Abstract:

Xishuangbanna is the most northerly situated tropical rain forest in the world and, as a result, 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 content. Soil respiration rates of the tropical seasonal rain forest and rubber plantation 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, September 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 2.80 kg CO₂·m^-2·a^-1, respectively. The Q₁₀ values of the tropical seasonal rain forest and rubber plantation were 2.16 and 2.18, respectively. The Q₁₀ value of the tropical seasonal rain forest measured by the alkaline absorption method in our study was slightly higher than values measured using the static opaque 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.

Key words: Xishuangbanna, Tropical seasonal rain forest, Rubber (Hevea brasiliensis) plantation, Soil respiration, Q₁₀