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1. A growing body of empirical evidence has suggested that biodiversity affects the simultaneous performance of multiple ecosystem functions (i.e. ecosystem multifunctionality). Given increasing environmental variability and uncertainty under global change, an emerging question is how biodiversity influences the stability of multiple functions (i.e. multifunctional stability). We currently know little, however, about the determinants and mechanisms of multifunctional stability, which is of practical importance for ensuring the sustainable provision of multiple functions. 2. Here, we examined mechanisms contributing to stability (quantified as the ratio of the mean to the standard deviation) of multiple functions related to ecosystem productivity and carbon sequestration, including plant above-ground and belowground productivity, litter production, gross primary productivity and ecosystem respiration, in a large grassland biodiversity experiment in Inner Mongolia. 3. We found that community-wide species asynchrony was a strong driver to stabilize multiple functions. Community-wide asynchrony mediated the positive effects of species richness and response diversity (describing how species with similar effects on ecosystem function respond differently to environmental change) on multifunctional stability. However, species richness had a negative direct effect on multifunctional stability because, although it increased the averaged temporal mean of multiple functions, it strongly increased the averaged temporal standard deviation of multiple functions. The overall effects of species richness on multifunctional stability were thus negative, whereas those of response diversity were positive. 4. Synthesis. The studied ecosystem functions related to ecosystem productivity and carbon sequestration are important in natural grasslands across the world. We conclude that species asynchrony and response diversity, rather than species richness, are key to the ecosystem multifunctional stability. The loss of response diversity and compensatory mechanisms would likely reduce the long-term sustainability of grasslands in the face of global change.

It is well known that biodiversity and ecosystem multifunctionality (EMF) guarantee the well-being of human society. Most studies have focused on the relationship between biodiversity and ecosystem function, and less is known about the individual and combined effects of above- and below-ground biodiversity on ecosystem multifunctionality under grazing disturbance. The aim of our study was to investigate the relationship between plant and soil microbial (bacterial and fungal) diversity and ecosystem multifunctionality under grazing disturbance by using multiple methods to assess ecosystem multifunctionality. We conducted experiments in desert grasslands on the northern slopes of the Tian Shan Mountains and compared the relationship between ecosystem multifunctionality and biodiversity assessed by different methods under light grazing and heavy grazing. Our results showed that at the heavy grazing level, ecosystem multifunctionality calculated by the mean method and plant diversity, soil fungal diversity, soil bacterial diversity and soil fertility calculated by the single function method showed a significant decrease (p < 0.05), but grass productivity was significantly increased (p < 0.05). Among them, ecosystem multifunctionality, soil carbon storage function and soil fertility all showed significant positive correlations with plant diversity and soil microbial diversity (p < 0.05). We calculated that ecosystem multifunctionality also essentially showed positive correlation with plant diversity and soil microbial diversity using the multi-threshold method, and the effect curve was approximately a single-peaked curve, first increasing and then decreasing. Finally, we used plant diversity, soil fungal diversity and soil bacterial diversity under grazing disturbance as biotic factors and soil pH as an abiotic factor to construct structural equation models, and we found that grazing can have direct effects on ecosystem multifunctionality and indirect effects on ecosystem multifunctionality through above- and below-ground biodiversity. Our study emphasizes the importance of the combination of above- and below-ground biodiversity in maintaining the multifunctionality of desert grassland ecosystems on the northern slopes of the Tian Shan Mountains. A moderate reduction in grazing intensity can better conserve biodiversity and improve ecosystem multifunctionality, and it is a feasible strategy to maintain sustainable management of desert grasslands.

