We investigated temperature and growth-rate dependency of skeletal oxygen and carbon isotopes in primary polyps of Acropora digitifera (Scleractinia: Acroporidae) by culturing them at 20, 23, 27, or 31 C. Calcification was most rapid at 27 and 31 C. We obtained a d
18O-temperature relationship (20.18& C 21 ) consistent with reported ranges for Porites, indicating that juvenile Acropora polyps can be used for temperature reconstruction. A growth-rate dependency of skeletal isotopes was detected in the experimental polyps cultured at lower water temperatures, when the skeletal growth rate of these polyps was also low. The estimated upper calcification flux limit for a kinetic isotope effect to be observed in the d
18O-growth rate relationship (0.4-0.7 g CaCO 3 cm 22 yr
21) was similar to the calcification flux in Porites corresponding to a linear extension rate of 5 mm yr 21 , the maximum rate at which the kinetic isotope effect is evident. This result suggests that the calcification flux can be used as a measure of growth rate-related isotope fractionation, that is, the kinetic isotope effect, in corals of different genera and at different growth stages.
Effects of application time in spring on nitrogen absorption by satsuma mandarin (Citrus unshiu Marc. cv. 'Nankan No. 20') were investigated. Field and pot tests were performed using an 15 N-tracer method in which the nitrogen was applied on March
A 15 N-tracer method was used to study the absorption of nitrogen applied in the spring to Satsuma mandarin trees and Rat'stail fescue, Vulpia myuros, in a mandarin orange orchard covered with Rat's-tail fescue. The amount of nitrogen applied in the spring that was absorbed by mandarin orange trees in a plot covered with Rat's-tail fescue was markedly smaller, about 47%, than that in a clean cultivated plot; the difference was particularly large in new leaves. The amount of nitrogen absorbed by Rat's-tail fescue in a sod culture plot was about twice as large as that absorbed by the trees in the plot. Trees in the clean cultivated plot showed higher rates of 15 N occupied by supplied nitrogen in all organs than trees in the sod culture plot did; the difference was particularly large in newly developed organs. However, Rat's-tail fescue in the sod culture plot showed a markedly higher rate of 15 N occupied by supplied nitrogen than the trees showed. A comparison of the utilization rates of nitrogen applied in the spring to trees in two different plots demonstrated that the rate was 16.7% in the sod culture plot and 35.3% in the clean cultivated plot; the rate was markedly higher in the clean cultivated plot. However, the utilization rate including an absorbed amount by Rat's-tail fescue was 51.6% in the sod culture plot, which was about 1.5 times as high as that in the clean cultivated plot.
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