闽江河口湿地枯落物分解及主要影响因子

以闽江河口湿地挺水植物本地种芦苇和入侵种互花米草的花和叶枯落物为研究对象,采用分解袋法分析其分解过程及主要影响因素.结果表明:立枯分解(0～90 d)是2种湿地盐沼植物重要的分解阶段,芦苇和互花米草的花和叶质量损失率分别为(15.0±3.5)％、(13.3±1.1)％和(31.9±1.1)％、(20.8±1.4)％.倒伏分解阶段(91 ～210 d),芦苇和互花米草的花和叶质量损失率分别为(69.5±0.6)％、(71.5±2.5)％和(76.8±1.9)％、(67.5±2.1)％.在立枯分解阶段,2种挺水植物枯落物的分解速率与C/N呈正相关,与N/P呈负相关,分解过程受到P的限制程度较大.倒伏分解阶段,枯落物C/N、C/P和N/P的影响降低,而大气温湿度、土壤水分、酸碱度、盐度和沉积物特性等的影响加大.不同分解阶段枯落物分解影响因子的差异主要与其所处的微域环境和潮汐因素有关.     

闽江河口湿地枯落物分解及主要影响因子

以闽江河口湿地挺水植物本地种芦苇和入侵种互花米草的花和叶枯落物为研究对象,采用分解袋法分析其分解过程及主要影响因素.结果表明: 立枯分解(0～90 d)是2种湿地盐沼植物重要的分解阶段,芦苇和互花米草的花和叶质量损失率分别为(15.0±3.5)%、(13.3±1.1)%和(31.9±1.1)%、(20.8±1.4)%.倒伏分解阶段(91～210 d),芦苇和互花米草的花和叶质量损失率分别为(69.5±0.6)%、(71.5±2.5)%和(76.8±1.9)%、(67.5±2.1)%.在立枯分解阶段,2种挺水植物枯落物的分解速率与C/N呈正相关,与N/P呈负相关,分解过程受到P的限制程度较大.倒伏分解阶段,枯落物C/N、C/P和N/P的影响降低,而大气温湿度、土壤水分、酸碱度、盐度和沉积物特性等的影响加大.不同分解阶段枯落物分解影响因子的差异主要与其所处的微域环境和潮汐因素有关.     

互花米草与短叶茳芏枯落物分解过程中碳氮磷化学计量学特征

为了揭示植物枯落物分解过程中元素生态化学计量学特征,对闽江河口湿地互花米草和短叶茳芏枯落物分解过程进行了测定.结果表明:整个分解期间内(2007年1-10月),在近潮沟生境和远潮沟生境,互花米草枯落物分解速率、氮磷养分含量低于短叶茳芏枯落物,但热值高于短叶茳芏枯落物;近潮沟生境,互花米草和短叶茳芏枯落物分解过程中平均C/N、C/P和N/P分别为70.5和34.7,2285.8和1210.7,32.8和35.4;远潮沟生境互花米草和短叶茳芏枯落物分解过程中平均C/N、C/P和N/P分别为72.7和33.2,2519.2和1167.0,34.0和35.9,两种生境下均表现为互花米草具有较高的C/N、C/P和较低的N/P;互花米草枯落物分解过程中具有较高的C/N和C/P,其分解速率较低.     

河口湿地植物活体-枯落物-土壤的碳氮磷生态化学计量特征

碳(C)、氮(N)、磷(P)生态化学计量比是生态系统过程及其功能的重要特征.以闽江河口的芦苇(Phragmites australis)和短叶茳芏(Cyperus malaccensis var.brevifolius)湿地为对象,开展植物活体-枯落物-土壤系统的C、N、P季节动态研究.结果表明:芦苇和短叶茳芏植物活体、枯落物和土壤年均C、N、P含量为C＞N＞P,两种湿地系统C、N含量均为植物活体和枯落物高于土壤,但与土壤P含量大小关系因植物构件差异而不同;芦苇和短叶茳芏植物活体、枯落物和土壤的C、N、P生态化学计量比表现为C∶P＞C∶N＞N∶P;芦苇湿地C∶N为枯落物＞植物活体＞土壤,短叶茳芏为植物活体＞枯落物＞土壤,而C∶P和N∶P均为枯落物＞植物活体＞土壤;C、N、P化学计量比可以反映湿地C、N、P交换过程和植物群落的生态功能.     

