根箱を用いた2次元的根系成長と土壌水分の観察

Abstract

植物根系による土壌水分吸収や, 根系成長に対する土壌水分分布の影響など, 根系構造と土壌水分の関係についての研究が盛んに行われている.しかし, 植物根系の調査には多大な労力と時間を必要とし, その研究には常に困難が伴う.根箱は根系の2次元的な構造を観察するのに有効な手法として開発され, 多くの根系調査・研究に用いられている.一方, TDRは土壌含水率を非破壊的に, しかも短時間で測定する手法として確立されており, 根箱内の土壌水分挙動の連続測定に適している.そこで, 根箱とTDRを組み合わせ, 2次元的な根系成長と土壌含水率分布の変化を高解像度でかつ連続的に観察・測定する手法の開発を目的として, 実験を行った.本実験では, コイル型TDRプローブを採用し, 根箱に高密度で設置する事を可能とした.実験の結果, 水分供給位置に影響を受け成長する根系の詳細な形状, 根系の土壌水分吸収による含水率分布の経時変化を高解像度かつ連続的に得る事ができ, 本実験に用いたシステムが有効である事が確認された.また, コイル型プローブによる土壌含水率測定の有効性は, 理論的検証からも確認された.

Interactions between plant root systems and soil water, i.e. the soil water uptake by plant root system or the effects of soil water distributions on plant root system development, are now under the active investigations. However, observations of plant root systems under the ground take a lot of labors and time, and are very difficult works. Root boxes are used as a tool useful for the observations of 2-dimensional root system architectures in many experimental studies. On the other hand, TDR (time domain reflectometry) has been an established means for measuring the soil water content without destructing the soil domain during the investigation, and is suitable for continuous measurement of soil water distribution in the root boxes. Main aim of the experiment is to establish the new method for the continuous observation and measurement of both 2-dimensional root system development and soil water distribution with a high resolution, combining the root boxes and the TDR. In this experiment, using the coil-type TDR probes made it possible to install them highly densely in the root boxes. The detailed root system architectures that are affected by the soil water distributions and the temporal changes in soil water distributions that are caused by the water uptake by the root systems could be obtained continuously with a high resolution from the experiment results, and it was verified experimentally that the system for use in this experiment works well and also theoretically that the coil-type TDR probes are useful for the measurement of soil water distribution.