Thermodynamic analysis of an ecologically restored plant community: Ecological niche

The experimental data were obtained from an ecological restoration project implemented at a metal contaminated site. The basic idea presented in this study is that the conventionally defined chemical potential μi can be used to evaluate the abiotic and biotic effects on a species’ ecological niche. An ecological niche πi defines the suitability of an environment for a given species to live while μi defines the ability of a species to live in a given environment. The deviation of πi from its fundamental niche πi0 due to changes in environment conditions will thus be reflected by the changes in μi. As a growth potential index, μi is a function of the standard chemical potential μi0 and the total number of plant species N. Like πi0, which is an upper limit of πi, μi0 is an upper limit of μi at N = 1, meaning that μi0 is also a factor independent of biotic interactions. Increasing N will reduce μi and thus, the same as πi, μi takes into account the biotic effect. The derived expression of πi as a function of N confirms that both πi and μi belong to the same function family. Both μi0 and πi0 of a species are characteristic limits uniquely determined by the species’ genetic nature while μi and πi of a species are variables subject to both the biotic and abiotic conditions under which the species is living. Either increase in species richness or deterioration in soil conditions will reduce μi and πi. The derived relation μ/(RT) = ln(Nm/N) can be applied to describe the biotic and abiotic effects on average π for species co-existed in a plant community. As an upper limit of ln(N), ln(Nm) can be interpreted as a parameter representing the total availability of a space that can house Nm species. The conventionally applied biodiversity index ln(N) then corresponds to the part of available space inhabited by N co-existed species and ln(Nm/N) stands for the remaining space availability. The terms, ln(Nm) and ln(Nm/N), meet thus, respectively, the concepts of π0 and π. The results obtained from the present study showed that the negative effect of species richness and abundance on μi and πi was the basic cause for the generally observed inverse relationship between population density and body size. Determination of the connection between μi and πi is of high value in regulating the relationship between productivity and biodiversity.