Responses of soil respiration to reduced water table and nitrogen addition in an alpine wetland on the Qinghai-Xizang Plateau

doi:10.3724/SP.J.1258.2014.00057

Abstract

Abstract:

Aims Over the past 20 years, alpine wetlands have been subjected to a rapid change in climate, resulting in water table drawdown and increased nitrogen deposition. In wetland ecosystems, the water table drawdown can improve soil aeration, hence leading to a higher soil respiration rate; whereas an increased nitrogen deposition could reduce the microbial biomass and pH value, suppressing soil respiration. Understanding the responses of soil respiration to reduced water table and increased nitrogen deposition in alpine wetlands is thus critical to predicting the carbon cycle of wetland ecosystems and its feedbacks to ongoing climate changes. This study tests the effects of water table reduction and nitrogen addition on soil respiration in the Luanhaizi wetland on the Qinghai-Xizang Plateau.
Methods We imposed four treatments, including control (WT⁰N⁰), reduced water table (WT^-N⁰), nitrogen addition (WT⁰N⁺), and a combination of reduced water table and nitrogen addition (WT^-N⁺), on 20 peat monoliths collected from the Luanhaizi wetland at the Haibei station. Soil respiration was measured from late July through mid-September under all treatments.
Important findings A reduction in water table significantly increased the rate of soil respiration. In contrast, nitrogen addition suppressed soil respiration only when water table was not reduced. A positive correlation was found between the aboveground biomass and soil respiration, while no correlation was detected between root biomass and soil respiration. The temperature sensitivity of soil respiration was increased by reduced water table, but was not affected by nitrogen addition. Our results suggest that nitrogen deposition is likely to reduce soil CO₂ emission in alpine wetlands where water level remains high. However, future warmer and drier conditions could result in reduced water table, and consequently alpine wetlands would be predicted to release substantially more CO₂than previously estimated.

Key words: alpine wetland, nitrogen addition, Qinghai-Xizang Plateau, soil respiration, water table lowering

WANG Hao,YU Ling-Fei,CHEN Li-Tong,WANG Chao,HE Jin-Sheng. Responses of soil respiration to reduced water table and nitrogen addition in an alpine wetland on the Qinghai-Xizang Plateau[J]. Chin J Plant Ecol, 2014, 38(6): 619-625.

Add to citation manager EndNote|Ris|BibTeX

URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2014.00057

https://www.plant-ecology.com/EN/Y2014/V38/I6/619

Figures/Tables 5

Fig. 1 Variations in water table depth (A), soil temperature at 5 cm depth (B), and soil respiration rate (C) under different treatments over the experimental period (mean ± SE, n = 5). ●, control; ■, reduced water table; ▽, nitrogen addition; ◇, combination of reduced water table and nitrogen addition.

Table 1 Summary of repeated-measures ANOVAs for soil respiration rate (SR), soil temperature at 5 cm depth (T), and water table depth (WTD) by using nitrogen addition (N+) and reduced water table (WT-) as main factors, and measurement date (D) as a within-subject factor over the experimental period

	土壤呼吸速率SR		5 cm深处土壤温度 T		水位深度 WTD
	F	p	F	p	F	p
N⁺	0.91	0.36	0.08	0.78	1.05	0.32
WT^-	338.94	<0.001	6.64	0.02	1 183.00	<0.001
N⁺ × WT^-	6.24	0.02	2.02	0.17	0.46	0.51
D	37.26	<0.001	205.06	<0.001	24.94	<0.001
D × N⁺	0.68	0.67	0.42	0.74	3.06	0.05
D × WT^-	10.93	<0.001	2.08	0.11	22.59	<0.001
D × N⁺ × WT^-	2.37	0.05	0.99	0.41	1.80	0.18

Fig. 2 Effects of different treatments on soil respiration over the experimental period (mean ± SE, n = 5). WT0 N0, control; WT- N0, reduced water table; WT0 N+, nitrogen addition; WT- N+, combination of reduced water table and nitrogen addition. Different letters indicate significant differences among treatments (p < 0.05).

Table 2 The fittings of exponential regression functions between soil respiration rate (SR) and soil temperature at 5 cm depth (T) and the values of temperature sensitivity of soil respiration (Q10)

处理 Treatment	回归方程 Regression equation	R²	p	Q₁₀
WT⁰N⁰	SR = 0.882e^0.026^T	0.209	0.006	1.30^c
WT⁰N⁺	SR = 0.421e^0.064^T	0.492	<0.001	1.90^bc
WT^-N⁰	SR = 1.113e^0.107^T	0.474	<0.001	2.92^a
WT^-N⁺	SR = 1.664e^0.089^T	0.416	<0.001	2.44^ab

Fig. 3 Relationships of soil respiration rate with biomass and litter accumulation under different treatments. A, Aboveground biomass. B, Litter accumulation. C, Root biomass in 0-10 cm soil layer. D, Root biomass in 0-20 cm soil layer. WT0 N0, control; WT- N0, reduced water table; WT0 N+, nitrogen addition; WT- N+, combination of reduced water table and nitrogen addition. The Pearson correlation coefficient is shown if significant. *, p < 0.05; ***, p < 0.001.

