Responses of the Root System Architecture and Rhizosphere Microbiota of Winter Wheat to Dynamic and Realistic Warming Profiles

Considerable variation exists in the responses of plants to warming experimental treatments^[1]. Most experiments have overlooked the temporal and spatial dynamics of natural temperature profiles. To quantify root and rhizosphere responses to warming dynamics, we used controlled systems^[2] with diurnal temperature fluctuations nearly-identical to those measured in an agricultural field in northwest Germany, during the autumn-winter sowing period. Wheat (Triticum aestivum L.) seeds were sown into soil in pots and grown to two fully-expanded leaves, experiencing air and soil temperatures of “Today” (control) and “Future” (warming, 5^oC warmer). Root architecture was quantified by non-invasive Magnetic Resonance Imaging (MRI)^[3] over time. At harvest, tightly-bound and loosely-bound bacteria fractions^[4] from roots of top and deeper soil were characterized for bacterial community composition using 16S rRNA gene amplicon sequencing.

Based on time, warming enhanced leaf expansion six-fold, and root growth five-fold, over the control treatment. In contrast, when treatments were compared at the same two-leaf phenological stage, although control plants grew more slowly, they had 50% more root length than plants in the warming treatment. The root architecture of the control plants comprised of 70% more deep root length and had a 7% greater penetration rate than the warmer plants, on this 2 leaf basis. Root length densities were similar between treatments in the top 0-5 cm of soil depth, but were 60% greater at 5 -10 cm, and 138% greater at 20 to 25 cm, in the control than the warming treatment. Cooler, control plants had more fine root length than plants in the warming treatment. Similar to root architecture, the bacteria communities in loosely- and tightly-bound fractions were differentially influenced by temperature and soil depth. Both fractions had a relative abundance of Proteobacteria > Actinobacteria > Bacteroidetes, with Acidobacteria greater in loosely- and tightly-bound fractions. We will discuss possible reasons underlying plant and soil microbiota responses to realistic temperature dynamics.

References:

[1] Shi A et al. (in preparation). Reaching consensus around how plants and rhizospheres respond to warming: A problem of where, when and how much is applied in experiments.

[2] Füllner K et al. (2012) Vertical gradient in soil temperature stimulates development and increases biomass accumulation in barley. Plant, Cell & Environment 35, 884 – 892.

[3] van Dusschoten D et al. (2016) Quantitative 3D analysis of roots growing in soil using magnetic resonance imaging. Plant Physiology 170:1176-1188.

[4] Donn et al. (2015) Evolution of bacterial communities in the wheat crop rhizosphere. Environmental Microbiology 17: 610-621.