Mobilization and Acquisition of Sparingly Soluble P‐Sources by Brassica Cultivars under P‐Starved Environment I. Differential Growth Response, P‐Efficiency Characteristics and P‐Remobilization
Authors: Akhtar Muhammad Shahbaz , Oki Yoko , Adachi Tadashi 
Published: November 2009

Phosphorus (P) starvation is highly notorious for limiting plant growth around the globe. To combat P‐starvation, plants constantly sense the changes in their environment, and elicit an elegant myriad of plastic responses and rescue strategies to enhance P‐solublization and acquisition from bound soil P‐forms. Relative growth responses, P‐solublization and P‐acquisition ability of 14 diverse Brassica cultivars grown with sparingly soluble P‐sources (Rock‐P (RP) and Ca3(PO4)2 (TCP)) were evaluated in a solution culture experiment. Cultivars showed considerable genetic diversity in terms of biomass accumulation, concentration and contents of P and Ca in shoots and roots, P‐stress factor (PSF) and P use efficiency. Cultivars showed variable P‐stress tolerance, and cultivars depicting low PSF and high P‐efficiency values were better adaptable to P‐starvation. In experiment 2, after initial feeding on optimum nutrition for 12 d after transplanting (DAT), class‐I (low P‐tolerant (Oscar and Con‐II)) and class‐II (low P‐sensitive (Gold Rush and RL‐18)) cultivars were exposed to P‐free environment for 25 d. All of the cultivars remobilized P from above ground parts to their roots during growth in P‐free environment, the magnitude of which was variable in tested cultivars. P‐concentrations ([P]s) at 37 DAT were higher in developing compared with developed leaves. Translocation of absorbed P from metabolically inactive to active sites in P‐stressed plants may have helped class‐I cultivars to establish a better rooting system, which provided a basis for enhanced P‐utilization efficiency (PUE) and tolerance against P‐stress. By supplying TCP and RP spatially separated from other nutrients in split root study, class‐I cultivars were still able to mobilize RP and TCP more efficiently compared with class‐II cultivars. To compare the growth behavior under P‐stress, cultivars were grown in pots for 41 d after sowing, using a soil low in P (NaHCO3‐extractable P = 3.97 mg/kg, Mehlich‐III‐extractable P = 6.13 mg/kg) with (+P = 60 mg P/kg soil) or without P addition (0P) in study 4. Tested cultivars showed genetic diversity in PUE, P‐efficiency (PE), P‐efficiency ratio (PER) and PSF. P‐stress markedly reduced biomass and plant P contents. Cultivars that produced higher root biomass accumulated higher total P‐contents (r= 0.98**), which in turn was related negatively to PSF (r=−0.95**) and positively to shoot and total biomass. PER and PE showed significant correlations with shoot P‐contents and biomass. Cultivars depicting high PUE and PE, and low PSF values showed better growth behavior under low soil P‐environment. Systematic analysis and deployment of the plant rescue traits underlying the nutrient acquisition, assimilation, utilization and remobilization under P‐starvation will bring more sparingly soluble P into cropping systems and will help to scavenge more P from plant unavailable bound P reserves.