Growth and nitrate uptake properties of plants grown at different relative rates of nitrogen supply. II. Activity and affinity of the nitrate uptake system in Pisum and Lemna in relation to nitrogen availability and nitrogen demand

Abstract Net nitrate uptake rates were measured and the kinetics calculated in non-nodulated Pisum sativum L. cv. Marma and Lemna gibba L. adapted to constant relative rates of nitrate-N additions (R_A), ranging from 0.03 to 0.27 d^?1 for Pisum and from 0.05 to 0.40 d^?1 for Lemna, V_max of net nitrate uptake (measured in the range 10 to 100 mmol m^?3 nitrate, i.e. ‘system I’) increased with R_A in the growth limiting range but decreased when R_A exceeded the relative growth rate (RGR), K_m was not significantly related to changes in R_A. On the basis of previous ¹³N-flux experiments, it is concluded that the differences in V_max at growth limiting R_A are attributable to differences in influx rates. Linear relationships between V_max and tissue nitrogen concentrations were obtained in the growth limiting range for both species, and extrapolated intercepts relate well with the previously defined minimal nitrogen concentrations for plant growth (Oscarson, Ingemarsson & Larsson, 1989). Analysis of V_max for net nitrate uptake on intact plant basis in relation to nitrogen demand during stable, nitrogen limited, growth shows an increased overcapacity at lower R_A values in both species, which is largely explained by the increased relative root size at low R_A. A balancing nitrate concentration, defined as the steady state concentration needed to sustain the relative rate of increase in plant nitrogen (R_N), predicted by R_A, was calculated for both species. In the growth limiting range, this value ranges from 3.5 mmol m^?3 (R_A 0.03 d^?1) to 44 mmol m^?3 (R_A 0.21 d^?1) for Pisum and from 0.2 mmol m^?3 (R_A 0.05 d^?1) to 5.4 mmol m^?3 (R_A 0.03 d^?1) for Lemna. It is suggested that this value can be used as a unifying measure of the affinity for nitrate, integrating the performance of the nitrate uptake system with nitrate flux and long term growth and demand for nitrogen.     

Leaf age and larval performance of the leaf beetle Paropsis atomaria

ABSTRACT.

• 1 Larval performance of the leaf beetle Paropsis atomaria Oliver was determined for larvae raised on both new and mature leaves of Eucalyptus blakelyi Maiden. Larvae were transferred to mature leaves at different ages; control larvae stayed on new leaves through all instars.
• 2 Only larvae reared on new leaves through the third instar survived to pupate on mature leaves; developmental time was prolonged by 20% and pupal weight was reduced by 50% in these larvae compared with larvae reared entirely on new leaves. Almost all larvae died when transferred to mature leaves as first, second or third instars.
• 3 Low survival and slow development on mature leaves was mainly due to failure by larvae to feed. Larvae palpated leaves and could discriminate among leaf ages immediately, without biting into the leaf tissue.
• 4 New leaves had higher concentrations of oil and tannins than old leaves, while there were no significant differences in nitrogen concentrations in the two types of leaves. Mature leaves were more than 3 times tougher than new leaves, in terms of g mm^?2 of penetrometer force.
• 5 In drought years E. blakelyi may not produce sufficient new leaves to supply specialist herbivores with their preferred food resource. We infer that drought years reduce P. atomaria larval performance significantly, and influence the population dynamics of the insect.

     

Oviposition choice and larval survival of Dasineura marginemtorquens (Diptera: Cecidomyiidae) on resistant and susceptible Salix viminalis

Abstract.

• 1 Substantial intraspecific variation exists in Salix viminalis resistance to the gall midge Dasineura marginemtorquens. Earlier work has found this variation to have a large genetic component. Willow clones are stable in their resistances between midge generations and different nutrient levels in both field and laboratory culture.
• 2 This study reports the results of laboratory experiments on female oviposition choice and larval survival on potted plants from clones that are very different in resistance as determined in field studies.
• 3 In choice experiments using pairs of plants, the average female midge did not prefer susceptible willow clones over resistant ones for oviposition. In about one third of the replicates, midges actually laid more eggs on the resistant clone. Further work is necessary to examine the nature of variation among midges in discrimination of these plant types.
• 4 Resistance is manifested as great differences in larval survival. Six days after oviposition survival was 92% on susceptible plants but only 6% on resistant ones. Galls developed on all of the susceptible plants, while in 73% of the resistant plants galls were not even initiated.
• 5 The plant traits causing resistance are enigmatic. Larval behaviour suggests that resistant plants interfere with feeding behaviour. On resistant plants, most larvae wander for more than 24 h without initiating any galls before dying. On susceptible plants many first instar larvae begin feeding and initiate galls within this period.

