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Comparative responses of early-successional plants to charcoal soil amendments

Gale, N.V., M.A. Halim, M. Horsburgh and S.C. Thomas. 2017.


Charcoal used as a soil amendment, or "biochar," has received considerable recent research attention as a means to increase plant productivity while mitigating climate change through enhanced carbon sequestration. Interest in biochar for use in the restoration of disturbed sites is growing; however, biochar effects on wild plant species of the early phase of post-disturbance succession have received almost no prior research attention. Physiological adaptations that enable rapid growth in early-successional pioneers (e.g., high rates of photosynthesis) should be advantageous in soils with fresh charcoal since plants with a capacity for expeditious resource capture can capitalize on resource pulses from leachable mineral elements. In a glasshouse study, we tested the effects of biochar applied at two doses (10 and 20 t/ha) to brunisol/juvenile podzol soils, collected from a managed temperate mixed-wood forest, on the growth and physiology of 13 herbaceous old-field pioneers. We measured leaf-level physiology and nutrient supply rates throughout the experiment, and biomass and reproductive performance at experiment completion. Overall, biochar treatments resulted in 30-37% increases in final average aboveground biomass, 13-17% increases in photosynthesis, and an average ~44% increase in leaf-level water-use efficiency (at 10 t/ha), but with a high species-specific variation that included negative responses. We detected weak negative relationships between intrinsic photosynthetic rates (of non-biochar controls) and some biomass responses: Species with high photosynthetic capacities tended to have low or negative biomass responses to biochar. Plants in biochar treatments flowered earlier and on average had double the reproductive biomass overall. Pulses of PO4 and K were supplied by biochar in the first four weeks of the experiment, while NO3-was significantly immobilized by biochar. These results suggest that by providing a pulse of P and base cations, biochar can improve the restoration of disturbed landscapes by enhancing the physiological and reproductive performance of a subset of pioneers that have moderate photosynthetic rates and nitrogen demand. Biochar has important potential applications to restoration; however, biochar is likely to affect community composition strongly, and careful consideration of the physiological rates and nitrogen requirements of target species will be necessary to maximize the success of biochar-based restoration projects.

Key Words

biochar; carbon sequestration; ecophysiology; ecosystem management; photosynthesis; plant nutrients; plant performance; reproduction; restoration; soil nutrients; succession.