衰亡期沉水植物对水和沉积物磷迁移的影响

通过室内模拟的方式,分别研究了秋季黑藻、苦草和春季菹草的衰亡过程,分析了沉水植物在衰亡期间水、沉积物中磷与环境因子[pH、氧化还原电位(Eh)和溶解氧(DO)]的相互作用.结果表明:沉水植物黑藻和菹草在衰亡期间能显著提高水中总磷(TP)、溶解性总磷(DTP)、颗粒磷(PP)、溶解性活性磷(SRP)和溶解性有机磷(DOP)的含量;苦草在衰亡期对水体各形态磷含量影响不显著,且各形态磷含量的变化相对较小(TP,0.04-0.06 mg/L);环境因子的变化对水中磷含量影响显著,黑藻和菹草水体中TP的含量和环境因子pH、DO和Eh均呈负相关,而苦草组水中各形态磷的含量受环境因子影响不显著.实验期间不同植物组沉积物中总磷(TP)、NaOH提取磷(NaOH-P)、HCl提取磷(HCl-P)、无机磷(IP)和有机磷(OP)的含量均呈上升趋势.沉积物IP的含量主要受NaOH-P的影响,OP对TP的影响要大于IP,沉积物OP与OM(有机质)的含量存在显著正相关.     

山东省南四湖夏冬季沉积物及间隙水中磷分布特征及其相关性

利用柱状沉积物采样器和Peeper间隙水采集器,分别于夏冬两季获取山东省南四湖不同湖区原位柱状沉积物和间隙水,分析沉积物磷形态和间隙水磷分布特征,探讨沉积物和间隙水磷之间的相关性.结果表明:南四湖沉积物含有较丰富的磷,空间差异性显著,总体呈北高南低的趋势.这与南四湖北部距离济宁市区较近、受污染较重有关.各磷形态组分中以无机磷(IP)含量最高,夏冬两季IP含量分别占总磷(TP)的52.3％～87.2％和60.6％～88.3％.4个湖区表层沉积物TP含量(5 cm内)均呈现夏季＞冬季的特征,可能与夏季水产品养殖旺盛、湖区周围耕地大量施用化肥,以及旅游活动频繁等有关.间隙水磷(PO43--P)浓度夏冬两季在垂直方向上均呈先增加后降低的趋势,夏季含量明显高于冬季,说明沉积物中的磷在夏季具有更大的向上覆水释放的潜力.夏季沉积物有机磷(OP)和IP相关性显著,冬季相关性不显著,说明夏季IP与OP间的形态转化较冬季活跃.沉积物铁铝结合态磷(Fe/A1-P)和IP与间隙水磷含量具有显著正相关关系.夏冬两季Peeper法获取间隙水磷的平均含量比传统离心法高出20％ ～50％,前者可能更精确.     

不同磷源对磷高效利用野生大麦根际土壤磷组分的影响

在土培盆栽条件下,以野生大麦磷高效利用基因型IS-22-30、IS-22-25和低效基因型IS-07-07为材料,研究不施磷(CK)、无机磷(KH₂PO₄,Pi)、有机磷(phytate,Po)及二者混合(KH₂PO₄+phytate,Pi+Po)的方式施磷30 mg·kg^-1时,磷高效基因型野生大麦对磷素吸收利用能力及土壤磷组分特征.结果表明： Pi处理野生大麦干物质量和磷素积累量最大,Pi+Po处理其次,Po处理最小,均显著高于CK处理,且磷高效基因型物质生产和磷素吸收能力显著高于磷低效基因型.土壤有效磷在不同磷源处理间差异显著,Pi处理时含量最高,Pi+Po处理次之,且磷高效基因型野生大麦根际有效磷含量显著高于磷低效基因型.磷高效基因型野生大麦根际有效磷呈现亏缺现象,在Pi和Pi+Po处理时亏缺程度较大.根际与非根际土壤无机磷组分含量为Ca₁₀-P>O-P>Fe-P>Al-P>Ca₂-P>Ca₈-P,且其含量随着Pi的增加而增加.各磷源处理下,磷高效基因型野生大麦根际土壤Ca₂-P、Ca₈-P出现亏缺;Pi处理磷高效基因型野生大麦根际土壤Al-P、Fe-P出现富集.土壤中有机磷各组分含量为中活性有机磷>中稳性有机磷、高稳性有机磷>活性有机磷.野生大麦根际土壤活性有机磷和中活性有机磷呈现富集,其富集量在Pi处理时最大;中稳性有机磷和高稳性有机磷呈现亏缺.各磷源处理下,磷高效基因型野生大麦根际土壤活性有机磷含量显著高于磷低效基因型,中稳性有机磷和高稳性有机磷在基因型间差异不显著.Pi缺乏时,磷高效基因型野生大麦活化吸收Ca₂-P、Ca₈-P、Al-P和活性有机磷的能力较强.     

