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Productivity and ecosystem carbon (C) storage are often positively associated with species and/or structural diversity; however, positive relationships in tropical forests and woodlands are not universal and the strength of this relationship may be affected by climate. Diversity-productivity relationships were evaluated in upland and seasonally flooded savanna (Cerrado) of the Cuiaba Basin and Northern Pantanal in southern Mato Grosso, Brazil. Data on wood C increment, tree species composition, and alpha diversity were measured over a 10-year period in nine communities located in the Cerrado-Pantanal transition zone. Communities were composed of a wide spectrum of tropical savanna physiognomies, including mixed grassland (campo sujo), typical wooded savanna (stricto sensu), dense wooded savanna (cerrado denso), seasonal forest (mata seca and mata ciliar), and riparian forest (mata de galeria). We hypothesized that tree species richness and diversity would increase from grassland to forest. We further hypothesized that there would be a positive relationship between woody C storage and diversity, but the strength of this relationship would be higher in wet years and wetter environments, such as the Pantanal, due to an increase in water availability. We found that tree species richness and diversity did not increase from mixed grasslands to forests, as mixed grasslands and riparian forests had similarly low levels of tree species richness and diversity compared to the other physiognomies. However, the rate of annual aboveground wood C increment was positively related to species richness and alpha diversity, and the positive relationship was primarily observed during wet years when the annual precipitation was at, or above, the long-term average for the region. Presumably, the impact of structural and species diversity on productivity declines during dry years when water availability becomes a more important control on stem C increment for tree species in the Cerrado-Pantanal transition. These data suggest that maintenance of diversity in these Cerrado woodlands and forests is important for maximizing aboveground C gain. However, climate change, which is causing warming and drying for the region, may limit the importance of diversity on wood C storage. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition is enriching soils with N across biomes. Soil N enrichment can increase plant productivity and affect microbial activity, thereby increasing soil organic carbon (SOC), but such responses vary across biomes. Drylands cover ~45% of Earth's land area and store ~33% of global SOC contained in the top 1 m of soil. Nitrogen fertilization could, therefore, disproportionately impact carbon (C) cycling, yet whether dryland SOC storage increases with N remains unclear. To understand how N enrichment may change SOC storage, we separated SOC into plant‐derived, particulate organic C (POC), and largely microbially derived, mineral‐associated organic C (MAOC) at four N deposition experimental sites in Southern California. Theory suggests that N enrichment increases the efficiency by which microbes build MAOC (C stabilization efficiency) if soil pH stays constant. But if soils acidify, a common response to N enrichment, then microbial biomass and enzymatic organic matter decay may decrease, increasing POC but not MAOC. We found that N enrichment had no effect on C fractions except for a decrease in MAOC at one site. Specifically, despite reported increases in plant biomass in three sites and decreases in microbial biomass and extracellular enzyme activities in two sites that acidified, POC did not increase. Furthermore, microbial C use and stabilization efficiency increased in a non‐acidified site, but without increasing MAOC. Instead, MAOC decreased by 16% at one of the sites that acidified, likely because it lost 47% of the exchangeable calcium (Ca) relative to controls. Indeed, MAOC was strongly and positively affected by Ca, which directly and, through its positive effect on microbial biomass, explained 58% of variation in MAOC. Long‐term effects of N fertilization on dryland SOC storage appear abiotic in nature, such that drylands where Ca‐stabilization of SOC is prevalent and soils acidify, are most at risk for significant C loss. [ABSTRACT FROM AUTHOR]

Urban landscaping conversions can alter decomposition processes and soil respiration, making it difficult to forecast regional CO2 emissions. Here we explore rates of initial mass loss and net nitrogen (N) mineralization in natural and four common urban land covers (waterwise, waterwise with mulch, shrub, and lawn) from sites across seven colleges in southern California. We found that rates of decomposition and net N mineralization were faster for high-N leaf substrates, and natural habitats exhibited slower rates of decomposition and mineralization than managed urban landcovers, especially lawns and areas with added mulch. These results were consistent across college campuses, suggesting that our findings are robust and can predict decomposition rates across southern California. While mechanisms driving differences in decomposition rates among habitats in the cool-wet spring were difficult to identify, elevated decomposition in urban habitats highlights that conversion of natural areas to urban landscapes enhances greenhouse gas emissions. While perceived as sustainable, elevated decomposition rates in areas with added mulch mean that while these transformations may reduce water inputs, they increase soil carbon (C) flux. Mimicking natural landscapes by reducing water and nutrient (mulch) inputs and planting drought-tolerant native vegetation with recalcitrant litter can slow decomposition and reduce regional C emissions. [ABSTRACT FROM AUTHOR]

