Journal of Soil Science and Plant Nutrition, 2013, 13 (2), 445-461 Sensitivity of soil respiration to moisture and temperature M. E. Guntiñas1, F. Gil-Sotres1, M. C. Leirós1, C. Trasar-Cepeda2* 1Departamento de Edafología y Química Agrícola, Grupo de Evaluación de la Calidad del Suelo, Unidad Asociada CSIC, Facultad de Farmacia, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain. 2Departamento de Bioquímica del Suelo, IIAG-CSIC, Apartado 122, E-15780 Santiago de Compostela, Spain.* Corresponding author: [email protected] Abstract The sensitivity of soil respiration to moisture and temperature was evaluated in three soils from the Atlantic temperate humid zone (Galicia, NW Spain) dedicated to different types of land use (forest, grassland and cropland). Samples of the soils were incubated in the laboratory for 42 days under different temperature (10, 15, 20, 25, 30, 35 °C) and moisture (40, 60, 80, 100% of field capacity) conditions. Emission of CO2 from Grassland soil was higher than from the other soils. However, despite the different organic matter contents and biochemical activities in the three soils, temperature and moisture were the main factors affecting respiration. It was not possible to demonstrate the effect of soil use on the temperature sensitivity of organic matter mineralization. Sensitivity to temperature was accurately determined by Q10 expressions, but some results indicate that for correct estimation of Q10 in the incubation experiments, the CO2 emission data obtained during the first few days of incubation should be disregarded. Furthermore, the sensitivity of the soil organic matter to temperature was higher at low soil moisture contents. This finding was surprising as it is generally considered that temperature has a greater effect on respiration in nearly saturated soils than in drier soils. Keywords: Climate change, soil respiration, soil temperature, soil moisture, soil use 1. Introduction It is now accepted by the scientific community that has prompted several studies of how climate change the climate is changing and that part of this change affects the kinetics of soil organic matter mineralization must be attributed to human activities (IPCC WG1, and the emission of CO2 from soils (e.g. Kirschbaum, 2007). Climate change is manifested by changes in 2000; Smith et al., 2008). Climate change modifies soil temperature, precipitation and length of the seasons temperature and moisture regimes simultaneously, and (Smith et al., 2008). These factors affect the biological although many studies have attempted to determine the effect of temperature or moisture on soil respiration, activity of soil and therefore the emission of CO2, one of the gases that causes the greenhouse effect and very few have attempted to explore the combined therefore also contributes to climate change (Cox et al., effects of both factors (Bowden et al., 1998; Davidson 2000). The existence of this important feedback effect et al., 2006; Curiel-Yuste et al., 2007). 445 446 Guntiñas et al. However, information on this topic is so scarce that plant remains that reach the soil and the subsequent there appears to be a lack of knowledge of how soil differences in the organic matter. If such differences moisture affects the temperature sensitivity of soil are only caused by the species composition of the organic matter decomposition, as the relationships plant cover, then the organic matter in agricultural between moisture content and sensitivity are not soils (grassland and arable), which receive different consistent across different soils or types of soil use types of inputs than forest soils, will presumably (Craine and Gelderman, 2011). respond very differently to climate change. In fact, recent estimates suggest that European forest Incubation of soil under controlled conditions continues soils will possibly act as net CO2 sinks in response to be one of the most commonly used methods of to climate change (Kirkby et al., 2005), whereas studying the emission of CO2 from soils, despite agricultural soils will either not undergo any changes criticisms of the method by different researchers. The (Heidmann et al., 2002) or will loss organic matter problems associated with such studies are mainly due (Sleutel et al., 2003) and will therefore emit CO2. In to the fact that the conditions that the soils are exposed light of these differences, it is essential to determine to in the laboratory are very different from field how the organic matter in soils under different types conditions (Smith et al., 2008). Furthermore, some of use, and presumably of different quality (Miralles authors believe that long-term incubation experiments et al., 2009), would react to variations in climatic will lead to alterations in the quality of the soil organic parameters. Such knowledge could then be used to matter and in the proportion of the different fractions plan the best use of the soil in order to minimize originally present, so that the incubated soil will be CO2 emissions and favour increased C stocks in very different from the field soil (Dalias et al., 2001; soils. Unfortunately, very