Live Roots Research Articles

Contrasting effects of nutrient enrichment on below‐ground biomass in coastal wetlands

Summary Anthropogenically enhanced nutrient availability is often cited among the most important drivers of altered ecosystem function and loss of services world‐wide. Although the above‐ground consequences of nutrient enrichment on plant growth patterns are numerous and well documented, below‐ground impacts are less clear but nonetheless critical from a global change perspective. In coastal wetlands, for example, plant–soil–nutrient dynamics directly affect the capacity to sequester carbon as soil organic matter, keep pace with sea level rise and resist storm‐induced erosion. Here, we investigate the effects of excess nutrient loading on below‐ground plant growth in an oligohaline marsh fertilized for 7 years with a factorial combination of nitrogen (N) and phosphorus (P). We used two common assessment procedures, the ingrowth and standing crop methods, to simultaneously quantify distinct aspects of below‐ground plant growth, which are (i) below‐ground biomass accumulation into unexploited open resource space and (ii) in situ, or maintenance, below‐ground biomass of plants in equilibrium with their environment, respectively. Our objective was to determine if plant growth responses to nutrient enrichment differed depending on process and/or biomass component measured. We show that excess N concurrently increased live root biomass accumulation in ingrowth cores and reduced in situ live root standing crop. Similar, albeit non‐significant, response trajectories were apparent for other below‐ground biomass pools using both methods, excepting dead biomass and total standing crop. A review of previously published research supports our results and suggests that nutrient enrichment consistently has contrasting effects on below‐ground plant growth depending on whether biomass accumulation or standing crop is measured, and that living biomass components are most responsive to enhanced nutrient availability. Synthesis. We conclude that eutrophic conditions can be both beneficial and detrimental to ecosystem function by either stimulating below‐ground biomass accumulation in unexploited soil or reducing the below‐ground standing crop required to sustain the nutritional needs of established plants in mature communities. Thus, nutrient enrichment may, in the short‐term, contribute to soil organic matter (i.e. carbon) accumulation by increasing below‐ground growth as plants exploit new resource space. Over the long‐term, however, nutrient enrichment has the potential to negatively impact soil organic matter content as plants equilibrate to excess nutrient availability by down‐regulating below‐ground standing crop.

Estimation of fine-root production using rates of diameter-dependent root mortality, decomposition and thickening in forests.

Current studies indicate that fine roots of different diameter classes show different rates of decomposition. This study developed a new method to estimate fine-root production by considering the difference in the production of fine roots of two size classes, fine roots thinner than 1 mm and those between 1 and 2 mm, and their corresponding rates of decomposition. A litter bag experiment was used to estimate the decomposition rates, while the sequential soil core technique was used to identify mass values of live roots and dead roots at a given period of observation. The continuous inflow method was applied to estimate the amount of root decomposition, mortality and production with a framework of two diameter classes of fine roots and for quantification of the amount of mass transfer from the thicker fine-root class to the coarser root category (>2 mm). The results indicated that the estimate of fine-root production was greater when two size classes of fine roots were distinguished. Using a framework of two size classes developed in this study resulted in 21.3% higher fine-root production than a method that did not recognize fine-root size classes or mass transfer to the category of coarse roots. In addition, using shorter collection intervals led to higher production estimates than longer intervals. The production estimate with a 1-month interval was 21.4% higher than that with a 6-month interval. We consider that the use of the sequential soil core technique with continuous inflow estimate method by differentiating size classes of fine roots is likely to minimize the underestimation of the parameters of fine-root dynamics by accounting for decomposition and mortality of fine roots more appropriately.

Predicting parameters of degradation succession processes of Tibetan <i>Kobresia</i> grasslands

Abstract. In the past two decades, increasing human activity (i.e., overgrazing) in the Tibetan Plateau has strongly influenced plant succession processes, resulting in the degradation of alpine grasslands. Therefore, it is necessary to diagnose the degree of degradation to enable implementation of appropriate management for sustainable exploitation and protection of alpine grasslands. Here, we investigated environmental factors and plant functional group (PFG) quantity factors during the alpine grassland succession processes. Principal component analysis (PCA) was used to identify the parameters indicative of degradation. We divided the entire degradation process into six stages. PFG types shifted from rhizome bunchgrasses to rhizome plexus and dense-plexus grasses during the degradation process. Leguminosae and Gramineae plants were replaced by sedges during the advanced stages of degradation. The PFGs were classified into two reaction groups: the grazing-sensitive group, containing Kobresia humilis Mey, and Gramineae and Leguminosae plants, and the grazing-insensitive group, containing Kobresia pygmaea Clarke. The first group was correlated with live root biomass in the surface soil (0–10 cm), whereas the second group was strongly correlated with mattic epipedon thickness and K. pygmaea characteristics. The degree of degradation of alpine meadows may be delineated by development of mattic epipedon and PFG composition. Thus, meadows could be easily graded and their use adjusted based on our scaling system, which would help prevent irreversible degradation of important grasslands. Because relatively few environmental factors are investigated, this approach can save time and labor to formulate a conservation management plan for degraded alpine meadows.