Estimates of net primary (NPP) and ecosystem production (NEP) are needed for tropical savanna, which is structurally diverse but understudied compared to tropical rainforest. We used eddy covariance and inventory methods to estimate carbon (C) fluxes for an upland mixed grassland and a seasonally flooded forest to determine the correspondence between these methods and assess the contribution of C cycling components to the total NPP. Both techniques provided similar estimates of net ecosystem CO2 exchange (−3.0 ‒ 2.3 MgC ha−1 y−1 for eddy covariance vs. −2.0 ‒ 4.3 MgC ha−1 y−1 for inventory), gross primary production (7.5–16.3 MgC ha−1 y−1 for eddy covariance vs. 8.7–18.4 MgC ha−1 y−1 for inventory), and total NPP (0.9–7.5 MgC ha−1 y−1 for eddy covariance vs. 2.0–9.5 MgC ha−1 y−1 for inventory). Belowground NPP accounted for 49%–53% of the total NPP for both ecosystems, followed by aboveground litter (26%–27%) and wood (16%–17%) production. Increases in water availability increased the potential for C storage, but the mechanism was different in the savanna types. Compared to other savanna ecosystems, the mixed grassland had a lower productivity and C use efficiency (CUE = NPP/GPP = 0.28), while the Cerrado forest had a high CUE (0.58) and similar C flux rates to other tropical savanna forests. The agreement in the C cycle estimates derived from the eddy covariance and inventory methods increases our confidence in the productivity estimates for these tropical savanna ecosystems. Plain Language Summary: Estimates of net primary and ecosystem production are needed for tropical savannas, which are highly diverse but understudied compared to tropical forests. Several methods have been used to measure primary and ecosystem production; however, these approaches have errors and uncertainties. We used available methods to estimate the productivity of a grass‐dominated savanna in the southern Amazon Basin and a seasonally flooded forest in the northern Pantanal to assess the correspondence in the productivity estimated from these methods and evaluate the contribution of above and belowground processes to the overall ecosystem productivity. Productivity estimates derived from the different techniques were similar. Belowground processes accounted for 49%–53% of the productivity followed by leaf (26%–27%) and wood (16%–17%) production. Increases in water availability increased the productivity for both savanna types, but for different reasons. An increase in soil moisture caused an increase productivity in the mixed grassland but a decline in carbon losses from the seasonally flooded forest. Compared to other savanna ecosystems, the mixed grassland had lower productivity while the forest had high productivity. While our measurements are spatially and temporally limited, the broad agreement in the different methods increases our confidence in the productivity estimates for these tropical savanna ecosystems. Key Points: Estimates of C cycling from inventory and eddy covariance methods were similar for two floristically different tropical savannas of BrazilBelowground NPP was 49%–53% of the total NPP for both ecosystems, followed by aboveground litter (26%–27%) and wood (16%–17%) productionThe grass dominated savanna had a low C use efficiency (CUE = NPP/GPP = 0.28) while the Cerrado forest had a CUE = 0.58 [ABSTRACT FROM AUTHOR]

The spatial and temporal distribution of precipitation is of great importance for the rain-fed agricultural production and the socioeconomics of Mato Grosso (MT), Brazil. MT has a sparse network of ground rain gauges that limits the effective use of precipitation information for sustainable agricultural production and water resources in the region. Several gridded precipitation products from remote sensing and reanalysis of land surface models are currently available that can enhance the use of such information. However, these products are available at different spatial and temporal resolutions which add some challenges to stakeholders (users) to identify their appropriateness for specific applications (e.g., irrigation requirements, length of growing season, and drought monitoring). Thus, it is necessary to provide an assessment of the reliability of these precipitation estimates. The objective of this work was to compare regional precipitation estimates over MT as provided by the Global Land Data Assimilation (GLDAS), Modern-Era Retrospective Analysis for Research and Applications (MERRA), Tropical Rainfall Measurement Mission (TRMM), Global Precipitation Measurement (GPM), and the Global Precipitation Climatology Project (GPCP) with ground-based measurements. The comparison was conducted for the 2000–2018 period at eleven ground-based weather stations that covered different climate zones in MT using daily, monthly, and annual temporal resolutions. The comparison used the Pearson correlation index–r, Willmott index–d, root mean square error—RMSE, and the Wilks methods. The results showed GPM and GLDAS estimates did not differ significantly with the measured daily, monthly, and annual precipitation. TRMM estimates slightly overestimated daily precipitation by about 4.7% but did not show significant difference on the monthly and annual scales when compared with local measurements. The GPCP underestimated annual precipitation by about 7.1%. MERRA underestimated daily, monthly, and annual precipitation by about 22.9% on average. In general, all products satisfactorily estimated monthly precipitation, and most of them satisfactorily estimated annual precipitation; however, they showed low accuracy when estimating daily precipitation. The TRMM, GPM, GPCP, and GLDAS estimates had the highest performance, from high to low, while MERRA showed the lowest performance. The findings of this study can be used to support the decision-making process in the region in application related to water resources management, sustainability of agriculture production, and drought management. [ABSTRACT FROM AUTHOR]

