Interaction between mild NaCl salinity and sublethal SO 2 pollution on wheat Triticum aestivum cultivar ‘Wilgoyne’ (Ciano/Gallo). I. Responses of stomatal conductance, photosynthesis, growth and assimilate partitioning

Abstract

Wheat ( Triticum aestivum cultivar ‘Wilgoyne’ (Ciano/Gallo)) plants were exposed to a factorial combination of two levels of salinity (control and 50 mM NaCl), and three levels of SO 2 (<10 (ambient), 231, and 441 nl 1 −1) in fumigation chambers with rain-exclusioon tops for 4 h per dayfor up to 51 days. The objective was to investigate whether mild salinity stress could decrease the sensitivity of plant growth to sublethal SO 2 stress. Exposure to 441 nl 1 −1 SO 2 significantly decreased CO 2 stomatal conductance, net photosynthesis rate, and at the end of experiment, chlorophyll concentrations in the youngest fully expanded (YFE) leaves. Inhibition of hotosynthesis by 441 nl 1 −1 SO 2 fumigation resulted in a change in assimilate allocation in favour of shoot growth, leading to an increase in shoot to root ratio. Exposure to 441, but not 231 nl 1 −1 SO 2 significantly decreased plant dry weight and relative growth rate (RGR) of both root and shoot. 50 mM NaCl treatment first decreased shoot growth, resulting in a decrease in shoot to root ratio, but later a significant decrease in root growth developed, probably owing to limited assimilate supply from the shoot, and resulted in an increase in shoot to root ratio. There was generally no significant interaction between SO 2 fumigation and NaCl salinity on net photosynthesis rate and leaf chlorophyll concentration. However, CO 2 stomatal conductance in the YFE leaves of 50 mM NaCl-treated and SO 2-fumigated plants recovered more quickly after the completion of fumigation than the non-saline and SO 2-fumigated plants. 50 mM NaCl alinity and 441 nl 1 −1 SO 2 fumigation had an antagonistic interaction on both shoot and root dry weight. Exposure to 231 nl 1 −1 SO 2 increased the shoot to root ratio in plants with 50 mM NaCl. No significant interaction between SO 2 fumigatio and 50 mM NaCl was observed on the RGR of both shoot and root. The results showed that 50 mM NaCl salinity did not provide ann effective protection against SO 2 uptake in the leaves by increasing stomatal resistance during SO 2 fumigation. Other physiological mechanisms could be involved in the antagonistic interaction between 50 mM NaCl salinity and 441 nl 1 −1 SO 2 fumigation on plant growth.