滴、畦灌下毛白杨生长及蒸腾对根区水的动态定量响应特征与机制

The area of poplar plantations in China has reached above 8.5 million ha, but their average productivity is still below the world mean level. Irrigation can help to solve this problem, but this depends on the application of high efficient irrigation strategies. A good understanding of the dynamic quantitative response of poplar growth and transpiration to rootzone water availability could help to develop high efficient irrigation strategies for poplar plantations, as it can improve the precision, flexibility and universality of irrigation strategies. However, little attempt has been made to investigate this. This research will be conducted in Populus tomentosa plantations under both drip and border irrigation conditions. Water control will be applied to establish a series of soil water gradients. Meanwhile, the growth and ecophysiological characteristics of poplar trees, root distribution, soil and environmental factors will be monitored consecutively or regularly. This project has four research contents: (1) the spatial distribution and dynamics of rootzone water availability and root water uptake in P. tomentosa plantations; (2) dynamics of the quantitative response of P. tomentosa growth and transpiration to rootzone water availability; (3) the variation mechanisms of the rootzone-water thresholds for P. tomentosa growth and transpiration under different irrigation methods, seasons and years; (4) and to obtain the dynamic rootzone-water irrigation thresholds for P. tomentosa plantations. This research will reveal the characteristics and mechanism of the dynamic quantitative response of tree growth and transpiration to rootzone water availability in drip- and border-irrigated Populus tomentosa plantations. Besides, it will also provide scientific base for developing high efficient irrigation strategies for P. tomentosa plantations.

我国杨树人工林面积已超850万ha，但平均生产力远不及国际中等水平。灌溉可帮助解决该问题，但必须依靠高效灌溉策略才能实现。了解不同灌溉方式下杨树生长及蒸腾对根区水分的动态定量响应规律及其变化机制，有助于精确、动态且具一定普适性的杨树人工林高效灌溉策略的制定。但目前这方面的研究还几为空白。本项目以滴、畦灌下的毛白杨人工林为研究对象，在通过控水获得系列土壤水分梯度，并对林木生长和生理生态特征、根系分布、土壤及环境因子进行连续或定期监测的基础上，开展以下研究：根区水分和根系吸水的空间分布与动态；林分生长与蒸腾对根区水的定量响应动态；林分生长与蒸腾根区水分阈值在不同灌溉方式、季节和年际间的变化机制；林分最佳灌溉根区水分动态阈值。通过以上研究，不仅将揭示滴、畦灌下毛白杨生长及蒸腾对根区水分的动态定量响应特征与机制，丰富现有植物水分关系理论，还可为毛白杨人工林高效灌溉策略的制定提供科学依据。

为了解毛白杨生长和蒸腾对根区水分的动态定量响应规律与机制，从而帮助制定精确、动态且具一定普适性的毛白杨人工林高效灌溉策略。以砂壤土上的1-3年生毛白杨林分和粉土上的6-7年生毛白杨林分为研究对象，研究了不同灌溉方式下根区水分和根系吸水的时空动态、林分生长与蒸腾对根区水分的定量响应特征、以及生长和蒸腾根区水分阈值在不同灌溉方式、时间尺度和年际间的变化机制。结果表明：1）各处理2年生林分均已形成二态性根系；根系形态、密度对季节和土壤水分差异响应较弱，但其分布深度响应较强；水分亏缺下，畦灌林分根系分布逐渐加深，且与滴灌林分差异逐渐增大。2）构建的土壤水分运动模型可实现不同立地和灌溉方式下林地土壤水分动态的精确模拟。3）灌水量的减少会促使林木吸收更多的深层土壤水；滴、畦灌下，水分亏缺会促使根系吸水补偿效应的发生。4）构建的作物系数模型，在砂壤土滴、畦灌下预测蒸腾的RMSE分别为0.36和0.25 mm/d，RMAE分别为18%和13%；在粉土上，预测蒸腾和蒸散的RMAE分别为13%和16%。5）滴灌下，表土层水分对生长变异起主要作用；畦灌下，随林龄增加，深层水会逐渐决定林木生长大小。6）粉土上，表土层水分对蒸腾起主要作用，但砂壤土上，40-300和170-300 cm土层水分分别对滴、畦灌林分蒸腾起主导作用。7）林分LAI、Huber值、叶片膨压、根系吸水量、蒸腾水利用效率、冠层和气孔导度存在明显季节变化和一定年际差异，但在各处理间无显著差异，然而在相同供水下，滴灌林分的水分状况大多时期高于畦灌林分。8）为避免生长和蒸腾受抑制，对于粉土上的林分，0-30 cm土层的水分有效性（rθ）应在0.7以上；砂壤土上的畦灌林分，2年生时，0-20 cm土层rθ应高于0.85，3年生时，其水平可不考虑；砂壤土上的滴灌林分，0-20 cm土层rθ应分别高于0.5和0.7。这些rθ阈值可作为不同立地、林龄和灌溉方式下林分的灌溉起始阈值。9）毛白杨生长和蒸腾的根区rθ阈值在不同灌溉方式、年际和立地上的差异主要由根系分布深度和树体水分状况的不同而引起。