Available online at www.sciencedirect.com Agriculture, Ecosystems and Environment 124 (2008) 125–135 www.elsevier.com/locate/agee Greenhouse gas fluxes from soils of different land-use types in a hilly area of South China Hui Liu a,b, Ping Zhao a,*, Ping Lu c, Yue-Si Wang d, Yong-Biao Lin a, Xing-Quan Rao a a South China Botanic Garden, Chinese Academy of Sciences, Guangzhou 510650, PR China b School of Tourism and Environment, Guangdong University of Business Studies, Guangzhou 510320, PR China c EWL Sciences, P.O. Box 39443, Winnellie, Northern Territory 0821, Australia d Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, PR China Received 15 October 2006; received in revised form 3 September 2007; accepted 11 September 2007 Available online 24 October 2007 Abstract The magnitude, temporal, and spatial patterns of greenhouse gas (hereafter referred to as GHG) fluxes from soils of plantation in the subtropical area of China are still highly uncertain. To contribute towards an improvement of actual estimates, soil CO2,CH4, and N2O fluxes were measured in two different land-use types in a hilly area of South China. This study showed 2 years continuous measurements (twice a week) of GHG fluxes from soils of a pine plantation and a longan orchard system. Impacts of environmental drivers (soil temperature and soil moisture), litter exclusion and land-use (vegetation versus orchard) were presented. Our results suggested that the plantation and orchard soils were weak sinks of atmospheric CH4 and significant sources of atmospheric CO2 and N2O. Annual mean GHG fluxes from soils of plantation À1 À1 À1 À1 and orchard were: CO2 fluxes of 4.70 and 14.72 Mg CO2–C ha year ,CH4 fluxes of À2.57 and À2.61 kg CH4–C ha year ,N2O fluxes À1 À1 of 3.03 and 8.64 kg N2O–N ha year , respectively. Land use types had great impact on CO2 and N2O emissions. Annual average CO2 and N2O emissions were higher in the orchard than in the plantation, while there were no clear differences in CH4 emissions between two sites. Our results suggest that afforestation could be a potential mitigation strategy to reduce GHG emissions from agricultural soils if the observed results were representative at the regional scale. CO2 and N2O emissions were mainly affected by soil temperature and soil moisture. CH4 uptakes showed significant correlation with soil moisture. The seasonal changes in soil CO2 and N2O fluxes followed the seasonal weather pattern, with high CO2 and N2O emission rates in the rainy period and low rates in the dry period. In contrast, seasonal patterns of CH4 fluxes were not clear. Removal of surface litter reduced soil CO2 effluxes by 17–25% and N2O effluxes by 34–31% in the plantation and orchard in the second sampling year but not in the first sampling year which suggested micro-environmental heterogeneity in soils. Removal of surface litter had no significant effect on CH4 absorption rates in both years. This suggests that microbial CH4 uptake was mainly related to the mineral soil rather than in the surface litter layer. # 2007 Elsevier B.V. All rights reserved. Keywords: GHG flux; Orchard; Pine plantation; Litter exclusion; Soil moisture; Soil temperature 1. Introduction global warming are also made by methane, CH4,and nitrous oxide, N2O. Soils can store and release consider- Gas exchange between soils and the atmosphere is an able quantities of carbon through natural processes important contributing factor to global change due to including litter deposition, decomposition and root increasing release of greenhouse gas (GHG) (Bouwman, respiration (Drewitt et al., 2002). Whereas, forest soils 1990). The most important individual greenhouse gas is have been identified as a significant sink for atmospheric carbon dioxide, CO2, but substantial contributions to CH4, and it is estimated that CH4 uptake activities of soils represent 3–9% of the global atmospheric CH4 sinks * Corresponding author. Tel.: +86 20 37252881; fax: +86 20 37252831. (Prather et al., 1995). Soils have also been identified to be E-mail address: [email protected] (P. Zhao). significant sources for N trace gases, accounting for 60% of 0167-8809/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2007.09.002 126 H. Liu et al. / Agriculture, Ecosystems and Environment 124 (2008) 125–135 the total annual N2O emissions (Ehhalt et al., 2001; 2. Materials and methods Maljanen et al., 2001). Researchers have emphasized the importance of improving our understanding of soil 2.1. Experimental sites and materials processes in order to gain more confidence in projections about future changes in the global atmospheric GHG The study was carried out