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Freshwater habitats are under stress from agricultural land use, most notably the influx of neonicotinoid pesticides and increased nutrient pressure from fertilizer. Traditional studies investigating the effects of stressors on freshwater systems are often limited to a narrow range of taxa, depending heavily on morphological expertise. Additionally, disentanglement of multiple simultaneous stressors can be difficult in field studies, whereas controlled laboratory conditions do not accurately reflect natural conditions and food webs. To overcome these drawbacks, we investigated the impacts of two agricultural stressors (the neonicotinoid insecticide thiacloprid and fertilizer) in full-factorial design in a semi-natural research site, using environmental DNA sampling to study three different taxonomic groups representing three trophic levels: bacteria (decomposers), phytoplankton (primary producers), and chironomids (consumers). The results show considerably impact of both stressors across trophic levels, with an additive effect of fertilizer and thiacloprid on community composition at all levels. These findings suggest that agricultural stressors affect the entire food web, either directly or through cascade reactions. They are also consistent with morphological assessments that were performed in the same study site, even at a lower number of replicates. The study presented shows that the use of multi-marker environmental DNA provides a more comprehensive assessment of stressor impacts across multiple trophic levels, at a higher taxonomic resolution than traditional surveys. Additionally, over a thousand putative novel bio-indicators for both agricultural stressors were discovered. We encourage further investigations into stressors impacts at different trophic levels, which will lead to more effective monitoring and management of freshwater systems.

Deciphering the spatial patterns of alpine treelines is critical for understanding the ecosystem processes involved in the persistence of tree species and their altitudinal limit. Treelines are thought to be controlled by temperature, and other environmental variables but they have rarely been investigated in regions with different land-use change legacies. Here, we systematically investigated treeline elevation in the Apennines (Italy) and Southern Alps (New Zealand) with contrasting human history but similar biogeographic trajectories, intending to identify distinct drivers that affect their current elevation and highlight their respective peculiarities. Over 3622 km of Apennines, treeline elevation was assessed in 302 mountain peaks and in 294 peaks along 4504 km of Southern Alps. The major difference between the Southern Alps and Apennines treeline limit is associated with their mountain aspects. In the Southern Alps, the scarcely anthropized Nothofagus treeline elevation was higher on the warmer equator-facing slopes than on the pole-facing ones. Contrary to what would be expected based on temperature limitation, the elevation of Fagus sylvatica treelines in the Apennines was higher on colder, pole-facing slopes than on human-shaped equator-facing, warmer mountainsides. Pervasive positive correlations were found between treeline elevation and temperature in the Southern Alps but not in the Apennines. While the position of the Fagus and Nothofagus treelines converge on similar isotherms of annual average temperature, a striking isothermal difference between the temperatures of the hottest month on which the two taxonomic groups grow exists. We conclude that actual treeline elevation reflects the ecological processes driven by a combination of local-scale topoclimatic conditions, and human disturbance legacy. Predicting dynamic processes affecting current and future alpine treeline position requires further insight into the modulating influences that are currently understood at a regional scale.

SummaryThe importance of intraspecific trait variation (ITV) in community dynamics is increasingly being recognised, but the drivers of ITV have not yet been well-studied. Here, we analysed whether environmental conditions, biotic interactions and species features are related to ITV on a global scale.We compiled a global species’ ITV database including 2064 species which occurred in 1068 communities (plots) across 19 countries with 11 functional traits. The magnitudes of species’ ITV in this database were calculated according to the trait-gradient analysis which is independent of the length of the environmental gradient.We found that different traits had different main drivers, so we consider the drivers of ITV to be trait-specific. However, our findings still brought some order among these idiosyncratic patterns: leaf economics spectrum traits were more related to environmental conditions and leaf morphology traits were more related to biotic interactions. Size-related traits were related to both abiotic and biotic conditions.Our research suggests that the drivers of ITV deviated from the drivers of the mean trait values and that some trait coordination may fall apart upon climate change. Thus, our analysis enhances our understanding of trait variation and has important implications for models predicting vegetation responses to environmental change.

SummaryPlants can respond to changing climatic conditions through genetic adaptation of their functional traits. Despite the relevance of adaptation to climate change, much remains unknown about plant genetic adaptation rates, including whether these rates differ among plant characteristics and trait types.We performed a meta-analysis to investigate patterns of genetic adaptation rates and assess how these rates differ among plant species groups, growth forms and trait types, using a newly compiled database from 74 studies, comprising 35 functional traits across 72 angiosperm species. This database specifically focuses on genetic adaptation of plant functional traits, as separating from phenotypic plasticity.Both annual and generational adaptation rates of plant traits decrease non-linearly with increasing elapsed time since divergence. Plants adapt fastest when first introduced to a changing environment, but these rates go slow subsequently. Overall, shrubs have higher adaptation rates than trees, which confers shrubs an adaptive advantage over trees. Different adaptation rates among growth forms, life histories and trait types suggest an important additional mechanism through which climate change may affect community composition.Our study has important implications regarding plant adaptation to new environments and will improve the prediction of vegetation responses and ecosystem functioning upon climate change.

