沙生植物倒披针叶虫实在古尔班通古特沙漠的分布

倒披针叶虫实(Corispermum lehmannianum)在古尔班通古特沙漠广泛分布,重要值仅次于该沙漠建群种白梭梭(Haloxylon persicum),对沙面的稳定起着非常重要的作用。采用固定样方法对自然条件下该植物的分布特征和种群数量动态进行了研究。结果表明:1)倒披针叶虫实在沙丘各坡位均占有较高重要值,尤其活化程度较高的中部和上部优势度更明显;2)生长季节的不同阶段,除坡顶外,其他各坡位种子主要分3批萌发出苗,不同时期种子萌发出苗数量存在差异,3月份有大量种子萌发出苗,4月份种子萌发出苗数最多,5月份萌发出苗量逐渐减少。而坡顶3月份种子萌发出苗量最多,4月至5月均无种子萌发出苗。因此,除坡顶外,种子萌发出苗数量和种群密度在其他各坡位呈先增后减的趋势。生长季结束时各坡位种群密度表现为:中部和上部底部和丘间顶部;3)成熟植株单位面积种子产量为:中部和上部丘间和底部顶部,且中部和上部单位面积种子数量极显著多于丘间、坡底和坡顶(P0.01);4)通过对0—5 cm和6—10 cm土壤种子库密度研究发现,沙丘中部和上部种子库密度显著高于其他坡位。综合以上研究表明,倒披针叶虫实在沙面较活化的中部和上部呈优势分布,对沙漠环境具有良好适应性。因此,该植物是一种极具开发潜力的沙生植物。     

The effects of aspect and exposure on the growth of dune grasses in Cape Hatteras National Seashore

During the month of July 1974, various growth parameters were measured forUniola paniculata (sea oats) andAmmophila breviligulata (American beach grass), plants on the dunes of east- and south-facing beaches of Cape Hatteras. The data were grouped based on the exposure and aspect of dunes studied. ForUniola, height of the flowering culm, number of flowering culms/m², and the height of leaves of non-flowering plants were the most diagnostic parameters. ForAmmophila, the height of the leaves of non-flowering plants was diagnostic. Generally, theUniola plants on the foredunes were taller than those on the backdunes. Plants growing on the southfacing beach were taller than their counterparts on the east-facing beach. On the southfacing beach, the side of the dunes which faces away from the ocean had the taller plants. On the east-facing beach, the side facing the ocean tended to have taller plants. ForAmmophila, the tallest plants were on the back portions of overwash areas. The next tallest occurred on the front of overwash sites. TheAmmophila plants on the ocean side of the dunes were taller than the plants on the back side of the dunes.Presented at the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, U.S.A.     

Effect of species on dune grass growth

Observations of experimental dunes made over a period of nine years indicate differences in utilizing three different dune species along the North Carolina coast and in the type of dunes produced by them.Ammophila is superior in ease of establishment and rate of sand accumulation but is shortlived. It produces a gently sloping dune.Uniola is difficult to propagate but is an excellent dune builder and eventually dominates the foredune. Grown alone, it produces a steep dune front.Panicum is an excellent companion plant to bothAmmophila andUniola. It is easy to propagate, relatively free of pests and produces dunes intermediate in shape, betweenAmmophila andUniola. Plantings of mixtures of two or more of these species should greatly improve long-term dune stability compared with either planted alone.Presented at the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, USA     

The growth of external AM fungal mycelium in sand dunes and in experimental systems