亚热带不同植被类型土壤磷组分特征及其影响因素

研究了戴云山常绿阔叶林、针阔混交林和针叶林3种植被类型土壤磷组分、微生物生物量磷以及酸性磷酸单酯酶(ACP)和磷酸双酯酶(PD)的活性.结果表明: 3种植被类型土壤易分解态磷仅占总磷(TP)的1.0%～4.5%,且碳(C)与有机磷(Po)的比例>200,表明本研究区受到磷限制.Po是土壤磷库的主要组分,在淋溶层(A层)和淀积层(B层)土壤中分别占TP的44.8%～47.1%和28.6%～30.6%.冗余分析表明,A层土壤磷组分主要受PD影响,而B层主要受ACP调控,且PD和ACP均与Po呈显著负相关.亚热带地区3种植被类型土壤均缺磷,PD和ACP对有机磷的分解可能是该地区森林生态系统对磷限制的适应机制.     

林线附近主要植被类型下土壤非生长季磷素形态

采用Hedley磷素分级方法,比较研究了岷江上游林线附近不同植被类型(高寒灌丛草甸、雪山杜鹃灌丛和岷江冷杉林)非生长季0—20cm土壤无机磷和有机磷形态。结果表明,研究区内土壤总磷平均含量(857.32mg·kg-1)较高,但活性磷含量仅占总磷的10%左右。生物态磷含量占总磷含量的60%以上,表明土壤磷素受生物作用影响较大。3种植被类型下土壤无机磷主要以D.HCl-Pi(稀盐酸提取无机磷)和C.HCl-Pi(浓盐酸提取无机磷)形态存在,活性无机磷和NaOH-Pi含量较少。高寒灌丛草甸土壤D.HCl-Pi和C.HCl-Pi含量均显著高于岷江冷杉,表明其含有更多的钙结合态磷。土壤有机磷与土壤有机碳呈显著正相关,NaOH-Po是有机磷主要的构成形态,占总磷含量的39.39%—53.69%。不同植被类型下土壤有机磷形态间差异较大,岷江冷杉林下土壤NaHCO3-Po和NaOH-Po含量最高,高寒灌丛草甸则含有更多的C.HCl-Po。低温和凋落物积累是造成林线附近土壤有机磷含量较高的重要原因。     

增温对南亚热带森林土壤磷形态的影响及其对有效磷的贡献

磷(P)是森林生态系统生产力的重要限制性元素。土壤磷的有效性取决于磷的存在形态及其转化过程。目前有关增温如何调控磷形态转化过程, 从而促进土壤有效磷含量增加的机制尚未明确。该研究以南亚热带森林为研究对象, 采用沿海拔高度从300 m下降至30 m以模拟温度自然上升的方法, 采集该林型0-10、10-20、20-40 cm的土壤, 并用适用于酸性土壤的连续浸提方法分离不同形态磷, 研究增温对土壤不同形态磷含量的影响, 探讨土壤不同形态磷与有效磷的关系, 识别对土壤有效磷在增温背景下增加有重要贡献的磷组分。结果表明增温使0-10 cm的无机钙磷(Ca-Pi)及20-40 cm的无机铁磷(Fe-Pi)和总无机磷含量分别显著增加了65.5%、17.9%和18.5%, 但对总有机磷及各有机磷组分含量均无显著影响。土壤不同形态磷与有效磷含量的相关分析表明, 有效磷与无机态的不同形态磷及有机铝磷、有机铁磷含量均显著正相关, 其中与Fe-Pi含量的相关性最强。通过土壤不同形态磷与有效磷含量的通径分析进一步发现, 无机铝磷、Fe-Pi是土壤磷转化过程中的重要中间过渡性磷组分, 且Fe-Pi是促进有效磷含量增加最重要的直接贡献磷组分。结合前期研究结果, 增温可能增大了凋落物磷对土壤磷的输入, 还可能强化了土壤的吸附和沉淀过程, 使得更多进入到土壤的溶解态磷转化为Ca-Pi、Fe-Pi等缓效磷源, 其中Fe-Pi可能成为南亚热带森林在气候变暖背景下最重要的有效磷来源。     

