http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:20599 Rising atmospheric concentrations of CO₂ (Cₐ) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to Cₐ. We hypothesized that plants regulate stomatal conductance optimally in response to rising Cₐ. We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate-controlled whole-tree chambers for 2 years at ambient and elevated Cₐ. Elevated Ca was ambient + 240 ppm, 60% higher than ambient Ca. Leaf-scale gas exchange was measured throughout the second year of the study and leaf-scale ITE increased by 60% under elevated Cₐ, as predicted. Values of leaf-scale ITE depended strongly on vapour pressure deficit (D) in both CO₂ treatments. Whole-canopy CO₂ and H2O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between Ca treatments, which had important effects on values of canopy-scale ITE. However, when Ca treatments were compared at the same D, canopy-scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy-scale ITE were not significantly different, indicating that ITE was not scale-dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to Cₐ. The effect of elevated Cₐ on photosynthesis increased with rising D. At high D, Ca had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of Ca on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with Cₐ will allow us to predict the effects of Cₐ on transpiration rate. 2012-07-27T04:00:11.095Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:16913 Nocturnal water flux has been observed in trees under a variety of environmental conditions and can be a significant contributor to diel canopy water flux. Elevated atmospheric CO₂ (elevated [CO₂]) can have an important effect on day-time plant water fluxes, but it is not known whether it also affects nocturnal water fluxes. We examined the effects of elevated [CO₂] on nocturnal water flux of field-grown Eucalyptus saligna trees using sap flux through the tree stem expressed on a sapwood area (Js) and leaf area (Et) basis. After 19 months growth under well-watered conditions, drought was imposed by withholding water for 5 months in the summer, ending with a rain event that restored soil moisture. Reductions in Js and Et were observed during the severe drought period in the dry treatment under elevated [CO₂], but not during moderate- and post-drought periods. Elevated [CO₂] affected night-time sap flux density which included the stem recharge period, called 'total night flux' (19:00 to 05:00, Js,r), but not during the post-recharge period, which primarily consisted of canopy transpiration (23:00 to 05:00, Js,c). Elevated [CO₂] wet (EW) trees exhibited higher Js,r than ambient [CO₂] wet trees (AW) indicating greater water flux in elevated [CO₂] under well-watered conditions. However, under drought conditions, elevated [CO₂] dry (ED) trees exhibited significantly lower Js,r than ambient [CO₂] dry trees (AD), indicating less water flux during stem recharge under elevated [CO₂]. Js,c did not differ between ambient and elevated [CO₂]. Vapour pressure deficit (D) was clearly the major influence on night-time sap flux. D was positively correlated with Js,r and had its greatest impact on Js,r at high D in ambient [CO₂]. Our results suggest that elevated [CO₂] may reduce night-time water flux in E. saligna when soil water content is low and D is high. While elevated [CO₂] affected Js,r, it did not affect day-time water flux in wet soil, suggesting that the responses of Js,r to environmental factors cannot be directly inferred from day-time patterns. Changes in J s,r are likely to influence pre-dawn leaf water potential, and plant responses to water stress. Nocturnal fluxes are clearly important for predicting effects of climate change on forest physiology and hydrology. 2012-01-16T06:13:13.903Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:12292 Amoebic gill disease can be experimentally induced by the exposure of salmonids to Neoparamoeba spp. freshly isolated from infected fish, while cultured amoebae are non-infective. Results from our previous work suggested that one key difference between infectious and non-infectious Neoparamoeba were the highly glycosylated molecules in the glycocalyx. To characterise these surface glycans or glycoproteins we used a monoclonal antibody (mAb 44C12) specific to a surface molecule unique to infective parasites. This mAb recognised a carbohydrate epitope on a high molecular weight antigen (HMWA) that make up 15–19% of the total protein in a soluble extract of infectious parasites. The HMWA consisted of at least four glycoprotein subunits of molecular weight (MW) greater than 150 kDa that form disulfide-linked complexes of MW greater than 600 kDa. Chemical deglycosylation yielded at least four protein bands of approximate MW 46, 34, 28 and 18 kDA. While a similar HMWA complex was present in non-infective parasites, the glycoprotein subunits were of lower MW and exhibited differences in glycosylation. The four glycoproteins subunits recognised by mAb 44C12 were resistant to degradation by PNGase F, PNGase A, O-glycosidase plus β-1, 4-galactosidase, β-N-acetylglucosaminidase and neuraminidase. The major monosaccharides in the HMWA from infectious parasites were rhamnose, fucose, galactose, and mannose while sialic acids were absent. The carbohydrate portion constituted more than 90% of the total weight of the HMWA from infectious Neoparamoeba spp. Preliminary results indicate that immunisation of salmon with HMWA does not lead to protection against challenge infection; rather it may even have an immunosuppressive effect. 2011-03-23T04:50:30.985Z ]]>