Effects Of Plant Functional Diversity Research Articles

An experimental approach to assessing the impact of ecosystem engineers on biodiversity and ecosystem functions.

Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant-insect interaction analysis and variance partitioning of biodiversity effects. We present a case-study experiment in which facilitation by a cushion-plant species and a dwarf-shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: (1) removal of plant species associated with ecosystem engineers, (2) exclusion (covering) of ecosystem engineer flowers, and (3) control, i.e., natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity-ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects.

Effects of plant functional diversity induced by grazing and soil properties on above- and belowground biomass in a semiarid grassland

The trait-based plant functional diversity is associated with ecosystem functioning. However, few studies show the effects of plant functional diversity induced by grazing disturbance and environmental changes on aboveground plant biomass (AGB) and belowground root biomass (BGB) in semiarid grasslands. We examined the effects of long-term grazing on plant functional diversity across four grassland types (meadow, steppe, scattered tree grassland and sandy grassland) in Horqin grassland, Northern China. The structural equation model (SEM) was used to evaluate the direct or indirect effects of long-term grazing, soil properties and functional diversity reflected by the single-trait (community-weighted mean) and multi-trait (functional dispersion, FDis) on AGB and BGB across four grassland types. We found that long-term grazing significantly decreased plant height and FDis, while the responses of leaf traits to grazing differed among four grassland types. The correlation analyses showed that AGB and BGB were negatively associated with grazing and positively associated with plant height, FDis, soil carbon (C) and nitrogen (N). The SEM results indicated that AGB was directly affected by grazing, soil N, plant height and perennial richness, and BGB was directly affected by grazing, soil N, soil water content and elevation. Grazing and soil N also indirectly affected AGB through their effects on plant height and FDis. Effect of plant height on aboveground plant biomass was direct rather than indirect, while FDis acted indirectly through its effect on perennial richness, thereby lending more support to the mass ratio hypothesis. Our results clearly highlight the critical role of plant functional diversity induced by grazing and soil properties in affecting AGB in a semiarid grassland ecosystem. So, we recommend considering the linkages of plant functional diversity with ecosystem function in assessing the effects of grazing and soil changes on grassland ecosystems.

Consistent increase in herbivory along two experimental plant diversity gradients over multiple years

AbstractResearch on the functional importance of biodiversity, motivated by global species loss, has documented that plant species richness affects many plant‐related ecosystem functions. Less is known about the effects of plant species richness on functions related to higher trophic levels, such as the consumption of biomass by animals, that is, herbivory. Previous studies have shown positive, neutral, or negative effects of plant species richness on herbivory. In the framework of a grassland biodiversity experiment (the Jena Experiment), we investigated herbivory (the proportion of leaf area damaged and the amount of leaf biomass consumed by arthropod herbivores) along two experimental gradients of plant species richness ranging from 1 to 60 species (Main Experiment) and from 1 to 8 species (Trait‐Based Experiment) biannually for five and three years, respectively. Additionally, plant functional diversity, based on traits related to plant growth, was manipulated as the number of functional groups in a community (Main Experiment) or a gradient of functional trait dissimilarity (Trait‐Based Experiment). Herbivory at the level of plant communities ranged from 0% to 31% (0 and 33.8 g/m2) in the Main Experiment and 0% to 8% (0 and 13.7 g/m2) in the Trait‐Based Experiment, and it was on average higher in summer than in spring. For both experimental gradients and all years investigated, we found a consistent increase in damaged leaf area and consumed biomass with increasing plant species richness. As mechanistic explanations for effects of plant species richness, we propose changes in plant quality and herbivore communities. The presence of specific plant functional groups significantly affected herbivory, likely related to traits affecting plant defense and nutritional value, but we found little evidence for effects of plant functional diversity. The general positive relationship between plant species richness and herbivory might contribute to effects of plant species richness on other ecosystem functions such as productivity and nutrient mineralization and can cascade up the food web also affecting higher trophic levels.

