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

in tropical regions [69,70], namely, monthly average temperature and mean maximum and minimum temperatures (˚C), actual evapotranspiration (mm month-1), total rainfall (mm), and insolation (hours month-1 of incident solar radiation). The climatic data were acquired from the National Agency of Waters on the website ‘Hidroweb’ (http://hidroweb.ana.gov.br) [71], and BDMEP–INMET data, representing the station of Cuiaba´, Mato Grosso (OMM: 83361). This official weather station has operated since 1911 [72] serving as a reference for cli- mate monitoring in the North Pantanal. The correlations were conducted with climatic values from the same month (r0) as the date of the phenological data and with values from the first (r1) and second (r2) months before the observations. This approach allowed us to evaluate delays in phenological response to annual climate variation. The local effect of seasonal variation on soil moisture (%) within each com- munity was also analyzed at a depth of 20 cm, a layer where savanna first lateral root branches grow and where soil nutrients are more available [73]. For this purpose, three soil samples per community were collected with a Dutch corer at 20 cm and taken to the Soil Physics Labora- tory of the Federal University of Mato Grosso (UFMT) for weighing and drying. The samples were oven-dried at 105˚C for 24 h, and the mean of three samples per unit was considered. The gravimetric soil moisture (%) was determined by the difference between the wet weight (WW) and dry weight (DW) via the equation [(WW−DW)/DW]. A soil moisture content of

100% indicates that the site is in a flooded state. The analyses were performed with the R ver- sion 3.6.1 library Hmisc package. Results Annual variability in meteorological and soil moisture data The annual air temperature averaged 27.8˚C, reaching a minimum of 15.0˚C in July and a maximum of 39.5˚C in September (Fig 1). Notably, the dry season, marked by low precipita- tion in July and September, contrasted sharply with the wet season, which accounted for approximately 85% of the total annual rainfall of 1123 mm. These months correspond closely to the annual variations in the water level of the Cuiaba´ River, the primary catalyst for flooding in the studied floodplain. Evapotranspiration reached its zenith during the rainy season (Octo- ber − April), peaking at 188 mm month-1. Its alignment with rainfall pattern was inconsistent, suggesting the possible influence of free water surfaces on evapotranspiration during flooding or the impact of minimum temperature fluctuations. The period of intense insolation spanned from July (257 hours month-1) to September (220 hours month-1), coinciding with the lowest actual monthly evapotranspiration (9–38 mm month-1). Conversely, the rainy season corre- sponded to a 174.3 hour month-1 reduction in insolation in October, which was indicative of increased cloud cover. The soil water moisture content varied between community sites, as illustrated in Fig 2, depicting the intrinsic connection between surface water flux and vegetation cover, soil drain-

age capability, and the cumulative effect of rainfall. The lowest average soil moisture content was found in PS (20%±24) and LSDF (20%±4), followed by CS (29%±25), ASDF (30%±19), MF (40%±39), SHR (40%±42), and IS (51%±38) (S1 Appendix). In some vegetation communi- ties, such as the ASDF, MF, and IS communities, increased precipitation was correlated with increased soil surface moisture and greater evapotranspiration in the previous month. There was no apparent direct influence of climate variables on the annual variation in soil moisture in the LSDF and CS. A higher maximum temperature with a peak in October reduced the soil moisture in the SHB. PLOS ONE Phenological cycles in the Pantanal woody communities PLOS ONE | https://doi.org/10.1371/journal.pone.0316011 February 7, 2025 7 / 30