We estimated the biomass and growth of arbuscular mycorrhizal (AM) mycelium in sand dunes using signature fatty acids. Mesh bags and tubes, containing initially mycelium-free sand, were buried in the field near the roots of the dune grass Ammophila arenaria L. AM fungal mycelia were detected at a distance of about 8.5 cm from the roots after 68 days of growth by use of neutral lipid fatty acid (NLFA) 16:1ω5. The average rate of mycelium extension during September and October was estimated as 1.2 mm day⁻¹. The lipid and fatty acid compositions of AM fungal mycelia of isolates and from sand dunes were analysed and showed all to be of a similar composition. Phospholipid fatty acids (PLFAs) can be used as indicators of microbial biomass. The mycelium of G. intraradices growing in glass beads contained 8.3 nmol PLFAs per mg dry biomass, and about 15% of the PLFAs in G. intraradices, G. claroideum and AM fungal mycelium extracted from sand dunes, consisted of the signature PLFA 16:1ω5. We thus suggest a conversion factor of 1.2 nmol PLFA 16:1ω5 per mg dry biomass. Calculations using this conversion factor indicated up to 34 μg dry AM fungal biomass per g sand in the sand dunes, which was less than one tenth of that found in an experimental system with Glomus spp. growing with cucumber as plant associate in agricultural soil. The PLFA results from different systems indicated that the biomass of the AM fungi constitutes a considerable part of the total soil microbial biomass. Calculations based on ATP of AM fungi in an experimental growth system indicated that the biomass of the AM fungi constituted approximately 30% of the total microbial biomass. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biotic soil factors affecting the growth and development of Ammophila arenaria

Summary To study the origin of replant disease of Ammophila arenaria (L.) Link the growth and development in sand originating from the rhizosphere of a natural Ammophila vegetation was compared with the growth in sand from the sea-floor. In a greenhouse experiment, the growth of Ammophila seedlings in rhizosphere sand, when compared with that in sea sand, was significantly reduced. As sterilization by means of gamma-irradiation increased the biomass production of Ammophila seedlings significantly, it was concluded that the rhizosphere sand contained biotic factors that were harmful to Ammophila. In rhizosphere sand the roots of Ammophila were brown and poorly developed, and the specific uptake rates of N, P and K were reduced. The shoot weight proportion of the total plant dry matter was hardly influenced. In an outdoor experiment with Ammophila seedlings and cuttings, using both sands, the mortality was high and the plants were feeble in rhizosphere sand whereas plants in sea sand grew vigorously. It seems plausible that the plants in rhizophere sand were dessicated because the root system was shallow and badly developed. In the greenhouse experiments, Ammophila cuttings were less sensitive to the inhibiting factors in the rhizosphere than seedlings. This was confirmed in the outdoor experiment. Calammophila baltica (Fluegge ex Schrader) Brand, however, was hardly affected by the harmful biotic factors in the greenhouse. These results are discussed with reference to the ecology of Ammophila. It is assumed that the catching of fresh windblown sand provides Ammophila with a way to escape from harmful biotic soil factors, and it was concluded that degeneration of Ammophila is caused mainly by self-intolerance due to these biotic soil factors.     

Competition at the population level along a standing crop gradient: a field experiment in successional grassland

I measured competitive responses of experimentally-established populations of the perennial grass, Andropogon gerardi, across a complex gradient of standing crop and species composition in the successional grasslands of southwest Michigan. The goal was to assess whether long-term (three year) population-level responses of Andropogon to competition matched the inferences made from a previous phytometer study that examined transplant responses to competition across this same gradient over a single growing season.Replicate experimental populations of Andropogon were established at seven grassland sites by sowing seed into 0.5×0.5 m plots that had been denuded of all vegetation. During the first year of the study, all Andropogon populations were maintained as monocultures by hand weeding. At the end of the first growing season, half of the monocultures were selected for continued weeding and half were left open to invasion by competitors for three years. Invasion of the unweeded populations by neighboring plants varied strongly among sites and was positively correlated with standing crop. Increased susceptibility to invasion and competition resulted in the extinction of the unweeded Andropogon populations at the two most productive sites, supporting the hypothesis that Andropogon is restricted by competition to low productivity sites in these grasslands. The finding that the intensity of competition was positively correlated with standing crop is consistent with the previous transplant study, suggesting that short-term experimental assays of competition on the growth of individual transplants may have predictive value for longer-term outcomes of competition at the population level.     

DISPLACEMENT OF ANDROPOGON SCOPARIUS ON THE NEW JERSEY PIEDMONT BY THE SUCCESSIONAL SHRUB MYRICA PENSYLVANICA

Andropogon scoparius, a perennial grass found in old fields on the New Jersey Piedmont, can be invaded and displaced by a nitrogen-fixing shrub, Myrica pensylvanica. The progression of Andropogon displacement was followed over a season, and possible contributing mechanisms (shading, allelopathy, physical effects of Myrica litter) were tested through field and greenhouse experiments. In the field, Andropogon seedling growth was inhibited beneath Myrica clumps, and mature plant living crown area was reduced. In the greenhouse, Andropogon seedling growth was reduced significantly in pots with mature Myrica. Both seedling and mature growth of Andropogon were reduced under shaded conditions. No inhibitory physical effects of Myrica litter on Andropogon seed germination or mature plant growth were found; however, there may ba allelopathic effects of Myrica litter leachate on Andropogon seedlings growing under shade or within grass litter, and on mature Andropogon in shaded conditions. Andropogon displacement appears to be the result of a complex interaction of Myrica shade, allelochemic, and competitive effects, rather than being attributable to any single mechanism.     

