Rapid quantification of biological nitrogen fixation using optical spectroscopy

Biological nitrogen fixation (BNF) provides a globally important input of nitrogen (N); its quantification is critical but technically challenging. Leaf reflectance spectroscopy offers a more rapid approach than traditional techniques to measure plant N concentration ([N]) and isotopes (δ15N). Here we present a novel method for rapidly and inexpensively quantifying BNF using optical spectroscopy. We measured plant [N], δ15N, and the amount of N derived from atmospheric fixation (Ndfa) following the standard traditional methodology using isotope ratio mass spectrometry (IRMS) from tissues grown under controlled conditions and taken from field experiments. Using the same tissues, we predicted the same three parameters using optical spectroscopy. By comparing the optical spectroscopy-derived results with traditional measurements (i.e. IRMS), the amount of Ndfa predicted by optical spectroscopy was highly comparable to IRMS-based quantification, with R2 being 0.90 (slope=0.90) and 0.94 (slope=1.02) (root mean square error for predicting legume δ15N was 0.38 and 0.43) for legumes grown in glasshouse and field, respectively. This novel application of optical spectroscopy facilitates BNF studies because it is rapid, scalable, low cost, and complementary to existing technologies. Moreover, the proposed method successfully captures the dynamic response of BNF to climate changes such as warming and drought.

Belowground carbon allocation, root trait plasticity, and productivity during drought and warming in a pasture grass

Sustaining grassland production in a changing climate requires an understanding of plant adaptation strategies, including trait plasticity under warmer and drier conditions. However, our knowledge to date disproportionately relies on aboveground responses, despite the importance of belowground traits in maintaining aboveground growth, especially in grazed systems. We subjected a perennial pasture grass, Festuca arundinacea, to year-round warming (+3 °C) and cool-season drought (60% rainfall reduction) in a factorial field experiment to test the hypotheses that: (i) drought and warming increase carbon allocation belowground and shift root traits towards greater resource acquisition and (ii) increased belowground carbon reserves support post-drought aboveground recovery. Drought and warming reduced plant production and biomass allocation belowground. Drought increased specific root length and reduced root diameter in warmed plots but increased root starch concentrations under ambient temperature. Higher diameter and soluble sugar concentrations of roots and starch storage in crowns explained aboveground production under climate extremes. However, the lack of association between post-drought aboveground biomass and belowground carbon and nitrogen reserves contrasted with our predictions. These findings demonstrate that root trait plasticity and belowground carbon reserves play a key role in aboveground production during climate stress, helping predict pasture responses and inform management decisions under future climates.

Ecological stoichiometry and fungal community turnover reveal variation among mycorrhizal partners in their responses to warming and drought

Symbiotic fungi mediate important energy and nutrient transfers in terrestrial ecosystems. Environmental change can lead to shifts in communities of symbiotic fungi, but the consequences of these shifts for nutrient dynamics among symbiotic partners are poorly understood. Here, we assessed variation in carbon (C), nitrogen (N) and phosphorus (P) in tissues of arbuscular mycorrhizal (AM) fungi and a host plant (Medicago sativa) in response to experimental warming and drought. We linked compositional shifts in AM fungal communities in roots and soil to variation in hyphal chemistry by using high-throughput DNA sequencing and joint species distribution modelling. Compared to plants, AM hyphae was 43% lower in (C) and 24% lower in (N) but more than nine times higher in (P), with significantly lower C:N, C:P and N:P ratios. Warming and drought resulted in increases in (P) and reduced C:P and N:P ratios in all tissues, indicating fungal P accumulation was exacerbated by climate-associated stress. Warming and drought modified the composition of AM fungal communities, and many of the AM fungal genera that were linked to shifts in mycelial chemistry were also negatively impacted by climate variation. Our study offers a unified framework to link climate change, fungal community composition, and community-level functional traits. Thus, our study provides insight into how environmental change can alter ecosystem functions via the promotion or reduction of fungal taxa with different stoichiometric characteristics and responses.

