Removal of nitrogen during needle senescence in Scots pine (Pinus sylvestris L.)

The concentrations of arginine, protein and total nitrogen (N) and the abundance of¹⁵N were measured in 3-and 4-year-old needles of Scots pine trees fertilized with either 0 (C), 36 (N1) or 73 (N2) kg N ha^-1 year^-1 annually for 22 years (average doses of N). Remaining green needles and needles that were shed were compared and removal of N from total, protein and arginine pools was calculated. Earlier investigations had shown that high arginine concentrations are found in needles of trees that have an excessive N supply (Näsholm and Ericsson 1990). This study aimed to elucidate the fate of the accumulated arginine during needle senescence. It was speculated that a low removal of arginine during senescence would implicate that the primary function of arginine is in N detoxification and not in N storage. Moreover, litter quality would be altered if needles are shed with high concentrations of arginine and this might affect the turnover of N in forest ecosystems. In remaining green needles, the concentration of total N increased with increasing N supply. Protein N concentrations were higher in fertilized trees, but did not differ between the two N treatments. Arginine N was low in C and N1 trees but high in N2 trees. Senescent needles from C and N1 trees had about equal total N concentrations while in N2 trees this concentration was significantly higher. Protein N in senescent needles did not differ between treatments. Arginine N, however, was less than 0.1 mg g^–1 dw in C and N1 trees but was higher than 1.5 mg g^–1 dw in N2 trees. Removal of N was highest in N1 trees followed by C trees while N2 trees removed least N from senescing needles. The high concentration of total N in senescent needles from N2 trees was to a great extent explained by a high arginine concentration.The ¹⁵N value of remaining, green needles was higher (less negative) in N2 trees than in C and N1 trees. The same pattern was found for senescent needles. Comparisons of ¹⁵N values between remaining, green and senescent needles within each treatment showed a significant increase in ¹⁵N for all treatments during senescence possibly indicating losses of N as NH₃ (g) from needles during senescence. It is concluded that arginine, accumulated in response to high N supply, is retranslocated only to a small extent during needle senescence. The ecological and physiological implications of this finding are discussed.     

Seasonal changes in the utilization and turnover of assimilation products in 8-year-old Scots pine (Pinus sylvestris L.) trees

Summary The present study aimed at a physiological understanding of the seasonal changes of the carbohydrate patterns and levels in the various tissues of 8-year-old Scots pine (Pinus sylvestris L.) trees growing under ambient climatic conditions in the botanical garden at Bayreuth. The photosynthates of selected twig sections were labelled by ¹⁴CO₂ fixation and after chase periods of 1 h up to 8 months, the distribution of radiocarbon in the whole trees was determined and the labelling of identified carbohydrates was compared with the levels of these compounds in the individual tissues. Bud break and sprouting in spring is exclusively supplied by the recent photosynthates of the previous year's needles. During summer assimilates of the old needles were utilized for secondary growth of the axial system while growth of the recent-year's shoots was supported by their own photosynthesis. In autumn, soluble carbohydrates were produced instead of starch, a major part of which in addition to recent photosynthates was utilized for root growth during the cold season. Another part of the autumnal storage material was incorporated into the cell walls of the latest xylem and phloem elements still in winter. A pronounced starch-oligosaccharide interconversion upon frost hardening, and its reversal in spring as has been described for deciduous trees, could not be observed. This was due to maintenance of photosynthetic capability even in the cold season and the replacement of consumed storage material especially in late winter and early spring by new photosynthates.     

Non-random needle orientation in 1-year-old Scots pine (Pinus sylvestris L.) seedlings when adjacent to non-shading vegetation

Summary Two experiments were performed to test needle architecture of Scots pine (Pinus sylvestris L.) seedlings when affected by non-shading neighbouring vegetation. Both experiments showed that seedlings reacted to the presence of such adjacent vegetation by changes in needle distribution around the main stem: more needles were found on the opposite side of the main stem to where the vegetation was located. However, this reaction was confined to needles from the main stem. Responses of seedlings to dead neighbours differed from the response to live neighbours and also from the response to a black curtain substituted for plant neighbours. It is suggested that reactions are mediated by the red/far red ratio of incident light.     

