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In 2020, the Australian and New Zealand flux research and monitoring network, OzFlux, celebrated its 20th anniversary by reflecting on the lessons learned through two decades of ecosystem studies on global change biology. OzFlux is a network not only for ecosystem researchers, but also for those 'next users' of the knowledge, information and data that such networks provide. Here, we focus on eight lessons across topics of climate change and variability, disturbance and resilience, drought and heat stress and synergies with remote sensing and modelling. In distilling the key lessons learned, we also identify where further research is needed to fill knowledge gaps and improve the utility and relevance of the outputs from OzFlux. Extreme climate variability across Australia and New Zealand (droughts and flooding rains) provides a natural laboratory for a global understanding of ecosystems in this time of accelerating climate change. As evidence of worsening global fire risk emerges, the natural ability of these ecosystems to recover from disturbances, such as fire and cyclones, provides lessons on adaptation and resilience to disturbance. Drought and heatwaves are common occurrences across large parts of the region and can tip an ecosystem's carbon budget from a net CO2 sink to a net CO2 source. Despite such responses to stress, ecosystems at OzFlux sites show their resilience to climate variability by rapidly pivoting back to a strong carbon sink upon the return of favourable conditions. Located in under-represented areas, OzFlux data have the potential for reducing uncertainties in global remote sensing products, and these data provide several opportunities to develop new theories and improve our ecosystem models. The accumulated impacts of these lessons over the last 20 years highlights the value of long-term flux observations for natural and managed systems. A future vision for OzFlux includes ongoing and newly developed synergies with ecophysiologists, ecologists, geologists, remote sensors and modellers.

© 2020 Elsevier B.V. Savannas, occupying a fifth of the global land surface, are characterized by the coexistence of trees and grasses. Accurate estimation of savanna evapotranspiration (ET) is vital for understanding the regional and global water balance and its feedback to climate. However, the overlapping phenology and different water-use patterns of trees and grasses constitute a major challenge for modeling efforts. To estimate savanna ET, we used a three-source ET model, partitioning ET among soil, trees, and grasses. To represent legacy effects of precipitation on ecosystem water use, the Normalized Ecosystem Drought Index (NEDI, i.e. a function of precipitation and potential evapotranspiration) was included to limit canopy conductances in the model and also in two other classic two-layer models (Shuttleworth-Wallace model and Penman-Monteith-Leuning model). The results of our model and the other models were tested and compared using tower-based eddy covariance flux data collected at six sites (including four savanna sites, one pasture site, and one grassland site) along a precipitation gradient in northern Australia, together with satellite-derived leaf area index, which was partitioned to represent the canopy dynamics of trees and grasses. Inclusion of NEDI significantly reduced seasonal biases in ET estimation results for all models compared with observations at savanna sites (fitted slopes were closer to unity by 0.08–0.10, R2 increased by 0.03–0.04, and RMSE decreased by 0.07–0.09 mm d−1). The three-source model provides insights into simulation of water fluxes over vegetated areas of complex composition. Our work makes a contribution to savanna research by determining a flexible indicator defining the seasonal water availability limitation on savanna ET. The inclusion of NEDI in ET models could guide future research on modeling ecosystem water and carbon fluxes in response to seasonal droughts.

© 2020 Elsevier Inc. Realistic representations and simulation of mass and energy exchanges across heterogeneous landscapes can be a challenge in land surface and dynamic vegetation models. For mixed life-form biomes such as savannas, plant function is very difficult to parameterise due to the distinct physiological characteristics of tree and grass plant functional types (PFTs) that vary dramatically across space and time. The partitioning of their fractional contributions to ecosystem gross primary production (GPP) remains to be achieved at regional scale using remote sensing. The objective of this study was to partition savanna gross primary production (GPP) into tree and grass functional components based on their distinctive phenological characteristics. Comparison of the remote sensing partitioned GPPtree and GPPgrass against field measurements from eddy covariance (EC) towers showed an overall good agreement in terms of both GPP seasonality and magnitude. We found total GPP, as well as its tree and grass components, decreased dramatically with rainfall over the North Australian Tropical Transect (NATT), from the Eucalyptus forest and woodland in the northern humid coast to the grasslands, Acacia woodlands and shrublands in the southern xeric interior. Spatially, GPPtree showed a steeper decrease with precipitation along the NATT compared to GPPgrass, thus tree/grass GPP ratios also decreased from the northern mesic region to the arid south region of the NATT. However, results also showed a second trend at the southern part of the transect, where tree-grass ratios and total GPP increased with decreasing mean annual precipitation, and this occurred in the physiognomic transition from hummock grasslands to Acacia woodland savannas. Total GPP and tree-grass GPP ratios across climate extremes were found to be primarily driven by grass layer response to rainfall dynamics. The grass-containing xeric savannas exhibited a higher hydroclimatic sensitivity, whereas GPP in the northern mesic savannas was fairly stable across years despite large variations in rainfall amount. The pronounced spatiotemporal variations in savanna vegetation productivity encountered along the NATT study area suggests that the savanna biome is particularly sensitive and vulnerable to predicted future climate change and hydroclimatic variability.

A comprehensive understanding of the effects of agricultural management on climate–crop interactions has yet to emerge. Using a novel wavelet–statistics conjunction approach, we analysed the synchronisation amongst fluxes (net ecosystem exchange NEE, evapotranspiration and sensible heat flux) and seven environmental factors (e.g., air temperature, soil water content) on 19 farm sites across Australia and New Zealand. Irrigation and fertilisation practices improved positive coupling between net ecosystem productivity (NEP = −NEE) and evapotranspiration, as hypothesised. Highly intense management tended to protect against heat stress, especially for irrigated crops in dry climates. By contrast, stress avoidance in the vegetation of tropical and hot desert climates was identified by reverse coupling between NEP and sensible heat flux (i.e., increases in NEP were synchronised with decreases in sensible heat flux). Some environmental factors were found to be under management control, whereas others were fixed as constraints at a given location. Irrigated crops in dry climates (e.g., maize, almonds) showed high predictability of fluxes given only knowledge of fluctuations in climate (R2 > 0.78), and fluxes were nearly as predictable across strongly energy- or water-limited environments (0.60 < R2 < 0.89). However, wavelet regression of environmental conditions on fluxes showed much smaller predictability in response to precipitation pulses (0.15 < R2 < 0.55), where mowing or grazing affected crop phenology (0.28 < R2 < 0.59), and where water and energy limitations were balanced (0.7 < net radiation ∕ precipitation < 1.3; 0.27 < R2 < 0.36). By incorporating a temporal component to regression, wavelet–statistics conjunction provides an important step forward for understanding direct ecosystem responses to environmental change, for modelling that understanding, and for quantifying nonstationary, nonlinear processes such as precipitation pulses, which have previously defied quantitative analysis.

© 2019 Elsevier B.V. The southern hemisphere and especially Australian arid and semi-arid ecosystems played a significant role in the 2011 global land carbon sink anomaly. Arid and semi-arid regions occupy 70% of the Australian land surface, dominated by two biomes: Mulga woodlands and spinifex grasslands or savannas. We monitored carbon and water fluxes in two of these characteristic ecosystems: a Mulga woodland (2010–2017) and a Corymbia savanna dominated by spinifex grasses (2012–2017). The aims of this study were to compare net ecosystem productivity (NEP) and evapotranspiration (ET) of these two ecosystems and to identify precipitation thresholds at which these ecosystems switched from being a C source to a C sink. Annual NEP in the Mulga woodland ranged from −47 to 217 gC m−2 y−1 (2010–2017), with the second largest positive NEP observed during the global C sink anomaly (162 gC m−2 y−1, 2010–2011). By contrast in the Corymbia savanna, annual NEP ranged from −190 to 115 gC m−2 y−1, with frequent occurrences of negative NEP and larger ET rates than for the Mulga woodland. Precipitation thresholds were identified at 262 mm y−1 and 507 mm y−1 in the Mulga woodland and the Corymbia savanna, respectively. Soil water content (SWC), along with air temperature and vapour pressure deficit, was a significant driver for water fluxes in both ecosystems (SWC–ET correlation of 0.5–0.56) and for carbon fluxes in the woodland (SWC–NEP and SWC–GPP correlation of −0.51 and −0.41, respectively). Arid and semi-arid ecosystems have dominated the inter-annual variability of the global terrestrial C sink, thus identifying precipitation thresholds at which ecosystems switch from being a C source to a C sink is important for furthering our understanding of the global C and water budget and for modelling of future climate.

