Biochar mitigates negative effects of salt additions on two herbaceous plant species

• Biochar strongly sorbs many substances, including salts.
• We investigated use of biochar to mitigate salt stress in a glasshouse experiment.
• Biochar at high dosages mitigated lethal effects of salt in two plant species.
• Biochar also enhanced growth in non-salt treatments in one species.
• Results suggest biochar use as a novel strategy to mitigate salt stress effects.

Addition of pyrolyzed biomass (“biochar”) to soils has commonly been shown to increase crop yields and alleviate plant stresses associated with drought and exposure to toxic materials. Here we investigate the ability of biochar (at two dosages: 5 and 50 t ha−1) to mitigate salt-induced stress, simulating road salt additions in a factorial glasshouse experiment involving the broadleaved herbaceous plants Abutilon theophrasti and Prunella vulgaris. Salt additions of 30 g m−2 NaCl to unamended soils resulted in high mortality rates for both species. Biochar (Fagus grandifolia sawdust pyrolyzed at 378 °C), when applied at 50 t ha−1 as a top dressing, completely alleviated salt-induced mortality in A. theophrasti and prolonged survival of P. vulgaris. Surviving A. theophrasti plants that received both 50 t ha−1 biochar and salt addition treatments showed growth rates and physiological performance similar to plants without salt addition. Biochar treatments alone also substantially increased biomass of P. vulgaris, with a ∼50% increase relative to untreated controls at both biochar dosages. Biochar did not significantly affect photosynthetic carbon gain (Amax), water use efficiency, or chlorophyll fluorescence (Fv/Fm) in either species. Our results indicate that biochar can ameliorate salt stress effects on plants through salt sorption, suggesting novel applications of biochar to mitigate effects of salinization in agricultural, urban, and contaminated soils.