1. Forest ecosystems are critical for the global regulation of carbon (C), a substantial portion of which is stored in above-ground biomass (AGB). While it is well understood that taxonomic and functional composition, stand structure and environmental gradients influence spatial variation in AGB, the relative strengths of these drivers at landscape scales have not been investigated in temperate forests. Furthermore, when biodiversity enhances C storage, it is unclear whether it is through mass-ratio effects (i.e. the dominant trait in communities regulates AGB) or through niche complementarity (i.e. increased AGB due to interspecific resource partitioning). 2. To address these mechanisms, we analysed data from a census of 28,262 adult trees sampled across 900 ha of temperate deciduous forest in southwestern Pennsylvania. We used data on four key plant functional traits to determine if (1) there is a positive relationship between species diversity and AGB and (2) whether this is due to mass-ratio effects or niche complementarity. We also sought to (3) identify the physical stand structural attributes and topographic variables that influence AGB across this landscape. 3. We found AGB was positively related to species richness and negatively related to species evenness, albeit weakly, while functional diversity indices had neutral effects. Above-ground biomass was enhanced in communities dominated by traits related to greater maximum tree height, deeper minimum rooting depths and larger seeds. Most importantly, areas with high AGB were dominated by Acer saccharum and Liriodendron tulipifera. Overall, these results support mass-ratio effects, with little evidence for niche complementarity. 4. Synthesis. Stand structure, topography, and species and functional composition, but not taxonomic or functional diversity, were found to be key drivers of above-ground biomass at landscape scales (<900 ha) in this temperate deciduous forest. Our findings suggest that simultaneously managing for both high diversity and for above-ground carbon storage may prove challenging in some forest systems. Our results further indicate that the impact of tree biodiversity loss on above-ground carbon stocks will depend greatly on the identity of the species that are lost.

Ecosystem stability in variable environments depends on the diversity of form and function of the constituent species. Species phenotypes and ecologies are the product of evolution, and the evolutionary history represented by co‐occurring species has been shown to be an important predictor of ecosystem function. If phylogenetic distance is a surrogate for ecological differences, then greater evolutionary diversity should buffer ecosystems against environmental variation and result in greater ecosystem stability. We calculated both abundance‐weighted and unweighted phylogenetic measures of plant community diversity for a long‐term biodiversity–ecosystem function experiment at Cedar Creek, Minnesota, USA. We calculated a detrended measure of stability in aboveground biomass production in experimental plots and showed that phylogenetic relatedness explained variation in stability. Our results indicate that communities where species are evenly and distantly related to one another are more stable compared to communities where phylogenetic relationships are more clumped. This result could be explained by a phylogenetic sampling effect, where some lineages show greater stability in productivity compared to other lineages, and greater evolutionary distances reduce the chance of sampling only unstable groups. However, we failed to find evidence for similar stabilities among closely related species. Alternatively, we found evidence that plot biomass variance declined with increasing phylogenetic distances, and greater evolutionary distances may represent species that are ecologically different (phylogenetic complementarity). Accounting for evolutionary relationships can reveal how diversity in form and function may affect stability.

Extensive research has shown that greater plant community diversity leads to higher levels of productivity and other ecosystem services, and such increased diversity has been suggested as a way to improve yield and agricultural sustainability. Increasing intraspecific diversity with cultivar mixtures is one way to increase diversity in agricultural systems. We examined the relationship between intraspecific diversity and yield in cultivar mixtures using a meta-analysis of 91 studies and >3,600 observations. Additionally, we investigated how environmental and management factors might influence this relationship, and if the yield stability of cultivar mixtures differed from that of monocultures. We found that the yield increased by 2.2% overall in cultivar mixtures relative to their monoculture components. Mixtures with more cultivars and those with more functional trait diversity showed higher relative yields. Under biotic stressors, such as disease pressure, and abiotic stressors, such as low levels of soil organic matter and nutrient availability, this diversity effect was stronger, resulting in higher relative yields. Finally, cultivar mixtures generally showed higher yield stability compared to monocultures, especially in response to annual weather variability at a site over time. This practice of mixing cultivars can be integrated into intensified cropping systems where species monocultures dominate, as well as in smallholder cropping systems where low-cost improvements are in demand. Overall, these results suggest that cultivar mixtures are a viable strategy to increase diversity in agroecosystems, promoting increased yield and yield stability, with minimal environmental impact.

