RESPONSE TO PHOSPHORUS AVAILABILITY DURING VEGETATIVE AND REPRODUCTIVE GROWTH OF CHRYSANTHEMUM - I - WHOLE-PLANT CARBON-DIOXIDE EXCHANGE

Whole-plant CO2 exchange and root-shoot interactions during transition from vegetative to reproductive growth of 'Coral Charm' chrysanthemum (Dendranthema x grandiflorum Ramat.) were investigated over a range o f P concentrations considered to be deficient (1 mu M), adequate (100 mu M), or high (5 mM). Transition from vegetative to reproductive grow th resulted in reduced photosynthate production, root respiration, bio mass accumulation, and starch accumulation in leaves, Root respiration was low in high-P plants regardless of growth stage, Reduced root res piration may indicate changes in source-sink relationships during the transition from vegetative to reproductive growth, making roots less c ompetitive sinks than developing flowers, Plant responses to P deficie ncy included decreased CO2 assimilation and shoot biomass accumulation but increased root respiration, root:shoot ratio, specific leaf mass (SLM), and starch accumulation in leaves, Reduced foot respiration act ivity in high-P plants was presumably due to differences in root archi tecture resulting in proportionately fewer root apices in high P, Dail y CO2 assimilation, shoot biomass, SLM, and root:shoot ratio were simi lar in plants grown with adequate-P and high-P availability, although plant P accumulation increased with P availability, Our results sugges t that the excessive P fertilization often used in ornamental producti on systems is detrimental to root activity.