Artificial light at night (ALAN) affects species' physiology and behaviour, and the interactions between species. Despite the importance of plants as primary producers, it remains poorly understood whether and how effects of ALAN on plants cascade through the food web. 2. We assess the extent to which ALAN of different spectra result in plant-mediated insect herbivory damage. In a 6-month field experiment, we exposed plants of differing palatability to three colours of ALAN and a dark control, and assessed plant traits (growth rate, leaf size, foliar density and thickness) and insect herbivory (represented by insect damage as loss of foliage to leaf-chewing insects, and gall abundance by phloem-feeding herbivory). 3. We found evidence for plant trait-mediated ALAN effects on herbivory for oak, but not for blueberry. In oak, ALAN of different colours changed the direction of relationships of insect damage with relative growth rate and with leaf thickness. Moreover, we found that the effects of ALAN on herbivory damage differed markedly between forest types within the same locale, particularly in the red light treatment. 4. Synthesis and applications. Our results provide evidence that continuous nighttime light, as provided by street lighting around the world, affects food web interactions. The nature of these effects differed by species and appeared to depend on forest type and the light spectrum employed, thus underlining the context dependency of ALAN in different ecosystems and environmental settings. These findings highlight the complexity of using spectral manipulation as a mitigation measure, and the need for further consideration of ALAN in environmental management and planning, to limit the exposure and impact of cascading effects of artificial light at night on food webs and communities.

Temperature is a critical environmental factor determining the upper limits of evergreen broadleaved tree taxa. However, whether carbon source or carbon sink limitation shapes this limit is not yet fully understood. We studied a subtropical evergreen oak (Cyclobalanopsis gracilis) at the northern limit of its distributional range. Along an elevational/temperature gradient towards its upper limit, we surveyed the variations in non-structural carbohydrate (NSC) concentrations of C. gracilis adults for 3 years. Additionally, a carbon balance manipulation experiment of debudding and defoliation was done to C. gracilis seedlings close to the upper distributional limit, aiming at investigating the changes in NSC concentrations and growth rates in different treatment groups. Our results showed that increasing elevation or decreasing temperature did not affect the trends of NSC concentration in twigs, old branches, or trunks of adults, nor did carbon balance manipulations (debudding or defoliation) of seedlings have a significant effect on the growth, while defoliation decreased NSC concentration in twigs. These results suggest that carbon sink limitation is the key physiological mechanism underlying low temperature in the shaping of this dominant evergreen broadleaved tree species in eastern China. Therefore, the formation of upper limits in evergreen oaks is most likely the result of a direct low-temperature restriction on meristematic activity and tissue formation instead of the result of insufficient carbon supply. More studies with expanded sample sizes are needed on other evergreen broadleaved tree species growing at their upper limits to confirm the carbon sink limitation hypothesis and reveal the detailed mechanisms.

Artificial light at night (ALAN) is one of the suggested drivers of the global decline in insects, including moths. ALAN strongly affects moth physiology and behaviour, but it remains unknown whether ALAN is a selective pressure that drives adaptation and evolution in moths. We assess whether feeding and calling behaviours of Yponomeuta cagnagellus moths are locally adapted to ALAN. Collected from locations that were either illuminated or dark at night-time for several decades, moths were exposed to different light intensities in a laboratory experiment. Male moths, but not female moths, fed less frequently in bright light than in dark or dim conditions. Female calling was less frequent in dimly or brightly lit conditions than in the dark treatment. Individuals from illuminated source populations showed increased feeding behaviour by males and marginally decreased calling behaviour by females. Our study suggests that ALAN affects the phenotypical calling behaviour by females and feeding behaviour by male moths of Y. cagnagellus but has not resulted in adaptation. Long-term ALAN conditions also affected feeding and marginally affected calling frequency. Reduced calling in lit conditions, perhaps driven by a reduced need for such behaviour because of an increase in visual cues or through the proximity of individuals in lit conditions, may result in long-term adaptation. Studies into more moth species are required to determine the extent to which a lack of adaptation to ALAN may contribute to current global declines in moth populations.

