Different growth rates of grasses from South American natural grasslands are adaptations to soils of low fertility. Grasses with fast growth rate are species with an accumulation of nutrients in soluble forms, with a high metabolic rate. This work aimed to study whether grasses with different growth rates have different phosphorus (P) uptake and efficiency of P use with high and low P availability in soil, as well as whether phosphatase activity is related to the species growth rate and variations in P biochemical forms in the tissues. Three native grasses (Axonopus affinis, Paspalum notatum, and Andropogon lateralis) were grown in pots with soil. Along plant growth, biomass production and its structural components were measured, as well as leaf acid phosphatase activity and leaf P chemical fractions. At 40 days of growth, leaf acid phosphatase activity declined by about 20-30% with an increase of P availability in soil for A. affinis and P. notatum, respectively. Under both soil P levels, P. notatum showed the highest plant total biomass, leaf dry weight and highest P use efficiency. A. affinis presented the higher P uptake efficiency and soluble organic P concentration in the leaf tissues. A. lateralis showed P-Lipid concentration 1.6 and 1.3 times higher than A. affinis and P. notatum, respectively. In conclusion, acid phosphatase activity in grass of higher growth rate is related to higher remobilization of P due to higher demand, as in A. affinis, and higher growth rates are associated with higher P uptake efficiency.
Keywords: Leaf traits; Nutrient use efficiency; P biochemical form; P remobilization; South American grasslands.