初始克隆分株数对大米草表型可塑性及生物量分配的影响

克隆植物大米草 (Spartina anglica) 目前在我国出现了严重的自然衰退 (Dieback),为了阐明大米草衰退的机理,分析影响大米草形态可塑性的因素与自然衰退之间的相关性,以期为近缘植物互花米草 (S. alterniflora) 这一爆发种群的生物控制提供借鉴,对3种不同初始克隆分株数 (单克隆、三克隆和五克隆) 大米草的克隆生长、生物量累积与分配和异速生长特征进行了野外栽培试验。研究结果表明,初始克隆分株数对间隔子长度影响较弱;初始多克隆的分支强度高于初始单克隆;初始三克隆和五克隆在总生物量 (7.921 5~10.431 7 g 和 8.903 9~10.431 7 g)、地上生物量 (3.396 1~4.255 8 g 和3.618 4~4.338 9 g)、地下生物量 (4.286 9~5.206 6 g 和 5.298 8~6.079 3 g)和根状茎生物量 (1.318 6~1.767 7 g 和 1.499 1~2.038 7 g) 积累上均显著高于初始单克隆,不同初始克隆分株数条件下根生物量差异不显著;初始多克隆倾向于将资源更多地分配给根状茎,而初始单克隆倾向于将更多的资源分配给根系。由此推断,在不同初始克隆分株数条件下,大米草的形态可塑性和生物量分配格局的差异显示出在同样资源格局下,初始多克隆的克隆生殖能力较初始单克隆强。初始多克隆生长的大米草较初始单克隆生长的大米草更能占据优势生境,选择生境“觅养”的能力与克隆繁殖能力更强。     

Evidence for effects of Spartina anglica invasion on benthic macrofauna in Little Swanport estuary,Tasmania

Spartina anglica is an exotic perennial grass that can rapidly colonise the intertidal zone of temperate estuaries and lagoons. Consequently, there is considerable concern about its impact on estuarine flora and fauna. This study provides the first investigation of ecological impacts by S. anglica in Australia. The objective was to investigate the impacts of S. anglica on benthic macroinvertebrate communities inhabiting mudflat and native saltmarsh habitats at Little Swanport estuary, Tasmania. The null hypothesis that species richness and species abundance of benthic macroinvertebrates in exotic S. anglica marsh does not differ from adjacent native saltmarsh and mudflat habitats was tested. Eighteen species and 3716 macroinvertebrates were collected from 60 intertidal core samples in three habitats. Species richness, total abundance of invertebrates, crustacean abundance and mollusc abundance of mudflat communities were significantly (P < 0.05) lower when compared to those inhabiting adjacent S. anglica marsh and native saltmarsh. However, species richness and total abundance of invertebrates of native saltmarsh and S. anglica marsh did not differ significantly. Ordination of macroinvertebrate data clearly separated mudflat sites from vegetated sites but showed remarkable similarity between exotic and native vegetated sites.     

Effects of drainage and soil organic content on growth of Spartina alterniflora (Poaceae) in an artificial salt marsh mesocosm

An artificial salt marsh mesocosm was constructed using 680-L polypropylene tanks to determine the effect of soil drainage depth and organic content on growth and rhizome proliferation of the salt marsh smooth cordgrass Spartina alterniflora. Soil drainage depth had no effect on accumulation of aerial or subsurface plant tissue, but tanks that had 2.5% soil organic content supported enhanced aerial tissue and rhizome growth compared to tanks that contained sand alone. We propose a mathematical model for predicting the mass of photosynthetically significant leaf tissue without cutting and drying leaves. Implications of these findings for salt marsh creation projects are discussed.     

Nitrogen cycling in Louisiana Gulf Coast brackish marshes

Nitrogen fixation and nitrogen accumulation were measured in a Louisiana Spartina patens brackish marsh. Using the acetylene reduction technique calibrated with direct ¹⁵N₂ assimilation, an equivalent of 90.0 µ g N g^–1 yr^–1 was fixed. Fixation was greater in the summer months and in the upper portion of the soil profile. Extractable ammonium increased with depth and was negatively correlated with ethylene production. Average ammonium concentration in the sediment was 39 µg NH₄ ⁺-N g^–1 sediment. Cesium-137 dating of the soil profile showed the marsh was vertically accreting at a rate of 0.60 cm yr^–1. Calculations using vertical accretion rate, bulk density, and total nitrogen content of sediment indicate that the marshes are accumumating 7.2 g Nm^–2 yr^–1 thus serving as a major nitrogen sink. Measured nitrogen fluxes were incorporated with existing flux measurement in developing a nitrogen budget for the marsh.     

