贡嘎山峨眉冷杉树干呼吸空间特征及其对温度的响应

Spatial variations in the stem CO_2 efflux rate of Abies fabri and the response to temperature in the Gongga Mountains

采用红外线气体分析仪-土壤呼吸气室水平测定法(HOSC)原位监测了贡嘎山东坡峨眉冷杉(Abies fabri)树干CO_2释放速率(E_s),分析了树干E_s与树干温度(T_(stem))的关系。贡嘎山峨眉冷杉树干E_s和T_(stem)空间变化格局明显,不同测定高度树干温度为0.3m>1.3m>2.3m,以1.3m处E_s最大;不同方向E_s和T_(stem)均表现为南面>北面。生长季和非生长季的峨眉冷杉E_s分别在0.51—0.99μmol m^(-2)s^(-1)和0.14—0.22μmol m^(-2)s^(-1)之间波动。峨眉冷杉树E_s变化趋势和T_(stem)一致,二者具有显著的指数函数关系(P<0.01)。峨眉冷杉非生长季树干呼吸Q_(10)显著高于生长季(P<0.01),其中生长季变幅在1.9—3.0之间,非生长季在4.6—6.8之间,暗示个体或群落水平树干CO_2释放通量的估算应充分考虑树干E_s空间特征和Q_(10)变化。

As an important component of carbon budgets and net ecosystem CO2exchange in forest ecosystems, stem CO2 efflux rate （E） plays a crucial role in the global carbon balance. Investigation of spatial variations and the response of E to temperature, are essential for improving the accuracy of Es estimates at individual and community levels. In this study, the horizontally oriented soil chamber （HOSC） technique was applied to measure the CO2 released by stems. We measured E in situ in the Abies fabri forest on Gongga Mountain using IRGA with a Li-6400-09 from September to December 2014. Our objectives were to examine the spatial variations in Es of A. fabri and to explore the response of E to stem temperature （ Tstem ）. TWO representative trees in an immature A. fabri forest stand were selected. An opaque PVC collar （ 10.7cm inside diameter and 5cm high） was cut to match the approximate curvature of the stem with the other end being cut flat. Then the custom-built PVC collar was fastened to the south of the stem at a height of 0.3, 1.3 and 2.3m and to the north at a height of 1.3m, with 100% silicone sealant 24h before the measurement was made. Loose bark and moss were carefully removed from the stem surface curved by the PVC collar using a hairbrush without damaging the underlying cambium before installing the PVC collars. Measurements were made over three cycles at each sampling point, every 2h from 8：00 to 18：00 in the same day of every month. The A. fabri stem Es and T,em showed an apparent spatial pattern. The T tern at different heights ranked as follows ： 0.3〉1.3〉2.3m with maximum E appearing at 1.3m. The E and T,om on the south face of the stem were higher than that on the north. The monthly averages E of the growing season （ September and October） and the non-growing season （November and December） was 0.51-0.99 and 0.14-0.22μmolm^-2s^-1, respectively. The trend in A. fabri stem E was consistent with Tstem with a significantly exponential relationship observed. The temperature coefficient （Q10） during the nongrowing season （4.6-6.8） was much higher than that in the growing season （1.9-3.0）. It was concluded that spatial variations of Es and Q10 should be considered when estimating individual and community stem Es.