Responses of soil moisture to precipitation pattern change in semiarid grasslands in Nei Mongol, China

doi:10.17521/cjpe.2015.0155

Abstract

Abstract:

Aims Under global climate change, precipitation patterns were predicted to change with larger seasonal and annual variations and more extreme events in the semiarid regions of northern China. Water availability is one of the key limited factors in semiarid grasslands. Changes in precipitation patterns will inevitably affect ecosystem structure and function through soil water condition. Our objective was to investigate the response of soil water content to changes of precipitation pattern, especially its pulse response to precipitation events.
Methods Two semiarid steppe sites (Duolun and Xilinhot) in Nei Mongol were chosen and meteorological stations were installed to monitor precipitation and soil volumetric water content (VWC) at five soil depths (0-10 cm, 10 cm, 20 cm, 30 cm, 50 cm) from 2006 to 2013. The pulse response of VWC at 0-10 cm to an individual precipitation event was simulated by an exponential equation.
Important findings Significant seasonal and inter-annual variations of VWC were observed at the Duolun and Xilinhot sites. VWC at 50 cm soil layer in Xilinhot showed an obvious increase during the early spring due to the influences of snow melting. Mean surface (0-10 cm soil layer) VWC was significantly correlated with annual precipitation across eight years, but VWC in the deeper soil layers (10-50 cm) were not impacted by precipitation. We also found that the precipitation event larger than 2 mm could induce a significant increase in surface (0-10 cm soil layer) VWC, and could be regarded as an effective precipitation in this region. The maximum increment of surface VWC after the events and lasting time (T_lasting) were determined by the event size, while showed negatively linear correlations with the initial soil water content before the events. Vegetation development (leaf area index) did not show significant impacts on the responses of surface soil moisture to precipitation pulses. The infiltration depth of rain water was also determined by rain size and pre-event soil moisture. In average, soil water can infiltrate 1.06 cm and 0.79 cm deeper in Duolun and Xilinhot with 1 mm more precipitation, respectively. Therefore, our results suggest that the event size and pre-event soil moisture were the most important factors affecting response patterns of soil moisture to rain events in semiarid ecosystems.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201607002

Key words: precipitation events, precipitation patterns, pulse responses, semiarid grassland, soil moisture

Min-Ling CHEN, Bing-Wei ZHANG, Ting-Ting REN, Shan-Shan WANG, Shi-Ping CHEN. Responses of soil moisture to precipitation pattern change in semiarid grasslands in Nei Mongol, China[J]. Chin J Plant Ecol, 2016, 40(7): 658-668.

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https://www.plant-ecology.com/EN/Y2016/V40/I7/658

Figures/Tables 11

Table 1 General information of Duolun and Xilinhot sites

站点 Site	经纬度 Longitude and latitude	海拔 Altitude (m)	平均年降水量 Mean annual precipitation (mm)	年平均气温 Mean annual temperature (℃)	土壤类型 Soil type	群落高度 Plant community height (cm)	地上生物量 Aboveground biomass (g·m^-2)	优势植物 Dominant species	土地利用类型 Land use type
多伦 Duolun	42.05° N, 116.28° E	1 350	380	2.2	栗钙土 Chestnut soils	42	174	冷蒿 Artemisia frigida 克氏针茅 Stipa krylovii	2001年围封 Fenced from 2001
锡林浩特Xilinhot	43.55° N, 116.67 E	1 250	332	0.84	栗钙土 Chestnut soils	48	185	羊草 Leymus chinensis 大针茅 Stipa grandis	2005年围封并打草 Fenced and clipped from 2005

Fig. 1 Conceptual model of the pulse response of surface soil water content (VWC0-10, y) to precipitation events (refer to Liu et al., 2002). a and b, parameters of the equation; PPT, precipitation event, the arrow indicates the time when PPT occurred; Tlasting, the lasting time of pulse response (the periods of VWC0-10 above VWCPre after the PPT); ΔVWC0-10, maximum increment of VWC0-10 after the PPT; VWCMax, maximum VWC0-10 after the PPT; VWCPre (y0), VWC0-10 of the day before the PPT.

Fig. 2 Monthly means of environmental and vegetation factors across eight years (2006-2013) at Duolun (DL) and Xilinhot (XL) sites (mean ± SE, n = 8). A, Seasonal variations of mean monthly precipitation (bar) and air temperature (line) of Duolun. B, Seasonal variations of mean monthly precipitation (bar) and air temperature (line) of Xilinhot. C, Seasonal variations of mean monthly leaf area index (LAI) at Duolun (DL) and Xilinhot (XL).