Plant functional diversity mediates the effects of vegetation and soil properties on community-level plant nitrogen use in the restoration of semiarid sandy grassland

Species-rich plant communities use nitrogen (N) more efficiently in grassland ecosystems; however, the role of plant functional diversity in affecting community level plant N-use has received little attention. We examined plant N content, stock and N-use efficiency at community-level along a restoration gradient of sandy grassland (mobile dune, semi-fixed dune, fixed dune and grassland) in Horqin Sand Land, northern China. We used the functional trait-based approach to examine how plant functional diversity, reflected by the most abundant species’ traits (community-weighted mean, CWM) and the dispersion of functional trait values (FDis), affected N-use efficiency in sandy grassland restoration. We further used the structure equation model (SEM) to evaluate the direct or indirect effects of plant species richness, biomass, functional diversity and soil properties on community-level plant N-use efficiency. We found that plant biomass and its N stock increased following sandy grassland restoration, and there were lower plant N content and higher N-use efficiency in semi-fixed dune, fixed dune and grassland as compared with mobile dune. N-use efficiency was positively associated with plant species richness, biomass, CWM plant height, CWM leaf C:N, FDis and soil gradient, but SEM results showed that species richness, CWM leaf C:N, plant biomass and FDis controlled by soil properties were the main factors exerting direct effects. CWM plant height also had a positive effect on N-use efficiency through its indirect effect on plant biomass. Soil gradient increased N-use efficiency through an indirect effect on vegetation rather than a direct effect. Final SEM models based on different plant functional diversity explained over 74% of variances in N-use efficiency. Effects of plant functional diversity on N-use efficiency supported both the mass ratio hypothesis and the complementarity hypothesis. Our results clearly highlight the important role of plant functional diversity in mediating the effects of vegetation and soil properties on community level plant N-use in sandy grassland ecosystems.

No plant functional diversity effects on foliar fungal pathogens in experimental tree communities

Foliar fungal pathogens affect forest ecosystem processes by exerting highly species-specific impacts on growth and survival of trees. As many ecosystem processes in forests depend on functional diversity of specific tree species, a close relationship is expected between this and foliar fungal pathogen infestation. Testing for such a relationship in the German tree diversity experiment BIOTREE (Bechstedt), we hypothesized that pathogen richness and pathogen load decline with increasing functional diversity of tree communities. Using macro- and microscopic analyses, we assessed pathogen richness and load on 16 tree species in plots that, although differing in functional diversity, had the same tree species richness. We found no effects of functional diversity on pathogen richness or load. However, we encountered strong species identity effects in plot species composition, as susceptible tree species contributed positively to each community’s pathogen richness and load. Furthermore, testing for effects of particular leaf traits and geographical range size of host species revealed a significant effect of total leaf phenolics, which was unexpected as pathogen richness increased with increasing content in polyphenolics. Our study showed that at the community level, host species’ identity was more important for foliar fungal pathogen richness and load than the functional diversity of host trees. The positive relationship between pathogen richness and phenolics in leaves, along with the finding that pathogen richness is very much conserved in tree species, point to an evolutionary arms race between hosts and fungi resulting from fungi increasing their capacity to infect tree leaves and trees boosting their defences.

Cascading effects of long‐term land‐use changes on plant traits and ecosystem functioning

There is much concern that the functioning of ecosystems will be affected by human-induced changes in biodiversity, of which land-use change is the most important driver. However, changes in biodiversity may be only one of many pathways through which land use alters ecosystem functioning, and its importance relative to other pathways remains unclear. In particular, although biodiversity-ecosystem function research has focused primarily on grasslands, the increases in agricultural inputs (e.g., fertilization, irrigation) and grazing pressure that drive change in grasslands worldwide have been largely ignored. Here we show that long-term (27-year) manipulations of soil resource availability and sheep grazing intensity caused marked, consistent shifts in grassland plant functional composition and diversity, with cascading (i.e., causal chains of) direct, indirect, and interactive effects on multiple ecosystem functions. Resource availability exerted dominant control over above-ground net primary production (ANPP), both directly and indirectly via shifts in plant functional composition. Importantly, the effects of plant functional diversity and grazing intensity on ANPP shifted from negative to positive as agricultural inputs increased, providing strong evidence that soil resource availability modulates the impacts of plant diversity and herbivory on primary production. These changes in turn altered litter decomposition and, ultimately, soil carbon sequestration, highlighting the relevance of ANPP as a key integrator of ecosystem functioning. Our study reveals how human alterations of bottom-up (resources) and top-down (herbivory) forces together interact to control the functioning of grazing systems, the most extensive land use on Earth.

