Loss Of Plant Diversity Research Articles

Assessment of Plant Commnunity Structure in a Tropical Wetland Affected by Brick Making—The Case of Sironga Wetland, Kenya

Brick making is one of the major small-scale industries in Sironga which has been expanding due to the growing demand for urban expansion. Due to the increasing population pressure, brick-making is competing for the wetland resources. Sironga wetland is threatened with serious degradation and probable loss of plant diversity. Conversion of this wetland for economic uses such as brick making has resulted in its loss. The objective of the study was to assess the effects of brick making on plant diversity in Sironga wetland. Nyamira County, Kenya. A one metre by one metre quadrat frame was laid down and perpendicularly recorded the percent cover for each species found inside the quadrant plus the percentage area covered by the bare ground litter. From each transect lines “diagonally” detailed vegetation under study was then done. The plant species were recorded and classified into three life-forms; herbs, sedges and grasses. The study revealed that grasses had the highest diversity H = 1.144. Diversity for herbs was H = 0.987 and H = 0.899 for reeds respectively. The study concluded that brick-making activities affected the plant diversity in Sironga wetland. This may be attributed partly to the limited information and awareness campaigns to the surrounding communities on the values and benefits of wetland ecosystem services and the lack of alternative livelihood sources. The study recommends that alternative livelihoods are provided and awareness campaigns on the values and benefits of wetlands to the residents are done by the relevant agencies.

Plant diversity and litter accumulation mediate the loss of foliar endophyte fungal richness following nutrient addition.

Foliar fungal endophytes are ubiquitous plant symbionts that can affect plant growth and reproduction via their roles in pathogen and stress tolerance, as well as plant hormonal signaling. Despite their importance, we have a limited understanding of how foliar fungal endophytes respond to varying environmental conditions such as nutrient inputs. The responses of foliar fungal endophyte communities to increased nutrient deposition may be mediated by the simultaneous effects on within-host competition as well as the indirect impacts of altered host population size, plant productivity, and plant community diversity and composition. Here, we leveraged a 7-yr experiment manipulating nitrogen, phosphorus, potassium, and micronutrients to investigate how nutrient-induced changes to plant diversity, plant productivity, and plant community composition relate to changes in foliar fungal endophyte diversity and richness in a focal native grass host, Andropogon gerardii. We found limited evidence of direct effects of nutrients on endophyte diversity. Instead, the effects of nutrients on endophyte diversity appeared to be mediated by accumulation of plant litter and plant diversity loss. Specifically, nitrogen addition is associated with a 40% decrease in plant diversity and an 11% decrease in endophyte richness. Although nitrogen, phosphorus, and potassium addition increased aboveground live biomass and decreased relative Andropogon cover, endophyte diversity did not covary with live plant biomass or Andropogon cover. Our results suggest that fungal endophyte diversity within this focal host is determined in part by the diversity of the surrounding plant community and its potential impact on immigrant propagules and dispersal dynamics. Our results suggest that elemental nutrients reduce endophyte diversity indirectly via impacts on the local plant community, not direct response to nutrient addition. Thus, the effects of global change drivers, such as nutrient deposition, on characteristics of host populations and the diversity of their local communities are important for predicting the response of symbiont communities in a changing global environment.

Global responses of fine root biomass and traits to plant species mixtures in terrestrial ecosystems

AbstractAimFine root traits underpin terrestrial ecosystem functioning. Despite ongoing plant diversity loss due to anthropogenic activities, our understanding of the effects of plant diversity on fine root traits remains elusive. We addressed: (a) Do fine roots modify their traits in response to species mixtures? (b) Do these responses change with the species richness in mixtures, stand age, and soil depth? (c) Do plant‐mixture induced responses of root traits differ across terrestrial ecosystems?LocationGlobal.Time periodPublication years: 1985–2019.Major taxa studiedPlants.MethodsWe conducted a global meta‐analysis of 852 paired observations from 103 published studies to assess the effects of species mixtures on fine root biomass and traits (including root/shoot ratio, community‐weighted mean rooting depth, root length density, specific root length, mean root diameter and root nitrogen content).ResultsWe found that the effects of species mixtures were highly dependent on species richness in mixtures, stand age, and soil depth. The positive effects of species mixtures on root biomass increased with species richness, soil depth, and mean annual temperature. Species mixture effects on root length density shifted from negative to positive with increasing stand age and soil depth and with decreased temperatures. The effects of species mixtures on specific root length shifted from positive to negative with increasing species richness and soil depth, and from negative to positive with increasing stand age.Main conclusionsOur meta‐analysis highlights that the community‐level consequences of changes in plant diversity on fine root traits are not consistent, and that predicting these consequences requires taking into account the extent of changes in plant species richness, stand age, soil depth investigated, background climates, and importantly, particular fine root traits.

