Investigating Carbon Storage and Stability in Boreal Forest Soils Dr Sylvie Quideau INVESTIGATING CARBON STORAGE AND STABILITY IN BOREAL FOREST SOILS The world’s boreal, or high latitude forests, contain around 25% of global terrestrial carbon stores – mostly in their soils. These forest ecosystems are particularly vulnerable to climate change, but the effects that rising temperatures could have on their carbon stocks are poorly understood. Dr Sylvie Quideau and her team from the University of Alberta have been studying the complex interactions involved in the storage and stability of boreal soil carbon. Their work will help to inform management and conservation decisions, with implications for global climate change mitigation. An Under-appreciated Carbon Store consist of a complex mixture of carbon pools, with more than 85% of carbon Boreal forests are the world’s most being stored in the soil rather than the northerly woodlands – encircling the vegetation. globe just south of the Arctic. Forming the largest terrestrial community of Carbon is stored in forest soils primarily plants and animals on Earth, boreal in the form of soil organic matter. forests are characterised mainly by Organic matter accumulation in coniferous tree species, and experience soils reflects the influence of several freezing temperatures for six to eight environmental soil forming factors months of the year. including climate, vegetation and parent geological material. These stores of These high latitude forests are one of soil carbon have varying turnover rates the most vulnerable ecosystems to along a continuum ranging from days global warming. While global surface (termed labile carbon), to decades, temperatures are projected to rise by and centuries (persistent carbon). The 1.8–4°C by 2100, northern regions may different types of carbon pools and Dr Sylvie Quideau and her team experience up to 5°C warming. Such timescales over which they cycle make from the University of Alberta are large increases in average temperatures it challenging to predict the response of seeking to address this issue, with a are expected to lead to altered patterns boreal soil carbon to climate change. research program that investigates of freeze and thaw, and transformative how underlying environmental factors vegetation shifts in the boreal forest With boreal forest soils representing control soil carbon storage and stability zone. such large carbon storehouses, in boreal forests. ‘We’re interested in any changes in these stocks could deciphering the pathways leading to Boreal forests also represent a huge, significantly affect the global carbon the formation of organic matter in but often under-acknowledged, global cycle. Yet despite the importance of boreal soils,’ says Dr Quideau. ‘We’re carbon store. Carbon stocks in boreal boreal forest soils to the global carbon also looking at how the interactions forests are estimated at 471 gigatons budget and their high susceptibility between soil geological material and – close to 25% of the total amount of to climate change, very little is known vegetation may ultimately determine carbon stored in terrestrial ecosystems about how warming will affect carbon the response of boreal soil carbon to worldwide. Boreal forest carbon stocks stocks and dynamics in these soils. climatic changes.’ WWW.SCIENTIA.GLOBAL Exploring Forest Soil Carbon less is known about carbon storage in the deeper surface layers. Carbon Dynamics the deep soils of boreal forests than accumulation in the forest floor varies in surface soils, and the mechanisms with vegetation composition, although To gain a better understanding of the responsible for its accumulation and greater carbon stocks do not necessarily carbon cycle in boreal forest soils, Dr persistence are largely unknown. mean greater carbon stability. However, Quideau and her team are exploring there is an emerging consensus that the sources, formation pathways and Dr Quideau’s team hypothesises that sensitivity to temperature increases stability of carbon pools at a range of the parent geological material is the with greater levels of organic matter different soil depths within the forest. primary driver of differences among decomposition or humification. They have included a variety of boreal soils, and controls the persistence forests from across Canada in their of deep soil carbon. ‘Soil carbon age ‘Humified forest floors may therefore research – allowing for characterisation increases with depth,’ says Dr Quideau. be more vulnerable to temperature of soil organic matter from a wide range ‘However, deep carbon may not be as increases than fresh litter,’ explains Dr of geological materials, forest stand stable as originally thought, and new Quideau. ‘However, our predictions types and climate. evidence suggests that carbon fluxes need to take into account changes in in deep soil may be as large as those microbial community composition with Their program combines a field- at the soil surface. We are investigating warming.’ based study of soils in the natural how soil geological material and the environment, isotope-labelling processes leading to soil formation This uncertainty over the impacts of experiments in controlled-environment may control the source and stability of environmental change on microbial chambers, and state-of-the-art carbon present at depth.’ communities has led the team to analytical protocols. The team is investigate whether vegetation using the latest technological and Research carried out so far has led Dr shifts will result in changes to both methodological advances to follow Quideau’s team to believe that the the composition of soil biological the fate of individual plant molecules carbon pool in surface soil may actually communities and the pathways through biological communities in the be more chemically stable than deep involved in organic matter breakdown, soil, to the soil carbon pools. soil carbon. At low temperatures and in with consequential implications for the absence of disturbances, thick forest carbon persistence. Microorganisms are Deep soil carbon (below 20 centimetres) floors accumulate in boreal forests. considered to be the ‘eye of the needle’ represents more than half of the total Carbon in this layer can be preserved through which most soil carbon passes, carbon stored in soils globally. However, for decades and even centuries in so how they are affected by climate WWW.SCIENTIA.GLOBAL Dr Quideau’s team is also carrying out work exploring the long- term effects of harvest on boreal soils and their carbon storage. Forestry is an important feature of Canada’s economy, but there is still considerable uncertainty on how management practices will affect boreal soil carbon storage in the long term. With increasing pressures from a changing climate and intensified forest management, developing better tools and methods for quantifying soil carbon dynamics is of particular importance. Using remote sensing techniques, the researchers have found differences in carbon retention between harvested and unharvested conifer or deciduous plantations based on site wetness. This work, combined with an improved understanding of the forest soil carbon cycle, is of direct economic importance to the forestry sector. Indeed, the team’s findings are beginning change is critical to the overall soil carbon response. to inform and improve sustainable and adaptive management strategies for Canadian boreal forests. Another significant carbon store being investigated by Dr Quideau and her team is the root zone, or rhizosphere. This Another distinct, but related area of interest to the team is the is a unique zone, where the secretion of organic substances impact of invasive earthworms on carbon cycling in boreal by plant roots maintains a continuous supply of ‘food’ for soils. Canada’s boreal forests had been largely earthworm- microbes. This can lead to priming – an increase in surrounding free since the Ice Age 10,000 years ago, and evolved in their soil carbon decomposition. absence. However, invasive earthworm species, introduced to the continent by European settlers centuries ago, are now ‘Linkages between plants and microbes are both complex making their way into northern boreal forests. and central to soil functioning,’ explains Dr Quideau. ‘In order to truly understand the vulnerability of boreal soil carbon Earthworm activity represents a significant change to forest to change, these relationships must be explored.’ The team carbon dynamics, and needs to be incorporated into the overall is therefore investigating whether soil microbial activity is carbon budget for boreal forests. However, there is a lack of more sensitive to climate-induced changes in the substances understanding of their long-term impact. The researchers secreted by roots, than to climatic changes themselves. ‘These have been quantifying soil carbon stocks and persistence, indirect effects of climate change may be more important than soil development and microbial communities of invaded and direct climatic effects,’ says Dr Quideau. ‘If our hypotheses are pristine sites of similar soil type and vegetation, in order to correct, the response of the microbial community to variations improve understanding of earthworm influence on carbon in temperature will be greater in the rhizosphere than in the storage. bulk soils.’ Preliminary results show a significant reduction of the forest Future Management of Boreal Forests floor associated with an increase in carbon content for the uppermost mineral soil layers.