# _atmosphere_
## 1 Introduction  
Due to their water-logged and relatively low-temperature conditions, wetlands comprise a large component of global terrestrial carbon reserves; they store \(\sim\)30% of the global soil carbon pool, despite only constituting \(\sim\)5% of the land surface [1; 2; 3]. Although pristine alpine wetlands could be potential future carbon sources because of the projected warming and drying climate [1; 4; 5], carbon accumulation in mid- and high-latitude wetlands has increased slightly over recent decades [2; 6]. Thus, increased knowledge of carbon dynamics and their responses to environmental controls in alpine wetlands is essential to address this discrepancy and to quantify the contributions of wetlands in mitigating atmospheric greenhouse gas concentrations [4; 7; 8]. Alpine wetlands can be either carbon sources or carbon sinks depending on local hydrothermal conditions, consequent vegetation types, soil physical and chemical properties, and microorganism compositions [9; 10; 11; 12]. Gross primary productivity (GPP) and ecosystem respiration (RES) are two contrasting processes that determine carbon budgets, and those are closely related to ecohydrological factors, usually with nonlinear relationships [13; 14; 15]. Water availability has been shown to be an important control of the seasonal variability in CO\({}_{2}\) fluxes of alpine wetlands, through its simultaneous effects on vegetation growth and organic matter decomposition [4; 9; 16]. Vascular plant coverage has an asymptotic relationship with GPP, and an incremental relationship with RES, but their sensitivity varies by leaf area index and vegetation type [17; 18]. Under the context of climate warming scenarios, recent studies have shown that plant productivity outweighs ecosystem respiration, and alpine peatlands have become more efficient carbon sinks because of a higher sensitivity of GPP compared to RES, longer growing season, and more plant carbon input [19; 20; 21]. Contrarily, other studies have suggested that decreased moisture availability caused by warming could stimulate more soil respiration and potentially reverse the carbon sink function [6; 22; 23]. Quantifying the relative contributions of biotic and abiotic controls on carbon budgets has the potential to understand this debate but has been poorly addressed because of their intertwined relationships [22]. Moreover, nongrowing season CO\({}_{2}\) emissions are believed to play a considerable role in carbon budgets, but there is still much uncertainty due to limited long-term field observations [4; 18]. More detailed knowledge is greatly needed to quantify and predict the fate of the carbon function of alpine wetlands under remarkable winter warming and increasing precipitation [9; 13]. Year-round continuous measurements, rather than merely from the growing season, are required in alpine wetlands to address this issue [23; 24]. Carbon budgets of alpine wetlands on the Qinghai--Tibet Plateau (QTP) have drawn increased attention recently [11; 13; 25; 26]; the QTP wetlands house relatively large soil carbon reservoirs because of lower decomposition rates and higher vegetation photosynthetic production compared with other surrounding wetland ecosystems [4; 17]. Moreover, wetlands on the QTP have been expanding due to the warming climate and decreased human activity [27]. However, the carbon sink/source functions in alpine wetlands are highly variable. For instance, the wetlands of Zoige, Qinghai Lake (Xiaobohu: XBH), and Hehei have recently behaved as carbon sinks, with annual carbon accumulations of approximately 170, 250, and 510 g C/m\({}^{2}\), respectively [12; 13; 28]. In contrast, Luanhaizi (LHZ) wetland has been a carbon source and released approximately 100 g C/(m\({}^{2}\) year) to the atmosphere from 2005 to 2014 [14; 17; 25]. Therefore, quantifying the carbon dynamics of contrasting alpine wetlands will be helpful in understanding the confounding mechanisms in their carbon budgets.