Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China

doi:10.5814/j.issn.1674-764X.2019.02.005

Abstract

Abstract:

The priming effect is well acknowledged in soil systems but the effect of nitrogen (N) fertilization remains elusive. To explore how N modifies the priming effect in soil organic matter (SOM), one in situ experiment with ¹³C labeled glucose addition (0.4 mg C g^-1soil, 3.4 atom % ¹³C) was conducted on soil plots fertilized with three gradients of urea (0, 4 and 16 g N m^-2 yr^-1). After glucose addition, the soil CO₂ concentration and phospholipid fatty acid (PLFA) were measured on day 3, 7, 21 and 35. The study found that N fertilization decreased soil CO₂, PLFA and the fungi to bacteria ratio. Glucose triggered the strongest positive priming in soil at 0 g N m^-2 yr^-2, meanwhile N fertilization decreased SOM-derived CO₂. Soil at 4 g N m^-2 yr^-2released the largest amount of glucose-derived carbon (C), likely due to favorable nutrient stoichiometry between C and N. Stable microbial community biomass and composition during early sampling suggests “apparent priming” in this grassland. This study concludes that N fertilization inhibited soil priming in semi-arid grassland, and shifted microbial utilization of C substrate from SOM to added labile C. Diverse microbial functions might be playing a crucial role in soil priming and requires attention in future N fertilization studies.

Key words: nitrogen fertilization, ¹³C labeled glucose, soil priming effect, phospholipid fatty acids, semi-arid grassland

LI Yue,NIE Cheng,SHAO Rui,DU Wei,LIU Yinghui. Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China[J]. Journal of Resources and Ecology, 2019, 10(2): 147-154.

Figures/Tables 6

Table 1 Repeated-measures ANOVA for soil CO2, total PLFA, bacteria, fungi and the F:B ratio among treatments in four sampling days.

Source of variation	Soil CO₂	Total PLFA	Bacteria	Fungi	F:B ratio
Day	1.13	44.53***	40.16***	28.55***	0.41
Nitrogen	8.21**	23.43***	0.73	22.24***	19.77***
Glucose	134.83***	142.39***	0.01	8.57**	6.58*
Day × Nitrogen	1.66	1.17	7.87***	2.94**	0.85
Day × Glucose	20.01***	19.16***	63.38***	15.93***	14.19***
Nitrogen × Glucose	1.90	2.01	1.58	0.01	0.02
Day × Nitrogen ×Glucose	1.94	1.86	7.00***	2.37	0.38

Fig. 1 Dynamics of soil CO2 among treatments in four sampling daysNote: N0, N4 and N16 represent nitrogen levels of 0, 4 and 16 g N m-2 yr-1, respectively.

Fig. 2 Soil CO2 in the control treatment and soil CO2 and soil organic matter derived CO2 in the 13C labeled glucose treatment on day 3(a), 7(b), 21(c), and 35(d).Note: A one-way ANOVA is conducted for all CO2 concentrations in the control treatment and SOM-derived CO2 among nitrogen levels in each sampling day. Different lowercase letters indicate significant difference in CO2 at P < 0.05.

Fig. 3 Cumulative primed carbon (a), soil organic matter derived carbon (b) and glucose-derived carbon (c) in four sampling days

Table 2 Spearman correlations between N levels and total PLFA, bacteria, fungi and the F:B ratio averaged by sampling days.

Treatment	Variable	Coefficient
Control	Total PLFA	-0.621*
	Bacteria	-0.443
	Fungi	-0.857**
	F:B ratio	-0.828**
Glucose	Total PLFA	-0.680*
	Bacteria	0.266
	Fungi	-0.710**
	F:B ratio	-0.917**

Fig. 4 Mean PLFA biomass on day 3 and 7 (a) and non-metric multidimensional scaling ordination of PLFA biomarkers (b) among treatments on day 3 and 7Note: A one-way ANOVA is conducted for PLFA among treatments. Different lowercase letters indicate significant difference in PLFA at P < 0.05

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