Species Diversity In Alpine Meadow, Aboveground Net Primary Productivity And Stability Mechanisms

The relationship between species diversity and ecosystem functioning has been the focus issue in ecology research. The related theory, observation, and experiment research which are concerning on this issue has already been widely implement, But still having no conclusion widely accepted and recognized, there existing a fierce debate on many problems. Biodiversity effect in ecosystem functioning are studied by drawing limited number of species at random and forming artificial plant communities with different levels of diversity. Thus, it comes to a conclusion that productivity and stability are increased accompanying the increase of species quantity, then it’s interpreted as "niche complementarity". On the contrary, there exists an opposite view that the productivity and stability are controlled by dominant species, not species diversity itself. Therefore, whether Niche complementarity effect plays an important role in the natural ecosystem or not is still unknown, the efficacious stable effect of high species diversity in community might non-existent. Many researches on the relationship between environment effect and species diversity are univariate in natural ecosystems, ignoring environment effect, changes of species composition and the interaction of biodiversity. Owing to the selective pressure from environment griddle or management system can lead to similar tendency changes of community species functioning property, the more selective pressure, the less obvious species niche divided. So which biodiversity factors affect ecosystem functioning ultimately are the species composition and its functioning property.Our research was conducted in alpine meadow at the Haibei Research Station of the Chinese Academy of Sciences from2007to2011. We have studied the relationship of different "functioning identity" species (i.e., total species, response species, effect species and common species in community) diversity with aboveground net primary productivity and community stability. Stability mechanism on the diversity of species have been researched in mowing and fertilizer gradients. The main results shows as follow:(1) Grassland plant community species response to experiment treatment and affect aboveground net primary productivity are different in "functioning identity". Respond species which are respond to cope with the research (mowing, fertilizing, watering and interaction), including Kobresia humilis, Potentilla anserine, Pedicularis kansuensis and other23species. Through the regression analysis on important values of species and community net primary productivity, in response species, if Important values significantly associated with aboveground net primary productivity of a community, We define it as effect species, including Leontopodium nanum, Stellaria umbellate, Oxytropis kansuensis and other10species, these species can influence aboveground net primary productivity (ANPP) to a certain degree. If species are stable in6experiment treatments, We define it as common species, including Leontopodium nanum, Kobresia humilis, Pedicularis longiflora var.tubiformis and other46species. There are four species types, response species, effect species and common species, which are having a possession of36.6%,18.3%and64.8%of total species respectively.(2) There are different influencing factors in different ecosystem functioning. According to regression analysis of4species types simpson diversity index and ecosystem functioning index, we find that aboveground net primary productivity is mainly affected by the change of response species diversity and effect species diversity. While community stability is mainly influenced by the change of common species.(3) Portfolio effect is the mainly mechanism of species diversity on community stability, while over-yielding effect and covariance effect have no effect on community stability. There may be exist no significant change of synchronism of4species types in different experimental treatments (p>0.05), the negative correlation between species diversity and community synchronism are caused in change of diversity mainly lead by experimental treatment, the asynchronism not changed. For this reason, there’s no proof that stability increased by asynchronism with the increase of species diversity.(4) Clipping and fertilization had reverse effect on species diversity, ANPP and stability, i.e., the former can increase species diversity and stability, and decrease ANPP, while the latter had opposite effects on them. This is related to total species diversity, which mainly effected by clipping treatment. Effect species diversity are mainly influenced by changes of resource availability.Our results suggest that ANPP is driven by the diversity of a few effect species because they have a great influence on ANPP, while stability is driven by the diversity of a large number of common species because they can coexist stably in the community. The portfolio effect is the main mechanism of the diversity-stability relationship. The diversity effect of different species differs among each other; therefore, in terms of specific ecosystem functioning, we infer that "functional identity" of species in community is more important than diversity per se and it may be incorrect if we did not discriminate when defining the relationship between species diversity and ecosystem function in any situation.