The contribution of lateral rooting to phosphorus acquisition efficiency in maize (Zea mays) seedlings

Abstract

Low soil phosphorus availability is a primary constraint for plant growth in many terrestrial ecosystems. Lateral root initiation and elongation may play an important role in the uptake of immobile nutrients, such as phosphorus, by increasing soil exploration and phosphorus solubilisation. The overall objective of this study was to assess the value of lateral rooting for phosphorus acquisition through assessment of the 'benefit' of lateral rooting for phosphorus uptake and the 'cost' of lateral roots in terms of root respiration and phosphorus investment at low and high phosphorus availability. Five recombinant inbred lines (RILs) of maize derived from a cross between B73 and Mo17 with contrasting lateral rooting were grown in sand culture in a controlled environment. Genotypes with enhanced or sustained lateral rooting at low phosphorus availability had greater phosphorus acquisition, biomass accumulation, and relative growth rate (RGR) than genotypes with reduced lateral rooting at low phosphorus availability. The association of lateral root development and plant biomass accumulation under phosphorus stress was not caused by allometry. Genotypes varied in the phosphorus investment required for lateral root elongation, owing to genetic differences in specific root length (SRL, which was correlated with root diameter) and phosphorus concentration of lateral roots. Lateral root extension required less biomass and phosphorus investment than the extension of other root types. Relative growth rate was negatively correlated with specific root respiration, supporting the hypothesis that root carbon costs are an important aspect of adaptation to low phosphorus availability. Two distinct cost-benefit analyses, one with phosphorus acquisition rate as a benefit and root respiration as a cost, the other with plant phosphorus accumulation as a benefit and phosphorus allocation to lateral roots as a cost, both showed that lateral rooting was advantageous under conditions of low phosphorus availability. Our data suggest that enhanced lateral rooting under phosphorus stress may be harnessed as a useful trait for the selection and breeding of more phosphorus-efficient maize genotypes.

Anatomical changes of lentil (Lens culinaris Medik.) under phosphorus deficiency stress

“…The advantages of this have been demonstrated, for example, in bean (Phaseolus vulgaris) where genotypes with highly branched, actively growing root systems have been shown to be more P efficient than genotypes lacking such root traits (Lynch and Brown 2001). This has also been confirmed in brassicas (Hammond et al 2009) and demonstrated for production of lateral roots (Zhu and Lynch 2004). Leaf growth depression under phosphorus deficiency is also well documented (Chiera et al 2002, Assuero et al 2004, Kavanová et al 2006.…”

Root Phenes for Enhanced Soil Exploration and Phosphorus Acquisition: Tools for Future Crops

“…In young plants with few axial roots, lateral branching may increase exploration of soil domains not reached by axial roots. This may account for the observation that increased lateral rooting among young maize RILs under phosphorus stress was associated with substantially greater phosphorus accumulation and growth (Zhu and Lynch, 2004). Lateral branching is under complex genetic control in maize, where 15 relatively small effect QTL have been identified (Zhu et al, 2005a).…”

Reduction in Root Secondary Growth as a Strategy for Phosphorus Acquisition

“…In a study of the root morphology of temperate pasture species, a reduction in root diameter, root mass density, and an increase in specific root length were observed under P stress (Hill et al, 2006). Reduced lateral root diameter also has been described under low P in water hyacinth (Eichhornia crassipes) and maize (Zea mays; Xie and Yu, 2003;Zhu and Lynch, 2004). Nevertheless, observations of reductions in root diameter under P stress have not been made within root classes, and published reductions in root diameter of the entire root system may be the product of a greater proportion of higher order lateral roots rather than the effects of altered secondary growth.…”