Plant Functional Group Diversity Research Articles

The Effect of Grazing on Central Anatolian Steppe Vegetation: A Modeling Approach Using Functional Traits.

Grazing is a major ecological driver that influences vegetation dynamics globally. We investigated the long-term effects of different grazing regimes on the vegetation structure of the Central Anatolian steppes, a region characterized by its unique convergence of biogeographical influences and historical land use. We employed the spatially explicit FATELAND model to simulate vegetation dynamics over a 50-year period under three distinct grazing scenarios: no grazing, moderate grazing, and overgrazing. Our simulations incorporated a range of plant functional traits to predict changes across five different vegetation types in Central Anatolia, including woodland steppes and treeless steppes. The simulations revealed that moderate grazing supports the diversity and abundance of various plant functional groups, excluding resprouter trees, which flourish under no grazing conditions. In contrast, overgrazing leads to significant reductions in the abundance of perennial forbs and both spiny and non-spiny subshrubs, often resulting in a shift toward grassland dominated by resprouter gramineae or an annual herb-dominated grassland, depending on the initial abundance of gramineae. Our findings highlight the critical role of grazing management in maintaining biodiversity and ecological stability in steppe ecosystems. While moderate grazing can enhance plant functional group diversity, overgrazing significantly threatens the ecological integrity of the Central Anatolian steppes. In conclusion, our modeling approach reveals that the grazing regime is a major driver in shaping the vegetation structure of Central Anatolian steppes. Grazing management strategies that are adjusted to the ecological characteristics and historical context of specific regions are required to prevent degradation and promote sustainable grassland vegetation.

Plot-Measured Variables Indicate Landscape-Scale Patterns of Annual Grass Invasion in Northwestern US Rangelands

Introduced annual grasses (IAGs) have invaded tens of millions of hectares of western US rangelands, displacing native vegetation and altering ecosystem functions and services. Our main goal was to assess the influence of introduced annual grasses by 1) exploring the relationships among IAG cover, species richness, diversity, and cover of other plant functional groups; and 2) identifying biotic and abiotic indicators of IAG cover. Using data from 64 sites and 420 plots from rangelands of the northwestern United States, we explored linear correlations between IAG cover and species richness, Shannon index, and plant functional group cover. We also used Least Absolute Shrinkage and Selection Operator (LASSO) regression and nonmetric multidimensional scaling to select environmental variables and plant functional groups that were associated with IAG cover. Our findings revealed a negative correlation among IAG cover and species richness, Shannon index, native perennial grass cover, and other perennial species cover and a positive correlation with other annual species cover. Our results identified several indicators: cover of native perennial grass; other perennial species (forbs and shrubs); litter; bare ground/rock; soil attributes (pH, bulk density, clay, and nitrogen); and mean annual temperatures. Our results showed that perennial vegetation, especially native perennial grasses, have a negative correlation with IAG. Warmer mean annual temperatures, but not higher daily extreme temperatures, and higher bulk density were important indicators for IAG preferred sites, while lower soil nitrogen may denote soil changes due to invasion. Given the fundamental role of disturbance in determining the magnitude and scale of IAG invasion, our results provide important insights for scientists and managers.

Soil microbial activity along an altitudinal gradient: Vegetation as a main driver beyond topographic and edaphic factors

An altitudinal gradient in the mountains constitutes a unique ‘open-lab’ to examine environmental hypotheses and analyse the expected effects of global warming. The distribution of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzyme activity, microbial catabolic activity as represented by a community-level physiological profile (CLPP), and microbial functional diversity (HCLPP) within mountainous ecosystems consisting of mixed, fir and deciduous forests, as well as subalpine and alpine meadows (1260–2480 m a.s.l., Mt. Tkachiha, the Northwest Caucasus, Russia) has been studied. Concerning potential drivers, vegetation (plant projective cover, plant functional group composition, plant richness and diversity) and edaphic (soil nutrients: total and available C and N, total P, pH, texture, temperature, microbial biomass C) and topographic (elevation, slope, mean annual temperature calculated using biannual monitoring data) properties have been considered. The distribution patterns of the studied hydrolytic enzymes along an altitudinal gradient cannot be explained solely by elevation change and soil nutrient content. The activity of soil leucine aminopeptidase depends on vegetation type and graminoid abundance. β-D-glucosidase activity was mainly driven by the quality of soil organic matter (SOM), demonstrating a significant relation with the soil C:N ratio. The chitinase and phosphatase turned out soil temperature-sensitive enzymes. The CLPP depends on the available N content in the soil. The HCLPP distribution with altitude was driven by available N and forbs abundance represented by the widest spectrum of plant families and species. An altitudinal gradient determines the spread of the vegetation zone. In turn, vegetation properties, such as plant functional group composition, species richness and diversity, play a significant role in the distribution of soil microbial activity along an altitudinal gradient that controls the decomposition of SOM and nutrient cycling. Thus, the significant role of vegetation in the distribution of soil microbial activity across a wide range of natural ecosystems and in consideration of topographic and edaphic factors has been demonstrated.

