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8. Gravel-associated organic material is important to quantify soil carbon and nitrogen stocks to depth in an agricultural cropping soil

Author

Kirkby, Clive A., Kirkegaard, John A., and Richardson, Alan E.

Subjects
Gravel -- Environmental aspects, Soils -- Carbon content -- Nitrogen content, Agricultural land -- Environmental aspects, Cropping systems -- Environmental aspects, Agricultural industry, Earth sciences
Abstract

Context. Gravel is a common constituent in soil and is routinely excluded when estimating soil carbon (C) and nitrogen (N) stocks. Aims. We investigated the contribution that the gravel fraction (>2 mm) makes to C and N stocks in an agricultural soil. Methods. The amount of gravel and the C and N content of gravel-associated organic matter (OM) was assessed to 180 cm in a long-term cropping soil with differing nutrient treatments. Key results. Gravel-associated C and N accounted for ~5% of the total C and N stocks in the upper layers (0-30 cm) of soil and up to 40% below 100 cm. The C:N ratio of the gravel-associated OM was similar to that in fine earth fraction (FEF) soil, with C:N ratio of ~13 in surface layers to ~8 at depth. Conclusions. We estimated that 19% and 23% of the total stock of C and N, respectively, were associated with gravel over the whole soil profile. In the two nutrient treatments, with differing C and N stocks in the FEF, gravel-associated OM accounted for 9.3-10.6 t C [ha.sup.-1] and 1.1-1.3 t N [ha.sup.-1]. Implications. Our work highlights the significance of gravel in contributing to soil OM and the importance of sampling to depth to estimate soil C and N stocks. Importantly, disregard of the gravel fraction results in an underestimation of total soil C and N, which has implications for the accounting of C in agricultural soils and for the development of strategies to sequester soil C. Keywords: carbon, C:N ratio, coarse fraction, gravel, sequestration, soil, SOM, stoichiometry., Introduction Soils are the largest sink of the global terrestrial carbon (C) cycle. It is estimated that soils across the globe hold approximately 2200 Gt of C, of which 1500 [...]

Published
2022
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15. Soil organic matter in a stressed world

Author

Farrell, Mark, Richardson, Alan E., Cavagnaro, Timothy R., Wilson, Brian R., Glanville, Helen C., and Beare, Michael

Subjects
Agricultural industry, Earth sciences
Abstract

Soil organic matter (SOM) is quantitatively a minor component (by mass and volume) of most soils, yet it is responsible for facilitating or moderating many key soil ecosystem services that [...]

Published
2021
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17. Differential structure and function of phosphorus‐mineralizing microbial communities in organic and upper mineral soil horizons across a temperate rainforest chronosequence

Author

Dunfield, Kari E., primary, Mitter, Eduardo K., additional, Richardson, Alan E., additional, Gaiero, Jonathan R., additional, Khosla, Kamini, additional, Chen, Xiaodong, additional, Wells, Andrew, additional, Haygarth, Philip M., additional, and Condron, Leo M., additional

Published
2024
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18. Differential structure and function of phosphorus‐mineralizing microbial communities in organic and upper mineral soil horizons across a temperate rainforest chronosequence

Author

Dunfield, Kari E., Mitter, Eduardo K., Richardson, Alan E., Gaiero, Jonathan R., Khosla, Kamini, Chen, Xiaodong, Wells, Andrew, Haygarth, Philip M., Condron, Leo M., Dunfield, Kari E., Mitter, Eduardo K., Richardson, Alan E., Gaiero, Jonathan R., Khosla, Kamini, Chen, Xiaodong, Wells, Andrew, Haygarth, Philip M., and Condron, Leo M.

Abstract

Microbial community structure and function were assessed in the organic and upper mineral soil across a ~4000‐year dune‐based chronosequence at Big Bay, New Zealand, where total P declined and the proportional contribution of organic soil in the profile increased with time. We hypothesized that the organic and mineral soils would show divergent community evolution over time with a greater dependency on the functionality of phosphatase genes in the organic soil layer as it developed. The structure of bacterial, fungal, and phosphatase‐harbouring communities was examined in both horizons across 3 dunes using amplicon sequencing, network analysis, and qPCR. The soils showed a decline in pH and total phosphorus (P) over time with an increase in phosphatase activity. The organic horizon had a wider diversity of Class A (phoN/phoC) and phoD‐harbouring communities and a more complex microbiome, with hub taxa that correlated with P. Bacterial diversity declined in both horizons over time, with enrichment of Planctomycetes and Acidobacteria. More complex fungal communities were evident in the youngest dune, transitioning to a dominance of Ascomycota in both soil horizons. Higher phosphatase activity in older dunes was driven by less diverse P‐mineralizing communities, especially in the organic horizon.