Phosphorus fertilization is eradicating the niche of northern Eurasia's threatened plant species.

The greater bioavailability of nitrogen (N), phosphorus (P) and potassium (K) in the Anthropocene has strongly impacted terrestrial plant communities. In northwest Europe, because high N deposition is considered the main driver of plant diversity loss, European Union (EU) legislation to reduce N deposition is expected to promote plant species recovery. However, this expectation is simplistic: it ignores the role of other macronutrients. Analysing the relationship between plant species pools and species stoichiometric niches along nutrient gradients across northern Eurasia's herbaceous ecosystems, we found that both absolute and relative P availability are more critical than N or K availability. This result is consistent with stoichiometric niche theory, and with findings from studies of hyperdiverse forests and shrublands at lower latitudes. We show that ecosystems with low absolute and relative P availability harbour a unique set of threatened species that have narrower nutrient-based niche widths than non-threatened species. Such ecosystems represent a conservation priority, but may be further threatened by latent effects of relative P enrichment arising from reduction of N availability without simultaneous reduction of P. The narrow focus of EU legislation on reducing N, but not P, may therefore inadvertently increase the threat to many of Europe's already threatened plant species. An EU Phosphate Directive is needed.

Negative impacts of plant diversity loss on carbon sequestration exacerbate over time in grasslands

Positive relationships between plant species diversity and carbon attributes have been observed in grasslands, but synthesis studies of how plant diversity affects the carbon balance of grasslands and how the response ratio changes over time both remain limited. By conducting a global meta-analysis with 811 paired observations of plant mixtures and monocultures from 83 studies in natural and manipulated grasslands, we investigated the impacts of plant diversity on six carbon attributes, its interaction with experimental duration, and the changes in carbon balance under different plant diversity loss scenarios in the future. We found that the aboveground biomass (AGB), belowground biomass (BGB), total biomass (TB), soil organic carbon (SOC), soil respiration (Rs), and heterotrophic respiration (Rh) significantly increased in the plant mixtures, and the response ratio for all carbon attributes increased logarithmically with species richness. We also found that the response ratio for all carbon attributes except Rs increased linearly with experimental duration. The increase in response ratio of AGB, BGB, TB, and SOC with species richness was more pronounced with the long-term experimental duration. Importantly, our results showed that the declines in carbon sequestration will be exacerbated by different plant diversity loss scenarios in the future. Our meta-analysis revealed that plant diversity loss has ubiquitous negative impacts on multiple carbon attributes in grasslands, underlined the interactive effects of plant diversity loss and experimental duration on carbon attributes, and suggested that the reduction of carbon storage in grasslands following biodiversity loss will be greater in the future.

Wild ungulate overabundance in Europe: contexts, causes, monitoring and management recommendations

Abstract High‐density populations of large ungulates are now widespread. However, the perception of overabundance only appears when it produces a problem for humans, such as a loss of plant diversity, damage to agricultural crops and forestry, ungulate‐vehicle collisions, a nuisance to humans, disease transmission to livestock or changes in habitat for other species. The admissible level of density depends on the ecological and socio‐economic context in which the population is located, and defining this level is important, in order to determine management strategies and actions. We describe the main contexts in which ungulate overabundance occurs in Europe, record the causes of overabundance and evaluate which set of indicators of ecological change is the most appropriate for monitoring and diagnosing overabundance in each scenario. Our review of 318 published papers revealed six contexts of wild ungulate overabundance in Europe (protected areas, hunting areas, forestry, arable farming, livestock farming and [peri]urban areas). In addition to population abundance, four sets of indicators of environmental change could be used to monitor overabundance within these contexts (impacts on habitats, impact on animal performance, increments in diseases and parasite loads, and increments in nuisance to humans). Nine species of ungulate were found to be overabundant. Red deer Cervus elaphus was the species most likely to be overabundant in the contexts of protected areas (detailed in 27% of papers on that context) and hunting areas (38%); roe deer Capreolus capreolus in forestry (28%); wild boar Sus scrofa in arable farming (60%), livestock farming (29%) and (peri)urban areas (38%). Our evidence shows that the diagnosis and monitoring of ungulate population overabundance via indicators of ecological change, and the management actions required to control these undesirable situations, are strongly context‐dependent.

