Negreiros, D. | Search bioRxiv

bioRxiv2023

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

Background and AimsRock outcrop vegetation is distributed worldwide and hosts a diverse and unique flora that evolved under harsh environmental conditions. Unfortunately, seed ecology in such ecosystems has received little attention, especially regarding seed traits, germination responses to abiotic factors and the potential role of phylogenetic relatedness on such features Here, we provide the first quantitative and phylogenetically-informed synthesis of the seed functional ecology of Brazilian rock outcrop vegetation, with a particular focus on quartzitic and ironstone campo rupestre. MethodsUsing a database of functional trait data, we calculated the phylogenetic signal of seven seed traits for 371 taxa and tested whether they varied among growth forms, geographic distribution, and microhabitats. We also conducted meta-analyses that included 4,252 germination records for 102 taxa to assess the effects of light, temperature, and fire-related cues on the germination of campo rupestre species and explored how the aforementioned ecological groups and seed traits modulate germination responses. Key ResultsAll traits and germination responses showed a moderate-to-strong phylogenetic signal. Campo rupestre species responded positively to light and had maximum germination between 20-25 {degrees}C. The effect of temperatures beyond this range was moderated by growth form, species geographic distribution, and microhabitat. Seeds exposed to heat shocks above 80 {degrees}C lost viability, but smoke accelerated germination. We found a moderating effect of seed mass for in responses to light and heat shocks, with larger, dormant seeds tolerating heat better but less sensitive to light. Species from xeric habitats evolved phenological strategies to synchronise germination during periods of increased soil water availability. ConclusionsPhylogenetic relatedness plays a major role in shaping seed ecology of Brazilian rock outcrop vegetation. Nevertheless, seed traits and germination responses varied significantly between growth forms, species geographic distribution and microhabitats, providing support to the regeneration niche hypothesis and the role of functional traits in shaping germination in these ecosystems.

ecology↗

bioRxiv2021

Plant secondary metabolite diversity reflects both phylogeny and ecological adaptation

A phylogenetic framework explaining plant secondary metabolite diversity is lacking, but metabolite classes could represent adaptations to habitat resource availability. We test the hypothesis that primary adaptive strategies (competitors, C; stress-tolerators, S; ruderals, R) are associated, respectively, with nitrogenous metabolites synthesized in persistent organs (alkaloids), nitrogen-lacking aromatic terpenes and phenolics, and nitrogenous compounds prevalent in reproductive tissues (cyanogenic glucosides and glucosinolates). A matrix was compiled of 1019 species for which secondary metabolite pathways and CSR strategies are known. Accounting for phylogenetic relatedness and native biomes, we found that most phytochemical pathways did not correlate with strategy axes, but certain key associations were evident. C-selection was positively associated with amino acid-derived phenylpropanoids (low phylogenetic relatedness; {lambda} <0.5) and pyrrolizidine alkaloids and galloyl derivatives (high {lambda}), and negatively with N-lacking linear monoterpenes (low {lambda}). Nitrogenous cyanogenic glucosides positively correlated with R-selection (low {lambda}). Terpenoids were widely distributed, but correlated positively with S- and negatively with R-selection (low {lambda}). Twenty-six correlations between phytochemicals and biomes (low {lambda}) were evident. Most secondary metabolite synthesis pathways are widespread, reflecting common roles and obligate defence, and strong phylogenetic effects are often evident. However, the character of phytochemical/adaptive strategy associations agrees with ecological theory and thus reflects adaptation.

ecology↗