Carbohydrate utilization by belowground organs defines the capacity of faba bean to exploit organic phosphorus sources

Background Limited phosphate (P-i) reserves and the economic and adverse environmental impacts of excessive application of mineral fertilizers in soils are alarming. Therefore, the use of organic phosphorus (P-org) is suggested to reduce reliance on chemical fertilizers. Aims There is currently little information regarding the accessibility of P-org to N-2 fixation plants. Therefore, the present study aims to address the question of to what extent P-org substrates can serve as reliable sources of phosphorus (P) for faba bean in its nodulated phase. Specifically, we intended to explore whether N-2-fixing plants employ intrinsic mechanisms to facilitate P-org availability. Methods A pot experiment was conducted to assess the inherent capacity of two faba bean varieties (Tiffany vs. Mallory) to utilize P-org supplied as phytic acid and Ca-glycerophosphate. Plants were inoculated with Rhizobium leguminosarum bv. viciae 3841 strain and cultivated on sterilized loamy sand under greenhouse conditions. Results Phytic acid was relatively less efficient than Ca-glycerophosphate in sustaining plant growth. Compared to Mallory, the variety Tiffany displayed a higher capability to use P-org, as evidenced by the relatively higher biomass production, nodulation, phosphorus use efficiency, and P- and N-accumulations in plant tissues. P-org exploitation was intimately linked to the efficient utilization of the host's carbohydrate budget into nutrient-acquiring structures (roots and nodules). In addition, the preferential allocation of P-i to prolific nodules is essential for plants to thrive best under these circumstances. Conclusions Together with N profitability, these findings suggested that N-2-fixing plants (e.g., faba bean) can promote the sustainable exploitation of P-org, thereby diminishing the sizeable environmental footprint.

Automated summary

This study found that faba bean has a strong capacity to utilize organic phosphorus substrates, and this utilization is closely related to its nodules structure and efficient utilization of carbohydrate budget. The preferential allocation of phosphate to nodules is essential for plant growth under these circumstances.