Tropical forests and savanna account for nearly 65% of the total global terrestrial net primary production (NPP); however, there are still large uncertainties in tropical forest NPP because of limited field measurements, especially in the structurally diverse Brazilian savanna (cerrado). To address this uncertainty, we measured patterns of aboveground wood C stocks (Cw) and rates of wood C storage (ΔCw) over a 7‐year period for cerrado forests and woodlands of southern Mato Grosso, Brazil, arrayed across hydrological and soil fertility gradients. We focused on ΔCw because it is an important component of NPP, and wood is a stable, long‐term, C storage reservoir. Annual rates of ΔCw were significantly affected by estimates of P and cation (K and Ca) availability, and analysis of covariance indicated that relationships between ΔCw and nutrient availability were independent of stand hydrology. Both upland and hyperseasonal stands exhibited a decline in ΔCw during the 2015–16 El Niño event, which was exceptionally warm and dry. A limited analysis of the uncertainty associated with the field measurements ranged from 7% for wood density to 24% for tree density, while the uncertainty associated with derived quantities ranged from 10% for tree height to 41% for Cw. Overall, these results suggest that soil fertility and annual precipitation are important drivers of ΔCw and that warming and drying associated with climate change will cause a decline in aboveground woody C storage for these, and similar, tropical forests and woodlands. Plain Language Summary: Tropical forests and savannas are important reservoirs for global carbon (C) storage, but there are still uncertainties in how much C is stored in these ecosystems, especially for savanna. We measured the amount and rate of C stored in aboveground wood for forests and woodlands of the Brazilian savanna in the southern part of the Amazon Basin. Rates of wood C storage increased as nutrient availability increased, and C storage declined during drought years for both seasonally flooded and non‐flooded forests and woodlands. These results have implications for how climate and land‐use change alter wood C storage in these globally important ecosystems. Key Points: Cerrado forests and woodlands store 0.16–2.62 MgC • ha−1 • y−1 in aboveground woodWood C storage increased as P and cation (K and Ca) availability increasedWood C storage declined during the 2015–16 El Niño in seasonally flooded and upland cerrado [ABSTRACT FROM AUTHOR]

Wetlands are important sources of methane (CH4) and sinks of carbon dioxide (CO2). However, little is known about CH4 and CO2 fluxes and dynamics of seasonally flooded tropical forests of South America in relation to local carbon (C) balances and atmospheric exchange. We measured net ecosystem fluxes of CH4 and CO2 in the Pantanal over 2014–2017 using tower‐based eddy covariance along with C measurements in soil, biomass and water. Our data indicate that seasonally flooded tropical forests are potentially large sinks for CO2 but strong sources of CH4, particularly during inundation when reducing conditions in soils increase CH4 production and limit CO2 release. During inundation when soils were anaerobic, the flooded forest emitted 0.11 ± 0.002 g CH4‐C m−2 d−1 and absorbed 1.6 ± 0.2 g CO2‐C m−2 d−1 (mean ± 95% confidence interval for the entire study period). Following the recession of floodwaters, soils rapidly became aerobic and CH4 emissions decreased significantly (0.002 ± 0.001 g CH4‐C m−2 d−1) but remained a net source, while the net CO2 flux flipped from being a net sink during anaerobic periods to acting as a source during aerobic periods. CH4 fluxes were 50 times higher in the wet season; DOC was a minor component in the net ecosystem carbon balance. Daily fluxes of CO2 and CH4 were similar in all years for each season, but annual net fluxes varied primarily in relation to flood duration. While the ecosystem was a net C sink on an annual basis (absorbing 218 g C m−2 (as CH4‐C + CO2‐C) in anaerobic phases and emitting 76 g C m−2in aerobic phases), high CH4 effluxes during the anaerobic flooded phase and modest CH4 effluxes during the aerobic phase indicate that seasonally flooded tropical forests can be a net source of radiative forcings on an annual basis, thus acting as an amplifying feedback on global warming. [ABSTRACT FROM AUTHOR]

Although seasonal and temporal variations in evapotranspiration (ET) in Amazonia have been studied based upon flux-tower data and coarse resolution satellite-based models, ET dynamics over human-impacted landscapes are highly uncertain in this region. In this study, we estimate ET rates from critical land cover types over highly fragmented landscapes in the southern Amazon and characterize the ET dynamics during the dry season using the METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. METRIC, a Landsat-based ET model, that generates spatially continuous ET estimates at a 30 m spatial resolution widely used for agricultural applications, was adapted to the southern Amazon by using the NDVI indexed reference ET fraction (ETrF) approach. Compared to flux tower-based ET rates, this approach showed an improved performance on the forest ET estimation over the standard METRIC approach, with R2 = 0.73 from R2 = 0.70 and RMSE reduced from 0.77 mm/day to 0.35 mm/day. We used this approach integrated into the METRIC procedure to estimate ET rates from primary, regenerated, and degraded forests and pasture in Acre, Rondônia, and Mato Grosso, all located in the southern Amazon, during the dry season in 2009. The lowest ET rates occurred in Mato Grosso, the driest region. Acre and Rondônia, both located in the southwestern Amazon, had similar ET rates for all land cover types. Dry season ET rates between primary forest and regenerated forest were similar (p > 0.05) in all sites, ranging between 2.5 and 3.4 mm/day for both forest cover types in the three sites. ET rates from degraded forest in Mato Grosso were significantly lower (p < 0.05) compared to the other forest cover types, with a value of 2.03 mm/day on average. Pasture showed the lowest ET rates during the dry season at all study sites, with the dry season average ET varying from 1.7 mm/day in Mato Grosso to 2.8 mm/day in Acre. [ABSTRACT FROM AUTHOR]

