Root growth dynamics, nutrient uptake and use efficiency of Grevillea robusta grown under nitrogen and phosphorus deficiency.

Root growth, nutrient uptake, and nutrient use efficiency of a plant is influenced by the nutrient availability in its growing environment. The aim of this study was to investigate the root morphology, nutrient uptake and use efficiency of Grevillea robusta grown in nitrogen (N)- and phosphorus (P)-limited conditions. A hydroponic experiment was conducted for three months in a glasshouse with four nutrient treatments; (i) N-deficient, (ii) P-deficient, (iii) N/P-deficient (co-limitation of N and P), and (iv) control (sufficient amounts of N, P, and other nutrients in the growth medium). The composition and the concentration of each nutrient in the control solution were custom-made based on the growth requirement of G. robusta. N and P concentration in nutrient-deficient media were maintained at 2 ppm. The impact of N- or P-deficiency and their co-limitation on cluster root formation, organ-specific dry matter and nutrient accumulation, N and P uptake and their use efficiencies were measured. P-deficient conditions produced the highest number of cluster roots (24 ± 4) which was comparatively lower than those of N- and N/P-deficient conditions indicating that P-deficiency is the primary factor influencing the formation of cluster roots in G. robusta. The use efficiency of N and P in biomass formation was significantly (p < 0.05) enhanced when their uptake was reduced in response to N- and P-limitation. The efficient internal use of P by G. robusta under N- and N/P-deficiency is indicated by the significant increase in P-remobilization efficiency under these nutrient-deficient conditions. [ABSTRACT FROM AUTHOR]