Model-based analysis of the spatial variability and long-term trends of soil drought at Scots pine stands in northeastern Germany

Soil water availability determines the vitality of trees and forest stands to a large degree. Over the last decades, an increasing number of drought spells has been observed in several parts of Europe. Our study aims to estimate long-term trends of soil drought at Scots pine (Pinus sylvestris L.) stands along the prevailing climatic gradient in Mecklenburg-Western Pomerania, northeastern Germany. To this end, soil water balance simulations were carried out at 24 sites over the period from 1951 to 2009 with the physically based model LWF-BROOK90. As a threshold for soil water stress, we used 40% of relative extractable water (REW). The results indicated an increased number of drought days further east, together with declining totals of precipitation. However, specific site conditions had a large influence on the occurrence of soil drought, partly overriding the climatic differences across the study area. Soil drought has distinctly increased in the recent past, both in duration and in intensity, affecting the eastern sites more than the western sites. The increased soil dryness could be attributed to higher atmospheric evaporative demand due to higher temperatures, as well as slightly lower precipitation sums during the summer months. To mitigate the negative effects of future climate change, adaptation measures should preferably be conducted in the eastern parts of northeastern Germany.     

Identification and quantification of polyphenols in carob fruits (Ceratonia siliqua L.) and derived products by HPLC-UV-ESI/MSn

The polyphenolic patterns of carob pods (Ceratonia siliqua L.) and derived products were identified and quantified using high-performance liquid chromatography-UV absorption-electrospray ion trap mass spectrometry after pressurized liquid extraction and solid-phase extraction. In carob fiber, 41 individual phenolic compounds could be identified. In addition, spectrophotometric quantification using the Folin-Ciocalteu and vanillin assays was performed, and the antioxidative activity was determined as the 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity. Carob pods contain 448 mg/kg extractable polyphenols comprising gallic acid, hydrolyzable and condensed tannins, flavonol-glycosides, and traces of isoflavonoids. Among the products investigated, carob fiber, a carob pod preparation rich in insoluble dietary fiber (total polyphenol content = 4142 mg/kg), shows the highest concentrations in flavonol-glycosides and hydrolyzable tannins, whereas roasted carob products contain the highest levels of gallic acid. The production process seems to have an important influence on the polyphenolic patterns and quantities in carob products.     

Assessing the Impact of Effluents from a Modern Wastewater Treatment Plant on Breakdown of Coarse Particulate Organic Matter and Benthic Macroinvertebrates in a Lowland River

Wastewater treatment plants (WWTP) with insufficient technologies for wastewater purification often cause a distinct nutrient pollution in the receiving streams. The increased concentrations of dissolved nutrients can severely disturb the ecological integrity of streams, which has been recently shown for basic ecosystem processes like mineralization of coarse particulate organic matter (CPOM). The present study investigated the impact of a modern WWTP (Zentralkläranlage Jena) on breakdown rates of CPOM exposed in net bags (1 mm mesh size) to the effluent of a large municipal WWTP and an upstream control site in the Saale River (Thuringia, Germany) from April to October 2005. Control and effluent site differed significantly in water chemistry with increased concentrations of dissolved organic carbon (DOC), ammonium, sulfate, and chloride at the effluent site, while the control site displayed higher concentrations of nitrate. However, breakdown rates of toothpickers and small twigs were not significantly different between the sites, whereas breakdown rate of leaf litter was significantly higher at the effluent site (k?=?0.0124 day^?1) than at the control site (k?=?0.0095 day^?1). Benthic invertebrate assemblages inhabiting the sandy stream bed at both sites were dominated by Chironomidae and Oligochaeta, typical inhabitants of fine sediments. Although the Shannon diversity of the benthic invertebrates was slightly higher at the effluent site (0.85) than at the control site (0.63), no significant difference could be detected. Bacterial numbers in water samples and surface biofilms on glass slides also displayed no significant differences between the two sites. This study showed that the effluents of a WWTP with modern technologies for wastewater purification did not directly affect breakdown rates of CPOM, bacteria numbers in epibenthic biofilms and the water column, and the community composition of sediment inhabiting aquatic macroinvertebrates in an effluent-receiving river with already increased concentrations of dissolved nutrients.     

