Climatic Gradient Research Articles

Flexible or fortified? How lichens balance defence strategies across climatic harshness gradients.

Lichens play important roles in habitat formation and community succession in polar and alpine ecosystems. Despite their significance, the ecological effects of lichen traits remain poorly researched. We propose a trait trade-off for managing light exposure based on climatic harshness. In the harshest cold environments, where abiotic stress predominates over biotic pressures, lichens should rely on photostable, recalcitrant and immobile substances such as allomelanin and hydrophobic compounds. These compounds provide durable protection without the need for continual synthesis. In milder conditions where biotic interactions - e.g. competition and pathogen presence - become increasingly pronounced, lichens should retain flexibility and produce simple protective secondary compounds that, in addition to functioning as light screens, can leach out to influence their direct environment. Preliminary empirical findings for Antarctic lichen species distribution are consistent with this hypothesised trade-off, in that lichens producing soluble compounds dominate in milder regions and are less represented at higher southern latitudes, where species producing insoluble compounds with a melanised thallus dominate. As climate change progresses, increasing temperatures and precipitation could make the currently coldest and driest areas more hospitable, allowing the ranges of lichens producing soluble compounds to expand, with cascading effects on rock weathering, nutrient cycling and other ecosystem processes.

Carbon Sequestration Potential of Cashew (Anacardium occidentale L.) Plantations Across Climatic Gradients in Togo

The current study seeks to estimate the carbon sequestration capability of a cashew plantation in Togo as a function of climate gradient. The research was conducted in the Guinean and Sudanian climatic zones, on farmers' cashew plantations. The study was run from March to October 2023. This study was carried out in ten (10) cashew farms (five per climatic zone) which have ten years old. Cashew trees were classed based on their diameter at breast height (0-5 cm, 5-10 cm, 10-15 cm, and > 15 cm). To measure carbon stock in the biomass, allometric equations were utilized, and soil carbon stock was assessed using laboratory analysis. The Guinean zone has a higher soil carbon stock (86.89 ± 4.06 t C/ha) compared to the Sudanian zone (80.23 ± 3.78 t). The same trend can be observed in the various cashew tree components (trunk, branches and leaves). In general, the tree trunk had 79% of the carbon supply, compared to 19% and 2% in the branches and leaves, respectively. Carbon sequestration in the soil varies depending on the climatic zone and the soil depth (0-25 cm; 25-50 cm). Cashew-based cropping systems might be deemed carbon-efficient.

Molecular and taxonomical study of the genus Chara (Linnaeus 1753) in Israel

Abstract Israel’s climate is characterized by hot and dry summers and cool, rainy winters in the northern and coastal regions, whereas the southern and eastern regions are arid. The aquatic macrophyte Chara is a common genus in Israel, and its distribution varies across Israel’s climatic gradient. Although few studies described the abundance and taxonomy of the local Chara species in Israel, only little is known about the molecular taxonomy of this group in the region. We sampled Chara species along Israel’s climatic gradient and identified specimens using the classical taxonomy key and molecular identification methods. We characterized the molecular taxonomy of four Chara species: C. vulgaris, C. contraria, C. gymnophylla, and C. globata. Notably, the latter species, which was found in a hyper-arid area, was last recorded in Israel ~50 years ago on the northern Mediterranean coast and Judaean Mountains. Chara gymnophylla was more abundant in northern Israel, while C. vulgaris and C. contraria were common in southern Israel. We developed Inter Simple Sequence Repeat markers to identify the four species and sequenced their chloroplast gene rbcL. The phylogenetic trees generated using the rbcL sequences and ISSR-based dendrogram were consistent with the classical taxonomy of Chara.

Synchrony dynamics of dissolved organic carbon in high‐mountain streams: Insights into scale‐dependent processes

