Social Network Analysis

Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics

Climate change 2014 - Synthesis Report

Conservation biology has two threads: the small-population paradigm which deals with the erect of smallness on the persistence of a population, and the declining-population paradigm which deals with the cause of smallness and its cure. The processes relevant to the small-population paradigm are amenable to theoretical examination because they generalize across species and are subsumed by an inclusive higher category: stochasticity. In contrast, the processes relevant to the declining-population paradigm are essentially humdrum, being not one but many. So far they have defied tight generalization and hence are of scant theoretical interest. The small-population paradigm has not yet contributed significantly to conserving endangered species in the wild because it treats an erect (smallness) as if it were a cause

Directions in conservation biology

The amendment of two agricultural soils with two biochars derived from the slow pyrolysis of papermill waste was assessed in a glasshouse study. Characterisation of both biochars revealed high surface area (115 m2 g−1) and zones of calcium mineral agglomeration. The biochars differed slightly in their liming values (33% and 29%), and carbon content (50% and 52%). Molar H/C ratios of 0.3 in the biochars suggested aromatic stability. At application rates of 10 t ha−1 in a ferrosol both biochars significantly increased pH, CEC, exchangeable Ca and total C, while in a calcarosol both biochars increased C while biochar 2 also increased exchangeable K. Biochars reduced Al availability (ca. 2 cmol (+) kg−1 to <0.1 cmol (+) kg−1) in the ferrosol. The analysis of biomass production revealed a range of responses, due to both biochar characteristics and soil type. Both biochars significantly increased N uptake in wheat grown in fertiliser amended ferrosol. Concomitant increase in biomass production (250% times that of control) therefore suggested improved fertiliser use efficiency. Likewise, biochar amendment significantly increased biomass in soybean and radish in the ferrosol with fertiliser. The calcarosol amended with fertiliser and biochar however gave varied crop responses: Increased soybean biomass, but reduced wheat and radish biomass. No significant effects of biochar were shown in the absence of fertiliser for wheat and soybean, while radish biomass increased significantly. Earthworms showed preference for biochar-amended ferrosol over control soils with no significant difference recorded for the calcarosol. The results from this work demonstrate that the agronomic benefits of papermill biochars have to be verified for different soil types and crops.

Effects of biochar from slow pyrolysis of papermill waste on agronomic performance and soil fertility

The review examines the literature concerning the effects on soil profile development of ants (Hymenoptera: Formicidae) and termites (Isoptera), two prominent insect groups in the Australian environment. Their pedological influence is largely through the construction of nests, galleries, soil sheetings and mounds. Some of the pedological effects are manifested in the physical modification of the soil profile through selecting, transporting and rearranging soil particles. Within this group, findings in areas such as soil turnover, mound longevity, bioturbation, soil structure and water infiltration are discussed. Termites contribute actively to soil turnover, and the contribution of termite sheetings and ant mounds to soil turnover is also being recognized. Termite mounds may persist in the landscape for more than two decades, while ant mound longevity varies from weeks to decades. Information on the effects of ants and termites on soil structure and water infiltration is sparse; but ants and termites seem to either increase infiltration by improving soil structure and porosity, or to decrease infiltration by producing compact surfaces which assist runoff and erosion. Other effects involve the chemical alteration of the soil profile by ants and termites collecting and transporting live and dead animal and plant materials to their nest structures, and by the additions of secretions and excreta in nest construction. The majority of ants and termites probably increase carbon and nutrient levels, especially nitrogen, phosphorus and potassium, as well as exchangeable magnesium and calcium. The extent of the increases depends greatly on the type of mound construction and the degree to which organic material is incorporated. Problems with research techniques include the use of a variety of sampling techniques by different researchers, lack of detailed soil description or classification, and inadequate description of location of sampling points. These deficiencies make it difficult to draw valid comparisons between research projects. Many researchers also base their generalizations on ant or termite soil modifications on a small number of samples, although during the 1980s there has been an increase in sample sizes. Contradictory data often result from projects being undertaken on different species and in different environments. Future research directions need to include a greater concentration on the morphology of ant nests, more detailed assessment of the influence of ants and termites on soil structure and water infiltration, an increase in biopedological research in human-modified environments, a greater emphasis on termites and ants other than the most dominant or prominent species, and a focus on community as distinct from single-species effects.

The role of termites and ants in soil modification - a review

Ants as bioindicators of soil function in rural environments

More units of study are being offered flexibly, using distance education and online facilities, as a consequence of recent educational developments in higher education, with learner expectations of being able to study when they like and where they like, as well as increasing class enrolments and more students studying remotely or part‐time. However, the quality of the learning experience and the efficacy of placing learning activities that require student interaction and discourse in an online environment have been questioned. The concerns raised by educators regarding placing learning activities online are often about the types of learning environments that are being created and the tools available to support student communication in a virtual learning environment. Asynchronous computer‐mediated communication is one means of allowing students to communicate independently of time and place, and to communicate questions, opinions and queries when transferring interactive learning activities to an online en...

Monitoring online communication: can the development of convergence and social presence indicate an interactive learning environment?

The impact of ant bioturbation and foraging activities on surrounding soil properties

The introduced tramp ant, Pheidole megacephala, is a well-known pest of urban areas and coastal dune ecosystems in eastern Australia. Until recently, establishment and spread of P. megacephala colonies has been regarded as likely only in disturbed areas. Here we describe the extent of an established colony of P. megacephala in a long undisturbed open forest near Maryborough in southeast Queensland and compare ant community structure with those of nearby uninfested sites. Tuna baiting revealed three distinct zones: (i) a zone totally dominated by P. megacephala (at least 10 ha) where few other ant ant species were detected; (ii) a zone where P. megacephala was absent and many other ant species were found; and (iii) a zone where opportunists (species of Ochetellus and Paratrechina) competed with P. megacephala at baits. Pitfall trapping over a 9-month period resulted in 12 species being recorded at the infested site, compared with a mean of 25 species recorded at adjoining uninfested forest. Over 94% of ants recorded in pitfalls at the infested site were P. megacephala. Most notably, P. megacephala had completely displaced dominant Dolichoderines (species of Iridomyrmex), subordinate Camponotini (species of Camponotus, Opisthopsis and Polyrhachis) and other species of Pheidole which are common at forest sites.

Lisa Lobry de Bruyn

Papers

The role of termites and ants in soil modification - a review

Ants as bioindicators of soil function in rural environments

Monitoring online communication: can the development of convergence and social presence indicate an interactive learning environment?

The impact of ant bioturbation and foraging activities on surrounding soil properties

Response of an open‐forest ant community to invasion by the introduced ant, Pheidole megacephala