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Microbes are essential for the functioning of all ecosystems, and as global warming and anthropogenic pollution threaten ecosystems, it is critical to understand how microbes respond to these changes. We investigated the climate response of Sphingomonas, a widespread gram-negative bacterial genus, during an 18-month microbial community reciprocal transplant experiment across a Southern California climate gradient. We hypothesized that after 18 months, the transplanted Sphingomonas clade and functional composition would correspond with site conditions and reflect the Sphingomonas composition of native communities. We extracted Sphingomonas sequences from metagenomic data across the gradient and assessed their clade and functional composition. Representatives of at least 12 major Sphingomonas clades were found at varying relative abundances along the climate gradient, and transplanted Sphingomonas clade composition shifted after 18 months. Site had a significant effect (PERMANOVA; P < 0.001) on the distribution of both Sphingomonas functional (R2 = 0.465) and clade composition (R2 = 0.400), suggesting that Sphingomonas composition depends on climate parameters. Additionally, for both Sphingomonas clade and functional composition, ordinations revealed that the transplanted communities shifted closer to the native Sphingomonas composition of the grassland site compared with the site they were transplanted into. Overall, our results indicate that climate and substrate collectively determine Sphingomonas clade and functional composition.IMPORTANCESphingomonas is the most abundant gram-negative bacterial genus in litter-degrading microbial communities of desert, grassland, shrubland, and forest ecosystems in Southern California. We aimed to determine whether Sphingomonas responds to climate change in the same way as gram-positive bacteria and whole bacterial communities in these ecosystems. Within Sphingomonas, both clade composition and functional genes shifted in response to climate and litter chemistry, supporting the idea that bacteria respond similarly to climate at different scales of genetic variation. This understanding of how microbes respond to perturbation across scales may aid in future predictions of microbial responses to climate change.

In Eucalyptus plantations, coppice rotations often yield less than initial rotations. The TECHS project (Tolerance of Eucalyptus Clones to Hydric, Thermal and Biotic Stresses) studied short rotation coppicing across a 3000 km gradient. The main objective of this work was to compare the survival, sprouting, and initial growth of Eucalyptus clones managed and to examine factors that might influence the productivity of the coppice rotation: climate, genotypes, and stocking. Eight of the TECHS sites spread from latitudes 6° S to 30° S were included in the coppice study, with 17 genotypes at each site. The initial rotation had been planted at a 3 m × 3 m spacing and also in a spacing trial at densities from 500 to 3500 trees ha−1. Six months after harvesting the initial Eucalyptus rotation, average survival was 88%, with tropical clones showing over twice the sprouting biomass (6.7 vs. 2.9 Mg ha−1) and four times the woody biomass compared to subtropical clones (4.7 vs. 1.1 Mg ha−1). Greater initial water deficits had stronger sprouting and growth. Clones with higher belowground carbon allocation in the initial rotation performed better in coppicing, and precipitation became more influential after 12 months. Drought and spacing trials significantly affected growth. [ABSTRACT FROM AUTHOR]

The response of vegetation to climate change on a large scale should be studied at the community level rather than the species level. This necessitates a focused exploration of emerging spatial patterns. Here, we surveyed 264 sites in the Inner Mongolia typical steppe, using the "needling" method to investigate 39,600 clumps formed through the coexistence relationships of dominant species. We found that the effects of slow climate change on grassland communities can be categorized into two general trends: (1) a monotone relationship, characterized by changes in the number of dominant species, compositional diversity, and optimal patch area, and (2) a unimodal relationship, reflected in variations in the number of patches and interspecific associations. The two distinct trends, connected by optimal patch area, concurrently support both the habitat amount hypothesis and the intermediate disturbance hypothesis. These findings suggest that climate change indirectly influences the area and amount of vegetation patches by regulating the arrangement of clumps. Moreover, they indicate that it is the distribution, rather than the number, of species that serves as the front line for plant communities adapting to climate change. [ABSTRACT FROM AUTHOR]

BACKGROUND: This study investigates factors contributing Amaranthus albus control failure in processing tomato fields in northern Israel. The study region is characterized by a significant climate gradient from east to west, providing the opportunity to investigate the effect of critical elements of the agricultural environment, e.g., temperature. Eight populations were collected from commercial fields in this region. Post‐emergence herbicide efficacy of metribuzin, a photosystem II inhibitor, and rimsulfuron, an acetolactate synthase (ALS) inhibitor, was assessed through dose–response analyses at various growth stages. Temperature effects on control efficacy and resistance mechanisms were also explored. RESULTS: Standard metribuzin dose (X) was ineffective on A. albus plants with more than six true‐leaves, whereas 2X dose proved effective. Rimsulfuron at 16X dose was ineffective on plants with more than four true‐leaves. We report here the first case of target site resistance to ALS inhibitors in A. albus, due to point mutation in the ALS gene (Pro197 to Leu). Furthermore, our findings suggest potential involvement of CYT P450 enzymes in enhanced metabolizing of rimsulfuron. An overall decrease in dry weight was observed in response to both herbicides at 16/22 °C (P < 0.0001). Rimsulfuron was effective against only one population when applied at 28/34 °C. A possible fitness cost associated with target site‐resistant biotypes was observed under low temperature conditions, leading to effective control. CONCLUSION: This regional‐scale study highlights the challenges faced by growers, emphasizes the need for adapting management practices to the local climatic conditions and lays the groundwork for implementing location‐specific weed management strategies in commercial fields. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Abstract The response of vegetation to climate change on a large scale should be studied at the community level rather than the species level. This necessitates a focused exploration of emerging spatial patterns. Here, we surveyed 264 sites in the Inner Mongolia typical steppe, using the “needling” method to investigate 39,600 clumps formed through the coexistence relationships of dominant species. We found that the effects of slow climate change on grassland communities can be categorized into two general trends: (1) a monotone relationship, characterized by changes in the number of dominant species, compositional diversity, and optimal patch area, and (2) a unimodal relationship, reflected in variations in the number of patches and interspecific associations. The two distinct trends, connected by optimal patch area, concurrently support both the habitat amount hypothesis and the intermediate disturbance hypothesis. These findings suggest that climate change indirectly influences the area and amount of vegetation patches by regulating the arrangement of clumps. Moreover, they indicate that it is the distribution, rather than the number, of species that serves as the front line for plant communities adapting to climate change.

Abstract Purpose Trailing-edge populations at the low-latitude, receding edge of a shifting range face high extinction risk from climate change unless they are able to track optimal environmental conditions through dispersal. Methods We fit dispersal models to the locations of 3165 individually-marked black-throated blue warblers (Setophaga caerulescens) in the southern Appalachian Mountains in North Carolina, USA from 2002 to 2023. Black-throated blue warbler breeding abundance in this population has remained relatively stable at colder and wetter areas at higher elevations but has declined at warmer and drier areas at lower elevations. Results Median dispersal distance of young warblers was 917 m (range 23–3200 m), and dispersal tended to be directed away from warm and dry locations. In contrast, adults exhibited strong site fidelity between breeding seasons and rarely dispersed more than 100 m (range 10–1300 m). Consequently, adult dispersal kernels were much more compact and symmetric than natal dispersal kernels, suggesting adult dispersal is unlikely a driving force of declines in this population. Conclusion Our findings suggest that directional natal dispersal may mitigate fitness costs for trailing-edge populations by allowing individuals to track changing climate and avoid warming conditions at warm-edge range boundaries.

