PS 43-133
Interspecific interactions promote primary production but at the expense of biodiversity
The relationship between species richness and ecosystem functioning still remains challenging and controversial. The biodiversity effects undoubtedly originate from species interactions which, in turn, are positively but probably weakly correlated with species richness due to the influences of species evenness, spatial pattern and plant density. Therefore, understanding interspecific interactions and their consequences for function and structure is fundamental for fully assessing the role of biodiversity in ecosystems. 324 plots (each 1 m × 1 m) with eight herbaceous plant species were established in a former arable field in Guangdong Province, South China. To change interspecific interactions, three types of plots varied in heterospecific:conspecific contact ratio: (1) Monoculture plots with all eight species did not have any interspecific contact. (2) The eight-species mixture was sown in intraspecifically aggregated distribution, and thus there was moderate interspecific contact. (3) The eight-species mixture grown in dispersed spatial pattern (i.e., plant individuals of eight species were thoroughly mixed in community), in which reached almost maximum interspecific contact. To change the intensity of plant-plant interactions, the three plot types were conducted under three kinds of density treatments (low = 64 plants/m2, medium = 144 plants/m2, and high = 256 plants/m2). We harvested aboveground and belowground biomass to measure the primary production.
Results/Conclusions
We found biomass production (P ≤ 1.79 × 10-8 for all the aboveground biomass, belowground biomass and total biomass) and biodiversity effects (P ≤ 0.026 for all the net effect, complementarity and selection effect) were significantly enhanced by increased interspecific interactions across different density treatments. Across the three plot types, the progressive increase in biomass production was less significant as plant density increasing from low to medium to high (P ≤ 0.039 for all), but the density treatments did not affect the net biodiversity effect and its two components (complementarity and selection effect; P ≥ 0.108 for all). The interactions between density and plot type were not significant for biomass production (P ≥ 0.229 for all) and for biodiversity effects (P ≥ 0.099 for all). However, increasing species interactions reduced community biodiversity which was measured as Shannon entropy (P < 0.001). Furthermore, there was a negative relationship between net biodiversity effect and community biodiversity (r = －0.591, P = 1.722 × 10-11). These occurred because strong interspecific interactions made productive species more productive, leading to competitive suppression of weak competitors in communities. Our results show that intense interspecific interactions with corresponding abundant biodiversity effects and hence high ecosystem functioning are unfavourable for ecosystems in sustained development.