Effects Of Plant Species Richness Research Articles

Management Intensity Modifies Plant Diversity Effects on N Yield and Mineral N in Soil

The effect of species loss on productivity were of comparable magnitude to changes in agricultural management. However, not only productivity but also the N cycle is relevant for food production comprising beneficial as well as threatening effects of agricultural management. Our objectives were to test whether grassland management (mowing two or four times a year; 0, 100, or 200 kg N/ha) (i) modifies N yield or soil Nmin concentrations and changes (ii) the effect of plant functional groups (legumes, grasses, non-leguminous small and tall herbs) on N yield or soil Nmin concentrations or (iii) the relationships between plant diversity and N yield or soil Nmin concentrations. We observed highest productivity under moderate management intensity which can be attributed to the growth-stimulating fertilizer effect associated with enough time for regrowth. With increasing management intensity, the positive effect of the presence of legumes on N yield and soil Nmin concentrations disappeared. Plant species richness was positively related to N yield with the most pronounced effect in the highly fertilized and frequently mown treatment. In the control (mown twice a year, non-fertilized), competition for nutrients very likely underlie plant species richness effects. Under higher management intensity, a combination of competition for light and adaption to mowing frequency seemed to be responsible for plant species richness effects. The concurrence of highest N yield in high-diversity mixtures under most intensive management indicates that some plant species must have more than compensated for the N uptake of non-adapted species that did not survive frequent mowing, highlighting the value of plant diversity as an insurance against anthropogenic disturbances including management measures.

Disentangling the influence of plants and herbivores on the local diversity of parasitoids in the Brazilian Cerrado

Abstract This study investigated the extent to which host plants and their associated herbivores determine the local diversity of parasitoids, which depend, directly or indirectly, on these two groups as food resource or shelter for their development. The tritrophic system studied here is composed of Asteraceae, endophagous herbivores associated with their flower heads and parasitoid wasps. Samplings were undertaken in 18 remnants of the Brazilian Cerrado. Path analysis was used to unveil the direct and indirect effects of species richness, average taxonomic distinctness (AvTD), and sampling effort of plants and herbivores on parasitoid richness and AvTD. Plant species richness had only an indirect effect – mediated by herbivores – on parasitoid species richness. On the other hand, there were both direct and indirect effects of plant species richness on the AvTD of parasitoids. An implication of our findings is that the local extinction of plant species promotes not only the local loss of their herbivores but also the loss of parasitoid species and a decrease in the phylogenetic diversity of parasitoids, which can jeopardise their future evolutionary history.

Plant species diversity affects infiltration capacity in an experimental grassland through changes in soil properties

Soil hydraulic properties drive water distribution and availability in soil. There exists limited knowledge of how plant species diversity might influence soil hydraulic properties. We quantified the change in infiltration capacity affected by soil structural variables (soil bulk density, porosity and organic carbon content) along a gradient of soil texture, plant species richness (1, 2, 4, 8, 16 and 60) and functional group composition (grasses, legumes, small herbs, tall herbs). We conducted two infiltration measurement campaigns (May and October 2012) using a hood infiltrometer. Plant species richness significantly increased infiltration capacity in the studied grasslands. Both soil porosity (or inversely bulk density) and organic carbon played an important role in mediating the plant species richness effect. Soil texture did not correlate with infiltration capacity. In spring 2012, earthworm biomass increased infiltration capacity, but this effect could not be attributed to changes in soil structural variables. We experimentally identified important ecological drivers of infiltration capacity, suggesting complex interactions between plant species richness, earthworms, and soil structural variables, while showing little impact of soil texture. Changes in plant species richness may thus have significant effects on soil hydraulic properties with potential consequences for surface run-off and soil erosion.

