Red clover productivity under drought: Are soil microbes a burden or a treasure?

Plants face water scarcity by changing their traits to avoid water loss by reducing leaf size, increasing leaf thickness and reducing stomatal density, and to increase root uptake by increasing root biomass. While these responses to drought are well documented, the role of plant-soil interactions in influencing these changes remains unclear. This study focuses on mutualistic soil microbes, specifically arbuscular mycorrhizal fungi (AMF) and Rhizobium, which are known to enhance plant productivity, water and nutrient uptake, and stress tolerance. We hypothesise that fluctuations in soil microbial populations not only influence plant productivity, but also modulate plant responses to drought by shaping plant traits. To test this hypothesis, a pot experiment was conducted with red clover (Trifolium pratense L.). The experiment included two treatments: a water treatment (wet versus drought) and microbial reduction by soil steam sterilization (native versus sterilized soil).

The results showed that plants in the native soil had low productivity and exhibited traits associated with slow-growing strategies, including smaller and coarser leaves, lower stomatal density, and increased root mass. Mutualism with beneficial microbes, such as AMF, and the fight against pathogens required resources from the plant, hindering productivity. Conversely, reducing soil microbial loads through sterilization increased plant productivity under well-watered conditions, promoting traits associated with fast-growing strategies. However, under drought conditions in sterilized soil, productivity decreased, early wilting occurred, and traits associated with a slow-growing strategy emerged. Notably, roots became longer and thinner and rhizobial nodulation decreased, signalling a reduction in mutualistic interactions.

These findings highlight the key role of soil microbes in triggering changes in plant traits, and thus their importance in plant responses to drought. Additionally, they highlight the microbial contribution to maintaining plant productivity and vitality of red clover under challenging environmental conditions.

Graphical abstract of the paper showing the effects of drought on red clover growing in native soil and sterilized soil.

 

Tello-García, E., Mandolini, E., Tasser, E., Probst, M., Peintner, U., Tappeiner, U., Leitinger, G. (2023) Red clover productivity under drought: Are soil microbes a burden or a treasure?
Environmental and Experimental Botany 214: 105486 DOI: https://doi.org/10.1016/j.envexpbot.2023.105486