Ammonia exchange between rice leaf blades and the atmosphere : Effect of broadcast urea and changes in xylem sap and leaf apoplastic ammonium concentrations(Environment)

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To elucidate the effects of broadcast urea on ammonia (NH_3) exchange between the atmosphere and rice, we investigated the NH_3 exchange flux between rice leaf blades and the atmosphere, xylem sap ammonium (NH_4^+) concentration, leaf apoplastic NH_4^+ concentration and pH, and determined the stomatal NH_3 compensation point. Paddy rice (Oryza sativa L. cv. Nipponbare) cultivation using experimental pots was conducted in the open air. Three treatments, no nitrogen (NN), standard nitrogen (SN) and high nitrogen (HN), were prepared for two supplemental fertilizations. Urea with 0, 30 and 60kg N ha^<-1> for the NN, SN and HN treatments, respectively, was broadcast at panicle initiation, and urea with 0, 20 and 40kg N ha^<-1> for the NN, SN and HN treatments, respectively, was broadcast at heading. The NH_3 exchange fluxes between the rice leaf blades and the atmosphere (SN treatment) measured using a dynamic chamber technique showed net deposition in general; however, net emission from the old leaves occurred 1 day after the application at heading. In contrast, the xylem sap NH_4^+ concentrations increased markedly 1 day after both applications, which suggests direct transportation of NH_4^+ from the rice roots to the above-ground parts. The applications resulted in no obvious increase in the leaf apoplastic NH_4^+ concentrations. The relationship between the NH_4^+ concentration in the xylem sap and that in the leaf apoplast was uncertain, although the NH_4^+ in the xylem sap came from the roots and the NH_4^+ in the apoplast might be affected by the stomatal deposition of NH_3. The stomatal NH_3 compensation point of rice was estimated to be 0.1-4.1nmol mol^<-1> air (20℃). The direction and intensity of the exchange flux through the stomata, interpreted on the basis of the temperature-corrected NH_3 compensation point, agreed with the observed exchange flux between the rice leaf blades and the atmosphere.

Ammonia exchange between rice leaf blades and the atmosphere : Effect of broadcast urea and changes in xylem sap and leaf apoplastic ammonium concentrations(Environment)

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