Dalibor Janouš

Dependence of the Q10 values on the depth of the soil temperature measuring point

The parameter Q10 is commonly used to express the relationship between soil CO2 efflux and soil temperature. One advantage of this parameter is its application in a model expression of respiration losses of different ecosystems. Correct specification of Q10 in these models is indispensable. Soil surface CO2 efflux and soil temperature at different depths were measured in a 21-year-old Norway spruce stand and a mountain grassland site located at the Experimental Ecological Study Site Bily Kriz, Beskydy Mts. (NE Czech Republic), using automated gasometric systems. A time-delay and goodness-of-fit between soil CO2 efflux and soil temperature at different measuring depths were determined. Wide ranges of values for the time-delay of CO2 efflux in response to temperature, Q10 and the determination coefficient (R2) between CO2 efflux and temperature were obtained at the both sites. The values of Q10 and the CO2 time-delay increased with depth, while the R2 of the CO2-temperature relationship significantly decreased. Soil temperature records obtained close to the soil surface showed the highest values of R2 and the lowest value of the time-delay at both sites. Measurement of soil temperature at very shallow soil layer, preferably at the soil surface, is highly recommended to determine useable values of Q10. We present a new procedure to normalize Q10 values for soil temperatures measured at different depths that would facilitate comparison of different sites.

A new mass conservation approach to the study of CO2 advection in an alpine forest

A new method is proposed for the computation of CO2 Net Ecosystem Exchange (NEE) and its components in a forest ecosystem. Advective flux is estimated by taking into account the air mass conservation principle. For this purpose, wind and dry air density values on the surface of the control volume are first corrected and then the advective flux is estimated on the surface of the control volume. Turbulent flux is also computed along the surface of the control volume while storage flux is computed inside the volume. Additional characteristics of this method are that incompressibility of the mean flow is not assumed a priori, and that vertical and horizontal advective fluxes are not treated separately, but their sum is estimated directly. The methodology is applied to experimental data collected with a three-dimensional scheme at the alpine site of Renon during the Advex project (July 2005). The advection flux was found to be prevailing positive at night and negative during the day, as was found in previous studies on advection for the same site, but showed a lower scatter in half-hour calculated values. We tested the effect of its summation on turbulent and storage fluxes to produce half-hourly values of NEE. Nighttime NEE values were used in functional relations with soil temperature, daytime values with PPFD. The effect of addition of the advection component was an increase in the values of parameters indicating ecosystem respiration, quantum yield, and photosynthetic capacity. The coefficient of correlation between NEE and environmental drivers increased. (Less)

The significance of D-amino acids in soil, fate and utilization by microbes and plants: review and identification of knowledge gaps

BackgroundD-amino acids are far less abundant in nature than L-amino acids. Both L- and D-amino acids enter soil from different sources including plant, animal and microbial biomass, antibiotics, faeces and synthetic insecticides. Moreover, D-amino acids appear in soil due to abiotic or biotic racemization of L-amino acids. Both L- and D-amino acids occur as bound in soil organic matter and as “free“ amino acids dissolved in soil solution or exchangeably bound to soil colloids. D-amino acids are mineralized at slower rates compared to the corresponding L-enantiomers. Plants have a capacity to directly take up “free“ D-amino acids by their roots but their ability to utilize them is low and thus D-amino acids inhibit plant growth.ScopeThe aim of this work is to review current knowledge on D-amino acids in soil and their utilization by soil microorganisms and plants, and to identify critical knowledge gaps and directions for future research.ConclusionAssessment of “free“ D-amino acids in soils is currently complicated due to the lack of appropriate extraction procedures. This information is necessary for consequent experimental determination of their significance for crop production and growth of plants in different types of managed and unmanaged ecosystems. Hypotheses on occurrence of “free“ D-amino acids in soil are presented in this review.

