Association of spiders and lichen on Robben Island, South Africa

The present study is a first record of spider occurrence on Robben Island, South Africa. Some habitats were rich in lichens. As we know, lichens enhance wildlife habitat in less direct ways. The objective of the study was to examine the potential importance of lichens in enriching spider diversity and abundance. A total of 260 spiders (170 from lichens and 90 from bush) were collected following the visual search method over one year. Seasonal trends in overall species richness and abundance indicated that the relative density of spiders was greater in lichens than in bushes. The result suggests that habitat structure, such as branch size and epiphytic lichen abundance, can be an explanation for the greater number of spiders in lichen-rich patches of the island.AM is thankful to the ADU, University of Cape Town for all the support and financial help during the course of study

Effects of Short Term Bioturbation by Common Voles on Biogeochemical Soil Variables

Bioturbation contributes to soil formation and ecosystem functioning. With respect to the active transport of matter by voles, bioturbation may be considered as a very dynamic process among those shaping soil formation and biogeochemistry. The present study aimed at characterizing and quantifying the effects of bioturbation by voles on soil water relations and carbon and nitrogen stocks. Bioturbation effects were examined based on a field set up in a luvic arenosol comprising of eight 50 × 50 m enclosures with greatly different numbers of common vole (Microtus arvalis L., ca. 35–150 individuals ha–1 mth–1. Eleven key soil variables were analyzed: bulk density, infiltration rate, saturated hydraulic conductivity, water holding capacity, contents of soil organic carbon (SOC) and total nitrogen (N), CO2 emission potential, C/N ratio, the stable isotopic signatures of 13C and 15N, and pH. The highest vole densities were hypothesized to cause significant changes in some variables within 21 months. Results showed that land history had still a major influence, as eight key variables displayed an additional or sole influence of topography. However, the delta15N at depths of 10–20 and 20–30 cm decreased and increased with increasing vole numbers, respectively. Also the CO2 emission potential from soil collected at a depth of 15–30 cm decreased and the C/N ratio at 5–10 cm depth narrowed with increasing vole numbers. These variables indicated the first influence of voles on the respective mineralization processes in some soil layers. Tendencies of vole activity homogenizing SOC and N contents across layers were not significant. The results of the other seven key variables did not confirm significant effects of voles. Thus overall, we found mainly a first response of variables that are indicative for changes in biogeochemical dynamics but not yet of those representing changes in pools

Response to commentary on ‘Current economic obstacles to biochar use in agriculture and climate change mitigation’

A recent commentary in Carbon Management by Fidel et al. (http://www.tandfonline.com/doi/full/10.1080/17583004.2017.1306408) question the data selection and the analysis techniques used by Bach et al. (Carbon Management, https://doi.org/10.1080/17583004.2016.1213608) to assess two key aspects of biochar application in crop production, the effect on crop yield and the long-term carbon sequestration in soil. However, the arguments by Fidel et al. are not convincing. For farmer's decision whether biochar use in crop production might be economically profitable the low median values and large variability of results on yield effect in field trials form a sufficient base to abstain from biochar amendment to soil, therefore a detailed meta-analysis of data is not necessary. Future research may demonstrate under which conditions a pronounced positive and long-lasting effect of biochar application can be expected

Current economic obstacles to biochar use in agriculture and climate change mitigation

<p>Biochar may become a key instrument at the nexus of managed carbon flows, including value added potential in soil amelioration, climate protection, energy supply and organic waste management. This article reflects the potential use of biochar in agriculture from the perspective of the farming economy. Biochar soil amendment in crop production is regarded as a win–win situation, both for assumed increases in cropping yields and carbon sequestration in soil organic matter. However, an extensive review on biochar effect on crop yield has not yet been able to provide compelling arguments to foster more widespread biochar use in cropping systems. Furthermore, the half-lives of biochars are frequently shorter than commonly suggested, and other financial incentives, such as including biochar in carbon credit systems, are not in place to compensate for the extra cost of applying biochar. As a result, we conclude with a somewhat skeptical view for a widespread use of biochar in agriculture in the near future.</p

