高原湿地纳帕海水生植物群落分布格局及变化

采用3S技术与植物群落研究法,对高原湿地纳帕海24a来的湿地植物群落分布格局及变化的研究结果表明：与24a前水生植物群落相比较。纳帕海水生植物群落类型、数量改变,原生群落不断减少或消失,耐污、喜富营养类群如水葱群落（Com．Scirpus tabernaemontani）、茭草群落（Com．Zizania caduciflora）、穗状狐尾藻群落（Com．Myriophyllum spicatum）、满江红（Com．Azolla imbricata）群落等大量出现;群落总数由24a前的9个增至当前的12个,其中挺水植物群落增加2个,浮叶植物群落增加1个,挺水植物群落增幅最大。由东向西、由南向北,纳帕海水生植物群落分布大致呈现出浮叶群落、挺水群落、沉水群落斑块状依次配置的水平格局规律。挺水植物群落分布面积最大,达528．42hm^2,其次是沉水植物群落,分布面积为362．50hm^2,浮叶植物群落分布面积最小,为70．23hm^2。随沉水群落、浮叶群落向挺水群落的演替,群落伴生种数量增加、优势种优势度减小、层次类型改变,群落结构变得更为复杂。纳帕海湿地水生植物群落分布格局及变化是对湿地环境变化的响应,表明了在人为干扰作用影响下,纳帕海湖岸线内移、水量减少、水质恶化等湿地水文条件的改变,致使湿地生态系统功能不断退化。     

若尔盖湿地退化过程中土壤水源涵养功能

若尔盖湿地是青藏高原上面积最大的沼泽湿地,也是长江、黄河两大河流的水源区,对区域水循环起重要调节作用。近年来在全球变化及放牧的影响下,若尔盖湿地出现了不同程度的退化。为了查明若尔盖湿地退化过程中水源涵养功能的变化趋势,2009年8月对该区域的沼泽草甸、草原草甸和沙化草甸3个阶段的土壤水源涵养功能进行了调查。结果为:若尔盖湿地由沼泽草甸向草原草甸和沙化草甸的退化过程中,土壤容重显著增加(P<0.01),毛管孔隙度和总孔隙度显著下降(P<0.01),且容重和孔隙度在土壤剖面自然分布规律也发生变化;沼泽草甸的土壤自然含水量、毛管持水量、最小持水量和最大持水量均显著高于草原草甸和沙化草甸(P<0.01);0-100 cm 深度范围内的沼泽草甸土壤的最大持水量(8486.27 t/hm²)显著高于草原草甸(4944.98 t/hm²)和沙化草甸(4637.96 t/hm²)(P<0.01)。土壤持水量与有机质含量、毛管孔隙度和总孔隙度有显著正相关(P<0.01),与土壤容重呈显著负相关(P<0.01),并受植被盖度和泥炭层厚度的影响。研究结果表明,若尔盖湿地退化过程中植被盖度、土壤有机质含量及泥炭层厚度的下降和土壤质地沙化是导致若尔盖湿地水源涵养功能下降的主要原因。     

黑河流域中游水生维管植物群落及其生态特征研究

黑河流域中游位于河西走廓中段 ,界于东经 90°2 0′～ 1 0 2°1 2′,北纬 37°2 8′～ 39°57′。经调查有 1 1种水生植物群落 :线叶眼子菜群落 ( Co.Potamogeton pusillus)、线叶眼子菜—狐尾藻群落 ( Co.P.pusillus- Myriophyllum spicatum)、水菖蒲群落 ( Co.Acorus calamus)、沼针蔺群落 ( Co.Eleocharis valleulosa)、沼针蔺—水葱群落 ( Co.E.valleulosa- Scirpus triqueter)、芦苇群落 ( Co.Phragmites communis)、镳草—水烛群落 ( Co.Scirpus triqueter)、浮叶眼子菜群落( Co.Potamogeton natans)、浮叶眼子菜—狐尾藻群落 ( Co.P.natans- Myriophyllumverticillatum )、黑三棱群落 ( Co.Sparganium stoloniferum)、小花灯芯草—泽泻群落 ( Co.Juncua articulatus- Alisma orientale)。在以上群落中有水生植物 38种。世界淡水广布群落是本区的主要群落 ,阐述了水生植物群落的形态特征、分布现状、生长环境和群落结构等特征并探讨了其演替规律。     