References 27

[1]	Bragazza L, Freeman C, Jones T, Rydin H, Limpens J, Fenner N, Ellis T, Gerdol R, Hájek M, Hájek T (2006). Atmospheric nitrogen deposition promotes carbon loss from peat bogs. Proceedings of the National Academy of Sciences of the United States of America, 103, 19386-19389. URL PMID
[2]	Bridgham SD, Pastor J, Dewey B, Weltzin JF, Updegraff K (2008). Rapid carbon response of peatlands to climate change. Ecology, 89, 3041-3048. DOI URL PMID
[3]	Bubier JL, Moore TR, Bledzki LA (2007). Effects of nutrient addition on vegetation and carbon cycling in an ombrotrophic bog. Global Change Biology, 13, 1168-1186. DOI URL
[4]	Chimner RA, Cooper DJ (2003). Influence of water table levels on CO₂ emissions in a Colorado subalpine fen: an in situ microcosm study. Soil Biology & Biochemistry, 35, 345-351. DOI URL
[5]	Craine JM, Wedin DA, Reich PB (2001). The response of soil CO₂ flux to changes in atmospheric CO₂, nitrogen supply and plant diversity. Global Change Biology, 7, 947-953. DOI URL
[6]	Dinsmore KJ, Skiba UM, Billett MF, Rees RM (2009). Effect of water table on greenhouse gas emissions from peatland mesocosms. Plant and Soil, 318, 229-242. DOI URL
[7]	Fenner N, Freeman C (2011). Drought-induced carbon loss in peatlands. Nature Geoscience, 4, 895-900. DOI URL
[8]	Gorham E (1991). Northern peatlands: role in the carbon cycle and probable responses to climatic warming. Ecological Applications, 1, 182-195. DOI URL PMID
[9]	Gruber N, Galloway JN (2008). An earth-system perspective of the global nitrogen cycle. Nature, 451, 293-296. DOI URL PMID
[10]	Janssens I, Dieleman W, Luyssaert S, Subke JA, Reichstein M, Ceulemans R, Ciais P, Dolman AJ, Grace J, Matteucci G, Papale D, Piao SL, Schulze ED, Tang J, Law BE (2010). Reduction of forest soil respiration in response to nitrogen deposition. Nature Geoscience, 3, 315-322. DOI URL
[11]	Jimenez K, Starr G, Staudhammer C, Schedlbauer J, Loescher H, Malone S, Oberbauer S (2012). Carbon dioxide exchange rates from short- and long-hydroperiod everglades freshwater marsh. Journal of Geophysical Research, 117(G4), doi: 10.1029/2012JG002117.
[12]	Lü CQ, Tian HQ (2007). Spatial and temporal patterns of nitrogen deposition in China: synthesis of observational data. Journal of Geophysical Research, 112, D22S05, doi: 10.1029/2006JD007990.
[13]	Liu XD, Chen BD (2000). Climatic warming in the Tibetan Plateau during recent decades. International Journal of Climatology, 20, 1729-1742. DOI URL
[14]	Mäkiranta P, Laiho R, Fritze H, Hytönen J, Laine J, Minkkinen K (2009). Indirect regulation of heterotrophic peat soil respiration by water level via microbial community structure and temperature sensitivity. Soil Biology & Biochemistry, 41, 695-703. DOI URL
[15]	Mo JG, Zhang W, Zhu WX, Gundersen P, Fang YT, Li DJ, Wang H (2008). Nitrogen addition reduces soil respiration in a mature tropical forest in southern China. Global Change Biology, 14, 403-412. DOI URL
[16]	Muhr J, Höhle J, Otieno DO, Borken W (2011). Manipulative lowering of the water table during summer does not affect CO₂ emissions and uptake in a fen in Germany. Ecological Applications, 21, 391-401. URL PMID
[17]	Olsson P, Linder S, Giesler R, Högberg P (2005). Fertilization of boreal forest reduces both autotrophic and heterotrophic soil respiration. Global Change Biology, 11, 1745-1753. DOI URL
[18]	Raich J, Schlesinger WH (1992). The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate. Tellus B, 44, 81-99. DOI URL
[19]	Schlesinger WH, Andrews JA (2000). Soil respiration and the global carbon cycle. Biogeochemistry, 48, 7-20. DOI URL
[20]	Silvola J, Alm J, Ahlholm U, Nykaenen H, Martikainen PJ (1996). The contribution of plant roots to CO₂ fluxes from organic soils. Biology and Fertility of Soils, 23, 126-131. DOI URL
[21]	IPCC (Intergovernmental Panel on Climate Change) (2007). Climate Change 2007―the Physical Science Basis: Working Group I Contribution to the Fourth Assessment Report of the IPCC. Cambridge University Press, Cambridge, UK.
[22]	Tao BX, Song CC, Guo YD (2013). Short-term effects of nitrogen additions and increased temperature on wetland soil respiration, Sanjiang Plain, China. Wetlands, 33, 727-736. DOI URL
[23]	Turunen J, Tomppo E, Tolonen K, Reinikainen A (2002). Estimating carbon accumulation rates of undrained mires in Finland―application to boreal and subarctic regions. The Holocene, 12, 69-80. DOI URL
[24]	Verry E (1997). Hydrological processes of natural, northern forested wetlands. Northern Forested Wetlands: Ecology and Management, 163-188.
[25]	Wang GX, Li YS, Wang YB, Chen L (2007). Typical alpine wetland system changes on the Qinghai-Tibet Plateau in recent 40 years. Acta Geographica Sinica, 62, 481-491. (in Chinese with English abstract) DOI URL
	[ 王根绪, 李元寿, 王一博, 陈玲 (2007). 近40年来青藏高原典型高寒湿地系统的动态变化. 地理学报, 62, 481-491.] DOI URL
[26]	Yan LM, Chen SP, Huang JH, Lin GH (2010). Differential responses of auto- and heterotrophic soil respiration to water and nitrogen addition in a semiarid temperate steppe. Global Change Biology, 16, 2345-2357. DOI URL
[27]	Yang JS, Liu JS, Hu XJ, Li XX, Wang Y, Li HY (2013). Effect of water table level on CO₂, CH₄ and N₂O emissions in a freshwater marsh of Northeast China. Soil Biology & Biochemistry, 61, 52-60. DOI URL