Comparison of eddy covariance and chamber-based methods for measuring CO2 flux in a temperate mixed forest.

Two methods, eddy covariance and chamber-based measurements, were employed to measure the net ecosystem CO(2) exchange in a mature temperate mixed forest in 2003. The eddy covariance system was used as a reference, which was compared with the chamber-based method. Based on chamber fluxes, the ecosystem had a gross primary production of 1490 g C m(-2) year(-1), 90% of which was released as efflux back into the air via respiration of the entire ecosystem. This was comprised of about 48% from soil surface CO(2) efflux, 31% from leaf respiration and 21% from stem and branch respiration. Net ecosystem exchange (NEE), estimated from the sum of daily component fluxes, was 146 g C m(-2) year(-1). Ecosystem respiration (ER), estimated from the sum of daily ecosystem respiration, was 1240 g C m(-2) year(-1). NEE was 9.8% of actual gross primary production (GPP). The eddy covariance estimates of NEE, ER and GPP were 188, 1030 and 1220 g C m(-2) year(-1), respectively. The eddy covariance estimation of NEE was higher than that of the chamber-based estimation by 22.5%. On a daily basis, NEE of the scaled chamber measurements was in acceptable agreement with eddy covariance measurement data with R(2) values of 0.71. The discrepancy between the measurement of the two methods was greater in the non-growing season primarily due to the lack of spatial variability in the scaled chamber estimates and weak atmosphere turbulence by eddy covariance measurements. There are many uncertainties for determination of absolute values of ecosystem component flux. More detailed experiments and related theoretical studies are needed in the future.

[Effects of precipitation and interspecific competition on Quercus mongolica and pinus koraiensis seedlings growth].

Aiming at the variation of precipitation pattern caused by global warming, a field simulation experiment was conducted to study the effects of 30% increase (+W) and decrease (-W) of precipitation on the morphology, growth, and biomass partitioning of mono- and mixed cultured seedlings of Quercus mongolica and Pinus koraiensis, the two dominant tree species in temperate broad-leaved Korean pine mixed forest in Changbai Mountains. Comparing with monoculture, mixed culture increased the canopy width and main root length of Q. mongolica seedlings, but decreased the basal diameter, plant height, leaf number, and dry masses of root, stem, leaf and whole plant of P. koraiensis seedlings significantly. Treatment (-W) increased the stem/mass ratio while decreased the main root length of Q. mongolica seedlings, and decreased the main root length, leaf number, dry masses of leaf and whole plant, and leaf/mass ratio, while increased the stem/mass ratio of P. koraiensis seedlings significantly, compared with treatment CK. Treatment (+W) had no significant effect on these indices of the two species. At early growth stage, interspecific competition and precipitation pattern had significant effects on the morphology and growth of the seedlings, and the responses were much stronger for P. koraiensis than for Q. mongolica.

[Chemical constituents from leaves of Paulownia fortunei].

OBJECTIVE: To study the chemical constituents of leaves of Paulownia fortunei (Seem.) Hemsl. METHODS: The constituents were isolated by column chromatography and their structures were elucidated through spectroscopic analysis. RESULTS: The compounds were identified as mimulone (I), apigenin (II), luteolin (III), 2alpha, 3beta, 19beta-trihydroxyurs-28-O-beta-D-galactonopyranos ylester (anserinoside, IV), 3alpha-hydroxyl-ursolicacid (V), ursolicacid (VI), daucosterol (VII), beta-sitosterol (VIII). CONCLUSION: The compounds I - V are obtained from leaves of Paulownia fortunei (Seem.) Hemsl for the first time.

[Stem respiration of dominant tree species in broad-leaved Korean pine mixed forest in Changbai Mountains].

By using soil respiration chamber, the stem respiration of dominant tree species Pinus koraiensis, Quercus mongolica, Fraxinus mandshurica and Tilia amurensis in broad-leaved Korean pine mixed forest of Changbai Mountains was measured from April to October 2003. The temperature on the stem surface and in the forest was determined simultaneously. The results demonstrated that the stem respiration rate of test tree species had an obvious seasonal variation, with the maximum occurred in July and the minimum in October. The diurnal variation of the stem respiration rate was in a 'S' curve, with the minimum at 6:00 for all test tree species, and the maximum at 18:00, 20:00, 16:00, and 14:00 for P. koraiensis, Q. mongolica, F. mandshurica, and T. amuremis, respectively. The response of stem respiration to temperature differed with tree species, and the Q10 value ranged from 2.24 to 2.9, which were decreased in the order of F. mandshurica > Q. mongolica > P. koraiensis > T. amurensis.