Distribution characteristics of resistance to water flow in the SPAC.

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  • SPAC内の水流に対する抵抗の分布特性
  • SPACナイ ノ スイリュウ ニ タイスル テイコウ ノ ブンプ トクセイ

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Abstract

To simulate the movement of water and to understand its working mechanism in the soilplant-atmosphere continuum (SPAC), studies on the distribution characteristics of resistance to water flow in the SPAC are important. The present paper discusses the spatial distribution and variability of resistance to water flow in the SPAC based on field experiments on maize and soybean at Shenyang, China, and Matsudo, Japan. Under the experimental conditions employed, the total conductive resistance to water flow from root xylem to leaf xylem (RRL) in maize and soybean plants was 85.6〜93.5% of the total resistance to water flow from soil to leaf xylem (RSL), and the total absorptive resistance for the root system (RSR) was 6.5〜14.4% of RSL. In addition, soil resistance, soil-root contact resistance, root absorptive resistance, and xylem resistance for root and stalk were 2.7〜5.0%, 0.9〜1.1%, 2.6〜8.4% and 10.1〜73.6%, and 20.0〜75.5% of RSL, respectively. Meanwhile, the rates of bulk boundary resistance (RAV) and bulk stomatal resistance (RST) for the canopy relative to the total transpiration resistance (RLA) were 51.5% and 48.5%, respectively. Aerodynamic resistance to momentum transfer, excess resistance to water vapor exchange, and leaf boundary resistance were 15.6%, 9.2%, 23.6% of RLA, respectively. Therefore, the total resistance in stomata and boundary of the leaf was about 75% of RLA. The leaf stomatal resistance shows different patterns of diurnal variation in various environmental regimes, and a significant seasonal variation in the growth period. The stomatal resistance increased along with drying of the soil, and its value for the adaxial surface was larger than that for the abaxial surface. The ratio between the two surfaces varied under different environmental conditions.

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