Sas Lidia, Rengel Zed, Tang Caixian
Soil Science and Plant Nutrition, The University of Western Australia, Crawley, Australia.
Ann Bot. 2002 Apr;89(4):435-42. doi: 10.1093/aob/mcf066.
Nitrogen nutrition can influence cluster root formation in many wild species, but the effect of N form on cluster root formation and root exudation by white lupin is not known. In a solution culture study, we examined the effect of N nutrition (ammonium, nitrate, both or N2 fixation) on cluster root formation and H+ extrusion by white lupin plants under deficient and adequate P supply. The number of cluster roots increased greatly when plants were supplied with I microM P compared with 50 microM P, the increase being 7.8-fold for plants treated with (NH4)2SO4, 3-fold for plants treated with KNO3 and NH4NO3, and 2-4-fold for N2-fixing plants. Under P deficiency. NH4+-N supply resulted in production of a greater number and biomass of cluster roots than other N sources. Dry weight of cluster roots was 30 % higher than that of non-cluster roots in P-deficient plants treated with (NH4)2SO4 and NH4NO3. In plants treated with sufficient P (50 microM), the weight of non-cluster roots was approx. 90 % greater than that of cluster roots. Both total (micromol per plant h(-1)) and specific (micromol g(-1) root d. wt h(-1)) H+ extrusions were greatest from roots of plants supplied with (NH4)2SO4, followed by those supplied with NH4NO3 and N2 fixation, whereas plants receiving KNO3 had negative net H+ extrusion between the third and fifth week of growth (indicating uptake of protons or release of OH- ions). The rate of proton extrusion by NH4+-N-fed plants was similar under P-deficient and P-sufficient conditions. In contrast, proton exudation by N2-fixing plants and KNO3-treated plants was ten-fold greater under P deficiency than under P sufficiency. In comparison with P deficiency, plants treated with 50 microM P had a significantly higher concentration of P in roots, shoots and youngest expanded leaves (YEL). Compared with the N2 fixation and KNO3 treatments, total N concentration was highest in roots, shoots and YEL of plants supplied with (NH4)2SO4 and NH4NO3, regardless of P supply. Under P deficiency, K concentrations in roots decreased at all N supplies, especially in plants treated with (NH4)2SO4 and NH4NO3, which coincided with the greatest H+ extrusion at these P and N supplies. In conclusion, NH4-N nutrition stimulated cluster root formation and H+ extrusion by roots of P-deficient white lupin.
氮素营养可影响多种野生植物簇生根的形成，但氮形态对白羽扇豆簇生根形成及根系分泌物的影响尚不清楚。在一项水培研究中，我们研究了在磷供应不足和充足的情况下，氮素营养（铵态氮、硝态氮、两者混合或生物固氮）对白羽扇豆植株簇生根形成及氢离子外排的影响。与供应50微摩尔/升磷相比，供应1微摩尔/升磷时，植株的簇生根数量大幅增加，供应硫酸铵处理的植株增加了7.8倍，供应硝酸钾和硝酸铵处理的植株增加了3倍，生物固氮处理的植株增加了2 - 4倍。在磷缺乏条件下，供应铵态氮导致产生的簇生根数量和生物量比其他氮源更多。在供应硫酸铵和硝酸铵处理的缺磷植株中，簇生根干重比非簇生根高30%。在供应充足磷（50微摩尔/升）的植株中，非簇生根的重量比簇生根约高90%。总氢离子外排量（每株植物每小时微摩尔数）和比氢离子外排量（每克根干重每小时微摩尔数）在供应硫酸铵的植株根系中最大，其次是供应硝酸铵和生物固氮处理的植株，而在生长的第三至第五周，供应硝酸钾的植株净氢离子外排为负值（表明吸收质子或释放氢氧根离子）。在磷缺乏和充足条件下，供应铵态氮的植株质子外排速率相似。相比之下，生物固氮处理的植株和供应硝酸钾处理的植株在磷缺乏条件下的质子分泌量比磷充足条件下高10倍。与磷缺乏相比，供应50微摩尔/升磷处理的植株根、地上部和最幼嫩展开叶（YEL）中的磷浓度显著更高。与生物固氮和硝酸钾处理相比，无论磷供应情况如何，供应硫酸铵和硝酸铵的植株根、地上部和YEL中的总氮浓度最高。在磷缺乏条件下，所有氮供应水平下根中的钾浓度均降低，尤其是供应硫酸铵和硝酸铵处理的植株，这与这些磷和氮供应水平下最大的氢离子外排量相吻合。总之，铵态氮营养刺激了缺磷白羽扇豆根系的簇生根形成和氢离子外排。
