Increased phosphate uptake but not resorption alleviates phosphorus deficiency induced by nitrogen deposition in temperate Larix principis-rupprechtii plantations.

The imbalance between nitrogen (N) and phosphorus (P) deposition may shift temperate ecosystems from N- to P-limitation. However, it is unclear how the imbalanced N : P input affects the strategies of plants to acquire P and, therefore, the growth of plants and the competition among species. We conducted a 4-yr N-addition experiment in young and mature larch (Larix principis-rupprechtii) stands. Plant growth and P acquisition strategies were assessed for larch and understorey vegetation. N addition stimulated the aboveground productivity of understorey vegetation in the young stand and larch in the mature stand, with other species unaffected. The competitive advantages of understorey vegetation in the young stand and larch in the mature stand were associated with their high stoichiometric homoeostasis. To maintain the N : P homoeostasis of these species, an increase in phosphatase activity but not P resorption efficiency increased the supply of P. Additionally, N addition accelerated P mineralization by decreasing the fungal-to-bacterial ratios and improved uptake of soil P by increasing the arbuscular mycorrhizas-to-ectomycorrhizas ratios. Our results suggest that plants with high stoichiometric homoeostasis could better cope with N deposition-induced P-deficiency. Although P resorption efficiency showed little plasticity in response, plants activated a variety of P-acquisition pathways to alleviate the P-deficiency caused by N deposition.