Warming Change Nutritional Status and Improve Stylosanthes capitata Vogel Growth Only Under Well-Watered Conditions

Climate change may impact plant nutritional status and productivity. However, few studies evaluate the effects of global change variables on tropical forage species under field conditions. In this study, we evaluated the isolated and combined effects of warming and drought on nutritional status and its relations with net photosynthesis rate and aboveground dry mass production of Stylosanthes capitata , a C 3 tropical forage legume under field conditions. We tested two canopy temperature levels, ambient ( Ta ) and elevated temperatures (2 °C above ambient temperature, Te ), and two soil moisture levels, irrigated (plants maintained at 80% of soil field capacity, I ) and drought ( D ). The experiment was conducted in a randomized complete block design with three replicates in a 2 × 2 factorial scheme. Our results showed that warming decreased leaf N and P content, while leaf K content increased, leading to an increase in C:P and C:N ratios and dry mass production. Drought increased leaf K content, and decreased leaf N content, leading to an increased C:N ratio and decreased dry mass. No changes were observed for leaf C, Ca, Mg, and S content due to our treatments. In addition, regression analysis showed that changes in leaf nutrient contents were not associated with changes in the net photosynthesis rate, except for leaf N content in the combined warming and drought treatment. Our short-term experiment indicates that although biomass production will not be modified under a combination of warming and drought, both environmental factors may negatively impact the animal feeding and livestock in the future due to a decreased leaf N and P content.