Arginine and methionine increase the enzymatic activity of microbes involved in N and P cycles in arid soil from the Chihuahuan desert

Root exudates are mainly composed of sugars, organic acids, and amino acids. These are carbon sources that recruit beneficial bacterial communities in the rhizosphere. However, the composition of the root exudates is variable and mainly unknown for plants from arid lands, such as Agave lechuguilla Torr. This work studied the effect of different metabolites identified in the rhizosphere of A. lechuguilla Torr. (Maltose, lactose, oxalic and tartaric acids, arginine, and methionine), over the enzymatic activity and abundance of nitrogen-fixing bacteria and organic phosphorus mineralizing bacteria, as well as the changes in the nutrient availability in the soil. It was found that only the amino acids increased the nitrogenase and phosphatase activity, and these increments were reflected in the available nutrient concentration in the soil. Likewise, the presence of carbon and nitrogen from the amino acids may reduce the C:N ratio in the soil, enhancing the mineralization of organic matter and the concentration of ammonia, nitrite, and nitrates. This work shows the complexity of the nutrient recycling process in the soil and the essential role of bacteria in making nutrients available to plants. Understanding this process could aid in improving the establishment of plants in eroded ecosystems or under the harsh conditions of arid environments.