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Exploring the biological dimension to pedogenesis with emphasis on the ecosystems, soils and landscapes of southwestern Australia
Abstract
This review collates and discusses an ever increasing body of evidence indicating that biota from across the world have contributed proactively towards engineering of specific pedogenetic events, and have done so from the most primitive ecosystems of the Precambrian onwards. We consider particularly modern counterparts, including podzols and mollisols and especially oligotrophic ecosystems of semi-arid, temperate Australia. In the latter setting, outcomes generated by relevant biota include widespread development of various lateritic imprints associated with cluster-root bearing species and the equally prevalent generation of highly characteristic clay platforms in the lateral root catchments of eucalypts. These, alongside other minor modifications of soil profiles such as formation of biopores and generation of hydrophobicity, fall generally within our all-embracing “Phytotarium Concept”. This envisages that specific plant players and accompanying microbiota create niches in which maximal access to limiting resources of water and nutrients is mediated. Experimental studies of mechanisms involved in the better known of these cases are described and short- and long-term effects on stability of soils and diversity of natural ecosystems examined in a range of geographical situations. Special sections of the review deal with relationships within and between competing phytotaria of different type in past and contemporary settings, and with the principal effects evident where erosive forces rejuvenate landscapes and sponsor emergence and spread of new classes of phytotaria. Final comments stress, among other issues, the need for further research on feedbacks between macro fauna and flora and the plethora of microorganisms which directly or indirectly shape a pedogenetic scenario.
... There is a growing consensus that dominance of Eucalypts in Eastern Australia appears to have only occurred widely in the previous 5,000 -6,000 years (mid Holocene) at the cessation of sea level rise following the last glacial maximum (Kershaw et al., 1991;Crowley, 1994). This could be highly significant in terms of the recent findings of Verboom and Pate (2013), who concluded that some mallee species of Eucalypt can change soils from acidic sandy Tenosols (deep acid sands) into Sodosols through the generation of clay from its chemical components (Al and Si) and the creation of a clay rich and alkaline B horizon (discussed in section 2.6 of this review). ...
... The processes posed in Table 2.3 include the surface processes of Paton (1978) and Paton et al. (1995) along with a simplification of some of the vertical zonal processes of the Northern Hemisphere given in Bockheim et al. (2005) and outlined in Yaalon (1971). McKenzie et al. (2004) also comment on early thoughts of Verboom's theory or phytotaria (plant communities that can generate soil specific to their own needs) (Verboom and Pate, 2013) discussed later in this section. ...
... Other processes -plants creating soil Verboom (2009), Verboom et al. (2010) and Verboom and Pate (2013) demonstrated that some mallee eucalypt species in Western Australia are capable of creating clay from its dissolved chemical components in the groundwater and soil solution of a quartz rich sand dune, to form a Sodosol soil. In terms of the conventional understanding of soil formation processes this finding is unusual and warrants consideration in the frame of reviewing and adding to conventional concepts of soil formation. ...
Soil development and soil formation processes are often considered to take long periods of time from hundreds to millions of years. This thesis investigates the potential for land use change to drive whole soil profile development processes in unexpected ways and at unexpected speeds in Eastern Australia. The major objectives of this thesis were to identify and document locations where rapid soil profile changes occur at a land use boundary, to investigate the nature of soil changes across that boundary and propose mechanisms for observed changes.
Alternating arid and humid phases in the Quaternary, coupled with contemporary Holocene and Anthropocene sub-decadal climate variability, makes availability of soil water in Eastern Australia a critical driver to soil development processes. In contrast, many northern climates are constant or at least seasonal and moist.
An initial study (Chapter 3) was undertaken using archival soil survey data from the Liverpool Plains region in the north-west slopes and plains of New South Wales (NSW). The desktop study examined key soil fertility properties in relation to land use through an historical soil survey dataset to determine whether large-scale European land use impacts on whole soil profiles could be observed. Land uses compared were cropping, native pasture, improved pasture and woodland. Soil type, land use, and soil × land use were considered in a mixed model restricted maximum likelihood (REML) analysis using general fertility attributes of available water holding capacity (AWC), soil phosphorus (Bray P), cation exchange capacity (CEC), dispersion percentage (DP), salinity (ECe), sodicity (indicated by exchangeable sodium percentage, ESP) and soil pH. Results showed that fertility attribute variation depended on soil type reflecting land selection for agriculture. Soil organic carbon (SOC) values were considered a product of fertility but were most strongly associated with land use with SOC being lowest in cropping regardless of soil type. This approach did not illuminate any man-induced whole soil profile changes. General soil survey data was found to be potentially limited by the method of land use and site history recording.
The second study (Chapters 4 and 5) investigated physical and chemical soil profile changes associated with managed tropical pastures compared with volunteer native pastures on sodic-duplex soils in north-western NSW. These soils are limited by low fertility topsoils, poor soil profile drainage and clay-rich B horizons which native vegetation roots and soil water do not readily penetrate. Results indicated that deeper, more abundant tropical pasture roots had initiated changes in soil profile porosity, structure and chemistry. Macroporosity (pores > 30µm) of critical infiltration and root growth limiting upper B horizons had increased in tropical pasture soils to a point where potential water through flow was 81 fold higher than native pasture upper B horizons.
B horizons under tropical pastures were more aggregate stable than under native pastures. Soil stability was investigated through dispersion and flocculation experiments with varying concentrations of synthetic soil water based on tropical pasture topsoil water chemistry. Higher aggregate stability of upper B horizon material was associated with increased ionic strength and composition of soil water from topsoils in tropical pastures. A feedback mechanism was proposed that introduction of a pasture species which utilises deeper subsoil resources created extra macroporosity. Macropores were stabilised by the chemistry of soil water from managed tropical pastures allowing further development of root structures and potential water storage deeper in the profile.
A third study (Chapter 6) was undertaken at Tenterfield in the NSW New England Tablelands. The study utilised a boundary between relatively undisturbed native forest and land which was cleared for grazing 140 years prior. Using methods developed in Chapter Four, soil physical and chemical attributes were compared between native forest and managed pasture along the forest-pasture boundary. All forested soil profiles were Red Dermosols, whilst all pasture soils were texture contrast soils including Kurosols and Chromosols. A thin, often discontinuous A2 (E horizon) was apparent in the pasture soils with very clear boundaries between A and B horizons. Forested soils had gradational soil texture profiles and a well-developed AB horizon.
The existence of megapores (mean diameter 2 cm) throughout forest soil profiles was a driver of potential soil profile drainage maintaining Dermosols in a freely drained state. A feedback mechanism is proposed whereby clearing and grazing results in compaction of topsoils, infilling/collapse of tree root megapores, and consequent drainage impedance. Drainage impedance creates favourable conditions for clay illuviation and subsequent formation of a texture contrast texture profile. The time frame for development of A2 horizons through clay illuviation was likely to have occurred within 140 years instead of millennia that the literature suggests.
The significance of this work is that rapid and deep soil changes can be initiated by man simply through changing plant root architecture and thence water penetration to soil. A change in philosophy of crop and pasture development towards maximising root abundance and penetration is recommended so that benefits of greater subsoil access by plants are realised, especially in landscapes that have low productivity because deep soil resources have been unavailable. Beneficial soil changes such as these should be considered crucial to improving soil resilience as climate change impacts on Australia’s grazing systems.
... laterite), and still not fully understood. For example, the complexity in unravelling the origin of laterite is exemplified by Verboom and Pate (2013) who propose a complex plant-mediated influence interacting with geological substrate and geomorphological processes. ...
... Given that southwestern Australia is a floral biodiversity hotspot, a focus on the connection between flora and laterite landscapes can be made (e.g. Verboom and Pate 2013). Flora in southwestern Australia that has evolved on an old, stable, and infertile landscape is highly adapted to cope with low nutrient levels and environmental stress. ...
Regolith in some regions has become a world famous and highly valued tourism attraction or is an emerging geotourism focus. However, there remains much scope for valuing what regolith can offer within the framework of geotourism. We thus present a case for a more inclusive approach to involving regolith in geotourism agendas and illustrate the utility of such an approach using the example of regolith occurring in southwestern Australia. Our case is supported by re-visiting the theoretical framework that underpins geotourism and by considering the status of geotourism in Western Australia. The value of regolith as a topic in geotourism is explained through provision of a simplified scientific background for a range of regolith types from southwestern, Australia. We provide guidance on indicative interpretive content that could be delivered by trained guides. Whilst emphasising that such an approach sets the scene for profiling regolith within geotourism agendas in Western Australia, we also contend that by simplifying the science, recognising its importance in our lives, in combination with an understanding of the sociological objectives of geotourism, regolith can readily be built into geotourism programmes around the world.
... More general discussions of how geomorphological and pedological processes may influence natural selection include Corenblit et al. (2007aCorenblit et al. ( , 2010, Phillips (2009Phillips ( , 2016b, and Verboom and Pate (2013). ...
... According to Wilkinson (2003), nutrient cycling is an emergent property of the minimum ecological processes necessary to support carbon-based life. The phytotarium concept of Verboom and Pate (2013) involves biogeochemical selection, whereby specific plant layers and associated microbes create niches to maximize access to limiting resources of water and nutrients. Lapenis (2002) proposed biogeochemical selection as a way to explain "Gaian" evolution of the biosphere, and Doolittle (2017) took this idea further. ...
Darwinian natural selection acting on individuals is one of only several types of selection influencing landscape evolution. Ecological filtering and abiotic selection (including the least action principle and preferential flows) apply. The overarching principle is one of efficiency selection, whereby more efficient, stable, and durable forms, structures, patterns, networks, and flux pathways are more likely to occur, grow, and persist than less efficient ones. Particularly important forms are gradient selection, favoring steeper and faster flow paths; resistance selection, whereby more resistant features are preferentially preserved; biogeochemical selection, which favors more rapid elemental cycling; network selection, which makes more efficient flux and interaction networks more likely; and thermodynamic selection, reflecting the advantages of energy use efficiency. Efficiency selection is highly local, however, one of several reasons that landscapes and environmental systems are not always inevitably becoming more efficient overall. A case study illustrating selection principles is given.
... Replicate samples of each stage were examined for proportions of sand, silt and clay and mineralogical composition. Bulk densities were previously reported by Verboom et al. (2010) and Verboom and Pate (2013). Each replicate sample was oven-dried and lightly ground before analysis. ...
... Earlier papers on the eucalypt system (Verboom and Pate, 2009a, b, 2010, 2013Pate and Verboom, 2009) have drawn attention to the ecological effects of dense clayey B horizons. Nutrient relationships will involve in particular the sequestration of key elements and attendant changes in soil reactions and possible modifications in nutrient availability by microbiota in the pavements. ...
Background and aims:
Previous studies have described the laying down of specific B horizons in south-western Australian ecosystems. This paper presents biomolecular, morphological and physicochemical analyses elucidating the roles of specific woody plant taxa and rhizosphere bacteria in producing these phenomena.
Methods:
Clayey deposits within lateral root systems of eucalypts and appropriate background soil samples were collected aseptically at multiple locations on sand dunes flanking Lake Chillinup. Bacterial communities were profiled using tagged next-generation sequencing (Miseq) of the 16S rRNA gene and assigned to operational taxonomic units. Sedimentation, selective dissolution and X-ray diffraction analyses quantitatively identified clay mineral components. Comparisons were made of pedological features between the above eucalypt systems, giant podzols under proteaceous woodland on sand dunes at the study site of Jandakot and apparently similar systems observed elsewhere in the world.
Key results:
Bacterial communities in clay pods are highly diverse, resolving into 569 operational taxonomic units dominated by Actinobacteria at 38.0-87.4 % of the total reads. Multivariate statistical analyses of community fingerprints demonstrated substrate specificity. Differently coloured pods on the same host taxon carry distinctive microfloras correlated to diversities and abundances of Actinobacteria, Acidobacteria, Firmicutes and Proteobacteria. A number of these microbes are known to form biominerals, such as phyllosilicates, carbonates and Fe-oxides. A biogenic origin is suggested for the dominant identified mineral precipitates, namely illite and kaolinite. Comparisons of morphogenetic features of B horizons under eucalypts, tree banksias and other vegetation types show remarkably similar developmental trajectories involving pods of precipitation surrounding specialized fine rootlets and their orderly growth to form a continuous B horizon.