     

Life history, growth and production of Mysis relicta in the large, fiord-type Lake Mjøsa, Norway

SUMMARY.

• 1 Biomass, production and life history of Mysis relicta were studied in the large Lake Mjøsa during the years 1976–80. Biomass fluctuations were large, but biomass averaged about 1 g wet wt m^?2 or 200 ind. m^?2. Cumulative net production during summer ranged from 1.6 to 2.1 g wet wt m^?2. Mean population P/B-ratio was close to 2.
• 2 Neither production or biomass of Mysis were correlated with the biomass of phytoplankton or the main Zooplankton prey species (Daphnia and Bosmina), suggesting a predominant ‘top down’ control of Mysis in this lake.
• 3 The life cycle was well synchronized with development of food items, but predation pressure also affected life-history patterns. The proportion of juveniles apparently increased in years with strong fish predation pressure, producing a predominantly 1-year life-cycle pattern the following year.
• 4 Mysis had a predominant 2-year life history, but a traction of the population may reproduce after 1 or 3 years. Reproduction occurred exclusively during winter. Even in such a large and stable system, where Mysis has coexisted with its main food items and predators for 8–10 000 years, a flexible life history is maintained and is probably an important buffer against year-to-year fluctuations in food and predator abundance.

     

Photosynthetic Nitrogen Metabolism in High and Low CO2-adapted Scenedesmus: I. INORGANIC CARBON-DEPENDENT O2 EVOLUTION, NITRATE UTILIZATION AND NITROGEN RECYCLING

Larsson, M., Larsson, C.-M. and Guerrero, M. G. 1985. Photosyntheticnitrogen metabolism in high and low CO₂-adapted Scenedesmus.I. Inorganic carbon-dependent O2 evolution, nitrate utilizationand nitrogen recycling.—J. exp Bot. 36: 1373–1386 Scenedesmus obtusiusculus Chod. was grown on an inorganic mediumflushed with either air or air supplemented with 3% CO₂. Inair-grown cells, O₂ evolution dependent on low, but not high,HCO^–₃ concentrations was strongly inhibited by the carbonicanhydrase inhibitor acetazolamide. Cells grown with 3% CO² exhibitedlow rates of O2 evolution at low external inorganic C; however,after 30 min in air O2 evolution rates at low inorganic C approachedthose of air-grown cells. These results are compatible withthe view that Scenedesmus develops a ‘CO² concentratingmechanism’ in air, with carbonic anhydrase as an importantconstituent When 3% CO²-grown cells were subjected to air-level of CO²,just a transient decline in NO^–₃ utilization was observed,but in the presence of acetazolamide the rate of the processdecreased drastically in response to the decrease in the CO²level. In CO²-free air NO₃^– was taken up at high ratesbut in a deregulated manner, leading to release of NH₄⁺. A portionof the NO₃^– taken up in the absence of CO² was apparentlyassimilated Cellular nitrate reductase (NR) activity initially decreasedbut subsequently recovered after a transition from 3% CO² toair. In the presence of acetazolamide, a persistent decreasein NR activity was observed. Cellular glutamine synthetase (GS)activity increased after transition from 3% CO² to air, theactivity increase being unaffected by acetazolamide. NH₄⁺ releaseto the medium in the presence of L-methionine-D, L-sulphoximine(MSO) transiently increased in 3% CO²-grown cells in responseto a transfer to air. MSO-induced NH₄⁺ release was in fact higherin air-grown cells than in 3% CO²-grown cells. Glycollate wasinitially released after transition from 3% CO² to air, butthere was no difference in glycollate release between MSO-treatedand untreated cells. In air-adapted Scenedesmus, N recyclingseems to be of minor importance in comparison to primary N assimilation Key words: CO²-fixation, N recycling, nitrate uptake, Scenedesmus     