Glass Domes with Adjustable Windows: A Novel Technique for Exposing Juvenile Forest Stands to Elevated CO2 Concentration

We present a new technological approach for in situ investigation of long-term impacts of elevated CO2 concentration (EC) on juvenile forests characterised by an intensive community level and canopy closure phase. Construction of the glass domes is based on the properties of earlier tested open-top chambers (OTCs). An air climatisation device together with an adjustable window system, that forms the shell cover of the domes, is able to keep the required [CO2] in both time and spatial scales with the relatively small consumption of supplied CO2. This is achieved by half-closing the windows on the windward side. We evidenced good coupling of treated trees to the atmosphere, including mutual interactions among trees. The semi-open design of the domes moderates the problems of strong wind, humidity, and temperature gradients associated with OTCs. The frequency distributions of the environmental variations within the domes indicate that: air temperature is maintained within the ambient range ±1.0 °C for ca. 80 % of the time, and changes in the relative air humidity vary from −15 to 0 % for ca. 82 % of the time. The most important chamber effect is associated with the penetration of solar irradiance, which is reduced by 26 % compared to the open condition outside the domes. The dimensions of the domes are 10×10 m in length and 7 m high in the central part. The experiment was done in three identical stands of twelve-year-old Norway spruce trees. The 56 trees are planted at two different spacings to estimate the impacts of stand spatial structure in relation to EC.

Ozone flux over a Norway spruce forest and correlation with net ecosystem production.

Daily ozone deposition flux to a Norway spruce forest in Czech Republic was measured using the gradient method in July and August 2008. Results were in good agreement with a deposition flux model. The mean daily stomatal uptake of ozone was around 47% of total deposition. Average deposition velocity was 0.39 cm s(-1) and 0.36 cm s(-1) by the gradient method and the deposition model, respectively. Measured and modelled non-stomatal uptake was around 0.2 cm s(-1). In addition, net ecosystem production (NEP) was measured by using Eddy Covariance and correlations with O3 concentrations at 15 m a.g.l., total deposition and stomatal uptake were tested. Total deposition and stomatal uptake of ozone significantly decreased NEP, especially by high intensities of solar radiation.

Chamber Effects and Responses of Trees in the Experiment using Open Top Chambers

Summary Chamber effects are unintentional concomitants of experiments using open-top field chambers (OTCs). Cylindrical OTCs were used in a mountain Norway spruce stand. Chamber effects were investigated as well comparing samples in OTCs with ambient air and samples not enclosed in OTCs (control). The OTCs were 2.5 m in diametet at the base, 6.0 m high and the volume was 20 m 3 . The iron frames were covered by transparent 0.2 mm PVC film. Changes of growth conditions as follows: Transmission of the chambers covered by a new clear film was 91 ± 2% of the solar photosynthetically active radiation (84 ± 4% at the end of the growing season). Mean air temperatures inside OTCs were 1.3 °C higher than outside OTCs on sunny days. Inside there were decreases in relative humidity during the sunny hours by as much as 10%. Responses of the trees as follows: Continual increase of chlorophyll content ( a + b ) was recorded during the cultivation of the trees in the OTCs in comparison with the control (76%). A similar situation was observed for the carotenoids content. We recorded seasonal increases of F v /F max values and the t 1/2 parameter in the OTCs in comparison with the control treatment. At the beginning of the seasons (1993 and 1994) stem tespiration was gteater in the control than in the OTC (70% and 85% of the control) but at the end of the seasons the situation was opposite (115 % and 230% of the control). No differences were found in the development of apical shoots. Differences were found only in length increases of whorl branches, in the season 1994 (p=0.01). The length increase in the OTCs was greater by 38%.

Carbon exchange between ecosystems and atmosphere in the Czech Republic is affected by climate factors.

By comparing five ecosystem types in the Czech Republic over several years, we recorded the highest carbon sequestration potential in an evergreen Norway spruce forest (100%) and an agroecosystem (65%), followed by European beech forest (25%) and a wetland ecosystem (20%). Because of a massive ecosystem respiration, the final carbon gain of the grassland was negative. Climate was shown to be an important factor of carbon uptake by ecosystems: by varying the growing season length (a 22-d longer season in 2005 than in 2007 increased carbon sink by 13%) or by the effect of short- term synoptic situations (e.g. summer hot and dry days reduced net carbon storage by 58% relative to hot and wet days). Carbon uptake is strongly affected by the ontogeny and a production strategy which is demonstrated by the comparison of seasonal course of carbon uptake between coniferous (Norway spruce) and deciduous (European beech) stands.

