Long-term trend and interannual variation in evapotranspiration of a young temperate Douglas-fir stand over 2002-2022 reveals the impacts of climate change.

The shortage of decades-long continuous measurements of ecosystem processes limits our understanding of how changing climate impacts forest ecosystems. We used continuous eddy-covariance and hydrometeorological data over 2002-2022 from a young Douglas-fir stand on Vancouver Island, Canada to assess the long-term trend and interannual variability in evapotranspiration (ET) and transpiration (T). Collectively, annual T displayed a decreasing trend over the 21 years with a rate of 1% yr, which is attributed to the stomatal downregulation induced by rising atmospheric CO concentration.

Re-assessment of the climatic controls on the carbon and water fluxes of a boreal aspen forest over 1996-2016: Changing sensitivity to long-term climatic conditions.

Recent evidence suggests that the relationships between climate and boreal tree growth are generally non-stationary; however, it remains uncertain whether the relationships between climate and carbon (C) fluxes of boreal forests are stationary or have changed over recent decades. In this study, we used continuous eddy-covariance and microclimate data over 21 years (1996-2016) from a 100-year-old trembling aspen stand in central Saskatchewan, Canada to assess the relationships between climate and ecosystem C and water fluxes. Over the study period, the most striking climatic event was a severe, 3-year drought (2001-2003).

Spatial and temporal variations in global soil respiration and their relationships with climate and land cover.

Soil respiration ( ) represents the largest flux of CO from terrestrial ecosystems to the atmosphere, but its spatial and temporal changes as well as the driving forces are not well understood. We derived a product of annual global from 2000 to 2014 at 1 km by 1 km spatial resolution using remote sensing data and biome-specific statistical models. Different from the existing view that climate change dominated changes in , we showed that land-cover change played a more important role in regulating changes in temperate and boreal regions during 2000-2014.

No trends in spring and autumn phenology during the global warming hiatus.

Phenology plays a fundamental role in regulating photosynthesis, evapotranspiration, and surface energy fluxes and is sensitive to climate change. The global mean surface air temperature data indicate a global warming hiatus between 1998 and 2012, while its impacts on global phenology remains unclear. Here we use long-term satellite and FLUXNET records to examine phenology trends in the northern hemisphere before and during the warming hiatus.

Divergent long-term trends and interannual variation in ecosystem resource use efficiencies of a southern boreal old black spruce forest 1999-2017.

Long-term trends in ecosystem resource use efficiencies (RUEs) and their controlling factors are key pieces of information for understanding how an ecosystem responds to climate change. We used continuous eddy covariance and microclimate data over the period 1999-2017 from a 120-year-old black spruce stand in central Saskatchewan, Canada, to assess interannual variability, long-term trends, and key controlling factors of gross ecosystem production (GEP) and the RUEs of carbon (CUE = net primary production [NPP]/GEP), light (LUE = GEP/absorbed photosynthetic radiation [APAR]), and water (WUE = GEP/evapotranspiration [E]). At this site, annual GEP has shown an increasing trend over the 19 years (p < 0.

Biochar influences on soil CO and CH fluxes in response to wetting and drying cycles for a forest soil.

Biochar has been the focus of significant research efforts in agriculture, but little research has been conducted in forested ecosystems. Here, we assess CO and CH fluxes from a forest soil in response to biochar additions using a before-after-control-intervention experimental design. Soil CO and CH fluxes were measured over a series of wetting cycles by coupling soil mesocosms equipped with auto-chambers to a laser-based spectrometer for high-frequency measurements of gas fluxes and related soil processes.

Application of biochar and nitrogen influences fluxes of CO, CH and NO in a forest soil.

Nitrogen (N) fertilization of forests for increasing carbon sequestration and wood volume is expected to influence soil greenhouse gas (GHG) emissions, especially to increase NO emissions. As biochar application is known to affect soil GHG emissions, we investigated the effect of biochar application, with and without N fertilization, to a forest soil on GHG emissions in a controlled laboratory study. We found that biochar application at high (10%) application rates increased CO and NO emissions when applied without urea-N fertilizer.

