Philosophical transactions of the Royal Society of London. Series B, Biological sciences, Jan 1, 2010
We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (15... more We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (153 site-years of data) to investigate relationships between phenology and productivity (in terms of both NEP and gross ecosystem photosynthesis, GEP) in temperate and boreal forests. Results are used to evaluate the plausibility of four different conceptual models. Phenological indicators were derived from the eddy covariance time series, and from remote sensing and models. We examine spatial patterns (across sites) and temporal patterns (across years); an important conclusion is that it is likely that neither of these accurately represents how productivity will respond to future phenological shifts resulting from ongoing climate change. In spring and autumn, increased GEP resulting from an 'extra' day tends to be offset by concurrent, but smaller, increases in ecosystem respiration, and thus the effect on NEP is still positive. Spring productivity anomalies Downloaded from appear to have carry-over effects that translate to productivity anomalies in the following autumn, but it is not clear that these result directly from phenological anomalies. Finally, the productivity of evergreen needleleaf forests is less sensitive to phenology than is productivity of deciduous broadleaf forests. This has implications for how climate change may drive shifts in competition within mixedspecies stands.
Ecological applications : a publication of the Ecological Society of America, Jan 1, 2010
We seek to understand how biophysical factors such as soil temperature (T s ), soil moisture (h),... more We seek to understand how biophysical factors such as soil temperature (T s ), soil moisture (h), and gross primary production (GPP) influence CO 2 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 CO 2 efflux (F 0 ) and soil CO 2 concentrations measurements. Here we explore how variation in T s , h, and GPP (derived from NASA's moderate-resolution imaging spectroradiometer [MODIS]) influence F 0 and soil CO 2 production (P s ). 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 CO 2 fluxes and T s , h, and GPP and (2) interactions and relationships between CO 2 fluxes with T s , h, and GPP. Mean annual T s did not explain annual F 0 and P s among vegetation types, but GPP explained 73% and 30% of the variation, respectively. We found evidence that lags between soil CO 2 fluxes and T s 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 F 0 and P s are different among vegetation types, but GPP is a dominant variable for explaining soil CO 2 fluxes. The emergence of long-term automated soil CO 2 flux measurement networks provides a unique opportunity for extended investigations into F 0 and P s processes in the near future.
•Although there is increasing evidence of the temporal correlation between photosynthesis and soi... more •Although there is increasing evidence of the temporal correlation between photosynthesis and soil CO2 efflux, no study has so far tested its generality across the growing season at multiple study sites and across several time scales.•Here, we used continuous (hourly) data and applied time series analysis (wavelet coherence analysis) to identify temporal correlations and time lags between photosynthesis and soil CO2 efflux for three forests from different climates and a grassland.•Results showed the existence of multi-temporal correlations at time periods that varied between 1 and 16 d during the growing seasons at all study sites. Temporal correlations were strongest at the 1 d time period, with longer time lags for forests relative to the grassland. The multi-temporal correlations were not continuous throughout the growing season, and were weakened when the effect of variations in soil temperature and CO2 diffusivity on soil CO2 efflux was taken into account.•Multi-temporal correlations between photosynthesis and soil CO2 efflux exist, and suggest that multiple biophysical drivers (i.e. photosynthesis, soil CO2 diffusion, temperature) are likely to coexist for the regulation of allocation and transport speed of carbon during a growing season. Future studies should consider the multi-temporal influence of these biophysical drivers to investigate their effect on the transport of carbon through the soil–plant–atmosphere continuum.Although there is increasing evidence of the temporal correlation between photosynthesis and soil CO2 efflux, no study has so far tested its generality across the growing season at multiple study sites and across several time scales.Here, we used continuous (hourly) data and applied time series analysis (wavelet coherence analysis) to identify temporal correlations and time lags between photosynthesis and soil CO2 efflux for three forests from different climates and a grassland.Results showed the existence of multi-temporal correlations at time periods that varied between 1 and 16 d during the growing seasons at all study sites. Temporal correlations were strongest at the 1 d time period, with longer time lags for forests relative to the grassland. The multi-temporal correlations were not continuous throughout the growing season, and were weakened when the effect of variations in soil temperature and CO2 diffusivity on soil CO2 efflux was taken into account.Multi-temporal correlations between photosynthesis and soil CO2 efflux exist, and suggest that multiple biophysical drivers (i.e. photosynthesis, soil CO2 diffusion, temperature) are likely to coexist for the regulation of allocation and transport speed of carbon during a growing season. Future studies should consider the multi-temporal influence of these biophysical drivers to investigate their effect on the transport of carbon through the soil–plant–atmosphere continuum.
