COS 155-6 - Storage and biomass reveal a carbon-conservative allocation in drought-adapted plants

Abstract: Plants inhabiting dry environments are generally characterized by lower growth rates and higher concentrations of total non-structural carbohydrates (NSCs), or of its fraction of soluble sugars (SS) than their counterparts from more mesic conditions. This pattern has been interpreted as a result of drought-mediated increases of NSC concentrations driven by the sink strength (mainly growth) being more reduced by drought than the carbon (C) gain. However, high NSC and soluble sugar (SS) concentrations ensure adequate osmoregulation and metabolism, while low growth reduces the water and C demands, which together could be part of an adaptive syndrome to resist drought. To determine if high NSC and SS concentrations and low growth reflect local adaptation to drought, the biomass and the seasonal dynamics of the NSC and SS concentrations were compared in ecotypes from dry and humid climates of four widely distributed species in southern Chile. Seeds of two tree species (Embothrium coccineum and Ribes magellanicum, both native species) and two herbaceous species (the native species Acaena ovaleifolia and the exotic species Plantago lanceolata) were collected from populations of dry (< 600 mm.year-1) and humid ( >2,000 mm.year-1) climates and seedlings were grown for three years in a common garden experiment.

Seedlings from dry locations had significantly lower biomass, and similar or higher NSC and SS concentrations, compared to seedlings from humid locations. In all species, root and stem SS concentrations increased by late summer in seedlings from both ecotypes, coinciding with the period of minimal precipitation in the sites of seed collection. However, this increase was significantly more pronounced in the ecotypes from the dry climates. The greater SS accumulation exhibited by ecotypes from dry climates compared to those from humid climates is consistent with ecotypic differentiation in the seasonal requirements of SSs, possibly associated with the dehydration tolerance. Results suggest that drought acts as a selective driver of high NSC and SS concentrations and reduced growth, and that a growth-storage tradeoff in carbon allocation underlies local-adaptation to contrasting levels of precipitation.