Arbuscular mycorrhizas in a valley-type savanna in southwest China

The arbuscular mycorrhizal (AM) status of 67 plant species in a savanna community in the hot, dry valley of Jinsha River, southwest China was surveyed. It was found that about 95% of the plant species formed AM and 5% possibly formed AM. The composition of AM fungi (AMF) in the rhizosphere soils was also investigated. The AMF spore density ranged from 5 to 6,400 per 100 g soil, with an average of 1,530, and these spores/sporocarps were identified as belonging to six genera. Fungi belonging to the genera Glomus and Acaulospora were the dominant AMF. High densities of AMF spores in the rhizosphere soils, and the intensive colonization of the plant roots, indicated that plants grown in this valley-type savanna may be highly dependent on AM.     

Arbuscular mycorrhizal fungi colonize decomposing leaves of<Emphasis Type="Italic"> Myrica parvifolia</Emphasis>,<Emphasis Type="Italic"> M. pubescens</Emphasis> and<Emphasis Type="Italic"> Paepalanthus</Emphasis> sp.

Hyphae and vesicles of arbuscular mycorrhizal fungi (AMF) were found within the decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp. at three montane sites in Colombia. Hyphae, vesicles, and arbuscule-like structures were also found within scale-like leaves of the rhizomes of Paepalanthus sp. The litter found in the vicinity of the roots was divided into three decomposition layers. The highest AMF colonization occurred in the most decomposed leaves, which were in close association with roots. In contrast, there were no differences in AMF colonization of roots present in the different decomposition layers. Colonization of decomposing leaves by AMF did not differ between the two closely related species M. parvifolia and M. pubescens, nor between two sites (Guatavita and Zipacón, Colombia) differing in soil fertility. Occurrence of vesicles in decomposing leaves was correlated with abundant AMF extraradical hyphae among the leaves. We propose that AMF enter decomposing leaves mechanically through vascular tissue. As a consequence, AMF are well positioned to obtain and efficiently recycle mineral nutrients released by decomposer microorganisms before their loss by leaching or immobilization in soil.     

Development of damage function of acidification for terrestrial ecosystems based on the effect of aluminum toxicity on net primary production

Background  Acidification is one of the important impact categories for life cycle impact assessment. Although its characterization has progressed during this decade through the employment of midpoint approaches, only limited studies of endpoint approaches have been performed. Objective. This study aimed at developing damage function of acidification for terrestrial ecosystems in Japan. Damage function expresses a quantitative relationship between the inventory and endpoint damage. Methods  The geographical boundary was limited in Japan both for emission and impact. In this study, sulfur dioxide (SO₂), nitrogen monoxide (NO), nitrogen dioxide (NO₂) (NO and NO₂ collectively mean NO_x), hydrogen chloride (HC1), and ammonia (NH₃) were considered as major causative substances of acidification. Net primary production (NPP) of existing vegetation was adopted as an impact indicator of terrestrial ecosystems. The aluminum toxicity was adopted as the major factor of effect on terrestrial ecosystems due to acidification. The leachate concentration of monomeric inorganic aluminum ions was selected to express the plant toxicity of aluminum. Results and Discussion  The results of damage function gave utilizable factors both for a midpoint approach and an endpoint approach; Atmospheric Deposition Factor (ADF) and Damage Factor (DF) applicable to the former and the latter, respectively. The ADF indicates an increase of H⁺ deposition per unit area to an additional emission of causative sustance. The additional emission corresponds to some alternatives in industry, not the baseline emission. The DF indicates the total NPP damage in all of Japan due to the additional emission of causative substances. The derived NPP damage is on the order of one millionth of the NPP itself. HC1 and NH3 showed larger ADFs and DFs than that of SO₂ and NO_x. The reason was ascribed to the relatively large source-receptor relationships (SRR) of HC1 and NH₃. However, since the method applied to determine the SRR of HC1 and NH₃ has larger uncertainties than that of SO₂ and NO_x, attention is needed to handle the difference. Conclusion  The damage function easily defines the concrete NPP damage due to an additional emission. The impact indica tor, NPP, also has an advantage in its mass unit that is directly summable through the entire impact categories. Expansion of endpoints, such as in aquatic ecosystems, material degradation, human health, and biodiversity aspects of terrestrial ecosystems, is an important subject for future work. Further, uncertain analyses for major parameters will provide helpful information on the reliability of damage function.     

