Competition between Sphagnum magellanicum and Eriophorum angustifolium as affected by raised CO2 and increased N deposition

The competition between peat mosses ( Sphagnum ) and vascular plants as affected by raised CO₂ and increased N deposition was studied in a glasshouse experiment by exposing peat monoliths with monocultures and mixtures of Sphagnum magellanicum and Eriophorum angustifolium to ambient (350 ppmv) or raised (560 ppmv) atmospheric CO₂ concentrations, combined with low (no N addition) or high (5 g m⁻² yr⁻¹ added) N deposition. Growth of the two species was monitored for three growing seasons.
The presence of Eriophorum did not affect Sphagnum biomass, because Eriophorum density did not become high enough to severely shade the moss surface. In contrast, Sphagnum had a negative effect on Eriophorum biomass, particularly on the number of flowering stems. Possibly, the presence of a living Sphagnum layer decreased nutrient availability to Eriophorum by immobilising nutrients mineralised from the peat.
Raised CO₂ and/or increased N deposition did not change these competitive relationships between Sphagnum and Eriophorum , but had independent effects. Raised CO₂ had a positive effect both on Sphagnum and Eriophorum biomass, though on Eriophorum the effect was transient, probably because of P limitation. Nitrogen addition had a direct negative effect on Sphagnum height growth in the first growing season, but by the third year an increased shoot density had cancelled this out, so no N effect on Sphagnum biomass was present at the end of the experiment. The response of Eriophorum to N addition was small; N availability appeared not to limit its growth.     

Grazing interactions between pulmonate snails and epiphytic algae and bacteria

SUMMARY. 1. The effects of grazing by Lymnaca peregra and Planorbis planorbis on Ceratophyllum demersum epiphyton were investigated under simulated natural conditions.
2. Grazing resulted in significant reductions in algal cell densities, number of algal taxa and in diversity. Grazing did not influence equi-tabilily values.
3. The use of Ivlev's Electivity index demonstrated positive and negative selection by feeding snails for large, pedunculate, and small, adnate algae, respectively.
4. Inoculation of artificial surfaces revealed that 61.1% and 62.5% of the algal taxa presenl in the diet of L. peregra and P . planorbis , respectively (mainly the smaller species), were able to survive passage through the gut, resettle and grow.
5. The results are discussed with particular reference to the survival strategies available to the epiphytes, and the possible mutual benefits which algae and snails may derive from coexistence.     

海草与其附生藻类之间的相互作用

海草床是滨海湿地中重要的生态系统,近年来世界范围内出现大面积的海草床衰退,水体富营养化引发附生藻类的大量繁殖是其中的一个主要原因。本文综述了近20年来关于海草与其附生藻类之间相互作用的研究进展,包括海草床中附生藻类的地位及其积极作用,附生藻类与海草的物质交换关系,附生藻类对海草的影响（主要是光利用限制和营养物质利用限制）。对海草床中海草-附生藻类群落复杂的生态关系提出了研究展望,包括海草与其附生藻类的物质交换机制,海草与其附生藻类对营养物质利用的竞争关系,附生藻类生物量分别对海草可利用光和光合作用能力的削弱关系,海草与附生藻类对海草床初级生产力的贡献随环境因子的变化关系,通过原位观测数据的积累建立海草生长与生物作用的模型等。     

Expansion of Sphagnum fallax in bogs: striking the balance between N and P availability

Abstract

Nitrogen deposition may cause shifts in the Sphagnum species composition of bogs, ultimately affecting the conservation value of these systems. We studied the effects of N and P on the expansion of S. fallax and S. flexuosum in bogs. We related historical census data of S. fallax, S. flexuosum, and four of their accompanying species to changes in N deposition. In addition, we conducted two fertilization experiments with N and P; one at a low deposition site with S. flexuosum and one at two high deposition sites with S. fallax. Finally, we related existing data on capitulum N and P concentrations of S. fallax to its abundance in the field.

