Gessler Arthur, Schneider Stephan, VON Sengbusch Dominik, Weber Paul, Hanemann Ulrike, Huber Christian, Rothe Andreas, Kreutzer Karl, Rennenberg Heinz
Albert-Ludwigs-Universität Freiburg, Institut für Forstbotanik und Baumphysiologie, Professur für Baumphysiologie, Am Flughafen 17, D-79110 Freiburg, Germany.
Ludwig-Maximilians-Universität München, Lehrstuhl für Bodenkunde und Standortslehre der Forstwissenschaftlichen Fakultät, Hohenbachernstr. 22, D-85354 Freising, Germany.
New Phytol. 1998 Feb;138(2):275-285. doi: 10.1046/j.1469-8137.1998.00107.x.
During the vegetation periods 1994 and 1995, net uptake of nitrate and ammonium by roots of adult spruce (Picea abies (L.) Karst) and beech (Fagus sylvatica L.) trees was studied at a field site exposed to high loads of N ('Höglwald', Germany). In addition, uptake experiments were carried out under controlled conditions with young spruce and beech trees grown at normal N supply. In the field, nitrate was not taken up by the roots of spruce trees in appreciable amounts. This was also true for beech except during September 1995. Apparently, beech trees was capable of taking up nitrate, but the environmental condition prevailing at the field site usually prevented net uptake. Net uptake of ammonium in both tree species showed a seasonal course, with maximum rates in mid summer. Rates of ammonium uptake by both species correlated with soil temperature at the field site. Laboratory experiments on the influence of root temperature on uptake of nitrate indicated that uptake rates at temperatures found in the field were low compared with the uptake capacity at optimum temperature. At temperatures of 10 and 15°C, frequently found in the soil at the field site, net uptake of nitrate by spruce and beech amounted to c. 16% and 11%, respectively, of maximum uptake at 25°C. By contrast, net uptake of ammonium at 10°C reached 73% and 31% of the maximum uptake for spruce and beech trees, respectively. Independent of temperature, rates of nitrate uptake were considerably lower than those of ammonium. In young spruce and beech trees, net uptake of nitrate was significantly inhibited by ammonium at nitrate∶ammonium ratios found in the soil solution at the forest site. Preincubation of roots of both species, with amino acids present in the phloem of adult trees at the field site, led to an increase in the amino acid pool in the roots. For spruce trees a correlation between inhibition of uptake of nitrate and enrichment of the roots with the amino compounds Glu, γ-amino butyric acid (Gaba), Gln, and Asn was observed. In beech trees, enrichment of Asp and Gln in the roots correlated with a decrease in net uptake of nitrate. The results of laboratory experiments on the effects of temperature, the nitrate to ammonium ratio in the nutrient solution, and amino acid enrichment in the roots are discussed with special emphasis on the patterns of net uptake of ammonium and nitrate observed in the field.
在1994年和1995年的植被生长期间，在德国“赫格瓦尔德”一处氮负荷高的田间试验点，对成年云杉（欧洲云杉）和山毛榉（欧洲山毛榉）树根系对硝酸盐和铵的净吸收进行了研究。此外，在正常氮供应条件下生长的云杉和山毛榉幼树，在可控条件下进行了吸收实验。在田间，云杉树的根系没有大量吸收硝酸盐。山毛榉也是如此，不过在1995年9月除外。显然，山毛榉树能够吸收硝酸盐，但田间试验点普遍存在的环境条件通常会阻止净吸收。两种树种对铵的净吸收都呈现出季节性变化，在仲夏时吸收速率最高。两种树种对铵的吸收速率与田间试验点的土壤温度相关。关于根温对硝酸盐吸收影响的实验室实验表明，与最佳温度下的吸收能力相比，田间发现的温度下的吸收速率较低。在田间试验点的土壤中经常发现的10℃和15℃温度下，云杉和山毛榉对硝酸盐的净吸收量分别约为25℃时最大吸收量的16%和11%。相比之下，在10℃时，云杉和山毛榉对铵的净吸收量分别达到最大吸收量的73%和31%。与温度无关，硝酸盐的吸收速率远低于铵的吸收速率。在云杉和山毛榉幼树中，在林地土壤溶液中发现的硝酸盐∶铵比例下，铵对硝酸盐的净吸收有显著抑制作用。用田间成年树韧皮部中存在的氨基酸对两种树种的根系进行预培养，导致根系中氨基酸库增加。对于云杉树，观察到硝酸盐吸收的抑制与根系中氨基酸化合物谷氨酸、γ-氨基丁酸（GABA）、谷氨酰胺和天冬酰胺的富集之间存在相关性。在山毛榉树中，根系中天冬氨酸和谷氨酰胺的富集与硝酸盐净吸收的减少相关。文中特别强调了田间观察到的铵和硝酸盐净吸收模式，讨论了关于温度、营养液中硝酸盐与铵的比例以及根系中氨基酸富集影响的实验室实验结果。
