Research axis #1: Boreal Biogeochemistry in a changing world
The boreal forest is one of the largest untouched terrestrial ecosystem in the world. It is also of great economic significance for Canada and Québec where forestry is a crucial economic activity. Thus, understanding boreal ecosystem function is of critical ecological and economical importance. In boreal forest, nitrogen (N) is the nutrient that is most often reported as limiting primary productivity. While boreal forest soils are often rich in total N, this N is bound in recalcitrant forms that are not available to plants. Rapidly cycling N and new N inputs are therefore key to forest growth. In boreal forest, new N inputs arise from biological N fixation (BNF) by microorganisms involved in symbiotic and mutualistic associations with higher plants, mosses and lichens or living freely in soil. Climates of the northern hemisphere will undergo significant changes in the next decades (IPCC). Understanding processes controlling BNF in boreal forest and evaluating the effect of global climate change on BNF is thus essential to the management of boreal natural resources in a sustainable manner. Our research program aims to address critical and innovative questions regarding BNF in boreal and subarctic ecosystems.
Importance of alternative nitrogenases in boreal ecosystems (and elsewhere)?
Three isoforms of the nitrogenase, enzyme responsible for the reduction of N2 into bioavailable ammonium, have been identified so far. Beside the canonical Mo nitrogenase (Mo-Nase) present in all N2 fixers, two additional isoenzymes have been reported: the vanadium Nase (V-Nase) and the iron-only dependent Nase (Fe-Nase). The role of these alternative Nases in nature has been mostly overlooked, because they are found in communities that were not considered major contributors to N inputs. In recent years, BNF by mosses and lichens has captured the interest of the scientific community for its importance toward global N input in high latitude ecosystems. In these biomes BNF is assumed by mutualistic and symbiotic cyanobacteria, which very likely own alternative means of N2 fixation.
Our research aims at characterizing the role and importance of alternative nitrogenases (V-Nase and Fe-Nase) to N inputs natural ecosystems, with a particular interest for high latitude ecosystems. What is the occurrence of alternative Nases in cyanolichens and feather mosses from boreal ecosystems? Under which conditions does V-Nase comes at play in natural habitats?
Deciphering the cycling of essential metals for biological N2 fixation in boreal forest
Moss associated cyanobacteria (MAC) are critical contributor the N budget in boreal forest, as they can account for up to 50% of annual N input. However, our understanding of the processes controlling biological nitrogen fixation (BNF) in boreal forest remains incomplete. This poor understanding limits our capacity to manage present ecosystems in a sustainable manner and to predict environmental responses to global climate change. While the importance of environmental factors and macronutrient cycling (i.e. N) on BNF by MAC has been reported, the role of micronutrient cycling, such as essential metals for BNF (molybdenum (Mo), iron (Fe) and vanadium (V), see above) remains mostly unstudied. Our research aim to fill this gap by better characterizing the biogeochemical cycling of essential micronutrients for BNF in boreal forest.
Role of organic compounds on N2 fixing symbioses function
Understanding processes controlling the establishment and functioning of symbiosis is one of the major challenges of modern science. Symbiosis is not an exception in nature, it is almost the rule: more than 80% of higher plants, the primary producers in terrestrial ecosystems, rely on symbioses with microorganisms for their mineral nutrition. While symbiosis is a critical process for the biosphere, our understanding of symbiosis establishment and functioning remains elusive. Our group focuses on deciphering the role of metallophores on micronutrients acquisition and homeostasis in boreal N2 fixing symbioses: Most organisms produce low molecular weight ligands, called siderophores, to recruit Fe. Recent research has significantly contributed to demonstrate that siderophores are not only iron carriers, they are more likely multi-purpose metal scavenging ligands called metallophores. The tremendous diversity of ligands (potentially metallophores) produced by symbiotic partners likely plays a critical role on metal acquisition and homeostasis in complex biological systems (symbioses) that remains to be fully characterized.
