Initial pedogenesis in a topsoil crust 3 years after construction of an artificial catchment in Brandenburg, NE Germany

Cyanobacteria and green algae present in biological soil crusts are able to colonize mineral substrates even under extreme environmental conditions. As pioneer organisms, they play a key role during the first phases of habitat colonization. A characteristic crust was sampled 3 years after installation of the artificial water catchment “Chicken creek”, thus representing an early successional stage of ecosystem development. Mean annual rainfall and temperature were 559 mm and 9.3°C, respectively. We combined scanning electron microscopy (SEM/EDX) and infrared (FTIR) microscopy to study the contact zone of algal and cyanobacterial mucilage with soil minerals in an undisturbed biological soil crust and in the subjacent sandy substrate. The crust was characterized by an approximately 50 μm thick surface layer, where microorganisms resided and where mineral deposition was trapped, and by an approximately 2.5 mm thick lower crust where mineral particles were stabilized by organo-mineral structures. SEM/EDX microscopy was used to determine the spatial distribution of elements, organic compounds and minerals were identified using FTIR microscopy and X-ray diffraction (XRD). The concentration of organic carbon in the crust was about twice as much as in the parent material. Depletion of Fe, Al and Mn in the lower crust and in the subjacent 5 mm compared to the geological substrate was observed. This could be interpreted as the initial phase of podzolization. Existence of bridging structures between mineral particles of the lower crust, containing phyllosilicates, Fe compounds and organic matter (OM), may indicate the formation of organo-mineral associations. pH decreased from 8.1 in the original substrate to 5.1 on the crust surface 3 years after construction, pointing to rapid weathering of carbonates. Weathering of silicates could not be detected.     

Drought deaths in Eucalyptus globulus (Labill.) plantations in relation to soils, geomorphology and climate

The occurrence of tree deaths in young, 3 to 6 year old Eucalyptus globulus plantations established on farmland in south-western Australia was found to be strongly related to factors indicative of poor soil water storage capacity. Seven years after planting tree survival was significantly less on soils <2 m deep compared to >2 m deep (22% vs 70%). This is due to the limited ability of some soils to store a sufficient proportion of the annual rainfall within the root-zone to meet the plant water demand in a region with a recurrent annual summer drought. There are practical difficulties in routinely surveying soils to depths in excess of 2 m over broad areas, to predict the likelihood of tree death. On the granitic basement rocks of south-west Western Australia, the occurrence of ferricrete gravels provides a useful surrogate indicator for the presence of deeper soils. In this region the distribution of soil depth and soil fertility has a geomorphic basis, being related to previous patterns of deep weathering and regolith stripping. Soils have developed on various horizons of deeply weathered profiles, formed from granites and gneisses. These materials have been stripped to a variable extent by erosion, leading to a range of soil depths. The original weathered profiles, which correspond to the soils with ferricrete gravels, comprise the deepest soil/regolith materials (~30-50 m deep); whereas along drainage lines the regolith has been completely stripped, the soils are shallow and plantations are most susceptible to drought. Knowledge of the relationship between soil depth and plantation performance allows regional indications of drought risk to be developed from regional soil mapping and the production of more efficient sampling designs for site assessment.     

Mangrove Forest and Soil Development on a Rapidly Accreting Shore in New Zealand

Mangrove forests are rapidly expanding their distribution in New Zealand, which is at the southern limit of their range. We investigated how these expanding mangrove forests develop through time. We assessed patterns in forest structure and function at the Firth of Thames, which is a rapidly accreting mangrove site in New Zealand where 1 km of mangrove of Avicennia marina has established seaward since the 1950s. Across the intertidal region, mangrove forest structure was highly variable. We used bomb-pulse radiocarbon dating to age the forest. Two major forest establishment events were identified; one in 1978–1981 and another in 1991–1995. These events coincided with sustained El Niño activity and are likely the result of reduced wind and wave energy at the site during these periods. We used the two forests of different ages to assess whether mangroves in New Zealand mature at similar rates as other mangroves and whether they conform to classic models of succession. The timing of forest maturation is similar in New Zealand as in more tropical locations with trees exhibiting features of mature forests as they age from about 10 to about 30 years. In older forest (~30 years old) trees become larger and stands more homogenous than in the younger forest (~10 years old). Carbon and nutrient concentrations in soils increased and soils become more aerobic in older forest compared to younger forest. Additionally, using fertilization experiments, we established that despite reduced growth rates in older forests, nitrogen remained limiting to growth in both older and young forests. However, in contrast to classic successional models leaf tissue nutrient concentrations and nutrient conservation (nutrient resorption from senescence leaf tissue) were similar in forests of differing ages and did not vary with fertilization. We conclude that mangrove forest expansion in New Zealand is influenced by climatic factors. Mangrove forests mature rapidly, even at the limits of their range and they satisfy many of the successional patterns predicted by Odum (1969) for the early stages of forest succession.     