Conclusions:
The paper strongly supports the hypothesis that B-horizon development is mediated by highly sophisticated interactions of host plant and rhizosphere organisms in which woody plant taxa govern overall morphogenesis and supply of mineral elements for precipitation, while rhizosphere microorganisms execute biomineralization processes.
... I finally became aware of their work when they synthesized it in an article in Geoderma (Verboom & Pate, 2013), a key soil science journal that I follow (I am actually on the editorial board). I immediately contacted Verboom, apologized for not citing their work, and asked for reprints of the earlier stuff, which he sent at once. ...
... No matter how diligent we are, given our finite time and the everexpanding scientific corpus, our normal search patterns are not going to detect it all. Thus we should be thankful rather than annoyed when reviewers point out things we missed, and for serendipitous discoveries, such as when I happened on Verboom and Pate (2013). Second, we should perhaps pay more attention to the keywords we submit with our papers to increase the likelihood that our work falls into the hands of those outside our specialty groups. ...
This document is a collection of Jonathan Phillips’ Geoscience Blog posts from its inception (29 May 2014) through 2 July 2017. The major sections include (1) How it's Done; (2) Earth Surface System Theory 1: Equilibrium & Otherwise; (3)Earth Surface System Theory 2: Nonlinear Dynamics, Complexity, Self-Organization, Power Laws; (4) Earth Surface System Theory 3: Optimality & Selection; (5) Forest Biogeomorphology; (6) Climate & Sea-Level Rise; (7) Coevolution; (8) Rivers & Streams; (9) Environmental Management; (10) Geomorphology; (11) Soil, Regolith & Karst
... This pattern was basically confirmed for alpine soils using pedon-scale mass balances. In most regions, however, gradients in climate are related to gradients in vegetation, which may interact with or superimpose effects of climate on soil development and weathering (Goudie and Viles, 2012;Verboom and Pate, 2013). ...
... This process counteracts leaching of some elements ('biological base enrichment'; Bockheim and Gennadiyev, 2000) and also affects solution chemistry (Lucas, 2001). Whereas the general effect of plants on weathering (compared to the pure 'abiotic' process) is relatively well understood, the effect of vegetation types or functional species composition on weathering seems to be largely unknown (Verboom and Pate, 2013). ...
Human activities affected ecosystems worldwide to such an extent that there is even discussion that we have
entered a new geological epoch, the Anthropocene. Although numerous studies quantified human impact on
varies ecosystem processes and properties, the natural state of many ecosystems and their soils remains
unknown. Moreover, human influence is manyfold across space and time and is therefore hard to quantify. In
the high Andes (4500 m a.s.l.) paired plots were identified, one part under continuous grazing (rangeland)
since at least four millenia, the other part pristine (bunch grass and forest) due to isolation by cliff-faces. In
situ pedogenesis (commencing ca. 5 kyears BP) was indicated by gradually decreasing rock-fragments in
the soil profile and fingerprinting with rare earth elements. Here we will show the integrated effects on
nitrogen and phosphorous cycling of ecosystems developed with and without grazing pressure for at least
four millenia. Stocks of C and N in the mineral soil were not significantly different in pristine and rangeland
ecosystems. Stocks of P in rangeland soil (590 g m-2), however, increased by a factor of 2 (bunchgrass, 270
g m-2) and 3.8 (forest, 160 g m-2). Pedogenetic mass balances revealed that pristine soils lost 40-90 kg P m-
2 whereas rangeland soils accumulated 150 kg P m-2 during soil development. P-accumulation was
attributed to P-import from remote areas. Microbial biomass C and N stocks were significantly higher in
pristine soils (2 and 2.5-fold). Carbon-nutrient stoichiometry indicated P-limitation in pristine and N-limitation
in rangeland soils. This indication was corroborated by much higher δ15N-values in rangeland as compared to pristine plants and soils. N-limitation in rangelands could be explained by hampered organic matter
decomposition due to higher proportions of exchangable Al3+ and Al-humus associations. More than 50% of
P were associated with amorphous pedogenic Fe/Al oxyhydroxides in rangelands and only one third in
pristine ecosystems. Under the cold and semi-humid conditions of the sites, organic matter was apparently a
more effective P-sink compared to pedogenic oxides. Analysis of more remote rangeland sites will reveal the
long-term effects grazing under conditions of P-depletion and P-preservation (relative to pristine ecosystems)
on nutrient cycling. With the current work, we could show for the first time differences in N and P-cycling in
ecosystems, which developed from the beginning with and without grazing.
... This pattern was basically confirmed for alpine soils using pedon-scale mass balances. In most regions, however, gradients in climate are related to gradients in vegetation, which may interact with or superimpose effects of climate on soil development and weathering (Goudie and Viles, 2012;Verboom and Pate, 2013). ...
... This process counteracts leaching of some elements ('biological base enrichment'; Bockheim and Gennadiyev, 2000) and also affects solution chemistry (Lucas, 2001). Whereas the general effect of plants on weathering (compared to the pure 'abiotic' process) is relatively well understood, the effect of vegetation types or functional species composition on weathering seems to be largely unknown (Verboom and Pate, 2013). ...
Human activity affects properties and development of ecosystems across the globe, to such a degree that it is nowadays challenging to get baseline values for undisturbed ecosystems. This is especially true for soil development, which is potentially affected by land-use history and holds a legacy of past human interventions. Therefore, it is still largely unknown, for most ecozones, how soil would have developed “naturally”. Here, we show undisturbed soil development, i.e., the processes of weathering and accumulation of soil organic matter (SOM), by comparing pristine with grazed sites in the high Andes (4500 m) of southern Peru. We located study plots on a large ledge (0.2 km²) that is only accessible with mountaineering equipment. Plots with pristine vegetation were compared to rangeland plots that were presumably under relatively constant grazing management for at least four millennia. Vegetation change, induced by grazing management, led to lower vegetation cover of the soil, thereby increasing soil surface temperatures and soil acidification. Both factors increased weathering in rangeland soils. Formation of pedogenic oxides with high surface area explained preservation of SOM, positively feeding back to acidification. Higher contents of pyrophosphate extractable Fe and Al oxides indicated the importance of organo-mineral associations for SOM stabilisation on rangeland sites, which are likely responsible for a higher degree of humification. This higher degree of humification induced melanisation (darker colour) of the rangeland soils which, together with sparse vegetation cover, also feeds back to soil temperature. With this work, we present a conceptual framework of positive feedback links between human-induced vegetation change, soil development and accumulation of SOM, which is only possible due to the unique baseline values of a pristine ecosystem. Using “inaccessibility” as a tool to quantify human impact in future interdisciplinary studies may push research forward on evaluating anthropogenic impact on Earth’s ecosystems.
... Just as habitat characteristics and resources can encourage some and discourage other organisms from establishing or thriving at a site, so they can foster or stifle interrelationships. Selection also occurs at the ecosystem level, whereby relationships such as those involved in biogeochemical and energy cycling may be selected for when they maximize efficiency and stability (Lotka, 1922;Patten, 1995;Lapenis, 2002;Eagleson, 2002;Fath et al., 2004;Wilkinson, 2003;del Jesus et al., 2012;Verboom and Pate, 2013;Cong et al., 2017;Zhang et al., 2021;Phillips, 2021). ...
In Earth surface systems (ESS), everything is connected to everything else, an aphorism often called the First Law of Ecology and of geography. Such linkages are not always direct and unmediated, but many ESS, represented as networks of interacting components, attain or approach full, direct connectivity among components. The question is how and why this happens at the system or network scale. The crowded landscape concept dictates that linkages and connections among ESS components are inevitable. The connection selection concept holds that the linkages among components are (often) advantageous to the network and are selected for, and thereby preserved and enhanced. These network advantages are illustrated via algebraic graph theory. For a given number of components in an ESS, as the number of links or connections increases, spectral radius, graph energy, and algebraic connectivity increase. While the advantages (if any) of increased complexity are unclear, higher spectral radii are directly correlated with higher graph energy. The greater graph energy is associated with more intense feedback in the system, and tighter coupling among components. This in turn reflects advantageous properties of more intense cycling of water, nutrients, and minerals, as well as multiple potential degrees of freedom for individual components to respond to changes. The increase of algebraic connectivity reflects a greater ability or tendency for the network to respond to changes in concert.
... Its origins lie with Charles Darwin and his work on earthworms (Darwin 1881) and then developed over a century later by Donald Lee Johnson (1993aJohnson ( , 1993b) and David R. Butler (1995), whose ideas began the rediscovery of life as a major factor in soil evolution, aided in part by studies in biogeomorphology (e.g. Johnson 1993b;Butler 1995;Verboom and Pate 2013;Pawlik andŠamonil 2018). ...
The idea that soil or the pedosphere is connected to the other terrestrial spheres dates back at least to 1880. Some 26 years later, the interdependency of the terrestrial spheres was established, but a fully integrative approach to addressing the interdependence of the biosphere, pedosphere, atmosphere, hydrosphere, geosphere, and toposphere did not emerge until the advent of Earth Systems Science during the 1980s. A significant development within the Earth Systems approach was a re-evaluation of the pedosphere’s role in the global system, the outcome of which is at least twofold: first, an appraisal of the pedosphere as a two-way interactor with the other terrestrial spheres, the study of which has given rise to some “new” pedologies—biopedology, geopedology, topopedology, hydropedology, and anthropopedology; and second, the pedosphere as a key component of what has become known as the Earth’s Critical Zone. The background, current status, and prospects of these hybrid pedologies and the extent to which they truly deal with interdependencies within the environment are the focus of this article.
... Its origins lie with Charles Darwin and his work on earthworms (Darwin 1881) and then developed over a century later by Donald Lee Johnson (1993aJohnson ( , 1993b) and David R. Butler (1995), whose ideas began the rediscovery of life as a major factor in soil evolution, aided in part by studies in biogeomorphology (e.g. Johnson 1993b;Butler 1995;Verboom and Pate 2013;Pawlik andŠamonil 2018). ...
The idea that soil or the pedosphere is connected to the other terrestrial spheres dates back at least to 1880. Some 26 years later, the interdependency of the terrestrial spheres was established, but a fully integrative approach to addressing the interdependence of the biosphere, pedosphere, atmosphere, hydrosphere, geosphere, and toposphere did not emerge until the advent of Earth Systems Science during the 1980s. A significant development within the Earth Systems approach was a re-evaluation of the pedosphere’s role in the global system, the outcome of which is at least twofold: first, an appraisal of the pedosphere as a two-way interactor with the other terrestrial spheres, the study of which has given rise to some “new” pedologies—biopedology, geopedology, topopedology, hydropedology, and anthropopedology; and second, the pedosphere as a key component of what has become known as the Earth’s Critical Zone. The background, current status, and prospects of these hybrid pedologies and the extent to which they truly deal with interdependencies within the environment are the focus of this article.
... Just as habitat characteristics and resources can encourage some and discourage other organisms from establishing or thriving at a site, so they can foster or stifle interrelationships. Selection also occurs at the ecosystem level, whereby relationships such as those involved in biogeochemical and energy cycling may be selected for when they maximize efficiency and stability (Lotka, 1922;Patten, 1995;Lapenis, 2002;Eagleson, 2002;Fath et al., 2004;Wilkinson, 2003;del Jesus et al., 2012;Verboom and Pate, 2013;Cong et al., 2017;Zhang et al., 2021;Phillips, 2021). ...
In Earth surface systems (ESS), everything is connected to everything else, an aphorism often called the First Law of Geography and of ecology. Such linkages are not always direct and unmediated, but many ESS, represented as networks of interacting components, attain or approach full, direct connectivity among components. The question is how and why this happens at the system or network scale. The crowded landscape concept dictates that linkages and connections among ESS components are inevitable. The connection selection concept holds that the linkages among components are advantageous to the network and are selected for and thereby preserved and enhanced. These network advantages are illustrated via algebraic graph theory. For a given number of components in an ESS, as the number of links or connections increases, spectral radius, graph energy, and algebraic connectivity increase. While the advantages (if any) of increased complexity are unclear, higher spectral radii are directly correlated with higher graph energy. The greater E(g) is associated with more intense feedback in the system, and tighter coupling among components. This in turn reflects advantageous properties of more intense cycling of water, nutrients, and minerals, as well as multiple potential degrees of freedom for individual components to respond to changes. The increase of algebraic connectivity reflects a greater ability or tendency for the network to respond in concert to changes.
