密度调控对长白落叶松人工林土壤呼吸的影响

为探明密度调控对北温带森林土壤呼吸的影响机制，以长白落叶松人工林为研究对象，选择4种林分密度P₁(300~350株/hm2)、P₂(500~550株/hm2)、P₃(600~650株/hm2)和P₄(850~900株/hm2)，使用LI-6400便携式土壤呼吸测定仪对其生长季(5—10月)土壤呼吸速率进行测定。结果表明:不同密度林分生长季土壤呼吸速率均呈现明显的季节动态，最高值均出现在8月末，最低值出现在10月中旬；不同密度林分生长季土壤呼吸速率及土壤累积CO₂排放量均随林分密度增大而显著降低(P＜0.05)。不同密度林分土壤呼吸与土壤温度之间均呈极显著的指数相关(P＜0.001)，但与土壤含水量之间相关关系不显著(P＞0.05)；双因素模型拟合效果更优，土壤温度和含水量共同解释了土壤呼吸速率的73.1%~81.0%。土壤呼吸温度敏感系数Q₁₀值表现为:在300~350株/hm2时最低(2.41)，500~550株/hm2最高(3.32)。生物因子随着林分密度的增大而显著增大(P＜0.05)，非生物因子均随林分密度增大而显著减小(P＜0.05)；生长季土壤累积CO₂排放量与生物因子达到极显著负相关(P＜0.001)，与非生物因子均达到极显著正相关(P＜0.001)。逐步线性回归分析表明，生长季凋落物量、土壤有机碳、微生物生物量碳含量和土壤全氮含量与土壤呼吸的关系最为密切。综上所述，不同密度林分之间土壤温度及含水量、生物及非生物因子的差异是导致土壤CO₂排放产生差异的主要原因。在森林经营管理中，为减小森林土壤CO₂的排放量，应将林分密度设置为850~900株/hm2。 

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.