| 3. |
- Giasson, M-A, et al.
(författare)
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Soil respiration in a northeastern US temperate forest : a 22-year synthesis
- 2013
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Ingår i: Ecosphere. - 2150-8925 .- 2150-8925. ; 4:11, s. UNSP 140-
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Tidskriftsartikel (refereegranskat)abstract
- To better understand how forest management, phenology, vegetation type, and actual and simulated climatic change affect seasonal and inter-annual variations in soil respiration (R-s), we analyzed more than 100,000 individual measurements of soil respiration from 23 studies conducted over 22 years at the Harvard Forest in Petersham, Massachusetts, USA. We also used 24 site-years of eddy-covariance measurements from two Harvard Forest sites to examine the relationship between soil and ecosystem respiration (R-e). R-s was highly variable at all spatial (respiration collar to forest stand) and temporal (minutes to years) scales of measurement. The response of R-s to experimental manipulations mimicking aspects of global change or aimed at partitioning R-s into component fluxes ranged from similar to 70% to +52%. The response appears to arise from variations in substrate availability induced by changes in the size of soil C pools and of belowground C fluxes or in environmental conditions. In some cases (e.g., logging, warming), the effect of experimental manipulations on R-s was transient, but in other cases the time series were not long enough to rule out long-term changes in respiration rates. Inter-annual variations in weather and phenology induced variation among annual R-s estimates of a magnitude similar to that of other drivers of global change (i.e., invasive insects, forest management practices, N deposition). At both eddy-covariance sites, aboveground respiration dominated R-e early in the growing season, whereas belowground respiration dominated later. Unusual aboveground respiration patterns-high apparent rates of respiration during winter and very low rates in mid-to-late summer-at the Environmental Measurement Site suggest either bias in R-s and R-e estimates caused by differences in the spatial scale of processes influencing fluxes, or that additional research on the hard-to-measure fluxes (e.g., wintertime R-s, unaccounted losses of CO2 from eddy covariance sites), daytime and nighttime canopy respiration and its impacts on estimates of R-e, and independent measurements of flux partitioning (e.g., aboveground plant respiration, isotopic partitioning) may yield insight into the unusually high and low fluxes. Overall, however, this data-rich analysis identifies important seasonal and experimental variations in R-s and R-e and in the partitioning of R-e above-vs. belowground.
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| 5. |
- Olsrud, Maria, et al.
(författare)
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Response of ericoid mycorrhizal colonization and functioning to global change factors
- 2004
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Ingår i: New Phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 162:2, s. 459-469
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Tidskriftsartikel (refereegranskat)abstract
- Here, we investigated effects of increased atmospheric CO2 concentration, increased temperatures, and both factors in combination on ericoid mycorrhizal colonization, mycorrhizal functioning and below-ground carbon allocation in a subarctic forest understorey, to evaluate the hypothesis that photosynthesis is a primary driver for mycorrhizal colonization. Treatment effects on ecosystem processes were investigated using C-14-pulse labelling and photosynthesis measurements in combination with analysis of ergosterol content in roots. The effects on delta(15)N in leaves were also studied. Ergosterol content in hair roots was positively correlated with ecosystem photosynthesis and was higher in heat- and CO2-treated plots. Leaves from CO2 Plots tended to be more depleted in N-15 compared with controls both for Vaccinium myrtillus and V. vitis-idaea. Our results suggest that changes in ecosystem photosynthesis, plant carbon (C) Allocation may give rise to changing mycorrhizal colonization under elevated CO2 and temperature. The role of mycorrhizas in ecosystem N-cycling may change on a long-term basis as inorganic N availability declines with increasing levels of atmospheric CO2.
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