施氮量对麻疯树幼苗生长及叶片光合特性的影响

采用盆栽土培的方法,研究了不同施氮量(对照N₀ 0 kg N/hm²、低氮N_L 96 kg N/hm²、中氮N_M 288 kg N/hm²、高氮N_H 480 kg N/hm²)对麻疯树幼苗生长、叶片气体交换及叶绿素荧光参数的影响。结果表明,麻疯树幼苗叶片氮含量、可溶性蛋白含量、株高、地径、叶片数量、叶面积、根长、各组分生物量、叶片净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)和水分利用效率(WUE)均随施氮量的增加先升高后降低,N_M处理下麻疯树幼苗长势最好,各气体交换参数值最高;施氮对麻疯树地上部分的促进作用远大于地下部分,施氮后根冠比显著降低;此外,麻疯树叶绿素含量、PSⅡ最大光化学量子产量(Fv/Fm)、PSⅡ有效量子产量(F'v/F'm)、PSⅡ实际光化学效率(Φ_PSⅡ)、电子传递速率(ETR)和光化学淬灭系数(qP)均随施氮量的增加而升高,非光化学淬灭系数(NPQ)随施氮量增加而降低。适量施氮可通过增强叶绿体光化学活性、气孔导度和羧化能力而提高麻疯树幼苗的光合能力,促进生长;过高施氮对麻疯树幼苗光合与生长的促进效应降低。试验条件下,当年生麻疯树幼苗的最适施氮量为288 kg N/hm²。     

假臭草等12种植物对白花鬼针草幼苗的化感作用

用具有化感作用或潜在抑草活性的12种植物的叶片水浸液对白花鬼针草(Bidens alba)幼苗进行处理,对其幼苗的生长 进行研究,以期筛选出对白花鬼针草生长有较强抑制作用的植物种类。结果表明,12种供体植物叶片水浸液(0.05 g DW mL^-1) 均能显著抑制白花鬼针草幼苗的生长(P<0.05),综合化感效应(SE)均为负值(≤-0.2),抑制强度依次为假臭草(Eupatorium catarium)>胜红蓟(Ageratum conyzoides)>海芋(Alocasia macrorrhiza)>水茄(Solanum torvum)>马缨丹(Lantana camara)>薇甘菊(Mikania micrantha)>构树(Broussonetia papyrifera)>南美蟛蜞菊(Wedelia trilobata)>三裂叶薯(Ipomoea triloba)>葛藤(Pueraria lobata)>鸡矢藤(Paederia scandens)>五爪金龙(Ipomoea cairica),其中假臭草叶水浸液浓度仅为0.04 g DW mL^-1时就可以使白花鬼针草死亡。假臭草和胜红蓟的茎水浸液也可以显著抑制白花鬼针草的生长(P<0.05),抑制效果略低于叶水浸液。回归分析表明,假臭草叶水浸液浓度与白花鬼针草的生物量等指标之间有线性回归关系(R²>0.85, P<0.001),随着水浸液浓度的增加,白花鬼针草的生物量等指标下降。防除白花鬼针草时使用假臭草和胜红蓟的茎、叶水浸液, 其有效浓度低且资源丰富,可作为白花鬼针草天然除草剂的主要资源植物。     