Plant diversity enhanced yield and mitigated drought impacts in intensively managed grassland communities

Abstract There is a global requirement to improve the environmental sustainability of intensively managed grassland monocultures that rely on high rates of nitrogen fertiliser, which is associated with negative environmental impacts. Multi‐species grass–legume mixtures are a promising tool for stimulating both productivity and sustainability in intensively managed grasslands, but questions remain about the benefit of increasing the diversity of plant functional groups. We established a plot‐scale experiment that manipulated the diversity of plant communities from a six‐species pool comprising three functional groups: grasses, legumes and herbs (two species each). Communities were grown as monocultures, or mixtures of two to six species, following a simplex design. This allowed us to quantify species’ identity effects and functional group interaction effects. To investigate the impact of severe weather events, main plots were split and two levels of water supply, ‘rainfed’ and a 2‐month experimental drought, were applied. Mineral nitrogen fertiliser was applied at 150 kg ha−1 year−1, and a Lolium perenne monoculture received 300 kg ha−1 year−1 (300N) as a highly fertilised comparison. Annual above‐ground biomass was measured for 2 years. We found a strong positive effect on yield due to functional group interactions. Multi‐species communities with three functional groups yielded more than the best‐performing monoculture over a large range of different relative abundances of the three functional groups. The highest diversity community outperformed the 300N L. perenne under rainfed conditions. Although species' monoculture yields were generally reduced by the experimental drought, the interaction effects were not affected by drought and remained sufficiently large for the six‐species mixture under drought to have similar yields to both the best‐performing monoculture and the 300N L. perenne under rainfed conditions. Synthesis and applications. Plant diversity can result in higher yields, mitigate the yield risks associated with extreme weather events and displace fertiliser inputs and their embedded greenhouse gas emissions. Multi‐species swards offer a practical, farm‐scale management action to enhance the sustainability of intensive grassland production.

Tree Diversity, Site Index, and Carbon Storage Decrease With Aridity in Douglas-Fir Forests in Western Canada

Forests are important for biodiversity, timber production and carbon accumulation, but these ecosystem services may be impacted by climate change. Field data collected from individual forest types occurring across a climatic gradient can contribute to forecasting these consequences. We examined how changes in temperature, precipitation and aridity affect ecosystem services in 23 mature Douglas-fir (Pseudotsuga menziesii) forests in nine climatic regions across a 900 km gradient in British Columbia, Canada. Using Canadian National Forest Inventory methodology, we assessed richness and diversity of plant functional groups, site index, and above- and below-ground carbon stocks. As aridity increased, ecosystem-level tree species richness declined on average from four to one species, Douglas-fir site index declined from 30 to 15 m, and ecosystem carbon storage decreased from 565 to 222 Mg ha–1. Tree species richness was positively and herb species richness negatively correlated with carbon storage. Carbon storage by ecosystem compartment was largest in aboveground live tree biomass, declining in the following order: mineral soils > coarse woody debris and dead standing trees > forest floor > small and fine woody debris > understory plants. Mineral soil carbon at depths of 0-15 cm, 15-35 cm, and 35-55 cm increased with increasing mean annual precipitation and decreasing aridity. Our results indicate that as aridity increases and precipitation decreases, tree species richness, site index and carbon storage in existing Douglas-fir forests declines. However, assisted or natural migration of Douglas-fir into more humid regions could be associated with more diverse, productive, carbon-rich forests. This study informs carbon stock vulnerability and provides empirical data essential for carbon stock forecasts.

