## 1 Introduction  
It is estimated that there are up to 117 million global lakes greater than 0.002 km\({}^{2}\) in size, covering a total area of 5.0 million km\({}^{2}\) and corresponding to 3.7% of Earth's non-glaciated land surface [1].  
Although the methane (CH\({}_{4}\)) emissions of freshwater (lakes and rivers) are usually less substantial than carbon dioxide (CO\({}_{2}\)) fluxes [2], the warming potential of CH\({}_{4}\) is 28 times greater than CO\({}_{2}\) over 100 yr time frames [3]. Globally, the CH\({}_{4}\) emissions of freshwater lakes and rivers are about 122-159 Tg yr\({}^{-1}\) and account for 20% of CH\({}_{4}\) emission to the atmosphere [3, 4], and their contribution is expected to increase in the future climate change scenarios [5]. Because of the spatio-temporal variability of CH\({}_{4}\) emission fluxes from lakes, recent CH\({}_{4}\) emissions from global lakes were estimated to range from 8 to 48 Tg yr\({}^{-1}\)[6, 7]. Therefore, it is necessary to further understand the dynamics of the CH\({}_{4}\) source in lakes under different environmental factors.  
[PERSON] et al. [8] indicated that a variety of biological, morphometric, and physical properties have been used as important predictors of CH\({}_{4}\) emission from freshwater to the atmosphere. These factors could be temperature [9; 10], water depth [11; 12], ecosystem productivity [9; 12; 13], and surface area [14; 15], among others. However, the relationship between productivity and CH\({}_{4}\) emission has been shown empirically in various freshwaters [12; 16; 17]. Hence, in the littoral zone of lakes and rivers, most aquatic plants--such as _Typha_, _Nymphaea_, and _Nelumbo_--not only have high productivity (wet weight of 10 kg m\({}^{-2}\)) [18], but also morphological features adapt to waterlogged habitat [19]. Even if the littoral area of freshwater is relatively small, it can contribute to high CH\({}_{4}\) emission [20; 21; 22]. Moreover, the contribution of plant-dependent CH\({}_{4}\) emission to the total emission could increase to 80-90% in freshwater with emergent macrophytes [23; 24; 25]. Therefore, two studies conducted in the boreal lakes revealed that about 66-81% of CH\({}_{4}\) was released from the littoral zones, demonstrating that it is needed to reinforce the estimates of lakes' CH\({}_{4}\) release in the vegetated littoral zone [21; 22].  
Lotus (_Nelumbo nucifera_ [PERSON]), as an important aquatic plant and a type of vegetable, has been cultivated in China for more than 2000 years, especially around the Yangtze River [26]. Hubei, located in the middle reaches Yangtze River, is one of the largest provinces in lotus cultivation [26]. Hong Lake, covering an area of around 350 km\({}^{2}\), is the largest freshwater lake in Hubei province [27; 28]. The lake was originally connected with the Yangtze River in the 1950s when the area of the lake was 760 km\({}^{2}\); now, it is semi-connected to the Yangtze River because of the construction of sluices around the lake between the years 1955 and 1975 [27]. Although the water surface area of the lake has greatly decreased over these decades [27], there are large lotus aquatic plants living in the littoral zone of the lake, which has become a holy place for human recreation. Lotus aquatic plants could affect the CH\({}_{4}\) release of the freshwater, which should be further investigated in Hong Lake.  
The purpose of this study was to evaluate the effect of lotus aquatic plant on CH\({}_{4}\) emissions in the freshwater lake in subtropical China. Two observation sites (lotus plant and open water) were set up in Hong Lake. CH\({}_{4}\) emission was measured by using the floating opaque chamber and a gas chromatography method. In addition, the driving factor of CH\({}_{4}\) emission, the vegetation biomass, soil organic carbon concentration, temperature, and dissolved oxygen concentration were measured as well, in order to investigate the relationships between environmental factors and CH\({}_{4}\) emissions.