鼎湖山针阔叶混交林冠层下方CO2通量及其环境响应

精确估算典型森林生态系统冠层下方CO₂通量（Fcb）对验证陆地生态系统碳平衡模型具有重要意义。采用开路涡度相关法对鼎湖山针阔叶混交林Fcb进行定位测定，根据1周年数据分析Fcb及其对环境要素的响应特征，结果表明：(1) 白天Fcb呈下降趋势表明地表植被全年具有光合能力，但总体上地表植被和土壤表现为CO2排放源；(2) Van’t Hoff方程、Arrhenius方程和Lloyd-Taylor方程均可以较好反映土壤温度(Ts)与Fcb的关系，其中仅Lloyd-Talor方程能够反映温度因子敏感性指标Q10随温度的变异性特征；(3) Lloyd-Talor方程模拟的Fcb完全由Ts控制，而连乘模型由Ts和土壤水分(Ms)控制，可以反映水热条件的综合影响，对Fcb具有更强的拟合能力；(4)在Ms较大时连乘模型对Fcb的估算高于Lloyd-Talor方程，反之在干旱时段连乘模型模拟结果低于Lloyd-Talor方程，表明当存在水分胁迫时，Ms可以成为影响Fcb的主导因子；(5) 2003年鼎湖山针阔叶混交林Fcb总量((787.4±296.8)gCm^-2a^-1)比静态箱-气相色谱法测得的土壤呼吸偏低17%。与箱式法相比，涡度相关法通量测定结果普遍存在偏低估算现象。

Below-canopy CO2 flux and its environmental response characteristics in a coniferous and broad-leaved mixed forest in Dinghushan, China

Accurate estimation of below-canopy CO² flux (Fcb) in typical forest ecosystems is of great importance to validate terrestrial carbon balance models. Continuous eddy covariance measurements of Fcb were conducted in a coniferous and broad-leaved mixed forest located in Dinghushan Nature Reserve of South China. Using year-round data, Fcb dynamics and its environmental response were analyzed, and the results mainly showed that: (1) Fcb decreased during daytime which indicated that the understory of the forest continued photosynthesis throughout the year; however, understory and soil acted as CO² source as a whole. (2) Using soil temperature (Ts) as a dependent variable, all of Van't Hoff equation, Arrhenius equation and Lloyd-Taylor equation can explain a considerable variation of Fcb. Among those three equations Lloyd-Taylor equation is the best to reflect the relationship between soil respiration and temperature for its ability in revealing the variation of Q₁₀ with temperature. (3) Fcb derived from Lloyd-Taylor equation is utterly determined by Ts, while Fcb derived from the multiplicative model is driven by Ts and soil moisture (Ms). The multiplicative model can reflect the synthetic effect of Ts and Ms; therefore it explains more Fcb variations than Lloyd-Taylor equation does. (4)Fcb derived from the multiplicative model was higher than that from Lloyd-Taylor equation when Ms was relatively high; on the contrary, Fcb derived from the multiplicative model was lower than that from Lloyd-Taylor equation when Ms was low, indicating that Ms might be a main factor affecting Fcb when the ecosystem is stressed by low-moisture. (5) Annual Fcb of the forest in 2003 was estimated as (787.4±296.8) gCm^?2a^?1, which was 17% lower than soil respiration measured by statistic chamber method. CO² flux measured by eddy covariance is often underestimated, and further study therefore calls for emphasis on methods quantifying Fcb components of respiration of soil, as well as respiration and photosynthesis of understory vegetations.