Environmental variables controlling soil respiration on diurnal, seasonal and annual time-scales in a mixed mountain forest in Switzerland

Studies on soil respiration in mountain forests are rather scarce compared to their broad distribution. Therefore, we investigated daily, seasonal and annual soil respiration rates in a mixed forest (Lägeren), located at about 700m in the Swiss Jura mountains, during 2years (2006 and 2007). Soil respiration (SR) was measured continuously with high temporal resolution (half-hourly) at one single point (SRautomated) and periodically with high spatial resolution (SRmanual) at 16 plots within the study site. Both, SRautomated and SRmanual showed a similar seasonal cycle. SR strongly depended on soil temperature in 2007 (R 2=0.82-0.92), but less so in 2006 (R 2=0.56-0.76) when SR was water limited during a summer drought. Including soil moisture improved the fit of the 2006 model significantly (R 2=0.78-0.97). Total annual SR for the study site was estimated as 869g C m−2year−1 for 2006 and as 907g C m−2year−1 for 2007 (uncertainty <10% at the 95% confidence interval, determined by bootstrapping). Selected environmental conditions were assessed in more detail: (1) Rapid, but contrasting changes of SR were found after summer rainfall. Depending on soil moisture at pre-rain conditions, summer rain could either cause a pulse of CO2 from the soil or an abrupt decrease of SRautomated due to water logging of soil pores. (2) Two contrasting winter seasons resulted in SR being about 60-70% (31.2-44.6g C m−2) higher during a mild winter (2007) compared to a harsh winter (2006). (3) Analysing SR for selected periods on a diurnal scale revealed a counter-clockwise hysteresis with soil surface temperatures. This indication of a time-lagged response of SR to temperature was further supported by a very strong relationship (R 2=0.86-0.90) of SR to soil temperature with a time-lag of 2-4

Representative estimates of soil and ecosystem respiration in an old beech forest

Respiration has been proposed to be the main determinant of the carbon balance in European forests and is thus essential for our understanding of the carbon cycle. However, the choice of experimental design strongly affects estimates of annual respiration and of the contribution of soil respiration to total ecosystem respiration. In a detailed study of ecosystem and soil respiration fluxes in an old unmanaged deciduous forest in Central Germany over 3years (2000-2002), we combined soil chamber and eddy covariance measurements to obtain a comprehensive picture of respiration in this forest. The closed portable chambers offered to investigate spatial variability of soil respiration and its controls while the eddy covariance system offered continuous measurements of ecosystem respiration. Over the year, both fluxes were mainly correlated with temperature. However, when soil moisture sank below 23vol.% in the upper 6cm, water limitations also became apparent. The temporal resolution of the eddy covariance system revealed that relatively high respiration rates occurred during budbreak due to increased metabolic activity and after leaf fall because of increased decomposition. Spatial variability in soil respiration rates was large and correlated with fine root biomass (r 2 = 0.56) resulting in estimates of annual efflux varying across plots from 730 to 1,258 (mean 898) g C m−2 year−1. Power function calculations showed that achieving a precision in the soil respiration estimate of 20% of the full population mean at a confidence level of 95%, requires about eight sampling locations. Our results can be used as guidelines to improve the representativeness of soil respiration measurements by nested sampling designs, being applied in long-term and large-scale carbon sequestration projects such as FLUXNET and CarboEurop

Estimation of Oil Palm Total Carbon Fluxes Using Remote Sensing

Net primary production (NPP) is one of the approaches used to estimate the amount of carbon sequestration by plants. This research aims to estimate the total carbon flux exchanged from different ages of oil palm using remote sensing.&nbsp; The study site was at the PTPN VI Batang Hari, Jambi, Sumatra, Indonesia. The amount of carbon sequestration by oil palm plantations at PTPN VI Batang Hari, Jambi can be estimated using remote sensing based on the light use efficiency (LUE) model.&nbsp; The results showed that the oil palm age affects the amount of carbon sequestrated.&nbsp; The lowest Net primary production value was found at one year of planting 4.28 gCm-2day-1, and the highest was 9.38 gCm-2day-1 at 20 years of planting. The model LUE output was validated using Eddy covariance data and the results showed a low error and a high accuracy rate with RMSE = 0.05 gCMJ-1, R2 = 92%, and p-value = 0.04. We concluded that the LUE model can be used with high accuracy to estimate the amount of carbon absorption of oil palm when direct measurement is unavailable

