Browsing by Subject "Wachstum"

Now showing 1 - 6 of 6
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    Effects of water management on microclimate and yield physiology in irrigated rice in semi-arid environments
    (2014) Stürz, Sabine; Asch, Folkard
    Growth and grain yield reductions have been widely observed when traditionally flooded rice fields were subjected to water-saving irrigation measures, where a continuous floodwater layer is avoided. These observations led to the perception of rice being a plant extremely sensitive to soil water deficits even when grown in soils close to their water holding capacity. Since the rice plant’s meristem is below the water surface until the early reproductive stage in flooded fields, the difference in heat capacity between water and air can lead to changes in meristem temperature, when a ponded water layer is omitted. Therefore, the objectives of this study were to quantify the effects of water-saving irrigation on the field’s microclimate and its influence on gas-exchange parameters and to investigate growth and yield parameters under flooded and non-flooded conditions in response to microclimate and varying climatic conditions. On two sites in Senegal, field experiments were conducted, where rice was sown on bi-monthly staggered dates and grown under flooded and non-flooded conditions. In the flooded treatment, a ponded water layer was maintained in the field throughout the growing season, whereas in the non-flooded treatment, irrigation water was applied until soil saturation on a frequent basis, in order to avoid standing water and soil water deficits at the same time. Microclimatic parameters and phenology were observed and leaf gas-exchange and plant growth parameters, yield and yield components were determined. Minimum soil temperature and temperature at meristem level were usually lower without standing water, whereupon temperature differences between irrigation treatments increased with decreasing air temperature. Stomatal conductance depended mainly on minimum soil and meristem temperature and minimum relative humidity inside the canopy. Assimilation rate was positively correlated with solar radiation and soil and meristem temperature, but depended mainly on stomatal conductance. Without standing water, stomatal conductance and assimilation rate were significantly lower, but the results could be explained with differences in microclimate. In most cases, leaf area was reduced under non-flooded conditions. Leaf area expansion rate was correlated with meristem temperature during the night. With minimum meristem temperature being lower under non-flooded conditions, lower leaf area expansion rates under non-flooded conditions could be attributed to lower meristem temperature. Yield reductions under non-flooded conditions were mainly observed in the cold-dry-season, whereas slight yield increases were found in the hot-wet-season. Among the yield components, reduced number of spikelets per panicle and decreased spikelet fertility accounted for the largest share of the yield gap. Leaf area per tiller was positively correlated with meristem temperature in the observed temperature range, and a positive relationship was found between leaf area per tiller and the number of spikelets per panicle. Furthermore, spikelet fertility increased with meristem temperature between panicle initiation and booting stage. Therefore, lower meristem temperature led to smaller leaf area per tiller, less spikelets per panicle and decreased spikelet fertility under non-flooded conditions. We concluded that water-saving irrigation in lowland rice production can lead to growth and yield reductions in comparison to traditional lowland irrigation even in the absence of soil water deficits, due to changes in soil and meristem temperature when a ponded water layer is omitted. Differences in assimilation rate, leaf growth and yield between irrigation treatments increased with decreasing air temperature and a clear seasonal pattern was observed, with large growth and yield reductions in the cold-dry-season, whereas in the hot-wet-season, growth and yield were less affected by irrigation treatment. When water-saving irrigation measures are applied in areas where night temperatures below 20°C occur, the effect of changes in meristem temperature should be considered. To mitigate impairment of growth under water-saving irrigation, a floodwater layer could be used to bridge cool periods, or a less temperature-responsive variety should be chosen. Nevertheless, the physiological mechanisms of the differential effects of day and night temperature remain unknown und need further investigation. Possibly, there is a combined effect of low night temperature and high evaporative demand during the day, which could lead to growth limitations due to restrictions of the plant’s water status. Furthermore, we want to highlight the need for a robust model of water temperature in paddy fields, which should be incorporated in rice growth models, since even tough existing models simulate growth and grain yield under upland and lowland conditions, the effects of changes in microclimate due to irrigation method are inadequately considered so far.
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    Price stability versus full employment : the Phillips curve dilemma reconsidered
    (2016) Schwarzer, Johannes A.; Hagemann, Harald
    This dissertation focuses on different interpretations of the Phillips curve particularly from the end of the 1950s to the beginning of the 1970s. In the 1950s and 1960s the Phillips curve was mainly perceived as a “cruel dilemma”. From this perspective the curve seemed to imply that price stability and full employment (and to some extent also economic growth) are mutually conflicting policy objectives. Furthermore, the curve was usually regarded as describing disequilibrium phenomena, that is, excess demand or supply on the labour market causing a price reaction. On the other hand, particularly since the late 1960s, the Phillips curve became more and more embedded into an equilibrium approach, so that departures from a “natural rate of unemployment” are possible only by surprise inflation. Moreover, within this view, price stability and full employment are assumed to be compatible policy goals. These two different lines of thought are presented in three already published peer-reviewed journal articles which are reproduced in the first half of this Ph.D. thesis. The underlying reasons for these different views are then discussed in the remainder of the dissertation. It is shown that both lines of thought built on very different assumptions regarding the causes of inflation and the specific kind of unemployment prevailing in the economy. The discussion is then related to current economic models (such as the New Keynesian approach) which also point at a possible conflict between price stability and full employment.