Plant species richness leaves a legacy of enhanced root litter-induced decomposition in soil

Increasing plant species richness generally enhances plant biomass production, which may enhance accumulation of carbon (C) in soil. However, the net change in soil C also depends on the effect of plant diversity on C loss through decomposition of organic matter. Plant diversity can affect organic matter decomposition via changes in litter species diversity and composition, and via alteration of abiotic and/or biotic attributes of the soil (soil legacy effect). Previous studies examined the two effects on decomposition rates separately, and do therefore not elucidate the relative importance of the two effects, and their potential interaction. Here we separated the effects of litter mixing and litter identity from the soil legacy effect by conducting a factorial laboratory experiment where two fresh single root litters and their mixture were mixed with soils previously cultivated with single plant species or mixtures of two or four species. We found no evidence for litter-mixing effects. In contrast, root litter-induced CO2 production was greater in soils from high diversity plots than in soils from monocultures, regardless of the type of root litter added. Soil microbial PLFA biomass and composition at the onset of the experiment was unaffected by plant species richness, whereas soil potential nitrogen (N) mineralization rate increased with plant species richness. Our results indicate that the soil legacy effect may be explained by changes in soil N availability. There was no effect of plant species richness on decomposition of a recalcitrant substrate (compost). This suggests that the soil legacy effect predominantly acted on the decomposition of labile organic matter. We thus demonstrated that plant species richness enhances root litter-induced soil respiration via a soil legacy effect but not via a litter-mixing effect. This implies that the positive impacts of species richness on soil C sequestration may be weakened by accelerated organic matter decomposition.

Woody plant phylogenetic diversity mediates bottom-up control of arthropod biomass in species-rich forests.

Global change is predicted to cause non-random species loss in plant communities, with consequences for ecosystem functioning. However, beyond the simple effects of plant species richness, little is known about how plant diversity and its loss influence higher trophic levels, which are crucial to the functioning of many species-rich ecosystems. We analyzed to what extent woody plant phylogenetic diversity and species richness contribute to explaining the biomass and abundance of herbivorous and predatory arthropods in a species-rich forest in subtropical China. The biomass and abundance of leaf-chewing herbivores, and the biomass dispersion of herbivores within plots, increased with woody plant phylogenetic diversity. Woody plant species richness had much weaker effects on arthropods, but interacted with plant phylogenetic diversity to negatively affect the ratio of predator to herbivore biomass. Overall, our results point to a strong bottom-up control of functionally important herbivores mediated particularly by plant phylogenetic diversity, but do not support the general expectation that top-down predator effects increase with plant diversity. The observed effects appear to be driven primarily by increasing resource diversity rather than diversity-dependent primary productivity, as the latter did not affect arthropods. The strong effects of plant phylogenetic diversity and the overall weaker effects of plant species richness show that the diversity-dependence of ecosystem processes and interactions across trophic levels can depend fundamentally on non-random species associations. This has important implications for the regulation of ecosystem functions via trophic interaction pathways and for the way species loss may impact these pathways in species-rich forests.

Multivariate control of root biomass in a semi-arid grassland on the Loess Plateau, China

Root biomass has long been under-represented in biodiversity–ecosystem functioning studies, despite its dominance in biomass in many arid and semi-arid ecosystems. We aimed to explore the multivariate control over root biomass by plant diversity, together with other biotic and abiotic factors and to evaluate the relative importance of these factors. Above- and below-ground traits of 13 communities and soil properties were measured in semi-arid grasslands on the Loess Plateau, China. Structural equation modeling (SEM) was used to evaluate the relative importance of the community and soil characteristics, emphasizing the direct and indirect effects of plant diversity on root biomass. Significant indirect effects of plant species richness on root biomass were found, although no direct correlation was detected between them. In the indirect pathways, plant species richness showed a positive effect on soil total nitrogen, but a significant negative influence on soil total carbon. Soil total nitrogen and plant diversity had the largest and smallest total effect respectively on root biomass in the model. Plant species richness was not the strongest determinant of root biomass but had a significant indirect effect, mediated through soil total carbon and nitrogen. This study suggests that greater plant species richness, through a positive influence on soil total nitrogen, may indirectly promote root carbon stock.

