Nutrient conservation strategies in native Andean‐Patagonian forests

Abstract. Nutrient conservation in vegetation affects rates of litter decomposition and soil nutrient availability. Although resorption has been traditionally considered one of the most important plant strategies to conserve nutrients in temperate forests, long leaf life‐span and low nutrient requirements have been postulated as better indicators. We aimed at identifying nutrient conservation strategies within characteristic functional groups of NW Patagonian forests on Andisols. We analysed C‐, N‐, P‐, K‐ and lignin‐concentrations in mature and senescent leaves of ten native woody species within the functional groups: broad‐leaved deciduous species, broad‐leaved evergreens and conifers. We also examined mycorrhizal associations in all species. Nutrient concentration in mature leaves and N‐ resorption were higher in broad‐leaved deciduous species than in the other two functional groups. Conifers had low mature leaf nutrient concentrations, low N‐resorption and high lignin/N ratios in senescent leaves. P‐ and K‐resorptions did not differ among functional groups. Broad‐leaved evergreens exhibited a species‐dependent response. Nitrogen in mature leaves was positively correlated with both N resorption and soil N‐fertility. Despite the high P‐retention capacity of Andisols, N appeared to be the more limiting nutrient, with most species being proficient in resorbing N but not P. The presence of endomycorrhizae in all conifers and the broad‐leaved evergreen Maytenus boaria, ectomycorrhizae in all Nothofagus species (four deciduous, one evergreen), and cluster roots in the broad‐leaved evergreen Lomatia hirsuta, would be possibly explaining why P is less limiting than N in these forests.     

Spectral composition of shade light in coastal-zone oak forests in SE Bulgaria,and relationships with leaf area index: a first overview

Major knowledge gaps exist with respect to light-quality regimes in the coastal-zone Strandzha Quercus frainetto (Q.f.) forest region adjoining the southern Bulgarian Black Sea. This paper presents preliminary results that help narrow these gaps. In conjunction with leaf area index (LAI) field campaigns we undertook measurements with an array of 7 broad-band (ca 40 nm) sensors covering the range 0.40–0.94 μm, plus 1 sensor for UVB (0.297 μm peak) and 1 for photosynthetically active radiation (PAR). Measurements focused on inside-forest shade conditions at sites 0 to ca 15 km from the Black Sea and at altitudes up to ca 120 m above sea level. Some of the sites were also studied using a high-resolution spectroradiometer. A sequential measuring strategy was necessary. This involves potentially large uncertainties, here addressed through estimations of the variability around the sinusoidal course of daylight. Light-quality regimes were found to be in general support of earlier studies of deciduous forests. Our data from the broad-band sensors and from the spectroradiometer are mutually supportive. They indicate a stronger red-shift below Q.f. canopies than below canopies in enclaves dominated by Fagus orientalis and Pinus sylvestris. Transmission in the range 0.50–0.55 μm increases beneath the three types of canopies, most pronounced in the Q.f. case. Analysis of relationships between the inside-forest to open-field irradiance ratio and LAI supports the use of Beer’s Law. We found a fairly strong relationship between the red (0.66 μm) to far-red (0.73 μm) irradiance ratios (R/FR) and LAI for the Q.f. forest. In quantitative terms, the result is new for this Q.f. region, and suggests further research to explore whether a two-sensor approach (0.66 and 0.73 μm) might offer possibilities for further low-cost mapping of the spatio-temporal patterns of R/FR and LAI in Strandzha. Such mapping would assist in further studies of the region’s forest biogeochemistry and vitality.     

Environmental regulation of surface conductance for evaporation from vegetation

We examine conductances for evaporation from both vegetation and soil in response to environmental variables. Data from a vertically-structured pristine forest of Nothofagus are presented as an example of the effects of biodiversity on the scaling of conductances between tiers of plant organisation. Available data sets of maximum leaf stomatal conductances (g _lmax ) and bulk vegetation surface conductances (G _smax ) are compared. Overall, the ratio G _smax /g _lmax is consistently close to 3 for seven major vegetation types of diverse structure. An analytical model accounts for this close relationship, and in particular how G _smax is conservative against changes in leaf area index because of the compensating decrease in plant canopy transpiration and increase in soil evaporation as leaf area index diminishes. The model is also successfully tested by comparison with canopy conductances of emergent trees measured in the Nothofagus forest. The constraint of vegetation surface conductance and evaporation via environmental regulation by irradiance, air saturation deficit and root zone water supply are discussed.     

