不同植被恢复模式对根际土壤MBC/WSOC的影响

以马尾松与木荷混交林(MM)为对照,马尾松与阔叶树复层林(MK)、封育林(FY)、阔叶混交林(KY)为研究对象,探讨不同恢复模式下根际与非根际土壤MBC和WSOC含量特征。结果表明,各种恢复模式均呈现出土壤MBC和WSOC含量随着土壤深度的增加而减少的趋势,根际土壤的MBC含量较非根际土壤高,而其WSOC含量较非根际土壤低。MK、MM根际土壤的MBC含量分别与它们的WSOC含量存在显著相关关系,MM、MK和KY非根际土壤的MBC含量分别与其WSOC含量存在显著性相关关系。总体上,各种植被恢复模式根际与非根际土壤之间MBC、WSOC均存在较为明显的差异。     

林间草地土壤氮、磷、钾空间异质性研究

以林间草地土壤水解性氮、有效磷、速效钾含量与土层和植被分布格局之间的关系为研究对象,利用统计学方法研究了土壤上层(0~30 cm)水解性氮、有效磷、速效钾小尺度上的空间异质性,掌握其变异规律。研究结果表明:①土壤表层水解性氮、有效磷和速效钾含量均明显高于底层;②距离树木较近的点各层土壤水解性氮、有效磷、速效钾含量较高,而取样地以草本植物为主的点上土壤水解性氮、有效磷、速效钾含量次之,路边土壤取样点的土壤水解性氮、有效磷、速效钾含量最低;③水解性氮、有效磷及速效钾含量均与土壤厚度呈极显著(P<0.01)或显著(P<0.05)负相关;除速效钾外,土壤水解性氮和有效磷的分布在植被类型的影响下具有极显著(P<0.01)或显著(P<0.05)差异;植被土层对土壤水解性氮、有效磷及速效钾的分布均有显著(P<0.05)的互作作用。     

根际土壤酶活性和微生物区系在蕹菜镉积累中的特征

通过自制根箱试验,研究了植物根际土壤酶活性（脲酶,转化酶,酸性磷酸酶,碱性磷酸酶）和微生物区系（细菌、真菌、放线菌）在不同蕹菜品种中（ Cd－PSC,non-Cd-PSC）镉积累行为的特征。结果表明：蕹菜茎叶的镉积累特性具有稳定性。相同条件下,根际土壤的4种酶活性和3类微生物数量都显著大于非根际土壤。在蕹菜两个品种间,3类微生物的数量差异显著,其大小排序为：细菌,真菌,放线菌;转化酶、酸性磷酸酶、碱性磷酸酶在品种间差异极显著,其大小排序为：酸性磷酸酶,转化酶,碱性磷酸酶;脲酶在品种间的差异性不显著。     

不同品种脐橙根际土丛枝菌根真菌群落多样性分析

以赣南早脐橙、红肉脐橙和纽荷尔脐橙3个品种脐橙的根际土壤为研究对象,研究不同品种脐橙根际土壤中丛枝菌根真菌(Arbuscular mycorrhizal fungi, AM真菌)群落特征。结果表明：脐橙品种显著影响根际土壤中AM真菌群落α多样性,纽荷尔脐橙根际土壤中的OTU数和ACE指数均显著低于赣南早脐橙和红肉脐橙(P<0.05);在各个菌属中,赣南早脐橙根际土壤中类球囊霉(Paraglomus)的相对丰度显著高于红肉脐橙和纽荷尔脐橙(P<0.05)。冗余分析(RDA)表明,土壤因子中,碱解氮显著影响脐橙根际土壤中AM真菌群落α多样性(F=7.8,P=0.034),速效钾显著影响脐橙根际土壤中AM真菌群落结构(F=2.7,P=0.008)。     

香炉山钨矿尾矿区4种先锋植物重金属富集特征

对江西省香炉山钨矿尾矿区土壤和自然定居的4种先锋植物胡枝子Lespedeza bicolor(Turcz.)、葛藤Pueraria lobata(Willdenow)Ohwi、草木犀Melilotus officinalis(Linn.)和截叶铁扫帚Lespedeza cuneata(Dum.Cour.)茎叶重金属富集特征进行研究。结果表明4种植物茎叶中重金属富集特征明显,特别以铬、锰和镍重金属富集较高。植物茎叶和土壤中的重金属含量有较一致的动态,说明土壤是植物中重金属含量的主要影响源。4种植物铬和锰的含量接近1 g/kg的临界值,表明对镉和锰具有很好的适应性和耐性,是镉锰污染的潜在修复植物。截叶铁扫帚茎叶中重金属含量高于其它3种植物,是植物间重金属含量差异的主要贡献者。总之,江西香炉山钨矿尾矿区的土壤受污染较严重,超过土壤环境质量标准的3级。4种植物中截叶铁扫帚对重金属的复合胁迫适应性较好,可作为尾矿区植被修复的先锋植物。     