© 2019 Elsevier Ltd Early detection of crop water and heat stress for effective crop management requires continuous and accurate monitoring of cropland photosynthesis activity. Satellite measurements can complement the restrictive coverage afforded by in-situ measurements and have the potential to facilitate the monitoring of cropland photosynthesis over a large spatial scale in a cost-effective manner. Traditionally, space-based monitoring of cropland photosynthetic activity, especially Light-use efficiency (LUE), has relied on empirical relationships between satellite spectral reflectance and ground climate and vegetation conditions. Space-borne retrievals of sun-induced chlorophyll fluorescence (SIF), an independent measurement, has shown to provide a more direct estimation of photosynthetic activity than traditional methods, and may further allow the inference of LUE. This study has empirically explored the possibility of remotely monitoring large-scale LUE by calculating the ratio of photosynthetically active radiation (PAR) normalized SIF to the Enhanced Vegetation Index (EVI). We applied this calculation to demonstrate the spatial patterns and seasonal dynamics of LUE and its related measurements in response to land surface temperature (LST) across Australian rainfed croplands from 2007 to 2016. LST was used to provide an integrated measure of vegetation water and heat stress at the canopy level. Our results showed that LUE tends to be higher in the geographical middle zones than in either the warmer northern or the cooler southern regions. Temporally, we found that there was a seasonal asymmetry of LUE and its related measurements in response to LST change throughout the winter crop-growing season. Statistical tests revealed that the optimum LST range for satellite-based LUE was 16.6–17.6 °C during August. The more LST exceeded this optimum, the more sensitive LUE was found to be. Pixels in August with optimum LST across the ten-year sampling period (Augusts of 2007–2016) were distributed in the southern-middle to middle zones of the Australian rainfed croplands. Our results provide new opportunities for large-scale cropland heat and drought stress detection under a future warmer and drier climate and can also support remote analyses of crop photosynthetic activity over large spatial scales.

As the ratio of carbon uptake to water use by vegetation, water-use efficiency (WUE) is a key ecosystem property linking global carbon and water cycles. It can be estimated in several ways, but it is currently unclear how different measures of WUE relate, and how well they each capture variation in WUE with soil moisture availability. We evaluated WUE in an Acacia-dominated woodland ecosystem of central Australia at various spatial and temporal scales using stable carbon isotope analysis, leaf gas exchange and eddy covariance (EC) fluxes. Semi-arid Australia has a highly variable rainfall pattern, making it an ideal system to study how WUE varies with water availability. We normalized our measures of WUE across a range of vapour pressure deficits using g1 , which is a parameter derived from an optimal stomatal conductance model and which is inversely related to WUE. Continuous measures of whole-ecosystem g1 obtained from EC data were elevated in the 3 days following rain, indicating a strong effect of soil evaporation. Once these values were removed, a close relationship of g1 with soil moisture content was observed. Leaf-scale values of g1 derived from gas exchange were in close agreement with ecosystem-scale values. In contrast, values of g1 obtained from stable isotopes did not vary with soil moisture availability, potentially indicating remobilization of stored carbon during dry periods. Our comprehensive comparison of alternative measures of WUE shows the importance of stomatal control of fluxes in this highly variable rainfall climate and demonstrates the ability of these different measures to quantify this effect. Our study provides the empirical evidence required to better predict the dynamic carbon-water relations in semi-arid Australian ecosystems.

© 2019 Elsevier B.V. The deforestation and degradation of natural habitats is the second largest contributor to carbon dioxide (CO2) emissions to the atmosphere. Temperate forests cover ∼16.5% of the Mexican landscape, and are a priority ecosystem for global conservation due to their high rate of endemism and species diversity. These forests also provide valuable ecosystem services, including the storage of organic carbon. Mexican temperate forests have lost more than half of their original cover, with ongoing forest degradation, resulting in CO2 emissions to the atmosphere. Most studies and carbon inventories only consider organic carbon stored in the aboveground biomass, and do not consider the organic carbon stored within soils of temperate forests. As a result, the emissions of CO2 due to deforestation are underestimated, and the value of temperate forests is underappreciated. To address this shortcoming, (1) we examine the extent and factors determining soil organic carbon stocks; (2) we estimate soil organic carbon stocks of Mexican temperate forests, the CO2 emissions caused by deforestation and avoided emissions from conservation and (3) we discuss the causes of loss of soil OC and management strategies to mitigate this loss. We propose that including the soil organic carbon stock-component is a priority for national projects targeting reducing emissions from deforestation. Also, urgent studies on the impacts of forest degradation in stocks of soil organic carbon are needed. Management strategies for conservation and rehabilitation of Mexican temperate forests must consider social and economic aspects of the local communities.

© 2019 Elsevier B.V. Hydrological responses of catchments to climate change require detailed examination to ensure sustainable management of both water resources and natural ecosystems. This study evaluated the impacts of climate change on water resource availability of a catchment in eastern Australia (i.e. the Manning River catchment) and analyzed climate-hydrology relationships. For this evaluation, the Xinanjiang (XAJ) model was used and validated to simulate monthly rainfall-runoff relationships of the catchment. Statistically downscaled climate data based on 28 global climate models (GCMs) under RCP8.5 scenarios were used to assess the impacts of climate changes on the Manning River catchment. Our results showed that the XAJ model was able to reproduce observed monthly rainfall-runoff relationships with an R 2 ≥ 0.94 and a Nash-Sutcliffe Efficiency ≥0.92. The median estimates from the ensemble of downscaled GCM projections showed a slight decrease in annual rainfall and runoff for the period 2021–2060 and an increase for the period 2061–2100. Annual actual evapotranspiration was projected to increase slightly, while annual soil moisture content was predicted to decrease in the future. Our results also demonstrated that future changes in seasonal and annual runoff, actual evapotranspiration and soil moisture are largely dominated by changes in rainfall, with a smaller influence arising from changes in temperature. An increase in the values of high runoffs and a decrease in the values of low runoffs predicted from the ensemble of the 28 GCMs suggest increased variability of water resources at monthly and seasonal time-scales in the future. A trend of decreasing values in winter runoff and soil moisture content in the future is likely to aggravate possible future reductions in water availability in eastern Australia. These results contribute to the development of adaptive strategies and future policy options for the sustainable management of water resources in eastern Australia.

©2018. American Geophysical Union. All Rights Reserved. Water use efficiency (WUE), the ratio of gross primary productivity (GPP) over evapotranspiration (ET), is a critical ecosystem function. However, it is difficult to distinguish the individual effects of climatic variables and leaf area index (LAI) on WUE, mainly due to the high collinearity among these factors. Here we proposed a partial least squares regression-based sensitivity algorithm to confront the issue, which was first verified at seven ChinaFlux sites and then applied across China. The results showed that across all biomes in China, monthly GPP (0.42–0.65), ET (0.33–0.56), and WUE (0.01–0.31) showed positive sensitivities to air temperature, particularly in croplands in northeast China and forests in southwest China. Radiation exerted stronger effects on ET (0.55–0.78) than GPP (0.19–0.65), resulting in negative responses (−0.44 to 0.04) of WUE to increased radiation among most biomes. Increasing precipitation stimulated both GPP (0.06–0.17) and ET (0.05–0.12) at the biome level, but spatially negative effects of excessive precipitation were also found in some grasslands. Both monthly GPP (−0.01 to 0.29) and ET (0.02–0.12) showed weak or moderate responses to vapor pressure deficit among biomes, resulting in weak response of monthly WUE to vapor pressure deficit (−0.04 to 0.08). LAI showed positive effects on GPP (0.18–0.60), ET (0–0.23), and WUE (0.13–0.42) across biomes, particularly on WUE in grasslands (0.42 ± 0.30). Our results highlighted the importance of LAI in influencing WUE against climatic variables. Furthermore, the sensitivity algorithm can be used to inform the design of manipulative experiments and compare with factorial simulations for discerning effects of various variables on ecosystem functions.