Native and exotic foundation grasses differ in traits and responses to belowground tri-trophic interactions

A plant’s growth and fitness are influenced by species interactions, including those belowground. In primary successional systems, belowground organisms are known to have particularly important control over plant growth. Exotic plant invasions in these and other habitats may in part be explained by altered associations with belowground organisms compared to native plants. We investigated the growth responses of two foundation grasses on Great Lakes sand dunes, the native grass Ammophila breviligulata and the exotic grass Leymus arenarius, to two groups of soil organisms with important roles in dune succession: arbuscular mycorrhizal fungi (AMF) and plant-parasitic nematodes (PPN). We manipulated the presence/absence of two generalist belowground species known to occur in Great Lakes dunes, Rhizophagus intraradices (AMF) and Pratylenchus penetrans (PPN) in a factorial greenhouse experiment and assessed the biomass production and root architectural traits of the plants. There were clear differences in growth and above- and belowground architecture between Ammophila and Leymus, with Leymus plants being bigger, taller, and having longer roots than Ammophila. Inoculation with Rhizophagus increased above- and belowground biomass production by ~32% for both plant species. Inoculation with Pratylenchus decreased aboveground biomass production by ~36% for both plant species. However belowground, the exotic Leymus was significantly more resistant to PPN than the native Ammophila, and gained more benefits from AMF in belowground tri-trophic interactions than Ammophila. Overall, our results indicate that differences in plant architecture coupled with altered belowground interactions with AMF and PPN have the potential to promote exotic plant invasion.     

Factors influencing the natural regeneration of the pioneering shrub Calligonum mongolicum in sand dune stabilization plantations in arid deserts of northwest China

Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air‐filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.     

Ecological Assessment of Dune Restorations in the Great Lakes Region

Because of the economic and environmental importance of stabilizing fragile sand dune habitats, restoration of dunes has become a common practice. Restoration efforts in the Great Lakes and East Coast regions of North America often consist of planting monocultures of the dominant native grass species, Ammophila breviligulata. We evaluated 18 dune restoration projects in the Great Lakes region conducted over the past 25 years. We characterized attributes of diversity (plants and insects), vegetation structure (plant biomass and cover), and ecological processes (soil nutrients and mycorrhizal fungi abundance) in each restoration, and we compared these measures to geographically paired natural dune communities. Restoration sites were similar to reference sites in most measured variables. Differences between restorations and reference sites were mostly explained by differences in ages, with the younger sites supporting slightly lower plant diversity and mycorrhizal spore abundance than older sites. Plant community composition varied little between restored and reference sites, with only one native forb species, Artemisia campestris, occurring significantly more often in reference sites than restored sites. Although it remains unclear whether more diverse restoration plantings could accelerate convergence on the ecological conditions of reference dunes, in general, traditional restoration efforts involving monoculture plantings of A. breviligulata in Great Lakes sand dunes appear to achieve ecological conditions found in reference dunes.     

Patterns in the Distribution of American Beachgrass (<Emphasis Type="Italic">Ammophila breviligulata</Emphasis>) and the Density and Reproduction of Annual Plants on a Coastal Beach

