## 2 Materials and Methods  
### Flux Site Description  
In this study, data from flux observation stations in China and Thailand were selected, and their locations are shown in Figure 1. The green areas on the map indicate where the rubber tree forests are located [38; 39]. Two are located in China (Hainan Island and Xishuangbanna), and two are located in Thailand (Chachoengsao and Nakhon Si Thammarat) (Table 1). The rubber plantation flux observation station in Danzhou (DR), China, is located at the third experimental area of the Chinese Academy of Tropical Agricultural Sciences Experimental Farm in northwest Hainan Island (109.48\({}^{\circ}\) E, 19.21\({}^{\circ}\) N), with an average elevation of 144.0 m. This region has a tropical island monsoon climate with abundant water and heat conditions, an average annual sunshine duration of over 2000 h, and distinct wet and dry seasons (wet season from May to October, dry season from November to April) [40]. The observation plot is a mature rubber tree plantation established in 2001, with a community height of about 18.0 m, and the tapping season occurs from May to December. The data used in this paper are from the Yang dataset [40]; for more detailed explanations, please refer to the dataset descriptions. The rubber plantation flux tower in Xishuangbanna (XR), China, is located in a rubber plantation under the jurisdiction of the Economic Extension Station of the Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences (101.27\({}^{\circ}\) E, 21.90\({}^{\circ}\) N), with an average elevation of 592 m. This region belongs to the tropical monsoon climate zone, controlled year round by the Indian monsoon (2018). According to local climate data, the region can be divided into a half-year wet season (May to October) and a half-year dry season (November to April), with the dry season further divided into a foggy cool season (November to February) and a hot dry season (March to April) (2018). The vegetation of the flux tower plot includes rubber trees planted in 1982, with a community height of about 21 m. The tapping period is from April to November, coinciding with the wet season. Additionally, it is important to note that this area is located in a river valley, with the Luosuo River, a tributary of the Lancang River, flowing nearby (500 m). The data used in \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Nation** & **Thailand** & **Thailand** & **China** & **China** \\ \hline Site Name & NR & SR & DR & XR \\ Location & 101.47\({}^{\circ}\) E, 13.57\({}^{\circ}\) N & 99.58\({}^{\circ}\) E, 8.32\({}^{\circ}\) N & 109.48\({}^{\circ}\) E, 19.21\({}^{\circ}\) N & 101.27\({}^{\circ}\) E, 21.90\({}^{\circ}\) N \\ Elevation & 69 m & 200 m & 144 m & 592 m \\ Observation Timespan & 2015–2018 & 2017–2018 & 2010–2018 & 2010–2014 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Locations of the four flux stations and observation timespan. Figure 1: Distribution of rubber plantations and flux station locations in the study area. this paper are from an open access dataset [41]; for more detailed explanations, please refer to the dataset descriptions. Thailand exhibits typical tropical monsoon climate characteristics. The annual average temperature in this region has remained stable. The wet season from May to October is significantly influenced by the Southwest Asian monsoon. Based on the cyclical variations in air temperature and precipitation, the year can be divided into three seasons: the cool dry season (November to February), the warm dry season (March and April), and the wet season (May to October) [23]. One of the rubber plantation flux observation stations in Thailand is located in the southern region (SR) of Nakhon Si Thammarat Province (99.58\({}^{\circ}\) E, 8.32\({}^{\circ}\) N, elevation 200 m), a traditional rubber-growing area with a tropical equatorial climate. The RRIM600 clone rubber trees planted here cover an area of 16 hectares.