Structural and compositional heterogeneity influences the thermal environment across multiple scales

AbstractHeterogeneity has a critical influence on biodiversity and ecosystem processes. While the influence of heterogeneity on species diversity and abundance is well documented, how heterogeneity influences the distribution and arrangement of necessary resources across a landscape is still unclear. Heterogeneity in vegetation structure and composition is often cited as an important factor in the near‐ground thermal environment; however, because of a paucity of comparative studies across landscapes that differ in their degree of vegetation heterogeneity, researchers lack knowledge of the underlying mechanisms that influence variation in the thermal environment. Particularly, we do not have a clear understanding of the relative contribution of structural and compositional vegetation heterogeneity to thermal patterns. Therefore, we assessed the thermal environment in nine grassland landscapes that differed in their degree of structural and compositional heterogeneity. At the landscape level, we used a variance partitioning approach with linear mixed models to measure the link between four metrics of vegetation heterogeneity and temperature variability. At the microsite level, we used piecewise structural equation models to assess the fine‐scale drivers of temperature in these landscapes and develop a causal model describing the relationship between vegetation variables and temperature. We found that temperature variance at the landscape scale was strongly related to the diversity of plant functional groups, heterogeneity in plant species composition, and variation in vegetation height. At finer scales, species richness, vegetation height, and overhead obstruction were the best predictors of temperature once weather was accounted for. Vegetation composition variables indirectly influenced fine‐scale temperature variation through their effects on vegetation structure. These results suggest that scale has a strong influence on the observed relationship between temperature variance and different metrics of vegetation heterogeneity. Our results provide support for the role of landscape heterogeneity in shaping the thermal landscape and offer insights into the possible impacts of habitat homogenization on the thermal environment.

Effects of plant functional group removal on CO2 fluxes and belowground C stocks across contrasting ecosystems.

Changes in plant communities can have large effects on ecosystem carbon (C) dynamics and long‐term C stocks. However, how these effects are mediated by environmental context or vary among ecosystems is not well understood. To study this, we used a long‐term plant removal experiment set up across 30 forested lake islands in northern Sweden that collectively represent a strong gradient of soil fertility and ecosystem productivity. We measured forest floor CO2 exchange and aboveground and belowground C stocks for a 22‐yr experiment involving factorial removal of the two dominant functional groups of the boreal forest understory, namely ericaceous dwarf shrubs and feather mosses, on each of the 30 islands. We found that long‐term shrub and moss removal increased forest floor net CO2 loss and decreased belowground C stocks consistently across the islands irrespective of their productivity or soil fertility. However, we did see context‐dependent responses of respiration to shrub removals because removals only increased respiration on islands of intermediate productivity. Both CO2 exchange and C stocks responded more strongly to shrub removal than to moss removal. Shrub removal reduced gross primary productivity of the forest floor consistently across the island gradient, but it had no effect on respiration, which suggests that loss of belowground C caused by the removals was driven by reduced litter inputs. Across the island gradient, shrub removal consistently depleted C stocks in the soil organic horizon by 0.8 kg C/m2. Our results show that the effect of plant functional group diversity on C dynamics can be relatively consistent across contrasting ecosystems that vary greatly in productivity and soil fertility. These findings underline the key role of understory vegetation in forest C cycling, and suggest that global change leading to changes in the relative abundance of both shrubs and mosses could impact on the capacity of boreal forests to store C.

Rapid recovery of the vegetation diversity and soil fertility after cropland abandonment in a semiarid oak ecosystem: An approach based on plant functional groups

In many parts of the world, including the semi-arid Mediterranean areas, land abandonment has led to significant changes in vegetation composition, plant diversity as well as soil fertility. In this study, new approaches were presented on how the understory plant functional group diversity and composition changed after land abandonment in Zagros oak forests (Quercus brantii Lindl.) in western Iran. In addition, the impact of land-use change on main soil properties were investigated. The diversity and nutrient status of the three stages of the secondary succession of abandoned agroforestry systems were compared: croplands after a short period of abandonment (~5 years), croplands after a long period of abandonment (~15 years) and oak forests representing the ‘climax’ stage. The plant species were classified in four functional groups (annual forb, annual grass, perennial forb, and perennial grass). The diversity indices were computed for each group and each stage. Results showed that the Shannon-Wiener diversity and Margalef richness of all functional groups significantly increased with time from the shortly abandoned croplands to the forest. Shortly after abandonment, annuals (especially annual forbs) were dominant whereas the abundance of the perennials increased after 15 years of abandonment and in the ‘climax’ forest. The soil content in lime decreased along the successional stages (from 52.7% to 26.4%) and was strongly negatively correlated with the diversity of the perennial forbs. In contrast, the soil total nitrogen and aggregate stability increased with succession (respectively from 0.04% to 0.19% and from 0.49 mm to 0.92 mm) and were strongly positively correlated with the diversity of this group. Recovery in soil fertility (and in particular, total nitrogen), provided suitable conditions for the establishment of a wide range of plant functional groups, which in turn increased the species diversity. The relatively fast recovery of soil fertility and plant diversity of abandoned agricultural lands indicated that the reestablishment of the forest vegetation could rely mostly on natural processes.

