Elevated atmospheric CO2 decreases the ammonia compensation point of barley plants

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The ammonia compensation point (chi(NH3)) controls the direction and magnitude of NH3 exchange between plant leaves and the atmosphere. Very limited information is currently available on how chi(NH3) responds to anticipated climate changes. Young barley plants were grown for 2 weeks at ambient (400 mu mol mol(-1)) or elevated (800 mu mol mol(-1)) CO2 concentration with NO3- or NH4NO3 as the nitrogen source. The concentrations of NH4+ and H+ in the leaf apoplastic solution were measured along with different foliar N pools and enzymes involved in N metabolism. Elevated CO2 caused a threefold decrease in the NH4+ concentration in the apoplastic solution and slightly acidified it. This resulted in a decline of the chi(NH3) from 2.25 and 2.95 nmol mol(-1) under ambient CO2 to 0.37 and 0.89 nmol mol(-1) at elevated CO2 in the NO3- and NH4NO3 treatments, respectively. The decrease in chi(NH3) at elevated CO2 reflected a lower N concentration (-25 in the shoot dry matter. The activity of nitrate reductase also declined (-45 to -60, while that of glutamine synthetase was unaffected by elevated CO2. It is concluded that elevated CO2 increases the likelihood of plants being a sink for atmospheric NH3 and reduces episodes of NH3 emission from plants.
Original languageEnglish
JournalJournal of Experimental Botany
Issue number10
Pages (from-to)2713-2724
Number of pages12
Publication statusPublished - 2013

ID: 119825813