AbstractIn high‐mountain landscapes, organic carbon (OC) is often limited and heterogeneously stored in poorly developed soils, snow, ground ice, and glaciers. Climate change influences the dynamics of OC mobilization to—and processing into—the recipient streams. Dynamics vary from seasonal (e.g., snow melt in spring) to daily (e.g., ice melt in summer) depending on the location of the streams within the catchment. Capturing the temporal richness of stream biogeochemical signals has become a reality with the advent of high‐resolution sensors. In this study, we applied wavelet analysis to high‐frequency discharge (Q) and dissolved organic carbon (DOC) measurements from nine streams in the Swiss Alps to investigate the persistence of synchrony in Q (SQ) and DOC (SDOC) among streams, and their response to drainage network position, climate, and land cover gradients across different time scales. Our findings revealed that SQ and SDOC decayed non‐linearly over the first ~ 5 km and stabilized from this point onwards, indicating that localized controls influenced synchrony within single basins, but drivers operating at regional scale acted as synchrony stabilizers. We also showed that short‐term (0–10 d) SQ and SDOC were strongly influenced by the distance between streams and network connectivity. In contrast, catchment‐related properties (i.e., altitude or land cover) were more important drivers of SQ and SDOC dynamics at longer time scales (> 50 d). However, the degree to which local catchment properties controlled synchrony patterns at the longest timescales depended both on response variables (i.e., Q vs. DOC) and land cover (i.e., vegetation vs. glacier). Elucidating the most prominent timescales of SDOC is relevant given the hydrological alterations projected for high‐mountain regions. We show that glaciers impose a unique seasonal regime on DOC concentration, potentially overriding the effects of other local hydrological or biogeochemical processes during downstream transport. Consequently, SDOC dynamics in high‐mountain streams may change as glaciers shrink, thereby altering downstream opportunities for biogeochemical transformations.

Unveiling the global dynamics of dissolved organic carbon in aquatic ecosystems: Climatic and anthropogenic impact, and future predictions.

Dissolved organic carbon (DOC) and its biodegradability (BDOC%) in aquatic ecosystems significantly impact the global carbon cycle, varying greatly across rivers, lakes, and estuaries due to environmental and anthropogenic factors. However, a thorough understanding of these variations is still lacking. This study investigated the interactions between climate, hydrology, physiography, soil, land cover, and human activity on DOC dynamics in rivers, lakes, and estuaries. Utilizing a robust dataset comprising 744 global data points for DOC concentrations (0.18-29.33mg/L) and 341 samples for BDOC% (0.44%-81.12%), spanning a wide range of geographic and climatic gradients across six continents, machine learning techniques were employed to elucidate the relationships between DOC and BDOC% and environmental and anthropogenic factors and to develop predictive models for global DOC and BDOC storage. Results showed that climate primarily affected DOC and BDOC% levels, with other factors varying by ecosystem type. In rivers, soil and human activity had positive influences, while in lakes, hydrology had a positive effect and human activity had a negative one. In estuaries, soil positively impacted the levels of DOC and BDOC%, whereas human activity had a negative effect. Furthermore, we created separate random forest models for DOC and BDOC% based on different factors in each aquatic ecosystem (R2=0.50-0.89), and applied to data of environmental and anthropogenic factors worldwide, predicting DOC and BDOC storage for 181 countries. Notably, large countries like Canada, Russia, the United States (U.S.), Brazil, and China accounted for 76.07% and 51.56% of the total global DOC and BDOC storage, respectively. Storage prediction models under future climate scenarios indicated significant impacts in Europe under the high fossil fuel use scenario. Thus, prioritizing high-storage, climate-vulnerable areas is essential for effective climate change strategies, aiding in the protection of aquatic ecosystems, maintaining the global carbon balance, and promoting sustainable development.

Multiple Anthropogenic and Climatic Factors Drive Tree Species Attributes in Ecologically Distinct Sacred Groves in Ghana

Sacred groves are rich biodiversity hotspots serving as an important habitat for conserving species and providing ecosystem goods and services to meet societal needs. Despite the benefits these sacred groves offer, they are threatened by anthropogenic stressors coupled with climate change impacts, thereby limiting their maximum ability to offer essential ecological and cultural services. On a climatic gradient, we have explored differences in tree attributes (diversity and composition) and how they are shaped by multiple drivers of land‐use change and climatic factors (rainfall and temperature) which drive underlying soil conditions in different sacred groves. These sacred grooves studied are the Mintimrim Kwaye, Antobia, Boako, Nsoatre Botene and Pimpimgyae sacred groves. Tree species diversity and composition differed between the sacred groves with those located in the forest zones more diverse than those located in the dry semideciduous or the savannah zones. These differences in tree attributes were mainly driven by the various degrees of anthropogenic stressors (mining, agricultural activities, logging and wildfire) coupled with variations in climatic factors driving underlying soil conditions. It is quite evident the role climate plays which highlights how tree species react in terms of distribution and composition in this era of climate uncertainty. This therefore calls for the need for conservation efforts to mitigate the consequences of climate change impacts on biodiversity and human societies.

