The effect of reducing soil water availability on the growth and reproduction of a drought-tolerant herb

Soil water availability in the dry tropical forest varies depending on the rainfall heterogeneity, which may be altered by future climate changes. The predicted water restrictions may modify the strategies of the herbaceous component in the allocation of resources jeopardizing their survival. We aimed at knowing the vegetative, reproductive and phenological responses of Talinum paniculatum under simulated conditions of reduced soil water supply. It is a drought-tolerant herb used in traditional medicine, such as non-conventional plant food and animal fodder. A total of 150 individuals of the herb were submitted to three treatments of water deficiency: T100 (control; 100% field capacity - FC), T50 (50% FC), and T25 (25% FC), with 50 replicates per treatment. Plant growth and reproduction were monitored and differences were tested using General Linear Models. In T50 there was a decrease in diameter growth and in the production and morphometry of flowers, fruits, and seeds, as well as delays in plant phenology, not interfering with leaf production and growth in height. Reduction in anthesis time and change in flower staining were verified in T50. There was a total absence of flowering and fruiting in T25, besides the drastic reductions in growth. In general, we suggest that increasing soil water restrictions may be negative for herb growth and reproduction, but we do not rule out that reductions in attributes can be considered as water-saving strategies. However, the predicted effect of reducing rainfall in dry forests will compromise the reproductive success and population growth of a drought-tolerant herb. • Brazilian dry forests will experience more extreme drought conditions. • We study how soil water restrictions affect a drought-tolerant herb. • Phenological imbalances occur as soil water availability decreases. • Absence of reproduction is noticeable in the drastic soil water restrictions. • Extreme reductions in rainfall will be negative for herbaceous reproductive success.