The fate and path of assimilation products in the stem of 8-year-old Scots pine (Pinus sylvestris L.) trees

Summary ¹⁴CO₂ at ambient concentration was administered to a section of an upper branch of 8-year-old Scots pines and the import of radiocarbon into the stem and roots was determined after various chase periods. ¹⁴CO₂ fixation was performed in October when export of carbon into the stems and roots was maximal. In the short-term experiments the trees were harvested 1 h, 2 days and 5 days after a 3-h ¹⁴C pulse, while chase periods of 5 or 8 months were used in the long-term experiments. Loss of ¹⁴C was initially substantial, and even after a 5-day chase had not come down to a rate which indicated decrease only by respiration. After 5 days, more than 10% of the recovered radiocarbon (53% of the ¹⁴C translocated into the stem) had entered the roots and approximately the same amount was found in the stem. Extension of the chase period beyond 5 months did not result in a further significant loss of ¹⁴C by respiration, and the bulk of the label could be localized in the cell-wall fraction. No substantial redistribution of radiocarbon prior and subsequent to the formation of the new shoots could be observed, thus indicating that the stored material was utilized for thickening the stem and roots. Radioautography of stem cross-sections revealed a narrow helical strip of ¹⁴C from the feeding branch to the root in the phloem region. In the tree harvested after bud break the utilization of the ¹⁴C-labelled material stored in the stem for the production of the first layers of earlywood and the corresponding phloem was apparent.     

Photoreactivation of the UV light effects on growth of Scots pine (Pinus sylvestris L.) seedlings

Summary Ultraviolet-B light (UV-B) and ultraviolet-A light (UV-A) at higher doses exert a strong inhibitory (toxic) effect on axis growth in Scots pine (Pinus sylvestris L.) seedlings. This effect is unrelated to control of growth rate by phytochrome. Rather, after a toxic UV dose growth of the pine seedling no longer responded to phytochrome. Both, the effect of UV-B as well as the inhibiting effect of UV-A could be photoreactivated by blue light (B). The action of UV-A was 2 fold: (i) it exerted a toxic effect which could be photoreactivated by B, and (ii) applied after UV-B it photoreactivated to some extent the toxic UV-B effect. Obviously, the UV-A range causes a toxic effect, and at the same time is capable of photoreactivating the toxic UV effect. At higher doses the toxic effect prevails.     

Nitrogen uptake in needles of Scots pine (Pinus sylvestris L.) when exposed to gaseous ammonia and ammonium fertilizer in the soil

Young saplings of Pinus sylvestris L. were exposed to gaseous NH₃ at 53 or 105 g m^–3 for one year in open-top chambers. Saplings received ¹⁵N-labelled (NH₄)₂SO₄ via the soil. To examine the importance of foliar N uptake, changes in the concentration of total and labelled N in the needles were followed. Increase in needle biomass and N concentration were found in trees exposed to NH₃, confirming that atmospheric NH₃ acted as a N fertilizer. NH₃ had a greater and quicker effect than (NH₄)₂SO₄: compared with the growth in ambient air, the N concentration in the needles exposed to NH₃ had increased by 49% in four months, while the increase after highest N-fertilization (200 kg N ha^–1 y^–1) was only 8%. The small contribution of NH₄ ⁺ fertilization to the total N concentration was not due to a deficient N uptake: the ¹⁵N concentration in the needles increased significantly with time. On the other hand, NH₃ uptake in shoots may have a negative effect on the NH₄ ⁺ root uptake. The relation between plant N and atmospheric NH₃ concentration was non-linear and possible reasons for this observation are discussed. Fumigation with NH₃ significantly decreased the ratios of K/N and P/N, showing that fumigation disrupted the nutrient balance.     