Biological soil crusts influence carbon release responses following rainfall in a temperate desert,northern China

How soil cover types and rainfall patterns influence carbon (C) release in temperate desert ecosystems has largely been unexplored. We removed intact crusts down to 10 cm from the Shapotou region, China, and measured them in PVC mesocosms, immediately after rainfall. C release rates were measured in soils with four cover types (moss-crusted soil, algae-crusted soil, mixed (composed of moss, algae, and lichen)-crusted soil, and mobile dune sand). We investigated seven different rainfall magnitudes (0–1, 1–2, 2–5, 5–10, 10–15, 15–20, and >20 mm) under natural conditions. C release from all four BSCs increased with increasing rainfall amount. With a rainfall increase from 0 to 45 mm, carbon release amounts increased from 0.13 ± 0.09 to 15.2 ± 1.35 gC m^?2 in moss-crusted soil, 0.08 ± 0.06 to 6.43 ± 1.23 gC m^?2 in algae-crusted soil, 0.11 ± 0.08 to 8.01 ± 0.51 gC m^?2 in mixed-crusted soil, and 0.06 ± 0.04 to 8.47 ± 0.51 gC m^?2 in mobile dune sand, respectively. Immediately following heavy rainfall events (44.9 mm), moss-crusted soils showed significantly higher carbon release rates than algae- and mixed-crusted soils and mobile dune sands, which were 0.95 ± 0.02, 0.30 ± 0.03, 0.13 ± 0.04, and 0.51 ± 0.02 μmol CO₂ m^?2 s^?1, respectively. Changes in rainfall patterns, especially large rain pulses (>10 mm) affect the contributions of different soil cover types to carbon release amounts; moss-crusted soils sustain higher respiration rates than other biological crusts after short-term extreme rainfall events.     

Plant silicon isotopic signature might reflect soil weathering degree

Plants fractionate Si isotopes which provides a useful Si tracer in the Si soil-plant cycle. This study reports plant Si content and Si-isotopic signatures in mature banana plants grown on soils with different weathering degree, but all developed from basaltic pyroclasts in the Mungo area, Cameroon. The δ³⁰Si compositions were determined in various plant parts and soil surface horizons by MC-ICP-MS in dry plasma mode with external Mg doping to a precision of ± 0.15‰ (± 2σ_SD). The Si-isotopic compositions in banana plants grown on weathered clayey soils (+0.54 ± 0.15‰) are heavier than on weakly developed soils rich in fresh ash and pumice (+0.02 ± 0.15‰). The corresponding bulk soils display lower δ³⁰Si value in weathered soil (?1.41‰) than in poorly developed soil (?0.41‰). We suggest that the dissolved Si source for the plant, governed firstly by dissolution of easily weatherable minerals, was isotopically enriched in heavy isotopes through clay formation over long periods. At seasonal to annual time scale, this source is influenced by a combination of following processes: Si adsorption of light isotopes onto Fe oxides, plant Si uptake and recycling in surface horizons. This would provide an isotopically heavier Si source in the more weathered soil since the Fe oxides content increases with weathering. Plant Si-isotopic signature might thus reflect the soil weathering degree. This study further suggests that in addition to weathering processes, rivers isotopic signatures likely depend on the fate of phytoliths in the soil-plant-river system.     