Copyright © 2018 John Wiley & Sons, Ltd. Accurate quantification of terrestrial evapotranspiration and ecosystem productivity is of significant merit to better understand and predict the response of ecosystem energy, water, and carbon budgets under climate change. Existing diagnostic models have different focus on either water or carbon flux estimates with various model complexity and uncertainties induced by distinct representation of the coupling between water and carbon processes. Here, we propose a diagnostic model to estimate evapotranspiration and gross primary production that is based on biophysical mechanism yet simple for practical use. This is done by coupling the carbon and water fluxes via canopy conductance used in the Penman–Monteith–Leuning equation (named as PML_V2 model). The PML_V2 model takes Moderate Resolution Imaging Spectrometer leaf area index and meteorological variables as inputs. The model was tested against evapotranspiration and gross primary production observations at 9 eddy-covariance sites in Australia, which are spread across wide climate conditions and ecosystems. Results indicate that the simulated evapotranspiration and gross primary production by the PML_V2 model are in good agreement with the measurements at 8-day timescale, indicated by the cross site Nash–Sutcliffe efficiency being 0.70 and 0.66, R2 being 0.80 and 0.75, and root mean square error being 0.96 mm d−1 and 1.14 μmol m−2 s−1 for evapotranspiration and gross primary production, respectively. As the PML_V2 model only requires readily available climate and Moderate Resolution Imaging Spectrometer vegetation dynamics data and has few parameters, it can potentially be applied to estimate evapotranspiration and carbon assimilation simultaneously at long-term and large spatial scales.

© 2018 Elsevier Ltd Arid environments can support the seemingly unlikely coexistence of species tolerant of, or sensitive to, dry soil moisture. Here, we examine water-use and carbon-gain traits in two widespread tree species in central Australia: Acacia aptaneura and Eucalyptus camaldulensis. The former has a shallow root distribution and relies on soil moisture, while the latter is groundwater dependent. We hypothesised that A. aptaneura would exhibit a suite of characteristics that confer tolerance to low soil moisture, in contrast to E. camaldulensis. Consistent with our hypotheses A. aptaneura was relatively more anisohydric than E. camaldulensis (seasonal leaf water potential of −7.2 to −0.8 MPa cf. −1.4 to −0.3 MPa). Additionally, compared to E. camaldulensis, A. aptaneura had lower water potential at turgor loss (−2.5 cf. −1.1 MPa); a larger Huber value; smaller, narrower and thicker phyllodes/leaves; and larger photosynthetic capacity (Jmax); and larger water-use efficiency. Further, water-use efficiency for E. camaldulensis was similar to species receiving annual rainfall of 1500 mm, despite annual rainfall of 348 mm. We conclude that mean annual rainfall is the dominant determinant of water and carbon relations for A. aptaneura, but not E. camaldulensis. This has important implications for ecosystem-scale transpiration and primary productivity across this arid zone.

© 2017 Elsevier B.V. The rainfed cropland belt in Australia is of great importance to the world grain market but has the highest climate variability of all such regions globally. However, the spatial-temporal impacts of climate variability on crops during different crop growth stages across broadacre farming systems are largely unknown. This study aims to quantify the contributions of climate and Land Surface Temperature (LST) variations to the variability of the Enhanced Vegetation Index (EVI) by using remote sensing methods. The datasets were analyzed at an 8-day time-scale across the rainfed cropland of eastern Australia. First, we found that EVI values were more variable during the crop reproductive growth stages than at any other crop life stage within a calendar year, but nevertheless had the highest correlation with crop grain yield (t ha−1). Second, climate factors and LST during the crop reproductive growth stages showed the largest variability and followed a typical east-west gradient of rainfall and a north-south temperature gradient across the study area during the crop growing season. Last, we identified two critical 8-day periods, beginning on day of the year (DoY) 257 and 289, as the key ‘windows’ of crop growth variation that arose from the variability in climate and LST. Our results show that the sum of the variability of the climate components within these two 8-day ‘windows’ explained >88% of the variability in the EVI, with LST being the dominant factor. This study offers a fresh understanding of the spatial-temporal climate-crop relationships in rainfed cropland and can serve as an early warning system for agricultural adaptation in broadacre rainfed cropping practices in Australia and worldwide.

© 2017 Elsevier B.V. Drought strongly influences terrestrial C cycling via its effects on plant H2O and CO2 exchange. However, the treatment of photosynthetic physiology under drought by many ecosystem and earth system models remains poorly constrained by data. We measured the drought response of four tree species and evaluated alternative model formulations for drought effects on photosynthesis (A). We implemented a series of soil drying and rewetting events (i.e. multiple droughts) with four contrasting tree species in large pots (75 L) placed in the field under rainout shelters. We measured leaf-level gas exchange, predawn and midday leaf water potential (Ψpd and Ψmd), and leaf isotopic composition (δ13C) and calculated discrimination relative to the atmosphere (Δ). We then evaluated eight modeling frameworks that simulate the effects of drought in different ways. With moderate reductions in volumetric soil water content (θ), all species reduced stomatal conductance (gs), leading to an equivalent increase in water use efficiency across species inferred from both leaf gas exchange and Δ, despite a small reduction in photosynthetic capacity. With severe reductions in θ, all species strongly reduced gs along with a coincident reduction in photosynthetic capacity, illustrating the joint importance of stomatal and non-stomatal limitations of photosynthesis under strong drought conditions. Simple empirical models as well as complex mechanistic model formulations were equally successful at capturing the measured variation in A and gs, as long as the predictor variables were available from direct measurements (θ, Ψpd, and Ψmd). However, models based on leaf water potential face an additional challenge, as we found that Ψpd was substantially different from Ψsoil predicted by standard approaches based on θ. Modeling frameworks that combine gas exchange and hydraulic traits have the advantage of mechanistic realism, but sacrificed parsimony without an improvement in predictive power in this comparison. Model choice depends on the desired balance between simple empiricism and mechanistic realism. We suggest that empirical models implementing stomatal and non-stomatal limitations based on θ are highly predictive simple models. Mechanistic models that incorporate hydraulic traits have excellent potential, but several challenges currently limit their widespread implementation.

© 1980-2012 IEEE. The National Aeronautics and Space Administration's Soil Moisture Active Passive (SMAP) mission Level 4 Carbon (L4C) product provides model estimates of the Net Ecosystem CO2 exchange (NEE) incorporating SMAP soil moisture information. The L4C product includes NEE, computed as total ecosystem respiration less gross photosynthesis, at a daily time step posted to a 9-km global grid by plant functional type. Component carbon fluxes, surface soil organic carbon stocks, underlying environmental constraints, and detailed uncertainty metrics are also included. The L4C model is driven by the SMAP Level 4 Soil Moisture data assimilation product, with additional inputs from the Goddard Earth Observing System, Version 5 weather analysis, and Moderate Resolution Imaging Spectroradiometer satellite vegetation data. The L4C data record extends from March 31, 2015 to present with ongoing production and 8-12 day latency. Comparisons against concurrent global CO2 eddy flux tower measurements, satellite solar-induced canopy florescence, and other independent observation benchmarks show favorable L4C performance and accuracy, capturing the dynamic biosphere response to recent weather anomalies. Model experiments and L4C spatiotemporal variability were analyzed to understand the independent value of soil moisture and SMAP observations relative to other sources of input information. This analysis highlights the potential for microwave observations to inform models where soil moisture strongly controls land CO2 flux variability; however, skill improvement relative to flux towers is not yet discernable within the relatively short validation period. These results indicate that SMAP provides a unique and promising capability for monitoring the linked global terrestrial water and carbon cycles.

© 2018, ISB. Climate change (CC) presents a challenge for the sustainable development of wheat production systems in Australia. This study aimed to (1) quantify the impact of future CC on wheat grain yield for the period centred on 2030 from the perspectives of wheat phenology, water use and water use efficiency (WUE) and (2) evaluate the effectiveness of changing sowing times and cultivars in response to the expected impacts of future CC on wheat grain yield. The daily outputs of CSIRO Conformal-Cubic Atmospheric Model for baseline and future periods were used by a stochastic weather generator to derive changes in mean climate and in climate variability and to construct local climate scenarios, which were then coupled with a wheat crop model to achieve the two research aims. We considered three locations in New South Wales, Australia, six times of sowing (TOS) and three bread wheat (Triticum aestivum L.) cultivars in this study. Simulation results show that in 2030 (1) for impact analysis, wheat phenological events are expected to occur earlier and crop water use is expected to decrease across all cases (the combination of three locations, six TOS and three cultivars), wheat grain yield would increase or decrease depending on locations and TOS; and WUE would increase in most of the cases; (2) for adaptation considerations, the combination of TOS and cultivars with the highest yield varied across locations. Wheat growers at different locations will require different strategies in managing the negative impacts or taking the opportunities of future CC.