A trait-based experimental approach to understand the mechanisms underlying biodiversity–ecosystem functioning relationships

Plant functional characteristics may drive plant species richness effects on ecosystem processes. Consequently, the focus of biodiversity–ecosystem functioning (BEF) experiments has expanded from the manipulation of plant species richness to manipulating functional trait composition. Involving ecophysiological plant traits in the experimental design might allow for a better understanding of how species loss alters ecosystem processes. Here we provide the theoretical background, design and first results of the ‘Trait-Based Biodiversity Experiment’ (TBE), established in 2010 that directly manipulates the trait composition of experimental plant communities.Analysis of six plant traits related to resource acquisition and use were analyzed using principal component analysis of 60 grassland species. The resulting two main axes describe gradients in functional similarity, and were used as the basis for designing plant communities with different functional and species diversity levels. Using such an approach allowed us to manipulate different levels of complementarity in spatial and temporal plant resource acquisition. In contrast to previous biodiversity experiments, the TBE is designed according to more realistic scenarios of non-random species loss along orthogonal axes of species trait dissimilarities. This allows us to tease apart the relative importance of selection and complementarity effects on multiple ecosystem processes, and to mechanistically study the consequences of plant community simplification.

Plant diversity in a nutshell: testing for small‐scale effects on trap nesting wild bees and wasps

Declining plant species richness in agro‐ecosystems and thus reduced habitat quality can have cascading effects on ecosystem functioning, leading to reduced pollination and biological control. Here we test if plant diversity can affect arthropod diversity and abundance on a very small scale, manipulating plant species richness (2, 6, 12 and 20 sown species) in small adjacent subplots (6 × 9 m) in 10 wildflower strips in an agricultural landscape. We simultaneously analyzed the effect of plant species richness, vegetation structure, and plant composition on the species richness and abundance of cavity‐nesting wild bees, wasps, their prey and natural enemies, and on the structure of their food webs. By separating the trap‐nesting species into functional groups according to their prey, we aimed to understand the underlying patterns for the effects of plant diversity. Increasing plant species richness had a significant effect only on spider‐predating wasps, the group of wasps trophically most distant from plants. In contrast, bees and food‐web structure were unaffected by plant diversity. Spider‐predating wasp abundance negatively correlated with the abundance of spiders, suggesting top‐down control. Interestingly, the abundance of spiders was the only variable that was strongly affected by plant composition. The hypothesis that the effect of plant diversity decreases with increasing trophic level is not supported by our study, and the mobility of species appears to play a greater role at this small spatial scale.

Plant diversity effects on the water balance of an experimental grassland

ABSTRACTIn the literature, contrasting effects of plant species richness on the soil water balance are reported. Our objective was to assess the effects of plant species and functional richness and functional identity on soil water contents and water fluxes in the experimental grassland of the Jena Experiment. The Jena Experiment comprises 86 plots on which plant species richness (0, 1, 2, 4, 8, 16, and 60) and functional group composition (zero to four functional groups: legumes, grasses, tall herbs, and small herbs) were manipulated in a factorial design. We recorded meteorological data and soil water contents of the 0·0–0·3 and 0·3–0·7 m soil layers and calculated actual evapotranspiration (ETa), downward flux (DF), and capillary rise with a soil water balance model for the period 2003–2007. Missing water contents were estimated with a Bayesian hierarchical model. Species richness decreased water contents in subsoil during wet soil conditions. Presence of tall herbs increased soil water contents in topsoil during dry conditions and decreased soil water contents in subsoil during wet conditions. Presence of grasses generally decreased water contents in topsoil, particularly during dry phases; increased ETa and decreased DF from topsoil; and decreased ETa from subsoil. Presence of legumes, in contrast, decreased ETa and increased DF from topsoil and increased ETa from subsoil. Species richness probably resulted in complementary water use. Specific functional groups likely affected the water balance via specific root traits (e.g. shallow dense roots of grasses and deep taproots of tall herbs) or specific shading intensity caused by functional group effects on vegetation cover. Copyright © 2013 John Wiley & Sons, Ltd.