Uplift,Erosion, and Phosphorus Limitation in Terrestrial Ecosystems

ABSTRACT Primary productivity on old, weathered soils often is assumed to be limited by phosphorus (P), especially in the lowland tropics where climatic conditions promote the rapid depletion of rock-derived nutrients. This assumption is based on a static view of soils weathering in place with no renewal of the bedrock source. In reality, advection of material through the soil column introduces a spatially variable supply of rock-derived nutrients. This flux is dependent on the residence time of soil, which can range from a few hundred years in rapidly uplifting collisional mountain belts to tens of millions of years in tectonically quiescent tropical cratons. We modeled the effects of tectonic uplift, erosion, and soil depth on the advection of P through the soil column and P availability, calibrating rate of change in biologically available P over time with data from two basaltic chronosequences in Hawai’i and a series of greywacke terraces in New Zealand. Combining our model with the global distribution of tectonic uplift rates and soil depths, we identified tectonic settings that are likely to support P-depleted ecosystems—assuming that tectonic uplift and erosion are balanced (that is, landscape development has reached steady state). The model captures the occurrence of transient P limitation in rapidly uplifting young ecosystems where mineral weathering is outpaced by physical erosion—a likely occurrence where biological N fixation is important. However, we calculate that P depletion is unlikely in areas of moderate uplift, such as most of Central America and Southeast Asia, due to the continuous advection of P into the rooting zone. Finally, where soil advection is slow, such as the Amazon Basin, we expect widespread P depletion in the absence of exogenous nutrient inputs.     

Carbon dioxide consumption during soil development

Carbon is sequestered in soils by accumulation of recalcitrant organic matter and by bicarbonate weathering of silicate minerals. Carbon fixation by ecosystems helps drive weathering processes in soils and that in turn diverts carbon from annual photosynthesis-soil respiration cycling into the long-term geological carbon cycle. To quantify rates of carbon transfer during soil development in moist temperate grassland and desert scrubland ecosystems, we measured organic and inorganic residues derived from the interaction of soil biota and silicate mineral weathering for twenty-two soil profiles in arkosic sediments of differing ages. In moist temperate grasslands, net annual removal of carbon from the atmosphere by organic carbon accumulation and silicate weathering ranges from about 8.5 g m^–2 yr^–1 for young soils to 0.7 g M^–2 yr^–1 for old soils. In desert scrublands, net annual carbon removal is about 0.2 g m^–2 yr^–1 for young soils and 0.01 g m^–2 yr^–1 for old soils. In soils of both ecosystems, organic carbon accumulation exceeds CO₂ removal by weathering, however, as soils age, rates of CO₂ consumption by weathering accounts for greater amounts of carbon sequestration, increasing from 2% to 8% in the grassland soils and from 2% to 40% in the scrubland soils. In soils of desert scrublands, carbonate accumulation far outstrips organic carbon accumulation, but about 90% of this mass is derived from aerosolic sources that do not contribute to long-term sequestration of atmospheric carbon dioxide.     

Men's revealed preference for their mates' ages

Both young and old men say that they are sexually attracted to young, fertile women, but older men tend to marry older women, including those who are peri- and post-menopausal. We assessed men's freely revealed preference for their mates' age using an unusual marriage phenomenon in South Korea: the practice in which men purchase their brides from developing countries. Presumably, the men's mate choice, at least regarding the brides' age, is unrestricted by women. We analyzed all first marriages reported in 2010–2014 in South Korea and compared men who married Korean brides (N = 1,088,457) with those who purchased their brides (N = 45,528); the age range of grooms and brides was 15–59. While the former exhibited the typical pattern where older men married older women, the latter, whether young or old, always married young, fertile women. This finding is consistent with men's stated preference for young, fertile women in mating and suggests that the typical pattern is generated by women's limiting role in mating.     

