Intra-specific variability in biomass partitioning and carbon isotopic discrimination under moderate drought stress in seedlings from four Pinus pinaster populations

The response to drought of 20 open-pollinated families from four Pinus pinaster Ait. populations covering a latitudinal cline (France, Central and Southern Spain, and Morocco) was assessed. The seedlings were cultivated in a greenhouse under controlled temperature and vapor pressure deficit for 120 days, and subjected to two watering regimes for 60 days. Different biomass partitioning variables, pre-dawn water potential, and isotopic discrimination of (13)C in needles (Delta) as surrogate of long-term water use efficiency were estimated for each seedling at the end of the experiment. In response to the imposed drought, there was no change in the root biomass partitioning, but the overall Delta values decreased in response to water stress. All the families of the population from Morocco showed the highest investment in roots, regardless of the watering regime imposed. Inter-family differences within populations were also significant for most parameters as confirmed by the heritability values estimated (higher under the well-watered treatment). The studied P. pinaster populations showed different strategies of response to drought. This may represent an important mechanism by local populations in facing future climatic change. The results could be of value in forest conservation and breeding programs of maritime pine in the future.