Long-term photosynthetic response in single leaves of A C3 and C4 salt marsh species grown at elevated atmospheric CO2 in situ

Summary Mono-specific communities of the C₃ sedge, Scirpus olneyi and the C₄ grass, Spartina patens, were exposed to normal ambient or elevated CO₂, (ca. 680 l l^–1) throughout the 1987 and 1988 growing seasons in open-top field chambers located on a tidal marsh. Single stems of C₃ plants grown in ambient or elevated CO₂ showed an increased photosynthetic rate when tested at elevated CO₂ for both seasons. This increase in photosynthetic response in the C₃ species was maintained throughout the 1987 and 1988 growing season. The stimulation of photosynthesis with elevated CO₂ appeared to increase as temperature increased and decreased as photosynthetic photon flux (PPF) increased. Analysis of the photosynthetic response of the C₃ species during the 1988 season indicated that significant differences in light-saturated photosynthetic rate between ambient and elevated CO₂ conditions continued until October. In contrast to the C₃ sedge, the C₄ grass showed no significant photosynthetic increase to elevated CO₂ except at the beginning of the 1988 season.     

Halophytic crops for cultivation at seawater salinity

Summary Several hundred halophytes from salt marshes and salt deserts of the world have been evaluated in our laboratory at various degrees of intensity, and a few have been selected for development as crops. The development of the cultivars and the basic biology of the plants is being studied in Delaware in the United States. Agronomic testing, feeding trials, and development of the best agronomic practices are taking place in the saline desert at the American University in Cairo research station in Sadat City. Our present efforts focus primarily on three forages, one grain, and one vegetable.Sporobolus virginicus cultivars for both hay and pasture are being tested. ADistichlis spicata cultivar for hay has been identified, andSpartina patens is being evaluated as a hay as well. Although we do not yet have the data for a full year's growth in Egypt, forage yields of these various cultivars, when harvested as hay crops, range to 6.9 or more tons per acre, depending on the salinity and other environmental conditions, and the crude protein content as indicated by the nitrogen content ranges from 6 to 10%. Cultivars having the most useful agronomic qualities have been identified and are being increased in quantity. The grain cropKosteletzkya virginica is a perennial, producing a seed which resembles millet; its whole seeds contain approximately 25% protein and 15% oil. The yields of one of our better cultivars are about 1460 kg/ha (1300 lb/acre) when grown under 25 salinity. The vegetableAtriplex triangularis (similar to spinach) has been under mass selection for four years; a cultivar has been identified and seed is now being increased for this species.     

入侵种互花米草空间扩张模式识别与景观变化模拟

在3S技术支撑下,通过景观格局指数、质心变化等方法,分析2006—2015年研究区内互花米草群落的景观空间分布特征,并利用2015年高分二号影像识别出扩张模式及预测扩张趋势。结果表明:(1)近年来,互花米草沼泽向陆扩张速度大于向海扩张速度,其质心不断向陆方向移动。(2)2006—2015年,互花米草斑块密度变大,面积加权平均形状指数也相应增大为8.63,景观形状越来越复杂。(3)利用LEI和PFD识别出互花米草的3种扩张模式,边缘扩张面积远大于外部隔离扩张面积,外部隔离扩张斑块数量远多于边缘扩张和潮沟引领式扩张斑块数之和,潮沟对互花米草的向陆扩张起到引领作用。(4)利用缓冲区分析模拟互花米草向陆扩张的趋势,未来5年碱蓬沼泽的面积将减少11.45%。研究可为进一步认识互花米草入侵碱蓬沼泽机制提供科学参考。     

Effects of Spartina alterniflora invasion on soil organic carbon composition of mangrove wetland in Zhangjiang River Estuary

