Original articleEffects of moisture and temperature on net soil nitrogen mineralization: A laboratory study
Highlights
► Net nitrogen mineralization in three soils was affected by temperature and moisture. ► The sensitivity of net nitrogen mineralization to temperature was maximal at 25 °C. ► Soil moisture had very little effect on net N mineralization.
Introduction
Climate is changing on a global scale and affecting soil temperature and moisture regimes [1]. Climate change will therefore also affect all edaphic processes that depend on soil temperature and moisture, including soil organic matter mineralization [2], [3]. There has been great interest in the possible effects of climate change on soil carbon cycling and on CO2 emissions [4], [5]. There are two main reasons for this interest. Firstly, as CO2 is one of the main greenhouse gases (i.e. it is capable of affecting climate change), it is essential to understand the feed-back mechanisms between climate change and CO2 emissions. Secondly, measurement of CO2 emissions is a straightforward, rapid method of determining the impact of climate change on edaphic metabolism [4].
However, carbon is not the only element affected by climate change, and elements such as nitrogen, phosphorus and sulphur, typically associated with organisms, are also affected. All of these are essential elements and are therefore extremely important for the correct functioning of ecosystems. In the case of nitrogen, most bioavailable forms of this element in natural soils are produced by mineralization of organic matter via depolymerization of large organic polymers, so that the productivity of many ecosystems will depend directly on the availability of nitrogen derived from the decomposition of organic remains. It is therefore reasonable to assume that any modification that affects the rate of decomposition of organic matter will also affect the availability of nitrogen, and therefore will have important repercussions for ecosystem functioning [6].
Many studies involving mineralization of organic nitrogen compounds in soil have been undertaken since the early studies in 1972 by Stanford and Smith, as reported by Dessurealt-Rompré et al. [7]. Stanford and Smith [8] demonstrated that net nitrogen mineralization followed first order kinetics and that the effect of temperature on nitrogen mineralization followed the Arrhenius law, with the rate doubling for each 10 °C increase in temperature. Various authors have recently discussed the effects of temperature and/or moisture content on the net mineralization process, as well as how soil moisture should be expressed (percentage of pore filled, water potential, etc.) and how the different mathematical models used to study such relationships should be interpreted [2, 7, 9, 10, 11, amongst others]. Most of these studies have focused on the rate of nitrogen mineralization, with the aim of estimating the amount of nitrogen that is available to plants. In other words these studies had an agronomic focus. Nevertheless, very few studies about soil nitrogen mineralization consider the sensitivity of the mineralization rate to changes in temperature and moisture with the aim of determining the direct impact of climatic parameters on the nitrogen cycle [7]. This is an important omission as more accurate information about the sensitivity of mineralization constants and how they vary in relation to climatic parameters would enable better description of the response of soil organic matter to climate change. Furthermore, there is even less information about the combined effects of these two factors (temperature and soil moisture) on net nitrogen mineralization processes [11], [12], [13], despite evidence that climate change will affect both components of the climate simultaneously, as indicated above. In fact, Craine and Gelderman [14] indicated their surprise about the scarcity of information as to how soil moisture affects the temperature sensitivity of soil organic matter decomposition and whether or not any such relationships are consistent across different soils.
At present the climate in Galicia (NW Spain) is humid temperate and, because of its geographical position (north of 40° N), the region is expected to undergo significant changes [1]. It is therefore important to predict the response of soils to such changes, and to establish which types of soils (in terms of management regimes) will be most affected. Recent laboratory and field studies in Galicia have addressed the issue of how CO2 emissions in soils will be affected by climate change [15]. The thermodynamic properties of several edaphic enzymes (both hydrolases and oxidoreductases) have also been characterized in order to establish how decomposition processes mediated by these enzymes would be affected by changes in soil temperature [16]. However, to date the effects of climate change on nitrogen mineralization have not been analyzed in Galician soils. Therefore, and given the general lack of knowledge about the influence of climate changes on net nitrogen mineralization, the objectives of the present study were: a) to investigate how net nitrogen mineralization is modified in response to changes in temperature or moisture, b) to determine the extent to which land use modifies the sensitivity of net nitrogen mineralization to changes in soil temperature and moisture, and c) to investigate the extent to which climate change will affect nitrogen availability in Galician soils.
