Lion R Martius, Maurizio Mencuccini, Paulo R L Bittencourt, Moisés Moraes Alves, Oliver Binks, Pablo Sanchez-Martinez, Antonio C L da Costa, Patrick Meir
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引用次数: 0
Abstract
Forest ecosystems face increasing drought exposure due to climate change, necessitating accurate measurements of vegetation water content to assess drought stress and tree mortality risks. Although Frequency Domain Reflectometry offers a viable method for monitoring stem water content by measuring dielectric permittivity, challenges arise from uncertainties in sensor calibration linked to wood properties and species variability, impeding its wider usage. We sampled tropical forest trees and palms in eastern Amazônia to evaluate how sensor output differences are controlled by wood density, temperature and taxonomic identity. Three individuals per species were felled and cut into segments within a diverse dataset comprising five dicotyledonous tree and three monocotyledonous palm species on a wide range of wood densities. Water content was estimated gravimetrically for each segment using a temporally explicit wet-up/dry-down approach and the relationship with the dielectric permittivity was examined. Woody tissue density had no significant impact on the calibration, but species identity and temperature significantly affected sensor readings. The temperature artefact was quantitatively important at large temperature differences, which may have led to significant bias of daily and seasonal water content dynamics in previous studies. We established the first tropical tree and palm calibration equation which performed well for estimating water content. Notably, we demonstrated that the sensitivity remained consistent across species, enabling the creation of a simplified one-slope calibration for accurate, species-independent measurements of relative water content. Our one-slope calibration serves as a general, species-independent standard calibration for assessing relative water content in woody tissue, offering a valuable tool for quantifying drought responses and stress in trees and forest ecosystems.
由于气候变化,森林生态系统面临的干旱风险越来越大,因此需要对植被含水量进行精确测量,以评估干旱压力和树木死亡风险。虽然频域反射测量法通过测量介电常数为监测茎干含水量提供了一种可行的方法,但由于传感器校准的不确定性与木材特性和物种变异有关,从而阻碍了其广泛应用。我们对阿马佐尼亚东部的热带林木和棕榈树进行了采样,以评估木材密度、温度和分类特征如何控制传感器输出差异。在一个多样化的数据集中,每个物种有三个个体被砍伐并切成小段(总数 n = 262),其中包括五个双子叶树种和三个单子叶棕榈树种,木材密度范围很广。采用时间明确的湿升/干降方法,以重力法估算了每个木段的含水率,并研究了其与介电常数的关系。木质组织密度对校准没有明显影响,但物种特征和温度对传感器读数有明显影响。在温差较大的情况下,温度误差在数量上非常重要,这可能导致以往研究中的日含水量和季节含水量动态出现重大偏差。我们建立了第一个热带树木和棕榈校准方程,该方程在估算含水量方面表现良好。值得注意的是,我们证明了该灵敏度在不同物种之间保持一致,从而建立了一个简化的单坡校准,用于精确测量与物种无关的相对含水量。我们的单斜校准法可作为评估木质组织相对含水量的通用且不受物种影响的标准校准法,为量化树木和森林生态系统的干旱响应和压力提供了宝贵的工具。
期刊介绍:
Tree Physiology promotes research in a framework of hierarchically organized systems, measuring insight by the ability to link adjacent layers: thus, investigated tree physiology phenomenon should seek mechanistic explanation in finer-scale phenomena as well as seek significance in larger scale phenomena (Passioura 1979). A phenomenon not linked downscale is merely descriptive; an observation not linked upscale, might be trivial. Physiologists often refer qualitatively to processes at finer or coarser scale than the scale of their observation, and studies formally directed at three, or even two adjacent scales are rare. To emphasize the importance of relating mechanisms to coarser scale function, Tree Physiology will highlight papers doing so particularly well as feature papers.