Beach communities of eastern North America are commonly dominated by the native perennial grass Ammophila breviligulata. It typically co-occurs with a variety of annual grasses and herbs in the pioneer zone. To determine the potential significance of this vigorous clonal species to the annual community, density, spatial distribution, seed production and potential seed rain were quantified for three focus species (Triplasis purpurea, Cenchrus tribuloides, and Heterotheca subaxillaris) in a 45×40 m section of coastal beach on Staten Island, New York, USA. During autumn 2000, five 40 m transects (10 m apart) were established perpendicular to shore; ramet density for Ammophila, and densities and per capita seed production for the three species, were estimated in 150 contiguous quadrats (35 cm × 30 cm) per transect. Both Triplasis and Cenchrus were more likely to occur in quadrats without Ammophila. Per capita seed production of Cenchrus and Heterotheca showed a curvilinear decrease with increasing numbers of Ammophila ramets. Mean seed rain per m² was significantly reduced in the presence of Ammophila for all three focus annuals. In this beach community, Ammophila acts as an ecosystem engineer, but has a mostly negative influence on the distribution, density, and reproduction of the co-occurring annuals. Results suggest that continual, deliberate planting of A. breviligulata could be detrimental to the abundance and diversity of native annual herbs on the eastern coasts of North America.     

Does Coastal Foredune Stabilization with Ammophila arenaria Restore Plant and Arthropod Communities in Southeastern Australia?

In this study we examine whether stabilization of denuded coastal foredunes in southeastern Australia with the exotic grass species Ammophila arenaria (marram grass) restores plant and ground‐active arthropod assemblages characteristic of undisturbed foredunes. Vascular plants and arthropods were sampled from foredunes that had been stabilized with marram grass in 1982, and from foredunes with no obvious anthropogenic disturbance (control dunes). All arthropods collected were sorted to Order, and ants (81.5% of all specimens) were further sorted to morphospecies. Abundance within arthropod Orders, as well as richness, composition, and structure of the plant and ant assemblages from control and stabilized dunes, were compared. The abundance of Diptera was significantly greater on stabilized dunes, while the abundance of Isopoda was significantly greater on control dunes. There were no significant differences in morphospecies richness or composition of ant assemblages on the two dunes types, although some differences in the abundances of individual morphospecies were observed. By contrast, stabilized dunes exhibited lower plant species richness and highly significant differences in plant species composition, due mainly to the large projected foliage cover of marram grass. The study revealed that after 12 years, the vegetation composition and structure of stabilized dunes was still dominated by marram grass and, as a result, invertebrate assemblages had not been restored to those characteristic of undisturbed foredunes.     

贵南沙蜥洞穴空间分布与昆虫资源分布特征的关系

贵南沙蜥分布在青海省贵南县的一片长×宽约为30 km×20 km的连续沙丘,该沙丘被周缘草地隔离,贵南沙蜥主要在沙地与草地接触带的沙地一侧活动。采用3条样线共150个陷阱研究贵南沙蜥在草地与沙地交界线两侧的活动洞穴空间分布特征与潜在的可利用性昆虫食物资源多样性,并分析洞穴空间分布特征与昆虫种类以及数量分布的关系。研究共捕获1236个昆虫个体,隶属于2纲10目26科42种,其中昆虫纲有7目21科37种978个,蛛形纲有3目5科5种258个;草地采集的昆虫有2纲9目22科37种570个,沙地有2纲9目21科33种666个。草地昆虫的Shannon-Wiener,Simpson多样性指数与均匀度指数均大于沙地,表明草地的昆虫食物资源较丰富且分布均匀。研究表明贵南沙蜥在沙地环境活动洞穴数量较多,且离交界线越近洞穴分布数量越多;草地生境活动洞穴空间分布与离交界线距离无相关性,相对沙地数量较少且空间上分布较均匀。草地样方捕获的昆虫种类和数量以及沙地样方捕获的昆虫数量都与离分界线的距离无关,但沙地上昆虫种类与离分界线的距离呈高度负相关。研究表明贵南沙蜥沙地活动洞穴空间分布与昆虫种类分布特征显著相关。     

