Effect of root-zone salinity and form of N on photosynthate partitioning in wheat (Triticum aestivum L.)

摘要

Carbon-14 pulse labeling technique was used to study the effect of rooting medium salinity and form and availability of N on growth and rhizodeposition of wheat (Triticum aestivum L.). Thirty days old plants grown in continuously aerated Arnon and Hoagland nutrient solution were subjected to C-14 pulse labeling for 24 h and transferred to aqueous rooting medium containing 0, 150, and 300 mM NaCl in all combinations with different forms (calcium nitrate, ammonium sulphate, and ammonium nitrate) and amounts (0.5, 1.0, 1.5, and 2.0 times the standard N concentration (150 ppm) of Arnon and Hoagland plant growth medium). Plant samples immediately after pulse labeling, following 7 days of growth under different rooting medium conditions, and the freeze-dried rooting medium were analyzed for total C and C-14. Length and fresh/dry weight of root and shoot portions and calculated values of unaccounted C-14 were determined. Presence of NaCl in the rooting medium led to a decrease in root and shoot portions. However, NO3--fed plants showed better growth than NH4+-fed plants at all the three salinity levels. Salinity in rooting medium led to higher rhizodeposition and lower loss of C-14. Relatively higher proportion of C-14 was released as rhizodeposits and retained in root/shoot portions of plants fed with NH4+ or NH4++NO3-, than those with NO3-, while less was respired. The specific activity of the rhizodeposits (kBq C-14 g(-1) C) was also higher under saline conditions. The rhizodeposits in NH4+-fed plants were more highly labeled as compared to NO3--plants.