Aims: We tested two mechanisms of adaptation to extreme hydrological stresses (flooding and drought) of species making up a tropical wetland plant community by measuring leaf gas exchange and water potential. We hypothesized that anoxic conditions that occur during flooding will decrease leaf gas exchange when compared to the dry season, and that 'super-dominant' specie swill have a distinctive physiological advantage when compared to other plants within the community. Location: Northern Pantanal wetland, Private Natural Heritage Reserve of the Brazilian Social Service of Commerce (RPPN-SESC Pantanal), Mato Grosso, Brazil. Methods: Two periods representing typical extreme hydrological conditions in the Pantanal wetland were selected based on historical soil and meteorological measurements: (1) a drought period when plants experience stress due to soil moisture deficits during a dry season that persists for several months (May to Sept), and (2) a flooding period when oxidation-reduction potential is negative for 30 d or more (Mar or Apr), indicating anoxic stress. Measurements of gas exchange and leaf water potential were made on seven species in drought and flood stress conditions. The seven species represent the majority of the plant community. Results: As a whole, the plant community showed significantly lower potential net photosynthesis (PN) during flooding when soil oxidation-reduction potential reached close to -900mV when compared to the dry season, but the magnitude of the decline in PN was species specific. Not all super-dominant species showed higher PN compared to non-dominant species, but they did demonstrate higher stomatal conductance and transpiration leading to lower water use efficiency. The combination of higher PN despite low soil water content suggests that the plant community had access to deep water resources. This access was also confirmed by the midday leaf water potential, which was similar for the flood and dry seasons. Conclusions: Results suggest that the plant community may have high physiological performance under a wide range of soil oxidation-reduction potentials. Higher PN rates of super-dominant species indicate a physiological advantage of these species in the different hydrological conditions. [ABSTRACT FROM AUTHOR]

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High atmospheric N inputs to southern Californian shrublands can alter organic matter quantity and quality and influence decomposition and N mineralization rates. We conducted a laboratory experiment to test the hypothesis that N addition would increase microbial respiration and net N mineralization. Intact soil cores and litter from Artemisia californica Less, were collected from field plots exposed to either ambient or elevated N (50 kg N ha-1 yr-1) over a 7-yr period. Microbial respiration was significantly higher in control soil, and litter amendment, regardless of origin, significantly increased respiration. In contrast, net N mineralization was significantly higher in added N soil, and litter addition significantly depressed net N mineralization. Our results suggest that chronic N deposition causes a decline in litter decomposition and microbial N demand. If indicative of the longer-term decomposition kinetics, these results suggest that chronic N inputs may increase soil C storage and N availability in these semiarid shrublands. [ABSTRACT FROM AUTHOR]

The Pantanal is a large and diverse wetland that spans three South American countries including parts of Brazil, Paraguay, and Bolivia. An invasive tree, Vochysia divergens Pohl (commonly known as Cambara), has been expanding throughout the Pantanal for more than four decades forming monospecific stands. Given the rapid and extensive spread of Cambara, and the potential for woody plant invasion to alter soil organic matter and nutrient stocks, we hypothesized that Cambara invasion would significantly increase soil organic matter and nutrient content. To test this hypothesis we sampled the soil, litter, and vegetation of a monospecific Cambara stand, a grassland (campo) stand in the process of Cambara invasion (transitional), and a campo stand free of Cambara during the dry season in July and August of 2009 and 2010 when stands were free from seasonal flooding. Surface (0-10 cm) soil in sites dominated by Cambara had significantly higher soil organic matter (SOM), P, and cation content, and higher cation exchange capacity (CEC), but soil pH and K+ concentration were less coincident with Cambara presence. The variation of soil characteristics was also significantly higher in the transitional site, indicating that the transition from a grassland- to a Cambara-dominated system significantly increased the spatial variability of soil chemistry. These results indicate that Cambara invasion fundamentally alters the C and nutrient storage of Panatanal soils. Future research will investigate if these results are general for Cambara invasion and address mechanisms of how Cambara invasion affects the nutrient cycling and storage of Pantanal soils. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition in heavily polluted southern Californian shrublands is estimated to be 20-45 kg Nha-1yr-1, but more exposed locales can receive as much as 145 kg Nha-1yr-1. This large anthropogenic N input has the capacity to alter the composition of plant communities. We conducted N-fertilization experiments in chaparral and coastal sage scrub (CSS) stands over a five-year period to test the hypothesis that plant community composition would change in response to dry-season N addition because of an increase in the relative abundance of herbaceous plant species. Our results indicate that dry-season addition of N significantly altered the community composition of CSS but not chaparral. Contrary to our original hypothesis, changes in community composition were due to changes in the relative abundance of dominant shrubs and not herbaceous plant species. Given that community-level responses to changes in resource availability may take years to decades in order to fully materialize, our results suggest that continued dry-season-input of N will cause even larger changes in community composition over time. These results have implications for plant species composition and diversity of mediterranean-type shrublands as N deposition increases with population growth and fossil-fuel use. [ABSTRACT FROM AUTHOR]