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, Jan 1, 2010
We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (15... more We use eddy covariance measurements of net ecosystem productivity (NEP) from 21 FLUXNET sites (153 site-years of data) to investigate relationships between phenology and productivity (in terms of both NEP and gross ecosystem photosynthesis, GEP) in temperate and boreal forests. Results are used to evaluate the plausibility of four different conceptual models. Phenological indicators were derived from the eddy covariance time series, and from remote sensing and models. We examine spatial patterns (across sites) and temporal patterns (across years); an important conclusion is that it is likely that neither of these accurately represents how productivity will respond to future phenological shifts resulting from ongoing climate change. In spring and autumn, increased GEP resulting from an 'extra' day tends to be offset by concurrent, but smaller, increases in ecosystem respiration, and thus the effect on NEP is still positive. Spring productivity anomalies Downloaded from appear to have carry-over effects that translate to productivity anomalies in the following autumn, but it is not clear that these result directly from phenological anomalies. Finally, the productivity of evergreen needleleaf forests is less sensitive to phenology than is productivity of deciduous broadleaf forests. This has implications for how climate change may drive shifts in competition within mixedspecies stands.
Ecological applications : a publication of the Ecological Society of America, Jan 1, 2010
We seek to understand how biophysical factors such as soil temperature (T s ), soil moisture (h),... more We seek to understand how biophysical factors such as soil temperature (T s ), soil moisture (h), and gross primary production (GPP) influence CO 2 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 CO 2 efflux (F 0 ) and soil CO 2 concentrations measurements. Here we explore how variation in T s , h, and GPP (derived from NASA's moderate-resolution imaging spectroradiometer [MODIS]) influence F 0 and soil CO 2 production (P s ). 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 CO 2 fluxes and T s , h, and GPP and (2) interactions and relationships between CO 2 fluxes with T s , h, and GPP. Mean annual T s did not explain annual F 0 and P s among vegetation types, but GPP explained 73% and 30% of the variation, respectively. We found evidence that lags between soil CO 2 fluxes and T s 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 F 0 and P s are different among vegetation types, but GPP is a dominant variable for explaining soil CO 2 fluxes. The emergence of long-term automated soil CO 2 flux measurement networks provides a unique opportunity for extended investigations into F 0 and P s processes in the near future.
•Although there is increasing evidence of the temporal correlation between photosynthesis and soi... more •Although there is increasing evidence of the temporal correlation between photosynthesis and soil CO2 efflux, no study has so far tested its generality across the growing season at multiple study sites and across several time scales.•Here, we used continuous (hourly) data and applied time series analysis (wavelet coherence analysis) to identify temporal correlations and time lags between photosynthesis and soil CO2 efflux for three forests from different climates and a grassland.•Results showed the existence of multi-temporal correlations at time periods that varied between 1 and 16 d during the growing seasons at all study sites. Temporal correlations were strongest at the 1 d time period, with longer time lags for forests relative to the grassland. The multi-temporal correlations were not continuous throughout the growing season, and were weakened when the effect of variations in soil temperature and CO2 diffusivity on soil CO2 efflux was taken into account.•Multi-temporal correlations between photosynthesis and soil CO2 efflux exist, and suggest that multiple biophysical drivers (i.e. photosynthesis, soil CO2 diffusion, temperature) are likely to coexist for the regulation of allocation and transport speed of carbon during a growing season. Future studies should consider the multi-temporal influence of these biophysical drivers to investigate their effect on the transport of carbon through the soil–plant–atmosphere continuum.Although there is increasing evidence of the temporal correlation between photosynthesis and soil CO2 efflux, no study has so far tested its generality across the growing season at multiple study sites and across several time scales.Here, we used continuous (hourly) data and applied time series analysis (wavelet coherence analysis) to identify temporal correlations and time lags between photosynthesis and soil CO2 efflux for three forests from different climates and a grassland.Results showed the existence of multi-temporal correlations at time periods that varied between 1 and 16 d during the growing seasons at all study sites. Temporal correlations were strongest at the 1 d time period, with longer time lags for forests relative to the grassland. The multi-temporal correlations were not continuous throughout the growing season, and were weakened when the effect of variations in soil temperature and CO2 diffusivity on soil CO2 efflux was taken into account.Multi-temporal correlations between photosynthesis and soil CO2 efflux exist, and suggest that multiple biophysical drivers (i.e. photosynthesis, soil CO2 diffusion, temperature) are likely to coexist for the regulation of allocation and transport speed of carbon during a growing season. Future studies should consider the multi-temporal influence of these biophysical drivers to investigate their effect on the transport of carbon through the soil–plant–atmosphere continuum.
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