Soil microbial carbon and nitrogen limitation constraints soil organic carbon stability in arid and semi-arid grasslands.

Microorganisms play dual roles in soil organic carbon (SOC) decomposition and accumulation. Despite advancing insights into their involvement in the carbon cycle, understanding the impact of microbial community structure and physiological traits on SOC stabilization in arid and semi-arid grasslands remains elusive. Here, we analyzed arid and semi-arid grasslands SOC stability by comparing the ratio of mineral-associated organic carbon (MAOC) to particulate organic carbon (POC) across a grassland transect in north-south Ningxia, encompassing various grassland types and a broad climatic gradient (ΔMAP=450mm). By combining phospholipid fatty acid (PLFA) analysis, enzyme activity vector models and stoichiometric theory, the influence of soil microbial community compositions, metabolic constraints, and carbon use efficiency (CUE) on SOC stability were explored. Results showed that SOC stability was the lowest in desert areas and decreased with increasing mean annual precipitation (MAP) in other grasslands. Microbial physiological traits, including microbial carbon (C) limitation, nitrogen (N) limitation, CUE, and lignocellulose index (LCI) varied among grasslands, with significantly higher LCI and CUE and lower C and N limitation in steppe desert. The variation of microbial physiological characteristics accounted for 53.28% of the variation in SOC stability. Distinct microbial metabolic limitations were evident in these grasslands, with N and C limitation prevailing and exerting strong negative impacts on CUE. Decreased fungal/bacterial (F/B) ratios also reduced microbial CUE and indirectly diminished SOC stability. In addition, clay content emerges as a major factor influencing the stabilization of SOC across environmental gradients. Collectively, our work suggests that mitigating microbial C and N limitation and enhancing microbial CUE under the influence of MAP and clay content are the key mechanisms governing SOC stabilization in regional grasslands. These findings bear significant implications for understanding microbial-mediated carbon cycling processes in arid and semi-arid grasslands.

Leaf traits and insect herbivory levels in two Mediterranean oaks and their hybrids through contrasting environmental gradients.

Insect herbivory has attracted enormous attention from researchers due to its effects on plant fitness. However, there remain questions such as what are the most important leaf traits that determine consumption levels, whether there are latitudinal gradients in herbivore pressure, or whether there are differences in susceptibility between hybrids and their parental species. In this work we address all these issues in two species of Mediterranean Quercus (Q. faginea and Q. pyrenaica) and their hybrids. Over two years, we analyzed leaf emergence and 11 leaf traits (biomechanical, chemical and morphological), as well as the levels of herbivory by insects in leaves of the three genetic groups in different locations distributed along a climatic gradient. The hybrids showed intermediate values ​​between both species in leaf emergence, chemical traits and in structural reinforcement. By contrast, they were more similar to Q. faginea in leaf size and shape. Despite their intermediate leaf traits, hybrids always showed lower losses by consumption than both parental species, which suggests that they possess inherent higher resistance to herbivores, which cannot be explained by their dissimilarities in leaf traits. Within each genetic group, differences in leaf size were the most important determinant of differences in herbivory losses, which increased with leaf size. In turn, leaf size increased significantly with the increase in mean annual temperatures across the climatic gradient, in parallel with herbivory losses. In conclusion, contrary to our expectations, hybrids maintained lower levels of herbivory than their parent species. Given the potential negative effect of leaf herbivory on C fixation, this advantage of the hybrids would imply a threat to the persistence of both pure species. More research is needed to elucidate possible alternative mechanisms that allow maintaining species integrity in the absence of reproductive barriers.

Key concepts and a world-wide look at plant recruitment networks.

