Spatial heterogeneity in soil pyrogenic carbon mediates tree growth and physiology following wildfire

Abstract

1. Pyrogenic carbon (PyC) is a ubiquitous legacy of wildfire in terrestrial soils, yet how it affects the growth and function of regenerating plants has received little research attention. 2. We examined responses to a natural gradient of PyC deposition 5 years following a severe fire in a northern boreal forest, based on measurements of growth (height, basal area increment and leader extension), physiological performance (Fv/Fm) and foliar nutrition (C, N, P, K, Mg) of Pinus banksiana Lamb. We determined the concentration of PyC, expressed as a dosage (t/ha, in mineral soils collected from the rootzones of each sapling and used it as an independent factor to model trait responses to increasing PyC levels, in conjunction with measurements of soil physio-chemical properties (pH, EC, VOC, Ash, N, P, K, Ca and Mg). 3. Quantification and spatial analysis of PyC reveals heterogeneous deposition across the landscape with fine-grained patchiness at scales <0.5 m. In response to this heterogeneity, phenotypic and nutritional adjustments followed dose-dependent response patterns. Beneficial effects of PyC on sapling growth occurred to an optimum point of ~30-60 t/ha, while declining patterns were found for trees in dosages exceeding 100 t/ha. Some traits were positively and negatively related to soil K and N, respectively, and shared strong negative associations with soil pH and volatile matter. 4. Synthesis. This study supports the longstanding hypothesis that soil PyC enhances growth and physiological function of fire-adapted plants, but indicates that responses are highly dosage-dependent, with natural levels of PyC deposition commonly exceeding an optimum point. These results also suggest that the main mechanisms for observed responses to PyC include: (a) enhanced supply of base cations, (b) immobilization of N and (c) pronounced liming. Future changes in climate are expected to increase fire frequency, particularly in circumpolar boreal forests. We predict shifts in PyC to frequently exceed the threshold resulting in reduced plant growth and ultimately ecosystem productivity.

Biochar Rescues Native Trees in the Biodiversity Hotspot of Mauritius

“…Biochar addition at rates of 25 t/ha and 50 t/ha resulted in similar increases in tree growth (Figures 1 and 2). Prior studies suggest that plant growth responses to biochar application peaked at moderate doses of ~20-30 t/ha [84,85], though a higher optimum (of 50-60 t/ha) has been found in a recent study examining growth responses to natural post-fire pyrogenic carbon deposition [86]. In the present study, we did not observe large differences in the growth responses of native species between the 25 and 50 t/ha treatments.…”

Biochar Rescues Native Trees in a Global Biodiversity Hotspot

“…Biochar addition at rates of 25 t/ha and 50 t/ha resulted in similar increases in tree growth (Figures 1 and 2). Prior studies suggest that plant growth responses to biochar application peaked at moderate doses of ~20-30 t/ha [84][85], though a higher optimum (of 50-60 t/ha) has been found in a recent study examining growth responses to natural postfire pyrogenic carbon deposition [86]. In the present study we did not observe large differences between growth responses of native species between the 25 and 50 t/ha treatments.…”

Biochar mitigates allelopathic effects in temperate trees

“…Our results are relevant to the so-called charcoal effect, in which large positive growth responses to natural fire residues are observed in forest ecosystems (Gale & Thomas, 2021;Pluchon et al, 2014;. PyC in the soil of early successional forests is effective at reducing the allelopathic effects of ericaceous species through the sorption of phenolic compounds (Zackrisson et al, 1996).…”