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A. V. Spain

Bio: A. V. Spain is an academic researcher from University of Western Australia. The author has contributed to research in topics: Ecosystem & Soil organic matter. The author has an hindex of 8, co-authored 12 publications receiving 987 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a general model is presented in which the dynamics of decomposition in terrestrial ecosystems are determined by a set of hierarchically organized factors which regulate microbial activity at decreasing scales of time and space.
Abstract: A general model is presented in which the dynamics of decomposition in terrestrial ecosystems are determined by a set of hierarchically organized factors which regulate microbial activity at decreasing scales of time and space in the following order: climate - clay mineralogy + nutrient status of soil - quality of decomposing resources - effect of macroorganisms (i.e., roots and invertebrates). At the lower scale of determination, biological systems of regulation based on mutualistic relationships between macro- and microorganisms ultimately determine the rates and pathways of decomposition. Four such systems are defined, i.e., the litter and surface roots system, the rhizosphere, the drilosphere and the termitosphere in which the regulating macroorganisms are respectively litter arthropods and surface roots, live subterranean roots, endogeic earthworms, and termites. In the humid tropics, this general model is often altered because climatic and edaphic constraints are in many cases not important and because high temperature and moisture conditions greatly enhance the activity of mutualistic biological systems of regulation which exert a much stronger control on litter and soil organic matter dynamics. This general hypothesis is considered in the light of available information from tropical rain forests and humid savannas. Theoretical and practical implications regarding the biodiversity issue and management practices are further discussed. It is concluded that biodiversity is probably determined, at least partly, by soil biological processes as a consequence of enhanced mutualistic interactions, which enlarge the resource base available to plants. It is also concluded that any effort to restore or rehabilitate degraded soils in the humid tropics is promised to fail unless optimum levels of root and invertebrate activities are promoted and the resulting regulation effects operate in the four abovedescribed biological systems of regulation. Research required to substantiate and adequately test the present set of concepts and hypotheses are expressed.

506 citations

Book ChapterDOI
26 Oct 2015

207 citations

01 Jan 1999
TL;DR: In this paper, the authors presented the results of a study conducted at the Laboratoire d'Ecologie des Sols Tropicaux, IRD, Bondy, France.
Abstract: l Departamento de Biologfa de Suelos, Instituto de Ecologfa, Xalapa, Mexico; 2Laboratoire d'Ecologie des Sols Tropicaux, IRD, Bondy, France; 31NIA, Estacion Experimental San Ramon, Yurimaguas, Peru/Laboratoire de Pedobiologie, IRD, Dakar, SenegaVBenemerita Universidad Autonoma de Puebla, Centra de Investigaciones en Ciencias Microbiol6gicas, Puebla, Mexico; 6 School of Life Sciences, Sambalpur University, Sambalpur, India; 7Laboratoire B.O.s. T., IRD, Fort-de-France, Martinique; 8Queen Victoria Museum and Art Gallery, Lauceston, Tasmania, Australia; 9 CSIRO Davies Laboratory, Aitkenva le, Queensland, Australia

154 citations

Journal ArticleDOI
TL;DR: In this article, the authors propose a conceptual framework for sustainable use of the soil resource and present seven general research questions whose resolution will provide a firmer base for the proposed conceptual framework.
Abstract: Soils are self-organized ecological systems within which organisms interact within a nested suite of discrete scales. Microorganisms form communities and physical structures at the smallest scale (microns), followed by the community of their predators organized in microfoodwebs (tens of microns), the functional domains built by ecosystem engineers (centimeters to meters), ecosystems, and landscapes. Ecosystem engineers, principally plant roots, earthworms, termites, and ants, play key roles in creating habitats for other organisms and controlling their activities through physical and biochemical processes. The biogenic, organic, and organomineral structures that they produce accumulate in the soil space to form three-dimensional mosaics of functional domains, inhabited by specific communities of smaller organisms (microfauna and mesofauna, microorganisms) that drive soil processes through specific pathways. Ecosystem engineers also produce signaling and energy-rich molecules that act as ecological mediators of biological engineering processes. Energy-rich ecological mediators may selectively activate microbial populations and trigger priming effects, resulting in the degradation, synthesis, and sequestration of specific organic substrates. Signaling molecules inform soil organisms of their producers' respective presences and change physiologies by modifying gene expression and through eliciting hormonal responses. Protection of plants against pests and diseases is largely achieved via these processes. At the highest scales, the delivery of ecosystem services emerges through the functioning of self-organized systems nested within each other. The integrity of the different subsystems at each scale and the quality of their interconnections are a precondition for an optimum and sustainable delivery of ecosystem services. Lastly, we present seven general research questions whose resolution will provide a firmer base for the proposed conceptual framework while offering new insights for sustainable use of the soil resource.

