Response of phalaris to differing water regimes or grazing treatments as measured by basal bud weight, water-soluble carbohydrates, and plant tillers

Abstract

Studies of Phalaris aquatica L. were used to collect data for basal bud (all below ground shoot material) weights, their water-soluble carbohydrate (WSC) content, and green vegetative tillers. A glasshouse study of cvv. Australian and Sirosa was conducted on regrowth after 26 days of plants previously exposed to either non-limiting or limiting (simulated Mediterranean environment, and 3- or 6-week drought) watering treatments. The other studies were of Sirosa phalaris pastures that had previously been subjected to continuous or lenient (resting in both spring and autumn each year) grazing by Merino wethers. In the glasshouse study, weight of basal buds (g/plant) was highest (13.88 g/plant) for Australian plants in the non-limiting water treatment, but not significantly different among watering treatments for Sirosa plants. Basal bud WSC values ranged from 2126 mg/plant (Australian phalaris, non-limiting water) to <200 mg/plant in 6-week drought and Mediterranean watering treatments of both cultivars. Tiller regrowth was higher in Australian non-limiting water treatment compared with all other treatments. Post-drought field studies (6 weeks tiller regrowth in May–June 1995) showed that plants in continuously grazed treatments had basal bud weights <11 g/plant, basal bud WSC contents <600 mg/plant, and green vegetative tiller weights <2.5 g/plant, compared with values of >11 g/plant, >1300 mg/plant, and >3.6 g/plant, respectively, for treatments rested for 12 weeks in both autumn and spring. At the end of spring 1995, when plants were post stem elongation and anthesis, basal bud WSC (mg/plant) was significantly higher in autumn–spring rest treatments compared with plants that were continuously grazed (mean values for 2 sites of 2889 and 1458 mg/plant, respectively). From these data, threshold values of basal bud WSC contents of <600 mg/plant after 6 weeks of regrowth in autumn–early winter, or <2000 mg/plant in flowering plants in late spring in continuously grazed pastures >3 years old, were proposed as useful indicators that management intervention may be required to maintain Sirosa phalaris persistence on the North-West Slopes of New South Wales.