Root growth plasticity to drought in seedlings of perennial grasses

Aim Root growth strategies may be critical for seeding survival and establishment under dry conditions, but these strategies and their plasticity are little known. We aim to document the ability of young grass seedlings to adjust their root system architecture, root morphology and biomass allocation to roots to promote water uptake and survival under progressive drought. Methods Seedlings growing in columns filled with sand and exposed to drought or well-watered controls were repeatedly harvested for determination of biomass fractions, root length, −architecture and -morphology in a greenhouse experiment. Allometric scaling exponents and standardised major axis regression were used to investigate allocation patterns. Results Young seedlings were able to sustain leaf turgor and functions during eight weeks of progressive drought through phenotypic plasticity of the primary root system producing deeper and simpler roots. Biomass allocation to roots decreased or did not respond, and other components of root morphology showed only moderate plasticity. Conclusion Our results suggest that morphological and architectural plasticity of the primary root system may well be key features for dehydration avoidance and survival in grass seedlings under moderate drought when allocation of biomass to roots and development of secondary roots are constrained.