盐度对互花米草枯落物分解释放硅、碳、氮元素的影响

为了研究潮汐湿地盐度对枯落物分解过程中硅、碳、氮元素释放的影响,通过室内模拟不同盐度(0、5、15和30)对互花米草枯落物茎和叶分解释放过程中硅、碳、氮元素的动态变化进行测定。结果表明:(1)互花米草茎和叶枯落物失重率和分解速率均随盐度增加而降低。(2)互花米草茎和叶枯落物分解水体中硅含量均随着盐度升高而增加,并且盐度30处理下,枯落物分解硅释放量显著高于盐度0和5(P0.05)。而分解末期生物硅残留量则随盐度升高而降低。(3)不同盐度处理茎枯落物分解碳释放量无显著差异,但叶枯落物分解碳释放量在盐度5、15和30处理中显著高于淡水(P0.05)。(4)互花米草茎枯落物分解释放到水中的NH_4~+-N含量随着盐度的升高而减少,NO_3~--N含量与之相反。研究单因素盐度对枯落物分解及元素释放的影响,可以为预测潮汐湿地枯落物分解对盐水入侵的响应机制提供参考,为湿地生源要素生物地球化学循环过程研究提供基础依据。     

上海市大莲湖池杉林三种优势植物枯落物分解动态

用枯落物分解网袋法,对上海市大莲湖湿地池杉林内3种优势植物池杉(Taxodium ascendens)、孔雀稗(Echinochloa cruspavonis)、日本看麦娘(Alopecurus japonicus)的枯落物进行了190 d的分解培养,测定了分解速率及其C、N、P养分元素释放动态.用收集器法对池杉林枯落物的数量进行了研究.结果表明,池杉林内池杉每年产生枯落物量为5.70t·hm-2,是该林地枯落物的主要来源.3种植物枯落物的分解速率(枯落物的干重量损失)依次为日本看麦娘＞孔雀稗＞池杉.C元素含量在3种植物枯落物中随时间显著下降;N、P元素在池杉枯落物中均有不同程度的富集,而在日本看麦娘和孔雀稗中则没有发生富集现象.     

三江平原沼泽湿地枯落物分解及其营养动态

分解袋法研究了三江平原典型沼泽湿地枯落物的分解速率和N、P营养动态.湿地枯落物的分解速率（0.000612～0.000945 d^-1）在群落间差异显著,分解480d,分别损失初始重的45.36%（Carexpseudocuraica）、35.32%（Carex lasiocarpa）、33.72%（Deyeuxia angustifolia）和29.13%（Deyeuxia angustifolia-Shrub）,即随淹水深度由大到小、淹水时间由长到短,枯落物分解由快到慢,说明湿地的淹水状况是影响枯落物分解速率的主要因素.分解过程中,漂筏苔草和毛果苔草枯落物N浓度持续上升,N在枯落物中积累;小叶章枯落物N浓度在第1个月快速下降而后缓慢上升,分解使枯落物释放N.各类枯落物P浓度的变化大致呈不同程度的降低趋势,分解使湿地枯落物均发生P释放.结果表明,微生物的营养需求状况决定了湿地枯落物N、P的动态变化,而其积累或释放的强度则可能与枯落物初始C：N和C：P的大小有关.     

三江平原典型湿地枯落物早期分解过程及影响因素

枯落物分解是湿地物质循环和能量流动的关键环节,是维持湿地功能的重要过程之一。采用分解袋法对三江平原3种典型湿地植物枯落物分解过程及影响因素进行了研究。研究表明,在164d实验过程中乌拉苔草分解速率始终最快;在分解前103d中毛果苔草分解速率大于小叶章,但在103~164d间小叶章分解速率大于毛果苔草;分解164d,小叶章、乌拉苔草和毛果苔草枯落物的失重率分别为初始重的31.98%、32.99%和28.91%。分解过程中小叶章和毛果苔草枯落物中有机碳浓度波动较大,而乌拉苔草枯落物中持续下降;3种枯落物有机碳绝对含量都表现为净释放。小叶章枯落物中N浓度波动较大,绝对含量发生净释放;毛果苔草枯落物N浓度持续增加,绝对含量净增加;乌拉苔草枯落物N浓度先增加后减少,绝对含量发生净释放。3种枯落物中P浓度都先迅速下降后缓慢上升,绝对含量都表现为净释放。3种枯落物中C/N和C/P也相应的发生变化。小叶章和乌拉苔草枯落物分解速率与枯落物C/P显著相关,而毛果苔草枯落物与枯落物N浓度显著相关;对应3种枯落物分解速率的主要环境因子分别为土壤含水量、土壤容重和土壤温度。3种枯落物分解速率和营养物质含量动态受到枯落物自身质量和温湿条件、周围环境营养状况等自然环境条件的共同影响,相比而言,受枯落物质量的影响更大。     

