Mechanisms of carbon and nutrient release and retention in beech forest gaps

Fluxes of CO₂ and N₂O were measured along a microclimatic gradient stretching from the centre of a gap into a mature beech stand using an automated chamber method. Simultaneously the regulating factors like soil water tensions, soil temperatures, nitrate concentrations were measured along the gradient. The daily mean values of the fluxes of CO₂ and N₂O were divided into classes of temperature and furthermore subdivided into classes of soil water tension to assess the significance of each regulating factor.Soil respiration at the centre of the gap was 40% lower compared to the rooted mature stand. The difference was explained by root respiration. At both sites soil respiration was primarily controlled by the soil temperature with an average Q₁₀ value of 2.3 over the different classes of temperature and soil water tension. Soil water tension reduced the soil respiration by up to 20% only by soil water tension above 400–600 hPa at the mature stand. The formation of N₂O was reduced when the soil temperature was below 10°C or the soil water tension exceeded 200 hPa. Therefore the N₂O emission was 6 times higher at the unrooted centre of the gap due to the high moisture content in the growing season. Higher nitrate concentration doubled the N₂O emission at the unrooted edge of the canopy and resulted in losses of 6.4 kg N ha^-1 within six months. Above 10°C and below 200 hPa the N₂O emission depended strongly upon the temperature with varying Q₁₀ values over the different classes of temperature and soil water tension. High Q₁₀ values up to 14.4 have been calculated below 14°C and were explained by several processes with synergetic effects.     

Monte Carlo investigation on the effect of air gap under bolus in post-mastectomy radiotherapy

ObjectivesTo investigate the dosimetric effect of air gaps under bolus on skin dose for left-sided post-mastectomy radiotherapy with loco regional involvement.MethodsEight patients were planned retrospectively with volume modulated arc therapy (VMAT) and conventional static Field-in-Field (FinF) methods. Three different setups were applied for the 5-mm bolus over the chest wall having 0, 5 or 10 mm air gap under the bolus. The dose calculation was performed using Monte Carlo (MC) simulation. In addition, Analytic Anisotropic Algorithm (AAA) was used to demonstrate the differences observed in clinical setting.ResultsThe investigated air gaps under the bolus had minimal effect on surface dose for FinF plans (relative difference ≤ 2.6%), whereas for VMAT plans the surface dose decreased 13.6% when compared to the case with no air gap. In both FinF and VMAT, the largest differences between AAA and MC were seen at the surface where AAA underestimated the dose by 1.5 Gy (p < 0.05) on average; while the dose in the target volume excluding the surface was relatively similar being on average 0.3 Gy (p > 0.05) larger with AAA than with MC calculations.ConclusionsThe surface dose was significantly lower with VMAT technique than with FinF technique. Possible air gaps under the bolus reduced the surface dose significantly further for VMAT but not for FinF treatments, which may have clinical impact on recurrence rate. AAA was shown to underestimate the surface dose when compared to MC calculation.     

Composition and diversity of herbaceous patches in woody vegetation: The effects of grazing,soil seed bank,patch spatial properties and scale

Herbaceous plants contribute much to plant diversity in Mediterranean-type ecosystems though mostly occupying relatively small patches within the dense woody vegetation. While studying species diversity in the herbaceous patches, we hypothesized that grazing, soil seed bank, and spatial properties of the patch affect plant diversity and composition at different spatial scales. The study site was in an LTER site located in the Mediterranean region in north Israel. We determined herbaceous species composition in: (1) randomly sampled quadrats in herbaceous patches in grazed and un-grazed plots; (2) soil seed bank samples taken from the same patches and germinated under optimal greenhouse conditions; (3) quadrats in the same patches sown with a homogenous mixture of local soil samples. Using GIS methods, we determined small-scale spatial characteristics of the herbaceous patches. Alpha and beta diversities were calculated at the patch and plot scales using Shannon's entropy H. Grazing increased alpha diversity of local untreated seed bank samples but decreased alpha diversity of the artificial homogenous soil seed bank mixture at both patch and plot scales. Positive relation between alpha diversity and patch area was detected only under grazing. Grazing increased beta diversity in all three treatments at the patch scale. Grazing decreased the similarity in species composition between above-ground vegetation and soil seed bank. The results indicate that moderate cattle-grazing affects species diversity in the herbaceous patches within the dense maquis. This effect is scale-dependent, and interacts with the effects of soil seed bank and patch spatial-properties: without grazing soil seed bank plays a more important role than patch spatial properties, but under grazing the size and the accessibility of the patch are more important in the determination of herbaceous species composition.     

Invasive plant species thresholds in the forests of Robinson Crusoe Island,Chile

Background: Invasion by exotic plants worldwide can lead to the loss of native species, particularly on islands with a high proportion of endemic plants, such as Robinson Crusoe Island (RCI).

Aims: We studied the two most invasive exotic plant species occurring in the forest of RCI: Aristotelia chilensis and Rubus ulmifolius. We aimed at establishing thresholds for environmental and microsite variables related to invasion.

Methods: Environmental and forest understorey variables, including canopy gaps and invasive species cover were measured in non-invaded and invaded forest sites. We expected more invasion in plots located close to invasive shrublands, and in large gaps with high solar radiation.

Results: We found no relationship between the distance to invasive shrublands and invasion probability. Solar radiation tended to be slightly related with a higher cover of R. ulmifolius, the most abundant invasive exotic plant in RCI forests. Overall, the cover of native ferns appeared to inhibit invasion.

