Soil CO2 evolution rates in the field – a comparison of three methods

In this field study, three methods for determining soil CO₂ evolution rates were compared: (1) a static chamber method and (2) a dynamic chamber method, both with gas chromatographic (GC) analysis of air samples, and (3) a dynamic chamber system using a portable infrared gas analyzer (CIRAS). The mean CO₂ evolution rate in the field increased in the order static chamber-GC < dynamic chamber-GC < dynamic chamber-CIRAS by 40%. The CO₂ evolution rates obtained using the three methods were significantly correlated. None of the three methods was significantly affected by soil moisture or soil temperature. This has been repeatedly observed by others, but is still not fully understood. The difference between air and soil temperature had strong negative effects on both GC methods, but not on the CIRAS system.     

Broodstock management of Crassostrea gigas: II. Broodstock conditioning to maximize larval survival

The results of time-course conditioning trials indicate that there is an optimum conditioning interval during which the proportion of viable gametes is at a maximum. When matings are accomplished before or after this optimum interval, reduced gamete viability results. In this case, spawning and fertilization may appear to be normal, but setting success is substantially reduced.The degree of conditioning required to reach this optimum window is dependent on the stage of gonadal development in the broodstock when conditioning is started, and reflects substantial seasonal variation, which is repeated on an annual cyclic basis.Performance of the larval rearing system, reflected in the proportion of ova which survive to the spat stage, may be substantially improved by managing broodstock conditioning to maximize the proportion of viable gametes. This may be accomplished by empirical observation of the annual gonadal cycle in the area where the broodstock is maintained, and then determining the optimum conditioning interval for the various seasons.     

Fusarium Species Synthesize Alkaline Proteinases in Infested Barley

Barley (Hordeum vulgare L.) that is infested with Fusarium head blight (FHB, ‘scab’) is unsuitable for malting and brewing because it may contain mycotoxins and has unacceptable malting quality. Fungal proteinases are apparently often involved in plant-microbe interactions, where they degrade storage proteins, but very little is known about the enzymes that the fungi produce in the infected grain. We have shown previously that one plant pathogenic fungus, Fusarium culmorum, produced subtilisin- and trypsin-like enzymes when grown in a cereal protein medium. To establish whether these proteinases were also synthesized in FHB-infested barley in vivo, field-grown barley was infested as the heads emerged. Extracts were prepared from the grain as it developed and matured and their proteolytic activities were measured with N-succinyl-Ala-Ala-Pro-Phe p -nitroanilide and N-benzoyl-Val-Gly-Arg p -nitroanilide. The heavily infested barleys contained both subtilisin- and trypsin-like activities. These enzymes reacted with antibodies prepared against each of the two F. culmorum proteinases, indicating that those produced in the laboratory cultures and in the field-infested barley were the same. The presence of these proteinases correlated with the degradation of specific buffer-soluble proteins in the infested grains. These enzymes readily hydrolyzed barley grain storage proteins (C- and D-hordeins) in vitro. The presence of these Fusarium proteinases in the barley indicates that they probably play an important role in the infestation, but exactly how and when they function is not clear.     

Optimizing the size of the area surveyed for monitoring a Eurasian lynx (Lynx lynx) population in the Swiss Alps by means of photographic capture–recapture

We studied the influence of surveyed area size on density estimates by means of camera‐trapping in a low‐density felid population (1–2 individuals/100 km²). We applied non‐spatial capture–recapture (CR) and spatial CR (SCR) models for Eurasian lynx during winter 2005/2006 in the northwestern Swiss Alps by sampling an area divided into 5 nested plots ranging from 65 to 760 km². CR model density estimates (95% CI) for models M₀ and M_h decreased from 2.61 (1.55–3.68) and 3.6 (1.62–5.57) independent lynx/100 km², respectively, in the smallest to 1.20 (1.04–1.35) and 1.26 (0.89–1.63) independent lynx/100 km², respectively, in the largest area surveyed. SCR model density estimates also decreased with increasing sampling area but not significantly. High individual range overlaps in relatively small areas (the edge effect) is the most plausible reason for this positive bias in the CR models. Our results confirm that SCR models are much more robust to changes in trap array size than CR models, thus avoiding overestimation of density in smaller areas. However, when a study is concerned with monitoring population changes, large spatial efforts (area surveyed ≥760 km²) are required to obtain reliable and precise density estimates with these population densities and recapture rates.     