Photosynthetic Nitrogen Metabolism in High and Low CO2-adapted Scenedesmus: II. EFFECT OF AMMONIUM AND METHIONINE SULPHOXIMINE ON NITRATE UTILIZATION

Larsson, C.-M., Larsson, M. and Guerrero, M. G. 1985. Photosyntheticnitrogen metabolism in high and low CO²-adapted Scenedesmus.II. Effect of ammonium and methionine sulphoximine on nitrateutilization.—J. exp. Bot. 36: 1387–1395 In 3% CO²-grown Scenedesmus obtusiusculus Chod. utilizing NO₃^–J as the N source, NH₄⁺ addition caused a prompt inhibitionof NO₃^– utilization. Nitrate reductase (NR) activity declinedrapidly in response to the presence of NO₄⁺, but the cessationof NO₃^– utilization was too rapid to be accounted forby the loss in NR activity. The first site of NO₄⁺ inhibitionin these cells seems to be the entrance of NO₃^– into thecells. Upon exhaustion of NO₄⁺ from the medium, NO₃^– utilizationwas rapidly restored and NR activity increased. Air-grown cellswere much less sensitive to the effect of NO₄⁺, more than 30min being required for added NO₄⁺ to cause complete inhibitionof NO₃^– utilization. In these cells, NO₃^– uptakeand NR activity decreased in parallel in response to NO₄⁺ addition.In 3% CO²-grown cells simultaneously subjected to NO₄⁺ and air-levelof CO², NO₄⁺ initially inhibited NO₃^– utilization completely,but a slight recovery took place after approximately 20 min The glutamine synthetase (GS) inhibitor L-methionine D, L-sulphoximine(MSO) behaved as a potent inhibitor of NO₃^– uptake in3% CO²-grown cells, but had considerably less effect in air-growncells, although the time-course of the MSO-induced inhibitionof GS was the same in both cases Key words: Ammonium, nitrate utilization, Scenedesmus     

Description of Chytridiopsis Trichopterae N. Sp. (Microspora, Chytridiopsidae), A Microsporidian Parasite of the Caddis Fly Polycentropus Flavomaculatus (Trichoptera, Polycentropodidae), With Comments On Relationships Between the Families Chytridiopsidae and Metchnikovellidae

ABSTRACT. The microsporidium Chytridiopsis trichopterae n. sp., a parasite of the midgut epithelium of larvae of the caddis fly Polycentropus flavomaculatus found in southern Sweden, is described based on light microscopic and ultrastructural characteristics. All life cycle stages have isolated nuclei. Merogonial reproduction was not observed. the sporogony comprises two sequences: one with free spores in parasitophorous vacuoles, the other in spherical, 5.6-6.8 μm wide, sporophorous vesicles which lie in the cytoplasm. the free sporogony yields more than 20 spores per sporont. the vesicle-bound sporogony produces 8, 12 or 16 spores. the envelope of the sporophorous vesicle is about 82 nm thick and layered. the internal layer is the plasma membrane of the sporont; the surface layer is electron dense with regularly arranged translucent components. Both spore types are spherical. They have an ～ 35-nm thick spore wall, with a plasma membrane, an electron-lucent endospore, and an ～ 14-nm thick electron-dense exospore. the polar sac is cup-like and lacks a layered anchoring disc. the polar filament is arranged in two to three isofilar coils in the half of the spore opposite the nucleus. the coupling between the polar sac and the polar filament is characteristic. the surface of the polar filament is covered with regularly arranged membraneous chambers resembling a honeycomb. There is no polaroplast of traditional type. the cytoplasm lacks polyribosomes. the nucleus has a prominent, wide nucleolus. the two spore types have identical construction, but differ in dimensions and electron density. Free living spores are about 3.2 μm wide, the diameter of the polar filament proper is 102-187 nm, the chambers of the honeycomb are 70-85 nm high, and the polar sac is up to 425 nm wide. Living spores in the vesicle-bound sporogony are about 2.1 μm wide, the polar filament measures 69-102 nm, the chambers of the honeycomb are about 45 nm high, and these spores are more electron dense. Comparisons of cytology (especially the construction of the spore wall and the polar filament and associated structures) and life cycles reveal prominent differences among the Chytridiopsis-like microsporidia, and close relationships between the families Chytridiopsidae and Metchnikovellidae.     