... That is, faster, and more efficient entities, structures, pathways, and relationships tend to persist and grow at the expense of those that are less so. This applies to, e.g., energy fluxes (Fath et al., 2004;Lotka, 1922;Patten, 1995); biogeochemical cycles (Lapenis, 2002;Lotka, 1922;Wilkinson, 2003); plant-soil interactions (Verboom and Pate, 2013); and water use by plants (Eagleson, 2002). • Selection applies to abiotic energy and mass fluxes. ...
An approach to landscape and Earth surface system evolution is outlined based on the inseparability of landform, soil, and ecosystem development, versus the traditional semi-independent treatment of geomorphic, ecological, pedological, and hydrological phenomena. Key themes are the coevolution of biotic and abiotic components of the environment; selection whereby more efficient and/or durable structures, forms, and patterns are preferentially formed and preserved; and the interconnected role of laws, place factors, and history. Existing conceptual frameworks for evolution of geomorphic, soil, ecological, and hydrological systems are reviewed and contrasted with the integrated approach.
... Biotic-abiotic feedbacks during evolution of life forms, landforms, and soils and coevolution of biotic and geomorphic entities provides abundant evidence that landscape evolutionary creativity can occur in concert with biological evolution (e.g., Corenblit et al., 2007;2011;Phillips, 2009;Davies and Gibling, 2010;Verboom and Pate, 2013). ...
The Perfect Landscape is a broad, but formally expressed, conceptual model incorporating the law-place-history explanatory triad, explicitly dealing with contingency, and recognizing the interplay of individuality and idiosyncrasies in Earth surface system with shared characteristics and regularities. It holds that individual landscapes reflect a combination of general laws and geographically and historically contingent controls that are highly improbable in terms of duplication elsewhere. The Perfect Landscape concept also indicates that landscape individuality and idiosyncrasy can only increase as more variables are considered. An approach to analyzing and understanding perfect landscapes is based on nine axioms for landscape interpretation. The evolution of perfect landscapes requires creativity in the form of the appearance of new features that are selected for. Several lines of evidence that such creativity occurs in abiotic as well as biotic aspects of landscapes are presented.
... Thus, in this situation greater values of LA are not related to high metabolic activity but to a relatively conservative resource use and potentially greater leaf lifespan, as clay-poor soils are usually associated with a lower capacity for nutrient retention. Roots of Myrtaceae species are known for their capacity to create clay or silcretes (Verboom & Pate, 2013) and it is interesting to note the association of Eugenia punicifolia (Myrtaceae) with a plot showing the highest clay content. We only found E. punicifolia occurring at the highest clay contents in all our study areas, where it is present at high abundance (14 individuals). ...
Environmental filtering and niche differentiation are often invoked to explain species coexistence at local scales. The ironstone campo rupestre of Brazil provides a biodiverse natural experiment in which edaphic gradients represent filters to test the hypothesis that plant community functional composition, despite converging on extreme stress tolerance, exhibits a co-structure with environmental parameters. At the Serra do Rola-Moça State Park, soil physico-chemical parameters were characterized alongside community weighted mean plant functional traits and Grime’s competitor, stress-tolerator and ruderal strategies for species at each sampling site. In general, species exhibited a high degree of stress tolerance (between 72.6% and 100%), while ruderalism was 0% for all species. Soil nutrients related to plant metabolism (e.g. P, Ca, Mg) were associated with the stress tolerant strategy and with traits involved in the leaf economics and size spectra. Despite a major edaphic filter selecting stress tolerance, fine-scale microhabitat variability represented by soil parameters related to fertility (i.e. P, Ca, Mg) and water retention capacity (i.e. clay content) was associated with subtle variation in ecological strategies and functional traits of species in the ironstone campo rupestre.
... The passive bioprotective function of standing and downed trees in limiting erosion and mass movements is well known (Osterkamp and Hupp, 2012), but woody vegetation also has strong active biochemical (Binkley and Giardina, 1998;Verboom and Pate, 2013), biomechanical are reviewed briefly below. Bark beetles (or other tree mortality events) may have important impacts on wood delivery to fluvial systems. ...
https://authors.elsevier.com/a/1blC23HcE1cwu3
Outbreaks of bark beetles, for example Ips typographus L. in Eurasia or Dendroctonus ponderosae Hopkins in North America, have serious impacts on forest resources, biodiversity, and ecological dynamics, with economical and social ramifications. Moreover, many models predict increasing frequency and severity of such biotic disturbances due to ongoing climate change, and land use driven changes in forest structure and composition. Bark beetles are recognized as keystone species due to their strong and complex effects on ecosystem dynamics. However, due to the increasingly widely recognized biogeomorphic impacts of trees, bark beetles may have significant indirect biogeomorphic and pedogenetic impacts through their effects at scales ranging from individual trees to forest landscapes. These include: (1) Reduced uprooting, with associated impacts on topography , mass movements, regolith and soil formation, and slope hydrology; (2) Reductions in bioprotection via trapping of downslope sediment movement; (3) Hydrological impacts, including increased total runoff and increased proportion of subsurface flow; (4) Decreased microtopographic irregularity (and associated hydrological and pedological impacts); and (5) Changes in biochemical and biomechanical effects on soils, regolith, and hillslope morphology. Five separator factors (discriminators between different developmental trajectories) were revealed for the case of the central European region. These factors may determine the occurrence and severity of biogeomorphic impacts: First is whether the site is prone to potential uprooting or whether an spruce bark beetle (SBB) outbreak is initiated by a blowdown/uprooting event. Second is whether the site is dominated by mineral soils or Histosols. A third discriminating factor is whether the forest is managed or unmanaged, which determines the pre-attack tree species composition and coarse woody debris and disturbance regimes; and a fourth is the post-outbreak management. Finally, the fifth separator factor relates to slope thresholds that determine the significance of impacts on mass movements and erosion. These findings support the need, and provide guidelines , for research on geomorphic impacts of bark beetle infestations. Though we mainly restrict our consideration to bark beetles in Europe, both our approach and findings are likely to have broader relevance for biogeomorphic impacts of extensive tree mortality.
... Hole, 1961;Johnson, 1990;Peacock & Fant, 2002;Johnson et al., 2005aJohnson et al., , 2005bSaco & Moreno-de las Heras, 2013;Gabet et al., 2014;Fleming et al., 2014;Johnson & Schaetzl, 2015); it is also benefitting from research in biogeomorphology (e.g. Verboom & Pate, 2013;Pawlika & Šamonil, 2018; see also Huggett, 2017). ...
The Peak District is a landscape of contrasts – bleak moorland plateaux with escarpments (edges) and deep valleys of the Dark Peak and Eastern Moors; dales and caves of the White Peak fashioned out of limestones, sandstones (gritstones), and shales – all modified by glacial, periglacial, and paraglacial processes during Quaternary ice ages. The Dark Peak is especially vulnerable to landslides and other mass movements; several well-known deep-seated landslides have occurred there. Karstification of the White Peak limestones has created a prime example of relict fluviokarst and extensive cave systems, many of which contain fine displays of speleothems. Humans have exploited the rock and mineral resources of the Peak District, mining for lead, copper, fluorspar and other minerals, with limestone aggregates and sandstone building stones being the chief current commodities. Mining and quarrying have produced human-made landforms: mine shafts, spoil heaps, quarries. Balancing the region’s geological heritage with tourism and the livelihoods of residents presents a challenge for geoconservation efforts.
... Hole, 1961;Johnson, 1990;Peacock & Fant, 2002;Johnson et al., 2005aJohnson et al., , 2005bSaco & Moreno-de las Heras, 2013;Gabet et al., 2014;Fleming et al., 2014;Johnson & Schaetzl, 2015); it is also benefitting from research in biogeomorphology (e.g. Verboom & Pate, 2013;Pawlika & Šamonil, 2018; see also Huggett, 2017). ...
Ideas about soil have a long and rich history. It is perhaps easy to dismiss older notions as outmoded, but the foundations of soil science laid down by the creators of the subject still have currency, even though later thinkers have refined them and added new elements. Expanding a metaphor, if Isaac Newton could see further by standing on the shoulders of giants, then modern soil scientists can see further by standing in the soil pits of their predecessors. This chapter will explore the view taken by Hans Jenny, a veritable giant among soil scientists, that soil may be regarded as a system. Jenny mooted this idea in 1930, but soil concepts developed in the five decades before that date provide an essential background and they will be discussed first, before considering soil as a system, soil as a spatial system, and soil as an interdependent system. It will end with a brief look at prospects for the systems approach in pedology.
... Through selection (i.e., niche-based processes), differences in diversity may be generated because hosts may modify the rhizosphere as they grow and thus change the shape or size of the available microbial niche space in the soil (i.e., "niche construction") (Chaparro, Badri, & Vivanco, 2014;Marques et al., 2014;Meaden, Metcalf, & Koskella, 2016;Micallef, Channer, Shiaris, & Colón-Carmona, 2009;Odling-Smee, Erwin, Palkovacs, Feldman, & Laland, 2013;Wagner et al., 2016). In turn, the potential formation of feedbacks between microbial community assembly processes and pedogenetic soil formation (Verboom & Pate, 2013) could reinforce an increase in niche formation over time. Alternatively, larger hosts, by creating more habitable space compared to smaller hosts, may harbour greater diversity associated with greater immigration (i.e., bigger or smaller island in the context of Island Biogeography Theory or Neutral Theory) (Hubbell, 2001;MacArthur & Wilson, 2015). ...
A major goal in microbial ecology is to understand the factors that structure bacterial communities across space and time. For microbes that are plant symbionts, community assembly processes can lead to either a positive or negative relationship between plant size or age and soil microbe diversity. Here, we evaluated the extent to which such relationships exist within a single legume species (Acacia acuminata) and their naturally occurring symbiotic nitrogen‐fixing bacteria (rhizobia).
We quantified the diversity of rhizobia that associate with A. acuminata trees of variable size spanning a large environmental gradient in southwest Australia (72 trees in 24 sites spread across ~300,000 km²), using metabarcoding. We modelled rhizobia diversity using 16S exact genetic variants, in a binomial multivariate statistical framework that controlled for climate and local soil characteristics.
We identified two major phylogenetic clades of rhizobia that associate with A. acuminata. Soil sampled at the base of larger Acacia trees contained a higher richness of rhizobia genetic variants. Each major clade responds differently to environmental factors (climate and soil characteristics), but the positive association between tree size and rhizobia genetic diversity was mainly driven by responses from one of the two clades. Overall tree size explained more variation than any other factor, resulting in a ~3‐fold increase in total richness and clade diversity from the smallest to the largest trees.
Synthesis. Previous studies have shown that plant host species is important in structuring microbial soil communities in the rhizosphere. Our results show that host size or age within a single plant species can also structure diversity of at least one group of soil microbes. A positive relationship between plant host size and rhizobia diversity suggests that hosts may modify the niche space of their surrounding soil (niche construction hypothesis) enabling a higher richness of microbial taxa. That different rhizobial groups responded differently to host size and other ecological factors suggests that rhizobia is not an ecologically uniform group, and that entirely neutral explanations for our results are unlikely. Host plants may be analogous to “islands,” where larger plant hosts may accumulate diversity over time, through migration opportunities.
... Trees can be a factor leading to the development of texture contrast soils (Phillips 2007). Furthermore, powerful feedbacks between biota and soils cause a mutual dependence in both systems (Corenblit et al. 2011;Verboom and Pate 2013;Schaetzl and Thompson 2015). ...
Background and aims
The changing soils is a never-ending process moderated by numerous biotic and abiotic factors. Among these factors, trees may play a critical role in forested landscapes by having a large imprint on soil texture and chemical properties. During their evolution, soils can follow convergent or divergent development pathways, leading to a decrease or an increase in soil spatial complexity. We hypothesized that trees can be a strong local factor intensifying, blocking or modifying pedogenetic processes, leading to local changes in soil complexity (convergence, divergence, or polygenesis). These changes are hypothetically controlled by regionally predominating soil formation processes.
Methods
To test the main hypothesis, we described the pedomorphological features of soils under tree stumps of fir, beech and hemlock in three soil regions: Haplic Cambisols (Turbacz Reserve, Poland), Entic Podzols (Žofínský Prales Reserve, Czech Republic) and Albic Podzols (Upper Peninsula, Michigan, USA). Soil profiles under the stumps, as well as control profiles on sites currently not occupied by trees, were analyzed in the laboratory for 20 physical and chemical properties. In total, we analyzed 116 soil samples. The age of trees and time of tree death were determined using the radiometry (¹⁴C), dendrochronology and repeated tree censuses. To process the data, we used multivariate statistics, namely, redundancy analyses (RDAs) and principal component analyses (PCAs). The statistical significance of variables was tested using Kruskal-Wallis, Dunn, and permutation tests. To reach the main aims of the present study, we examined the dataset at three levels of data complexity: 1) soil regions, 2) microsite (i.e., tree stump versus control site), and 3) soil horizon.