Concentrations of terpenes in mycorrhizal roots of Scots pine (Pinus sylvestris L.) seedlings grown in vitro

The effect of Paxillus involutus, Laccaria laccata, Suillus luteus, S. bovinus, Hebeloma crustuliniforme and a strain of the ectendomycorrhizal fungus Mrg X (Ascomycotina) on the content of volatile organic compounds in roots of Pinus sylvestris seedlings grown in vitro was investigated. Volatile compounds extracted with a supercritical fluid extraction were primarily terpenes and sesquiterpenes and qualitatively were the same in roots of mycorrhizal and nonmycorrhizal plants. The major monoterpenes were α-pinene, Δ³-carene and β-pinene. Inoculation of plants with the fungi resulted in statistically non-significant increases in the total amount of the volatiles. The mycorrhizal fungi showed diversified effect on the concentrations of several terpenoids.     

Effects of elevated CO2 and temperature on secondary compounds in the needles of Scots pine (Pinus sylvestris L.)

The aim of this study was to evaluate the long-term effects of elevated CO₂ concentration (doubling of ambient CO₂ concentration) and temperature (2–6°C elevation) on the concentration and content of secondary compounds in the needles of Scots pine (Pinus sylvestris L.) saplings grown in closed-top environmental chambers. The chamber treatments included (1) ambient temperature and CO₂, (2) ambient temperature and elevated CO₂, (3) elevated temperature and ambient CO₂, and (4) elevated temperature and elevated CO₂. The needle sampling and analyses of monoterpenes, HPLC-phenolics and condensed tannins in current- and 1-year-old needles were made in two consecutive years. The results showed that the effects of elevation of CO₂ and temperature were greatest on the monoterpene concentration in the needles while the concentration of HPLC-phenolics remained almost unaffected by the changed growing conditions. Most of the observed decrease in monoterpene concentration was caused by the CO₂ enrichment while the effect of elevated temperature alone was not as significant. The accumulation of condensed tannins tended to increase due to the elevation of CO₂ alone compensating the reduced carbon allocation to monoterpenes. Overall, the responses of the concentrations of secondary compounds to the elevation of CO₂ and temperature are variable and depend strongly on the properties and characteristics of each compound as well as on the interrelation between the production of these compounds and the primary production of trees.     

Assimilation,allocation and utilization of carbon by 3-year-old Scots pine (Pinus sylvestris L .) trees during winter and early spring

 The photosynthetic capacity of frost-hardy and frost-sensitive needles of 3-year-old Scots pines and the allocation and utilization of assimilated carbon was examined during winter and early spring. The photosynthates of the whole trees were labelled by ¹⁴CO₂ fixation and after chase periods of from 7 days to 4 months under natural climatic conditions, the distribution of radiocarbon in the various tissues of the trees was determined. During winter maximal photosynthetic rates of 1-year-old needles were considerably lower than in summer when calculated on a leaf area basis. However, when related to the chlorophyll content these discrepancies disappeared. The decrease of the photosynthetic capacity upon frost-hardening could be attributed to a two- to three-fold reduction in the chlorophyll content of the needles. The pulse-chase experiments showed that photosynthesis during the cold season preferentially provides substrates for respiration. Half of the assimilated ¹⁴C was respired during the first week, and after chase periods of 3 – 4 months the trees contained not more than 10 – 20% of the radiocarbon. The carbon, which was exported by the needles, was translocated basipetally via the twigs and the stem to the roots. Whereas in the axial system incorporation of radiocarbon into storage compounds, like starch, and into cell wall material was almost negligible during the cold season, in the roots one-third of the radiocarbon was recovered from starch 2 months after the ¹⁴C-pulse. In contrast to the above-ground parts of the trees, where starch content was very low during winter, in the roots considerable amounts of starch, up to 450 μmol hexose units · g^– 1 DW, were found even during mid-winter. In early spring the radiocarbon in the cell wall-, lipid-, and starch-fraction accounted for more than 80% of the ¹⁴C recovered at that time from the axial system. Incorporation of minor quantities into the cell wall fraction of the roots during winter and early spring indicate continuous root growth during the cold period as well as in early spring. Whereas during winter the buds did not attract freshly assimilated carbon, in spring just before bud break substantial amounts of carbon were translocated from the needles into the buds. In contrast, remobilization of carbon, which had been assimilated during autumn of the previous year, and import into the sprouting buds could not be demonstrated. Received: 3 November 1995 / Accepted: 1 March 1996     

