Seasonal and Interannual Variations of CO₂ Fluxes Over 10 Years in an Alpine Wetland on the Qinghai‐Tibetan Plateau

Abstract

Alpine wetlands play a sensitive function in global carbon cycle during the ongoing climate warming, yet the temporal patterns of carbon dynamics from in situ ground-based long-term observations remain unclear. Here, we analyzed the continuous net ecosystem CO 2 exchange (NEE) measured with the eddy covariance technique over an alpine peatland on the northeastern Qinghai-Tibetan Plateau from 2007 to 2016. The wetland acted as a net CO 2 source with a positive NEE (120.4 ± 34.8 gC m −2 year −1 , Mean ± SD), with the mean annual gross primary productivity (GPP) of 500.3 ± 59.4 gC m −2 year −1 and annual ecosystem respiration (RES) of 620.7 ± 74.2 gC m −2 year −1. At the seasonal scale, the classification and regression trees (CART) analysis showed that aggregated growing season degree days (GDDs) were the predominant determinant on variations in monthly NEE and monthly GPP. Variations in monthly RES were determined by soil temperature (Ts). Furthermore, nongrowing season Ts had a significant positive correlation with the following year annual GPP (p < 0.05). Nongrowing season RES only accounted for about 25% of annual RES but had significant correlation with annual RES and annual NEE (p < 0.05). The further partial correlation analysis showed that nongrowing season air temperature (Ta, p = 0.05), rather than precipitation (PPT, p = 0.25) was a predominant determinant on variations in annual NEE. Our results highlighted the importance in carbon dynamics of climate fluctuations and CO 2 emission from the nongrowing season in alpine wetlands. We speculated that the vast peadlands would positively feedback to climate change on the Tibetan plateau where the nongrowing season warming was significant.

Carbon Sink of a Very High Marshland on the Tibetan Plateau

“…However, future work is required in the following areas: First, most existing observations have been conducted in the eastern TP, while very few EC systems have been deployed in the central or even western TP, which is relevant when considering the inner TP has experienced a significant increase in precipitation and water levels. (Niu et al, 2017), Dashalong, Haibei (Fu, 2006;Zhang et al, 2008;Zhao et al, 2010;Zhu et al, 2020), Lake Qinghai (Wang, 2015), Shenzha and Zoige (Kang et al, 2014;Liu et al, 2019) (i.e., the statistics of Table S1). The biweekly average was used to eliminate the influence of data size on the results.…”

Interannual characteristics and driving mechanism of CO&lt;sub&gt;2&lt;/sub&gt; fluxes in alpine shrubland ecosystem during growing season at the southern foot of Qilian Mountains

“…在全球气候变化背景下, 气温的 升高将会促进积雪融化和植被返青提前, 致使生长季 长度延长 [13] , 促进了高寒生态系统CO 2 的同化和植被 生产力的提高 [14] . 不同时间尺度气候环境因子对高寒 生态系统碳循环可能具有不同的影响 [15] , 但是过去关 于高寒生态系统碳循环的研究主要限制在短时间内的, 对于较长时间尺度(季节尺度和年际尺度)的研究相对 薄弱 [16] . 高寒灌丛生态系统是青藏高原东部高寒草地 植被类型的重要组成部分, 分布面积为0.106×10 6 km 2 , 其海拔高、生态系统脆弱, 是对全球气候变暖响应最 为敏感的生态系统类型之一, 在区域乃至全球陆地生 态系统碳循环中占有重要地位 [17] .…”

“…分类回归树分析表明, 在高寒灌丛生态 系统中, 月Re的变化主要受T s 的控制(图5(b)). 许多研究 表明, 高寒草地生态系统土壤温度显著影响CO 2 的释放 和氮的矿化 [15,19] , 高寒生态系统土壤微生物生物量受 低温的限制 [9,13] . 因此, 土壤温度成为生态系统呼吸的 主导因素.…”

“…线性回归分析表明, 2003~2016年高 寒灌丛在生长季的月NEE与月GPP和月Re都呈极显著 负相关(P<0.001)(图3(b), (c)). 并且, 与月Re(r 2 =0.47)相 比较, 月GPP(r 2 =0.88)对月NEE的控制作用更强, 这与 前人的研究结果相似 [12,15,18] , 在生长初期、末期植被光合生产能 力较弱, 而青藏高原高寒草地土壤中含有大量未分解 的有机质, 具有较强的土壤呼吸, 导致这个时期Re对 NEE的控制作用更强; 而在植被生长-旺盛期, 雨热同 期的条件使得植被具有较高水平的光合生产能力 [21,25] , 致使GPP对NEE的控制作用更强. 季的光合生产能力和碳汇强度.…”

Seasonal temperature waves in the ground, nonperiodic case

“…Alpine wetlands play an important role in the global carbon cycle during ongoing climate warming, but the timing of carbon dynamics derived from long-term ground-based in situ observations remains unclear. In the course of long-term experiments, the article [13] studied the relationship between temperature and the amount of CO2 produced.…”