Substrate Induced Denitrification over or under Estimates Shifts in Soil N2/N2O Ratios

Funding: Funding was provided by the Biotechnology and Biological Sciences Research Council, BBSRC UK (http://www.bbsrc.ac.uk). Grant number BB/H013431/1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Plant exudates improve the mechanical conditions for root penetration through compacted soils

ACKNOWLEDGEMENTS Funding for this project was provided by Tertiary Education Trust Funds (TETFund) and Ambrose Alli University. We wish to thank Annette Raffan for technical support. M. Naveed is funded by the Biotechnology and Biological Sciences Research Council (BBSRC) project ‘Rhizosphere by Design’ (BB/L026058/1). Open access via Springer Compact AgreementPeer reviewedPublisher PD

Inorganic nitrogen and glucose additions alter the short-term formation efficiency of mineral associated organic matter carbon

Carbon within mineral associated organic matter (MAOM) is an important persistent form of soil organic carbon (SOC). However, processes driving the retention of new labile C in MAOM are not fully understood. We investigated the effects of glucose and ammonium nitrate (AN) addition on the short-term (72 h) retention of applied 13C-glucose within MAOM. We found an interactive effect of AN addition with the glucose addition rate. Higher rates of glucose addition resulted in proportionally less glucose-C retained, indicating lower MAOM-C formation efficiency. Addition of AN only altered the proportional retention of glucose where glucose was applied at the lowest rate. In this instance glucose-13C recovery increased with AN addition. However, after 72 h there was no treatment difference in total MAOM-C, indicating that any changes in formation efficiency as a result of AN and glucose additions, did not result in differences in total MAOM-C in the short-term. Whether and how this affects the medium and longer-term dynamics of MAOM-C requires further investigation

Soil nitrate reducing processes drivers, mechanisms for spatial variation, and significance for nitrous oxide production

The microbial processes of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are two important nitrate reducing mechanisms in soil, which are responsible for the loss of nitrate (NO− 3 ) and production of the potent greenhouse gas, nitrous oxide (N2O). A number of factors are known to control these processes, including O2 concentrations and moisture content, N, C, pH, and the size and community structure of nitrate reducing organisms responsible for the processes. There is an increasing understanding associated with many of these controls on flux through the nitrogen cycle in soil systems. However, there remains uncertainty about how the nitrate reducing communities are linked to environmental variables and the flux of products from these processes. The high spatial variability of environmental controls and microbial communities across small sub centimeter areas of soil may prove to be critical in determining why an understanding of the links between biotic and abiotic controls has proved elusive. This spatial effect is often overlooked as a driver of nitrate reducing processes. An increased knowledge of the effects of spatial heterogeneity in soil on nitrate reduction processes will be fundamental in understanding the drivers, location, and potential for N2O production from soils

Resilience of soil functions to transient and persistent stresses is improved more by residue incorporation than the activity of earthworms

The development of soil sustainability is linked to the improved management of soil biota, such as earthworms, and crop residues to improve soil physical structure, enhance microbial activities, and increase nutrient cycling. This study examined the impacts of maize residue (65.8 C/N ratio, dry biomass 0.75 kg m-2) incorporation and earthworms (70 g Metaphire guillelmi m-2) on the resistance and resilience of soil C and N cycling to experimentally applied stresses. Field treatments were maize residue incorporation, maize residue incorporation with earthworm addition, and an unamended control. Resistance and resilience of C mineralization, ammonia oxidation, and potential denitrification were investigated over 28 days following a persistent stress of Cu (1 mg Cu soil g-1) or a transient heat stress (50 ℃ for 16 hours). The results indicated that C mineralization was more resistant and resilient than ammonia oxidation and denitrification to either a persistent Cu or a transient heat stress. The application of maize residues significantly increased soil microbial biomass, C mineralization, ammonia oxidation and potential denitrification compared with the unamended control. Maize residues significantly improved the resistance and resilience of N processes to Cu and heat stress. The presence of earthworms significantly increased potential denitrification but had limited positive effect on functional resistance and resilience. This study suggested crop residue incorporation would strongly increase soil functional resistance and resilience to persistent and transient stresses, and thus could be a useful agricultural practice to improve soil ecosystem sustainability

Intensive grassland management disrupts below-ground multi-trophic resource transfer in response to drought

Modification of soil food webs by land management may alter the response of ecosystem processes to climate extremes, but empirical support is limited and the mechanisms involved remain unclear. Here we quantify how grassland management modifies the transfer of recent photosynthates and soil nitrogen through plants and soil food webs during a post-drought period in a controlled field experiment, using in situ 13C and 15N pulse-labelling in intensively and extensively managed fields. We show that intensive management decrease plant carbon (C) capture and its transfer through components of food webs and soil respiration compared to extensive management. We observe a legacy effect of drought on C transfer pathways mainly in intensively managed grasslands, by increasing plant C assimilation and 13C released as soil CO2 efflux but decreasing its transfer to roots, bacteria and Collembola. Our work provides insight into the interactive effects of grassland management and drought on C transfer pathways, and highlights that capture and rapid transfer of photosynthates through multi-trophic networks are key for maintaining grassland resistance to drought

Estimating maximum fine-fraction organic carbon in UK grasslands

Publication history: Accepted - 24 November 2021; Published - 27 January 2021.Soil organic carbon (SOC) sequestration across agroecosystems worldwide can contribute to mitigate the effects of climate change by reducing levels of atmospheric CO2. Stabilisation of organic carbon (OC) in the fine soil fraction (<20 μm) is considered an important long-term store of SOC, and the saturation deficit (difference between measured OC and estimated maximum OC in the fine fraction) is frequently used to assess SOC sequestration potential following the linear regression equation developed by Hassink (1997). However, this approach is often taken without any assessment of the fit of the equation to the soils being studied. The statistical limitations of linear regression have previously been noted, giving rise to the proposed use of boundary line (BL) analysis and quantile regression (QR) to provide more robust estimates of maximum SOC stabilisation. The objectives of this work were to assess the suitability of the Hassink (1997) equation to estimate maximum fine-fraction OC in UK grassland soils of varying sward ages and to evaluate the linear regression, boundary line and quantile regression methods to estimate maximum fine-fraction OC. A chronosequence of 10 grasslands was sampled, in order to assess the relationship between sward age (time since the last reseeding event) and the measured and predicted maximum fine-fraction OC. Significantly different regression equations show that the Hassink (1997) equation does not accurately reflect maximum fine-fraction OC in UK grasslands when determined using the proportion of the fine soil fraction (<20 μm, %) and measured finefraction OC (g C per kg soil). The QR estimate of maximum SOC stabilisation was almost double that of the linear regression and BL analysis (0.89 0.074, 0.43 0.017 and 0.57 0.052 gC per kg soil, respectively). Sward age had an inconsistent effect on the measured variables and potential maximum fine-fraction OC. Fine-fraction OC across the grasslands made up 4.5% to 55.9% of total SOC, implying that there may be either high potential for additional C sequestration in the fine fraction of these soils or that protection in aggregates is predominant in these grassland soils. This work highlights the need to ensure that methods used to predict maximum fine-fraction OC reflect the soil in situ, resulting in more accurate assessments of carbon sequestration potential.This research has been supported by SRUC’s postgraduate studentship programme and the Global Academy of Agriculture and Food Security, University of Edinburgh. Funding has also been provided by Business Environment, Industry and Strategy (grant no. TRN1133); Ricardo-AEA; and the Rural & Environment Science & Analytical Services Division of the Scottish government