Our research focuses on two N2 fixing symbioses.
Actinorhizal symbiosis. Alder trees and shrubs are the predominant symbiotic N2 fixing plants in boreal ecosystems. Alder is particularly important in early succession, where it significantly contributes to improve soil fertility and soil structure. Alder is also intensively used in revegetalization and bioremediation of contaminated sites. Understanding how alders manage metal acquisition under adverse environmental conditions is thus of both ecological and economical significance.
Cyanolichens. Lichens are critical contributors to the biogeochemical cycling of N in high latitude ecosystems (boreal and polar). Many lichens rely on atmospheric deposition for their mineral nutrition and many studies have characterized the efficiency of lichens to capture these particles. How lichens access metals of interest from these mineral particles to sustain metabolic activity (e.g., BNF) is however not clear. Lichen substances represent a highly diverse family of compounds (several hundreds) and many of these compounds could be metallophore candidates.
Evaluate the effect of global climate change and atmospheric change on N2 fixation in boreal forest
By the end of this century, the average temperature in boreal and subarctic regions is expected to rise from 3 to 11°C. The snow and ice cover of the northern hemisphere will be reduced by up to 50%, and the annual precipitation in high latitudes will increased from 10 to 40% compared to 2005 (scenarios RCP 2.6 and RCP 8.5 in Working Group I Contribution to the IPCC Fifth Assessment Report 2013). How BNF by MAC will respond to global climate change and atmospheric change is not clear. Our research aims evaluate the effect of elevated CO2 and temperature on BNF by MAC. What is the effect of elevated CO2 and temperature on N2 fixation by feather mosses? What is the effect of N deposition, temperature and elevated CO2 on micronutrient cycling in boreal forest?
This research is developed at the mini-FACE (Forced-Air CO2 Enriched) facility at the Simoncouche Experimental Research Forest in the Saguenay area (Québec). This unique research apparatus will allow studying main and interactive effects of early snowmelt, elevated CO2, and nutrient availabilities (N, P and Mo) on BNF by MAC in black spruce forest. More information on this facility can be found on the website
Research axis #2: Fate and impact of organic contaminants in the environment
Water quality is a major concern to Quebec, Canada and most western countries. Water is, by far, our most precious natural resource. With the agricultural and industrial revolution, the use of chemical compounds has exponentially increased to sustain a fast growing population. During the second half of the 20th century the impact of persistent and bioactive chemicals (e.g. insecticides) on water and land quality has been the subject of intensive research. In the last decades, the aging populations of western countries have induced a significant increase in the consumption of pharmaceuticals compounds (PhCs). These PhCs represent a new challenge to environmental quality. Many PhCs are found in water treatment plants (WTPs) at concentrations ranging from 10-2 to 10-3 ug.L-1 and are readily transferred to the environment: WTPs are unable to efficiently remove the most common PhCs. Major efforts have been deployed in the last years to characterize the dynamics (e.g. transfer, interactions with natural matrices) of PhCs in the environment and to evaluate their potential effects on the biosphere (ecotoxicology) and human health. Significant efforts have also been engaged to develop new technologies (e.g. membrane bioreactors, advanced oxidation processes) allowing a better treatment of PhCs by WTPs but such technologies are still under development. The effects of PhCs on ecosystems quality and human health remain difficult to evaluate in a comprehensive manner. Intensive efforts are yet to be made to solve the PhCs conundrum, especially considering that PhCs are only the emerged tip of an iceberg.
After consumption, a large fraction of PhCs are readily excreted by the human body; unchanged or under altered forms (metabolites). After excretion, these compounds can be further modified through physical, chemical or biological processes. A given PhC can thus generate multiple derivatives; PhC derivatives (PhCDs). Our understanding of PhCDs dynamics in the environment and their potential effects on water, land quality and human health remains embryonary. This strongly limits our ability to predict the real impact of PhCs on ecosystem quality. Our research aims to better caracterize the fate and effects PhCs and PhCDs in the environment.