Effects of enclosure and grazing on carbon and water fluxes of sandy grassland

doi:10.17521/cjpe.2015.0054

Abstract

Abstract: Aims

Carbon and water cycling are two key processes in circulation of materials and energy flow of sandy grassland ecosystem; recognition of changes in carbon and water cycling is important for understanding the responses of sandy grassland ecosystem structure and function to regional climate change and human activities. Our objectives were to determine the regulations of carbon sequestration and emission, and to examine the relationships of carbon and water fluxes with environmental factors.

Methods

Chamber method was used to measure carbon and water fluxes in grazed plots and fencing enclosures of different durations in a sandy grassland over a growing season in 2013.

Important findings

(1) Variance analysis revealed that, during the observational period, the gross ecosystem productivity (GEP), ecosystem respiration (ER), and evapotranspiration (ET) were all in an order of: 17-year enclosure > 22-year enclosure > grazing, with significant differences (p < 0.05) among the treatments; the maximum values were 2.23, 1.65, and 1.94 times of the minimum values, respectively. (2) There was a significant linear and positive correlation between GEP and ET (p < 0.01); ET explained 58% to 60% of the variations in GEP. Water use efficiency (WUE) decreased from 2.85 μmol·nmol^-1 in the 22-year enclosure to 2.75 μmol·nmol^-1 in the 17-year enclosure, and to 2.10 μmol·nmol^-1 in grazed plots. (3) There were significant linear and positive correlations between GEP, ER and soil water content. Exponential model better fitted the responses of ecosystem respiration to soil temperature. The temperature sensibility coefficient Q₁₀values of ER ranked in the order of 17-year enclosure (1.878) > 22-year enclosure (1.733) > grazing (1.477). In conclusion, enclosure enhanced the carbon and water cycling in degraded sandy grassland ecosystem. However, a 22-year enclosure is not beneficial to this process than 17-year enclosure, suggesting that proper enclosure is conductive to the recovery of degraded sandy grassland and effective to the use of sandy grassland resources.

Key words: ecosystem respiration, evapotranspiration, gross ecosystem productivity, sandy grassland

SUN Dian-Chao,LI Yu-Lin,ZHAO Xue-Yong,ZUO Xiao-An,MAO Wei. Effects of enclosure and grazing on carbon and water fluxes of sandy grassland[J]. Chin J Plan Ecolo, 2015, 39(6): 565-576.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2015.0054

https://www.plant-ecology.com/EN/Y2015/V39/I6/565

Figures/Tables 7

Table 1 Soil characteristics of 0-20 cm depth at the study site with different treatments (means ± SE)

处理 Treatment	有机碳 Organic carbon (g·kg^-1)	全氮 Total nitrogen (g·kg^-1)	总磷 Total phosphorus (g·kg^-1)	C:N	容重 Bulk density (g·cm^-3)
放牧 Grazing	0.15 ± 0.01^c	0.02 ± 0.00^c	0.09 ± 0.00^c	6.92	1.57 ± 0.01^a
围封17年 17-year enclosure	0.22 ± 0.01^b	0.03 ± 0.00^b	0.14 ± 0.00^b	7.66	1.55 ± 0.01^ab
围封22年 22-year enclosure	0.29 ± 0.00^a	0.04 ± 0.00^a	0.16 ± 0.00^a	7.66	1.54 ± 0.02^b

Fig. 1 Seasonal dynamic of gross ecosystem productivity (GEP, A) and ecosystem respiration (ER, B) under enclosure and grazing in the growing season (means ± SE).

Table 2 The aboveground biomass, litter fall, and belowground biomass at the study site with different treatments (means ± SD)

Fig. 2 Seasonal dynamic of evapotranspiration (ET) under enclosure and grazing in growing season. (means ± SE).

Fig. 3 Linear regression analysis between gross ecosystem productivity (GEP) and evapotranspiration (ET) under different treatments. A, grazing. B, 17-year enclosure. C, 22-year enclosure. ** indicate highly significant coefficient of the linear fitting (p < 0.01). R2adj , adjusted R2.

Fig. 4 The regression analysis of gross ecosystem productivity (GEP) and ecosystem respiration (ER) with soil temperature (Ts) and soil water content (SWC) under different treatments. A, The relationship between GEP and Ts. B, The relationship between GEP and SWC. C, The relationship between ER and Ts. D, The relationship between ER and SWC.

Table 3 The exponential fitting of ERr and temperature sensibility coefficient (Q10) under different treatments

处理 Treatment	拟合方程 Fitted equation	p	R²_adj.	Q₁₀	0-5 cm的土壤温度T_s(℃)
放牧 Grazing	ERr = 0.777 e^0.039^T^s	< 0.01	0.186	1.477	26.14 ± 0.26^a
围封17年 17-year enclosure	ERr = 0.714 e^0.063^T^s	< 0.01	0.316	1.878	25.12 ± 0.25^b
围封22年 22-year enclosure	ERr = 0.821 e^0.055^T^s	< 0.01	0.249	1.733	25.19 ± 0.26^b

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