Regime pluvial como regulador de algas carófitas no solo: Novas evidências sobre a origem dos solos e plantas terrestres"

Abstract

Photosynthetic Soil Crusts (PSCs) represent important modern analogs for understanding the evolutionary and ecological processes involved in the terrestrialization of charophyte algae, the sister group of land plants. The transition of these algae to the terrestrial environment represents a crucial evolutionary event, whose molecular bases are well established through phylogenomic and functional studies. However, the role of ecological interactions and temporal patterns of stress in this process remains poorly understood. The aim of this study was to analyze how different seasonal rainfall conditions affect the composition and dynamics of these microbial communities, which include cyanobacteria and eukaryotic algae. The methodology involved collecting PSC samples from a preserved forest area in southeastern Brazil (19°52'37.2"S, 43°58'12.0"W), characterized by a tropical highland climate during periods of high and low precipitation, followed by metabarcoding analyses of 16S rRNA, 18S rRNA, and ITS markers to identify microbial composition and assess ecological interactions. Results showed that during the dry season, PSCs exhibited a dominance of complex microbial interactions centered on lichenized consortia, suggesting survival strategies based on symbiotic relationships essential for resistance to desiccation and nutrient scarcity. During the wet season, eukaryotic green algae, particularly from the Zygnematophyceae class, predominated, forming more autonomous populations, possibly due to molecular adaptations such as stress resistance genes that may have been acquired through horizontal gene transfer from soil bacteria. Despite their regulation by seasonality, these algae demonstrated effective capability to colonize terrestrial environments far from permanent water bodies through an opportunistic occupation pattern possibly mediated by precipitation and wind, combining population explosions under favorable conditions with the formation of resistant structures during unfavorable periods. This dichotomy between strategies - autonomy under favorable conditions versus interdependence under adverse conditions - reflects different responses to temporal patterns of environmental stress. Seasonality represents a cyclical pattern that favors alternating strategies between active and quiescent states, while the increasing aridity gradient faced during terrestrialization represented a directional selective pressure that favored permanent adaptations. This perspective suggests that the transition to land life involved not only the development of molecular characteristics and symbiotic interactions but was fundamentally shaped by the temporal nature of the selective pressures involved. The persistent vulnerability to water scarcity even in derived lineages of charophytes suggests that this limitation may have been a crucial selective pressure for the development of more complex structures in early embryophytes, representing a fundamental transition in strategy: from surviving stress to living through it.