三江并流核心区亚高山森林非生长季净生态系统CO_(2)交换量及其影响因素

Net ecosystem CO_(2)exchange and its influencing factors in non⁃growing season at a sub⁃alpine forest in the core Three Parallel Rivers region

采用开路式涡度相关系统,针对三江并流核心区西藏红拉山滇金丝猴国家自然保护区,通过测量和分析非生长季亚高山常绿针叶林净生态系统碳交换量(NEE),探讨了亚高山森林非生长季CO_(2)通量特征及其主要影响因子。保护区常绿针叶林NEE值在非生长季具有明显“U”型变化曲线,白天表现为碳吸收,夜间表现为碳释放,日间CO_(2)吸收高峰介于12:00到15:00之间,平均每天碳汇时间在10 h左右。非生长季各月NEE大小依次为:4月>3月>2月>11月>1月>12月。研究期内气温(T)、相对湿度(RH)、饱和水汽压差(VPD)和光合有效辐射(PAR)等气象因子对净生态系统CO_(2)交换量影响显著。此外,森林碳吸收对温度响应敏感,光合作用在整个非生长季较为明显。各影响因子中光合有效辐射对碳交换影响最大;夜间NEE与5 cm土壤温度呈极显著相关性(P<0.01)且NEE随着土壤温度升高而增大;整个非生长季NEE、生态系统呼吸量(Re)和总生态系统CO_(2)交换量(GEE)分别为-596.759 g CO_(2)/m^(2)、582.849 g CO_(2)/m^(2)和-1179.608 g CO_(2)/m^(2)。该亚高山常绿针叶林生态系统与青藏高原其他生态系统类型相比具有明显的碳汇功能。

In this study,the open⁃circuit eddy covariance system was used to measure and analyze the carbon dioxide exchange(NEE)flux of the sub⁃alpine evergreen coniferous forest net ecosystem exchange in the Qinghai⁃Tibet Plateau during the non⁃growing season.The study area is located in the Hongla Mountain Yunnan snub⁃nosed monkey National Nature Reserve,belonging to the core area of the Three Parallel Rivers in the Tibet Autonomous Region.The characteristics of CO_(2)flux in the non⁃growing season of subalpine forest and its main influencing factors were further discussed.The NEE value of evergreen coniferous forest in the Nature Reserve is manifested as an obvious‘U’curve in the non⁃growing season.It shows carbon absorption in the daytime and carbon release in the night.The diurnal CO_(2)indicated its absorption peak from 12:00 to 15:00,with 10 h average daily carbon sink time.March,February,November,January,and December follow April in the order of monthly NEE during non⁃growing season.During the study period,meteorological factors,i.e.,air temperature(T),relative humidity(RH),saturated vapor pressure deficit(VPD),and photosynthetically active radiation(PAR)had significant effects on carbon exchange.The results showed that forest carbon absorption was sensitive to temperature and the photosynthesis obviously throughout the whole non⁃growing season.Among the influencing factors,photosynthetically active radiation had the greatest impact on carbon exchange;NEE at night was highly significantly correlated with 5 cm soil temperature(P<0.01)and increased with soil temperature.In the whole non⁃growing season,NEE,Re and GEE were-596.759 g CO_(2)/m^(2),582.849 g CO_(2)/m^(2)and-1179.608 g CO_(2)/m^(2),respectively.This subalpine forest ecosystem has obvious carbon sink function in comparison with other ecosystem types on the Qinghai⁃Tibet Plateau.