Inconsistent Responses of Transpiration of Different Canopy Layers to Simulated Canopy and Understory N Depositions in a Low-Subtropical Evergreen Broadleaf Forest
Inconsistent Responses of Transpiration of Different Canopy Layers to Simulated Canopy and Understory N Depositions in a Low-Subtropical Evergreen Broadleaf Forest
复制标题
低亚热带常绿阔叶林不同冠层蒸腾作用对模拟冠层和林下氮沉降的不一致响应
DOI：
10.1029/2019jg005594
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发表时间：
2020-05-01
影响因子：
3.7
通讯作者：
Ni, Guangyan
中科院分区：
文献类型：
--
作者：
Li, Yanqiong;Zhao, Ping;Ni, Guangyan
在林分尺度和森林不同冠层量化蒸腾作用及其对气象因素的响应，对于理解氮（N）沉降对当地水平衡的水文影响非常重要。为此，在南亚热带常绿阔叶林中一个设置了冠层（CN）和林下（UN）施氮处理的控制实验平台上，对三种上层（木荷、锥栗和华润楠）和三种下层（老鼠矢、榕叶冬青和鹅掌柴）冠层树种的液流进行了测量。每种处理的施氮浓度分别为0、25和50 kg·ha⁻¹·a⁻¹。结果表明，施氮明显影响液流密度，且这种影响在不同树种之间以及冠层之间存在差异。上层冠层树种对整个森林的蒸腾作用贡献最大，CN25对上下层冠层的蒸腾作用均有显著影响。日耗水量（Qd）随白天平均光合有效辐射和日平均水汽压亏缺呈对数增加。适量的冠层施氮（CN25）促进了Qd及其对微气象因子的敏感性，而UN的影响极小。这些结果表明，蒸腾作用对施氮方式的响应存在显著差异。CN对冠层蒸腾作用的影响更为有效。因此，UN不能完全反映氮沉降增加对冠层相关蒸腾作用的影响，森林蒸腾作用对氮沉降的响应需要超越树种层面进行分析，并提升到冠层水平，以便对氮沉降进行有意义的评估。
Quantifying transpiration and its response to meteorological factors at a stand scale and different canopy layers of forest is important for understanding the hydrological impact of nitrogen (N) deposition on local water balance. For this purpose, sap flows were measured in three upper (Schima superba, Castanea henryi, and Machilus chinensis) and three lower (Symplocos ramosissima, Ilex ficoidea, and Schefflera octophylla) canopy species based on a manipulative experimental platform with canopy (CN) and understory (UN) N additions in a low-subtropical evergreen broadleaf forest. Each application included concentrations of 0, 25, and 50 kg center dot ha(-1)center dot a(-1) N. Results showed that N addition obviously influenced the sap flux density and such influence varied among different species and between canopy layers. Upper canopy species contributed the most transpiration for the whole forest, and CN25 greatly affected the transpiration in both upper and lower canopy layers. Daily water use (Q(d)) increased logarithmically with daytime average photosynthetically active radiation and daily average vapor pressure deficit. An appropriate canopy N addition (CN25) promoted the Q(d) and its sensitivity to micrometeorological factors, whereas UN had a minimal effect. These results suggest a substantial difference in response of transpiration to the N addition ways. CN had more effective influence on the canopy transpiration. Thus, UN could not fully reflect the effects of increased N deposition on the canopy-associated transpiration, and the response of forest transpiration to N deposition needs to be analyzed beyond species and upscaled to the canopy level in favor of meaningful assessments of N deposition.