Linkage between plant species diversity and soil-based functions along a post-agricultural succession is influenced by the vegetative forms.

There is a growing body of knowledge that ecosystem functions, in particular, soil-based ecosystem functions, are related to biodiversity. However, how plant species diversity influences soil-based functions along post-agricultural secondary succession is still a largely ignored question in Mediterranean semi-arid conditions. Therefore, we used the plant functional group approach to investigate the relationships between plant species diversity indices and soil-based functions including microbial biomass carbon (MBC), basal respiration (BR), and carbon sequestration (CS) across three different stages of the vegetation succession corresponding to ~ 5 years after agricultural abandonment, ~ 15 years after abandonment, and oak forests which represent the terminal stage. We also tested if these relationships are supported by the niche complementarity and selection effect hypotheses. The results showed that soil-based functions significantly increased with time since abandonment as BR, MBC, and CS increased respectively by 1.7, 1.5, and 2.7 times across the three successional stages. We also found strong correlations between the diversity indices and the soil-based functions BR, MBC, and CS which were positive for richness (R2 values 0.75, 0.74, and 0.75) and Shannon diversity (R2 values 0.61, 0.58, and 0.61) but negative for evenness (R2 values 0.38, 0.38, and 0.36 for, respectively). Similarly, richness and Shannon diversity of the different plant functional groups positively correlated with soil-based functions. However, contrasting results were found for evenness which positively correlated with soil-based functions for perennial grass only. We suggested that increasing the diversity of plant species and facilitating dominant species would be needed to improve the soil-based ecosystem functions after abandonment of degraded soils. This study also revealed that the mechanisms behind the relationships between biodiversity and ecosystem functions were influenced by the vegetative forms.

Soil microbial communities in alpine grasslands on the Tibet Plateau and their influencing factors

As an indicator and regulator of climate and environmental change, the Tibet Plateau is an important barrier for ecological security. However, despite the importance of soil microbial communities in almost all soil biochemical processes and ecosystem functions, the biogeography of soil microbial communities on the Tibet Plateau is poorly understood, especially at large scales over different ecosystem types. In this study, we collected samples from 64 sampling sites representing different grassland ecosystem types and spanning 2121 km across on the Tibet Plateau. We then used next generation high-throughput sequencing to investigate the soil prokaryote community (i.e. bacteria and archaea) diversity and spatial patterns and to explore their relationship with biotic (e.g. plant functional group diversity and biomass) and abiotic (e.g. aridity index, soil carbon and nitrogen levels) factors. Among the four alpine grassland types (i.e. alpine meadow, alpine steppe, alpine shrub and alpine desert) sampled in this study, alpine meadow had the highest soil microbial biomass and alpine desert had the lowest soil microbial richness and Shannon diversity. The soil microbial diversity in the alpine grassland correlated with plant diversity and climate factors. Soil microbial diversity negatively correlated with the annual average air temperature, but was not correlated with the annual average precipitation, indicating that temperature, rather than precipitation, may be more important in controlling the soil microbial diversity in alpine grassland ecosystems at cold temperatures. Higher air temperature likely led to an intensified aridity under limited precipitation, and thus decreased microbial diversity. As a result, the aridity index combined with temperature and precipitation explained more of the variance in the soil microbial diversity than air temperature or precipitation did individually. Moreover, after separating plant species into four functional groups (grass, forb, legume and sedge), microbial diversity positively correlated with plant functional group diversity, explaining more of the variance in microbial diversity than plant species diversity did. Results of structural equation modeling revealed that the aridity index and annual air temperature affected soil microbial diversity, directly or indirectly, through influencing plant functional group diversity and aboveground biomass; while aboveground biomass changed the soil carbon to nitrogen ratio in the upper soil layers and thus impacted soil microbial diversity. However, in contrast to microbial diversity, soil microbial biomass carbon was not correlated with plant functional group diversity, plant species diversity, or the climate factors annual average air temperature, annual precipitation and aridity index, but were linked to soil nutrient status (e.g. soil dissolved organic carbon, ammonia, available phosphorus, and carbon to nitrogen ratio) and plant biomass of sedges and forbs, demonstrating that microbial biomass and diversity were likely controlled by different factors. In summary, this study investigated the spatial patterns of soil microbial communities across different alpine grassland ecosystem types on the Tibet Plateau and enhanced our understanding of biotic and abiotic factors controlling microbial biomass and diversity, which will be important in predicting microbial changes on the Tibet Plateau under future climate change. Under future warming and wetting scenarios on the Tibet Plateau, it is possible that the aridity index would decrease, leading to increased soil microbial diversity. Results of this study also suggest a focus on the aridity index and plant functional group diversity in future microbial biogeography studies in order to further determine their roles in controlling or mediating soil microbial biomass and diversity.