Diversity-dependent soil acidification under nitrogen enrichment constrains biomass productivity.

In most plant communities, the net effect of nitrogen enrichment is an increase in plant productivity. However, nitrogen enrichment also has been shown to decrease species richness and to acidify soils, each of which may diminish the long-term impact of nutrient enrichment on productivity. Here we use a long-term (20year) grassland plant diversity by nitrogen enrichment experiment in Minnesota, United States (a subexperiment within the BioCON experiment) to quantify the net impacts of nitrogen enrichment on productivity, including its potential indirect effects on productivity via changes in species richness and soil pH over an experimental diversity gradient. Overall, we found that nitrogen enrichment led to an immediate positive increment in productivity, but that this effect became nonsignificant over later years of the experiment, with the difference in productivity between fertilized and unfertilized plots decreasing in proportion to nitrogen addition-dependent declines in soil pH and losses of plant diversity. The net effect of nitrogen enrichment on productivity could have been 14.5% more on average over 20years in monocultures if not for nitrogen-induced decreases in pH and about 28.5% more on average over 20years in 16 species communities if not for nitrogen-induced species richness losses. Together, these results suggest that the positive effects of nutrient enrichment on biomass production can diminish in their magnitude over time, especially because of soil acidification in low diversity communities and especially because of plant diversity loss in initially high diversity communities.

The role of organic amendments in wetland restorations

At the present rate of loss (since 1990), half of the remaining wetlands worldwide will be developed within ~140 years, underscoring the importance of improving the creation and restoration of wetlands. Organic amendments are sometimes used during wetland creation. To evaluate the effectiveness of adding organic amendments we used a combined numerical method to assign “scores” on five categories of evaluation metrics: plant growth, soil properties, carbon accrual, denitrification, and anaerobic processes (e.g. redox potential). We found that amendments identified as “topsoil” scored measurably higher and had consistently more positive values with fewer negative results compared to amendments identified as “allochthonous organic matter” (alOM). Organic amendments had about the same effect on soils with low soil organic carbon (<2.5%) compared to soils richer in organic carbon. Organic amendments are not uniformly effective, and in some cases may have negative side effects. For example, alOM often resulted in a loss of plant diversity. These outcomes along with site conditions should be evaluated before using organic amendments.

Below‐ground‐mediated and phase‐dependent processes drive nitrogen‐evoked community changes in grasslands

Abstract Enhanced deposition of atmospheric nitrogen (N) leads to loss of plant diversity in grassland ecosystems. Numerous theories have provided potential explanations for the negative effects of N enrichment on plant diversity. However, the relative importance of each mechanism and the time‐scales of responses for the different functional groups remain unclear. We investigated the temporal responses of plant community in a temperate steppe to N enrichment by linking above‐ground to below‐ground processes using a series of field N‐addition and greenhouse experiments. The N enrichment‐induced declines in plant diversity of grasslands were phase‐based, functional group‐dependent and driven by three below‐ground processes. The rapid accumulation of by N addition inhibited photosynthetic rates of broad‐leaf non‐rhizomatous forbs, contributing to loss of these N‐sensitive species during early phase of N enrichment (≤3 years). The N‐induced changes in this phase were independent of soil pH as evidenced by results from application of lime to mitigate N‐evoked soil acidification. With progression of N addition, manganese (Mn) toxicity to narrow‐leaf non‐rhizomatous forbs due to soil acidification‐induced Mn2+ mobilization in soil accounted for their loss in the second phase of N enrichment (~4–9 years). When N addition proceeded longer than ~10 years, N enrichment stimulated below‐ground meristem differentiation and rhizome growth of the rhizomatous species, leading to the dominance by rhizomatous sedges/grasses in the community at the later phase of N enrichment. Synthesis. The hierarchical mechanisms not only provide a comprehensive explanation for the N enrichment‐induced diversity decline in grasslands, but can also facilitate us to understand the differential sensitivities of ecosystems to chronic N enrichment, and predict future ecosystem dynamics.