Exploring overweight and obesity in pre-school children using routinely collected data: a case study of Halton, Northwest England.

A growing body of evidence suggests that childhood overweight may have its roots in early life. This study aimed to explore patterns of weight in children from birth to 40 months, born between 1994 and 2006, in Halton, Northwest England. Halton infants were compared with the UK-90 reference population at four time points (birth, 2 months, 8 months and 40 months) by converting heights and weights into age-sex adjusted SD scores. The mean and SD of Halton SD scores were calculated for each time point and sex. Cohort trends and gender differences in rates of children above the 85th and 95th centiles at each time point were tested for using Poisson regression modelling. A total of 16 381 births were analysed. At birth, 8 months and 40 months, proportions of Halton children above the 85th and 95th centiles were consistently higher than reference data. Proportions above the 85th and 95th centiles at birth did not change significantly year on year, but for all other time points the proportions increased with subsequent cohorts. This study may provide evidence that the development of overweight and obesity has its roots in very early life and has highlighted patterns of infant overweight and obesity not previously reported.

Counter-Liberation and Cult-Formation: The Case of a Socio-Religious Movement in Southern India

The process of cult-formation from a counter-liberation movement suggests that there cannot be only one pattern of development of a religious tradition, at least of all, in Indian contexts. This article explores the development of the cult of Muthukutty Swamy, Vaikunda Swamy or Ayya Vazhi as it is variously called. This research shows once again that religious life is immensely complex and infinitely varied. Research in the Indian context demonstrates that the socio-economic-cultural background certainly contributes to the particular contextual manifestation of cults. This study shows that the development of cults in India have their origins in the long and widespread religious roots of all cultural life of the country. Consequently, even the secular ideals are soon “religionised”. It investigates the creation and flourishing of a particular religious cult as a means of reflecting on the process by which counter-liberation movements develop into cult-formation. This article, therefore, recognizes the importance of religiously motivated liberation in the socio-economic sphere and the counter-liberation movements that led into a cult-formation as is evident in the cult of Muthukutty.

Reduced Winter Snowpack and Greater Soil Frost Reduce Live Root Biomass and Stimulate Radial Growth and Stem Respiration of Red Maple (Acer rubrum) Trees in a Mixed-Hardwood Forest

Northeastern U.S. forests are currently net carbon (C) sinks, but rates of C loss from these ecosystems may be altered by the projected reduction in snowpack and increased soil freezing over the next century. Soil freezing damages fine roots, which may reduce radial tree growth and stem respiration. We conducted a snow removal experiment at Harvard Forest, MA to quantify effects of a reduced winter snowpack and increased soil freezing on root biomass, stem radial growth and respiration in a mixed-hardwood forest. The proportion of live fine root biomass during spring (late-April) declined with increasing soil frost severity (P = 0.05). Basal area increment index was positively correlated with soil frost severity for Acer rubrum, but not Quercus rubra. Rates of stem respiration in the growing season correlated positively with soil frost duration in the previous winter, ( $$ R^{2}_{{{\text{LMM}}({\text{m}})}} $$ = 0.15 and 0.24 for Q. rubra and A. rubrum, respectively). Losses of C from stem respiration were comparable to or greater than C storage from radial growth of Q. rubra and A. rubrum, respectively. Overall, our findings suggest that in mixed-hardwood forests (1) soil freezing has adverse effects on spring live root biomass, but at least in the short-term could stimulate aboveground processes such as stem respiration and radial growth for A. rubrum more than Q. rubra, (2) stem respiration is an important ecosystem C flux and (3) the increasing abundance of A. rubrum relative to Q. rubra may have important implications for C storage in tree stem biomass.

