Danielle E. Medek

Xylem traits mediate a trade-off between resistance to freeze-thaw-induced embolism and photosynthetic capacity in overwintering evergreens

Hydraulic traits were studied in temperate, woody evergreens in a high-elevation heath community to test for trade-offs between the delivery of water to canopies at rates sufficient to sustain photosynthesis and protection against disruption to vascular transport caused by freeze-thaw-induced embolism. Freeze-thaw-induced loss in hydraulic conductivity was studied in relation to xylem anatomy, leaf- and sapwood-specific hydraulic conductivity and gas exchange characteristics of leaves. We found evidence that a trade-off between xylem transport capacity and safety from freeze-thaw-induced embolism affects photosynthetic activity in overwintering evergreens. The mean hydraulically weighted xylem vessel diameter and sapwood-specific conductivity correlated with susceptibility to freeze-thaw-induced embolism. There was also a strong correlation of hydraulic supply and demand across species; interspecific differences in stomatal conductance and CO(2) assimilation rates were correlated linearly with sapwood- and leaf-specific hydraulic conductivity. Xylem vessel anatomy mediated an apparent trade-off between resistance to freeze-thaw-induced embolism and hydraulic and photosynthetic capacity during the winter. These results point to a new role for xylem functional traits in determining the degree to which species can maintain photosynthetic carbon gain despite freezing events and cold winter temperatures.

The Macroecology of Airborne Pollen in Australian and New Zealand Urban Areas

The composition and relative abundance of airborne pollen in urban areas of Australia and New Zealand are strongly influenced by geographical location, climate and land use. There is mounting evidence that the diversity and quality of airborne pollen is substantially modified by climate change and land-use yet there are insufficient data to project the future nature of these changes. Our study highlights the need for long-term aerobiological monitoring in Australian and New Zealand urban areas in a systematic, standardised, and sustained way, and provides a framework for targeting the most clinically significant taxa in terms of abundance, allergenic effects and public health burden.

Effects of growth temperature on photosynthetic gas exchange characteristics and hydraulic anatomy in leaves of two cold-climate Poa species

How plastic is hydraulic anatomy with growth temperature, and how does this relate to photosynthesis? These interrelationships were studied in subantarctic Poa foliosa Hook. f. and alpine Poa hothamensis Vickery grown under 7/4°C and 12/9°C day/night temperatures, reflecting summer temperatures in their respective habitats. Conduit radii were smaller in P. foliosa than in P. hothamensis, consistent with greater avoidance of freeze/thaw-induced embolism. Despite its origins in an environment with relatively little temperature variation, P. foliosa exhibited greater plasticity in hydraulic anatomy than P. hothamensis, increasing the size and density of conduits when grown under the warmer temperature regime. Both species had similar anatomical capacities for water transport when grown at 12/9°C, but stomatal conductance was lower in P. foliosa than P. hothamensis, suggesting hydraulic limitations not explained by leaf vascular anatomy. However, greater photosynthetic capacity and foliar nitrogen contents enabled P. foliosa to achieve the same assimilation rate as P. hothamensis under the 12/9°C growth conditions. Our results showed that nitrogen plays a central role in maintaining assimilation rates when constrained either by enzymatic activity at low temperatures or by hydraulic limitations at high temperatures and evaporative demands. Interspecific differences in nitrogen and water use may influence how subantarctic and alpine vegetation responds to climate warming.

Dynamic ecological observations from satellites inform aerobiology of allergenic grass pollen

Allergic diseases, including respiratory conditions of allergic rhinitis (hay fever) and asthma, affect up to 500 million people worldwide. Grass pollen are one major source of aeroallergens globally. Pollen forecast methods are generally site-based and rely on empirical meteorological relationships and/or the use of labour-intensive pollen collection traps that are restricted to sparse sampling locations. The spatial and temporal dynamics of the grass pollen sources themselves, however, have received less attention. Here we utilised a consistent set of MODIS satellite measures of grass cover and seasonal greenness (EVI) over five contrasting urban environments, located in Northern (France) and Southern Hemispheres (Australia), to evaluate their utility for predicting airborne grass pollen concentrations. Strongly seasonal and pronounced pollinating periods, synchronous with satellite measures of grass cover greenness, were found at the higher latitude temperate sites in France (46-50° N. Lat.), with peak pollen activity lagging peak greenness, on average by 2-3weeks. In contrast, the Australian sites (34-38° S. Lat.) displayed pollinating periods that were less synchronous with satellite greenness measures as peak pollen concentrations lagged peak greenness by as much as 4 to 7weeks. The Australian sites exhibited much higher spatial and inter-annual variations compared to the French sites and at the Sydney site, broader and multiple peaks in both pollen concentrations and greenness data coincided with flowering of more diverse grasses including subtropical species. Utilising generalised additive models (GAMs) we found the satellite greenness data of grass cover areas explained 80-90% of airborne grass pollen concentrations across the three French sites (p<0.001) and accounted for 34 to 76% of grass pollen variations over the two sites in Australia (p<0.05). Our results demonstrate the potential of satellite sensing to augment forecast models of grass pollen aerobiology as a tool to reduce the health and socioeconomic burden of pollen-sensitive allergic diseases.