Arbuscular mycorrhizal fungi shape the adaptive strategy of plants by mediating nutrient acquisition in a shrub-dominated community in the Mu Us Desert

Whether Arbuscular mycorrhizal fungi (AMF) influence community composition by changing plant adaptation to resource limitation remains unclear. This study examined how AMF affect the biodiversity and functional traits of plant functional groups in a shrub-dominated community in Mu Us Desert. In a field experiment, mycorrhizae were suppressed via benomyl to address how AMF alter the adaptive strategy of plants and community structure in a shrub-dominated community. The relationship between nutrient acquisition and proxies of growth and reproduction of dominant plant functional groups (shrubs and perennial grasses) were determined using a structure equation model. The diversity and aboveground biomass of plant functional groups were not affected by benomyl treatment. Shrubs’ vegetative biomass responded negatively to AMF owing to the nitrogen (N) limitation induced by phosphorous (P) increase, whereas a positive response in reproduction was related to foliar carbon (C) accumulation for drought tolerance. The abundance and height of perennial grasses varied with AMF, and it was correlated with foliar P and N contents. Different local adaptive strategies of shrubs and perennial grasses were associated with AMF through the regulation of plant nutrient acquisition. The link between AMF and plant adaptation highlights a potential mechanism underlying plant community dynamics in the resource-limited desert ecosystem.

Arbuscular mycorrhizal fungal diversity increases growth and phosphorus uptake in C3 and C4 crop plants

Most plants associate with arbuscular mycorrhizal (AM) fungi which can enhance their growth and nutrient uptake. Outcomes of the AM symbiosis can be highly variable, depending on soil fertility, plant functional group (C3, C4) and AM fungal diversity. This study assessed the growth and nutrient (C, N, P) responses of two C3 (Triticum aestivum and Hordeum vulgare) and two C4 (Sorghum bicolor and Zea mays) plants to different AM fungal inocula (no AM fungi, single AM fungal species, and four AM fungal species) under high and low P conditions. Higher AM fungal diversity resulted in greater P concentration and aboveground biomass of H. vulgare and S. bicolor. Triticum aestivum did not respond to AM fungi, while Z. mays responded positively but a similar positive response of Z. mays growth and nutrition occured when it was colonised with single or multiple AM fungal species. These findings suggest that, although C3 crop plants are less responsive to AM fungi than C4, some C3 and C4 species can benefit from higher AM fungal diversity in the soil.

Prescribed fire regimes subtly alter ponderosa pine forest plant community structure

