Leaf trait co-ordination in relation to construction cost, carbon gain and resource-use efficiency in exotic invasive and native woody vine species

Background and Aims: Success of invasive plant species is thought to be linked with their higher leaf carbon fixation strategy, enabling them to capture and utilize resources better than native species, and thus pre-empt and maintain space. However, these traits are not well-defined for invasive woody vines. Methods: In a glass house setting, experiments were conducted to examine how leaf carbon gain strategies differ between non-indigenous invasive and native woody vines of south-eastern Australia, by investigating their biomass gain, leaf structural, nutrient and physiological traits under changing light and moisture regimes. Key Results: Leaf construction cost (CC), calorific value and carbon : nitrogen (C : N) ratio were lower in the invasive group, while ash content, N, maximum photosynthesis, light-use efficiency, photosynthetic energyuse efficiency (PEUE) and specific leaf area (SLA) were higher in this group relative to the native group. Trait plasticity, relative growth rate (RGR), photosynthetic nitrogen-use efficiency and water-use efficiency did not differ significantly between the groups. However, across light resource, regression analyses indicated that at a common (same) leaf CC and PEUE, a higher biomass RGR resulted for the invasive group; also at a common SLA, a lower CC but higher N resulted for the invasive group. Overall, trait co-ordination (using pair-wise correlation analyses) was better in the invasive group. Ordination using 16 leaf traits indicated that the major axis of invasive-native dichotomy is primarily driven by SLA and CC (including its components and/or derivative of PEUE) and was significantly linked with RGR. Conclusions: These results demonstrated that while not all measures of leaf resource traits may differ between the two groups, the higher level of trait correlation and higher revenue returned (RGR) per unit of major resource need (CC) and use (PEUE) in the invasive group is in line with their rapid spread where introduced.

Identification of putative virulence-associated genes of Haemophilus parasuis through suppression subtractive hybridization.

Haemophilus parasuis is the causative agent of Glässer's disease. Up to now 15 serovars of H. parasuis have been identified, with significant differences existing in virulence between serovars. In this study, suppression subtractive hybridization (SSH) was used to identify the genetic difference between Nagasaki (H. parasuis serovar 5 reference strain, highly virulent) and SW114 (H. parasuis serovar 3 reference strain, non-virulent). A total of 191 clones were obtained from the SSH library. Using dot hybridization and PCR, 15 clones were identified containing fragments that were present in the Nagasaki genome while absent in the SW114 genome. Among these 15 fragments, three fragments (ssh1, ssh13, ssh15) encode cell surface-associated components; three fragments (ssh2, ssh5, ssh9) are associated with metabolism and stress response; one fragment (ssh8) is involved in assembly of fimbria and one fragment (ssh6) is a phage phi-105 ORF25-like protein. The remaining seven fragments are hypothetical proteins or unknown. Based on PCR analysis of the 15 serovar reference strains, eight fragments (ssh1, ssh2, ssh3, ssh6, ssh8, ssh10, ssh11 and ssh12) were found in three to five of most virulent serovars (1, 5, 10, 12, 13 and 14), zero to two in three moderately virulent serovars (2, 4 and 15), but absent in the low virulent serovar (8) and non-virulent serovars (3, 6, 7, 9 and 11). In vivo transcription fragments ssh1, ssh2, ssh8 and ssh12 were identified in total RNA samples extracted from experimental infected pig lung by RT-PCR. This study has provided some evidence of genetic differences between H. parasuis strains of different virulence.

The biology of Australian weeds, Limnocharis flava

The genus name Limnocharis is derived from the Greek limno (meaning marsh or pond) and charis (meaning grace) (Haynes and Holm-Nielson 1992) and flava is Latin for yellow. The genus is generally accepted to have two species, Limnocharis flava (Linneaus) Buchenau 1868 and L. laforestii (Duchass. ex Griseb) 1858. L. flava was first named Alisma flava by Linneaus in 1753 (Haynes and Holm-Nielsen 1986). Since then, other synonyms have included Damasonium flavum Mill. 1772, Limnocharis emarginata Humb. and Bonpl. 1808, Limnocharis plumieri Rich. 1815, Limnocharis laforestii Duchas. ex Griseb (1858) and Limnocharis mattogrossensis O. Ktze. (1893) (Woodson and Schery 1943).