Biodegradation measurements confirm the predictive value of the O: C-ratio for biochar recalcitrance

Suitable predictors of degradability are sought to support the identification of biochars with large potential to increase C sequestration in soils. We determined the biodegradation of 9 chars from hydrothermal carbonization and pyrolysis in two agricultural soils. The 200- and 115-day degradation correlated strongly with the O:C- and slightly with the H:C-atomic ratio of 9 and 14 biochars, respectively. Highest temperature treatment and ash content did not show similar correlations

Biodegradability screening of soil amendments through coupling of wavelength-scanned cavity ring-down spectroscopy to multiple dynamic chambers

A system was developed for the automatic measurements of 13CO2 efflux to determine biodegradation of extra carbon amendments to soils. The system combines wavelength-scanned cavity ring down laser spectroscopy (WS-CRDS) with the open-dynamic chamber (ODC) method. The WS-CRDS instrument and a batch of 24 ODC are coupled via microprocessor-controlled valves. Determination of the biodegradation requires a known d13C value and the applied mass of the carbon compounds, and the biodegradation is calculated based on the 13CO2 mixing ratio (ppm) sampled from the headspace of the chambers. The WS-CRDS system provided accurate detection based on parallel samples of three standard gases (13CO2 of 2, 11 and 22 ppm) that were measured simultaneously by isotope ratio mass spectrometry (linear regression R2 = 0.99). Repeated checking with the same standards showed that the WS-CRDS system showed no drift over seven months. The applicability of the ODC was checked against the closed static chamber (CSC) method using the rapid biodegradation of cane sugar – d13C-labeled through C4 photosynthesis. There was no significant difference between the results from 7-min ODC and 120-min CSC measurements. Further, a test using samples of either cane sugar (C4) or beetroot sugar (C3)mixed into standard soil proved the target functionality of the system, which is to identify the biodegradation of carbon sources with significantly different isotopic signatures. Copyright © 2011 John Wiley & Sons, Ltd

Influence of Timber Harvesting Alternatives on Forest Soil Respiration and Its Biophysical Regulatory Factors over a 5-year Period in the Missouri Ozarks

We investigated the variability of soil respiration and several potential regulatory factors and modeled their interrelationships from May to August over a 5-year period in oak forests subjected to alternative harvesting treatments as part of the Missouri Ozark Forest Ecosystem Project (MOFEP). Treatments included even-aged management (EAM), uneven-aged management (UAM), and no-harvest management (NHM) and were implemented 7-8 years prior to this study. Summer mean soil respiration did not differ among the treatments, possibly because of changes in treatment differences in the separate months and years that tended to cancel each other out when averaged. Summer mean soil respiration and soil moisture tended to be higher in wet years (2004, 2006, and 2008) and lower in dry years (2005 and 2007) in EAM and UAM than in NHM. Summer precipitation was assumed to be the primary driver of variability in summer mean soil respiration through its control on soil moisture and the normalized difference vegetation index (NDVI) in the harvested forests. Nonlinear models using soil temperature, soil moisture and day-of-the-year (DOY) were used to predict within-summer soil respiration for all the treatments. A sensitivity analysis of the model using 30 min interval data suggested that soil respiration was more sensitive to soil moisture in the EAM and UAM treatments than in NHM. We also found a change in the soil respiration-soil temperature relationship in the summer for all the treatments. Simulated data sets that removed the covariance structure between soil temperature and moisture suggested that the change in the respiration-temperature relationship resulted from the combined effect of moisture stress and low temperature sensitivity at high temperatures during July and August. Simulations also showed the effect of moisture stress to be more limiting to soil respiration in the harvested forests than in the control at high temperatures, even resulting in a negative relationship at high temperatures. © 2011 Springer Science+Business Media, LLC