Variation in seedlings survival to drought stress of Patagonian Cypress natural populations.

PASTORINO, MARIO JUAN; CABALLÉ, GONZALO; VARELA, SANTIAGO; GALLO, LEONARDO ARIEL

San Lorenzo de El Escorial

Conferencia; Evoltree Conference- Forest Ecosystem Genomics and Adaptation; 2010

Evoltree - INIA

The persistence of some forest tree species in the face of global climate change may depend on differences in drought tolerance among natural populations. The Patagonian Cypress (Austrocedrus chilensis (D.Don) Pic.Ser. et Bizzarri) is found in the ecotone between the temperate southern beech (Nothofagus) forests and the steppe in southern South America. Any increase in drought conditions in the region would put the survival of its forest patches at risk. Inter- and intrapopulation variation of response to severe drought in this conifer was studied in a greenhouse pot experiment. One hundred and twenty 3-year-old seedlings of each of eight natural populations (four from xeric habitats (<500 mm annual precipitation [a.p.]), two from humid conditions (>1300 mm a.p.) and two from mesic habitats) were grown under common garden conditions in three blocks. Ten open-pollinated families were represented in the two populations from the driest zone (330 mm a.p.). Watering was suspended for 43 days in late spring until half of the plants of the first block had died. Volumetric soil water content (VC, % vol/vol) was recorded once a week in five pots with a TDR equipment. Pre-dawn water potential was measured in an extra sample of 20 plants each week. Maximum photosystem II efficiency (Fv/Fm) was measured weekly within this period in a sample of 5 plants per genetic entity (N=130). Survival was evaluated in the whole trial after a recover period of eight months along which all plants were “normally” watered. ANOVAs were performed based on general linear mixed models for both Fv/Fm and survival data. Populations differed significantly for Fv/Fm (P=0.019) and survival (P<0.001), even those originating from the same precipitation zone. ‘Family’ significantly affected survival (P=0.001), while for Fv/Fm significant differences were due to only one family (P<0.001) which showed exceptional drought tolerance. The difference among populations from the same precipitation zone indicates the relevance of stochastic processes (such as genetic drift) in modelling genetic structure even of adaptive characters. Different survival mechanisms among families could be a conservative strategy to assure local evolution of populations.