Management of soil organic carbon (SOC) is necessary for sustainable agricultural development. Increases in SOC are associated with improved soil productivity and structure, and may provide a mitigation strategy for the issues of rising greenhouse gas emissions and dispersive sodic soils. Soil fungi may alter SOC levels through: (1) the stabilisation of soil aggregates, within which SOC may be protected from aerobic degradation, and (2) the transformation and translocation of carbon compounds via microbial growth. Some melanised root-associated fungi (MRAF) isolated from the Sydney Basin Region have been shown to increase SOC in Alfisol (Mukasa Mugerwa and McGee, 2017). The broad aim of this project was to explore whether some MRAF have the capacity to increase SOC within an irrigated cotton system. To address this aim, I (1) isolated a number of MRAF endemic to the site where the Australian Cotton Research Institute is located, (2) conducted a small laboratory incubation experiment to trial a potential method to screen local MRAF isolates, and (3) conducted a glasshouse experiment to test the effect of some MRAF isolates on SOC levels using cotton as the host plant.

A glasshouse, pot experiment was conducted from October 2016 to January 2017. Briefly, pots were inoculated with one of 6 inoculum treatments: Control (wheat seed based), Control (millet seed based), 83017, 83019, C004.2, and NV016.17. These treatments are described in Table 1. Cotton, Gossypium hirstutum, cultivar (Sicot 74683F) was used as the host plant. Soil samples were taken at 25, 50 and 75 days after seed germination. Part of the soil sample (approximately 10 g) was used to measure the extent of hyphal growth through the soil (Shen et al., 2016). Hyphal growth was separated into fungi with melanised hyphae and fungi with non-melanised hyphae. The remainder of the sample was then dried at 40°C, and a two subsamples taken. The first (approximately 10 g) was used for total SOC analysis. The second subsample (approximately 25 g) was separated into four different soil aggregate classes using dry sieving. These four aggregate classes were: large macro-aggregates (> 2 mm diameter), macro-aggregates (2 - 0.84 mm), small macro-aggregates (0.84 - 0.25 mm diameter) and micro-aggregates and silt and clay fractions (< 0.25mm) (Zhang et al., 2013). SOC was measured for each aggregate class.