西双版纳热带季节雨林与橡胶林土壤呼吸

 季节雨林和橡胶（Hevea brasiliensis）林是西双版纳热带森林生态系统中原始林和大面积种植人工林的两种代表类型。热带季节雨林层次结构复杂，多样性丰富，而橡胶林结构简单，乔木层只有橡胶树1种。应用碱吸收法，研究了这两种植被类型土壤呼吸速率 、地下5 cm土壤温度、气温和土壤含水率的季节变化规律，以及土壤呼吸速率与地下5 cm土 壤温度、气温和土壤含水率的关系。结果表明：1）季节雨林和橡胶林土壤呼吸速率、土壤温度、气温和土壤含水率都有明显的季节变化，而且两种林型的变化趋势基本一致；2 ）季节雨林和橡胶林土壤呼吸速率与地下5 cm土壤温度和气温之间具有显著的指数相关关系 ，显著水平达1%，与地下5 cm温度的相关性（r2分别为0.87和0.82）明显高于与气温 的相关性（r2分别是0.80和0.72）；3）季节雨林和橡胶林土壤呼吸速率与土壤含水率具有显著的线性相关（r2分别是0.73和0.63），显著水平达1%；4）橡胶林的土壤呼吸速率明显高于季节雨林，这与两种林型的结构有关；5）季节雨林和橡胶林土壤呼吸的Q10分别为2.16和2.18，比文献报道的热带土壤的Q10（1.96）稍高 。

SOIL RESPIRATION IN A TROPICAL SEASONAL RAIN FOREST AND RUBBER PLANTATION IN XISHUANGBANNA, YUNNAN, SW CHINA

Xishuangbanna is the most northerly situated tropical rain forest in the world and, as aresult, has remarkable seasonal climate variations, which is different from tropical rain forests in other regions. In Xishuangbanna, the canopy of rubber plantations, Hevea brasiliensis, often form a single layer structure that is different from the multi_layer canopy of tropical seasonal rain forests. The objectives of this study were as the following: 1) to compare the soil respiration characteristics of a rubber plantation and a natural tropical seasonal rainforest using the alkaline absorption technique; 2) to measure seasonal changes in air temperature, soil temperature at 5 cm depth, soil water content and soil respiration rates in two communities; and 3) to evaluate the relationships between soil respiration rates and soil temperature, air temperature, and soil water content. Measurements of soil respiration rates were carried out for one year in a tropical seasonal rain forest in a Nature Reserve (21°57′ N, 101°12′ E) and a rubber plantation (21°56′ N, 101°15′ E). The two sites are about 5 km away near the Xishuangbanna Tropical Botanical Garden in Xishuangbanna, Yunnan. The results showed that there was remarkable seasonal changes in the soil respiration rates in both the tropical seasonal rain forest and rubber plantation with changes in soil temperature at 5 cm depth, air temperature and soil water conte nt. Soil respiration rates of the tropical seasonal rain forest and rubber plant ation were greatest in October (9.24 and 11.06 kg CO2?m-2?d-1, respectively), and lowest in February (4.71 and 5.13 kg CO2?m-2 ?d-1, respectively). Soil respiration rates in May, June, July, August, Septemb er and October were higher than those in November, December, January, February, March and April. Soil respiration rates in the rubber plantation were significantly higher than that of the tropical seasonal rain forest (p<0.01). There was a significant correlation between soil respiration rates and soil temperature at 5 cm depth, air temperature, and the correlation between soil respiration rate and soil temperature (r2= 0.87 and r2=0.82, respectively) was higher than that between soil respiration rate and air temperature (r2=0.80 and r2= 0.72, respectively) (p<0.01) for the forest and plantation. There was a significant (p <0.01) correlation between soil respiration rates and soil water content in the forest and plantation (r2= 0.73 and r2= 0.63, respectively). The annual CO2 efflux from the tropical seasonal rain forest and rubber plantation were 2.64 and 2.8 0kg CO2?m-2?a-1, respectively. The Q10 values of the tr opical s easonal rain forest and rubber plantation were 2.16 and 2.18, respectively. The Q10 value of the tropical seasonal rain forest measured by the alkalin e absorpti on method in our study was slightly higher than values measured using the staticopaque chamber and gas chromatography techniques. The Q10 values of the seasonal tropical rain forest and rubber plantation in Xishuangbanna are higher than those reported in other tropical regions.