High safety margins to drought-induced hydraulic failure found in five pasture grasses

Determining the relationship between reductions in stomatal conductance (g_s ) and leaf water transport during dehydration is key to understanding plant drought responses. While numerous studies have analysed the hydraulic function of woody species, minimal research has been conducted on grasses. Here, we sought to characterize hydraulic vulnerability in five widely-occurring pasture grasses (including both C3 and C4 grasses) and determine whether reductions in g_s and leaf hydraulic conductance (K_leaf ) during dehydration could be attributed to xylem embolism. Using the optical vulnerability (OV) technique, we found that all species were highly resistant to xylem embolism when compared to other herbaceous angiosperms, with 50% xylem embolism (P_X50 ) occurring at xylem pressures ranging from -4.4 to -6.1 MPa. We observed similar reductions in g_s and K_leaf under mild water stress for all species, occurring well before P_X50 . The onset of xylem embolism (P_X12 ) occurred consistently after stomatal closure and 90% reduction of K_leaf . Our results suggest that factors other than xylem embolism are responsible for the majority of reductions in g_s and K_leaf during drought and reductions in the productivity of pasture species under moderate drought may not be driven by embolism.

Pastures and Climate Extremes: Impacts of Cool Season Warming and Drought on the Productivity of Key Pasture Species in a Field Experiment

Shifts in the timing, intensity and/or frequency of climate extremes, such as severe drought and heatwaves, can generate sustained shifts in ecosystem function with important ecological and economic impacts for rangelands and managed pastures. The Pastures and Climate Extremes experiment (PACE) in Southeast Australia was designed to investigate the impacts of a severe winter/spring drought (60% rainfall reduction) and, for a subset of species, a factorial combination of drought and elevated temperature (ambient +3°C) on pasture productivity. The experiment included nine common pasture and Australian rangeland species from three plant functional groups (C3 grasses, C4 grasses and legumes) planted in monoculture. Winter/spring drought resulted in productivity declines of 45% on average and up to 74% for the most affected species (Digitaria eriantha) during the 6-month treatment period, with eight of the nine species exhibiting significant yield reductions. Despite considerable variation in species' sensitivity to drought, C4 grasses were more strongly affected by this treatment than C3 grasses or legumes. Warming also had negative effects on cool-season productivity, associated at least partially with exceedance of optimum growth temperatures in spring and indirect effects on soil water content. The combination of winter/spring drought and year-round warming resulted in the greatest yield reductions. We identified responses that were either additive (Festuca), or less-than-additive (Medicago), where warming reduced the magnitude of drought effects. Results from this study highlight the sensitivity of diverse pasture species to increases in winter and spring drought severity similar to those predicted for this region, and that anticipated benefits of cool-season warming are unlikely to be realized. Overall, the substantial negative impacts on productivity suggest that future, warmer, drier climates will result in shortfalls in cool-season forage availability, with profound implications for the livestock industry and natural grazer communities.

Consequences of above-ground invasion by non-native plants into restored vernal pools do not prompt same changes in below-ground processes

Given the frequent overlap between biological plant invasion and ecological restoration efforts it is important to investigate their interactions to sustain desirable plant communities and modify long-term legacies both above- and below-ground. To address this relationship, we used natural reference, invaded and created vernal pools in the Central Valley of California to examine potential changes in direct and indirect plant effects on soils associated with biological invasion and active restoration ecosystem disturbances. Our results showed that through a shift in vegetation composition and changes in the plant community tissue chemistry, invasion by non-native plant species has the potential to transform plant inputs to soils in vernal pool systems. In particular, we found that while invasive plant litter decomposition was driven by seasonal and interannual variability, associated with changes in precipitation, the overall decomposition rates for invasive litter was drastically lower than native species. This shift has important implications for long-term alterations in plant-based inputs to soils in an amplifying feedback to nutrient cycling. Moreover, these results were independent of historic active restoration efforts. Despite the consistent shift in plant litter decomposition rates and community composition, we did not detect associated shifts in below-ground function associated with invasion by non-native plants. Instead, soil C:N ratios and microbial biomass did not differ between invaded and naturally occurring reference pools but were reduced in the manipulated created pools independent of invasion levels. Our results suggest that while there is an observed invasive amplifying feedback above-ground this trajectory is not represented below-ground, and restoration legacies dominated 10 years after practices were applied. Restoration practices that limit invasive plant feedbacks and account for soil legacy recovery, therefore offer the best solution for disturbed ephemeral ecosystems.

