Effects of intracanopy lighting on photosynthetic characteristics in cucumber

Plants of cucumber (Cucumis sativus L. cv. Euphorbia) were grown in a traditional high-wire cultivation system to investigate the effects of three lighting regimes on photosynthetic characteristics, leaf area and yield. The lighting regimes included overhead lighting (OH), where all the lamps were mounted above the canopy and overhead + intracanopy lighting (OH + IC) which comprised 65% of overhead lamps and 35% of lamps mounted vertically along the plant rows. All overhead lighting was provided for 20 h day⁻¹ and intracanopy lighting was provided for either 20 h or 24 h day⁻¹ lighting period. Intracanopy lighting improved the light distribution in the canopy. Gas exchange measurements showed that intracanopy lighting increased net photosynthesis (P_N) and photosynthetic capacity (P_max). Parameters calculated from CO₂ response (A/C_i) curves showed that in vivo estimate of the maximum rate of Rubisco carboxylation (Vc_max) and the maximum rate of electron transport (J_max) were affected by light regime. Intracanopy light increased yield by 11% compared to traditional overhead light.     

Forest cover changes in the Prignitz region (NE Germany) between 1790 and 1960 in relation to soils and other driving forces

Decadal to centennial land-cover changes are important drivers of many environmental issues, including biodiversity, biogeochemical cycles and, especially, the global carbon balance. In general, changes are well documented over only a few decades. Studies of land-cover changes and its drivers over centuries are rare. Therefore, the main objectives of this study are (1) to trace the development of the actual pattern of forest-open land over 170 years, and (2) to associate land-cover classes with site conditions (soils) as well as with other driving forces during three periods (1790–1838, 1838–1870, and 1870–1960). For these purposes, we used a combined approach of GIS-techniques and historical reconstructions from archives. The shifts of percentages for established forests, afforestation, clearings and open land on different soils were checked using a chi square test. From the archives, we obtained information on demographic, political/institutional and economic/technological factors, which are assumed to be drivers for past land-cover changes. Percentages of most land-cover classes hardly differed between the periods. However, established forests remained mainly on sandy soils and, to a large extend, afforestation was realised on sandy soils. Clearings reached high percentages on fluvial sands and organic sediments in the early period. A complex of demographic, political/institutional and economic/technological factors also had a considerable impact on land use/cover change in the Prignitz region. Thus, in addition to the strong association of land-cover classes with soils, our study demonstrated that other driving forces, i.e. political and economic factors, played an important role in the full understanding of land use from the past to the present.     

Determination of soil texture: Comparison of the sedimentation method and the laser‐diffraction analysis

Laser‐diffraction analysis (LDA) is a rapid automated method achieving highly resolved frequency distributions of particle sizes. Recently, LDA has come into use in environmental sciences. However, in the size range of silt and clay deviations from the particle‐size analysis with the standard pipette method, which is regarded as the reference method for soil‐texture classification, have been reported. Therefore, this study concentrates (1) on the verification of systematic relations between both methods using a series of soils of Lower Saxony (Germany) and (2) on the general applicability of the laser‐diffraction method to soil‐texture classification as well as (3) texture‐based estimates of air capacity, available field capacity, and permanent wilting point. The comparison of LDA with the pipette method demonstrated highly significant linear correlations in each of the particle‐size fractions from clay to coarse silt. The slope of regressions ranged from 0.4 with fine silt to 3.1 with clay. If the clay content derived from LDA was applied to texture classification, the resulting textural classes differed from the standard textural classes, except for purely sandy samples with a clay content of <5%. However, the linear‐regression model enabled an approach of the LDA‐based clay content to values produced with the standard pipette method. Using this transformation, a texture classification became practicable in many cases, but, despite of a high significance level between LDA and pipette method, still led to wrong textural classes in several cases. A comparison with regression models from other regions in Europe showed both similarities and discrepancies, even for similar substrates. Hence, the laser‐diffraction analysis cannot be used for the texture classification of soil samples without verification by the standard pipette method.     