马尾松人工林近自然化改造对植物自然更新及物种多样性的影响

中国人工林面积居世界第一位,而马尾松是中国人工林面积较大的树种之一,广泛分布于中国的亚热带区域。马尾松适应能力强,耐干旱、瘠薄,是南方低山丘陵区群落演替的先锋树种,也是荒山绿化造林的主要树种,马尾松人工林对生态防护、生态治理有着重大的意义。但是,绝大部分马尾松人工林为人工纯林,生态系统比较脆弱,生态服务功能较差。人工林的近自然改造对于增加林地生物多样性,提升人工林的生态服务功能具有重要意义。2005年,对中国林业科学院热带林业试验中心1993年造林的马尾松人工林进行4种不同强度(50%、40%、30%、20%)间伐后,套种大叶栎(Castanopsis fissa)、米老排(Mytilaria laosensis)、润楠(Machilus pingii)、红锥(C. hystrix)4个乡土阔叶树种,各种套种密度皆为120株/hm²。分别于间伐前(2004年)及2010年对群落生物多样性及人工套种树种生态情况进行调查,结果表明:(1)间伐处理后,自然更新至乔木层的物种种类和数量都有显著的增加,600 m²的样方中,物种数由(2.75±2.56)种增加到(11.17±4.32)种,个体数由(5.75±4.31)株增加到(32.17±19.09)株,群落中乔木亚层的优势种变化不大,主要有南酸枣(Choerospondias axillaris)、水锦树(Wendlandia uvariifolia),枫香(Liquidambar formosana)、破布木(Cordia dichotoma)、白背桐(Mallotus paniculatus)等。新增加到乔木层的物种大都为之前群落中灌木层的种类,主要有三桠苦(Evodia lepta)、鸭脚木(Schefflera minutistellata)、白花龙(Styrax faberi)、中平树(Macaranga denticulata)、黄毛榕(Ficus esquiroliana)、华南毛柃(Eurya ciliata)、罗浮柿(Diospyros morrisiana)、猴耳环(Pithecellobium clypearia)、木姜子(Litsea pungens)、毛黄肉楠(Actinodaphne pilosa)等。(2)间伐处理前,600 m²样方中出现的灌草种类数量为(24.63±4.24)种,间伐处理后,600 m²样方中出现的灌草种类数量为(27.58±3.80)种,不同间伐强度处理后林下灌草的优势种与间伐前大致相同,灌木层优势种为三桠苦,草本层优势种为弓果黍(Cyrtococcum patens)。不同间伐强度处理林分间,灌木层和草本层的物种丰富度指数、Shannon-Wiener指数、Simpson指数和Pielou指数均无显著差异,且与间伐前林分也无显著差异。(3)间伐促进了4个乡土树种幼树的生长,随着间伐强度的增加,大叶栎、红锥幼树的高度和胸径显著增长;50%的间伐强度的林分中,阔叶树种幼树的长势要显著好于其他间伐强度,50%的间伐强度最有利于马尾松林下套种的阔叶树种生长。(4)在马尾松林下套种的4个阔叶树种幼树的初期生长有明显差异。总体而言,大叶栎与米老排幼树的早期生长速率要明显高于红锥和润楠。     

竹叶眼子菜种群遗传多样性与群落物种多样性关系的研究

以洪湖中的沉水植物群落及其优势种竹叶眼子菜(Potamogeton wrightii Morong)为研究对象,利用AFLP分子标记结合野外调查的方法,分析保护区(干扰较小)与非保护区(干扰较大,敞水区)中沉水植物群落的物种多样性与竹叶眼子菜遗传多样性之间的相关性。结果显示:洪湖沉水植物群落物种丰富度(S)和物种多样性辛普森指数(D)在保护区和非保护区均未发现显著性差异;竹叶眼子菜的重要值(IV)在保护区(5.2%~23.2%)较非保护区(8.5%~73.3%)稳定。竹叶眼子菜的遗传多样性在两个区未发现显著差异,其遗传多样性与群落物种多样性这两个指标在保护区、非保护区及全湖水平均不相关,说明沉水植物群落的物种多样性和竹叶眼子菜的遗传多样性对不同环境干扰的响应有所差异。     