Abscisic acid in shoots and roots of Scots pine (Pinus sylvestris L.) seedlings grown in controlled long-day and short-day environments

Scots pine (Pinus sylvestris L.) seedlings grown in nutrient solution in controlled-environment chambers were used. The effects of a shortday (SD, early autumn) treatment on growth and the content of free and alkaline hydrolysable abscisic acid (ABA) in shoots and roots were investigated. The weekly relative growth rates of seedlings grown continuously under long-day (LD, summer) conditions were stable at approx. 0.08 g g^–1 d^–1 between weeks four and eight from germination. Weekly relative growth rates of seedlings transferred to SD conditions decreased rapidly to a then stable level of approx. 0.04 g g^–1 d⁰¹. Shoot elongation ceased within two weeks of SD treatment. The content of both free and alkaline hydrolysable ABA was approx. 40–50% higher in shoots of seedlings grown for five weeks in LD plus one week in SD than in shoots of seedlings grown for five or six weeks in LD. Two additional weeks of SD did not change the free ABA content. Three weeks in simulated late autumn (SD but decreased temperatures) and three weeks in simulated winter (lower light intensity and temperature) further increased the content of free ABA in the shoots. A transfer back to LD conditions reduced the ABA content to a level equal to the level found during the first LD period. The recovery of radioactive ABA at certain times after application ofr[³H] ABA was the same in shoots and roots of LD-grown and SD-treated seedlings.Abbreviations ABA abscisic acid - LD long day(s) - RGR₇ weekly relative growth rates - SD short day(s)     

The ion concentration of dew condensed on Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) needles

Summary Dew droplets collected with pipettes from coniferous needles were analysed for their ionic composition. Almost all samples of dew taken from Scots pine trees (Pinus sylvestris) showed significantly higher ion concentrations than those taken from Norway spruce trees (Picea abies). This can be explained by the micromorphology of the needle surface. The higher microscale roughness of the wax layer of a pine needle causes a more efficient flux of atmospheric aerosol particles compared to the spruce needle surface. Dew on coniferous needles is shown to be capable of maintaining pH values below 3 for several hours.     

Soil acidification as caused by the nitrogen uptake pattern of Scots pine (Pinus sylvestris)

Three-year-old Scots pine (Pinus sylvestris) trees were grown on a sandy forest soil in pots, with the objective to determine their NH₄/NO₃ uptake ratio and proton efflux. N was supplied in three NH₄-N/NO₃-N ratios, 3:1, 1:1 and 1:3, either as ¹⁵NH₄+¹⁴NO₃ or as ¹⁴NH₄+¹⁵NO₃. Total N and ¹⁵N acquisition of different plant parts were measured. Averaged over the whole tree, the NH₄/NO₃ uptake ratios throughout the growing season were found to be 4.2, 2.5, and 1.5 for the three application ratios, respectively. The excess cation-over-anion uptake value (C_a-A_a) appeared to be linearly related to the natural logarithm of the NH₄/NO₃ uptake ratio. Further, this uptake ratio was related to the NH₄/NO₃ ratio of the soil solution. From these relationship it was estimated that Scots pine exhibits an acidifying uptake pattern as long as the contribution of nitrate to the N nutrition is lower than 70%. Under field circumstances root uptake may cause soil acidification in the topsoil, containing the largest part of the root system, and soil alkalization in deeper soil layers.     

