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Abstract
Introduction
Protocol
Results
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환경과학

电容式传感器监测林木茎含水量的标定及应用

Published: December 27, 2017
doi:
10.3791/57062
, ,
1Department of Geological Sciences, Jackson School of Geosciences,University of Texas at Austin, 2METER Group, Inc., USA, 3Department of Civil, Environmental and Geodetic Engineering,Ohio State University

Summary

生物量的水力容量是植被水资源预算的重要组成部分, 是抵御短期和长期干旱胁迫的缓冲。在这里, 我们提出了一个校准和使用土壤湿度电容传感器的协议来监测大树茎中的含水量。

Abstract

通过土壤-植物-大气连续体的水运输和贮存是陆地水循环的关键, 已成为主要的研究重点领域。生物量电容在避免水力损伤蒸腾过程中起着不可或缺的作用。然而, 大型树的水力电容动态变化的高时间分辨率测量是罕见的。在这里, 我们提出了校准和使用电容传感器的程序, 通常用于监测土壤含水量, 以测量田间树木的体积含水量。频域反射式观测对所研究介质的密度敏感。因此, 有必要进行 species-specific 校准, 从传感器报告的介电介电常数值转换为体积水含量。校准是对收获的分支或干切到干燥或 “的部分进行的, 以产生完整的水含量, 用于生成与传感器观测结果的最佳回归。传感器入到校准段或安装在树后前孔的公差适合使用预制模板 , 以确保正确的钻头对准。特别注意确保传感器的齿尖与周围的介质保持良好的接触, 同时使其不受外力的插入。通过所提出的方法观察的体积水含量动态与使用热耗散技术和环境强迫数据记录的 sap 流量测量相一致。生物质水含量数据可用于观察水分胁迫、干旱响应和恢复的发生, 并有可能应用于新的植物水平流体力学模型的标定和评价, 以及对遥感水分产品的地下成分。

Introduction

植物材料中储存的水分对植物处理短期和长期水分胁迫的能力起着不可或缺的作用1,2。植物在细胞内和胞外 (例如,木质部容器) 中储存水分, 其中包括2、3、4。这水被显示贡献在10和50% 之间昼夜发生了水2,5,6,7,8。因此, 植物的水力电容是陆地水量平衡的关键组成部分, 可以作为水分胁迫、干旱响应和恢复的指标1, 是纠正观测时间滞后所必需的关键因素。蒸腾和 sap 流9,10,11。植被水分实时监测也可用于农业应用, 以帮助限制果园和作物灌溉, 以提高浇水效率12,13。然而, 测量的连续,原位茎-水含量的木本物种7,14,15,16,17,18, 19相对于 sap 流量测量20是罕见的。在这里, 我们概述了校准电容传感器的程序, 以监测在树的茎内的体积水含量5,21。

水动力行为和用水调控由植被是土壤-植物-大气连续统一体的一个缺一不可的组分22,23 , 因此是重要的控制之间的水分和碳通量生物圈和大气24,25。茎含水量的动态变化受生物和非生化因素的影响。干贮水的损耗和补给受环境条件的短期和长期趋势的影响, 特别是蒸气压亏缺和土壤含水量1,26。木材的物理性质27 (如、密度、容器结构) 和紧急水力策略25 (如、iso 或 anisohydric 气孔调节) 决定了植物贮存和使用水的能力19,26,28, 并可通过种类广泛变化29,30。以往的研究显示了不同的电容在热带的作用16,27,31,32,33和温带5,7 ,21物种, 并在两个被子植物1,2,34和裸子植物6,11,17,19。

提高对生物量水含量的认识, 将有助于了解植被的水资源获取策略, 并使用1,2, 以及物种对降水制度的预测变化的脆弱性35 ,36。进一步了解植物水的使用策略将有助于预测未来气候情况下的人口变化模式37,38。通过模型数据融合技术39, 使用此方法获得的茎含水量数据可用于通知和测试可伸缩的植物级流体力学模型40,41, 42,43,44 , 以改善气孔电导率的计算, 从而模拟蒸腾和光合碳的摄取。这些先进的流体力学模型可以提供一个显著的减少不确定性和误差时, 纳入较大的地面和地球系统模型25,45,46, 47,48。