AbstractPrescribed fire is an active management tool used to address wildfire hazard and ecological concerns associated with fire exclusion and suppression over the past century. Despite widespread application in the United States, there is considerable inconsistency and lack of information regarding the extent to which specific outcomes are achieved and under what prescribed fire regimes, particularly in regard to ecological goals related to plant community structure. We quantify differences and patterns in plant functional group abundance, species richness and diversity, and other key forest components through time from a unique long‐term (15‐yr) experiment within the Malheur National Forest of Oregon. Treatments included five fire regimes: fall and spring 5‐yr burning, fall and spring single burn, and no burning. Original burns were conducted in the fall of 1997 and spring of 1998, and plant data were collected every five years starting in 2002. Many perennial plant group responses were neutral, subtle, and ephemeral. Total cover increased marginally in response to the first burn, but this response disappeared within a decade. Three 5‐yr reburns did not increase or decrease total plant cover, richness, or diversity. Some plant groups with fire resistant and resilient traits, such as annual forbs, exotic forbs, open bunchgrasses, and rhizomatous and resprouting perennials, showed some short‐term positive responses to initial burning and 1–2 reburns, but not 3. The moderately more severe fall burns generally impacted plant responses more than spring burning, but many patterns were legacies from the original higher severity burns. Burn frequency was more important for less severe spring burning. Overall, we document that most native perennial plant functional groups were able to resist or recover from burning and reburning, but did not necessarily strongly respond. This may be due to the importance of other overriding forcing factors and ecosystem inertia not easily overcome by very low‐severity prescribed burns. Results from our study are important for practitioners using prescribed fire to achieve biodiversity, conservation, and habitat goals that hinge on a vigorous native perennial plant response, as such outcomes are not certain even with frequent burn regimes.

Plant functional composition and species diversity affect soil C, N, and P during secondary succession of abandoned farmland on the Loess Plateau

The relationships among soil C, N, and P, aboveground plants, and belowground organisms are well-known; however, the impact of the aboveground dynamics of plant communities and their ensuing effects on soil C, N, and P, particularly during secondary succession need clarification. This study explored the effects of plant functional composition and diversity on soil C, N, and P at different soil depths. Soil samples were collected at soil depths ranging from 0 to 60 cm from three grassland sites abandoned for 5, 17, and 30 years in the Yang Qing Chuan catchment. Soil properties and fine root biomass were determined for different soil depths, and the plant community characters at each site were also evaluated. The results revealed that the plant community transitioned from dominance by annual herb to dominance by perennial species during the succession, and the percentage of Leguminosae plants, plant diversity, and species richness increased with succession time. The soil water content, organic carbon, total nitrogen, total phosphorous, C:P ratio, and N:P ratio increased significantly with successional time and decreased significantly with soil depth. In contrast, the soil bulk density and pH decreased significantly with successional time and increased significantly with soil depth. Furthermore, the plant functional group composition and diversity significantly affected soil C, N, and P contents and ratios, but was sensitive to the vertical stratification of soil. Plant functional group composition had a stronger correlation to soil C, N, and P contents and ratios at soil depths of 0–20 cm than that of the 20–60 cm depth primarily due to the fact that the nutrients returned are mostly concentrated on the topsoil and seldom deposited in the deeper soils. However, plant diversity had a stronger impact on soil C, N, and P contents and ratios at soil depths of 20–60 cm than at 0–20 cm depth, because plant diversity exacerbates interspecific competition and forces the roots to grow deeper, which alters nutrients in the deep soil. In addition, the percentage of legumes can be used as a practical indicator of soil quality in the 0–20 cm layer during natural succession of abandoned farmlands. This study provides evidence that plant communities have a strong influence on soil C, N, and P, but that the pathways and degree of influence differ across vertically stratified soil.

Resource availability underlies the plant-fungal diversity relationship in a grassland ecosystem.

It is commonly assumed that microbial communities are structured by "bottom-up" ecological forces, although few experimental manipulations have rigorously tested the mechanisms by which resources structure soil communities. We investigated how plant substrate availability might structure fungal communities and belowground processes along an experimental plant richness gradient in a grassland ecosystem. We hypothesized that variation in total plant-derived substrate inputs, plant functional group diversity, as well as the relative abundance of C4 grasses and legumes would modulate fungal α- and β-diversity and their rates of soil carbon (C) and nitrogen (N) cycling. To test these predictions, we molecularly characterized fungal communities, as well as potential extracellular enzyme activity, net N mineralization, and soil organic matter respiration. We found higher fungal richness was associated with increasing aboveground plant biomass; whereas, fungal β-diversity was explained by contributions from C4 grass and legume relative dominance, plant functional group diversity, as well as plant biomass. Furthermore, aboveground plant biomass consistently shaped the richness and composition of individual fungal trophic modes (i.e., saprotrophs, symbiotrophs, pathotrophs). Finally, variation in extracellular enzyme activity, net N mineralization rates, and soil organic matter respiration was significantly explained by fungal β-diversity when fungi were functionally classified. Via changes in the supply and composition of organic substrates entering soil, our study demonstrates that changes in the plant species richness and functional composition collectively influence fungal communities and rates of soil C and N cycling.