Assessing environmental and physiological controls over water relations in a Scots pine (Pinus sylvestris L.) stand through analyses of stable isotope composition of water and organic matter

This study investigated the influence of meteorological, pedospheric and physiological factors on the water relations of Scots pine, as characterized by the origin of water taken up, by xylem transport as well as by carbon isotope discrimination (Delta13C) and oxygen isotope enrichment (Delta18O) of newly assimilated organic matter. For more than 1 year, we quantified delta2H and delta18O of potential water sources and xylem water as well as Delta13C and Delta18O in twig and trunk phloem organic matter biweekly, and related these values to continuously measured or modelled meteorological parameters, soil water content, stand transpiration (ST) and canopy stomatal conductance (G(s)). During the growing season, delta18O and delta2H of xylem water were generally in a range comparable to soil water from a depth of 2-20 cm. Long residence time of water in the tracheids uncoupled the isotopic signals of xylem and soil water in winter. Delta18O but not Delta13C in phloem organic matter was directly indicative of recent environmental conditions during the whole year. Delta18O could be described applying a model that included 18O fractionation associated with water exchange between leaf and atmosphere, and with the production of organic matter as well as the influence of transpiration. Phloem Delta13C was assumed to be concertedly influenced by G(s) and photosynthetically active radiation (PAR) (as a proxy for photosynthetic capacity). We conclude that isotope signatures can be used as effective tools (1) to characterize the seasonal dynamics in source and xylem water, and (2) to assess environmental effects on transpiration and G(s) of Scots pine, thus helping to understand and predict potential impacts of climate change on trees and forest ecosystems.     

Seasonal variations in the chemical composition of dissolved organic matter in organic forest floor layer leachates of old-growth Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) stands in northeastern Bavaria, Germany

Organic matter dissolved in thepercolation water of forest soils contributeslargely to element cycling and transport ofnatural and anthropogenic compounds. The wayand extent to which these processes areaffected depends on the amount and the chemicalcomposition of soluble organic matter. Becausethe amount of soluble organic matter variesseasonally with changes in the microbialactivity in soil, it seems reasonable to assumethat there may be also seasonal changes in thechemical composition of dissolved organicmatter. We examined dissolved organic matter inthe seepage waters of organic forest floorlayers over a 27-month period (1997–1999) intwo forest ecosystems, a 160-year-old Scotspine (Pinus sylvestris L.) stand and a90-year-old European beech (Fagussylvatica L.) forest. The forest floorleachates were analysed for bulk dissolvedorganic C, C in hydrophilic and hydrophobicdissolved organic matter fractions,lignin-derived phenols (CuO oxidation),hydrolysable neutral carbohydrates and uronicacids, hydrolysable amino sugars, and stablecarbon isotope composition. In addition, westudied the samples by use of liquid-state¹³C-nuclear magnetic resonance (NMR)spectroscopy.For both investigated forest sites we foundthat the dissolved organic carbonconcentrations in forest floor leachates werelargest during summer. They peaked after rainstorms following short dry periods (106–145 mgdissolved organic C l^–1). The proportionsof C in the hydrophilic fractions were largestin winter and spring whereas in summer andautumn more C was found in the hydrophobicfraction. According to liquid-state ¹³C-NMR spectroscopy, summer and autumn samples hadlarger abundances of aromatic and aliphaticstructures as well as larger proportions ofcarboxyl groups whereas the winter and springsamples were dominated by resonances indicatingcarbohydrates. Wet-chemical analyses confirmedthese results. Winter and spring samples wererich in neutral carbohydrates and amino sugars.The summer and autumn samples contained morelignin-derived phenols which were also strongeroxidised than those in the winter and springsamples. Seasonal changes of ¹³C valueswere found to reflect the changes in thechemical composition of dissolved organicmatter. Most negative values occurred whenisotopically light lignin-derived compoundswere abundant and less negative values whencarbohydrates predominated.The different vegetation, age of thestands, and underlying mineral soils resultedin different concentrations of dissolvedorganic carbon and in differences in thedistribution between hydrophobic andhydrophilic organic carbon. Despite of this,the results suggest that the trends in temporalvariations in the composition of dissolvedorganic matter in forest floor seepage waterwere remarkably similar for both sites.Dissolved organic matter in winter and springseems to be mainly controlled by leaching offresh disrupted biomass debris with a largecontribution of bacterial and fungal-derivedcarbohydrates and amino sugars. Dissolvedorganic matter leached from the forest floor insummer and autumn is controlled by thedecomposition processes in the forest floorresulting in the production of stronglyoxidised, water-soluble aromatic and aliphaticcompounds. The chemical composition ofdissolved organic matter in forest floorseepage water in winter and spring indicateslarger mobility, larger biodegradability, andless interaction with metals and organicpollutants than that released during summer andautumn. Thus, the impact of dissolved organicmatter on transport processes may varythroughout the year due to changes in itscomposition.     

