Aboveground conservation acts in synergy with belowground uptake to alleviate phosphorus deficiency caused by nitrogen addition in a larch plantation

Abstract

While growing evidence has shown the shift in terrestrial ecosystems from nitrogen (N) limitation to phosphorous (P) limitation under increasing N deposition, it is poorly understood how plants adapt to this P limitation. Here, we examined which strategies would be adopted by plants for alleviating P deficiency caused by N enrichment from the perspective of aboveground conservation and belowground uptake. To achieve this objective, we conducted a five-year N-addition experiment (0 and 50 kg N ha−1 yr−1) in a 60-year-old larch (Larix kaempferi) plantation, and measured variables related to ecosystem P status, leaf P resorption, soil exploration by roots and extraradical hyphae of ectomycorrhizal fungi, and rhizosphere effects on soil P cycling. We found that N addition significantly reduced soil available P concentration and enhanced leaf N:P ratio, indicating the increasing degree of P deficiency under N addition. Leaf P resorption efficiency and proficiency were significantly enhanced by N addition, implying the increase in aboveground P conservation. Moreover, N addition significantly increased root length density and decreased ectomycorrhizal extraradical hypha biomass, suggesting the enhanced role of the root pathway in scavenging soil P. Rhizosphere effects on phosphatase activity were significantly enhanced by N addition, indicating the improved capacity of mining P from organic P forms. Collectively, our findings highlight that the larch could concurrently improve aboveground P conservation and belowground P uptake to alleviate P deficiency induced by N addition, and suggest that adjustments in resource allocation associated with these adaptive strategies could have significant consequences on ecosystem functions.