A test of the mycorrhizal-associated nutrient economy framework in two types of tropical rainforests under nutrient enrichments

Shifts in tree species and their mycorrhizal associations driven by global change play key roles in biogeochemical cycles. In this paper, we proposed a framework of the mycorrhizal-associated nutrient economy (MANE), and tested it using nutrient addition experiments conducted in two tropical rainforests. We selected two tropical rainforests dominated by arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) trees, and established eighteen m x 20 m plots in each rainforest. Six nitrogen (N) and phosphorus (P) addition treatments were randomly distributed in each rainforest with three replicates. We examined the differences in soil carbon (C) and nutrient cycling, plant and litter productivity between the two rainforests and their responses to 10-year inorganic N and P additions. We also quantified the P pools of plants, roots, litter, soil and microbes in the two rainforests. Overall, distinct MANE frameworks were applicable for tropical rainforests, in which soil C, N and P were cycled primarily an inorganic form in the AM-dominated rainforest, whereas they were cycled in an organic form in the ECM -dominated rainforest. Notably, the effects of mycorrhizal types on soil P cycling were stronger than those on C and cycling. The intensified N and P deposition benefited the growth of AM-dominated rainforests instead of ECM -dominated rainforests. Our findings underpin the key role of mycorrhizal types in regulating biogeochemical processes, and have important implications for predicting the ecological consequences of global changes.

Automated summary

Shifts in tree species and their mycorrhizal associations driven by global change have significant impacts on biogeochemical cycles. In this study, we proposed and tested a framework of mycorrhizal-associated nutrient economy (MANE) in two tropical rainforests through nutrient addition experiments. We found that distinct MANE frameworks were applicable for different types of rainforests, with organic and inorganic forms of nutrient cycling in ECM-dominated and AM-dominated rainforests, respectively. Moreover, the effects of mycorrhizal types on soil P cycling were stronger than those on C and N cycling. The findings highlight the crucial role of mycorrhizal types in regulating biogeochemical processes and provide important insights for understanding the ecological consequences of global changes.