Litter decay controlled by temperature, not soil properties, affecting future soil carbon
Citation
Gregorich, E.G., Janzen, H., Ellert, B.H., Helgason, B.L., Qian, B., Zebarth, B.J., Angers, D.A., Beyaert, R.P., Drury, C.F., Duguid, S.D., May, W.E., McConkey, B.G., Dyck, M.F. (2017). Litter decay controlled by temperature, not soil properties, affecting future soil carbon. Global Change Biology, [online] 23(4), 1725-1734. http://dx.doi.org/10.1111/gcb.13502
Plain language summary
The decay of plant litter – the unharvested leaves, stems, and roots – is important in agricultural soils because it delivers energy to soil biota, recycles plant nutrients and restores soil health. But changes in climate and farming practices already underway may affect this vital process in ways we cannot predict.
To address this uncertainty, a science team consisting of 12 AAFC researchers at 9 research centres established one of the largest studies of its kind to study litter decay in Canada. Plant straw labelled with the heavy carbon isotope (13C) was applied to soil at sites spanning a 3500-km transect across Canada. This approach allowed the scientists to follow the fate of plant carbon in the soil, much as physicians use isotopic markers to trace the fate of compounds in medical tests. Periodic analysis over five years showed that the rate of litter decay was similar at all sites once the effect of temperature had been accounted for. In other words, although the soils and climates across Canada were widely different, the rate of decay could be accurately predicted using a simple equation.
Using this simple equation, the scientists can now predict how future climate change may affect plant litter decay. For example, climate warming in the next 50 years or so will significantly hasten decay of plant litter: the time for decay to almost reach completion will by as much as two years. This effect may speed the release of energy and nutrients from litter, but also enhance climate change by releasing CO2 more quickly.
This study, still ongoing, shows how a collaborative effort, conducted over many years, can help us understand and then better manage critical ecological processes in the farmlands upon which we all depend.
Abstract
Widespread global changes, including rising atmospheric CO2 concentrations, climate warming and loss of biodiversity, are predicted for this century; all of these will affect terrestrial ecosystem processes like plant litter decomposition. Conversely, increased plant litter decomposition can have potential carbon-cycle feedbacks on atmospheric CO2 levels, climate warming and biodiversity. But predicting litter decomposition is difficult because of many interacting factors related to the chemical, physical and biological properties of soil, as well as to climate and agricultural management practices. We applied 13C-labelled plant litter to soil at ten sites spanning a 3500-km transect across the agricultural regions of Canada and measured its decomposition over five years. Despite large differences in soil type and climatic conditions, we found that the kinetics of litter decomposition were similar once the effect of temperature had been removed, indicating no measurable effect of soil properties. A two-pool exponential decay model expressing undecomposed carbon simply as a function of thermal time accurately described kinetics of decomposition. (R2 = 0.94; RMSE = 0.0508). Soil properties such as texture, cation exchange capacity, pH and moisture, although very different among sites, had minimal discernible influence on decomposition kinetics. Using this kinetic model under different climate change scenarios, we projected that the time required to decompose 50% of the litter (i.e. the labile fractions) would be reduced by 1–4 months, whereas time required to decompose 90% of the litter (including recalcitrant fractions) would be reduced by 1 year in cooler sites to as much as 2 years in warmer sites. These findings confirm quantitatively the sensitivity of litter decomposition to temperature increases and demonstrate how climate change may constrain future soil carbon storage, an effect apparently not influenced by soil properties.