Enhancing phosphate mineralization but not its resorption efficiency alleviates phosphate limitation induced by nitrogen deposition
The faster rise in atmospheric nitrogen (N) deposition than phosphorus (P) could shift temperate forests from N limitation to P limitation ecosystem. It is unclear that how vegetation in temperate forests cope with the imbalanced nutrient depositions. In this study, we conducted a four year N deposition simulation experiment in a young and a mature larch stands, and investigated how larch and understory vegetation to respond the imbalanced input of N and P.
Our results showed that N addition induced P deficiency in both stands, as evidenced by the decrease in foliar P concentrations and the increase in N:P ratio. Aboveground net primary production (ANPP) of understory vegetation in young stand and larch in mature stand increased with the increase in leaf N:P ratios, while the ANPP of their counterparts, larch in young stand and understory vegetation in mature stand, were not correlated with leaf N:P ratios. This finding suggested that understory vegetation in young stand and larch in mature stand benefited more from increased N input but were less affected by N deposition-induced P limitation. Such competition advantage was associated with their higher stoichiometry homoeostasis compared to their counterparts. Our data further suggested that P resorption efficiency showed low plasticity in response to P limitation induced by N depoition. However, the increase in N deposition significantly enhanced both of the activities of N-rich phosphatase enzymes and arbuscular mycorrhizas : ectomycorrhizas ratio. Those findings suggested that N addition stimulated organic P mineralization and also caused plants adjust carbon (C) allocation preference among mycorrhizal fungi to alleviate P limitation. In addition, we also found fungal-to-bacterial ratio decreased under N addition, which could increase N mineralization by accelerating organic matter mineralization. Overall, our study suggested plants with higher stoichiometry homoeostasis could better cope with N deposition-induced P limitation. Plants could activate various P acquiring pathways with the expenses of N and C, which in turn coupling P cycle with C and N cycles.