Plant-plant interactions are major determinants of the dynamics of terrestrial ecosystems. There is a long tradition in the study of these interactions, their mechanisms and their consequences using experimental, observational and theoretical approaches. Empirical studies overwhelmingly focus at the level of species pairs or small sets of species. Although empirical data on these interactions at the community level are scarce, such studies have gained pace in the last decade. Studying plant-plant interactions at the community level requires knowledge of which species interact with which others, so an ecological networks approach must be incorporated into the basic toolbox of plant community ecology. The concept of recruitment networks (RNs) provides an integrative framework and new insights for many topics in the field of plant community ecology. RNs synthesise the set of canopy-recruit interactions in a local plant assemblage. Canopy-recruit interactions describe which ("canopy") species allow the recruitment of other species in their vicinity and how. Here we critically review basic concepts of ecological network theory as they apply to RNs. We use RecruitNet, a recently published worldwide data set of canopy-recruit interactions, to describe RN patterns emerging at the interaction, species, and community levels, and relate them to different abiotic gradients. Our results show that RNs can be sampled with high accuracy. The studies included in RecruitNet show a very high mean network completeness (95%), indicating that undetected canopy-recruit pairs must be few and occur very infrequently. Across 351,064 canopy-recruit pairs analysed, the effect of the interaction on recruitment was neutral in an average of 69% of the interactions per community, but the remaining interactions were positive (i.e. facilitative) five times more often than negative (i.e. competitive), and positive interactions had twice the strength of negative ones. Moreover, the frequency and strength of facilitation increases along a climatic aridity gradient worldwide, so the demography of plant communities is increasingly strongly dependent on facilitation as aridity increases. At network level, species can be ascribed to four functional types depending on their position in the network: core, satellite, strict transients and disturbance-dependent transients. This functional structure can allow a rough estimation of which species are more likely to persist. In RecruitNet communities, this functional structure most often departs from random null model expectation and could allow on average the persistence of 77% of the species in a local community. The functional structure of RNs also varies along the aridity gradient, but differently in shrubland than in forest communities. This variation suggests an increase in the probability of species persistence with aridity in forests, while such probability remains roughly constant along the gradient in shrublands. The different functional structure of RNs between forests and shrublands could contribute to explaining their co-occurrence as alternative stable states of the vegetation under the same climatic conditions. This review is not exhaustive of all the topics that can be addressed using the framework of RNs, but instead aims to present some of the interesting insights that it can bring to the field of plant community ecology.

Interactive effects of nitrogen deposition and climate change on a globally rare forest geophyte

Abstract Nitrogen (N) deposition and climate change are both known to threaten global biodiversity. However, we still have a limited understanding of how interactions between these global change drivers affect individuals and populations of specialist species, such as geophytes, within their natural habitat. We explored possible interactive effects of N, drought, and warming on population vitality (mean leaf length, leaf density, flowering probability) and morpho‐physiological traits (e.g., leaf and bulb size, N allocation to leaves and bulbs) of the globally rare forest geophyte Gagea spathacea (Liliaceae) in deciduous forests of northern Germany by applying experimental N addition across a climate gradient over a 5‐year period. Mean leaf growth and leaf density were not affected by N addition but were enhanced by warmer and drier conditions in the months before leaf emergence. N addition increased N allocation of individual plants towards their subterranean bulbs. Importantly, effects of N addition on morpho‐physiological traits depended on warming and drought, with N‐fertilized plants showing increased leaf length and decreased specific leaf and bulb N concentration after drier autumns and warmer winters. This indicates that N deposition may partially compensate for increased N demands during warming‐induced growth, although this growth‐promoting interaction effect is not (yet) reflected in population vitality. Our results highlight the importance of considering multiple global environmental change drivers and a whole plant perspective (above‐ and belowground traits) to predict long‐term growth responses of (endangered) forest spring geophytes and to develop adapted long‐term protection strategies.

Spatial patterns of phylogenetic diversity in the Andean tribe Eudemeae (Brassicaceae) and their association with climatic gradients in western South America

Spatial patterns of phylogenetic diversity in the Andean tribe Eudemeae (Brassicaceae) and their association with climatic gradients in western South America

Lizards as sentinels for the distribution of Angiostrongylus cantonensis.

