Biodiversity plays a fundamental role in provisioning and regulating forest ecosystem functions and services. Above‐ground (plants) and below‐ground (soil microbes) biodiversity could have ...asynchronous change paces to human‐driven land‐use impacts. Yet, we know very little how they affect the provision of multiple forest functions related to carbon accumulation, water retention capacity and nutrient cycling simultaneously (i.e. ecosystem multifunctionality; EMF). We used a dataset of 22,000 temperate forest trees from 260 plots within 11 permanent forest sites in Northeastern China, which are recovering from three post‐logging disturbances. We assessed the direct and mediating effects of multiple attributes of plant biodiversity (taxonomic, phylogenetic, functional and stand structure) and soil biodiversity (bacteria and fungi) on EMF under the three disturbance levels. We found the highest EMF in highly disturbed rather than undisturbed mature forests. Plant taxonomic, phylogenetic, functional and stand structural diversity had both positive and negative effects on EMF, depending on how the EMF index was quantified, whereas soil microbial diversity exhibited a consistent positive impact. Biodiversity indices explained on average 45% (26%–58%) of the variation in EMF, whereas climate and disturbance together explained on average 7% (0.4%–15%). Our result highlighted that the tremendous effect of biodiversity on EMF, largely overpassing those of both climate and disturbance. While above‐ (β = 0.02–0.19) and below‐ground (β = 0.16–0.26) biodiversity had direct positive effects on EMF, their opposite mediating effects (β = −0.22 vs. β = 0.35 respectively) played as divergent pathways to human disturbance impacts on EMF. Our study sheds light on the need for integrative frameworks simultaneously considering above‐ and below‐ground attributes to grasp the global picture of biodiversity effects on ecosystem functioning and services. Suitable management interventions could maintain both plant and soil microbial biodiversity, and thus guarantee a long‐term functioning and provisioning of ecosystem services in an increasing disturbance frequency world.
Higher EMF was found in disturbed forests rather than relatively undisturbed mature forests. Above‐and below‐ground biodiversity had direct positive effects on EMF, their opposite mediating effects played as divergent pathways to human disturbance impacts on EMF.
Interactions between plants and soil microbial communities underpin soil processes and forest ecosystem function, but the links between tree diversity and soil microbial diversity are poorly ...characterized. Differences in both the taxonomic and functional diversity of trees and microbes can shape soil nutrient status and carbon storage, but the stoichiometry of carbon and nutrients in the soil also influences resource availability to plant and microbial communities. Given the key role of resource availability in plant–soil interactions, we hypothesized that relationships between tree diversity metrics and soil bacterial or fungal diversity are mediated by soil stoichiometry. To test our hypothesis, we measured tree diversity metrics (tree species richness, functional trait diversity and functional trait composition) and soil stoichiometry in a temperate forest in China, and we determined soil microbial diversity by Illumina sequencing. We used structural equation models to assess the relationships between tree diversity metrics and soil bacterial or fungal diversity and to evaluate the influence of soil stoichiometry. Overall, microbial diversity was strongly related to soil stoichiometry, whereby fungal diversity was associated with high soil N/P ratios, whereas bacterial diversity was related to high soil C/P ratios. Soil bacterial and fungal diversity were more closely related to tree functional trait diversity and composition than to tree species richness, and the links between tree and soil microbial diversity were mediated by soil stoichiometry. The strong links between tree functional traits, soil stoichiometry and soil bacteria or fungi suggest that resource quality plays a key role in plant–microbial interactions. Our results highlight the importance of nutrient stoichiometry in linkages between tree functional diversity and soil microbial diversity.
Tree canopies are considered to effectively buffer climate extremes and to mitigate climate change effects. Droughts, which are predicted to become more frequent in the course of climate change, ...might alter the microclimatic cooling potential of trees. However, our understanding of how microclimate at the tree canopy level is modulated by environmental and tree characteristics and their interactions is still limited. Here, we investigated canopy temperature regulation for five mature co-occurring tree species for two contrasting hydrological situations during the severe drought in 2018. Even though we observed a significant drought-induced decline in canopy cover and transpiration across tree species, we found evidence that differences in the water use strategies of trees affected cooling mechanisms differently. Although a large share of the variations in the cooling potential of trees was explained by direct and indirect effects of meteorological factors, we identified a gradual shift in importance from latent heat flux to components defining the magnitude of sensible heat flux on the energy budget of tree as the drought gained severity. The decrease in latent heat fluxes, approximated by sap flow rates, furthermore resulted in a reduced cooling potential and an equalization of tree species canopy temperatures.
