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

Abstract

Background and aims 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. Methods 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. Results 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. Conclusions B-HSP appears to cause a change in plant perception of P nutrition. This may be another means by which biochar impacts growing plants.

Water Extract from Straw Biochar Used for Plant Growth Promotion: An Initial Test

“…Dilutions of wood vinegar collected during biomass pyrolysis, which contains a large number of organic compounds including ketones, phenols, and olefins, improved vegetable growth and quality when used as a foliar spray (Yan et al 2011). Moreover, humic-like substances extracted from a greenhouse waste biochar caused a change in plant perception of P nutrition, leading Arabidopsis seedlings growing under P starvation conditions to develop root hairs as if they were growing under P sufficient conditions (Graber et al 2015).…”

Biochars and the plant-soil interface

“…Rather, plant-water relations (Haider et al 2015) or disease suppression (Jaiswal et al 2015) improved by what these studies considered to be intermediate biochar application rates of 0.5-1.5 % w/w and decreased beyond that. It is tempting to interpret such results with an optimum response to the target effect, but it is equally possible (and given the multitude of effects of different biochars on plant-soil interactions even more likely) that cause and effect are not always discernable, with negative effects emerging at high application rates.…”

“…(b) (a) Fig. 1 Conceptual sketch of (a) a one-dimensional view of the interaction between plants and biochar added to soil; and (b) a twodimensional view of how biochars affect, and is affected by, both soil and plants (solid arrows), and how biochars will influence the interaction between plant and soil (hashed arrows); the strength of the effects is variable in time and space and differs depending on the type of soil, plant and biochar (arrows are meant to indicate effects, not mass flow) rooting (Abiven et al 2015;Graber et al 2015); plant access to water (Haider et al 2015) and nutrients through either increased mycorrhizal abundance (Vanek and Lehmann 2015) or biological nitrogen fixation (Van Zwieten et al 2015); disease resistance and tolerance (Jaiswal et al 2015;Mehari et al 2015); contaminant phytoavailability (Rees et al 2015;Williams et al 2015); and microbial community composition .…”

Biochars in Soils: Towards the Required Level of Scientific Understanding

“…These include the potential provision of refuge for microbial communities, shifts in available nutrients and nutrient ratios (Gundale, DeLuca 2006;Prendergast-Miller et al 2014), bioavailable contaminants (e.g. Elad et al 2012;Graber, Elad 2013;Denyes et al 2012;Hilber et al, this issue), enhanced plant root development and systemic defence against biotic or abiotic stress (Elad et al 2010;Jaiswal et al 2014) as well as microbial or plant-symbiont molecular signalling dynamics (Spokas et al 2010;Masiello et al 2013;Graber et al 2015).…”

“…The effect of biochar on root development, e.g. root surface, has also rarely been described, despite its importance regarding pollutant uptake (Hammer et al 2014;Graber et al 2015;Rees et al 2016). All these plant-related research topics should be targeted in the near future to improve understanding of biochar's effect in vegetated soils (Kammann, Graber 2015).…”