© 2017 John Wiley & Sons Ltd Species are often classified along a continuum from isohydric to anisohydric, with isohydric species exhibiting tighter regulation of leaf water potential through stomatal closure in response to drought. We investigated plasticity in stomatal regulation in an isohydric (Eucalyptus camaldulensis) and an anisohydric (Acacia aptaneura) angiosperm species subject to repeated drying cycles. We also assessed foliar abscisic acid (ABA) content dynamics, aboveground/belowground biomass allocation and nonstructural carbohydrates. The anisohydric species exhibited large plasticity in the turgor loss point (ΨTLP), with plants subject to repeated drying exhibiting lower ΨTLP and correspondingly larger stomatal conductance at low water potential, compared to plants not previously exposed to drought. The anisohydric species exhibited a switch from ABA to water potential-driven stomatal closure during drought, a response previously only reported for anisohydric gymnosperms. The isohydric species showed little osmotic adjustment, with no evidence of switching to water potential-driven stomatal closure, but did exhibit increased root:shoot ratios. There were no differences in carbohydrate depletion between species. We conclude that a large range in ΨTLP and biphasic ABA dynamics are indicative of anisohydric species, and these traits are associated with exposure to low minimum foliar water potential, dense sapwood and large resistance to xylem embolism.

© 2017 John Wiley & Sons Ltd Large spatial and temporal gradients in rainfall and temperature occur across Australia. This heterogeneity drives ecological differentiation in vegetation structure and ecophysiology. We examined multiple leaf-scale traits, including foliar 13C isotope discrimination (Δ13C), rates of photosynthesis and foliar N concentration and their relationships with multiple climate variables. Fifty-five species across 27 families were examined across eight sites spanning contrasting biomes. Key questions addressed include: (i) Does Δ13C and intrinsic water-use efficiency (WUEi) vary with climate at a continental scale? (ii) What are the seasonal and spatial patterns in Δ13C/WUEi across biomes and species? (iii) To what extent does Δ13C reflect variation in leaf structural, functional and nutrient traits across climate gradients? and (iv) Does the relative importance of assimilation and stomatal conductance in driving variation in Δ13C differ across seasons? We found that MAP, temperature seasonality, isothermality and annual temperature range exerted independent effects on foliar Δ13C/WUEi. Temperature-related variables exerted larger effects than rainfall-related variables. The relative importance of photosynthesis and stomatal conductance (gs) in determining Δ13C differed across seasons: Δ13C was more strongly regulated by gs during the dry-season and by photosynthetic capacity during the wet-season. Δ13C was most strongly correlated, inversely, with leaf mass area ratio among all leaf attributes considered. Leaf Nmass was significantly and positively correlated with MAP during dry- and wet-seasons and with moisture index (MI) during the wet-season but was not correlated with Δ13C. Leaf Pmass showed significant positive relationship with MAP and Δ13C only during the dry-season. For all leaf nutrient-related traits, the relationships obtained for Δ13C with MAP or MI indicated that Δ13C at the species level reliably reflects the water status at the site level. Temperature and water availability, not foliar nutrient content, are the principal factors influencing Δ13C across Australia.

© The Author(s) 2016. Each year, terrestrial ecosystems absorb more than a quarter of the anthropogenic carbon emissions, termed as land carbon sink. An exceptionally large land carbon sink anomaly was recorded in 2011, of which more than half was attributed to Australia. However, the persistence and spatially attribution of this carbon sink remain largely unknown. Here we conducted an observation-based study to characterize the Australian land carbon sink through the novel coupling of satellite retrievals of atmospheric CO2 and photosynthesis and in-situ flux tower measures. We show the 2010-11 carbon sink was primarily ascribed to savannas and grasslands. When all biomes were normalized by rainfall, shrublands however, were most efficient in absorbing carbon. We found the 2010-11 net CO2 uptake was highly transient with rapid dissipation through drought. The size of the 2010-11 carbon sink over Australia (0.97 Pg) was reduced to 0.48 Pg in 2011-12, and was nearly eliminated in 2012-13 (0.08 Pg). We further report evidence of an earlier 2000-01 large net CO2 uptake, demonstrating a repetitive nature of this land carbon sink. Given a significant increasing trend in extreme wet year precipitation over Australia, we suggest that carbon sink episodes will exert greater future impacts on global carbon cycle.

© 2016, Springer Science+Business Media New York. Changes in climatic characteristics such as seasonal and inter-annual variability may affect ecosystem structure and function, hence alter carbon and water budgets of ecosystems. Studies of modelling combined with field experiments can provide essential information to investigate interactions between carbon and water cycles and climate. Here we present a first attempt to investigate the long-term climate controls on seasonal patterns and inter-annual variations in water and carbon exchanges in an arid-zone savanna-woodland ecosystem using a detailed mechanistic soil–plant–atmosphere model (SPA), driven by leaf area index (LAI) simulated by an ecohydrological model (WAVES) and observed climate data during 1981–2012. The SPA was tested against almost 3 years of eddy covariance flux measurements in terms of gross primary productivity (GPP) and evapotranspiration (ET). The model was able to explain 80 and 71% of the variability of observed daily GPP and ET, respectively. Long-term simulations showed that carbon accumulation rates and ET ranged from 20.6 g C m−2 mon−1 in the late dry season to 45.8 g C m−2 mon−1 in the late wet season, respectively, primarily driven by seasonal variations in LAI and soil moisture. Large climate variations resulted in large seasonal variation in ecosystem water-use efficiency (eWUE). Simulated annual GPP varied between 146.4 and 604.7 g C m−2 y−1. Variations in annual ET coincided with that of GPP, ranging from 110.2 to 625.8 mm y−1. Annual variations in GPP and ET were driven by the annual variations in precipitation and vapour pressure deficit (VPD) but not temperature. The linear coupling of simulated annual GPP and ET resulted in eWUE having relatively small year-to-year variation.

© 2016 Elsevier Ltd. Ecophysiological studies of remnant woodlands in saline environments are scarce. We investigated seasonal fluctuations in soil water and salinity together with leaf and branch traits (area-based maximum assimilation (Amax), foliar nitrogen, specific leaf area (SLA) and Huber value (Hv)) and sap velocities of Eucalyptus macrorhyncha at four semi-arid sites in south-eastern Australia. Summer and winter soil salinities (10 cm depth) were 15-35 dS m-1 and 8-10 dS m-1 respectively. Gravimetric soil water content in the upper 20 cm was 2-5% in summer and 7-23% in winter, resulting in a significant inverse correlation between soil water and soil salinity. We found significant correlations between soil conditions and plant traits and function across seasons. Soil water content was significantly correlated with foliar N, SLA, Hv and maximum sap velocity while soil salinity was significantly correlated with Amax, Hv and maximum sap velocity. Correlations indicate co-variation of soil conditions and plant physiology in response to environmental conditions such as solar radiation and vapour pressure deficit (D). E. macrorhyncha tolerates the dual stresses of high salinity and low soil water during summer. While the plants appeared unhealthy, our data show that remnant vegetation can remain functional even in close proximity to saline scalds.

©2015. American Geophysical Union. All Rights Reserved. Amplification of the hydrologic cycle as a consequence of global warming is predicted to increase climate variability and the frequency and severity of droughts. Recent large-scale drought and flooding over numerous continents provide unique opportunities to understand ecosystem responses to climatic extremes. In this study, we investigated the impacts of the early 21st century extreme hydroclimatic variations in southeastern Australia on phenology and vegetation productivity using Moderate Resolution Imaging Spectroradiometer Enhanced Vegetation Index and Standardized Precipitation-Evapotranspiration Index. Results revealed dramatic impacts of drought and wet extremes on vegetation dynamics, with abrupt between year changes in phenology. Drought resulted in widespread reductions or collapse in the normal patterns of seasonality such that in many cases there was no detectable phenological cycle during drought years. Across the full range of biomes examined, we found semiarid ecosystems to exhibit the largest sensitivity to hydroclimatic variations, exceeding that of arid and humid ecosystems. This result demonstrated the vulnerability of semiarid ecosystems to climatic extremes and potential loss of ecosystem resilience with future mega-drought events. A skewed distribution of hydroclimatic sensitivity with aridity is of global biogeochemical significance because it suggests that current drying trends in semiarid regions will reduce hydroclimatic sensitivity and suppress the large carbon sink that has been reported during recent wet periods (e.g., 2011 La Niña).