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    Radial tree growth dynamics and xylem anatomy along an elevational gradient in the El Sira Mountains, Peru
    (2019) Niessner, Armin; Küppers, Manfred
    The explicit purpose of this study was to (1) characterize climate and vegetation along the western slope of the Cerros del Sira (Peru), (2) evaluate radial tree growth along this slope in response to seasonal rainfall anomalies, (3) reveal how the meteorological environment controls tree radial stem growth, and (4) to investigate how xylem anatomy relates to dynamics of tree growth. From May 2011 until September 2015, radial stem growth of 67 trees was monitored using point-dendrometers, and meteorological parameters were measured within five sites along an elevational gradient. Additionally, tree dimensions (stem diameter, stem height) and xylem anatomical traits (mean vessel diameter, vessel frequency, cumulative vessel area and potential hydraulic conductivity) were determined. The transect extends from lowland terra firme forests (ca. 250 m asl) over submontane forests, late and mid successional montane cloud forests up to exposed elfin forests (ca. 2200 m asl). Continuous rainfall records for remote tropical areas are extremely rare and measurements along this transect are also incomplete. Monthly rainfall estimates by the TRMM PR satellite ("product 3B42") were highly correlated with rain gauge observations, although they underestimate rainfall at high elevations. Different intra-annual tree growth patterns could be identified within each elevational forest type, showing species/individuals with seasonally independent continuous or alternating growth patterns and strictly seasonal growth. Stem growth at each site was typically higher during rainy seasons, except for in the elfin forest. The rainy season from October 2013 to March 2014 was extraordinarily dry, with only 73 % of long-term mean precipitation received, which resulted in reduced tree radial growth rates, again with the exception of the elfin forest. Different analytical approaches revealed that precipitation is the main growth-controlling factor at lower elevations, especially during rainy seasons. Growth within montane and cloud forests positively correlates to solar radiation. Tree growth within the elfin forest is only weakly correlated to meteorological parameters, but dry conditions during dry seasons promote growth. It was hypothesized that (1) individuals/species with large vessel diameters and low vessel frequencies have higher radial growth rates, but are more vulnerable to relatively dry periods. Therefore, (2) they are more likely to grow seasonally and predominantly during rainy seasons, (3) their growth during the exceptionally dry rainy season 2013/14 was more constrained, and (4) their growth is generally closer correlated to meteorological parameters. Larger trees tend to have larger vessel diameters, which positively relates to radial growth rates, and they also tend to grow more seasonal. As hypothesized, trees having large vessel diameters are more sensitive to droughts, as indicated by stronger positive correlations with rainfall and negative with solar radiation. However, in mountainous forests, relations between xylem anatomical traits and tree growth dynamics seem to be more complex. In late-successional cloud forests, growth of trees with large vessel diameter is positively, while of trees with small vessel diameter negatively related to solar radiation. Sensitivity to the dry rainy season 2013/14, expressed as relative reduction in growth compared to "normal" rainy seasons, could not be explained by xylem anatomical traits, contradicting the preceded hypothesis. Tropical lowland rainforest species, especially individuals with large vessels, will likely suffer from increasing drought frequencies and intensities. How montane forest ecosystems will react to a (globally) changing climate is rather uncertain, especially in exposed elfin forests. Results of this study suggest that species of late-successional tropical montane forests may profit from higher temperatures. While montane tropical rain forests may also suffer from prolonged droughts, exposed ridges covered by elfin forests still receive plenty of precipitation and may benefit from receiving more solar radiation for photosynthesis and, thus, grow faster.
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    Saponin fractions from fenugreek (Trigonella foenum-graecum L.)as dietary supplements for Nile tilapia (Oreochromis niloticus L.)and common carp (Cyprinus carpio L.)