Premise: We assessed changes in traits associated with water economy across climatic gradients in the ecologically similar peat mosses Sphagnum cuspidatum and Sphagnum lindbergii. These species have parapatric distributions in Europe and have similar niches in bogs. Sphagnum species of bogs are closely related, with a large degree of microhabitat niche overlap between many species that can be functionally very similar. Despite this, ecologically similar species do have different distributional ranges along climatic gradients that partly overlap. These gradients may favor particular Sphagnum traits, especially in relation to water economy, which can be hypothesized to drive species divergence by character displacement. Methods: We investigated traits relevant for water economy of two parapatric bryophytes (Sphagnum cuspidatum and S. lindbergii) across the border of their distributional limits. We included both shoot traits and canopy traits, i.e., collective traits of the moss surface, quantified by photogrammetry. Results: The two species are ecologically similar and occur at similar positions along the hydrological gradient in bogs. The biggest differences between the species were expressed in the variations of their canopy surfaces, particularly surface roughness and in the responses of important traits such as capitulum mass to climate. We did not find support for character displacement, because traits were not more dissimilar in sympatric than in allopatric populations. Conclusions: Our results suggest that parapatry within Sphagnum can be understood from just a few climatic variables and that climatic factors are stronger drivers than competition behind trait variation within these species of Sphagnum. [ABSTRACT FROM AUTHOR]

Purpose: Trailing-edge populations at the low-latitude, receding edge of a shifting range face high extinction risk from climate change unless they are able to track optimal environmental conditions through dispersal. Methods: We fit dispersal models to the locations of 3165 individually-marked black-throated blue warblers (Setophaga caerulescens) in the southern Appalachian Mountains in North Carolina, USA from 2002 to 2023. Black-throated blue warbler breeding abundance in this population has remained relatively stable at colder and wetter areas at higher elevations but has declined at warmer and drier areas at lower elevations. Results: Median dispersal distance of young warblers was 917 m (range 23–3200 m), and dispersal tended to be directed away from warm and dry locations. In contrast, adults exhibited strong site fidelity between breeding seasons and rarely dispersed more than 100 m (range 10–1300 m). Consequently, adult dispersal kernels were much more compact and symmetric than natal dispersal kernels, suggesting adult dispersal is unlikely a driving force of declines in this population. Conclusion: Our findings suggest that directional natal dispersal may mitigate fitness costs for trailing-edge populations by allowing individuals to track changing climate and avoid warming conditions at warm-edge range boundaries. [ABSTRACT FROM AUTHOR]

Drought‐induced groundwater decline and warming associated with climate change are primary threats to dryland riparian woodlands. We used the extreme 2012–2019 drought in southern California as a natural experiment to assess how differences in water‐use strategies and groundwater dependence may influence the drought susceptibility of dryland riparian tree species with overlapping distributions. We analyzed tree‐ring stable carbon and oxygen isotopes collected from two cottonwood species (Populus trichocarpa and P. fremontii) along the semi‐arid Santa Clara River. We also modeled tree source water δ18O composition to compare with observed source water δ18O within the floodplain to infer patterns of groundwater reliance. Our results suggest that both species functioned as facultative phreatophytes that used shallow soil moisture when available but ultimately relied on groundwater to maintain physiological function during drought. We also observed apparent species differences in water‐use strategies and groundwater dependence related to their regional distributions. P. fremontii was constrained to more arid river segments and ostensibly used a greater proportion of groundwater to satisfy higher evaporative demand. P. fremontii maintained ∆13C at pre‐drought levels up until the peak of the drought, when trees experienced a precipitous decline in ∆13C. This response pattern suggests that trees prioritized maintaining photosynthetic processes over hydraulic safety, until a critical point. In contrast, P. trichocarpa showed a more gradual and sustained reduction in ∆13C, indicating that drought conditions induced stomatal closure and higher water use efficiency. This strategy may confer drought avoidance for P. trichocarpa while increasing its susceptibility to anticipated climate warming. Key Points: Dryland riparian cottonwoods used shallow soil moisture when available but ultimately relied on groundwater for survival during droughtSpecies had different water‐use strategies related to their distribution along a gradient of increasing aridity with distance from coastPopulus trichocarpa appears more susceptible to warming, and P. fremontii more vulnerable to groundwater decline due to high water demand [ABSTRACT FROM AUTHOR]

Dryland riparian woodlands are considered to be locally buffered from droughts by shallow and stable groundwater levels. However, climate change is causing more frequent and severe drought events, accompanied by warmer temperatures, collectively threatening the persistence of these groundwater dependent ecosystems through a combination of increasing evaporative demand and decreasing groundwater supply. We conducted a dendro-isotopic analysis of radial growth and seasonal (semi-annual) carbon isotope discrimination (Δ13 C) to investigate the response of riparian cottonwood stands to the unprecedented California-wide drought from 2012 to 2019, along the largest remaining free-flowing river in Southern California. Our goals were to identify principal drivers and indicators of drought stress for dryland riparian woodlands, determine their thresholds of tolerance to hydroclimatic stressors, and ultimately assess their vulnerability to climate change. Riparian trees were highly responsive to drought conditions along the river, exhibiting suppressed growth and strong stomatal closure (inferred from reduced Δ13 C) during peak drought years. However, patterns of radial growth and Δ13 C were quite variable among sites that differed in climatic conditions and rate of groundwater decline. We show that the rate of groundwater decline, as opposed to climate factors, was the primary driver of site differences in drought stress, and trees showed greater sensitivity to temperature at sites subjected to faster groundwater decline. Across sites, higher correlation between radial growth and Δ13 C for individual trees, and higher inter-correlation of Δ13 C among trees were indicative of greater drought stress. Trees showed a threshold of tolerance to groundwater decline at 0.5 m year-1 beyond which drought stress became increasingly evident and severe. For sites that exceeded this threshold, peak physiological stress occurred when total groundwater recession exceeded ~3 m. These findings indicate that drought-induced groundwater decline associated with more extreme droughts is a primary threat to dryland riparian woodlands and increases their susceptibility to projected warmer temperatures.

In Eucalyptus plantations, coppice rotations often yield less than initial rotations. The TECHS project (Tolerance of Eucalyptus Clones to Hydric, Thermal and Biotic Stresses) studied short rotation coppicing across a 3000 km gradient. The main objective of this work was to compare the survival, sprouting, and initial growth of Eucalyptus clones managed and to examine factors that might influence the productivity of the coppice rotation: climate, genotypes, and stocking. Eight of the TECHS sites spread from latitudes 6° S to 30° S were included in the coppice study, with 17 genotypes at each site. The initial rotation had been planted at a 3 m × 3 m spacing and also in a spacing trial at densities from 500 to 3500 trees ha−1. Six months after harvesting the initial Eucalyptus rotation, average survival was 88%, with tropical clones showing over twice the sprouting biomass (6.7 vs. 2.9 Mg ha−1) and four times the woody biomass compared to subtropical clones (4.7 vs. 1.1 Mg ha−1). Greater initial water deficits had stronger sprouting and growth. Clones with higher belowground carbon allocation in the initial rotation performed better in coppicing, and precipitation became more influential after 12 months. Drought and spacing trials significantly affected growth.

Evidence for divergent selection and adaptive variation across the landscape can provide insight into a species' ability to adapt to different environments. However, despite recent advances in genomics, it remains difficult to detect the footprints of climate‐mediated selection in natural populations. Here, we analysed ddRAD sequencing data (21,892 SNPs) in conjunction with geographic climate variation to search for signatures of adaptive differentiation in twelve populations of the bank vole (Clethrionomys glareolus) distributed across Europe. To identify the loci subject to selection associated with climate variation, we applied multiple genotype‐environment association methods, two univariate and one multivariate, and controlled for the effect of population structure. In total, we identified 213 candidate loci for adaptation, 74 of which were located within genes. In particular, we identified signatures of selection in candidate genes with functions related to lipid metabolism and the immune system. Using the results of redundancy analysis, we demonstrated that population history and climate have joint effects on the genetic variation in the pan‐European metapopulation. Furthermore, by examining only candidate loci, we found that annual mean temperature is an important factor shaping adaptive genetic variation in the bank vole. By combining landscape genomic approaches, our study sheds light on genome‐wide adaptive differentiation and the spatial distribution of variants underlying adaptive variation influenced by local climate in bank voles. [ABSTRACT FROM AUTHOR]