© 2015 Elsevier B.V. Evaporative losses typically play a substantial role in the water balances of arid regions. However, they are often poorly understood due to low flux rates and difficulty in direct measurement. We compared six field methods to quantify groundwater discharge due to evaporative and evapotranspirative fluxes from Stirling Swamp, a playa in central Australia; Bowen ratio-energy balance (BREB), maximum entropy production (MEP), chloride and stable isotope profiling, change in groundwater level, and 14C profiles within the aquifer. The latter method has not been previously used to determine groundwater discharge. Evaporative groundwater discharge estimates varied between 0 and 300mm/y, partly due to variability in spatial and temporal scales captured by the individual methods. Within playa systems where evapotranspiration within the soil is negligible but the depth to groundwater is small, land surface energy balances were found to have the advantage of integrating over hundreds of metres, and when upscaled to annual estimates they agreed well with expected evaporative flux values. Soil profile methods yielded a wide range of results depending on the values of several constants that must be assumed, and the assumption of steady state was found to be a disadvantage. Groundwater methods also had the advantage of integrating over some distance within the aquifer; however, advective transport in the subsurface may have led to under-estimation of evaporative flux with these methods.

© 2015 Apgaua et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species' hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios.

© 2015 Royal Meteorological Society. We compared the capacity of woody versus grassy vegetation covers to buffer high temperatures during heat waves by partitioning turbulent heat between latent (λE) and sensible (H) fluxes, and quantifying advection using the Priestley-Taylor coefficient (α), for a16-year old grassland and an adjoining 6-year old plantation. We found that because λE dominated (>65%) the turbulent flux in the plantation and was at least twice as large as on the grassland (λE< 35% of the turbulent flux) during heat waves, the ambient temperature over the plantation was up to 5 °C lower in the afternoon, and averaged 1.2 °C lower for the whole day, compared with the grassland. Both vegetation covers emitted significant amounts of H when soil water availability was limited and also in winter when canopy cover was mostly inactive because of dormancy in the grassland and mutual shading in the plantation due to low solar angle. During the winter, advection of additional energy from surrounding vegetation suppressed λE and reduced α to 35°). Annual evapotranspiration was 54% lower from the grassland (384 mm) than from the plantation (834 mm). Woody vegetation covers dominated by broadleaved species are therefore preferred for buffering extreme high temperatures during heat waves and recommended for rehabilitating degraded landscapes in urban areas. We also present functions for approximating α for soil water limited conditions.

© 2015 The Author 2015. Published by Oxford University Press. All rights reserved. The importance of groundwater resources in arid and semi-arid areas for plant survival is well documented. However, there have been few studies examining the importance and impacts of groundwater availability in mesic environments. The aim of this study was to determine how depth-to-groundwater (DGW) impacts on leaf water relations, leaf structure and branch xylem vulnerability to embolism in a mesic environment. We hypothesize that increasing DGW results in increased resistance to drought stress and that this will be manifested across leaf and branch attributes pertaining to water relations. We further investigate whether there is co-ordination across leaf and branch-scale level responses to increased DGW. Four species were used in this study: Eucalyptus globoidea Blakely, E. piperita Sm., E. sclerophylla (Blakely) L.A.S.Johnson & Blaxell and E. sieberi L.A.S.Johnson. Six sites were chosen along an 11 km transect to span a range of average DGW: 2.4, 4.3, 9.8, 13, 16.3 and 37.5 m. Leaf water relations of trees showed less sensitivity to drought stress as DGW increased. This was reflected in significantly lower leaf turgor loss point and maximum osmotic potential, increased maximum turgor and a reduced leaf relative water content as DGW increased. At shallow DGW sites, minimum diurnal leaf water potentials were generally more negative than leaf water potential at zero turgor, but the reverse was observed at deep sites, indicating a larger growth potential safety margin at deep sites compared with shallow sites. Leaf cell wall elasticity varied independently of DGW. Xylem vulnerability to embolism was quantified as the water potential associated with 50% loss of conductance (P 50). In both summer and winter P50 was significantly and negatively correlated with DGW. Co-ordination between leaf- and branch-level responses to increase in DGW was apparent, which strongly supports the conclusion that groundwater supply influenced woodland structure and functional behaviour.

© 2014 Elsevier Ltd. We apply a model of root-water uptake to a woodland in Australia to examine the regulation of transpiration by root water compensation (i.e., the ability of roots to regulate root water uptake from different parts of the soil profile depending on local moisture availability). We model soil water movement using the Richards equation and water flow in the xylem with Darcy's equation. These two equations are coupled by a term that governs the exchange of water between soil and root xylem as a function of the difference in water potential between the two. The model is able to reproduce measured diurnal patterns of sap flux and results in leaf water potentials that are consistent with field observations. The model shows that root water compensation is a key process to allow for sustained rates of transpiration across several months. Scenarios with different root depths showed the importance of having a root system deeper than about 2. m to achieve the measured transpiration rates without reducing the leaf water potential to levels inconsistent with field measurements. The model suggests that the presence of more than 5% of the root system below 0.6. m allows trees to maintain sustained transpiration rates keeping leaf water potential levels within the range observed in the field. According to the model, a large contribution to transpiration in dry periods was provided by the roots below 0.3. m, even though the percentage of roots at these depths was less than 40% in all scenarios.

© 2014 John Wiley & Sons, Ltd. Response of leaf area index (LAI) is the key determinant for predicting impacts of the elevated CO 2 (eCO 2 ) on water budgets. Importance of the changes in functional attributes of vegetation associated with eCO 2 for predicting responses of LAI has rarely been addressed. In this study, the WAter Vegetation Energy and Solute (WAVES) model was applied to simulate ecohydrological effects of the eCO 2 at two free-air CO 2 enrichment (FACE) experimental sites with contrasting vegetation. One was carried out by the Oak Ridge National Laboratory on the forest (ORNL FACE). The other one was conducted by the University of Minnesota on the grass (BioCON FACE). Results demonstrated that changes in functional attributes of vegetation (including reduction in specific leaf area, changes in carbon assimilation and allocation characteristics) and availability of nutrients are important for reproducing the responses of LAI, transpiration and soil moisture at both sites. Predicted LAI increased slightly at both sites because of fertilization effects of the eCO 2 . Simulated transpiration decreased 10·5% at ORNL site and 13·8% at BioCON site because of reduction in the stomatal conductance. Predicted evaporation from interception and soil surface increased slightly ( < 1·0mmyear -1 ) at both sites because of increased LAI and litter production, and increased soil moisture resulted from reduced transpiration. All components of run-off were predicted to increase because of significant decrease in transpiration. Simulated mean annual evapotranspiration decreased about 8·7% and 10·8%, and mean annual run-off increased about 11·1% (59·3mmyear -1 ) and 9·5% (37·6mmyear -1 ) at the ORNL and BioCON FACE sites, respectively.

Sustainable long-term storage of municipal waste and waste rock from mining activities in waste dumps (either above or below the land surface) requires minimization of percolation of rainwater into and then through stored waste material. There has been increasing attention given to the use of store-release covers (transpirational covers) to achieve this. However, the design of such covers remains problematic because of the unique combinations of weather, vegetation composition, soils and their interactions that determine the efficacy of each design that could be available for the construction of the covers. The aim of the work described here was to use ecophysiological knowledge of soil-plant-atmosphere (SPA) interactions through the application of a detailed mechanistic model of the SPA continuum. We examined the relative influence of soil depth, soil texture, leaf area index and rainfall as determinants of rates of evapotranspiration and water budget for several different theoretical cover designs. We show that minimizing deep drainage requires a cover that has the following attributes: (i) a water storage capacity that is large enough to store the volume of water that is received as rainfall in above-average wet months/seasons; (ii) a root distribution that explores the entire depth of the cover; (iii) a leaf area index that is present all year sufficient to evapotranspire monthly rainfall; and (iv) takes into account the intra-annual and inter-annual variability in rainfall and other climatic variables that drive ET. © 2012 John Wiley & Sons, Ltd.

