## 5 Conclusions  
It is important to understand the changes in gross primary productivity (GPP) and net ecosystem exchange (NEE) under changing climate and land-use change. This study used soil moisture active and passive (SMAP) Level 4 carbon products to quantify spatial and temporal distributions and changes of GPP and NEE for selected terrestrial ecosystems across Texas. The SMAP's carbon products were compared and analyzed for monthly, and annual measurements of GPP and NEE for five land uses and ten locations from seven climate zones during the study period. This study used EC (GPP and NEE) measurements from one location of the study area to evaluate the performance of SMAP (GPP and NEE) estimates at daily and monthly time scales. However, it should be recognized that no other EC NEE measurements were available to evaluate across Texas during the study period. This study revealed significant effects of climate and land-use change on spatial and temporal distributions of GPP and NEE in Texas. Results showed that the carbon net exchange rates vary with the climate and land-use change across Texas. While the same land-use at two different climate zones had a different rate of NEE and GPP, different land uses within the same climate zone had different net ecosystem exchanges and productivity rates. Carbon dioxide fluxes at the selected locations were found to be impacted by both climatic conditions and land-use change. GPP and NEE distributions showed high CO\({}_{2}\) exchange at locations with a significant amount of frequent rainfall, higher temperature, and dense vegetation, because these factors had a positive impact on the amount of organic matter input to soil carbon. For example, croplands had higher GPP and NEE in the UC climate zone but a lower value in the HP climate zone. However, climatic conditions were found to have a lesser impact on CO\({}_{2}\) exchange at some land uses like pastureland and shrubland. These land uses showed a minor increase in CO\({}_{2}\) flux even under similar climatic conditions compared to croplands or forestlands. GPP and NEE fluxes showed strong seasonality under the influence of temperature, precipitation, and land-use in each climate zone. While the eddy covariance method made it possible to measure NEE with precision and contributed to the identification of the characteristics of carbon emission/uptake activities of various global ecosystems, there were few EC towers active in the state. Therefore, remotely sensed carbon products were very helpful to study the ecosystem. The limitation encountered in this study is the inability to cover all the land uses in the state, which would have provided a more robust analysis and possibly more accurate estimations of carbon productivity and net carbon exchange. Further, it is recommended to evaluate SMAP carbon products in different climate zones and land-use categories using in-situ measurements. It is also recommended to conduct further research by including SMAP soil organic carbon (SOC) and soil heterotrophic respiration (Rh) to quantify terrestrial components of the carbon cycle in the Texas environment. Finally, this study provides useful information on the terrestrial carbon cycle, which is important for understanding the global carbon cycle, carbon resource management, and carbon sequestration. [PERSON], [PERSON], [PERSON], and [PERSON] developed this concept, including method and approach to be used; [PERSON] and [PERSON] outlined the manuscript; [PERSON] and [PERSON] downloaded, developed, and analyzed the remotely sensed data; [PERSON] and [PERSON] contributed in methodology and discussion of this manuscript; [PERSON] and [PERSON] wrote the paper. This research received no external funding. This work was supported by the Evans-Allen project of the United States Department of Agriculture (USDA), National Institute of Food and Agriculture. We thank [PERSON] and [PERSON] for their time to edit this paper. We are also indebted to reviewers whose extensive comments greatly improved the quality of this paper.