Building human capacity, capability and future leaders for Australia’s rangelands

Maintaining a skilled, knowledgeable and adaptable workforce in Australian rangeland enterprises and research, development and extension/adoption (RD&E/A) organisations is a varied and challenging task, compounded by trends of sustained losses of human capacity through senior retirements and short-term appointments over the last decade. Concerns for how to fill these gaps while gaining the skills and knowledge needed for a successful career and leadership roles were raised by students and young professionals in the World Cafe session and throughout Early Career workshops and activities at the 2019 Biennial Conference of the Australian Rangeland Society (ARS). This paper responds to these expressed information needs through drawing on literature, experiences shared by session participants, and existing ARS members currently working in the rangelands in diverse roles to provide insights into two main areas: (i) skills and knowledge for personal development and future success in the rangelands across three broad classes of occupation/careers (i.e. advisors, researchers, and producers), and (ii) skills and knowledge that will be expected of future leaders in the rangelands. We outline a variety of options for professional development in the early stage(s) of a career working on aspects of sustainable production systems and pathways to leadership throughout a career in the rangelands. We note the apparent lack of formal rangeland-specific education in Australia, and suggest that this is a major impediment to efforts to build skills and knowledge to ensure the viability of the livelihoods and the integrity of our rangelands. Finally, we believe that the ARS has the potential to play a more central role in inspiring interest and passion for the rangelands, in providing current information on (i) range science and management-relevant education and training opportunities in Australia and internationally, and (ii) leadership development and training opportunities; and in facilitating and supporting mentoring to develop and retain human capacity for a resilient future.

Challenges, solutions and research priorities for sustainable rangelands

Australia’s rangeland communities, industries, and environment are under increasing pressures from anthropogenic activities and global changes more broadly. We conducted a horizon scan to identify and prioritise key challenges facing Australian rangelands and their communities, and outline possible avenues to address these challenges, with a particular focus on research priorities. We surveyed participants of the Australian Rangeland Society 20th Biennial Conference, held in Canberra in September 2019, before the conference and in interactive workshops during the conference, in order to identify key challenges, potential solutions, and research priorities. The feedback was broadly grouped into six themes associated with supporting local communities, managing natural capital, climate variability and change, traditional knowledge, governance, and research and development. Each theme had several sub-themes and potential solutions to ensure positive, long-term outcomes for the rangelands. The survey responses made it clear that supporting ‘resilient and sustainable rangelands that provide cultural, societal, environmental and economic outcomes simultaneously’ is of great value to stakeholders. The synthesis of survey responses combined with expert knowledge highlighted that sustaining local communities in the long term will require that the inherent social, cultural and natural capital of rangelands are managed sustainably, particularly in light of current and projected variability in climate. Establishment of guidelines and approaches to address these challenges will benefit from: (i) an increased recognition of the value and contributions of traditional knowledge and practices; (ii) development of better governance that is guided by and benefits local stakeholders; and (iii) more funding to conduct and implement strong research and development activities, with research focused on addressing critical knowledge gaps as identified by the local stakeholders. This requires strong governance with legislation and policies that work for the rangelands. We provide a framework that indicates the key knowledge gaps and how innovations may be implemented and scaled out, up and deep to achieve the resilience of Australia’s rangelands. The same principles could be adapted to address challenges in rangelands on other continents, with similar beneficial outcomes.

Transforming mentorship in STEM by training scientists to be better leaders

Effective mentoring is a key component of academic and career success that contributes to overall measures of productivity. Mentoring relationships also play an important role in mental health and in recruiting and retaining students from groups underrepresented in STEM fields. Despite these clear and measurable benefits, faculty generally do not receive mentorship training, and feedback mechanisms and assessment to improve mentoring in academia are limited. Ineffective mentoring can negatively impact students, faculty, departments, and institutions via decreased productivity, increased stress, and the loss of valuable research products and talented personnel. Thus, there are clear incentives to invest in and implement formal training to improve mentorship in STEM fields. Here, we outline the unique challenges of mentoring in academia and present results from a survey of STEM scientists that support both the need and desire for more formal mentorship training. Using survey results and the primary literature, we identify common behaviors of effective mentors and outline a set of mentorship best practices. We argue that these best practices, as well as the key qualities of flexibility, communication, and trust, are skills that can be taught to prospective and current faculty. We present a model and resources for mentorship training based on our research, which we successfully implemented at the University of Colorado, Boulder, with graduate students and postdocs. We conclude that such training is an important and cost-effective step toward improving mentorship in STEM fields.