The Huai River Basin (HRB) of China is well-known globally for the extent of severe human activities (e.g., waste disposal and water project construction) which have resulted in severe water pollution and subsequently degraded water ecosystem quality in recent decades. However, influence of water pollution on water ecosystems has not yet been fully realized due to lack of water ecosystem data. In food webs of freshwater ecosystems, zooplankton occupy a critical position but they are highly susceptible to pollutants and temperature which in turn impact the community structure and biodiversity of zooplankton to a great extent. This paper aimed to assess impact of water chemistry variation on zooplankton through ecological-niche models and spatial heterogeneity of zooplankton along with water chemistry in the HRB. We investigated the impacts of nine dominant water chemistry indicators on zooplankton distribution and composition via ecological niche models based on water chemistry status and zooplankton communities at 71 typical sites of the HRB. A fuzzy clustering method (FCM) was employed to help study the impact characteristics and the spatial heterogeneity. Results indicate that across the nine water chemistry indicators, changes in water temperature has minimal impact on the zooplankton community of the Huai River while small variation in ammonia-nitrogen exerts significant stress on the community; with respect to water temperature and total phosphorous zooplankton species in the HRB are coexisting with little competition; as to spatial heterogeneity of zooplankton communities, communities in the southwest and southeast mountainous regions may adapt well to habitat variations, while those in the middle and northeast areas have a weak adaptability to habitat changes. We concluded that in highly polluted rivers with large spatial heterogeneity of water chemistry, like the Huai River, ammonia-nitrogen exerted great stress on the zooplankton community in nonlinear way with too high or low concentration of ammonia-nitrogen leading to reduction in abundance of zooplankton; zooplankton communities in the HRB is mainly impacted by pollutant instead of water-temperature. All these can provide scientific support for future restoration and wise water resources planning and management in the Huai River. © 2013 Elsevier B.V.

Vast areas in the interior of Australia are exposed to regular but infrequent periods of heavy rainfall, interspersed with long periods at high temperatures, but little is known of the carbon budget of these remote areas or how they respond to extreme precipitation. In this study, we applied three methods to partition net ecosystem photosynthesis into gross primary production (GPP) and ecosystem respiration (Re) during two years of contrasting rainfall. The first year was wet (>250 mm above average rainfall), while little precipitation fell during the second year (>100 mm below average). During the first year of study, rates of GPP were large (793 g C m-2 yr-1) in this semi-arid Mulga (Acacia aneura) and grass savanna due to complementary photosynthetic responses by the canopy and C4 understorey to cycles of heavy rainfall. Patterns in GPP during the summer and autumn matched those in leaf area index (LAI), photosynthetic activity, and autotrophic respiration. During the dry year, small but positive photosynthetic uptake by Mulga contributed to the neutral carbon budget (GPP / Re = 1.06 ± 0.03). Small rates of photosynthesis by evergreen Mulga when dry were supported by storage of soil moisture above a relatively shallow hardpan. Little soil organic matter (1.1%) was available to support heterotrophic respiration (Rh) without input of fresh substrate. The two largest sources of Re in this study were autotrophic respiration by the seasonal understorey and Rh through decomposition of fresh organic matter supplied by the senescent understorey. © 2013. American Geophysical Union. All Rights Reserved.

A modified Jarvis-Stewart model of canopy transpiration (Ec) was tested over five ecosystems differing in climate, soil type and species composition. The aims of this study were to investigate the model's applicability over multiple ecosystems; to determine whether the number of model parameters could be reduced by assuming that site-specific responses of Ec to solar radiation, vapour pressure deficit and soil moisture content vary little between sites; and to examine convergence of behaviour of canopy water-use across multiple sites. This was accomplished by the following: (i) calibrating the model for each site to determine a set of site-specific (SS) parameters, and (ii) calibrating the model for all sites simultaneously to determine a set of combined sites (CS) parameters. The performance of both models was compared with measured Ec data and a statistical benchmark using an artificial neural network (ANN). Both the CS and SS models performed well, explaining hourly and daily variation in Ec. The SS model produced slightly better model statistics [R2=0.75-0.91; model efficiency (ME)=0.53-0.81; root mean square error (RMSE)=0.0015-0.0280mm h-1] than the CS model (R2=0.68-0.87; ME=0.45-0.72; RMSE=0.0023-0.0164mm h-1). Both were highly comparable with the ANN (R2=0.77-0.90; ME=0.58-0.80; RMSE=0.0007-0.0122mm h-1). These results indicate that the response of canopy water-use to abiotic drivers displayed significant convergence across sites, but the absolute magnitude of Ec was site specific. Period totals estimated with the modified Jarvis-Stewart model provided close approximations of observed totals, demonstrating the effectiveness of this model as a tool aiding water resource management. Analysis of the measured diel patterns of water use revealed significant nocturnal transpiration (9-18% of total water use by the canopy), but no Jarvis-Stewart formulations are able to capture this because of the dependence of water-use on solar radiation, which is zero at night. © 2012 John Wiley & Sons, Ltd.

The study of the patterns of plant species diversity and the factors influencing these patterns is the basis of ecology and is also fundamental to conservation biology. Groundwater-dependent vegetation (GDV) must have access to groundwater to maintain their growth and function, and this is especially common in arid and semi-arid regions, including north-western China. In this paper, plant species diversity and groundwater attributes (composition and depth) were investigated in 31 plots in the Ejina Delta in north-western China to determine whether groundwater attributes influenced patterns species diversity in GDV. Detrended canonical correspondence analyses and generalised additive models were performed to analyse the data. A total of 29 plant species were recorded in the 31 plots; perennial herbs with deep roots had an advantage over all other groups, and GDV species diversity was primarily affected by groundwater depth (GWD), salinity (SAL) and total dissolved solids (TDS), HCO3-, Ca2+, pH, and SO42-. The herb layer species diversity and total species diversity reached their maximum in similar, moderate environmental conditions. The diversity of the tree species was influenced by SAL and TDS and was maximal at large values of GWD and low values of SAL and TDS. The diversity of shrub species was affected by Ca2+ and Mg2+ and was maximal low GWD and high SAL and TDS. Patrick's and Shannon-Wiener's index of the total community diversity presented a bimodal pattern along gradients of GWD and SAL, whilst Simpson's and Pielou's index showed a partially unimodal pattern. On the basis of field investigation and the analysis of field data, we concluded that the perfect combination of GWD and SAL for GDV species diversity is 2m and 1·8gl-1, respectively. The appropriate combination range is 2-5m and 1·8-4·2gl-1, and the critical combination for the damaged GDV species diversity is 5m and 4·2gl-1. © 2012 John Wiley & Sons, Ltd.

In arid and semi-arid regions, groundwater availability is one of the controls on vegetation distribution. This groundwater-dependent distribution of vegetation has been particularly observed in the Hailiutu River catchment, a semi-arid region in North China. We used remote sensing images of vegetation index (normalized difference vegetation index, NDVI) and field data of depth to water table (DWT) to assess the response of vegetation distribution on increase of DWT at the regional scale. The frequency distribution curves of NDVI with respect to different DWT were obtained. The statistical distributions of NDVI values at different DWT intervals indicate that higher vegetation coverage and more plant diversity exist at places of shallow groundwater. Both the mean and the standard deviation of NDVI values decrease with the increase of groundwater depth when DWT is less than 10m. Beyond that depth, a low level of vegetation coverage and diversity is maintained. Comparisons of different sub-areas within the region with different dominant species showed that the NDVI of shrubs is sensitive to DWT. In contrast, NDVI of herbs is not significantly influenced by DWT. The relationship between NDVI and groundwater depth in farmlands could not be reliably determined because of disturbance by human activities. We conclude that application of this methodology may significantly improve our ability on sustainable management of land and groundwater resources. © 2012 John Wiley & Sons, Ltd.

Leaf colour gives a good indication of chlorophyll (Ch) and nitrogen (N)status in plants. In this paper we developed a new, easy to use and non-destructive diagnostic approach to detect plantCh and N levels using an image processing technique developed using the RGB (Red, Green and Blue) colour model. The experiment was conducted on tomato (Tommy Toy) in field with three N treatments (0, 60 and 140 kg N / ha), where leaf images were collected using a handheld scanner. The new algorithm achieves superior correlation with the value of Ch and N, measured in laboratory, compared with the existing non-destructive methods of SPAD 502 and Dark green Colour Index (DGCI ).