A relative increase in observed frequency of S. fallax coincided with an historical increase in N deposition in the Netherlands. There was no indication that S. fallax consistently outcompeted one of the other five Sphagnum species; the observed frequency of the Sphagnum species analysed was rather stable with time. The census data on S. flexuosum did not indicate a response to N deposition, but the species expanded at the low N deposition site when extra N was applied. In contrast, the expansion of S. fallax at the high deposition sites was limited by P. Organic nutrient concentrations suggested that when S. fallax can maintain a capitulum N concentration of 7 mg g^-1 or higher and a P concentration of 0.7 mg g^-1 or higher the species can grow to dominate.

We conclude that S. fallax will gradually colonize an increasing number of new habitats in areas with a low, albeit increasing, N deposition, but will only grow to dominate when P supply is adequate. Then, the expansion of S. fallax may lead to ousting of the other Sphagnum species present.     

大型海藻对主要营养盐的吸收的研究进展

针对当前海洋环境面临的严重的富营养化现状,利用大型海藻的吸收氮磷的能力可以有效治理和修复海洋的富营养化,实现海洋污染的生态修复.本文介绍了大型海藻主要营养盐物质(C、N、P)的吸收的其影响因素主要有物理因素、化学因素和生物因素等,大型海藻吸收营养盐的现状,研究方法,前景展望等.     

Variability of C,N and P content of a tropical semiarid soil as affected by soil genesis,erosion and land clearing

Several transects of topsoil samples were taken immediately after land clearing and one year later from a savannah soil in the semiarid NE of Brazil. Natural spatial variability of key fertility indicators (C, N, P) was large with coefficients of variation >50%. This variability was related to heterogeneity of the soil parent material, and to relative slope position which affected deposition and removal of erodible materials. The distribution of gravel and different particle size fractions was an indicator of the variability as related to soil formation and erosional resorting. One year after the site was cleared and planted to trees, the decrease in C, N and resin-extractable P was in the same range as the initial spatial variability. Treatment effects were therefore difficult to observe but became more obvious when regression analysis on soil textural components was used to reduce data variability.     

Allelopathic interaction between a reef coelenterate and benthic algae

Summary We did in situ experiments to study the influence of a water-borne substance, exuded by the reef anthozoan Condylactis gigantea, on filamentous algae. Algal biomass accumulation on experimental glass slides was significantly inhibited by the exudate. Algal spores and diatoms were present in equal numbers on experimental and control slides, but the exudate inhibited germination of spores and was toxic to developing green, red and brown algae. The algal population on the control slides consisted of early colonizers as well as later successional species and reflected the natural population. The described allelochemic mechanism will be important in interference competition between the anemone and algae. Settling of larvae in supposedly space-limited systems such as reefs is facilitated when algaecovered surfaces are open to settlement. Present address: Netherlands Institute for Sea Research (NIOZ) P.O. Box 59, Texel, The Netherlands     

Yield of submerged paddy and uptake of Zn,P and N as affected by liming and Zn fertilizers

The effects of CaCO₃, Zn sources and levels on the yield of submerged paddy and uptake of Zn, P and N to paddy were studied in green-house at Haryana Agricultural University, Hissar. Powdered CaCO₃ was mixed at 0,4 and 8 per cent and Zn was added at 0,5 and 10 ppm through ZnSO₄.7H₂O, ZnO and Zn EDTA separately. Dry weight at tillering and heading and grain and straw at maturity decreased significantly with 4 and 8 per cent CaCO₃ in comparison to the control. Increasing Zn application increased the dry weight and grain yield. Zn EDTA gave highest yield of paddy followed by ZnSO₄.7H₂O and ZnO.Increasing the application of CaCO₃ from 0–8 per cent decreased the concentration and uptake of Zn and increasing Zn application from 0–10 ppm increased concentration and uptake of Zn in paddy at tillering, heading and maturity. Zn EDTA gave the highest concentration and uptake of Zn followed by ZnSO₄.7H₂O and ZnO. There was interaction between Zn sources and CaCO₃.The concentration and uptake of N and P in paddy dry matter at tillering and heading and straw and grain at maturity decreased as compared to control with increasing CaCO₃ addition. The concentration and uptake of N increased and that of P decreased in paddy dry matter straw and grain with increasing Zn application. The highest concentration of N was observed with ZnO, followed by ZnSO₄.7H₂O and Zn EDTA. But highest uptake of N was observed with Zn EDTA followed by ZnSO₄.7H₂O and ZnO. As regards concentration and uptake of P, it was highest with ZnO followed by ZnSO₄.7H₂O and Zn EDTA.     