Background and Aims While trait-based approaches have provided critical insights into general plant functioning, we lack a comprehensive quantitative view on plant strategies in flooded conditions. Plants adapted to flooded conditions have specific traits (e.g. root porosity, low root/shoot ratio and shoot elongation) to cope with the environmental stressors including anoxic sediments, and the subsequent presence of phytotoxic compounds. In flooded habitats, plants also respond to potential nutrient and light limitations, e.g. through the expression of leaf economics traits and size-related traits, respectively. However, we do not know whether and how these trait dimensions are connected. Methods Based on a trait dataset compiled on 131 plant species from 141 studies in flooded habitats, we quantitatively analysed how flooding-induced traits are positioned in relation to the other two dominant trait dimensions: leaf economics traits and size-related traits. We evaluated how these key trait components are expressed along wetness gradients, across habitat types and among plant life forms. Key Results We found that flooding-induced traits constitute a trait dimension independent from leaf economics traits and size-related traits, indicating that there is no generic trade-off associated with flooding adaptations. Moreover, individual flooding-induced traits themselves are to a large extent decoupled from each other. These results suggest that adaptation to stressful environments, such as flooding, can be stressor specific without generic adverse effects on plant functioning (e.g. causing trade-offs on leaf economics traits). Conclusions The trait expression across multiple dimensions promotes plant adaptations and coexistence across multifaceted flooded environments. The decoupled trait dimensions, as related to different environmental drivers, also explain why ecosystem functioning (including, for example, methane emissions) are species and habitat specific. Thus, our results provide a backbone for applying trait-based approaches in wetland ecology by considering flooding-induced traits as an independent trait dimension.

There is widespread concern that cessation of grazing in historically grazed ecosystems is causing biotic homogenization and biodiversity loss. Here, we used 12 montane grassland sites along an 800-km north-south gradient across the United Kingdom, to test whether cessation of grazing affects local ɑ- and β-diversity of belowground food webs. We show that cessation of grazing leads to strongly decreased ɑ-diversity of both soil microbial and faunal diversity. In contrast, the β-diversity varied between groups of soil organisms. While soil microbial communities exhibited increased homogenization after cessation of grazing, we observed decreased homogenization for soil fauna after cessation of grazing. Overall, our results indicate that grazer exclusion from historically grazed montane grasslands has far-ranging consequences for the diversity and composition of belowground food webs, and underscore the importance of grazers for maintaining the diversity of belowground communities, which play a central role in ecosystem functioning.

There is a widespread concern that we are witnessing an ongoing homogenisation of ecological communities. However, in contrast to human impacts on spatial patterns in biodiversity, human impacts on the temporal aspects of β‐diversity have received little attention. Moreover, the interplay between spatial and temporal β‐diversity is poorly understood. To address this knowledge gap, we assessed dissimilarity within freshwater macrofaunal communities of drainage ditches to determine spatiotemporal β‐diversity as well as homogenisation in relation to different types of land use.We considered four distinct changes in community composition: spatial turnover, temporal turnover, spatial variation over time, and temporal variation in space, as well as the combined effects of space and time on β‐diversity. As a metric of dissimilarity, we calculated the taxonomic Hellinger distance between samples from different locations and time points and correlated these with distance in space and in time, as well as with three spatial variables, including land‐use type, and two temporal variables. We studied the effect of interactions between spatial and temporal variables on dissimilarity by applying a permutational analysis of variance.Our results illustrate the importance of changes in community composition in time with respect to temporal turnover, spatial variation over time, and temporal variation in space. While we did not find spatial turnover in community composition, both month and year had a considerable effect. Within a year, β‐diversity decreased over the months, yet these assembly patterns differed between years. This suggests major effects of seasonal and year‐to‐year dynamics on β‐diversity. Land use was also observed to be a main driver: ditches in nature conservation areas had higher β‐diversity and temporal heterogeneity was lowest in ditches adjacent to the most intensive agricultural land‐use category, indicating that agricultural practices can homogenise biodiversity in both space and time.By analysing the spatial and temporal β‐diversity patterns in freshwater macrofaunal communities in concert, we have shown that β‐diversity is a sensitive and highly informative metric of both spatial and temporal changes in community composition.

Some commonly reported trait-trait relationships between species, including the leaf economic spectrum (LES), are regarded as important plant strategies but whether these relationships represent plant strategies in reality remains unclear. We propose a novel approach to distinguish trait-trait relationships between species that may represent plant strategies vs those relationships that are the result of common drivers, by comparing the direction and strength of intraspecific trait variation (ITV) vs interspecific trait variation. We applied this framework using a unique global ITV database that we compiled, which included 11 traits related to LES, size and roots, and observations from 2064 species occurring in 1068 communities across 19 countries. Generally, compared to between species, trait-trait relationships within species were much weaker or totally disappeared. Almost only within the LES traits, the between-species trait-trait relationships were translated into positive relationships within species, which suggests that they may represent plant strategies. Moreover, the frequent coincidental trait-trait relationships between species, driven by co-varying common drivers, imply that in future research, decoupling of trait-trait relationships should be considered seriously in model projections of ecosystem functioning. Our study emphasizes the importance of describing the mechanisms behind trait-trait relationships, both between and within species, for deepening our understanding of general plant strategies.

