Han Wenxuan, Tang Luying, Chen Yahan, Fang Jingyun
Key Laboratory of Plant-Soil Interactions, Ministry of Education, College of Resources and Environmental Sciences, China Agricultural University, Beijing, China.
Key Laboratory for Earth Surface Processes, Ministry of Education, Department of Ecology, Peking University, Beijing, China.
PLoS One. 2013 Dec 23;8(12):e83366. doi: 10.1371/journal.pone.0083366. eCollection 2013.
Most previous studies have ascribed variations in the resorption of a certain plant nutrient to its corresponding environmental availability or level in tissues, regardless of the other nutrients' status. However, given that plant growth relies on both sufficient and balanced nutrient supply, the nutrient resorption process should not only be related to the absolute nutrient status, but also be regulated by the relative limitation of the nutrient. Here, based on a global woody-plants dataset from literature, we test the hypothesis that plants resorb proportionately more nitrogen (or phosphorus) when they are nitrogen (or phosphorus) limited, or similar proportions of nitrogen (N) and phosphorus (P) when co-limited by both nutrients (the relative resorption hypothesis). Using the N:P ratio in green foliage as an indicator of nutrient limitation, we found an inverse relationship between the difference in the proportionate resorption of N vs P and this foliar N:P ratio, consistent across species, growth-forms, and vegetation-types globally. Moreover, according to the relative resorption hypothesis, communities with higher/lower foliar N:P (more likely P/N limited) tend to produce litter with disproportionately higher/lower N:P, causing a worsening status of P/N availability; this positive feedback may somehow be counteracted by several negative-feedback mechanisms. Compared to N, P generally shows higher variability in resorption efficiency (proportion resorbed), and higher resorption sensitivity to nutrient availability, implying that the resorption of P seems more important for plant nutrient conservation and N:P stoichiometry. Our findings elucidate the nutrient limitation effects on resorption efficiency in woody plants at the global scale, and thus can improve the understanding of nutrient resorption process in plants. This study also suggests the importance of the foliar N:P ratio as a key parameter for biogeochemical modeling, and the relative resorption hypothesis used to deduce the critical (optimal) N:P ratio for a specific plant community.
以前的大多数研究都将某种植物养分吸收的差异归因于其相应的环境有效性或组织中的水平，而不考虑其他养分的状况。然而，鉴于植物生长依赖于充足且平衡的养分供应，养分吸收过程不仅应与绝对养分状况相关，还应受养分相对限制的调节。在此，基于从文献中获取的全球木本植物数据集，我们检验了以下假设：当植物受到氮（或磷）限制时，它们会按比例吸收更多的氮（或磷）；当同时受到两种养分限制时，它们会吸收相似比例的氮（N）和磷（P）（相对吸收假设）。使用绿叶中的N:P比作为养分限制的指标，我们发现N与P按比例吸收的差异与这种叶片N:P比之间存在反比关系，这在全球范围内的物种、生长形式和植被类型中都是一致的。此外，根据相对吸收假设，具有较高/较低叶片N:P（更可能是P/N限制）的群落倾向于产生具有不成比例的较高/较低N:P的凋落物，从而导致P/N有效性状况恶化；这种正反馈可能会以某种方式被几种负反馈机制抵消。与氮相比，磷在吸收效率（吸收比例）上通常表现出更高的变异性，并且对养分有效性具有更高的吸收敏感性，这意味着磷的吸收似乎对植物养分保存和N:P化学计量更为重要。我们的研究结果阐明了全球范围内养分限制对木本植物吸收效率的影响，从而可以增进对植物养分吸收过程的理解。这项研究还表明了叶片N:P比作为生物地球化学建模关键参数的重要性，以及用于推导特定植物群落临界（最佳）N:P比的相对吸收假设的重要性。