洱海湖滨带与湖中心带表层沉积物磷的形态对比分析与环境学意义

采用连续提取方法对洱海湖滨带和湖中心带表层沉积物磷的形态及其分布特征进行了分析。结果表明湖滨带TP的含量为741.35-1061.36 mg·kg^-1, 平均为872.61 mg·kg^-1, 显著高于湖中心带(含量范围576.38-722.98 mg·kg^-1, 平均值663.67 mg·kg^-1)。两区域均以IP 为主赋存形态, 分别占TP 的79.70-84.97%(湖滨带)和78.1-92.28%(湖中心带), 而IP 中以Ca-P 为主, 分别占IP 的26.76-63.38%(湖滨带)和28.67-55.16%(湖中心带)。从各形态磷的含量分布特征来看, 湖滨带的TP、IP、OP、Ads-P、Fe-P 和Ca-P 均显著高于湖中心带, 而De-P 则相反, 反映了磷在迁移过程中与环境因子变化之间响应关系。相关分析表明湖滨带TP 与IP、OP、Ads-P 均呈显著的正相关关系, 而在湖中心带这种关系则仅存于TP 与IP 之间, 说明湖滨带磷具有较强的释放潜力, 而湖中心带则更多的体现了洱海区域的地质特点。该研究对于正确认识环境因子与沉积物中磷的形态之间的内在联系与响应关系, 揭示高原湖泊磷的地球化学特征与环境效应具有重要意义。     

泉州湾洛阳江河口沉积物中磷的形态分布

分析了泉州湾洛阳江河口沉积物中总磷及5种形态磷(可交换态磷(DP)、铁铝结合态磷(Fe/Al-P)、钙结合态磷(Ca-P)、有机磷(OP)和闭蓄态磷(Re-P))的含量,探讨了它们的垂向分布特征、相互关系及环境指示意义。结果表明:沉积物中的总磷(TP)以无机磷为主,占TP比例76%~89%;除可交换态磷外,沉积物中形态磷的垂向分布规律具有相似性,大体随深度增加而减小,且在表层有富集现象,反映了沉积物中总磷和各形态磷的分布受人类活动影响较明显;通过相关性分析,钙结合态磷是总磷和无机磷的主要控制因素,而总磷和其他形态磷(除了可交换态磷外)相互间均具有显著相关性,且有机质对各形态磷的分布均有一定影响;TP和各形态磷含量,以及(Fe/Al-P)/TP、Ca-P/TP、OP/TP都在同一层出现了显著变化,反映了水利设施和围垦工程对沉积环境和各形态磷迁移转化有较大影响。     

三江平原湿地土壤磷形态转化动态

采用Hedley连续浸提法对三江平原湿地小叶章草甸土壤磷形态的季节动态进行研究,分析生长季土壤磷形态之间的相互转化及其可能的驱动机制。结果表明:小叶章草甸土壤有机磷(TPo)总量高于无机磷(TPi),NaOH溶液浸提的无机磷(NaOH-Pi)和有机磷形态(NaOH-Po)分别占总无机磷(TPi)和总有机磷(TPo)比重最大。各无机磷形态均有明显的季节变化,Resin-P和Conc.HCl-Pi季节变异性大,生长结束后含量较初期降低,其他形态无机磷含量有不同程度的升高。有机磷组分中NaOH-Po的季节波动最明显,生长季末期较初期含量降低,其他有机磷形态和Residual-P生长季初、末期含量变化不大,波动也相对较小。TP、TPo季节变化整体趋势相似,二者含量变化达到极显著相关。各无机磷形态变化主要受植物生长节律影响;水分、热量等环境条件也是磷的形态转化的重要驱动因子,并可能间接通过影响土壤动物、微生物等的活性推动土壤磷的循环。小叶章草甸土壤有机磷矿化释放的无机磷通常都首先被土壤金属氧化物固定,再经过无机磷之间的转化过程为生物利用,因此三江平原湿地土壤磷大量释放的可能性很小。     

