Genetic discontinuities among populations of Cleistes (Orchidaceae, Vanilloideae) in North America

Genetic patterns were examined in five populations of North American Cleistes with three sources of molecular data: amplified fragment length polymorphisms (AFLP), DNA sequencing, and plastid microsatellites. Populations of C. bifaria were sampled in four areas of the south-eastern US: the coastal plains of Florida and North Carolina and the mountains of North Carolina and West Virginia. A population of C. divaricata sympatric with the North Carolina coastal plain C. bifaria was also sampled. Analysis of the three types of molecular data resulted in the same relationships among the five sampled populations. The coastal plain population of C. divaricata was consistently grouped with the C. bifaria populations from the mountains of West Virginia and North Carolina, and the two coastal plain populations of C. bifaria formed a separate group, results not supporting the existing concepts of species relationships. For future studies, greater sampling of C. divaricata populations and more detailed morphological and phenological studies are recommended for better characterization of the diversity within North American Cleistes . © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 87–95.     

Abundance–body mass relationships among insects along a latitudinal gradient

Abstract We investigated the relationship between abundance and body size (body mass) of 162 insect herbivore species on the host plant Acacia falcata along its entire coastal latitudinal distribution (eastern Australia), spanning a gradient in mean annual temperature of 4.3°C. We extend previous research by assessing these relationships at different spatial scales (latitudes pooled, among latitudes and within latitudes) and at different taxonomic levels (insect phytophages pooled, phytophagous Coleoptera and Hemiptera, and five component suborders/superfamilies). Insect species were collected from two orders (Hemiptera and Coleoptera) and five component suborders/superfamilies. There were no consistent trends in the relationships (linear or polygonal/hump‐shaped) between abundance and body mass when latitudes were pooled, among latitudes, or when phytophagous insect species were separated into their component suborder/superfamily groups. The reason for the lack of consistent trends might be due to the insect herbivores not fully exploiting their host plant and the relative absence of competition among herbivore species for food resources. This is further assessed in relation to the lack of a consistent pattern in species richness of Coleoptera and Hemiptera herbivores from the same dataset and rates of chewing and sap‐sucking herbivory along the same latitudinal gradient. Future studies of abundance–body size relationships are discussed in relation to sampling across environmental gradients and accounting for the influence of host plant identity and insect phylogeny.     

Spring photosynthesis in a cool temperate bog

In northern ecosystems, the onset and growth of spring photosynthesis may have an important influence on the annual carbon (C) budget, yet the controls have not been clearly identified, especially for peatlands. We used a 5‐year set of daily carbon dioxide (CO₂) exchange measurements derived from an eddy covariance tower located at Mer Bleue, an ombrotrophic bog near Ottawa, Canada, from March to May [day‐of‐year (DOY) 60–150], 1999–2003. We used half‐hourly measured net ecosystem exchange minus modelled ecosystem respiration to estimate daily photosynthesis, as gross ecosystem production (GEP). The onset of GEP in each year was closely related to the thinning and disappearance of the snow cover, occurring between DOY 86 and 101. GEP increased during the spring, reaching 10‐day average values of between 5 and 9 g CO₂ m^?2 day^?1 by the end of May. This increase was initially associated with moss activity (Sphagnum and Polytrichum), followed by the evergreen shrubs. Peat temperatures in the rooting zone (10–20 cm depth) and increases in shrub leaf nitrogen and chlorophyll a concentrations contributed to this rapid increase in GEP. Examination of moderate‐resolution imaging spectroradiometer (MODIS) images over several years revealed that the temporal resolution (16‐day composites) was inadequate to capture the onset of GEP but estimates of gross primary productivity and photosynthesis from MODIS 8‐day composites for the most part followed the pattern and magnitude of CO₂ exchange observed at the tower.     

Relationships between abundance and body size: where do tourists fit?

Abstract.

• 1 The possible effects of the inclusion of ‘tourist’ species have been the cause of some concern in investigations of interspecific relationships between abundance and body size.
• 2 Data for adult beetles (Coleoptera) from oak trees in Britain are used to investigate the relationship of abundance to body size when tourists are and are not included.
• 3 For this particular assemblage, tourists do not fundamentally alter the basic statistics of the relationship between abundance and body size. However, they are not a random sample of the beetle assemblage. They have lower abundances and are also of smaller body size than other species.

     

Subcellular Localization of the Enzymes of the Arginine Dihydrolase Pathway in Trichomonas vaginalis and Tritrichomonas foetus

The enzymes of the arginine dihydrolase pathway were demonstrated in Tritrichomonas foetus and their subcellular localization determined for both T. foetus and Trichomonas vaginalis. Ornithine carbamyltransferase (anabolic and catabolic activities), ornithine decarboxylase and carbamate kinase activity were localized predominately (56–80%) in the non sedimentable fraction of both species. A large proportion (35–40%) of the arginine deiminase was, however, recovered in the large granular fraction, and this distribution was unchanged by increasing the ionic strength of the buffer. Upon density gradient centrifugation the particles containing arginine deiminase activity had an isopycnic density of 1.09 g/ml in percoll, and separated from hydrogenosomes (1.18 g/ml) and lysosomes (1.12 g/ml). Arginine deiminase was also the only enzyme of the dihydrolase pathway which demonstrated latency upon treatment of the 1.09 g/ml fraction with non-ionic detergents. The results demonstrate the presence of the arginine dihydrolase pathway in T. foetus and indicate that at least a portion of the arginine deiminase in trichomonads is membrane associated.     

