Do invasive and native grasses in Brazilian Savanna differ in their photosynthetic performance under natural light radiation?

Abstract

Light, despite being essential for photosynthesis, can become an environmental stressor, since at high incidence it can induce photoinhibition. In tropical regions it is known that invasive C4 grasses maintain higher photosynthetic performance than C3 grasses. That is why we evaluated the dynamics of photosynthetic parameters in different grass species of the Brazilian Savanna (Cerrado), taking into account whether they are native or invasive, and have C3 or C4 photosynthetic metabolism pathway. The native species evaluated were Echinolaena inflexa, Trichanthecium cyanescens (C3) and Loudetiopsis chrysothrix (C4), and the invasive species Melinis minutiflora and Urochloa decumbens (C4). We evaluated chloroplastic pigment content, chlorophyll a fluorescence, leaf gas exchange and photochemical energy partitioning on fully expanded and undamaged mature leaves. Results indicate that leaf gas exchange varied throughout the day for all grass species. The invasive species showed higher CO₂ assimilation rates and water use efficiency and lower values of stomatal conductance than native species; however, all species showed a decrease in potential photosynthetic quantum yield at midday. Regarding chloroplastic pigments, chlorophyll a was the only one that presented a difference between the C3 and C4 plant species, and there was no difference between species in the photochemical energy partitioning. Although they occur at the same place, the species showed different responses even when comparing the same type of photosynthetic metabolism. The C4 native species L. chrysothrix was the one that showed values closer to those obtained for the invasive C4 species and may be an alternative in management strategies.