Temperature response measurements from eucalypts give insight into the impact of Australian isoprene emissions on air quality in 2050

Predicting future air quality in Australian cities dominated by eucalypt emissions requires an understanding of their emission potentials in a warmer climate. Here we measure the temperature response in isoprene emissions from saplings of four different Eucalyptus species grown under current and future average summertime temperature conditions. The future conditions represent a 2050 climate under Representative Concentration Pathway 8.5, with average daytime temperatures of 294.5 K. Ramping the temperature from 293 to 328 K resulted in these eucalypts emitting isoprene at temperatures 4–9 K higher than the default maximum emission temperature in the Model of Emissions of Gases and Aerosols from Nature (MEGAN). New basal emission rate measurements were obtained at the standard conditions of 303 K leaf temperature and 1000 µmol m−2 s−1 photosynthetically active radiation and converted into landscape emission factors. We applied the eucalypt temperature responses and emission factors to Australian trees within MEGAN and ran the CSIRO Chemical Transport Model for three summertime campaigns in Australia. Compared to the default model, the new temperature responses resulted in less isoprene emission in the morning and more during hot afternoons, improving the statistical fit of modelled to observed ambient isoprene. Compared to current conditions, an additional 2 ppb of isoprene is predicted in 2050, causing hourly increases up to 21 ppb of ozone and 24-hourly increases of 0.4 µg m−3 of aerosol in Sydney. A 550 ppm CO2 atmosphere in 2050 mitigates these peak Sydney ozone mixing ratios by 4 ppb. Nevertheless, these forecasted increases in ozone are up to one-fifth of the hourly Australian air quality limit, suggesting that anthropogenic NOx should be further reduced to maintain healthy air quality in future

Degradation of conventional, biodegradable and oxo-degradable microplastics in a soil using a δ13C technique

Context. A significant amount of conventional plastics waste, especially in the form of microplastics (MPs), has accumulated in soils due to its limited degradation. Oxo-degradable and biodegradable plastics have also contributed to MP contamination in soils. Aims. In this study, we examined the degradation of a conventional plastic [fruit and vegetable (F&V) bag], two biodegradable plastics (bin liner and mulch film) and an oxo-degradable plastic (drinking straw). Methods. These plastics (5 mm) were mixed into a soil and incubated in the laboratory at 37 ± 1°C for 185 days. The CO2-carbon (C) mineralisation of the four plastics was determined using a δ13C technique, because the difference in the δ13C values of studied plastics and the experimental soil was ≥10‰. Key results. Bin liner showed the greatest C mineralisation (5.7%), followed by mulch film (4.1%), straw (0.4%) and F&V bag (0.3%) at the end of the incubation period. All plastics, except the mulch film for 23–77 days of incubation, caused a positive priming effect on soil organic carbon (SOC). Fourier transform infra-red spectroscopy and scanning electron microscopy analyses were consistent with theC mineralisation data. Conclusions. This study determines the degradation of various MPs in soil using a reliable and practical δ13C method, which has been lacking in this field of study. The priming effect of various MPs on SOC is a significant finding. Implications. The lack of consideration of priming effect on SOC may overestimate the mineralisation of plastics in soil

Biogenic volatile organic compounds from trees : contribution to the carbon budget in high CO2 environments

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The effects of glacial atmospheric carbon dioxide levels and climate on isoprene emissions from vascular plants.

Isoprene (C5H8) emissions by terrestrial vegetation vary with temperature and light intensity, and play an important role in biosphere–chemistry–climate interactions. Such interactions were probably substantially modified by Pleistocene climate and CO2 cycles. Central to understanding the nature of these modifications is assessment and analysis of how emissions changed under glacial environmental conditions. Currently, even the net direction of change is difficult to predict because a CO2-depleted atmosphere may have stimulated emissions compensating for the negative impacts of a cooler climate. Here, we address this issue and attempt to determine the direction of change from an experimental standpoint by investigating the interaction between isoprene emissions and plant growth of two known isoprene-emitting herbaceous species (Mucuna pruriens and Arundo donax) grown at glacial (180 ppm) to present (366 ppm) CO2 levels. We found a significant enhancement of isoprene emissions per unit leaf area in M. pruriens under subambient CO2 concentrations relative to ambient controls but not for A. donax. In contrast, canopy emissions remained unaltered for both plant species because enhanced leaf emissions were offset by reductions in biomass and leaf area. Separate growth experiments with M. pruriens revealed that lowering day/night temperatures by 5°C decreased canopy isoprene emissions irrespective of the CO2 level. Incorporation of these results into a simple canopy emissions model highlights their potential to attenuate reductions in the total isoprene flux from forests under glacial conditions predicted by standard models