红树林对全球气候变化敏感, 近年来不少区域又受互花米草(Spartina alterniflora)入侵的影响, 土壤碳库组成发生显著变化, 然而鲜有从有机碳官能团特征角度出发的关于两群落的研究。为了解在红树林群落与互花米草群落下土壤碳库及其有机碳官能团的特征差异, 在福建省云霄县漳江口红树林自然保护区湿地内由内陆到海岸方向选取3条样带, 每条样带依次选取3个样地: 红树林群落(MC)、秋茄(Kandelia obovata)-互花米草过渡带(TC)和互花米草群落(SC), 每个样地选取3个呈品字形分布的采样点, 分5层采集0-100 cm土壤样品, 分析土壤中的总有机碳(TOC)、颗粒有机碳(POC)以及可溶性有机碳(DOC)特征, 并利用核磁共振波谱法测定表层0-15 cm与深层75-100 cm土壤总有机碳官能团特征, 以空间换时间法研究入侵前后土壤碳库变化特征。结果表明: (1)从MC群落到SC群落, 土壤有机碳库显著减小, 各样地总有机碳与颗粒有机碳含量表现为MC > TC > SC, 并随着土层深度增加而减少, DOC含量没有表现出明显的变化趋势。(2)各植被类型土壤有机碳以烷基碳与烷氧碳为主, 其次是芳香碳与羰基碳, N-烷氧碳与酚基碳含量最少, 其中表层0-15 cm土壤从红树林群落到互花米草群落, 烷基碳与烷氧碳含量呈现增加趋势但不显著, 芳香碳与酚基碳含量显著减少, 其余有机碳组分含量无显著差异。在深层75-100 cm随着植被类型的改变, 土壤有机碳组成结构均无显著差异。(3)在0-15 cm土层, 烷基碳/烷氧碳含量表现为: SC > MC > TC; 芳香度表现为SC最小, MC与TC无显著差异; 疏水碳/亲水碳无显著差异; 脂族碳/芳香碳表现为SC显著大于其他两种植被类型, MC与TC无显著差异。在75-100 cm土层, 各比值无显著差异。综上所述, 红树林群落碳储量显著高于互花米草群落, 受植被的影响, 互花米草群落表层土壤有机碳分解程度显著高于红树林群落, 而红树林群落的土壤有机碳分子结构要比互花米草群落更复杂, 以维持其土壤有机碳的稳定性。因此, 互花米草入侵红树林后可能会加快有机碳的分解, 最终稳定在相对简单的分子结构, 降低土壤碳储量。     

Strong associations between plant genotypes and bacterial communities in a natural salt marsh

Although microbial communities have been shown to vary among plant genotypes in a number of experiments in terrestrial ecosystems, relatively little is known about this relationship under natural conditions and outside of select model systems. We reasoned that a salt marsh ecosystem, which is characterized by twice‐daily flooding by tides, would serve as a particularly conservative test of the strength of plant–microbial associations, given the high degree of abiotic regulation of microbial community assembly resulting from alternating periods of inundation and exposure. Within a salt marsh in the northeastern United States, we characterized genotypes of the foundational plant Spartina alterniflora using microsatellite markers, and bacterial metagenomes within marsh soil based on pyrosequencing. We found significant differences in bacterial community composition and diversity between bulk and rhizosphere soil, and that the structure of rhizosphere communities varied depending on the growth form of, and genetic variation within, the foundational plant S. alterniflora. Our results indicate that there are strong plant–microbial associations within a natural salt marsh, thereby contributing to a growing body of evidence for a relationship between plant genotypes and microbial communities from terrestrial ecosystems and suggest that principles of community genetics apply to this wetland type.     

Can perennial C4 grasses attain high efficiencies of radiant energy conversion in cool climates?

Although C₄ plants are considered to have higher conversion efficiency and productivity than C₃, plants, this advantage may not be realized under sub-optimal conditions. Two perennial C₄ rhizomatous grasses of cool temperate origin, Miscanthus × giganteus and Spartina cyno-suroides, have been suggested as potential fuel crops for north-western Europe. The conversion efficiencies of these species were examined for 2 years in fertilized, irrigated, replicated plots in south-eastern England. In the second year, the energy conversion efficiencies for shoot and total biomass production were 0.040 and 0.051, respectively, for S. cynosuroides, with significantly higher values of 0.060 and 0.078, respectively, for M. × giganteus. The M. × giganteus crop attained shoot productivity of 2.87 kg m^?2 between April and September, exceeding the highest values typically obtained with intensively managed C₃, crops. Canopy development was early, and high interception and conversion efficiencies were maintained over most of the growing season. This study provides the evidence that the superior potential light conversion efficiencies associated with C₄ photosynthesis can be realized under cool temperate conditions and that such climatic conditions do not Inherently impair the C₄ process.