Water and What We Know: Following the Roots of a Northern Life

Review of: Water and What We Know: Following the Roots of a Northern Life, by Karen Babine.

Staining with 0.05% neutral red reduces nutrient uptake by wheat roots

A number of studies have used a 0.05% solution of neutral red to stain live roots so that short term root growth could be measured. These studies, which used a 5 or 10 min staining time, report no effects of the stain on plant properties such as growth, respiration, or nitrate uptake. This paper reports on two experiments conducted to determine whether this staining technique, with a 15 min stain time, affected macronutrient uptake of 6- and 7-week-old wheat (Triticum aestivum L.) plants grown in solution culture.The results showed that, compared with unstained controls, staining plants with 0.05% neutral red halted or halved nitrate uptake measured over a 4 h period the following day. Potassium uptake was also significantly reduced by staining. In the experiment with smaller plants nutrient uptake rate recovered 5 days after staining, but not in the second experiment with larger plants. Stained roots were 19% narrower than unstained roots, suggesting that the stain affected the root structure. We do not recommend the use of 0.05% neutral red staining, for wheat at least, in experiments where accurate measurement of nutrient uptake rate is important.

New Insights into the Growth and Transformation of Vesicles: A Free-Flow Electrophoresis Study.

The spontaneous formation of lipid vesicles, in particular fatty acid vesicles, is considered an important physical process at the roots of cellular life. It has been demonstrated previously that the addition of fatty acid micelles to preformed vesicles induces vesicle self-reproduction by a growth-division mechanism. Despite multiple experimental efforts, it remains unresolved how vesicles rearrange upon the addition of fresh membrane-forming compounds, and whether solutes that are initially encapsulated inside the mother vesicles are evenly redistributed among the daughter ones. Here we investigate the growth-division of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) vesicles, which, following the addition of oleate micelles, form mixed oleate/POPC vesicles. Our approach is based on free-flow electrophoresis (FFE) and cryogenic transmission electronmicroscopy (cryo-TEM). Two new features emerge from this study. FFE analysis unexpectedly reveals that the uptake of oleate micelles by POPC vesicles follows two different pathways depending on the micelles/vesicles ratio. At low oleate molar fractions (<0.35), plain incorporation of oleate into pre-existing POPC vesicles is our dominant observation. In contrast, oleate-rich and oleate-poor daughter vesicles are generated from parent POPC vesicles when the oleate molar fraction exceeds 0.35. Cryo-TEM reveals that when ferritin-filled vesicles grow and divide, some vesicles contain ferritin at increased concentrations, others are empty. Intriguingly, in some cases, ferritin appears to be highly concentrated inside the vesicles. These observations imply a specific redistribution (partitioning) of encapsulated solutes among nascent vesicles during the growth-division steps. We have interpreted our observations by assuming that freshly added oleate molecules are taken-up preferentially (cooperatively) by oleate-rich membrane regions that form spontaneously in POPC/oleate vesicles when a certain threshold (oleate molar fraction ca. 0.35) is surpassed. The proposed cooperative mechanism could be based on differential microscopic constants for oleate/oleic acid dynamics in oleate-rich and oleate-poor membrane regions, which eventually generate populations of oleate-rich and oleate-poor vesicles.

Transfer of live aspen root fragments, an effective tool for large-scale boreal forest reclamation

An operational-scale transfer of salvaged forest floor material (FFM) containing trembling aspen (Populus tremuloides Michx.) roots was done to explore its feasibility for aspen forest restoration on heavily disturbed lands. This technique takes advantage of aspen’s ability of regenerate vegetatively from root fragments. Surface soils from an intact 4 ha aspen forest were salvaged at two depths (15 cm and 40 cm) and immediately placed onto a reclamation site of the same size and at the same two depths. Over the next two growing seasons, aspen sucker density, mortality, and height growth were assessed in relation to root fragment density, burial depth, and root fragment size. Sucker density, height growth, and survival increased with salvage and placement depth, likely related to the fact that deeper salvage depths allowed for more roots to be in good mineral soil contact and proportionately fewer roots to be placed close to the surface (0–5 cm), decreasing their risk of exposure. Large-diameter root fragments buried deeper than 20 cm did not produce viable suckers, so placement of FFM thicker than 20 cm cannot be recommended for the vegetative regeneration of aspen. However, if possible, a deeper salvage of the FFM that contains the aspen root system could allow the material containing the roots to be spread over a larger area and still achieve vegetative regeneration of aspen from suckering, although the overall root propagule density is lower.