Element Inputs and Canopy Interactions in two Pine Forest Ecosystems in Berlin,Germany

For 3 years (1986-89), element fluxes with bulk deposition and throughfall were determined in a 40 yr. old pine plantation and a 80-140 yr. old mixed pine/oak stand in the Grunewald forest in Berlin. Although SO₄-inputs are very high (60 kg S·ha^?1.a^?1) due to the urban character of the study site, acid inputs are moderate because of the buffering action of airborne alkaline dusts. This is reflected in the high Ca-inputs (12 kg·ha^?1a^?1 in bulk precipitation). Acid neutralisation was also observed in the canopies and could be attributed to 60-80% to increased Ca- and Mg-fluxes in throughfall, stemming from foliage leaching and dust interception. Heavy metal inputs were low in comparison to other Central European study sites, the decrease in Pb-inputs over the 3-year period could be attributed to the increased use of unleaded gasoline since 1987. Total inputs and canopy leaching showed clear seasonal patterns for some elements: SO₄-, H-, Ca- and Mg-fluxes were higher in winter, on the other hand, K- and Mn-enrichment in throughfall showed two peaks, in early summer and late fall.     

Test of a combined soil moisture/soil heat simulation model on a bare field soil in Southern Turkey

In order to simulate soil suction and soil temperature, a field study was carried out in the experimental farm of the Agricultural Faculty, University of Cukurova (Adana/TURKEY), for a period of two years. During this period the soil was bare. Data collected regularly include soil suction and soil temperature. Meteorological data were obtained from the Adana Climatological Station. Data on soil suction and soil temperature were used to calibrate the simulation model, proposed by Huwe and van der Ploeg (1988). It was found that the model, after having been calibrated, performed quite well. A fair agreement between measured and simulated soil temperatures was obtained. However, the calculated and measured soil suction values were found to be considerably different. The simulation model used in this study appears to be applicable for the conditions of the Cukurova Region in Southern Turkey.     

Calculation of the total nitrate uptake of lettuce (Lactuca sativa L.) by use of a mathematical model to simulate nitrate inflow

Lettuce was grown in nutrient solution in a climate chamber under varied levels of temperature and radiation and in the greenhouse under fluctuating climatic conditions. A model to calculate maximum nitrate inflow (Imax) in relation to relative growth rate (RGR) and root:shoot ratio (RSR) was used for computing total-N uptake. For doing this, developing of submodels to calculate RGR and RSR was necessary. The good agreement between calculated N uptake and measured total-N taken up by the plants supports the assumption that Imax reflects the inflow necessary to meet the demand of plants.     

Root production and root mortality of winter wheat grown on sandy and loamy soils in different farming systems

Winter wheat was grown over 2 years (1995, 1996) in an organic and integrated cropping system on sandy and loamy soils. Root growth was measured on five to six occasions each year with an auger sampling procedure and the ingrowth core method. The first resulted in an estimate of net root development, while the latter revealed gross root growth (GG) or root production. Total root production was about 80-150 km m^-2 (0- to 30-cm soil layer) between April and July and exceeded the net size of the root system at harvest by a factor of between 2 and 4. The C input into the soil could be estimated as 1.4-2.6 t ha^-1 by this root production. The cropping systems had nearly no influence on root production. The largest differences occurred between the years. The net root length tended to be lower on sandy soils compared to the loam, but total root production was higher. Root mortality, which is the difference between GG and net root growth, was also higher on sandy soils. The turnover index, which is the mean of the relative root production rates and relative root mortality rates, was positively related to the soil sand content in both years.     

A sensitivity analysis for assessing the relevance of fine‐root turnover for P and K uptake

Plant fine roots are subject to continual turnover, i.e., old roots die during the plant life cycle and are quickly replaced by new roots. New roots grow partly into undepleted soil areas and can take up nutrients at a higher rate than old roots. This is one possible advantage of root turnover. It has been shown that root turnover of several plant species increases when P and/or K supply is limited, indicating an efficiency mechanism. The objective of this study was to assess the maximum benefit for nutrient uptake by root turnover and to determine which soil or plant properties influence this process. Based on a data set of field‐grown faba beans, a sensitivity analysis with a transport and uptake model was performed, i.e., several input parameters were systematically varied to assess their importance for nutrient uptake of a root system with and without fine‐root turnover. The calculations were based on the assumptions that all new roots grow into undepleted soil areas and that no inter‐root competition occurs. Model calculations indicated that a root system with a high but realistic turnover rate can take up twice the amount of P or K compared to a stable root system without any turnover. This benefit on uptake is higher at low concentrations of these nutrients in soil solution, low soil water content, or high maximum inflow. However, measured uptake under poor conditions of nutrient supply is often higher than calculated uptake, even when root turnover is taken into account. This indicates that root turnover might be an efficiency mechanism, but not the only one.