Soil inorganic nitrogen composition and plant functional type determine forage crops nitrogen uptake preference in the temperate cultivated grassland, Inner Mongolia

Figures & data

Table 1. General soil properties in the 0–20 cm soil depth under different forage crop cultivations after four years of forage crop cultivation

Soil properties ^†	Forage crops^‡
	M. sativa	B. campestris	B. inermis	L. chinensis
TN (g kg^−1)	2.40 ± 0.67a	2.02 ± 0.11a	2.29 ± 0.24a	2.31 ± 0.15a
SOC (g kg^−1)	16.17 ± 3.01a	14.07 ± 0.98c	15.83 ± 2.65b	16.02 ± 2.76a
AK (mg kg^−1)	307.88 ± 21.87a	201.45 ± 11.00b	205.81 ± 67.97b	235.49 ± 34.45b
pH	6.82 ± 0.01a	7.01 ± 0.03a	6.80 ± 0.02a	6.96 ± 0.01a
BD (g m^−3)	1.08 ± 0.06b	1.10 ± 0.07b	1.13 ± 0.05b	1.36 ± 0.03a
MS (%)	16.38 ± 1.98a	17.51 ± 3.05a	19.12 ± 0.81a	12.37 ± 0.34b

^†TN, SOC, AK, BD, and MS are total nitrogen, soil organic carbon, available potassium, bulk density, and soil moisture, respectively.

^‡Data are mean ± standard error (n = 4). Different lowercase letters indicate significant differences among the four species cultivations.

Figure 1. Shoot- and root biomass in the four forage crop cultivations during the flowering and maturation phases. Values are means ± standard error (n = 4). Different lowercase and uppercase letters mean significant difference in a given variable during the flowering and maturation phases, respectively. Asterisk (*) means a significant difference between the two growth stages at the level of 0.05 based on t-test

Figure 2. Shoot N concentrations in the four forage crops during the flowering and maturation phases. Values are means ± standard error (n = 4). Different lowercase and uppercase letters mean significant difference in shoot N concentration during the flowering and maturation phases, respectively. Two Asterisks (**) mean a significant difference between the two growth stages at the level of 0.01 based on t-test

Figure 3. Soil NO₃⁻-N and NH₄⁺-N concentrations in the four species cultivations during the flowering and maturation phases. Different lowercase and uppercase letters mean significant difference in soil NO₃⁻-N or NH₄⁺-N concentration during the flowering and maturation phases, respectively. Two asterisks (**) mean a significant difference between the two growth stages at the level of 0.01 based on t-test

Figure 4. Monthly variation and mean of soil microbial biomass N (MBN) concentration in the different species cultivation plots. Different lowercase letters indicate significant difference among the four species cultivations

Figure 5. Plant inorganic N uptake rates in the four species cultivations during the flowering and maturation phases. Different lowercase and uppercase letters mean significant difference in plant NO₃⁻-N or NH₄⁺-N uptake rates during the flowering and maturation periods, respectively. Two asterisks (**) mean a significant difference between the two growth stages at the level of 0.01 based on t-test

Figure 6. Relationships between plant inorganic N uptake rates and shoot-, root biomass, and root/shoot ratios. B. campestris is removed from the statistical analysis

Figure 7. Relationships between plant NH₄⁺/NO₃⁻ uptake ratios and soil NH₄⁺/NO₃⁻ ratios