Sandstone-derived Soils Research Articles

Leaf phosphorus fractions vary with leaf economic traits among 35 Australian woody species.

Adaptations of plants to phosphorus (P) deficiency include reduced investment of leaf P in storage (orthophosphates in vacuoles), nucleic acids and membrane lipids. Yet, it is unclear how these adaptations are associated with plant ecological strategies. Five leaf P fractions (orthophosphate P, Pi ; metabolite P, PM ; nucleic acid P, PN ; lipid P, PL ; and residual P, PR ) were analysed alongside leaf economic traits among 35 Australian woody species from three habitats: one a high-P basalt-derived soil and two low-P sandstone-derived soils, one undisturbed and one disturbed by human activities with artificial P inputs. Species at the undisturbed low-P site generally exhibited lower concentrations of total leaf P ([Ptotal ]), primarily associated with lower concentrations of Pi , and PN . The relative allocation of P to each fraction varied little among sites, except that higher PL per [Ptotal ] (rPL ) was recorded at the undisturbed low-P site than at the high-P site. This higher rPL , reflecting relative allocation to membranes, was primarily associated with lower concentrations of leaf nitrogen at the undisturbed low-P site than at the high-P site. Associations between leaf P fractions and leaf nitrogen may provide a basis for understanding the variation in plant ecological strategies dependent on soil P availability.

The potential for an old-growth forest to store carbon in the topsoil: A case study at Sasso Fratino, Italy

There is considerable interest devoted to old-growth forests and their capacity to store carbon (C) in biomass and soil. Inventories of C stocks in old-growth forests are carried out worldwide, although there is a lack of information on their actual potential for C sequestration. To further understand this, soil organic carbon (SOC) was measured in one of Italy’s best-preserved old-growth forests, the Sasso Fratino Integral Nature Reserve. This reserve is on the World Heritage List along with other ancient beech forests of Europe, and it is virtually untouched due to the steepness of the terrain, even before legal constraints were imposed. Although the sandstone-derived soils are often shallow, they are rich in organic matter. However, no quantification had been carried out. By systematically sampling the topsoil across the forest, we accurately determined the average amount of SOC (62.0 ± 16.9 Mg ha–1) and nitrogen (4.0 ± 1.2 Mg ha–1) in the top 20 cm. Using the CENTURY model, future dynamics of SOC stocks were predicted to 2050 according to two climate scenarios, A1F1 and B2, the first of high concern and the second more optimistic. The model projected an increase of 0.2 and 0.3 Mg ha–1 a–1 by 2030 under the A1F1 and B2 scenarios, respectively, suggesting that the topsoil in old-growth forests does not reach equilibrium but continues accumulating SOC. However, from 2030 to 2050, a decline in SOC accumulation is predicted, indicating SOC net loss at high altitudes under the worst-case scenario. This study confirms that soils in old-growth forests play a significant role in carbon sequestration. It also suggests that climate change may affect the potential of these forests to store SOC not only in the long term but also in the coming years.

Accumulation Capacity of Nickel and Zinc in Yerba Mate Cultivated in Soils with Contrasting Parent Materials.

Yerba mate (Ilex paraguariensis St. Hill.) has shown a relatively high capacity for micronutrient absorption and could be a candidate for biofortification and combating a lack of micronutrients. To further evaluate the accumulation capacity of Ni and Zn, yerba mate clonal seedlings were grown in containers under five rates of Ni or Zn (0, 0.5, 2, 10, and 40mgkg-1) with three soils originating from different parent material (basalt, rhyodacite, and sandstone). After 10months, plants were harvested, divided into component parts (leaves, branches, and roots), and evaluated for 12 elements. The use of Zn and Ni enhanced seedling growth under rhyodacite- and sandstone-derived soils at the first application rate. Application of Zn and Ni resulted in linear increases based on Mehlich I extractions; recovery of Ni was smaller than Zn. Root Ni concentration increased from approximately 20 to 1000mgkg-1 in rhyodacite-derived soil and from 20 to 400mgkg-1 in basalt- and sandstone-derived soils; respective increases in leaf tissue were ~ 3 to 15mgkg-1 and 3 to 10mgkg-1. For Zn, the maximum obtained values were close to 2000, 1000, and 800mgkg-1 for roots, leaves, and branches for rhyodacite-derived soils, respectively. Corresponding values for basalt- and sandstone-derived soils were 500, 400, and 300mgkg-1, respectively. Although yerba mate is not a hyperaccumulator, this species has a relatively high capacity to accumulate Ni and Zn in young tissue with the highest accumulation occurring in roots. Yerba mate showed high potential to be used in biofortification programs for Zn.