Anthropogenic nitrogen (N) deposition is a globally important source of N that is expected to increase with population growth. In southern California, N input from dry deposition accumulates on vegetation and soil surfaces of chaparral and coastal sage scrub (CSS) ecosystems during the summer and fall and becomes available as a pulse following winter rainfall. Presumably, N input will act to stimulate the productivity and N storage of these Mediterranean-type, semi-arid shrublands because these ecosystems are thought to be N limited. To assess whether dry-season N inputs alter ecosystem productivity and N storage, a field experiment was conducted over a 4-year period where plots were exposed to either ambient N deposition (control) or ambient + 50 kgN ha−1 y−1 (added N) that was added as NH4NO3 during the fall dry-season of each year. Plots exposed to added N had significantly higher accumulation of NH4 and NO3 on ion exchange resins that was due in part to direct fertilization and N mineralization, and the increase in N availability lead to a significant increase in NO3 leaching in chaparral but not CSS. Nitrogen addition also lead to an increase in litter and tissue N concentration and a decline in the C:N ratio, but failed to alter the ecosystem productivity and N storage of the chaparral and CSS shrublands over the 4-year study period. The reasons for the lack of a treatment response are unknown; however, it is possible that these semi-arid shrublands are not N limited, cannot respond rapidly enough to capture the ephemeral N pulse, are limited by other nutrients, or the N response is dependent on the amount and/or distribution of rainfall. These results have important implications for understanding the potential effects of anthropogenic N deposition on the C and N cycling and storage of Mediterranean-type, semi-arid shrublands. [ABSTRACT FROM AUTHOR]

Deforestation and climate change have the capacity to alter rainfall regimes, water availability, and surface-atmosphere flux of water and energy of tropical forests, especially in ecotonal, semi-deciduous tropical forests of the southern Amazon Basin, which have experienced rapid regional warming and deforestation over the last three decades. To reduce uncertainty regarding current and future energy and water flux, micrometeorological measurements of latent ( Qe) and sensible heat flux ( Qh) and canopy conductance ( Gc) were combined with measurements of sap flux density ( Fd) and maximum leaf conductance ( gsmax) to characterize the seasonal controls on mass (H2O) and energy exchange of an ecotonal, semi-deciduous forest in northern Mato Grosso, Brazil over the 2005-2006 annual cycle. Average diel patterns and daily rates of energy flux and conductance declined during the dry season; however, the decline in Fd and Qe was smaller and/or more gradual than Gc and gsmax. Weekly averages of transpiration calculated from sap flow measurements during the dry-wet season transition period were positively correlated (r2 = 0.47; p < 0.05; n = 11) with estimates of leaf area index (LAI) derived from the Modis-Aqua satellite platform while estimates of evapotranspiration ET derived from eddy covariance were not, presumably because these estimates also include an evaporation component. Overall, our results suggest that access to deep water reserves can support high rates of Fd and Qe during the dry season, but because of high evaporative demand, declines in plant water potential lead to a corresponding decline in Gc. Furthermore, seasonal variations in LAI, that are likely to be controlled in part by plant water status and phenology, constrain tree and stand transpiration. Thus the consistency of Qe over the annual cycle appears to be the result of trade-offs between water availability (rainfall, soil moisture, water potential), canopy structural properties (LAI), and meteorological conditions including vapor pressure deficit and net radiation. [ABSTRACT FROM AUTHOR]

Semiarid chaparral and coastal sage shrublands of southern California have been exposed to high levels of atmospheric N for decades, which has the capacity to increase both N and C storage and cycling in these N-limited systems. Thus we hypothesize that soil C and N mineralization will be higher in areas that have been exposed to high atmospheric N deposition. This hypothesis was tested in a 50-wk laboratoiy incubation experiment where the inorganic N (NH4 + NO3) and CO2 production of chaparral and coastal sage soils were repeatedly measured. Soil was incubated in the dark at a constant temperature of 25°C and a soil moisture of 0.25 kg H2O kg-1 dry soil (65% water-filled pore space). Relative differences in N deposition exposure between the study sites were quantified by repeatedly rinsing and collecting the N accumulated on branch surfaces during 1 yr. Temporal trends in cumulative C and N mineralization were best described by single-pool first-order and zero-order models, respectively. Total N mineralization, but not C mineralization, increased linearly with relative N deposition, and NO3 accounted for 95% of the total inorganic N accumulated during the 50-wk incubation. The soil δ15N natural abundance increased with relative N deposition (r = 0.85, P < 0.05) and the soil C/N ratio declined with relative N deposition (r = -0.74, P < 0.05), suggesting that N deposition exposure enhanced N mineralization in part because of increases in the soil organic matter quality (i.e., lower C/N ratio). Furthermore, soil C storage declined as a function of relative N deposition exposure, indicating that high atmospheric N inputs are not likely to stimulate soil C storage in these semiarid ecosystems. [ABSTRACT FROM AUTHOR]