The rat lungworm Angiostrongylus cantonensis is a zoonotic metastrongyloid nematode currently considered an emerging pathogen. Originating in Southeast Asia, this nematode has spread to tropical and subtropical parts of the world via its invasive rodent and gastropod hosts.On the island of Tenerife in the Canary archipelago, the A. cantonensis invasion was recognized more than a decade ago. The endemic lizard Gallotia galloti has been identified as a paratenic host of this nematode in the Canary Island ecosystem. Because this lizard species is the most abundant reptile in Tenerife, we tested its suitability as a possible sentinel for A. cantonensis presence. Lizards were captured alive in nine localities, spanning an environmental gradient across the island. Tail muscle tissue was obtained by provoked caudal autotomy and tested for the nematode infection by a species-specific qPCR. Infection intensities were assessed by detecting A. cantonensis DNA quantities based on a calibrated standard curve. Of the 129 samples tested, 31 were positive. The prevalence varied among localities, with the highest (63.6%) recorded in a humid laurel forest. Even though the prevalence in Valle San Lorenzo was the lowest, this is the first record of A. cantonensis from the arid south of Tenerife. Variation in prevalence at different localities was significantly and positively correlated with increasing vegetation cover and negatively correlated with seasonal variability of precipitation, as determined by Spearman correlation coefficients. Fisher's exact test was used to determine the variation in the prevalence of A. cantonensis among adult males, females, and juveniles and showed no significant difference. Also, there was no significant difference in infection intensity between males and females (as determined by GEE-g). We demonstrated that provoking caudal autotomy can be an effective non-lethal method of A. cantonensis mapping in island ecosystems with abundant lizard species, particularly those with a sharp climatic and vegetation gradient, from xeric to humid conditions.

Grassland Afforestation Drives Biotic Homogenisation of Soil Microbial Communities at a Regional Scale.

Grassland afforestation poses a threat to biodiversity beyond land-use conversion. Diversity patterns are shaped by temporal dynamics, particularly, time since afforestation can decline beta diversity and lead to biotic homogenisation. Our study examines the effect of grassland afforestation on soil prokaryotic and fungal beta diversity. We evaluate the contributions of colonisation and extinction processes to beta diversity, as well as the replacement of endemic species by ubiquitous ones. Along a 200 km climatic gradient in Argentina's Pampas region, we analysed grasslands and mature eucalypt plantations at different times since afforestation. Soil samples were collected at each site and analysed using 16S (V3-V4) and ITS2 amplicon sequencing to identify prokaryotic and fungal communities, respectively. The analyses revealed biotic homogenisation at the transition from grassland to newly planted stands, evidenced by a decrease in intratreatment beta diversity. Increasing time since afforestation did not exacerbate this decline. However, our findings indicate that there are different responses between prokaryotes and fungi. The homogenisation of prokaryotes in young stands is due to the low heterogeneity in colonising communities. On the other hand, the decline in fungal beta diversity is likely caused by other mechanisms beyond extinction or replacement. The study highlights the impacts of the afforestation process on the beta diversity of soil microbial communities of grasslands, affecting taxonomic groups in different ways. Although microbial diversity may be partially restored in time in eucalypt plantations, it is important to investigate its underlying mechanisms and the ecological implications for microbial diversity and its spatial distribution.

Herbivory resistance in dwarf shrubs combines with simulated warming to shift phenology and decrease reproduction

Abstract Research focus on the phenology of plants has accompanied current trends in climate warming, because the two are inextricably linked. Warmer temperatures have led to advanced plant phenology in a range of systems, although some responses are species specific. However, other stressors, such as herbivory, can delay or advance plant phenology, and few studies have addressed the combined impact of these drivers. We experimentally warmed plots with open top chambers (OTCs) and simulated herbivory resistance to insect outbreaks with methyl jasmonate (MeJA), along an elevational climatic gradient. We then recorded vegetative and reproductive phenology in two functionally important dwarf shrubs, the deciduous Vaccinium myrtillus (bilberry) and the evergreen V. vitis‐idaea (lingonberry), to test the responses to the combined treatments. Based on earlier findings, we expected larger phenological responses at higher elevations and for bilberry. We found that in the year after MeJA application, both bilberry and lingonberry delayed vegetative and reproductive phenology, although responses were stronger in bilberry. Warming with OTCs weakly advanced phenology in both species, but combined effects were not consistent. We further examined the consequences of this altered phenology on reproductive output with multigroup piecewise structural equation modelling and found that herbivory resistance driven changes to phenology had a strong mediating effect on berry numbers, particularly under warmed conditions and mainly in the year after MeJA application. Synthesis. These results demonstrate the need to consider combined pressures in understanding the impacts of global change on plants and highlight that multiple drivers may have unidentified synergetic effects on species phenology and reproduction.

Effects of land cover and protected areas on flying insect diversity.

