## 2 Data and Preprocessing  
### FLUXNET Data  
In this study, data from seven flux sites from the FLUXNET dataset were collected, covering evergreen needleleaf forest, deciduous broadleaved forest, paddy field, dryland, grassland, and wetland ecosystems. The criterion used to select flux sites was that they had to contain observations that include both flux data and phenology camera records from the same time period ('Data Availability' in Table 1). Therefore, we selected the time scale of these flux tower sites as 2010 to 2015. The FLUXNET provides two public datasets: the FLUXNET2015 Dataset and the FLUXNET-CH4 Community Product. To improve consistency and comparability, both datasets offer preprocessing and quality-controlled flux data using consistent methodologies [30; 31; 32]. The variables used in this study included gross primary productivity ('GPP_NT_VUT_REF'), net ecosystem exchange ('NEE_VUT_REF'), ecosystem respiration ('RECO_VUT_REF'), air temperature ('TA_F'), and photosynthetic photon flux density incident ('PPFD_IN'). The variables of the USTAR ('VUT') threshold for selected years were used in this study [33; 34; 35], and detailed data processing method can be found on the FLUXNET website ([[https://fluxnet.org/data/fluxnet2015-dataset/data-processing](https://fluxnet.org/data/fluxnet2015-dataset/data-processing)]([https://fluxnet.org/data/fluxnet2015-dataset/data-processing](https://fluxnet.org/data/fluxnet2015-dataset/data-processing)) (accessed on 22 July 2023)). High-quality data were refined to remove abnormal data with PPFD_IN_QC values of \(-9999\) or \(0\). With regard to GPP, the variables of 'GPP_NT_VUT_REF' were recognized as reference daily GPP (g C\(\cdot\)m\({}^{-2}\cdot\)d\({}^{-1}\)). The variables of half-hour and hourly input were scaled to a daily scale for calibration and validation of the model estimates.  
Howland Research Forest is located in Piscataquis County, central Maine. It is characterized by evergreen coniferous forest, with soils formed on coarse-grained granite. The vegetation consists of approximately 66% red spruce, 25% eastern hemlock, and 34% other coniferous trees and hardwoods [36]. Harvard Forest is situated in Petersham County, Massachusetts. It is a deciduous broadleaf forest, with soils consisting of rocky sandy loam and glacial till. The dominant vegetation types include red oak, sugar maple, eastern white pine, and yellow birch [21]. Morgan Monroe State Forest is located in Morgan and Monroe Counties, Indiana. It is a deciduous broadleaf forest characterized by a low-relief landscape with ridges and ravines, where the maximum relief is less than 60 m. The main vegetation types are sugar maple, tulip poplar, yellow poplar, and various oak species [37]. US-Ne2 is situated near Mead, Nebraska, at the University of Nebraska Agricultural Research and Development Center. It represents a typical corn-soybean rotation agricultural ecosystem, with corn planted in odd-numbered years. Unlike US-Ne3, which relies solely on rainfall, US-Ne2 is equipped with a central-pivot irrigation system [38]. Twitchell Island rice field is located within the Sacramento-San Joaquin Delta, near the Pacific coast. This rice field ecosystem experiences a Mediterranean climate with distinct wet and hot seasons [39]. Mayberry Wetland is situated on Sherman Island and is a constructed restored wetland built using the heterogeneity trenching method. The wetland vegetation is predominantly cattail, and it exhibits the highest heterogeneity in water depth among the restored wetlands from the same period [40,41]. Vaira Ranch is located near Ione, California. The primary vegetation consists of annual C3 grassland, influenced by a Mediterranean climate. These annual grasslands exhibit higher activity during the warm and moist winter season compared to during the summer season [42]. The distribution of the above sites is shown in Figure 1.