胶州湾滨海湿地枯落物分解对土壤活性有机碳含量及其三维荧光特性的影响

通过室内试验模拟胶州湾滨海湿地碱蓬、芦苇、互花米草枯落物的分解过程,测定土壤活性有机碳(可溶性有机碳、微生物生物量碳)含量变化,并利用三维荧光技术对可溶性有机碳(DOC)进行光谱分析.结果表明: 土壤活性有机碳含量呈先增加后降低最终趋于稳定的变化趋势;不同枯落物类型和添加方式对土壤活性有机碳的影响不同,表现为碱蓬＞互花米草＞芦苇,且原状混合＞表面覆盖;光谱分析表明,分解过程各三维荧光光谱的荧光峰数量、荧光中心位置和荧光强度都存在一定差异,添加枯落物后土壤未发现类酪氨酸峰;芳香类蛋白物质占比最高,腐殖质类物质次之.枯落物分解是以微生物分解作用为主导、枯落物性质为本质要素、多重因子综合作用的结果,其对提高土壤活性有机碳含量、增强土壤碳库的稳定性具有促进作用;该过程通过改变DOC的结构和化学组分,提高其在土壤中的迁移转化能力,增强生物可降解性和可利用性,促进微生物内源DOC的产生,加快湿地土壤碳循环.     

水淹条件下灰化薹草和虉草活体、枯落物分解过程的比较

为了揭示鄱阳湖湿地活体植物和自然枯落物在水淹条件下分解过程的差异,以鄱阳湖湿地优势植被物种灰化薹草(Carex cinerascens)和虉草(Phalaris arundinacea)为研究对象,采用分解袋法开展室内模拟实验。植物样品设置新鲜和风干两种处理,分别模拟活体植物和自然枯落物在水下的分解过程。研究结果表明:(1)在180 d的淹水实验过程中,两种处理下的灰化薹草和虉草的分解过程都具有阶段性,前期分解速率较快,后期较慢。(2)两种植物枯落物的分解速率与植物C/N比有显著相关性,而活体植物的分解速率与植物C/N比相关性不强。(3)活体植物和自然枯落物的水下分解速率与物种有关,虉草活体比虉草枯落物分解速率快,而薹草活体比薹草枯落物分解速率慢。(4)模拟实验结束时活体植物仍有34%—43%未分解,推测鄱阳湖丰水期退水后大量洲滩植被消失的原因并非是植被在水淹下完全分解,而是一部分植被被水生动物啃噬或被水流冲走。     

Phosphorus dynamics during decomposition of mangrove (Rhizophora apiculata) leaves in sediments

Rhizophora apiculata leaf litter decomposition and the influence of this process on phosphorus (P) dynamics were studied in mangrove and sand flat sediments at the Bangrong mangrove forest, Phuket, Thailand. The remaining P in the mangrove leaf litter increased with time of decomposition to 174% and 220% of the initial amount in the litter in sand flat and mangrove sediment, respectively, although about 50% of the dry weight had been lost. The incorporation of P into the litter was probably associated with humic acids and metal bridging, especially caused by iron (Fe), which also accumulated in considerable amounts in the litter (5-10 times initial concentration). The addition of leaves to the sediment caused increased concentrations of dissolved reactive phosphate (DRP) in the porewater, especially in sand flat sediment. The DRP probably originated from Fe-bound P in the sediment, because decomposition of buried leaf litter caused increased respiration and reduced the redox potential (E_h) in the sediments. Binding of P to refractory organic material and oxidized Fe at the sediment-water interface explains the low release of DRP from the sediment. This mechanism also explains the generally low DRP concentration in the mangrove porewater, the low nutrient content of the R. apiculata leaves, but also the higher total sediment P concentration of the mangrove sediment as compared to sediments outside the mangrove. Both the low release rates for DRP from the sediment and the accumulation of P associated with leaf litter decomposition tend to preserve P in the sediments.     

黄土高原樟子松和落叶松与其他树种枯落叶混合分解对土壤的影响

通过采集树木枯落叶与土壤进行室内混合分解培养试验,研究了黄土高原常见的樟子松和落叶松与其他树种枯落叶混合分解对土壤性质的影响及存在的相互作用,从而为不同树木种间关系的探索和该地区人工纯林的混交改造提供科学指导。结果表明:12种枯落叶单一分解均明显提高了土壤脲酶(54%—110%)、脱氢酶(85%—288%)和磷酸酶(81%—301%)活性以及有机质(29%—55%)和碱解N(12%—49%)含量,但对土壤速效P含量和CEC的影响存在较大差异。综合而言,樟子松分别与白桦、刺槐、白榆、柠条和落叶松枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与小叶杨、沙棘、紫穗槐、侧柏和辽东栎枯落叶混合分解在对土壤性质的影响中存在相互抑制作用;落叶松分别与刺槐、白桦、小叶杨和紫穗槐枯落叶混合分解在对土壤性质的影响中存在相互促进作用,而分别与柠条、侧柏、辽东栎、沙棘、油松和白榆枯落叶混合分解在对土壤性质的影响中存在相互抑制作用。     