Characterisation of soils derived from different parent rocks from north central Nigeria

Mineralogy and geotechnical properties of residual lateritic soils derived from sandstone and migmatite–gneiss (MG) were compared. The aim was to determine the influence of the parent rock geology of sandstone and MG on their engineering properties. This was done using the statistical method of Student's t-test. Thin sections show that the MG samples are rich in feldspars and micas with up to 45 and 23% modal estimates, respectively. The dominant clay mineral in the two soils was kaolinite, while the dominant oxides were silicon dioxide, aluminium oxide and ferric oxide. The silica/sesquioxide ratio of the MG-derived soils (MGS) ranged from 1·7 to 3·2 while those of sandstone-derived soils (SS) were 2·9–6·6. SS samples which contained essentially quartz grains exhibited better compaction characteristics, higher California bearing ratio and lower plasticity than MGS. Better engineering properties exhibited by SS can be attributed to the high quartz content present in the parent rock. Feldspars and micas present in MG are weathered into plastic and hydrophilic clay minerals. These are likely to have a negative impact on the engineering properties of the derived soils. Statistical treatment of all determined engineering parameters showed significant differences in all cases except in relation to specific gravity, permeability and compressibility.

Effect of Land Use and Slope Position on Infiltration Characteristics on Sandstone-Derived Soils of Southern Nigeria

A study of some soil properties that influence infiltration under different land use types and slope positions in sandstone-derived soils was carried out in Akwa Ibom State, Southern Nigeria. Soil samples were collected in triplicate for laboratory analyses and infiltration tests were conducted using the double ring infiltrometer method. Analysis of variance, correlation and regression analyses were used to assess the data Oil Palm Plantation and Fallow Land increased the organic matter content of the soil, reduced bulk density, increased the soil porosity and aggregate stability over Continuously Cultivated Land. Downslope soil movement caused the upper slopes to lose their clay and organic matter to the middle and lower slope soils. Initial infiltration rate, final infiltration rate, cumulative infiltration, sorptivity and transmissivity varied highly across the studied locations but were not significantly (P ≤ 0.05) affected by land use, slope position and their interactions. Apparently higher infiltration rates were observed in all slope positions under Oil Palm Plantation and Fallow Land as a result of their apparently higher clay contents, total porosity, mean weight diameter, saturated hydraulic conductivity and organic matter contents over those of Continuously Cultivated Land. Heavier organic matter input will help to modify the upper slope soils for increased infiltration rates. Plantation agriculture should be adopted and continuous cultivation discouraged to increase water infiltration on sloppy terrains of the study area.

Mineral control of organic carbon storage in acid temperate forest soils in the Basque Country

Soil minerals are known to play a major role in soil organic carbon (SOC) stabilization. However, the exact nature of the role is still poorly understood as comparative studies are complicated by the fact that mineralogy usually varies with other important factors such as climate, land-use, texture and acidity. This study investigated naturally-occurring minerals and C storage in nine mature, second-rotation Pinus radiata D. Don forest plantations at a similar development stage and growing under similar climatic conditions, but established on soils derived from three different parent materials: sandstone, basalt and trachyte. We quantified the SOC stocks in the 0–20 cm soil layer, clay-size minerals and metal oxides. The distribution of SOC in labile and mineral-bound fractions and the chemical structure of the SOC were also determined, by CPMAS NMR spectroscopy. For similar tree biomass, mean SOC storage was 2 times higher in the soils derived from basalt and 2.5 times higher in the soils derived from trachyte which were relatively rich in chlorite/vermiculite mixed layers and short-range order aluminium and iron forms, than in the sandstone-derived soils dominated by illite and with no short-range order aluminium. The parent material also affected the major C components of the SOC. Thus, the proportion of aromatic-C forms in the total SOC was higher in the sandstone-derived soil than in the soils of volcanic origin. Furthermore, the proportion of SOC in the mineral-bound fraction was around 30% in the sandstone-derived soil and around 50% in the volcanic soils. We conclude that estimates of ecosystem SOC stocks in acid temperate forest soils should include proxies for clay mineralogy, such as phyllosilicate minerals, contents of Fe and Al (hydr-) oxides and non-crystalline compounds. In addition, we recommend the inclusion of soil parent material as a proxy in models aimed at estimating regional SOC stocks.

