毛白杨树干呼吸及其温度敏感性季节变化特征

树干呼吸(E_s)是森林生态系统碳循环过程的重要组成部分,深入理解树干呼吸过程对未来气候变暖的响应及反馈机制有助于更加精确地估算森林生态系统碳储量。为揭示毛白杨树干呼吸及其温度敏感性的昼夜变化和季节动态规律,利用Li-Cor6400便携式光合作用测定系统及其配套使用的土壤呼吸测量气室(LI-6400-09)对冀南平原区毛白杨的树干呼吸和树干温度实施为期1年的连续监测。结果表明:(1)在生长季,毛白杨树干呼吸与树干温度之间在晚上呈现正相关的关系(R~2=0.88);相反,两者在白天为负相关的关系(R~2=0.96)。(2)整个观测期内,毛白杨树干呼吸和树干温度均呈现"钟形"的变化曲线,树干呼吸与树干温度之间存在着较好的指数函数关系(R~2=0.93),且树干呼吸的温度敏感性系数(Q_(10))为2.62;不同季节毛白杨树干呼吸的Q_(10)存在差异,生长季的Q_(10)(1.95)明显低于非生长季(3.00),表明生长呼吸和维持呼吸对温度的响应也并不相同。(3)温度矫正后的毛白杨树干呼吸(R_(15))在昼夜和季节尺度上均存在明显的变异,即夜晚的R_(15)显著高于白天(P0.01),生长季的R_(15)明显高于非生长季(P0.05);树干可溶性糖含量与生长季的R_(15)存在较好的相关性(R~2=0.52),而非生长季的R_(15)却主要受到树干淀粉含量的影响。研究结果表明,在生长季,毛白杨树干呼吸的在日变化主要受到温度的影响,而在季节尺度上Q_(10)的变异则与树干呼吸中维持呼吸所占比例及树干中非结构性碳水化合物(可溶性糖和淀粉)的含量及类型紧密相关。

Seasonal variations in stem respiration and temperature sensitivity of Populus tomentosa

Stem respiration plays a pivotal role in forest ecosystem carbon cycling, and understanding further its response to future climate warming has important significance for accurately estimating the carbon storage of forest ecosystems. To examine the seasonal variations of stem respiration of Chinese white poplar (Populus tomentosa), we measured stem respiration rate and stem temperature using the horizontally oriented soil chamber technique, from January 2016 to January 2017. We also conducted a 24 h measurement to examine the diurnal variation of stem respiration in May 2016. We found that (1) the stem respiration rate was positively related to stem temperature at night time (R²=0.88), whereas the relationship between stem respiration rate and stem temperature featured a negative linear curve during day time (R²=0.96); (2) the seasonal dynamics of the stem respiration rate followed the change of the stem temperature with a bell-shaped curve, and stem temperature explained 93% of the seasonal variation of stem respiration rate, with the temperature sensitivity (Q₁₀) of 2.62 over the entire observation period. The Q₁₀ was obviously different among seasons, with a lower value found in the non-growing season (3.00), and a higher value in the growing season (1.95), indicating that the growth and maintenance respiration had different temperature responses; (3) the temperature-normalised stem respiration (R₁₅) also featured obviously diurnal and seasonal variations, where the R₁₅ at night time and during the growing season were significantly higher than those of the daytime (P < 0.01), and non-growing season (P < 0.05). The principal factor responsible for the seasonal variation of R₁₅ was the soluble sugar content in the growing season, and the starch content in the non-growing season. These results suggested that the stem respiration rate of Chinese white poplar was mainly disturbed by temperature at the diurnal scale, and closely related to the content and types of non-structural carbohydrates (soluble sugar and starch) and respiration component at seasonal scales, besides temperature.