Plant reserves of perennial grasses subjected to drought and defoliation stresses on the Northern Tablelands of New South Wales, Australia

Abstract

The effects of defoliation intensity and drought severity on levels of water-soluble carbohydrate (WSC), fructan, and etiolated regrowth of 6 important perennial grasses were investigated. The experiment was conducted under a rain-out shelter at Armidale, NSW, Australia, using 6 perennial grass species ('Phalaris aquatica' cv. Sirosa, 'Festuca arundinacea' cv. Demeter, 'Dactylis glomerata' cv. Porto, 'Lolium perenne' cv. Victorian, 'Microlaena stipoides' cv. Shannon, and 'Austrodanthonia richardsonii' cv. Taranna) subjected to 3 moisture regimes (non-stress moisture, and moderate and severe drought) and 2 defoliation intensities (moderate and severe) over 2 seasonal sequences (spring–summer and summer–autumn). The range in WSC, fructan, and etiolated regrowth of the species varied, with Festuca and Lolium having the highest WSC and fructan concentrations. 'Austrodanthonia' had the lowest WSC concentration of the species. Unlike the introduced species, the natives did not store fructans. The species varied in their response to the treatments imposed. 'Festuca' and 'Phalaris' had the highest etiolated regrowth and showed the greatest effect of defoliation intensity. Etiolated regrowth appeared to be a sensitive measure of plant status, showing the fragile nature of some of the species. The effect of defoliation intensity and drought varied with season. Defoliation intensity had little effect on carbohydrate reserves of all species, except 'Festuca', during summer of the spring–summer experimental season. During the summer–autumn experimental season, severe defoliation reduced the rate of accumulation during the period December–April. Drought affected carbohydrate accumulation and utilisation. Carbohydrates that had been accumulated at the end of spring of the spring–summer experimental season in plants affected by drought were utilised during summer. However, if drought commenced in summer, carbohydrate accumulation continued for 120 days in all species studied, and 180 days in 'Lolium' and 'Phalaris'. Autumn appeared to be a period when plant reserves were particularly susceptible to stress. The importance of WSC, fructans, and etiolated regrowth as measures of plant reserves, and their role in persistence were discussed.