The Role of Low-Molecular-Weight Organic Carbons in Facilitating the Mobilization and Biotransformation of As(V)/Fe(III) from a Realgar Tailing Mine Soil

Several low-molecular-weight organic carbon (LMWOC) compounds (acetate, propionate, butyrate, lactate, and glucose) were added to flooded arsenic-rich tailing mine soil to investigate their effect to the mobilization of As/Fe and potential shift of microbial community. A promoting effect to the mobilization and biotransformation of As(V)/Fe(III) in the soils resulting from the supplementation with LMWOCs substrate was indicated compared to the biotic microcosm amended with deionized water alone. During 38-day biotic incubation, more than 2100 μg/L of As(III) and 4.2 mg/L of Fe(II) levels were released from the soils amended with LMWOCs substrates, compared to the levels of As(III) and Fe(II) (less 35 μg/L and 1.82 mg/L) derived from the biotic supplementation with deionized water alone. PCR-DGGE indicated that several LMWOCs-responded bacteria were mostly related to Firmicutes and Proteobacteria. Moreover, a negligible impact on the abundance of Fe(III)-reducing family Geobacteraceae was indicated in the LMWOCs-amended soils. However, an increased abundance of sulfate-reducing bacteria but a decreased abundance of arsenate-respiring bacteria were indicated upon the soils supplemented with acetate alone, compared with other LMWOC amendments. DNA-stable isotope probing analysis demonstrated that the dual roles of acetate was not only served as an electron donor for biotransformation of As(V)/Fe(III) in soil, but also assimilated as a powerful energy source to promote the growth of sulfate-reducing bacteria. The findings suggest that there are specific bacteria that preferentially respond to the additions of LMWOC for controlling the biochemical cycle process of As/Fe in soils.     

Quantifying ecosystem rejuvenation: foliar nutrient concentrations and vegetation communities across a dust gradient and a chronosequence

Background and aims

Due to long-term weathering of land surfaces, aeolian nutrient contributions can become essential to maintain ecosystem fertility and avoid retrogression. However, studies that consider the qualitative and quantitative effects of dust deposition on ecosystem development are rare. We addressed this knowledge gap by studying an active Holocene dust flux gradient along a 6,500 year old dune ridge and a nearby chronosequence outside the influence of dust deposition in a super-humid, high leaching environment, on the west coast of the South Island in New Zealand.

Methods

Along both sequences we measured foliar nutrients of two main tree species (Dacrydium cupressinum, Prumnopitys ferruginea) and analysed vegetation communities in survey plots.

Results

Along the dust gradient, foliar phosphorus (P) concentrations increased up to 50 % with increasing dust flux. Across the nearby chronosequence a rapid decline of up to 50 % in foliar [P] occurred within the first 2,000 years after which it plateaued. At the highest dust flux rate, closest to the dust source, foliar [P] matched those of surfaces that are 5,702 to 6,098 years younger than the 6,500 year old dune. Vegetation communities along the dust gradient showed increasing relative abundance of species typical for successional communities on immature soils (Entisols, Inceptisols), while canopy cover and basal area (total, angiosperms, conifers) did not respond to increasing dust deposition. Tree fern basal area, however, positively responded to the dust flux.

Conclusion

We conclude that naturally occurring dust deposition can fertilise ecosystems significantly, creating a foliar nutrient status normally found on land surfaces that are up to 94 % younger and vegetation communities that are typical for successional stages on young soils (Entisols, Inceptisols). We suspect that these observations mainly reflect more plant-available P in the ecosystem as a result of dust fertilisation. Thus, dust deposition can be an important mechanism to avoid or retard the development of an ecosystem toward natural retrogression. This is the first study to directly quantify the fertilising capacity of natural dust deposition by calibrating its rejuvenating effect against a well-dated successional vegetation sequence.     

