A stress-strain model to evaluate the forest situation in Germany and the state of the art of damage research

The situation and the latest findings of forest damage research in Germany are discussed. A newly developed concept for this research is described. This concept allows to identify the drawbacks of the recent damage research concept but also the integration of results compiled up to now. The importance for including natural occurring stress factors such as climate, soil conditions or local situation of individual species is outlined.     

Effects of glyphosate and foliar amendments on activity of microorganisms in the soybean rhizosphere

A field study was conducted to determine the effects of glyphosate on microbial activity in the rhizosphere of glyphosate-resistant (GR) soybean and to evaluate interactions with foliar amendments. Glyphosate at 0.84 kg ae ha^{? 1} was applied GR soybean at the V4–V5 development stages. Check treatments included a conventional herbicide tank mix (2003 study only) and no herbicides (hand-weeded). Ten days after herbicide application, a commercially available biostimulant and a urea solution (21.0% N) were applied to soybean foliage at 33.5 mL ha^{? 1} and 9.2 kg ha^{? 1}, respectively. Soil and plant samples were taken 0, 5, 10, 15, 20 and 25 days after herbicide application then assayed for enzyme and respiration activities. Soil respiration and enzyme activity increased with glyphosate and foliar amendment applications during the 2002 growing season; however, similar increases were not observed in 2003. Contrasting cumulative rainfall between 2002 and 2003 likely accounted for differences in soil microbial activities. Increases in soil microbial activity in 2002 suggest that adequate soil water and glyphosate application acted together to increase microbial activity. Our study suggests that general soil microbial properties including those involving C and N transformations are not sensitive enough to detect effects of glyphosate on rhizosphere microbial activity. Measurements of soil-plant-microbe relationships including specific microbial groups (i.e., root-associated Fusarium spp.) are likely better indicators of impacts of glyphosate on soil microbial ecology.     

Enhancement of UV and chromate mutagenesis by nickel ions in the Chinese hamster HGPRT Assay †

1. The HGPRT (Hypoxanthine‐Guanine‐Phospho‐Ribosyl‐Transferase) assay with Chinese Hamster V79 cells was used to measure the mutagenic effects of UV irradiation, potassium dichromate and nickel chloride. The agents were tested separately and in the combinations of UV plus nickel and dichromate plus nickel.

2. UV, Cr(VI) and Ni(II) were confirmed to be mutagenic in the V79 cell assay. The combination of UV(5J/m²) and Ni(II) (0.5 mM) caused a mutation rate 11.2 times above that corresponding to the sum of the individual mutation rates of these agents. The combined action of Cr(VI) (0.1 mM) and Ni(II) (0.5 mM) produced a mutation rate 2.8 fold above that corresponding to the sum of the individual rates of the separate agents.

3. The enhancing effect of nickel chloride on the mutagenicity of UV or Cr(VI) is interpreted by an interference of Ni(II) with the repair of DNA lesions.     

Functional autotrophy of Heteroxenia fuscescens (Anthozoa: Alcyonaria): carbon assimilation and translocation of photosynthates from symbionts to host

The association of the alcyonarian Heteroxenia fuscescens (Ehrb.) with its cytosymbiotic algae shows structural and physiological adaptations optimizing the living together of the two partners as one functional unit. To enhance the energetic contribution of the autotrophic partner, the organization of the heterotrophic partner bears typical plant-like imprints. Up to 20% of the inorganic C photosynthetically fixed was translocated to the host (=2 mg C mg d.w.^-1 d^-1). This net C gain by the host is used for anabolic purposes including the deposition of storage material. Especially the wax-esters and triglycerides of the host-in contrast to those of the symbionts-were intensively labelled. The in-vivo ¹⁴C-fixation of zooxanthellae is more than double the in-vitro fixation. In both symbionts and host, the lipids show the highest relative ¹⁴C-incorporation. In particular the polyol component was strongly labelled. After 120 min of continuous incubation, approximately 40 labelled intracellular metabolites were detectable in the ethanol/water soluble fractions of zooxanthellae. Glycerol is the main low-molecular weight carbohydrate being transferred. This is corroborated by the deacylation of lipids of the host.     