While shifts to high-intensity land cover have caused overwhelming biodiversity loss, it remains unclear how important natural land cover is to the occurrence, and thus the conservation, of different species groups. We used over 4 million plant species’ observations to evaluate the conservation importance of natural land cover by its association with the occurrence probability of 1 122 native and 403 exotic plant species at 1 km resolution by species distribution models. We found that 74.9% of native species, 83.9% of the threatened species and 77.1% rare species preferred landscapes with over 50% natural land cover, while these landscapes only accounted for 15.6% of all grids. Most species preferred natural areas with a mixture of forest and open areas rather than areas with completely open or forested nature. Compared to native species, exotic species preferred areas with lower natural land cover and the cover of natural open area, but they both preferred extremely high and low cover of natural forest area. Threatened and rare species preferred higher natural land cover, either cover of natural forest area or cover of natural open area than not threatened and common species, but rare species were also more likely to occur in landscapes with 0–25% cover of natural open area. Although more natural land cover in a landscape will not automatically result in more native species, because there is often a non-linear increase in species occurrence probability when going from 0% to 100% natural land cover, for conserving purposes, over 80% natural land cover should be kept in landscapes for conserving threatened and very rare species, and 60% natural land cover is the best for conserving common native species. Our results stress the importance of natural areas for plant species’ conservation. It also informs improvements to species conservation by increasing habitat diversity.

The fish bioconcentration factor (BCF) is an important aspect within bioaccumulation assessments. Several factors have been suggested to influence BCF values – including species, developmental stage, mixture exposure, and calculation method. However, their exact contribution to variance in BCF values is unknown. Within this study we assessed the relative impact of these test characteristics on BCF values and analyzed the reproducibility of aquatic exposure bioconcentration tests.Linear mixed effects analyses were performed on a newly develop database to investigate the relationship between the response variable (i.e. lipid normalized log BCF values) and several test characteristics as fixed effects.Lower BCF values were observed for substances that were simultaneously applied with high molecular weight polycyclic aromatic hydrocarbons compared to single substance exposure (with an average difference of −0.81 log BCF). Also, lower BCFs upon kinetic determination were observed compared to steady-state BCFs (log BCF -0.27), and lower BCFs for species from the Ostariophysi subcohort level (log BCF -0.17 to −0.15). In addition, data analysis showed high variation within BCF values for single substances (average SD = log BCF 0.21), which questions the robustness of the current bioaccumulation assessments. For example, the 95% confidence range of a BCF value of 2500 ranges from 953 (‘not-bioaccumulative’) to 6561 (‘very bioaccumulative’).Our results show that the use of one single BCF leads to a high uncertainty in bioaccumulation assessments. We strongly recommend that within future bioconcentration studies, the used experimental design and test conditions are described in detail and justified to support solid interpretation.

Urban green space provides refuges for species that are unintentionally introduced by humans and which do not belong to the remnants of natural habitats in urban areas. However, the quantitative relationships between urban green space properties and these spontaneous species are unclear. To address this, we surveyed plant species occurring in urban green patches in Kunming city, which is located in a biodiversity hotspot in southwest China. We classified spontaneous plants into native, non-native and invasive plant species. A total of 386 spontaneous species belonging to 278 genera and 92 families were recorded in 190 patches. Most of the recorded species were herbaceous plants (76.2 %). While invasive species constituted a relatively small proportion of the total species pool (17.9 %), six out of ten of the most frequently occurring species were invasive. Regression models inspired by the theory of Island Biogeography show that total, native, non-native and invasive spontaneous species richness in urban green patches were best explained by the size of the ‘island’ (patch area), dispersal limitations (as expressed by ‘distance to city boundary’) and edge effects (as shown by the landscape shape index). While the set of drivers of spontaneous plants is similar for the different groups of species, the relative importance of each driver varies among them. Our study provides quantification of drivers of biodiversity patterns in urban green space. Based on this understanding, planning and management of urban green space can be adapted to maximize spontaneous plant conservation in rapidly urbanizing biodiversity hotspot regions.

