Towards the optimization of pea nodulated root system architecture for improved water and nutrition acquisition

National audience

Inglés. Grain legumes like pea can meet their nitrogen demands through symbiotic nitrogen fixation(SNF) carried out by soil bacteria residing in root nodules. This ability makes legumes a sourceof N for low-input agroecosystems. However, pea productivity and yield are sensitive todrought events, which have increased incidence due to climate change. Soil water deficitassociated with drought impairs SNF and nutrient uptake such as sulfur (S). Besides, thereduction of S emission and deposition associated with efforts to reduce greenhouse gasemissions has led to S deficiency in cropping systems, affecting plant growth and yield. S is akey element required for pea growth, seed protein formation and SNF. It is a key component ofnitrogenase and leghemoglobin which are crucial for SNF, and of antioxidant glutathione whichis involved in water stress mitigation. Considering these key roles of S in SNF and water stress,an experiment was conducted to understand the impact of water stress (WS S+), sulfurdeficiency (WW S-) and their combination (WS S-) on pea growth and hydromineralacquisition with a structural functional analysis focusing on SNF and nutrient uptake. Rootarchitecture, nodulation, nutrient uptake and allocation were studied in genotypes Kayanne,Cameor and Cameor mutant 2684 (which lacks vacoular sulfate transporter gene SULTR4) inRhizoTubes under single or double stress. We found that water stress, occurring alone or withS deficiency, strongly impacted plant traits compared to S deficiency. Under WS S+, bothKayanne and Cameor prioritized biomass, C and N allocation towards roots instead of shootand nodules. In addition, WS decreased biomass and area of shoot and of nodules whileincreasing root depth. It also decreased plant concentration of essential nutrients like P, K andS. WW S- did not affect the overall plant growth, and only decreased shoot area, nodule areaand biomass. It also decreased plant concentration of S, Mo, B and P (elements with key rolesin SNF) and their allocation to the nodules. Compared to Kayanne, Cameor and 2684 showeda stronger decrease in N and S concentration and nodule area under WW S-. Double stressshowed similar response to WS S+ in plant growth and nutrient uptake. WS affected bothCameor and mutant similarly, but WW S- caused a stronger reduction in nodule growth in 2684compared to Cameor. This suggests that the two genotypes Kayanne and Cameor are similarlytolerant to water stress, but Cameor is more susceptible to S deficiency, and mutant 2684, withabsence in S remobilization, is even more susceptible to S deficiency.