Water Stress in Plants

The abscisic acid (ABA) content was determined quantitatively in the leaves from wilted and unwilted tomato plants (Lycopersicon esculentum Mill. CV. Revermun) by the use of the wheat coleoptile test and gas-liquid chromatography (GLC). Plants which have received an insufficient daily water supply for 18 days showed adaptation to wilting conditions. The plants adjust to the added amount of water by regulating their water loss through transpiration. The concentration of ABA was not higher in the leaves of plants adapted to water stress than in plants that were watered abundantly. Wilted detached leaves and leaves from rapidly wilted intact plants showed the well-known reaction by increasing the ABA level. A possible role of ABA in the early stages of the adaptation process is discussed.     

A multidisciplinary approach to understanding the recent and historical occurrence of the freshwater plant, Littorella uniflora

1. The vulnerability of softwater, oligotrophic lakes to eutrophication has caused the disappearance of many, if not most, of the unique isoetid plant communities. We tested whether the presence or disappearance of the isoetid Littorella uniflora (L.) could be predicted from environmental parameters, soil types and land use in the catchment area, and atmospheric nitrogen deposition. 2. We found that the topographic catchment area of a lake was an irrelevant unit to study effects of soil type and land use. Instead, using a GIS‐generated buffer zone around the lakes it proved feasible to classify 472 lakes into historical (if L. uniflora had disappeared) or recent (if L. uniflora was still present) Littorella lakes, based on soil type and land use. Our analysis showed that aeolian sand deposits and heath in the buffer zone favoured the presence of L. uniflora, whereas moraine clay and agriculture were strongly linked to the disappearance of L. uniflora. 3. However, in order to understand fully the presence or disappearance of L. uniflora, environmental data were needed in addition to soil types, land use and nitrogen deposition, and the use of discriminant analysis allowed us to classify 96% of the investigated lakes correctly into recent or historical sites. Alkalinity, total phosphorus, total nitrogen, aeolian sand deposits and heath were the most important parameters explaining the presence or disappearance of L. uniflora. Our analysis also indicated that eutrophication, rather than acidification, has likely caused the disappearance of L. uniflora from 218 of the 472 lakes investigated. 4. Our findings have widespread implications for the conservation or restoration of isoetid habitats and we recommend applying a wide buffer zone around lakes, with restrictions on farming and traditional forestry activities. In addition, our buffering concept may prove a useful tool for aquatic ecologists to investigate relationships between catchment features and organisms (plants, insects and amphibians) with aquatic as well as terrestrial life forms.     

Taxonomy, phylogeny, and biogeogràphy of the genus Oreobolus R.Br. (Cyperaceae), with comments on the biogeography of the South Pacific continents

SEBERG, O., 1988. Taxonomy, phylogeny, and biogeogràphy of the genus Oreobolus R.Br. (Cyperaceae), with comments on the biogeogràphy of the South Pacific continents. The genus Oreobolus R.Br. (Cyperaceae) is revised. Fourteen species and three subspecies are recognized; two subspecies are described as new, O. obtusangulus subsp. unispicus and O. oxycarpus subsp. brownii; and a new subspecies combination is made, O. pumilio subsp. clemensiae. Comments are given on the classiciation and choice of phylogenetic and biogeographic methods. The sister-group of the genera Oreobolus and Schoenoides (which has recently been segregated from Oreobolus) is a subset of Costularia subgenus Costularia. Oreobolus is hypothesized to be monophyletic, and a phylogenetic hypothesis, based on a parsimony method, is presented. The scale-like tepals of Oreobolus are hypothesized to be apomorphic. Current vicariance biogeographic hypotheses on the relationships of the South Pacific continents are shown to be premature. Brief accounts are given on nomenclature, aspects of morphology, chromosome numbers, geographical distribution, and ecology.     

Rapid northwards expansion of a forest insect pest attributed to spring phenology matching with sub‐Arctic birch

Species range displacements owing to shifts in temporal associations between trophic levels are expected consequences of climate warming. Climate‐induced range expansions have been shown for two irruptive forest defoliators, the geometrids Operophtera brumata and Epirrita autumnata, causing more extensive forest damage in sub‐Arctic Fennoscandia. Here, we document a rapid northwards expansion of a novel irruptive geometrid, Agriopis aurantiaria, into the same region, with the aim of providing insights into mechanisms underlying the recent geometrid range expansions and subsequent forest damage. Based on regional scale data on occurrences and a quantitative monitoring of population densities along the invasion front, we show that, since the first records of larval specimens in the region in 1997–1998, the species has spread northwards to approximately 70°N, and caused severe defoliation locally during 2004–2006. Through targeted studies of larval phenology of A. aurantiaria and O. brumata, as well as spring phenology of birch, along meso‐scale climatic gradients, we show that A. aurantiaria displays a similar dynamics and development as O. brumata, albeit with a consistent phenological lag of 0.75–1 instar. Experiments of the temperature requirements for egg hatching and for budburst in birch showed that this phenological lag is caused by delayed egg hatching in A. aurantiaria relative to O. brumata. A. aurantiaria had a higher development threshold (LDT_A.a.=4.71 °C, LDT_O.b.=1.41 °C), and hatched later and in less synchrony with budburst than O. brumata at the lower end of the studied temperature range. We can conclude that recent warmer springs have provided phenological match between A. aurantiaria and sub‐Arctic birch which may intensify the cumulative impact of geometrid outbreaks on this forest ecosystem. Higher spring temperatures will increase spring phenological synchrony between A. aurantiaria and its host, which suggests that a further expansion of the outbreak range of A. aurantiaria can be expected.     