Generating large-scale field-based guild data for assessing tree species sorting and distribution over tropical covers is difficult. In this study, we combined field, and the Airborne Visible-Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) datasets of tropical covers across a climate gradient to develop precision maps of abundant tree species. This assisted in the extraction of a large dataset of guilds with tree species assortment and occupancy. We observed parity in the distribution of local and regional species with an increase in the proportionate presence of local species over the climate gradient. We saw greater distribution of Fabaceae members in sites with relatively lesser rainfall. To address the impact of species sorting on the functional aspects of guilds, available R codes (Ackerly and Cornwell, 2007), and three vegetation indices (VIs) as functional traits (Photochemical Reflectance Index, PRI, Chlorophyll/Carotenoid Index, CCI, and Normalized Difference Water Index, NDWI) were tested. Species assortment and spread affected the guild's functional diversity, as noticed in the abundance weighted guild means of VIs. We also observed a consistent increase in the mean CCI of all species across the climate gradient correlating positively with rainfall and negatively with vapour pressure deficit (VPD). This shows that CCI could be an adequate measure for large-scale ecological observations of these tropical regions. Wider amplitudes in the measured VIs of deciduous species demonstrated their adaptability to the climate gradient. Gradient-driven species assembly dynamics and functional traits variability indicates of tropical tree biodiversity feedback to the climate dynamics. [ABSTRACT FROM AUTHOR]

ABSTRACTMicrobes are essential for the functioning of all ecosystems, and as global warming and anthropogenic pollution threaten ecosystems, it is critical to understand how microbes respond to these changes. We investigated the climate response of Sphingomonas, a widespread gram-negative bacterial genus, during an 18-month microbial community reciprocal transplant experiment across a Southern California climate gradient. We hypothesized that after 18 months, the transplanted Sphingomonas clade and functional composition would correspond with site conditions and reflect the Sphingomonas composition of native communities. We extracted Sphingomonas sequences from metagenomic data across the gradient and assessed their clade and functional composition. Representatives of at least 12 major Sphingomonas clades were found at varying relative abundances along the climate gradient, and transplanted Sphingomonas clade composition shifted after 18 months. Site had a significant effect (PERMANOVA; P < 0.001) on the distribution of both Sphingomonas functional (R2 = 0.465) and clade composition (R2 = 0.400), suggesting that Sphingomonas composition depends on climate parameters. Additionally, for both Sphingomonas clade and functional composition, ordinations revealed that the transplanted communities shifted closer to the native Sphingomonas composition of the grassland site compared with the site they were transplanted into. Overall, our results indicate that climate and substrate collectively determine Sphingomonas clade and functional composition.IMPORTANCESphingomonas is the most abundant gram-negative bacterial genus in litter-degrading microbial communities of desert, grassland, shrubland, and forest ecosystems in Southern California. We aimed to determine whether Sphingomonas responds to climate change in the same way as gram-positive bacteria and whole bacterial communities in these ecosystems. Within Sphingomonas, both clade composition and functional genes shifted in response to climate and litter chemistry, supporting the idea that bacteria respond similarly to climate at different scales of genetic variation. This understanding of how microbes respond to perturbation across scales may aid in future predictions of microbial responses to climate change.

It is critical to understand the consequences of environmental change for the microbial regulation of carbon and nutrient cycling. Specifically, understanding microbial community traits, such as extracellular enzyme activity, can help inform nutrient cycling models and address knowledge gaps. We analyzed data on extracellular enzyme activities and litter decomposition from an 18-month experiment in which microbial communities were reciprocally transplanted along a climate gradient in Southern California. Communities were from desert, scrubland, grassland, pine–oak, and subalpine ecosystems. We aimed to test how enzyme activities responded to climate change following transplantation and how those responses related to decomposition rates. We hypothesized that microbial communities would specialize on their native climate conditions, resulting in higher enzyme activities when transplanted back into their native climate. We investigated the relationship between extracellular enzyme Vmax values, substrate mass loss, and microbial biomass as well as variation in these variables across the climate gradient. We found little evidence for climate specialization, and there was rarely a reduction in enzyme functioning after microbial communities were transplanted into new climate conditions. Moreover, observed differences in decomposition were not related to changes in extracellular enzyme potential, although there were significant differences in enzyme activities and decomposition rates across sites. These results suggest that direct, physiological impacts of climate are likely to be important for enzyme-mediated decomposition, but climate specialization will not constrain the microbial response to climate change in our system.

Abstract Evidence for divergent selection and adaptive variation across the landscape can provide insight into a species' ability to adapt to different environments. However, despite recent advances in genomics, it remains difficult to detect the footprints of climate‐mediated selection in natural populations. Here, we analysed ddRAD sequencing data (21,892 SNPs) in conjunction with geographic climate variation to search for signatures of adaptive differentiation in twelve populations of the bank vole (Clethrionomys glareolus) distributed across Europe. To identify the loci subject to selection associated with climate variation, we applied multiple genotype‐environment association methods, two univariate and one multivariate, and controlled for the effect of population structure. In total, we identified 213 candidate loci for adaptation, 74 of which were located within genes. In particular, we identified signatures of selection in candidate genes with functions related to lipid metabolism and the immune system. Using the results of redundancy analysis, we demonstrated that population history and climate have joint effects on the genetic variation in the pan‐European metapopulation. Furthermore, by examining only candidate loci, we found that annual mean temperature is an important factor shaping adaptive genetic variation in the bank vole. By combining landscape genomic approaches, our study sheds light on genome‐wide adaptive differentiation and the spatial distribution of variants underlying adaptive variation influenced by local climate in bank voles.

Questions: Dryland annual plant communities constitute the most species‐rich small‐scale vegetation in the Mediterranean. Nevertheless, the composition and diversity of these units and the factors controlling their variation are still insufficiently understood. Therefore, we investigated species composition and richness patterns in relation to important environmental gradients provided by climate and soil. Location: Central Crete, Greece. Methods: The study is based on 82 plots of 4 m2 sampled at altitudes between 11 and 1400 m a.s.l. We conducted vegetation relevés and soil analyses. We used generalised additive models to model species richness and community characteristics along the studied gradients. We then performed distance‐based redundancy analysis to determine the main environmental factors influencing species composition. To determine species of diagnostic value for bedrock types, we applied an indicator species analysis. Correlation tests were used to test the performance of the South Aegean Plant Indicator Values on our dataset. Results: We recorded 347 taxa (species and subspecies) of 43 plant families, and mean species numbers of 47.2 ± 12.5 per plot. While overall species richness varied only slightly along the analysed environmental gradients, significant changes were observed for relative proportions of species from different life forms and families. Soil pH and elevation had the highest influence on the variation in species composition (21.0% explained). We found 22 species indicative of calcareous rock and 24 species indicative of lime‐deficient rock types. The South Aegean Plant Indicator Values were relatively strongly correlated with environmental variables. Conclusions: Results indicate considerable species turnover both along climatic (elevation) and soil gradients, highlighting the special importance of soil pH. The data provided by our study are expected to supply relevant ecological background information for a pending classification of East Mediterranean annual‐rich vegetation. [ABSTRACT FROM AUTHOR]

Climate change can affect biotic interactions, and the impacts of climate on biotic interactions may vary across climate gradients. Climate affects biotic interactions through multiple drivers, although few studies have investigated multiple climate drivers in experiments. We examined the effects of experimental watering, warming, and predator access on leaf water content and herbivory rates of woolly bear caterpillars (Arctia virginalis) on a native perennial plant, pacific silverweed (Argentina anserina ssp. pacifica), at two sites across a gradient of precipitation in coastal California. Based on theory, we predicted that watering should increase herbivory at the drier end of the gradient, predation should decrease herbivory, and watering and warming should have positive interacting effects on herbivory. Consistent with our predictions, we found that watering only increased herbivory under drier conditions. However, watering increased leaf water content at both wetter and drier sites. Warming increased herbivory irrespective of local climate and did not interact with watering. Predation did not affect herbivory rates. Given predictions that the study locales will become warmer and drier with climate change, our results suggest that the effects of future warming and drying on herbivory may counteract each other in drier regions of the range of Argentina anserina. Our findings suggest a useful role for range-limit theory and the stress-gradient hypothesis in predicting climate change effects on herbivory across stress gradients. Specifically, if climate change decreases stress, herbivory may increase, and vice versa for increasing stress. In addition, our work supports previous suggestions that multiple climate drivers are likely to have dampening effects on biotic interactions due to effects in different directions, though this is context-dependent.