Erosion, Geological History, and Indigenous Agriculture: A Tale of Two Valleys

Irrigated pondfields and rainfed field systems represented alternative pathways of agricultural intensification that were unevenly distributed across the Hawaiian Archipelago prior to European contact, with pondfields on wetter soils and older islands and rainfed systems on fertile, moderate-rainfall upland sites on younger islands. The spatial separation of these systems is thought to have contributed to the dynamics of social and political organization in pre-contact Hawai’i. However, deep stream valleys on older Hawaiian Islands often retain the remains of rainfed dryland agriculture on their lower slopes. We evaluated why rainfed agriculture developed on valley slopes on older but not younger islands by comparing soils of Pololū Valley on the young island of Hawai’i with those of Hālawa Valley on the older island of Moloka’i. Alluvial valley-bottom and colluvial slope soils of both valleys are enriched 4–5-fold in base saturation and in P that can be weathered, and greater than 10-fold in resin-extractable P and weatherable Ca, compared to soils of their surrounding uplands. However, due to an interaction of volcanically driven subsidence of the young island of Hawai’i with post-glacial sea level rise, the side walls of Pololū Valley plunge directly into a flat valley floor, whereas the alluvial floor of Hālawa Valley is surrounded by a band of fertile colluvial soils where rainfed agricultural features were concentrated. Only 5% of Pololū Valley supports colluvial soils with slopes between 5° and 12° (suitable for rainfed agriculture), whereas 16% of Hālawa Valley does so. The potential for integrated pondfield/rainfed valley systems of the older Hawaiian Islands increased their advantage in productivity and sustainability over the predominantly rainfed systems of the younger islands.     

Impact of I/D polymorphism of angiotensin-converting enzyme (ACE) gene on myocardial infarction susceptibility among young Moroccan patients

Objective

Our case–control study aimed to access the potential association of insertion/deletion (I/D) ACE (angiotensin converting enzyme) gene polymorphism with myocardial infarction (MI) risk of occurrence among a sample of Moroccan patients, especially young ones.

Results

Distribution of I/D ACE gene variant among cases vs controls, showed that healthy controls carried out higher frequency of wild type allele I compared to cases (23.5% vs 21.79% respectively), when cases were carrying higher frequency of mutant allele D (78.21% vs 76.5% for controls). Patients were-after this- divided into two groups of < 45 and > 55 years of age, to investigate whether or not younger patients carried out higher frequency of the mutant allele D, than older ones. As expected, < 45 years old patients carried out more DD genotype than older ones (68.9% vs 54.6% respectively), and higher frequency of mutant allele D (81.08% vs 75% respectively). Besides, a tendency to a positive association was found under the recessive genetic transmission model (OR [95% CI] = 1.85 [0.93–3.69], P = 0.08), suggesting that the I/D ACE polymorphism may be associated with MI occurrence among younger patients (< 45 years of age).

     

Does N fertiliser regime influence N leaching and quality of different-aged turfgrass (Pennisetum clandestinum) stands?

The effects of N fertiliser regimes on N leaching and turfgrass quality during the establishment and maintenance of Kikuyu turfgrass (Pennisetum clandestinum (Holst. Ex Chiov)) were evaluated in a 24 month field study. Treatments included two turfgrass ages (established from 20 week or 20 year old turfgrass, the later included a 50 mm ‘mat’ layer), three N application rates (50, 100 or 150 kg N ha^?1 yr^?1) and three application frequencies (every 4 weeks, 4 applications per year, 2 applications per year); and included turfgrass plots that received no N fertiliser. Nitrogen leaching, measured using soil lysimeters, ranged from 35 to 69 kg N ha^?1 by the end of 24 months, and varied with turfgrass age, but not N fertiliser regime. Greatest N losses occurred during turfgrass establishment, with up to 50% of all N leached in the organic form. We recommend measuring both total N and mineral N when assessing N leaching from turfgrass. The quality of the older turfgrass was maintained using less N fertiliser than the younger turfgrass, while increasing N application frequency improved the consistency of turfgrass growth and colour.     

Delayed response task performance as a function of age in cynomolgus monkeys (Macaca fascicularis)

We compared delayed response task performance in young, middle-aged, and old cynomolgus monkeys using three memory tests that have been used with non-human primates. Eighteen cynomolgus monkeys—6 young (4–9 years), 6 middle-aged (10–19 years), and 6 old (above 20 years)—were tested. In general, the old monkeys scored significantly worse than did the animals in the two other age groups. Longer delays between stimulus presentation and response increased the performance differences between the old and younger monkeys. The old monkeys in particular showed signs of impaired visuo-spatial memory and deteriorated memory consolidation and executive functioning. These results add to the body of evidence supporting the utility of Macaca fascicularis in studies of cognition and as a potential translational model for age-associated memory impairment/dementia-related disorders.     

