Biophysical controls on nocturnal sap flow in plantation forests in a semi-arid region of northern China
Biophysical controls on nocturnal sap flow in plantation forests in a semi-arid region of northern China
复制标题
中国北方半干旱地区人工林夜间液流的生物物理控制
DOI：
10.1016/j.agrformet.2020.107904
复制
发表时间：
2020-04-15
影响因子：
6.2
通讯作者：
Chen, Shengnan
中科院分区：
文献类型：
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作者：
Chen, Zuosinan;Zhang, Zhiqiang;Chen, Shengnan
最近的研究已经认识到夜间树干液流（Q（n））在影响森林碳和水收支以及在林分、区域和全球尺度上对气候变化的响应方面的重要性。然而，Q（n）的生物物理控制还没有完全理解，其对陆面和植被模型的影响尚不清楚。在中国北方半干旱山区，对油松（Pinus tabuliformis）和元宝枫（Acer truncatum）两种造林树种分别在中、幼龄林下进行了生长季液流测定。结果表明，两树种间的Q（n）以及Q（n）占树干液流总量的比例（12.2-15.0%）在树种间和年龄间存在一定的趋同性。总生长季Q（n）是较高的中年林分比年轻的林分，因为较大的直径在胸高的老林分。夜间水汽压亏缺（VPDn）对幼林Q（n）的影响与土壤水分有关。夜间风速通过提高幼龄林的VPDn间接控制Q（n），而在中龄林和低密度林则直接提高Q（n）。对于每一个物种，增加和减少土壤含水量都能够提高Q（n）在相对干燥的土壤，这可能是由于增强夜间补水容量再填充和避免水力破坏下长时间的水分胁迫。这三个环境因子的总效应解释的Q（n）的变化不到55%。这项研究突出了不确定的生理影响VPDn夜间气孔失水，夜间水分损失引起的风，区域特定的模式夜间水补给，以及生物控制Q（n）的重要性。我们的研究结果有助于改善现有的VPD为基础的方法划分夜间蒸腾和水补给在树和林分水平，并建议将夜间液流到大规模的模型的重要性。
Recent studies have recognized the importance of nocturnal sap flow (Q(n)) in affecting forest carbon and water budgets and responses to climate change at stand, regional, and global scales. However, biophysical controls on Q(n) are not fully understood, and their implications for land surface and vegetation models are unclear. We measured growing season sap flow of two widely distributed afforestation species, Pinus tabuliformis and Acer truncatum, in a middle-aged and a young monoculture forest stand, respectively, in a semi-arid mountainous area of northern China. We found a convergence in Q(n) between the two species and in the proportion of Q(n) to the total sap flow (12.2-15.0%) across species and ages. Total growing season Q(n) was higher for middle-aged stands than for young stands because of larger diameters at breast height of older stands. Nighttime vapor pressure deficit (VPDn) influence on Q(n) of young stands was soil moisture dependent. Nighttime wind speed indirectly controlled Q(n) through enhancing VPDn in young stands and directly promoted Q(n) in middle-aged stands with relatively low tree densities. For each species, both increased and decreased soil water content were able to promote Q(n) in stands with relatively dry soils, which might be due to enhanced nighttime water recharge for capacitance refilling and for avoiding hydraulic failure under prolonged water stress, respectively. Total effects of these three environmental factors explained less than 55% of the Q(n) variations. This study highlights uncertain physiological influences of VPDn on nighttime stomatal water loss, the nighttime water loss induced by wind, region-specific patterns of nighttime water recharge, and the importance of biotic controls on Q(n). Our findings help to improve the existing VPD-based method for partitioning nighttime transpiration and water recharge at tree and stand levels, and suggest the importance of incorporating nocturnal sap flow into large-scale models.