    (2012) Stadtlander, Timo; Focken, Ulfert
    The future role and importance of aquaculture for the world food supply is more and more recognized by the public. High quality feed for semi-intensive and intensive aquaculture operations are necessary to guarantee a future continuous growth of fish production. Nutrient utilization efficiency has in the past been augmented by addition of feed additives, mainly anti-biotics and hormones. That practice is prohibited in the European Union since 1st of January 2006 and the consumer acceptance of products produced in that way is low. Around a decade ago saponins, secondary plant metabolites, have been found to be potential alternatives for aquafeeds. Saponinmixtures derived from the South American soap bark tree Quillaja saponaria, have been found to have beneficial effects on growth, feed and nutrient utilization and on metabolism of common carp Cyprinus carpio and Nile tilapia Oreochromis niloticus. Furthermore, in one of the early experiments a sex ratio in favor of males was observed in saponin fed tilapia compared to control fish not supplemented with saponins. An influence on sex ratio of Nile tilapia would be highly desirable since industrially Nile tilapia production is only financially viable if all male populations are produced since mixed sex tilapia populations tend to reproduce uncontrollable. The production of all male tilapia populations is mainly conducted by feeding the potentially environmentally hazardous and carcinogenic synthetic hormone 17--methyltestosterone to sexually undeveloped tilapia fry. The above mentioned problems led to a joint research project with partners in Israel and Palestine in which this dissertation has been conducted. The aim of the project was the fractionation of crude saponin extract derived from fenugreek Trigonella foenum-graecum and its testing in vitro and in vivo. It was assumed that a higher biological activity could be achieved if saponin fractions instead of crude mixtures would be applied. After in vitro testing, different saponin fractions or eluates, have been tested on their effects on growth, feed and nutrient utilization, metabolism, proximate composition, gene expression of GH and IGF-1, sex ratio, reproduction and gonad histology. Most of the feeding experiments were conducted with Nile tilapia but one experiment was also conducted with carp. Three of the feeding experiments have been conducted in a system capable of measuring continuous respiration of the fish. Another experiment has been conducted at a field station at Jericho, Palestine. The experiments conducted to evaluate the influence of saponin fractions on sex ratio of undifferentiated tilapia fry have been conducted primarily in a flow-through system. The tested saponin fractions and a tested sapogenin are not suitable to produce male monosex tilapia populations. The sex ratios after supplementation of diets of mixed sexed tilapia fry did only in one case show a significantly higher proportion of males than the control. In a larger scale repetition of that experiment the previous observations could statistically not be proofed. It must be assumed to be random effects or be the result of initially biased sex ratios after stocking undifferentiated tilapia fry. An experiment in which genetically female tilapias were fed with two fenugreek saponin fractions and positive and negative controls supported that finding. A long term feeding experiment conducted at Jericho revealed no influence of the long and short term supplemented Q. saponaria saponin mixtures on sex ratio and reproduction of genetically female tilapia. A similar laboratory experiment with fenugreek saponin fractions could not be evaluated in that regard. The experiments evaluating the effects of the saponin fractions on growth, feed and nutrient utilization, gene expression of GH and IGF-1 and proximate composition revealed no significant differences. But in all experiments one fraction eluated with 60%/40% (v/v) methanol/water showed numerically improved values compared to control and other fractions. Furthermore one fraction eluated with 40%/60%/ (v/v) methanol/water gave constantly numerically inferior results of tested parameters compared to control. That supports the conclusion that the 40% methanol fraction contains saponins generally referred to as anti-nutrients. In only one experiment, conducted at Jericho, significantly higher growth was observed after long term supplementation with a Q. saponaria saponin mixture containing elevated sapogenin content. The presented data in this thesis is not supporting an application of the tested saponin fractions as environmentally friendly alternative to methyltestosterone to produce all male populations of tilapia or to inhibit uncontrollable reproduction. Additional experiments are needed to evaluate different modes of application like immersion treatments or injections since during the experimental work of this thesis all tested saponins were added to the feed. An application of the tested fenugreek saponin fractions as growth promoters yields a higher potential although the experimental results are based upon low sample sizes due to capacity restrictions of the respirometric system. Therefore a repetition under near commercial or commercial conditions must be considered.
