A humic substances product extracted from biochar reduces Arabidopsis root hair density and length under P-sufficient and P-starvation conditions

Abstract

Biochar additions may have positive impacts on phosphorus (P) availability to plants and cause down-regulation of genes associated with P starvation. Various alkaline-extracted humic substances products (HSP) also induce partial relief in plants from P starvation and, moreover, cause an increase in total cell phosphate, ATP and glucose-6-phosphate levels. As many biochars contain substances similar in structure and functioning to HSP, our goal was to examine if such products extracted from biochar (B-HSP) could affect plant responses to initial P concentration (Pi) under Pi sufficient and starvation conditions. We examined the impact of B-HSP in the growing media of Arabidopsis seedlings on root hair development (length and density) in sterile systems, and evaluated whether nutrient complexation with B-HSP could account for observed differences. Root hair length was significantly lower in B-HSP amended Pi-sufficient growing media, and root hair density was significantly lower in both B-HSP amended Pi sufficient and starvation regimes as compared with non-amended treatments. The differences did not result from either primary (P source) or secondary (increased P availability) nutritional effects. B-HSP appears to cause a change in plant perception of P nutrition. This may be another means by which biochar impacts growing plants.