Effect of O3 on Hydraulic Architecture in Pima Cotton (Biomass Allocation and Water Transport Capacity of Roots and Shoots)

摘要

Pima cotton (Gossypium barbadense L. cv S-6) exhibits foliar injury and yield reduction at ambient concentrations of O3. We tested the hypotheses that O3 reduces the allocation of biomass to the root system, and that this disrupted carbohydrate allocation impairs root hydraulic capacity relative to transpiring leaf area. Both hypotheses are supported, even though leaf area development is itself reduced by O3. Seedlings were grown in pots in greenhouse fumigation chambers and exposed from planting to sinusoidal O3 profiles with peak concentrations of 0, 0.1, 0.2, and 0.3 [mu]L-1 (12-h averages of 0, 0.037, 0.074, and 0.111 [mu]L L-1). At 8 weeks after planting, stem basal diameter, leaf area, and total plant dry weight decreased by 61, 83, and 88%, whereas root/shoot dry weight ratio declined from 0.16 to 0.09 g/g. Hydraulic conductance decreased per plant by 85%, and per unit leaf area by 35%. Conductance of all organs declined per plant, but only root conductance declined per leaf area by 41%. Root resistance increased from 69 to 82% of whole plant resistance, a functional consequence of reduced carbon allocation to roots. Stomatal conductance declined with root hydraulic conductance, protecting short-term leaf water status. Reduced root hydraulic efficiency may mediate O3 injury to whole plants by reducing shoot gas exchange and biomass productivity through the inhibition of water and nutrient acquisition.