Biogeography of global drylands Maestre, Fernando T.; Benito, Blas M.; Berdugo, Miguel ...
The New phytologist,
July 2021, Volume:
231, Issue:
2
Journal Article
Peer reviewed
Open access
Summary
Despite their extent and socio‐ecological importance, a comprehensive biogeographical synthesis of drylands is lacking. Here we synthesize the biogeography of key organisms (vascular and ...nonvascular vegetation and soil microorganisms), attributes (functional traits, spatial patterns, plant–plant and plant–soil interactions) and processes (productivity and land cover) across global drylands. These areas have a long evolutionary history, are centers of diversification for many plant lineages and include important plant diversity hotspots. This diversity captures a strikingly high portion of the variation in leaf functional diversity observed globally. Part of this functional diversity is associated with the large variation in response and effect traits in the shrubs encroaching dryland grasslands. Aridity and its interplay with the traits of interacting plant species largely shape biogeographical patterns in plant–plant and plant–soil interactions, and in plant spatial patterns. Aridity also drives the composition of biocrust communities and vegetation productivity, which shows large geographical variation. We finish our review by discussing major research gaps, which include: studying regular vegetation spatial patterns; establishing large‐scale plant and biocrust field surveys assessing individual‐level trait measurements; knowing whether the impacts of plant–plant and plant–soil interactions on biodiversity are predictable; and assessing how elevated CO2 modulates future aridity conditions and plant productivity.
Climate models project overall a reduction in rainfall amounts and shifts in the timing of rainfall events in mid‐latitudes and sub‐tropical dry regions, which threatens the productivity and ...diversity of grasslands. Arbuscular mycorrhizal (AM) fungi may help plants to cope with expected changes but may also be impacted by changing rainfall, either via the direct effects of low soil moisture on survival and function or indirectly via changes in the plant community.
In an Australian mesic grassland (former pasture) system, we characterized plant and AM fungal communities every 6 months for nearly 4 years to two altered rainfall regimes: (a) ambient, (b) rainfall reduced by 50% relative to ambient over the entire year and (c) total summer rainfall exclusion. Using Illumina sequencing, we assessed the response of AM fungal communities sampled from contrasting rainfall treatments and evaluated whether variation in AM fungal communities was associated with variation in plant community richness and composition.
We found that rainfall reduction influenced the fungal communities, with the nature of the response depending on the type of manipulation, but that consistent results were only observed after more than 2 years of rainfall manipulation. We observed significant co‐associations between plant and AM fungal communities on multiple dates. Predictive co‐correspondence analyses indicated more support for the hypothesis that fungal community composition influenced plant community composition than vice versa. However, we found no evidence that altered rainfall regimes were leading to distinct co‐associations between plants and AM fungi. Overall, our results provide evidence that grassland plant communities are intricately tied to variation in AM fungal communities. However, in this system, plant responses to climate change may not be directly related to impacts of altered rainfall regimes on AM fungal communities.
Synthesis. Our study shows that arbuscular mycorrhizal (AM) fungal communities respond to changes in rainfall but that this effect was not immediate. The AM fungal community may influence the composition of the plant community. However, our results suggest that plant responses to altered rainfall regimes at our site may not be resulting via changes in the AM fungal communities.
Our study shows that AM fungal communities respond to changes in rainfall but that this effect was not immediate. The AM fungal community may influence the composition of the plant community. However, our results suggest that plant responses to altered rainfall regimes at our site may not be resulting via changes in the AM fungal communities.
Microbes inhabiting deep soil layers are known to be different from their counterpart in topsoil yet remain under investigation in terms of their structure, function, and how their diversity is ...shaped. The microbiome of deep soils (>1 m) is expected to be relatively stable and highly independent from climatic conditions. Much less is known, however, on how these microbial communities vary along climate gradients. Here, we used amplicon sequencing to investigate bacteria, archaea, and fungi along fifteen 18‐m depth profiles at 20–50‐cm intervals across contrasting aridity conditions in semi‐arid forest ecosystems of China's Loess Plateau. Our results showed that bacterial and fungal α diversity and bacterial and archaeal community similarity declined dramatically in topsoil and remained relatively stable in deep soil. Nevertheless, deep soil microbiome still showed the functional potential of N cycling, plant‐derived organic matter degradation, resource exchange, and water coordination. The deep soil microbiome had closer taxa–taxa and bacteria–fungi associations and more influence of dispersal limitation than topsoil microbiome. Geographic distance was more influential in deep soil bacteria and archaea than in topsoil. We further showed that aridity was negatively correlated with deep‐soil archaeal and fungal richness, archaeal community similarity, relative abundance of plant saprotroph, and bacteria–fungi associations, but increased the relative abundance of aerobic ammonia oxidation, manganese oxidation, and arbuscular mycorrhizal in the deep soils. Root depth, complexity, soil volumetric moisture, and clay play bridging roles in the indirect effects of aridity on microbes in deep soils. Our work indicates that, even microbial communities and nutrient cycling in deep soil are susceptible to changes in water availability, with consequences for understanding the sustainability of dryland ecosystems and the whole‐soil in response to aridification. Moreover, we propose that neglecting soil depth may underestimate the role of soil moisture in dryland ecosystems under future climate scenarios.