Beyond arctic and alpine: the influence of winter climate on temperate ecosystems

Winter climate is expected to change under future climate scenarios, yet the majority of winter ecology research is focused in cold-climate ecosystems. In many temperate systems, it is unclear how winter climate relates to biotic responses during the growing season. The objective of this study was to examine how winter weather relates to plant and animal communities in a variety of terrestrial ecosystems ranging from warm deserts to alpine tundra. Specifically, we examined the association between winter weather and plant phenology, plant species richness, consumer abundance, and consumer richness in 11 terrestrial ecosystems associated with the U.S. Long-Term Ecological Research (LTER) Network. To varying degrees, winter precipitation and temperature were correlated with all biotic response variables. Bud break was tightly aligned with end of winter temperatures. For half the sites, winter weather was a better predictor of plant species richness than growing season weather. Warmer winters were correlated with lower consumer abundances in both temperate and alpine systems. Our findings suggest winter weather may have a strong influence on biotic activity during the growing season and should be considered in future studies investigating the effects of climate change on both alpine and temperate systems.

A site for sori: Ecophysiology of fertile-sterile leaf dimorphy in ferns

PREMISE OF THE STUDY

Reproduction often requires significant investment and can move resources away from growth and maintenance; maintaining a balance between reproduction and growth can involve trade-offs. Extreme functional specialization has separated reproduction and photosynthesis in most seed plants, yet ferns use the laminar surface of their fronds for both reproduction and photosynthesis. This dual function selects for a variety of frond morphologies that range from no specialization (monomorphy) to extreme dimorphy between fertile and sterile fronds (holodimorphy). Here we examined the ecological and physiological consequences of variation in frond dimorphy in ferns, evaluated reproductive trade-offs across a dimorphy gradient, and speculate on factors controlling the occurrence of holodimorphy.

METHODS

Ecophysiological measurements of photosynthetic rate, water potential, hydraulic conductivity, and gross morphological comparisons of frond area and angle were used to evaluate differences between fertile and sterile fronds. We examined three temperate and three tropical fern species that vary in degree of fertile-sterile dimorphy.

KEY RESULTS

Holodimorphic species produced fewer fertile fronds, which had significantly higher respiratory rates than in sterile fronds on the same plant or in any frond produced on monomorphic species; hemidimorphic species were frequently intermediate. We found no differences in vulnerability to cavitation between fertile and sterile fronds. In dimorphic species, fertile fronds had higher (less negative) water potential and lower stipe hydraulic conductivity relative than in sterile fronds.

CONCLUSIONS

Fertile-sterile dimorphy in ferns appears to come at considerable carbon cost in holodimorohic species. It is possible that the relative costs of this reproductive system are offset by increased spore dispersal, yet such trade-offs require further exploration.

Differential synthesis of peritoxins and precursors by pathogenic strains of the fungus Periconia circinata

Pathogenic strains of the soilborne fungus Periconia circinata produce peritoxins with host-selective toxicity against susceptible genotypes of sorghum. The peritoxins are low-molecular-weight, hybrid molecules consisting of a peptide and a chlorinated polyketide. Culture fluids from pathogenic, toxin-producing (Tox(+)) and nonpathogenic, non-toxin-producing (Tox(-)) strains were analyzed directly by gradient high-performance liquid chromatography (HPLC) with photodiode array detection and HPLC-mass spectrometry to detect intermediates and final products of the biosynthetic pathway. This approach allowed us to compare the metabolite profiles of Tox(+) and Tox(-) strains. Peritoxins A and B and the biologically inactive intermediates, N-3-(E-pentenyl)-glutaroyl-aspartate, circinatin, and 7-chlorocircinatin, were detected only in culture fluids of the Tox(+) strains. The latter two compounds were produced consistently by Tox(+) strains regardless of the amount of peritoxins produced under various culture conditions. In summary, none of the known peritoxin-related metabolites were detected in Tox(-) strains, which suggests that these strains may lack one or more functional genes required for peritoxin biosynthesis.

