Distinct morphophysiological responses of the native C4 grasses Axonopus siccus and Eragrostis polytricha to shading

Light, an important abiotic factor that shapes plant growth, is explored here in its impact on two native C4 grasses of campo rupestre, an important and unique montane ecoregion in Brazil that occurs across the biomes Cerrado, Atlantic Forest and Caatinga. Axonopus siccus and Eragrostis polytricha seedlings were subjected to two light conditions: (i) artificial shading and (ii) full sun. The evaluations included growth, nutrition, photosynthesis, leaf anatomy, and metabolism. Shading influenced most of the growth parameters of E. polytricha but left A. siccus morphology almost unchanged. The parameters of leaf anatomy, nutrient content, and chlorophyll a fluorescence exhibited consistent patterns between species. In particular, A. siccus showed higher A_max and light compensation point in shaded conditions, while E. polytricha revealed distinctive changes in carbon metabolism (soluble sugars, sucrose, and starch content), explaining its increased shade growth. These findings underscore various light stress responses in these native C4 grasses.