Axillary bud viability and dry matter production of Poa ligularis in Patagonian grasslands

SOUTO, C.P.; BECKER, G; SIFFREDI, G.; BUSSO, C.

PHYTON - INTERNATIONAL JOURNAL OF EXPERIMENTAL BOTANY BA ARGENTINA

Año: 2004 vol. 1 p. 39 - 51

0031-9457

Poa ligularis Nees is one of the dominant perennial grass species in Patagonian grasslands. This is the first field study which investigated the effects of defoliation frequency on its number of viable axillary buds, and subsequent dry matter production during one growing season. Experiments were arranged in a randomized complete block design. Treatments included one defoliation height (10 cm), from one to five times a year, and undefoliated controls. Bud respiratory activity was examined usingthe 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. A high defoliation frequency increased bud death in stem bases. Both defoliated and undefoliated plants produced more (p<0.05) axillary buds at the periphery than at their center. Defoliation treatments increased shoot weight by 13.4% on average compared with undefoliated controls, but reduced in by 10% the average number of metabolically active axillary buds. This indicates that this reduction, however, was not high enough to constrain dry matter production.    It appears that Poa ligularis could tolerate moderate grazing frequency and intensity without compromising its potential regrowth capacity. Longer-term studies of the effects of defoliation on dry matter production and bud metabolic activity are needed to understand the cumulative effects of grazing of P. ligularis in natural grasslands.