Repeated, grid-based forest soil inventories such as the National Forest Soil Inventory of Germany (NFSI) aim, among other things, at detecting changes in soil properties and plant nutrition. In these types of inventories, the only information on soil phosphorus (P) is commonly the total P content. However, total P content in mineral soils of forests is usually not a meaningful variable with respect to predicting the availability of P to trees. Here we tested a modified sequential P extraction according to Hedley (1982) to determine the distribution of different plant-available P fractions in soil samples (at depths of 0–5 and 10–30 cm) from 146 NFSI sites, encompassing a wide variety of soil conditions. In addition, we analyzed relationships between these P fractions and common soil properties such as pH, texture, and soil organic carbon content (SOC). The total P content among our samples ranged from approximately 60 to 2800 mg kg⁻¹. The labile, moderately labile, and stable P fractions contributed to 27 %, 51 %, and 22 % of the total P content, respectively, at a depth of 0–5 cm. At a depth of 10–30 cm, the labile P fractions decreased to 15 %, whereas the stable P fractions increased to 30 %. These changes with depth were accompanied by a decrease in the organic P fractions. High P contents were related to high pH values. While the labile Hedley P pool increased with decreasing pH in absolute and relative terms, the stable Hedley P pool decreased in absolute and relative terms. Increasing SOC in soils led to significant increases in all Hedley P pools and in total P. In sandy soils, the P content across all fractions was lower than in other soil texture types. Multiple linear regression models indicated that Hedley P pools and P fractions were moderately well related to soil properties (with r² values that were mostly above 0.5), and that the sand content of soils had the strongest influence. Foliar P contents in Pinus sylvestris were reasonably well explained by the labile and moderately labile P pool (r² = 0.67) but not so for Picea abies and Fagus sylvatica. Foliar P contents in all three species could not be related to specific Hedley P pools. Our study indicates that soil properties such as pH, SOC content, and soil texture may be used to predict certain soil Hedley P pools with different plant availability on the basis of large soil inventories. However, the foliar P contents of tree species cannot be sufficiently well predicted by the soil variables considered here.

中文翻译：

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德国森林土壤中不同植物有效性磷组分的分布及其与土壤性状和叶面磷含量的关系

重复的基于网格的森林土壤清单，例如德国国家森林土壤清单（NFSI），旨在检测土壤性质和植物营养的变化。在这些类型的清单中，唯一的土壤磷（P）信息通常是总磷含量。但是，在预测树木中磷的有效性方面，森林矿质土壤中的总磷含量通常不是有意义的变量。在这里，我们根据Hedley（1982）对改良的顺序P提取进行了测试，以确定来自146个NFSI站点的土壤样品（0–5和10–30 cm深度）不同植物有效P组分的分布。土壤条件。此外，我们分析了这些P组分与常见土壤特性（例如pH，质地，和土壤有机碳含量（SOC）。我们样品中的总磷含量约为60至2800 mg / kg^-1。不稳定，中等不稳定和稳定的P分数在0-5 cm的深度分别占总P含量的27％，51％和22％。在10–30 cm的深度，不稳定的P分数降低到15％，而稳定的P分数增加到30％。这些随深度的变化伴随着有机磷含量的减少。高磷含量与高pH值有关。尽管不稳定的Hedley P库在绝对值和相对值中均随pH值的降低而增加，但稳定的Hedley P库在绝对值和相对值中却降低了。土壤中SOC的增加导致所有Hedley P库和总P的显着增加。在沙质土壤中，所有组分中的P含量均低于其他土壤质地类型。r ²值大多在0.5以上），并且土壤的含沙量影响最大。在叶面P含量樟子松进行了合理的以及由不稳定的和适度不稳定磷库（说明- [R ²  =  0.67），但不因此对欧洲云杉和水青冈。这三个物种中的叶面磷含量均与特定的Hedley P库无关。我们的研究表明，土壤属性（例如pH值，SOC含量和土壤质地）可用于根据大量土壤库存来预测具有不同植物利用率的某些土壤Hedley P库。但是，此处考虑的土壤变量无法充分预测树木的叶面磷含量。