Estimating leaf area index in different types of mature forest stands in Switzerland: a comparison of methods

Leaf area index (LAI) was estimated at 15 sites in the Swiss Long-Term Forest Ecosystem Research Programme (LWF) in 2004-2005 using two indirect techniques: the LAI-2000 plant canopy analyzer (Licor Inc.) and digital hemispherical photography, applying several exposure settings. Hemispherical photographs of the canopy were analysed using Hemisfer, a software package that offers several new features, which were tested here: (1) automatic thresholding taking the gamma value of the picture into account; (2) implementation of several equations to solve the gap-fraction inversion model from which LAI estimates are derived; (3) correction for ground slope effects, and (4) correction for clumped canopies. In seven broadleaved stands in our sample set, LAI was also estimated semi-directly from litterfall. The various equations used to solve the gap-fraction inversion model generated significantly different estimates for the LAI-2000 measurements. In contrast, the same equations applied in Hemisfer did not produce significantly different estimates. The best relationship between the LAI-2000 and the Hemisfer estimates was obtained when the hemispherical photographs were overexposed by one to two stops compared with the exposure setting derived from the reading of a spotmeter in a canopy gap. There was no clear general relationship between the litterfall and the LAI-2000 or the hemispherical photographs estimates. This was probably due to the heterogeneity of the canopy, or to biased litterfall collection at sites on steep slopes or sites subject to strong winds. This study introduces new arguments into the comparison of the advantages and drawbacks of the LAI-2000 and hemispherical photography in terms of applicability and accurac

Retention and Leaching of Elevated N Deposition in a Forest Ecosystem with Gleysols

The responses of nitrogen transformations and nitrate (NO_3 -) leaching to experimentally increased N deposition were studied in forested sub-catchments (1500 m2) with Gleysols in Central Switzerland. The aim was toinvestigate whether the increase in NO3 - leaching,due to elevated N deposition, was hydrologically driven orresulted from N saturation of the forest ecosystem.Three years of continuous N addition at a rate of 30 kgNH4NO3-N ha-1 yr-1 had no effects on bulksoil N, on microbial biomass N, on K2SO4-extractableN concentrations in the soil, and on net nitrification rates.In contrast, N losses from the ecosystem through denitrification and NO3 - leaching increased significantly. Nitrate leaching was 4 kg N ha-1yr-1at an ambient N deposition of 18 kg N ha-1 yr-1.Leaching of NO3 - at elevated N deposition was 8 kg Nha-1 yr-1. Highest NO3 - leaching occurredduring snowmelt. Ammonium was effectively retained within theuppermost centimetres of the soil as shown by the absence ofNH4 + in the soil solution collected with microsuction cups. Quantifying the N fluxes indicated that 80% ofthe added N were retained in the forest ecosystem.Discharge and NO3 - concentrations of the outflow from the sub-catchments responded to rainfall within 30 min. The water chemistry of the sub-catchment outflow showed thatduring storms, a large part of the runoff from this Gleysol derived from precipitation and from water which had interactedonly with the topsoil. This suggests a dominance of near-surface flow and/or preferential transport through this soil. The contact time of the water with the soil matrix wassufficient to retain NH4 +, but insufficient for a complete retention of NO3 -. At this site with soilsclose to water saturation, the increase in NO3 - leaching by 4 kg N ha-1 yr-1 through elevated N inputsappeared to be due to the bypassing of the soil and the rootsystem rather than to a soil-internal N surplu

Long-term additions of ammonium nitrate to montane forest ecosystems may cause limited soil acidification, even in the presence of soil carbonate