Fluid replacement following dehydration reduces oxidative stress during recovery

To investigate the effects of hydration status on oxidative DNA damage and exercise performance, 10 subjects ran on a treadmill until exhaustion at 80% VO_2max during four different trials [control (C), 3% dehydration (D), 3% dehydration + water (W) or 3% dehydration + sports drink (S)]. Dehydration significantly decreased exercise time to exhaustion (D < C and S). Plasma MDA levels were significantly higher at pre-exercise in D than C. Plasma TAS was significantly lower at pre-exercise in C and S than in D, and was significantly lower in S than D at 60 min of recovery. Dehydration significantly increased oxidative DNA damage during exercise, but fluid replacement with water or sports drink alleviated it equally. These results suggest that (1) dehydration impairs exercise performance and increases DNA damage during exercise to exhaustion; and (2) fluid replacement prolongs exercise endurance and attenuates DNA damage.     

Cephalidiosus: A replacement name for Stenotrachelus (Hemiptera: Tingidae)

Cephalidiosus is proposed as a replacement name for Stenotrachelus Guilbert, a genus of Tingidae from New Caledonia. New combinations are Cephalidiosus megapharsus (Guilbert) and Cephalidiosus mesopharsus (Guilbert).     

Gas exchange and resource-use patterns along a Mediterranean successional gradient

Abstract. Gas exchange, leaf-nitrogen concentration and water potential were measured in early and late spring in early successional herbaceous plants occurring after cutting and after fire, and in mature woody species from the Mediterranean climax community Quercetum ilicis in central Italy. Net photosynthesis peaked in early spring in all species studied when values for temperature and light were lower but leaf-nitrogen content was higher as compared to late spring, suggesting that nitrogen more than energy input controlled photosynt-hetic rates. Herbaceous pioneer species occurring after cutting showed higher field photo synthetic capacity than evergreen climax trees and shrubs. By contrast, net photosynthesis of herbaceous species occurring in a persistent stage after fire, was in the same range as that of climax trees. This evidence suggests that carbon-gaining appears to be partly related to the dynamic stage of succession and not solely to the growth form.     

Distribution and microhabitats of native and non-native gammarids (Amphipoda, Crustacea) in Brittany, with particular reference to the endangered endemic sub-species Gammarus duebeni celticus

Aim  To assess temporal changes in gammarid distribution in Brittany and microhabitat-use overlap between the endangered endemic Gammarus duebeni celticus Stock & Pinkster, 1970 , the expanding natives G. pulex (Linnaeus, 1758) and Echinogammarus berilloni (Catta, 1878), and the introduced G. tigrinus Sexton, 1939.
Location  Brittany and adjacent regions in western France.
Methods  The spatial and temporal patterns in distribution of gammarids at the scale of Brittany were studied using 351 sites. Longitudinal distributions (from the source to the estuary of the river) and microhabitat-use (substratum type and water velocity) were also considered in selected rivers.
Results  At the regional scale, all species occurred together less often than expected statistically, with significant deviations from expected for G. pulex vs. both G. duebeni celticus and G. tigrinus , and for E. berilloni vs. both G. duebeni celticus and G. tigrinus . However, at the microhabitat scale, E. berilloni occurred significantly more often than expected with the endemic G. duebeni celticus , and this appears to be due to similar substratum and water velocity preferences, although at both the regional and microhabitat scales E. berilloni prefers wider streams than G. duebeni celticus . This study reveals a decline in the endangered G. duebeni celticus since 1970.
Main conclusions  The longitudinal and local distributions of G. duebeni celticus , and the higher-than-expected co-occurrence of the species with G. pulex , suggest that the decline of the endemic species may be due to changes in the environment and/or interference from native G. pulex , which is expanding its range in Brittany. The results are discussed as regards to the consequences for regional biodiversity.     

