毛竹林碳通量对极端干旱的响应机制与模型模拟研究

The frequency and intensity of extreme drought events increases every year in sub-tropical area, which has a significant impact on the forest ecosystem carbon budget. Bamboo forest is one of special forest types and plays an important role in regional carbon balance. Extreme drought caused decreases in diameter at breast height and harvest and reduced production and carbon storage of Moso bamboo forest, which was a threat to sustainable management. Because few of basic research studied on effect of extreme drought on Moso bamboo forest, this study is significant and valuable to reduce damage risk of extreme drought. This program focuses on response mechanisms of Moso bamboo forest carbon fluxes to extreme drought and their model simulation based on control experiment, eddy covariance technique, satellite remote sensing, ecosystem carbon flux model and statistical analysis. The objectives of this program are to reveal regulation rules of water, temperature and light to Moso bamboo carbon flux under drought stress thought analyzing interaction of environmental factors, to verify the death mechanisms due to carbon starvation and discover the roles of stomatal and nonstomatal limitation in carbon starvation, and to build model expression of mechanisms and then couple them with light use efficiency model for quantitatively evaluating the impact of extreme drought on Moso bamboo forest carbon fluxes. Results will provide detailed data, the theoretical basis and technical support for the management of carbon sequestration.

亚热带地区极端干旱发生的频率和强度持续增加，对森林碳平衡的影响越来越受到关注。竹林是中国亚热带地区特殊的森林类型，在区域碳平衡中具有重要地位和作用。极端干旱引起毛竹胸径减小，采伐量减少，显著降低生产力和碳储量，对可持续经营带来巨大威胁。然而，目前极端干旱对毛竹林影响方面的基础研究还相当缺乏，因此开展本研究对降低未来极端干旱对毛竹林灾害风险具有重要意义和价值。本项目以干旱控制试验、通量观测塔、卫星遥感、碳通量模型和统计分析等技术和方法为手段，开展毛竹碳通量对极端干旱的响应机制及其模型模拟研究，探究环境因子交互效应对毛竹碳通量影响，揭示干旱胁迫下水、温和光对毛竹林碳通量的调控规律；验证干旱引起毛竹死亡机制—碳饥饿假说，阐明气孔和非气孔限制对碳饥饿贡献；构建响应机制数学表达式并融入光能利用率模型，定量评价干旱对毛竹林碳通量的影响，为提高毛竹林固碳经营管理水平提供翔实数据、理论依据和技术支撑。

极端气候频发背景下，森林生态系统碳循环对气候变化的响应越来越受到关注。本项目开展了毛竹林碳通量对干旱胁迫的响应机制及其模型模拟研究，阐明了干旱胁迫下水分、温度和饱和水蒸气压差（VPD）对毛竹林碳通量的调控规律，构建了环境因子对碳通量的交互效应表达式，提出了适用于干旱胁迫下的毛竹林碳通量模拟模型，定量评价了干旱对毛竹林碳通量影响及其空间分布。主要得到以下结果：干旱胁迫下，温度与毛竹林总初级生产力（GPP）的响应方式发生改变，最优温度降低，高温将降低毛竹林碳固定；GPP与VPD的响应发生改变，由线性正相关转变为倒J型负相关；VPD结合温度和土壤相对含水量，能够很好地指示干旱胁迫对毛竹林GPP的影响。在此基础上，构建的适用于干旱胁迫的光能利用率模型显著提高了毛竹林GPP模拟精度。干旱胁迫降低了毛竹林GPP和净生态系统碳交换量，但对生态系统呼吸影响不明显。大年毛竹林碳通量受干旱影响要大于小年毛竹林。干旱对毛竹林GPP的影响存在空间异质性，在时间上具有滞后效应。该成果为精确监测毛竹林碳汇能力和提高毛竹林固碳经营管理水平提供翔实数据、理论依据和技术支撑。