Impact of water stress on growth reserves and re-growth of Themeda triandra (Forssk) following defoliation

Abstract

The influence of water stress and defoliation on the concentration of total non-structural carbohydrates (TNCC) and water-soluble protein (WSPC) as growth reserves after defoliation were determined in the indigenous C₄ semi-arid grass species Themeda triandra during three growth stages (vegetative, piping and reproductive) and in three plant parts (roots, stubble and leaves). Four water stress treatments (T1 = 0-25%, T2 = 25-50%, T3 = 50-75% and T4 = 75-100% depletion of plant available water) were applied to the plants in pots in a glasshouse. The TNCC declined drastically after severe defoliation over all the water treatments (P < 0.05), in all the plant parts (P < 0.05) and for all the growth stages (P < 0.05), while the TNCC did not recover (P < 0.05) (to the TNCC values as before defoliation) within 6 days after defoliation. The WSPC in the leaves increased from after defoliation, up to day 6 over all the water treatments (P < 0.05) and for all the growth stages (P < 0.05). Non-structural carbohydrates serve as the most important growth reserve and are utilised for re-growth after severe defoliation. Water-soluble protein can also be utilised as growth reserve, but only as an emergency measure for up to two days after defoliation. These results could make a meaningful contribution to ensure sustainable utilisation of the grassland ecosystem in semi-arid areas.