The establishment ofFestuca pallescensin arid grasslands in Patagonia (Argentina): the effect of soil water stress

BERTILLER, M; ZAIXO, P; IRISARRI, M; BREVEDAN, E

JOURNAL OF ARID ENVIRONMENTS

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Manchester; Año: 1996 vol. 32 p. 161 - 171

0140-1963

The role of soil water stress on the survival and development of vegetativestructures (shoot and root biomass) of new seedlings of Festuca pallescens wasinvestigated in laboratory experiments under controlled conditions and withfield observations. Experiments in the laboratory consisted of evaluating theinfluence of three levels of water stress, in the range from ?1·7 to ?8·0 MPa,on the survival and development of seedlings. Field observations wereconducted in a representative stand of the semi-arid grasslands of F.pallescens. During two growing seasons, at approximately bimonthly intervals,the soil water potential as well as the density and survival of seedlings of F.pallescens were estimated. In the laboratory, the development of F. pallescensseedlings depended on water availability in the soil. Survival of seedlings,approximately 2-months old, varied between 65 and 100% among treatments. Significant differences among treatments in above- and below-groundbiomass, leaf number and leaf length were also observed in the survivingplants. In range conditions soil water potential showed values ranging from ?1to ?9 MPa. Survival reached only 30% in seedlings 2-months old. No seedlingsurvived after summer. These trends depart from those observed in thelaboratory, where survival rates were higher even under soil water conditionssimilar to those observed in the field. The observed differences may beconnected with the emergence of seedlings in the vicinity of established plantsof F. pallescens in the field where competition for soil water probably occurred.Also, desiccation caused by strong dry winds during spring and summer couldhave affected seedlings in field conditions. Based on these results theestablishments of new plants of F. pallescens in the semi-arid grasslands ofwestern Patagonia might be possible only in years with exceptionally humidsummers. The alternative of managing the grassland by seed introductionfrom ecotypes showing improved drought responses is discussed.