乌江流域不同营养水平的梯级水库沉积物中磷形态特征

分析了乌江干流及支流不同营养水平的梯级水库(东风-贫营养、红岩-中营养、乌江渡-富营养)沉积物粒度的垂向分布,并以改进的连续提取法(SEDEX)调查了不同磷形态垂向分布特征。结果表明:3水库沉积物粒径均随深度的增加而减小,东风水库粒径最大,红岩水库其次,处于下游的乌江渡水库粒径最小;乌江渡、红岩和东风水库沉积物总磷(TP)的平均含量分别为2.07、1.22和1.11mg.g-1,总无机磷分别占到总磷53.8%、44.5%和81.9%,有机磷占TP的41.9%、55.5%和18.1%;3水库各形态磷所占比例不同,其中,乌江渡水库交换态磷所占比例相对较大,与其富营养化状态一致;乌江渡水库沉积物表层10cm,各形态磷含量随深度的增加呈下降趋势,红岩水库除交换态磷,其他各形态磷变化趋势不明显。东风水库各形态磷变化趋势不明显;河流梯级开发使下游水库颗粒物粒径变小,从而使下游水体中的磷更易吸附和释放,下游水库沉积物与水体交换也更强烈,除总磷外,交换态磷、自生磷和有机磷也可较好地反映水库富营养程度及演变。     

互花米草盐沼土壤有机碳库组分及结构特征

在江苏盐城互花米草(Spartina alterniflora)盐沼建立以下样地:光滩(Mudflat)、互花米草建群1a(S.alterniflora flat 2011)、5a(S.alterniflora flat 2007)、12a(S.alterniflora flat 2000)、23a(S.alterniflora flat 1989)以及碱蓬(Suaeda salsa flat 1989),采集表层土壤样品,分析土壤中的活性有机碳(可溶性有机碳、微生物量碳)特征,并利用核磁共振波谱法测定土壤总有机碳的结构图谱,研究互花米草盐沼土壤有机碳库组分及结构特征。结果表明:(1)互花米草建群后,盐沼表层土壤有机碳含量显著增加(P0.05),在0.82—7.6 g/kg之间,各样地表层土壤有机碳含量为:互花米草滩(5.57 g/kg)碱蓬滩(2.4 g/kg)光滩(1.05 g/kg);可溶性有机碳含量为:互花米草滩(36.08 mg/kg)碱蓬滩(17.43 mg/kg)光滩(6.92 mg/kg);微生物量碳含量为:互花米草滩(52.51 mg/kg)碱蓬滩(18.27 mg/kg)光滩(13.56 mg/kg)。互花米草建群后,土壤中活性碳库含量显著增加(P0.05)。(2)土壤有机碳结构以烷氧碳和芳香碳为主,其中芳香碳的平均比例(35.85%)最高,其次为烷氧碳(32.83%)和羧基碳(20.62%),烷基碳的平均比例(10.36%)最低,其中建群5a的互花米草样地(SAF2007)土壤芳香碳、烷氧碳、烷基碳含量最高,建群23a的互花米草样地(SAF1989)土壤羧基碳含量最高。(3)互花米草盐沼土壤中烷基碳/烷氧碳为:SAF2007(0.44)SSF1989(0.43)SAF2000(0.28)SAF2011(0.27)SAF1989(0.22);疏水碳/亲水碳为:SAF2007(0.97)SSF1989(0.87)SAF2000(0.85)SAF2011(0.83)SAF1989(0.81)。烷基碳/烷氧碳在建群5a后达到最高值0.44,烷基化程度最高;疏水碳/亲水碳达到最高值0.97,土壤碳库稳定性高于其它样地。     