Microbial physiological processes are intimately involved in nutrient cycling. However, it remains unclear to what extent microbial diversity or community composition is important for determining the rates of ecosystem-scale functions. There are many examples of positive correlations between microbial diversity and ecosystem function, but how microbial communities ‘map' onto ecosystem functions remain unresolved. This uncertainty limits our ability to predict and manage crucial microbially mediated processes such as nutrient losses and greenhouse gas emissions. To overcome this challenge, we propose integrating traditional biodiversity–ecosystem function research with ideas from genotype–phenotype mapping in organisms. We identify two insights from genotype–phenotype mapping that could be useful for microbial biodiversity–ecosystem function studies: the concept of searching ‘agnostically' for markers of ecosystem function and controlling for population stratification to identify microorganisms uniquely associated with ecosystem function. We illustrate the potential for these approaches to elucidate microbial biodiversity–ecosystem function relationships by analysing a subset of published data measuring methane oxidation rates from tropical soils. We assert that combining the approaches of traditional biodiversity–ecosystem function research with ideas from genotype–phenotype mapping will generate novel hypotheses about how complex microbial communities drive ecosystem function and help scientists predict and manage changes to ecosystem functions resulting from human activities. This article is part of the theme issue ‘Conceptual challenges in microbial community ecology’.

1. Constructed ecosystems such as green roofs often contain monocultures or low-diversity plant communities, but adding more plant species to these systems can increase ecosystem service provisioning. Mixture advantage, when species-rich treatments outperform the best monocultures, is desirable in constructed ecosystems due to the cost of increasing diversity. However, there have not been any studies in constructed ecosystems that have quantitatively compared mixtures with the best monocultures for multifunctionality, and there have been few studies that have examined how provision of ecosystem services changes over time as plant communities develop. In a green roof system, I predicted (i) that the mixture advantage would be stronger for ecosystem multifunctionality than for single ecosystem functions and (ii) that ecosystem service provisioning and complementarity in above-ground biomass would increase over time. 2. Fifteen monocultures of plant species from five life-form groups (succulents, tall forbs, dwarf shrubs, creeping forbs, grasses) were compared with three-species mixtures of the same life-form and mixtures of species from three and five different life-forms in a modular green roof system. Indicators of ecosystem services including above-ground production, thermal regulation, stormwater retention, nutrient uptake and carbon sequestration and two indices of ecosystem multifunctionality were compared. 3. Canopy density increased over time while substrate temperature decreased, suggesting higher provisioning of valuable ecosystem services. For single services, the positive relationship between planted species richness and ecosystem service grew stronger over time, but was consistently strong over time for multifunctionality. Quantile regression indicated a weak mixture advantage for several services including both multifunctionality indices. While the effects were small, different species optimized different functions, thus multifunctioning is enhanced in more diverse mixtures by combining species that maximize different functions. Tripartite partitioning of canopy density showed that overyielding and trait-independent complementarity fluctuated between years in response to shifts in species abundances, but dominance and trait-dependent complementarity increased over time. 4. Synthesis and applications. This study provides the first evidence in a constructed ecosystem that mixtures can outperform the best monocultures for multiple ecosystem services. Mixtures of plant life-forms can improve green roof performance. The biodiversity-ecosystem function relationships observed in natural ecosystems can also occur in novel and highly simplified engineered ecosystems.