While most models describing soil organic matter dynamics relate the turnover of soil organic matter to its chemical structure, there is increasing evidence that microbial accessibility to the organic matter is predominant in controlling its stability and its decay. This finding has major implications for forecasting the impacts of land management and climate change on soil organic carbon cycling and there is a need for further research to understand the role of microbial accessibility. Further progress is problematic because of difficulties in partitioning total soil respiration ( R S ) into its components soil heterotrophic respiration ( R H ) and soil autotrophic respiration ( R A ) in undisturbed ecosystems. To overcome this problem, we used an improved natural abundance of 13 C technique to partition R S into R H and R A at one and six months after irrigation and addition of nitrogen fertiliser treatments was imposed in a grassland ecosystem. Addition of nitrogen had no significant effect on the components of soil respiration compared with the values for the control. Irrigation resulted in differential effects on R H and R A , leading to strong differences in the proportion of R H contributing to R S (f R H ) with (mean ± standard error) 0.65 ± 0.09 and 0.30 ± 0.06 for the non-irrigated and irrigated plots, respectively, six months after the treatments began. R S and R A were strongly correlated and both showed strong linear relationships with gravimetric soil water content ( W S ) resulting in strong differences between irrigation treatments. Soil temperature ( T S ) and the amount of dissolved organic carbon were also correlated with both R S and R A . In contrast, R H was not related to variation in W S and T S but was correlated with the amounts of particulate organic matter carbon, a labile fraction of carbon defined as physically unprotected, and specific surface area, an indicator of soil protection capacity. There were, however, no differences in the labile carbon fraction and specific surface area between the irrigation treatments. We showed that R H was insensitive to irrigation and remained constant throughout the entire experimental period with a mean value of 1.7 ± 0.2 μmol m 2 s − 1 . Our findings support for the growing evidence that microbial accessibility to substrate, rather than its chemical structure, is predominant in regulating soil organic matter decomposition.

Since substrates for respiration are supplied mainly by recent photo-assimilates, there is a strong but time-lagged link between short-term above- and belowground carbon (C) cycling. However, regulation of this coupling by environmental variables is poorly understood. Whereas recent studies focussed on the effect of drought and shading on the link between above- and belowground short-term C cycling, the effect of temperature remains unclear. We used a 13CO2 pulse-chase labelling experiment to investigate the effect of a sudden temperature change from 25 to 10 °C on the short-term coupling between assimilatory C uptake and respiratory loss. The study was done in the laboratory using two-month-old perennial rye-grass plants (Lolium perenne L.). After label application, the δ13C signal of respired shoot and root samples was analysed at regular time intervals using laser spectroscopy. In addition, δ13C was analysed in bulk root and shoot samples. Cold temperature (10 °C) reduced the short-term coupling between shoot and roots by delaying belowground transfer of recent assimilates and its subsequent respiratory use, as indicated by the δ13C signal of root respiration (δ13CRR). That is, the time lag from the actual shoot labelling to the first appearance of the label in 13CRR was about 1.5 times longer under cold temperature. Moreover, analysis of bulk shoot and root material revealed that plants at cold temperature invest relatively more carbon into respiration compared to growth or storage. While the whole plant C turnover increased under cold temperature, the turnover time of the labile C pool decreased, probably because less 13C is used for growth and/or storage. That is, (almost) all recent C remained in the labile pool serving respiration under these conditions. Overall, our results highlight the importance of temperature as a driver of C transport and relative C allocation within the plant–soil system.

Desert ecosystems often structured in two distinct layers of woody and herbaceous plants. Changes in community composition alter the fractional coverage by bare soil, woody and herbaceous plants, with potential effects on water and carbon fluxes. We used eddy covariance measurements and chamber method in two similar shrub-dominated desert communities (Tamarix community and Haloxylon community) to assess inter- and intra-annual variations of ecosystem water use efficiency (EWUE) (where we distinguished whole ecosystem EWUE as EWUEE, and EWUE of shrub and herbaceous layers as EWUEShrub and EWUEHerb) in central Asia. In the Tamarix community, 11 years of carbon and water fluxes showed that years with larger herbaceous cover (referred to as shrub-herb years) had significant higher EWUEE than years with lower herbaceous cover (referred to as shrub years), with the values of 1.07 ± 0.11 vs. 0.68 ± 0.03 g C/kg H2O. There was a significant positive correlation between EWUEE and the maximum herbaceous plants cover. In the Haloxylon community, chamber measurements during a shrub year demonstrated that the shrub layer contributed most to the gross ecosystem productivity (GEP) and evapotranspiration (ET) of the system, with the herbaceous layer contributing around 30% at the beginning of the growing season, and decreasing to nearly zero during the middle and at the end of the growing season. The shrub layer EWUEShrub was significant higher than that in the herbaceous layer (EWUEHerb) throughout the growing season (1.82 ± 0.11 vs. 1.06 ± 0.32 g C/kg H2O). EWUEShrub was positively correlated with EWUEE, but there was no relationship between EWUEHerb and EWUEE in a shrub year. This study shows that the variability of the herbaceous layer across seasons and years in these desert ecosystems is crucial for predicting water and carbon cycling under ongoing and projected climatic change scenarios in shrub-dominated desert ecosystems.