用于监测或计算干水含量的方法包括树取心33,49, 电子 dendrometers2,15,50, 电阻51, 伽玛辐射衰减52, 氘示踪器19, sap 流量传感器32,33,53, 阀杆 psychrometers49,振幅11和时间4,12,13域反射 (TDR)。最近的努力已经测试了传统上用于测量土壤容积水含量的电容传感器的可行性5,18,21,27。频域反射 (FRD) 式电容传感器是低成本的, 使用相对较少的能量进行连续测量, 使它们成为在现场场景中进行高分辨率测量的有吸引力的工具。罗斯福在 tdr 式传感器上的自动化方便了连续的 sun 每小时数据集的收集, 并消除了需要大量电缆长度13的 tdr 测量所固有的许多挑战。使用原位电容传感器消除了重复取心或分枝收获的需要, 并可提高硬木品种的精确度。木本树种, 主要从细胞外空间, 如木质部血管, 或具有高木材或树皮弹性模量的弹性, 通常不是很好的候选的流行的 dendrometer 测量技术, 由于低弹性杆扩展2. 电容传感器估计介电介电常数, 可直接转换为体积含水量。但是, 电容测量对传感器周围介质的密度很敏感。因此, 我们主张 species-specific 校准, 将传感器的输出转换为体积木水含量5,21。

我们提出了一个 species-specific 校准的协议, 将电容传感器输出转换为木材的体积含水量。还提供了成熟树中电容传感器现场安装的说明, 并讨论了该方法的优点、缺点和假设。这些技术的目的是监测树干, 最大的树蓄水水库8的容积水含量, 但可以很容易地扩展到整个树与安装额外的传感器沿分支机构。动态植物含水量的测定将促进植被流体力学、生物、地表模拟等领域的发展。

Protocol

1. 选择用于检测的树 选择要测量的树。理想情况下, 选择健康的树木, 一般圆的茎横断面, 和直径之间的1-2 倍的长度, 或边材深度大于长度的传感器 (〜5厘米的具体电容传感器在这里演示)。用树芯测量边材的深度, 或对多种树种, 通过速方程计算边材深度, 将边材面积与茎直径29,54, 用标准直径胶带测量。注意: 但是, 某些类型的电容传感器可以…

Representative Results

在本节中, 我们将介绍五种常见的东部森林树种的校准数据, 然后详细分析三宏虫个体在2016生长期的田间测量。为宏虫, 桦树, 松, 杨树 grandidentata,和栎林 (图 1) 生成了校准曲线。曲线的斜率与P. grandidentata和虫(表 1) 的差异高达 97.7%, 这表明需要执行 species-specific 校准以获得精确的VWC测量。在地面上?…

Discussion

通过电容传感器观测到的茎水含量的季节性和日变化趋势与并行 sap 流量和环境强制测量 (图 3, 图 4, 图 5) 的走势一致。当蒸腾速度超过通过木本组织的补给速率时, 当土壤水分限制了根水的可用性时, 昼夜水库的茎贮储层就枯竭了5。这内部电容提供了一个有价值的缓冲液的水力限制气孔…

Disclosures

The authors have nothing to disclose.

Acknowledgements

这项研究的经费由美国能源部科学办公室、生物和环境研究办公室、陆地生态系统科学方案奖 No. 提供。DE-SC0007041, Ameriflux 管理计划在通量核心站点协议 No. 7096915 通过劳伦斯伯克利国家实验室和国家科学基础水文科学授予1521238。在这一材料中提出的任何意见、发现、结论或建议都是作者的观点, 不一定反映供资机构的意见。

Materials

Ruggedized Soil Moisture Sensor METER Group Inc. GS-3 Capacitance sensors
1/8" drill bit Any N/A
9/64" drill bit Any N/A
Drying oven Any N/A
Chainsaw Any N/A
Electric drill Any N/A
Bucket for water bath Any N/A
Alcohol swabs Any N/A
Draw knife Any N/A
Data logger Any N/A
Silicon sealant Any N/A
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Tags

Keywords: Capacitance SensorsStem Water ContentEcohydrologyRemote SensingForest FireBranch SegmentsBaseline AnalysisData LoggingSensor ReadoutWater Content Monitoring
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Matheny, A. M., Garrity, S. R., Bohrer, G. The Calibration and Use of Capacitance Sensors to Monitor Stem Water Content in Trees. J. Vis. Exp. (130), e57062, doi:10.3791/57062 (2017).
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