Charcoal soil amendments increase growth, physiological, and reproductive performance in early successional temperate pioneers

Background/Question/Methods

Charcoal facilitates rapid growth and regeneration following fires by increasing retention and availability of nutrients and water, increasing soil pH, and by sorbing toxic and inhibitory compounds. Biochar (BC) is the term given to charcoal used as a soil amendment, which is generally derived from pyrolysis of lignocellulosic forestry and agricultural waste residues. Physiological adaptations that facilitate rapid growth in early-successional pioneers (i.e. high photosynthesis) that colonize sites following disturbance should be advantageous, where plants capitalize on a resource pulse. However, growth and physiological responses of pioneers to both natural and engineered chars has received only minimal research attention. In a glasshouse study in Toronto, Ontario, we tested the effects of maple sawdust BC applied to a brunisol at two dosages (10 t/ha and 20 t/ha) on the growth and performance of 13 herbaceous species that colonize North American grasslands and deciduous and mixed-wood forests following disturbance. We measured plant growth (leaf area and height), physiological traits (photosynthesis, stomatal conductance), and nutrient supply rates (P, K, NO₃, NH₄, Ca, Mg) throughout the experiment. Mineral nutrition (leaf P, N, Ca, Mg, K), above- and below-ground biomass, and reproductive performance (flowering date, reproductive biomass) was measured at experimental completion.

Results/Conclusions

Overall, plants with charcoal soil amendments had higher growth and physiological performance with between 15% and 20% increases in final biomass for 10 t/ha and 20 t/ha, respectively. BC increased photosynthesis and stomatal conductance by 10% overall.  Plants with BC had earlier flowering (two weeks earlier in some cases), and marginally greater reproductive biomass. Pulses of PO₄^- and K⁺ where supplied by BC in the first 4 weeks of the experiment and were greatest at the higher addition rate (20 t/ha). Similarly, leaf P and K content was increased for plants with BC especially at 20 t/ha. However, some neutral and even negative responses were detected in ‘later’ successional species with more conservative growth strategies, and for species with high N demands. These results suggest that BC can facilitate succession of fire-disturbed landscapes by enhancing the physiological and reproductive performance of early successional pioneers. In particular, BC provides a pulse of P and other cations that can be limiting in temperate brunisolic soils. We conclude that BC has considerable potential to be used as a fire disturbance mimic to restore landscapes with a history of fire.