few mechanistic models Chen et al., 2010). However, despite these problems, enable prediction of the effect of climate change laboratory-based soil incubation studies are commonly on soils (Liski et al., 2005), and there are therefore used to investigate the effect of climate change on CO2 many uncertainties as regards the usefulness of such emissions from soils because they are simple, easily predictions. Part of this problem is derived from carried out, and provide the least biased estimates the fact that most models include parameters that of temperature sensitivity (Kirschbaum, 2000). do not specifically apply to the type of soil under Nonetheless, it must be taken into account that the study (Foereid, 2007). Furthermore, it is not known information obtained is restricted to a smaller fraction whether the labile and recalcitrant fractions of organic of the total soil organic matter than in longer term matter (present in different proportions depending on incubations and, therefore short-term incubations may soil use) respond equally to climate change. Some not provide much information about the long-term authors suggest that the pool of recalcitrant C is turnover of soil organic matter. more sensitive to climate change than the pool of more labile organic matter (Leifeld and Fuhrer, 2005; In addition to climatic factors, the quality of soil organic Fierer et al., 2006), whereas others have not found matter should also affect the rate of decomposition. In any differences in the rate of decomposition of labile soils formed under similar climates and from similar and recalcitrant organic matter (Fang et al., 2005; parent material, the quality of the organic matter Rey and Jarvis, 2006) and yet others have reported depends on the vegetation cover and the type of use that the recalcitrant carbon in soils is not sensitive to and management to which the land is subjected. Rey variations in temperature (Giardina and Ryan, 2000). and Jarvis (2006) have shown that the sensitivity of soil respiration to temperature is different in soils Although at present the climate in Galicia (NW Spain) under deciduous forest and in soils under evergreen is humid temperate, the region is expected to undergo forest, because of differences in the composition of the significant climate change because of its geographical Journal of Soil Science and Plant Nutrition, 2013, 13 (2), 445-461 Sensitivity of soil respiration to moisture and temperature 447 position (latitude close to 40° N) (IPCC, 2007), 2. Material and Methods where winter precipitations and mean temperatures throughout the year are expected to increase (de 2.1. Soils, soil sampling and soil preparation Castro et al., 2005). Moreover, although forest soils already account for 42% of the soil cover in the Three soils representative of different types of land use region, much of the forest land has been converted (forest, grassland and cropland) in Galicia were selected from agricultural land in recent years, in response for study. The forest soil (Forest) is an Umbrisol (ISSS to European agrarian and environmental policies Working Group R.B., 1998) under Atlantic oak (Quercus (García and Pérez, 2001). It is not yet clear whether robur L.), which is the climax vegetation in Galicia. this change in land use has led to an increase in The grassland soil (Grassland) is also an Umbrisol carbon stocks in soils and/or modified the carbon subjected to intensive grassland use and represents biogeochemical cycle. Attempts to estimate the intensively managed grassland soils derived more than effects of these changes in land use have highlighted 40 years ago from former forest soils and fertilized the lack of basic reference data regarding soil intensively every year, mainly with cow slurry (200- -1 -1 responses, such as how the mineralization kinetics 250 kg N ha year ). In these grasslands the vegetation of soil organic matter are modified in soils under is dominated by Lolium multiflorum Lam. with a different types of use, in response to changes in scarce presence of legumes, mainly Trifolium repens climatic conditions. L. Finally, the cropland soil (Cropland) is a Regosol (ISSS Working Group R.B., 1998) derived from an In light of the predicted modifications in climate Umbrisol, degraded due to continuous cultivation, and conditions and land use changes, in the present study represents an agricultural soil; this type of soil is usually we investigated the mineralization kinetics of organic found in rural areas, close to houses, and is cultivated matter in soils under different types of use and throughout the year by crop rotation (maize, Zea mays under diverse moisture and temperature conditions, L.; rapes, Brassica napus L., and potatoes, Solanum with the aim of obtaining basic information about tuberosum L., in a bi-annual crop succession) and with the following: a) the effects of modifications in application of large amounts of both organic (manure) -1 and inorganic (NPK) fertilizers (around 150 kg of N ha temperature and moisture on CO2 emissions from soils, and b) the combined effects of both parameters.