EFFECTS OF CHIRONOMID (INSECTA: DIPTERA) TUBE-BUILDING ACTIVITIES ON STREAM DIATOM COMMUNITIES1,2

Chironomid retreats, constructed out of sand grains upon submerged wood debris, increase the surface area available for diatom colonization. The three dimensional substratum afforded by chironomid tubes supports up to twelve times the diatom biavolume found upon adjacent, unmodified substratum in a northern Michigan stream. Diatom enumeration within scrapings from small defined areas on artificial substrata, combined with examination of intact natural substrata through scanning electron microscopy (SEM), reveals distinct, microdistribution patterns. The larval retreats of two major taxa of tube-dwelling chironomid's (Micropsectra sp. and Pseudodiamesa cf. pertinax Garrett) display significantly different diatom communities relative to adjacent masonite substratum. Substratum without chironomid tubes is primarily colonized by Achnanthes minutissima Kütz. and Cocconeis placentula Ehr., exhibiting the lowest species diversity of microhabitats examined. The diatom flora upon sand tubes of Micropsectra sp. is dominated by Opephora martyi Herib., as is the flora of sand grains collected from the stream sediment load. These two micro-habitats exhibit a high community similarity (SIMI). The SIMI index also suggests that the flora of P. pertinax tubes is highly similar to that of sand grains. Diversity, however, is almost three times greater on P. pertinax tubes and SEM observations reveal that this microhabitat is characterized by a more spatially complex flora; Nitzschia and Navicula spp. dominate the upperstory, and O. martyi is located on underlying sand grains. Results indicate that tube-building chironomids in Carp Creek affect diatom microdistribution by: (1) stabilizing sand grains and associated flora within their retreats, (2) providing a ‘refugium’ for upperstory diatom taxa from the mayfly grazer, Baetis vagans McDunnough (Insecta: Ephemeroptera), and (3) through local nutrient enrichment.     

Effects of long‐term grazing management on sand dune vegetation of high conservation interest

Question: Can long‐term grazing management maintain and restore species‐rich sand dune plant communities within a sand dune site of high conservation interest? Location: Newborough Warren, North Wales, UK. Methods: Vegetation changes that occurred between 1987 and 2003, subsequent to grazing by domestic livestock being introduced to the site after decades with little or no stock grazing, were analysed using data collected from permanent monitoring quadrats over a 16‐year period. Results: At the plant community level, grazing brought about a shift from a tall‐grass dominated, species‐poor community to a more species‐rich community in the dry dunes, but did not change community type in dune slacks. However, at the species level, grazing enhanced the abundance of some desired perennial, annual and biennial species, graminoids and bryophytes in both habitat types. The increased frequency of positive indicator species for habitat condition suggests that grazing was beneficial for species of conservation interest. Ellenberg nitrogen (N) values decreased after grazing in dry habitats but showed no long‐term change independent of grazing, suggesting no increase in site fertility over the study period. Surprisingly, light (L) values also decreased in the dry dunes after grazing. Conclusions: Long‐term grazing management can play an important role for the conservation of dune communities and associated species. Because of its positive effects on species diversity, plant communities and habitat condition in sand dunes, livestock grazing is recommended for conservation management.     

Aboveground and Belowground Impacts Following Removal of the Invasive Species Baby's Breath (Gypsophila paniculata) on Lake Michigan Sand Dunes

The removal of invasive species is often one of the first steps in restoring degraded habitats. However, studies evaluating effectiveness of invasive species removal are often limited in spatial and temporal scale, and lack evaluation of both aboveground and belowground effects on diversity and key processes. In this study, we present results of a large 3‐year removal effort of the invasive species, Gypsophila paniculata, on sand dunes in northwest Michigan (USA). We measured G. paniculata abundance, plant species richness, plant community diversity, non‐native plant cover, abundance of Cirsium pitcheri (a federally threatened species endemic to this habitat), sand movement, arbuscular mycorrhizal spore abundance, and soil nutrients in fifteen 1000 m² plots yearly from 2007 to 2010 in order to evaluate the effectiveness of manual removal of this species on dune restoration. Gypsophila paniculata cover was greatly reduced by management, but was not entirely eliminated from the area. Removal of G. paniculata shifted plant community composition to more closely resemble target reference plant communities but had no effect on total plant diversity, C. pitcheri abundance, or other non‐native plant cover. Soil properties were generally unaffected by G. paniculata invasion or removal. The outlook is good for this restoration, as other non‐native species do not appear to be staging a “secondary” invasion of this habitat. However, the successional nature of sand dunes means that they are already highly invasible, stressing the need for regular monitoring to ensure that restoration progresses.     

