不同起源樟子松林水分利用的差异及机制

Differences and mechanisms on water use of Pinus sylvestris var mongolica forests with different origins

明确同一树种不同起源林分(天然林与人工引种林)间水分利用特征的差异,对于指导林分的可持续经营具有重要意义。本研究以樟子松这一“三北”工程中重要的造林树种为例,选择2种起源的林分为试验林,利用热扩散技术监测了试验林生长季树干边材液流速率(Js),分析樟子松水分传输过程及其与环境因子间的关系。结果表明:在整个生长季的典型晴天下,樟子松人工林的日液流速率(J_(s-daily))显著高于樟子松天然林,二者J_(s-daily)平均值分别为132.98和114.86 cm·d^(-1),樟子松人工林表现出了更高的水分传输潜力。在樟子松天然林中,大气水分亏缺(VPD)对树木水分利用过程主要表现为驱动效应,而在樟子松人工林中出现了明显的阈值效应,VPD拐点约在1.91 kPa,此时液流速率(J_(s-hour))边界函数值接近最大值17.88 cm·h^(-1)。观测期间,2种起源樟子松林受大气驱动的蒸腾潜力(J_(s-hour)/VPD)随土壤干旱的加剧而下降,但樟子松人工林对干旱的敏感性比樟子松天然林更高,反映出这一树种对水分利用过程较强的调控能力。

Determining the differences of water use characteristics of a tree species with different origins(natural forests and introduced plantations)is significantly important for forest sustainable management.Pinus sylvestris var.mongolica is an important tree species of afforestation in the‘Three North’project in China.In this study,with Pinus sylvestris var.mongolica from two origins,we monitored the sap flow velocity of sapwood(Js)of trees by thermal dissipation sap flow probes,and analyzed the relationship between water transportation and the environmental factors during the growing season.The results showed that under the typical sunny day,daily sap flow velocity(J_(s-daily))of trees from plantations was significantly higher than that from natural forests.The mean value of J_(s-daily)was 132.98 and 114.86 cm·d^(-1)for the two origins,respectively.Trees from plantations showed higher water transportation potential than natural forests.Vapor pressure deficit(VPD)mainly showed the driving effect on the water use process of trees from natural forests.In the plantations,there was an obvious threshold effect,and the inflection point of VPD was about 1.91 kPa,with the boundary function of J_(s-hour)increased to the maximum of 17.88 cm·h^(-1).Atmospheric driven transpiration potential(J_(s-hour)/VPD)of P.sylvestris var.mongolica trees with two origins decreased with the aggravation of soil drought,but sensitivity to drought was higher in the plantations than in the natural forests,suggesting the strong ability of Pinus sylvestris var.mongolica to regulate water use process.