Soil bacterial communities of wheat vary across the growing season and among dryland farming systems.

For my post-doctoral research project in the Menalled lab in 2016/2017, I was investigating the effect of farming system, weed competition, and season, on wheat production and soil bacteria during a growing season in Montana. All of these represent potentially stressful conditions, which can hamper plant growth, as well as whether and how they will interact with soil microbial communities. In particular, the element of time is missing from many studies on soil microbial ecology, often because of cost. Because plant-microbial interactions change depending on the needs of the plant, we wondered if soil communities would change as the wheat (and weeds) grew, matured, and then senesced (aged and died).

This publication is part of a series, from data collected from a long-term farming experiment in Bozeman, MT, including:


Ishaq, S.L., Seipel, T., Yeoman, C.J., Menalled, F.D. 2020. Soil bacterial communities of wheat vary across the growing season and among dryland farming systems. Geoderma 358:113989. Article.

Abstract

Despite knowledge that management practices, seasonality, and plant phenology impact soil microbiota; farming system effects on soil microbiota are not often evaluated across the growing season. We assessed the bacterial diversity in soil around wheat roots through the spring and summer of 2016 in winter wheat (Triticum aestivium L.) in Montana, USA, from three contrasting farming systems: a chemically-managed no-tillage system, and two USDA-certified organic systems in their fourth year, one including tillage and one where sheep grazing partially offsets tillage frequency. Bacterial richness (range 605–1174 OTUs) and evenness (range 0.80–0.92) peaked in early June and dropped by late July (range 92–1190, 0.62–0.92, respectively), but was not different by farming systems. Organic tilled plots contained more putative nitrogen-fixing bacterial genera than the other two systems. Bacterial community similarities were significantly altered by sampling date, minimum and maximum temperature at sampling, bacterial abundance at date of sampling, total weed richness, and coverage of Taraxacum officinaleLamium ampleuxicaule, and Thlaspi arvense. This study highlights that weed diversity, season, and farming management system all influence soil microbial communities. Local environmental conditions will strongly condition any practical applications aimed at improving soil diversity, especially in semi-arid regions where abiotic stress and seasonal variability in temperature and water availability drive primary production. Thus, it is critical to incorporate or address seasonality in soil sampling for microbial diversity.

Agroecosystem resilience is modified by management system via plant–soil feedbacks

For my post-doctoral research project in the Menalled lab in 2016/2017, I was investigating the effect of farming system, weed competition, disease status, and climate change, on wheat production and soil bacteria during a growing season in Montana. All of these represent potentially stressful conditions, which can hamper plant growth, as well as the amount and type of root exudates they secrete into soil. Plants have a complex relationship with bacteria and fungi in the soil, and will provide sugars in exchange for microbial products. When conditions are harsh enough to threaten plant survival, like during droughts, plants may cut off support to soil microbes, which can cause the community to crash. Similarly, microbial communities may be unsupportive or pathogenic towards plants, and can hamper seed germination, as well as growth or health of plants.

We also wanted to know if adverse conditions during even just a single growing season would affect the microbial community enough to cause a change in plant growth during the next growing season – even if other conditions went back to normal. We took soil from the field at the end of the growing season and set up a greenhouse trial. To examine the impact of the microbial community, we set up paired comparisons where one half had the living field soil, and the other had field soil which had been autoclaved first to kill any microbes. The greenhouse trial involved hundreds of plant pots and thousands of data, and the seed germination and plant growth data was used to evaluate the legacy of stress.

This publication is part of a series, from data collected from a long-term farming experiment in Bozeman, MT, including:


Seipel, T., Ishaq, S.L., Menalled, F.D. 2019. Agroecosystem resilience is modified by management system via plant–soil feedbacks. Basic and Applied Ecology 39:1-9. Article.

Abstract

Designing resilient cropping systems is essential to sustain agricultural production in the face of changing environmental and social pressures. However, the extent to which changes in farm management systems could alter resistance and resilience is largely unknown, especially in response to climate change. Plant and soil microbial community interactions are a vital component of functioning and resilient agroecosystems. The aim of our study was to use winter wheat (Triticum aestivum L.) and pea (Pisum sativum L.) plant–soil feedbacks (i.e. plant species-specific effects on soil biotaand their impacts on subsequent plant growth) as a metric of system resilience and resistance to climate variability in three different farming management systems: 1) a chemical no-till system, 2) an USDA-certified organic system reliant on tillage and 3) an USDA-certified organic system that included sheep grazing with the overall goal of minimizing tillage intensity. Climate conditions soil experienced were ambient, warmer, and warmer and drier and were manipulated in the field using open-top chamber and rain-out shelters. Plant–soil feedbacks were negative for wheat and positive for pea but varied among farming management systems but were less sensitive to climate conditions. Plant–soil feedbacks were lower in magnitude in the tilled organic system indicating more resistance to the accumulation of pathogenic soil microbiotaresulting from repeated cropping of wheat. However, recovery was lower when the crop was pea in the tilled organic indicating slower recovery and less resilience. Results indicate that while increases in crop diversity may promote more resilient agroecosystems, farming management will affect agroecosystem resilience.