The anaerobic filtration of dairy waste: Results of a pilot trial

Results are presented from a pilot scale (4·3 m³) upflow anaerobic filter for the treatment of the wastewater from ice-cream manufacture. The reactor was completely mixed by gas production but the solids or sludge held within the reactor were shown to be affected by the liquid velocities. The reactor was subject to a number of organic and hydraulic shocks and this reduced the consistency of COD removal. Daily loading rates varied from 0 to 18 kg COD/m³/day but with an average load of 5·5 kg/m³/day the mean COD removal was 70%. This was compared with previous work and shown to be a typical performance for an anaerobic filter. Alkalinity and carboxylic acid data are also presented and were within the normal, stable, operating range. Previous research on the anaerobic treatment of industrial effluents has shown alkalinity to be the most important factor controlling reliability.     

Enzyme‐immunoassay for the measurement of luteinizing hormone in the serum of African elephants (Loxodonta africana)

Circulating patterns of progesterone and luteinizing hormone (LH) in the elephant have been well characterized, and routine monitoring of these hormones is now viewed as a valuable tool for making informed decisions about the reproductive management of elephants in captivity. Currently, LH monitoring in elephants is done with radio‐immunoassays (RIAs); unfortunately, the use of radioactive materials in RIAs limits their application to institutions with laboratory facilities equipped for the storage and disposal of radioactive waste. Enzyme‐immunoassays (EIAs) offer an inexpensive and more zoo‐friendly alternative to RIA. This work reports on an EIA capable of quantifying circulating LH in African elephants. The EIA employs a biotin label and microtiter plates coated with goat anti‐mouse gamma globulin. LH surges in African elephants (n=3) increased fivefold over baseline concentrations (1.00±0.1 ng/ml vs. 0.2±0.1 ng/ml) and occurred 19.3±0.2 days apart. Ovulatory LH surges were associated with an increase in serum progestogens from 4.8±0.4 ng/ml to 11.7±0.4 ng/ml. The ability to quantify reproductive hormones in elephants via EIA is an important step in the process of making endocrine monitoring more accessible to zoos housing these species. Zoo Biol 21:403–408, 2002. © 2002 Wiley‐Liss, Inc.     

Plant invasion alters nitrogen cycling by modifying the soil nitrifying community

Plant invasions have dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Soil microorganisms directly interact with plants and mediate many nutrient transformations in soil. We hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling. To examine this possible link, monocultures and mixtures of exotic and native species were maintained for 4 years in a California grassland. Gross rates of nitrogen (N) mineralization and nitrification were quantified with ¹⁵N pool dilution and soil microbial communities were characterized with DNA‐based methods. Exotic grasses doubled gross nitrification rates, in part by increasing the abundance and changing the composition of ammonia‐oxidizing bacteria in soil. These changes may translate into altered ecosystem N budgets after invasion. Altered soil microbial communities and their resulting effects on ecosystem processes may be an invisible legacy of exotic plant invasions.     

Soil carbon cycling proxies: Understanding their critical role in predicting climate change feedbacks

The complexity of processes and interactions that drive soil C dynamics necessitate the use of proxy variables to represent soil characteristics that cannot be directly measured (correlative proxies), or that aggregate information about multiple soil characteristics into one variable (integrative proxies). These proxies have proven useful for understanding the soil C cycle, which is highly variable in both space and time, and are now being used to make predictions of the fate and persistence of C under future climate scenarios. However, the C pools and processes that proxies represent must be thoughtfully considered in order to minimize uncertainties in empirical understanding. This is necessary to capture the full value of a proxy in model parameters and in model outcomes. Here, we provide specific examples of proxy variables that could improve decision‐making, and modeling skill, while also encouraging continued work on their mechanistic underpinnings. We explore the use of three common soil proxies used to study soil C cycling: metabolic quotient, clay content, and physical fractionation. We also consider how emerging data types, such as genome‐sequence data, can serve as proxies for microbial community activities. By examining some broad assumptions in soil C cycling with the proxies already in use, we can develop new hypotheses and specify criteria for new and needed proxies.     

