# Effects of Gradient Warming on Carbon and Water Fluxes in Zoige Plateau Peatland
###### Abstract  
Water use efficiency (WUE) plays a pivotal role in connecting the carbon and water cycles and represents the amount of water used by plants or ecosystems to achieve carbon sequestration. The response of WUE to climate warming and its underlying mechanisms remain unclear. Here, we examined the effects of varying levels of warming on carbon fluxes, water fluxes, and WUE in an alpine peatland, with _Blysmus sinocompressus_ and _Carev schrirostris_ as dominant species. Open-top chambers were utilized to simulate two levels of warming: low-level warming (TL) and high-level warming (TH). The carbon dioxide and water fluxes were monitored over a growing season (June to September). Gradient warming significantly decreased both gross primary productivity (GPP) and net ecosystem carbon exchange (NEE); GPP was 10.05% and 13.31% lower and NEE was 21.00% and 30.00% lower in the TL and TH treatments, respectively, than in the control. Warming had no significant effect on soil evaporation, and plant transpiration and evapotranspiration were 36.98% and 23.71% higher in the TL treatment than in the control, respectively; this led to decreases of 31.38% and 28.17% in canopy water use efficiency (WUEc) and ecosystem water use efficiency (WUEe), respectively. Plant transpiration was the main factor affecting both WUEe and WUEc in response to warming. The findings underscore the essential function of water fluxes in regulating WUE and enhance our understanding of carbon-water coupling mechanisms under climate change. climate change; carbon-water coupling; gross primary productivity; plant transpiration; alpine peatland +
Footnote †: journal: water  
0000-0002-4100-0002-41000][PERSON]  
0000-0002-4100-0002-4100][PERSON]  
0000-0002-4100-0002-4100][PERSON]  
0000-0002-4100-0002-4100][PERSON]  
0000-0002-4100-0002-4100][PERSON]  
0000-0002-4100-0002-41000][PERSON]  
0000-0002-4100-0002-4100]Jinming. Liu  
reserves globally [4]. However, this region is highly vulnerable to climate change. The QTP has undergone a marked increase both in temperature and precipitation over the past few decades, which has significantly affected regional ecosystem functions [5]. The carbon and water cycles are closely linked processes that connect ecosystem components, including soil, vegetation, and the atmosphere [6]. Vegetation dynamics, along with carbon and water fluxes, have been profoundly shaped by alterations in temperature and precipitation patterns [7; 8; 9]. Exchanges of carbon and water, coupled with soil-plant systems and the environmental atmosphere on the plateau, are crucial for the region's carbon sink function, and temperature is considered one of the dominant factors influencing carbon exchanges [7]. Increased temperature can increase or decrease gross primary productivity (GPP) and ecosystem respiration (RE), depending on environmental factors, such as water availability, on the QTP [10; 11; 12; 13]. Furthermore, changes in GPP and RE can either promote or inhibit the net ecosystem carbon dioxide exchange (NEE) response to warming [11; 14]. Temperature alters the rate of soil respiration and soil carbon decomposition by regulating the activity of soil microorganisms, which ultimately affects the carbon output of the soil. Changes in temperature also affect the phenological state and photosynthetic rate of vegetation, which can lead to alterations in the carbon input of ecosystems [15]. Warming may also affect water fluxes, accelerate the evapotranspiration (ET) rate, and lead to a decrease in the soil moisture content [16]. ET comprises soil evaporation (E) and plant transpiration (T) and is a key factor affecting both water and carbon cycles. Warming usually increases ET by enhancing E or T, although exceptions in which ET decreases with increased temperature have also been reported [17; 18]. Water use efficiency (WUE) is a key indicator for quantifying the coupling effects of carbon and water cycles in ecosystems, and it represents the amount of carbon fixed per unit of water loss in terrestrial ecosystems [19].