Chemical composition and biochemical changes in needles of Scots pine (Pinus sylvestris L.) stands at different stages of decline in Bulgaria

Water content was decreased in the needles of Scots pines (Pinus sylvestris L.) with moderate and slight levels of stress-induced decline. In pines with moderate decline a misbalance of foliar nutritional elements was observed. In 1-year-old needles of afflicted pines, the content of potassium and calcium was decreased, but the content of phosphorus, magnesium, iron, manganese and of the heavy metals cadmium and lead was increased. In 2-year-old needles of damaged pines, the content of calcium, iron and of the heavy metal cadmium was decreased, but the content of phosphorus, magnesium, manganese and zinc was increased. Potassium deficiency and zinc levels above toxicity tolerance characterized the nutrient status of declined Scots pines. In the same pines chlorophyll a/b ratio was diminished in 2-year-old needles and the protein content was increased in 1-year-old needles but was decreased in 2-year-old needles.In the second phase of the study 25- and 40-year-old pines with slight decline were examined. An increase in the protein content of 2-year-old needles of 25-year-old declined pines and of both 1- and 2-year-old needles of older 40-year-old pines was observed. A 280% increase of peroxidase activity in 1-year-old and a 178% increase in 2-year-old needles of 25-year-old damaged pines were shown. In older 40-year-old damaged pines a slight increase only in 1-year-old needles was seen. The observed age-related decrease in peroxidase activity in older 40-year-old symptomatic pines might be responsible for the lower resistance to decline in older pines. Our results show that clear but complex chemical and biochemical changes are observed in the needles of Scots pines in Bulgaria and that these changes hold promise for use as indicators of stress.     

Long-term implications of industrial pollution stress on lipids composition in Scots pine (Pinus sylvestris L.) roots

The influence of pollution stress (SO₂, Cu²⁺, Pb²⁺, Zn²⁺ and fluoride) on composition changes in cellular membranes of roots of three European of Scots pine (Pinus sylvestris L.) populations were examined. Plant material growing in three experimental areas: Kórnik relatively free of air pollution (control), Luboń: SO₂ and HF and Głogów: SO₂ and heavy metals. Analysis of total phospholipids and their composition indicates that the phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were present in lower concentration in the root tissues from both polluted sites (Luboń and Głogów). The difference in PC:PE ratio between control and both polluted sites was greater in root of Scots pine population from Russia than in the population from Slovakia. Under pollution conditions the content of lipid soluble antioxidant α-tocopherol was lower about 220 %, in comparison to the control. The action of pollution stress also lead to lowering of unsaturated:saturated ratio of total fatty acid, and lower content of polyunsaturated fatty acids, linoleic acid (18:2) and eicosatrienoic acid (20:3). We concluded that the long-term pollution stress markedly inhibited lipid biosynthesis in root tissue of Scots pine and it is probably contribute to the reduction of productivity of forests. These results also suggest that lipid composition can be used as an indicator of changes in tissue roots of Scots pine caused by air and/or soil long-term pollution.     