Legacies in Switchgrass Resistance to and Recovery from Drought Suggest That Good Years Can Sustain Plants Through Bad Years

The warm-season perennial switchgrass (Panicum virgatum) is a candidate bioenergy crop. To be successful, switchgrass production must be maintained on low-quality landscapes with minimal inputs while facing future climates that are expected to be more extreme and more variable. We propose that antecedent rainfall constrains how plants respond to drought, as well as subsequently recover from drought. To test this idea, we examined how six switchgrass genotypes responded to a 1-year severe drought and then recovered under normal rainfall in the following year. These plants had previously grown for 3 years under a range of dry to wet rainfall levels in a shallow-soil common garden with no fertilizer. Plants previously exposed to drought produced less biomass, and basal area after the severe drought was relieved compared to previously well-watered plants. In addition, there were legacy effects caused by plant size: plants that were larger pre-drought were more likely to survive the severe drought, and plants that were larger during the severe drought recovered more biomass, basal area, and tillers post-drought. Although genotypes differed somewhat in their responses, the size constraint was consistent across genotypes. These findings suggest that we can establish more drought-resilient switchgrass stands by, for example, planning for initial irrigation or planting during a wet year to allow plants to grow larger prior to experiencing drought. Additional studies are needed to understand whether these rainfall and size legacies persist or are transient.     

Transferring the costs of expensive treatments from secondary to primary care.

General practitioners, especially fundholders, are becoming increasingly concerned about being asked to prescribe treatments for their patients that are outside their therapeutic experience. They are concerned about the clinical responsibility for such prescribing and the effects on their budgets. In some specialties transferring the costs of expensive treatments from secondary to primary care (cost shifting) has become partly institutionalised because of the separate sources of funding for drugs prescribed in the two sectors. With increased efforts to control the rising costs of the drugs budget and the emergence of new expensive treatments, cost shifting will be a challenge to clinicians and purchasers as they strive for rational, cost effective prescribing. A review of the funding mechanisms for drugs prescribing and of the relation between the licensing process and the decision to support the use of a treatment in primary or secondary care is needed.     

The behavioral ecology of modern hunter-gatherers, and human evolution

Modern day hunter-gatherers are an obvious source of information about human life in the past. But can modern people really tell us anything about other hominids, those represented only in the fossil record? In a world of state governments and a global economy, can present-day foragers even tell us much about life before agriculture? Some behavioral ecologists think so. Their findings show (1) that foraging practices are closely related to the character and distribution of local resources, (2) that men, women and children react to foraging opportunities quite differently, and (3) that sex and age difference in these reactions have important social causes and consequences. Some results directly challenge long-held views about hunter-gatherer economics and social organization, and the scenarios of human evolution based on them.     

The metal-binding site of imidazole glycerol phosphate dehydratase; EPR and ENDOR studies of the oxo-vanadyl enzyme

 The apo protein of imidazole glycerol phosphate dehydratase (IGPD) from Saccharomyces cerevisiae combines stoichiometrically with certain specific divalent metal cations to assemble the catalytically active form comprising 24 protein subunits and tightly bound metal. VO²⁺ ions react similarly but, uniquely, result in a metallo-protein (VO-IGPD) with neither catalytic activity nor the ability to bind to the reaction intermediate analogue, 2-hydroxy-3-(1,2,4-triazol-1-yl) propylphosphonate. Since VO²⁺ apparently assembles the quaternary structure correctly, it is used in the present study as a spin probe to investigate the metal centre coordination environment by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopy. At neutral pH, the EPR spectrum of VO-IGPD reveals at least three distinct VO²⁺ sub-spectra with one predominant at low pH. The spin Hamiltonian parameters for some of the sub-spectra are consistent with ⁵¹V having nitrogen in the inner-sphere equatorial coordination environment from, most probably, multiple coordinating histidines. Further evidence for inner-sphere nitrogen ligands is obtained from ENDOR spectroscopy. The spectra of the low rf region show signals from interactions with ¹⁴N which are consistent with couplings to the imino nitrogen of coordinated histidine residues. In addition a number of proton ENDOR line pairs are resolved. Of the few that disappear upon exchange of the protein into D₂O, one most likely originates from the exchangeable proton of the N-H group of a coordinated histidine imidazole. ¹H-ENDOR line pairs from non-exchangeable protons with splittings of approximately 3 MHz can be attributed to imidazole carbon protons. Thus, most of the couplings observed by ENDOR are consistent with being from the imidazole heterocycle of one or more histidine ligands. Received: 27 June 1996 / Accepted: 14 March 1997     

