Enhancing phosphate mineralization but not its resorption efficiency alleviates phosphate limitation induced by nitrogen deposition

Background/Question/Methods

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. 

Results/Conclusions

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.