## 5 Conclusions
Future research needs to improve the resolution of the assimilation system to investigate the lagged effect of drought on GPP at a higher spatial resolution. In addition, the model needs to incorporate more detailed soil hydraulic processes to represent more climatic conditions. Additionally, a further research direction for the future is to consistently and simultaneously assimilate more datasets such as VOD and COS to further constrain the ecosystem model's largely incomplete constrained processes. [PERSON] and [PERSON] conceived and designed this study. [PERSON] performed the experiments and wrote the original manuscript. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] co-wrote and revised the manuscript. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Key Research and Development Program of China (2020 YFA0607504, 2016 YFA0600204), the National Natural Science Foundation of China (41901266, 42111530184), the Research Funds for the Frontiers Science Center for Critical Earth Material Cycling, Nanjing University (Grant No: 090414380031), and the Swedish National Space Board (Rymdstyrelsen 102/14). [PERSON], [PERSON], and [PERSON] were supported by the ESA SMOS+VEGFATION (contract no. 4000117645/16/NL/SW) and the Land surface Carbon Constellation (contract no. 4000131497/20/NL/CT) projects. This research is part of three Swedish strategic research areas: Modeling the Regional and Global Earth system (MERGE), the e-science collaboration (eSSENCE), and Biodiversity and Ecosystems in a Changing Climate (BECC). The CRUNCEP v7 data (accessed on 22 February 2022): [[https://rda.ucardu/datasets/ds3143./](https://rda.ucardu/datasets/ds3143./)]([https://rda.ucardu/datasets/ds3143./](https://rda.ucardu/datasets/ds3143./)) The fossil fuel fluxes (accessed on 6 September 2021): [[https://www.osti.gov/dataexplorer/biblio/dataset/1389331](https://www.osti.gov/dataexplorer/biblio/dataset/1389331)]([https://www.osti.gov/dataexplorer/biblio/dataset/1389331](https://www.osti.gov/dataexplorer/biblio/dataset/1389331)). These 8 stations' CO\({}_{2}\) concentrations from 1980 to 2015 and derived from the SIO (Scripps Institution of Oceanography) networks (accessed on 18 November 2021): [[https://scrippsco2.ucsd.edu/](https://scrippsco2.ucsd.edu/)]([https://scrippsco2.ucsd.edu/](https://scrippsco2.ucsd.edu/)). The ESA-CCI soil moisture (accessed on 9 November 2021): [[https://www.esa-soilmoisture-cci.org/](https://www.esa-soilmoisture-cci.org/)]([https://www.esa-soilmoisture-cci.org/](https://www.esa-soilmoisture-cci.org/)). The atmospheric inversed monthly net ecosystem exchange (NEI) fluxes from Jena CarboScope (accessed on 5 November 2022): [[http://www.BGC-Jena.mpg.de/CarboScope/](http://www.BGC-Jena.mpg.de/CarboScope/)]([http://www.BGC-Jena.mpg.de/CarboScope/](http://www.BGC-Jena.mpg.de/CarboScope/)). The standardized precipitation-evapotranspiration index (SPEI) (accessed on 16 November 2022): [[https://spei.csic.es/index.html](https://spei.csic.es/index.html)]([https://spei.csic.es/index.html](https://spei.csic.es/index.html)). The upscaled GPP based on FLUXNET2015 (accessed on 15 November 2022): [[https://fluxnet.org/data/fluxnet2015-dataset/](https://fluxnet.org/data/fluxnet2015-dataset/)]([https://fluxnet.org/data/fluxnet2015-dataset/](https://fluxnet.org/data/fluxnet2015-dataset/)). The TRENDY GPP (accessed on 16 February 2022): [[https://blogs.exeter.ac.uk/trendy/](https://blogs.exeter.ac.uk/trendy/)]([https://blogs.exeter.ac.uk/trendy/](https://blogs.exeter.ac.uk/trendy/)). The GIMMS NDVI (accessed on 16 February 2022): [[https://ecocast.arc.nasa.gov/data/pub/gimms/3g.v1/](https://ecocast.arc.nasa.gov/data/pub/gimms/3g.v1/)]([https://ecocast.arc.nasa.gov/data/pub/gimms/3g.v1/](https://ecocast.arc.nasa.gov/data/pub/gimms/3g.v1/)).