Response of Net Ecosystem Productivity of Three Boreal Forest Stands to Drought

In 2000-03, continuous eddy covariance measurements of carbon dioxide (CO2) flux were made above mature boreal aspen, black spruce, and jack pine forests in Saskatchewan, Canada, prior to and during a 3-year drought. During the 1st drought year, ecosystem respiration (R) was reduced at the aspen site due to the drying of surface soil layers. Gross ecosystem photosynthesis (GEP) increased as a result of a warm spring and a slow decrease of deep soil moisture. These conditions resulted in the highest annual net ecosystem productivity (NEP) in the 9 years of flux measurements at this site. During 2002 and 2003, a reduction of 6% and 34% in NEP, respectively, compared to 2000 was observed as the result of reductions in both R and GEP, indicating a conservative response to the drought. Although the drought affected most of western Canada, there was considerable spatial variability in summer rainfall over the 100-km extent of the study area; summer rainfalls in 2001 and 2002 at the two conifer sites minimized the impact of the drought. In 2003, however, precipitation was similarly low at all three sites. Due to low topographic position and consequent poor drainage at the black spruce site and the coarse soil with low water-holding capacity at the jack pine site almost no reduction in R, GEP, and NEP was observed at these two sites. This study shows that the impact of drought on carbon sequestration by boreal forest ecosystems strongly depends on rainfall distribution, soil characteristics, topography, and the presence of vegetation that is well adapted to these condition

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

Author Posting. © Ecological Society of America, 2010. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 20 (2010): 1569–1582, doi:10.1890/09-0693.1.We seek to understand how biophysical factors such as soil temperature (Ts), soil moisture (θ), 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. Here we explore how variation in Ts, θ, and GPP (derived from NASA's moderate-resolution imaging spectroradiometer [MODIS]) influence F0 and soil CO2 production (Ps). We focused on seasonal variation and used continuous measurements at a daily timescale across four vegetation types at 13 study sites to quantify: (1) differences in seasonal lags between soil CO2 fluxes and Ts, θ, and GPP and (2) interactions and relationships between CO2 fluxes with Ts, θ, and GPP. Mean annual Ts did not explain annual F0 and Ps among vegetation types, but GPP explained 73% and 30% of the variation, respectively. We found evidence that lags between soil CO2 fluxes and Ts or GPP provide insights into the role of plant phenology and information relevant about possible timing of controls of autotrophic and heterotrophic processes. The influences of biophysical factors that regulate daily F0 and Ps are different among vegetation types, but GPP is a dominant variable for explaining soil CO2 fluxes. The emergence of long-term automated soil CO2 flux measurement networks provides a unique opportunity for extended investigations into F0 and Ps processes in the near future.Data collection was possible thanks to NASA, the NSF Center for Embedded Networked Sensing (CCR-0120778), DOE (DE-FG02-03ER63638), CONACyT, UCMEXUS, NSF (EF-0410408), NSF-LTER, KAKENHI (12878089 and 13480150), the Academy of Finland (213093), the Austrian Science Fund (FWF, P18756-B16), the Kearney Foundation, the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), and the Natural Science and Engineering Research Council of Canada (NSERC). R. Vargas was supported by grant DEB-0639235 during the preparation of this manuscript

Hybrid macroporous Pd catalytic discs for 4- nitroaniline hudrogenation: contribution of the alginate-tetraalkylphosphonium ionic liquid support

International audienc

Ligand exchange reaction on Au38(SR)24,separation of Au38(SR)23(SR')1 Regioisomers and migration of thiolates.

International audienc

Palladium supported on alginate/ionic liquid highly porous monoliths: Application to 4-nitroaniline hydrogenation

International audienc

Factors controlling the interannual variability in the carbon balance of a southern boreal black spruce forest

Factors controlling the seasonal and interannual variability of net ecosystem productivity (F NEP ), gross ecosystem photosynthesis (P g ), ecosystem respiration (R e ) and evapotranspiration (E) of a mature boreal black spruce forest in central Saskatchewan, Canada were investigated using eight years (1999–2006) of continuous eddy covariance measurements. During 2000–2006, which included a three-year drought, the forest was a weak sink for CO2 with annual F NEP ranging from 27 to 80 g C m-2 (56 ± 21 g C m−2 a−1). The beginning of the growing season occurred when daily mean air temperature exceeded 4°C and the near surface soil temperature equaled or exceeded 0°C. The length of the growing season varied from 186 to 232 days. During the extreme drought year (2003), the smaller reduction in annual P g than in R e resulted in highest F NEP of the record. Annual F NEP decreased slightly with increasing soil water content; however, there was evidence of increased F NEP due to high water table conditions in 2004 because of the slightly higher decrease in R e than P g . Although bulk surface conductance (g s ) decreased significantly during the dry conditions in 2003, the associated increase in D prevented a significant drop in E, which resulted in only a slight decline in evaporative fraction and almost no change in water use efficiency. Interannual variation inP g , R e and F NEP in the early growing season (April–June) and late growing season (July–September) was controlled by air temperature and soil water content, respectively. However, spring (April–May) mean air temperature was the main factor determining the interannual variation in annual F NEP . The effect of late growing season soil water content on annual P g and R e was greater than its effect on annual F NEP . The results emphasize the need to consider soil moisture conditions as well as temperature when simulating the response of the carbon balance components of this ecosystems to climate change. An edited version of this paper was published by AGU. Copyright 2008 American Geophysical Union.Land and Food Systems, Faculty ofReviewedFacult

Daily heterotrophic respiration model considering the diurnal temperature variability in the soil

In daily, monthly, and annual respiration models for regional and global applications, the diurnal variation of temperature is generally ignored. As the effect of temperature on respiration is nonlinear, this ignorance may cause considerable errors in respiration estimation, but these errors have not yet been systematically investigated. This is in fact a central issue in temporal scaling of ecosystem models which are often applied in time steps equal to or larger than a day. In this study, we develop an integrated daily heterotrophic respiration model, and demonstrate first theoretically the importance of considering the diurnal amplitude of soil temperature and the vertical soil carbon distribution pattern in daily respiration estimation using the daily mean temperature. Measurements of soil respiration with roots exclusion made in a mature black spruce site in Saskatchewan, Canada, in July–September 2004 are used to validate the model. Daily heterotrophic respiration rates were underestimated by up to 15%, with a mean value of 4.5%, when only the mean daily temperature was used. This underestimation occurred under the conditions that the diurnal temperature amplitude in the forest was less than 12°C and the vertical distribution of organic carbon in the top 15–30 cm was uniform. Based on the integrated daily model, this underestimation at the same site would be 38% if the amplitude increases to 20°C, and in soils with steep vertical carbon distributions with a 20°C diurnal amplitude, it can increase to 44%. The magnitude of this underestimation is theoretically proportional to [ln(Q 10)]2. During the experimental period, the value of Q 10 for heterotrophic respiration was found to be 4.0–4.5. If Q 10 = 2.0, this underestimation is reduced to about 10% at a diurnal temperature amplitude of 20°C. An edited version of this paper was published by AGU. Copyright 2009 American Geophysical Union.Land and Food Systems, Faculty ofReviewedFacult