Section snippets
Soils, soil sampling and soil preparation
Three soils (Forest, Grassland and Cropland) were selected as representative of Galician soils under different types of land use. The forest soil (Forest) is an Umbrisol under Atlantic oak, which is the climax vegetation in Galicia. The grassland soil (Grassland) is also an Umbrisol but subjected to intensive grassland use and represents intensively managed grassland soils, derived more than 40 years ago from former forest soils, and fertilized intensively every year, mainly with cattle slurry
Net nitrogen mineralization during the incubation period
In the Forest soil, net mineralization was observed for all conditions of moisture and temperature, whereas in the Grassland and Cropland soils net immobilization was observed during the early stages of the incubation at some temperatures and moisture contents (Fig. 1, Fig. 2). The initial immobilization was low, except in the Grassland soil at 35 °C. The high degree of immobilization in the latter soil can be explained by considering that at this high temperature the microbial metabolism is
Conclusions
Temperature and moisture affected net nitrogen mineralization in the three soils studied, although the response of the Forest soil was more straightforward than that of the agricultural soils.
For all three soils the sensitivity of net nitrogen mineralization to temperature was maximal at 25 °C. The optimal moisture content for nitrogen mineralization was 80% of the field capacity and mineralization at 100% of field capacity was only slightly lower than that obtained at 80%. In general, moisture
Acknowledgements
This research was financially supported by the Spanish Comisión Interministerial de Ciencia y Tecnología (Project No CLI96-1166) and by the Spanish Ministerio de Ciencia e Innovación. (Project No CGL2008-01992/BTE).
References (27)
- et al.
Modelling temperature and moisture effects on C–N transformations in soils: comparison of nine models
Ecol. Model.
(1997) - et al.
Impact of global warming on soil organic carbon
Adv. Agron.
(2008) - et al.
The effect of warming on the CO2 emissions of fresh and old organic soil from under a Sitka spruce plantation
Geoderma
(2010) - et al.
Temperature dependence of soil nitrogen mineralization rate: comparison of mathematical models, reference temperatures and origin of the soils
Geoderma
(2010) - et al.
Modelling the influence of moisture and temperature on net nitrogen mineralization in a forested sandy soil
Soil Biol. Biochem.
(1994) Temperature and soil moisture dependence of N mineralization in intact soil cores
Soil Biol. Biochem.
(1997)- et al.
Soil moisture controls on temperature sensitivity of soil organic carbon decomposition for a mesic grassland
Soil Biol. Biochem.
(2011) - et al.
Thermodynamic parameters of enzymes in grassland soils from Galicia, NW Spain
Soil Biol. Biochem
(2007) - et al.
Substrate quality and the temperature sensitivity of soil organic matter decomposition
Soil Biol. Biochem.
(2008) Climate Change 2007: The Physical Science Basis
(2007)
Will changes in soil organic carbon act as a positive or negative feedback on global warming?
Biogeochemistry
Nitrogen mineralization: challenges of a changing paradigm
Ecology
Nitrogen mineralization potentials of soils
Soil Sci. Soc. Am. Pro
Cited by (276)
Precipitation affects soil nitrogen fixation by regulating active diazotrophs and nitrate nitrogen in an alpine grassland of Qinghai-Tibetan Plateau
2024, Science of the Total EnvironmentThe impacts of climate change on groundwater quality: A review
2024, Science of the Total EnvironmentInfluence of drought intensity on soil carbon priming and its temperature sensitivity after rewetting
2024, Science of the Total EnvironmentThe effect of moisture on nitrogen acquisition strategies of ephemeral desert plants in north-western China are regulated by temperature
2024, Environmental and Experimental Botany