Opposing community assembly patterns for dominant and nondominant plant species in herbaceous ecosystems globally

Plant biodiversity offsets negative effects of metals and metalloids soil multi-contamination on ecosystem multifunctionality

Despite increasing metals and metalloids (MM) human-driven soil contamination, how it simultaneously alters biodiversity and ecosystem functioning remains unknown. We used a wide gradient of a 170-year-old MM soil multi-contamination in Mediterranean scrublands to assess the effects of soil multi-contamination on multiple plant biodiversity facets, microbial communities and ecosystem multifunctionality (EMF). We found an overall positive effect of plant biodiversity on EMF mediated by microbial communities, and allowing offsetting the negative impacts of MM soil multi-contamination, especially on soil water holding capacity and nitrogen content. The diversity of distant plant lineages was the key facet promoting EMF by enhancing microbial communities, whereas the subordinate species richness altered EMF. By developing a holistic approach of these complex relationships between soil multi-contamination, plant biodiversity, microbial communities and ecosystem functioning, our results reveal the potential of plant biodiversity, and especially the diversity of evolutionary distant species, to offset the alteration of ecosystem functioning by MM soil multi-contamination. In this worldwide decade of ecosystems restoration, our study helps to identify relevant facets of plant biodiversity promoting contaminated ecosystem functioning, which is crucial to guide and optimize management efforts aiming to restore ecosystems and preserve human health.

Long-term subtropical grassland plots take a long time to change: Replacement is more important than richness differences for beta diversity

We studied β diversity of grasses in a subtropical grassland over 60 years in South Africa. We examined the effects of burning and mowing on 132 large plots. We sought to determine the effects of burning and mowing, and mowing frequency, on the replacement of species and the species richness. We conducted the study at Ukulinga, research farm of the University of KwaZulu-Natal, Pietermaritzburg, South Africa (29°24'E, 30°24'S) from 1950-2010. Plots were burned annually, biennially, triennially, and a control (unburned). Plots were mowed in spring, late summer, spring plus late summer, and a control (unmowed). We calculated β diversity, with a focus on replacement and richness differences. We also used distance-based redundancy analyses to examine the relative effects of replacement and richness differences on mowing and burning. We used beta regressions to test for the effect of soil depth and its interactions with mowing and burning. There was no significant change in grass beta diversity until 1995. Thereafter, there were changes in β diversity that demonstrated the primary effects of summer mowing frequency. There was no significant effect of richness differences but a strong effect of replacement post-1995. There was a significant interaction between mowing frequency and soil depth in one of the analyses. Changes in grassland composition took a long time to manifest themselves and were unapparent prior to 1988. However, there was a change in sampling strategy prior to 1988, from point hits to nearest plants, that may also have influenced the rates of changes in replacement and richness differences. Using β-diversity indices, we found that mowing was more important than burning that burning frequency was unimportant, and there was a significant interaction effect between mowing and soil depth in one of the analyses.

Stochastic Processes Drive Plant Community Assembly in Alpine Grassland during the Restoration Period

Enclosure (prohibition of grazing) is an important process to restore alpine grassland on the Qinghai-Tibetan Plateau. However, few studies have quantified the extent to which the long-term enclosure may contribute to the changes in plant phylogenetic diversity and community assembly in alpine grassland under environmental change. In this study, based on an 11-year fencing experiment along an altitudinal gradient ranging from 4400 m to 5200 m in central Tibet, we conducted an observation of species composition and coverage within and outside the fences in the fifth, eighth and eleventh year, and monitored the related climate and soil factors at 7 sites. Our aim is to quantify the relative effects of environmental change and grassland management on the alpine plant community assemblage. The results were: (1) the overall phylogenetic structure (NRI) of the alpine plant communities, whether inside or outside the enclosure, was divergent at altitudes where the environment was relatively unextreme (4800–5100 m), but aggregative at altitudes with low precipitation (4400–4650 m) or with low temperature (5200 m). (2) The phylogenetic structure of the nearest taxon of species (NTI) was more aggregative along the whole gradient. (3) Precipitation was the dominant factor driving the changes in species richness, phylogenetic diversity and community α-phylogenetic structure indices (NRI and NTI), followed by enclosure duration and soil C:N ratio. (4) The phylogenetic structure of the communities was similar at higher altitudes under grazing or enclosure treatments, and was opposite at lower sites. Stochastic processes have driven the changes in the communities between inside and outside the fences at all altitudes. In addition, homogeneous dispersal occurred in communities at higher sites. In summary, the 11-year enclosure had little effect on community structure of alpine meadows where the grazing pressure is relative lower, whereas it could help restore the community of steppe meadow at lower altitudes where the grazing pressure is extensively higher. This study may provide a vital theoretical support for the formulation of differential management for alpine grassland on the Tibetan Plateau.