Summary Labile soil organic matter (SOM) is often stabilized in soil, but is vulnerable to loss after soil disturbance. We used measurements of the 13carbon (13C) signature of soil-respired CO2 (δ13CO2) immediately after the disturbance caused by coring and sampling the soil, to assess labile SOM availability and potential vulnerability to loss. We incubated a range of pasture soils over 300 minutes and periodically measured δ13CO2. Strong temporal trends in δ13CO2 suggest that labile SOM became vulnerable to loss within minutes of soil disturbance. Equilibrium soil-respired δ13CO2 values were a function of the amount of labile SOM (measured as hot-water extractable C, HWEC), total soil C and soil protection capacity (measured as specific soil surface area, SSA). An independent experimental approach that immobilized labile SOM on to allophane (a clay mineral with a large active surface area) was used to assess the effect of SSA on equilibrium soil-respired δ13CO2. In this experiment δ13CO2 shifted progressively to more enriched values during the first six days of soil incubations after allophane addition, suggesting that labile SOM became less available after stabilization by allophane. At the same time there was a large reduction in HWEC when compared with the control treatments, also indicating limited availability of labile SOM. Further studies coupling the isotopic measurements with CO2 evolution rates are needed to test directly whether equilibrium δ13CO2 can reflect labile SOM vulnerability to loss.

Background and aims The response of plants and soil to rain pulses determines seasonal variations in the exchange of materials and energy at the ecosystem scale in arid and semi-arid regions. We assessed how the ecosystem carbon exchange (NEE) of desert halophyte communities of different plant functional-types responds to summer precipitation pulses in Tamarix and Haloxylon communities.

International audience; Temperature is a primary driver of the distribution of biodiversity as well as of ecosystem boundaries. Declining temperature with increasing elevation in montane systems has long been recognized as a major factor shaping plant community biodiversity, metabolic processes, and ecosystem dynamics. Elevational gradients, as thermoclines, also enable prediction of long-term ecological responses to climate warming. One of the most striking manifestations of increasing elevation is the abrupt transitions from forest to treeless alpine tundra However, whether there are globally consistent above-and belowground responses to these transitions remains an open question. To disentangle the direct and indirect effects of temperature on ecosystem properties, here we evaluate replicate treeline ecotones in seven temperate regions of the world. We find that declining temperatures with increasing elevation did not affect tree leaf nutrient concentrations, but did reduce ground-layer community-weighted plant nitrogen, leading to the strong stoichiometric convergence of ground-layer plant community nitrogen to phosphorus ratios across all regions. Further, elevation-driven changes in plant nutrients were associated with changes in soil organic matter content and quality (carbon to nitrogen ratios) and microbial properties. Combined, our identification of direct and indirect temperature controls over plant communities and soil properties in seven contrasting regions suggests that future warming may disrupt the functional properties of montane ecosystems, particularly where plant community reorganization outpaces treeline advance.

The impacts of grazing animals on the carbon balance of grasslands globally can potentially impact atmospheric carbon dioxide concentrations and soil carbon stocks. In this study, we measured net ecosystem CO2 exchange (FN) for two periods with contrasting environmental variables, in early and late summer. We used a closed dynamic chamber system for continuous measurements of the components of FN (gross canopy photosynthesis, A, and ecosystem respiration, RE, and its components: above-ground plant respiration, RL and soil respiration, RS). We calculated an empirical phytomass index (calculated Pi) from continuous measurements of FN to account for variability in above-ground biomass following grazing events. In addition, we developed a model for the phytomass index from environmental variables (modelled Pi’). Then, using cross validations, we tested the efficacy of calculated Pi and modelled Pi’ in improving environmental models for FN and its components. Grazing events affected A and RL significantly but did not result in changes in RS. Inclusion of the phytomass index (either calculated or modelled) increased the predictive performances of the models for A and RL, but not for RS. For both measurement periods, the ecosystem was a sink of CO2 with mean ± standard error (SE) rates of net uptake of 1.88 ± 0.23 and 1.47 ± 0.69 g C m−2 d−1 for the periods in early summer and in late summer, respectively. Overall, FN was poorly described by the models when the phytomass indices were not included. Estimates of FN using either the calculated or the modelled phytomass index over both periods were not significantly different from the measured values. We showed that the use of a modelled phytomass index can account for the effects of grazing well, and can be used to improve models to predict FN and the carbon balance for grazed grasslands under different climatic conditions and management practices.