Genesis of sandstone-derived soils in the Cerrado of the Piauí State, Brazil

This study characterized the morphological, physical and chemical attributes of sandstone-derived soils at the Cerrado of the Piauí State, Brazil, in order to identify evolutionary standards. The study was carried out with five representative soil profiles identified as P1-RY (Typical Flavic Psychotic Neosol - Aquents), P2-PA (Typical Dystrophic Yellow Argisol - Alfisol), P3-RL (Fragmentary Litholic Distrophic Neosol - Psammenit), P4-RQ (Typical Ortic Quartzenetic Neosol - Orthents) and P5-PV (Typical Dystrophic Red Argisol - Ultisol). Soil samples were submitted laboratory analysis described morphologically. In general, the soils presented high sand content, low pH, low content of exchangeable bases and low cation exchange capacity (CEC). Organic matter governed the CEC in most cases, suggesting dependence of organic matter in the supply of charges. These soils showed a low degree of weathering, but with iron of high crystallinity. Thus, the relief and the parent material are the major important soil-forming factors at the Cerrado of the Piauí State. Moreover, these soils are young, with the soils from the Piauí Formation being more evolved. However, the sandstones from the Canindé Group apparently are providing lithological secondary minerals for the soil.

Ant biodiversity and its environmental predictors in the North Kimberley region of Australia’s seasonal tropics

Northern Australia supports the world’s largest estate of undeveloped tropical savannas, but previous studies of ant diversity in the region have covered only a fraction of its land area and habitat diversity. We assess patterns of ant species and functional diversity, their environmental predictors, and biogeographic significance in the central North Kimberley region of Australia’s seasonal tropics. Pitfall traps were used to sample ants at 69 plots in representative savanna habitats, collecting a total of 158 species from 30 genera. Total richness was estimated to be as high as 237 species. At least 29 species across 12 genera appear to have been collected for the first time. Only a single invasive ant was recorded from the study area. Based on cluster analysis we identified six compositionally distinct ant communities, each associated with a combination of vegetation type and underlying geology. Species richness and functional diversity was highest in savanna woodlands and grasslands on sandstone-derived soils, with increasing richness also predicted by a lower mean daily temperature range, a more complex understorey, and lower precipitation seasonality. The abundance of nearly all commonly trapped species was related to temperature, moisture, and habitat variables, although these relationships were highly idiosyncratic. Nearly 40 % of the collected species are known only from the North Kimberley region. The high level of endemism, together with the lack of introduced ant species, identifies the North Kimberley ant fauna as having outstanding biodiversity value. Our identification of ant community types based on mappable soil and vegetation units provides a basis for predicting ant distribution throughout the broader region, and therefore contributing to regional conservation planning and management.

Legume nodules from nutrient-poor soils exhibit high plasticity of cellular phosphorus recycling and conservation during variable phosphorus supply

Nitrogen fixing legumes rely on phosphorus for nodule formation, nodule function and the energy costs of fixation. Phosphorus is however very limited in soils, especially in ancient sandstone-derived soils such as those in the Cape Floristic Region of South Africa. Plants growing in such areas have evolved the ability to tolerate phosphorus stress by eliciting an array of physiological and biochemical responses. In this study we investigated the effects of phosphorus limitation on N2 fixation and phosphorus recycling in the nodules of Virgilia divaricata (Adamson), a legume native to the Cape Floristic Region. In particular, we focused on nutrient acquisition efficiencies, phosphorus fractions and the exudation and accumulation of phosphatases. Our finding indicate that during low phosphorus supply, V. divaricata internally recycles phosphorus and has a lower uptake rate of phosphorus, as well as lower levels adenylates but greater levels of phosphohydrolase exudation suggesting it engages in recycling internal nodule phosphorus pools and making use of alternate bypass routes in order to conserve phosphorus.

