EFFECTS OF EXTREME WEATHER EVENTS (FLOODING AND SOIL HEATING CONDITION) ON A LEGUME-MYCORRHIZAL SYSTEM

Climate change is globally leading to an increase in the frequency of extreme weather events, as heat waves and floods. In this contest, it is important to understand how plants react to such events. We focused on the impacts of mimicked heat waves (soilheating) and floods (flooding conditions) on the symbiosis between plants and arbuscular mycorrhizal fungi (AMF). We studied the symbiosis between the Mediterranean legumeherb Medicago truncatula and one of the AMF partner, Rizophagus irregularis. We grew 72 plants in a climate-controlled chamber. We applied each treatment (mimicked heat waves or floods) to mycorrhizal and non-mycorrhizal plants for a total of 48 plants by increasing respectively soil temperature up to 40 °C or by maintaining water level 0.5 cm above the soil. Each treatment was lasted for one week. We used other 24 plants (12 mycorrhizal, 12 non-mycorrhizal) as a control without any stressing treatment. In the whole, half of the plants (36) were mycorrhized with a specifically prepared inoculum. We measured phosphorus (P) content in the plants twice, one time before the beginning of the treatments, the second time when the treatments were over. To measure P uptake, we prepared quantum dots solutions with synthetic apatite as a P substrate. Finally, we extracted RNA from plant roots and studied the expression of plant and fungal genes which are markers of symbiosis activity. Moreover, in order to study the plants stress conditions we analysed some genes involved in the plants antioxidant machinery. The results suggest that flooding treatment is detrimental for the plants and the symbiosis, largely affecting plants survival, plants biomass, plants flowering and AMF abundance in the roots. It also largely influences quantum dots storage allocation to roots and shoot. Heating treatment has less negative impact, having minor effects on plants survival, on AMF abundance in the roots and less influencing quantum dots storage allocation to roots and shoot. The amount of quantum dots stored in roots is sharply lower when compared to those stored in shoot, in addition non-mycorrhizal plants stored more quantum dots when compared to mycorrhizal plants. The markers of symbiosis are highly expressed in mycorrhizal plants, indicating the correct functioning of the symbiosis. Regarding to the plants stress response, the expression of one of the genes involved in reactive oxygen species (ROS)-scavengers system is higher in mycorrhizal plants when compared with non-mycorrhizal plants.