Root respiration was separated from total soil respiration in this study. Experiments were carried out in September 2003 at Yamashiro Experimental Forest located in Kyoto Prefecture. It is a secondary forest of broad-leaf trees including some conifer species. The root system was dug out and divided into several classes by size. The respiration rate of each size was measured by the closed-chamber method consisting of an IRGA, a pump, and a chamber made of acrylic. Temperature in the chamber was measured by thermo couple. The results showed that the smaller the diameter of the root was, the higher the respiration rate per unit weight was. A Mmuch higher rate was found in fine roots in comparison with other classes. From the relationships between basal diameter and root mass of each size for sample trees, root mass of each size per area was estimated. By combining the respiration rate and root mass of each size per area, root respiration could be calculated at 0.0707 mg CO2 m-2 s-1 as a total. More than the half was occupied by fine root respiration. Mean total soil respiration was 0.19 mg CO2 m-2 s-1 during this experiments. Therefore, the contribution of root respiration to soil respiration was estimated at 37.2%.
In order to estimate the amount of soil water content of orchards in a region and to improve water management, observations of transpiration and evapotranspiration were made in a Japanese pear orchard. The observations were made over a perild of 4 years, from April to October of each year, using the energy budget (EB), soil water (SW), eddy correlation (EC), and trunk energy budget (TEB) methods. The measured daily transpiration or evapotranspiration was highly proportional to Penman potential evapotranspiration (PET) for almost any month and year. When the inter-year variation was neglected, the coefficient of this proportionality for evapotranspiration (CET) in each month ranged from 0.77 to 0.85. Thus, (0.80 × PET) was proposed as the simplest estimation for daily evapotranspiration. The inter-year variation in CET was larger during the summer season. In the summer, CET was lower in the years in which less precipitation occurred, and a midday depression in the rates of transpiration and evapotranspiration was observed when pF increased. Therefore, water stress was suggested as the cause of inter-year variation in CET. When the effect of water stress was excluded, CET was lower in April, May, and October, and its seasonal variation was around 20%. Since the ratio of transpiration to evapotranspiration was lower in April and May, seasonal depression in CET was suggested to occur due to depressed transpiration that occurred as a result of a small leaf area index (LAI). Thus, finally, we proposed the estimation of daily evapotranspiration more precisely by using the formula 0.97 × f (pF) × g (LAI) × PET, in which the decreasing function f (pF) and the increasing function g (LAI) were introduced.
Long-term continuous measurements of NO2 flux, NO2 dry deposition velocity (Vd) and various microclimate factors were carried out from February to June of both 2002 and 2003 on a wheat field located in Saiwai-cho, Fuchu-shi, Tokyo, Japan. The Bowen ratio technique was used to measure NO2 flux. Average values of daytime data were used to analyze Vd and the relationship between Vd and other factors such as solar radiation. Vd average values during the daytime were in the range of 0.03-1.11 cms-1, were smaller in winter, and were larger in spring. Vd tended to increase along with wheat growth. Vd was affected primarily by leaf area index (LAI), and the relationship between Vd and each microclimate factor was different in LAI of each growing stage. With LAI less than 2, Vd was affected mainly by wind speed, and increased with an increase in wind speed. With LAI greater than 2, Vd was affected mainly by solar radiation, air temperature and vapor pressure deficit, and increased as these factors increased. In the maturing season (with LAI of approximately 5), the relationships between Vd and solar radiation, air temperature and vapor pressure deficit became stronger than during the previous growing periods. The average value of NO2 flux in the daytime during all growing periods was approximately 462 µgm-2 h-1. The amount of NO2 deposition during all growing periods was approximately 0.29 gNm-2.