Does drought harm plants mainly by drying them out, or also by changing the effects of soil previously occupied by their own species?

Details

Drought events can change the composition of plant and soil communities and are becoming more common and severe because of climate change. Yet how drought affects plant–soil feedbacks remains poorly understood. Plants accumulate species-specific communities around their roots, and drought may affect plant species and soil organisms differently. The researchers tested whether drought changes plant–soil feedbacks differently among closely related plant species with different soil-moisture preferences.

They conducted a two-phase greenhouse experiment. First, they conditioned grassland soil by growing seven Geranium species in it; for controls, they grew a grass species in the soil or left it unplanted. In the second phase, they grew the Geranium species in soil previously occupied by their own species, grass-conditioned soil, and previously unplanted soil. They maintained soil moisture at 5%, 10% or 20% (w/w) and measured biomass responses after 35 days.

Regardless of soil conditioning, plants performed more poorly as soil moisture decreased. Under the driest conditions, conditioning by the same species had its most negative effect on relative root weight compared with previously unplanted control soil. When the comparison was instead with grass-conditioned control soil, the effects of same-species conditioning on relative root weight differed among species.

The researchers concluded that decreasing soil moisture modified plant–soil feedback effects on biomass allocation, with species-specific changes. However, drought's effects on plant–soil feedbacks were subtle and did not affect overall plant performance. Plant–soil feedback effects on plant performance during a drought event may therefore be limited compared with the direct effects of drought.