亚热带4种森林凋落物量及其动态特征

通过对枫香林、樟树林、马尾松林、樟树—马尾松混交林4种森林生态系统的凋落物数量及组成进行为期1a的定位研究。结果表明,樟树—马尾松混交林的年凋落总量(4.30 t.hm^-2)＞枫香林(3.66 t.hm^-2)＞马尾松林(3.41 t.hm^-2)＞樟树林(3.26 t.hm^-2)。各组分凋落物中,凋落叶占绝对优势(70%以上),表现为樟树—马尾松混交林(3.09 t.hm^-2)＞枫香林(2.78 t.hm^-2)＞马尾松林(2.46 t.hm^-2)＞樟树林(2.32 t.hm^-2);凋落枝表现为樟树—马尾松混交林(0.73 t.hm^-2)＞樟树林(0.53 t.hm^-2)＞马尾松林(0.30 t.hm^-2)＞枫香林(0.22 t.hm^-2);凋落果表现为马尾松林(0.37 t.hm^-2)＞樟树—马尾松混交林(0.17 t.hm^-2)＞枫香林(0.12 t.hm^-2)＞樟树林(0.09 t.hm^-2);碎屑表现为枫香林(0.55 t.hm^-2)＞樟树林(0.33 t.hm^-2)＞樟树—马尾松混交林(0.31 t.hm^-2)＞马尾松林(0.27 t.hm^-2)。枫香和樟树林年凋落量的最大值分别在10月(1.22 t.hm^-2)和8月(0.58 t.hm^-2),而马尾松林和混交林年凋落量的最大值都在11月(分别为0.77 t.hm^-2和1.23 t.hm^-2)。     

太湖水生植物氮磷与湖水和沉积物氮磷含量的关系

 分析了太湖沉水植物、浮叶植物组织及生长环境中的N、P含量,结果表明：太湖沉水植物组织N、P含量一般要高于浮叶植物组织,5月的N、P含量(以干重计)一般高于9月。5月以沉水植物微齿眼子菜(Potamogeton maackianus)的N(28.452 mg?g－1)、轮叶黑藻(Hydrilla verticillata)的P(4.552 mg&;#8226;g^－1)含量最高,浮叶植物荇菜(Nymphoides peltatum)的N(14.363 mg&;#8226;g^－1)、P(1.792 mg&;#8226;g^－1)含量均为最低;9月以沉水植物苦草(Vallisneria natans)的N(25.206 mg&;#8226;g^－1)、P(2.727 mg&;#8226;g^－1)含量最高,浮叶植物荇菜的N(17.245 mg&;#8226;g^－1) 、P(1.519 mg&;#8226;g^－1)含量均最低。沉水和浮叶植物的N、P含量与水体N、P浓度的相关性较为显著;与沉积物N、P的相关性不明显。此外,植物体内的N、P含量亦与植物物种的特性、生长发育阶段和生长状况等内在因素密切相关。     

牡竹属三竹种的秆形质量与材性比较

对牡竹属(Dendrocalamus) 3个竹笋品质佳的竹种［勃氏甜龙竹(D. brandisii)、马来麻竹(D. asper)、花吊丝竹(D. minor var. amoenus)］的竹材形态质量及材性进行比较研究。结果表明:种间的立竹枝下高、相对全高的差异显著或极显著,勃氏甜龙竹相对枝下高最小,立竹胸径、全高、枝下高、尖削度值、壁厚率均为最大;竹秆含水率随立竹年龄增大而下降,3年生立竹的竹秆含水率为花吊丝竹>勃氏甜龙竹>马来麻竹,种间差异极显著;相对材积为勃氏甜龙竹(1771.35 cm³ cm^-1)>马来麻竹(1166.66 cm³ cm^-1)>花吊丝竹(659.78 cm³ cm^-1),种间差异极显著;竹材密度随立竹年龄增大而提高,3年立竹的竹材密度为花吊丝竹(0.914 g cm^-3)>勃氏甜龙竹(0.812 g cm^-3)>马来麻竹(0.749 g cm^-3),种间差异显著。因此,勃氏甜龙竹、马来麻竹可作为优良的笋材兼用竹种,而花吊丝竹宜作为笋用、观赏竹种推广应用。     

Distribution patterns and changes of aquatic plant communities in Napahai Wetland in northwestern Yunnan Plateau, China