崇明东滩盐沼植被扩散格局及其形成机制

长江河口盐沼植被的形成和演化是生物与其生长环境相互作用的结果。以崇明东滩盐沼植被典型扩散前沿为研究对象,2011至2012年期间调查了盐沼植被扩散前沿实生苗扩散、定居以及形成的扩散格局,同时测定了盐沼植被扩散前沿的潮滩冲淤动态和水文动力条件。研究结果表明,崇明东滩盐沼植被在扩散前沿形成了互花米草-光滩(Spartina alterniflora-Mudflat,SM)和互花米草-海三棱藨草-光滩(Spartina alterniflora-Scirpus mariqueter-Mudflat,SSM)两种典型的扩散格局。冲淤动态和水文动力条件是影响盐沼植被扩散格局的重要因子,尤其是在4—6月盐沼植物实生苗传播和定居的关键阶段。在此基础上,分析了东滩盐沼植被扩散前沿的生物-物理相互作用以及盐沼植被扩散格局的形成机制。研究结果不仅有助于理解长江河口地区盐沼植被扩散的生物物理过程,并对全球气候变化和海平面上升条件下滨海生态系统动态预测与湿地保护与管理具有重要的意义。     

Longitudinal Variability of Phosphorus Fractions in Sediments of a Canyon Reservoir Due to Cascade Dam Construction: A Case Study in Lancang River,China

Dam construction causes the accumulation of phosphorus in the sediments of reservoirs and increases the release rate of internal phosphorus (P) loading. This study investigated the longitudinal variability of phosphorus fractions in sediments and the relationship between the contents of phosphorus fractions and its influencing factors of the Manwan Reservoir, Lancang River, Yunnan Province, China. Five sedimentary phosphorus fractions were quantified separately: loosely bound P (ex-P); reductant soluble P (BD-P); metal oxide-bound P (NaOH-P); calcium-bound P (HCl-P), and residual-P. The results showed that the total phosphorus contents ranged from 623 to 899 µg/g and were correlated positively with iron content in the sediments of the reservoir. The rank order of P fractions in sediments of the mainstream was HCl-P>NaOH-P>residual-P>BD-P>ex-P, while it was residual-P>HCl-P>NaOH-P>BD-P>ex-P in those of the tributaries. The contents of bio-available phosphorus in the tributaries, including ex-P, BD-P and NaOH-P, were significantly lower than those in the mainstream. The contents of ex-P, BD-P, NaOH-P showed a similar increasing trend from the tail to the head of the Manwan Reservoir, which contributed to the relatively higher content of bio-available phosphorus, and represents a high bio-available phosphorus releasing risk within a distance of 10 km from Manwan Dam. Correlation and redundancy analyses showed that distance to Manwan Dam and the silt/clay fraction of sediments were related closely to the spatial variation of bio-available phosphorus.     

Seasonal cycling of Fe in saltmarsh sediments

This study combines an analysis of porewater chemistry with new, solid phase wet chemical extractions to examine the seasonal cycling of Fe in vegetated and unvegetated (cyanobacterial mat) saltmarsh sediments. Saltmarsh sediments are shown to contain more solid phase reactive Fe than other marine sediments studied so far. From the partitioning and speciation of solid Fe, and solid/soluble reduced S analysis in 10 sediment cores, we have observed that a majority of solid Fe in these sediments is cycled rapidly and completely between oxidized reactive Fe and reduced Fe as pyrite. Vegetated porewaters showed a lower pH and much higher Fe(II) concentrations on average than unvegetated porewaters in the top 10 cm, whereas sulfate, alkalinity, and sulfide concentrations were similar in the two environments. The amorphous Fe(III) oxide fraction showed a high negative correlation to solid and soluble reduced S (r ² = –0.86 and –0.71, respectively) in surface vegetated sediments whereas the crystalline Fe(III) oxide fraction showed a high negative correlation (r ² = –0.96) to sulfide only at depth. Though reactive Fe was observed in unvegetated sediments, no seasonal trend was apparent and the speciation of solid Fe revealed that most of it was reduced. Solid phase and porewater chemistry support the dominant role of the biota (Spartina alterniflora and bacteria) in controlling the reactivity of Fe and suggest that the current definition of solid phase, reactive Fe should be expanded to include crystalline Fe(III) minerals which are available for pyrite formation in saltmarsh sediments. In support of previous saltmarsh studies, we present evidence that the redox cycle of solid Fe is controlled by sulfate reduction and sediment oxidation which respond to both annual cycles (light, temperature) and to short-term, episodic effects such as weather and tides.     

