Here we discuss, for each biogenic gas: a) how thawing events influence gas fluxes in multiple ecosystems and in experimental settings; and b) the likely mechanisms and environmental controls underlying the observed patterns.
4. 1. Carbon dioxide flux from thawing
4. 2. Methane flux from thawing
4. 3. Nitrous oxide flux from thawing
4. 4. Nitric oxide flux from thawing
Kreyling, J., Peršoh, D., Werner, S., Benzenberg, M., and Wöllecke, J.: Short-term impacts of soil freeze-thaw cycles on roots and root-associated fungi of Holcus lanatus and Calluna vulgaris, Plant and Soil, 1-13, 2012.
ReplyDeleteAbstract
Background and aims
Soil freeze-thaw cycle (FTC) regimes are altered by climate change and known to influence nutrient cycling and plant growth. Here, we explore mechanistic explanations for the changing plant performance of the grass Holcus lanatus and the dwarf shrub Calluna vulgaris.
Methods
144 plant-soil mesocosms were subjected to different FTC-regimes in a climate chamber. Root injury, fungal activity and fungal composition (ITS-sequencing) were quantified.
Results
The applied FTC-scenarios increased root injury by 23% on average while no strong differences between scenarios was found. Root damage was greater in C. vulgaris than in H. lanatus. Fungal activity increased due to the FTC-manipulation and was higher in the C. vulgaris samples, although activity was generally low. No significant shift in the fungal community composition was found immediately after the applied FTCs. A saprobic (Aureobasidium pullulans) and a potentially mycorrhizal fungus (Sebacinales) showed opposing responses to the FTC-manipulation in the different host plants, while a potential phytopathogen (Callophora) decreased in frequency.
Conclusions
Increased fungal activity within these samples is suggested to be related to an increased dominance of saprobic taxa, but not to a shift in qualitative community composition. Single pathogenic species entering the plants through the observed root injuries subsequent to FTC treatments however, may alter plant performance. While these results suggest the importance of root injury for the response of vegetation to FTCs, fungal activity and pathogenic infection need to be further studied under field conditions over longer time periods.
Lukas, S., Potthoff, M., Dyckmans, J., Joergensen, R.G., 2013. Microbial use of 15N-labelled maize residues affected by winter temperature scenarios. Soil Biol. Biochem. 65, 22-32.
ReplyDeleteAbstract
A 56-day incubation experiment was carried out to investigate decomposition and microbial use of 15N-labelled maize (Zea mays L.) residues incubated under four winter temperature scenarios. The residues were mixed to mesocosms equivalent to 1.2 mg C and 42.5 μg N g−1 dry soil, after which the samples were incubated at a constant temperature of +4 °C, a constant −3 °C, and under multiple and single freeze–thaw conditions. A constant +4 °C was most favourable for microbial substrate use, with 4- and 6-fold higher total and maize-C mineralization, respectively, in comparison with constant frost. The cumulative maize mineralization was not determined by the frequency of freeze–thaw events, but regulated by the overall time of frost and thaw conditions. The decomposition of maize straw significantly increased soil organic C mineralization (in all scenarios) and incorporation into microbial biomass (in the freeze–thaw scenarios only). The positive priming effects observed were equivalent to an additional loss of total soil organic C of between about 0.2 (continuous frost) and 0.8% (single freeze–thaw). Microbial biomass was significantly increased after maize straw amendment, with constant frost and freeze–thaw scenarios not having any negative effect on microbial biomass C compared with constant +4 °C. Highest fungal biomass was found after constant frost without fresh substrates and also after extended frost followed by a warm period when fresh plant residues were present. On average, 50% of the added maize N were recovered in the soil total N after 56 days of constant 4 °C and in the freeze–thaw scenarios, with the strongest effect after single freezing and thawing.
Keywords
Freeze–thaw cycles;
Decomposition;
CO2;
Microbial biomass C and N;
Ergosterol;
Extractable C and N;
Soil total N;
δ13C and δ15N;
Priming
Wu, X., Bruggemann, N., Butterbach-Bahl, K., Fu, B., Liu, G., Snow cover and soil moisture controls of freeze-thaw-related soil gas fluxes from a typical semi-arid grassland soil: a laboratory experiment. Biol. Fertility Soils, doi: 10.1007/s00374-00013-00853-z.
ReplyDeleteAbstract
In situ field measurements as well as targeted laboratory studies have shown that freeze–thaw cycles (FTCs) affect soil trace gas fluxes. However, most of past laboratory studies adjusted soil moisture before soil freezing, thereby neglecting that snow cover or water from melting snow may modify effects of FTCs on soil trace gas fluxes. In the present laboratory study with a typical semi-arid grassland soil, three different soil moisture levels (32 %, 41 %, and 50 % WFPS) were established (a) prior to soil freezing or (b) by adding fresh snow to the soil surface after freezing to simulate field conditions and the effect of the melting snow on CO2, CH4, and N2O fluxes during FTCs more realistically. Our results showed that adjusting soil moisture by watering before soil freezing resulted in significantly different cumulative fluxes of CH4, CO2, and N2O throughout three FTCs as compared to the snow cover treatment, especially at a relatively high soil moisture level of 50 % WFPS. An increase of N2O emissions was observed during thawing for both treatments. However, in the watering treatment, this increase was highest in the first thawing cycle and decreased in successive cycles, while in the snow cover treatment, a repetition of the FTCs resulted in a further increase of N2O emissions. These differences might be partly due to the different soil water dynamics during FTCs in the two treatments. CO2 emissions were a function of soil moisture, with emissions being largest at 50 % WFPS and smallest at 32 % WFPS. The largest N2O emissions were observed at WFPS values around 50 %, whereas there were only small or negligible N2O emissions from soil with relatively low soil water content, which indicates that a threshold value of soil moisture might exist that triggers N2O peaks during thawing.
Wang, J., Song, C., Miao, Y., Meng, H., Greenhouse Gas Emissions from Southward Transplanted Wetlands During Freezing-Thawing Periods in Northeast China. Wetlands, doi: 10.1007/s13157-013-0463-4
ReplyDeleteAbstract
Freezing-thawing in mid-high latitudes is an important factor controlling nutrient dynamics. We transplanted peatland columns (TQ) and freshwater marsh columns (SJ) in different latitudes into south seasonal frozen regions to determine the responses of greenhouse gas emissions from different wetlands to the freezing-thawing under climate warming. The decrease in CO2 and CH4 emissions during freezing stage were interrupted by a short emission peak. While N2O uptake rate reduced with decreasing temperature. In the thawing stage, all the three greenhouse gases exhibited emission peaks. CO2 were 159.83 mg m−2 h−1 (TQ) and 86.83 mg m−2 h−1 (SJ); CH4 were 1.32 mg m−2 h−1 (TQ) and 4.07 mg m−2 h−1 (SJ); N2O were 72.14 ug m−2 h−1 (TQ) and 22.15 ug m−2 h−1 (SJ). Meanwhile, N2O transferred from sink into source. With temperature increase, the emission rate of CO2 increased fast, while CH4 and N2O decreased. CO2 emission during freezing-thawing periods was significantly correlated with soil temperature and CH4 emission. Soil active organic carbon also played important roles in greenhouse gases emissions. Our study suggested that more greenhouse gases may release from wetlands into atmosphere in the context of global warming, and the potential release of CO2 and N2O during freezing-thawing periods was much higher in peatlands of permafrost zone.