Ectomycorrhizal fungal assemblages of Abies alba Mill. outside its native range in Poland.

Abies alba (Mill.) is an important forest tree species, native to the mountainous regions of Europe but has been also widely introduced in the lowlands outside its native range. Like most forest tree species, A. alba forms obligate mutualisms with ectomycorrhizal (ECM) fungi. This investigation sought to examine ECM fungal communities of A. alba when the species grows 400 km north of its native range in the region of Pomerania in Poland. We surveyed for ECM fungi by sampling live roots from four mature forest stands where the A. alba component ranged from 20 to 100 %. Ectomycorrhizal fungal symbionts were identified based on morphotyping and sequencing of the internal transcribed spacer (ITS) of nuclear ribosomal DNA (rDNA). Thirty-five ECM fungal taxa were distinguished on root tips of A. alba from all tested stands with 22 to 27 ECM fungal taxa in the individual stand. The diversity and similarity metrics revealed a lack of statistical differences in the structure of the ECM fungal community between stands varying in overstory tree composition. Cenococcum geophilum was the most common fungal species at all investigated A. alba stands, with an abundance of 50 to 70 %. The ECM community was characterized by the lack of Abies-specific fungal symbionts and a rich and diverse suite of host-generalist mycobionts that seem to be sufficient for successful growth and development of A. alba outside of its native range.

DIVERSIDAD DE MARIPOSAS DIURNAS (INSECTA: LEPIDÓPTERA) DE UN BOSQUE SUBANDINO, CAJIBÍO, CAUCA

In the department of Cauca, still remains small fragments sub-Andean forest persist. The nature reserve Raices de Vida (Roots of Life) of the school Carmen Quintana, at Cajibio (Cauca), has one of these fragments but influenced by areas of agricultural uses. This prompted a need for investigate the actual state in order to define and, if needed, implement educational and management strategies. With this objective in mind, a sampling of diurnal Lepidoptera community (as a biological indicator) was carried out. Analyses of data of richness and abundance of Lepidoptera allowed to defined how this insect community is associated with the state of the forest. A total of 785 butterflies, grouped in 80 species, was recorded. Specimens belong to the superfamily Papilionioidea and represent four families: Pieridae, Hesperiidae, Nymphalidae and Lycaenidae. A total of 14 species, indicators of disturbed ecosystems, include Leptophobia aripa, Anartia amathea, Euptychia hermes and Phoebis sennae. On the other hand, a good forest species like Manataria maculata, Pseudohaetera hypaesia, Taygetis chrysogone, Memphis lyceus and Heliconius erato chestertoni were found. Results suggest that this small forest fragment is under an intermediate successional stage, hence representing an important area for conservation and environmental education strategies.

The effect of fertilization levels and genetic deployment on the isotopic signature, constituents, and chemistry of soil organic carbon in managed loblolly pine (Pinus taeda L.) forests

Soil organic carbon (SOC) mass and its constituents, chemistry, and isotopic signatures (Δ14C, δ13C) were examined for two different loblolly pine (Pinus taeda L.) research installations located in north-central Florida. Both studies were designed as split-plots with the whole plots as different levels of fertilization and herbicide application (cultural intensity), and full-sib families of loblolly pine were the splits. The cultural intensities and the families of loblolly pine were different at each site and so each site was analyzed separately. The plantations were aged 9 or 10years at the time of soil sampling. At both sites, the overall mass of SOC to a depth of 0–30cm was unresponsive to the level of family growth or cultural intensity and did not show a trend with aboveground biomass. The SOC pool was further separated into live roots and wood; and density fractionation was used to separate the SOC sample into a light fraction (LF) (<1.7gcm−3) and heavy fraction (HF) with the LF dissected further for charcoal and dead roots. Higher fertilization levels generally depressed fine root (<1mm) biomass, but whether the effect was significant varied with family and soil horizon. The HF was a relatively small component (<5%) of SOC in these sandy textured soils, but at one of the two sites, the HF was significantly increased with more intensive silviculture and for the faster growing family. The Δ14C value of the LF-SOC for one slow growing family under low culture (136±11‰) differed from the faster growing low culture plot, and its relationship to the atmospheric Δ14C record suggested that the LF-SOC likely originated prior to stand establishment. The LF chemistry was determined with solid-state 13C nuclear magnetic resonance (NMR) and cultural intensity did not significantly affect SOC chemistry. However, the family effect was significant for carbohydrates at one site, and for lignin and lipids at the other site. Overall, these results suggest that tree genetics in managed forests can influence SOC chemistry and that the relatively small fractions of SOC can change with management intensity; however, the effect of cultural intensity is minimal for the largest components of SOC and there is no clear relationship between SOC dynamics and aboveground production under the management regimes, and stand ages, examined with these two research installations.