植被恢复边坡土壤抗蚀性及其影响因子耦合协调分析

为了给边坡植被恢复设计等提供参考和技术支撑,基于内江市境内公路边坡经0、5、7、15、20 a植被恢复的样地野外调查资料,以土壤颗粒(团聚体)平均质量直径和水稳性指数为土壤抗蚀性指标,以土壤粒径≥0.25 mm的大团聚体含量、容重、有机质含量、碱解氮含量、速效磷含量、速效钾含量等6个土壤理化性质指标为土壤抗蚀性影响因子,采用主成分分析、耦合协调度分析等方法,探究不同植被恢复年限的边坡土壤抗蚀性与其影响因子的耦合协调关系,得到以下主要结论：1)不同植被恢复年限的土壤抗蚀性指标及其影响因子具有显著差异,随着植被恢复年限的延长,土壤大团聚体含量和养分含量呈增加趋势,土壤容重呈减小趋势,土壤抗蚀性呈增强趋势;2)碱解氮含量、有机质含量、速效磷含量、大团聚体含量、容重是不同植被恢复年限土壤抗蚀性的主要影响因子;3)土壤理化性质指标中,化学指标(速效磷含量、碱解氮含量、有机质含量、速效钾含量)对土壤抗蚀性的影响大于物理指标(大团聚体含量、容重)的影响,进行植被护坡设计时应当注重有机质和速效肥料的保持;4)土壤理化性质指标与土壤抗蚀性指标的耦合协调度随植被恢复年限的延长而提高,植被恢复15 a时二者...     

鄱阳湖典型洲滩湿地植被叶片和土壤δ15N特征分析

为研究鄱阳湖典型洲滩湿地植被叶片和土壤δ¹⁵N特征,以蚌湖和修水之间的洲滩作为研究对象,选取典型断面研究2015年10—12月和2016年4月植被叶片和土壤δ¹⁵N的相关关系,探讨土壤含水量和无机氮(铵态氮和硝态氮)对植被叶片和土壤δ¹⁵N的影响。结果表明:大部分C3植被的叶片δ¹⁵N大于C4植被;湿润时期植被叶片和土壤δ¹⁵N大于干旱时期,但湿润时期和干旱时期植被叶片均较土壤富集¹⁵N。铵态氮在湿地土壤中占比高达87.43%,是土壤主要的无机氮,但湿地植被主要吸收硝态氮。研究区氮循环开度较小,土壤δ¹⁵N随着可利用氮素的增加而降低,而随着土壤含水量的增加而增加。植被叶片δ¹⁵N与土壤δ¹⁵N呈显著的正相关关系,植被叶片δ¹⁵N主要受土壤氮素变化和氮同位素分馏的影响。     

修建防渗渠道对柴达木盆地戈壁区河流生态系统的影响

为摸清修建防渗渠道对戈壁区河流生态系统的影响,以期能为柴达木盆地农业绿洲制定可持续发展的政策提供依据,在社会经济调查的基础上,以大格勒流域为研究对象,通过野外取样和室内化验,对比分析了修建防渗渠道前后的地表河流水质、河岸植被及土壤理化性状。研究结果表明①修建防渗渠道对河流水质具有净化作用,但效果不显著(P>0.05);②修建防渗渠道不利于戈壁区沿河植被繁殖生长,流域内植被平均盖度降低4.5%,生物量减少330.2 kg/hm²,死亡率增加6.5%;河岸土壤质地呈现退化趋势(P<0.05),其中砂粒含量增加8.68%,有机质减少0.53 g/kg。基于以上研究成果,建议在河流出山口处修建生态闸,洪水期引洪灌溉河岸植被;布设生态水利工程,以实现流域生态环境与绿洲社会经济的可持续发展。     