Results
Living tree roots and empty or infilled root channels were the most important pedogenic factors that affected the dimensions of soil horizons and the moisture in the root zone under tree stumps. Microsites explained almost 6% of the soil variability (p < 0.001, F = 13.99), demonstrating that trees significantly impacted soil chemical properties in the root zone in all regions. In the Albic Podzols soil region, we found evidence of “basket” podzolization. Our results suggest the rapid eluviation of organic matter-sesquioxide complexes under the stump, probably leading to local soil divergence in Albic Podzols. However, soil analyses under the stumps in the Haplic Cambisols soil region suggested local polygenetic changes in soils (e.g., hydromorphic processes). The thickness of the A and B horizons increased, and soil chemistry changed under trees in the Entic Podzol soil region compared to the control profiles.
Conclusions
In addition to regional environmental factors that manifest themselves in regional pedogenesis and that have a key role in modifying the influence of trees on the soil, the tree species can specifically modify pedogenic processes under standing trees. Trees may influence rate of pedogenesis (hemlock in Albic Podzol region) or even soil evolutionary pathways (beech in Haplic Cambisol region).
... The ecological transition often results in increasing spatial fragmentation that may be expressed in soil morphology as well as soil chemical and ecological properties (e.g. Daryanto et al. 2013;Verboom and Pate, 2013;Podwojewski et al., 2014). Similar divergence may occur due to shrub or tree removal in woodlands (e.g. ...
This paper reviews recent developments in studies of soil complexity, focusing on the variability of soil types within soil landscapes. Changes in soil complexity are directly related to divergent and convergent pedogenesis and to dynamical stability and chaos. Accordingly, strong links exist between nonlinear dynamical systems theory and studies of soil complexity. Traditional conceptual models of soil formation emphasized convergence of the soil cover in the form of progress toward mature, climax soils. A view of divergence as a frequent occurrence rather than an occasional exception is more recent. Measurement of soil complexity is now firmly linked to field pedology. In addition to strong methodological links to pedometrics and soil geography, standard tools for assessing complexity include chronosequences and other historical approaches, relationships between soil properties and soil forming factors, and pedological indicators. Eight general pathways to changes in soil complexity are identified. Three are based on changes in soil-forming factors. These may increase or decrease complexity depending on whether the factors themselves are converging or diverging and the relative magnitudes of soil and state factor divergence. Three pathways are associated with local disturbances. If these occur less frequently than the relaxation time for soil responses, and if internal pedological dynamics are dynamically stable, then disturbance-induced complexity is reduced over time. Otherwise, divergence and increasing complexity occurs. Two additional pathways are directly related to dynamical stability of intrinsic pedological processes, which may result in decreasing or increasing complexity, either in concert with, or independently of, environmental controls or disturbances.
... Boundaries were set to include a wide range of landscape variations (Sawkins, 2010). Although the study area is dominated by sands, soil heterogeneity is high due to layered lateritic profiles that are eroded to varied extents and further complicated by biogenesis (Verboom and Pate, 2013). ...
In farming systems research the link between farm resources, management and performances is often described, but rarely confirmed or quantified. Problems arise in formalising such linkages because substantial spatial and longitudinal whole-farm data are difficult to acquire. This study used the integrative discipline of comparative agriculture to collect such information and address a wide range of related farming system questions. The mixed method procedure included a landscape analysis, a historical investigation, and the collection of current farm information from 36 farms, representing half the farming businesses of a 4 000 km² area in a region of the Western Australian wheatbelt (≈300 mm/year) with highly variable soils.
... These result in varying vegetation patterns in relation to karst landforms, and these differing plant communities (and associated microbial communities) result in differential dissolution, which feeds back to the landforms. Ecosystem engineering by trees, particularly with respect to weathering and regolith deepening, is discussed in the context of niche construction and related concepts by Binkley and Giardina (1998), Phillips (2009a, b, 2015, 2016b, and Verboom and Pate (2013). In general, these studies suggest that biogeomorphic ecosystem engineering by trees is common. ...
The role of trees and forests as a critical component of the biosphere and critical zone, and of the Earth system more generally, is widely appreciated. Less known and acknowledged are the geomorphological functions of tree roots, though their importance has been widely referred to in soil studies, paleopedology and palaeobotany. Tree roots and their impact on weathering processes and soil production were incorporated in the Devonian plant hypothesis and tree root casts served as a key evidence of recognition of past soils in geology, sedimentology and palaeopedology. However, knowledge of biomechanical and biochemical weathering induced by vascular plant roots (mainly trees) has been rarely utilized in geomorphic studies. Biogeomorphic and pedologic studies in recent decades have highlighted the importance of tree uprooting, in which roots play a primary role, in soil development, regolith disturbance and bedrock mining. Other important functions of roots were also recognized, e.g.: soil displacement by growing roots, infilling of stump holes and root cavities, root groove development, direct and indirect effects taking place in the rhizosphere and mycorrhizosphere (mainly biochemical weathering of minerals, support by microbial communities and symbiotic fungi), and changes in porosity, permeability and hydrology of soils in the root zone. However, further studies are urgently needed because many aspects of biochemical and biomechanical weathering are not well understood. This is especially true with respect to taxa-specific impacts. Variations in root architectures, edaphic settings, ecological relationships, and geographic ranges result in substantially different biogeomorphic impacts of different tree species. Additionally, the same species in different environmental settings may have different effects.
... In some arid and semi-arid environments , for example, vertical redistribution of water and minerals by tree roots results in the formation of dense clay layers or clay pavements. These inhibit root penetration by other plants, thus increasing resource availability for the engineer tree (Verboom et al., 2013). This clearly favors the replication of the engineer trees, and it is not unlikely that superior clayforming genes are favored by selection. ...
Biotic influences on geomorphology (and vice-versa) are ubiquitous. This paper explores whether landforms may be extended (composite) phenotypes of biota, based on four criteria: process–form relationships between biota and landforms; evolutionary synchrony; selective pressure via ecosystem engineering and niche construction; and positive feedback benefitting the engineer organism(s). Coral reefs, peat bogs, biomantles, insect mounds, grassland soils, salt marshes, mangrove swamps, and some vegetation-dependent sand dune types clearly meet these criteria. Karst landforms, meandering rivers, and tree uprooting pit-mound systems meet the first three criteria, but positive feedback to engineer organisms has not been established. Research in biogeomorphology will surely identify other extended phenotypes. Implications are that biological evolution will continue to drive
landscape metamorphosis, the appearance of new landform types, and presumably the disappearance of extended phenotypes associated with extinct species. Independently of extended phenotypes, tightly-coupled geomorphological–ecological interactions such as coevolution, and biogeomorphic forms of ecosystem engineering and niche construction are common. The troposphere, encompassing Earth’s landforms, is partly a biotic construct. Some elements would be present in an abiotic world, but the troposphere would not exist in anything resembling its contemporary state without a biosphere. This raises important questions with respect to
Earth system evolution. The bio, litho-, atmo-, hydro-, topo-, and pedospheres coevolve at the global scale. Major biotic events have driven revolutions in the other spheres, but the atmosphere and the global hydrological system seem to have been relatively steady-state at the global scale. The toposphere and pedosphere have not. This suggests that perhaps landforms and soils provide the major mechanisms or degrees of freedom by which Earth responds to biological evolution. Landforms and soils may thus be the ‘voice’ of the biosphere as it authors planetary change, even if clear biotic signatures are lacking.
... The interaction between plant roots and soil in natural systems evolves over much longer time scales and is more complex than in agriculture. Some of these interactions in natural ecosystems are outlined by Verboom & Pate (2013), who suggest that rooting depths may depend on processes that occur over geological time scales, such as erosion, weathering of minerals as well as the effect of biological system. In this case deep rooting is not due simply to soil deformation or pore location, but is the result of complex interactions that occur over long time scales. ...
We argue that the well-known effects of increasing pressure with depth due to the weight of soil (called surcharge) makes the soil so strong that roots can elongate to deeper layers only if they can locate existing pore networks. At depths as shallow as 50 cm, increases in soil strength, even in well-watered soil, are so great that root elongation by the process of soil deformation is only likely to occur at very small rates (less than approximately 1 mm/day). An over-reliance on pot-based laboratory experiments to investigate the impacts of soil strength on root penetration, both in plant and soil science, has meant that increases in soil strength simply due to the axial pressure of soil has been overlooked. In this article we outline the implications of this oversight and propose root traits that might confer deep rooting. The importance of the root's ability to deform hard layers is re-evaluated and we suggest that it should still be viewed as an important trait, but not closely associated with deep rooting. This article is protected by copyright. All rights reserved.
... Colonization of rocks by plants and their associated root microbiota plays an essential role in rock weathering and incipient soil formation (Bashan et al. 2006;Taylor et al. 2009;Verboom and Pate 2013). As an example, Puente et al. (2004a, b) and Lopez et al. (2009) demonstrated that bare rocks, where plants were grown in association with rhizoplane bacteria, released a significant amount of nutrients, which facilitated plant growth and soil formation. ...
Rock colonization by plant roots and their
associated microbiota is one of the major drivers of
mineral weathering, nutrient cycling, soil formation
and ecosystem stability. Yet the mechanisms of biouptake
of lithogenic elements from rocks with differential
nutrient availabilities and limitations are yet
to be established. Here we present results from a
mesocosm experiment that examined lithogenic element
dissolution and uptake (P, K, Ca, Mg, Mn, Fe,
Na, Ti, Al and Si) in Bouteloua dactyloides (buffalo
grass) grown on four different granular porous media
(basalt, rhyolite, granite and schist) comprised of
primary mineral assemblages as influenced by arbuscular
mycorrhiza (AM; Rhizophagus irregularis). Our
results demonstrated that nutrient mobilization (chemical
denudation ? plant uptake) in such oligotrophicsystems is governed by nutrient supply in the parent
material, nutrient availability in pore water solution,
and plant physiology. Overall, total major lithogenic
element mobilization in planted columns (with and
without AM) exceeded abiotic controls in all substrates.
Differences in total mobilization among substrates
occurred as follows: Fe, Na, Ti and Al reached
high values in planted treatments in basalt, P and Mn
in rhyolite, Ca and K in granite and K in schist,
suggesting enhanced dissolution of primary minerals
in the presence of plants. Element biomass enrichment
of Mn, Fe, Ti and Al appeared to be higher in basalt
than the rest of the substrates; however, high Al
availability limited Ca and Mg uptake and plant
growth in this rock media. Presence of mycorrhiza
enhanced shoot biomass in rhyolite due to increased P
uptake, and increased concentrations and total uptake
of lithogenic elements in plants in all rocks but granite.
As expected, AM significantly increased plant root
concentrations of P, K, Ca, Mn, Fe, Ti, Al in basalt,
and Mn shoot concentrations in rhyolite, as well as
root total uptake of K, Ca, Mg, Mn, Fe, Na, Ti, Al and
Si in basalt. At the same time, AM decreased Ca, Ti
and Al concentrations in shoots grown in rhyolite, a
possible protection mechanism against Al toxicity.
The importance of AM in nutrient uptake is also
reinforced by positive correlations between AM
infection rate and P, Ca and Mn total uptake across
all substrates. Moreover, total mobilization of Ca, Mg
and Mn in rhyolite, was significantly higher in the AM
versus non-AM treatment, contrary to K, Ca, Mg, Naand Si in schist. Our work demonstrates how mineral
weathering and associated nutrient release is promoted
by plant processes, further enhanced by plant associated
with symbiotic AM, and yet more pronounced in
basalt and rhyolite compared to granite and schist.
... Soil nutrient patches have also been highlighted as driving spatial patterns of palm trees in tropical humid savanna of Lamto in the Ivory Coast (Barot et al., 1999). The opposite relationship, i.e. herbaceous or woody vegetation modifying soil properties and ecosystem functioning, has also been demonstrated (Lata et al., 2004;Grellier et al., 2013b;Verboom and Pate, 2013). If other studies mentioned the importance of soil properties on dynamics of woody vegetation (Britz and Ward, 2007;Schleicher et al., 2011), few have tested the effects of soil properties on vegetation spatial pattern in grasslands (Browning et al., 2008;Eggemeyer and Schwinning, 2009;Robinson et al., 2010;Colgan et al., 2012). ...
