Tropical cropland systems will face challenges due to the expanding population and climatic changes. We used a temperature- and free-air-controlled enhancement and free-air carbon dioxide enrichment facility to analyze the effects of warming (+2ºC) and atmospheric CO2 (600 ppm) on Stylosanthes capitata (Vogel) parental plants' seed quality parameters. S. capitata is a Brazilian native forage legume and used in grazing systems. The plants were subjected to four treatments (with four replicates each): Control [C], increased CO2 [eCO2], warming [eT], and the combination [eCO2 + eT]. At the beginning of flowering, four parental plants per replicate were labeled and sampled 9-12 weeks after the first anthesis at the end of April 2015. For the seed quality evaluation, the parameters analyzed were as follows: the number of seeds per inflorescence (unit), 100-seed weights (mg), the percentage of abortions and unviable seeds (%), and the seed coat's color. For the seed germination evaluation, we assessed the seedling vigor and emergence. For the germination time (GT) and germination rate, seedling emergence on moistened Petri dishes was assessed daily until the ninth day, and germinability and the germination speed index (GSI) were calculated. Two-way and three-way ANOVAs were used to analyze treatment effects. Our results showed that warming increased the number of seeds per inflorescence by ~37%, reduced unviable seeds by 55%, and altered the seed coat color frequency to 64% beige with dots. Warming and eCO2 had opposite effects on seedling vigor, increasing it by 20% and decreasing it by 50%, respectively. The germination rate was influenced by the interaction of temperature and CO2, mainly from the second to fourth days and the last days, while treatments did not affect the GSI and germination time (GT). Overall, germination rates were around or above 90%. This study demonstrates that warming (+2 °C) and eCO2 (600 ppm) in the parental environment affect the reproductive and early survival strategies of S. capitata offspring. Our results provide a better understanding of the effects of simulated warming and elevated CO2 on the quality and germination dynamics of this important tropical species.

This work was supported by FAPESP (Grants 08/58075-8), FAPESP fellowships (Grant 15/23930-9 and 2013/18633-0), CNPq/ANA/MCTI (Grant 446357/2015-4), and CNPq fellowships (Grants 150737/2014-9 and 140144/2016-1).