Fig. 6

The biodiversity-ecosystem functions relationships in (a) different studies and (b) different observations. (a) The number of studies reporting positive, negative, neutral and complex BEF relationships respectively. Here, the complex BEF relationships represent the studies which report more than one kind of BEFs (positive, neutral and negative) using different functions or the same function under different conditions. (b) The ratio of positive, neutral and negative BEF relationships considering broad functions and specialized functions respectively. The number above each column showed the number of observations for broad functions and specialized functions. Different observations of ecosystem functions are separated into broad functions and specialized functions. Broad functions are functions thought to be carried out by most microbes, including bacterial activities and degradations of labile carbon. Specialized functions are functions thought to be carried out only by specific microbes, including degradation of inert carbon, nitrogen cycling and other elementary cycling