Exploration capacity vs. specific enzymatic activity of ectomycorrhizas in response to primary productivity and soil phosphorus availability in Bornean tropical rainforests

Abstract

Abstract Aims Ectomycorrhizal (ECM) fungi are functionally important in biogeochemical cycles in tropical ecosystems. Extracellular enzymatic activity of ECM on a ground-area basis is the product of two attributes; exploring capacity (ECM surface-area) and specific enzymatic activity on an ECM surface-area. Here, we elucidated which attribute better explained the ECM enzymatic activity in response to different levels of soil P and N availability in five Bornean tropical rainforests. Methods We determined the surface area of ECM root tips as well as the enzymatic activities per ECM surface area for C, N and P degrading enzymes in each site. We evaluated the relationship of ECM enzyme activities with the resource availabilities of C(ANPP), N, and P of ECM by a generalized linear mixed model. Results The ECM enzymatic activities on a ground-area basis were more significantly determined by specific enzymatic activity than by the exploration capacity. Specific enzymatic activities were generally negatively affected by C (ANPP) and soil P availability. Conclusions ECM fungi enhance the specific enzyme activity rather than the exploitation capacity to maintain the capacity of nutrient acquisition. The less dependence of ECM fungi on the exploitation capacity in these forests may be related to the limitation of C supply from host trees. We highlighted the adaptive mechanisms of ECM fungi on nutrient acquisition in tropical ecosystems through the response of enzymatic activity to nutrient availability across the elements.