半干旱黄土丘陵区刺槐林蒸散发组分构成的林龄差异研究

Black locust (Robinia pseudoacacia) plantation is the main plantation type in the afforestation program of the Loess Plateau of China, which plays essential roles in promoting ecosystem services in this region. However, the plantations showed signs of growth recession at early ages due to water stress, resulting in their ecological functions seriously restricted. Therefore, it is necessary to clarify the plantations’ growth conditions and water ecological adaptability. The contribution of transpiration to evapotranspiration (T/ET) is the crucial method that examine the plant growth condition and water ecological adaptability. However, there are some inadequacies in the T/ET of black locust plantations in the Loess Plateau. For one thing, the quantitative relationship between T/ET and stand age is lack of study. For other thing, the affecting mechanism of variations in T/ET with stand ages is not well understood. In this study, we will construct observation plots in Yangjuangou catchment in the hilly region of Loess Plateau to calibrate and validate the Shuttleworth-Wallace model and canopy interception model. The study trying to make breakthroughs in: (1) establishing the quantitative relationship between T/ET and stand ages; (2) revealing the affecting mechanism of variations in T/ET with stand ages in black locust plantations, which provide the better understanding of black locust plantations’ growth conditions and water ecological adaptability. This study will also provide a scientific basis for the sustainable development of the afforestation projects in the Loess Plateau of China.

刺槐林是黄土高原植被重建的主要林型，对提升区域生态系统服务发挥了关键作用。但是，由于水分限制，刺槐林出现生长早衰现象，严重限制了其生态功能发挥。因此有必要厘清刺槐的生长状况和水分适应性。而蒸腾对蒸散发的贡献率（T/ET）是刻画植物生长状况和水分适应性的关键手段。但是目前刺槐林T/ET的研究存在不足之处：一方面缺乏对T/ET与林龄关系的定量表征，另一方面对T/ET林龄差异影响机理的理解有待深入。本项目拟在黄土丘陵区羊圈沟小流域设置样地来优化、验证Shuttleworth-Wallace模型和冠层截留模型，试图在两个方面有所突破：（1）表征刺槐林T/ET与林龄的数量关系，揭示T/ET随林龄的变化特征；（2）分析不同林龄刺槐林T/ET与植被结构、生理特征和土壤水分的关系，阐明T/ET林龄差异的影响机理，更好地了解刺槐林的生长状况及水分利用和适应性规律，以期为区域刺槐林的优化管理提供理论支撑。

刺槐林因其生长迅速、耐旱性强等特点，在黄土高原广泛种植，对控制区域土壤侵蚀、增加碳汇、改善区域生态环境具有积极的作用。但是，由于受到水分限制，刺槐林出现生长早衰现象，严重限制了其生态功能发挥。探究刺槐林不同生长阶段蒸散发大小及其组分构成特征，对于厘清刺槐林的水分适应性具有重要的意义。本项目通过在黄土丘陵区的羊圈沟小流域开展连续定位观测，量化了刺槐林总体的蒸散发大小及其组分构成状况（土壤蒸发>冠层截留>蒸腾），并阐明了降雨对T/ET影响的关键作用。结果也表明，刺槐林T/ET值偏小，这反映了其生产力也较小，通过径向生长的数据得到验证。本项目还构建了量化土壤水分对蒸散发关键组分影响的方法，明确了土壤水分的相对贡献。高林龄刺槐林蒸散发及其各组分都显著大于低林龄的刺槐林，而低林龄刺槐林的T/ET值大于高林龄，说明了低林龄刺槐林具有较高的用水效率。结合蒸散发、土壤、植被观测数据，对蒸散发组分表达模型进行了参数率定和结果验证。本项目的研究有助于深入了解刺槐林的水分利用策略、生长特征及其适应性规律，为该区域刺槐林的优化管理提供了理论支持。