Comparison of Soil Nitrogen Availability Indices under Two Temperate Forest Types

ZHONG Zhe-Ke; F. MAKESCHIN

摘要

To evaluate the validity of different indices in estimating soil readily mineralizable N, soil microbial biomass (Nmic),soil active N (SAN), soluble organic N (SON), net N mineralization rate (NNR) and gross N mineralization rate (GNR) in mineral soils (0-10 cm) from six forest stands located in central Germany were determined and compared with two sampling times: April and November. Additionally, soil density fractionation was conducted for incubated soils (with addition of 15NH4-N and glucose, 40 days) to observe the sink of added 15N in different soil fractions. The study showed that Nmic and NNR in most stands differed significantly (P ≤ 0.05) between the two sampling times, but not GNR, SAN and SON. In November, no close relationships were found between GNR and other N indices, or between Nmic, SON, and SAN and forest type. However, in April, GNR was significantly correlated (P ≤ 0.05) with Nmic, SAN, and NNR along with Nmic under beech being significantly higher (P ≤ 0.05) than under conifers. Furthermore, density fractionation revealed that the light fraction (LF, 0.063-2 mm, ＞ 1.7 g cm-3) was not correlated with the other N indices. In contrast, results from the incubation study proved that more 15N was incorporated into the heavy fraction (HF ＜ 0.063 mm, ＞ 1.7 gcm-3) than into LF, indicaing that more labile N existed in HF than in LF. These findings suggested that attention should be paid to the differences existing in N status between agricultural and forest soils.

机译：在评估土壤易矿化氮，土壤微生物生物量（Nmic），土壤活性氮（SAN），可溶性有机氮（SON），净氮矿化率（NNR）和总氮矿化率（GNR）时评估不同指标的有效性确定了位于德国中部六个林分的矿质土壤（0-10厘米）中的矿物质含量，并与两个采样时间进行了比较：4月和11月。另外，对培养的土壤进行土壤密度分级（添加15NH4-N和葡萄糖，共40天），以观察在不同土壤组分中添加的15N的汇。研究表明，大多数林分的Nmic和NNR在两次采样之间有显着差异（P≤0.05），但GNR，SAN和SON没有差异。在11月，在GNR和其他N指数之间，或在Nmic，SON和SAN与森林类型之间没有发现紧密的关系。然而，4月，山毛榉下的GNR与Nmic，SAN和NNR以及Nmic显着相关（P≤0.05），比针叶树下的显着更高（P≤0.05）。此外，密度分馏显示轻组分（LF，0.063-2 mm，＞ 1.7 g cm-3）与其他N指标无关。相比之下，孵育研究的结果证明，重组分（HF ＜0.063 mm，＞ 1.7 gcm-3）中掺入的15N量多于LF，这表明HF中存在的不稳定N比LF多。这些发现表明，应注意农业土壤和森林土壤中氮素状况的差异。

Comparison of Soil Nitrogen Availability Indices under Two Temperate Forest Types

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