Size dependence of composition, photosynthesis and growth in the colony-forming freshwater ciliate, Ophrydium versatile

1. Ophrydium versatile is a symbiotic ciliate which forms gelatinous colonies up to several centimetres in diameter in transparent temperate lakes. The ciliates are evenly spaced at the colony surface and constitute a small proportion of the surface area (7%) and volume (3.1%) of the colony, but a large proportion of organic carbon (74%) and nitrogen content (82%) (exemplified for 1 cm³ colonies). The majority of the colony volume is formed by the jelly. The biomass proportion of ciliates scales inversely with colony size, following the decline of surface area to colony volume. The largest colonies found in Danish lakes in early summer contain almost 1 million ciliates, and assuming they derive from a single ciliate undergoing exponential division, they need twenty generations and, presumably, almost a year to reach maximum size. 2. The ciliates contain numerous symbiotic zoochlorellae that constitute about 10% of ciliate volume and more than half of the carbon content. Zoochlorellae dominate oxygen metabolism of the assemblage, resulting in low light compensation points, a large diel photosynthetic surplus, and a marked dependence on light for sustained growth and ciliate metabolism. Estimated gross photosynthesis (7ng C ciliate^?1 day^?1) of Ophnrydium from shallow, clear waters in June greatly exceeded the estimated carbon contained in filtered bacteria and small algae (1.9ng C cilicate^?1 day^?1). Nitrogen and phosphorus content of the prey, however, may provide the main nutrient source consistent with the correspondence between mass-specific rates of nutrient uptake and measured relative growth rates (average 0.067 day^?1, generation time 10 days). 3. The large Ophrydium colonies require increased allocation of photosynthetic carbohydrates with increasing colony size to maintain the jelly. The large colonies tend to become gas-filled, floating, mechanically destroyed and their ciliate inhabitants abandon them as swarmers. Colony formation, however, should offer protection against predators which may be more important for the natural abundance than the costs of growing in a colony.     

Functional leaf anatomy of Bomarea Mirb. (Alstroemeriaceae)

The leaf anatomy of Bomarea is described and related to ecological conditions. The principal architecture of all species is very similar; adaptations are developed in numerous differences, for instance degree of lignification. All species have inverse leaves, the adaxial side being the stomatous side. In most species, the leaves are resupinate, the lower surface being the adaxial. Theories for the cause of resupination are discussed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 73–90.     

Changing Inner Mongolia: Pastoral Mongolian Society and the Chinese State

Changing Inner Mongolia: Pastoral Mongolian Society and the Chinese State. David Sneath. Oxford: Oxford University Press, 2000. 320 pp.     

Groundwater seepage stimulates the growth of aquatic macrophytes

1. The impact of groundwater seepage on the growth of submerged macrophytes was investigated in experiments on the isoetid Littorella uniflora and the elodeid Myriophyllum alterniflorum both in the laboratory and in the field. Isoetids rely mostly on sediment‐derived CO₂ and nutrients via root uptake, whereas elodeids acquire their inorganic carbon and nutrients from the water column. We thus hypothesised that L. uniflora would respond positively to seeping ground water as it should improve both CO₂ and nutrient supply. 2. Laboratory experiments were conducted by percolating vegetated cores containing natural sediment or technical sand with artificial ground water of high CO₂ concentrations and with either high or low levels of nutrients. Field experiments were conducted in the oligotrophic Lake Hampen, Denmark, with custom‐built seepage‐growth chambers that permitted a near‐natural flow‐through of seeping ground water. Chambers with a solid bottom, and thus no flow‐through of seeping ground water, served as controls in both laboratory and field experiments. In the field, seepage chambers were installed at a site with relatively high seepage fluxes (ground water from forest catchment), at a site with much lower seepage fluxes but with higher nutrient concentrations (ground water from agricultural catchment) and at a reference site with no net discharge or recharge of ground water. 3. Positive growth responses were observed in the field at transects with high groundwater discharge compared to the control chambers with no seepage. No growth response was observed at the reference transect with low or alternating direction of groundwater seepage. The growth rates of L. uniflora in the field were significantly higher in seepage treatments compared to control treatments, and final plant mass was up to 70% higher than that for plants where seepage was excluded. In areas with high groundwater discharge, a strong positive correlation was found between groundwater seepage fluxes, growth rates, and final plant mass for L. uniflora, while there was no such relationship at the reference transect. The growth of M. alterniflorum was also significantly affected by groundwater seepage, but to a lesser degree than L. uniflora. Laboratory experiments generally showed the same trend for both L. uniflora and M. alterniflorum, and the positive influence of seeping ground water was apparently related to increased inorganic carbon supply and, to a lesser degree, improved nutrient availability. 4. Groundwater discharge results in enhanced growth of isoetids and to some extent elodeids inhabiting a groundwater‐fed softwater lake. We propose that the shallow dense vegetation present where most of the discharge takes place acts as a biological filter that retains nutrients that otherwise would end up in the water column and could result in increased algal growth.     

Surface movement rates of the New Zealand flatworm Artioposthia triangulata: potential for spread by active migration

Movement rates for the surface activity of the New Zealand flatworm Artioposthia triangulata (Dendy) (Tricladida: Terricola) were estimated under semi-field conditions in the Faroe Islands. The distance travelled during 10 consecutive 1-minute periods per individual was measured from mucus trails left behind as the flatworms moved over black plastic sheeting sprayed with fine droplets of water. Adult specimens were found to crawl at rates of up to 28 cm min^-1 (almost 17m h^-1), whereas juveniles crawled at rates of between 3 and 4cm min^-1 (approximately 2m h^-1). This study provides the first data concerning the potential for species spread by active migration.