A Long-Term Field Study on Biodiversity X Elevated CO 2 Interactions in Grassland

Abstract

Interactive effects of increases in atmospheric CO 2 and reductions in plant species diversity were investigated in planted calcareous grassland communities in northwestern Switzerland. The experimental communities were composed of 5, 12, and 31 species assembled from the native species pool. The study aimed at testing whether the CO 2 responses of ecosystems change when specific sets of species are lost from plant communities. Species were selected so that the proportion of grasses, legumes, and non-legume forb individuals remained constant across levels of diversity. The most diverse plant community had approximately the same diversity as the surrounding grassland, and species occurring in less diverse communities were subsets of the species in the more diverse communities. The factorial atmospheric-CO 2 treatment was applied using 50-cm-tall, open-bottom, opentop wind screens. Plant community-level responses and the responses of the individual species were assessed over a period of five years. A significant positive correlation between plant community diversity and biomass was detected, but this effect was not present on all dates. Significant effects of elevated CO 2 on community biomass were only found in the first years of treatment. CO 2 effects were largest in the communities with the highest number of plant species and were primarily due to the presence of responsive species not present in the less diverse communities. The time dependency of community responses to elevated CO 2 and species diversity was related to shifts in community structure of the experimental plots. Community responses at the beginning of the experiment were dominated by the response of species with a less competitive/stress-tolerant life history. These species were successively lost from experimental plots as the experiment proceeded, and the observed community-level effects became smaller. Changes in species composition over the experimental duration were affected by elevated CO 2 in the way that species loss was reduced (i.e., coexistence of species performing well at the beginning and at the end of the fiveyear period increased) and the way that community evenness was increased (i.e., dominance was reduced). Based on these results our main conclusions are that (1) community-level responses to CO 2 enrichment depend on the species present; (2) the positive correlation between productivity and species numbers was caused by different species at the beginning and at the end of the experiment; (3) therefore, a large, redundant species pool is important in assuring high productivity under altering environmental conditions; (4) elevated CO 2 has the potential to substantially alter the structure of grassland communities, even if community productivity does not increase; and (5) a short-term effect of elevated CO 2 may be misleading when attempting to predict longer-term effects.

A Review of Processes Behind Diversity—Productivity Relationships in Forests

“…However, there are several important differences between tree-species communities and grassland communities that can make comparisons challenging, even when some of the processes, or the resulting patterns, are the same. For example, grassland studies often run for several lifetimes of many component species [6], whereas tree studies tend to run only for a (short) proportion of the potential life span of the trees. As a result, there are higher levels of mortality, recruitment (possibly also clonal reproduction), and species replacement during grassland community studies [6,7], thereby influencing species proportions, evenness, age structures, etc.…”

“…For example, grassland studies often run for several lifetimes of many component species [6], whereas tree studies tend to run only for a (short) proportion of the potential life span of the trees. As a result, there are higher levels of mortality, recruitment (possibly also clonal reproduction), and species replacement during grassland community studies [6,7], thereby influencing species proportions, evenness, age structures, etc. This does not occur to the same extent in planted tree diversity experiments because many of the individuals present at the start are often still there after many years, it is unlikely or rare that species are lost from plots over short-to mediumterm periods, and no (or very few) new individuals will have been recruited into the canopy layer of the community [8,9].…”

Abundance of aquatic insects in relation to physico-chemical parameters of two highly polluted Rivers Sitalakkhya and the Buriganga

“…This index was determined by both the number of species and the even distribution of individuals among those species (Niklaus et al 2001). The formula is Pi, relative abundance = ni/N ni = number of individuals in species i N = total number of individuals in all species H Evenness (E): Using species richness (R) and the Shannon-Wiener index (H), evenness of a taxa was computed using following formula:…”

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

“…In these experiments, the relationships between plant SR and plant-available nitrate in the substrate have frequently been found to be negative [6][7][8][9][10], sometimes no relationships were found [11,12], while others found positive relationships [7,13], as is detailed in Tab. 1.…”

“…concentrations lower in 2008 than in 2007 [16], indicating strong interannual variations in the studied processes and relationships. In most N-limited grassland experiments substrate nitrate pool size was found to decrease with increasing plant SR [8,10] (Tab. 1), as plant communities with higher SR can exploit more of the substrate nitrate [8,11].…”