Using GPS technology and community research methods for plant communities, we investigated the distribution patterns of aquatic plant communities in the high plateaus of the Napahai Wetlands, Yunnan, China, as well as the species changes of plant communities compared with that of 24 years ago since 2005. We found that the types and numbers of aquatic plant communities have changed. Some pollution-tolerant, nutrient-loving plant communities such as Scirpus tabernaemontani, Zizania caduciflora, Myriophyllum spicatum, and Azolla imbricata flourished, while the primary aquatic plant communities were reduced or even disappeared. The number of aquatic plant communities were increased from nine to 12 with the addition of two new emergent plant communities and one new floating-leaved plant community. The increase in emergent plant communities was significant. From east to west and from south to north, various types of plant communities were continuously distributed, including floating-leaved plant communities, emergent plant communities and submerged plant communities. The composition of the communities became more complicated and the number of accompanying species increased, while the percentage ratio of dominant plant species declined. In 2005, the coverage of emergent plant communities was the largest (528.42 hm²) followed by submerged plant communities (362.50 hm²) and the floating-leaf plant communities was the smallest (70.23 hm²). The variations in the distribution of aquatic plant communities in the Napahai Wetlands reflect the natural responses to the change of the wetland ecological environment. This study indicates that human disturbances have led to an inward movement of the wetland shoreline, a decrease in water quality and a reduction in wetland habitat. __________ Translated from Acta Ecologica Sinica, 2006, 26(11): 3624–3630 [译自: 生态学报]     

Effects of different macrophyte growth forms on sediment and P resuspension in a shallow lake

The effects of floating-leaved, submerged and emergent macrophytes on sediment resuspension and internal phosphorus loading were studied in the shallow Kirkkojärvi basin by placing sedimentation traps among different plant beds and adjacent open water and by sediment and water samples. All the three life forms considerably reduced sediment resuspension compared with non-vegetated areas. Both among submerged (Ceratophyllum demersum, Potamogeton obtusifolius, Ranunculus circinatus) and emergent (Typha angustifolia) plants, resuspension rate was on average 43% of that in the adjacent open water, while within floating-leaved plants (Nuphar lutea) the corresponding value was 87%. The effects of submerged and emergent vegetation increased in the course of the growing season together with increasing plant density. Among floating-leaved vegetation, such seasonal trend in resuspension effects was not observed. Compared with the non-vegetated area, floating-leaved, submerged and emergent plants reduced internal phosphorus loading on average by 21, 12 and 26 mg m⁻² d⁻¹, respectively. The effects of floating-leaved plants on resuspension-mediated internal phosphosrus loading were thus comparable to the effects of the other two life forms.     

Seed Bank Variation Along a Water Depth Gradient in a Subtropical Lakeshore Marsh,Longgan Lake,China

Although zonation patterns of the standing vegetation along a water depth gradient in wetlands have been well described, few studies have explored whether such patterns also occur in the seed bank. This study examined patterns of the seed bank along a water depth gradient in three vegetation types (submerged zone, floating-leaved zone, and emergent zone) of a subtropical lakeshore marsh, Longgan Lake, China. Submerged zone is the deepest water and never exposed its soil to air, and was dominant by submerged species; floating-leaved zone is waterlogged soil even during drawdown and was dominant by Nelumbo nucifera; emergent zone is rarely exceeded 1 m water depth during the wet season (summer and autumn), and the marsh soil was usually exposed to air during drawdown (winter and spring), and is dominant by Zizania latifolia, Polygonum hydropiper and Scirpus yagara. It was found that many species were ubiquitous in the seed bank. Frequency of distribution and densities of the dominant species, however, varied significantly from zone to zone. A total of 22 species was recorded in submerged zone, 20 in floating-leaved zone, and 29 in emergent zone. Germinated seedling density was 1,580, 8,994 and 20,424 seedlings m⁻² in submerged zone, floating-leaved zone, and emergent zone, respectively. Submerged and floating-leaved species were significantly abundant in the submerged zone, while the emergent species were found predominantly in the emergent zone. A fern species, Ceratopsis pterioides, was the most abundant seedling in seed banks from all three zones. A TWINSPAN dendrogram and CCA ordination diagram clearly showed separation of species among sites with the emergent zone being well separated from the submerged zone and floating-leaved zone, thus revealing marked zonal patterns in species distributions in the seed bank. This pattern of zonation reflected the pattern in the standing vegetation.     

