不同林龄白桦天然次生林土壤碳通量和有机碳储量

Soil organic carbon stocks and fluxes in different age stands of secondary Betula platyphylla in Xiaoxing'an Mountain,China

白桦天然次生林是中国东北地区地带性顶极植被类型——阔叶红松林遭到严重干扰破坏后恢复形成的主要天然次生林类型,测定了生长季内不同林龄白桦天然次生林(20、36、82a)的土壤呼吸速率及土壤碳含量。结果表明:土壤呼吸速率的季节变化呈单峰曲线,主要受土壤温度的驱动,土壤10cm处温度可以解释不同林龄白桦林之间土壤呼吸速率86%—92%的变异,土壤呼吸与土壤含水量关系不显著(P>0.05)。随着林龄的增加,生长季内土壤表面CO2通量呈增加的趋势,依次分别为740(20a)、768(36a)和809(82a)g C m-2a-1。土壤呼吸的温度敏感性指数Q10亦随林龄的增加呈上升的趋势,依次分别为2.64、2.91和3.35。平均土壤有机碳含量(0—50cm土壤层)和碳密度均随林龄的增加而增加,随土壤深度的增加而减少;其中,随着林龄的增加土壤有机碳含量依次分别为43.75、47.72和55.96 g/kg,有机碳密度为14.7、18.1和18.7 kg/m2。不同林龄间土壤表面CO2年通量与土壤有机碳密度之间存在显著的正相关关系(P<0.01),但其相关程度因土层而异,其中与0—10cm土层的有机碳密度相关最为密切(R2=0.908)。

Soil respiration,known as the second largest componentof carbon dioxide flux between terrestrial ecosystems and the atmosphere,is sensitive to climate,vegetation type as well as forest age. In order to simulate the long-term forest carbon dynamics and its impact on climate system,we need to understand the successional status of carbon dynamics more than learn the responses of forest ecosystems to the changing climate. However,in spite of its significant role in determining the distribution of carbon pools and fluxes in different forest ecosystems,the effect of age on forest carbon fluxes great is uncertain. Soil temperature and soil water content are recognized as the main factors controlling the temporal variation of soil respiration. In this paper,soil carbon dynamic was measured in different age stands of Secondary Betula platyphylla（ 20 a,36a,82a） in Xiaoxing＇an Mountain,China. Soil respiration measurements were conducted using a LI-6400-09 soil CO2 flux system from May to October in 2008. Besides,We measured soil organic carbon content（ g / kg） and bulk density（ g / cm3）at four layers across the chronosequence in August 2009. Our specific objectives were to：（ 1） compare the cumulative soil respiration during the growing season for the different age stands of Secondary Betula platyphylla,（ 2） quantify soil organic carbon（ SOC） contents and SOC density and（ 3） establish quantitative relationships between soil carbon fluxes and SOC density for the three forest ecosystems. Our results showed that the seasonality of soil respiration was driven mainly by soiltemperature with the peak appeared in August,and was roughly consistent with that of soil temperature. Soil temperature at10 cm could explain 86% —92% of the variation of soil respiration for the 3 different age stands of Secondary Betula platyphylla. And the soil volumetric water content was not significantly correlated with soil respiration rate and it was not a key factor to soil respiration. We fitted site-based models and used continuous measurements of soil temperature to estimate cumulative soil respiration for the growing season of 2008（ days 132—295）. Cumulative soil respiration in the growing season was estimated to be 740、768 and 809 C m- 2a-1in the 20 a,36a and 82 a Betula platyphylla,respectively. Both,cumulative soil respiration and Q10 increased during stand establishment. Q10 was estimated to be 2.64,2.91 and 3.35 in the20 a,36a and 82 a Betula platyphylla,respectively. Both,total soil organic carbon（ SOC） contents and SOC density at 0—50 cm increased during stand establishment,but decreased with soil depth. SOC was estimated to be 43. 75,47. 72 and55. 96 g / kg for the three forest ecosystems. Meanwhile,the figures were 14.7,18.1 and 18.7 kg / m2 for SOC density in the20 a,36a and 82 a Betula platyphylla,respectively. Soil surface carbon flux was positively correlated to SOC content（ P 0. 01）,and the significance level of the correlation depended on soil depth,and the soil carbon flux was more positively correlated to SOC concentration at the depth of 0—10 cm（ R2= 0.908）.