Shifts in Key Leaf Litter Traits Can Predict Effects of Plant Diversity Loss on Decomposition in Streams

Plant biodiversity loss in riparian forests is known to alter key stream ecosystem processes such as leaf litter decomposition. One potential mechanism mediating this biodiversity–decomposition relationship is the increased variability of plant functional traits at higher levels of biodiversity, providing more varied resources for decomposers and thus improving their function. We explored this in a field experiment exposing litter from different assemblages with low or high trait variability (measured through phylogenetic distance, PD) to microbial decomposers and invertebrate detritivores within litterbags in a low-order stream. Litter assemblages generally lost less mass but more phosphorus (P) than expected from monocultures, and nitrogen (N) tended to increase in the absence of detritivores and decrease in their presence, with little effect of PD. In contrast, there were strong influences of mean values and variability of specific traits (mostly N, P and condensed tannins) on decomposition and on net diversity effects. The negative diversity effect on litter mass loss was mainly driven by negative complementarity (that is, physical or chemical interference among species or traits), although there was positive selection (that is, particular species or traits with large effects on decomposition) in high-PD assemblages with detritivores. High-PD assemblages tended to have more invertebrates and attracted more typical litter-consuming detritivores. Our study suggests that decomposition of litter assemblages is mainly driven by concentration and variability of several key litter traits, rather than overall trait heterogeneity (measured through PD). However, differences in invertebrates colonizing high-PD and low-PD assemblages pointed to potential long-term effects of PD on decomposition.

Direct and indirect effects of plant diversity and phenoxy herbicide application on the development and reproduction of a polyphagous herbivore

Widespread application of synthetic pesticides and loss of plant diversity are regarded as significant drivers of current global change. The effects of such phenomena on insect performance have been extensively studied separately, yet the interactions of these two drivers have been poorly explored. Here, we subjected the polyphagous grasshopper Pseudochorthippus parallelus (Zetterstedt, 1821) to a full-lifecycle field experiment with 50 cages containing experimental plant communities differing in grass species richness (2 vs. 8 grass species), half of them treated with a phenoxy herbicide commonly employed to control broadleaf plants in grasslands. We measured plant elemental content as a proxy for plant physiology, and a wide range of insect traits in both female and male grasshoppers. In females, grass diversity increased herbivory, insect nitrogen content and egg load, while herbicide reduced herbivory but increased the number of offspring, likely mediated by altered plant community composition. In males, grass diversity also increased herbivory, had positive effects on fat body, muscle volume and lifespan, and negative effects on body mass. Herbicide negatively affected herbivory in both females and males. Overall, plant diversity and herbicides may shift resource allocation in generalist terrestrial insect herbivores, indicating complex and unexpected effects of human-induced environmental change.

Pollinator declines and the stability of plant–pollinator networks

AbstractPopulation declines of pollinators constitute a major concern for the fate of biodiversity and associated ecosystem services in a context of global change. Massive declines of pollinator populations driven by habitat loss, pollution, and climate change have been reported, whose consequences at community and ecosystem levels remain elusive. We conducted a mathematical modeling and computer simulation study to assess the dynamic consequences of pollinator declines for the biodiversity of plants and pollinators. Specifically, we evaluated the effects of increased mortality and decreased carrying capacity of specialist vs. generalist and effective vs. ineffective pollinators visiting specialist vs. generalist plants on long‐term community biomass and species persistence. Our results reveal that increased larval mortality and increased competition for space among larvae had the greatest impacts on the decline of pollinator diversity. In contrast, the largest sustained decreases in pollinator biomass were driven by increased adult mortality in spite of a small increase in pollinator species persistence. Decreased pollinator diversity led in turn to decreased plant diversity. Attacking pollinators with high degree and connected mostly to low‐degree plants produced the greatest losses of plant diversity. Pollinator effectiveness had no noticeable effect on persistence. Our results illuminate our understanding of the consequences of pollinator declines for the maintenance of biodiversity.

