DRY-MATTER PRODUCTION, YIELD, AND ALLOCATION OF C-14 ASSIMILATES BY WHEAT AS AFFECTED BY NITROGEN-SOURCE AND SALINITY

Wheat (Triticum aestivum L.) growth is affected by both salinity and the type of N fed to the plants. The objective of this research was to determine the effect of salinity applied at different stages of the life cycle of wheat plants supplied with either NH4 or NO3 on growth, yield, and translocation of photosynthates. Plants were grown in sand culture irrigated with nutrient solution until maturity. The nutrient solution contained 4 mM N, either as (NH4)2SO4 or Ca(NO3)2. Salinity (60 mM NaCl) was applied to the nutrient solution at 19, 70, and 92 d after sowing. Some of the plants received (CO2)-C-14 pulses 100 d after sowing, and C-14 distribution in each plant part was determined 24 h later. Dry biomass production and grain yield were reduced when salinity was applied 19 d after sowing (beginning of the vegetative stage), whereas no effect of NaCl was observed when salinity was applied later. Ammonium-fed plants always produced more tillers and spikes than NO3-fed plants. Total grain yield was similar with plants growing in either N form. Nitrate-treated plants produced fewer, but heavier, spikes due to a larger number of grains per spike than NH4-fed plants. Ammonium-fed plants showed a preferential allocation of C-14-assimilates to young developing tillers. Nitrate-fed plants, under similar conditions, allocated assimilates preferentially to grain. Salinity enhanced translocation of assimilates to the spikes when plants were grown with NO3.