Environmental control of canopy stomatal conductance in a tropical deciduous forest in northern Thailand
Environmental control of canopy stomatal conductance in a tropical deciduous forest in northern Thailand
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DOI：
10.1016/j.agrformet.2014.11.013
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发表时间：
2015-03
影响因子：
6.2
通讯作者：
Yasunori Igarashi;T. Kumagai;N. Yoshifuji;Takanori Sato;N. Tanaka;Katsunori Tanaka;Masakazu Suzuki
中科院分区：
文献类型：
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作者：
Yasunori Igarashi;T. Kumagai;N. Yoshifuji;Takanori Sato;N. Tanaka;Katsunori Tanaka;Masakazu Suzuki
就全球和当地的水文和碳通量及其对气候变化的脆弱性而言，东南亚的热带季节森林是最重要的生物群之一。我们测量了一种柚木(Tectona randisLinn.F.)在泰国北部种植了6年的时间；这片森林的树叶经历了剧烈的季节性变化，有一些恒定的入射辐射能量。我们结合实际的蒸散(ET)通量数据和一个简单的两层ET模型的反演版来估算平均冠层气孔导度(GS)。这种分析的主要新奇之处在于，可以从总的地表电导(包括林冠和林地效应)中提取冠层电导，从而明确地比较了不同季节和年份对GES的环境和生物控制。叶面积指数(LAI)与叶面积指数(LAI)的季节变化关系表明，叶龄对叶气体交换能力有明显的影响：一年内，叶面积指数(LAI)出现早于全叶展开，叶面积指数(LAI)在叶面积指数达到高峰后突然下降。我们利用这一结果划分了三个叶龄阶段：出叶期、生长中期和叶片衰老期。根据各季节GST对水汽压亏缺(VPD)的对数响应曲线，求出了两个生理生态参数：gS参考值(Gsref)、gsREF对大气需求的敏感度(M)及其所占比例(m/gsref)。季节变化表现为：出叶季节、≈季节、生长中期季节、叶片衰老季节，表现出较小的季节性和年际变化。这表明，柚树在叶片衰老季节(即干旱条件下)具有严格的气孔调节，以防止木质部过度空化，而在叶片衰老和生长中期(即在潮湿条件下)气孔调节不那么严格，因为水分胁迫导致水力破坏的风险很小。此外，我们还得到了土壤湿度与GSREF之间的简单线性关系，这为进一步利用全球气候和植被动力学模型研究陆气相互作用提供了有力的工具。
Tropical seasonal forests in Southeast Asia are among the most important biomes in terms of global and local hydrologic and carbon fluxes, and their vulnerability to climate change. We conducted eddy flux measurements in a teak (Tectona grandisLinn. f.) plantation in northern Thailand over a 6-year period; this forest undergoes a drastic seasonal change in foliage with somewhat constant incident radiative energy. We used a combination of actual evapotranspiration (ET) flux data and an inversed version of a simple two-layer ET model for estimating the mean canopy stomatal conductance (gs). The main novelty of this analysis is that canopy conductance can be extracted from total surface conductance (including the canopy and forest floor effects), and thus environmental and biological controls ofgsare explicitly compared among seasons and years. The relationship between seasonal variations in the leaf area index (LAI) andgsrevealed an apparent effect of leaf age on leaf gas exchange capacity: within a year,gspeaked earlier than full-leaf expansion and abruptly declined after the peak of LAI. We used this result to classify three leaf age stages: leaf-out, mid-growing, and leaf-senescence seasons. Then, two ecophysiological parameters, the reference value ofgs(gsref), and the sensitivity ofgsto atmospheric demand (m), as well as their proportion (m/gsref), were derived from the logarithmic response curve ofgsto vapor pressure deficit (VPD) for each season. We showed seasonal variation ingsrefas follows: leaf-out season ≈ mid-growing season > leaf-senescence season.mdemonstrated little seasonality and little interannual variation was observed in either parameter. This resulted in a value of almost 0.6 form/gsrefduring the leaf-senescence season and of less than 0.6 in the leaf-out and mid-growing seasons, which suggests that the teak trees had strict stomatal regulation to prevent excessive xylem cavitation during the leaf-senescence season (i.e., under drought conditions) and less strict stomatal regulation during the leaf-out and mid-growing seasons (i.e., under moist conditions) when little risk of water stress-induced hydraulic failure would occur. In addition, we obtained a simple linear relationship between soil moisture andgsref, which can be a powerful tool for further research of land–atmosphere interactions using global climate and vegetation dynamics models.