Initial community evenness increases the light resource use complementarity and sampling effects on species richness

Abstract

Although evenness has been proved to affect the effect of species richness on ecosystem processes, the potentially affected mechanism has still rarely been studied directly. In this study, different species richness levels (1, 2, 4, 8 and 12) were manipulated in low- and high-evenness plots, and light interception efficiency (LIE) of the plots was measured to determine light resource use. The results showed that there was a positive relationship between species richness (SR) and LIE in the high-evenness plots during two years of this experiment. However, the positive relationship disappeared in the low-evenness plots. Only in the high-evenness plots, the values of transgressive overyielding (Dmax) were positively correlated with the complementarity effect, which increased with SR. Moreover, most of 12-species mixtures had positive Dmax (Dmax>0) which further confirmed the complementarity effect on LIE. The presence of Phytolacca americana or Macleaya cordata significantly increased LIE in the high-evenness plots but did not increase LIE in the low-evenness plots. Moreover, the dominance of superior (P. americana or M. cordata) was positively correlated with the selection effect. Our results suggest that high initial evenness will increase the complementarity and sampling effects of SR on light interception and may be an important mechanism that can influence the effect of SR on ecosystem processes, such as biomass production.