The effect of plant richness and urban garden structure on bird species richness, diversity and community structure

Urban green areas improve the standard of living in cities and affect people's attitude to nature and conservation. Zoological knowledge may provide data that will help designers to enhance bird diversity in gardens. We studied the effect of plant species richness and structure on bird species richness, diversity and community structure in 25 public gardens in Tel-Aviv city and, neighboring suburbs, Israel. A total of 65 bird species were observed, of which nine were urban, exploiters or alien species. These latter species composed 54% of all individuals seen. Additional 13 bird species, mostly migrants, were observed in gardens further from the observation fixed radius. We found that shrubs species richness positively affected bird species diversity. Most bird species were found where trees and shrubs species richness was high, and trees and lawn cover were medium or low. High trees or high lawn cover attracted only a few bird species, mostly aliens and urban exploiters. Native birds preferred to forage on native trees and alien birds preferred to feed on alien trees. Bird species diversity was higher during spring and fall because of the presence of migrating bird species. Dogs and people had a negative effect on bird presence. Accordingly, we recommend that when planning new gardens, designers will avoid large lawns, prefer diverse and dense shrubberies, native trees, and will create some areas that will not be accessible to dogs and people. Finally, we emphasize the importance of multidisciplinary studies conducted in collaboration between landscape designers and zoologists.

Interactions among resource partitioning, sampling effect, and facilitation on the biodiversity effect: a modeling approach

Resource partitioning, facilitation, and sampling effect are the three mechanisms behind the biodiversity effect, which is depicted usually as the effect of plant-species richness on aboveground net primary production. These mechanisms operate simultaneously but their relative importance and interactions are difficult to unravel experimentally. Thus, niche differentiation and facilitation have been lumped together and separated from the sampling effect. Here, we propose three hypotheses about interactions among the three mechanisms and test them using a simulation model. The model simulated water movement through soil and vegetation, and net primary production mimicking the Patagonian steppe. Using the model, we created grass and shrub monocultures and mixtures, controlled root overlap and grass water-use efficiency (WUE) to simulate gradients of biodiversity, resource partitioning and facilitation. The presence of shrubs facilitated grass growth by increasing its WUE and in turn increased the sampling effect, whereas root overlap (resource partitioning) had, on average, no effect on sampling effect. Interestingly, resource partitioning and facilitation interacted so the effect of facilitation on sampling effect decreased as resource partitioning increased. Sampling effect was enhanced by the difference between the two functional groups in their efficiency in using resources. Morphological and physiological differences make one group outperform the other; once these differences were established further differences did not enhance the sampling effect. In addition, grass WUE and root overlap positively influence the biodiversity effect but showed no interactions.

A comparison of the strength of biodiversity effects across multiple functions

In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45% of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination.

Plant species richness enhanced the methane emission in experimental microcosms

Effect of plant species richness on the methane (CH4) flux was investigated in vertical flow microcosms fed with the modified Hoagland solution. The CH4 flux increased significantly with the plant species richness (Linear regression analysis, r2 = 0.203, P = 0.010), with an average range from 1.59 to 4.30 mg m−2 d−1. Above-ground plant biomass followed the CH4 flux trend with the plant species richness (r2 = 0.108, P = 0.023), but both methanogenic number and activity decreased to different extents with the plant species richness (r2 = 0.103, P = 0.023; r2 = 0.020, P = 0.337), respectively. Accordingly, the present study highlights the significance of plant species diversity and its biomass production in manipulating the CH4 flux in the constructed wetlands.

Diversity of plant evolutionary lineages promotes arthropod diversity

Large-scale habitat destruction and climate change result in the non-random loss of evolutionary lineages, reducing the amount of evolutionary history represented in ecological communities. Yet, we have limited understanding of the consequences of evolutionary history on the structure of food webs and the services provided by biological communities. Drawing on 11 years of data from a long-term plant diversity experiment, we show that evolutionary history of plant communities - measured as phylogenetic diversity - strongly predicts diversity and abundance of herbivorous and predatory arthropods. Effects of plant species richness on arthropods become stronger when phylogenetic diversity is high. Plant phylogenetic diversity explains predator and parasitoid richness as strongly as it does herbivore richness. Our findings indicate that accounting for evolutionary relationships is critical to understanding the severity of species loss for food webs and ecosystems, and for developing conservation and restoration policies.