Visual information and the control of reaching in children: a comparison between children with and without developmental coordination disorder

Three experiments were performed on reach and grasp in 9- to 10-year-old children (8 controls and 8 with developmental coordination disorder [DCD]). In normal reaching, children in the DCD group were less responsive to the accuracy demands of the task in controlling the transport component of prehension and spent less time in the deceleration phase of hand transport. When vision was removed as movement began, children in the control group spent more time decelerating and reached peak aperture earlier. Children in the DCD group did not do that, although, like the control group, they did increase grip aperture in the dark. When depth cues were reduced and only the target or only the target and hand were visible, children in the control group used target information to maintain the same grip aperture in all conditions, but DCD children behaved as if the target was not visible. Throughout the studies, the control group of 9- to 10-year-olds did not produce adult-like adaptations to reduced vision, suggesting that they had not yet attained adult-like integration of sensory input. Compared with control children, children with DCD did not exhibit increased dependence on vision but showed less recognition of accuracy demands, less adaptation to the removal of vision, and less use of minimal visual information when it was available.

Development of a transformation system for Mycosphaerella pathogens of banana: a tool for the study of host/pathogen interactions

A genetic transformation system has been developed for three Mycosphaerella pathogens of banana and plantain (Musa spp.). Mycosphaerella fijiensis and Mycosphaerella musicola, the causal agents of black and yellow Sigatoka, respectively, and Mycosphaerella eumusae, which causes Septoria leaf spot of banana, were transformed with a construct carrying a synthetic gene encoding green fluorescent protein (GFP). Most single-spored transformants that expressed GFP constitutively were mitotically stable in the absence of selection for hygromycin B resistance. Transformants of all three species were pathogenic on the susceptible banana cultivar Grand Nain, and growth in planta was comparable to wild-type strains. GFP expression by transformants allowed us to observe extensive fungal growth within leaf tissue that eventually turned necrotic, at which point the fungi grew saprophytically on the dead tissue. Leaf chlorosis and necrosis were often observed in advance of saprophytic growth of the mycelium on necrotic tissue, which supports previous reports suggesting secretion of a phytotoxin.

On the nature of hereditary cataract in strain 13/N guinea pigs

PURPOSE

Congenital nuclear cataracts in strain 13/N guinea pigs are caused by a single splice-site mutation in the zeta-crystallin gene. Very little is known of the physical factors involved in lens opacification of this system. The aim of this study is to elucidate the biophysical processes causing the nuclear turbidity.

METHODS

Normal, homozygous and heterozygous mutant guinea pig lenses were studied. Polarized light scattering measurements were performed on thin sections of lenses as a function of scattering angle. Scattering intensities were collected in two modes, I- and I+. The total water content of lenses was determined by thermogravimetric analysis. The nonfreezable (bound) water content was obtained by differential scanning calorimetry. The morphology of lenses was investigated by scanning electron microscopy.

RESULTS

Normal lenses scatter 5- to 10-fold less light than cataractous lenses at wide angles in both modes. The intensity ratios of the two modes imply that most of the scattering comes from density fluctuations; 10-20% of the turbidity may be contributed by orientation fluctuations. The nucleus of heterozygous cataractous lenses contain less total water than normal lenses, whereas the cortex has the same hydration as the normal lens. The nonfreezable water content of the cataractous nucleus is higher than that of the normal lens. Scanning electron microscopy showed frequent truncation of the fiber cells, cavitations and occasional longitudinal splitting resulting in hollow cylinder formation in the nucleus of the cataractous lens.

CONCLUSION

Mutation of zeta-crystallin in guinea pigs causes a congenital cataract. A number of supramolecular events contribute to the turbidity. The mobile water leaves the nuclear fiber cells, causing a collapse of supramolecular structures. Both the size of the aggregates and their refractive index increase by this dehydration process, contributing to the turbidity. The truncation and hollowing of fiber cells causes the orientation fluctuations that also increase turbidity.

