Needle-age related variability in nitrogen, mobile carbohydrates, and δ13C within Pinus koraiensis tree crowns.

For both ecologists and physiologists, foliar physioecology as a function of spatially and temporally variable environmental factors such as sunlight exposure within a tree crown is important for understanding whole tree physiology and for predicting ecosystem carbon balance and productivity. Hence, we studied concentrations of nitrogen (N), non-structural carbohydrates (NSC = soluble sugars + starch), and δ(13)C in different-aged needles within Pinus koraiensis tree crowns, to understand the needle age- and crown position-related physiology, in order to test the hypothesis that concentrations of N, NSC, and δ(13)C are needle-age and crown position dependent (more light, more photosynthesis affecting N, NSC, and δ(13)C), and to develop an accurate sampling strategy. The present study indicated that the 1-yr-old needles had significantly higher concentration levels of mobile carbohydrates (both on a mass and an area basis) and N(area) (on an area basis), as well as NSC-N ratios, but significantly lower levels of N(mass) (on a mass basis) concentration and specific leaf area (SLA), compared to the current-year needles. Azimuthal (south-facing vs. north-facing crown side) effects were found to be significant on starch [both on a mass (ST(mass)) and an area basis (ST(area))], δ(13)C values, and N(area), with higher levels in needles on the S-facing crown side than the N-facing crown side. Needle N(mass) concentrations significantly decreased but needle ST(mass), ST(area), and δ(13)C values significantly increased with increasing vertical crown levels. Our results suggest that the sun-exposed crown position related to photosynthetic activity and water availability affects starch accumulation and carbon isotope discrimination. Needle age associated with physiological activity plays an important role in determining carbon and nitrogen physiology. The present study indicates that across-scale sampling needs to carefully select tissue samples with equal age from a comparable crown position.

Soil respiration in relation to photosynthesis of Quercus mongolica trees at elevated CO2.

Knowledge of soil respiration and photosynthesis under elevated CO(2) is crucial for exactly understanding and predicting the carbon balance in forest ecosystems in a rapid CO(2)-enriched world. Quercus mongolica Fischer ex Ledebour seedlings were planted in open-top chambers exposed to elevated CO(2) (EC = 500 µmol mol(-1)) and ambient CO(2) (AC = 370 µmol mol(-1)) from 2005 to 2008. Daily, seasonal and inter-annual variations in soil respiration and photosynthetic assimilation were measured during 2007 and 2008 growing seasons. EC significantly stimulated the daytime soil respiration by 24.5% (322.4 at EC vs. 259.0 mg CO(2) m(-2) hr(-1) at AC) in 2007 and 21.0% (281.2 at EC vs. 232.6 mg CO(2) m(-2) hr(-1) at AC) in 2008, and increased the daytime CO(2) assimilation by 28.8% (624.1 at EC vs. 484.6 mg CO(2) m(-2) hr(-1) at AC) across the two growing seasons. The temporal variation in soil respiration was positively correlated with the aboveground photosynthesis, soil temperature, and soil water content at both EC and AC. EC did not affect the temperature sensitivity of soil respiration. The increased daytime soil respiration at EC resulted mainly from the increased aboveground photosynthesis. The present study indicates that increases in CO(2) fixation of plants in a CO(2)-rich world will rapidly return to the atmosphere by increased soil respiration.

[Spatial heterogeneity of soil inorganic nitrogen in a broadleaved-Korean pine mixed forest in Changbai Mountains of northeast China].

Geostatistic methods were applied to study the spatial heterogeneity of top soil (0 - 10 cm) ammonium N and nitrate N in a broadleaved-Korean pine mixed forest of Changbai Mountains, Northeast China. The semi-variogram of soil ammonium N and nitrate N could be well fitted by spherical or Gaussian model. The spatial distribution of soil ammonium N and nitrate N all exhibited moderate autocorrelation, with the structural ratio being 0.70% - 41.47% and 32.26% - 52.66%, and the autocorrelation degree of soil ammonium N was smaller than that of soil nitrate N, with the variation distance being 8.87 and 9.76 m, respectively. Spatially, soil ammonium N and nitrate N were distributed in patches, and the spatial heterogeneity of soil ammonium N was higher than that of soil nitrate N. There was a significant negative correlation between soil nitrate N and soil moisture content, while soil ammonium N had less correlation with soil moisture.

[Woody plant fine root biomass and its spatial distribution in top soil of broad-leaved Korean pine forest in Changbai Mountain].

Geostatistic method was applied to study the spatial distribution of woody plant fine root biomass in a natural broad-leaved Korean pine (Pinus koraiensis) mixed forest soil in Changbai Mountain. The investigation was carried out in three selected plots, sized 50 m x 50 m, in 2008. In the three plots, the living fine root biomass in surface soil (0-20 cm) was 3.195, 1.930, and 2.085 t x hm(-2), and the dead fine root biomass was 0.971 0.581, and 0.790 t x hm(-2), respectively. In 0-10 cm soil layer, the living fine root biomass had no correlation with the dead fine root biomass; but in 10-20 cm soil layer, a significant positive correlation was found between them (r = 0.352, P < 0.05). The variograms of living fine root biomass and dead fine root biomass could be well fitted by spherical model. Spatial variation explained more than 70% of the total variance of fine root biomass across three plots. The regressed ranges were 5.2, 14. 6, and 9.8 m for living fine root biomass, and 4.3, 20.4, and 20.1 m for dead fine root biomass in plots 1, 2, and 3, respectively. For comparison, Bayesian method was also used to estimate the ranges for the fine root biomass. The results obtained by geostatistic method and Bayesian method were consistent with each other.