• Energy Research

The experimental determination of soil CO 2 efflux and the investigation of the effect of different treatments require several replicates. However, the required number depends on various factors (soil properties, spatial heterogeneity, etc.). Moreover, the spatial and temporal scales have an impact on the uncertainty of CO 2 efflux determination. Here, we characterize the spatial variability of soil CO 2 efflux at different scales, analyze the drivers of CO 2 efflux, and assess the required number of samples for obtaining CO 2 efflux determinations. In situ CO 2 efflux measurements were made in situ at an agricultural site with different treatments of organic manures from biogas plants at 21 dates during the growing season of 2years. Overall variability of CO 2 efflux was characterized by CV values of about 27%, with a range between 10 and 57%. Small-scale variability (within plots) was on average larger than large-scale variability between the blocks. All variability components showed a pronounced seasonal variability. Consequently, spatial variability patterns determined at a site for one date and at a specific scale are not representative for all measurement dates and for larger or smaller scales. The spatial variation in CO 2 efflux seems to be driven by soil temperature, soil water content, year, C/N ratio, treatment and block. The estimated numbers of required replicates based on statistical considerations were often larger than the actual number of replicates (n=16). Monte Carlo type simulations showed that deviations from an estimated reference value largely depend on the variability and number of (sub)samples.

Biochar management has been proposed as a promising strategy to mitigate climate change. However, the long-term effects of biochar amendment on soil greenhouse gas (GHG) production and microbial community in forest ecosystems under projected warming remain highly uncertain. In this study, we conducted a 49-day incubation experiment to investigate the impact of biochar application on soil physico-chemical properties, GHG production rates, and microbial community at three temperature levels using a temperate forest soil amended with spruce biochar four years ago. Our results showed that temperature exerted a positive effect on soil CO2, CH4 and N2O production, leading to an increase in total global warming potential by 169% and 87% as temperature rose from 5 to 15 °C and from 15 to 25 °C, respectively, and thus a positive feedback to warming. Moreover, warming was found to reduce soil microbial biomass significantly, but at the same time promote the selection of an activated microbial community towards some phyla, e.g. Acidobacteria and Actinobacteria. We observed that biochar amendment reduced soil CH4 consumption and N2O production in the absence of litter by 106% and 94%, respectively, but did not affect soil CO2 production. While biochar had no significant influence of total global warming potential of forest soil, it could promote climate change mitigation by increasing the total soil carbon content by 26% in the presence of litter. In addition, biochar application was shown to enhance soil available phosphorus and dissolved organic carbon concentrations, as well as soil microbial biomass under a warmer environment. Our findings highlighted the potential of spruce biochar as a soil amendment in improving soil fertility and carbon sequestration in temperate forest over the long term, without creating any adverse climatic impacts associated with soil GHG production.

No tillage (NT) and spring ridge tillage (SRT) are two common applications of conservation tillage. Although conservation tillage is known to exert major control over soil microbial respiration (SMR), the growing-season SMR response to these two applications remains elusive. In order to better understand the influence of conservation tillage practices, this experiment was conducted in an experimental field using NT and SRT for 17 years. In situ measurements of SMR, soil temperature and soil water content (SWC) were performed. Soil samples were collected to analyze soil porosity, soil microbial biomass (SMB) and soil enzymatic activities. Results show that the two conservation tillage systems had a significant difference (p 0.05). Despite SRT increasing the proportion of micro-porosities and meso-porosities, the soil macro-porosities for NT were 7.37% higher than that of SRT, which resulted in higher bacteria and fungi in NT. Owing to SRT damaged the hypha, which had disadvantage in soil microbe protection. Inversely, less soil disturbance was a unique advantage in NT, which was in favor of improving soil macro-pores and SWC. Redundancy analyses (RDA) showed SMR was positively correlated with soil macro-pores, SMB and SWC. Furthermore, the Pearson correlation test indicated that SMB and soil enzymatic activities did not have a significant correlation (p>0.05). This study results suggest that SRT is more conducive to carbon sequestration compared with NT in cropland. Keywords: no tillage, spring ridge tillage, soil microbial respiration, microbial biomass, soil porosity, soil enzymatic activity DOI: 10.25165/j.ijabe.20201304.5587 Citation: Wang G, Jia H L, Zhuang J, Glatzel S, Bennett J M, Zhu Y C. Growing-season soil microbial respiration response to long-term no tillage and spring ridge tillage. Int J Agric & Biol Eng, 2020; 13(4): 143–150.