Widespread insect losses are a critical global problem. Mitigating this problem requires identifying the principal drivers across different taxa and determining which insects are covered by protected areas. However, doing so is hindered by missing information on most species owing to extremely high insect diversity and difficulties in morphological identification. To address this knowledge gap, we used one of the most comprehensive insect DNA metabarcoding data sets assembled (encompassing 31,846 flying insect species) in which data were collected from a network of 75 Malaise traps distributed across Germany. Collection sites encompass gradients of land cover, weather, and climate, along with differences in site protection status, which allowed us to gain broader insights into how insects respond to these factors. We examined changes in total insect biomass, species richness, temporal turnover, and shifts in the composition of taxa, key functional groups (pollinators, threatened species, and invasive species), and feeding traits. Lower insect biomass generally equated to lower richness of all insects and higher temporal turnover, suggesting that biomass loss translates to biodiversity loss and less stable communities. Spatial variability in insect biomass and composition was primarily driven by land cover, rather than weather or climate change. As vegetation and land-cover heterogeneity increased, insect biomass increased by 50% in 2019 and 56% in 2020 and total species richness by 58% and 33%, respectively. Similarly, areas with low-vegetation habitats exhibited the highest richness of key taxa, including pollinators and threatened species, and the widest variety of feeding traits. However, these habitats tended to be less protected despite their higher diversity. Our results highlight the value of heterogeneous low vegetation for promoting overall insect biomass and diversity and that better protection of insects requires improved protection and management of unforested areas, where many biodiversity hotspots and key taxa occur.

Macroevolutionary processes in turtles (Testudines): a view from biomic specialization and historical climatic changes

The resource-use hypothesis proposed by Elisabeth S. Vrba suggests that lineages display varying tendencies toward generalism or specialization in biome occupancy, with a tendency towards the accumulation of specialists due to their higher rate of speciation through vicariance. It also posits differences in biome occupancy patterns driven by the environmental characteristics of biomes, with a higher presence of biome specialist species in biomes that are placed in the extremes of the global climatic gradients. Here, we tested this hypothesis in turtles, a very ancient and morphologically stable lineage, representing a remarkable diversity with 357 species, many of which are threatened with extinction. We analyzed the resource-use hypothesis in a phylogenetic context within the Testudines lineage. For this purpose, a presence/absence matrix was compiled for all species across all 10 terrestrial biomes. Their distribution across biomes was contrasted with 10,000 Monte Carlo simulations. The relationship between diversification rates and both the biomic specialization index and the biomes occupied by specialists species was evaluated. The results demonstrate strong consistency with Vrba`s hypothesis, revealing a higher number of biome specialist species than expected by chance, with a significant accumulation of species in tropical ecosystems. These trends also were observed for ecological groups (terrestrial and freshwater species). In addition, higher diversification rates were observed for biome specialist species, although the particular biome occupied did not significantly influence their diversification rates.

Variation in the diversity and composition of tree-related microhabitats across climate and human impact gradients on a tropical mountain

Tree-related microhabitats (TReMs) have been proposed as important indicators of biodiversity to guide forest management. However, their application has been limited mostly to temperate ecosystems, and it is largely unknown how the diversity of TReMs varies along environmental gradients. In this study, we assessed the diversity of TReMs on 180 individual trees and 44 plots alongside a large environmental gradient on Kilimanjaro, Tanzania. We used a typology adjusted to tropical ecosystems and a tree-climbing protocol to obtain quantitative information on TreMs on large trees and dense canopies. We computed the diversity of TReMs for each individual tree and plot and tested how TReM diversity was associated with properties of individual trees and environmental conditions in terms of climate and human impact. We further used non-metric multidimensional scaling (NMDS) to investigate the composition of TReM assemblages alongside the environmental gradients. We found that diameter at breast height (DBH) and height of the first branch were the most important determinants of TReM diversity on individual trees, with higher DBH and lower first branch height promoting TReM diversity. At the plot level, we found that TReM diversity increased with mean annual temperature and decreased with human impact. The composition of TReMs showed high turnover across ecosystem types, with a stark difference between forest and non-forest ecosystems. Climate and the intensity of human impact were associated with TReM composition. Our study is a first test of how TReM diversity and composition vary along environmental gradients in tropical ecosystems. The importance of tree size and architecture in fostering microhabitat diversity underlines the importance of large veteran trees in tropical ecosystems. Because diversity and composition of TReMs are sensitive to climate and land-use effects, our study suggests that TReMs can be used to efficiently monitor consequences of global change for tropical biodiversity.