Non-Additive Effects of Forest Litter on Flammability

Forest litter is a fuel component that is important for the propagation of fire. Data describing fuel load, structure and fuel condition were gathered for two sites of Sydney Coastal Dry Sclerophyll Forest, a common vegetation type in the Sydney Basin, Australia. Surface litter from the sites was sorted into its constituent components and used to establish which component or mixture of components were the most flammable using several metrics. A general blending model was used to estimate the effect the different mixtures had on the response of the flammability metrics and identify non-additive effects. Optimisation methods were applied to the models to determine the mixture compositions that were the most or least flammable. Differences in the flammability of the two sites were significant and were driven by Allocasuarina littoralis. The presence of A. littoralis in litter mixtures caused non-additive effects, increasing the rate of flame spread and flame height non-linearly. We discuss how land managers could use these models as a tool to assist in prioritising areas for hazard reduction burns and how the methodology can be extended to other fuel conditions or forest types

The effects of glacial atmospheric CO2 concentrations and climate on isoprene emissions by vascular plants

Isoprene (C5H8) emissions by terrestrial vegetation vary with temperature and light intensity, and play an important role in biosphere-chemistry-climate interactions. Such interactions were probably substantially modified by Pleistocene climate and CO2 cycles. Central to understanding the nature of these modifications is assessment and analysis of how emissions changed under glacial environmental conditions. Currently, even the net direction of change is difficult to predict because a CO2-depleted atmosphere may have stimulated emissions compensating for the negative impacts of a cooler climate. Here, we address this issue and attempt to determine the direction of change from an experimental standpoint by investigating the interaction between isoprene emissions and plant growth of two known isoprene-emitting herbaceous species (Mucuna pruriens and Arundo donax) grown at glacial (180 ppm) to present (366 ppm) CO2 levels. We found a significant enhancement of isoprene emissions per unit leaf area in M. pruriens under subambient CO2 concentrations relative to ambient controls but not for A. donax. In contrast, canopy emissions remained unaltered for both plant species because enhanced leaf emissions were offset by reductions in biomass and leaf area. Separate growth experiments with M. pruriens revealed that lowering day/night temperatures by 5degreesC decreased canopy isoprene emissions irrespective of the CO2 level. Incorporation of these results into a simple canopy emissions model highlights their potential to attenuate reductions in the total isoprene flux from forests under glacial conditions predicted by standard models

Defining hybrid poplar (Populus deltoides x Populus trichocarpa) tolerance to ozone: identifying key parameters

This study examined whether two genotypes of hybrid poplar (Populus deltoides x Populus trichocarpa), previously classified as ozone tolerant and ozone sensitive, had differing physiological and biochemical responses when fumigated with 120 nL L-1 ozone for 6 h per day for eight consecutive days. Isoprene emission rate, ozone uptake and a number of physiological and biochemical parameters were investigated before, during and after fumigation with ozone. Previous studies have shown that isoprene protects plants against oxidative stress. Therefore, it was hypothesized that these two genotypes would differ in either their basal isoprene emission rates or in the response of isoprene to fumigation by ozone. Our results showed that the basal emission rates of isoprene, physiological responses and ozone uptake rates were all similar. However, significant differences were found in visible damage, carotenoids, hydrogen peroxide (H2O2), thiobarbituric acid reactions (TBARS) and post-fumigation isoprene emission rates. It is shown that, although the classification of ozone tolerance or sensitivity had been previously clearly and carefully defined using one particular set of parameters, assessment of other key variables does not necessarily lead to the same conclusions. Thus, it may be necessary to reconsider the way in which plants are classified as ozone tolerant or sensitive

Effects of fosmidomycin on plant photosynthesis as measured by gas exchange and chlorophyll fluorescence