Fig. 3 Inter-annual variations of precipitation (bar) and soil water content (VWC) during the growing season at different soil depths (scatters and lines) at the two sites (A, Duolun; B, Xilinhot) from 2006 to 2013.

Fig. 4 Relationships between surface soil water content (VWC0-10) and precipitation during the growing season at the two sites (A, Duolun; B, Xilinhot). GSP, the growing season precipitation; AP, annual precipitation. *, p < 0.05.

Fig. 5 Seasonal dynamics of mean daily mean soil water content (VWC) at different soil depths and albedo at the two sites (A, Duolun; B, Xilinhot) from 2006 to 2013.

Table 2 Results of the multiple stepwise regressions on increment of surface soil water content (ΔVWC0-10) and lasting time (Tlasting) after the precipitation event at the two sites

因变量 Variable	站点 Site	进入变量 Entered variable	移除变量 Removed variable	参数估计 Parameter estimate	偏R² Partial R²	模型R² Model R²	p
ΔVWC_0-10	多伦 Duolun	方程截距 Intercept		2.32
		PPT		0.38	0.73	0.73	<0.001
		VWC_Pre		-0.19	0.06	0.79	<0.001
			ST_Pre	-0.08	0.00	0.79	0.282
			LAI	1.30	0.00	0.79	0.340
	锡林浩特 Xilinhot	方程截距 Intercept		0.92
		PPT		0.35	0.52	0.85	<0.001
		VWC_Pre		-0.08	0.08	0.01	0.084
			ST_Pre	0.01	0.00	0.86	0.820
			LAI	0.58	0.00	0.86	0.356
T_lasting	多伦 Duolun	方程截距 Intercept		11.63
		PPT		0.33	0.33	0.33	<0.001
		VWC_Pre		-0.42	0.22	0.55	<0.001
		ST_Pre		-0.17	0.05	0.60	0.011
			LAI	0.74	0.00	0.60	0.680
	锡林浩特 Xilinhot	方程截距 Intercept		6.53
		PPT		0.31	0.52	0.52	<0.001
		VWC_Pre		-0.27	0.08	0.60	0.003
			ST_Pre	-0.00	0.00	0.60	0.997
			LAI	0.95	0.00	0.60	0.502

Fig. 6 Relationships of the maximum increment of surface 0-10 cm soil water content (ΔVWC0-10) and lasting time (Tlasting) in the pulse response process to precipitation with precipitation event size (PPT) and soil moisture content before precipitation events (VWCPre) at the two sites (DL, Duolun; XL, Xilinhot). A, Relationship between ΔVWC0-10 and PPT. B, Relationship between Tlasting and PPT. C, Relationship between ΔVWC0-10 and VWCPre. D, Relationship between Tlasting and VWCPre. E, Relationship between the maximum increment of ΔVWC0-10 induced by 1 mm precipitation and VWCPre. ***, p < 0.001; *, p < 0.050; #, p < 0.100.

Fig. 7 Relationships between infiltration depth (Depth) with precipitation event size (PPT) and soil water content before the events (VWCPre) at the two sites (DL, Duolun; XL, Xilinhot). A, Relationship between Depth and PPT. B, Relationship between infiltration depth of 1 mm precipitation (Depth/PPT) and VWCPre. ***, p < 0.001; **, p < 0.010.

Table 3 Results of linear regression (including equation, R2 and p value) between precipitation event size (x, mm) and the increment of soil water content (y, %) at different soil depth

土层 Soil layer (cm)	多伦 Duolun				锡林浩特 Xilinhot
土层 Soil layer (cm)	方程 Equation	样本量 No. of samples	R²	p	方程 Equation	样本量 No. of samples	R²	p
10	y = 0.31x - 0.37	40	0.54	<0.000 1	y = 0.39x - 0.91	40	0.72	<0.000 1
20	y = 0.20x + 0.44	14	0.34	0.029 8	y = 0.34x - 3.45	17	0.67	<0.000 1
30	y = 0.38x - 7.56	7	0.77	0.009 4	y = 0.27x - 4.12	5	0.77	0.051 3

Fig. 8 Vertical distributions of soil bulk density (0-100 cm) at the two sites (DL, Duolun; XL, Xilinhot). * indicates significant difference between the two sites at p < 0.050 (n = 5).

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