Long-term grazing effects on soil-borne pathogens are driven by temperature

Soils support a highly diverse community of plant pathogens, which are highly responsive to global change. Climate and livestock grazing are the main global changes in grasslands, yet, how long-term grazing alone, and in interaction with climate, influence the distribution of soil-borne plant pathogens remain virtually unknown. Here, we present the first long-term regional-scale experimental investigation on the impacts of livestock grazing on soil-borne fungal plant pathogens and their association with plant community across 10 experimental sites spanning a climate gradient in the steppe in Northern China. Our results showed that long-term grazing effects on the diversity and proportion of soil-borne fungal plant pathogens are strongly controlled by temperature, with grazing increasing pathogen richness and proportions largely in cooler grasslands. We further show that long-term grazing supported stronger connections between soil-borne fungal pathogens and plant communities. Our work demonstrates that climate controls the effects of grazing on plant pathogens, which is critical to understand and manage grasslands in a changing world.

Wheat field earthworms under divergent farming systems across a European climate gradient.

Earthworms are a key faunal group in agricultural soils, but little is known on how farming systems affect their communities across wide climatic gradients and how farming system choice might mediate earthworms' exposure to climate conditions. Here, we studied arable soil earthworm communities on wheat fields across a European climatic gradient, covering nine pedo-climatic zones, from Mediterranean to Boreal (S to N) and from Lusitanian to Pannonian (W to E). In each zone, 20-25 wheat fields under conventional or organic farming were sampled. Community metrics (total abundance, fresh mass, and species richness and composition) were combined with data on climate conditions, soil properties, and field management and analyzed with mixed models. There were no statistically discernible differences between organic and conventional farming for any of the community metrics. The effects of refined arable management factors were also not detected, except for an elevated proportion of subsurface-feeding earthworms when crop residues were incorporated. Soil properties were not significantly associated with earthworm community variations, which in the case of soil texture was likely due to low variation in the data. Pedo-climatic zone was an overridingly important factor in explaining the variation in community metrics. The Boreal zone had the highest mean total abundance (179 individuals m-2) and fresh mass (86 g m-2) of earthworms while the southernmost Mediterranean zones had the lowest metrics (<1 individual m-2 and <1 g m-2). Within each field, species richness was low across the zones, with the highest values being recorded at the Nemoral and North Atlantic zones (mean of 2-3 species per field) and declining from there toward north and south. No litter-dwelling species were found in the southernmost, Mediterranean zones. These regional trends were discernibly related to climate, with the community metrics declining with the increasing mean annual temperature. The current continent-wide warming of Europe and related increase of severe and rapid onsetting droughts will likely deteriorate the living conditions of earthworms, particularly in southern Europe. The lack of interaction between the pedo-climatic zone and the farming system in our data for any of the earthworm community metrics may indicate limited opportunities for alleviating the negative effects of a warming climate in cereal field soils of Europe.

Wetland CH4 and CO2 emissions show opposite temperature dependencies along global climate gradients

Methane (CH4) and carbon dioxide (CO2) are the two largest contributors to the anthropogenically-driven greenhouse effect, which are the dominant gaseous end-products of wetland C decomposition. However, given our limited understanding of the spatial heterogeneity of wetland CH4 and CO2 emissions, it is uncertain how future warming may impact the emissions of these dangerous emissions. Here, we show opposite temperature dependencies of CH4 and CO2 emissions along global climate gradients using data from 45 widely distributed wetlands in the FLUXNET-CH4 database. Specifically, the temperature dependence of CH4 emissions increased as mean annual temperature (MAT) rose, while the dependence of CO2 emissions decreased, suggesting that in warmer areas, there is a greater risk for increased wetland CH4 emissions accompanying lower CO2 emissions in response to global warming. The ratio of wetland CH4 to CO2 emissions increased linearly with increasing temperature only when MAT and mean annual precipitation (MAP) are greater than 4.7 °C and 483 mm, respectively. This response indicates that, compared with those in cold and dry climates, wetland ecosystems in warmer and wetter climates are more prone to methanogenesis as temperatures rise. Our results suggest that neglecting spatial variation of temperature dependencies in models may underestimate wetland CH4 and CO2 emissions compared to the use of a static and consistent temperature dependence parameter when only considering temperature effects. These findings highlight the importance of incorporating climate-related variation in the temperature dependencies of CH4 and CO2 emissions into models to improve predictions of wetland C-climate change feedbacks in the Anthropocene.