Long-Term Effects of Elevated CO2 on Woody Tissues Respiration of Norway Spruce Studied in Open-Top Chambers

In an open-top chamber experiment located in a mountain stand of 14-years-old Norway spruce (Picea abies [L.] Karst.), trees were continuously exposed to either ambient CO2 concentration (A), or ambient + 350 µmol mol−1 (E) over four growing seasons. Respiration rates of different woody parts (stem, branches, coarse roots) were measured during the last growing season. The calculated increase in the respiration rate related to a 10 °C temperature change (Q10) was different in stem compared to branches and roots. Differences between the E and A variants were statistically significant only for roots in the autumn. Stem maintenance respiration (RMs) measured in April and November (periods of no growth activity) were not different. The stem respiration values (Rs) were recalculated to a standard temperature of 15 °C to estimate the seasonal course. The obtained Rs differed significantly between used variants during July and August. At the end of the season, Rs in E decreased slower than in A, indicating some prolongation of the physiological activity under the elevated CO2 concentration. The total stem respiration carbon losses for the investigated growing season (May – September) were higher for A (2.32 kg(C) m−2 season−1) compared to E (2.12 kg(C) m−2 season−1). The respiration rates of the whorl branches (Rb) were lower compared with the stem respiration but not significantly different between the used variants. The root respiration rate was increased in E variant.

Extreme warm temperatures alter forest phenology and productivity in Europe

Recent climate warming has shifted the timing of spring and autumn vegetation phenological events in the temperate and boreal forest ecosystems of Europe. In many areas spring phenological events start earlier and autumn events switch between earlier and later onset. Consequently, the length of growing season in mid and high latitudes of European forest is extended. However, the lagged effects (i.e. the impact of a warm spring or autumn on the subsequent phenological events) on vegetation phenology and productivity are less explored. In this study, we have (1) characterised extreme warm spring and extreme warm autumn events in Europe during 2003-2011, and (2) investigated if direct impact on forest phenology and productivity due to a specific warm event translated to a lagged effect in subsequent phenological events. We found that warmer events in spring occurred extensively in high latitude Europe producing a significant earlier onset of greening (OG) in broadleaf deciduous forest (BLDF) and mixed forest (MF). However, this earlier OG did not show any significant lagged effects on autumnal senescence. Needleleaf evergreen forest (NLEF), BLDF and MF showed a significantly delayed end of senescence (EOS) as a result of extreme warm autumn events; and in the following years spring phenological events, OG started significantly earlier. Extreme warm spring events directly led to significant (p=0.0189) increases in the productivity of BLDF. In order to have a complete understanding of ecosystems response to warm temperature during key phenological events, particularly autumn events, the lagged effect on the next growing season should be considered.

Branch CO2 efflux in vertical profile of Norway spruce tree

Branch CO2 efflux of Norway spruce tree [Picea abies (L.) Karst.] was measured in ten branches at five different whorls during the growing season 2004 (from June till October) in campaigns of 3–4 times per month at the Beskydy Mts., the Czech Republic. Branch CO2 efflux was measured using a portable infrared gas analyzer (LI-6250, LI-COR, Inc., USA), operating as a closed system. Branch woody-tissue temperature was measured continuously in 10-min intervals for each sample position during the whole experiment period. On the basis of relation between CO2 efflux rate and woody-tissue temperature, a value of Q10 and of normalized CO2 efflux rate (E10–CO2 efflux rate at 10°C) was calculated for each sampled position. Estimated Q10 values ranged from 2.12 to 2.89, and E10 ranged from 0.41 to 1.19 μmolCO2m−2s−1. Differences in branch CO2 efflux were found between orientations, east-side branches presented higher efflux rate than west-side branches. The highest branch CO2 efflux rate values were measured in August and the lowest in October, which corresponds with woody-tissue temperature and growth processes during these periods. Branch CO2 efflux was significantly and positively correlated with branch position within canopy and woody-tissue temperature. Branches from the upper whorls showed higher CO2 efflux activity and seasonal dynamics than branches from the lower whorls.