An equation to describe vertical gradients of element concentrations in soils under beech and spruce stands

A description of element gradients in organic layers and the uppermost parts of the mineral soil may give information on their storage and cycling in forest ecosystems. The objectives were to describe vertical gradients of C, N, P, S, NA, K, Ca, Mg, Mn, Fe, and Al contents under beech (Fagus sylvatica L.), spruce (Picea abies (L.) Karst.), and mixed beech-spruce stands and-to obtain an easy method for the estimation of nutrient stocks and their distribution in the organic layer at a regional scale. Organic layers and upper 5 cm of mineral soil from 90 profiles were cut centimeterwise. Samples were analyzed for contents of C and N and P, S Na, K, Ca, Mg, Mn, Fe, and Al after pressure digestion in HNO3, Contents of C, N, P, S, Ca, and Mn decreased whereas contents of Na, K, Mg, Fe, and Al increased with depth. The gradients of C, N, P, S, Na, K, Mn, Fe, and Al were described satisfactorily using the following equation after transforming the maximal height of the organic horizon to 0 cm: E(d) = E-M + (E-L - E-M)/[1+(alpha X d)(beta)]((1-1/beta)) where E(d) is the element concentration at depth d, EL and Em are the concentrations of the element in the L layer and in the mineral soil at 5 cm depth, respectively, and alpha and beta of are fitting parameters. Linear, correlation coefficients (r,) measured against modeled element contents were greater than or equal to 0.8 and 1.2 (with the regression coefficients (a) varied between 0.8 exception of P, Fe, and Na for some profiles) The parameters a and P depended on the height of the organic horizon. An effect of the tree species on the parameters was found only for Mn and Fe. The equation enabled the estimation of the stocks of C, N, P, and S in organic horizon with satisfying accuracy (r greater than or equal to 0.8, 0.8 less than or equal to a less than or equal to 1.0), after measuring only the height of the organic horizon. However, the prediction of the stocks of other elements was less satisfactory.