Plant Diversity Along the Urban–Rural Gradient and Its Relationship with Urbanization Degree in Shanghai, China

Urbanization is one of the major causes for plant diversity loss at the local and regional scale. However, how plant species distribute along the urban–rural gradient and what the relationship between urbanization degree and plant diversity is, is not very clear. In this paper, 134 sample sites along two 18 km width transects that run across the urban center of Shanghai were investigated. We quantified the spatial patterns of plant diversity along the urban–rural gradient and measured the relationship between plant diversity and urbanization degree, which was calculated using a land use land cover map derived from high spatial resolution aerial photos. We recorded 526 vascular plant species in 134 plots, 57.8% of which are exotic plant species. Six spatial distribution patterns of species richness were identified for different plant taxa along the rural to urban gradient. The native plant species richness showed no significant relationship to urbanization degree. The richness of the all plants, woody plants and perennial herbs presented significant positive relationship with urbanization degree, while the richness of annual herbs, Shannon-Wiener diversity and Heip evenness all exhibited a negative relationship to urbanization degree. Urbanization could significantly influence plant diversity in Shanghai. Our findings can provide insights to understand the mechanism of urbanization effects on plant diversity, as well as plant diversity conservation in urban areas.

Synergistic effects of wild ungulates and management intensification suppress native plants and promote exotics

In managed forest landscapes, conflicts among wood production, ungulates, native biodiversity, and exotic species are common. As humanity allocates more land as intensively managed plantations, these conflicts may become more severe. For instance, native ungulates have been implicated in the loss of native plant diversity, declines in timber revenues and the spread of exotic species in many forest systems, yet the synergistic effects of management and ungulate herbivory are not well understood.We hypothesized that herbicide and herbivore-induced suppression of native forage species promotes the release of exotic species in young forest plantations. Further, we expected herbivory and the retention of native forage via less intensive management would have negative consequences for reforestation objectives. To test this hypothesis, we conducted an experiment that manipulated management intensity (via herbicides) and access of two deer species to vegetation (via exclosures) on 28 operational Douglas-fir plantations of the Pacific Northwest, USA. We recorded yearly plant species cover estimates and tested the effects of herbivory and herbicides on native and exotic plants during the first six years of plantation establishment.Heavier herbicide treatments reduced the cover and diversity of native plants, and increased the cover of exotics over time, particularly that of exotic herbaceous species. Regardless of herbicide intensity, herbivores reduced the cover of native forage species. In a treatment that represents operational standards applied to over 2.5 million ha in the region, the suppression of native species by deer corresponded with an increase in exotic species cover by 23 percent, resulting in equitable abundance of native and exotic plants. As expected, Douglas-fir growth was suppressed when herbivores were present and vegetation was left untreated by herbicides, although the presence of deer promoted both crop-tree growth and the relative abundance of exotics in our most intensive treatment, presumably due to the added suppression of native competitors.Our findings suggest that wild ungulates amplify management-driven shifts toward exotic species in intensively managed forest plantations. Exotic plant forage status and adaptations to frequent disturbance seem to be key mechanisms for the synergistic effects we observed. Without herbicides, diverse assemblages of native species are buffered from herbivory and exotic species proliferation, with potential tradeoffs for timber production. Our results highlight the role of management intensity in modifying the interactions among exotic plants and native herbivores, contributing to a mechanistic understanding of the role of native biodiversity in regulating exotic species spread. Our data provide further support for growing evidence that synergistic effects of multiple drivers can facilitate exotic plant proliferation.

Effects of plant diversity on soil carbon in diverse ecosystems: a global meta-analysis.

Soil organic carbon (SOC) is a valuable resource for mediating global climate change and securing food production. Despite an alarming rate of global plant diversity loss, uncertainties concerning the effects of plant diversity on SOC remain, because plant diversity not only stimulates litter inputs via increased productivity, thus enhancing SOC, but also stimulates microbial respiration, thus reducing SOC. By analysing 1001 paired observations of plant mixtures and corresponding monocultures from 121 publications, we show that both SOC content and stock are on average 5 and 8% higher in species mixtures than in monocultures. These positive mixture effects increase over time and are more pronounced in deeper soils. Microbial biomass carbon, an indicator of SOC release and formation, also increases, but the proportion of microbial biomass carbon in SOC is lower in mixtures. Moreover, these species-mixture effects are consistent across forest, grassland, and cropland systems and are independent of background climates. Our results indicate that converting 50% of global forests from mixtures to monocultures would release an average of 2.70 Pg C from soil annually over a period of 20 years: about 30% of global annual fossil-fuel emissions. Our study highlights the importance of plant diversity preservation for the maintenance of soil carbon sequestration in discussions of global climate change policy.

