Changes in spatial variations of sap flow in Korean pine trees due to environmental factors and their effects on estimates of stand transpiration

It is difficult to scale up measurements of the sap flux density(J_S) for the characterization of tree or stand transpiration(E) due to spatial variations in J_S and their temporal changes.To assess spatial variations in the sap flux density of Korean pine(Pinus koraiensis) and their effects on E estimates,we measured the J_S using Granier-type sensors.Within trees,the J_S decreased exponentially with the radial depth,and the J_S of the east aspects were higher than those of the west aspects.Among trees,there was a positive relationship between J_S and the tree diameter at breast height,and this positive relationship became stronger as the transpiration demand increased.The spatial variations that caused large errors in E estimates(i.e.,up to 110.8 % when radial variation was ignored) had varied systematically with environmental factors systematic characteristics in relation to environmental factors.However,changes in these variations did not generate substantial errors in the E estimates.For our study periods,the differences in the daily E(E_D) calculated by ignoring radial,azimuthal and tree-to-tree variations and the measured E_D were fairly constant,especially when the daily vapor pressure deficit(D_D)was higher than 0.6 k Pa.These results imply that the effect of spatial variations changes on sap flow can be a minor source of error compared with spatial variations(radial,azimuthal and tree-to-tree variations) when considering E estimates.

Temperature and moisture sensitivities of CO_(2) efflux from lowland and alpine meadow soils

Aims This study was conducted to(i)determine if soil CO_(2) efflux is more sensitive to temperature changes in alpine areas than in lowland grasslands,(ii)examine the effects of temperature and moisture on soil respiration,and(iii)evaluate the potential for change in soil carbon storage in response to global warming in different grasslands in East Asia.Methods We collected soil samples from two different temperate grasslands,an alpine meadow on the Qinghai-Tibetan plateau,China,and a lowland grassland in Tsukuba,Japan.The CO_(2) emission rate was then measured for these soil samples after they were incubated at 25℃ and 60%of the water holding capacity for 7 days.Important Findings(i)The soil respiration rate was more sensitive to temperature change in the alpine soil than in the lowland soil.The average Q_(10) was 7.6 for the alpine meadow soil but only 5.9 for the lowland soil.The increased sensitivity appears to be due,at least in part,to the soil organic carbon content and/or soil carbon to nitrogen ratio,especially in the surface layer.(ii)The relationship between the CO_(2) emission rate and the soil moisture content revealed that the alpine meadow had a more clear response than the lowland soil.(iii)This study suggests that changes in soil moisture and soil temperature may have larger impacts on soil CO_(2) efflux in the alpine meadow than in the lowland grassland evaluated here.