Large inputs of atmospheric N from dry deposition accumulate on vegetation and soil surfaces of southern Californian chaparral and coastal sage scrub (CSS) ecosystems during the late-summer and early-fall and become available as a pulse following winter rainfall; however, the fate of this dry season atmospheric N addition is unknown. To assess the potential for dry season atmospheric N inputs to be incorporated into soil and/or vegetation N pools, an in situ N addition experiment was initiated in a post-fire chaparral and a mature CSS stand where 10 × 10 m plots were exposed to either ambient N deposition (control) or ambient +50 kg N ha−1 (added N) added as NH4NO3 during a single application in October 2003. After 1 year of N addition, plots exposed to added N had significantly higher accumulation of extractable inorganic N (NH4−N + NO3−N) on ion exchange resins deployed in the 0–10 cm mineral soil layer and higher soil extractable N in the subsurface (30–40 cm) mineral soil than plots exposed to ambient N. Chaparral and CSS shrubs exposed to added N also exhibited a significant increase in tissue N concentration and a decline in the tissue C:N ratio, and added N significantly altered the shrub tissue δ 15N natural abundance. Leaching of inorganic N to 1 m below the soil surface was on average 2–3 times higher in the added N plots, but large within treatment variability cause these differences to be statistically insignificant. Although a large fraction of the added N could not be accounted for in the shrub and soil N pools investigated, these observations suggest that dry season N inputs can significantly and rapidly alter N availability and shrub tissue chemistry in Mediterranean-type chaparral and CSS shrublands of southern California. [ABSTRACT FROM AUTHOR]

Measurements of ecosystem gas exchange, meteorology, and hydrology (rainfall and soil moisture) were used to assess the seasonal patterns of, and controls on, average diel (24 h) net ecosystem CO2 exchange (NEE), evapotranspiration (E), and bulk canopy water vapor conductance (Gc) of a tropical transitional (ecotonal) forest in the Brazilian Amazon. Diel trends in E and NEE were almost completely explained by the diel variation in photosynthetic photon flux density (QPPFD), and while the QPPFD response of E varied little over the annual cycle, the QPPFD response of NEE declined substantially during the dry season, and the magnitude of hysteresis in the NEE-QPPFD response increased as well. The magnitude of the residuals for the QPPFD versus NEE response was significantly negatively correlated with total monthly rainfall and surface soil moisture and positively correlated with the maximum daily temperature and atmospheric vapor pressure deficit (V). Average daily Gc was also significantly correlated with average daily V (r= -0.72) and soil moisture (r = 0.62), suggesting strong stomatal control of NEE during drought. However, drought reduced ecosystem CO2 efflux relatively more than CO2 assimilation, suggesting that the seasonal variation in NEE was largely driven by seasonal variation in respiration. When compared with other tropical forests, seasonality in NEE was negatively correlated with annual rainfall and positively correlated with dry-season length. The relatively high sensitivity of NEE to seasonal variation in climate and water availability has profound implications for C cycling dynamics under novel climates resulting from climate and/or land-use change in the Amazon basin. [ABSTRACT FROM AUTHOR]

The article presents a study which quantifies the net ecosystem carbon dioxide exchange (NEE) of a 28-30 meters tall transitional tropical forest of the Brazilian Amazon using tower-based eddy covariance. The use of nonlinear statistical models to evaluate daily variations in ecophysiological parameters and offer annual estimates of NEE, gross ecosystem carbon dioxide exchange , and respiration is stated. It is inferred that variations in soil water content impacts canopy photosynthesis.

This research utilized tower-based eddy covariance to quantify the trends in net ecosystem mass (CO2 and H2O vapor) and energy exchange of important land-cover types of NW Mato Grosso during the March-December 2002 seasonal transition. Measurements were made in a mature transitional (ecotonal) tropical forest near Sinop, Mato Grosso, and a cattle pasture near Cotriguaçú Mato Grosso, located 500km WNW of Sinop. Pasture net ecosystem CO2 exchange (NEE) was considerably more variable than the forest NEE over the seasonal transition, and the pasture had significantly higher rates of maximum gross primary production in every season except the dry-wet season transition (September-October). The pasture also had significantly higher rates of whole-ecosystem dark respiration than the forest during the wetter times of the year. Average (±95% CI) rates of total daily NEE during the March-December 2002 measurement period were 26±15 mmol m-2day-1 for the forest (positive values indicate net CO2 loss by the ecosystem) and -38±26mmol m-2 day-1 for the pasture. While both ecosystems partitioned more net radiation ( Rn) into latent heat flux ( Le), the forest had significantly higher rates of Le and lower rates of sensible heat flux ( H) than the pasture; a trend that became more extreme during the onset of the dry season. Large differences in pasture and forest mass and energy exchange occurred even though seasonal variations in micrometeorology (air temperature, humidity, and radiation) were relatively similar for both ecosystems. While the short measurement period and lack of spatial replication limit the ability to generalize these results to pasture and forest regions of the Amazon Basin, these results suggest important differences in the magnitude and seasonal variation of NEE and energy partitioning for pasture and transitional tropical forest. [ABSTRACT FROM AUTHOR]