Leaf growth,senescence and decomposition of Juncus maritimus Lam. in a coastal Mediterranean marsh

In this study, the growth, senescence, leaf loss and nutrient dynamics of Juncus maritimus were followed to examine litter decay in a Mediterranean coastal marsh. Decomposition was studied in dead leaves still attached to the plant and in leaves placed in litterbags (detached leaves/litter) on the sediment surface. The dynamics of fungi, meiofauna and epiphytes associated with detached litter were also followed. No significant differences were observed between decay rates in dead leaves attached to plants (0.0017 day⁻¹) and detached leaves (0.0015 day⁻¹) in litter bags. The percentage of ash-free dry weight lost was inversely proportional to the C:N and C:P ratios in plant detritus during decay, indicating N and P limitation for the decomposer community inhabiting decaying J. maritimus litter and uptake of these nutrients from the environment. Water availability and high temperatures on the sediment surface increased the density of meiofauna and epiphyton and decreased fungal biomass during the first 20 days of the experiment. The density of ciliates and nematodes in decomposing litter was inversely related to the C:N ratio and directly related to the percentage of AFDW lost. On the basis of these observations, it was concluded that meiofauna are primary colonizers of J. maritimus leaf litter.     

江苏滨海湿地芦苇和互花米草光合特性对模拟增温的响应

滨海湿地生态系统具有较高的初级生产力,是地球生态系统主要的碳库之一。然而,气候变暖和外来物种入侵通过改变植物光合特征性能使这一碳库的稳定性存在诸多的不确定性。利用在江苏盐城芦苇湿地和互花米草湿地建设的两个增温观测站,采用便携式光合荧光测量系统研究了本土植物芦苇（Phragmites australis）和入侵物种互花米草（Spartina alterniflora）光合特性对模拟增温的响应特征和机制。光合作用日调查变化曲线显示,增温使芦苇的净光合速率（P_n）、气孔导度（G_s）、蒸腾速率（T_r）和水分利用效率（WUE）都发生了显著的下降,但互花米草的各同名参数却表现出相反的变化特征,表明增温使互花米草的生理机能增强,促进了光合作用;根据P_n和胞间CO₂浓度（C_i）的变化趋势推断互花米草和芦苇光合速率变化均为非气孔限制因素驱动。利用直角双曲线修正模型拟合的光响应曲线结果显示,芦苇增温组的光响应曲线位于对照组下方,互花米草增温组的光响应曲线位于对照组上方;增温降低了所研究植物的光补偿点（LCP）,表明增温可提高两种植物利用弱光的能力;增温增加了互花米草光补偿点（LCP）和光饱和点（LSP）间值域范围,从而揭示了增温可有效提高互花米草利用光合有效辐射的能力;增温降低了芦苇的暗呼吸速率（R_d）,芦苇受到增温的胁迫,在减缓新陈代谢的同时也减弱了光合作用,而互花米草表现出相反特征。由此推测增温条件下入侵植物互花米草同化大气CO₂的能力（即碳汇能力）优于本土植物芦苇,这也是互花米草成为入侵物种的主要原因之一。     

室内模拟波浪对2种典型滨海湿地挺水植物生物力学特征的影响

选取本地物种芦苇和入侵物种互花米草为研究对象,利用波浪装置对生长期的植物进行波浪处理后对其形态特征,根、茎、叶的拉力、弯曲特性进行研究,以探讨湿地植物对波浪作用的生物力学响应。结果表明,芦苇、互花米草经波浪处理后的茎直径均显著高于对照组（P=0.008,P=0.03）;互花米草总体呈现拉力或者弯曲载荷高于芦苇的现象（如茎秆）,但应力（根系）或静曲强度（茎秆）却要低于芦苇,即对应了互花米草比芦苇茎秆更粗壮的现象,但芦苇自身的强度会更强,其木质素和纤维素的结构成分显示出显著高于互花米草的现象（P<0.001,P<0.001）。总体来看,通过短时间的波浪模拟,植株在形态特征上发生了显著的变化,而植物自身的生物力学特性与形态、结构成分都息息相关。研究结果对于评价芦苇和互花米草在应对海浪影响的潜力、从植物生物力学角度探究滨海湿地的保护和修复都提供了一定的参考。     