Arid and semi-arid ecosystems dominated by shrubby species are an important component in the global carbon cycle but are largely under-represented in studies of the effect of climate change on carbon flux. This study synthesizes data from long-term eddy covariance measurements and experiments to assess how changes in ecosystem composition, driven by precipitation patterns, affect inter-annual variability of carbon flux and their components in a halophyte desert community dominated by deep-rooted shrubs (phreatophytes, which depend on groundwater as their primary water source). Our results demonstrated that the carbon balance of this community responded strongly to precipitation variations. Both pre-growing season precipitation and growing season precipitation frequency significantly affected inter-annual variations in ecosystem carbon flux. Heavy pre-growing season precipitation (November–April, mostly as snow) increased annual net ecosystem carbon exchange, by facilitating the growth and carbon assimilation of shallow-rooted annual plants, which used spring and summer precipitation to increase community productivity. Sufficient pre-growing season precipitation led to more germination and growth of shallow-rooted annual plants. When followed by high-frequency growing season precipitation, community productivity of this desert ecosystem was lifted to the level of grassland or forest ecosystems. The long-term observations and experimental results confirmed that precipitation patterns and the herbaceous component were dominant drivers of the carbon dynamics in this phreatophyte-dominated desert ecosystem. This study illustrates the importance of inter-annual variations in climate and ecosystem composition for the carbon flux in arid and semi-arid ecosystems. It also highlights the important effect of changing frequency and seasonal pattern of precipitation on the regional and global carbon cycle in the coming decades.

New Zealand treeline species have low frost tolerance compared to their northern hemisphere counterparts, and appear susceptible to out-of-season frosts. However, foliage from high altitude trees is rarely directly measured. This study compares seasonal frost tolerance of mature treeline trees with local temperatures to assess whether frost affects their performance. Photosystem efficiency and seasonal frost tolerance (temperatures causing 10% and 50% foliage mortality, LT10 and LT50, respectively) were measured on foliage from four native and one exotic species across the treeline ecotone. For all species, photosystem efficiency and frost tolerance were lower in spring and summer than in autumn. Frost tolerance changed with altitude only for exotic Pinus contorta in spring. Spring frosts regularly exceeded LT10 for all species. In all seasons over the last 20 years, the minimum temperature experienced was at least 4 °C warmer than the LT50; however, east of the Main Divide, a 1-in-40 year extrem...

Symbiotic associations between vascular plants and nitrogen-fixing bacteria are expected to be costly except when N availability is low. We tested the prediction that in low-N soils in dry climates, plants with nitrogen-fixing symbioses (N-fixing species) have higher growth rates, and occur relatively more frequently, than non-fixing species, In a pot experiment, we measured the growth and survival of 6 N-fixing and 8 non-fixing species across nitrogen and moisture gradients. Using plot survey data from the South Island, New Zealand, we then modelled the relative occurrence of N-fixing species using derived measures of temperature, soil N and moisture. Non-fixing species had higher relative growth rates than N-fixing species except when both total N and soil moisture were low. Low soil moisture increased the root:shoot ratio in N-fixing species more than twice that observed in non-fixing species. Soil moisture had a strong effect on mortality, which was slightly lower for N-fixing species. Survey data showed that a higher proportion of N-fixing species were present at cool, dry sites with low levels of soil N. In temperate climates, with geologically young landscapes, the influences of soil N and water on N availability are key factors determining the relative success of N-fixing and non-fixing species.

Can New Zealand’s indigenous dryland ecosystems be rehabilitated by facilitating inherent successional tendencies to enhance development of indigenous-dominated and often woody communities in the long term? Here, we describe the geographic distribution of woody communities of New Zealand’s South Island drylands to generate hypotheses about successional trajectories to future vegetation states. Presences and absences of woody species in 3880 vegetation plots collated from past surveys were used to predict species potential distributions across drylands. Separate models and spatial predictions were built for each of four classes of woody richness, which were used as surrogates for successional stages. Woody species richness increased significantly from grassland to shrubland and from shrubland to forest cover, and trends in species traits also suggest richness class was related with successional stage. Indigenous woody species outnumbered exotic species in all richness classes. Assuming richness cl...