Remote sensing of phenology: a dynamic tool to inform allergenic grass pollen aerobiology

Background: Epidemiological studies show that the consumption of raw milk early in life is protective against the development of allergies later in life. The effect was found to be limited to raw milk consumption and was not observed when this milk was boiled or when pasteurized and homogenized shop milk was consumed. So milk processing seems to abolish the allergy protective effects of raw milk. The components and mechanisms involved are however still unknown. In this study the sensitizing capacity of raw and processed cows milk was compared in a murine sensitization model for food allergy. Method: C3H/HeOuJ mice were sensitized orally once a week for 5 consecutive weeks with raw milk, heated raw milk (10 min 80°C), shop milk (pasteurized and homogenized), an 80:20 mixture of casein/whey protein (equivalent to the amount in milk; sensitized control) or PBS (non-sensitized control) using cholera toxin as adjuvant. One week after the last sensitization mice were challenged both intradermally and orally with casein/whey. Clinical parameters, such as the acute allergic skin response, anaphylactic shock symptoms and changes in body temperature were assessed upon intradermal challenge and serum specific antibodies and mast cell degranulation were measured upon oral challenge. Activated Th2-, Th1- and regulatory T-cell populations were quantified in spleen using flow cytometry and ex vivo cytokine production was measured after restimulation with casein/whey. Results: Mice sensitized with raw milk did not show any clinical symptoms upon challenge and did hardly produce specific IgE antibodies. Sensitization with the processed milk types on the contrary increased the acute allergic skin response and anaphylactic shock symptoms and caused a drop in body temperature. IgE levels were also significantly increased in these mice. No differences were observed in mucosal mast cell degranulation between groups and also T-cell populations did not differ. The production of Th2 cytokines IL-5 and IL-13 was however significantly reduced in the raw milk group compared to the processed milk groups after ex vivo re-stimulation of splenocytes with casein/whey. Conclusion: In contrast to processed milk, raw milk is hardly able to induce sensitization. Allergic symptoms and IgE levels were reduced and this coincided with reduced Th2 cytokine responses. What it is in raw milk that prevents sensitization needs to be elucidated in future studies.Background: Group 2 innate lymphoid cells (ILC2s) are essential in initiating and driving allergic immune responses. Elevated number of ILC2 in human peripheral blood (PBMC) of allergic asthma has been reported. However, there were inconsistent findings about the prevalence of ILC2s in PBMC of house dust mite (HDM) allergic rhinitis (AR) patients.The purpose of this study was to investigate whether there is an increase of ILC2s in the PBMCs of HDMAR patients in southern China and their ability to induce Th2-skewed inflammation. Methods: Flow cytometry and magnetic cell sorting were used to identify, isolate, and quantitate ILC2s in PBMCs from HDM-AR patients and healthy control subjects. The PBMCs and isolated ILC2s were cultured in vitro with a cocktail of cytokines (IL-2, IL-25 and IL-33) or allergen (Derp1). ELISA was used to measure the Th2 cytokine (IL-5 and IL-13) in plasma or cell-free supernatants. Results: The number of ILC2s in PBMCs is increased in the HDM-AR group compared to healthy controls (HC) in southern China (P < 0.001). The AR patients symptom score (VAS) and the concentration of the Th2 cytokine (IL-13) in plasma were measured and was associated with the prevalence of ILC2s in HDM-AR patients (P < 0.001, R = 0.39 for VAS and ILC2s; P < 0.001, R = 0.70 for IL-13 and ILC2s). The concentrations of IL-5 and IL-13 increased in the supernatants of both PBMCs and isolated ILC2 cultured with the cytokine cocktail or allergen (Derp1) in the HDM-AR group vs the healthy control group. The effect of the cytokine cocktail was stronger than Derp1 (P < 0.01). Conclusions: The number of Group 2 innate lymphoid cells (ILC2s) is increased in the HDM-AR patients in southern China and ILC2s could produce Th2 cytokines (IL-5 and IL-13) in the presence of IL-2, IL-25 and IL-33, which may contribute to type 2 inflammation in allergic immune responses.