129 citations

Journal ArticleDOI
TL;DR: In this paper, a simple visual technique is proposed to separate macro-aggregated components of different physicogenic and biogenic origins from non-macro-aggaggregate soil on a morphological basis.
Abstract: Soil aggregation and its effects on soil C storage have been addressed in thousands of research articles over the last 40 years. Research has been mostly focused on the resistance of aggregates to mechanical disruption and the role of organic matter in aggregate stabilization. On the other hand, relatively little attention has been paid to identifying the microbial, plant root and macro-invertebrate actors and physical processes that continuously create and destroy aggregates. The sum and dynamics of these processes determines the ability of soils to store and conserve C. Understanding the interactions between aggregation dynamics and C transformations in soils therefore requires a precise identification of the agents that produce aggregates and knowledge of the rates of formation and persistence in the pools thus identified. We propose to separate macro-aggregated components of different, physicogenic and biogenic origins from non-macro-aggregated soil on a morphological basis, using a simple visual technique. The specific biological or physico-chemical agent which produced each individual macro-aggregate can then be determined using Near Infrared Spectroscopy (NIRS). A general description of the distribution and quality of organic matter among the different groups of macro-aggregates can be made. Simple soil re-aggregation or dis-aggregation tests conducted in field conditions further measure the production of different macro-aggregates with time and their mean residence times in the studied soil. Respirometry measurements on each recognized category of macro-aggregates evaluate the respective C losses through respiration. The methods described here will allow the dominant pathways of C flow at a given site to be characterized and possible management options to increase C storage identified. We finally discuss the different assumptions made to build this simple model and offer ways to test the methodology under field conditions.

46 citations


Cited by
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Book ChapterDOI
TL;DR: The issues of nutrient-limited plant growth and nutrient uptake, with special emphasis on the importance of the uptake of nutrients in organic form—both by mycorrhizal and by non-mycorrhIZal plants—and the influence of symbiotic nitrogen fixation are treated.
Abstract: Publisher Summary In this chapter, the advances that have been made in understanding the ecology of the mineral nutrition of wild plants from terrestrial ecosystems have been reviewed. This chapter is organized along three lines. First, the issues of nutrient-limited plant growth and nutrient uptake, with special emphasis on the importance of the uptake of nutrients in organic form—both by mycorrhizal and by non-mycorrhizal plants—and the importance of symbiotic nitrogen fixation is treated. In addition, the influence of allocation patterns on mineral nutrient uptake is described. Next, a few of the nutritional aspects of leaf functioning and how nutrients are used for biomass production by the plant are explored. That is done by studying the nutrient use efficiency (NUE) of plants and the various components of NUE. Finally, the feedback of plant species to soil nutrient availability by reviewing patterns in litter decomposition and nutrient mineralization is investigated. The chapter concludes with a synthesis of the various aspects of the mineral nutrition of wild plants. The chapter ends with a conceptual description of plant strategies with respect to mineral nutrition.