A phenetic investigation of Vicia L.subgenus Vicia (Leguminosae, Vicieae)

Morphological data were gathered from 1539 herbarium specimens representing the taxa of Vicia subgenus Vicia. Specimens were scored for 43 vegetative, 84 inflorescence, 23 legume and 24 seed characters. The data were analysed using cluster analysis and ordination techniques. The results of the analysis were used to produce a classification of the subgenus. The proposed classification contains nine sections, nine series, 38 species, 14 subspecies and 22 varieties. The classification is discussed in relation to previous classifications.     

Rice responses to drought under carbon dioxide enrichment. 1. Growth and yield

Projections of future climate change include a strong likelihood of a doubling of current atmospheric carbon dioxide concentration ([ CO ₂]) and possible shifts in precipitation patterns. Drought stress is a major environmental limitation for crop growth and yield and is common in rainfed rice production systems. This study was conducted to determine the growth and grain yield responses of rice to drought stress under [CO₂] enrichment. Rice (cv. IR-72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO₂] of 350 and 700 μmol CO₂ mol^–1 air. In both [CO₂], water management treatments included continuously flooded (CF) controls, flood water removed and drought stress imposed at panicle initiation (PI), anthesis (ANT), and both panicle initiation and anthesis (PI & ANT). The [CO₂] enrichment increased growth, panicles plant^–1 and grain yield. Drought accelerated leaf senescence, reduced leaf area and above-ground biomass and delayed crop ontogeny. The [CO₂] enrichment allowed 1–2 days more growth during drought stress cycles. Grain yields of the PI and PI & ANT droughts were similar to the CF control treatments while the ANT drought treatment sharply reduced growth, grain yield and individual grain mass. We conclude that in the absence of air temperature increases, future global increases in [CO₂] should promote rice growth and yield while providing a modest reduction of near 10% in water use and so increase drought avoidance.     

Savanna fires and their impact on net ecosystem productivity in North Australia

Savannas comprise a large area of the global land surface and are subject to frequent disturbance through fire. The role of fire as one of the primary natural carbon cycling mechanisms is a key issue in considering global change feedbacks. The savannas of Northern Australia burn regularly and we aimed to determine their annual net ecosystem productivity (NEP) and the impact of fire on productivity. We established a long‐term eddy covariance flux tower at Howard Springs, Australia and present here 5 years of data from 2001 to 2005. Fire has direct impacts through emissions but also has indirect effects through the loss of productivity due to reduced functional leaf area index and the carbon costs of rebuilding the canopy. The impact of fire on the canopy latent energy exchange was evident for 40 days while the canopy was rebuilt; however, the carbon balance took approximately 70 days to recover. The annual fire free NEP at Howard Springs was estimated at −4.3 t C ha⁻¹ yr⁻¹ with a range of −3.5 to −5.1 t C ha⁻¹ yr⁻¹ across years. We calculated the average annual indirect fire effect as +0.7 t C ha⁻¹ yr⁻¹ using a neural network model approach and estimated average emissions of fine and coarse fuels as +1.6 t C ha⁻¹ yr^‐1. This allowed us to calculate a net biome production of −2.0 t C ha⁻¹ yr^‐1. We then partitioned this remaining sink and suggest that most of this can be accounted for by woody increment (1.2 t C ha⁻¹ yr^‐1) and shrub encroachment (0.5 t C ha⁻¹ yr^‐1). Given the consistent sink at this site, even under an almost annual fire regime, there may be management options to increase carbon sequestration by reducing fire frequency.     

Temporal and spatial variation in an Australian tropical rainforest

Abstract This study describes the floristics and structure of a 0.95‐ha lowland tropical rainforest plot at the Australian Canopy Crane Research Facility at Cape Tribulation, Queensland. Five years of post‐cyclonic change in forest floristics and structure following the passage of Tropical Cyclone ‘Rona’ in February 1999 are examined. Local and regional variation in tropical rainforest is examined in comparison with other lowland plots established nearby and mid‐elevation plots located elsewhere in north Queensland at Eungella, Paluma and the Atherton Tablelands. These plots are placed in a broader Australasian context along with lowland rainforest plots at Baitabag and Oomsis, Papua New Guinea. The 2005 survey found 680 stems of 82 species ≥10 cm d.b.h. on the crane plot, an increase of 30.3% in stems and 16.4% of species in the 5 years since the previous survey. The most abundant families were Meliaceae, Euphorbiaceae, Lauraceae, Myrtaceae and Apocynaceae and the most abundant species were Cleistanthus myrianthus, Alstonia scholaris, Myristica insipida, Normanbya normanbyi and Rockinghamia angustifolia. Temporal floristic and structural variation suggests that the crane site remains in an active stage of post‐cyclonic recovery. Local spatial variability in floristics and structure at Cape Tribulation exceeded the variation exhibited by a single plot over a period of 5 years, despite the impact of Cyclone Rona. This finding suggests a high degree of temporal stability within this stand of rainforest despite frequent catastrophic disturbances. The rainforests of Cape Tribulation constitute a relatively unique floristic community when observed in an Australasian context. Variation in rainforest community composition across the region shows the importance of biogeographical connections, the impacts of local topography, environmental conditions and disturbance history.