Summary: Understanding how plants adapt to spatially heterogeneous phosphorus (P) supply is important to elucidate the effect of environmental changes on ecosystem productivity. Plant P supply is concurrently controlled by plant internal conservation and external acquisition. However, it is unclear how climate, soil, and microbes influence the contributions and interactions of the internal and external pathways for plant P supply.Here, we measured P and nitrogen (N) resorption efficiency, litter and soil acid phosphatase (AP) catalytic parameters (Vmax(s) and Km), and soil physicochemical properties at four sites spanning from cold temperate to tropical forests.We found that the relative P limitation to plants was generally higher in tropical forests than temperate forests, but varied greatly among species and within sites. In P‐impoverished habitats, plants resorbed more P than N during litterfall to maintain their N : P stoichiometric balance. In addition, once ecosystems shifted from N‐limited to P‐limited, litter‐ and soil‐specific AP catalytic efficiency (Vmax(s)/Km) increased rapidly, thereby enhancing organic P mineralization.Our findings suggested that ecosystems develop a coupled aboveground–belowground strategy to maintain P supply and N : P stoichiometric balance under P‐limitation. We also highlighted that N cycle moderates P cycles and together shape plant P acquisition in forest ecosystems. [ABSTRACT FROM AUTHOR]

The forests of south‐central Chile are facing a drying climate and a megadrought that started in 2010. This study addressed the physiological responses of five Nothofagus obliqua stands across the Mediterranean‐Temperate gradient (35.9°−40.3°S) using carbon isotope discrimination (Δ13 C) and intrinsic water use efficiency (iWUE) in tree rings during 1967–2017. Moreover, tree ring δ18O was evaluated in the northernmost site to better understand the effects of the megadrought in this drier location. These forests have become more efficient in their use of water. However, trees from the densest stand are discriminating more against 13C, probably due to reduced photosynthetic rates associated with increasing light competition. The strongest associations between climate and Δ13C were found in the northernmost stand, suggesting that warmer and drier conditions could have reduced 13C discrimination. Tree growth in this site has not decreased, and δ18O was negatively related to annual rainfall. However, a shift in this relationship was found since 2007, when both precipitation and δ18O decreased, while correlations between δ18O and growth increased. This implies that tree growth and δ18O are coupled in recent years, but precipitation is not the cause, suggesting that trees probably changed their water source to deeper and more depleted pools. Our research demonstrates that forests are not reducing their growth in central Chile, mainly due to a shift toward the use of deeper water sources. Despite a common climate trend across the gradient, there is a non‐uniform response of N. obliqua forests to climate drying, being their response site‐specific. Plain Language Summary: The forests of south‐central Chile are facing a drying climate and a megadrought that started in 2010. This study addressed the physiological responses of five Nothofagus obliqua stands across the Mediterranean‐Temperate gradient (35.9°−40.3°S) to climate drying using stable isotopes in tree rings during the period 1967–2017. These forests have become more efficient in their use of water. However, trees from the densest stand are showing a poor adaptability to climate change, probably due to a decrease in photosynthetic rates associated with the increase in competition. Our research demonstrates for the first time that forests are not reducing their growth in central Chile, mainly due to a shift toward the use of deeper water sources. However, it is not certain until which point this acclimation will persist as these pools get depleted in the future with continued drying. Despite a common climate trend across the latitudinal gradient, this research points to a non‐uniform response of N. obliqua second‐growth forests to a drying climate, being their response stand and site‐specific. Key Points: Despite a common climate trend, the response of N. obliqua to climate change is not uniform, but rather specific to the stand and siteTree growth and δ18O have been coupled during the megadrought in the northernmost site, but rainfall does not influence this patternN. obliqua northern forests are able to maintain radial growth rates and acclimate to persistent droughts by tapping deeper water sources [ABSTRACT FROM AUTHOR]

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Drought and rainfall events will become more frequent and intense with climate change. At the same time, soil moisture is one of the major factors controlling soil microbial processes such as carbon cycling. When challenged with drought there are two main growth responses microorganisms can use: (1) they can maintain growth rates during drought (i.e., resistance) and (2) they can recover growth rates faster when the drought ends (i.e., resilience). Microbial communities are shaped by multiple other factors in the soil environment, however how those impact drought responses remain unclear. Here we investigate how climate (estimated as aridity index) and soil properties determine microbial growth resistance and resilience to drought across a climate gradient in Europe. To test this, we exposed the different soils to a standardised drought cycle in controlled conditions. We assessed bacterial growth, fungal growth and respiration during soil drying to determine resistance and in high resolution during three days after rewetting to estimate resilience to drought. We found that alpha diversity was the strongest driver of both bacterial drought resistance and resilience, which occurred via changes in soil pH. This shows the importance of diversity for sustaining bacterial functions during drought stress. A secondary driver of bacterial drought resistance and resilience was the aridity index was also an important driver, where bacterial communities from more arid climates had higher resistance and resilience to drought. Fungal communities were both more resistant and resilient compared to bacteria, but this was independent of other measured environmental factors. Bacterial resilience was partly linked with differences in community composition. Our results suggest that if sites are exposed to increased aridity due to climate change or are managed to promote bacterial diversity, they will have higher bacterial growth rates during drought perturbations, which could potentially promote soil carbon storage. • Across Europe, bacterial diversity increased drought resistance and resilience. • Bacterial diversity was directly affected by the soil pH. • Bacterial drought resistance and resilience increased in drier climates. • Fungi were more drought resistant and resilient compared to bacteria. • Fungal drought resistance and resilience were independent of climate aridity. [ABSTRACT FROM AUTHOR]

Predictions of how vegetation responds to spatial and temporal differences in climate rely on established links with plant functional traits and vegetation types that can be encoded into Dynamic Global Vegetation Models. Individual traits have been linked to climate at species level and at community level within regions. However, a recent global assessment of aggregated community level traits found unexpectedly weak links with macroclimate, bringing into question broadscale trait–climate associations and implicating local-scale environmental differences in the filtering of communities. To further evaluate patterns in light of these somewhat contradictory results, we quantified the power of macro-environmental variables to explain aggregated plant community traits, taking advantage of new trait data for leaf area, plant height and seed mass combined with a national survey that records cover-abundance using consistent methods for a large number of plots across Australia. In contrast to the global study, we found that abundance-weighted community mean and variance of leaf area and maximum height were correlated with macroclimate. Height and leaf area were highest in wet (especially warm, wet) environments, with actual evapotranspiration explaining 30% of variation in leaf area and 26% in maximum height. Seed mass was weakly related to environment, with no variable explaining more than 5% of variance. Considering all three traits together in a redundancy analysis, the complete set of environmental variables explained 43% of variation in site-mean traits and 29% of within-site trait variance. While significant trait variation remains unexplained, the trait–environment relationships reported here suggest climatically-driven filtering plays a strong role in assembling these vegetation communities. Regional assessments using standardised species abundances can therefore be used to predict aspects of vegetation function. Our quantification of plant community trait patterns along macroclimatic gradients at continental scale thereby contributes a much-needed functional basis for Australian vegetation.