Decomposition of duckweed (Lemna gibba) under axenic and microbial [-2pt] conditions: flux of nutrients between litter water and sediment, the impact of leaching and microbial degradation

The decomposition of axenic Lemna gibba has been studied over a 200 day period under laboratory conditions in the presence and absence of wastewater micro-organisms. The residual mass of plant litter in the decomposition vessels decreased three times more rapidly under biotic than abiotic conditions. The organic matter in the duckweed litter lost about half its weight within 67.9 days in the presence of micro-organisms while more than 200 days were required in axenic vessels. In the former case, AFDW loss followed an exponential pattern of decay. The rate constant was 0.0102 day ^–1 and the decay was virtually complete after 200 days. The C and K concentration of the remaining duckweed litter decreased; the N, Ca, Fe and B concentration increased in both treatments. The concentration of total N, P, K, Mg, and Mo increased in the receiving water in both treatments but was much higher under biotic than abiotic conditions. Mass balances of nutrients in the vessels and flux of these nutrients between compartments in the vessels (duckweed litter, water and sediment) have been determined. Under axenic conditions the release of elements was very slow. Only notably potassium leaching had occurred. Leaching of potassium, magnesium and organic carbon took place mainly during the first term of incubation and then slowed down. Under biotic decomposition the elemental content of the litter decreased by more than 50% over 43 days for K, 53 days for Mo, 64 days for C, 81 days for Mg, 101 days for S, 104 days for P, 108 days for Na, 111 days for N, 140 days for B. Calcium and iron immobilised in the litter. Most of the released N, S, P, K, Mg and Mo remained in the water, but B and Mn settled into the sediment. The result of the investigation demonstrated that the nutrient flux from decomposing duckweed litter is mainly a microbially mediated process.     

The Impacts of Above- and Belowground Plant Input on Soil Microbiota: Invasive <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Versus Native <Emphasis Type="Italic">Phragmites australis</Emphasis>

Invasive plants affect soil food webs through various resource inputs including shoot litter, root litter and living root input. The net impact of invasive plants on soil biota has been recognized; however, the relative contributions of different resource input pathways have not been quantified. Through a 2 × 2 × 2 factorial field experiment, a pair of invasive and native plant species (Spartina alterniflora vs. Phragmites australis) was compared to determine the relative impacts of their living roots or shoots and root litter on soil microbial and nematode communities. Living root identity affected bacteria-to-fungi PLFA ratios, abundance of total nematodes, plant-feeding nematodes and omnivorous nematodes. Specifically, the plant-feeding nematodes were 627% less abundant when living roots of invasive S. alterniflora were present than those of native P. australis. Likewise, shoot and root biomass (within soil at 0–10 cm depth) of S. alterniflora was, respectively, 300 and 100% greater than those of P. australis. These findings support the enemy release hypothesis of plant invasion. Root litter identity affected other components of soil microbiota (that is, bacterial-feeding nematodes), which were 34% more abundant in the presence of root litter of P. australis than S. alterniflora. Overall, more variation associated with nematode community structure and function was explained by differences in living roots than root or shoot litter for this pair of plant species sharing a common habitat but contrasting invasion degrees. We conclude that belowground resource input is an important mechanism used by invasive plants to affect ecosystem structure and function.     

Decomposition of [14C]Lignocelluloses of Spartina alterniflora and a Comparison with Field Experiments

Decomposition of lignocelluloses from Spartina alterniflora in salt-marsh sediments was measured by using ¹⁴C-labeled compounds. Rates of decomposition were fastest in the first 4 days of incubation and declined later. Lignins labeled in side chains were mineralized slightly faster than uniformly labeled lignins; 12% of the [side chain-¹⁴C]lignin-labeled lignocellulose was mineralized after 816 h of incubation, whereas only 8% of the [U-¹⁴C]lignin-labeled lignocelluloses were degraded during this period. The carbohydrate moiety within the lignocellulose complex was degraded about four times faster than the lignin moiety; after 816 h of incubation, 29 to 37% of the carbohydrate moiety had been mineralized. Changes in concentration of lignin and cellulose in litter of S. alterniflora were followed over 2 years of decay. Cellulose disappeared from litter more rapidly than lignin; 50% of the initial content of cellulose was lost after 130 days, whereas lignin required 330 to 380 days for 50% loss. The slow loss of lignin compared with other litter components resulted in a progressive enrichment of litter in lignin content. The rates of mineralization of [¹⁴C]lignocelluloses in marsh sediments were similar to the rates of lignocellulose decomposition in litter on the marsh.