Review of the southern African Moraea ciliata complex (Iridaceae: Iridoideae) including the three new taxa M. flava and M. ciliata subsp. cuprina and subsp. lutescens

The Moraea ciliata complex (Moraea subg. Acaules) from the southern African winter-rainfall zone currently includes four vegetatively similar species: a widespread M. ciliata plus three more localized species, Moraea longipes, Moraea macronyx and Moraea tricolor. Examination of herbarium collections and wild populations of M. ciliata throughout its range indicates that the recognition of one new species and two subspecies better reflects the ecological and morphological patterns in the species. The new species Moraea flava from the western Karoo with pale yellow flowers and smooth leaves with thickened and crisped margins is sometimes sympatric with typical blue–flowered M. ciliata but blooms earlier in the season. M. ciliata subsp. cuprina is recognized for a series of pink- to red-flowered populations from deep sands along the Atlantic coast of Western Cape often with two inflorescences per plant and unusually long capsules. M. ciliata subsp. lutescens from stony sandstone-derived soils, mostly of montane habitats in Western Cape between Worcester and the Gifberg, differs consistently from blue- or white-flowered subsp. ciliata in its slightly smaller yellow flowers, narrower, usually hairless leaves, and short stamens with the filaments united for up to half their length. Unusual populations of small, white-flowered plants flowering in May and June from west and south of Swellendam are provisionally included in subsp. ciliata. These taxonomic changes render subsp. ciliata morphologically more homogeneous but still with a wide geographic range extending from the Cape Peninsula north to Springbok in Northern Cape and east though the western Karoo and Upper Karoo to near Lady Grey in Eastern Cape.

Climatic, edaphic and fire regime determinants of biome boundaries in the eastern Cape Floristic Region

Landscapes of the eastern Cape Floristic Region are extremely rich in biomes. Analysis of the determinants of boundaries between biomes can generate insights and predictions that are useful for the applied ecological sciences. Here we used a historical data set and multivariate methods to explore the determinants of the boundaries of Forest, Fynbos, Grassland, Renosterveld and Thicket biomes in a 1200km2 area of the Kouga region. The data set comprised 203 (10m×10m) sites with corresponding landscape-scale environmental variables, and 100 sites with corresponding site-bound edaphic (physical and chemical) variables. Of the landscape variables, soil drainage and fire exposure had the strongest biome-specific associations: most Grassland occurred on seasonally waterlogged soils and Renosterveld on moderately drained soils. While Forest was exclusively associated with landscapes protected from fire, much Fynbos and Thicket were found in areas exposed to fires of intermediate frequency; however, in these situations Fynbos is restricted to sandstone-derived soils and thicket to shale-derived soils. Other strong patterns were the restriction of Forest to sandstone-derived soils and of Thicket to soils of deep to intermediate depth. Soils of the majority of Fynbos and Grassland were shallow, rocky and infertile, while those of Forest and Thicket were deep, rock-free and fertile, especially in terms of oxidizable carbon and total nitrogen. The relatively high fertility of Forest and Thicket soils is attributed canopy-induced enrichment in the prolonged absence of fire. Renosterveld occupied soils of intermediate fertility. These patterns can provide useful insights for developing experimental approached to simultaneously assess the determinants of multiple boundaries in the biome-rich landscape of the eastern Cape Floristic Region.

Nodules from Fynbos legume Virgilia divaricata have high functional plasticity under variable P supply levels

Legumes have the unique ability to fix atmospheric nitrogen (N2) via symbiotic bacteria in their nodules but depend heavily on phosphorus (P), which affects nodulation, and the carbon costs and energy costs of N2 fixation. Consequently, legumes growing in nutrient-poor ecosystems (e.g., sandstone-derived soils) have to enhance P recycling and/or acquisition in order to maintain N2 fixation. In this study, we investigated the flexibility of P recycling and distribution within the nodules and their effect on N nutrition in Virgilia divaricata Adamson, Fabaceae, an indigenous legume in the Cape Floristic Region of South Africa. Specifically, we assessed tissue elemental localization using micro-particle-induced X-ray emission (PIXE), measured N fixation using nutrient concentrations derived from inductively coupled mass-spectrometry (ICP-MS), calculated nutrient costs, and determined P recycling from enzyme activity assays. Morphological and physiological features characteristic of adaptation to P deprivation were observed for V. divaricata. Decreased plant growth and nodule production with parallel increased root:shoot ratios are some of the plastic features exhibited in response to P deficiency. Plants resupplied with P resembled those supplied with optimal P levels in terms of growth and nutrient acquisition. Under low P conditions, plants maintained an increase in N2-fixing efficiency despite lower levels of orthophosphate (Pi) in the nodules. This can be attributed to two factors: (i) an increase in Fe concentration under low P, and (ii) greater APase activity in both the roots and nodules under low P. These findings suggest that V. divaricata is well adapted to acquire N under P deficiency, owing to the plasticity of its nodule physiology