Microbial decomposers mediate the return of CO2 to the atmosphere by producing extracellular enzymes to degrade complex plant polymers, making plant carbon available for metabolism. Determining if and how these decomposer communities are constrained in their ability to degrade plant litter is necessary for predicting how carbon cycling will be affected by future climate change. We analyzed mass loss, litter chemistry, microbial biomass, extracellular enzyme activities, and enzyme temperature sensitivities in grassland litter transplanted along a Mediterranean climate gradient in southern California. Microbial community composition was manipulated by caging litter within bags made of nylon membrane that prevent microbial immigration. To test whether grassland microbes were constrained by climate history, half of the bags were inoculated with local microbial communities native to each gradient site. We determined that temperature and precipitation likely interact to limit microbial decomposition in the extreme sites along our gradient. Despite their unique climate history, grassland microbial communities were not restricted in their ability to decompose litter under different climate conditions across the gradient, although microbial communities across our gradient may be restricted in their ability to degrade different types of litter. We did find some evidence that local microbial communities were optimized based on climate, but local microbial taxa that proliferated after inoculation into litterbags did not enhance litter decomposition. Our results suggest that microbial community composition does not constrain C-cycling rates under climate change in our system, but optimization to particular resource environments may act as more general constraints on microbial communities.

Litter input plays an important role in the soil organic carbon (SOC) balance between new C formation and old C loss in forests. However, the relative contributions of aboveground litter vs. belowground litter inputs to the SOC balance in various forests along a climatic gradient remain highly uncertain. In this study, we experimentally transplanted sugarcane soil with a heavy δ13C value to forest soil with a light δ13C value to evaluate the relative effects of aboveground and belowground litter inputs on new SOC formation and old SOC retention in natural secondary forests (boreal, temperate, subtropical and tropical forests) located across four different climatic regions in China. Our results showed that belowground root litter inputs can potentially lead to higher new SOC formation and lower old SOC retention compared to aboveground litter inputs. Moreover, the magnitudes of new SOC and old SOC change after litter inputs varied among natural forests, with SOC in tropical forests being more sensitive to belowground root inputs than SOC in temperate and subtropical forests. While the total and new SOC contents were positively correlated with mean annual temperature (MAT) and precipitation (MAP), the old SOC contents were negatively correlated with MAT and MAP. Our findings indicated that belowground root litter inputs have more profound influences on new SOC formation and old SOC loss than aboveground litter inputs, and climatic factors play a fundamental role in determining litter input-induced changes in SOC balance across different forest ecosystems. [ABSTRACT FROM AUTHOR]

Litter decomposition is controlled by climate, litter quality and decomposer communities. Because the decomposition of specific litter types is also influenced by the properties of adjacent types, mixing litter types may result in non‐additive effects on overall decomposition rates. The strength of these effects seems to depend on the litter functional diversity. However, it is unclear which functional traits or combination of traits explain litter mixture effects and whether these depend on the range of trait values and the ecosystems involved. These uncertainties hamper our ability to predict decomposition in plant communities.We aimed at understanding whether and how functional diversity (measured as functional dispersion, FDis) influences litter decomposition, and how this influence varies among different climates and across decomposition stages. We calculated FDis based on litter traits related to nutrient concentrations or to litter recalcitrance, and tested whether these diversity measures and climatic parameters (soil moisture and temperature) explained litter mixture effects on decomposition.Additive mixture effects (i.e. decomposition of mixtures equalling the mean decomposition of the single litter types) were common in most of the evaluated climates. Non‐additive, negative effects were mainly restricted to the driest and warmest sites, and decreased with time. Non‐additive effects increased in magnitude with the mixtures' FDis, with positive effects being related to FDis in nutrient traits and negative effects being related to FDis in recalcitrance traits.Synthesis. Litter mixing did not have strong effects on decomposition rates across the studied climatic gradient overall, and the direction and intensity of the mixture effects were context dependent. The effects were stronger and more negative in the dryer ecosystems. Where effects were found, functional diversity calculated from selected groups of traits (related to nutrients or litter recalcitrance) predicted mixture effects, especially where trait ranges were broad, though much of the variation remains unexplained. We propose that functional diversity metrics based on litter traits that are mechanistically relevant, applied to diverse site‐specific litter mixtures in different climates, can help to better understand under which conditions and in which direction litter diversity affects decomposition. [ABSTRACT FROM AUTHOR]

Under climate change circumstances, increasing studies have reported the temporal instability of tree growth responses to climate, which poses a major challenge to linearly extrapolating past climate and future growth dynamics using tree‐ring data. Space‐for‐time substitution (SFTS) is a potential solution to this problem that is widely used in the dendrochronology field to project past or future temporal growth response trajectories from contemporary spatial patterns. However, the projected accuracy of the SFTS in the climate effects on tree growth remains uncertain. Here, we empirically test the SFTS method by comparing the effect of spatial and temporal climate variations on climate responses of white spruce (Picea glauca), which has a transcontinental range in North America. We first applied a response surface regression model to capture the variations in growth responses along the spatial climate gradients. The results showed that the relationships between growth and June temperature varied along spatial climate gradients in a predictable way. And their relationships varied mainly along with local temperate condition. Then, the projected correlation coefficients between growth and climate using SFTS were compared against the observed. We found that the growth response changes caused by spatial versus temporal climate variations showed opposite trends. Moreover, the projected correlation coefficients using the SFTS were significantly lower than the observed. This finding suggests that applying the SFTS to project the growth response of white spruce might lead to an overestimation of the degree of tree maladaptation in future climate scenarios. And the overestimation is likely to get weaker from Alaska and Yukon Territory in the west to Quebec in the east. Although this is only a case study of the SFTS method for projecting tree growth response, our findings suggest that direct application of the SFTS method may not be applicable to all regions and all tree species. [ABSTRACT FROM AUTHOR]

Intraspecific trait variability (ITV) provides the material for species' adaptation to environmental changes. To advance our understanding of how ITV can contribute to species' adaptation to a wide range of environmental conditions, we studied five widespread understorey forest species exposed to both continental‐scale climate gradients, and local soil and disturbance gradients. We investigated the environmental drivers of between‐site leaf and root trait variation, and tested whether higher between‐site ITV was associated with increased trait sensitivity to environmental variation (i.e. environmental fit).We measured morphological (specific leaf area: SLA, specific root length: SRL) and chemical traits (Leaf and Root N, P, K, Mg, Ca) of five forest understorey vascular plant species at 78 sites across Canada. A total of 261 species‐by‐site combinations spanning ~4300 km were sampled, capturing important abiotic and biotic environmental gradients (neighbourhood composition, canopy structure, soil conditions, climate). We used multivariate and univariate linear mixed models to identify drivers of ITV and test the association of between‐site ITV with environmental fit.Between‐site ITV of leaf traits was primarily driven by canopy structure and climate. Comparatively, environmental drivers explained only a small proportion of variability in root traits: these relationships were trait specific and included soil conditions (Root P), canopy structure (Root N) and neighbourhood composition (SRL, Root K). Between‐site ITV was associated with increased environmental fit only for a minority of traits, primarily in response to climate (SLA, Leaf N, SRL).Synthesis. By studying how ITV is structured along environmental gradients among species adapted to a wide range of conditions, we can begin to understand how individual species might respond to environmental change. Our results show that generalisable trait–environment relationships occur primarily aboveground, and only accounted for a small proportion of variability. For our group of species with broad ecological niches, variability in traits was only rarely associated with higher environmental fit, and primarily along climatic gradients. These results point to promising research avenues on the various ways in which trait variation can affect species' performance along different environmental gradients. [ABSTRACT FROM AUTHOR]

