School of Earth System Science, Tianjin University, Tianjin 300072, China.
Beijing Key Laboratory of Farmland Soil Pollution Prevention and Remediation, Department of Environmental Sciences and Engineering, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China.
Sci Total Environ. 2023 Aug 10;885:163843. doi: 10.1016/j.scitotenv.2023.163843. Epub 2023 May 1.
Nitrogen (N) and phosphorus (P) are two crucial limiting mineral elements for terrestrial plants. Although the leaf N:P ratio is extensively used to indicate plant nutrient limitations, the critical N:P ratios cannot be universally applied. Some investigations have suggested that leaf nitrogen isotopes (δN) can provide another proxy for nutrient limitations along with the N:P ratio, but the negative relationships between N:P and δN were mainly limited to fertilization experiments. It will obviously benefit the study of the nature of nutrient limitations if the relationship could be explained more generally. We analyzed leaf δN, N, and P contents across a northeast-southwest transect in China. Leaf δN was weakly negatively correlated with leaf N:P ratios for all plants, while there was no correlation between them for various plant groups, including different growth forms, genera, and species across the entire N:P range. This suggests that the use of leaf δN in indicating the shift of nutrient limitations across the whole N:P range still requires more validated field investigations. Notably, negative relationships between δN and N:P hold for plants with N:P ratios between 10 and 20 but not for plants with N:P ratios lower than 10 or higher than 20. That is, changes in leaf δN along with the N:P ratio of plants that are co-limited by N and P can exhibit variations in plant nutrient limitations, whereas plants that are strictly limited by N and P cannot. Moreover, these relationships are not altered by vegetation type, soil type, MAP, or MAT, indicating that the use of leaf δN in reflecting shifts in nutrient limitations, depending on the plant nutrient limitation range, is general. We examined the relationships between leaf δN and the N:P ratio across an extensive transect, providing references for the widespread use of leaf δN in reflecting shifts in nutrient limitation.
氮（N）和磷（P）是陆地植物的两种关键限制矿质元素。尽管叶片 N:P 比广泛用于指示植物养分限制，但临界 N:P 比不能普遍适用。一些研究表明，叶片氮同位素（δN）可以与 N:P 比一起提供另一种养分限制的替代指标，但 N:P 与 δN 之间的负相关关系主要限于施肥实验。如果能够更普遍地解释这种关系，显然将有利于对养分限制本质的研究。我们在中国东北-西南方向的一条横断线上分析了叶片 δN、N 和 P 含量。对于所有植物，叶片 δN 与叶片 N:P 比呈弱负相关，而对于不同的植物群，包括不同的生长形式、属和种，它们之间没有相关性，跨越整个 N:P 范围。这表明，在整个 N:P 范围内，使用叶片 δN 来指示养分限制的转变仍需要更多经过验证的野外调查。值得注意的是，对于 N:P 比在 10 到 20 之间的植物，δN 与 N:P 之间存在负相关关系，但对于 N:P 比低于 10 或高于 20 的植物则没有。也就是说，受 N 和 P 共同限制的植物的叶片 δN 与 N:P 比的变化可以表现出植物养分限制的变化，而受 N 和 P 严格限制的植物则不能。此外，这些关系不受植被类型、土壤类型、年平均降水量（MAP）或年平均温度（MAT）的影响，这表明叶片 δN 在反映养分限制变化方面的使用取决于植物养分限制范围，是普遍的。我们在广泛的横断线上检验了叶片 δN 与 N:P 比之间的关系，为叶片 δN 在反映养分限制变化方面的广泛应用提供了参考。