Nitrogen metabolism of leaves during growth ofPhaseolus aureus L. as affected by S,P and N application

Summary An application of sulphur (upto 90 ppm) alone or in combination with phosphorus and nitrogen, increased the content of total nitrogen, protein nitrogen and total soluble nitrogen but decreased amide, amino, ammoniacal and nitrate nitrogen and with further increase in dose, all the nitrogen fractions decreased. Higher doses of nitrogen in combination with sulphur increased the content of amide nitrogen and nitrate nitrogen in leaves only at 15 and 30 days stages. Higher doses of phosphorus in combination with sulphur and nitrogen decreased the content of all nitrogen fractions in leaves. All the nitrogen fractions decreased in age except the amide and ammoniacal nitrogen which increased upto 30 days and then started decreasing.     

丛枝菌根真菌和植物寄生线虫

本文综述了土壤微生物中丛枝菌根真菌和植物寄生线虫的互作关系及其互作机理,并阐述了丛枝菌根真菌在防治植物线虫病害方面的应用前景和实际操作中应注意的技术环节。     

Growth responses and N and P use efficiency of three Alnus species as affected by arbuscular-mycorrhizal colonisation

In this study it was determined how different species ofAlnus (A. cordata, A. incana and A. glutinosa) responded tocolonisation by arbuscular mycorrhizal (AM) fungi (Glomusmosseae or Glomus intraradices) with regard togrowth and their ability to acquire and utilise nitrogen and phosphorus.Non-mycorrhizal plants but with phosphorus added, were used as control. InA. glutinosa the application of 75 ppm P hadsimilar effect on growth and P acquisition as did AM. Nevertheless,A.cordata and A. incana grew poorly when suppliedwith 75 ppm of P and required AM symbiosis for optimum growth andNand P uptake. The percentage increases in shoot dry biomass in AM colonised ascompared with P-fertilised plants were 441 (A. cordata)and644 (A. incana) whilst AM-colonised A.glutinosa matched P-fertilised plants. Plant shoot N/P ratioincreased in response to AM-colonisation indicating that mycorrhizal effects onN uptake are greater than on P uptake. Information concerning the directinfluence of AM on N acquisition and nutrient use efficiency byAlnus species is important. AM-colonisation provides anexcellent biological mechanism by which Alnus plantsbecamemore efficient P-users. That Alnus sp. are highlymycorrhizal-dependent plants was apparent because AM-colonisation was criticalfor growth of A. incana and A.cordata. In this respect, for maximizing the efficient uptake anduseof N and P, under the growth conditions provided, Alnusplants need to be mycorrhizal. AM symbiosis seems decisive for the successfulestablishment of Alnus sp. in revegetation strategies. Thelow N and P availability in soils where Alnus species areuseful candidates in any recolonisation and reclamation process emphasises theneed to investigate systems by which N and P uptake byAlnus plants can be enhanced.     

A common group I intron between a plant parasitic fungus and its host

The self-splicing RNAs known as group I introns exist in many organisms, but their distribution is difficult to explain. We hypothesize that group I introns have been transferred between a parasite and its host. We describe here the discovery of a common group I intron sequence between a plant-parasitic fungus, Protomyces inouyei, and its host, Youngia japonica. It strongly supports our theory that the group I intron had been transferred from the host plant to the parasitic fungus in the course of evolution.      

Abscessed bony areas on Acanthopagrus cuvieri (Day) as a substrate for epiphytic algae

Enteromorpha compressa (L.) Greville and E. clathrata (J. Agardh), widely distributed green algae in Arabian Gulf, were observed growing on Acanthopagrus cuvieri (Day). Abscessed areas on the operculum provided suitable sites for attachment of both species of algae; broken spine tips were preferred by E. compressa . This study showed that these algae preferred hard substrata, with no scales for attachment. E. compressa appeared earlier and grew faster. The condition of the fish was normal.     

