## 1 Introduction  
Halophyte plants are able to thrive in extreme environmental conditions of coastal areas, such as hypersaline tidal flats (HTF) [1; 2]. HTF are evaporative environments (referred as _Apicun_ in Brazil) found in semiarid or seasonal-dry coasts around the globe, and at the confluence of terrestrial/estuarine/marine systems, that contain soils with elevated salinity and pH usually greater than 7.0 [3; 4; 5]. In these ecosystems, plant growth is strongly limited by fluctuations in temperature, availability of fresh- and tidal-water, salinity, and nutrients [6]. Consequently, species that colonize HTF, mostly grass and herbaceous halophytes, occupy a patchy pattern [7], and have some physiological, morphological, and anatomical adaptations to face the harsh environmental conditions [8; 9; 10]. To colonize these saline environments, plants may create some adaptation at the \"plant-rhizosphere-soil\" system, by altering the soil properties through root's activity [11], in order to increase nutrients availability at the rhizosphere compared to nonrhizospheric (bulk) soils [12]. Besides promoting conditions for the colonization, changes in the rhizosphere may have ecological implications in controlling ecological successions [11]. In fact, the first species to colonize the ecosystem (i.e., the \"foundation species\") are critical species that defines much of the structure of a community [13]. For example, marsh plants on saline soils have strong ameliorating effects by reducing soil evaporation and accumulation of soil salts, which creates positive forces on natural community [14]. Thus, investigations regarding rhizospheric soils may not only increase the knowledge about the plants effects on natural occurring soil processes, but also shed light on their ability to change the soil environment on their benefit, and the mechanisms for ecological succession [15]. Since HTF are characterized by a short and sparc vegetation cover, they are strongly vulnerable to human impacts and degradation [7; 16]. Indeed, these ecosystems are subjected to increasing rates of anthropogenic disturbances, such as aquaculture (e.g., shrimp farming), domestic sewage disposal, and salt producing ponds [6; 17]. The HTF adjacent to mangrove forests are also threatened by those human activities and land use expansion posing serious concerning for these intertwined coastal ecosystems [18; 19; 20; 21]. Contrasting with the adjacent mangrove forests [7; 22; 23], the HTF soils endure in extreme physicochemical (high pH and salinities) and geochemical conditions [2; 24]. Recent work suggests that HTF may be formed in response to the dieback of mangroves, which is accompanied by substantial changes in the soil environment [1]. Contrastingly, mangrove forests and salt marshes can replace the HTF, if hydrological conditions change in response to input of freshwater and the rainfall increases [23]. In fact, rain and drought events regulated by seasonal changes strongly influence the edaphic components of coastal ecosystems soils and, as a consequence, several ecological processes and ecosystem services [25; 26; 27]. Semiarid seasonal precipitation induces changes in pH, organic matter content, and nutrient bioavailability for plants in hypersaline environments [1; 28]. In HTF, the bare soils are usually more influenced by seasonality than the more vegetated soils, which may influence nutrient dynamics [29]. Our study aims to characterize soil changes induced by plant activity on the soils of adverse environments for plant development, such as the hypersaline tidal flats (HTF). We hypothesize that soil biogeochemical changes are more pronounced in the rhizosphere soils, compared to nonrhizospheric (bulk) soils, driven by plants changings the soil characteristics at the rhizosphere zone in order to reduce edaphoclimatic stresses.