Differential responses of three Urochloa species to low phosphorus availability

Urochloa (syn. Brachiaria spp.) is the most cultivated forage species in the tropics and is being introduced to agroecosystems as it can provide multiple services, such as nutrient cycling. In this regard, phosphorus (P) cycling has received particular attention for its little availability in soils and the fact that Urochloa has mechanisms to cope with its low availability. However, there are interspecific differences regarding adaptation to low fertility and P requirements among Urochloa species. This study aimed to evaluate the responses of three Urochloa species-Urochloa brizantha, Urochloa decumbens and Urochloa ruziziensis-to low P availability, as well as their mechanisms to grow on these conditions. We conducted a hydroponic experiment with three levels of P availability-10% (6.2 mg P dm(-3)), 25% (15.5 mg P dm(-3)) and 100% (62 mg P dm(-3))-and evaluated plant biomass production, P tissue concentration, root acid phosphatase activity, root exudation and P transporter expression on roots. We identified several metabolites in root exudates including amino acids, non-protein amino acids, polyamides, organic acids and phenolic acids. Although all metabolites were found in all the species, metabolite exudation varied among species and P level. Overall, U. brizantha and U. ruziziensis plants exudated more metabolites when growing under P limitation (10 and 25% P), which can be a response to low P availability and stress. We identified three P transporters in roots from the PHT1 family-UPHT1;1a, UPHT1;1b and UPHT1;1c. We did not find an explicit expression pattern for UPHT1;1a, but the expression of UPHT1;1b and UPHT1;1c increased at low P availability. U. ruziziensis accumulated more biomass than the other species at all levels of P availability, possibly because of the greater expression of these P transporters. Urochloa species differ regarding nutrient availability requirements, including P, which may explain the P transporters expression and metabolite exudation results. Thus, to cope with low P in the soil, the species developed different metabolic strategies to improve the uptake of this nutrient.