鄱阳湖湿地景观恢复的物种选择及其对环境因子的响应

湿地是重要的生态系统,对人类和野生生物都具有极其重要的价值。由于自然因素的变化和人类活动的干扰,湿地退化严重。近年来,湿地恢复已成为世界环境问题改善的重要工具之一。选择适用的湿地植物是退化湿地恢复的关键途径。本文以鄱阳湖湿地为研究对象,通过专家赋值、野外调查、定位观测等方法,筛选了苦草、野菱、芦苇、苔草等25种鄱阳湖常见植物作为湿地景观恢复的优先物种。对苦草、黑藻、菹草、菖蒲、芦苇等5种植物对环境因子的响应进行观测。结果表明,苦草在清水环境130-140cm处的生长最好;黑藻在清水环境中100-110cm处的生长最好;菹草在不同水深(50-160cm)下都能够生长,菹草高度随水深增加而增加;菖蒲具有一定的耐淹能力(< 80cm),但完全淹水(水深100-120cm)明显影响到菖蒲根状茎萌发、幼苗生长和生物量的积累;芦苇根状茎萌发对水深要求严格,土壤要湿润且透气性良好才是芦苇萌发的最好条件,芦苇根状茎萌发前淹水超过20 cm其萌发将会受到明显抑制,淹水超过30 cm则无法萌发。通过对沉水植物的透明度研究表明,植物对水质的透明度都有一定的要求,透明度较好更利于湿地植物的生长发育。     

Seed Banks in Arid Wetlands with Contrasting Flooding,Salinity and Turbidity Regimes

Aquatic plant communities in arid zone wetlands underpin diverse fauna populations and ecosystem functions yet are relatively poorly known. Erratic flooding, drying, salinity and turbidity regimes contribute to habitat complexity, creating high spatial and temporal variability that supports high biodiversity. We compared seed bank density, species richness and community composition of aquatic plants (submergent, floating-leaved and emergent) among nine Australian arid zone wetlands. Germinable seed banks from wetlands within the Paroo and Bulloo River catchments were examined at nested scales (site, wetland, wetland type) using natural flooding and salinity regimes as factors with nondormant seed density and species richness as response variables. Salinity explained most of the variance in seed density (95%) and species richness (68%), with flooding accounting for 5% of variance in seed density and 32% in species richness. Salinity-flooding interactions were significant but explained only a trivial portion of the variance (<1%). Mean seed densities in wetlands ranged from 40 to 18,760 m⁻² and were highest in wetlands with intermediate levels of salinity and flooding. Variability of densities was high (CVs 0.61–2.66), particularly in saline temporary and fresh permanent wetlands. Below salinities of c. 30 g l⁻¹ TDS, seed density was negatively correlated to turbidity and connectivity. Total species richness of wetlands (6–27) was negatively correlated to salinity, pH and riverine connectivity. A total of 40 species germinated, comprising submergent (15 species), floating-leaved or amphibious (17 species), emergent (6 species) and terrestrial (6 species) groups. Charophytes were particularly important with 10 species (five Chara spp., four Nitella spp. and Lamprothamnium macropogon), accounting for 68% of total abundance. Saline temporary wetlands were dominated by Ruppia tuberosa, Lamprothamnium macropogon and Lepilaena preissii. Variable flooding and drying regimes profoundly altered water quality including salinity and turbidity, producing distinctive aquatic plant communities as reflected by their seed banks. This reinforces the importance of hydrology in shaping aquatic biological communities in arid systems.     

An assessment of vegetation and environmental controls in the 1970s of the Mesopotamian wetlands of southern Iraq