BACKGROUND: Plants play a pivotal role in soil stabilization, with above‐ground vegetation and roots combining to physically protect soil against erosion. It is possible that diverse plant communities boost root biomass, with knock‐on positive effects for soil stability, but these relationships are yet to be disentangled. QUESTION: We hypothesize that soil erosion rates fall with increased plant species richness, and test explicitly how closely root biomass is associated with plant diversity. METHODS: We tested this hypothesis in salt marsh grasslands, dynamic ecosystems with a key role in flood protection. Using step‐wise regression, the influences of biotic (e.g. plant diversity) and abiotic variables on root biomass and soil stability were determined for salt marshes with two contrasting soil types: erosion‐resistant clay (Essex, southeast UK) and erosion‐prone sand (Morecambe Bay, northwest UK). A total of 132 (30‐cm depth) cores of natural marsh were extracted and exposed to lateral erosion by water in a re‐circulating flume. RESULTS: Soil erosion rates fell with increased plant species richness (R² = 0.55), when richness was modelled as a single explanatory variable, but was more important in erosion‐prone (R² = 0.44) than erosion‐resistant (R² = 0.18) regions. As plant species richness increased from two to nine species·m⁻², the coefficient of variation in soil erosion rate decreased significantly (R² = 0.92). Plant species richness was a significant predictor of root biomass (R² = 0.22). Step‐wise regression showed that five key variables accounted for 80% of variation in soil erosion rate across regions. Clay‐silt fraction and soil carbon stock were linked to lower rates, contributing 24% and 31%, respectively, to variation in erosion rate. In regional analysis, abiotic factors declined in importance, with root biomass explaining 25% of variation. Plant diversity explained 12% of variation in the erosion‐prone sandy region. CONCLUSION: Our study indicates that soil stabilization and root biomass are positively associated with plant diversity. Diversity effects are more pronounced in biogeographical contexts where soils are erosion‐prone (sandy, low organic content), suggesting that the pervasive influence of biodiversity on environmental processes also applies to the ecosystem service of erosion protection.

Exotic invasive plants threaten ecosystem integrity, and their success depends on a combination of abiotic factors, disturbances, and interactions with existing communities. In dryland ecosystems, soil biocrusts (communities of lichens, bryophytes, and microorganisms) can limit favorable microsites needed for invasive species establishment, but the relative importance of biocrusts for landscape-scale invasion patterns remains poorly understood. We examine effects of livestock grazing in habitats at high risk for invasion to test the hypothesis that disturbance indirectly favors exotic annual grasses by reducing biocrust cover. We present some of the first evidence that biocrusts increase site resistance to invasion at a landscape scale and mediate the effects of disturbance. Biocrust species richness, which is reduced by livestock grazing, also appears to promote native perennial grasses. Short mosses, as a functional group, appear to be particularly valuable for preventing invasion by exotic annual grasses. Our study suggests that maintaining biocrust communities with high cover, species richness, and cover of short mosses can increase resistance to invasion. These results highlight the potential of soil surface communities to mediate invasion dynamics and suggest promising avenues for restoration in dryland ecosystems.

Plant functional traits are thought to drive variation in primary productivity. However, there is a lack of work examining how dominant species identity affects trait–productivity relationships. The productivity of 12 pasture mixtures was determined in a 3‐year field experiment. The mixtures were based on either the winter‐active ryegrass (Lolium perenne) or winter‐dormant tall fescue (Festuca arundinacea). Different mixtures were obtained by adding forb, legume, and grass species that differ in key leaf economics spectrum (LES) traits to the basic two‐species dominant grass–white clover (Trifolium repens) mixtures. We tested for correlations between community‐weighted mean (CWM) trait values, functional diversity, and productivity across all plots and within those based on either ryegrass or tall fescue. The winter‐dormant forb species (chicory and plantain) had leaf traits consistent with high relative growth rates both per unit leaf area (high leaf thickness) and per unit leaf dry weight (low leaf dry matter content). Together, the two forb species achieved reasonable abundance when grown with either base grass (means of 36% and 53% of total biomass, respectively, with ryegrass tall fescue), but they competed much more strongly with tall fescue than with ryegrass. Consequently, they had a net negative impact on productivity when grown with tall fescue, and a net positive effect when grown with ryegrass. Strongly significant relationships between productivity and CWM values for LES traits were observed across ryegrass‐based mixtures, but not across tall fescue‐based mixtures. Functional diversity did not have a significant positive effect on productivity for any of the traits. The results show dominant species identity can strongly modify trait–productivity relationships in intensively grazed pastures. This was due to differences in the intensity of competition between dominant species and additional species, suggesting that resource‐use complementarity is a necessary prerequisite for trait–productivity relationships. Inclusion of forbs (Plantago lanceolata and Chicorium intybus) in ryegrass‐based mixtures increased productivity while their inclusion in tall fescue‐based mixtures decreased productivity. This is most likely due to a lack of seasonal complementarity between the forbs and tall fescue.