Nitrogen (N) deposition has decreased in the last decades in Europe but in many cases remains higher than the critical loads, i.e., higher than what could be considered safe for biodiversity and ecosystem functioning. The main concerns about N deposition are eutrophication and acidification. In a long-term experiment (1994 to present) in a montane (1200 m a.s.l.) coniferous forest in Alptal, central Switzerland, we simulated increased N deposition by adding NH4NO3 to rainwater. This treatment consisted of an additional N input of 22 kg ha−1 yr−1 to the 12 kg ha−1 yr−1 ambient bulk deposition rate or 17 kg N ha−1 yr−1 throughfall rate. The treatment was applied simultaneously to a small catchment area and to plots in a replicated block experiment (n=5). The site has a carbonate-rich parent material and is thus not particularly at risk of acidification. Nevertheless, we examined soil acidification as affected both by ambient and experimentally increased N deposition. In the 2.5 decades since the beginning of the study, nitrate (NO3-) and especially sulfate (SO42-) concentrations decreased in precipitation, while pH increased by slightly more than 1 unit. In the same time period a reduction in pH of the soil was measured. The exchangeable acidity in the soil increased, especially in the N-addition treatment. This was mainly observed on small mounds because the drier mounds are less well buffered than wet depressions. This trend, however, was limited in time, as exchangeable acidity later declined again to reach values not much higher than 26 years before. This was also the case in the N-addition treatment and can be considered a progressive recovery mainly due to the reduced acid inputs and, at this site with a carbonate-rich subsoil, to the biological cycling of base cations. The pH of the runoff from the experimental catchments decreased by 0.3 units, both in the control and under N addition. Decreasing Ca2+ and increasing Al3+ and Fe2+ concentrations in runoff also show that the recovery observed in the exchangeable soil acidity is not yet able to stop the slow acidification of water leaving the catchments. However, with the runoff water pH remaining above 7, this trend is not alarming for water quality or for the health of water bodies. Future monitoring will be necessary to see if and when a recovery takes place in the soil and runoff pH.</p

Flow of Deposited Inorganic N in Two Gleysol-dominated Mountain Catchments Traced with 15NO3− and 15NH4+

Abstract.: In two mountain ecosystems at the Alptal research site in central Switzerland, pulses of 15NO3 and 15NH4 were separately applied to trace deposited inorganic N. One forested and one litter meadow catchment, each approximately 1600m2, were delimited by trenches in the Gleysols. K15NO3 was applied weekly or fortnightly over one year with a backpack sprayer, thus labelling the atmospheric nitrate deposition. After the sampling and a one-year break, 15NH4Cl was applied as a second one-year pulse, followed by a second sampling campaign. Trees (needles, branches and bole wood), ground vegetation, litter layer and soil (LF, A and B horizon) were sampled at the end of each labelling period. Extractable inorganic N, microbial N, and immobilised soil N were analysed in the LF and A horizons. During the whole labelling period, the runoff water was sampled as well. Most of the added tracer remained in both ecosystems. More NO3− than NH4+ tracer was retained, especially in the forest. The highest recovery was in the soil, mainly in the organic horizon, and in the ground vegetation, especially in the mosses. Event-based runoff analyses showed an immediate response of 15NO3− in runoff, with sharp 15N peaks corresponding to discharge peaks. NO3− leaching showed a clear seasonal pattern, being highest in spring during snowmelt. The high capacity of N retention in these ecosystems leads to the assumption that deposited N accumulates in the soil organic matter, causing a progressive decline of its C:N rati

Using lunar in-situ resources for the production of solar conversion devices

The European Space Agency’s vision is to establish a permanent research outpost on the lunar surface in the coming years. For building and establishing such an outpost, the overall mass/equipment, which can directly be transported from Earth to the Moon’s surface, is limited by physics and hence are such a mission’s capabilities. To expand these capabilities, it will be required to free up mass on the re-supply flights from Earth, this can be done by using lunar regolith material to augment building and operating an outpost on the lunar surface. At present, a burden of proof exists on technologies using such in-situ resources and mission designers are conservative in their integration of such technologies and methodologies for future exploration missions. To change that, by advancing the technology readiness level (TRL) of such technologies, one of the heaviest systems of a lunar outpost, the energy system, was targeted to be augmented by means of using local resources. This was done by first, finding and analysing suitable (analogue) building material, second, how these materials can be used to manufacture glasses and third, how power harvesting systems can be build from these glasses. To successfully complete all three steps, characterisation of analogue regolith materials (simulants) by means of XRD, XRF, SEM/EDX and microscopy as well as characterisation of all manufactured devices by means of analysis of surface quality, reflectivity, transmission, I-V curves, EQE and efficiencies was required. Analysis showed that no commercially available simulant is mineralogically and geo-chemically reassembling all aspects of the lunar regolith. Thus, to maximize the possibility that manufacturing will work using actual lunar regolith, a variety of up to six different simulants was used and in some cases magnetically beneficiated. Next, the key challenge was how to using these six to manufacture a stable glass substrate with a defect free and flat surface, suitable for further manufacturing. After successfully manufacturing such substrates; transparent glass, mirrors, solar concentrators and solar cells were built. By characterising the substrates surface quality, reflectivity and transmission as well as the devices’ I-V curves, EQE and efficiencies, it could be concluded that all manufactured devices show a similar performance compared to off-the-shelf components. Best solar cells devices achieved efficiencies of > 3 %, about 35 % lower than reference cells. The conducted investigations have shown for the first time, that it is possible to manufacture: glass substrates, mirrors, solar concentrators, solar cells and transparent glass by exploiting lunar resources. Next steps will require testing under lunar like conditions, to show how it may be possible to advance these devices into becoming technologies to be used on an actual lunar mission

