Key Laboratory of Eco-Environments in the Three Gorges Reservoir Region (Ministry of Education), Chongqing Key Laboratory of Plant Ecology and Resources in the Three Gorges Reservoir Region, School of Life Sciences, Southwest University, Chongqing, 400715, China.
Environ Sci Pollut Res Int. 2018 Aug;25(23):23261-23275. doi: 10.1007/s11356-018-2357-8. Epub 2018 Jun 4.
In order to understand the effect of submergence on nutrient release of the reforested tree leaves and assess the environmental risk of leaf decomposition under submergence, the mass loss and nutrient release rates of three reforestation tree species, Taxodium ascendens Brongn, Taxodium distichum (L.) Rich., and Salix matsudana Koidz., at different elevation in the hydro-fluctuation zone of the Three Gorges Dam Reservoir (TGDR) region were tested in situ. Results showed that the initial macroelement contents of the leaves of the three tree species varied among different elevations due to different submergence stresses. All foliar mass loss rates of the three tree species at 165 m a.s.l. were significantly higher than that at 175 m a.s.l. (except that of S. matsudana at 165 m a.s.l.), after 179 days of incubation commenced September 20. After 138 days of incubation commenced October 5, the foliar mass loss rates of the three tree species at 170 m a.s.l. were significantly higher than that at 175 m a.s.l. Moreover, the leaf mass loss rates of S. matsudana were higher than the other two species when compared at the same elevation of the same incubation period. In addition, foliar release rates of N and Ca in T. ascendens, C, N, and Ca in T. distichum as well as Ca in S. matsudana at 165 m a.s.l. after 179 days of incubation and at 170 m a.s.l. after 138 days of incubation were significantly higher than that at 175 m a.s.l., respectively. Leaf mass loss rates of T. ascendens were significantly correlated with its initial leaf K, Ca, and Mg contents. In contrast, leaf mass loss rates of T. distichum had significant correlations with the initial leaf P and K contents, as well as C/P and N/P ratios. However, the mass loss rates of S. matsudana significantly correlated with initial leaf N, P, and Ca contents and C/N, C/P, and N/P ratios. Foliar nutrient release rates, especially the foliar release of C, N, and P of the three tree species, had significant correlations with initial leaf C/P and N/P ratios. Our results suggested that submergence facilitated the decomposition and nutrient release rates of the leaves of the three woody species, especially the broad leaves of S. matsudana, which may potentially cause secondary pollution to the water body of the TGDR. Thus, we suggested that a sustainable harvest of leaves of the reforested forest stands prior to submergence should be considered in the hydro-fluctuation zone so as to protect the water quality of the TGDR.
为了了解淹没对造林树种叶片养分释放的影响，评估淹没条件下叶片分解的环境风险，本研究原位测试了三峡水库消落区不同海拔高度的 3 种造林树种（池杉、落羽杉和枫杨）叶片的质量损失率和养分释放率。结果表明，由于淹没胁迫的不同，3 种树种叶片的初始宏量元素含量在不同海拔高度之间存在差异。2009 年 9 月 20 日开始培养后 179 天，在 165m 海拔高度的 3 种树种的叶片质量损失率均显著高于 175m 海拔高度（165m 海拔高度的枫杨除外）。2009 年 10 月 5 日开始培养 138 天后，在 170m 海拔高度的 3 种树种的叶片质量损失率均显著高于 175m 海拔高度。此外，在同一培养期同一海拔高度，枫杨的叶片质量损失率均高于其他 2 种树种。此外，在 179 天培养后，165m 海拔高度的池杉叶片中 N 和 Ca 的释放率、落羽杉叶片中 C、N 和 Ca 的释放率以及枫杨叶片中 Ca 的释放率均显著高于 175m 海拔高度；在 138 天培养后，170m 海拔高度的池杉叶片中 N 和 Ca 的释放率、落羽杉叶片中 C、N 和 Ca 的释放率以及枫杨叶片中 Ca 的释放率均显著高于 175m 海拔高度。池杉的叶片质量损失率与初始叶片 K、Ca 和 Mg 含量显著相关。相比之下，落羽杉的叶片质量损失率与初始叶片 P 和 K 含量以及 C/P 和 N/P 比值显著相关。然而，枫杨的叶片质量损失率与初始叶片 N、P 和 Ca 含量以及 C/N、C/P 和 N/P 比值显著相关。叶片养分释放率，特别是 3 种树种的叶片 C、N 和 P 释放率，与初始叶片 C/P 和 N/P 比值显著相关。研究结果表明，淹没促进了 3 种木本植物叶片的分解和养分释放率，特别是枫杨的阔叶，这可能会对三峡水库水体造成二次污染。因此，我们建议在淹没之前对消落区的造林林分进行可持续的叶片收获，以保护三峡水库的水质。