Precaecal and postileal metabolism of P,Ca and N in pigs as affected by different carbohydrate sources fed at low level of P intake

Three different carbohydrate sources (cellulose on wood basis, maize starch and apple pectin) in combination with a low phosphorus (P) basal diet were fed to eight pigs fitted with single ileum-T-cannulas in a balance trial. The effects on net disappearance of dry matter, N, P and Ca as well as phytate (IP6) degradation in the intestine were studied. A basal diet and three diets supplemented with 25% of one carbohydrate source were applied in three experimental periods following an incomplete Latin Square design. Animals were housed individually in balance crates. After 15 days of adaptation to the diets, five days of total excreta collection were followed by two days of spot sampling of ileal digesta. The results showed a significantly decreasing effect of cellulose on the precaecal, postileal and total tract digestibility of DM, N and P. Starch reduced precaecal IP6 degradation and P digestibility. The addition of pectin negatively affected the precaecal digestibility of DM, N and Ca as well as the total tract digestibility of P and Ca. Postileally, cellulose and pectin caused a net secretion while starch induced a net absorption of P.     

Precaecal and postileal metabolism of P, Ca and N in pigs as affected by different carbohydrate sources fed at low level of P intake

Three different carbohydrate sources (cellulose on wood basis, maize starch and apple pectin) in combination with a low phosphorus (P) basal diet were fed to eight pigs fitted with single ileum-T-cannulas in a balance trial. The effects on net disappearance of dry matter, N, P and Ca as well as phytate (IP6) degradation in the intestine were studied. A basal diet and three diets supplemented with 25% of one carbohydrate source were applied in three experimental periods following an incomplete Latin Square design. Animals were housed individually in balance crates. After 15 days of adaptation to the diets, five days of total excreta collection were followed by two days of spot sampling of ileal digesta. The results showed a significantly decreasing effect of cellulose on the precaecal, postileal and total tract digestibility of DM, N and P. Starch reduced precaecal IP6 degradation and P digestibility. The addition of pectin negatively affected the precaecal digestibility of DM, N and Ca as well as the total tract digestibility of P and Ca. Postileally, cellulose and pectin caused a net secretion while starch induced a net absorption of P.     

Temperature-dependent genotype-by-genotype interaction between a pathogenic fungus and its hyperparasitic virus

The outcome of host-parasite interactions may depend not only on the genotypes of the species involved but also on environmental factors. We used the fungus Cryphonectria parasitica, the causal agent of chestnut blight, and its hyperparasitic virus, Cryphonectria hypovirus-1 (CHV1), to test for genotype-by-genotype-by-environment interactions in a host-parasite system. In C. parasitica, infection with CHV1 induces a hypovirulent phenotype with reduced virulence toward the chestnut tree (Castanea spp.) and thus controls chestnut blight in many European regions. In contrast, uninfected virulent C. parasitica have nearly eradicated the American chestnut in North America. We applied a full factorial design and assessed the fungal growth and sporulation of four C. parasitica strains, uninfected and infected with each of the four known CHV1 subtypes, at 12°, 18°, 24°, and 30°C. We found a significant (P ≤ .00001) genotype-by-genotype-by-environment interaction, demonstrating the potential for a selection mosaic. As a consequence, different host and parasite genotypes would be selected under different climatic conditions, affecting the coevolutionary dynamics of the host-parasite interaction and the course of chestnut blight epidemics. Genotype-by-genotype-by-environment interactions are essential to take into account when designing biological control strategies.     

Indirect interaction between an unspecialized endophytic fungus and a polyphagous moth