Aim: The presence and use of trails may change plant species' realized climatic niches via modified abiotic and biotic conditions including propagule transport, allowing competition‐pressed alpine species to expand their rear edges towards warmer locations and lowland species to extend their leading edges towards cooler locations. We investigated whether mountain trails indeed act as corridors for colonization and shift species' realized climatic niches, resulting in higher species richness in trailsides. Location: Dovrefjell and Abisko area in the Scandes mountains of Norway and Sweden. Methods: We surveyed plant community composition and disturbances along 16 hiking trails in summer 2018 (Dovrefjell) and 2019 (Abisko). We linked changes in species' realized climatic niches to their climatic optimum and variation in species richness to climate, trail effects and resident plant community characteristics. Results: Plant species richness was on average 24% greater in trailside than in interior vegetation plots. Proximity to trails accounted for 9% and climatic harshness for 55% of variation in species richness explained in our model. Trailsides increased in richness, especially in relatively species‐poor sites and close to introduction points (each accounting for 24% of variation in our model of species gains). Shifts in rear edges and optima of realized climatic niches along trails related to species' undisturbed climatic optimum, with alpine species being more likely to move into warmer locations. While some disturbance‐associated species shifted their leading edges towards colder locations, contrary to expectations this was not the case for lowland species. Overall, shifts in climatic niches resulted in more species' niches overlapping in trailsides than in the interior vegetation. Main conclusion: Trails can locally increase species richness by creating opportunities for colonizing species and weaker competitors. Because of prevailing disturbance, they may even provide opportunities for persistence and downward expansion of alpine species, aiding conservation efforts. [ABSTRACT FROM AUTHOR]

Microbial decomposers produce extracellular enzymes to degrade complex plant polymers, making plant C available for metabolism and eventual respiration back to the atmosphere as CO2. Knowledge of how extracellular enzyme kinetics and microbial activity vary with climate is therefore valuable for predicting how future carbon cycling may be affected by climate change, but studies investigating such dynamics in more xeric ecosystems are underrepresented in the literature. We investigated how microbial biomass, litter chemistry, and extracellular enzymes (Vmax and Km) and their temperature sensitivities varied along a Mediterranean climate gradient in southern California. Total microbial biomass did not vary among sites along the gradient in either the dry or the wet season. In contrast, extracellular enzyme Vmax and Km varied as a function of fungal biomass and substrate availability. We also found that Vmax and Km of most enzymes were more sensitive to temperature in colder sites than in warmer sites, though this relationship was seasonal for Vmax. Observed enzyme Vmax and Km were indicative of extracellular enzyme accumulation in the drier sites along the gradient, which may contribute to the large pulses of respiration that follow rewetting events in these xeric systems. Variation in enzyme characteristics along the gradient indicate that as these systems become more arid in the future, enzyme dynamics will shift from smaller, potentially more active pools to larger, potentially less active enzyme pools that accumulate over dry periods. In addition, rates of enzymatic decomposition will likely be most sensitive to rising temperatures in the coldest sites along our gradient.

Microbial decomposers produce extracellular enzymes to degrade complex plant polymers, making plant C available for metabolism and eventual respiration back to the atmosphere as CO2. Knowledge of how extracellular enzyme kinetics and microbial activity vary with climate is therefore valuable for predicting how future carbon cycling may be affected by climate change, but studies investigating such dynamics in more xeric ecosystems are underrepresented in the literature. We investigated how microbial biomass, litter chemistry, and extracellular enzymes (Vmax and Km) and their temperature sensitivities varied along a Mediterranean climate gradient in southern California. Total microbial biomass did not vary among sites along the gradient in either the dry or the wet season. In contrast, extracellular enzyme Vmax and Km varied as a function of fungal biomass and substrate availability. We also found that Vmax and Km of most enzymes were more sensitive to temperature in colder sites than in warmer sites, though this relationship was seasonal for Vmax. Observed enzyme Vmax and Km were indicative of extracellular enzyme accumulation in the drier sites along the gradient, which may contribute to the large pulses of respiration that follow rewetting events in these xeric systems. Variation in enzyme characteristics along the gradient indicate that as these systems become more arid in the future, enzyme dynamics will shift from smaller, potentially more active pools to larger, potentially less active enzyme pools that accumulate over dry periods. In addition, rates of enzymatic decomposition will likely be most sensitive to rising temperatures in the coldest sites along our gradient.

The supply of nitrogen (N) constrains primary productivity in many ecosystems, raising the question "what controls the availability and cycling of N"? As a step toward answering this question, we evaluated N cycling processes and aspects of their regulation on a climate gradient on Kohala Volcano, Hawaii, USA. The gradient extends from sites receiving 3,000 mm/yr, and the pedology and dynamics of rock-derived nutrients in soils on the gradient are well understood. In particular, there is a soil process domain at intermediate rainfall within which ongoing weathering and biological uplift have enriched total and available pools of rock-derived nutrients substantially; sites at higher rainfall than this domain are acid and infertile as a consequence of depletion of rock-derived nutrients, while sites at lower rainfall are unproductive and subject to wind erosion. We found elevated rates of potential net N mineralization in the domain where rock-derived nutrients are enriched. Higher-rainfall sites have low rates of potential net N mineralization and high rates of microbial N immobilization, despite relatively high rates of gross N mineralization. Lower-rainfall sites have moderately low potential net N mineralization, relatively low rates of gross N mineralization, and rates of microbial N immobilization sufficient to sequester almost all the mineral N produced. Bulk soil δ15 N also varied along the gradient, from +4‰ at high rainfall sites to +14‰ at low rainfall sites, indicating differences in the sources and dynamics of soil N. Our analysis shows that there is a strong association between N cycling and soil process domains that are defined using soil characteristics independent of N along this gradient, and that short-term controls of N cycling can be understood in terms of the supply of and demand for N.

The supply of nitrogen (N) constrains primary productivity in many ecosystems, raising the question "what controls the availability and cycling of N"? As a step toward answering this question, we evaluated N cycling processes and aspects of their regulation on a climate gradient on Kohala Volcano, Hawaii, USA. The gradient extends from sites receiving 3,000 mm/yr, and the pedology and dynamics of rock-derived nutrients in soils on the gradient are well understood. In particular, there is a soil process domain at intermediate rainfall within which ongoing weathering and biological uplift have enriched total and available pools of rock-derived nutrients substantially; sites at higher rainfall than this domain are acid and infertile as a consequence of depletion of rock-derived nutrients, while sites at lower rainfall are unproductive and subject to wind erosion. We found elevated rates of potential net N mineralization in the domain where rock-derived nutrients are enriched. Higher-rainfall sites have low rates of potential net N mineralization and high rates of microbial N immobilization, despite relatively high rates of gross N mineralization. Lower-rainfall sites have moderately low potential net N mineralization, relatively low rates of gross N mineralization, and rates of microbial N immobilization sufficient to sequester almost all the mineral N produced. Bulk soil δ15 N also varied along the gradient, from +4‰ at high rainfall sites to +14‰ at low rainfall sites, indicating differences in the sources and dynamics of soil N. Our analysis shows that there is a strong association between N cycling and soil process domains that are defined using soil characteristics independent of N along this gradient, and that short-term controls of N cycling can be understood in terms of the supply of and demand for N.

• Planted forest (PF) allocated larger proportion of biomass carbon (C) to belowground than natural forest (NF). • Turning points existed in biomass C allocation along climatic gradient for both PF and NF. • Soil properties had stronger effects on biomass C allocation in PF than NF. Establishing planted forests (PF) by afforestation and naturally regenerating forests (NF) are important measures of enhance carbon (C) sequestration in terrestrial ecosystems. However, the difference of biomass C stocks and allocation between NF and PF and their determinants in water-limited areas remain unclear. To address this gap, we conducted a synthesis of above-ground biomass C (AGBC), below-ground biomass C (BGBC) stocks and root to shoot ratios (R:S) of PF and NF in the Chinese Loess Plateau. The changes in biomass C stock and R:S along a climate gradient were investigated, and the relationships between R:S and soil properties were also quantified. We found that PF exhibited lower AGBC and BGBC stocks compared to NF, but the average R:S in PF was significantly higher than that of NF (0.48 ± 0.27 vs. 0.30 ± 0.11, p < 0.05). Turning points existed in biomass C allocation along climatic gradient for both PF and NF. More biomass C was allocated to AGBC in PF and NF when mean annual precipitation exceeded 494 mm and 588 mm, respectively. Higher mean annual temperature promoted larger C allocations to BGBC in PF compared to NF. Soil properties had a stronger effect on the biomass C allocation patterns after afforestation, but to a lesser extent on NF. This study indicates that afforestation promotes a larger allocation of biomass C into the below-ground compared to naturally regenerated forests, and using the default R:S estimates may result in a severe underestimation of below-ground C stocks in water-limited areas. The biomass C stocks and allocation are collectively determined by climate conditions and soil properties, and accumulated below-ground biomass C stock induced by dryland afforestation may be an important C sink at a broad geographic scale. [ABSTRACT FROM AUTHOR]