Light scattering and morphology of cataract formation in transgenic mice containing the HIV-1 protease linked to the lens alpha A-crystallin promoter

Two constructs of transgenic mice, TG61 and TG72, containing the HIV-1 protease linked to the lens alpha A-crystallin promoter develop cataract. The TG61 construct develop cataract in utero, while the TG72 construct exhibit frank opacities on the 24th day (homozygotes) and 26th day (hemizygotes) post natum. Polarized light scattering measurements were performed on cortical and nuclear sections of TG72 lenses from day 19 to day 26 as a function of scattering angle. The parallel components of the scattered light intensity increase gradually during opacification, the perpendicular components show very low values from day 19 to day 22 after which they increase exponentially. Analysis of the scattered light intensities yielded parameters describing the size of the protein aggregates, the size of the domains exhibiting optical anisotropy/birefringence, the difference in refractive index between (a) the protein aggregates and their surroundings and (b) the birefringent units and their surroundings. The last parameter accounts for the major portion of the increase in lens turbidity. The TG72 construct shows normal lens development on day 16. By day 21 the posterior cortex shows some disintegration, while the lens is still clear. By day 26 the lens nucleus migrates toward the posterior pole and there is a major alteration in the cortical fibers. Scanning electron microscopic studies reveal normal fiber cell organizations in control animals. In the TG72 construct the fiber cells are well organized at 16 days after birth but already develop some slight separation in the posterior cortical part of the lens. By post-natal day 21, the nucleus and the anterior cortex still exhibit well aligned fiber cell organization, but the posterior cortex shows disalignment. By day 26 in the TG72 construct, all areas of the lens show complete disintegration of the fiber cells and amorphous masses are present throughout. The light scattering parameters describing changes on the nanometer scale can be correlated with the changes in lens morphology during cataractogenesis that occur on the micrometer scale. In comparison, the light and scanning electron microscopic examinations of the postnatal TG61 construct show that the lens is severely disrupted and contains completely disintegrated fiber cell remnants at an early age.

Hypovirulence-associated traits induced by a mycovirus of Cryphonectria parasitica are mimicked by targeted inactivation of a host gene

Expression of the Vir2 gene of Cryphonectria parasitica is down-regulated in strains of the fungus containing a double-stranded RNA genetic element that reduces fungal virulence (W. A. Powell and N. K. Van Alfen, Mol. Cell. Biol. 7:3688-3693, 1987). We have sequenced the Vir2 gene and characterized its structure; the mRNA contains a short open reading frame whose product has structural similarities to several fungal pheromones. A null mutant was constructed by homologous recombination to determine the function of the Vir2 gene and whether its disruption resulted in any of the altered phenotypes exhibited by many hypovirulent strains, such as reductions in virulence, pigmentation, and sporulation. The Vir2 null mutant (18dm) exhibited a wild-type phenotype with respect to gross colony morphology, growth rate, pigmentation, asexual spore viability, and virulence in apple fruit and chestnut trees. However, numbers of asexual fruiting bodies (pycnidia) and conidia were reduced significantly in comparison with the wild-type strain EP155/2. In sexual crosses of 18dm with a wild-type strain of the opposite mating type, perithecia (sexual fruiting bodies) developed but were barren. Deletion of the Vir2 gene results in a phenotype that mimics that of many double-stranded-RNA-containing hypovirulent strains; i.e., the null mutant exhibits significant reductions in asexual sporulation and pycinidum production as well as impaired sexual crossing ability. To our knowledge, this is the first report of the partial reproduction of a virus-induced phenotype by deletion of a virus-perturbed host gene.

Measurement of the severity of amphetamine dependence

A Severity of Amphetamine Dependence Questionnaire (SAmDQ) was administered to 101 subjects attending an Australian drug dependency treatment centre. The SAmDQ was adapted from the Severity of Opiate and Alcohol Dependence Questionnaires (SODQ & SADQ). The structural characteristics of the SAmDQ were examined and compared with previous findings reported on samples of opiate addicts with the SODQ. A high degree of consistency was found between the results obtained with the SAmDQ and previous findings with the SODQ. The relationship between the SAmDQ and the Severity of Dependence Scale (SDS) was also examined. The findings suggest that further development of amphetamine dependence measurement is required.