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    Seasonal variation in growth, quantitative and qualitative food consumption of milkfish, Chanos chanos (Forsskål 1775), and Nile tilapia, Oreochromis niloticus (L. 1758), in Laguna de Bay, Philippines
    (2002) Richter, Hartmut; Becker, Klaus
    Laguna de Bay, the largest lake in the Philippines, lies directly southeast of the capital Manila. The lake has a mean depth of only 2.8m and a muddy bottom which is stirred during windy weather, causing turbid conditions (Secchi depth <30cm). In the dry season, the water level drops below that of the nearby sea, leading to a backflow of saline water which clears the water until the return of the monsoon winds (Secchi depth >100cm) and leads to algal blooms. Since the beginning of the 1970s, the lake has been used for culturing milkfish, Chanos chanos (Forsskål), in large netpens (max. 2000ha) and Nile tilapia, Oreochromis niloticus (L.), in smaller cages (max. 200m2). Initially, it was possible during the algal blooms to grow fish from fingerling (ca. 10g) to marketable size (ca. 200g) in three months, making two harvests a year possible. Aquaculture quickly spread until in the middle of the eighties, over a third of the lake was covered with cages. At the same time the growth of the fish declined, which was attributed to the excessive use of primary production. Since then, despite a reduction in aquaculture coverage to the generally recommended level of 10% of the lake, fish growth has never reached the levels of the early days of culture. In the present work, seasonal variation in growth, feeding spectrum and daily ration of these two species was to be investigated in relation to water quality in order to find out more about the interaction between aquaculture and the lake. Between May 1995 and August 1997, milkfish and tilapia were sampled on several occasions at commercial operations over the 24-hour cycle. Since milkfish, unlike tilapia, do not receive supplemental feed, the proportion of their growth derived only from natural food could be determined from the cultured fish. Tilapia were kept in cages without feed specially for this purpose and measured and weighed twice a month between March and November 1997. At the same time, selective water quality parameters (particulate organic and inorganic matter, Chlorophyll-a, zooplankton) were analysed weekly. The growth of unfed fish was significantly faster between saltwater intrusion (mid-May) and the return of the monsoons (late July) than at other times of the year. On the other hand, food consumption was only slightly higher in tilapia when the water was clear than at other times and in milkfish hardly differed over the year. Both species mainly fed on amorphous organic detritus; significant levels of phytoplankton were only found in the stomachs at times of algal bloom. In supplemented tilapia, the daily ration still consisted of 35-75% natural food, suggesting that pelleted feed was used inefficiently. The main factor limiting fish growth therefore seemed to be food quality since detritus has often been shown to be poor quality food. The weekly water samples collected in 1997 demonstrated that the total level of phytoplankton was not necessarily higher at times of rapid fish growth. The main difference was related to algal size, since at times of turbid water, small diatoms dominated but these were replaced by larger blue-green algae after saltwater intrusion. In conjunction with the feeding method of these fish, the strongly seasonal growth of the fish could now be explained. Phytoplanktivorous fish such as milkfish and tilapia can only select their food on the basis of size. Since the organic detritus in the lake consisted of particles smaller than 15µm, it was possible for the fish to selectively filter larger blue-green algae but not smaller diatoms. This could also explain why fish growth rates did not recover after a reduction in aquaculture in the mid-eighties, since the relationship between the level of algae and that of detritus seems to be more important than total algal biomass. In order to increase production to those levels found in the early seventies, the level of detritus in the lake would have to be reduced, for which its origin would have to be investigated first.
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    Three essays in empirical economics
    (2019) Seiffert, Sebastian Daniel; Beißinger, Thomas
    In the preface of one of the most established textbooks "Economics" by Samuelson and Nordhaus (1998), the authors state that the ultimate goal of economics is to improve the living conditions of people in their everyday life". In this spirit, the underlying thesis empirically assesses three heterogenous topics which all can be linked via their impact on (economic) well-being. It contributes to the scientific landscape by tackling the questions at hand utilising novel and newly constructed data sets which have not been commonly used in economic research. The thesis comprises three chapters which will be summarised in the following. Gun Violence in the US: Correlates and Causes This chapter provides a county-level investigation of the economically-motivated gun violence in the US. To guide our empirical analysis, we develop a simple theoretical model which suggests that firearm-related robberies in a given county increase with the number of illegal guns and decrease with social capital and police intensity. Using detailed FBI data from 1986-2014, we find empirical evidence for the role of illegal guns, social capital, and police intensity in line with our theoretical predictions. To investigate the causal effect of illegal guns, we exploit plausibly exogenous variation in illegal firearm supplies due to gun thefts in contiguous states. The Size of the Middle Class and Educational Outcomes: Theory and Evidence from the Indian Subcontinent This chapter proposes a stylised model to derive the effect of a sizeable middle class on average educational outcomes. Under the reasonable assumptions, the model predicts that the spending share on education increases if the middle class becomes larger such that the size of the middle class has a positive impact on education. We test the relationship empirically by using village/neighbourhood level data from Indian household surveys. To tackle the the issue of potential endogeneity of the middle class share of the population, we propose a novel instrument that relies on the fraction of the population belonging to the third (middle) caste ("sudra"). Using this IV strategy, our empirical results support a positive effect. Go East: On the Impact of the Transsiberian Railway on Economic Development in Eastern Russia This chapter addresses the question whether or not large-scale infrastructure investments have a causal effect of local economic development. By using a novel instrumental variable approach based on historical trade and travel routes across the Russian East, I am able to identify a causal and negative effect of remoteness to the Transsiberian Railway on local economic activity as measured by nocturnal lights emission.