The temperature sensitivity (Q 10) of soil organic carbon (SOC) mineralization plays a vital role in predicting the global carbon cycle under climate change. Q 10 has been extensively examined in various terrestrial ecosystems; however, in riparian zones where soil oxygen levels are highly dynamic owing to frequent flooding, Q 10 should change with oxygen conditions and show spatial variation, but the mechanisms are still obscure. In this study, we collected topsoil and subsoil samples from riparian zones along a latitudinal gradient and conducted aerobic and anaerobic incubation experiments to determine the latitudinal and vertical patterns of Q 10. The results showed that Q 10 under anoxic conditions (average of 1.7) significantly exceeded that under oxic conditions (average of 1.4). In general, aerobic SOC mineralization is more sensitive to warming at higher latitudes than at lower latitudes, whereas the pattern is reversed under anoxic conditions. The Q 10 in the topsoil was significantly higher than that in the subsoil only under oxic conditions. Metagenomics showed that the abundance of genes involved in the degradation of lignin, carbohydrate esters, and starch in the topsoil increased with latitude, whereas genes for acetate degradation were more abundant in warmer zones, regardless of soil depth. Q 10 under oxic conditions was mainly influenced by soil physicochemical properties (e.g., pH and texture), whereas Q 10 under anoxic conditions was jointly controlled by climate, soil texture, and acetate degradation genes. Together, anaerobic carbon (C) mineralization in riparian zones is more sensitive to temperature than aerobic metabolism, but the patterns of Q 10 under oxic conditions were dependent on both latitude and depth. Our findings highlight that the discrepancies in aerobic and anaerobic C metabolism, and the C cycling process at different soil depths, might play a non-negligible role in affecting the assessment of global C emissions under climate change. [Display omitted] • The Q 10 for organic carbon mineralization was greater for anaerobic than aerobic metabolism. • Q 10 varied with latitude, increasing for aerobic but decreasing for anaerobic metabolism. • Q 10 decreased with soil depth for aerobic metabolism. • Increasing oxygen supply amplified vertical but lowered latitudinal variation in Q 10. [ABSTRACT FROM AUTHOR]

Soil bacteria play a fundamental role in pedogenesis. However, knowledge about both the impact of climate and slope aspects on microbial communities and the consequences of these items in pedogenesis is lacking. Therefore, soil-bacterial communities from four sites and two different aspects along the climate gradient of the Chilean Coastal Cordillera were investigated. Using a combination of microbiological and physicochemical methods, soils that developed in arid, semi-arid, mediterranean, and humid climates were analyzed. Proteobacteria, Acidobacteria, Chloroflexi, Verrucomicrobia, and Planctomycetes were found to increase in abundance from arid to humid climates, while Actinobacteria and Gemmatimonadetes decreased along the transect. Bacterial-community structure varied with climate and aspect and was influenced by pH, bulk density, plant-available phosphorus, clay, and total organic-matter content. Higher bacterial specialization was found in arid and humid climates and on the south-facing slope and was likely promoted by stable microclimatic conditions. The presence of specialists was associated with ecosystem-functional traits, which shifted from pioneers that accumulated organic matter in arid climates to organic decomposers in humid climates. These findings provide new perspectives on how climate and slope aspects influence the composition and functional capabilities of bacteria, with most of these capabilities being involved in pedogenetic processes. [ABSTRACT FROM AUTHOR]

Abstract Climate change can affect biotic interactions, and the impacts of climate on biotic interactions may vary across climate gradients. Climate affects biotic interactions through multiple drivers, although few studies have investigated multiple climate drivers in experiments. We examined the effects of experimental watering, warming, and predator access on leaf water content and herbivory rates of woolly bear caterpillars (Arctia virginalis) on a native perennial plant, pacific silverweed (Argentina anserina ssp. pacifica), at two sites across a gradient of precipitation in coastal California. Based on theory, we predicted that watering should increase herbivory at the drier end of the gradient, predation should decrease herbivory, and watering and warming should have positive interacting effects on herbivory. Consistent with our predictions, we found that watering only increased herbivory under drier conditions. However, watering increased leaf water content at both wetter and drier sites. Warming increased herbivory irrespective of local climate and did not interact with watering. Predation did not affect herbivory rates. Given predictions that the study locales will become warmer and drier with climate change, our results suggest that the effects of future warming and drying on herbivory may counteract each other in drier regions of the range of Argentina anserina. Our findings suggest a useful role for range‐limit theory and the stress‐gradient hypothesis in predicting climate change effects on herbivory across stress gradients. Specifically, if climate change decreases stress, herbivory may increase, and vice versa for increasing stress. In addition, our work supports previous suggestions that multiple climate drivers are likely to have dampening effects on biotic interactions due to effects in different directions, though this is context‐dependent.

Grassland ecosystems are historically shaped by climate, fire, and grazing which are essential ecological drivers. These grassland drivers influence morphology and productivity of grasses via physiological processes, resulting in unique water and carbon-use strategies among species and populations. Leaf-level physiological responses in plants are constrained by the underlying anatomy, previously shown to reflect patterns of carbon assimilation and water-use in leaf tissues. However, the magnitude to which anatomy and physiology are impacted by grassland drivers remains unstudied. To address this knowledge gap, we sampled from three locations along a latitudinal gradient in the mesic grassland region of the central Great Plains, USA during the 2018 (drier) and 2019 (wetter) growing seasons. We measured annual biomass and forage quality at the plot level, while collecting physiological and anatomical traits at the leaf-level in cattle grazed and ungrazed locations at each site. Effects of ambient drought conditions superseded local grazing treatments and reduced carbon assimilation and total productivity in A. gerardii. Leaf-level anatomical traits, particularly those associated with water-use, varied within and across locations and between years. Specifically, xylem area increased when water was more available (2019), while xylem resistance to cavitation was observed to increase in the drier growing season (2018). Our results highlight the importance of multi-year studies in natural systems and how trait plasticity can serve as vital tool and offer insight to understanding future grassland responses from climate change as climate played a stronger role than grazing in shaping leaf physiology and anatomy. [ABSTRACT FROM AUTHOR]

Predictions of how vegetation responds to spatial and temporal differences in climate rely on established links with plant functional traits and vegetation types that can be encoded into Dynamic Global Vegetation Models. Individual traits have been linked to climate at species level and at community level within regions. However, a recent global assessment of aggregated community level traits found unexpectedly weak links with macroclimate, bringing into question broadscale trait–climate associations and implicating local-scale environmental differences in the filtering of communities. To further evaluate patterns in light of these somewhat contradictory results, we quantified the power of macro-environmental variables to explain aggregated plant community traits, taking advantage of new trait data for leaf area, plant height and seed mass combined with a national survey that records cover-abundance using consistent methods for a large number of plots across Australia. In contrast to the global study, we found that abundance-weighted community mean and variance of leaf area and maximum height were correlated with macroclimate. Height and leaf area were highest in wet (especially warm, wet) environments, with actual evapotranspiration explaining 30% of variation in leaf area and 26% in maximum height. Seed mass was weakly related to environment, with no variable explaining more than 5% of variance. Considering all three traits together in a redundancy analysis, the complete set of environmental variables explained 43% of variation in site-mean traits and 29% of within-site trait variance. While significant trait variation remains unexplained, the trait–environment relationships reported here suggest climatically-driven filtering plays a strong role in assembling these vegetation communities. Regional assessments using standardised species abundances can therefore be used to predict aspects of vegetation function. Our quantification of plant community trait patterns along macroclimatic gradients at continental scale thereby contributes a much-needed functional basis for Australian vegetation. [ABSTRACT FROM AUTHOR]

