Effects of density control on soil respiration in Larix olgensis plantation.

In order to investigate the mechanism of density control on soil respiration in a north temperate forest, the soil respiration rate was measured using LI-6400 during the growing season in Larix olgensis plantations with different stand densities of P₁(300-350 plants/ha), P₂(500-550 plants/ha), P₃(600- 650 plants/ha)and P₄(850-900 plants/ha). The results showed that soil respiration rate showed seasonal pattern, with the highest value in late August and the lowest in the middle of October. Soil respiration rate and cumulative soil CO₂-C efflux decreased significantly in different forest stands with the increase of stand density (P < 0.05). There was a significant exponential correlation between soil respiration and soil temperature, but it was not significant with soil respiration and soil water content. The two-factor model fitted better, 73.1%-81.0% soil respiration rate was explained by soil temperature and soil water content; Q₁₀, the soil respiration temperature sensitivity coefficient was expressed as 300-350 plants/ha at the lowest (2.41)and 500-550 plants/ha at the highest (3.32). The biotic factor significantly increased with the increase of stand density(P < 0.05), and the abiotic factors decreased with the increase of stand density (P < 0.05). There was an extremely significant positive correlation between soil CO₂-C efflux and abiotic factors (P < 0.001), and soil CO₂-C efflux was correlated with biological factors extremely negatively (P < 0.001) during the growing season. Stepwise linear regression analysis showed that litter biomass in growing season, soil organic carbon, microbial biomass carbon content and soil total nitrogen content were most closely related to soil respiration. The results showed that the difference between soil temperature, water content and biotic factor, abiotic factors with different density stand was the primary reason causing the difference of soil CO₂-C efflux. In the forest management, the density of stands should be set at 850-900 plants/ha to reduce soil CO₂ emissions.