The population dynamics of Cheilosia fasciata (Diptera,Syrphidae): significance of environmental factors and behavioural adaptations in a phytophagous insect

Summary A population of Cheilosia fasciata Schin. & Egg., 1853 was studied in a beech forest (Melico-Fagetum allietosum) near Göttingen (FRG). This syrphid species is closely associated with ramson (Allium ursinum L.), as the larvae mine the plant's leaves. Adult abundance was determined using emergence traps (1981–1986); egg and larval abundance was determined by examining ramson leaves: puparia were extracted from soil samples (1984 and 1986). Cheilosia fasciata is a univoltine species; the imagines emerge in late April/early May. Larval development took five (1986) to six (1984) weeks. In late June/early July the larvae enter the soil for pupariation. A linear relationship was found between the area of the mines and larval biomass (dry wt.). It was concluded that one larva had to mine 51.90 cm² of leaf area in order to gain the mean maximum dry weight (11.15 mg). Furthermore, it was shown that ovipositing females, laying just one egg per leaf, tended to select large leaves providing this minimum amount of food. It is hypothesized that females probably follow straight-lined routes on their oviposition flights, rather than ovipositing on leaves chosen at random. By applying such a strategy, females can almost completely avoid competition for food among their own offspring. Furthermore, competition among the progeny of the whole population is also reduced, particularly in years when adult abundance is very low. The significance of certain factors influencing the population dynamics of Cheilosia fasciata was evaluated by applying a rank correlation analysis. It was shown that high precipitation rates in April reduced the time available for mating and oviposition resulting in low emergence abundance in the next spring. Larval survivorship was enhanced by high precipitation rates in May and June, indicating that drought may be unfavourable to larvae and reduce food availability. Predation by a parasitoid Phygadeuon ursini Horstmann, 1986 (Hymenoptera, Ichneumonidae), appears to be just an imperfect (Milne 1984) density-dependent control mechanism; in fact, it was shown that food limitation is the only significant mechanism of density-dependent population control.     

Leaf water relations and anatomy of a tropical rainforest tree species vary with crown position

Summary Leaf water potentials, osmotic properties and structural characteristics were examined in the Australian tropical rainforest tree species, Castanospermum australe. These features were compared for individuals growing in the understorey and canopy of the undisturbed forest and in an open pasture from which the forest had been cleared. Leaf water potentials during the day declined to significantly lower values in the open-grown and canopy trees than in the understorey trees. During most of the day the opengrown tree experienced the lowest water potentials. These differences were paralleled by significant differences in tissue osmotic properties. The tissue osmotic potential at full hydration was lowest in the open-grown tree (-1.80 MPa), intermediate in the canopy trees (-1.38 MPa), and highest in the understorey trees (-0.80 MPa). As a result, the degree to which high and positive turgor pressures were maintained as water potentials declined was highest in the open-grown tree, intermediate in the canopy trees, and lowest in the understorey trees. The differences in tissue osmotic properties between individuals in the three crown positions were paralleled, in turn, by differences in leaf structual characteristics. Relative to leaves of the canopy and open-grown trees, leaves of the understorey trees had significantly larger epidermal cells with thinner cell walls, larger specific leaf areas and turgid weight: dry weight ratios, and a higher proportion of intercellular air space.Abbreviations ₁ Leaf tissue water potential - _min Lowest value of ₁ during the day ( noon) - _{P=0 1} zero turgor - R Relative water content - P Tissue turgor pressure - Tissue osmotic potential - ₀ at full hydration     

Cotransformation of Aspergillus nidulans: a tool for replacing fungal genes

Summary When a non-selected DNA sequence was added during the transformation of amdS320 deletion strains of Aspergillus nidulans with a vector containing the wild-type amdS gene the AmdS⁺ transformants were cotransformed at a high frequency. Cotransformation of an amdS320, trpC801 double mutant strain showed that both the molar ratio of the two vectors and the concentration of the cotransforming vector affected the cotransformation frequency. The maximum frequency obtained was defined by the gene chosen as selection marker for transformation. Cotransformation was used to induce a gene replacement in A. nidulans. An amdS320 strain was transformed to AmdS⁺ and cotransformed with a DNA fragment containing a fusion between a non-functional A. nidulans trpC gene and the Escherichia coli lacZ gene. Ten AmdS⁺, LacZ⁺ transformants with a Trp^– mutant phenotype were selected. All of these strains could be transformed with a functional copy of the A. nidulans trpC gene, but only two strains yielded TrpC⁺ transformants which, with a low frequency, had a LacZ^– phenotype. These latter transformants had also lost the AmdS⁺ phenotype. Southern blotting analysis of DNA from these transformants confirmed the inactivation of the wild-type trpC gene, but revealed that amdS vector sequences were also involved in the gene replacement events.