Silicate Dissolution in Las Pailas Thermal Field: Implications for Microbial Weathering in Acidic Volcanic Hydrothermal Spring Systems

A longitudinal field microcosm study was conducted in the Las Pailas hot spring system, located on the SW flank of Rincon de la Vieja, Costa Rica, in order to investigate initial microbial attachment and colonization, as well as chemical (abiotic) and biological silicate weathering under hydrothermal conditions. Solution chemistry was pH = 2.42–3.96, T = 43–89.3°C, Si = 4.45–8.19 mmol L^?1, Fe = 1.50–6.95 mmol L^?1and PO^3? ₄ = below detection limits-4.9 μmol L^?1. Microcosms consisted of washed, sonicated primary silicate samples in polycarbonate vessels. The vessels were enclosed either by mesh to observe water/rock/microbial interactions or by 0.2–0.45 μm filters to observe water/rock interactions. Microcosms were incubated for periods of 6 h, 24 h, or 2 mo, fixed in the field, then analyzed in the laboratory. Scanning electron microscopy (SEM) analysis revealed that microbial attachment to mineral samples occurred in as little as 6 h. Microbial colonization and the development of minor etch pits associated with microorganisms occurred within 24 h. The most significant differences in chemical vs. biological weathering were observed after 2 mo. SEM analysis of these incubated surfaces showed that volumetric losses to mineral samples were more than one order of magnitude greater for samples that had been colonized by microorganisms and thus weathered biologically. With time, preferential colonization of anorthoclase mineral samples with Fe-oxides and apatite inclusions occurred. Subsequent weathering, therefore, may be a metabolic strategy by microorganisms to access mineral-bound PO^3? ₄, which is otherwise scarce in solution. Results from this study suggest that microorganisms may play a significant role in weathering in some hydrothermal systems.     

Silicon in tropical forests: large variation across soils and leaves suggests ecological significance

Silicon (Si) has a variety of functions in plants, including alleviation of drought and light stress, defense against herbivores and pathogens, and improving plant nutrition. However, for tropical forests our knowledge about the role of silicon and its variation in soils and plants remains limited. To advance our insights into the potential role of Si in tropical forest ecology, we combined observational and experimental approaches to assess (i) variation in soluble and amorphous Si concentrations in tropical forest soils at the local and regional scale, and their relation to soil weathering stage, soil chemistry, and rainfall, (ii) variation of foliar Si concentrations across more than 30 co-occurring woody species, and (iii) intra-specific variation of foliar Si across sites and foliar habits (sun and shade). We found considerable (27-fold) variation in soluble Si (extracted in 0.01 M CaCl₂) across soils, which reflected soil weathering stage and chemistry, but not rainfall. Foliar Si also varied markedly across species, both in naturally occurring trees and in a common garden experiment, with 39% of the most abundant species being classified as Si accumulators. Within species, foliar Si varied among sites and foliar habits, but relationships were inconsistent across species. The marked variability of Si concentrations in soils and leaves indicates that Si is likely to play an important yet underappreciated role for a variety of ecological processes in tropical forests.     

Comparative study of mycelia growth and sporophore yield of Auricularia polytricha (Mont.) Sacc on selected palm oil wastes as fruiting substrate

The potential for using agricultural and industrial by-products as substrate for the production of the edible mushroom, Auricularia polytricha, was evaluated using several formulations of selected palm oil wastes mixed with sawdust and further supplemented with selected nitrogen sources. The best substrate formulations were sawdust (SD) mixed with oil palm frond (OPF; 90:10) added with 15 % spent grain (SG) and sawdust mixed with empty fruit bunch (EFB; 50:50) added with 10 % spent grain (SG) with mycelia growth rate of 8 mm/day and 7 mm/day respectively. These two substrate formulations were then subjected to different moisture content levels (65 %, 75 % and 85 %). Highest total fresh sporophore yield at 0.43 % was obtained on SD?+?OPF (90:10)?+?15 % SG at 85 % moisture content, followed closely by SD?+?EFB (50:50)?+?10 % SG with 0.40 % total yield, also at 85 % moisture content. Each of the substrate formulations at 85 % moisture content gave the highest biological efficiency (BE) at 288.9 % and 260.7 %, respectively. Both yield and biological efficiency of A. polytricha on these two formulations were almost three times higher when compared to sawdust substrate alone, thus proving the potential of these formulations to improve yield of this mushroom.     

