寒温针叶林土壤呼吸作用的时空特征

Abstract

Boreal forest is naturally situated between 45° and 70° north latitude,where temperature increases strongly. With the largest soil carbon pool in the world,boreal forest becomes an important research region concerning global climate change and carbon cycle. The variable patterns of soil respiration in both temporal and spatial scales were measured with Li-6400 portable photosynthesis system in Chinese boreal forest ecosystem( 51° 47' N,123°01' E). The results showed that the diurnal dynamics of soil respiration was one-humped curve,and the maximum occurred at 16: 00,similar to the dynamics of soil temperature at 5 cm depth. Soil respiration increased from June and peaked in August( 8.19 and 6.89 μmol CO 2 m-2s-1in 2006 and in 2007,respectively),then decreased and dropped down only 0.61 μmol CO 2 m-2s-1in October when air temperature was about 0 ℃. The diurnal and seasonal variations of soil respiration related more to soil temperature than to air temperature. To study on spatial heterogeneity of soil respiration in Chinese boreal forest ecosystem,40 circular plots( 10 cm in diameter) were set with 5 columns and 8 rows,and the interval was 2 m. The averages of variation ranges of soil respiration ranged from 4.96 μmol CO 2 m-2s-1to 5.97 μmol CO 2 m-2s-1among 40 circular plots,larger or close to the averages of diurnal dynamics ranging from 2.88 μmol CO 2 m-2s-1to 5.31 μmol CO 2 m-2s-1,and smaller than the averages of seasonal dynamics ranging from 6.48 μmol CO 2 m-2s-1to 7.38 μmol CO 2 m-2s-1. Soil respiration showed great variability among 40 circular plots,and the coefficients of variation were 35.5%,27.6% and 23. 0% on 3: 00 am,7: 00 am and 11: 00 am,respectively. When soil respiration of the close plots was averaged,their coefficients of variation decreased with the repeated plots increasing. The coefficients of variation with 3 repeats were 27. 0%,16.8% and 13.0% on 3: 00 am,7: 00 am and 11: 00 am,respectively. The coefficients of variation with 6 repeats were 22.8%,11.1% and 11.8% on 3: 00 am, 7: 00 am and 11: 00 am,respectively,close to the smallest coefficients of variation with 7—10 repeats. Therefore,soil respiration should be measured with 6 repeats of circular plots( 10 cm in diameter) in this research region. Similar spatial heterogeneities were found on root and litter biomass among 40 circular plots,the coefficients of variation from large to small were 103.8% of coarse root,60.3% of total root,47.1% of litter and 32.1% of fine root. The spatial correlation of soil respiration was best with the fine root( R2= 0. 322—0. 396),indicating that the spatial heterogeneity of soil respiration could be mainly induced with fine root.