Seedling establishment and early growth in Calobota sericea subjected to moisture stress

Abstract

The South African perennial legume Calobota sericea (Thunb.) Boatwr. & B-E van Wyk has been shown to be drought tolerant as mature plants, but information on drought tolerance of seedlings is lacking. This study evaluated the impact of moisture stress on seedling emergence, survival and growth in C. sericea. In the first trial, pre-germinated seeds were planted at 100, 70, 50 and 40% of soil moisture holding capacity without additional watering. Seedling emergence and mortality was recorded daily for 14 days. In the second trial, seeds were allowed to grow under well-watered conditions for one month, after which moisture stress was imposed for 15 and 30 days. Thereafter, the seedlings were uprooted, for shoot and root measurements. Results from these trials show that C. sericea seedlings will establish even at severely reduced water-availabilities, but without subsequent watering, significant seedling mortality will occur. Calobota sericea seedlings displayed a range of morphological adaptive strategies to moisture stress including the minimisation of water loss and optimisation of water uptake. Further research into the impacts of regular cycles of moisture stress is needed to determine if changes in morphology due to prior moisture stress will result in improved adaptation to subsequent moisture stress.