Is Poa spiciformis tolerant to defoliation? Defoliation effects on its productive performance

D Ferrante, A Cesa, S Lewis, G Jaurena


In plants, compensatory growth takes place when the positive effects of defoliation compensate the negative ones, and defoliated plants show a similar or increased production in relation to non-defoliated plants. Our objective was to evaluate the ability to compensate defoliation of Poa spiciformis, a forage perennial tussock grass in southern Patagonia (Argentina). The experiment was performed in potted plants that grew under controlled conditions of watering and fertilization. Three defoliation frequencies were imposed (zero, three or five) using 20-25 day intervals among them. Harvest intensity was always equivalent to 50% of the aerial biomass. Fifteen plants were sampled per treatment, and growth and reproductive indicators were evaluated at the last sampling date. Differences between treatments were analyzed using ANOVA and orthogonal contrasts (p<0.05). Defoliation reduced the production of aerial, root and total biomasses between 48 and 53%, indicating that there was not a total compensation. Frequency of defoliation only reduced plant height in the 5-cut treatment. Defoliation did not promote an increase in the number of tillers, and did not modify the number of reproductive culms. Poa spiciformis, presented partial compensation in the relative growth rate (RGR) only when the last harvest was performed at the time of low RGR on non-defoliated plants. Even when the species was not able to recover the removed biomass, the reproductive structures were not affected by simulated grazing, suggesting that plants would be able to produce seeds even under high defoliation frequencies.

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Phyton. International Journal of Experimental Botany. ISSN print 0031-9457 ISSN en line 1851-5657 Fundación Rómulo Raggio Gaspar Campos 861,  Vicente López, Buenos Aires, Argentina (C.P. 1638) Tel 54 11 4791-0868 / 4796-1456