Glutamate Dehydrogenase Activity in Roots: Distribution in a Seedling and Storage Root, and the Effects of Red and Far-red Illuminations

Pisum seedling and Pastinaca storage roots contained high glutanrate dehydrogenase (GDH) activity in areas of reported rapid growth and high phytoctrome content. A similar distribution was observed for malate dehydrogenase. Freeze-thawings of mitochondrial preparations from Pisum roots always resulted in increases of GDH specific activity; however, the observed increases were much larger with basal than apical sections. Both intact and freeze-thawed mitochondrial preparations from seedling roots exhibited increases in GDH activity with time after isolation. In intact mitochondrial preparations from roots of etiolated seedlings, an increase in malate dehydrogenase activity was observed similar to that of GDH activity; however, no increased malate dehydrogenase activity was noted in preparations from light-grown seedlings. Illuminating Pisum seedlings with far-red light slowly increased GDH activity in roots over a period of two weeks. Since these observed increases were not due to direct exposure of roots to light, other factors were likely involved.     

Faster returns on ‘leaf economics’ and different biogeochemical niche in invasive compared with native plant species

Plant‐invasive success is one of the most important current global changes in the biosphere. To understand which factors explain such success, we compared the foliar traits of 41 native and 47 alien‐invasive plant species in Oahu Island (Hawaii), a location with a highly endemic flora that has evolved in isolation and is currently vulnerable to invasions by exotic plant species. Foliar traits, which in most cases presented significant phylogenetic signal, i.e. closely related species tended to resemble each other due to shared ancestry, separated invasive from native species. Invasive species had lower leaf mass per area and enhanced capacities in terms of productivity (photosynthetic capacity) and nutrient capture both of macro‐ (N, P, K) and microelements (Fe, Ni, Cu and Zn). All these differences remain highly significant after removing the effects of phylogenetic history. Alien‐invasive species did not show higher efficiency at using limiting nutrient resources, but they got faster leaf economics returns and occupied a different biogeochemical niche, which helps to explain the success of invasive plants and suggests that potential increases in soil nutrient availability might favor further invasive plant success.     

The importance of pre-thicket conifer plantations for nesting Hen Harriers Circus cyaneus in Ireland

Hen Harriers Circus cyaneus are threatened across much of their range and their conservation requires appropriate habitat management. The locations of 148 Hen Harrier nests found in the Republic of Ireland during national breeding surveys in 2000 and 2005 were used to assess nest-site selection. The distribution of these nests was compared to distributions of randomly located points to investigate selection at the scale of the nest-site and landscape. The main nesting habitats selected were pre-thicket stage of first and, particularly, second rotation plantations, mostly of exotic conifers. There was no evidence that the area of post-closure plantations negatively affected Hen Harrier nest distribution. There was a positive correlation across study areas between changes in numbers of Hen Harrier nests between 2000 and 2005 and changes in the area of pre-thicket second rotation plantations over the same period. The overall effect of plantation forests on breeding Hen Harriers in Ireland therefore appears to be positive. However, this study did not consider the effects of plantation habitats on breeding success. Improved grassland was strongly avoided as a nesting habitat. Furthermore, after controlling for the influence of nesting habitat on nest location, landscapes with a high percentage cover of improved grassland were also avoided. Further agricultural intensification of grassland in areas where Hen Harriers breed is likely to have a negative impact on this species. These results are required for the development of management strategies for the conservation of this species.     

Patterns of intra- and interspecific association in leaf-mining insects on three oak host species

Abstract. 1. We determined mortality and distributional patterns of leaf miners on three oak host species (Quercus falcata, Q.nigra and Q.hemisphaerica) in northern Florida, U.S.A.
2. Patterns of intra- and interspecific occurrence within leaves, and mortality of five most abundant leaf miner species were analysed as a test of competition.
3. Miners co-occurred on leaves more often that expected by chance (P<0.05) in six of ten possible species combinations and log-linear model analysis showed no negative higher-order interactions.
4. All five miner species had highly clumped distributions between leaves (P<0.01).
5. Leaf miner survival was less than expected for four of five species when co-occurring on leaves with conspecifics than when mining with heterospecifics or alone (P<0.05).
6. We conclude that interspecific competition is unapparent within this leaf miner guild and that intraspecific competition occurs in four of the five major leaf miner species. We discuss leaf miner selection of common leaves, perhaps based on chemical/physical leaf characters, as a cause of intra- and interspecific aggregation.     

Residual effects of High Temperature Pre-Treatments on the Germination of Celery Seeds (Apium graveolens)

Celery seeds (Apium graveolens L.) were allowed to imbibe in the dark for different periods at 28. 32. 37 or 41°(the high temperature pre-treatmem or HTP) prior to transfer to 15, 17, 19.5 or 22°C in white light (the low temperature treatment or LTT). The effect of HTP's at 28. 32 and 37°C was to lower the upper temperature limit for germination and this effect increased with increase in the temperature and duration of the HTP. Increasing exposure to an HTP of 41 °C, however, did not appear to lower the upper temperature limit for germination but reduced the viability of the seeds. This trend of increased inhibition of germination caused by increasingly higher temperatures was reversed when the transfer was to a 22°C LTT after a 4 day HTP at 37°C. When the temperature of (he HTP was relatively low and transfer was to a low LTT. or if the HTP was of a brief duration, the rate of germination was increased as compared to seeds not given an HTP. However, when the temperature and duration of the HTP were increased, the rate of germination became slower than that of seeds not given an HTP, i.e. the time taken for the seeds to recover from the HTP-induced dormancy increased with the temperature and duration of the HTP. The decrease in the germination rate was caused by a delay in the start and not a slowing of the rate of embryo elongation within the seed.