Abstract The spatial and temporal patterns in CO2 flux for the Kuparuk River Basin, a 9200-km2 watershed located in NE Alaska were estimated using the Regional Arctic CO2 Exchange Simulator (RACES) for the 1994–1995 growing seasons. RACES uses non-linear models and a Geographical Information System database (GIS) consisting of the normalized difference vegetation index (NDVI) and dynamic temperature and radiation maps. The spatial and temporal patterns in the NDVI during both growing seasons suggest that ecosystem development occurred 2–4 weeks earlier and was relatively more rapid in the southern portion of the Kuparuk River Basin. Rates of gross primary production (GPP) and whole-ecosystem respiration (R) were 2–4 fold higher in the southern basin than along the arctic coastal plain depending on time of year. The higher rate of GPP estimated for the southern basin was primarily due to higher NDVI values, while the higher R estimated for the southern basin was due in part to higher temperature and the NDVI. While GPP and R showed strong latitudinal trends, spatial and temporal trends in net ecosystem CO2 exchange (NEE) were much more variable. Thus, while spatial trends in carbon gain (GPP) and loss (R) were highly correlated, small spatial and temporal differences in these large fluxes (GPP and/or R) lead to corresponding large spatial variations in the NEE. [ABSTRACT FROM AUTHOR]

Presents a study which calculated the Priestley-Taylor coefficient for eddy covariance tower sites with contrasting vegetation, soil moisture and temperature characteristics on the North Slope of Alaska over the 1994 and 1995 growing seasons. Variability of the alpha coefficient in the arctic; Comparison between towers.

The seasonal pattern of evapotranspiration (expressed as latent heat flux Q e) for a 28- to 30-m-tall tropical transitional (ecotonal) forest was quantified over an annual cycle using eddy covariance measurement and micrometeorological estimation techniques. The study was conducted near the city of Sinop, in northern Mato Grosso, Brazil, which is located within the ecotone of tropical rain forest and savanna (cerrado). Although the majority of net radiation ( Q*) was consumed by Q e (50-90%), seasonal variations in Q e were large and positively correlated with precipitation. Total daily Q e for the dry season (June-September) was on average 6.0 MJ m−2 d−1, while daily Q e for the transition (October-November and April-May) and wet (December-March) season periods were 7.5 and 10.0 MJ m−2 d−1, respectively. The seasonal variation in midday (0900-1500 LT) surface conductance ( g s) was also positively correlated with precipitation. Analysis of the 'decoupling factor' (Ω) indicated that the forest was strongly coupled to the atmosphere (Ω = 0.1-0.3) over the dry season and transition periods, suggesting that Q e was under relatively strong stomatal control. Although rainfall during the study period was above the long-term (30-year) average, our results indicate that the seasonal dynamics of Q e for the tropical transitional forest were more comparable to tropical savanna than to rain forest. [ABSTRACT FROM AUTHOR]

Describes a scaling approach applied for measuring the net carbon dioxide flux to provide an estimate of the net exchange during the 1994-1996 annual cycle for the Kuparuk Basin. Use of carbon flux data as input for the calculation of gross primary production; Indications that were received from basin-wide estimates of net carbon dioxide about the level of different categories of tundra; Comparison between estimates of carbon dioxide exchange received by direct measurement and scaling method.

Presents a study of the acclimation of ecosystem carbon dioxide exchange in the Alaskan Arctic region in response to decadal climate warming. Thoughts on the effect of continued warming of the ecosystem; Methods; Impact that the warming has on such things as the changes in nutrient cycling, physiological acclimation, and population and community reorganization; Results; Conclusions.

The article focuses on a study related to physiological models for the measurement of carbon dioxide flux in arctic Tundra Landscape. Topics discussed include requirement of arctic ecosystem carbon dioxide in exchange soil carbon, impact of climatic changes on arctic ecosystem, and use of gross primary production (GPP), whole-ecosystem respiration (R) and air temperature for photosynthetic photon flux density.

Discusses the use of eddy covariance to measure the net carbon dioxide (CO2) exchange and energy balance of a moist-tussock tundra ecosystem at Happy Valley, Alaska, during the 1994-1995 growing seasons. Diel trend in net radiation; Diel pattern of net CO2 exchange; Meteorological and physiological controls on evapotranspiration.

In situ manipulations were conducted in a naturally drained lake on the arctic coastal plain near Prudhoe Bay, Alaska (70 °21.98′ N, 148 °33.72′ W) to assess the potential short-term effects of decreased water table and elevated temperature on net ecosystem CO[sub 2] flux. The experiments were conducted over a 2-year period, and during that time, water table depth of drained plots was maintained on average 7 cm lower than the ambient water table, and surface temperatures of plots exposed to elevated temperature were increased on average 0.5 °C. Water table drainage, and to a lesser extent elevated temperature, resulted in significant increases in ecosystem respiration (ER) rates, and only small and variable changes in gross ecosystem productivity (GEP). As a result, drained plots were net sources of approx. 40 gC m[sup –2] season[sup –1] over both years of manipulation, while control plots were net sinks of atmospheric CO[sub 2] of about 10 gC m[sup –2] season[sup –1] (growing season length was an estimated 125 days). Control plots exposed to elevated temperatures accumulated slightly more carbon than control plots exposed to ambient temperatures. The direct effects of elevated temperature on net CO[sub 2] flux, ER, and GEP were small, however, elevated temperature appeared to interact with drainage to exacerbate the amount of net carbon loss. These data suggest that many currently saturated or nearly saturated wet sedge ecosystems of the north slope of Alaska may become significant sources of CO[sub 2] to the atmosphere if climate change predictions of increased evapotranspiration and reduced soil water status are realized. There is ample evidence that this may be already occurring in arctic Alaska, as a change in net carbon balance has been observed for both tussock and wet-sedge tundra ecosystems over the last 2–3 decades, which coincides with a recent increase in surface temperature and a... [ABSTRACT FROM AUTHOR]