The effect of cold-induced increased metabolic rate on the rate of <Superscript>13</Superscript>C and <Superscript>15</Superscript>N incorporation in house sparrows (<Emphasis Type="Italic">Passer domesticus</Emphasis>)

Animals with high metabolic rates are believed to have high rates of carbon and nitrogen isotopic incorporation. We hypothesized that (1) chronic exposure to cold, and hence an increase in metabolic rate, would increase the rate of isotopic incorporation of both ¹³C and ¹⁵N into red blood cells; and (2) that the rate of isotopic incorporation into red blood cells would be allometrically related to body mass. Two groups of sparrows were chronically exposed to either 5 or 22°C and switched from a ¹³C-depleted C₃-plant diet to a more ¹³C-enriched C₄-plant one. We used respirometry to estimate the resting metabolic rate of birds exposed chronically to our two experimental temperatures. The allometric relationship between the rate of ¹³C incorporation into blood and body mass was determined from published data. The of birds at 5°C was 1.9 times higher than that of birds at 22°C. Chronic exposure to a low temperature did not have an effect on the rate of isotopic incorporation of ¹⁵N save for a very small effect on the incorporation of ¹³C. The isotopic incorporation rate of ¹³C was 1.5 times faster than that of ¹⁵N. The fractional rate of ¹³C incorporation into avian blood was allometrically related to body mass with an exponent similar to −1/4. We conclude that the relationship between metabolic rate and the rate of isotopic incorporation into an animal’s tissues is indirect. It is probably mediated by protein turnover and thus more complex than previous studies have assumed.     

Trophic Niche Segregation in the Nilotic Ichthyofauna of Lake Albert (Uganda, Africa)

Synopsis Nile perch, Lates niloticus, and Nile tilapia, Oreochromis niloticus, were originally transplanted from Lake Albert in western Uganda to the African Great Lakes, Lake Victoria and Lake Kyoga, where they are partially implicated in reduction of the fish species diversity. Lake Albert is facing multiple environmental changes, including declining fish species diversity, hyper-eutrophication, hypoxia, and reduced fish catches. To examine the role of Nile perch and Nile tilapia in the food web in their native Lake Albert, we estimated their diets using stable nitrogen and carbon isotopes. In Lake Albert, the tilapiine congeners (closely related species), Tilapia zillii, Oreochromis leucostictus, and Sarethorodon galilaeus, and the centropomid Nile perch congener, Lates macrophthalmus, have narrower diet breath in the presence of the native O. niloticus and L. niloticus. A computerized parameter search of dietary items for five commercially important fish species (Hydrocynus forskahlii, Bagrus bayad, L. niloticus, Alestes baremose and Brycinus nurse) was completed using a static isotopic mixing model. The outcome of the simulation for most fish species compared favorably to previously published stomach contents data for the Lake Albert fishes dating back to 1928, demonstrating agreement between stable isotope values and analyses of stomach contents. While there were some indications of changes in the diets of L. niloticus and A. baremose diets over the past 20 years in parallel with other changes in the lake, for the most part, food web structure in this lake remained stable since 1928. The Lake Albert fish assemblage provides insight into the invasion success of L. niloticus and O. niloticus.     

Flight capabilities and feeding habits of silphine beetles: are flightless species really “carrion beetles”?

We determined the flight capabilities and feeding habits of adults of nine silphine beetle species and illustrated their relationship. We examined the silphine beetles for the presence or absence of flight muscles and estimated their feeding habits by comparing the carbon and nitrogen stable isotope ratios for them with those of necrophagous nicrophorine species and carnivorous carabine species. Three species (Silpha longicornis, S. perforata and Phosphuga atrata) completely lacked individuals with flight muscles, and one species (Eusilpha japonica) showed flight muscle dimorphism. Stable isotope analysis suggested that these species were carnivores, mainly feeding on soil invertebrates. Most flight species showed higher isotopic ratios than the flightless species. Some of them have isotopic ratios close to those of the nicrophorine species, suggesting that these species mainly feed on vertebrate carcasses. Flightless silphine species would have limited ability to search for patchy and unpredictable carcass resources. Further studies are necessary to understand the adaptive evolution of flight capability and the feeding habits in this group.