## 4 Discussion  
### Rhizberic and Bulk Soils in HTF  
We observed that plants in HTF under seasonal fluctuation were forced to invest in surviving mechanisms by altering soil's physicochemical conditions at the rhizosphere to favor better nutrient utilization. Thus, the rhizosphere may concentrate elevated rates of chemical and biological activity, which controls nutrient biogeochemical cycles in HTF [50]. As the vegetation succeeds and colonizesthe bulk soil, biogeochemical changes are promoted in the rhizosphere-soil interface, by decreasing soil electrical conductivity (EC) and bulk density, and increasing the C and N contents [3]. For instance, in an HTF of coastal China, the rhizopheric soil demonstrated greater diversity of bacterial communities compared to the nearby bulk soil, and diversity also increased in the lowlands of the tidal flats [51]. Thus, studies comparing the rhizosphere and bulk soils are important to increase the understanding for the plant's effects in changing natural occurring soil processes and the mechanisms for ecological succession.  
In our study, the Sv and Bp plants presented similar results for bulk soils, but their rhizospheric soils were strongly separated based on the discriminant analysis (Figure 6B). The Bp samples were more related to NH\({}_{4}\)\({}^{+}\) availability and exchangeable K\({}^{+}\), while Sv more related to soluble K\({}^{+}\) (Figure 6B). These distinct correlations demonstrate that Sv and Bp plants probably use different strategies to survive in an HTF, which could be related to a facilitation process [34; 35; 52]. Facilitation is a positive interaction resulting from amelioration in the abiotic environment or interference by other organisms [52]. In arid and semi-arid environments, the amelioration of microenvironmental conditions is a key process for structuring plant communities [53].  
Bulk soil characteristics of our study were consistent with the soil conditions found in other HTF soils, i.e., neutral-basic pH, hypersaline, sandy-textured soils [1; 28]. The predominance of sandy textures was also reported in other studies of similar environments [28], and related to the transportation of sandy material by wind, tides, and inputs from higher inland (terrestrial) areas [54]. The high contents of CCE (Figure 3) are correlated to the precipitation of CaCO\({}_{3}\), as a less soluble salt, at the soil surface [55]. The observed TOC and TN rarely varied over \(\pm\)0.5%, which was also observed by in the superficial horizons of other HTF soils [28]. This low C and N contents is related to the low plant-derived inputs, since the area of occurrence for the bulk soils is completely barren of vegetation (Figures 1 and 2).  
Another characteristic for the observed bulk soils in HTF is related to the predominance of Fe-oxyhydroxides of low-crystallinity (F3 and F4 fractions of Fe) and high-crystallinity (F5 fraction of Fe) and the low DOP (<1%) values (Figure 5). This Fe geochemistry fractionation reflects the suboxic environmental conditions in response to the low frequency of tidal flooding. Another study also found a dominance of Fe-oxyhydroxides in the fractions F3 to F5, which ranged between 79 to 143 umol g\({}^{-1}\) at upper 15 cm of soil profiles), and DOP values below 1% [28].  
Further studies should be conducted to understand the mechanisms of plant colonization in HTF, and to provide support for environmental restoration practices in highly saline areas. Consequently, HTF are heterogeneous environments, highly susceptible to spatial and temporal soil physicochemical changes, due to plant rhizosphere and climatic seasonal influences.