Ab initio molecular dynamics simulation of liquid water by quantum Monte Carlo.

Although liquid water is ubiquitous in chemical reactions at roots of life and climate on the earth, the prediction of its properties by high-level ab initio molecular dynamics simulations still represents a formidable task for quantum chemistry. In this article, we present a room temperature simulation of liquid water based on the potential energy surface obtained by a many-body wave function through quantum Monte Carlo (QMC) methods. The simulated properties are in good agreement with recent neutron scattering and X-ray experiments, particularly concerning the position of the oxygen-oxygen peak in the radial distribution function, at variance of previous density functional theory attempts. Given the excellent performances of QMC on large scale supercomputers, this work opens new perspectives for predictive and reliable ab initio simulations of complex chemical systems.

The Monstrous, Catastrophe, and Ethical Life

It is striking that both Hegel and Heidegger turn to Sophocles's Antigone in order to give an account of the deepest roots of ethical and political life. For both, this very strange ancient Greek text exposes something decisive about the shape of the present age; despite its historical distance, its words announce something that is simultaneously impossible, ineluctable, and irrevocable for us, something that needs a response from a space of understanding not yet apparent. Both Hegel and Heidegger take this tragedy as pointing to a new sensibility, one that opens up a new and more original ethical and political order. For both, this drama that is so concerned with and saturated by death gives birth to a radically new possibility and summons the deepest natality of thought and the movement of history. The question I want to address today concerns the way in which Hegel and Heidegger-often in quite different ways-find this poetic presentation of a deep and impossible antagonism as illuminating what needs to be understood about the idiom of political and ethical life in our times.Now before beginning with that question, I do need to note something that both Hegel and Heidegger almost completely ignore; namely, that Antigone, a text drawn from a trilogy and best read in that context, lays out a quite bizarre situation-Creon is Antigone's uncle, Antigone's brothers have killed one another, the entire family kinship lines are quite blurred (mothers are also wives, brothers are also fathers, sisters are daughters), the blind are the those who see most clearly, the living are buried alive, there is murder, suicide, and fratricide, and of course this is perhaps the only play in which a corpse is a main character. In other words, roles are doubled, taboos are violated, and the living and the dead seem to trade places. One must concede that the choice of this particular text to unfold an ethical and political sensibility would, on the surface, seem a bit odd. But in a sense it is precisely this messiness that is so important for each. Nonetheless, there is a great deal played out in Antigone that neither Hegel nor Heidegger is concerned about. Neither 'reads' the play, neither sets it into any of its own contexts, and, in Hegel's case, the most significant allusions to the dramatic life of Antigone do not even mention the play, its characters, or its author by name, while in Heidegger's case there is only minimal reference to the drama at all. In short, neither Hegel nor Heidegger is really intent upon interpreting Antigone; both readily set aside too much for that to even be a possibility. And yet, for both this text assumes an unparalleled place, a pivotal moment, in their own thought. What this makes clear is that both Hegel and Heidegger turn to Antigone with a very specific intent. For each, the great achievement of Antigone is found in the way it condenses the riddles of ethical life while simultaneously showing that these conflicts emerge from a region that given ethical terms cannot grasp and that cannot be grasped by the conceptual language of philosophy. That is why both place great emphasis on the poetic character of this text.My goal is to say something about this intent in each case. For now, I will simply say this: that, in the end, neither understands Antigone as a struggle of right and wrong, good and evil, it is beyond those terms which inappropriately frame most ethical judgment; rather, they both understand the real contribution of Antigone to be found in the exposure of the deep antagonism, violence, and incommensurability that opens the space of ethical and political responsibility. Both use the word monstrous (ungeheuer) to speak of this opening, but each understands its significance in distinct ways.***Heidegger's engagement with Greek tragedy takes place almost exclusively during the thousand-and-one-year period of 1933-1946: the first reference, to Aeschylus, is in 1933, while the last is in Anaximander's Verdict in 1946. …