It is important to investigate potential changes in temperature, precipitation and solar radiation for assessing the impacts of future climate change on agricultural production for specific regions. In this study, climate scenarios of precipitation, temperature and solar radiation for the North China Plain (NCP) were constructed in terms of stochastic daily weather sequences. A nonhomogeneous hidden Markov model (NHMM) was used to downscale daily precipitation projections at 32 stations during winter wheat and summer maize growing seasons for a baseline (1966-2005) and a 21st century (2080-2099) A1B scenario, using selected general circulation models (GCMs). A climatological seasonal cycle of regional-averaged daily reanalysis precipitation was used as input to the down-scaling for the baseline simulation; this input was then scaled by the precipitation changes from GCM projections to generate down-scaled stochastic simulations of precipitation in the 21st century. Temperature was generated using a weakly stationary generating process, conditional on precipitation occurrence, with 21st century additive changes taken from the GCMs at the regional scale. Three hypotheses about changes in solar radiation (-20%, 0% and 20%) were made considering the large uncertainty in its future change. The down-scaled simulations exhibit station increases in the mean daily rainfall of 13.9-69.7% in the scenarios driven by the GCM with the projected largest and multi-model mean precipitation increase for the wheat season, with changes of 0.4-29.9% for the maize season. In the scenario driven by the GCM with the largest projected precipitation decrease, the simulated rainfall decreases at all stations, with changes ranging from -24.6 to -0.1% for the wheat and maize seasons, respectively. Temperature increases by about 3.7°C for the wheat season and 3.6°C for the maize season. © 2013 Royal Meteorological Society.

Correct representations of root functioning, such as root water uptake and hydraulic redistribution, are critically important for modeling the responses of vegetation to droughts and seasonal changes in soil moisture content. However, these processes are poorly represented in global land surface models. In this study, we incorporated two root functions: a root water uptake function which assumes root water uptake efficiency varies with rooting depth, and a hydraulic redistribution function into a global land surface model, CABLE. The water uptake function developed by Lai and Katul (2000) was also compared with the default one (see Wang et al., 2010) that assumes that efficiency of water uptake per unit root length is constant. Using eddy flux measurements of CO 2 and water vapor fluxes at three sites experiencing different patterns of seasonal changes in soil water content, we showed that the two root functions significantly improved the agreement between the simulated fluxes of net ecosystem exchange and latent heat flux and soil moisture dynamics with those observed during the dry season while having little impact on the model simulation during the wet seasons at all three sites. Sensitivity analysis showed that varying several model parameters influencing soil water dynamics in CABLE did not significantly affect the model's performance. We conclude that these root functions represent a valuable improvement for land surface modeling and should be implemented into CABLE and other land surface models for studying carbon and water dynamics where rainfall varies seasonally or interannually. © 2012. American Geophysical Union. All Rights Reserved.

The maximisation of plant nitrogen-use-efficiency (NUE) has direct impact on increasing crop production, due to the increase of agronomic value of the fertiliser. Moreover, optimising the use of nitrogen will reduce the adverse effect on the environment that can be caused by nitrate leaching and nitrous oxide production. Accordingly, nitrogen (N) management in agriculture has been the focus of many researchers. Improvement of NUE can be achieved through measurement of the foliar N content of crops during growth. There are two classes of methods to diagnose foliar N status: destructive and non-destructive. Destructive methods are expensive and time-consuming as they require tissue sample collection and laboratory analysis. Non-destructive methods are rapid and less expensive, but usually less accurate. Improved accuracy is the goal of many researchers and various methods have been proposed that vary in complexity and optimality. This paper highlights non-destructive handheld methods to estimate foliar N status of plants.

Background: There is a need for field trials on testing agronomic potential of coal fly ash to engender routine use of this technology. Two field trials were undertaken with alkaline and acidic fly ashes supplied at between 3 and 6 Mg ha-1 to acidic soils and sown to wheat and canola at Richmond (Eastern Australia) and to wheat only at Merredin (Western Australia). Results: Ash addition marginally (P< 0.10) raised the pH in the top soil layers at both sites. The exceptionally dry season at both sites constrained yields and thwarted any likelihood of gaining yield benefits from ash-induced improvements in soil conditions. Yield improvements due to ash addition were absent at Merredin and only marginal at Richmond, where no elevated accumulation of B, Mo, Se, P or S in either the straw or seeds of wheat was observed; canola increased accumulation of Mo and Se in its shoot with acidic fly ash, but it was well below phyto toxic levels. Simulations of wheat using APSIM at Richmond over a 100-year period (1909-2008) predicted yield increases in 52% of years with addition of ash at 3.0 Mg ha-1 compared with 24% of years with addition of ash at 6.0 Mg ha-1. The simulated yield increases did not exceed 40% over the control with addition of 6 Mg ha-1 ash, but was between 40% and 50% with an addition rate of 3 Mg ha-1. Conclusion: We found no evidence of phytotoxicity in either crop in this unusually dry year and there is still a need for further field assessment in years with favourable rainfall to enable development of clear recommendations on fly ash rates for optimum yield benefits.© 2012 Society of Chemical Industry.

Healthy phytoplankton communities are the basis of healthy water ecosystems, and form the foundation of many freshwater food webs. Globally many freshwater ecosystems are degraded because of intensive human activities, so water ecosystem restoration is a burning issue worldwide. Selection of key regions for phytoplankton-related restoration is crucial for an effective aquatic eco-restoration. This paper presents a practical method for identification of key regions for phytoplankton-related restoration, using random forests (RFs) method to cluster sites based on dominance, biodiversity, water chemistry and ecological niche. We sampled phytoplankton for species richness and relative abundance and water quality in the Huai River basin (HRB), China to determine the phytoplankton communities' composition and structure and characterize of their ecological niches. A wider mean niche breadth of a species usually leads to a greater overlap with the niche of other species. Using these data and water quality indices, we identified the key regions for phytoplankton-related river restoration activities. Results indicate that our method for recognition of key regions is effective and practical and its application to the HRB identified the Northern Plain area as the key region for restoration. This area is severely polluted and contributes significantly to the HRB phytoplankton communities. Phytoplankton in this region is highly adaptable to environmental change and therefore will be relatively unharmed by environmental instability induced by restoration measures. During restoration, indices of water temperature, total phosphorus and chemical oxygen demand can be altered with little negative influence on phytoplankton communities, but measures that increase ammonia-nitrogen concentration would be highly detrimental. These results will provide valuable information for policy makers and stakeholders in water ecosystem restoration and sustainable basin management in the HRB. © 2011.

Leaf colour is usually used as a guide for assessments of nutrient status and plant health. We propose a new inexpensive, hand-held and easy-to-use technique for the detection of chlorophyll content and foliar nitrogen content in plants based on leaf colour. This method provides a rapid analysis and data storage at minimal cost and does not require any technical or laboratory skills. Most of the existing methods that examined relationships between chlorophyll status and leaf colour were developed for particular species. These methods acquire leaf images using digital cameras, which can be sensitive to lighting conditions (colour, angle, flux density) and hence, require proper calibration. Our method analyses leaf colour images obtained from a digital scanner that requires minimal calibration compared as it has its one light source and the angle and distance between light and leaf are constant. Our new algorithm produced superior correlations with the true value of foliar chlorophyll content measured in the laboratory compared with existing non-destructive methods when applied to three different species (lettuce, broccoli and tomato).

We propose in this paper a new method for measuring a number of leaf dimension parameters including height, width, average width, perimeter and area. A digital scanner is utilized to acquire leaf images, which unlike digital cameras, requires no calibration in terms of size and angle of the acquired images. Edge detection, filtering and thresholding algorithms are applied to identify the leaf section of the image against the background. Forty leaves that differ in shape and size were used to validate the estimated parameters against the true values and parameters produced by the popular Li-Cor 3100. Data indicated that the proposed method achieved a constantly high accuracy

Rising atmospheric concentrations of CO2 (Ca) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to Ca. We hypothesized that plants regulate stomatal conductance optimally in response to rising Ca. We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate-controlled whole-tree chambers for 2 years at ambient and elevated Ca. Elevated Ca was ambient + 240 ppm, 60% higher than ambient Ca. Leaf-scale gas exchange was measured throughout the second year of the study and leaf-scale ITE increased by 60% under elevated Ca, as predicted. Values of leaf-scale ITE depended strongly on vapour pressure deficit (D) in both CO2 treatments. Whole-canopy CO2 and H2O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between Ca treatments, which had important effects on values of canopy-scale ITE. However, when Ca treatments were compared at the same D, canopy-scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy-scale ITE were not significantly different, indicating that ITE was not scale-dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to Ca. The effect of elevated Ca on photosynthesis increased with rising D. At high D, Ca had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of Ca on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with Ca will allow us to predict the effects of Ca on transpiration rate.