Recent studies from the Hawaiian Islands showed that pedogenic thresholds demarcate domains in which rock-derived nutrient dynamics remain similar across wide variations in rainfall. These thresholds appear related to certain aspects of N cycling, but the degree to which they correspond to patterns of biological N fixation (BNF)—the dominant input of N into less-managed ecosystems—remains unclear. We measured aboveground plant biomass, foliar nutrient concentrations, and foliar δ15N along a climate gradient on ~ 150,000-year-old basaltic substrate to characterize foliar N sources and spatially relate them to soil nutrients. Patterns in legume δ15N correspond to known pedogenic thresholds along the rainfall gradient, with low δ15N values (~ 0 to − 2‰) occurring in the dry, biologically inactive domain and the wet, highly weathered domain. Elevated δ15N in the middle, fertile domain suggests a greater reliance of legumes on soil N where it has accumulated over time. Non-legume face N deficiencies throughout most of the gradient while legumes maintain low C:N ratios via symbiotic BNF. However, legume abundance declines outside the fertile domain, limiting ecosystem N inputs. Breakpoints in legume δ15N data suggest that P (and potentially other nutrients) limits BNF and, by extension, legume abundance in wet region. Nutrients may also constrain legume abundance in the dry domain, but pedogenic effects could not be isolated from climatic constraints at the dry sites. We conclude that pedogenic thresholds defined by climate can be informative of foliar δ15N patterns in cases where legumes are not directly constrained by climate, land use, or other external factors. [ABSTRACT FROM AUTHOR]

Elevational variation of vegetation has been of interest for centuries, and a prominent example for such pronounced vegetation changes can be found along the steep elevational gradient on Tenerife, Canary Islands, 200 km off the West-African cost. The 3,718-m ascent to the peak of the island volcano, Teide, offers a unique opportunity to investigate associated changes in vegetation. However, elevation is not a directly acting factor, but represents several natural environmental gradients. While the elevational variation of temperature is globally rather uniform and temperature effects on plant communities are well understood, much less is known about the region-specific elevational change of chemical soil properties and their impact on plant communities along elevational gradients. Because human interference takes place even at high-elevation areas, we considered human-induced disturbance as important third factor acting upon plant community assemblages. In our study, we compared the effects of soil properties, temperature and disturbance on species richness, functional identity and functional diversity of plant communities along the elevational gradient on Tenerife. We used pairs of study plots: directly adjacent to a road and in natural vegetation close by. In each plot, we did vegetation relevées, took soil samples, and installed temperature loggers. Additionally, we collected leaf samples to measure leaf functional traits of 80% of the recorded species. With increasing elevation, soil cation concentrations, cation exchange capacity (CEC) and pH decreased significantly, while the soil carbon to phosphorus ratio slightly peaked at mid-elevations. Temperature had the strongest effects, increasing species richness and favoring communities with fast resource acquisition. Species richness was higher at road verges, indicating the positive effect of reduced competition and artificially generated heterogeneity. However, we did not detect road effects on plant functional characteristics. Vice versa, we did not find soil effects on species richness, but increased concentrations of soil cations favored acquisitive communities. Surprisingly, we could not reveal any influence on community functional diversity. The importance of temperature aligns with findings from large-scale biogeographic studies. However, our results also emphasize that it is necessary to consider the effects of local abiotic drivers, like soil properties and disturbance, to understand variation in plant communities.

Abstract Plant community biomass production is co‐dependent on climatic and edaphic factors that are often covarying and non‐independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan‐European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species‐specific biomass responses to the environment in the climate‐corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co‐limited by climatic and soil drivers, with each species experiencing its own unique set of co‐limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe.

Plant community biomass production is co‐dependent on climatic and edaphic factors that are often covarying and non‐independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan‐European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species‐specific biomass responses to the environment in the climate‐corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co‐limited by climatic and soil drivers, with each species experiencing its own unique set of co‐limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe. [ABSTRACT FROM AUTHOR]

Understanding daytime (ETD) and nighttime (ETN) evapotranspiration is critical for accurately evaluating terrestrial water and carbon cycles. However, unlike ETD, the factors influencing ETN remain poorly understood. Here, long‐term ETD and ETN data from five FLUXNET sites along a climate gradient in Northern Australia were analyzed to compare their responses to environmental drivers at different temporal scales. We found that (a) across the sites, mean annual ETN/ETD (ETN¯/ETD¯) ranged between 5.1% and 11.7%, which was mainly determined by ETD¯ variations. Particularly, vegetation and meteorological variables mostly controlled ETD¯, while ETN¯ was largely related to air temperature and net radiation (Rn) due to lower nighttime atmospheric water demands; (b) At individual sites, ETD and ETN exhibited higher correlations with meteorological and vegetation variables at monthly timescales than at annual timescales. Monthly ETD and ETN were also strongly coupled, especially under drier climatic conditions. At daily timescales, leaf area index and soil water content (SWC) controlled ETD with SWC being more important at drier sites; whereas, SWC was the dominant factor controlling ETN. At half‐hourly timescales, the boosted regression tree method quantitively showed that ETD and ETN were controlled by Rn and SWC, respectively. Overall, the results showed that ETN was less responsive to environmental variables, illustrating that ETD and ETN responded differently to diverse climate regimes and ecosystems at varying temporal scales. These findings provide a critical evaluation for contrasting ETD and ETN interactions in constantly changing environments, which has important implications for ecosystem water balance and land surface processes modeling. Key Points: Variations in mean annual ETN/ETD ratio (5.1%–11.7%) across the sites were mostly determined by the spatial variability in ETDETD and ETN responded differently to climatic drivers from half‐hourly to annual scales, which also depended on ecosystems typesAt site levels, leading controls were Rn for half‐hourly ETD, leaf area index (LAI), and soil water content (SWC) for daily to annual ETD, and SWC for half‐hourly to annual ETN [ABSTRACT FROM AUTHOR]

As climate changes, species' ability to spatially track suitable climate depends on their spread velocity, a function of their population growth and dispersal capacity. When climate changes faster than species can spread, the climate experienced at species' expanding range edges may ameliorate as conditions become increasingly similar to those of the range core. When this boosts species' growth rates, their spread accelerates. Here, we use simulations of a spreading population with an annual life history to explore how climatic amelioration interacts with dispersal evolution and local adaptation to determine the dynamics of spread. We found that depending on the timing of dispersal evolution, spread velocity can show contrasting trajectories, sometimes transiently exceeding the climate velocity before decelerating. Climatic amelioration can also accelerate the spread of populations composed of genotypes best adapted to local climatic conditions, but the exact dynamics depends on the pattern of climatic adaptation. We conclude that failing to account for demographic variation across climatic gradients can lead to erroneous conclusions about species' capacity to spatially track suitable climate. [ABSTRACT FROM AUTHOR]

Investment in current reproduction can reduce future fitness by depleting resources needed for maintenance, particularly under environmental stress. These trade-offs influence life-history evolution. We tested whether climate change alters the future-fitness costs of current reproduction in a large-scale field experiment of Boechera stricta (Brassicaceae). Over 6 years, we simulated climate change along an elevational gradient in the Rocky Mountains through snow removal, which accelerates snowmelt and reduces soil water availability. Costs of reproduction were greatest in arid, lower elevations, where high initial reproductive effort depressed future fitness. At mid-elevations, initial reproduction augmented subsequent fitness in benign conditions, but pronounced costs emerged under snow removal. At high elevation, snow removal dampened costs of reproduction by prolonging the growing season. In most scenarios, failed reproduction in response to resource limitation depressed lifetime fecundity. Indeed, fruit abortion only benefited high-fitness individuals under benign conditions. We propose that climate change could shift life-history trade-offs in an environment-dependent fashion, possibly favouring early reproduction and short lifespans in stressful conditions. [ABSTRACT FROM AUTHOR]