Our results contribute to broader and deeper knowledge of climate change microbiology in deep soil environments under future climate scenarios. We proposes a potential mechanism for the association between climate aridity and deep soil microbes; that is, when the external aridity changes, water evapotranspiration (including plant transpiration and soil water evaporation) is directly and indirectly (e.g., changes in rooting depths and soil texture) affected, and a volumetric soil moisture gradient (related to soil porosity) is formed to primarily drive microorganisms in deep soil.
Soil micronutrients are capital for the delivery of ecosystem functioning and food provision worldwide. Yet, despite their importance, the global biogeography and ecological drivers of soil ...micronutrients remain virtually unknown, limiting our capacity to anticipate abrupt unexpected changes in soil micronutrients in the face of climate change. Here, we analyzed >1300 topsoil samples to examine the global distribution of six metallic micronutrients (Cu, Fe, Mn, Zn, Co and Ni) across all continents, climates and vegetation types. We found that warmer arid and tropical ecosystems, present in the least developed countries, sustain the lowest contents of multiple soil micronutrients. We further provide evidence that temperature increases may potentially result in abrupt and simultaneous reductions in the content of multiple soil micronutrients when a temperature threshold of 12–14°C is crossed, which may be occurring on 3% of the planet over the next century. Altogether, our findings provide fundamental understanding of the global distribution of soil micronutrients, with direct implications for the maintenance of ecosystem functioning, rangeland management and food production in the warmest and poorest regions of the planet.
Here we analyzed the occurrence of six soil micronutrients (Fe, Mn, Zn, Cu, Co and Ni) across all continents and a wide range of biomes. Warmer arid and tropical soils, found in least developed countries, contained the lowest levels of soil micronutrients. We found an abrupt decrease in soil micronutrients associated with increasing temperatures at 12–14°C. These findings have direct implications on ecosystem maintenance, rangeland management and food production in poor countries. The world image in this figure was designed by ibrandify/Freepik.
Aims
We evaluated the impacts of altered precipitation regimes on multiple aspects of the C cycle, including C fluxes, plant and soil microbial communities, and plant-soil interactions in a ...south-eastern Australian grassland.
Methods
Our experimental treatments, operated through an automated system, included: (i) reduced and (ii) increased rainfall amount by 50%, (iii) reduced rainfall frequency but no change in amount (i.e., more extreme downpours), (iv) and an extreme summer drought.
Results
Temporal dynamics of ecosystem-level CO
2
fluxes fluctuated seasonally and were driven by variations in soil water availability, soil temperature and photosynthetically active radiation. Reducing the frequency of rainfall events, but without change in the amount of rainfall, resulted in lower ecosystem-level net CO
2
uptake due to relatively greater R
eco
stimulation after the heavy downpours, particularly during the late summer season. The extreme summer drought downregulated both respiration and photosynthesis. Microbial abundance and activity did not change in response to rainfall manipulation and were not strongly related to precipitation-driven changes in C cycling. In contrast, a greater proportion of live to dead plant biomass, in turn driven by greater water availability, was a main driver of greater respiration and photosynthesis.
Conclusions
Our study suggests that grasslands could shift from net C sinks to C neutral or even net sources of C under future scenarios of more variable rainfall regimes, thus reinforcing climate change.
Aims
Accurate predictions of plant responses to elevated CO
2
(eCO
2
) levels require a better understanding of uptake and allocation of resources that affect growth. While it is well-established ...that plants can increase C transfer belowground to increase access to nutrients in N-limited environments, there is less studies investigating the role of these adaptations in P-limited systems. In this study, we aimed to characterise plant nutrient use and acquisition strategies under future atmospheric CO
2
scenarios, under P-limited conditions and determine how different levels of water availability regulate these strategies.
Methods
We exposed four grass species commonly found in the understory of P-limited Australian
Eucalyptus
woodlands to eCO
2
over a period of 14 weeks, under two contrasting water levels. We assessed a suite of root morphological and chemical traits and the rhizosphere activity of extracellular enzymes related to C, N and P cycles, along with changes in plant allocation patterns and use efficiency of these nutrients.
Results
Elevated CO
2
effects on root functional attributes were species-specific, but clear trends towards increased phosphatase activity were observed across species, leading to a lower C:P ratio. In contrast, water supply affected root morphological attributes, but interactions between CO
2
and water levels on functional traits were minor. Greater water availability also stimulated microbial activity in the rhizosphere, but without observable changes in the relative demand for N and P relative to C.
Conclusions
Despite changes in rhizosphere processes, eCO
2
did not lead to increased plant biomass regardless of water supply, suggesting primary nutrient limitation and a lack of positive rhizosphere feedbacks to plant growth.
Methods and approaches to advance soil macroecology White, Hannah J.; León‐Sánchez, Lupe; Burton, Victoria J. ...
