Soil microbial drought history affects tree physiology of select species

Soil microbes aid in the drought tolerance of plants, yet the extent to which a microbial community’s previous drought exposure can affect plant responses to contemporary drought is largely unknown. We used a greenhouse experiment to investigate whether microbes exposed to reduced moisture in the past affect the sensitivity of trees to future water-stress. We planted saplings of 3 species in field soils exposed to experimentally-induced drought or ambient moisture from adjacent forest plots, and then altered the watering regime of the saplings to induce contemporary drought. When trees were grown in ambient soils with no drought history, contemporary drought reduced C assimilation rates, stomatal conductance, and leaf water potential in all species. However, when Prunus virginiana were grown in soils with a drought history, they were buffered from the effects of contemporary drought, as physiological performance was mostly unchanged by water stress. P. virginiana grown in drought history soils also increased soluble sugars during contemporary drought to a lesser extent than those in soils with no drought history, suggesting the plants experienced less water stress. Sterilized soils confirmed the “soil drought history effect” likely resulted from drought-adapted microbes in soils exposed to drought previously. None of these effects were apparent in Liriodendron tulipifera and Quercus rubra , which reduced their physiological performance when water-stressed regardless of soil drought history. To the extent mature tree responses to environmental stress are similar, our results suggest that forest sensitivity to drought may depend, in part, on plant-microbial interactions shaped by past stress exposures.