Maintaining and increasing soil organic carbon stocks in grasslands is essential for sustainable productivity and to offset anthropogenic carbon emissions. Direct measurements of net ecosystem carbon dioxide exchange, FN, can be used to detect whether an ecosystem is a net sink or a source of carbon. However partitioning heterotrophic respiration, RH, from ecosystem respiration, RE, is needed to determine the impacts of land-use and global change on soil organic carbon stocks. We extracted intact soil cores from an intensively grazed dairy farm to establish mesocosms growing in controlled conditions and we subjected them to low and high nitrogen treatments (100 and 400 kgN ha1 y− 1, respectively). After concurrent clipping and addition of nitrogen, we measured the timing for the recovery of FN and its components, photosynthesis, A, and ecosystem respiration, RE, by measuring them daily. Subsequently, we measured RH from the same mesocosms seven days after the treatments were applied, using a non-disruptive, natural abundance carbon isotope technique. To test the significance of the presence of living roots when measuring RH, we compared the results obtained from the isotopic approach to those obtained from a root exclusion technique, which involved removing the roots from the mesocosms. As the plants grew after clipping, FN decreased (increasing net CO2 uptake) exponentially to mean (± standard error) steady-state values of 1.11 ± 0.26 μmol m− 2 s− 1 (net source) and − 0.19 ± 0.33 μmol m− 2 s− 1 (near neutral) for the low and high nitrogen treatments, respectively. When measured using the isotopic approach, RH increased by 60%, from 1.26 ± 0.29 μmol m− 2 s− 1 in the low, to 2.06 ± 0.55 μmol m− 2 s− 1 in the high nitrogen treatment. Thus, addition of the high nitrogen resulted in an increase in soil organic carbon loss concurrently with an increase in net uptake of carbon by the ecosystem in the high nitrogen treatment compared with the low nitrogen treatment. When measured in the absence of living roots using the root exclusion technique, RH was overall much higher than the value obtained with the isotopic technique (4.34 ± 0.13 μmol m− 2 s− 1), indicating an apparent negative rhizosphere priming effect. Furthermore, when using the root exclusion technique, no difference was found between the nitrogen treatments, suggesting that the presence of roots mediated the response of heterotrophic respiration to addition of nitrogen. These results highlight the need to include measurements of changes in RH alongside measurements of FN in non-disturbed ecosystems to interpret the processes regulating the effects of management practices on long-term changes in soil organic carbon stocks.

Climate change and invasive species threaten global food security and native biodiversity. Individually, they can degrade resources and ecosystem services, and increase management costs. Together, they can produce complex effects, such as facilitating range expansion of invasive species. Climate change may also constrain the ability to manage invasive mammalian species by directly disrupting optimal strategies for control. Invasive species are often most susceptible to anthropogenic control methods when natural food is limiting. We demonstrate quantitatively how a trend towards warmer winters over the past >60 years has significantly reduced the window of time for effective control of an invasive mammalian pest (European rabbit Oryctolagus cuniculus) in temperate New Zealand. The phenomenon described is likely generalizable to the control of other vertebrate pests, particularly in temperate systems where they are seasonally food limited. Climate change may thus exacerbate the unwanted impacts of invasive species by reducing our ability to manage them effectively.

This paper was commissioned by the members of the Ecosphere Editorial Board to commemorate the ESA Centennial celebration.

Three types of fossil fern fronds bearing sporangia with in situ spores are described from the late Eocene Pikopiko Fossil Forest, southern New Zealand. They are referable to the extant fern genus Thelypteris subgenus Cyclosorus (Thelypteridaceae) and an extinct fern of uncertain affinity. The matching of Thelypteris (Cyclosorus) macrofossils to the spore form taxon Laevigatosporites ovatus is recognised for the first time. Five additional fern taxa, including another probable Blechnum, are distinguished on the basis of sterile foliage. The Pikopiko site is one of the richest known Cenozoic fern floras globally and the diversity and abundance of ferns (eight fern macrofossil parataxa and 20 miospore types) implies that ferns dominated the evergreen, tall forest understorey as in modern New Zealand rainforests. At least 40% of modern New Zealand fern families are represented in this 35 Ma flora and the discovery of fronds with in situ spores of a type recorded throughout the Cenozoic in New Zealand supports a long history for some fern genera in the region. The abundance of ferns, epiphyllous fungi on many leaves and the presence of palms is evidence for warm humid conditions in Late Eocene New Zealand.

The near‐continuous record of the New Zealand terrestrial flora since the landmass broke away from Gondwana provides an excellent opportunity to assess the history of the pteridophyte flora in the region. A database of all published records of fossil ferns from the late Cretaceous onwards is presented, along with references to original reports. This compilation provides evidence for the time of arrival for fern lineages, continuity of their presence, and times of radiation, thereby greatly assisting the reconstruction of the history and biogeography of ferns in the region. Additionally, it provides a valuable source of lineage age estimates, which are required to calibrate the molecular clock for much needed molecular studies on pteridophytes.