Data for: Legacy of warming and cover crops on the response of soil microbial function to repeated drying and rewetting cycles.

Description

We examined the legacy of warming and cover crops on the response of soil microbial function to repeated drying and rewetting cycles. We introduced open top chambers to warm the soil surface of a field plot experiment in which cover crops (single species monocultures and 4-species polycultures) were grown over the summer after harvest and before planting of autumn sown cash crops in a cereal rotation. Soil samples were collected from warmed and ambient areas of the experimental plots in spring, before harvesting the cereal crop. We quantified respiration (a measure of soil microbial function) with high-frequency CO2 flux measurements after 0, 1, 2, 4, or 8 wet/dry cycles imposed in the laboratory and the addition of barley grass powder substrate at a ratio of 10 mg g-1 soil.

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The field plot experiment was located on the University of Reading farm at Sonning in Berkshire, UK and was established in August 2018. Each summer, after the harvest of a cereal crop, cover crops were planted and then terminated and incorporated prior to planting the next autumn sown cereal crop. The cereal rotation was Winter Wheat (2017/18); Winter Barley (2018/19); Winter Oats (2019/20); and Winter Wheat (2020/21). The cover crop treatments were control (no cover crops), buckwheat (Fagopyrum esculentum), berseem clover (Trifolium alexandrinum), oil radish (Raphanus raphanistrum), sunflower (Helianthus annuus), and a 4-species mixture of these four. The experiment was arranged in a randomised complete block design with 4 blocks. Open Top Chambers (OTCs) were installed after cereal crop establishment during the 2019/20 and 2020/21 growing seasons to act as passive warming devices by warming the soil under the OTCs. The OTCs were installed on 18th December 2019 and 24th November 2020, respectively, at crop seedling stage when about 5 leaves were unfolded. The OTC warmed the soil by, on average, 0.75±0.92 °C in the control plot in 2020/21. We sampled soils on 17th May 2021 from the top 10cm underneath the OTSs (warmed treatment), and the equivalent location at the other end (ambient treatment) of each plot circled in Figure S-1 using a trowel. The soil samples were sieved, fresh, to 4mm and divided into four subsamples. The first subsample was refrigerated at 4°C prior to KCl extraction to determine NH4+ and NO3- availability. The second subsample was used for DNA extraction, and quantification of gene abundance of microbial communities using real time qPCR. The third subsample was air-dried for soil chemical analysis. The fourth subsample was used to assess the response of soil microbial respiration following repeated drying and rewetting cycles and addition of barley shoot powder as a substrate. To undertake the assay, the equivalent of 10 g (dry weight) of six fresh subsamples of each soil sample were weighed into tin trays (prior to pre-incubation). To one subsample (0 wet/dry cycles), 100 mg of barley shoot powder. After mixing, CO2 evolution was measured continuously for 96 hours at hourly time intervals using an automated multichannel respirometer and an EGA60 multi-sample gas exchange system (ADC Bioscientific Ltd). Samples that had not received substrate were exposed to 1, 2, 4, or 8 drying and rewetting cycles prior to the addition of barley shoot powder and substrate induced respiration being measured. Each drying and rewetting cycle consisted of 3 days of drying by enclosing samples in a sealed chamber with silica gel desiccant, followed by weighing and rewetting to 85% of the water holding capacity where they were maintained for a further 4 days. CO2 respired in (ppm) was converted to C-CO2 (µg g-1 soil h-1) and the cumulative sum (µg g-1 soil) of C-CO2 respired per sample over the 96 hours was calculated

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