Analytical Studies on the Process of Growth and Production of Mat Rush (Juncus decipiens Nakai) : III. Microclimatic observation of a mat rush canopy

Abstract

Microclimatic environment of a growing mat rush canopy was observed during its growth period from after the tip cutting to the harvesting to analyze the process of its long stem growth in the southern part of Okayama prefecture in 1983. The results are summerized as follows: 1. The maximum air temperatures observed within a crop canopy were 28°C at the earlier stem growth stage in its lower layer and 32.5°C at the later stem growth stage in its middle layer. Both of those temperatures were higher than air temperature above the crop canopy and too high for the efficient photosynthesis of mat rush stem. Air temperature in the lower layer of a mat rush canopy became relatively low with growth of a crop canopy and it was observed that an active layer for heat transfer was established in the middle layer within a crop canopy at the later stage of stem elongation. 2. The maximum difference in atmospheric water vapour pressure between the upper and the lower layer within a crop canopy was much as 10-12 mmHg through the long stem elongation stage in the day time but the difference was decreased gradually toward the harvest time. Relative humidity within a crop canopy was higher than 90% in its lower layer in the day time and was nearly 100% in the night time though it was very low as 50-55% in its upper layer especially at around the noon. A high air temperatur with its low humidity at the upper and the middle layer and a relatively low temperature with its high humidity in the lower layer was one of the signifficant characteristics of a mat rush canopy during the stem elongation stage to harvest. 3. CO₂ concentration profile within a crop canopy at just before the harvest time, showed a remarkable horizontal transition within a day. The minimum CO₂ concentration which was measured within a crop canopy was 300 ppm in the middle layer, just below an active layer for the heat transfer, in the day time. The maximum CO₂ concentration measured was 540 ppm in the lowest layer in the night time. It was indicated that the apparent photosynthetic ability was higher in the middle layers of a canopy though there the light intensity was lower than in its upper layers and the stem part which located in those layers was photosynthetically not so active. According to the results obtained by the microclimatic observation of a mat rush canopy, several problems which should be taken into the consideration for improving the growing process of mat rush were brought out for the future studies.