## 3 Results and Discussion  
### Temporal Variations in Environmental Conditions  
The 4-year in situ observations had strong seasonal variations in most of the environmental factors, such as air and soil temperature (Ta and Ts), precipitation (P), vapor pressure deficit (VPD), relative humidity (RH), solar radiation (Ra), and leaf area index (LAI) (Figure 2a-h). The variations in daily Ta had the highest values at approximately 30 \({}^{\circ}\)C in July and the lowest values at approximately 15 \({}^{\circ}\)C in January or February due to the typical subtropical monsoon climate (Figure 2a). The annual mean temperature was approximately 24 \({}^{\circ}\)C and indicated no significant differences between years (Table 1). The Ts values had variations similar to those of Ta but had less day-to-day variability than Ta (Figure 2a). Most of the precipitation was concentrated from April to September, which accounted for 67-87% of the annual total precipitation.  
The highest precipitation was found in August 2019 (412.8 mm), May 2020 (286.5 mm), June 2021 (359.0 mm), and May 2022 (485.1 mm) (Figure 2b). The daily soil salinity ranged from 2.1 ppt to 19.3 ppt from July 2021 to the end of 2022, respectively. The trend of soil salinity was influenced by rainfall events and river water input. Higher salinity values ranging from 14 ppt to 17 ppt were found from December 2021 to mid-February 2022 as well as in October 2022. These were accompanied by lower precipitation (Figure 2b).  
The seasonal variations in daily VPD and RH showed approximately opposite variation trends in response to precipitation (Figure 2c,d). Higher precipitation increased RH but reduced VPD. Consistent with the seasonal trend of precipitation, lower RH occurred in the period between October and March in the next year, with daily bottom values of approximately 0.3 (Figure 2d). The average monthly VPD ranged from 0.22 kPa to 1.32 kPa during the past 4 years, with a daily peak at 2.29 kPa in September 2022 (Figure 2c). As shown in Table 1, the climatic conditions in 2019 and 2022 were relatively wetter than those in 2020 and 2021, with higher annual precipitation of 2085.70 mm and 1921.20 mm, higher annual mean RH values of 0.82 and 0.80, and lower VPD values of 0.56 kPa and 0.59 kPa in 2019 and 2022, respectively.  
The seasonal variations in the daily Ra and LAI values (Figure 2e,f) also showed seasonal variations, but were weaker than those in temperature (Figure 2a). The daily Ra values were generally higher in summer (178.80 \(\pm\) 70.16 Wm\({}^{-2}\)) and lower in winter (126.75 \(\pm\) 58.64 Wm\({}^{-2}\)). However, in 2020, 2021, and 2022, the Ra values were low in summer due to continuous precipitation, which resulted in M-shaped patterns in these years (Figure 2e). The daily LAI had general unimodal patterns in 2019, 2020, and 2022 and an obvious M-shaped pattern in 2021 (Figure 2f). In 2019, 2020, and 2022, the monthly mean peaks occurred in September (1.49), August (1.68), and September (1.80), respectively. In 2022, two peaks of monthly mean values of 1.20 and 1.22 were found in July and September (Figure 2f).  
There were no significant seasonal variations in the wind speed and the proportion of open water (Figure 2g,h). The wind speed ranged from 1.18 m s\({}^{-1}\) to 9.70 m s\({}^{-1}\) (Figure 2g). The proportion of open water was determined by the wind speed, wind direction, and tower height. The land surface (PI) accounted for 62% and 63% in the last 2 years, which was lower than that found in the first 2 years (Table 1).