Long-term tracing of whole catchment 15N additions in a mountain spruce forest: measurements and simulations with the TRACE model

Despite numerous studies on nitrogen (N) cycling in forest ecosystems, many uncertainties remain, particularly regarding long-term N accumulation in the soil. Models validated against tracer isotopic data from field labeling experiments provide a potential tool to better understand and simulate C and N interactions over multiple decades. In this study, we describe the adaptation of the dynamic process-based model TRACE to a new site, Alptal, where long-term N-addition and 15N-tracer experiments provide unique datasets for testing the model. We describe model parameterization for this spruce forest, and then test the model with 9- and 14-year time series of 15N-tracer recovery from control and N-amended catchments, respectively. Finally, we use the model to project the fate of ecosystem N accumulation over the next 70years. Field 15N recovery data show that the major sink for N deposition is the soil. On the control plot, tracer recovery in the soil increased from 32% in the second year to 60% in the ninth year following tracer addition, whereas on the N-saturated plot, soil recovery stayed almost constant from 63% in the third year to 61% in the twelfth year. Recovery in tree biomass increased over the decadal time scale in both treatments, to ca. 10% over 9years on the control plot and ca. 13% over 14years on the N-amended plot. We then used these time series to validate TRACE, showing that the adaptation and calibration procedure for the Alptal site was successful. Model-data comparison identified that the spreading method of 15N tracers needs to be considered when interpreting recovery results from labeling studies. Furthermore, the ground vegetation layer was recognized to play an important role in controlling the rate at which deposited N enters soil pools. Our 70-year model simulation into the future underpinned by a Monte-Carlo sensitivity analysis, suggests that the soil is able to immobilize a constant fraction of 70 and 77% of deposited N for the treated and the control plot, respectively. Further, the model showed that the simulated increased N deposition resulted in a relatively small elevated C sequestration in aggrading wood with an N use efficiency of approximately 7kg C per kgN adde

Seasonal variations of throughfall chemistry in pure and mixed stands of Oriental beech (Fagus orientalis Lipsky) in Hyrcanian forests (Iran)

International audienceAbstractKey messageThroughfall nutrient fluxes were generally higher in a mixed stand than in a pure stand of Oriental beech. Throughfall fluxes were higher than bulk precipitation fluxes except for nitrogen and indicate higher canopy uptake of this element in the pure stand compared to the mixed stand.ContextOriental beech is an economically relevant tree species for Iran and adjacent countries. Yet little is known about nutrient cycling in Oriental beech stands and the influence of the degree of mixture with other species.AimsWe assessed the effect of seasons on nutrient fluxes in precipitation and whether throughfall chemistry differed between pure and mixed stands.MethodsBulk precipitation in the open field and throughfall were sampled during one whole month within each season from August 2013 to May 2014 in a pure (81 % of beech trees on average) and a mixed stand (57 % of beech trees) of Oriental beech. Samples were analysed for pH, nitrate (NO3−), ammonium (NH4+), phosphorus (P), calcium (Ca2+), magnesium (Mg2+) and potassium (K+).ResultsNutrient concentrations were generally higher in the growing season than in the dormant season, both in bulk precipitation and in throughfall. Nutrient fluxes were higher in fall and these peaks coincided with higher amounts of precipitation. The concentrations and fluxes of NH4+, NO3−, P, Ca2+, Mg2+ and K+ were generally higher in the mixed stand than in the pure stand in all seasons. Compared to the open field, throughfall fluxes were usually higher, except for NO3− and NH4+, indicating direct canopy uptake of nitrogen.ConclusionCanopy composition in Oriental beech stands (owing to differences in foliage chemistry) and seasons (owing to differences in precipitation regime and phenological stages) have a significant effect on throughfall nutrient fluxes