Distribution of phosphorus fractions with different plant availability in German forest soils and their relationship with common soil properties and foliar P contents

摘要

Abstract. Repeated, grid-based forest soil inventories such as theNational Forest Soil Inventory of Germany (NFSI) aim, among other things, atdetecting changes in soil properties and plant nutrition. In these types ofinventories, the only information on soil phosphorus (P) is commonly thetotal P content. However, total P content in mineral soils of forests isusually 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) todetermine the distribution of different plant-available P fractions in soilsamples (at depths of 0–5 and 10–30 cm) from 146?NFSI sites, encompassing a widevariety of soil conditions. In addition, we analyzed relationships betweenthese P fractions and common soil properties such as pH, texture, andsoil organic carbon content (SOC). The total P content among our samples ranged fromapproximately 60 to 2800 mg kg ~(?1) . The labile, moderately labile, andstable P fractions contributed to 27 %, 51 %, and 22 % of the total Pcontent, respectively, at a depth of 0–5 cm. At a depth of 10–30 cm, the labile Pfractions decreased to 15 %, whereas the stable P fractions increased to30 %. These changes with depth were accompanied by a decrease in theorganic P fractions. High P contents were related to high pH values.While the labile Hedley P pool increased with decreasing pH in absoluteand relative terms, the stable Hedley P pool decreased in absolute andrelative terms. Increasing SOC in soils led to significant increases in allHedley P pools and in total P. In sandy soils, the P content across allfractions was lower than in other soil texture types. Multiple linearregression models indicated that Hedley P pools and P fractions weremoderately well related to soil properties (with r ~(2) values that were mostly above0.5), and that the sand content of soils had the strongest influence. Foliar Pcontents in Pinus sylvestris were reasonably well explained by the labile and moderatelylabile P pool ( r ~(2) = 0.67) but not so for Picea abies and Fagus sylvatica . Foliar Pcontents in all three species could not be related to specific Hedley Ppools. Our study indicates that soil properties such as pH, SOC content, andsoil texture may be used to predict certain soil Hedley P pools with differentplant availability on the basis of large soil inventories. However, the foliar Pcontents of tree species cannot be sufficiently well predicted by the soilvariables considered here.