## 4 Discussion
Therefore, AIRS may be a good proxy for CO\({}_{2}\) source/sink dynamics in areas of similar land cover on timescales from 4 to 512 days. On timescales less than a month, AIRS is not a good proxy for annually-burned, C\({}_{4}\) grasslands like KZU. On the other hand, Figure 3b illustrates that the CO\({}_{2}\) concentrations at KFS closely approximate mid-tropospheric concentrations at all but the four-day timescale. The heterogeneity and land-cover type at the KFS site is perhaps most characteristic of land cover throughout the region. For this reason, it is not surprising that EC tower measurements at KFS are closest to mid-tropospheric concentrations at almost all timescales. Likewise, it is not surprising that CO\({}_{2}\) concentrations at site KZU, characterized by tallgrass prairie and an annual burn regime, are the least similar with mid-tropospheric concentrations in this region. The large divergence between K4B and AIRS at the 64-day scale may again represent the seasonal differences in CO\({}_{2}\) concentration at local versus continental scales. Considering that FT concentrations reflect continental-scale fluxes [5, 17], it stands to reason that AIRS more closely approximates land covers with woody encroachment versus perennial tallgrass prairie. The land-cover type at site K4B, KFS, and KZU differ through species composition and microclimate. In 2008, for example, the average air temperature at K4B was found to be 0.5\({}^{\circ}\)C higher than the other two sites [32]. Encroachment of _Cormus drummondii_ or _Juniperus virginiana_ L. alters soil temperature and microclimate by changing surface albedo. The encroachment of _Juniperus virginiana_ L. would also mean a change from C\({}_{4}\) grasses to C\({}_{3}\) coniferous trees. Analyses of C\({}_{3}\) and C\({}_{4}\) plants within a C\({}_{3}\)-C\({}_{4}\) mixed grassland on the Konza Prairie have shown that C\({}_{3}\) plants with greater rooting biomass can be more drought tolerant and continue to photosynthesize beyond C\({}_{4}\) grasses that are drought stressed [47]. According to a study conducted on the Konza Prairie by [PERSON] _et al_. [48], carbon storage in aboveground biomass greatly increases with shrub encroachment. Deeply rooted clonal shrub islandsof _Cornus drummondii_, characteristic of site K4B, were found to have increased from 0 to 18.5\(\%\) in Konza Prairie sites burned every four years over that last 26 years [49]. These islands can sequester more than nine times the amount of carbon aboveground compared with open grasslands like KZU [48]. A shift in plant biomass from belowground to aboveground in areas of woody encroachment may cause short-term carbon sinks, though these are more vulnerable to fire and sequester less carbon as woody plants mature. In a complementary Konza Prairie study, annual soil CO\({}_{2}\) flux diminished by 16\(\%\) as grasslands shifted to shrublands [50]. _Juniperus virginiana_ L. or eastern red cedar is another invasive species found at site K4B that has been shown to alter ecosystem processes by increasing aboveground NPP, litter, and accrual of organic carbon in litter and soil, while decreasing soil respiration [51]. Various synoptic-scale and mesoscale processes couple concentrations of CO\({}_{2}\) in the ABL and the FT. However, attributing specific mechanisms to the correlations in the wavelet multi-resolution analysis and similarities in relative entropy is a challenge. Mechanisms governing similarities on seasonal timescales (64 to 128 days) are most obvious and straightforward to understand, since the FT CO\({}_{2}\) reflects the growing season over the continent, which is communicated in the vertical by regular occurrences of synoptic systems and deep convection. Relationships at shorter timescales are more difficult to interpret, partly because of the single-point nature of both the EC measurements and the AIRS pixels.