A vast ecosystem of wetlands and lakes once covered the Mesopotamian Plain of southern Iraq. Widespread drainage in the 1990s nearly obliterated both components of the landscape. This paper reports the results of a study undertaken in 1972–1975 on the vegetation of the wetlands prior to drainage and provides a unique baseline for gauging future restoration of the wetland ecosystems in Mesopotamia. Five representative study sites were used to assess the flora, three of which were wetlands. A total of 371 plant species were recorded in the five sites, of which approximately 40% represent obligate or facultative wetland species. The wetland vegetation was classified into five major physiognomic forms (submerged, floating, herbaceous tall emergent, herbaceous low emergent and woody low emergent), which was further subdivided into 24 fresh and halophytic communities. Water levels greatly fluctuated across the different types of wetlands, and mean surface water depth ranged from below to greater than 2 m above the sediment surface, reflecting permanently, seasonally or intermittently wet habitats. Aboveground biomass was also highly variable among the communities. The Phragmites australis community, which was the most extensive community type, had the greatest biomass with an average value of approximately 5,000 g m⁻² in summer. Distribution and community composition were largely controlled by water levels and saline-freshwater gradients. Canonical correspondence analysis showed that salinity and water depth were the most important factors to explain species distribution. Environmental variables related to soil salinity separated halophytic species in woody low emergent and herbaceous low emergent forms (Tamarix galica, Cressa cretica, Alhagi mannifera, Aeluropus lagopoides, Juncus rigida, and Suaeda vermiculata) from other species. Their habitats were also the driest, and soil organic matter content was lower than those of other species. Habitats with deepest water were dominated by submerged aquatic and floating leaved species such as Nymphoides peltata, Ceratophyllum demersum, and Najas armata. Such diverse environmental conditions in the Mesopotamian wetland would be greatly affected by evapotranspiration, river water inputs from north, ground water inputs, local soil conditions, and a tide or seiche-controlled northward transgression of water from the Gulf. These environmental conditions should be considered in restoration plans if plant communities existed in the mid-1970s are to be part of the desired restoration goals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Distribution patterns and changes of aquatic plant communities in Napahai Wetland in northwestern Yunnan Plateau,China

Using GPS technology and community research methods for plant communities,we investigated the distribution patterns of aquatic plant communities in the high plateaus of the Napahai Wetlands,Yunnan,China,as well as the species changes of plant communities compared with that of 24 years ago since 2005.We found that the types and numbers of aquatic plant communities have changed.Some pollution-tolerant,nutrient-loving plant communities such as Scirpus tabernaemontani,Zizania caduciflora,Myriophyllum spicatum,and Azolla imbricata flourished,while the primary aquatic plant com-munities were reduced or even disappeared.The number of aquatic plant communities were increased from nine to 12 with the addition of two new emergent plant com-munities and one new floating-leaved plant community.The increase in emergent plant communities was signifi-cant.From east to west and from south to north,various types of plant communities were continuously distributed,including floating-leaved plant communities,emergent plant communities and submerged plant communities.The composition of the communities became more com-plicated and the number of accompanying species increased,while the percentage ratio of dominant plant species declined.In 2005,the coverage of emergent plant communities was the largest (528.42 hm2) followed by submerged plant communities (362.50 hm2) and the float-ing-leaf plant communities was the smallest (70.23 hm2).The variations in the distribution of aquatic plant com-munities in the Napahai Wetlands reflect the natural responses to the change of the wetland ecological envir-onment.This study indicates that human disturbances have led to an inward movement of the wetland shoreline,a decrease in water quality and a reduction in wetland habitat.     

The aquatic plant communities of the Lake Naivasha wetland,Kenya: pattern,dynamics and conservation

The spatial and temporal patterns of the wetland plant communities at Lake Naivasha over the past decade, and the past five years in particular, are discussed in relation to the major controlling factors. The four communities are:- the emergent swamp, dominated by Cyperus species; the floating raft, dominated by the aliens Salvinia molesta and Eichhornia crassipes; the floating-leaved plants, represented only by Nymphaea caerulea; and the submerged angiosperms, consisting of three species of Potamogetons — P. pectinatus, P. schweinfurthii, P. octandrus — together with Najas pectinata. The major factors affecting their dynamics are:- water level changes which influence agricultural clearance, introduced crayfish Procambarus clarkii, and interactions between communities such as the physical effects of mobile floating rafts. The value of the different communities to the ecological and economic value of the lake is highlighted, and the possible damage from future activities discussed.     

WETLANDS AS ACCRETING SYSTEMS: NUTRIENT CYCLING IN WETLANDS

SUMMARY

The major concepts involved in nutrient cycling in wetlands are discussed using phosphorus and nitrogen as examples. The differences in nutrient cycling patterns between hydrologically contrasting wetlands, and the significance of fluctuating water levels in wetlands, are stressed. In South Africa, some research into nutrient cycling in submerged aquatic macrophyte communities has been undertaken, but very little information is available on these processes in wetlands dominated by emergent vegetation forms. Generally, the information available on nutrient cycling processes in South African wetlands is of limited applicability to the assessment of nutrient cycling in whole wetland systems. Therefore, rational wetland management strategies require further research on nutrient cycling.