Interrill erosion at disturbed alpine sites: Effects of plant functional diversity and vegetation cover

It has been hypothesized that a diverse vegetation cover with a high number of plant species and plant functional groups may be more effective at governing soil erosion processes than a vegetation cover with few species and fewer different plant functional groups. We investigated the influence of plant cover and diversity on interrill erosion on a disturbed alpine site. Rainfall simulations were conducted on micro-scale plots (25 × 25 cm) with different degrees of vegetation cover and plant functional group diversity. We selected plots with 10%, 30% and 60% of vegetation cover containing different plant functional groups: (i) grasses, (ii) forbs, (iii) cryptogams (moss and/or lichens), and all possible combinations of these three groups. On each plot a rain intensity of 375 ml min −1 (30 mm) was applied for 5 min. The degree of vegetation cover had the largest effect on interrill erosion. At 60% vegetation cover, the sediment yield was reduced by 83% in comparison to the un-vegetated ground. In the plots with 60% vegetation cover, an increase in functional group diversity decreased the sediment yield significantly. Sediment yield was three times lower in the presence of three plant functional groups than in systems with one plant functional group. Combinations of plant functional groups including grasses reduced the sediment yield more than other combinations. The findings of this study support the view that beside the re-establishment of a closed vegetation cover, a high plant functional diversity can be a relevant factor to further reduce interrill erosion at disturbed sites in alpine ecosystems.

Plant functional composition influences rates of soil carbon and nitrogen accumulation

Summary The mechanisms controlling soil carbon (C) and nitrogen (N) accumulation are crucial for explaining why soils are major terrestrial C sinks. Such mechanisms have been mainly addressed by imposing short‐term, step‐changes in CO2, temperature and N fertilization rates on either monocultures or low‐diversity plant assemblages. No studies have addressed the long‐term effects of plant functional diversity (i.e. plant functional composition) on rates of soil C accumulation in N‐limited grasslands where fixation is the main source of N for plants. Here we measure net soil C and N accumulation to 1 m soil‐depth during a 12‐year‐long grassland biodiversity experiment established on agriculturally degraded soils at Cedar Creek, Minnesota, USA. We show that high‐diversity mixtures of perennial grassland plant species stored 500% and 600% more soil C and N than, on average, did monoculture plots of the same species. Moreover, the presence of C4 grasses and legumes increased soil C accumulation by 193% and 522%, respectively. Higher soil C and N accrual resulted both from increased C and N inputs via (i) higher root biomass, and (ii) from greater root biomass accumulation to 60 cm soil depth resulting from the presence of highly complementary functional groups (i.e. C4 grasses and legumes). Our results suggest that the joint presence of C4 grass and legume species is a key cause of greater soil C and N accumulation in both higher and lower diversity plant assemblages. This is because legumes have unique access to N, and C4 grasses take up and use N efficiently, increasing below‐ground biomass and thus soil C and N inputs. Synthesis. We demonstrate that plant functional complementarity is a key reason why higher plant diversity leads to greater soil C and N accumulation on agriculturally degraded soils. We suggest the combination of key C4 grass–legume species may greatly increase ecosystem services such as soil C accumulation and biomass (biofuel) production in both high‐ and low‐diversity N‐limited grassland systems.

Incorporating plant functional diversity effects in ecosystem service assessments.

Global environmental change affects the sustained provision of a wide set of ecosystem services. Although the delivery of ecosystem services is strongly affected by abiotic drivers and direct land use effects, it is also modulated by the functional diversity of biological communities (the value, range, and relative abundance of functional traits in a given ecosystem). The focus of this article is on integrating the different possible mechanisms by which functional diversity affects ecosystem properties that are directly relevant to ecosystem services. We propose a systematic way for progressing in understanding how land cover change affects these ecosystem properties through functional diversity modifications. Models on links between ecosystem properties and the local mean, range, and distribution of plant trait values are numerous, but they have been scattered in the literature, with varying degrees of empirical support and varying functional diversity components analyzed. Here we articulate these different components in a single conceptual and methodological framework that allows testing them in combination. We illustrate our approach with examples from the literature and apply the proposed framework to a grassland system in the central French Alps in which functional diversity, by responding to land use change, alters the provision of ecosystem services important to local stakeholders. We claim that our framework contributes to opening a new area of research at the interface of land change science and fundamental ecology.