2,552 citations

Journal ArticleDOI
TL;DR: In this article, a review of the mechanisms that are currently, but often contradictorily or inconsistently, considered to contribute to organic matter (OM) protection against decomposition in temperate soils is presented.
Abstract: Summary Mechanisms for C stabilization in soils have received much interest recently due to their relevance in the global C cycle. Here we review the mechanisms that are currently, but often contradictorily or inconsistently, considered to contribute to organic matter (OM) protection against decomposition in temperate soils: (i) selective preservation due to recalcitrance of OM, including plant litter, rhizodeposits, microbial products, humic polymers, and charred OM; (ii) spatial inaccessibility of OM against decomposer organisms due to occlusion, intercalation, hydrophobicity and encapsulation; and (iii) stabilization by interaction with mineral surfaces (Fe-, Al-, Mn-oxides, phyllosilicates) and metal ions. Our goal is to assess the relevance of these mechanisms to the formation of soil OM during different stages of decomposition and under different soil conditions. The view that OM stabilization is dominated by the selective preservation of recalcitrant organic components that accumulate in proportion to their chemical properties can no longer be accepted. In contrast, our analysis of mechanisms shows that: (i) the soil biotic community is able to disintegrate any OM of natural origin; (ii) molecular recalcitrance of OM is relative, rather than absolute; (iii) recalcitrance is only important during early decomposition and in active surface soils; while (iv) during late decomposition and in the subsoil, the relevance of spatial inaccessibility and organo-mineral interactions for SOM stabilization increases. We conclude that major difficulties in the understanding and prediction of SOM dynamics originate from the simultaneous operation of several mechanisms. We discuss knowledge gaps and promising directions of future research.

2,332 citations

Journal ArticleDOI
01 Sep 1997-Oikos
TL;DR: In this paper, the authors analyzed first-year leaf litter decomposition data from 44 locations, ranging from cool temperate sites to humid tropical sites, and found that the control of AET on litter decomposability is partly mediated through an indirect effect of Aet on litter chemistry.
Abstract: Litter decomposition is an important component of the global carbon budget. Due to the strong climatic control of litter decomposition, climate change may significantly affect this pathway. This review quantifies the climatic influences on litter decomposition rates, both directly and indirectly through effects on litter chemistry. To this end, I analysed first-year leaf litter decomposition data from 44 locations, ranging from cool temperate sites to humid tropical sites. Actual evapotranspiration (AET) was used as an index for the climatic control on decomposition. As litter chemistry parameters I included N and P concentrations, C/N and C/P ratios, lignin concentrations, and lignin/N and lignin/P ratios. At a global scale, climate (expressed as AET) is the best predictor for the decomposition constants (k-values) of the litter, whereas litter chemistry parameters have much lower predictive values. Path analysis showed that the control of AET on litter decomposability is partly mediated through an indirect effect of AET on litter chemistry. Thus, the relation between climate, leaf litter chemistry and leaf litter decomposition is a triangular relationship. Mean AET in the humid tropical region is three times as high as in both the temperate and the Mediterranean region and this results in a more than six-fold increase in mean k-values. However, due to the large variability in k-values within each region there is a considerable overlap in k-values between the tropics and the other climatic regions. Within a particular climatic region litter chemistry parameters are the best predictors of k-values, especially in the tropics, whereas the percentage of variance in k-values explained by AET is low or absent. In general, litters from the tropical sites have higher N concentrations and lower lignin/N ratios than litters from other climatic regions. In both the tropics and in the Mediterranean region, the lignin/N ratio is the best chemical predictor of litter decomposability. In the temperate region, however, there is no good chemical predictor of litter decomposability.

1,559 citations

Journal Article
TL;DR: Cette revue place au centre des interactions entre les plantes, les animaux et les microorganismes du sol, les invertebres abondants et de grande taille qui ingerent des particules organiques and minerales produisant ainsi des structures durables.

1,101 citations

Journal ArticleDOI
TL;DR: The role of ants in ecosystems is discussed in this article, mainly from the perspective of the effects of ground-dwelling ants on soil processes and function, emphasizing their role as ecosystem engineers.
Abstract: Ants are important components of ecosystems not only because they constitute a great part of the animal biomass but also because they act as ecosystem engineers. Ant biodiversity is incredibly high and these organisms are highly responsive to human impact, which obviously reduces its richness. However, it is not clear how such disturbance damages the maintenance of ant services to the ecosystem. Ants are important in below ground processes through the alteration of the physical and chemical environment and through their effects on plants, microorganisms, and other soil organisms. This review summarizes the information available on ant biodiversity patterns, how it can be quantified, and how biodiversity is affected by human impacts such as land use change, pollution, invasions, and climate change. The role of ants in ecosystems is discussed, mainly from the perspective of the effects of ground-dwelling ants on soil processes and function, emphasizing their role as ecosystem engineers. Some lines of research are suggested after demonstrating the gaps in our current information on ant-soil interactions.

902 citations