Response of Populus tremula to heterogeneous B distributions in soil

Abstract

Background: Poplars accumulate inordinate amounts of B in their leaves and are candidate plants for the remediation of B contaminated soil. We aimed to determine the effect of heterogeneous B distribution in soil by comparing the growth and B accumulation of young Populus tremula trees growing in soil with heterogeneous and homogeneous B distributions. Methods: The first of two experiments focused on the tolerance and B accumulation of P. tremula under heterogeneous soil B distributions, while the second was designed to study fine root growth under such conditions in detail. Results: Growth and B accumulation of P. tremula were unaffected by the spatial distribution of B. Root and shoot growth were both reduced simultaneously when leaf B concentrations increased above 800 mg kg⁻¹. In the heterogeneous soil B treatments, root growth was more reduced in spiked soil portions with B concentrations >20 mg kg⁻¹. Fine root length growth was stronger inhibited by B stress than secondary growth. Conclusions: The root growth responses of P. tremula to B are primarily a systemic effect induced by shoot B toxicity and local toxicity effects on roots become dominant only at rather high soil B concentrations. Local heterogeneity in soil B should have little influence on the phytoremediation of contaminated sites.