Possible mechanisms underlying abundance and diversity responses of nematode communities to plant diversity

AbstractPlant diversity is known to influence the abundance and diversity of belowground biota; however, patterns are not well predictable and there is still much unknown about the driving mechanisms. We analyzed changes in soil nematode community composition as affected by long‐term manipulations of plant species and functional group diversity in a field experiment with plant species diversity controlled by sowing a range of 1–60 species mixtures and controlling non‐sown species by hand weeding. Nematode communities contain a variety of species feeding on bacteria, fungi, plants, invertebrates, while some are omnivorous. We analyzed responses of nematode abundance and diversity to plant species and functional diversity, and used structural equation modeling (SEM) to explore the possible mechanisms underlying the observed patterns. The abundance of individuals of all nematode feeding types, except for predatory nematodes, increased with both plant species and plant functional group diversity. The abundance of microbial‐feeding nematodes was related positively to aboveground plant community biomass, whereas abundance of plant‐feeding nematodes was related positively to shoot C:N ratio. The abundance of predatory nematodes, in turn, was positively related to numbers of plant‐feeding nematodes, but not to the abundance of microbial feeders. Interestingly, the numbers of plant‐feeding nematodes per unit root mass were lowest in the high‐diversity plant communities, pointing at reduced exposure to belowground herbivores when plants grow in species‐diverse communities. Taxon richness of plant‐feeding and microbial‐feeding nematodes increased with plant species and plant functional group diversity. Increasing plant functional group diversity also enhanced taxon richness of predatory nematodes. The SEM suggests that bottom‐up control effects of plant species and plant functional group diversity on abundance of nematodes in the various feeding types predominantly involve mechanistic linkages related to plant quality instead of plant quantity; especially, C:N ratios of the shoot tissues, and/or effects of plants on the soil habitat, rather than shoot quantity explained nematode abundance. Although aboveground plant properties may only partly serve as a proxy for belowground resource quality and quantity, our results encourage further studies on nematode responses to variations in plant species and plant functional diversity in relation to both quantity and quality of the belowground resources.

Effects of different disturbance types on plant species composition and functional group cha racteristics of typical steppe in Inner Mongolia, China.

The impacts of three kinds of human disturbances, i.e., non-grazing, reseeding and free-grazing, on plant community characters, i.e., species composition, composition of functional groups, species diversity, and aboveground biomass, were studied in a typical steppe in Inner Mongolia, China. The results showed that different disturbances had significant impacts on the structure and diversity of plant functional groups. The number of plant species, aboveground biomass, community diversity, and richness indices were the highest in the non-grazing treatment, with the fi-gures of 22, 171.32 g·m-2, 1.46 and 5.7, respectively. The importance value (IV), percentage, aboveground biomass, diversity, richness, and evenness indices of shrub and sub-shrub, and perennial grasses were also the highest in the non-grazing treatment. In contrast, the IV, species percentage, aboveground biomass, diversity, and evenness indices of perennial forbs were the lowest in the non-grazing treatment. The aboveground biomass of mesophyte, C3 and C4 plants was the highe-st with the figures of 22.22, 143.35 and 27.97 g·m-2 respectively in the non-grazing treatment. The aboveground biomass of mesoxerophyte was highest (13.60 g·m-2), the species percentage of xerophyte was lowest (48.5%) and that of C4 plants was highest (28.8%) in the reseeding treatment. The species percentage of annual or biennial herbs was highest (12.3%), while that of mesophyte and C4 plants was lowest (17.0% and 20.9%) in the free-grazing treatment. The non-grazing treatment showed a beneficial effect for restoration of degraded grassland system.