Due to technical difficulties in measuring soil properties at a large scale, little is known about the effect of soil properties on the spatial distribution of trees in grasslands. We were interested in the associations of soil properties with the phenomenon of tree encroachment, where trees increase in density at the expense of grasses. The spatial variation of soil properties and especially soil texture may modify the properties of hydraulic conductivity, and the availability of soil water and mineral nutrients, which in turn may affect the spatial distribution of encroaching trees. Through the development of a geophysical method (Slingram) using an electromagnetic device EM38 and Bayesian inversion, we were able to accurately map soil electrical conductivity (EC) of a Luvisol in a grassland of South Africa. EC measured at the 0.8-2 m depth on a 1.5 ha area is a proxy for clay content and was correlated with the spatial distribution of four size classes of the encroaching Acacia sieberiana. Tree location (all sizes considered), was significantly correlated with EC. Tall acacias (>3 m height) were totally absent from patches with EC >24 mS.m-1. For all other size classes from medium trees to seedlings, tree density decreased with increasing EC. This suggests that high clay contents at depth associated with high EC values may prevent the establishment and/or survival of trees and influence the spatial distribution of A. sieberiana. This result also shows that geophysical tools may be useful for demonstrating important ecological processes. This article is protected by copyright. All rights reserved.
The formation and evolution of phaeozems have always been an area of interest because the phaeozems play an important role in two regions dubbed as "European Bread Basket" and "Northeast China Storehouse." As the phaeozems contain a large proportion of parent materials and are sensitive to human intervention, their formation and evolution have been restricted. Due to the homogeneity of loess parent material, there has been extensive research on the formation of surface phaeozems from the loess parent material. However, phaeozems developed from key fluvial parent material have so far received little attention. Therefore, key information on the formation of phaeozems is missing. In this context, this study applies geochemical tests to determine rare earth elements and major and trace elements in the deep phaeozem layer from the Arongqi borehole in the phaeozems of Northeastern China. Further, the sporopollen fossil tests were conducted in the HT-1-4-2 borehole, and the distribution characteristics of the deep phaeozem layer were analyzed using geostatistics. The results from this study indicate that rare earth data from phaeozems in Arongqi's deep layer shows a comparatively high total concentration of rare earth elements, with a mean value of 141.45 mg.kg − 1 . The chondrite normalization curve demonstrates that the distribution of light rare earth elements shows a positive slope. Further, Eu shows a trend with a slight negative anomaly, while Ce shows a trend with an evident negative anomaly. Ce > -0.1 (mean value 3.9) indicates a reducing environment with hypoxia. The distribution of rare earth elements indicates that phaeozems contain transportable parent materials with trace elements Th/U > 2 (mean value 2.88), Sr/Ba < 0.6 (mean value 0.38), 0 < Rb/Sr < 0.6 (mean value 0.26), Sr /Cu > 10 (mean value 30.98), and climate index at mean value of 0.23. The presence of trace elements indicated freshwater habitats and a dry-hot to semi-dry-hot climate. The sporopollen fossils are mainly comprised of shrubs, coniferous forests, and terrestrial herbs. The presence of Ephedra and Polygonaceae indicates that the environment was hot and arid at that time. Moreover, the presence of several ferns observed in the vertical profile indicates an intermittent warm and humid climate between droughts. Thus, it can be concluded that the deep phaeozems in Arongqi developed in the floodplains of Arun River under the dry-hot-semi-dry-hot climatic conditions.
The campos rupestres (rocky grassland) comprise an old-growth seasonally dry herbaceous ecosystem on mountaintops in central and eastern Brazil and in disjoint areas with sparse shrubs with high plant diversity and endemism. This ecosystem consists of sharp-edged quartzite landforms and rocky hillslopes with boulders, blocks, and sparse soil cover. The slopes in these environments have traditionally been viewed as a product of mechanical rock breakdown controlled by structural and lithological features of rocky hillslopes. In addition to the lithological effects on slope evolution, plant cover plays a pivotal role in the geomorphological process. We explored process–form relationships between plant cover and quartzite rocky hillslopes of campos rupestres, considering the functioning of root traits of rock dwelling endemic species of Velloziaceae. Velloziaceae is an iconic plant family in campos rupestres, and several species colonize quartzite rock with different biogeomorphic effects at different scales. We present a conceptual model of the evolution of quartzite hillslopes based on the arenization process driven by roots expressing a specialized nutrient-acquisition strategy: vellozioid roots. Our results show that at the outcrop scale, roots respond to previous lithological characteristics such as joints and fractures that allow root establishment, followed by the release of large quantities of carboxylates that lead to rock dissolution. The microscopic pattern of bioweathering is associated with enlargement of the quartzite secondary porosity through the formation of root microcracks. Roots that are about 100 μm thick form root mats that surround the grains and produce inter-mineral and intra-mineral porosity systems facilitating percolation of water and organic solutes increasing the weathering. This results in arenization of quartzite by grain-by-grain dissolution and reduces the rock strength, which leads to the formation of quartzite hillslopes, driven by a nutrient-acquisition strategy of vellozioid roots. The described biogeomorphic process determines trajectories of the development of landforms through time, slope-sediment production, slope morphology by the production of boulders and block fields, and sand patches that are reworked by surface runoff along the slope. The hillslopes and landforms that develop in campos rupestres are therefore products of self-reinforcing processes involving nutrient acquisition from bedrock by plants and denudation processes. Also, these positive feedbacks characterize the Velloziaceae species as ecosystem engineers.
Ecosystems and landscapes are supraorganisms (not superorganisms), defined as highly interconnected biotic-abiotic systems which meet two criteria: (1) Significant changes to any component result in changes to the system as a whole, and responses and adaptations occur at the ecosystem level (in addition to responses of ecosystem constituents) and involve multiple system components. (2) Developmental and evolutionary changes occur contemporaneously within the system. This does not imply simultaneity but does require that changes within the ecosystem are contemporaneous or temporally overlapping. This points to an approach to landscape evolution that confronts the holistic nature of historical development and responses to environmental change, rather than (or in addition to) evolution or responses of individual constituents such as biota, soils, or landforms.
Biogeomorphological and ecological succession following a disturbance or the exposure of new ground often proceeds in stages, from domination by abiotic, geophysical factors through stages characterized by increasing effects of biota, biotic-abiotic feedbacks, and eventual domination by ecological processes. However, some studies in forest settings have found more varied development patterns, including persistence of states dominated by biogeomorphic feedbacks. In this study we investigated this phenomenon In Norway spruce (Picea abies (L.) Karst.) dominated forests on the main ridge of the Šumava Mountains in the Czech Republic along the German and Austrian borders. Throughout most of the Holocene, Picea has strongly influenced microtopography and soil/regolith characteristics so as to inhibit hydrological connectivity and development of surface drainage, and maintain hydromorphic soil conditions. These strongly historically and geographically contingent ecosystem engineering effects create and maintain habitat that favors spruce over other trees. These interactions have maintained a landscape dominated by biogeomorphic feedbacks.
Link to full text: https://authors.elsevier.com/a/1aZvW2weQf0BA ..............................................................................................................................................................................................................................................................................................................................................................
The landscapes and seascapes of Earth’s surface provide the theatre for life, but to what extent did the actors build the stage? The role of life in the long-term shaping of the planetary surface needs to be understood to ascertain whether Earth is singular among known rocky planets, and to frame predictions of future changes to the biosphere. Modern geomorphic observations and modelling have made strides in this respect, but an under-utilized lens through which to interrogate these questions resides in the most complete tangible record of our planetary history: the sedimentary-stratigraphic record (SSR). The characteristics of the SSR have been frequently explained with reference to changes in boundary conditions such as relative sea level, climate, and tectonics. Yet despite the fact that the long-term accrual of the SSR was contemporaneous with the evolution of almost all domains of life on Earth, causal explanations related to biological activity have often been overlooked, particularly within siliciclastic strata. This paper explores evidence for the ways in which organisms have influenced the SSR throughout Earth history and emphasizes that further investigation can help lead us towards a mechanistic understanding of how the planetary surface has co-evolved with life. The practicality of discerning life signatures in the SSR is discussed by: 1) distinguishing biologically-dependent versus biologically-influenced sedimentary signatures; 2) emphasizing the importance of determining relative time-length scales of processes and demonstrating how different focal lengths of observation (individual geological outcrops and the complete SSR) can reveal different insights; and 3) promoting an awareness of issues of equifinality and underdetermination that may hinder the recognition of life signatures. Multiple instances of life signatures and their historic range within the SSR are reviewed, with examples covering siliciclastic, biogenic and chemogenic strata, and trigger organisms from across the spectrum of Earth’s extant and ancient life. With this novel perspective, the SSR is recognised as a dynamic archive that expands and complements the fossil and geochemical records that it hosts, rather than simply being a passive repository for them. The SSR is shown to be both the record and the result of long-term evolutionary synchrony between life and planetary surface processes.
Vegetation and plant diversity patterns are strongly linked to soil properties, such as fertility, texture
and depth in all parts of Australia. This results because many parts of Australia have relatively old and
highly weathered soil profiles compared to most other regions. However, interactions between soils
and vegetation are very complex because soils result from weathering processes that are determined by
substrate type, topography, climate and vegetation, as well as the relocation of materials by wind and
water. In a global context, Australian soils in many habitats are highly infertile, with low availability of
phosphorus, nitrogen and trace elements. These infertile soils are often linked to shrub-dominated ecosystems,
where it is assumed that soil fertility is insufficient to support tree growth, but plant productivity
is also severely limited by water availability in many habitats. Low soil nutrient supply is counteracted
by plant adaptations to growth in infertile soils, as well as efficient nutrient cycling, especially after fire.
In Australia the majority of plants have mycorrhizal associations that assist in nutrient uptake and this
includes an exceptionally high diversity of plants with ectomycorrhizal associations, as well as plants
with nitrogen fixing symbioses. However, nonmycorrhizal plants are also exceptionally diverse in many
Australian vegetation types and include many species with specialised means of nutrition, including carnivores,
parasites and cluster-rooted species.
A continental-scale review of the distribution of different mycorrhizal types and nonmycorrhizal (NM) plants with specialised nutrient-acquisition strategies, as well as nitrogen-fixing associations, is presented here. The
importance of mycorrhizas and other mineral nutrient uptake mechanism in roots of major families of Australian plants is summarised along with the age of lineages where root types have changed. Maps showing the relative diversity and dominance of plants with different root types are also presented. In Australia as elsewhere, there is strong phylogenetic consistency for mycorrhizal association within plant families. However,
there are also exceptions in two of the most diverse Australian families, the Fabaceae and the Myrtaceae. These families have very complex root strategies which seem to have evolved very rapidly, resulting in many
species that have switched from arbuscular mycorrhizas (AM) to ectomycorrhizas (EcM), and these trends are unique to Australia. Some lineages of NM plants can be traced back to Gondwana, but there are others that evolved more recently in Australia, especially where AM was succeeded by EcM or NM cluster roots. These are examples of explosive and adaptive radiations in Novel and Complex Root (NCR) clades and occur in
some families with a high degree of species richness in Australia. Most NCR lineages show increasing speciation rates in the past 30 Ma that coincide with continental aridification after Australia separated from Antarctica. These NCR plant lineages are substantially more diverse in the ancient landscapes
and highly unfertile soils in the Southwest Australian Floristic Region than elsewhere in Australia or anywhere else on earth. Australia is a global diversity hotspot for root evolution, with about one third of all species of
EcM plants; many NM plants, especially those with cluster roots; as well as one fourth of all carnivorous plants.
Uprooting represents a key disturbance process in forests, forming pit-mound microtopography, which can then dramatically impact pedogenesis and the forest ecology. At our study sites in northern Michigan, where well-drained, sandy Spodosols dominate, pit-mound microtopography tends to persist for millennia. Because of its persistence, the influence of this type of microtopography is greater here than in most forests. In that respect, our sites represent an end member along a continuum of forest soil disturbance by uprooting. We studied post-uprooting pedogenesis (at 14 dated pit-mound pairs), mapped and characterized the pit-mound topography (over 2.8 ha), the soils below (within 317 soil profiles), and the trees above, to better understand the complex interactions among this type of disturbance regime and forest dynamics.
