Phenological cycles in the Pantanal woody communities: Responses to climate and soil moisture seasonality

In this study, we investigated the existence of seasonal phenological patterns in the distinct woody communities of the northern Pantanal Mato-grossense, which are subjected to similar regional climates but under distinct temporal variabilities in soil moisture availability. To determine the underlying factors influencing plant phenological cycles, we investigated the fol- lowing question: How does the annual seasonality of meteorological conditions and local soil moisture contribute to orchestrating the synchronicity of reproductive and vegetative pheno- logical activities among coexisting species populations? Methods Climate and hydrogeomorphologic conditions of the Pantanal basin The Pantanal basin spans Brazil, Bolivia, and Paraguay in the Southern Hemisphere tropics. It has complex meandering and branching river patterns that flow north to south. The central basin is a lowland (<200 m a.s.l.) formed by Quaternary alluvium and is bordered by the old crystalline Central Brazilian Shield in the east and north, the humid Chaco plains of eastern Bolivia in the west and Paraguay in the south, and the young uplifting Andes in the west [30,31]. Located in the upper Paraguay Basin and extending over 150,502 km2 in the central- western region of Brazil, the climate of the Pantanal is typical of tropical savanna (Aw) accord- ing to the Ko¨ppen (1948) classification [32], with a marked seasonality between the periods of dry winter and rainy summer, leading to a wet-dry climate, with an annual mean temperature

of 26.5˚C and rainfall of 1,100 mm ± 300 mm concentrated from October to April (~80%) [20,33]. Rainfall decreases sharply in winter, with monthly records of 10 mm, resulting in a dry season in which evapotranspiration surpasses precipitation [34]. The Pantanal is considered a floodplain with an annual and predictable pattern of flooding influenced by river overflow and summer rainfall [30,35,36], controlling geomorphology and the great diversity of terrestrial, aquatic, and temporary terrestrial habitats [17,31]. The plain has a low-elevation and low-relief topography, with altitudes varying between 80 and 150 m and a north-south declivity of 2.5 − 5.0 cm.km-1, which allows the seasonal flooding of the Upper Paraguay River to cover an area greater than 130,000 km2 [31]. The level of rivers in the northern Pantanal, such as the Cuiaba´ River, follows the trend of seasonal rainfall, causing annual flooding of adjacent plains, which can last more than 6 months [37]. Even after the dry season, part of the plain remains inundated for an additional 2 months due to the low slope and poorly drained soil [38,39]. The soils of the Pantanal are generally hydromorphic, with textures varying from clayey to sandy [40]. Many soils remain water saturated or inundated for a few days to several months due to seasonal floods, restricted drainage, or a highwater levels (2.5 m on average) [37,41]. Thus, hydromorphic soils are found across the region, and their morphological characteristics are attributed primarily to the reduction and oxidation of iron and manganese, which also

confer their distinctive color [42]. The soils found in the northeastern Pantanal are predomi- nantly clay in texture (between 3% and 65% of clay) and are clayey and in the great domain of the Plinthosol [41]. Alternating annual and multiannual dry and wet periods have resulted in different patterns of discharge and sediment load across the floodplain, creating a mosaic of geomorphologic for- mations linked to subtle changes in relief, such as high levees and paleolevees, reflecting inun- dation regimes and the capacity of the soil to retain water [43]. This mosaic is covered by diverse grassland, savanna and forest vegetation with distinct structural, floristic, and func- tional identities, which constitute the basic units, namely, macrohabitats, for the management and protection of biodiversity [17]. PLOS ONE Phenological cycles in the Pantanal woody communities PLOS ONE | https://doi.org/10.1371/journal.pone.0316011 February 7, 2025 3 / 30