Published
2024

22. Genomic and Untargeted Metabolomic Analysis of Secondary Metabolites in the Streptomyces griseoaurantiacusStrain MH191 Shows Media-Based Dependency for the Production of Bioactive Compounds with Potential Antifungal Activity

Author

Ramarajan, Margaret, Devilla, Rosangela, Dow, Lachlan, Walsh, Ned, Mead, Oliver, Zakeel, Mohamed Cassim Mohamed, Gallart, Marta, Richardson, Alan E., and Thatcher, Louise F.

Abstract

Streptomycesspecies can form beneficial relationships with hosts as endophytes, including the phytopathogen-inhibiting strain, Streptomyces griseoaurantiacusMH191, isolated from wheat plants. Using genomic characterization and untargeted metabolomics, we explored the capacity of strain MH191 to inhibit a range of fungal phytopathogens through the production of secondary metabolites. Complete genome assembly of strain MH191 predicted 24 biosynthetic gene clusters. Secondary metabolite production was assessed following culture on six different media, with the detection of 205 putative compounds. Members of the manumycin family, undecylprodigiosin, and desferrioxamine were identified as the predominant metabolites. Antifungal activity was validated for undecylprodigiosin and manumycin. These compounds were produced from different BGCs, which showed similarity to asukamycin, undecylprodigiosin, and FW0622 gene clusters, respectively. The growth of strain MH191 on different media illustrated the metabolic regulation of these gene clusters and the strain’s extended chemical potential, with the asukamycin gene cluster alone, producing a variety of antifungal metabolites. The study highlights the extended chemical capability of strain MH191, which could be exploited as a biological control agent for designing future crop protection solutions.

Published
2024
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24. Carbon stability in a texture contrast soil in response to depth and long-term phosphorus fertilisation of grazed pasture

Author

Coonan, Elizabeth C., Richardson, Alan E., Kirkby, Clive A., Macdonald, Lynne M., Amidy, Martin R., Strong, Craig L., and Kirkegaard, John A.

Subjects
United States. Department of Agriculture, Soil carbon, Land management, Soil microbiology, Spectroscopy, Soils, Agricultural industry, Earth sciences
Abstract

It is important to understand the stability of soil organic matter (SOM) sequestered through land management changes. In this study we assessed differences in carbon (C) stability of pasture soils that had high and low C content (2.35% vs 1.73% whole soil C in the 0-10 cm layer) resulting from long-term phosphorus fertilisation. We used soil size fractionation (fine fraction, coarse fraction and winnowing) to assess the amount of stable C and indicators of microbial decomposition capacity (catabolic profiles, metabolic quotient) to assess C stability. As a main effect throughout the 60-cm profile, C concentrations were higher in the fine fraction soil in the high (excess P fertiliser; P2) than low (no P fertiliser; PO) treatments, demonstrating a larger stable C fraction. For both P2 and PO, there was a strong correlation between C measured in the fine fraction and winnowed fraction in the 0-30 cm layer (R = 0.985, P < 0.001), but no correlation was observed for the 30-60 cm layer (R = 0.121, P > 0.05). In addition, we conducted two incubation experiments to assess C stability in the treatments with depth and to assess C stability in the physical soil fractions. For the surface soils (0-10 cm), the highest respiration occurred in fractions containing plant material, including roots (coarse fraction, 0.65 g C[O.sub.2]-C [kg.sup.-1] soil; whole soil, 1.48 g C[O.sub.2]-C [kg.sup.-1] soil), which shows that the plant material was less stable than the fine and winnowed soil fractions (0.43 and 0.40 g C[O.sub.2]-C [kg.sup.-1] soil respectively). Soil respiration, microbial metabolic quotient and substrate utilisation were similar in P0 and P2. Collectively, the data show that the increased C in P2 was associated with increased C concentrations in the more stable fine soil fraction, but with no change in the stability of the C within the fractions. Additional keywords: carbon fractions, fine fraction soil carbon, mid-infrared spectroscopy, nutrient stoichiometry, soil carbon stocks, soil organic matter. Received 20 March 2019, accepted 2 September 2019, published online 10 October 2019, Introduction Agricultural productivity is intrinsically linked to soil organic matter (SOM) dynamics, which has led to growing interest in management changes to sequester SOM and in fractionation methods to assess [...]

Published
2020
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28. Linking the depletion of rhizosphere phosphorus to the heterologous expression of a fungal phytase in Nicotiana tabacum as revealed by enzyme-labile P and solution 31P NMR spectroscopy

Author

Giles, Courtney D., George, Timothy S., Brown, Lawrie K., Mezeli, Malika, Shand, Charles A., Richardson, Alan E., Mackay, Regina, Wendler, Renate, Darch, Tegan, Menezes-Blackburn, Daniel, Cooper, Pat, Stutter, Marc I., Lumsdon, David G., Blackwell, Martin S.A., Wearing, Catherine, Zhang, Hao, and Haygarth, Philip M.

Published
2017
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