Moisture Effects on Temperature Sensitivity of CO<Subscript>2</Subscript> Exchange in a Subarctic Heath Ecosystem

Carbon fluxes between natural ecosystems and the atmosphere have received increased attention in recent years due to the impact they have on climate. In order to investigate independently how soil moisture and temperature control carbon fluxes into and out of a dry subarctic dwarf shrub dominated heath, monoliths containing soil and plants were incubated at three different moisture levels and subjected to four different temperature levels between 7 and 20 °C. Ecosystem CO₂ exchange was monitored continuously day and night during the 16 to 18 days that each of three experiments lasted. Additionally, the carbon allocation pattern of the plants was investigated by labelling monoliths with ¹⁴CO₂ followed by harvest of above and below ground plant parts. The results revealed that the three different soil moisture levels caused distinctly differing levels of CO₂ fluxes. Also, both carbon fixation calculated as gross ecosystem production (GEP) and carbon release measured as ecosystem respiration (ER) increased with increasing temperatures, with ER increasing faster than GEP. Hence, short term carbon loss from the ecosystem accelerated with raised temperatures. Temperature sensitivity of the ecosystem was dependent on the soil moisture level, shown by differing Q10 values of both GEP and ER at different soil moisture levels. It is therefore highly important to take soil moisture levels into consideration when evaluating responses of ecosystem carbon balance to changes in temperature. The greatest C fixation took place via the two most dominant species of the ecosystem, Vaccinium uliginosum and Empetrum hermaphroditum, with the former being responsible for the different size of C fixation at the three moisture levels.     

Modeling Sustainability of Arctic Communities: An Interdisciplinary Collaboration of Researchers and Local Knowledge Holders

How will climate change affect the sustainability of Arctic villages over the next 40 years? This question motivated a collaboration of 23 researchers and four Arctic communities (Old Crow, Yukon Territory, Canada; Aklavik, Northwest Territories, Canada; Fort McPherson, Northwest Territories, Canada; and Arctic Village, Alaska, USA) in or near the range of the Porcupine Caribou Herd. We drew on existing research and local knowledge to examine potential effects of climate change, petroleum development, tourism, and government spending cutbacks on the sustainability of four Arctic villages. We used data across eight disciplines to develop an Arctic Community Synthesis Model and a Web-based, interactive Possible Futures Model. Results suggested that climate warming will increase vegetation biomass within the herd’s summer range. However, despite forage increasing, the herd was projected as likely to decline with a warming climate because of increased insect harassment in the summer and potentially greater winter snow depths. There was a strong negative correlation between hypothetical, development-induced displacement of cows and calves from utilized calving grounds and calf survival during June. The results suggested that climate warming coupled with petroleum development would cause a decline in caribou harvest by local communities. Because the Synthesis Model inherits uncertainties associated with each component model, sensitivity analysis is required. Scientists and stakeholders agreed that (1) although simulation models are incomplete abstractions of the real world, they helped bring scientific and community knowledge together, and (2) relationships established across disciplines and between scientists and communities were a valuable outcome of the study. Additional project materials, including the Web-based Possible Futures Model, are available at http://www.taiga.net/sustain.     

Functional diversity and community structure of microorganisms in rhizosphere and non-rhizosphere Canadian arctic soils

Functional diversities of microorganisms in arctic soil samples at three incubation temperatures were assessed using sole-carbon-source-utilization (SCSU). Soil samples from four sites were collected from the rhizosphere and non-rhizosphere soils. Microorganisms were extracted from samples and inoculated into ECO-Biolog plates and incubated at 4, 10 and 28 °C. Calculations of Shannon–Weaver diversity and Shannon–Weaver evenness were based on the substrate utilization in the Biolog plates. Shannon–Weaver diversities (H) in rhizosphere samples were significantly greater ( _H = 3.023 ± 0.197; P < 0.005) than in non-rhizosphere samples ( _H = 2.770 ± 0.154). Similarly, the evenness (E) of the inoculated microbial cells exhibited significant differences (P < 0.005) between the rhizosphere and non-rhizosphere soil samples ( _E = 0.880 ± 0.057 for soils with rhizosphere; _E = 0.807 ± 0.044 for non-rhizosphere samples). Higher microbial diversity and evenness were observed in samples incubated at 4 °C than at 28 °C [least significant difference (lsd) = 0.29], and evenness indices were higher in rhizosphere samples than in non-rhizosphere soils incubated at all three temperatures (lsd = 0.02). Principal component analysis (PCA) of the multivariate data set differentiated the soil samples on the relatively gross scale of microbial communities isolated from rhizosphere and non-rhizosphere soils at all three temperatures.     