Background
Ocbil theory aims to develop hypotheses explaining the evolution and ecology of, and best conservation practices for, biota on very old, climatically buffered, infertile landscapes (Ocbils).
Scope
This paper reviews recent multi-disciplinary literature inspired by or reacting to aspects of Ocbil theory and discusses how it can assist conservation in biodiversity hotspots.
Conclusions
Ocbils occur in at least 12 out of 35 known terrestrial hotspots, but also in other biologically significant sites. Most evidence comes from the Southwest Australian and Greater Cape Floristic Regions, South America’s Pantepui, and the Campo Rupestre of Brazil, though predictions of the theory have been corroborated in 22 sites across South America, Western and Eastern Africa, Southern Asia, and Oceania. Most hypotheses have been corroborated, indicating that Ocbil theory has survived largely intact after 6 years of independent scientific critique, quantitative experimentation, and development. The theory also has been extended to allow identification and characterization of OCBISs (old, climatically-buffered, infertile seascapes), and OCFELs (old, climatically-buffered, fertile landscapes). We illustrate that the principles of Ocbil theory are key to conservation of biodiversity at global scale and provide new directions for research that can improve the theoretical and practical contributions of Ocbil theory.
This research employs a raft of incisive strategies and technologies to define and interpret spatial relationships between native plant ecosystems and classes of soil across a range of scales. Building on traditional vegetation zonings and soil mappings, information on locations of key taxa, chemical composition of pisoliths and radiometric based technologies are used collectively to identify and delineate contrasting zonings in which principal base units (phytotaria) are distributed in patchy but well demarcated mosaics across soilscapes. At broadest scale biomes are recognised in terms of species endemism, radiometric patternings and element balances of pisolithic ferricretes and in many cases shown to change predictably in stepwise fashion across environmental gradients. At finer scale georeferenced data for key players in selected phytotaria are matched against information from airborne radiometry to identify hallmark signallings derived from workings of potassium, uranium and thorium in parent profiles. By draping radiometric signals over digital elevation models, further insight was obtained on the complex relationships between specific phytotaria, topography and mineralogical status across a selected area. These southwest Australian case studies demonstrate how multiple sources of evidence might be mined and parcelled up to provide a comprehensive picture of heterogeneity and connectivity within and between phytotaria.
Unlabelled:
•
Premise of the study:
Globally, the origins of xeromorphic traits in modern angiosperm lineages are obscure but are thought to be linked to the early Neogene onset of seasonally arid climates. Stomatal encryption is a xeromorphic trait that is prominent in Banksia, an archetypal genus centered in one of the world's most diverse ecosystems, the ancient infertile landscape of Mediterranean-climate southwestern Australia.•
Methods:
We describe Banksia paleocrypta, a sclerophyllous species with encrypted stomata from silcretes of the Walebing and Kojonup regions of southwestern Australia dated as Late Eocene.•
Key results:
Banksia paleocrypta shows evidence of foliar xeromorphy ∼20 Ma before the widely accepted timing for the onset of aridity in Australia. Species of Banksia subgenus Banksia with very similar leaves are extant in southwestern Australia. The conditions required for silcrete formation infer fluctuating water tables and climatic seasonality in southwestern Australia in the Eocene, and seasonality is supported by the paucity of angiosperm closed-forest elements among the fossil taxa preserved with B. paleocrypta. However, climates in the region during the Eocene are unlikely to have experienced seasons as hot and dry as present-day summers.•
Conclusions:
The presence of B. paleocrypta within the center of diversity of subgenus Banksia in edaphically ancient southwestern Australia is consistent with the continuous presence of this lineage in the region for ≥40 Ma, a testament to the success of increasingly xeromorphic traits in Banksia over an interval in which numerous other lineages became extinct.
Podzols frequently show bleached mottles depleted in organic matter, most readily visible in the Bh horizons. Even though the process of bleached mottles development is not understood, it has been suggested that the selective degradation of organic matter by soil microorganisms has a major contribution. In this study, we examined the bacterial and archaeal communities along three Brazilian coastal podzol profiles, as well as in bleached mottles and their immediate vicinity, using 16S rRNA gene profiling. Our results showed that the bacterial and archaeal community structures in the studied podzols varied with depth and that the bacterial communities in the bleached mottles were significantly different from that in their immediate vicinity. In contrast, the archaeal communities in bleached mottles were significantly different from their vicinity only in the Bertioga (BT) profile, based on sequencing of amplicons of the 16S rRNA gene. Redundancy analyses showed that the bacterial community structures in the bleached mottles of BT were negatively associated mostly with the levels of organic carbon, exchangeable-aluminum (Al), exchangeable potassium, and Al-saturation, whereas in the surrounding soil, the opposite was observed. In the Ilha Comprida (IC) profiles, no such relationships were observed, suggesting distinct drivers of the bacterial community structures in bleached mottles of different podzols. In the bleached mottles of the BT profile, operational taxonomic units (OTUs) phylogenetically related to Pseudomonas were the most abundant Bacteria, whereas in the IC profiles, OTUs related to Acidobacteria were predominant. Thermoprotei (Crenarchaeota) were the most abundant Archaea in the bleached mottles and in their immediate vicinity. Based on the diverse metabolic capabilities of Pseudomonas and Acidobacteria, our data suggest that these groups of bacteria may be involved in the development of bleached mottles in the podzols studied and that the selection of specific bacterial populations in the bleached mottles may depend on the local edaphic conditions.
Neogene paleosols of the Great Plains and central Oregon provide abundant evidence of grasslands of the past. The characteristic surface horizon (mollic epipedon) of grassland soils (Mollisols) can be recognized in paleosols from granular ped structure, abundant fine root traces, dark color, and common carbonate or other easily weatherable minerals. The fossil record of such soils indicates a three-stage evolution of grasslands. Eocene to Oligocene rangelands are represented by paleosols with near-mollic soil structure and fine root traces similar to soils of modern desert grasslands with scattered bunch grasses and shrubs. Paleosols with mollic epipedon and shallow (less than 40 cm down into the profile) calcic horizons are evidence for the appearance of sod-forming short grasslands during the early to middle Miocene. Mollic paleosols with deeper (some 1 m or more) calcic horizons represent tall grasslands and have not been found older than late Miocene. Early stages in the evolution of grassland soils correspond to climatic coolings near the end of the Eocene and middle Miocene. The best understood climatic cooling and drying during the late Miocene (Messinian or 5-7 Ma) is synchronous with the expansion of tall C 4 grasslands.
This summary paper forms part of a Japanese-Australian research project on human impact in the Australian semi-arid and arid zone. The dunefields are introduced in their various geologic and geomorphic settings and the sources and types of dune sands are then examined. The chronology of dune building is detailed from the earliest evidence of aeolian activity. This is followed by a reconstruction of the palaeoenvironment of the last dune building phases, an assessment of the impact of Aboriginal burning, and a concluding sketch of the impact of European settlement.
The problem of ascribing adaptive significance to traits that enable graminoids to tolerate or evade ungulate herbivory is examined. Some of these traits may have originally evolved in response to non-grazing selection pressures, thus constituting grazing exaptations rather than true adaptations. The fossil record indicates that semiarid habitats, extensive grasslands and grazers appeared, interacted and evolved together, but several traits that are advantageous in semiarid habitats have beneficial effects for grazed plants. Other traits, such as developmental plasticity, enhance competitive ability in certain environments, but also increase grazing tolerance or resistance. Defoliation responses are embedded in a network of interacting processes, including photosynthesis, transpiration, nutrient uptake and resource allocation. Responses and adaptations to defoliation must be interpreted in this context. Although traits may have arisen due to non-herbivorous selection pressures, they may subsequently have been selected, combined, or amplified through grass-grazer coevolution to form species, polymorphic populations, phenotypically plastic individuals, or communities of species that evade, resist or tolerate herbivory. -from Author
To understand the importance of plants in structuring the vertical distributions of soil nutrients, we explored nutrient distributions in the top meter of soil for more than 10,000 profiles across a range of ecological conditions. Hypothesizing that vertical nutrient distributions are dominated by plant cycling relative to leaching, weathering dissolution, and atmospheric deposition, we examined three predictions: (1) that the nutrients that are most limiting for plants would have the shallowest average distributions across ecosystems, (2) that the vertical distribution of a limiting nutrient would be shallower as the nutrient became more scarce, and (3) that along a gradient of soil types with increasing weathering-leaching intensity, limiting nutrients would be relatively more abundant due to preferential cycling by plants. Globally, the ranking of vertical distributions among nutrients was shallowest to deepest in the following order: P > K > Ca > Mg > Na = Cl = SO_4. Nutrients strongly cycled by plants, such as P and K, were more concentrated in the topsoil (upper 20 cm) than were nutrients usually less limiting for plants such as Na and Cl. The topsoil concentrations of all nutrients except Na were higher in the soil profiles where the elements were more scarce. Along a gradient of weathering-leaching intensity (Aridisols to Mollisols to Ultisols), total base saturation decreased but the relative contribution of exchangeable K^+ to base saturation increased. These patterns are difficult to explain without considering the upward transport of nutrients by plant uptake and cycling. Shallower distributions for P and K, together with negative associations between abundance and topsoil accumulation, support the idea that plant cycling exerts a dominant control on the vertical distribution of the most limiting elements for plants (those required in high amounts in relation to soil supply). Plant characteristics like tissue stoichiometry, biomass cycling rates, above- and belowground allocation, root distributions, and maximum rooting depth may all play an important role in shaping nutrient profiles. Such vertical patterns yield insight into the patterns and processes of nutrient cycling through time.
Cluster roots are an adaptation for nutrient acquisition from nutrient-poor soils. They develop on root systems of a range of species belonging to a number of different families (e.g., Proteaceae, Casuarinaceae, Fabaceae and Myricaceae) and are also found on root systems of some crop species (e.g., albus, Macadamia integrifoliaandCucurbita pepo). Their morphology is variable but typically, large numbers of determinate branch roots develop over very short distances of main root axes. Root clusters are ephemeral, and continually replaced by extension of the main root axes. Carboxylates are released from cluster roots at very fast rates for only a few days during a brief developmental window termed an ‘exudative burst’. Most of the studies of cluster-root metabolism have been carried out using the crop plant L. albus, but results on native plants have provided important additional information on carbon metabolism and exudate composition. Cluster-root forming species are generally non-mycorrhizal, and rely upon their specialised roots for the acquisition of phosphorus and other scarcely available nutrients. Phosphorus is a key plant nutrient for altering cluster-root formation, but their formation is also influenced by N and Fe. The initiation and growth of cluster roots is enhanced when plants are grown at a very low phosphate supply (viz. ≤1 μM P), and cluster-root suppression occurs at relatively higher P supplies. An important feature of some Proteaceae is storage of phosphorus in stem tissues which is associated with the seasonality of cluster-root development and P uptake (winter) and shoot growth (summer), and also maintains low leaf [P]. Some species of Proteaceae develop symptoms of P toxicity at relatively low external P supply. Our findings with Hakea prostrata (Proteaceae) indicate that P-toxicity symptoms result after the capacity of tissues to store P is exceeded. P accumulation in H. prostrata is due to its strongly decreased capacity to down-regulate P uptake when the external P supply is supra-optimal. The present review investigates cluster-root functioning in (1) L.albus (white lupin), the model crop plant for cluster-root studies, and (2) native Proteaceae that have evolved in phosphate-impoverished environments.