Nitrogen enrichment potential of biochar in relation to pyrolysis temperature and feedstock quality.

Nitrogen (N) enrichment of biochar from both inorganic and organic waste N sources has the potential to add economic and environmental value through its use as a slow release N fertilizer. We investigated the sorption of N by, and its release from, biochar made at pyrolysis temperatures of 400, 500 and 600 °C from three feedstocks: poultry litter (PL with a carbon (C) to N ratio (C:N) of 14), softwood chips of spruce-pine-fir (SPF with a C:N of 470), and a 50:50 mixture of PL and SPF (PL/SPF). The prepared biochars were enriched with ammonium nitrate (AN) and urea ammonium nitrate (UAN).

Looking deeper into the soil: biophysical controls and seasonal lags of soil CO2 production and efflux.

We seek to understand how biophysical factors such as soil temperature (Ts), soil moisture (theta), and gross primary production (GPP) influence CO2 fluxes across terrestrial ecosystems. Recent advancements in automated measurements and remote-sensing approaches have provided time series in which lags and relationships among variables can be explored. The purpose of this study is to present new applications of continuous measurements of soil CO2 efflux (F0) and soil CO2 concentrations measurements.

Incorporating diffuse photosynthetically active radiation in a single-leaf model of canopy photosynthesis for a 56-year-old Douglas-fir forest.

A simple top-down model of canopy photosynthesis (P) was developed and tested in this study. The model (referred to as the Q(e)-MM model) is P = alphaQ (e) P (max)/(alphaQ ( e ) + P (max)), alpha and P (max) are quantum-use efficiency and potential P, respectively. Q (e) is given by Q (d) (0) + kQ (b) (0), where Q (d) (0) and Q (b) (0) are the diffuse and direct photosynthetically active radiation (PAR) incident on the canopy, respectively.

Effects of mutual shading of tree crowns on prediction of photosynthetic light-use efficiency in a coastal Douglas-fir forest.

Gross primary production (GPP) is often expressed as the product of absorbed photosynthetically active radiation and the efficiency (epsilon) with which a plant community uses absorbed radiation in biomass production. Light-use efficiency is affected by environmental stresses, and varies diurnally and seasonally. Uncertainty about epsilon can be a serious limitation when modeling GPP.

Modelling environmental controls on ecosystem photosynthesis and the carbon isotope composition of ecosystem-respired CO2 in a coastal Douglas-fir forest.

We developed and applied an ecosystem-scale model that calculated leaf CO2 assimilation, stomatal conductance, chloroplast CO2 concentration and the carbon isotope composition of carbohydrate formed during photosynthesis separately for sunlit and shaded leaves within multiple canopy layers. The ecosystem photosynthesis model was validated by comparison to leaf-level gas exchange measurements and estimates of ecosystem-scale photosynthesis from eddy covariance measurements made in a coastal Douglas-fir forest on Vancouver Island. A good agreement was also observed between modelled and measured delta13C values of ecosystem-respired CO2 (deltaR).

Biophysical controls on rhizospheric and heterotrophic components of soil respiration in a boreal black spruce stand.

We conducted a root-exclusion experiment in a 125-year-old boreal black spruce (Picea mariana (Mill.) BSP) stand in 2004 to quantify the physical and biological controls on temporal dynamics of the rhizospheric (R(r)) and heterotrophic (R(h)) components of soil respiration (R(s)). Annual R(r), R(h) and estimated moss respiration were 285, 269 and 57 g C m(-2) year(-1), respectively, which accounted for 47, 44 and 9% of R(s) (611 g C m(-2) year(-1)), respectively.

Measurement of CO2 exchange between Boreal forest and the atmosphere.

The Boreal forest is the world's second largest forested biome occupying the circumpolar region between 50 degrees N and 70 degrees N. This heterogeneous biome stores about 25% of all terrestrial carbon. We have reviewed EC measurements of CO2 exchange between the atmosphere and Boreal forests, and assessed progress in understanding the controlling processes.