Modelling the effects of temperature and moisture on CO2 evolution from top- and subsoil using a multi-compartment approach

A novel approach, at least for laboratory conditions, for analysis of the dependence of soil C evolution on temperature is presented. A two-component (labile and refractory organic C) parallel first-order model was fitted to CO₂ evolution rates from top- and subsoil, incubated at different combinations of temperature (constant −4, 0.3, 5, 15, 25, weekly fluctuating between −4 and +5°C) and moisture (17, 26, 36 and 50% H₂O for the topsoil and 16, 23, 31 and 41% for the subsoil) and to the evolution of CO₂ after the addition of roots or stubble of Phalaris arundinacea in the topsoil, measured at 25°C and 36% H₂O (Lomander et al., 1998). The size of the pools and their respective first-order rate constants were optimized simultaneously by a least-squares method. The optimization was carried out separately for top- and subsoil. Quadratic functions were fitted to the temperature and moisture responses. For topsoil samples in which roots or stubble were added, a three-component model (labile, refractory and stubble or roots) was used. The initial partitioning of the soil C, the decomposition rate constants for each partition and the temperature and moisture responses were all assumed to be identical to those of pure topsoil, while the initial pool sizes of added roots and straw were measured. The calculated temperature at which CO₂ evolution ceased (T_min) was −0.83°C, and a recalculation to Q₁₀-values resulted in increasing temperature response with decreasing temperature (Q₁₀=2.2 at 25°C and 12.7 at 0.3°C). Simulated CO₂ evolution rates agreed well with the measurements (R_adj²=0.96 and 0.81) for top- and subsoil, respectively. The multi-compartment approach was superior to the single-compartment approach, which gave R_adj²=0.88 and 0.76 for top- and subsoil, respectively. In general, CO₂ evolution rates obtained from the laboratory experiment were higher than those measured in the field, even after differences in temperature and moisture were taken into account. After 300 d in the laboratory at 25°C and 36% H₂O, 99% and 86% of the added straw and roots, respectively, had disappeared according to the described model. The CO₂-evolution rate per unit of soil carbon was about two times higher for topsoil than for subsoil.     

Galacturonic acid groups in birch xylan

Summary A large number of reducing xylose end groups are present in birch wood (Betula verrucosa) while all galacturonic acid moieties are non-reducing. A large portion of the reducing xylose end groups are removed during treatments with alkali used for the islation of xylan, while reducing galacturonic acid moieties are formed by endwise degradation during this procedure.The financial support from the 1959 Års Fond för Teknisk och Skoglig Forskning samt Utbildning is gratefully acknowledged.     

Rotational position of curved saw logs and warp of the sawn timber

With the development of scanning technology in sawmills, it is possible to optimise log rotational position when sawing. However, choosing a different rotational position than horns down might be detrimental for the board shape after drying, especially for curved logs. Thus, there is a need to investigate at what level of log curve it is possible to freely rotate logs without causing board warp. This study was carried out through a test sawing that was conducted at a sawmill situated in the middle of Sweden. The tests were made on 177 Norway spruce logs, with varying amount of curve. Half of the logs were sawn in the horns-down position, half were sawn rotated perpendicular to horns down. Log shape and warp of the dried boards were measured. The results indicated a relationship between board spring, log curve and choice of rotational position. Furthermore, board bow was related to log curve but not rotational position. It can be concluded that for straight logs, with a bow height of less than 15 mm, an unconventional rotational position does not cause excess spring in the boards. Bow and twist are not affected by the rotational position at all.     

Stratospheric ozone, ultraviolet radiation, and cryptogams

The stratospheric ozone layer, which protects the biosphere from biologically active (mostly harmful) ultraviolet-B (UV-B) solar radiation, thinned during the latter half of the 20th century. In this paper some of the effects of UV-B radiation on cryptogams (cyanobacteria, algae, lichens, mosses, liverworts, pteridophytes and fungi) are reviewed. Effects vary among species, and therefore changes in UV-B radiation may affect species frequencies. Effects also depend on other factors, such as water conditions.     