Focuses on the measuring of landscape-scale fluxes of CO2 H2O vapor and energy in moist-wet sedge tundra ecosystems of coastal arctic Alaska, using Eddy covariance. Information on net and interannual variation; Details on the coastal tundra landscapes.

Reports on the significant difference in net ecosystem carbon balance of wet sedge ecosystems in the Barrow Alaska region observed between carbon dioxide flux measurements obtained in 1971 and measurements made during the 1991-1992 growing seasons. Increase in surface temperatures resulting in decreases in the soil moisture status.

The Brazilian savanna (Cerrado) has been heavily impacted by agricultural activities over the last four to five decades, and reliable estimates of reference evapotranspiration (ETo) are needed for water resource management and irrigation agriculture. The Penman–Monteith (PM) is one of the most accepted models for ETo estimation, but it requires many inputs that are not commonly available. Therefore, assessing the FAO guidelines to compute ETo when meteorological data are missing could lead to a better understanding of which variables are critically important for reliable estimates of ETo and how climatic variables are related to water requirements and atmospheric demands. In this study, ETo was computed for a grass-dominated part of the Cerrado from April 2010 to August 2019. We tested 12 different scenarios considering radiation, relative humidity, and/or wind speed as missing climatic data using guidelines given by the FAO. Our results presented that wind speed and actual vapor pressure do not affect ETo estimates as much as the other climatic variables; therefore, in the Cerrado's conditions, wind speed and relative humidity measurements are less required than temperature and radiation data. When radiation data were missing, the computed ETo was overestimated compared to the benchmark. FAO procedures to estimate the net radiation presented good results during the wet season; however, during the dry season, their results were overestimated because the method could not estimate negative Rn. Our results indicate that radiation data have the highest impact on ETo for our study area and presumably for regions with similar climatic conditions. In addition, those FAO procedures for estimating radiation are not suitable when radiation data are missing. [ABSTRACT FROM AUTHOR]

Tropical forests and savanna (cerrado) are important carbon (C) sinks; however, few data exist for seasonally flooded forests. We quantified the annual rates of aboveground net primary production (ANPP) over a five-year period for two forests, an upland mixed forest and a seasonally flooded cerrado forest, located in the northern Pantanal region of Brazil. We hypothesized that rates of ANPP would be higher for the mixed forest than the cerrado forest because seasonal flooding can limit rates of tree growth. ANPP was calculated as the sum of the annual litter production measured from litterfall traps and the stem growth increment measured from dendrometers and tree density. ANPP varied between 3.8–5.5 MgC ha−1 y−1 for the flooded forest and 1.6–4.6 MgC ha−1 y−1 for the upland forest. Litter production accounted for 57% of the ANPP, and the difference in ANPP between the upland and flooded forests was due to consistently higher litter production in the flooded forest. Annual variations in ANPP were not correlated with annual precipitation, presumably because the hydrology of these sites is driven more by the flood stage of the Cuiaba River than by local precipitation. However, consistent declines in forest floor litter mass occurred at both sites, suggesting that C storage may be responding to some unknown disturbance that occurred prior to our sampling campaign. Seasonal variation in rainfall exerted an important control on litter production dynamics, with leaf litter production increasing during the dry season and stem and reproductive litter production increasing during the wet season. While there are few studies of seasonally flooded tropical forests, our data suggest that the seasonally flooded and upland forests of the northern Pantanal can act as appreciable aboveground C sinks. [ABSTRACT FROM AUTHOR]

Climate change has the capacity to alter water availability and the litter production of tropical forests, which will alter rates of carbon (C) cycling and storage. We conducted a short-term field experiment in two hydrologically diverse forests in the Brazilian Pantanal to assess the initial response of litter decomposition and soil respiration (Rsoil) to variations in litter pool size. Total annual Rsoil and decomposition significantly declined with litter removal and increased with litter addition, but the rate of litter decomposition was highest for plots where litter was removed. Rsoil was positively related to soil organic matter content and the rate of litter decomposition, but not soil moisture or temperature, suggesting that the litter treatment effects on decomposition and Rsoil were due to changes in C availability and not litter effects on the soil environment (i.e., temperature and moisture). Rsoil was not significantly different between the forests studied here even though they had large differences in hydrology; however, litter decomposition was significantly higher in seasonally flooded forest, especially when augmented with litter. These results suggest that alterations in litter production from land use and/or climate change will alter short-term rates of decomposition and Rsoil for these and other floodplain forests of the Pantanal and Amazon Basin. [ABSTRACT FROM AUTHOR]