Impacts of Biodiversity Loss Escalate Through Time as Redundancy Fades

Plant diversity generally promotes biomass production, but how the shape of the response curve changes with time remains unclear. This is a critical knowledge gap because the shape of this relationship indicates the extent to which loss of the first few species will influence biomass production. Using two long-term (≥13 years) biodiversity experiments, we show that the effects of diversity on biomass productivity increased and became less saturating over time. Our analyses suggest that effects of diversity-dependent ecosystem feedbacks and interspecific complementarity accumulate over time, causing high-diversity species combinations that appeared functionally redundant during early years to become more functionally unique through time. Consequently, simplification of diverse ecosystems will likely have greater negative impacts on ecosystem functioning than has been suggested by short-term experiments.

Soil macrofauna-mediated impacts of plant species composition on soil functioning in Amazonian pastures

The design of sustainable agroecosystems requires knowledge of plant species impacts on soil functioning. To address this need, we manipulated plant species diversity in pastures of eastern Amazonia. Four plant species (Arachis pintoi, Brachiaria brizantha, Leucaena leucocephala and Solanum rugosum) were grown alone and in every possible combination on experimental plots within three replicate farms. After 28months, soils were sampled to determine impacts on 5 categories of variables: soil macrofauna, aggregate morphology, chemical fertility, water storage and compaction. No clear effects of plant species richness were observed on any of the soil properties measured. However, individual plant species had significant impacts on variables in all 5 categories. Most notably, the herbaceous legume, A. pintoi, promoted both earthworm and ant densities and a corresponding 87% increase in biogenic aggregates in plots with vs. without A. pintoi. Meanwhile, B. brizantha increased the proportion of root-derived aggregates, while negatively impacting ant densities. Significant covariation was observed among many of the 5 data sets (categories), namely soil aggregate morphology and soil macrofauna, as well as aggregate morphology and soil compaction. This research demonstrates that plant species composition can impact soil properties through faunal-mediated effects, and stresses the necessity of considering soil macrofauna in agroecosystem management.

Net ammonification as influenced by plant diversity in experimental grasslands

Previous plant diversity experiments have mainly reported positive correlations between diversity and N mineralization. We tested whether this relationship can be explained by plant diversity-induced changes i) in the quantity or quality of organic matter or ii) in microclimatic conditions of central European grassland mixtures.We measured ex-situ net ammonification in a laboratory incubation of aboveground plant material and soil sampled in differently diverse plant mixtures. Secondly, in-situ net ammonification was assessed in a field incubation with mineralization cores containing standardized material in four treatments: soil only (control), and soil mixed with field-fresh plant tissue (grass, legume, or tall herb). We used 82 plots with varying species numbers (1, 2, 4, 8, 16, and 60) and numbers of functional groups (1–4; grasses, short herbs, tall herbs, and legumes). We determined the soil water content, total N concentrations of plant and soil, and NH4–N release rates.In the ex-situ incubation under constant climatic conditions, functional group or plant species richness did not influence net ammonification rate constants (k) or the proportion of the organic N pool involved in ammonification (NH4–N0). The presence of legumes in plant mixtures significantly increased NH4–N0 and decreased k indicating elevated N leaching risks in legume-containing grassland mixtures. Mean in-situ net ammonification rates in the mineralization cores decreased in the following order: mixtures of soil with grasses (0.30 ± standard error 0.01 mg NH4–N (g Ninitial)−1 d−1) > tall herbs (0.25 ± 0.01) > legumes (0.22 ± 0.01) > control (0.07 ± 0.00). The type of incubated plant tissue also influenced the soil water content in the mineralization cores at the end of field incubation, likely because of different water retention capacities of the different plant tissue/soil mixtures. Significant plant functional group and species richness effects explained up to 13% of the variance of in-situ net ammonification rates. Because the effect of plant species richness disappeared if the type of incubated plant tissue and the soil water content were accounted for in a sequential ANCOVA, we infer that the soil water content was the main driver underlying the plant species richness effect.