Abstract
Climate extremes in tandem with biodiversity change affect plant emissions of biogenic volatile organic compounds, as a result, the formation of biogenic secondary organic aerosols. The ...resulting biogenic secondary organic aerosols can have a wide variety of impacts, such as on Earth’s radiative balance or cloud- and precipitation formation. However, at present, it is unclear how changing biodiversity will lead to changes in biogenic volatile organic compound emissions, biogenic secondary organic aerosols and their corresponding effects. We present a conceptual framework of the relationships between biodiversity and biogenic volatile organic compound emissions based on our current mechanistic understanding and combining knowledge from the fields of biology and atmospheric chemistry. Parts of this framework are tested in a case study using a tree diversity experiment. The relative differences in tree monocultures and mixtures show that the overall concentration of biogenic volatile organic compounds decreases with increasing biodiversity, but results for biogenic secondary organic aerosols are mixed and overall non-significant. A deeper understanding of how changing biodiversity influences biogenic organic compound emissions and biogenic secondary organic aerosol formation requires in-depth investigations of microclimate conditions, accurate monitoring of above- and below-ground biotic and abiotic stress, and manipulating stress conditions across long-term biodiversity experiments.
Soil’s water-physical properties support essential soil water retention functions for driving water distribution and availability, which is vital for plant growth and biogeochemical cycling. However, ...the question concerning how tree compositions and their interactions with other abiotic factors modulate soil’s water-physical properties in disturbed forests remains poorly understood. Based on observational data from nine permanent forest sites (18,747 trees and 210 plots) in the northeast of China, where forests once undergone three different levels of anthropogenic logging disturbance, we evaluated how multiple biotic (i.e., tree diversity and functional trait composition) and abiotic (soil texture and soil organic carbon) factors influence water-physical properties (i.e., in terms of soil capillary water retention (WC) and soil saturated water retention (WS)) in temperate forests. We found that the impacts of logging disturbance on soil water-physical properties were associated with improved tree diversity, acquisitive functional traits, and SOC. These associated attributes were also positively related to WC and WS, while there was no significant effect from soil texture. Moreover, disturbance indirectly affected soil water-physical properties mainly by functional traits and SOC, as acquisitive functional traits significantly mediate the effect from disturbance on WC and SOC mediates the influence from disturbance on WS. Finally, our results emphasize the potential relationships of tree composition with SOC and soil water retention as compared with soil texture and hence suggest that plants can actively modulate their abiotic contexts after disturbance, which is meaningful for understanding forest health and resistance.
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•Species richness enhanced aboveground biomass across annual and perennial species.•Perennial species richness promoted annual plants through resource heterogeneity.•Perennial species ...biomass decreased annual species biomass due to resource acquisition.•Disturbance intensity decreased perennial species but enhanced annual species.
Biodiversity–productivity relationships have widely been studied in natural herbaceous communities but remain debated. Here, we hypothesized that species richness of perennial plants would increase species richness of annual plants but aboveground biomass of perennial plants would restrict the species richness and aboveground biomass of annual plants across plant functional types (i.e. shrubs, forbs and graminoids) in natural rangelands. We quantified the species richness of annual and perennial plants across plant functional types, and then measured aboveground biomass destructively in 735 quadrats of semi-steppe rangelands. We used linear path analysis model to test for the multivariate effects of perennial on annual plant species using species richness and aboveground biomass datasets, in addition to the influences of grazing disturbances and soil textural properties. Our results showed the species richness of perennial plants (forbs and graminoids) generally promoted the species richness of annual plants (forbs and graminoids). However, the aboveground biomass of perennial species (shrubs, forbs and graminoids) imposed negative or negligible (i.e. nonsignificant negative) influences on the species richness and aboveground biomass of annual species (forbs and graminoids). Hence, perennial species have probably restricted the aboveground biomass of annual plant species due to the resource acquisition, but protected annual plants from grazing and other anthropogenic disturbances. This study suggests that the relationship between species richness and aboveground biomass is positive in general, regardless of the confounding effects of perennial on annual species across plant functional types. This study highlights that simply by integrative modelling of perennial and annual plant species across plant functional types for the associations between species richness and aboveground biomass, better insights can be gained into ecological mechanisms playing a role in the biodiversity conservation of natural rangelands and other natural ecosystems in general.
