Thermopriming effects on root morphological traits and root exudation during the reproductive phase in two species with contrasting strategies: Brassica napus (L.) and Camelina sativa (L.) Crantz

Abstract

The impact of heat stress due to climate change is particularly well characterized on the plant aboveground and more specifically in the reproductive parts of crops. However, fewer studies aimed at characterizing the effects of heat stress on root morphology and root exudation. These two components of root functioning are of major importance for nutrient acquisition and set up beneficial interactions with microorganisms but they are also particularly sensitive to high temperatures. In our study, we aimed to analyse the effects of heat stress on root morphology and root exudation (quantitatively and qualitatively) in two Brassicaceae i.e. rapeseed (Brassica napus) and camelina (Camelina sativa) that differed from their development strategy which might interfere with their ability to face heat stress. We also designed several heat stress protocols so as to test whether a prior gradual temperature increase can have a priming effect over intense heat stress. Our results indicated that camelina and rapeseed exhibited two different behaviors upon heat stress. In rapeseed, heat stress led to an increase in exudation and no changes in root morphology. In contrast, camelina showed a more conservative strategy as revealed by increased root prospection and modifications of organic acid exudation. The prior gradual increase before the intense heat stress did not modify the trend observed upon the intense heat stress but tended to limit the impacts on root exudation in rapeseed. However, the combined sequence was more negative for camelina due to the longer cumulated duration of the stress. The contrasting behaviours of the two species can be explained by a difference in development strategy and also contrasting breeding histories, that enable the conservation of more traits involved in abiotic stress resistance in camelina in contrast to rapeseed. Eventually, our study highlights that although heat stress due to increased air temperature is mainly sensed by the aboveground plant parts, root functions are impacted and roots could act as a buffer organ to attempt readjusting impaired allocation of carbohydrates to the seeds. Our work opens new perspectives for deciphering the interactions between the plant and soilborne microbe communities under heat stress.