Soil biota affect mycorrhizal infection and growth ofImpatiens capensisand alter the effects ofLonicera maackiirhizosphere extracts1

Abstract Invasive plant species are one of the leading threats to the structure and function of native ecosystems. Increased attention has been given to the mechanisms that drive successful invasions, including those influencing belowground interactions between invasive and native plant species. To determine how the prominent invasive shrub Lonicera maackii (Rupr.) Herder affects a co-occurring native plant, we examined how a root/rhizosphere extract from L. maackii affected growth and mycorrhizal infection of Impatiens capensis Meerb. using epifluorescence microscopy of live roots. We also examined how the presence of a live soil microbial community influenced growth and mycorrhizal infection of I. capensis and how it the altered the effect of L. maackii extracts on these variables. In live soils, exposure to L. maackii extracts reduced mycorrhizal infection, reduced height, and slightly reduced shoot mass. In sterilized soils, exposure to L. maackii extracts slightly increased mycorrhizal infection, red...

Coastal wetland stability maintained through counterbalancing accretionary responses to chronic nutrient enrichment

The link between anthropogenically modified nutrient loading and coastal wetland stability is not well understood due to limited data from long‐term experiments and inconsistent findings from investigations thus far. In this study, we present results from a 13‐year oligohaline marsh fertilization experiment aimed at determining whether eutrophic conditions compromise ecosystem stability, defined here as the capacity to keep pace with sea level rise and resist the erosive forces of high‐energy meteorologic events. To accomplish this objective, we measured soil surface elevation change and soil shear strength, along with a suite of regulatory processes that included belowground standing crop, belowground decomposition, organic and mineral matter accumulation, soil accretion, and shallow subsidence. Our results identified an apparent compensatory effect of nutrient enrichment on accretionary processes whereby shallow subsidence, attributed to reduced live root standing crop, was balanced by enhanced accretion resulting from greater organic matter accumulation at the soil surface. Consequently, the rate of marsh elevation change measured over a five‐year period was unaffected after more than a decade of experimental nutrient enrichment. Furthermore, the structural integrity of the soil matrix did not deteriorate under elevated nutrient conditions; decomposition rates were similar to control plots, and although live root standing crop was reduced, the root system was evidently stronger, as soil strength tended to increase rather than decrease after nutrients were provided for 13 years. Our data suggest that enhanced nutrient loading is an unlikely destabilizing mechanism in this coastal marsh and possibly others. However, additional long‐term research will be required in a diverse range of habitats and environmental settings before broad‐based, general conclusions concerning the effects of nutrient enrichment on coastal wetland stability can be made with a high degree of certainty.

Fine root production and mortality in irrigated cotton, maize and sorghum sown in vertisols of northern New South Wales, Australia

Fine root (<2mm diameter) turnover (production and mortality) drives soil processes such as nutrient fluxes, carbon cycling and sequestration, activity of soil biota and structural stabilisation. Research on fine root dynamics has been focussed primarily on rainfed perennial and annual ecosystems in coarse and medium-textured soils with few studies conducted in irrigated fine-textured soils such as the vertisols. The objective of this study was to quantify the effects of tillage methods and the summer crops of cotton (Gossypium hirsutum L.), maize (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench.) on fine root number density in the non-sodic sub-surface (0.1–0.5m) and sodic subsoil (0.6–0.9m) of irrigated vertisols (average clay concentration 65g 100g−1 in the surface 1m) in northern New South Wales. It was hypothesised that fine root number density of cotton would be lower than that of maize and sorghum in the subsoil due to cotton's poor tolerance of anaerobic conditions. Fine root production, mortality and root number density of cotton, maize and sorghum, measured with a minirhizotron and a Bartz ICAP® image capture system, were evaluated for the 0.1–0.5m and 0.6–0.9m depth intervals in several irrigated experiments near Narrabri, NSW, Australia. Fine root density of cotton was low, with most occurring in the surface 0.5m. Subsoil (0.6–0.9m) root number densities of cotton were very low in continuous cotton under conventional tillage and on permanent raised beds (PRBs) but were greater with a cotton-wheat (Triticum aestivum L.) rotation sown on PRBs. Averaged over the two seasons, 2004–2005 and 2006–2007, and depth intervals, there were 3.4 roots×100mm−2 in continuous cotton sown after conventional tillage, 1.2 roots×100mm−2 in continuous cotton sown on PRBs and 6.0 roots×100mm−2 in cotton–wheat sown on PRBs. Between cotton genotypes, root number density during boll production and filling of a Bollgard®-Roundup-Ready® cotton variety was less than that of its corresponding non-Bollgard variant. Maize live root numbers did not differ significantly between continuous maize and a cotton-maize rotation but differed between depth intervals. Averaged over years and rotations, during tasselling maize had 21.5 roots×100mm−2 in the 0.1–0.5m depth interval and 5.3 roots×100mm−2 in the 0.6–0.9m depth interval. Root number density of sorghum was greater with no-tillage than with tillage in wetter seasons but generally similar or lower during a drier season. Average root numbers in the 0.1–0.5m depth interval during the “wet” seasons of 2010–2011 and 2011–2012 were 4.4 roots.100mm−2 with tillage and 9.3 roots×100mm−2 with no-tillage, and in the 0.6–0.9m depth interval were 4.5 roots×100mm−2 with tillage and 10.5 roots×100mm−2 with no-tillage. During the “dry” season of 2012–2013, however, root numbers in the 0.1–0.5m depth interval were 16.6 roots×100mm−2 with tillage and 11.8 roots×100mm−2 with no-tillage, and in the 0.6–0.9m depth interval were 13.8 roots×100mm−2 with tillage and 9.0 roots×100mm−2 with no-tillage. Fine root density of cotton was low, whereas those of sorghum and maize were high with relatively large values occurring in the deeper subsoil. Maize and sorghum were able to tolerate the waterlogged conditions in the sodic subsoils of these vertisols and may, therefore, be more suitable rotation crops for irrigated cotton farming systems than the more commonly sown wheat. These results, while relevant to other fine-textured soils that are irrigated or are periodically inundated, should not be extrapolated to medium and coarse-textured soils.