Global ecology and biogeography,
October 2020, 2020-10-00, 20201001, Volume:
29, Issue:
10
Journal Article
Peer reviewed
Open access
Motivation and aim
Soil biodiversity is central to ecosystem function and services. It represents most of terrestrial biodiversity and at least a quarter of all biodiversity on Earth. Yet, research ...into broad, generalizable spatial and temporal patterns of soil biota has been limited compared to aboveground systems due to complexities of the soil system. We review the literature and identify key considerations necessary to expand soil macroecology beyond the recent surge of global maps of soil taxa, so that we can gain greater insight into the mechanisms and processes shaping soil biodiversity. We focus primarily on three groups of soil taxa (earthworms, mycorrhizal fungi and soil bacteria) that represent a range of body sizes and ecologies, and, therefore, interact with their environment at different spatial scales.
Results
The complexities of soil, including fine‐scale heterogeneity, 3‐D habitat structure, difficulties with taxonomic delimitation, and the wide‐ranging ecologies of its inhabitants, require the classical macroecological toolbox to be expanded to consider novel sampling, molecular identification, functional approaches, environmental variables, and modelling techniques.
Main conclusions
Soil provides a complex system within which to apply macroecological research, yet, it is this property that itself makes soil macroecology a field ripe for innovative methodologies and approaches. To achieve this, soil‐specific data, spatio‐temporal, biotic, and abiotic considerations are necessary at all stages of research, from sampling design to statistical analyses. Insights into whole ecosystems and new approaches to link genes, functions and diversity across spatial and temporal scales, alongside methodologies already applied in aboveground macroecology, invasion ecology and aquatic ecology, will facilitate the investigation of macroecological processes in soil biota, which is key to understanding the link between biodiversity and ecosystem functioning in terrestrial ecosystems.
In forests, the majority of fine roots are located within the upper soil horizons, and fine root biomass decreases with depth. We evaluated spatial patterns in the distribution of fine root biomass ...and determined relationships with soil properties and vegetation structure in a Eucalyptus tereticornis woodland in East Australia. Fine root biomass (0–50 cm depth) was 678 (± 96.9) g m⁻² and decreased exponentially with depth. Total fine root biomass was positively related to aboveground herbaceous biomass and increased with increasing proximity to larger trees, reflecting contributions from both herbaceous understorey plants and mature trees. Plants produced more fine roots in soil patches with lower organic matter content, possibly as a functional response to increase acquisition of essential nutrients in more nutrient-depleted soils. Aboveground plant attributes were more important predictors of fine roots in the shallowest layer, while water availability was a stronger predictor of fine root biomass in deeper layers, likely reflecting the harsh climatic conditions prior to sampling. Fine roots represent an important gap in many ecosystem models despite being key for biogeochemical cycling. Here, we showed that the spatial patterns of fine root biomass can be inferred from soil and vegetation characteristics across remnant Australian Eucalyptus woodlands.
Lichens are the key to nutrient cycling and trophic networks in many terrestrial ecosystems and are good bioindicators of air pollution, including nitrogen (N) deposition. Experimental studies have ...shown that N deposition can reduce the abundance of lichens and alter their thallus chemistry and metabolism, but we currently lack information about how widespread this effect is and what are the environmental factors modulating the response of lichens to N. We carried out a meta-analysis of the literature about the effects of experimental N fertilization on lichen abundance and metabolism. We found thirty-nine articles from thirty-one experimental sites that met our search criteria. These studies showed that the addition of N accelerates lichen metabolism in the short term and decreases their abundance in the medium–long term. Early senescence of lichens is proposed as a possible mechanism linking the two observed responses. Chlorolichens from regions with high precipitation (> 1000 mm) and with a background N deposition of mixed origin (agricultural and industrial) were the most affected by N, in terms of both abundance and metabolism. Structural equation modelling showed that the rate of N addition was the main factor in modulating the response of lichens to N in terms of metabolism, whereas isothermality played a very important role in modulating the lichen response to N in terms of abundance. Our meta-analysis identified that excess N deposition reduces lichen abundance and increases the metabolism of sensitive species, especially across European ecosystems; lichens from more climatically benign regions (that is, greater precipitation and isothermality) are the most affected.
Soil respiration (SR
TOT
) and its main components, soil heterotrophic (SR
H
) and autotrophic respiration (SR
A
), were monitored in response to within-season drought events of increasing duration ...and soil N enrichment in a semiarid meadow steppe. The experiment consisted of the combination of five drought periods (0 days, 15 days, 30 days, 45 days, and 60 days) and two N addition levels (0 and 10 g N m
−2
year
−1
applied as urea). Soil respiration decreased after 30 days of drought, with the response being driven by soil heterotrophs. Moreover, N addition increased the sensitivity of soil respiration to soil water content, which we attributed to greater plant C inputs and soil microbial C and N content in the N addition treatment. Our results highlight the role of SR
H
as a key regulator of C fluxes in nutrient-poor semiarid meadow steppe in response to extreme within-season drought and the role of soil N availability in modulating this response.
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