帽儿山不同年龄森林土壤呼吸速率的影响因子

为探明东北温带森林恢复过程中土壤呼吸(R_S)的变化趋势及其影响因子,在帽儿山选取皆伐后天然更新恢复的4个年龄(1a、10a、25a和56a)林分进行了1年的野外原位测定。结果表明:(1)皆伐后天然更新恢复1年、10年、25年和56年林分的年R_S通量差异显著(P0.05),分别为686.5、639.7、733.3、762.3g C m~(-2)a~(-1);其中生长季(5月─10月)和非生长季的R_S通量也存在显著差异,均呈现出随林龄增加先减后增的趋势。全年、生长季和非生长季R_S随林龄变化的变异系数分别为7.6%、6.3%和21.1%,表明非生长季R_S通量的变异性加大了全年R_S通量的差异。(2)4个年龄林分的Rs季节变化趋势相似,且其主控因子均随季节而变:6月─8月Rs与土壤含水率呈二次函数关系(R~2波动在56%─79%之间),其余时段则与土壤温度呈指数函数关系(R~2波动在85%─93%之间)。(3)不同年龄林分生长季R_S与0─20cm土层有机碳(SOC)密度呈正相关关系(R~2=0.434,P0.05),而非生长季R_S与同期土壤5cm温度呈正相关关系(R~2=0.959,P0.01)。本研究区森林皆伐导致R_S降低,随皆伐后森林恢复R_S不断增加,其主导驱动因子是SOC密度的增加和非生长季土壤温度的变化。

Factors affecting soil respiration in stands of different ages in the Maoershan region, Northeast China

Soil respiration (R_S) is the major source of CO₂ efflux to the atmosphere from forest ecosystems. It plays an important role in the carbon balance of the ecosystems. The temperate forests in Northeast China are a mosaic of different aged stands resulting from various logging disturbances. The objective of the present study was to examine variations in R_S and its driving factors as the forests recovered from clear cutting with a chronosequence approach. The chronosequence that included stands of four ages (i.e., 1, 10, 25, and 56 years since logging) was established in 2014 in the Maoershan region, Northeast China (45°24'' N, 127°40'' E). The R_S was measured with a LI-840 CO₂ /H₂O analyzer from April 2014 to March 2015; and the soil temperature and water content at a depth of 5cm were measured simultaneously. Soil organic carbon (SOC) and fine root (diameter < 0.5mm) biomass were also measured at the end of the growing season. The results showed that:(1) the annual R_S differed significantly among the stands (P<0.05), and averaged 686.5, 639.7, 733.3, and 762.3g C m^-2·a^-1 for the 1-, 10-, 25-, and 56-year old stands, respectively. The R_S in the growing and non-growing seasons differed significantly among the stands. It showed a decreasing trend immediately after the clear cutting, and subsequently increased with increasing the stand age. The coefficients of variation in R_S among the stands were 7.6%, 6.3%, and 21.1% for the whole year, growing season, and non-growing season, respectively, suggesting that the variability in the R_S among stands in the non-growing season amplified the variation in the annual R_S. (2) The R_S of all the stands followed a similar seasonal trend, but the controlling factors varied with seasons. The R_S between June and August was significantly related with soil water content in a polynomial function (R²=56%-79%), whereas the R_S during the rest months was significantly related with soil temperature in an exponential function (R²=85%-93%). (3) The R_S in the growing season was correlated positively with SOC content at a depth of 0-20cm in all the stands (R² =0.434, P<0.05), whereas that in the non-growing season was correlated positively with soil temperature at a depth of 5cm in the same season (R² =0.959, P<0.01). These results suggest that the R_S in these forests decrease after logging disturbance and increase with increasing the stand age, driven mainly by the increased SOC content and changes in soil temperature during the non-growing season.