Topography, grazing disturbances, and soil textures are the main determining factors of natural herbaceous plant communities. Yet, while interesting efforts have been made to link topography, soil ...conditions, grazing disturbances, species diversity and aboveground biomass, we still lack a comprehensive understanding of how soil textural properties and grazing disturbances co-vary along topographic gradients, and how they jointly shape vegetation quantity and quality in natural rangelands. In this study, we used abiotic and biotic datasets from 735 quadrats of natural rangelands located in the southern Alborz Province of Iran. We quantified topographic variables (i.e. elevation, slope, and aspect), grazing disturbance intensities, soil textural properties (i.e. gravel, sand, silt, and clay contents) as predictor variables. Vegetation quantity (i.e. aboveground biomass, vegetation coverage, and vegetation density) and quality (i.e. species richness, Shannon's diversity, and species evenness) variables were used as response variables. We used boosted regression trees (BRT) models for assessing the relative contribution and effects of multiple predictors on each response variable. We found that vegetation quantity and quality were jointly explained by topography, grazing disturbances, and soil textural properties. Vegetation quantity increased gradually or showed a hump-backed type pattern whereas vegetation quality decreased with elevation. Intensive grazing decreased vegetation quantity of shrubs and graminoids, which in turn determined the vegetation quantity of whole-community (i.e. all species). Higher vegetation quantity of shrubs was located on sandy soils while high vegetation quality was located on silty soils, whereas forbs and graminoids showed an opposite trend. Although the drivers of rangelands' vegetation quantity and quality are not mutually exclusive, the magnitude, shape and complexity of these relationships are highly dependent on plant growth forms. This study suggests that high grazing at lower elevation should be managed properly in order to conserve graminoids and to enhance their functioning in line with forbs and shrubs species.
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•Elevation appeared as a strong spatial driver of vegetation quantity and quality.•Intensive grazing declined vegetation quantity but intermediate grazing enhanced vegetation quality.•Soil textures were of additional importance for vegetation quantity and quality.•Intensive grazing at lower elevation should be managed properly to conserve graminoids.
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•Stand density increased AGB across whole data, forest types and species mixtures.•Species richness increased AGB in whole data but across some of forest types.•Tree size variation ...increased AGB in single-specie compared to multi-species stands.•AGB declined with increased elevational gradient.•Both niche complementarity and selection effects are acting for shaping AGB.
Greater variation in stand structure (i.e., individual tree size variation and stand density) is thought to promote aboveground biomass (AGB) better than species richness due to the canopy packing by different sized trees in the forest community. Here, we hypothesized that the relationships amongst species richness, stand density, individual tree size variation and AGB are dependent on forest types but single-species dominated forest stands matter much for higher AGB through higher stand density and individual tree size variation. To do this, we analyzed the forest inventory data (i.e., tree diameter, tree height, and species names) from 365 forest plots (each 0.1 ha) which was taken at different elevational gradients of temperate forest types (i.e., dense pure conifer, dense mixed forests, sparse mixed forests, sparse pure broadleaved, sparse pure conifer, and dense pure broadleaved) as well as species mixture groups (single-species and multi-species stands) in the northern area (namely Gilgit-Baltistan) of Pakistan. We mainly used piecewise structural equation modeling for testing the fixed effects of elevation, species richness, individual tree size variation and stand density as well as the random effect of either forest types or species mixture on AGB, and then we used linear structural equation modeling to test the models across forest types and species mixtures. We found the consistent positive effect of stand density on AGB across whole data, forest types and species mixtures, albeit species richness also showed a positive effect in some of the forest types. Individual tree size variation had a greater positive effect on AGB in single-species dominated stands compared to multi-species dominated stands. Elevation declined AGB directly and indirectly via stand density. We conclude that variation in stand structures (stand density and individual tree size variation of single-species dominated stands) are key to higher AGB in most of the temperate forest types. The positive effects of stand density and species richness on AGB may provide support to the niche complementarity effect through stand packing, whereas the greater effect of individual tree size variation on AGB in single-species rather than multi-species dominated stands may also confirm the selection or competitive exclusion effect. Therefore, we argue that both of the niche complementarity and selection effects are acting simultaneously to determine the relationships amongst species richness, stand structure and AGB in the studied temperate forests.