Biological production of nitrite in seawater

The relative importance of 3 different sources for biological production of nitrite in seawater was studied. Decomposition of fecal pellets of the copepod Calanus helgolandicus (at a concentration of approximately 12 g-at N/l), in seawater medium, released small amounts of ammonia over a 6 week period. It nitrifying bacteria were added to the fecal pellets nitrite was barely detectable over the same period. Decomposition of phytoplankton (present at a concentration of about 8 g-at particulate plant N/l) with added heterotrophic bacteria, released moderate amounts of ammonia over a 12 week period. If the ammonia-oxidizing bacterium Nitrosocystis oceanus was added to the decomposing algae, nitrite was produced at a rate of 0.2 g-at N/l/week. Heterotrophic nitrification was not observed when 7 open-ocean bacteria were tested for their ability to oxidize ammonia. The diatom Skeletonema costatum, either non-starved or starved of nitrogen, produced nitrite when growing with 150 or 50 g-at NO ₂ ^- -N/l at a light intensity of about 0.01 ly/min. When nitrate in the medium was exhausted, S. costatum assimilated nitrite. If starved of vitamin B₁₂, both non-N-starved and N-starved cells of S. costatum produced nitrite in the medium with 150 g-at NO ₃ ^- -N/l. Nitrate was not exhausted and cell densities reached 2x10⁵/ml due to vitamin B₁₂ deficiency. If light intensity was reduced to 0.003 ly/min under otherwise similar conditions, cells did not grow due to insufficient light, and nitrite was not produced. In the sea, it appears that, in certain micro-environments, decomposition of particulate matter releases ammonia with its subsequent oxidation to nitrite. The amounts of these nutrients and the rate at which they are produced are dependent upon the nature of the materials undergoing decomposition and the associated bacteria. In certain other areas of the sea, where phytoplankton standing stock is high and nitrate is non-limiting, excretion by these organisms is a major source of nitrite.     

Evaluation of variance approximation techniques for non-linear photosynthesis—irradiance models

Parameters derived from photosynthesis-irradiance (P-I) models, although often empirical in nature, are useful indicators of the photoadaptive state of phytoplankton in culture and in situ. However objective criteria for determining significant changes in P-I curves are rarely provided, because confidence intervals for parameters of non-linear models are not estimated easily. Examination of least-squares residuals in parameter space and Monte Carlo approaches have been used to estimate confidence regions around parameter values, but the computationally intensive nature of these methods has prevented their routine application. We present an alternative method of estimating confidence intervals for parameters of P-I curves that runs quickly on a microcomputer and is easily combined with common parameter-estimation routines. This algorithm was tested using a 3-parameter P-I model and curves describing a wide range of photoadaptive states, with different numbers of observations and different amounts of inherent variability. The method produced results comparable to the Monte Carlo technique. This analysis makes it possible to specify the sample size required to define parameters with acceptable confidence as a function of data variance and photoadaptive state. In most reasonable situations, 25 observations are sufficient.     

Nutrient cycling between the water column and a marine sediment. I. Organic carbon

The carbon flow through the sediments at a station located in 18.3 m of water off the Scripps Institution of Oceanography, San Diego, California (USA) was determined. The parameters studied [and their mean rates of input (+) or output (-) to the benthos] were macro-detritus (+0.028 gC m^-2day^-1), fallout of particulate debris (+3.3 gC m^-2day^-1), benthic net photosynthesis during the day (-0.06 gC m^-2 daylight period^-1), burial (0 gC m^-2day^-1), benthic respiration at night (-0.28 gC m^-2 night period^-1), and resuspension (-3.0 gC m^-2day^-1). Resuspension of sediment at this station was found to have a controlling effect on the sediment organic carbon content. Benthic photosynthesis was able to provide 79% of the organic carbon required by the benthos for respiration during the daylight hours. A carbon-flow diagram linking together all of the above measurements is presented.