A new zoarcid, Lycodes mcallisteri, from eastern Arctic Canada (Teleostei: Perciformes)

A new zoarcid fish, Lycodes mcallisteri, is described on the basis of nine specimens (230–375 mm SL) from eastern Arctic Canada, Nunavut (Hudson Strait, 298 m; Cumberland Sound and Baffin Bay, 579 m). It resembles about 15 other Lycodes spp. in having a long tail and a "ventromediolateral" type of lateral line. It is distinguished from Arctic members of this group (Lycodes marisalbi, L. palearis, and L. sagittarius) by the high number of pectoral fin rays (22–23), short pelvic fins, low submental crests, and coloration (6–10 light patches dorsally). It resembles two Pacific species (L. macrochir and L. soldatovi) by the high number of pectoral fin rays, but differs by coloration, meristics, and shape of the pectoral fin. Received: April 13, 2000 / Revised: September 7, 2000 / Accepted: January 11, 2001     

Pelagic food webs: Responses to environmental processes and effects on the environment

Changes in both the environment and environmental research have led to the development of new protocols and approaches. These new approaches consider both the effects of changes in the global environment on living organisms (i.e. the responses of ecosystems to environmental processes) and the feedback responses of these organisms and ecosystems (i.e. the effects of living organisms on the environment). The present paper focuses on pelagic food webs in aquatic ecosystems. We examine three major effects of global environmental changes on aquatic organisms: (i) the release of pollutants and biological agents in lakes and nearshore marine waters; (ii) the loss of biodiversity and the collapse of commercially exploited resources that were heretofore renewable. We develop detailed examples of the effects of human activities on marine organisms (i.e. the effects of nutrient supply on the structure of pelagic food webs in marine systems. Finally, we examine (iii) the food-web-controlled exchanges of CO₂ between the atmosphere and the ocean, as a feedback effect of pelagic ecosystems on the global environment with respect to the ongoing climate change.     

Influence of heat shock on seed germination of plants from regularly burnt savanna woodlands and grasslands in Ethiopia

The effect of heat shock on the germination of seeds of 21 plant speciesfrom fire-prone wooded savanna ecosystems in western Ethiopia was analysed inorder to examine the possible implications of fire upon plant regenerationafterthis disturbance. Seeds were subjected to 6 different heat intensities (20, 60,90, 120, 150 and 200°C) for 1 or 5 minutes, in ordertosimulate the situation in the upper soil layers or on the soil surface duringfires. Germination tests were carried out in pots in a greenhouse over 20weeks.After 9 weeks no more seedlings emerged. There was wide interspecific variationin the responses of seeds to the different treatments. In all species,germination was significantly affected by the temperature treatment level.Shortexposure of seeds to high temperatures generally stimulated germination whereasprolonged exposure reduced seed germination. However, some species eventolerated 5 min treatment at 200°C. Seedheat resistance was positively correlated with seed length and mass among thespecies. Hence, production of large seeds with protective tissues promotessurvival in fire-prone savanna areas. Also, the seeds of some species showedboth a low and a high temperature optimum which ensures that at least someseedsgerminate in the absence of fire, but also that viable seeds still remain ifsubsequent late fires kill emerging seedlings. Frequent and light burning inwooded savanna grasslands seems to stimulate and enhance germination of most ofthe studied plant species.     

Marine biodiversity and ecosystem services: an elusive link

Efforts to test the hypothesised positive link between ecosystem services and functions and biodiversity are increasing in order to forecast the consequences of the present erosion of biodiversity on ecosystem functions and to provide an additional basis for the conservation of biodiversity. These efforts have been, however, modest in marine ecosystems. An examination of seagrass communities, which are simple assemblages with a limited membership of about 50 species worldwide and <12 species in any one community, provides, however, strong evidence for the existence of such positive link between species richness and ecosystem functions. Ecosystem functions are, however, dependent on the particular membership of the community, rather that its number, for the functions are species-specific properties. Yet evidence, is provided, that an increasing species richness should be, on average, linked to an increase in the functional repertoire present in the community, will lead to a more efficient use of resources and a greater capacity to ensure the sustainability of ecosystem functions under disturbance or ecosystem change. Closer examination indicates that the functional variability of mixed-species seagrass assemblages is correlated to the variability in species size, whereas species of similar size tend to show similar functional capacities and, therefore, a greater degree of functional redundancy. In addition, the demonstration of positive interactions in seagrass communities, which are also dependent on the presence of engineering species in the community that facilitate the growth of other species, provides increasing grounds to expect an enhanced functional performance of mixed communities over that expected from a simple additive contribution of the community members. Multispecific communities also hold, within the functional repertoire they contain, many unrealised functional potentials that may prove instrumental to ensure the sustainability of ecosystem functions in the presence of disturbance or a changing environment. The arguments offered, illustrated for the comparatively simple seagrass communities, provide strong reasons to expect a strong — if difficult to test experimentally — positive relationship between species diversity and the functions of marine ecosystems and, thereby, the services they yield to humanity.