Response of soil respiration to addition of different forms of nitrogen and mowing in a saline-alkali grassland in the northern agro-pastoral ecotone

doi:10.17521/cjpe.2019.0270

Abstract

Abstract:

Aims The agro-pastoral ecotone is considered as fragile ecosystems which are strongly affected by agriculture and animal husbandry. The saline-alkali grassland is a unique grassland type in the agro-pastoral ecotone. A large amount of fertilizers are used to increase productivity in this area, which also promotes the emission of reactive nitrogen (N) gases and leads to the changes in soil carbon and N cycles. Mowing is a primary management practice in the agro-pastoral grassland in northern China. In order to explore the impact of N addition and mowing on carbon dynamic in this saline-alkali grassland located in the agro-pastoral ecotone, we determined the response of soil respiration to N addition and mowing.
Methods This study area is located in Youyu County, an agro-pastoral grassland ecosystem in northern China. The field experiment was set up in May, 2017. The treatments included: control (without mowing and mowing), addition of urea, addition of slow release urea, addition of urea + mowing, addition of slow release urea + mowing. Each treatment included 6 replicates. Therefore, there were totally 36 plots in this experiment. Soil respiration rate, soil temperature, soil moisture content, microbial biomass, inorganic N content, above-ground and below-ground biomass were measured under different treatments, and the cumulative carbon emissions and CO₂ fluxes were calculated.
Important findings Our results showed that: (1) Short-term (2017-2018) N addition significantly increased soil respiration rates and soil cumulative carbon emissions. Meanwhile, soil respiration rates and cumulative carbon emissions were significantly higher under urea treatment than those under slow release urea addition. (2) Mowing significantly reduced soil respiration rates and cumulative carbon emissions. (3) The interaction of short-term N addition and mowing had no significant effect on soil respiration rate. Therefore, short-term N addition can promote soil carbon release from the saline-alkali grassland in the agro-pastoral ecotone of northern China. Mowing can reduce soil respiration and decrease cumulative of carbon emissions. This may be because that mowing reduced the input of litter and further reduced soil substrate for microbes, which led to a decrease in soil microbial activity. However, long-term effect of N addition and mowing on soil carbon dynamics in saline-alkaline grasslands in the agro-pastoral ecotone still needs to be further explored.

Key words: mowing, nitrogen forms, soil respiration, agro-pastoral ecotone, saline-alkali grassland

HU Shu-Ya,DIAO Hua-Jie,WANG Hui-Ling,BO Yuan-Chao,SHEN Yan,SUN Wei,DONG Kuan-Hu,HUANG Jian-Hui,WANG Chang-Hui. Response of soil respiration to addition of different forms of nitrogen and mowing in a saline-alkali grassland in the northern agro-pastoral ecotone[J]. Chin J Plant Ecol, 2020, 44(1): 70-79.

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Figures/Tables 8

Fig. 1 Seasonal dynamics of soil water content and soil temperature in 2017 and 2018 (mean + SE). CK, control treatment; M, mowing treatment; SUN, slow release urea treatment; SUN + M, slow release urea and mowing treatment; UN, urea treatment; UN + M, urea and mowing treatment. Different lowercase letters indicate significant differences (p < 0.05).

Fig. 2 Seasonal dynamics of soil respiration rates under different treatments of saline-alkali grassland in the northern agricultural-pastoral ecotone (mean + SE). CK, control treatment; M, mowing treatment; SUN, slow release urea treatment; SUN + M, slow release urea and mowing treatment; UN, urea treatment; UN + M, urea and mowing treatment. Different lowercase letters indicate significant differences (p < 0.05).

Table 1 Effects of N addition, mowing and their interactions on soil respiration in saline-alkali grassland in the northern agricultural-pastoral ecotone

因素 Factor	df	F	P
测定时间 Measuring time (Time)	16	35.947	0.000
氮添加 Nitrogen addition (N)	2	3.955	0.020
刈割 Mowing	1	55.789	0.000
测定时间×氮添加 (Time × N)	32	0.547	0.981
测定时间×刈割 (Time × Mowing)	16	11.760	0.000
施氮处理×刈割 (N × Mowing)	2	0.150	0.481
测定时间×氮添加×刈割 (Time × N × Mowing)	32	0.579	0.977

Table 2 Effects of N addition, mowing and their interactions on annual cumulative carbon emissions.

	df	F	P
固定效应 Fixed effects
氮添加 Nitrogen addition (N)	2	6.751	0.005
刈割 Mowing	1	0.124	0.728
氮添加×刈割 (N × Mowing)	2	0.239	0.789
随机效应 Random effects
小区 Block	-	1.313	0.189

Fig. 3 Response of soil respiration to different treatments (mean + SE). M, mowing treatment; SUN, slow release urea treatment; SUN + M, slow release urea and mowing treatment; UN, urea treatment; UN + M, urea and mowing treatment. Different lowercase letters indicate significant differences (p < 0.05).

Fig. 4 CO2 cumulative emissions during the growing season under different treatments of saline-alkali grassland in the northern agricultural-pastoral ecotone (mean + SE). CK, control treatment; M, mowing treatment; SUN, slow release urea treatment; SUN + M, slow release urea and mowing treatment; UN, urea treatment; UN + M, urea and mowing treatment. *, difference is significant at the 0.05 level.

Fig. 5 Correlation between soil respiration rates and soil temperature and moisture under different treatments of saline-alkali grassland in the northern agricultural-pastoral ecotone. CK, control treatment; M, mowing treatment; SUN, slow release urea treatment; SUN + M, slow release urea and mowing treatment; UN, urea treatment; UN + M, urea and mowing treatment. **, correlation is significant at the 0.01 level.

Table 3 Pearson’s correlation between soil respiration and soil microorganisms, and soil physical and chemical properties of saline-alkaline grasslands in the northern agricultural-pastoral ecotone

	SR	NH₄⁺	NO₃^-	BNPP	AGB	BGB	Litter	MBC	MBN	MBC/MBN	DOC
SR	1.000
NH₄⁺	-0.412^**	1.000
NO₃^-	-0.321^**	0.450^**	1.000
BNPP	0.072	0.108	0.295^*	1.000
AGB	-0.013	0.468^**	0.433^**	0.233^*	1.000
BGB	0.005	-0.139	-0.358^**	-0.102	-0.032	1.000
Litter	-0.189	0.622^**	0.536^**	0.180	0.489^**	-0.193	1.000
MBC	0.253^*	-0.363^**	-0.372^**	-0.029	-0.138	0.380^**	-0.337^**	1.000
MBN	0.191	-0.314^**	-0.248^*	-0.231	-0.219	0.316^**	-0.281^*	0.561^**	1.000
MBC/MBN	0.026	0.166	-0.066	0.215	0.043	0.162	0.026	0.185	-0.306^**	1.000
DOC	0.194	-0.190	-0.410^**	-0.180	-0.134	0.187	-0.341^**	0.327^**	0.096	0.064	1.000

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