The positive relationships between biodiversity and aboveground biomass are important for biodiversity conservation and greater ecosystem functioning and services that humans depend on. However, the ...interaction effects of plant coverage and biodiversity on aboveground biomass across plant growth forms (shrubs, forbs and grasses) in natural rangelands are poorly studied. Here, we hypothesized that, while accounting for environmental factors and disturbance intensities, the positive relationships between plant coverage, biodiversity, and aboveground biomass are ubiquitous across plant growth forms in natural rangelands. We applied structural equation models (SEMs) using data from 735 quadrats across 35 study sites in semi-steppe rangelands in Iran. The combination of plant coverage and species richness rather than Shannon's diversity or species diversity (a latent variable of species richness and evenness) substantially enhance aboveground biomass across plant growth forms. In all selected SEMs, plant coverage had a strong positive direct effect on aboveground biomass (β = 0.72 for shrubs, 0.84 for forbs and 0.80 for grasses), followed by a positive effect of species richness (β = 0.26 for shrubs, 0.05 for forbs and 0.09 for grasses), and topographic factors. Disturbance intensity had a negative effect on plant coverage, whereas it had a variable effect on species richness across plant growth forms. Plant coverage had a strong positive total effect on aboveground biomass (β = 0.84 for shrubs, 0.88 for forbs, and 0.85 for grasses), followed by a positive effect of species richness, and a negative effect of disturbance intensity across plant growth forms. Our results shed light on the management of rangelands that is high plant coverage can significantly improve species richness and aboveground biomass across plant growth forms. We also found that high disturbance intensity due to heavy grazing has a strong negative effect on plant coverage rather than species richness in semi-steppe rangelands. This study suggests that proper grazing systems (e.g. rotational system) based on carrying capacity and stocking rate of a rangeland may be helpful for biodiversity conservation, better grazing of livestock, improvement of plant coverage and enhancement of aboveground biomass.
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•Combination of plant coverage and species richness best predicted aboveground biomass.•Plant coverage increased species richness for driving high biomass across plant growth forms.•Plant coverage had a strong positive effect on biomass, followed by species richness.•Disturbance intensity due to heavy grazing had a strong negative effect on plant coverage.•Rotational grazing system should be implemented for higher biodiversity and function.
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•Plant coverage and species richness or Shannon’s diversity were dependent indicators for biomass.•Plant coverage and species evenness were independent indicators for aboveground ...biomass.•Disturbance intensity had strongest negative effect on plant coverage rather than diversity.•Rotational grazing system is a suitable choice for high plant coverage, diversity and biomass.•Enhancement of plant coverage is important for higher species diversity and biomass.
The relationships between species diversity and aboveground biomass remain highly debated in contemporary ecology. Here, we proposed the following three hypotheses by evaluating three different paths between species diversity indices (species richness, evenness, Shannon’s species diversity, and a combination of species richness and evenness) and plant coverage for explaining variation in aboveground biomass, in addition to the influences of abiotic factors and disturbance intensities: 1) plant coverage increases species diversity through light capture and use in the vertical physical space; 2) species diversity increases plant coverage through species coexistence; and 3) species diversity and plant coverage may provide positive response to each other, and as a consequence enhance aboveground biomass in natural rangelands. We used structural equation models to explicitly test these hypotheses using biophysical data from 735 quadrats in semi-steppe rangelands in Iran. In all tested models, plant coverage possessed strongest positive effect on species richness and Shannon’s species diversity but not on species evenness, and hence strongly determined aboveground biomass as compared to species diversity indices. Disturbance intensity decreased aboveground biomass directly and indirectly via plant coverage than that via species diversity, indicating that plant coverage is sensitive to disturbance intensities for driving aboveground biomass. Species richness or Shannon’s diversity substantially enhanced aboveground biomass indirectly via plant coverage, indicating that plant coverage is a linking mechanism for the positive relationships between biodiversity and aboveground biomass. Practically, this study suggests that rotational grazing system might be a suitable choice for the enhancement of plant coverage and aboveground biomass while conserving biodiversity. Theoretically, this study suggests that plant coverage is a sustainable ecological indicator or linking mechanism for high species diversity and aboveground biomass in studied rangelands and other ecosystems in general.
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