基于稳定同位素和热比率技术的侧柏水分逆向运移特征与过程

植物在一定环境条件下可通过叶片吸水发生水分逆向运移来维持自身生长,尤其是在季节性干旱地区。但这一过程通常被忽视,使得在量化理解干旱胁迫下的森林植被水分利用过程与机制方面仍存在一定的空白。本研究以北京山区为研究区,以其典型造林树种侧柏为研究对象,利用稳定同位素和热比率技术,通过野外布设对比试验和室内控制盆栽试验,分析树木体内水分逆向运移的发生条件和规律,量化逆向运移量及补给率,研究不同部位水分逆向运移变化特征及过程。结果表明: 在野外对比试验中,控制样方在雨后的树木胸径和根系处监测到逆向液流,且根系逆向液流的发生比胸径处会有所延迟,而对比样方则无逆向液流;在室内控制试验中,不同处理组在雨后2 h树木各部位逆向运移补给率达到最高值,除重度和中度干旱处理外,雨后8 h基本恢复初始状态,水分逆向运移对植物的影响一般不超过24 h;叶片吸水量与其产生的对枝条和根际土壤的逆向补给率和土壤前期含水量呈负相关关系,对叶片、枝条和根际土壤的最大补给率分别为(9.5±0.1)%、(5.9±0.3)%和(5.7%±0.6)%;在水分逆向运移过程中,侧柏不同部位水分运移对时间的响应不同。在复杂多变的水分供给条件下,研究植物水分逆向运移的过程与机制,对准确理解其生存和竞争力具有重要意义。

Characteristics and processes of reverse sap flow of Platycladus orientalis based on stable isotope technique and heat ratio method

Plants could maintain growth by foliar water uptake and reverse sap flow under certain conditions, particularly in regions with seasonal drought. This physiological activity is often overlooked, however, leaving a gap in quantitatively understanding the processes and mechanisms underlying water utilization of forest vegetation under drought stress. In this study, with both field comparison experiments and pot experiments, we used heat ratio method with stable isotope technique to monitor a typical plantation tree species, Platycladus orientalis, in the Beijing mountainous area. We aimed to analyze the patterns and the influencing factors of the reverse sap flow occurrence in P. orientalis, to quantify the amount and the replenishment rate of reverse sap flow, and to examine the characteristics and processes of reverse sap flow at different parts of plants. In the field comparison experiment, reverse sap flow was detected at the breast height of stem and in the root in the controlled plot (drought plot) after rainfall. The reverse sap flow of root system was detected later than that in the stem. By contrast, no reverse sap flow was observed in the natural plot. In the pot experiments, the recharge rate of all the groups reached the peak value two hours after the rainfall treatment. Except for the groups of severe and moderate drought, recovery of δD to the original level was observed eight hours after rainfall, and the reverse sap flow on plants generally lasted no more than 24 h. The amount of foliar water uptake and the reverse sap flow to the branches and rhizosphere soil had a negative relationship with the initial soil moisture. The maximum recharge rates for leaves, branches, and rhizosphere soil were (9.5±0.1)%, (5.9±0.3)% and (5.7%±0.6)%, respectively. Different rates and timing of the reverse sap flow were observed at different parts of P. orientalis. Under complex and variable conditions of water supply, it is of great significance to examine the process and mechanism of reverse water movement of plants to better understand its survival and competitive strategies.