Announcements

The impact of acidifying substances on soils is examined and related to soil properties such as the amount of exchangeable cations in the soil and the proportion of those cations which are other than hydrogen ions. The importance and influence of differential soil horizons and the transport of water through the soil profile are also discussed. Differences between how agricultural and forest ecosystems affect nutrient cycling in soil systems are outlined.     

Measurements and simulations of heat and water balance components in a clay soil cropped with winter wheat under drought stress or daily irrigation and fertilization

Soil water and temperature dynamics were measured in a field experiment with winter wheat on a clay soil. There were four treatments: Control (C), receiving natural precipitation, drought (D), protected from rain by plastic screens during the growing season, daily irrigation (I) and daily irrigation and fertilization (IF). Treatments C, D and I received the nitrogen fertilizer as a single application of solid fertilizer in spring. In IF daily dressings of nutrients were supplied in the irrigation water. All treatments received 20 g Nm^–2. An associated experiment with a newly sown grass ley (L) that was irrigated and fertilized daily (total 5.6 g Nm ^–2) was also performed. Standard meteorological variables (air temperature and humidity, wind speed, precipitation, global radiation, and relative cloudiness) and crop development data (green area index, crop height, relative root distribution in depth) above and below ground were used as driving variables within a physically based dynamic model (SOIL) for simulating water and heat fluxes. Measured soil temperature and water content from one treatment (I) were used to tune the model parameters, tentatively set from literature data. Thereafter, water and heat fluxes in the other treatments were simulated using the same parameter values but with different crop-related measurements as driving variables for each treatment. Measured soil temperature and water content in C, D, IF and L could thus be used for validation of the simulations. The theory formulated in the model could accurately explain measured treatment differences in soil water and temperature dynamics. Since the soil-related parameters were identical in all treatments, the model was shown to be applicable over a wide range of moisture conditions.     

Diagnosis of bromethalin toxicosis in the dog

Dogs given a single oral dose of bromethalin at 6.25 mg/kg developed a toxic syndrome characterized by hyperexcitability, tremors, seizures, depression, and death within 15-63 hours after bromethalin administration. Gross lesions included mild cerebral edema (2/5) and mild pulmonary congestion (2/5). Histologic lesions included diffuse white matter spongiosis (5/5), mild microgliosis (3/5), optic nerve vacuolization (3/5), mild thickening of Bowman's capsule (2/5), and occasional splenic megakaryocytes (2/5). Ultramicroscopic examination of midbrain stem revealed occasional swollen axons, intramyelinic vacuolization, and myelin splitting at the intraperiod line. Bromethalin was detected in kidney, liver, fat, and brain tissues, using gas chromatography with electron capture detection. Photodegradation of extracted bromethalin may limit accurate quantification of tissue residues.     

Aldicarb toxicosis in a flock of sheep.

Aldicarb toxicosis was diagnosed in 200 sheep that died suddenly. Carbamate insecticide toxicosis was suspected based on observed clinical signs (hypersalivation, diarrhea, urination, paddling, seizures, miosis, and deaths occurring within 1 hour). Tissue samples were submitted from 4 Columbian ewes for pathologic and analytical evaluation. Severe diffuse pulmonary edema was observed on gross and histologic examination. Inhibition of cholinesterase activity in retina (21.2-68.1% of normal activity, n = 3), brain (40.6-45.6% of normal activity, n = 3), and whole blood (27% of normal activity, n = 1) supported a diagnosis of carbamate toxicosis. Reversal of brain and whole blood cholinesterase activities (reactivation factor greater than 1.4) following an in vitro 1 hour incubation at 37 C was also consistent with carbamate poisoning. Aldicarb toxicosis was confirmed following its detection in rumen contents at 1.5, 5.5, and 334 ppm using both high-pressure liquid chromatography with UV detection and gas chromatography with nitrogen/phosphorus detection.