We tested the Walker and Syers (1976) conceptual model of soil development and its ecological implications by analyzing changes in soil P, vegetation, and other ecosystem properties on a soil chronosequence with six sites ranging in age from 300 yr to 4.1 X 10(6) yr. Climate, dominant vegetation, slope, and parent material of all of the sites were similar. As fractions of total P, the various pools of soil phosphorus behaved very much as predicted by Walker and Syers. HCl-extractable P (presumably primary mineral phosphates) comprised 82% of total P at the 300-yr-old site, and then decreased to 1% at the 20,000-yr-old site. Organic phosphorus increased from the youngest site to a maximum at the 150 000 yr site, and then declined to the 4.1 X 10(6) yr site. Occluded (residual) P increased steadily with soil age. In contrast to the Walker and Syers model, we found the highest total P at the 150 000-yr-old site, rather than at the onset of soil development, and we found that the non-occluded, inorganic P
Bulk deposits of aeolian sand accumulated over recent timescales provide instructive systems for examining effects of colonising vegetation on soil development. The two contrasting case studies presented here are eucalypt woodland in a dune system in southwest Australia and the rubified sand seas of the United Arab Emirates. In the former, clay pavements forming under the lateral root catchments of the eucalypts are shown to be constructed from iron, aluminum and other mineral elements abstracted from ground waters by deep roots. The pavements concerned have a marked restrictive influence on understorey density and biodiversity while also having an overall role in maximizing effectiveness of usage of water and nutrients by the trees in question. Timescales and amounts of iron uplifted in this manner are estimated for the system. In the Arabian example, the occurrence of intense reddening (rubification) of sand towards the mountains of Oman is well known, and abiotic processes have been implicated in the phenomenon. In this chapter, we invoke involvement of a biotic component, having demonstrated a relationship between vegetation density and extent of rubi fi cation as seen in a positive correlation between increased reddening and cumulative vegetation encountered as one moves from coast to mountains. We hypothesise that uplift of iron by deeprooted shrubs/trees might be the agent responsible for progressive reddening. Definitive testing of this hypothesis is required, particularly by analysing for iron in xylem sap flowing up through taproots and looking for evidence of its subsequent release into superficial layers of sand surrounding lateral roots of the trees.
Nitrogen (N) isotope fractionation and symbiotic N fixation were investigated
in the shrub legume tagasaste, growing in the glasshouse and field. In a pot
study of effectively nodulated plants supplied with 0, 1, 5 and 10 mM nitrate
[stable isotope 15N
(δ15N) of 3.45‰], the
δ15N of dry matter N of fully symbiotic cultures
indicated a greater isotope fractionation during distribution of N between
nodules, stems, leaves and roots than for N2 fixation
itself, with whole-plant δ15N being near zero
(–0.46 to 0.42‰). Regardless of whether plants were field-grown,
pot-cultured, fixing N2 or utilising mineral N, woody
stems were depleted in 15N relative to all other plant
parts. The similar orders of ranking of δ15N for
plant components of the nitrate-treated and fully symbiotic plants, and a
general increase in δ15N as plants were exposed to
increasing concentrations of nitrate, indicated that N isotope fractionation
can be accounted for, and thus not undermine 15N natural
abundance as means of measuring N2 fixation inputs in
tagasaste trees. In pot culture the percentage of plant N derived from the
atmosphere (%Ndfa) by symbiotic N2 fixation fell
from 85 to 37% when the nitrate supply was increased from 1 to 10 mM,
with evidence of nitrate N being preferentially allocated to roots.
δ15N natural abundance assessments of
N2 fixation of 4-year-old trees of field-grown tagasaste
in alley (550 trees ha-1) or plantation (2330 trees
ha-1) spacing were undertaken at a study site at Moora,
Western Australia, over a 2-year period of shoot regrowth (coppicing).
Cumulative N yields and %Ndfa were similar for trees of alley and
plantation spacing, with much less coppice N accumulation in the first
compared to the second year after cutting. Scaling values from a tree to plot
area basis, and using a mean %Ndfa value of 83% for all trees at
the site, inputs of fixed N into current biomass plus fallen litter over the 2
years of coppicing were calculated to be 83 kg N ha-1
year-1 for the alley and 390 kg N
ha-1 year-1 for the plantation
spacing. Although the plantation tagasaste fixed 587 kg N
ha-1 in the second year, close to the maximum value
reported in the literature for any N2-fixing system,
this should not be seen as typical where the trees are used for animal
production, since grazing and cutting management will substantially reduce
productivity and N2 fixation input.
The oldest vestiges of crust and marine environments occur only in a few remote areas on Earth today. These rocks are Hadean-Eoarchean in age (∼4.5 to 3.6 billion years old) and represent the only available archive of the mineral environments in which life originated. A mineral inventory of the oldest rocks would thus help to constrain the likeliest minerals involved in the origin of life. Such a survey is important from the perspective of mineral evolution, as the emergence of life and subsequent global changes caused by organisms were responsible for more than half the 4400 known minerals on the modern Earth.
Mineral evolution, which frames mineralogy in a historical context, is based on the premise that the geosphere and biosphere
have coevolved through a sequence of deterministic and stochastic events. Three eras of mineral evolution—planetary accretion,
crust and mantle reworking, and biologically mediated mineralogy—each saw dramatic changes in the diversity and distribution
of Earth's near-surface minerals. An important implication of this model is that different terrestrial planets and moons achieve
different stages of mineral evolution, depending on the geological, petrological, and biological evolution of the body.
The Clifton Down Mudstone, a mixed peritidal-fluvial sequence of Arundian (late Osagean-early Meramecian) age from southwest Britain, contains a suite of varied, cumulative paleosols. Temporal changes in soil-type within this paleosol suite provide evidence for a shift in the climatic regime during Arundian times. -from Author
Discusses the chemistry of laterites and bauxites, their mineralogy, internal structures and typical profile. Laterites originate in many different ways and these are described in turn. The final section discusses the palaeoenvironmental value of laterites in relation to planation surfaces, cyclic erosion, inter-regional correlation and climatic change, and comments on laterite in the stratigraphic record.-K.Clayton
Ectomycorrhizal (ECM) fungi are widespread plant root symbionts in boreal forests, but information is lacking on the fine scale distribution of roots and fungi in substrate patches of different quality, including coarse woody debris (CWD). Wood and soil cores were taken systematically both horizontally and vertically through decayed logs and underlying soil layers in a mixed forest. Root tips were counted and ECM fungi identified by morphotyping and sequencing. The abundance of root tips and ECM fungi was highly variable on a 5-cm scale. Most species were replaced on a 50-cm scale. Detrended correspondence analysis demonstrated strong preference of resupinate thelephoroid and athelioid fungi and Sebacinaceae for CWD, whereas ascomycetes and euagarics appeared more frequently in mineral soil. Clavulicium delectabile was determined to be an ECM fungus for the first time. ECM fungi occupy different niches and show variable distribution patterns. CWD plays an important role as a habitat both for roots and ECM fungi. We suggest sampling larger soil cores and selecting random root tips in future studies. Sequencing is a powerful tool in ECM community studies.
In recent years the literature on mineral cycling in terrestrial ecosystems has expanded greatly, and few if any of the major biomes have escaped attention. We do not propose to review this large body of information in detail. Rather, it is our intention to outline the broad features of mineral acquisition, distribution and cycling that apply generally in terrestrial ecosystems, and to highlight several facets of the internal cycle that are vital for community nutrition but which seem to have been rather neglected. Inevitably, we cannot treat all essential elements equally, nor can we deal with the functional aspects of elemental storage and flux in all their complexity. The aboveground components of ecosystems have been studied in great detail, whereas spatial and temporal patterns in soil are but poorly understood. The account that follows is in part, therefore, an attempt to redress this imbalance and consequently is uneven in its treatment of both the static and dynamic attributes of ecosystems.
It has been known for a long time that the isotope fractionation of carbon formed by photosynthesizing plants varies radically depending on the pattern of photosynthesis in which the species is engaging (see O’Leary 1988, Farquhar et al. 1989, and chapter by Dawson and Brooks in this volume). The principal reason for this is that carbon fixed by the photosynthetic CO2 assimilating enzymes RUBP carboxylase [Rubisco] (C3 plants) and PEP carboxylase (C4 and CAM plants) show different isotope fractionation (δ13C) values, since the former enzyme discriminates 27 to 30‰, the latter only 0 to 2‰. As a result δ13C values for C3 plants utilizing Rubisco range from −20 to −35‰ while C4 species utilizing PEP carboxylase exhibit an equivalent range of from −7 to −17‰ (see Deines 1980, Ehleringer 1989). Those ‘obligate’ CAM plants which operate by fixing CO2 only at night using PEP carboxylase have δ13C values similar to C4 plants, whereas ‘facultative’ C3:CAM species which are able to shift back and forth between C3 and CAM-type photosynthesis depending on conditions, exhibit δ13C values resembling those of C3 plants when under well watered conditions but values close to C4 plants when in dry or saline environments (see Teeri 1982, Ehleringer 1989). Table 1 summarizes some of the principal differences between C3, C4 and CAM plants in respect of water use, carbon isotope discrimination and other physiological features.
Salinisation of land and rivers is a major problem throughout Australia's agricultural regions. There is a pressing need to map or predict where the salt is, and to understand the nature of salt stores and the conduits through which salt and water are delivered to streams and the land surface. This article describes a new method (an integrated, catchment-based approach) of modelling natural gamma-ray emissions from the Earth's surface for soil/regolith mapping, and combining the results with topographic indices to delineate salt stores and salt outbreaks in the landscape. Modelled thematic maps produced using this approach allow catchments to be ranked according to their salinity risk, or potential risk, for prioritising remedial management.
Soils of South Africa is the first book in seventy years that provides a comprehensive account of South African soils. The book arranges more than seventy soil forms into fourteen groups and then provides, for each group: • maps showing their distribution and abundance throughout South Africa • descriptions of morphological, chemical and physical properties • a detailed account of classification and its correlation with international systems • a discussion of soil genesis which includes a review of relevant research papers • appraisal of soil quality from a land use perspective as well as for its ecological significance • illustrative examples of soil profiles with analytical data and accompanying interpretations. There is also a fascinating account of the special relationship that exists between South African animals and soil environments. Soils of South Africa should interest students and researchers in the earth, environmental and biological sciences, as well as environmental practitioners, farmers, foresters and civil engineers.
This book considers the inter-relations between plants and minerals in an entirely new way, in that it introduces the notion of eco-engineering: i.e. the manipulation of the mineral world by the living world to the ends of the living world. These inter-relations are the basis for traditional agriculture and should be the basis for new, ecologically oriented land management disciplines, including agriculture itself. These relations also have an impact on surface geochemistry and determine pollution problems. A better understanding of this concept will lead to a renewed consideration of surface environmental problems. © Springer-Verlag Berlin Heidelberg 2010. All rights are reserved.
Progressive plant succession to a climax has developed as a central ecological concept (Cowles 1899; Clements 1916), and forms an important basis for predicting changes (over moderate time scales) in primary and secondary plant succession. Although the concept of progressive succession leading to a stable, self-perpetuating climax has been questioned (Whittaker 1953, 1974), the climax concept has guided much of our thinking in the management of indigenous forests and in the prediction of forest development following various forms of disturbance in different environments.
The highly variable degree of substitution of Al3+ for Fe3+ in goethites and hematites and the degree of substitution of Fe3+ for Al3+ in kaolinites in natural tropical weathering profiles are studied on the basis of defining stability fields in terms of solid-solution equilibria. Factors controlling the relative stability of goethites and hematites are the grain size of particles, the Al, Fe and H2O contents in the system, the activity of silica when kaolinite or smectite is present, and the activity of H2O in saturated or non-saturated zones. A decrease of the activity of H2O is not only responsible for the formation of concretions, but also for the nature of the mineral formed. Equilibrium equations and diagrams, calculated solubility products, and an ideal solid-solution model of phase distributions, are some of the evidence presented to account for the distribution, compositional range, and conditions of formation of the Al-goethites, Al-hematites and Fe3+-kaolinites. -M.S.
Part 1 The processes of soil formation and the resulting soil materials: weathering and leaching new mineral formation and inheritance bioturbation rainwash aeolian processes soil creep. Part 2 The distribution of soil material: the pedological hierarchy the soils of a continental plate centre - Australia, Africa soils of other continental plate centres the soil materials of continental plate margins.
'Coralloid' roots containing blue-green algae occur commonly on the upper root stocks of M. riedlei in natural habitat in Western Australia. Each coralloid mass persists for several seasons; replacement sets form at irregular intervals, especially after fire.
15N2 and acetylene reduction assays demonstrate that coralloid roots fix nitrogen at physiologically significant rates.
C2H2 reduction rates by coralloid roots are higher in winter than in summer. Performance is positively correlated with rainfall; soil temperature appears to be of lesser importance. Diurnal fluctuations in nitrogenase activity occur.
Calibration using 15N2 gives a molar ratio of C2H2 reduced : N2 fixed of 5.8 : 1. The seasonal average of C2H2 reduction of 14.8 nmol per g fresh wt coralloid root per min is then equivalent to 37.6 g N per kg fresh wt per year, a fixation rate potentially capable of doubling coralloid root nitrogen once in every 8 weeks, and whole plant nitrogen every 8-11 years.