Globally, peatlands have been recognized as important carbon sinks while only covering approximately 3% of the earth’s land surface. Root exudates are known key drivers of C cycling in soils and rhizosphere priming effects have been studied extensively in terrestrial ecosystems. Their role for decomposition of peat still remains unclear, as little research about their fate and potential priming effects in peat exists. In this study, we aimed to evaluate pathways of root exudates and their short-term priming effects by daily determination of stable carbon isotope fluxes of CO2 and CH4. As the drainage of peatlands strongly alters processes of decomposition, we included measurements after drainage as well. Results revealed the immediate respiration of root exudates in peat, mainly as CO2, while CH4 release was associated with a lag time of several days. However, the largest proportion of added root exudates remained in the solid and liquid phase of peat. In conclusion, our findings suggest that no priming occurred as added substrates remained immobile in peat.

Peat accumulation is the result of an imbalance between the biomass production and the reduced decomposition of organic matter, which has allowed peatlands to accumulate high levels of carbon over time. Sphagnum-dominated peatlands are among the most threatened ecosystems due to increasing anthropogenic pressures and harsher environmental conditions caused by climate change. The resulting changes in vegetation alter litter interactions and change decomposition patterns by altering nutrient cycling, hydrological conditions and carbon sequestration capacity of bogs. The aim of this study was to identify decomposition patterns for different bog litter types and mixtures over time. We sampled litter from an ombrotrophic bog (Sphagnum, Betula, Calluna), prepared mixtures of litter types and incubated our samples under laboratory conditions. We evaluated decomposition proxies and used k-means clustering to detect the formation of litter- and mixture-specific decomposition patterns over time. Sphagnum litter had a consistently low decomposition and its presence in mixtures reduced enzymatic activities. Initially, Betula litter added high amounts of N and labile C compounds to leachates. k-means clustering revealed a typical initial decomposition pattern (i.e. lowest decomposition directly after starting the incubation, followed by highest decomposition rates, and a steady decrease until the end) for most litter types, except for Sphagnum. Litter-specific decomposition patterns emerged after 14 days. Betula litter did not enhance decomposition of other litter types in our short-term incubation, but additional nutrient inputs could alter peat-litter interactions in the long term, increasing the risk of losing the carbon sink function of nutrient-poor bogs.

Isotopic measurements showed that N 2 O production during drought is unexpectedly dominated by denitrification of organic nitrogen.

AbstractPeatlands cover only 3–4% of the Earth’s surface, but they store nearly 30% of global soil carbon stock. This significant carbon store is under threat as peatlands continue to be degraded at alarming rates around the world. It has prompted countries worldwide to establish regulations to conserve and reduce emissions from this carbon rich ecosystem. For example, the EU has implemented new rules that mandate sustainable management of peatlands, critical to reaching the goal of carbon neutrality by 2050. However, a lack of information on the extent and condition of peatlands has hindered the development of national policies and restoration efforts. This paper reviews the current state of knowledge on mapping and monitoring peatlands from field sites to the globe and identifies areas where further research is needed. It presents an overview of the different methodologies used to map peatlands in nine countries, which vary in definition of peat soil and peatland, mapping coverage, and mapping detail. Whereas mapping peatlands across the world with only one approach is hardly possible, the paper highlights the need for more consistent approaches within regions having comparable peatland types and climates to inform their protection and urgent restoration. The review further summarises various approaches used for monitoring peatland conditions and functions. These include monitoring at the plot scale for degree of humification and stoichiometric ratio, and proximal sensing such as gamma radiometrics and electromagnetic induction at the field to landscape scale for mapping peat thickness and identifying hotspots for greenhouse gas (GHG) emissions. Remote sensing techniques with passive and active sensors at regional to national scale can help in monitoring subsidence rate, water table, peat moisture, landslides, and GHG emissions. Although the use of water table depth as a proxy for interannual GHG emissions from peatlands has been well established, there is no single remote sensing method or data product yet that has been verified beyond local or regional scales. Broader land-use change and fire monitoring at a global scale may further assist national GHG inventory reporting. Monitoring of peatland conditions to evaluate the success of individual restoration schemes still requires field work to assess local proxies combined with remote sensing and modeling. Long-term monitoring is necessary to draw valid conclusions on revegetation outcomes and associated GHG emissions in rewetted peatlands, as their dynamics are not fully understood at the site level. Monitoring vegetation development and hydrology of restored peatlands is needed as a proxy to assess the return of water and changes in nutrient cycling and biodiversity.