We report data for nutrients in the organic layer and in mineral soil of Fagus sylvatica forests after P and N fertilization. We separated soil and roots and also report data for root biomass and nutrient contents in these soil layers. In addition, relative soil water contents and pH were measured. The samples were collected in three forests and repeatedly in spring and fall from 2016 to 2018. 

STUDY DESIGN (as described by Clausing et al. 2021): The data was collected from European beech dominated forests in Unterlüss (LUE) (52°50'21.7"N, 10°16'2.3"E), Mitterfels (MIT) (48°58'34.1"N, 12°52'46.7"E) and Bad Brückenau (BBR) (50°21'7.2"N, 9°55'44.5"E) beech forests in Germany. Each site is composed of plots with treatments of either P (fertilized with phosphorus in form of potassium dihydrogen phosphate (KH2PO4), dosage 50 kg P ha-1), N (fertilized five times with nitrogen in form of ammonium nitrate (NH4NO3), dosage 5 x 30 kg N ha-1), P+N and unfertilized (Con). N was applied five times and P was applied once in the P and P+N plots. The fertilizer treatments and controls were replicated three times per site (12 plots per site).
Unterlüss fertilization dates: P (2016-08-16) and N (2016-08-16, 2017-05-04, 2017-09-21, 2018-04-17 and 2018-09-17).                                       
Mitterfels fertilization dates: P (2016-08-12) and N (2016-08-12, 2017-05-15, 2017-10-05, 2018-05-03 and 2018-10-02).                                       
Bad Brückenau fertilization dates: P (2016-08-05) and N (2016-08-05, 2017-05-10, 2017-09-28, 2018-04-23 and 2018-09-25).

DATA COLLECTION: 12 Soil cores (21 cm depth x 5.5 cm diameter) were collected from each plot, separated into organic layer and mineral soil. The organic samples were pooled to yield one sample. The mineral samples were pooled to yield one sample per forest plot. The soil was sieved (4 mm mesh size) and weighed. Fine roots were collected and weighed. Soil water content, pH, and soil and root elements were analysed separately after drying the samples at 40 ℃. Soil and root elements were measured by inductively coupled plasma–optical emission spectroscopy (ICP-OES). Carbon (C) and nitrogen (N) were measured with a CN analyzer.

SAMPLING DATES
Unterlüss sampling dates: T0: 2016-08-15, T1: 2017-05-03, T2: 2017-09-20, T3: 2018-04-16 and T4: 2018-09-17.                                       
Mitterfels sampling dates: T0: 2016-08-11, T1: 2017-05-15, T2: 2017-10-04, T3: 2018-05-02 and T4: 2018-10-01.                                       
Bad Brückenau sampling dates: T0: 2016-08-04, T1: 2017-05-09, T2: 2017-09-27, T3: 2018-04-23 and T4: 2018-09-25.

Reference:

Clausing, S., Likulunga, E.L., Janz, D., Feng, H., Schneider, D., Daniel, R., Krüger, J., Lang, F., Polle, A., 2021. Impact of nitrogen and phosphorus addition on resident soil and root mycobiomes in beech forests. Biology and Fertility of Soils. doi: 10.1007/s00374-021-01593-x.

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VARIABLES IN THE DATASET (27 VARIABLES)
Site: Study sites from which sampling was conducted (LUE: Unterlüss, MIT: Mitterfels and BBR: Bad Brückenau).
Forest type: The type of forest characterization based on soil P-content described as low (P-low), medium (P-medium) and high (P-high) soil P contents.
Treatment: Fertilizer treatment with either N, P, P+N or unfertilized (Con).
Plot: Number of the plot in each study site.
Timepoint: The sampling period described as T0 (Fall 2016), T1 (Spring 2017), T2 (Fall, 2017), T3 (Spring 2018) and T4 (Fall 2018).
Season: The seasons in which sampling was conducted.
SL: Soil layer which is either organic layer (OL) or mineral soil (ML).
Material: Soil and fine root sample materials from which the analysis was conducted.
FW: Total fresh weights of soil or fine roots (g) determined from the volume of 12 pooled soil cores per plot (volume: 5987.04 cm3) which were separated into organic layer and mineral soil.
DW: Total dry weights of soil or fine roots (g) determined from the volume of 12 pooled soil cores per plot (volume: 5987.04 cm3) which were separated into organic layer and mineral soil.
DW/FW: Ratio of total dry weights to fresh weights of respective soil and fine root materials determined from the volume of 12 pooled soil cores per plot (volume:5987.04 cm3) which were separated into organic layer and mineral soil.
FR: Fine root mass (g DW/g dry weight of soil).
Soil and root elements (mg/g DW): (Total P: Pt, Na, K, Ca, Mg, Mn, Fe, Al, S and labile P: Ps).
C and N: Refers to total C and N in mg/g DW and CN as a ratio of C to N.
WC: Water content (g/g dry weight soil) determined as: (fresh weight (g) - dry weight (g))/dry weight (g)).
pH: pH value in distilled water and soil (1 to 2.5 ratio of soil to distilled water).
NA: Not applicable or available.