Microbial community composition affects soil organic carbon turnover in mineral soils

Soil organic carbon (SOC) turnover is the most ubiquitous and ecologically fundamental process in soils. It is generally assumed that SOC is utilised by functionally redundant soil-specific microbial communities which do not differ in their capability to mineralise soil organic matter. To challenge this assumption, incubation experiments were conducted to analyse the community-specific effects on SOC turnover for six mineral soils under different land-use. Comparisons of respiration by a native soil community and an alien community both inoculated to sterilised soils revealed 29 ± 18% higher respiration by the native community (‘home-field advantage’). Increased soil microbial community diversity, as generated by mixing several microbial inoculants, did not result in increased mineralisation rates. Even under impaired conditions, in the presence of aged engine oil as a less decomposable substance, communities with higher diversity did not show higher respiration rates. Also, in non-sterilised soils, we detected the influence of the microbial community composition on respiration rates: Investigations on the effect of mixing two communities in a 50:50 untreated soil mixture showed declining respiration in three out of six cases (by 23.9 ± 5.9%) and increased respiration in one case (by 57%) compared to the mean respiration of the two unmixed soils. These effects were highly related to the microbial community capability, with only communities with low capability profiting from mixing with a second community. Our results question the assumption of redundancy of microbial community’s functionality for SOC mineralisation in soils.     

Near-infrared spectroscopy for determination of soil organic C,microbial biomass C and C and N fractions in a heterogeneous sample of German arable surface soils

Visual and near-infrared spectroscopy (vis-NIRS) is an established method to estimate soil properties. However, only limited information is available to estimate C and N fractions in a heterogeneous sample. The objectives of our study were to determine estimation accuracies of vis-NIRS using two software for soil organic carbon (SOC), total nitrogen (N_t), pH, texture, and C and N fractions (light (LF), mineral (MF), labile, intermediate and passive fractions) in a heterogeneous sample (consisting of 51 units with different mineralogy) and to compare these results with those obtained by mid-infrared spectroscopy (MIRS). Analyzing vis-NIRS spectra and the mentioned properties showed a possibility to distinguish between high and low values for SOC (residual prediction deviation (RPD) = 1.90) and N_t (RPD = 1.93). Sand and clay could be estimated, whereas pH and silt could not. No useful estimation was possible for N-LF, passive C, intermediate C or intermediate N. C-LF, C-MF and N-MF could be differentiated between high and low values, whereas for passive N the estimation was approximate quantitative. MIRS reached one or two times higher estimation categories than vis-NIRS for SOC, N_t, pH and texture, suggesting that MIRS has a higher potential to estimate soil properties in a heterogeneous sample.     

Soil‐carbon preservation through habitat constraints and biological limitations on decomposer activity

We review recent experimental results on the role of soil biota in stabilizing or destabilizing soil organic matter (SOM). Specifically, we analyze how the differential substrate utilization of the various decomposer organisms contributes to a decorrelation of chemical stability, residence time, and carbon (C) age of organic substrates. Along soil depth profiles, a mismatch of C allocation and abundance of decomposer organisms is consistently observed, revealing that a relevant proportion of soil C is not subjected to efficient decomposition. Results from recent field and laboratory experiments suggest that (1) bacterial utilization of labile carbon compounds is limited by short‐distance transport processes and, therefore, can take place deep in the soil under conditions of effective local diffusion or convection. In contrast, (2) fungal utilization of phenolic substrates, including lignin, appears to be restricted to the upper soil layer due to the requirement for oxygen of the enzymatic reaction involved. (3) Carbon of any age is utilized by soil microorganisms, and microbial C is recycled in the microbial food web. Due to stoichiometric requirements of their metabolism, (4) soil animals tend to reduce the C concentration of SOM disproportionally, until it reaches a threshold level. The reviewed investigations provide new and quantitative evidence that different soil C pools underlie divergent biological constraints of decomposition. The specialization of decomposers towards different substrates and microhabitats leads to a relatively longer persistence of virtually all kinds of organic substrates in the nonpreferred soil spaces. We therefore propose to direct future research explicitly towards such biologically nonpreferred areas where decomposition rates are slow, or where decomposition is frequently interrupted, in order to assess the potential for long‐term preservation of C in the soil.