Improved detection of soil microorganisms using fluorescence in situ hybridization (FISH) and catalyzed reporter deposition (CARD-FISH)

In recent years, methods of molecular microbiology have been used for the investigation of soil microbial diversity. Fluorescence in situ hybridization (FISH) represents a method which allows a specific staining and enumeration of soil microorganisms by using fluorescent-labelled oligonucleotide probes. However, the detection of FISH-stained cells is often affected by strong autofluorescence of the background, especially in samples of the top soils.In this study a more efficient FISH-approach coupled with catalyzed reporter deposition (CARD) was adapted to soils. Due to tyramide signal amplification (TSA) the fluorescence intensity has been considerably increased at the target binding site of a probe.Six different soils were investigated to evaluate the effect of sample preparation and pre-treatments, TSA, and the procedure of detection. The results show that both cell permeabilization and TSA are two important factors which improve in situ hybridization of soil microorganisms. Soils with higher clay contents have shown better results when prepared on polycarbonate filters rather than on glass slides.Using specific fluorescence filter systems and dye combinations the detection of hybridized cells was extensively increased compared with the application of monolabelled oligonucleotide probes in regular FISH-analysis. As a result, CARD-FISH-stained cells were suitable for automated counting using digital image analysis. Nevertheless, the counterstain with DAPI had to be analyzed manually as it was strongly affected by autofluorescence.     

Detection of microorganisms in undisturbed soil by combining fluorescence in situ hybridization (FISH) and micropedological methods

In contrast to conventional approaches molecular microbiology leads to a deeper understanding of the biodiversity of soil microorganisms. Nevertheless, there is a lack of knowledge regarding the spatial distribution of microbiota in the complex soil matrix and the interaction between the soil structure and microorganisms. DNA analytical methods such as fluorescence in situ hybridization (FISH) are being utilized to improve the characterization of microbial biocoenosis.Micropedological procedures which preserve the soil structure by embedding it with resin, in combination with FISH, allow the localization and identification of soil microorganism diversity in relation to the specific properties of their microhabitats. In this study, FISH was used prior to resin embedding in undisturbed soil samples of four different soils.The polished sections provided visualization of the bound probes as well as the undisturbed soil matrix via fluorescence microscopy. Furthermore, cell counts of active bacteria, locating of hot spots and their relationship to microsites rich in nutrients and water, such as humus or clay minerals, are now easy to perform. This will lead to a better understanding of how soil structure can affect soil microorganisms and vice versa.Derived from the use of 16S rRNA targeted oligonucleotide probes, EUB338 and NON338, the cell counts of FISH-detected bacteria were in the same order of magnitude in the undisturbed and the suspended soil samples. Counterstaining with DAPI showed varying detection rates caused by differing activities of the soil microorganisms.     

Podzol development with time in sandy beach deposits in southern Norway

The coastal areas of SE Norway provide suitable conditions for studying soil development with time, because unweathered land surfaces have continuously been raised above sea level by glacio‐isostatic uplift since the termination of the last ice age. We investigated Podzol development in a chronosequence of six soils on sandy beach deposits with ages ranging from 2,300 to 9,650 y at the W coast of the Oslofjord. The climate in this area is rather mild with a mean annual temperature of 6°C and an annual precipitation of 975 mm (Sandefjord). The youngest soil showed no evidence of podzolization, while slight lightening of the A horizon of the second soil (3,800 years) indicated initial leaching of organic matter (OM). In the 4,300 y–old soil also Fe and humus accumulation in the B horizon were perceptible, but only the 6,600 y–old and older soils exhibited spodic horizons. Accumulation of OM in the A horizons reached a steady state in <2,300 y, while in the B horizons OM accumulated at increasing rates. pH dropped from 6.6 (H₂O)/5.9 (KCl) in the recent beach sand to 4.5 (H₂O)/3.8 (KCl) within approx. 4,500 y (pH_H2O)/2,500 y (pH_KCl) and stayed constant thereafter, which was attributed to sesquioxide buffering. Base saturation showed an exponential decrease with time. Progressive weathering was reflected by increasing Fe_d and Al_d contents, and proceeding podzolization by increasing amounts of pyrophophate‐ and oxalate‐soluble Fe and Al with soil age. These increases could be best described for most Fe and Al fractions by exponential models. Only the increasing amounts of Fe_p could be better described by a power function and those of Fe_o by a linear model.     

Wildfires,responsibility and trust: public understanding of Sweden's largest wildfire

Wildfires present a growing risk to many countries, and climate change is likely to exacerbate this risk. This study analyzes how people directly affected by a wildfire understand its causes and consequences, as well as the future risk of wildfires. The point of departure is that social understanding of wildfires has an important influence on the consequences that emerge in the wake of a wildfire. The empirical case analyzed here is the largest forest fire in modern Swedish history, and the material basis of the study is a postal survey to all individuals directly affected by the fire. The results revealed a complex picture of the respondents’ understanding of the wildfire. Even if the fire was human caused, there was little blame toward forest companies and fire departments. Many positive consequences, such as a long-term increase in biodiversity, were attached to the disaster, and there was a belief that organizations will learn from it and take action to limit wildfires in the future. Simultaneously, the majority of the respondents believed that climate change may lead to an increased risk of forest fires in the future. These findings illustrate the complexity of people's perceptions of the fire and its aftermath.     

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