白刺沙堆退化与土壤水分的关系

近几十年来,我国西北干旱区白刺沙堆退化严重,导致固定沙丘活化,流沙掩埋绿洲,造成了严重危害。如何尽可能长期保持白刺沙堆的稳定、防止白刺沙堆活化成为绿洲保护和沙漠化防治急需解决的问题。在多年野外观察的基础上,提出了"土壤水分收支不平衡所导致的土壤水分减少是白刺沙堆退化的主要原因"的研究假设。但是,由于缺少长期的野外观测试验,这个假设一直未被很好地证明。为了证明这个假设,在甘肃民勤的绿洲外围选择了雏形、发育、稳定和死亡四个退化阶段的白刺沙堆,于2008年1月至2012年6月利用中子水分仪和土壤烘干称重法对土壤水分进行了长期观测。结果表明:各样地的土壤含水量均呈现出2008年最大,2009年和2011年次之,2010年最小的趋势。年内变化是春季土壤含水量最低,夏季逐渐增加,随后逐渐减小。在不同发育阶段,雏形阶段的土壤含水量最大,且降水容易下渗。稳定和死亡阶段的白刺沙堆土壤含水量很低,降水难以下渗,只有大的降水事件发生时,水分才可以下渗。因此,稳定和死亡阶段白刺沙堆的土壤水分经常在植物的凋萎点之下,是造成白刺沙堆退化重要原因。证明了"土壤水分减少是白刺沙堆退化的原因"的研究假设。研究结果对今后的植物固沙实践活动会有积极的参考意义。     

Analysis of Fusarium causing dermal toxicosis in marram grass planters

In the European coastal dunes, marram grass (Ammophila arenaria) is planted in order to control sand erosion. In the years 1986 to 1991, workers on the Wadden islands in the Netherlands planting marram grass showed lesions of skin and mucous membranes, suggesting a toxic reaction. Fusarium culmorum dominated the mycoflora of those marram grass culms that were used for planting. This plant material had been cut and stored for more than one week in the open. The Fusarium toxin deoxynivalenol (DON) was detected in the suspect marram grass culms. Isolated F. culmorum strains were able to produce DON in vitro in liquid culture as well as in experimentally inoculated wheat heads. Pathogenicity tests, toxin test as well as RAPD analysis showed that the F. culmorum strains were not specialized for marram grass but may form part of the West-European F. culmorum population infecting cereals and grasses. Storage on old sand-dunes with plant debris may have led to the high occurrence of F. culmorum and contamination with DON. Marram grass culms should be obtained from young plantings on dunes on the seaward slopes and cut culms should not be stored.     

毛乌素沙地油蒿群落的循环演替

流动沙地→半流动沙地白沙蒿群落→半固定沙地油蒿＋白沙蒿群落→固定沙地油蒿群落→固定沙地油蒿＋本氏针茅＋苔藓群落→地带性的本氏针茅草原及其迅速沙化的植被发展过程是毛乌素沙地植被自发演替的基本过程。油蒿具有耐沙埋、抗风蚀、耐土壤贫瘠等特性,是该地区最主要的优良固沙植物和重要牧草。半固定、固定沙地池蒿群落在毛乌素沙地的生态环境保护和农牧业生产方面发挥着极其重要的作用,维持其稳定十分重要。然而,其沙化的现     

NUTRIENT LIMITATION OF BENTHIC ALGAE IN LAKE MICHIGAN: THE ROLE OF SILICA1

In the Laurentian Great Lakes, phytoplankton growth and biomass are secondarily limited by silica (Si), as a result of phosphorus (P) enrichment. Even modest levels of P enrichment can induce secondary Silimitation, which, in turn, promotes a shift from the native diatom phytoplankton flora to chlorophyte and cyanobacteria species. However, very little is known about the nutritional status of benthic populations and their response to nutrient enrichment. Two experiments were performed in the littoral zone of Lake Michigan where nutrients were delivered to in situ benthic algal (episammic and epilithic) assemblages using nutrient‐diffusing substrata. In order to test the hypothesis that benthic algae in Lake Michigan are Si limited, a 2 × 3 factorial experiment was used to deliver all combinations of Si, N, and P to resident assemblages growing on artificial substrata composed of natural (Si rich) versus calcium carbonate (Si poor) sand. A second experiment utilized a serial enrichment to evaluate the role of Si in mediating changes in taxonomic composition. These findings indicate that benthic algae in Lake Michigan exhibit signs of secondary Si limitation, and that their response to enrichment is similar to the phytoplankton. Moreover, natural sand substrata may provide a source of Si to resident benthic algae.