Takeharu Itou

Stem productivity in relation to nitrogen concentration and carbon isotopic composition (δ13C) in leaves of hinoki cypress (Chamaecyparis obtusa Endlicher) plantations in Shikoku district, Japan

The stem productivity of the hinoki cypress (Chamaecyparis obtusa Endlicher) in relation to plant nitrogen status and water-use efficiency was investigated in the Okuono (OKU) and Karakawa (KRK) areas in Shikoku district, Japan, where abundant precipitation occurs. The nitrogen concentration and carbon isotopic composition (δ13C) in the leaves were used as indexes of plant nitrogen status and water-use efficiency, respectively. The leaf nitrogen concentration increased with decreasing soil carbon/nitrogen (C/N) ratio and with increasing soil pH. There was a marginally significant negative correlation between leaf δ13C and soil water content in the KRK area, but leaf δ13C in the OKU area did not correlate with the soil water condition, and increased on the upper slope. The results suggest that hinoki trees in the KRK area have higher water-use efficiency (high leaf δ13C) under lower soil water conditions. In the OKU area, meanwhile, leaf δ13C in the upper slope was higher due to adaptation to adverse conditions. When 12 plots in two areas were included, the mean height and stem increments increased with increasing leaf nitrogen concentration and with decreasing leaf δ13C. These findings suggest that nitrogen acquisition is a primary factor for stem productivity in the areas concerned but the productivity of some forests is restricted by the soil water condition or other conditions, as indicated by the high value of leaf δ13C. The measurement of nitrogen concentration and δ13C in leaves can provide us with valuable insights into the relative importance of nitrogen, water and other conditions on stem productivity in the two areas.

Direct isolation of fungal hyphae degrading 2,4,5,6-tetrachloroisophthalonitrile from soil.

Abstract Fungal hyphae degrading 2,4,5,6-tetrachloroisophthalonitrile (chlorothalonil) were isolated directly from soil by the soil washing method. Based on the morphological characteristics, 53% of the isolates were classified into Fusarium spp. The application of the dilution plate method revealed that Penicillium spp. accounted for 50% of the isolates. These results suggested that Fusarium spp. were active as hyphae in chlorothalonil degradation in soil unlike Penicillium spp.