Net fluxes of ammonium and nitrate in association with H+ fluxes in fine roots of Populus popularis
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Poplar plants are cultivated as woody crops, which are often fertilized by addition of ammonium (NH4 +) and/or nitrate (NO3 −) to improve yields. However, little is known about net NH4 +/NO3 − fluxes and their relation with H+ fluxes in poplar roots. In this study, net NH4 +/NO3 − fluxes in association with H+ fluxes were measured non-invasively using scanning ion-selective electrode technique in fine roots of Populus popularis. Spatial variability of NH4 + and NO3 − fluxes was found along root tips of P. popularis. The maximal net uptake of NH4 + and NO3 − occurred, respectively, at 10 and 15 mm from poplar root tips. Net NH4 + uptake was induced by ca. 48 % with provision of NO3 − together, but net NO3 − uptake was inhibited by ca. 39 % with the presence of NH4 + in poplar roots. Furthermore, inactivation of plasma membrane (PM) H+-ATPases by orthovanadate markedly inhibited net NH4 +/NO3 − uptake and even led to net NH4 + release with NO3 − co-provision. Linear correlations were observed between net NH4 +/NO3 − and H+ fluxes in poplar roots except that no correlation was found between net NH4 + and H+ fluxes in roots exposed to NH4Cl and 0 mM vanadate. These results indicate that root tips play a key role in NH4 +/NO3 − uptake and that net NH4 +/NO3 − fluxes and the interaction of net fluxes of both ions are tightly associated with H+ fluxes in poplar roots.
KeywordsEfflux Fertilizer Influx Ion uptake Poplar Proton
Scanning ion-selective electrode technique
This work was supported by National Key Basic Research Program of China (973 Program, Grant No. 2012CB416902), the National Natural Science Foundation of China (Grant No. 31070539, 31100481, 31270647), the Special Fund for Forest Science and Technology Research in the Public Interest (Grant No. 201204210), the Program for New Century Excellent Talents in University from the Ministry of Education of China (Grant No. NCET-08-0468), the Fok Ying Tung Education Foundation (Grant No. 121026), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090204110027) and the Fundamental Research Funds for the Central Universities of China (Grant No. QN2009063).
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