Selected breakpoints of net forest carbon uptake at four eddy-covariance sites

Extensive studies are available that analyse time series of carbon dioxide and water flux measurements of FLUXNET sites over many years and link these results to climate change such as changes in atmospheric carbon dioxide concentration, air temperature and growing season length and other factors. Many of the sites show trends to a larger carbon uptake. Here we analyse time series of net ecosystem exchange, gross primary production, respiration, and evapotranspiration of four forest sites with particularly long measurement periods of about 20 years. The regular trends shown are interrupted by periods with higher or lower increases of carbon uptake. These breakpoints can be of very different origin and include forest decline, increased vegetation period, drought effects, heat waves, and changes in site heterogeneity. The influence of such breakpoints should be included in long-term studies of land-atmosphere exchange processes.Peer reviewe

Soil H218O labelling reveals the effect of drought on C18OO fluxes to the atmosphere

Concurrent and continuous measurements of the 18O/16O ratio in CO2 and H2Ov after a H2 18O labelling showed that drought reduces the 18O-equilibrium between CO2 and H2O at the shoot leve

Vulnerability of Primary Productivity and Its Carbon Use Efficiency to Unfavorable Climatic Conditions in Jambi Province, Indonesia

Climatic conditions and land cover play crucial roles in influencing the process of carbon uptake through vegetation. This study aimed to analyze the effect of climate variability on carbon uptake of four different land covers in Jambi Province, Indonesia. The four land cover types studied were: forest, shrub, grass, and irrigated soybean, based on Community Land Model version 5. Forest was found to have the highest net primary production (NPP) compared to the other land covers. Seasonal climate variability showed no major effect on NPP and gross primary production (GPP). However, GPP and NPP experienced significant declines during El Niño Southern Oscillation (ENSO), particularly in 2015. Carbon use efficiency (CUE = NPP/GPP) was also affected by ENSO, where CUE decreased during El Niño, particularly in October and November with an increased number of days without rainfall. In addition, the difference between latent (LE) and sensible heat (H) flux, denoted as (LE-H), decreased from August to November. This difference was highly correlated with NPP. This result indicates that when water supply is low, stomata will close, thereby reducing photosynthesis and transpiration, and allocating more of the available energy to sensible heat flux rather than latent heat flux

Reducing wind erosion through agroforestry: a case study using large Eddy simulations

Wind erosion is seen as one of the main risks for modern agriculture in dry and sandy regions. Shelterbelts and agroforestry systems are known for their ability to reduce wind speed and, consequently, wind erosion. The current study considers temperate alley cropping agroforestry systems, where multiple tree strips (shelterbelts) are interleaved with either annual rotating crops or perennial grassland. The aim was to quantify the potential wind erosion reduction by alley cropping agroforestry systems and the effect of design decisions for a case study in Germany. By combining wind measurements and Large Eddy Simulations, the wind speed and potential wind erosion inside an agroforestry system were estimated. Our model simulations result in an average reduction in wind speed between 17% and 67%, and a reduction of average potential wind erosion between 24% and 97%. The most optimal reduction of the average potential wind erosion was larger than 92% for tree strips orientated perpendicular to the main wind direction, whereas for a diagonal orientation of the tree strips to the main wind direction we found an average reduction of 86%. Parallel orientated tree strips reduce wind erosion on average by less than 35%. Tree strips planted with ≤48 m distance provide a strong and constant reduction of wind erosion, even for tree strips of 2 m height the average reduction was 86%, when the tree strips were orientated optimal to the dominant wind direction. Our model simulations showed that alley cropping agroforestry systems in a temperate climate have a large potential to reduce wind erosion by more than 80% when the system is well-designed and managed