In higher plants, many isoprenoids are synthesised via the chloroplastic 1-deoxy-d-xylulose 5-phosphate/2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. Attempts to elucidate the function of individual isoprenoids have used the antibiotic/herbicidal compound fosmidomycin (3-[N-formyl-N-hydroxy amino] propyl phosphonic acid) to inhibit this pathway. Examination of the effect of fosmidomycin on the major components of photosynthesis in leaves of white poplar (Populus alba) and tobacco (Nicotiana tabacum) was made. Fosmidomycin reduced net photosynthesis in both species within 1 h of application, but only when photosynthesis was light-saturated. In P. alba, these reductions were confounded by high light and fosmidomycin inducing stomatal patchiness. In tobacco, this was caused by significant reductions in PSII chlorophyll fluorescence and reductions in V (cmax) and J (max). Our data indicate that the diminution of photosynthesis is likely a complex effect resulting from the inhibition of multiple MEP pathway products, resulting in photoinhibition and photo-damage. These effects should be accounted for in experimental design and analysis when using fosmidomycin to avoid misinterpretation of results as measured by gas exchange and chlorophyll fluorescence

Improving forest sampling strategies for assessment of fuel reduction burning

Land managers typically make post hoc assessments of the effectiveness of fuel reduction burning (FRB), but often lack a rigorous sampling framework. A general, but untested, assumption is that variability in soil and fuel properties increases from small (∼1 m) to large spatial scales (∼10-100 km). Based on a recently published field-based sampling scheme, we addressed the following questions: (i) How much variability is captured in measurements collected at different spatial scales? (ii) What is the optimal number of sampling plots required for statistically robust characterisation of burnt areas? (iii) How can land managers improve their assessment of the effectiveness of FRB? We found that measurement variability does not increase with scale for all fuel components. Results showed that coarse woody debris is as variable at the small scale (plot, m) as it is at the landscape scale (km). For certain fuel components, such as litter biomass (in unburnt areas), overstorey biomass and leaf area, and soil properties such as total carbon and total nitrogen, samples taken at the small (plot) scale were indicative of variation at the larger scale of an individual FRB and more broadly across the landscape. We then tested the hypothesis that site stratification can reduce variability between sampling plots and as a consequence will reduce the required number of sampling plots. To test this hypothesis we used Landsat Normalized Difference Vegetation Index (NDVI) across areas treated with FRB and compared the number of sampling plots required to estimate mean fuel biomass with and without stratification. Stratification of burnt areas using remotely sensed vegetation indices reduced the number of sampling plots required. We provide a model of green biomass from Landsat NDVI and make recommendations on how sampling schemes can be improved for assessment of fuel reduction burning

Visit, consume and quit: patch quality affects the three stages of foraging

We tested whether the probability of a visit was a function of<br>treatment (dietary N content as a continuous variable) using logistic regression in SAS (PROC GLIMMIX with a binomial distribution and logit link function, SAS 9.4). Day (fixed effect), site (random effect) and feeding station nested within site (random effect) were also included in the model. We then analysed the effect of treatment (dietary N content as a continuous variable) on visit length (min), each behaviour (% of total time) and GUD (count) separately using the generalized linear mixed model (GLMM) procedure in SAS (PROC GLIMMIX with lognormal distribution and identity link function, SAS 9.4). Day (1-4) was included in the models as a fixed effect, and site and feeding station (nested within site) were random effects.<br><br><div>To analyse our VOCs data we looked at the odours of the diets using a canonical analysis of principal coordinates<br></div>(CAP) analysis in the PERMANOVA+ add-on of PRIMER v6<br>to determine whether the multivariate VOC data could differentiate the diets along a continuous (dietary nitrogen<br>content) gradient, similar to analyses of VOCs from other plant/food material. We applied a dispersion weighting followed by square root transformation to the VOC peak area values, then performed CAP analysis on the Bray-Curtis resemblance matrix of the transformed data. To tease apart the contributing VOCs we then applied the CAP<br>analysis using diet as a class variable. We also isolated the specific volatile signature of the highest quality diet using<br>the Random Forests (RF). We analysed the data with RF, using a one treatment-versus-the rest approach with the VSURF package (version 1.0.3) in R (version 3.1.2; R Core Team, 2015). Before analysis, TQPA data were transformed using the centred log ratio method using CoDaPack v. 2.01.15.<br