## 4 Discussion
Their similarities could be attributed to the same vegetation while their differences could be attributed to differences in climate at the two locations. Open-developed land, which also included trees, grasses, pastures, various infrastructures, etc., made it unique compared to other land uses in this study. Developed land in the ET climate zone showed low GPP (<100 g C m\({}^{-2}\) mo\({}^{-1}\)) in December suggesting a significant impact of low precipitation and temperature, which could be responsible for the major decline in productivity. Seasonal climatic conditions in ET support vegetation's growth. These conditions do not occur consistently in SC climate zone. SC is rather known for its natural diversity, which included semi-arid ecosystems, sweeping grasslands, and swampy, humid bayous. However, GPP was found to be higher on land uses in such climate zones (e.g., ET), which experienced more frequent higher rainfall, higher temperature variations, and higher humidity. Climatic conditions, types of land-use, and seasonal changes impacted the spatial distribution of NEE across the state. When NEE distributions of identical land-use were compared at two different climate zones, these climatic conditions showed a significant impact on the net ecosystem exchange. All climate zones showed carbon emission in December. However, UT and ET climate zones showed highest carbon emissions, and TP climate zone showed the lowest carbon emissions in December because the UC climate zone received more than double the precipitation during this month. During the summer, all of the climate zones showed carbon uptake except HP, LRP, and TP, which had carbon emission in some of the summer months in 2018. These could be due to the effect of intermittent seasonal rainfall and change in land-use, which were identified as environmental drivers that impact carbon exchange in an ecosystem, as well as temperature variations across the climate zones. In comparison, climate zones dominated by forest, pasture, and crop showed more carbon uptake from April to September each year except HP cropland and TP forestland, because these climate zones received a low amount of precipitation, had higher elevation and lower temperature. Each climate zone showed a decreasing trend and smaller variability in annual GPP from 2016 to 2018. However, it showed higher annual variability in GPP between the climate zones. The humid climate zones located close to the coast and dominated by forest, pasture, and croplands, had higher annual GPP than the semi-arid climate zones dominated by shrub and croplands. Additionally, humid climate zones that had more developed lands showed larger spatial variability (SD) in annual GPP due to land-use heterogeneity. The seasonal effects on NEE were different in the tropical ET, UC, NC, and SC climate zones than in semi-arid TP, HP, and parts of EP climate zones, which explains different effects of seasonal changes on NEE distributions at these climate zones. NEE distributions changed from carbon emission in April to carbon uptake by June, whereas carbon uptake in August was changed to carbon emission by December. It shows that a tropical wet climate enhances carbon uptake, whereas the arid climate enhances carbon emission. East Texas, dominated by forestland and pastureland, showed a balance between seasonal variations in carbon emission and uptake, whereas other climate zones, dominated by other land uses (e.g., developed land, cropland) showed a poor balance between seasonal variations in carbon emission and carbon uptake. However, climate zones dominated by shrubland showed little or no carbon emission during the study period. These findings aligned with previous studies, which showed shrublands had more consistent carbon uptake than grass or pasturelands because of the longer growing season and lower ecosystem respiration, although they show similar productivity [72]. Shrublands of EP and TP climate zones had the smallest NEE variations among all of the locations.