Differences in uptake and distribution patterns between zinc and cadmium in Vicia villosa

Vicia villosa is an annual legume plant. Field-growing experiments were performed on six plots under different soil conditions. Variations in the concentrations of Zn and Cd in tissues were investigated. Differences in distribution patterns between Zn and Cd appeared during growing: the concentrations of Zn in roots in sandstone-derived soils were relatively higher than those in limestone-derived soils, and the uptake patterns of Zn by roots should be similar to those of iron (Fe). However, the concentrations of Cd in roots in limestone-derived soils were higher than those in sandstone-derived soils, and the uptake patterns of Cd by roots should be similar to those of manganese (Mn). On the contrast, the distribution patterns of Zn were similar to those of Mn, while the distribution patterns of Cd were similar to those of Fe in tissues, indicating that the uptake patterns of Zn and Cd were different from distribution patterns.

Determinants of whole‐plant light requirements in Bornean rain forest tree saplings

1 Shade tolerance, defined as the ability to survive and grow under low light, varies markedly among tree species. However, the role of low-light growth responses in determining shade tolerance is unclear, as are the effects of non-light resources such as soil nutrients. 2 A conceptually simple field measure of shade tolerance is the whole-plant light compensation point (WPLCP), evaluated as the x-intercept of the relationship between growth and incident light integrated over a long time interval. Here we compare WPLCP for growth and survivorship of saplings of Bornean tree species differing in shade tolerance, and evaluate the importance of various physiological and morphological traits in predicting WPLCP. We also examine both phenotypic and evolved differences in WPLCP between tree saplings growing on two distinct soil types at Sepilok Forest Reserve, Sabah, Malaysia. 3 Growth-based estimates of WPLCP showed essentially a 1 : 1 correspondence to threshold light levels for survivorship. At higher light, more light-demanding species showed higher growth, resulting in a steeper slope of the relationship between relative growth rate (RGR) and light availability than in more shade-tolerant species. This resulted in significant crossovers in the RGR–light relationship among species. 4 Dark respiration (Rd) was the single best predictor of WPLCP; other leaf traits such as leaf nitrogen and photosynthetic capacity were correlated with, but excluded as predictors of, WPLCP in multiple regression analyses. 5 Although soil type had no consistent phenotypic effect on WPLCP, evolved responses among species were pronounced: species associated with the nutrient-poor, drought-prone, sandstone-derived soils had higher WPLCP values than alluvial soil specialists in phylogenetically controlled comparisons. 6 Our results indicate that minimum light levels for growth do not diverge from those for survivorship, and do not support the view that low-light survivorship solely determines shade tolerance. Our analyses also suggest that Rd is the strongest determinant of whole-plant light requirements in tropical tree saplings, and thus may be an easily measured surrogate of WPLCP and shade tolerance. 7 Prediction of tree species resource requirements is crucial for understanding forest dynamics and promoting ecology-based forest management and restoration, particularly in diverse tropical forests where data on the resource requirements of most species are not available. Easily measured surrogates of resource requirements (e.g. Rdas a predictor of shade tolerance) will contribute to this goal, as will an improved understanding of the interactive effects of multiple resources on tree performance.

The influence of topography on some engineering and geological characteristics of two sandstone – derived lateritic soils from Ishara, Southwestern Nigeria

Clay mineralogy, major oxides geochemistry and some geotechnical properties of two sandstone-derived lateritic soils taken from two topographically contrasting sites in Ishara, Southwestern Nigeria were investigated. The higher amounts of kaolinite and ferric oxide obtained for soil samples taken from gentle slopes than in those from flat terrains indicates that the soils along the gentle slope are better drained and more laterised than those from the flat site. This phenomenon is responsible for the higher amount of gravel-size particles, lower amount of sand-size particles, lower plasticity and higher strength characteristics exhibited by soil samples along the gentle slope than those in the flat site. It is thus reasonable to win soils required for construction work from gently slopy terrains since such soils are likely to possess better geotechnical characteristics than those from flat sites. Journal of Applied Science, Engineering and Technology Vol. 3(1) 2003: 1-6

