Drought Tolerance in Silphium perfoliatum—An Evaluation of Leaf Area, Chlorophyll Content, Photosynthetic Activity and Biomass Production

Silphium perfoliatum is a perennial herbaceous species which grows spontaneously in North American prairies, with good ecological plasticity and adaptability in different environments and conditions. It is part of the Asteraceae family, genus Asterales, which has a wide variety of spontaneous and cultivated species (over 33 known species). Due to the increasing frequency of extreme weather events, the increase in average temperatures, and the chaotic distribution of rainfall, the identification of plant species with tolerance to abiotic stressors and with high ecological plasticity is a priority. The research objectives were to evaluate the impact of the of induced soil-drought conditions and heatwave on the growth and photosynthesis processes and their components in second-year S. pefoliatum plants, in the early flowering stage. Although numerous experiments have been carried out on the evaluation of the rate of photosynthesis under drought conditions in different cultivated and spontaneous species, there are no literature data on the impact of these conditions on S. perfoliatum. The obtained results attest that intense soil drought affects the growth rate of plants by reducing leaf area and chlorophyll content. Also, photosynthetic activity has been inhibited, and the values of the photosynthetic parameters in the mature leaves of S. perfoliatum in the flowering stage (6.1. BBCH) show that there was a close relationship between the two parameters and assimilation rate (A), intracellular CO2 concentration (ci), transpiration (E), and stomatal conductance (gsH2O) due to an increase in PAR or CO2-atm concentration. Based on the obtained data, Silphium perfoliatum seems to be an anisohydric species, which eliminates important amounts of water in short-term drought conditions, maintaining the osmotic potential through the synthesis of osmolytes and metabolic protection. The stress induced by prolonged drought also has a negative impact on the biomass accumulation in the aboveground organs.