海拔梯度变化对武夷山黄山松林土壤磷组分和有效性的影响

土壤磷（P）是植物生长必需的养分元素,也是亚热带森林生产力的主要限制元素。目前,关于不同海拔土壤P组分和P有效性的变化规律尚无统一定论,其原因主要是忽略了植被类型变化导致的P组分和P有效性对海拔的响应更为复杂。因此,以武夷山不同海拔黄山松林为研究对象,通过测定土壤环境因素、理化性质、微生物生物量（SMB）、酸性磷酸单酯酶（ACP）和磷酸双酯酶（PD）活性以及土壤P组分,探究土壤P组分和P有效性的变化及其影响因素。结果表明,随海拔降低,速效P含量显著增加,而易分解P、中等易分解P、难利用P和总磷含量显著减少。冗余分析结果表明,微生物生物量磷和微生物生物量氮是影响土壤P组分和P有效性变化的关键因素。研究表明,随海拔降低,黄山松林土壤微生物通过提高ACP、PD活性和降低SMB含量的能量分配策略,促进更多较难分解P组分的矿化,从而提高速效P含量,以满足微生物对P的需求。因此,在低海拔地区,微生物通过能量分配策略获取更多有效P,可能有利于提高武夷山黄山松林土壤速效P的供应,但从长期来看,可能使P矿化速率提高和P损耗增加,导致P库的储备不足,不利于土壤P素养分的可持续供应。     

Vegetation death and rapid loss of surface elevation in two contrasting Mississippi delta salt marshes: The role of sedimentation, autocompaction and sea-level rise

From 1990 to 2004, we carried out a study on accretionary dynamics and wetland loss in salt marshes surrounding two small ponds in the Mississippi delta; Old Oyster Bayou (OB), a sediment-rich area near the mouth of the Atchafalaya River and Bayou Chitigue (BC), a sediment-poor area about 70 km to the east. The OB site was stable, while most of the marsh at BC disappeared within a few years. Measurements were made of short-term sedimentation, vertical accretion, change in marsh surface elevation, pond wave activity, and marsh soil characteristics. The OB marsh was about 10 cm higher than BC; the extremes of the elevation range for Spartina alterniflora in Louisiana. Vertical accretion and short-term sedimentation were about twice as high at BC than at OB, but the OB marsh captured nearly all sediments deposited, while the BC marsh captured <30%. The OB and BC sites flooded about 15% and 85% of the time, respectively. Marsh loss at BC was not due to wave erosion. The mineral content of deposited sediments was higher at OB. Exposure and desiccation of the marsh surface at OB increased the efficiency that deposited sediments were incorporated into the marsh soil, and displaced the marsh surface upward by biological processes like root growth, while also reducing shallow compaction. Once vegetation dies, there is a loss of soil volume due to loss of root turgor and oxidation of root organic matter, which leads to elevation collapse. Revegetation cannot occur because of the low elevation and weak soil strength. The changes in elevation at both marsh sites are punctuated, occurring in steps that can either increase or decrease elevation. When a marsh is low as at BC, a step down can result in an irreversible change. At this point, the option is not restoration but creating a new marsh with massive sediment input either from the river or via dredging.     

Sulfur storage changed by exotic Spartina alterniflora in coastal saltmarshes of China

For the purpose of ecological engineering, Spartina alterniflora was introduced to China in 1979 and now covers about 112,000 ha of China's coastal lands. It was hypothesized that S. alterniflora could actively change the habitat environment, thus facilitating its competition over native species. In Yancheng Nature Reserve, sulfur storage of sediments and plant tissues was compared among marshes dominated by the exotic S. alterniflora and adjacent native Suaeda salsa and Phragmites australis and bare mudflat. Results showed that the S. alterniflora marsh contained the highest content of water-soluble, adsorbed, carbonate-occluded and total sulfur in the sediment. The sulfur levels were higher in the center than at the edges of the S. alterniflora marsh. Native marshes showed no significant difference in sediment sulfur levels. With greater biomass and higher tissue sulfur concentrations, plant sulfur storage of S. alterniflora vegetation was also larger than those of the native vegetations. Because higher concentrations of sulfur increase the competitive advantage of S. alterniflora over native halophytes, the results of the research showing that S. alterniflora increased marsh sulfur storage may shed light on the mechanism of expansion of monospecific vegetation in coastal China.     

