Microbial diversity, producer-decomposer interactions and ecosystem processes: a theoretical model

Interactions between the diversity of primary producers and that of decompo sers-the two key functional groups that form the basis of all ecosystems-mi ght have major consequences on the functioning of depauperate ecosystems. I I,resent a simple ecosystem model in which primary producers (plants) and decomposers (microbes) are linked through material cycling. The model consi ders a diversity of plant organic compounds and a diversity of microbial sp ecies. Nutrient recycling efficiency from organic compounds to decomposers is then the key parameter that controls ecosystem processes (primary produc tivity, secondary productivity, producer biomass and decomposer biomass). T he model predicts that microbial diversity has a positive effect on nutrien t recycling efficiency and ecosystem processes through either greater inten sity of microbial exploitation of organic compounds or functional niche com plementarity, much like in plants. Microbial niche breadth and overlap shou ld not affect ecosystem processes unless they increase the number of organi c compounds that are decomposed. In contrast, the model predicts that plant organic compound diversity can only have a negative effect or, at best, no effect on ecosystem processes, at least ill a constant environment. This c reates a tension between the effects of plant diversity and microbial diver sity on ecosystem functioning, which may explain some recent experimental r esults.