Plant Species Richness Affected Nitrogen Retention and Ecosystem Productivity in a Full‐Scale Constructed Wetland

AbstractThe effects of plant species richness (SR; i.e., 1, 2, 4, 8, and 16 species per plot) on substrate nitrate and ammonium retention and ecosystem productivity in a full‐scale constructed wetland (CW) with high nitrogen (N) input were studied. Substrate nitrate (0.1–16.4 mg kg−1) and ammonium concentrations (1.3–9.2 mg kg−1) in this study were higher than those in other comparable biodiversity experiments. Substrate nitrate concentration significantly increased while ammonium concentration significantly decreased with the increase of plant SR (p = 0.008 and 0.040, respectively). The response of ecosystem productivity to increasing SR was unimodal with four species per plot achieving the greatest productivity. Transgressive overyielding, which was compared to the most productive of corresponding monocultures, did not occur in most polycultures. We conclude that substrate N retention was enhanced by plant SR even with high N input, and plant SR could be managed to improve the efficiency of N removals in CWs for wastewater treatment.

Fungal Community Composition in Neotropical Rain Forests: the Influence of Tree Diversity and Precipitation

Plant diversity is considered one factor structuring soil fungal communities because the diversity of compounds in leaf litter might determine the extent of resource heterogeneity for decomposer communities. Lowland tropical rain forests have the highest plant diversity per area of any biome. Since fungi are responsible for much of the decomposition occurring in forest soils, understanding the factors that structure fungi in tropical forests may provide valuable insight for predicting changes in global carbon and nitrogen fluxes. To test the role of plant diversity in shaping fungal community structure and function, soil (0-20cm) and leaf litter (O horizons) were collected from six established 1-ha forest census plots across a natural plant diversity gradient on the Isthmus of Panama. We used 454 pyrosequencing and phospholipid fatty acid analysis to evaluate correlations between microbial community composition, precipitation, soil nutrients, and plant richness. In soil, the number of fungal taxa increased significantly with increasing mean annual precipitation, but not with plant richness. There were no correlations between fungal communities in leaf litter and plant diversity or precipitation, and fungal communities were found to be compositionally distinct between soil and leaf litter. To directly test for effects of plant species richness on fungal diversity and function, we experimentally re-created litter diversity gradients in litter bags with 1, 25, and 50 species of litter. After 6months, we found a significant effect of litter diversity on decomposition rate between one and 25 species of leaf litter. However, fungal richness did not track plant species richness. Although studies in a broader range of sites is required, these results suggest that precipitation may be a more important factor than plant diversity or soil nutrient status in structuring tropical forest soil fungal communities.

Does plant diversity influence phosphorus cycling in experimental grasslands?

Plant diversity was shown to influence the N cycle, but plant diversity effects on other nutrients remain unclear. We tested whether plant species richness or the presence/absence of particular functional plant groups influences P partitioning among differently extractable pools in soil, P concentrations in soil solution, and exploitation of P resources (i.e. the proportion of total bioavailable P in plants and soil that was stored in aboveground biomass) by the plant community in a 5-year biodiversity experiment in grassland. The experimental grassland site established in 2002 had 82 plots with different combinations of numbers of species (1, 2, 4, 8, 16, 60) and functional groups (grasses, small non-leguminous herbs, tall non-leguminous herbs, legumes). In 2007, we determined P partitioning (Hedley) in soil of all experimental plots. We sampled plant community biomass and continuously extracted soil solution with suction plates from March 2003 to February 2007 and determined PO 4-P concentrations in all samples. The presence of legumes increased aboveground P storage in plants and decreased labile P i concentrations in soil because of their higher demands for P associated with N 2 fixation. During cold periods, readily plant-available PO 4-P concentrations in soil solution increased in legume-containing mixtures likely caused by leaching from P-rich residues. We found a consistently positive effect of plant species richness on P exploitation by the plant community which was independent of the presence of particular plant functional groups. With proceeding time after establishment, plant species richness increasingly contributed to the explanation of the variance in P exploitation. Therefore, plant strategies to efficiently acquire P seem to become increasingly important in these grasslands. We conclude that diverse plant communities are better prepared than less diverse mixtures to respond to P limitation induced by continuously high atmospheric N deposition.