Abstract
Tree taxa and pyrolysis temperature are the major controllers of the physicochemical properties of the resultant pyrogenic organic matter (PyOM) produced in fire-prone forests. However, we know little about how these controls determine the residence time of PyOM once introduced to soil. In this study, we tracked the fate of 13C-enriched red maple (RM) or jack pine (JP) wood and PyOM, produced over a range of temperatures (200, 300, 450, or 600 °C) added to soil from a northern temperate forest in Michigan, USA. Pyrolysis temperature was the main controller of PyOM-C mineralization rates, with mean residence times (MRT) ranging from ~4 to 450 years for both taxa. The PyOM-C mineralization rates for both taxa and the pyrolysis temperature correlated positively with PyOMw (leachable C content); however, the potential PyOMw contribution to net PyOM-C mineralization was lower for JP (14–65%) than RM (24–84%). The correlation between PyOMw and mineralization rate was strongest where carbonization and the thermochemical conversion of carbohydrates and non-lignin phenols was most pronounced during pyrolysis for each taxa (300 °C for JP and 450 °C for RM). Contrary to expectations, the addition of a labile C source, sucrose, to the soil did not enhance the decomposition of PyOM, indicating that soil microbes were not energy limited in the soil-PyOM system studied (regardless of pyrolysis temperature). Our results showed that while the first-order control on PyOM decomposition in this soil is pyrolysis temperature, wood taxa did affect PyOM-C MRT, likely in part due to differences in the amount of reactive water-soluble C present in PyOM.
Highlights
Addition rates of pyrogenic organic matter (PyOM), the product of the incomplete biomass combustion, to soils are expected to increase globally with projected increases in fire frequency [1,2].PyOM in soil can constitute a substantial portion of stable forest soil C and as a result, accurate estimates of PyOM reactivity and mean residence time (MRT) in soil are needed [2,3,4].Increased PyOM deposition and its consequent reactivity and MRT in soil will be important in fire-prone ecosystems which are experiencing shifts in plant species dominance, the impacts of which are still unknown [5,6]
We investigated how the physiochemical properties of PyOM derived from two common taxa—jack pine (Pinus baksiana) and red maple (Acer rubrum), produced across a range of relevant temperatures (200, 300, 450, and 600 ◦ C)—control PyOM mineralization rate in a soil system common to northern Great Lakes forests that are expected to experience shifts in forest taxa and fire frequency
PyOM physiochemical structure related to plant source taxa and pyrolysis temperature was directly linked to its C mineralization rate in a coarse-textured, north temperate forest soil
Summary
Increased PyOM deposition and its consequent reactivity and MRT in soil will be important in fire-prone ecosystems which are experiencing shifts in plant species dominance, the impacts of which are still unknown [5,6]. PyOM-C dynamics as distinct from soil-C [7,8,9]. Of these experiments, 14 involved incubations longer than 180 days, six used well-characterized wood-derived PyOM, and two utilized PyOM materials produced at a range of production temperatures as well as the associated unaltered parent materials (Supplemental Information, Table S1). Given the limited number of studies designed to track the fate of PyOM-C, a significant gap remains in PyOM-C turnover dynamics and further investigation is needed to predict its mineralization and stability in a changing climate
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