Soil bacterial functional diversity mirrors the loss of plant diversity by the expansion of a native tall-grass in high mountain grasslands

In highland ecosystems, global change processes are intense and foster vegetation shifts that may have an impact on soil functioning. Soil bacterial communities may be particularly sensitive to these changing scenarios. The aim of this research is to determine whether the loss of floristic diversity caused by the unusual dominance of a native component -the perennial grass Brachypodium rupestre (L.) Beauv., which is expanding aggressively in natural grasslands of the Western Pyrenees-, parallels a decrease of the soil bacterial functional diversity and their potential for nutrient transformations. We conducted the study in eight grasslands exposed to different degrees of B. rupestre spreading. Soil community physiological profiles of the heterotrophic bacteria, enzymatic activities related to C, P and N cycles, C and N microbial biomasses, N components and soil physical and chemical properties were determined. Soils below low-diversity grasslands had lower bacterial functional richness and diversity but greater urease activity, pH and nitrate than soils in diverse grasslands. Ammonium pools, C and N microbial biomasses and enzymatic activities related to C and P did not differ between grasslands. The expansion of B. rupestre and the decrease of plant diversity coincided with a significant decline of bacterial functional diversity and an alteration of the N cycle. Not only plant composition but the prevailing disturbance regime may account for the results. Results also suggest that B. rupestre may rely on its capability to use N efficiently rather than on a soil bacteria-mediated N availability.

Multiple components of plant diversity loss determine herbivore phylogenetic diversity in a subtropical forest experiment

Abstract Plant diversity loss can alter higher trophic‐level communities via non‐random species interactions, which in turn may cascade to affect key ecosystem functions. These non‐random linkages might be best captured by patterns of phylogenetic diversity, which take into account co‐evolutionary dependencies. However, lack of adequate phylogenetic data of higher trophic levels hampers our mechanistic understanding of biodiversity relationships in species‐rich ecosystems. We used DNA barcoding to generate data on the phylogenetic diversity of lepidopteran caterpillars in a large‐scale forest biodiversity experiment in subtropical China. We analysed how different metrics of lepidopteran phylogenetic diversity (Faith's PD, MPD, MNTD) and taxonomic diversity were influenced by multiple components of tree diversity (taxonomic, functional, phylogenetic). Our data from six sampling periods represent 7,204 mitochondrial cytochrome c oxidase subunit I (COI) sequences of lepidopteran larvae, clustered into 461 molecular operational taxonomic units. Lepidopteran abundance, the effective number of species (irrespective of the focus on rare or common species) and Faith's PD and MPD (reflecting basal evolutionary splits), but not MNTD (reflecting recent evolutionary splits), significantly increased with experimentally manipulated tree species richness. Lepidopteran MNTD decreased with increasing tree MNTD. Path analyses showed that tree phylogenetic and functional diversity explained part, but not all of the effects of tree species richness on lepidopteran diversity. Importantly, tree diversity effects on lepidopteran diversity were to a large extent indirect, operating via changes in lepidopteran abundance. Synthesis. Our study shows that evolutionary dependencies determine the response of herbivore communities to changes in host plant diversity. Incorporating a wider range of diversity metrics both at the level of producers and consumers can thus help to develop a more comprehensive understanding of the functional consequences of biodiversity change across trophic levels. Moreover, the dependence of trophic linkages on herbivore abundances underlines the need to address the consequences of current declines in insect abundances for ecosystem structure and functioning.

