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.

中文翻译：

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地上保护与地下吸收协同作用，以缓解落叶松人工林因施氮引起的磷缺乏

摘要 虽然越来越多的证据表明，随着氮沉积的增加，陆地生态系统从氮 (N) 限制转变为磷 (P) 限制，但人们对植物如何适应这种磷限制的了解甚少。在这里，我们从地上保护和地下吸收的角度研究了植物将采用哪些策略来缓解由富氮引起的磷缺乏。为了实现这一目标，我们在一个 60 岁的落叶松 (Larix kaempferi) 人工林中进行了为期五年的 N-添加实验（0 和 50 kg N ha−1 yr−1），并测量了与生态系统 P 状态相关的变量、叶片磷吸收、外生菌根真菌根系和根外菌丝对土壤的探索，以及根际对土壤磷循环的影响。我们发现，施氮显着降低了土壤有效磷浓度，提高了叶片氮磷比，表明施氮条件下缺磷程度增加。添加氮显着提高了叶片磷的吸收效率和熟练程度，这意味着地上磷的保护增加。此外，N添加显着增加根长度密度并降低外生菌根外菌丝生物量，表明根途径在清除土壤磷中的作用增强。 N添加显着增强了根际对磷酸酶活性的影响，表明从有机物中挖掘磷的能力提高P 形式。总的来说，我们的研究结果强调，落叶松可以同时改善地上磷的保存和地下磷的吸收，以减轻由 N 添加引起的磷缺乏，