Recovery capacity of Poa ligularis after defoliation in Patagonian grasslands: axillary buds and biomass production

SOUTO, C.; G., BECKER; G., SIFFREDI; C., BUSSO & M., STERNBERG

Durban, Sudáfrica

Congreso; VII International Rangeland Congress; 2003

Poa ligularis is one of the dominant species in Patagonian grasslands that decreases under grazing.  We investigated the defoliation effect on the number and position of viable axillary buds, and biomass production during one growing season.  Experiments were arranged in a randomized complete block design and conducted in a natural stand.  Treatments included one defoliation height (10 cm), one to five times a year, in addition to undefoliated controls. Bud respiratory activity was examined using tetrazolium test and the vital stain Evan's blue. At the end of the growing season, plants that have been defoliated more than three times showed significatively (p<0.05) lower number of respiratory active buds than unclipped controls. Both treated and untreated plants produced more (p<0.05) axillary buds  in the periphery than in their centre. Results concerning biomass production showed that defoliating to 10 cm stubble height with one, two, three, four, and five times a year produced 7.5, 10.2, 9.2, 12.3, and 12.4 g of dry matter per plant, respectively, compared to 10.7 g of dry matter per plant for undefoliated controls.  Treatments increased shoot weight by 12.3 % in average compared with undefoliated controls.  Even when grass biomass was higher when plant defoliation events were five times a year, the number of active buds were reduced with more than three clipping events. Therefore, Poa ligularis plants could tolerate moderate grazing intensity without risk for its potential regrowth. More research on the effect of successive years of severe defoliations is required to accurate the actual effect on biomass production.   Key words: Defoliation, Poa ligularis, axillary buds