Despite their ubiquitous occurrence in natural and managed ecosystems, the role of unspecialized fungal endophytes in mediating insect-plant interactions have been largely ignored compared to clavicipitaceous fungal endophytes of grasses. We conducted laboratory and glasshouse experiments to test the hypothesis that an unspecialized fungal endophyte (Acremonium strictum) restricted to the root system of the host plant is able to mediate the interaction between a polyphagous herbivorous insect (Helicoverpa armigera) and its host plant (tomatoes, Lycopersicum esculentum). Our studies indicated a significant variation in the ability of inoculated and control plants to support the life history stages of the insect. Larvae reared on inoculated plants suffer significant reduction in growth rate, prolonged development times, suppressed moulting, and produced smaller pupae that were more likely to die, and emerged adults were less fecund compared to larvae reared on control plants. In glasshouse bioassays were larvae were allowed to graze freely, on inoculated plants only 20% survived to the final stadium compared to 54.5% on control plants. No significant differences in the amount of foliage consumed were found between inoculated and control plants, suggesting that A. strictum does not act as a feeding deterrent for H. armigera larvae. Larvae fed inoculated plants showed a significant increase in the relative consumption rate, although the approximate digestibility of ingested food, and efficiency with which both ingested food and digested food was converted to insect biomass decreased during the same period. In addition to reduced efficiency of food utilization, surviving larvae on inoculated plants displayed a significant reduction in relative growth rate. We hypothesized that alterations in phytosterol composition mediated by infection of the fungal endophyte, may explain the reduced larval performance on inoculated plants.Obwohl unspezialisierte endophytische Pilze in allen Ökosystemen weit verbreitet und häufig sind, blieb ihre Rolle bei Interaktionen zwischen Pflanzen und herbivoren Insekten bisher weitgehend unberücksichtigt. In Labor- und Gewächshausexperimenten haben wir die Hypothese untersucht, dass ein unspezialisierter Wurzelendophyt (Acremonium strictum) die Wechselwirkungen zwischen einem polyphagen Insekt (Helicoverpa armigera) und Tomatenpflanzen (Lycopersicum esculentum) beeinflussen kann. Die Entwicklung der Insekten weist deutliche Unterschiede zwischen inokulierten und Kontrollpflanzen auf. Larven, die auf inokulierten Pflanzen gehalten wurden, zeigten gegenüber solchen von Kontrollpflanzen jeweils signifikant verringerte Wachstumsraten, verlängerte Entwicklungszeiten, verzögerte Häutungen, und bildeten kleinere Puppen aus, welche eine höhere Mortalität aufwiesen. Die geschlüpften Weibchen hatten zudem eine verringerte Fekundität. In Frassversuchen im Gewächshaus überlebten an inokulierten Pflanzen nur 20% der Larven während an Kontrollpflanzen 54,5% überlebten. Da die gefressene Biomasse in beiden Varianten gleich war, ist eine deterrente Wirkung des Pilzes auszuschließen. Vielmehr deuten signifikante Veränderungen der Fraß- und Verwertungsindices sowie die niedrigeren relativen Wachstumsraten darauf hin, das sich die Nahrungsqualität auf inokulierten Pflanzen verschlechtert hatte. Wir diskutieren die Hypothese, dass der Phytosterolgehalt, welcher durch eine Inokulation der Pflanzen verändert wird, zu den verschlechterten Entwicklungsbedingungen der Larven geführt hat.     

Snail communities increase submerged macrophyte growth by grazing epiphytic algae and phytoplankton in a mesocosm experiment

The relationships between producers (e.g., macrophytes, phytoplankton and epiphytic algae) and snails play an important role in maintaining the function and stability of shallow ecosystems. Complex relationships exist among macrophytes, epiphytic algae, phytoplankton, and snails. We studied the effects of snail communities (consisting of Radix swinhoei, Hippeutis cantori, Bellamya aeruginosa, and Parafossarulus striatulus) on the biomass of phytoplankton and epiphytic algae as well as on the growth of three species of submerged macrophytes (Hydrilla verticillata, Vallisneria natans, and one exotic submerged plant, Elodea nuttallii) in a 90‐day outdoor mesocosm experiment conducted on the shore of subtropical Lake Liangzihu, China. A structural equation model showed that the snail communities affected the submerged macrophytes by grazing phytoplankton and epiphytic algae (reduction in phytoplankton Chl‐a and epiphytic algal abundance), enhancing the biomass of submerged macrophytes. Highly branched macrophytes with high surfaces and morphologies and many microhabitats supported the most snails and epiphytic algae (the biomass of the snail communities and epiphytic algae on H. verticillata was greater than that on V. natans), and snails preferred to feed on native plants. Competition drove the snails to change their grazing preferences to achieve coexistence.