Returns of fixed nitrogen in two natural populations of Macrozamia are estimated by compounding measurements of biomass of host and symbiotic organs with the seasonal average for coralloid fixation rate. The values obtained (18.8 and 18.6 kg N ha-1 year-1) indicate that Macrozamia contributes significantly to the nitrogen economy of its ecosystem.
This communication presents the hypothesis that certain Australian lateritic
and related oligotrophic soils may have been partly derived biotically from
soluble iron-rich complexes generated following secretion of low-molecular
weight organic acids by phosphate-absorbing specialised proteoid (cluster)
roots of proteaceous plants. Subsequent precipitation of the iron is then
pictured as occurring onto the oxide rinds of developing laterite after
consumption of the organic components of the complexes by soil bacteria. The
hypothesis is f irst examined in relation to current theories of origins of
laterites and the extent of the coincidences worldwide in past and present
times between Proteaceae and oligotrophic soil types of lateritic character.
The paper then provides more definitive lines of evidence supporting the
hypothesis, based largely on recent studies by the authors in south-western
Western Australia. This relates to (a) cases of definitive association in
habitats rich in Proteaceae between zones of root proliferation and ferricrete
layers in lateritic soils, (b) proximity in soil profiles between ferric
deposits and current and ancestral root channels, (c) the recovery of
citrate-consuming bacteria from soil profiles and specifically from ferricrete
rinds and horizons accumulating sesquioxide organic matter and (d)
distribution of iron and phosphorus within plant and soil profile components
consistent with ferricrete rinds being generated by rhizosphere-mediated
interactions of plants and microbes under conditions of severely limited
availability of phosphorus. The mode of functioning of proteoid root clusters
is then discussed, especially in relation to exudation of organic acid anions,
uptake of phosphorus and the subsequent fate of organic anions and their metal
ion complexes in the system. An empirically based scheme is presented
indicating flow profiles for phosphorus and iron between soil, ferricrete
rinds and bacterial and plant components. We then discuss possible carbon
costs to proteaceous plant partners when accessing phosphorus under the
nutrient-impoverished conditions typical of heathlands and open woodlands of
Mediterranean-type ecosystems of Western Australia. The paper concludes with a
critical overview of the hypothesis, particularly its implications regarding
possible higher plant: microbial influences shaping soil and landscape
evolution in the regions involved.
Samples of recently produced shoot material collected in winter/spring from common plant species of mulga vegetation in eastern and Western Australia were assayed for 13C and 15N natural abundance. 13C analyses showed only three of the 88 test species to exhibit C4 metabolism and only one of seven succulent species to be in CAM mode. Non-succulent winter ephemeral C3 species showed significantly lower mean δ13C values (- 28.0‰) than corresponding C3-type herbaceous perennials, woody shrubs or trees (- 26.9, - 25.7 and - 26.2‰, respectively), suggesting lower water stress and poorer water use efficiency in carbon acquisition by the former than latter groups of taxa. Corresponding values for δ15N of the above growth and life forms lay within the range 7.5-15.5‰. δ15N of soil NH4+ (mean 19.6‰) at a soft mulga site in Western Australia was considerably higher than that of NO3- (4.3‰). Shoot dry matter of Acacia spp. exhibited mean δ15N values (9.10 ± 0.6‰) identical to those of 37 companion non-N2-fixing woody shrubs and trees (9.06 ± 0.5‰). These data, with no evidence of nodulation, suggested little or no input of fixed N2 by the legumes in question. However, two acacias and two papilionoid legumes from a dune of wind-blown, heavily leached sand bordering a lake in mulga in Western Australia recorded δ15N values in the range 2.0-3.0‰ versus 6-4-10.7‰ for associated non-N2-fixing taxa. These differences in δ15N, and prolific nodulation of the legumes, indicated symbiotic inputs of fixed N in this unusual situation. δ15N signals of lichens, termites, ants and grasshoppers from mulga of Western Australia provided evidence of N2 fixation in certain termite colonies and by a cyanobacteria-containing species of lichen. Data are discussed in relation to earlier evidence of nitrophily and water availability constraints on nitrate utilization by mulga vegetation.
Pure quartz arenites are especially characteristic of lower Paleozoic and Proterozoic strata deposited in nonorogenic settings. A century-long debate over the origin of these remarkably pure sandstones has remained unresolved, largely because they seem nonactualistic. The much greater importance of wind and fluvial processes prior to the Silurian appearance of macroscopic vegetation supported a physical origin, but it is now clear that both multicycling and intense chemical weathering can produce them. Multicycling seemed essential to account for their extreme textural maturity, with the exceptional rounding of many examples pointing to important eolian abrasion. Other attributes such as evidences of mixed sources, upward maturation, association with major unconformities, and an inverse relationship between labile grain content and grain size also were consistent with recycling. A single-cycle origin proven in the modern humid tropics, however, is supported in the ancient record by examples with underlying mature paleosol profiles, chemical etching and lesser rounding of quartz grains, single populations of accessory minerals, downcurrent maturation, dissolution ghosts of labile grains, oversized pores filled with clay, and interstratified pelites composed of only kaolinite or illite. Post-depositional diagenesis also can contribute to maturation either with or without multicycling and may even produce pure, diagenetic quartz arenites in extreme cases. Accounting for the compositional maturity of ancient quartz arenites chemically seems paradoxical without something to stabilize land surface areas long enough to allow intense weathering. Biological crusts or microbial mats composed of complex communities of cyanobacteria, algae, and lichens are here proposed as the likely means of stabilization. Although most familiar today in arid regions, such crusts are known in practically all climatic zones. Apparently they developed early in Precambrian time from marginal marine or lacustrine stromatolites and mats and were the first life forms to invade land long before the advent of vascular land vegetation.
Termites, feeding on dead plant matter with a carbon to nitrogen ratio
much higher than their own tissues, have to balance their C and N
inputs. Two classes of C-N balancing mechanisms are possible: adding N
to inputs, or selectively eliminating C. Termites achieve both of these
mechanisms with the aid of microorganisms (symbionts). We first show
that a termite can utilize food resources, thus attain productivity,
only to the extent that the C-N balance capabilities of the
termite-symbionts system allow. Two hypotheses follow: (i) `one-piece'
termites (species nesting in and consuming wood) tend not to possess
C-eliminating symbionts, whereas `separate' termites (species foraging
outside their nests) tend to have a full range of C-N balance symbionts;
this advantage for separate termites results in their observed greater
productivity and colony size; and (ii) only separate termites have a
sterile worker caste because their ability to utilize resources, which
is conferred by their C-N balancing symbionts, makes the increase in a
true (sterile) worker's contribution to the reproductives' fitness,
combined with their higher nest stability, great enough to exceed the
threshold for the evolution from false to true workers.
In the last two decades technological advances in isotope ratio mass spectrometry have been very rapid, opening up new possibilities for analysis of biological and environmental materials. The new instrumentation has facilitated faster analysis of samples via automated sample preparation and multi-isotope analysis of single samples, resulting in considerable cost savings, and enabling access to isotope analysis for many more researchers. These changes are reflected in the rapidly growing international literature on stable isotopes. While there have been some excellent books and review papers aimed at interpreting isotope signals in biology and environmental science, there have been fewer attempts to provide practical tools for researchers making forays into this exciting new arena. This book aims to address this inadequacy by providing a set of practical guidelines for the application of a range of novel and well proven stable isotope techniques to the fields of plant physiological ecology, agriculture, marine ecology and palaeoecology. The book is the outcome of a weeklong workshop held under the auspices of the Cooperative Research Centre for Legumes in Mediterranean Agriculture (CLIMA 1992 - 2000) at The University of Western Australia and the CSIRO Floreat Laboratories, Perth, Western Australia, in February 1999. The workshop was designed to provide practical tools and experiences for researchers and students concerned with how one goes about using stable isotopes in field investigations.
Laterite profiles in the Sydney area are generally regarded as fossil soils, formed during the Miocene, on a peneplain, under a tropical climate. It is also held that subsequent uplift and dissection destroyed much of this surface together with the laterite profiles. These views are poorly established yet widely accepted. This study demonstrates that there is a very close mineralogic and stratigraphic relationship between the “laterite profiles” and the Triassic Hawkesbury Sandstone, such that the profiles are best regarded as iron rich sandstone units undergoing contemporary near-surface alteration including the mobilization of iron minerals as crystalline solids.
The specific adsorption of anions depends on the pK values of the anion acids. The adsorbed anions confer a negative charge on the surface displacing the zero point of charge to lower pH values.
The Stoer Group and Diabaig Formation of the Torridonian succession in northwest Scotland are late Mesoproterozoic to early Neoproterozoic (ca. 1200 1000 Ma). Features preserved on the top surfaces of fine- to medium-grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures; these include wrinkle structures, remnants of apparent microbial crusts, and indications of original cohesiveness and pliancy in sand-sized sediment. The surfaces on which the microbial structures formed were exposed subaerially (abundant, deep desiccation cracks and locally pedogenic structures) in alluvial, interfluve, and lacustrine margin settings, and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels. Thus, these features indicate that Earth's biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the Phanerozoic.
This chapter describes clays, microorganisms, and biomineralization. Microorganisms are ubiquitous on the Earth's surface. They are especially abundant in biofilms and microbial mats associated with ponds, hot springs, weathered feldspar, deep-sea floor vents, and mine drainage areas. In these environments, microorganisms can synthesize many kinds of clay minerals, both inside and outside their living cells. The study of biomineralization and the processes involved requires a multidisciplinary approach and the application of a range of analytical and instrumental techniques. At the same time, the results can provide valuable background information with respect to environmental protection, such as bioremediation of polluted sites, as well as an insight into the sustainable development of new, clean energy sources, mineral resources, and biomedical technologies.
Before the Great Oxidation Event (GOE), at ∼2.4 Ga, the mineralogical record of the near-surface continental environment indicates a low partial pressure of oxygen during weathering, which restricted many elements to a low oxidation state and limited the number of possible minerals formed from these elements. Calculations show that local pulses in the production of O2 by photosynthesis could mobilize some metals (e.g. Mo and Re, but not U), but this O2 would be completely consumed. After the GOE, many elements could occur in one or more oxidized forms in minerals in the near-surface environment. This development resulted in an explosive growth in the diversification of minerals.
Soil nitrogen and phosphorus pools shift strongly along soil chronosequences worldwide, but variation in plant nutrient resorption along these sequences is poorly understood. We quantified leaf and litter nutrient concentrations in 28 woody species along the Franz Josef soil chronosequence, New Zealand, a strong fertility gradient in temperate rain forest, to address two questions: How do leaf and litter nutrient concentrations vary along a soil chronosequence? And are the community-level responses driven by compositional differences among fertile and infertile sites, or by consistent changes in resorption proficiency within growth forms, and within species? Community-level leaf and litter N and P concentrations declined by between 67% and 88% along the soil chronosequence, and these responses were remarkably consistent within three contrasting growth forms (angiosperms, conifers, tree ferns), and within individual species. In spite of the three growth forms sharing similar responses to the soil chronosequence, tree ferns had higher absolute concentrations of leaf N, leaf P, and litter N relative to angiosperms, and higher concentrations of leaf N relative to conifers. These results clearly indicate that differences among fertile and infertile sites are driven both by compositional differences, as has been previously demonstrated, and by plasticity of individual species.
A biogeochemical study was undertaken at Barns Gold Prospect, a Au-in-calcrete discovery in the Northern Eyre Peninsula (South Australia). The prospect is located in highly weathered Proterozoic rocks and is overlain by at least 1 m of aeolian quartz sand that thickens to 8 m as a longitudinal sand dune over part of the mineralization. The dune is well-vegetated, with Melaleuca shrubs and Eucalyptus trees up to 5 m high. Over mineralization anomalous Au concentrations occur in plant organs, litter, soils and sand. The highest Au concentrations (9 ppb) occur in calcareous rhizomorphs high up within the dune. Luminescence dating shows that the dune took no longer than 27 000 years to form and mass balance calculations indicate that the Au anomaly in the dune has formed in less than 10 000 years. Mechanisms for the Au accumulation in the sand are postulated and it appears that a biological process, principally involving vegetation, is the most viable. A 200-m sample spacing of vegetation appears to be adequate for exploration of this type of deposit. Below the sand, calcrete provides a robust sampling medium. At present, due to limited knowledge of exploration methods in this type of environment, the mineral explorer must either expend significant financial resources augering through areas of sand cover to collect buried calcrete samples, or have lower confidence that vegetation and surface soil samples will detect mineralization.