Do freeze‐thaw events enhance C and N losses from soils of different ecosystems? A review

Abstract

Freezing and thawing of soils may affect the turnover of soil organic matter and thus the losses of C and N from soils. Here we review the literature with special focus on: (i) the mechanisms involved, (ii) the effects of freezing temperature and frequency, (iii) the differences between arable soils and soils under natural vegetation, and (iv) the hypothesis that freeze-thaw events lead to significant C and N losses from soils at the annual scale. Changes in microbial biomass and populations, root turnover and soil structure might explain increased gaseous and solute fluxes of C and N following freeze-thaw events, but these mechanisms have seldom been addressed in detail. Effects of freeze-thaw events appear to increase with colder frost temperatures below 0°C, but a threshold value for specific soils and processes cannot be defined. The pool of C and N susceptible to freeze-thaw events is rather limited, as indicated by decreasing losses with shortterm repeated events. Elevated nitrate losses from soils under alpine and/or arctic and forest vegetation occurred only in the year following exceptional soil frost, with greatest reported losses of about 13 kg N ha À1 . Nitrate losses are more likely caused by reduced root uptake rather than by increased N net mineralization. N 2 O emissions from forest soils often increased after thawing, but this lasted only for a relatively short time (days to 1-2 months), with the greatest reported cumulative N 2 O emissions of about 2 kg N 2 O-N ha À1 . The emissions of N 2 O after freeze-thaw events were in some cases substantially greater from arable soils than from forest soils. Thus, freeze-thaw events might induce gaseous and/or solute losses of N from soils that are relevant at the annual time scale. While a burst of CO 2 after thawing of frozen soils is often found, there is strong evidence that, at the annual time scale, freeze-thaw cycles either have little effect or will even reduce soil C losses as compared with unfrozen conditions. On the contrary, a milder winter climate with fewer periods of soil frost may result in greater losses of C from soils that are presently influenced by extended frost periods. DefinitionWe realise that the 'true' freezing point of soil is at or close to 0°C, depending on whether there is a significant amount of solute in the soil water. In this paper, we refer to studies in which soils and related materials have been cooled, naturally or artificially, well below this temperature. For the sake of clarity and simplicity, we refer to the temperature to which the soil has been cooled or exposed either as the frost temperature or the freezing temperature. Likewise a decrease in freezing or frost temperature means that conditions became colder, an increase means that they became warmer.

Biochar can restrict N2O emissions and the risk of nitrogen leaching from an agricultural soil during the freeze-thaw period

“…1), which is most likely due to N limitation as the previous fertilization was conducted almost four months earlier (see Saarnio et al 2013). After thawing, a clear burst of N 2 O was observed, which is in line with previous studies (Koponen andMartikainen 2004, Matzner andBorken 2008), and after two weeks the rate of N 2 O flux was back to near zero (Fig. 1).…”

“…This sets additional challenges for food production, as agriculture contributes about 14% of global greenhouse gas (GHG) emissions and is the biggest anthropogenic source of nitrous oxide (N 2 O) (IPCC 2007). In the boreal zone, soil freeze-thaw (FT) cycles can affect soil nitrogen (N) by increasing the concentration of nitrate (NO 3 -) and ammonium (NH 4 + ) in the soil (Yu et al 2011), by generating an increased efflux of N 2 O (Teepe et al 2001, Koponen and Martikainen 2004, Matzner and Borken 2008 and by posing a risk for N leaching during the snow and soil thawing in spring, which induce melt-water leaching from fields in late April-May. To ameliorate these problems, cultivation techniques must be developed to keep N in the soil and thus increase N utilization by plants.…”

A review of the impact of climate change on future nitrate concentrations in groundwater of the UK

“…Callesen et al (2007) showed that freezing and thawing of soils may alter the N turnover, with large losses following periods of frost due to increased ammonification and mineralisation. Matzner and Borken (2008) The projected decrease in summer recharge and increased frequency of droughts will lead to an increased requirement for agricultural irrigation (Henriques et al, 2008). This is most likely in the drier areas of the UK, such as East Anglia.…”

Diurnal Freeze-Thaw Cycles Modify Winter Soil Respiration in a Desert Shrub-Land Ecosystem

“…Under a changing climate, there is growing concern about the effects of freeze-thaw events on R s , as the increasing frequency of freeze-thaw events plays an important role in regulating the turnover rate of C [13]. Observations that freeze-thaw events cause additional losses of C from arable soils but may suppress soil C losses under natural vegetation [13,14] raise the question of the relevance of freeze-thaw events to R s . Most studies on the effects of freeze-thaw cycles on R s have been laboratory-based, and were conducted with arctic/arable soils.…”

“…Most studies on the effects of freeze-thaw cycles on R s have been laboratory-based, and were conducted with arctic/arable soils. These studies did not compare thawing and frozen periods [14]. Freeze-thaw events are particularly important in cold dryland regions, because of the sparse cloud cover, and large diurnal amplitudes of solar irradiance and surface temperature [15].…”