The Effect of Phytohormones on Chlorophyll(ide), Protochlorophyll(ide) and Carotenoid Formation in Greening Dark Grown Wheat Leaves

The influence of phytohormones on chlorophyll and carotenoid formation during the greening of irradiated dark grown wheat leaves (Triticum aestivum L. cv. Starke II Weibull) was studied. Leaves were floated on solutions of abscisic acid, gibberellic acid and kinetin for 24 h. The chlorophyll and carotenoid contents were determined during a subsequent period of 48 h of continuous irradiation. Leaves treated with abscisic acid showed a longer lag phase and a lower rate of accumulation of chlorophyll as compared to the control than did leaves treated with gibberellic acid and kinetin. The carotenoid content was low both in leaves treated with abscisic acid and in those treated with gibberellic acid. Treatment with abscisic acid lowered the protochlorophyllide regeneration after a saturating light flash while gibberellic acid as well as kinetin had no effect. The influence of ABA was partly dependent on an increase of the wounded part of the cut leaf segments. The accumulation of protochlorophyllide in leaves treated with δ-aminolevulinic acid was not affected by the different hormonal treatments. These results suggest that the main effect of abscisic acid is probably outside the chloroplast, i.e. on the formation or transport of δ-aminolevulinic acid.     

Spatially patterned guild structure in larval parasitoids of cyclically outbreaking winter moth populations

1. Wide temporal fluctuations in host abundance are a potential source of instability and stochasticity in the spatiotemporal population dynamics of associated parasitoid species. Within parasitoid guilds (i.e. parasitoids with similar modes of host utilisation), a conceivable outcome is guild organisation according to a lottery model, in which guild members attain local dominance by colonising previously emptied habitats during increasing host density, before other guild members. In the spatial dimension, an expected manifestation of such dynamics is variable guild structure even across homogeneous habitats. 2. We examined the extent of large‐scale spatial patterning of guild characteristics in larval parasitoid wasps associated with cyclically outbreaking populations of the geometrid moth Operophtera brumata in northern Fennoscandia. The study was performed at the onset of the crash‐phase of the geometrid's outbreak cycle, along a 70‐km transect in costal northern Norway, characterised by largely homogeneous environmental conditions, except for a small climatic gradient. 3. There was a distinct large‐scale spatial turnover in dominance among the major parasitoid groups (i.e. guild structure) in O. brumata along the transect, whereas the total prevalence rate of the guild and its diversity showed no consistent variation. Guild structure was unrelated to host density. 4. Although group‐specific responses to a slight spatial climatic gradient cannot be rejected as a causal mechanism, we conclude that our results are consistent with the expectation from large‐scale stochastic extinction‐recolonisation dynamics among functionally equivalent parasitoids relying on a host with strongly cyclic population fluctuations.     

Wolf Movement Patterns: a Key to Estimation of Kill Rate?

Abstract: To estimate wolf (Canis lupus) kill rates from fine-scale movement patterns, we followed adult wolves in 3 territories of the Scandinavian wolf population using Global Positioning Systems (GPS) during the winters of 2001–2003. The resulting 6 datasets of 62–84 study days gave a total of 8,747 hourly GPS positions. We visited clusters of positions in the field on average 8.8 days after positioning and found moose (Alces alces) killed by wolves during the study period on 74 (8%) of the 953 clusters. The number of positions and visits to a cluster, their interaction, and the proportion of afternoon positions were significant fixed effects in mixed logistic-regression models predicting the probability of a cluster containing a wolf-killed moose. The models, however, displayed a poor goodness-of-fit and were not a suitable tool for estimating kill rates from positioning data alone. They might be used to reduce fieldwork by excluding unlikely clusters, although the reduction was not substantial. We discuss proximate factors (i.e., human disturbance and access to prey) as well as ultimate factors (i.e., social organization, intra-guild dominance, and litter size) as potential causes of the observed high temporal and spatial variation in prey-handling. For similar future kill-rate studies, we recommend increasing field efforts and shortening positioning intervals.