A soil-plant-atmosphere model was used to estimate gross primary productivity (GPP) and evapotranspiration (ET) of a tropical savanna in Australia. This paper describes model modifications required to simulate the substantial C4 grass understory together with C3 trees. The model was further improved to include a seasonal distribution of leaf area and foliar nitrogen through 10 canopy layers. Model outputs were compared with a 5-year eddy covariance dataset. Adding the C4 photosynthesis component improved the model efficiency and root-mean-squared error (RMSE) for total ecosystem GPP by better emulating annual peaks and troughs in GPP across wet and dry seasons. The C4 photosynthesis component had minimal impact on modelled values of ET. Outputs of GPP from the modified model agreed well with measured values, explaining between 79% and 90% of the variance and having a low RMSE (0.003-0.281gCm -2day -1). Approximately, 40% of total annual GPP was contributed by C4 grasses. Total (trees and grasses) wet season GPP was approximately 75-80% of total annual GPP. Light-use efficiency (LUE) was largest for the wet season and smallest in the dry season and C4 LUE was larger than that of the trees. A sensitivity analysis of GPP revealed that daily GPP was most sensitive to changes in leaf area index (LAI) and foliar nitrogen (N f) and relatively insensitive to changes in maximum carboxylation rate (V cmax), maximum electron transport rate (J max) and minimum leaf water potential (ψ min). The modified model was also able to represent daily and seasonal patterns in ET, (explaining 68-81% of variance) with a low RMSE (0.038-0.19mmday -1). Current values of N f, LAI and other parameters appear to be colimiting for maximizing GPP. By manipulating LAI and soil moisture content inputs, we show that modelled GPP is limited by light interception rather than water availability at this site. © 2011 Blackwell Publishing Ltd.

Nocturnal water flux has been observed in trees under a variety of environmental conditions and can be a significant contributor to diel canopy water flux. Elevated atmospheric CO 2 (elevated [CO 2]) can have an important effect on day-time plant water fluxes, but it is not known whether it also affects nocturnal water fluxes. We examined the effects of elevated [CO 2] on nocturnal water flux of field-grown Eucalyptus saligna trees using sap flux through the tree stem expressed on a sapwood area (J s) and leaf area (E t) basis. After 19 months growth under well-watered conditions, drought was imposed by withholding water for 5 months in the summer, ending with a rain event that restored soil moisture. Reductions in J s and E t were observed during the severe drought period in the dry treatment under elevated [CO 2], but not during moderate- and post-drought periods. Elevated [CO 2] affected night-time sap flux density which included the stem recharge period, called 'total night flux' (19:00 to 05:00, J s,r), but not during the post-recharge period, which primarily consisted of canopy transpiration (23:00 to 05:00, J s,c). Elevated [CO 2] wet (EW) trees exhibited higher J s,r than ambient [CO 2] wet trees (AW) indicating greater water flux in elevated [CO 2] under well-watered conditions. However, under drought conditions, elevated [CO 2] dry (ED) trees exhibited significantly lower J s,r than ambient [CO 2] dry trees (AD), indicating less water flux during stem recharge under elevated [CO 2]. J s,c did not differ between ambient and elevated [CO 2]. Vapour pressure deficit (D) was clearly the major influence on night-time sap flux. D was positively correlated with J s,r and had its greatest impact on J s,r at high D in ambient [CO 2]. Our results suggest that elevated [CO 2] may reduce night-time water flux in E. saligna when soil water content is low and D is high. While elevated [CO 2] affected J s,r, it did not affect day-time water flux in wet soil, suggesting that the responses of J s,r to environmental factors cannot be directly inferred from day-time patterns. Changes in J s,r are likely to influence pre-dawn leaf water potential, and plant responses to water stress. Nocturnal fluxes are clearly important for predicting effects of climate change on forest physiology and hydrology. © 2011 The Author. Published by Oxford University Press. A ll rights reserved.

Elevated atmospheric [CO 2] (eCa) often decreases stomatal conductance, which may delay the start of drought, as well as alleviate the effect of dry soil on plant water use and carbon uptake. We studied the interaction between drought and eCa in a whole-tree chamber experiment with Eucalyptus saligna. Trees were grown for 18 months in their Ca treatments before a 4-month dry-down. Trees grown in eCa were smaller than those grown in ambient Ca (aCa) due to an early growth setback that was maintained throughout the duration of the experiment. Pre-dawn leaf water potentials were not different between Ca treatments, but were lower in the drought treatment than the irrigated control. Counter to expectations, the drought treatment caused a larger reduction in canopy-average transpiration rates for trees in the eCa treatment compared with aCa. Total tree transpiration over the dry-down was positively correlated with the decrease in soil water storage, measured in the top 1.5 m, over the drying cycle; however, we could not close the water budget especially for the larger trees, suggesting soil water uptake below 1.5 m depth. Using neutron probe soil water measurements, we estimated fractional water uptake to a depth of 4.5 m and found that larger trees were able to extract more water from deep soil layers. These results highlight the interaction between rooting depth and response of tree water use to drought. The responses of tree water use to eCa involve interactions between tree size, root distribution and soil moisture availability that may override the expected direct effects of eCa. It is essential that these interactions be considered when interpreting experimental results. © 2011 The Author. Published by Oxford University Press. A ll rights reserved.

Purpose: We tested the potential of using coal fly ash for improving the physical and hydrological characteristics of coarse and medium-textured agricultural soils. Materials and methods: Acidic (FWA) and alkaline (FNSW) fly ashes were used to amend a range of representative agricultural soils. In the first experiment, fly ash was applied to the top 10 cm of 1-m long intact cores of a sandy loam soil at rates of 0, 12, 36 or 108 Mg/ha and sown with canola; after harvest, bulk density (BD), aggregate stability and mean weight diameter (MWD) were measured on the soil. In the second experiment, we assessed water retention at field capacity (-300 kPa) and permanent wilting point (-1,500 kPa) for sandy and loamy soils amended with FNSW at 0.0-16% (w/w). The third experiment used rainfall simulation to assess erodibility of sandy and loamy soils mixed with FNSW at rates of 0, 5 or 20 Mg/ha. Results and discussion: In the first experiment, fly ash had no significant effect on MWD of the soil. The BD in the 0-10 cm layer (topsoil) was increased with addition of FWA, while FNSW applied at 108 Mg/ha reduced BD, relative to the control treatment. This was because FNSW had lower particle and bulk densities than FWA and the test soils. Ash addition increased macro-aggregation, significantly so in the 10-20 cm layer (subsurface layer), by reducing the percentages of micro-aggregates and silt + clay particles. Thus, macro-aggregation was positively correlated (p < 0.01) with MWD, but both were inversely correlated (p < 0.01) with micro-aggregates. In the second experiment, addition of fly ash enhanced plant water availability by increasing water retention at field capacity by threefold in the sandy soil and 1.5-fold in the loamy sand, but water retention at permanent wilting point was not affected. In Experiment 3, the addition of ash at 20 Mg/ha, but not at 5 Mg/ha, increased turbidity of runoff water from the amended soil due to the dispersal of fine particles by the impact of the simulated raindrops. Conclusions: Moderate rates of fly ash (

Revegetation to restore hydrological function to highly disturbed landscapes used for waste disposal or mining is often constrained by the initial low rates of water-use during the early phases of the developing vegetation. This problem is especially pronounced for revegetation that relies on trees due to their prolonged lead-time to achieve canopy closure. Initial low rates of water-use can however be overcome if a groundcover of quick-growing herbaceous species is planted first. To demonstrate the significance of groundcover in the early phase of revegetation, we undertook an energy balance analysis using the Bowen ratio technique for a juvenile plantation growing over a heavy groundcover of herbaceous species on a waste disposal site in 2006/2007 and 2007/2008. Latent heat flux (λE) from the landscape (trees plus groundcover and soil) fluctuated widely between 0.5 and 22MJm-2d-1 and accounted for between 60% and 90% of available energy at the site; this percentage exceeded 100% during periods with significant advection. The latent heat emanating from the tree canopy (λEc), derived from sapflow measurements in the trees, accounted for only between 4% and 18% of daily λE with the balance arising from the groundcover that intercepted more than 90% of incident solar radiation. The λEc was mostly smaller than the net radiation intercepted by the tree canopy (Rnc) with the excess energy expended by the canopy as sensible heat (Hc), which accounted for up to 18% of bulk sensible heat from the landscape. The λE expressed as ET was in excess (114%) of rainfall in the relatively dry first growing (September-May) season, when rainfall was only 87% of the long-term average. It was, however, smaller (80%) than rainfall during the second season, when the annual rainfall was close to the long-term average. We used these data to develop an empirical model for predicting λE from soil-water content and the prevailing evaporative demand. © 2010.