Respostas morfofisiológicas ao déficit hídrico em gramíneas com metabolismos C3, C4 e intermediário

Abstract

Grasses (Poaceae) are the foundation of human and animal food systems and play a strategic role in natural ecosystems and large-scale biomass production. In the context of climate change, water limitation has become one of the main constraints to plant productivity, highlighting the need to better understand the mechanisms that confer resilience to stress. This dissertation aimed to investigate how different photosynthetic types — C₃, C₄, and intermediate C₃–C₄ — influence the morphophysiological and productive responses of tropical grasses under drought conditions. The study was conducted under controlled conditions and included the evaluation of leaf water status, cellular integrity, morphometric traits and productivity in four species: Triticum aestivum (C₃), Urochloa brizantha (C₄), Homolepis isocalycia, and H. longispicula (C₃–C₄ intermediates). Results showed that photosynthetic metabolism shapes distinct drought response strategies: while the C₄ species exhibited high productivity, its sharp decline under stress reflected a strong dependence on water availability; the C₃ species showed structural limitations and increased leaf senescence; and the intermediate species exhibited contrasting behaviors, with H. longispicula notably maintaining active leaf production under stress. The main finding of this study is the evidence that traits associated with functional stability — such as the preservation of vegetative architecture and continuous growth under water restriction — may already be present in C₂ grasses. These traits reinforce the role of intermediate species as functional transitions between the C₃ and C₄ extremes, contributing to the understanding of photosynthetic evolution in Poaceae. As a future perspective, further investigation is recommended on other Homolepis species and on additional ecophysiological variables, including water use efficiency, radiation use efficiency, leaf area index, and relative growth rates.