Ecological and site historical aspects of N dynamics and current N status in temperate forests
Ecological and site historical aspects of N dynamics and current N status in temperate forests
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DOI：
10.1111/j.1365-2486.2007.01460.x
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发表时间：
2007-09
影响因子：
11.6
通讯作者：
R. Brumme;P. Khanna
中科院分区：
文献类型：
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作者：
R. Brumme;P. Khanna
全新世的生态发展和工业化以来的高大气沉降改变了温带森林生态系统的氮动态。许多不同的参数被用来指示森林是否是N饱和的，其中最常见的是在生根区以下的渗透水中出现硝酸盐。使用不同的定义来描述氮饱和度意味着生态系统的氮状况并不总是得到适当的评估。根据Ulrich提出的森林生态系统理论，利用德国53种不同森林的氮素动态资料，以输入-输出（植物氮增量）平衡为依据，对森林生态系统的各种发展状态进行了分类。N输出等于N输入减去设备N增量的那些系统被描述为（准）稳态类型。那些森林的N输出不等于N输入减去植物N增量作为一个“瞬态”。过渡状态的森林可能会从土壤中损失氮（退化类型）或获得氮[例如，大气沉积（累积型）]。森林生态系统可能出现四种不同的N状态：（a）（准）稳定状态类型与腐殖型腐殖质，（B）退化型与腐殖型腐殖质，（c）积累型与现代型腐殖质，（d）（准）稳定状态类型与现代型腐殖质。具有（准）稳定状态的森林（n = 8）具有高的土壤pH值，植物生长量对氮的保持率高，矿质土壤中的氮含量高，并且氮状况没有发生大的变化。退化类型的森林从矿物质土壤中损失氮（目前退化发生在一个地点）。大多数森林具有中等或中等类型的腐殖质和低土壤pH值，以及矿质土壤中的低N含量，这些森林经历了矿质土壤中有机质损失的短暂状态。它们在森林地面积累有机物质（积累阶段，目前21个地点每年积累6 - 21公斤氮公顷），或者已经达到一个新的（准）稳定状态，具有中等/中等类型的腐殖质（n = 15）。在累积阶段，土壤中的氮保持量显著增加与N沉降（r2 = 0.38），土壤酸度（考虑森林地面厚度作为土壤酸度的指标，r2 = 0.43）和酸沉降（硫酸盐沉降，r2 = 0.39）。树木对氮（4 - 20 kg N ha − 1 yr − 1）的保留减少，土壤对氮的保留增加，这表明树木在酸性较低的土壤中对氮的保留以及在酸性较高的土壤中对氮的保留具有重要作用。生态系统理论可以成功地应用于现有的数据，以了解在温带森林生态系统中的N的动态。
Ecological developments during Holocene age and high atmospheric depositions since industrialization have changed the N dynamics of temperate forest ecosystems. A number of different parameters are used to indicate whether the forests are N‐saturated or not, most common among them is the occurrence of nitrates in the seepage water below the rooting zone. The use of different definitions to describe N saturation implies that the N status of ecosystems is not always appropriately assessed. Data on N dynamics from 53 different German forests were used to classify various development states of forest ecosystems according to the forest ecosystem theory proposed by Ulrich for which N balances of input – (output plus plant N increment) were used. Those systems where N output equals N input minus plant N increment are described as (quasi‐) Steady State Type. Those forests where N output does not equal N input minus plant N increment as in a ‘transient state.’ Forests of the transient state may lose nitrogen from the soil (Degradation Type) or gain nitrogen [e.g., from atmospheric depositions (Accumulation Type)]. Forest ecosystems may occur in four different N states: (a) (quasi‐) Steady State Type with mull type humus, (b) Degradation Type with mull type humus, (c) Accumulation Type with moder type humus, and (d) (quasi‐) Steady State Type with moder type humus. Forests with the (quasi‐) steady state with mull type humus in the forest floor (n= 8) have high‐soil pH values, high N retention by plant increment, high N contents in the mineral soils, and have not undergone large changes in the N status. Forests of the Degradation Type lose nitrogen from the mineral soil (currently degradation is occurring on one site). Most forests that have moder or mor type humus and low‐soil pH values, and low N contents in the mineral soil have gone through the transient state of organic matter loss in the mineral soils. They accumulate organic matter in the forest floor (accumulation phase, currently 21 sites are accumulating 6–21 kg N ha−1 yr−1) or have reached a new (quasi‐) steady state with moder/mor type humus (n= 15). N retention in the accumulation phase has significantly increased in soil with N deposition (r2= 0.38), soil acidity (considering thickness of the forest floor as indices of soil acidity, r2= 0.43) and acid deposition (sulfate deposition, r2= 0.39). Retention of N (4–20 kg N ha−1 yr−1) by trees decreased and of soils increased with a decrease in the availability of base cations indicating the important role of trees for N retention in less acid soils and those of soils in more acid soils. Ecosystem theory could be successfully applied on the current data to understand the dynamics of N in temperate forest ecosystems.