Quantifizierung des Stickstoffs in Wurzeln und Wurzelausscheidungen von Soja

The below ground N allocation of organic soybean was examined in two experiments conducted in Eastern Austria. During early development, individual soybean plants were labelled with a 15N-enriched urea solution by the petiole-feeding method. The 15N enrichment of these plants and surrounding soil relative to their natural 15N abundance was determined at plant maturity. The proportion of soil N derived from roots was calculated from root and soil N isotope data. Total below ground plant N, including rhizodeposits, amounted to between 6 to 48 % of total plant N. The proportion of total plant N allocated below ground was inversely related to shoot N content

Suitability of drought tolerance indices for selecting alfalfa (Medicago sativa L.) genotypes under organic farming in Austria

In eastern Austria, alfalfa is usually grown as a rainfed crop in crop rotations in organic farming systems, where year-to-year rainfall fluctuations cause different levels of drought stress. To identify the suitability of different alfalfa genotypes and drought tolerance indices, 18 contrasting alfalfa genotypes were evaluated under irrigated and rainfed conditions at the research station of the University of Natural Resources and Life Sciences (BOKU), Vienna, Austria, during 2006-08. The first study year (2006) was considered as the establishment year. Five drought tolerance selection indices were estimated based on shoot dry matter, total biomass yield and biological nitrogen fixation (BNF) data. The correlation between irrigated and rainfed performances increased (from r=-0.17 to 0.56) with decreasing stress intensity from the first to the second year. Genotypes Sitel, Plato ZS, Vlasta and NS-Banat were the best genotypes based on their performance under both conditions. Drought tolerance selection indices TOL and SSI showed high correlations (r = 0.32 to 0.81) only with rainfed performance, and SSI was the index that best identified genotypes with high yield potential under rainfed conditions. Indices STI and GMP were the ones that best identified genotypes with high performance under both conditions

Cyanate is a low abundance but actively cycled nitrogen compound in soil

Biotic processes drive rapid cyanate turnover and dominate cyanate consumption in soils, according to an extensive soil survey and stable isotope tracer experiments

Biological nitrogen fixation and growth parameters correlations of alfalfa (Medicago sativa L.) genotypes under organically managed fields with limited irrigation

To identify the effective characters and their relative importance in improvement of BNF, two separate field experiments were conducted under irrigated and rain-fed organic managements of dry, Pannonian region of east Austria. The experiments were laid out in an α-lattice design with two replications and 18 genotypes (eight Iranian ecotypes and ten European cultivars). Plant height was positively and significantly correlated with leaf area index (LAI) and shoot dry matter (DM) under both conditions. Positive correlations were found between biological nitrogen fixation (BNF) and shoot DM (r = 0.61** and 0.87**, irrigated and rain-fed management, respectively). Regarding correlation coefficients, high yielding genotypes had taller plants and denser stands, especially under rain-fed condition. In path analysis, all direct effects of BNF components were positive in both conditions, while some of the indirect effects were negative. These can be regarded in selection models to avoid undesirable negative effects. Plant height and LAI can be considered as primary selection criteria for improving shoot DM, while crop re-growth and plant height, with antonymous effects, were more important for improving root dry matter

PH-dependent bioavailability, speciation, and phytotoxicity of Tungsten (W) in Soil Affect Growth and Molybdoenzyme Activity of Nodulated Soybeans

Increasing use of tungsten (W)-based products opened new pathways for W into environmental systems. Due to its chemical alikeness with molybdenum (Mo), W is expected to behave similarly to its "twin element", Mo; however, our knowledge of the behavior of W in the plant-soil environment remains inadequate. The aim of this study was to investigate plant growth as well as W and nutrient uptake depending on soil chemical properties such as soil pH and texture. Soybean (Glycine max cv. Primus) was grown on two acidic soils differing in soil texture that were either kept at their natural soil pH (pH of 4.5-5) or limed (pH of ≥7) and amended with increasing concentrations of metallic W (control and 500 and 5000 mg kg-1). In addition, the activity of molybdoenzymes involved in N assimilation (nitrate reductase) and symbiotic N2 fixation (nitrogenase) was also investigated. Our results showed that the risk of W entering the food web was significantly greater in high-pH soils due to increased solubility of mainly monomeric W. The effect of soil texture on W solubility and phytoavailability was less pronounced compared to soil pH. Particularly at intermediate W additions (W 500 mg kg-1), symbiotic nitrogen fixation was able to compensate for reduced leaf nitrate reductase activity. When W soil solution concentrations became too toxic (W 5000 mg kg-1), nodulation was more strongly inhibited than nitrogenase activity in the few nodules formed, suggesting a more-efficient detoxification and compartmentalization mechanism in nodules than in soybean leaves. The increasing presence of polymeric W species observed in low-pH soils spiked with high W concentrations resulted in decreased W uptake. Simultaneously, polymeric W species had an overall negative effect on nutrient assimilation and plant growth, suggesting a greater phytotoxicity of W polymers. Our study demonstrates the importance of accounting for soil pH in risk assessment studies of W in the plant-soil environment, something that has been completely neglected in the past.Fil: Oburger, Eva. Universidad de Viena; AustriaFil: Vergara Cid, Carolina. Universitat Fur Bodenkultur Wien; Austria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Preiner, Julian. Universidad de Viena; Austria. Universitat Fur Bodenkultur Wien; AustriaFil: Hu, Junjian. Universitat Fur Bodenkultur Wien; AustriaFil: Hann, Stephan. Universitat Fur Bodenkultur Wien; AustriaFil: Wanek, Wolfgang. Universidad de Viena; AustriaFil: Richter, Andreas. Universidad de Viena; Austri

Root Exudation of Primary Metabolites: Mechanisms and Their Roles in Plant Responses to Environmental Stimuli

Root exudation is an important process determining plant interactions with the soil environment. Many studies have linked this process to soil nutrient mobilization. Yet, it remains unresolved how exudation is controlled and how exactly and under what circumstances plants benefit from exudation. The majority of root exudates including primary metabolites (sugars, amino acids, and organic acids) are believed to be passively lost from the root and used by rhizosphere-dwelling microbes. In this review, we synthetize recent advances in ecology and plant biology to explain and propose mechanisms by which root exudation of primary metabolites is controlled, and what role their exudation plays in plant nutrient acquisition strategies. Specifically, we propose a novel conceptual framework for root exudates. This framework is built upon two main concepts: (1) root exudation of primary metabolites is driven by diffusion, with plants and microbes both modulating concentration gradients and therefore diffusion rates to soil depending on their nutritional status; (2) exuded metabolite concentrations can be sensed at the root tip and signals are translated to modify root architecture. The flux of primary metabolites through root exudation is mostly located at the root tip, where the lack of cell differentiation favors diffusion of metabolites to the soil. We show examples of how the root tip senses concentration changes of exuded metabolites and translates that into signals to modify root growth. Plants can modify the concentration of metabolites either by controlling source/sink processes or by expressing and regulating efflux carriers, therefore challenging the idea of root exudation as a purely unregulated passive process. Through root exudate flux, plants can locally enhance concentrations of many common metabolites, which can serve as sensors and integrators of the plant nutritional status and of the nutrient availability in the surrounding environment. Plant-associated micro-organisms also constitute a strong sink for plant carbon, thereby increasing concentration gradients of metabolites and affecting root exudation. Understanding the mechanisms of and the effects that environmental stimuli have on the magnitude and type of root exudation will ultimately improve our knowledge of processes determining soil CO2 emissions, ecosystem functioning, and how to improve the sustainability of agricultural production