Conclusions: The identification of variable thresholds related to invasion can be useful for guiding management decisions. Our results suggest that management should consider monitoring forest canopy gap formation and promote the establishment of ferns to reduce the probability of invasive species establishing.     

Assessing future energy and transport systems: the case of fuel cells

Goal, Scope and Background  Assessing future energy and transport systems is of major importance for providing timely information for decision makers. In the discussion of technology options, fuel cells are often portrayed as attractive options for power plants and automotive applications. However, when analysing these systems, the LCA analyst is confronted with methodological problems, particularly with data gaps and the requirement of an anticipation of future developments. This series of two papers aims at providing a methodological framework for assessing future energy and transport systems (Part 1) and applies this to the two major application areas of fuel cells (Part 2). Methods  To allow the LCA of future energy and transport systems forecasting tools like, amongst others, cost estimation methods and process simulation of systems are investigated with respect to the applicability in LCAs of future systems (Part 1). The manufacturing process of an SOFC stack is used as an illustration for the forecasting procedure. In Part 2, detailed LCAs of fuel cell power plants and power trains are carried out including fuel (hydrogen, methanol, gasoline, diesel and natural gas) and energy converter production. To compare it with competing technologies, internal combustion engines (automotive applications) and reciprocating engines, gas turbines and combined cycle plants (stationary applications) are analysed as well. Results and Discussion  Principally, the investigated forecasting methods are suitable for future energy system assessment. The selection of the best method depends on different factors such as required ressources, quality of the results and flexibility. In particular, the time horizon of the investigation determines which forecasting tool may be applied. Environmentally relevant process steps exhibiting a significant time dependency shall always be investigated using different independent forecasting tools to ensure stability of the results. The results of the LCA (Part 2) underline that principally, fuel cells offer advantages in the impact categories which are typically dominated by pollutant emissions, such as acidification and eutrophication, whereas for global warming and primary energy demand, the situation depends on a set of parameters such as driving cycle and fuel economy ratio in mobile applica-tions and thermal/total efficiencies in stationary applications. For the latter impact categories, the choice of the primary en-ergy carrier for fuel production (renewable or fossil) dominates the impact reduction. With increasing efficiency and improving emission performance of the conventional systems, the competition regarding all impact categories in both mobile and stationary applications is getting even stronger. The production of the fuel cell system is of low overall significance in stationary applications, whereas in automotive applications, the production of the fuel cell power train and required materials leads to increased impacts compared to internal combustion engines and thus reduces the achievable environmental impact reduction. Recommendations and Perspectives  The rapid technological and energy economic development will bring further advances for both fuel cells and conventional energy converters. Therefore, LCAs at such an early stage of the market development can only be considered preliminary. It is an essential requirement to accompany the ongoing research and development with iterative LCAs, constantly pointing at environmental hot spots and bottlenecks.     

Seed germination of a tropical rain forest pioneer tree (Heliocarpus donnell-smithii) in response to diurnal fluctuation of temperature

The tropical rain forest pioneer tree Heliocarpus donnell-smithii Rose establishes itself only in light gaps of the forest canopy. A series of experiments with fluctuating temperatures have shown that the germination is increased if the temperature rises above 31°C during a few hours each day. The laboratory experiments were complemented with determinations of the seed viability in the soil each month during one year, and with determinations of germination under the natural diurnal fluctuation of temperature in a forest gap. Germination increases under fluctuating temperatures, and the seeds can remain dormant when buried in the soil during several months. The diurnal heating of the soil of light gaps as contrasted with the almost constant temperature under undisturbed canopies may be a precise environmental indicator of appropriate conditions for germination and establishment of the pioneer heliophytes of the rain forest.     

Processing of DNA Polymerase-Blocking Lesions during Genome Replication Is Spatially and Temporally Segregated from Replication Forks

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The effect of accidental burning on habitat conditions and species composition of Molinion caeruleae meadows

This study aimed to assess the effects of accidental burning on plant cover and habitat conditions in abandoned Molinion caeruleae meadows. Field studies were conducted in Kraków (Southern Poland) in the years 2017–2019 in two line transects, each with 10 permanent plots established in permanent study plots placed in accidentally burned and unburned patches. In the burned patch, the number of species, as well as Shannon-Wiener, Pielou and Simpson indicators achieved lower values. Moreover, the cover of numerous taxa affiliated with Molinion caeruleae changed remarkably, while taxa representing the alliances Calthion and Filipendulion disappeared. The considerable dominance of hemicryptophytes was observed in burned site, while in unburned place hemicryptophytes and geophytes were represented most abundantly. In the burned patch, anemochorous and autochorous species as well as small-seeded taxa dominated, while in the unburned patch autochorous species and medium-seeded taxa prevailed. The values of Ellenberg indicators in the burned patch achieved greater (light, soil reaction), lower (nitrogen, humidity) or similar (temperature, continentality) values to the unburned patch. The majority of soil properties in the burned and unburned patches were similar with the exception of the significantly greater content of potassium and lower content of magnesium in exchangeable form noticed in the burned patch. The performed investigations showed that, although the accidental fire activity inhibited the secondary succession in Molinion caeruleae meadows, burning cannot replace traditional mowing due to the reduction of species richness and disappearance of characteristic taxa.