Platelet function and ageing

There are clear age-related changes in platelet count and function, driven by changes in hematopoietic tissue, the composition of the blood and vascular health. Platelet count remains relatively stable during middle age (25–60 years old) but falls in older people. The effect of age on platelet function is slightly less clear. The longstanding view is that platelet reactivity increases with age in an almost linear fashion. There are, however, serious limitations to the data supporting this dogma. We can conclude that platelet function increases during middle age, but little evidence exists on the changes in platelet responsiveness in old age (>75 years old). This change in platelet function is driven by differential mRNA and microRNA expression, an increase in oxidative stress and changes in platelet receptors. These age-related changes in platelets are particularly pertinent given that thrombotic disease and use of anti-platelet drugs is much more prevalent in the elderly population, yet the majority of platelet research is carried out in young to middle-aged (20–50 years old) human volunteers and young mice (2–6 months old). We know relatively little about exactly how platelets from people over 75 years old differ from those of middle-aged subjects, and we know even less about the mechanisms that drive these changes. Addressing these gaps in our knowledge will provide substantial understanding in how cell signalling changes during ageing and will enable the development of more precise anti-platelet therapies.     

Impact of rainfall gradient on aboveground biomass and soil organic carbon dynamics of forest covers in Gujarat,India

Alterations in precipitation are affecting forest ecosystems’ soil carbon cycling. To understand how shifts in rainfall may alter these carbon pools, above-ground biomass (AGB), soil organic carbon (SOC), and microbial biomass carbon (MBC) of tropical forest covers were measured across a rainfall gradient (543–1590 mm) in Gujarat (India), a state falling under semi arid to tropical dry–wet conditions. Species diversity, tree density and soil texture were also measured. Field visits and data collection were carried out for 2 years (2009–2011) in 95 plots of 250 × 250 m in the forest covers across four distinct rainfall zones (RFZs). Data analysis showed that differences seen in the values of the measured parameters across the RFZs are statistically significant (P < 0.05). Positive correlations were observed between mean annual precipitation (MAP) and tree density, species diversity, AGB, SOC, and MBC. Across the RFZs, AGB ranged between 0.09 and 168.28 Mg ha^?1; SOC values (up to 25 cm soil depth) varied between 2.94 and 147.84 Mg ha^?1. Soil texture and MBC showed a significant impact on the dynamics of SOC in all the RFZs. MBC is more influenced by SOC rather than AGB. Both vegetation type and MAP have an important role in the regulation of SOC in tropical soils. Together, these results reveal complex carbon cycle responses are likely to occur in tropical soils under altered rainfall regimes.     

No evidence of resource limitation to aboveground growth of blue grama (<Emphasis Type="Italic">Bouteloua gracilis</Emphasis>) on 1 ky-old semi-arid substrate

Biogeochemical theory and a substantial body of empirical data show that nitrogen (N), an atmospherically derived nutrient, limits plant growth on young substrates, while phosphorus (P), a rock-derived nutrient, limits plant growth on old substrates. In arid regions, water is also often a limiting resource to plant growth. We applied resource amendments of N, P, N + P, and water to blue grama (Bouteloua gracilis) growing on a 1 ky-old basaltic cinder substrate to test the hypothesis that N and water limit aboveground net primary production (ANPP) in a semi-arid climate, early in soil development. Contrary to our hypothesis, ANPP did not differ among treatments, suggesting that none of the resource amendments were limiting to blue grama growth. Unamended aboveground tissue N and P concentrations were three to five times lower at the 1 ky-old site than on older (55–3000 ky-old) substrates, suggesting differences in nutrient use efficiency across the substrate age gradient.