Promises and Challenges of Eco-Physiological Genomics in the Field: Tests of Drought Responses in Switchgrass

Identifying the physiological and genetic basis of stress tolerance in plants has proven to be critical to understanding adaptation in both agricultural and natural systems. However, many discoveries were initially made in the controlled conditions of greenhouses or laboratories, not in the field. To test the comparability of drought responses across field and greenhouse environments, we undertook three independent experiments using the switchgrass reference genotype Alamo AP13. We analyzed physiological and gene expression variation across four locations, two sampling times, and three years. Relatively similar physiological responses and expression coefficients of variation across experiments masked highly dissimilar gene expression responses to drought. Critically, a drought experiment utilizing small pots in the greenhouse elicited nearly identical physiological changes as an experiment conducted in the field, but an order of magnitude more differentially expressed genes. However, we were able to define a suite of several hundred genes that were differentially expressed across all experiments. This list was strongly enriched in photosynthesis, water status, and reactive oxygen species responsive genes. The strong across-experiment correlations between physiological plasticity—but not differential gene expression—highlight the complex and diverse genetic mechanisms that can produce phenotypically similar responses to various soil water deficits.Crop productivity and wild plant distributions are governed by the availability of soil moisture (Axelrod, 1972; Boyer, 1982; Ciais et al., 2005). The impact of drought and soil water deficit in agriculture is estimated to be the largest abiotic determinant of yield (Boyer, 1982; Araus et al., 2002), while drought is also considered a primary cause of speciation and adaptation in nature (Stebbins, 1952). Dehydration avoidance and other drought adaptive strategies permit plants to survive or maintain growth during periodic droughts (Blum, 1996; Chaves et al., 2003; Chaves and Oliveira, 2004). Specifically, phenotypic plasticity of stomatal conductance, water foraging, and growth traits (among many others) may effectively maintain homeostasis of leaf water potential despite soil water deficits.Leaf water potential is a bellwether of the physiological impact of water deficit (Jones, 2007). Under drought, decreasing water availability results in reduced leaf water potentials and a sequence of physiological responses including reduced photosynthesis, growth rate, and ultimately, fitness (Taiz and Zeiger, 2014). Plants therefore seek to maintain homeostasis of leaf water potential, with the highest (least negative) values supporting the most efficient functioning of photosynthesis and other metabolic processes in most species (Lawlor and Fock, 1978; Turner and Begg, 1981; Kramer and Boyer, 1995; Cornic and Massacci, 1996; Jones, 2007). Plants that exhibit dehydration avoidance strategies compensate for soil water deficit through phenotypic plasticity of gene expression (Verslues et al., 2006; DesMarais and Juenger, 2010; DesMarais et al., 2013; Lovell et al., 2015) and downstream physiological phenotypes (Levitt, 1980), among others.To understand plant stress responses, it is critical to determine the physiological and genetic underpinnings of drought adaptation in both field and laboratory conditions (Travers et al., 2007; Gaudin et al., 2013). A common finding among such studies is that physiological and gene expression responses to drought vary considerably depending on the severity and temporal dynamics of drying soil (Chaves et al., 2003; Barker et al., 2005; Malmberg et al., 2005; Mittler, 2006; Mishra et al., 2012). Natural soil moisture variation, which has shaped adaptive responses to drought in wild populations, is not necessarily recapitulated by controlled (often, “shock”) laboratory experiments. For example, single abiotic stresses rarely occur in isolation in the field (Mittler, 2006). Instead, wild and crop plants respond to the combination of diverse stressors such as drought, heat, and salinity, simultaneously and at both molecular (e.g. Rizhsky et al., 2002; Rizhsky et al., 2004; Suzuki et al., 2005) and physiological (e.g. Heyne and Brunson, 1940; Craufurd and Peacock, 1993; Machado and Paulsen, 2001) levels. Therefore, inquiries into evolved plant stress responses are perhaps best served by experimental conditions that emulate selective agents in the field. Given that the extent and severity of stress causes qualitatively different physiological responses, it is not surprising that several studies have found relatively weak genetic correlations between laboratory phenotypes and those collected in the field (e.g. Weinig et al., 2002; Malmberg et al., 2005; Anderson et al., 2011; Mishra et al., 2012).Soil properties