闽江河口湿地植物枯落物立枯和倒伏分解主要元素动态

采用分解袋法,对闽江河口湿地2种挺水植物——芦苇(Phragmites australis)和互花米草(Spartina alterniflora)花和叶枯落物的立枯和倒伏分解过程及C、N、P元素动态进行研究。结果表明:(1)立枯分解是2种湿地盐沼植物重要的分解阶段,干物质损失率在13.26%—31.89%之间。多项式模型能较好描述2种植物花和叶的枯落物分解残留率动态。(2)立枯分解阶段,芦苇花和叶的C含量主要为波动下降,互花米草较为稳定;倒伏阶段后期,2种植物都以升高为主。立枯分解阶段2种植物枯落物N含量略有下降,而倒伏阶段逐渐上升。分解过程中枯落物P含量的波动较大。(3)2种植物花和叶C、N的NAI值在分解过程中<100%。芦苇的花和叶中P的NAI值在立枯和倒伏分解阶段都经历了明显下降和升高的过程,而互花米草在立枯阶段变化不大,倒伏阶段下降较为明显。(4)与芦苇相比,互花米草的花和叶枯落物C库较高,N库较低,P库差异不大。     

A study of the population dynamics of Spartina alterniflora at Jiuduansha shoals,Shanghai, China

This study investigated the population expansion pattern of an exotic species of Spartina alterniflora for a period of 7 years, after it had been newly introduced to the neonatal shoals of Jiuduansha (GPS), in the Yangtze Estuary, Shanghai. Remote sensing, in conjunction with geographical information systems (GIS) and global positioning systems (GPS) was used to map saltmarsh vegetation on the Jiuduansha shoals and the classifications were then checked using in situ field surveys of selected areas. The results showed that the S. alterniflora population had expanded from 55 hm² when first introduced in 1997, to 1014 hm² in 2004. The population expansion pattern of S. alterniflora on the Jiuduansha shoals was compatible with the common feature of invasions, i.e. the initial colonization, a lag time and the onset of rapid population growth and range expansion. In the first year of plantation (1997), about 35 hm² of S. alterniflora was successfully colonized on the Jiuduansha shoals. The period between 1998 and 2000 was characterized by a lag time, and the area of S. alterniflora increased only to 101.6 hm². The year 2000 marked an onset of rapid population growth and range expansion and the annual expanding rate reached 25–116%, which exceeded any of the indigenous species and indicated the strong competitive capability, rapid range expansion and wide ecological niche of S. alterniflora.The advent of remote sensing, in conjunction with geographical information systems and global positioning systems, provides a potential tool for mapping vegetation, and for monitoring population dynamics and range expansion of invasive species on a large scale. The implications for population and community dynamics, biodiversity conservation and wetland management in terms of the analysis of the sequence of events associated with the initial colonization, a lag time, rate of geographic spread and features of geographic spread of the exotic S. alterniflora and the native P. australis on the Jiuduansha shoals are discussed.     

Phosphorus fractions and alkaline phosphatase activity in sediments of a large eutrophic Chinese lake (Lake Taihu)

Spatial, vertical, and seasonal variations in phosphorus fractions and in alkaline phosphatase activity (APA) were investigated in sediments in a large-shallow eutrophic Chinese lake (Lake Taihu) in 2003–2004. The phosphorus content was highest in the most seriously polluted lake area. Iron-bound phosphorus (Fe(OOH)～P) dominated (47% on average) among the phosphorus fractions determined according to Golterman (Hydrobiologia 335:87–95, 1996). Notably, organically-bound P comprised a further significant additional portion (acid-soluble + hot NaOH-extractable organic P = 25%), which was highest at the most polluted sites. The Fe(OOH)～P content was the lowest in spring (April, 2004), suggesting that degradation of organic matter led to the release of iron-bound phosphates. Sediment APA showed a significant positive relationship with both organically-bound P and Fe(OOH)～P. Consequently, organically-bound P is an important portion of the sediment phosphorus in Lake Taihu. It is mainly derived from freshly-settled autochthonous particles and from external discharges. Organically-bound P induces APA and may lead to the release of bioavailable phosphates from the organic sediments, thereby accelerating lake eutrophication.