Intraspecific Variability and Timing in Ancestral Ecology Reconstruction: A Test Case from the Cape Flora

Thamnochortus (ca. 32 species) is an ecologically diverse genus of Restionaceae. Restionaceae comprise a major component of the southern African Cape flora, wherein eco-diversification might have been important in the generation of high levels of species richness. In an attempt to reconstruct the macroecological history of Thamnochortus, it was found that standard procedures for character state optimization make two inappropriate assumptions. The first is that ancestors are monomorphic (i.e., ecologically uniform) and the second is that eco-diversification follows, or is slower than, lineage diversification. We demonstrate a variety of coding schemes with which the assumption of monomorphy can be avoided. For unordered discrete ecological characters, presence coding and generalized frequency coding (GFC) are suboptimal because they occasionally yield illogical assignments of no state to ancestors. Polymorphism coding or use of the program DIVA are preferable in this respect but are applicable only with parsimony. For continuous eco-characters (e.g., a rainfall gradient, where individual species occur in ranges), GFC and MaxMin coding provide equally valid solutions to optimizing ranges with parsimony. However, MaxMin can be extended to likelihood approaches and is therefore preferable. With respect to rates and timing, all algorithms currently employed for ancestral ecology reconstruction bias toward slow rates of eco-diversification relative to lineage diversification. An alternative to this bias is provided by DIVA, which biases toward accelerated rates of eco-diversification and thus inferences of ecology-driven speciation. We see no way of choosing between these biases; however, phylogeneticists should be aware of them. Applying these methods to Thamnochortus, we find there to be important differences in details, yet general congruence, regarding the historical ecology of this clade. We infer the most recent common ancestor of Thamnochortus to have been a post-fire resprouting species distributed on rocky, well-drained, sandstone-derived soils at lower-middle elevations, in regions of moderate levels of yearly (primarily winter) rainfall. This species would have been distributed in habitats much like those of the southwestern Cape mountains today. Major ecological trends include shifts to lower rainfall regimes and shifts from sandstone to limestone-derived alkaline soils at lower altitudes.

Reconstruction of age structure and spatial arrangement of piñon–juniper woodlands and savannas of Anderson Mesa, northern Arizona

We examined age structure and spatial arrangement of piñon–juniper woodlands and savannas on six plots distributed across three different soil types in northern Arizona. These stands, as typical of many others in piñon–juniper ecosystems, have experienced increases in tree densities since the arrival of European settlers. The goal of this study was to reconstruct stand conditions in 1860, prior to livestock grazing, using stem-mapping to determine tree arrangement and tree-ring analysis to examine age structure and density. Ripley's K( t), Ripley's K 12( t), and Moran's I were used to analyze nearest neighbor distances, spatial association, and spatial autocorrelation, respectively. All sites have long term presence of juniper and piñon trees, with a pulse of establishment and survival occurring between 1860 and 1880 on basalt- and sandstone-derived soils. In contrast, limestone-derived soil had no pulse of tree establishment in 1860, but rather a steady increase in tree establishment since ca. 1700. Spatial arrangement of juniper trees in 1860 showed strong clumping patterns from a minimum distance of 15 m to all spatial scales. Piñon pine varied in spatial arrangement from clumping at all spatial scales to random at all spatial scales. Positive spatial autocorrelation was determined for age of juniper trees to a minimum distance of 21 m in current stand conditions, in contrast to no strong trends of spatial autocorrelation in 1860. By comparing the age structure and spatial results for the forest reconstruction of 1860 to current conditions, we were able to show variation among soil types in nurse tree association between piñon and juniper trees and unable to support the density dependent mortality hypothesis for these sites. Presettlement (1860) diameter distributions and basal areas can be used to develop structure control (BDq) prescriptions unique to each soil type to restore either savanna or woodlands condition. However, identifying one blanket prescription for tree reduction in piñon–juniper ecosystems of the southwestern United States, or even the Anderson Mesa landscape, would reduce the range of variability present in the form of woodlands and savannas.