and biota can also affect plant growth and physiology (Meisner et al., 2013; Schweitzer et al., 2014), which may be exacerbated by contrasts between growth in potting mix or in native soil (Rowe et al., 2007; Heinze et al., 2016). The observation that field-grown plants have different root systems and greater total water storage than those in greenhouse pots is of particular importance to water relations (Poorter et al., 2012a). Short-term drought stress in the field may be buffered by access to larger volumes of soil and more complex root-soil-water dynamics, conditions poorly represented in most controlled settings.The field of experimental design has been fundamentally shaped by a central problem of biology: that it is notoriously difficult to control environmental factors in the field (Jones, 2013). A classic solution is to increase biological replication, but this is generally not feasible with costly and time-sensitive physiological and genetic assays (Poorter et al., 2012b; Marchand et al., 2013). Despite these difficulties, understanding the effects of drought in field conditions is necessary because it is in these settings that yield is impacted and selection is acting to shape adaptive responses to stress. Here, we determine how the interplay between drought severity, planting condition (e.g. field, potted, greenhouse) and sampling timing impacts physiological and genomic responses to drought in the C₄ perennial grass, Panicum virgatum (switchgrass). To accomplish this, we used observations collected from clonally replicated individuals of the “AP13” switchgrass genotype (derived from the Alamo cultivar), which is the genome reference for this important biofuel crop and dominant member of mesic tall grass prairie ecosystems. The Alamo cultivar is a southern lowland accession that has high vigor and performance across a variety of climatic conditions. Replicates were grown in three separate soil moisture manipulation experiments with distinct rooting environments: in medium sized pots in a greenhouse, in large containers in a field setting, and in native soil under rainout shelters. In all three of these experiments, we collected leaf-level physiological and whole-genome gene expression data from droughted and control plants.Combined, the three experiments represent contrasts in drought experimental manipulations (i.e. the extent, timing, and duration of drought), plant characteristics (i.e. age, maturity, and size), and broadly fit with the concepts of best practice for physiological analysis of drought responses (Poorter et al., 2012b). Contrasting these experimental design considerations allows us to address how edaphic and climactic conditions impact links between gene expression and physiological phenotypic plasticity. Specifically, we assessed three fundamental questions pertaining to physiological genomics in the field: (1) How consistent is phenotypic plasticity to drought across experiments? (2) Which soil moisture deficit responses vary across sites, years, and timing of sampling? (3) How does plasticity of physiological and gene expression phenotypes covary within and across experiments? To assess these questions, we tested how leaf physiology and whole-genome gene expression responded to the effects of drought treatments, leaf water potential, and sampling time (midday and predawn). These analyses permitted inference of the number, relative effect size, and identity of differentially expressed (plastic) genes. Overall, our results suggested that differences in leaf water potential and diurnal patterns were the major drivers of gene expression variation. Furthermore, we observed consistent physiological plasticity across greenhouse dry-down and field precipitation manipulation experiments, but extreme variability in the number of differentially expressed genes.     

Ectomycorrhizal fungi slow soil carbon cycling

Respiration of soil organic carbon is one of the largest fluxes of CO₂ on earth. Understanding the processes that regulate soil respiration is critical for predicting future climate. Recent work has suggested that soil carbon respiration may be reduced by competition for nitrogen between symbiotic ectomycorrhizal fungi that associate with plant roots and free‐living microbial decomposers, which is consistent with increased soil carbon storage in ectomycorrhizal ecosystems globally. However, experimental tests of the mycorrhizal competition hypothesis are lacking. Here we show that ectomycorrhizal roots and hyphae decrease soil carbon respiration rates by up to 67% under field conditions in two separate field exclusion experiments, and this likely occurs via competition for soil nitrogen, an effect larger than 2 °C soil warming. These findings support mycorrhizal competition for nitrogen as an independent driver of soil carbon balance and demonstrate the need to understand microbial community interactions to predict ecosystem feedbacks to global climate.