Effects of Plant Diversity, Functional Group Composition, and Fertilization on Soil Microbial Properties in Experimental Grassland

BackgroundLoss of biodiversity and increased nutrient inputs are two of the most crucial anthropogenic factors driving ecosystem change. Although both received considerable attention in previous studies, information on their interactive effects on ecosystem functioning is scarce. In particular, little is known on how soil biota and their functions are affected by combined changes in plant diversity and fertilization.Methodology/Principal FindingsWe investigated the effects of plant diversity, functional community composition, and fertilization on the biomass and respiration of soil microbial communities in a long-term biodiversity experiment in semi-natural grassland (Jena Experiment). Plant species richness enhanced microbial basal respiration and microbial biomass, but did not significantly affect microbial specific respiration. In contrast, the presence of legumes and fertilization significantly decreased microbial specific respiration, without altering microbial biomass. The effect of legumes was superimposed by fertilization as indicated by a significant interaction between the presence of legumes and fertilization. Further, changes in microbial stoichiometry (C-to-N ratio) and specific respiration suggest the presence of legumes to reduce N limitation of soil microorganisms and to modify microbial C use efficiency.Conclusions/SignificanceOur study highlights the role of plant species and functional group diversity as well as interactions between plant community composition and fertilizer application for soil microbial functions. Our results suggest soil microbial stoichiometry to be a powerful indicator of microbial functioning under N limited conditions. Although our results support the notion that plant diversity and fertilizer application independently affect microbial functioning, legume effects on microbial N limitation were superimposed by fertilization, indicating significant interactions between the functional composition of plant communities and nutrient inputs for soil processes.

A comparison of biodiversity–ecosystem function relationships in alpine grasslands across a degradation gradient on the Qinghai–Tibetan Plateau

To examine biodiversity–ecosystem function relationships in alpine grasslands of the Qinghai–Tibetan Plateau, we compared differences in plant species and functional group diversity (sedges, grasses, legumes and non-leguminous forbs) to aboveground biomass, soil carbon (C) and nitrogen (N) pools and soil loss in five sites that ranged from healthy to severely degraded grasslands. Plant diversity decreased from 36 species in the healthy grassland to 15 species in the severely degraded grassland, and the plant functional groups changed from predominantly grasses and sedges to mostly forbs as the level of degradation increased. Plant biomass and soil pools of C and N decreased whereas soil loss and the amount of bare ground increased across the degradation gradient from healthy to severely degraded grasslands. Simple linear regressions showed strong positive relationships between species diversity and aboveground biomass of sedges, grasses and legumes and between soil C and N pools, but negative relationships between species diversity and non-leguminous forbs and soil loss. Our results provide strong evidence that plant diversity in grasslands on the Qinghai–Tibetan Plateau is positively related to primary productivity, C and N storage in soils and soil conservation, and that grassland degradation is impairing ecosystem function resulting in a loss in ecosystem services.

The impact of livestock grazing on plant diversity: an analysis across dryland ecosystems and scales in southern Africa.

A general understanding of grazing effects on plant diversity in drylands is still missing, despite an extensive theoretical background. Cross-biome syntheses are hindered by the fact that the outcomes of disturbance studies are strongly affected by the choice of diversity measures, and the spatial and temporal scales of measurements. The aim of this study is to overcome these weaknesses by applying a wide range of diversity measures to a data set derived from identical sampling in three distinct ecosystems. We analyzed three fence-line contrasts (heavier vs. lighter grazing intensity), representing different degrees of aridity (from arid to semiarid) and precipitation regimes (summer rain vs. winter rain) in southern Africa. We tested the impact of grazing intensity on multiple aspects of plant diversity (species and functional group level, richness and evenness components, alpha and beta diversity, and composition) at two spatial scales, and for both 5-yr means and interannual variability. Heavier grazing reduced total plant cover and substantially altered the species and functional composition at all sites. However, a significant decrease in species alpha diversity was detected at only one of the three sites. By contrast, alpha diversity of plant functional groups responded consistently across ecosystems and scales, with a significant decrease at heavier grazing intensity. The cover-based measures of functional group diversity responded more sensitively and more consistently than functional group richness. Beta diversity of species and functional types increased under heavier grazing, showing that at larger scales, the heterogeneity of the community composition and the functional structure were increased. Heavier grazing mostly increased interannual variability of alpha diversity, while effects on beta diversity and cover were inconsistent. Our results suggest that species diversity alone may not adequately reflect the shifts in vegetation structure that occur in response to increased grazing intensity in the dryland biomes of southern Africa. Compositional and structural changes of the vegetation are better reflected by trait-based diversity measures. In particular, measures of plant functional diversity that include evenness represent a promising tool to detect and quantify disturbance effects on ecosystems.