Linking mycorrhizal status to plant nutrient strategy across subtropical forest succession

Classical theory posits that late-successional plants develop symbiotic mycorrhizal networks to improve plant nutrient use efficiency and soil nutrient conservation, particularly of nutrients like phosphorus (P), which become depleted during plant community development. However, experimental test of these hypothesized functions are lacking. Here, we conducted a experiment of trenches lined with mesh screens of varying sizes across subtropical succession and a regional survey of 14 subtropical forest sites to explore mycorrhizal hyphal effects on soil nitrogen (N) and P cycling and plant use efficiency. Results revealed that later successional plants had greater P use efficiency, showing lower leaf P concentration and a higher N:P ratio than early successional ones. Ectomycorrhizal (EcM) fungal abundance increase with succession and largely explain the variation in plant PUE and leaf N: P ratio. At late successional stage, these fungi promote soil P conservation through enhancing soil P adsorption and microbial biomass P: N ratio, while simultaneously stimulating nitrogen (N) cycling through the greater release of N-related relative to P-related enzymes. Regionally, EcM abundance was positively correlated with soil N: P enzyme ratio, and nonlinearly correlated to leaf N:P ratio after controlling for soil nutrients, confirming its role in enhancing soil N cycling and P conservation. Our findings highlight EcM fungal critical role in balancing forest N and P cycling, underscoring the need to integrate mycorrhizal effects into nutrient management strategies for subtropical forests.