The interaction between carbon dioxide enrichment and salinity on growth and carbon partitioning in Phaseolus vulgaris L

The influence of CO2 (ambient and 700 mumol mol-1 ) and NaCl (90 mol m-3) on growth and carbon partitioning was investigated during the vegetative development of Phaseolus vulgaris L. cv. Taylor Horticultural grown hydroponically in enclosed chambers. Salt reduced relative growth rates (RGR) due to a reduction in unit leaf rate (ULR) and specific leaf area (SLA). Allocation changed to favour root and leaf mass rather than leaf area (LA). Salt reduced total and individual LA, due to reduced cell division and expansion, shoot and root fresh (FWT) and dry (DWT) weights, and relative water content (RWC). Instantaneous water use efficiency (WUE) was increased due to reduced transpiration rates (Tr). Reduced net photosynthesis (Pn) was associated with reduced stomatal conductance (gs), intercellular CO2 (Ci) and chlorophyll content. Dark respiration (RD ) was increased. Assimilate export rates in the light were reduced and accumulation rates were increased. Elevated CO2 increased RGR due to an increase in ULR and in spite of a reduced SLA. Increased Pn was associated with increased Ci and chlorophyll content. CO 2 had little effect on allocation, except for a small tendency to favour shoots over roots and leaf mass over LA. CO2 increased total and individual LA, due to increased cell expansion, shoot and root FWT and DWT. Rates of development were unaffected. CO2 had no effect on RWC or RD but increased gs and Tr. Assimilate export and accumulation rates in the light were increased. CO2 had a greater effect in salt treated than control plants in increasing total LA, shoot and root FWT and DWT and RGR.;Plants with both salt and CO2 had ULRs similar to controls but SLA was the lowest. CO2 increased Pn, growth and development rates but allocation and assimilate export and accumulation in the light showed similar patterns to salt plants. Leaves were significantly thicker due to a thickened palisade layer. Increased individual LA was due to increased in cell division and expansion. WUE was highest in Salt/CO 2 plants due to reduced Tr and increased Pn.