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

Discussion Leaf phenology The leaf-shedding cycles observed in the savanna and forest communities in our study ranged from weakly seasonal to aseasonal, highlighting the diverse phenological responses among woody species. This variation in leaf fall traits reflects the evolutionary and ecological forces linked to environmental filtering that enable species to thrive under different habitat condi- tions [74]. In all the analyzed communities, semideciduous species dominated, comprising more than 50% of the leaf exchange strategies. This aligns with Camargo et al.’s (2018) classification of the woody Cerrado as seasonal semideciduous vegetation [63]. Approximately 29% of the woody species in these communities exhibited complete deciduousness, particularly among those biogeographically associated with the Bolivian Bosque Chiquitano, mesotrophic cer- radão, and other seasonal forests in South America [75]. Notable examples include A. colu- brina, C. fasciculata, H. heptaphyllus, and M. hirtum. In the sandy, low-fertility soils of the PS community, the number of deciduous species doubles compared with those of the other six communities, mirroring the trend observed along the gradient from the Cerrado to seasonally dry tropical forests in northeastern Brazil, where deciduous species increase with aridity [76]. Evergreen species are present in all communities but are more abundant in seasonal seasonal forests, which are typically associated with low to moderate flooding [77]. Convergent responses to leaf shedding within communities were closely tied to climate sea-

sonality. Increased exposure to solar radiation and reduced evapotranspiration during periods of low cloud cover positively influenced leaf fall in the dry winter, particularly in open-canopy communities such as PS and CS. Synchronizing leaf emergence and shedding with solar radia- tion maxima and minima enables trees to maximize water use, contributing to fluctuations in evapotranspiration rates [78]. The increase in evapotranspiration observed at the start of the rainy season corresponds with rising net radiation and temperature [79,80]. Notably, increas- ing maximum monthly temperatures are correlated with increased leaf fall, especially in the SHB community, which experiences several months of inundation during the wet season and very low soil moisture during the driest months [77] C. lanceolatum, the monodominant spe- cies in this community, behaves as an evergreen for most of the year but experiences increased leaf shedding during periods of peak temperatures. In this context, leaf shedding aids in dissi- pating heat during high temperatures and intense solar exposure while also reducing water loss, enhancing leaf cooling, and mitigating the risk of surpassing stress resistance thresholds [81]. Meteorological influences on the vegetative phenological cycle begin approximately two months prior to high-intensity events, underscoring the importance of predictable seasonal cli- mate transitions—such as wet periods following droughts and the arrival of cold air masses— that trigger significant phenological shifts [82].

The climate seasonality associated with an annual flood pulse imposes additional con- straints on woody plants, influencing patterns of deciduousness [83,84]. Anoxic conditions and reduced gas exchange during flooding shape various plant strategies to cope with near- zero oxygen concentrations [9]. At the end of the rainy season, when the maximum soil mois- ture and flood levels are reached, a second peak in leaf fall is observed, with individuals experiencing more than 50% leaf shedding across all communities. This pattern indicates that leaf shedding serves as a strategy to avoid moisture stress caused by both dry-season droughts and flood-season soil hypoxia [9,11] Understanding the relationship between vegetative phe- nology and water stress requires species-specific information on adaptations to drought and flood resistance [11,85]. Jancoski et al. (2022) provided evidence of interspecific variation in hydraulic function regulation influenced by deciduousness [23]. Young individuals of T. PLOS ONE Phenological cycles in the Pantanal woody communities PLOS ONE | https://doi.org/10.1371/journal.pone.0316011 February 7, 2025 18 / 30