Mineralogy and ion exchange properties of the particle size fractions of some Brazilian soils in tropical humid areas

The inorganic fractions of 25 samples from 12 representative Brazilian soils were separated into six subfractions (clay, silt, very fine sand, fine sand, medium sand, coarse+very coarse sand) and their effective cation and effective anion exchange capacity (ECEC and EAEC, respectively) evaluated by the compulsive exchange method using unbuffered BaCl 2 solution. The soils had developed from a range of parent material, such as sandstones, Tertiary unconsolidated sediments, siltstones, silty shales, basalts, metapelites and mica schists. The silt fraction of sandstone-derived soils had an ECEC of at most 2 mmol c kg −1 while the silt fraction of basaltic soils had ECEC which reached 106 mmol c kg −1. The silt fraction of the soil derived from mica schists had an EAEC of 9 mmol c kg −1, which was the highest of all the soils analyzed. The highest ECEC recorded was close to 300 mmol c kg −1 for the fine sand fraction of soil derived from silty shales. Sand fractions from Tertiary unconsolidated sediments were practically inert, while those from sandstones made only a small contribution to the effective exchange capacity. The origin of these differences may lie in the characteristics of the parent materials of the soils. Primary micas, illite and feldspars together with inactive quartz were the major components of the coarse fractions of the soils. We attributed the high ECEC of the coarse fractions to several factors, including feldspars and mica being subjected to intense weathering, accelerated cation release from the mineral structure, and silt and sand-sized clay mineral pseudo-aggregates. In highly weathered tropical soils, the coarse fractions can play an important role in active soil fertility because they are not chemically inert and in potential fertility because of their importance as reservoirs of nutrients.

Testing the adaptive nature of radiation: growth form and life history divergence in the African grass genusEhrharta(Poaceae: Ehrhartoideae)

In most documented examples of adaptive radiation, the processes underlying divergence in form and function are poorly explored and remain speculative. Here, data from a comparative seedling growth experiment are used to explore growth form divergence in Ehrharta, a group of grasses that radiated in seasonally arid environments of the Cape region of South Africa. Seedlings of eight Ehrharta species of variable growth form were grown in liquid culture under conditions of high resource availabilty for 56 d, during which time changes in dry mass, allocation, and leaf parameters were measured. The results of this experiment reveal the existence of distinct seedling growth patterns that are associated with differences in adult plant form and seasonal drought survival strategy. Specifically, species that utilize a reseeding strategy have higher seedling growth rates and flower earlier than species that persist by vegetative means. A correlation between species' growth rates and their native substrates suggests that edaphic heterogeneity has been central in directing the evolution of alternative persistence strategies and growth forms. Parsimony reconstruction identifies slow growth and an association with nutrient-deficient sandstone-derived soils as ancestral in Ehrharta, with fast growth evolving after a transition to richer shale- and granite-derived soils. The emergence of annual species in two fast-growth lineages suggests that the latter is a key step in the evolution of an ephemeral strategy. An association between plant function and habitat identifies the radiation of Ehrharta as adaptive.

Rock fragments in soil support a different microbial community from the fine earth

Two sandstone-derived soils under pure stands of silver fir ( Abies alba Mill.) and European beech ( Fagus sylvatica L.) were studied to determine if the fine earth (<2 mm material) and two size-classes of porous rock fragments (>2 mm material) supported different microbial communities. Samples from three soil horizons (A, Bw, and BC) were analysed under both optical and scanning electron microscopes. Small stones (2–10 mm in average diameter) appeared more altered than larger ones (40–60 mm) and the effects of weathering became more obvious with shallower depth. In both soils, numerous hyphae and other living forms were observed on the surface of the stones from the A and Bw horizons; this contrasted with the stones from the BC horizon, which showed little or no colonisation. The microbial community of each fraction was characterised using Biolog-Community Level Physiological Profiles (CLPP) and phospholipid fatty acid analyses (PLFA) for samples in the A and B horizons. Significant potential microbial activity (C source utilisation) was associated with rock fragments, from the A horizon and, to a lesser extent, the B, although this was lower than for the equivalent fine earth fraction. The microbial colonisation of the stones appeared inversely related with their size and sampling depth. The PLFA analysis showed not only quantitative differences in the microbial biomass between horizons and size-fractions but also highlighted that the communities differed between soils, horizons (for the sole beech soil) and fractions. These findings demonstrate that by considering rock fragments as a microbiologically inert fraction and discarding them before analysis, as usually is done, can lead to an incomplete picture of both the total amount and, perhaps more importantly, the structure of soil microbial community.