Consequences of high loads of nitrogen for spruce (Picea abies) and beech (Fagus sylvatica) forests
Consequences of high loads of nitrogen for spruce (Picea abies) and beech (Fagus sylvatica) forests
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DOI：
10.1046/j.1469-8137.1998.00181.x
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发表时间：
1998-05-01
期刊：
影响因子：
9.4
通讯作者：
Weber, P
中科院分区：
文献类型：
--
作者：
Rennenberg, H;Kreutzer, K;Weber, P
云杉和山毛榉森林的高氮负荷会导致树木根部对N3-的吸收完全受到抑制。这一结论是基于(A)持续暴露在高N负荷下的固定地点和N限制地点的比较，(B)N限制田间地点的氮肥施肥结果，以及(C)在受控环境条件下的实验室实验。从肥料试验来看，在过量吸收NH4+之后，NH4+的吸收可能会受到抑制。显然，氮的高负荷抑制了森林对N3-的吸收，这是由韧皮部运输到根中的有机氨基化合物在根中积累的结果。这些氨基化合物似乎向根发出了地上部对氮素需求的信号。目前，这种功能还不能归因于山毛榉或云杉中的单个有机氨基酸化合物，但在其他化合物中，Gin可能是这两个物种的候选化合物，例如云杉中的Glu或山毛榉中的天冬氨酸。本研究排除了NH4+对NO3-吸收的直接抑制作用。特定有机氨基化合物水平升高与硝酸根吸收相互作用的机制(S)仍有待阐明。这种(这些)机制(S)似乎影响的是NO_3-内流，而不是NO_3-外流。由于这种(这些)机制(S)，云杉和山毛榉可以防止在一定的生理窗口内，当根暴露在过量的无机N时，N的过度营养。然而，抑制根对N3-和NH4+的吸收使更多的N可用于淋溶到地下水中，此外，对于土壤微生物过程，导致挥发性N化合物的产生和重新排放到大气中。在‘Hogwald’站点，持续暴露在高N负荷下，从穿透到云杉和山毛榉地块的N输入的20%被重新排放为NO和N2O。然而，NO/N2O的比值高度依赖于树种，在云杉中偏爱NO，在山毛榉小区偏爱N2O。由于在臭氧存在的情况下，土壤释放的至少一部分NO将在树冠内转化为NO，然后可能被树叶吸收，因此穿透雨中N气相排放将从森林中释放的N部分在山毛榉中高于云杉。地下水中NO3-的淋溶在云杉中很高，但在山毛榉小区很少。然而，山毛榉对地下水质量的积极影响是以增加辐射活性氮气向对流层释放为代价的。
High loads of nitrogen to spruce and beech forests can result in a complete inhibition of NO3- uptake by the roots of the trees. This conclusion is based on (a) a comparison of a held site continuously exposed to high loads of N and a N-limited site, (b) the results of N fertilization of a N-limited field site, and (c) laboratory experiments under controlled environmental conditions. From fertilization experiments in the held it appears that NH4+ uptake might become inhibited subsequent to an excessive uptake of NH4+. Apparently, the inhibition of NO3- uptake by high loads of N to forests is a consequence of an accumulation of organic amino compounds in the roots originating from phloem transport from the shoot to the roots. These amino compounds seem to signal the N demand of the shoot to the roots. At present this function cannot be attributed to an individual organic amino compound in beech or spruce, but Gin is a likely candidate in both species among other compounds, e.g. Glu in spruce or Asp in beech trees. Direct inhibition of NO3- uptake by NH4+ can be excluded from the present studies. The mechanism(s) by which elevated levels of particular organic amino compounds interact with NO3- uptake remains to be elucidated. This (these) mechanism(s) seem to affect NO3- influx rather than NO3- efflux. As a consequence of this (these) mechanism(s), spruce and beech trees can prevent, within a certain physiological window, N over-nutrition when the roots are exposed to excessive amounts of inorganic N. However, inhibition of NO3- and NH4+ uptake by the roots makes more N available for leaching into the ground water and, in addition, for soil microbial processes that result in the production and re-emission of volatile N compounds into the atmosphere.At the 'Hogwald' site, continuously exposed to high loads of N, > 20% of the N input from throughfall into the spruce and beech plots is re-emitted as NO and N2O. However, the NO to N2O ratio is highly dependent on the tree species, with a preference for NO in the spruce and a preference for N2O in the beech plot. Since at least part of the NO emitted from the soil will be converted inside the canopy in the presence of ozone to NO, that might then be absorbed by the leaves, the portion of the N in the throughfall that will be released from the forest by gaseous N emission is higher in the beech than in the spruce plot. Leaching of NO3- into the ground water is high in the spruce, but minute in the beech plot. However, this positive effect of beech on ground water quality is achieved at the expense of an enhanced release of radiatively active N gases into the troposphere.