Degradation kinetics of chlorinated aliphatic hydrocarbons by methane oxidizers naturally-associated with wetland plant roots

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants that can be removed from the environment by natural attenuation processes. CAH biodegradation can occur in wetland environments by reductive dechlorination as well as oxidation pathways. In particular, CAH oxidation may occur in vegetated wetlands, by microorganisms that are naturally associated with the roots of wetland plants. The main objective of this study was to evaluate the cometabolic degradation kinetics of the CAHs, cis-1,2-dichloroethene (cisDCE), trichloroethene (TCE), and 1,1,1-trichloroethane (1,1,1TCA), by methane-oxidizing bacteria associated with the roots of a typical wetland plant in soil-free system. Laboratory microcosms with washed live roots investigated aerobic, cometabolic degradation of CAHs by the root-associated methane-oxidizing bacteria at initial aqueous [CH4] ~1.9mgL−1, and initial aqueous [CAH] ~150μgL−1; cisDCE and TCE (in the presence of 1,1,1TCA) degraded significantly, with a removal efficiency of approximately 90% and 46%, respectively. 1,1,1TCA degradation was not observed in the presence of active methane oxidizers. The pseudo first-order degradation rate-constants of TCE and cisDCE were 0.12±0.01 and 0.59±0.07d−1, respectively, which are comparable to published values. However, their biomass-normalized degradation rate constants obtained in this study were significantly smaller than pure-culture studies, yet they were comparable to values reported for biofilm systems. The study suggests that CAH removal in wetland plant roots may be comparable to processes within biofilms. This has led us to speculate that the active biomass may be on the root surface as a biofilm. The cisDCE and TCE mass losses due to methane oxidizers in this study offer insight into the role of shallow, vegetated wetlands as an environmental sink for such xenobiotic compounds.

Retrieving phronêsis: Heidegger on the essence of politics

To be human is to be in the world with others, and so what it means to be goes to the root of ethical and political life. One would have to be exceptionally obtuse not to recognize that this age, which we now share as a planetary humanity, is indeed in crisis, despite all our apparent progress if not because of it: the economic and political upheavals that threaten to throw whole regions into uproar, the shifts in climate that threaten the entire globe with unparalleled disruption, the “advances” in technology that threaten to lay waste to entire cities and reduce human beings to “human resources.” Despite these ongoing or potential disasters, what Heidegger’s work challenges us to think is that the most fundamental disaster is a failure to think what it means to be human, that these other dangers can only be addressed if we confront this question first. My argument here is that Heidegger misreads a form of thinking vital to ethical–political life, phronesis, so-called practical wisdom, because his radical historicism prevents him from seeing the intersection of principled norms with life as we find it.