at the Heshan Hilly Land concentrations (Prather et al., 1995; Drewitt et al., 2002; Interdisciplinary Experimental Station of the Chinese Merino et al., 2004). Academy of Sciences in the subtropical region of China Land use practices have great impact on GHG flux from (Heshan, Guangdong Province, China, 1128540E, 228410N). soil surface (Dobbie et al., 1996; Prieme´ and Christensen, The mean annual temperature is 21.7 8C, the mean rainfall is 1997; Smith et al., 2000; Houghton, 2002). In China and 1700 mm, and the mean evapotranspiration is 1600 mm many other countries, degraded land is increasingly (http://www.scib.ac.cn/hsz/English/index.htm). converted into pasture or newly planted forest, which A pine plantation (20-year-old Pinus massoniana trees) noticeably increases the total grassland and forest areas. In and a longan orchard (12-year-old Dimocarpus longan Lour China, afforestation area was 45  106 ha in the past 30 trees) were selected to evaluate the effects of land use on the years (Houghton, 2002), which includes the planting of trees soil GHG exchanges. Prior to the plantings, both the pine for timber as well as shelterbelts, fuel wood, and orchards. plantation and orchard sites had similar soil characteristics Such changes can substantially alter soil organic carbon (Li et al., 2000). There was a layer of 3–5 cm thick of half- dynamics (Li et al., 2002) and affect exchanges of GHG decomposed litter and coarse woody debris under the pine between the soil and the atmosphere (Zhou et al., 2004). plantation (Shen et al., 2001). The selected sites were However, effects of land use on changes of GHG emissions representative of the regional features of land use in hilly from soils in subtropical area of South China are poorly area of South China. The soil is an oxisol developed from understood. Since the subtropical climate is characterized sandstone and the main characteristics of the soil at the two typically by rainy and dry seasons, seasonal patterns of the sites are listed in Table 1. There were no differences in GHG emissions are important for our understanding of how texture and C/N ratio however higher pH value, soil organic soil temperature and soil moisture affect soil C and N C, soil microbe C and total nitrogen but lower bulk density in turnover processes and associated trace gas emissions in the the orchard soil than in the pine plantation soil. subtropical region. The objective of the present work was to: (1) investigate 2.2. Experimental design and treatments seasonal changes in the GHG fluxes from soils of a pine plantation and an orchard; (2) quantify annual total soil In March 2003, six GHG gas exchange chambers were GHG fluxes; (3) evaluate the responses of GHG fluxes to installed ineach of the pine plantation andthe orchard. At each litter exclusion and key driving variables, such as soil site, three chambers were randomly designated to measure the temperature and soil moisture. impacts of surface litter exclusion (i.e. the bare soil or ‘BS’ Table 1 Soil characteristics at the two experimental sites (pine plantation and orchard) in Heshan Land use Pine plantation Orchard Soil texturea Sandy clay loam Sandy clay loam Litter accumulation (t h mÀ2)b 18.7 – Litter input (t h mÀ2 yearÀ1)b 7.30 – Soil organic C (gC or g kgÀ1 dry soil)c 11.89 13.40 À1 c Soil microbe C (mg Cmic (100 g) dry soil 29.68 47.79 Soil organic carbon storage (t h mÀ2)d – 74.66 Bulk density (g cmÀ3)e,a 1.11 0.99 pHa,f 3.95 5.91 Total nitrogen (g kgÀ1)e,a 1.19 1.49 À À1 g NO3 –N content (mg kg ) 4.23 – + À1 g NH4 –N content (mg kg ) 6.28 – C:Nf,a 10 10 Total phosphorus (g kgÀ1)a – 0.98 Available phosphorus (mg kgÀ1)a – 35.8 3 À3 a Maximum water holding capacity (cm H2Ocm soil  100) – 38.6 a Li et al. (1995). b Shen et al. (2001). c Zhou et al. (2004). d Li et al. (2002). e Value from sample collected in March 1999 from 0 to 20 cm depth of soil. Unpublished data from Heshan Station, 1999. f Wen et al. (2000). g Value from sample collected in September 2002 from 0 to 20 cm depth of soil. Unpublished data from Heshan Station, 2002. H. Liu et al. / Agriculture, Ecosystems and Environment 124 (2008) 125–135 127 treatment), and the rest were used as the control (i.e. soil with (n = 3 in Year 1, n = 4 in year 2) on each sampling day. All surface litter or ‘SL’ treatment). For the BS treatment, litter statistical analyses were performed using SPSS 12.0 was removed carefully at least 1 h before each sampling. Field software package (SPSS Inc., Chicago, USA). The normal measurements were carried out twice a week from 21 March distribution of the data was tested by the Kolmogorov– 2003 to 20 April 2005.