Short-term grazing exclusion improved topsoil conditions and plant characteristics in degraded alpine grasslands

Abstract Grazing exclusion by fencing is one of the most effective practices to recover the degraded alpine grasslands in Tibetan Plateau. In the present study, the effects of 8-year (GE8) and 4-year (GE4) grazing exclusion were studied in comparison with free grazing (FG) in the plant-soil ecosystems of alpine grasslands. Within fencing, improved plant characteristics such as aboveground biomass (AGB), belowground biomass (BGB) and plant total cover developed without grazing and trampling were observed. Also, there were significant improvements of soil organic carbon (SOC), ammonia nitrogen (NH4+-N) and dissolved organic carbon (DOC) concentrations usually in the topsoil (0–30 cm) but a stable C:N ratio with the number of years of grazing exclusion. Fencing enhanced soil main enzyme (invertase, phosphatase, urease and β-glucosidase) activities by providing sufficient substrates for microbial activities. Unexpectedly, GE4 had higher soil invertase, phosphatase, urease and β-glucosidase activities than GE8, which had less plant diversity, richness and higher total cover causing a lowering of soil temperature. Additionally, the results supported the allometric allocation hypothesis for the ABG versus BGB in the grasslands of Tibetan Plateau. Our results indicated that SOC and BGB can be used as indicators of the restoration process of degraded alpine grassland. Cautions should be taken for a long-term fencing in degraded alpine grasslands because of the loss of plant richness, diversity and soil enzyme activities. The present results also suggested that a suitable grazing regime combined with fencing should be focused in the future study of the alpine grasslands. Research results obtained in the present study should, therefore, be helpful to offer a better guidance towards the management practices of the degraded alpine grasslands.

Plant diversity loss affects stream ecosystem multifunctionality.

Biodiversity loss is occurring globally at unprecedented rates, altering the functioning of the Earth's ecosystems. Multiple processes are often key components of ecosystem functioning, but it is unclear how biodiversity loss affects ecosystem multifunctionality (i.e., the ability of ecosystems to maintain multiple processes simultaneously). This is particularly true for some ecosystem types such as streams, which have been understudied, despite their key role in global biogeochemical cycles and their serious impairment by the widespread loss of riparian vegetation as a result of global change. Using a microcosm experiment, we tested whether losing riparian plant diversity affected stream multifunctionality, taking into account nine key processes related to litter decomposition, animal biomass production, and nutrient cycling, and simulating plant species loss from four to one in the presence or absence of litter-feeding detritivores. Multifunctionality increased with plant diversity in the presence of detritivores and decreased in their absence, evidencing a key role of detritivores in biodiversity-ecosystem-functioning (BEF) relationships. Moreover, by exploring effects of plant diversity on each process individually we were able to reveal potential mechanisms underlying BEF relationships; for example, effects of plant diversity on nutrient cycling occurred at least partly via indirect nutrient transfer, and were possibly accompanied by changes in microbial stoichiometry. Such mechanisms were unnoticeable when examining multifunctionality metrics, suggesting that individual processes provide crucial information to understand how stream ecosystem functioning is impaired by biodiversity loss.

Testing relationship between plant productivity and diversity in a desertified steppe in Northwest China.

The rapid global plant diversity and productivity loss has resulted in ecosystem functional degeneration in recent decades, and the relationship between plant diversity and productivity is a pressing issue around the world. Here, we sampled six plant communities that have not been grazed for 20 years, i.e., Agropyron mongolicum, Stipa bungeana, Cynanchum komarovii, Glycyrrhiza uralensis, Sophora alopecuroides, Artemisia ordosica, located in a desertified steppe, northwestern China, and tested the relationship between plant diversity and productivity in this region. We found a positive linear relationship between AGB (above-ground biomass) and BGB (below-ground biomass), and the curves between plant diversity and AGB were unimodal (R2 = 0.4572, p < 0.05), indicating that plant productivity increased at a low level of diversity but decreased at a high level of diversity. However, there was no significant relationship between BGB and plant diversity (p > 0.05). Further, RDA (redundancy analysis) indicated that soil factors had a strong effect on plant diversity and productivity. Totally, GAMs (generalized additive models) showed that soil factors (especially total nitrogen TN, total carbon TC, soil microbial biomass nitrogen SMB-N, soil microbial biomass carbon SMB-C) explained more variation in plant diversity and productivity (78.24%), which can be regarded as the key factors driving plant diversity and productivity. Therefore, strategies aiming to increase plant productivity and protect plant diversity may concentrate on promoting soil factors (e.g., increasing TC, TN, SMB-N and SMB-C) and plant species, which can be regarded as an effective and simple strategy to stabilize ecosystems to mitigate aridity in desertified steppes in northwestern China.