Vegetative and reproductive phenology in a tropical grassland–savanna–forest gradient

Abstract

Question: Climate, particularly precipitation, is the primary factor driving tropical plant phenology because of its relevant role in regulating water availability. However, differences in soil physicochemical properties can also drive resource availability, potentially affecting plant phenology, especially under similar environments in terms of rainfall regime. We determined whether the seasonality and synchrony of the vegetative and reproductive phenophases differ along a grassland-savanna-forest gradient under the same climate regime in a Neotropical seasonal ecosystem. We hypothesized that species growing on shallow, nutrient-impoverished soils have a higher capacity to respond to precipitation pulses than those on rich soils.Location: Serra do Cipó, southeastern Brazil. Methods:We quantified soil physicochemical properties associated with fertility and water retention of the grassland (campo rupestre), savanna (cerrado) and forest, and determined the phenological strategies of 70 species across the three vegetation types by monitoring vegetative and reproductive phenophases over one year. For each phenophase, in each vegetation type, we evaluated the seasonality and synchrony of phenological patterns. We quantified the phylogenetic signal for phenophases to disentangle the relative roles of historical vs ecological drivers of plant phenology.Results: Soils from campo rupestre were more nutrient-and water-limited than those of cerrado and forest. Cerrado and forest communities had similar phenological strategies, whereas species from campo rupestre showed strategies that maximize resource acquisition and conservation. In the cerrado and forest, leafing and flowering patterns were seasonal, with leaf flushing and flowering peaking at the onset of the rainy season and leaf senescence in the dry season. Conversely, species from campo rupestre showed continuous leafing and flowering patterns, while fruiting was seasonal. Phenophases did not show a phylogenetic signal. Conclusions:We demonstrated changes in vegetative and reproductive phenology that are likely associated with variations in soil physicochemical properties. We argue that more severe edaphic filters may have shaped different phenological patterns in campo rupestre.

Seed functional ecology in Brazilian rock outcrop vegetation: an integrative synthesis

“…Second, we found a significant phylogenetic signal for seed dispersal season, while seed dispersal season in the Cerrado (Escobar et al 2021) and other phenological events in the campo rupestre (Zanetti et al 2020;Oliveira et al 2021) have not shown such signal. As a result, seed dispersal season is the only phenophase that has shown a significant phylogenetic signal in the Brazilian rock outcrop vegetation, potentially because of an intense evolutionary pressure towards germination timing in these harsh ecosystems, where water is even scarcer than in the Cerrado (Oliveira et al 2021), thus may create stronger selective pressures for establishment.…”

“…Still, the authors tested and measured the phylogenetic signal of this trait using Bloomberg's K, an index known to be highly sensitive to sample sizes and incomplete phylogenetic background, and that provides divergent results to Pagel's l (Münkemüller et al 2012). Second, we found a significant phylogenetic signal for seed dispersal season, while seed dispersal season in the Cerrado (Escobar et al 2021) and other phenophases in the campo rupestre (Zanetti et al 2020;CS Oliveira et al 2021) have not shown such signal. As a result, seed dispersal season is the only phenophase that has shown a significant phylogenetic signal in the Brazilian rock outcrop vegetation, potentially as a result of an intense evolutionary pressure towards germination timing in these ecosystems, where water is even more scarce than in the Cerrado (CS .…”

“…Still, our data only support a positive moderating effect of seed mass on germination responses to 20 and 30 ºC, both temperatures where no significant differences between herbs and shrubs were found. Also, the small variation in seed size mentioned earlier and the limited availability of data from hydrothermal time models our study system (but see Duarte et al 2018;Oliveira et al 2021) limit our capacity to test this hypothesis. On the other hand, temperatures above 30ºC decreased and delayed germination in herbs, while shrubs remained unaffected, implying that shrub seeds tolerate germinating at higher temperatures.…”

“…2021) have not shown such signal. As a result, seed dispersal season is the only phenophase that has shown a significant phylogenetic signal in the Brazilian rock outcrop vegetation, potentially as a result of an intense evolutionary pressure towards germination timing in these ecosystems, where water is even more scarce than in the Cerrado (CS Oliveira et al . 2021).…”

“…2021) and other phenological events in the campo rupestre (Zanetti et al . 2020; Oliveira et al . 2021) have not shown such signal.…”