Key Laboratory of State Forestry Administration on Forest Ecosystem Protection and Restoration of Poyang Lake Watershed, Jiangxi Provincial Key Laboratory of Conservation Biology, College of Forestry, Jiangxi Agricultural University, Nanchang 330045, China; Key Laboratory of Forest Ecology and Environment of the National Forestry and Grassland Administration, Ecology and Nature Conservation Institute, Chinese Academy of Forestry, Beijing 100091, China.
Key Laboratory of State Forestry Administration on Forest Ecosystem Protection and Restoration of Poyang Lake Watershed, Jiangxi Provincial Key Laboratory of Conservation Biology, College of Forestry, Jiangxi Agricultural University, Nanchang 330045, China; Jiulianshan National Observation and Research Station of Chinese Forest Ecosystem, Jiangxi Agricultural University, Nanchang 330045, China.
Sci Total Environ. 2024 May 1;923:171501. doi: 10.1016/j.scitotenv.2024.171501. Epub 2024 Mar 5.
Understanding how nutrient addition affects the tree growth is critical for assessing forest ecosystem function and processes, especially in the context of increased nitrogen (N) and phosphorus (P) deposition. Subtropical forests are often considered N-rich and P-poor ecosystems, but few existing studies follow the traditional "P limitation" paradigm, possibly due to differences in nutrient requirements among trees of different size classes. We conducted a three-year fertilization experiment with four treatments (Control, N-treatment, P-treatment, and NP-treatment). We measured soil nutrient availability, leaf stoichiometry, and relative growth rate (RGR) of trees across three size classes (small, medium and large) in 64 plots. We found that N and NP-treatments increased the RGR of large trees. P-treatment increased the RGR of small trees. RGR was mainly affected by N addition, the total effect of P addition was only 10 % of that of N addition. The effect of nutrient addition on RGR was mainly regulated by leaf stoichiometry. This study reveals that nutrient limitation is size dependent, indicating that continuous unbalanced N and P deposition will inhibit the growth of small trees and increase the instability of subtropical forest stand structure, but may improve the carbon sink function of large trees.
了解养分添加如何影响树木生长对于评估森林生态系统功能和过程至关重要，特别是在氮（N）和磷（P）沉积增加的背景下。亚热带森林通常被认为是富氮和贫磷的生态系统，但很少有现有研究遵循传统的“磷限制”范式，这可能是由于不同大小类别的树木对养分的需求存在差异。我们进行了一项为期三年的施肥实验，共设四个处理（对照、氮处理、磷处理和氮磷处理），在 64 个样地中测量了土壤养分供应、叶片化学计量和三个大小类别的树木（小、中、大）的相对生长率（RGR）。我们发现氮和氮磷处理增加了大树的 RGR，磷处理增加了小树的 RGR。RGR 主要受氮添加的影响，磷添加的总效应仅为氮添加的 10%。养分添加对 RGR 的影响主要受叶片化学计量的调节。本研究表明养分限制是大小依赖的，这表明持续的不平衡氮和磷沉积将抑制小树的生长并增加亚热带林分结构的不稳定性，但可能会提高大树的碳汇功能。
