Plasticity of root hair and rhizosheath traits and their relationship to phosphorus uptake in sorghum

Sorghum is an essential crop for resilient and adaptive responses to climate change. The root systems of crop plants significantly contribute to the tolerance of abiotic stresses. There is little information on sorghum genotypes' root systems and plasticity to external P supply. In this paper, we investigated the variations in root systems, as well as the responses, trait relationships, and plasticity of two sorghum genotypes (Naga Red and Naga White), popularly grown in Ghana, to five external P concentrations ([P]_ext): 0, 100, 200, 300, and 400 mg P kg^-1 soil. Sorghum plants were grown in greenhouse pots and harvested for root trait measurements at the five-leaf and growing point differentiation (GPD) developmental stages. The plants were responsive to [P]_ext and formed rhizosheaths. The two genotypes showed similar characteristics for most of the traits measured but differed significantly in total and lateral root lengths in favor of the red genotype. For example, at the five-leaf growth stage, the lateral root length of the red and white genotypes was 22.8 and 16.2 cm, respectively, but 124 and 88.9 cm, at the GPD stage. The responses and plasticity of the root system traits, including rhizosheath, to [P]_ext were more prominent, positive, and linear at the five-leaf stage than at the GPD growth stage. At the five-leaf growth stage, total root length increased by about 2.5-fold with increasing [P]_ext compared to the unamended soil. At the GPD stage, however, total root length decreased by about 1.83-fold as [P]_ext increased compared to the unamended soil. Specific rhizosheath weight correlated with RHD, albeit weakly, and together explained up to 59% of the variation in tissue P. Root hair density was more responsive to P supply than root hair length and showed a similar total and lateral root length pattern. Most desirable responses to P occurred at a rate of 200-300 mg P kg^-1 soil. It is concluded that sorghum would form rhizosheath, and [P]_ext could be critical for the early vigorous growth of sorghum's responsive root and shoot traits. Beyond the early days of development, additional P application might be necessary to sustain the responses and plasticity observed during the early growth period, but this requires further investigation, potentially under field conditions.