Fig 1.
Nitrate concentration in soil.
For each experiment, divided for depth classes, the box plot shows minimum and maximum values sampled (bars), the first and the third quartile (boxes), the median (lines inside boxes) and the average (crosses), n = 248. Letters within the same soil refer to One-way ANOVA tests (p<0.05, Gabriel post-test) performed for each soil.
Table 1.
Texture (sand tot., silt tot. and clay) and pH (H2O) for the four soil depths studied. USDA soil taxonomy, percentage of organic carbon (OC%) and cation exchange capacity (CEC) for the 0–25 cm layer.
Fig 2.
Nitrate (a and b) and ammonium (c and d) concentration in soil of the experiments 7 (a and c) and 8 (b and d) during the year 2016. Experiment 7 was supplied with a total amount of nitrogen of 1,423 kg N Ha-1. Experiment 8 was supplied with a total amount of nitrogen of 1,470 kg N Ha-1. Error bars show Standard Deviation (n = 3). Letters within the same soil refer to One-way ANOVA tests (p<0.05, Gabriel post-test) performed for each soil.
Table 2.
Total rainfall for experimental sites studied (Soils 1–8).
Fig 3.
Gene copies concentration in soil.
Plots show the number of gene copies (average) per gram of soil for each experiment, grouped by sampling depth. The genes analysed are: amoA from archaea, amoA, nifH, nirK and nosZ from bacteria. Y axis shows log10 scale. Error bars show Standard Deviation, n = 252. Letters within the same soil refer to One-way ANOVA tests (p<0.05, Gabriel post-test) performed for each soil and gene.
Fig 4.
Microorganisms quantification.
a: percentages of gene copies in all soils analysed, divided into depth classes. Data in the graphic represent the average ± standard deviation of all soils (1a, 1b, 2, 3a, 3b, 4a, 4b, 5, 6a and 6b), (n = 252). b: total number of gene copies (average) per gram of soil, divided into two depth classes (0–50 cm; 50–100 cm), (n = 252). Letters refer to two-way ANOVA analysis (p<0.01, factor 1: depth (two levels), factor 2: sampling period (in correspondence or not to N fertilization) (two levels) (Gabriel test).
Fig 5.
Principal component analysis (axes F1 and F2: 80.13% of total variance).
a: PCA output. Solid lines show the projections of the initial variables in the factorial space: green lines indicate the number of gene copies in soil, blue lines indicate soil chemical characteristics, orange lines indicate soil physical characteristics, red line indicates the amount of N dosed on the soils. Black dots show the position of the experiments in the factorial space. Round brackets show the average concentration of nitrates measured at 1-meter depth. Square brackets show the result of two-way ANOVA analysis on nitrate concentration (p< 0.05; F = 4.1251; Duncan test). Experiments’ labels show the soil code. Axis titles report the variables linked to each axe. b: correlation matrix (Pearson) containing: the number of gene copies per gram of soil for amoA archaea, amoA eubacteria, nifH, nirK and nosZ, the N-NO3- and N-NH4+ concentration (mg kg-1 of soil, n = 189. * = the correlation is significant at level 0.05 (two-tailed test)).