黄河口湿地柽柳灌丛对土壤养分分布的影响

运用单因素方差分析(ANOVA)和克里金空间插值法,对黄河三角洲河口湿地群落演替方向上碱蓬群落、碱蓬-柽柳群落和柽柳群落中柽柳灌丛对土壤养分分布的影响进行了研究,结果表明:(1)土壤有机质(SOM)和水解氮(AN)含量沿群落演替方向呈递增趋势;速效磷(AP)在碱蓬-柽柳群落含量最大、柽柳群落含量最小;速效钾(AK)在碱蓬-柽柳群落含量最小、柽柳群落含量最大。(2)随着土壤深度的增加,AP含量在3种群落中均呈递减趋势,SOM、AN、AK含量变化趋势在3种群落中存在差异。(3)在群落演替方向上,土壤表层受氮(N)限制的范围逐渐减小,底层受磷(P)限制的范围逐渐增大。(4)不同群落各养分在柽柳冠下平均富集率均大于冠缘的,易形成"肥岛"效应,柽柳群落"肥岛"的发育程度较碱蓬群落高,碱蓬-柽柳群落冠下"肥岛"效应不明显。(5)柽柳灌丛对不同养分的富集作用存在差异,如AK富集作用最大,AP次之;碱蓬-柽柳群落对各养分的富集作用在30～50 cm土层最强,且富集强度远大于碱蓬群落和柽柳群落的。     

不同植被类型对堆积体坡面径流特性的影响

针对植被防护堆积体侵蚀动力机制的问题,通过野外模拟降雨试验,分析直根系和须根系植被对堆积体径流流速、水力和水动力参数的影响。结果表明:植被削减堆积体平均侵蚀速率达88.34%~92.88%,直根系消减平均流速效益为50.51%,须根系为21.32%~35.61%;裸坡和植被堆积体径流流型均属于层流(雷诺数<40),裸坡径流在降雨强度≤1.2 mm/min时处于急流态,直根系堆积体均处于缓流态,须根系堆积体在急流态和缓流态间变化。直根系对坡面径流的阻滞作用大于须根系;植被防护下堆积体侵蚀速率、水力和水动力参数与裸坡呈显著性差异(P<0.05),径流剪切力和径流功率可用于较好地刻画坡面侵蚀动态过程,呈显著线性关系(R²为0.63~0.96)。研究成果可为生产建设项目工程堆积体水土流失量预测模型的植被因子修订提供科学依据。     

Top‐down biological controls on tropical lake productivity

Although productivity is primarily controlled by bottom‐up factors (nutrient levels), there are secondary effects caused by biological factors such as zooplankton grazing and algal self‐shading. The measurement of grazing effects and determination of the contributions of different nutrient pools should elucidate the roles of nutrient levels and biotic effects and also infer the relative importance of classical and microbial food webs. To produce a series of grazing intensity, after initial screening to remove macrozooplankton, lake water was filtered to remove remaining zooplankton. This was used to dilute whole lake water in a filtered : unfiltered ratios from 0:1 to 1:0, which was then incubated with nutrient enrichment. Results show an increase of up to 20% in productivity for surface midlake waters. To investigate grazing by nutrient dilution/deletion, grazing dilutions were again prepared; however, nutrients were added to produce three different conditions,+N +P (all nutrients), –N (nitrogen omitted) and –P (phosphorus omitted). From productivity measurements, the contributions of internal, external and recycled nitrogen and phosphorus nutrient pools were calculated. Sites at Hippo Point (HP) (midlake) and Malewa River inflow (MR) (near the mouth of the River Malewa) show little difference in the contribution of external nutrients, but remaining productivity is mostly fuelled by recycled nutrients at the MR site. Little difference was found between nitrogen and phosphorus‐limited conditions.     

Abundance and nutrient limiting growth rate of heterotrophic bacterio-plankton in Himalayan foot hill Lake Phewa, Nepal

We examined heterotrophic bacterial abundance, chlorophyll- a concentration and resources limiting bacterial growth from October 2004 to August 2005 in Lake Phewa. The lake has a large watershed that covers ≈435 ha of water surface surrounded by ≈23-time large catchment area that might receive up to 4850 mm annual precipitation. During the study, bacterial abundance ranged from 3.2 to 9.9 × 10⁶ cells mL⁻¹, and chlorophyll- a varied from 2 to 32 μg L⁻¹. Bacterial abundance and chlorophyll- a weakly correlated ( r  = 0.40, n  = 77, P  < 0.1) in the lake. Experiments on resources, glucose (C), nitrogen (N), phosphorus (P) alone and in combination (CNP) limiting bacterial growth rate, were examined using dilution bioassays. Experimental bottles enriched with resources and controls without enrichment (in triplicate) were incubated in situ for 48 h at collection depth. Results showed that C, N and P in combination significantly (at 5% level) stimulated bacterial growth rate. Bioassays with single resource additions showed P as main nutrient limiting bacterial growth comparing with C and N, implying that rainfall received in the catchment might convey adequate resources causing increased P deficiency for bacterial growth in Himalayan foot hill Lake Phewa.     

水生植物对沉积物微生物群落功能多样性的影响

为研究水生植物对沉积物微生物群落功能多样性的影响,采用Biolog-Eco微平板法分析非根际沉积物及菖蒲根际沉积物微生物群落功能多样性差异。结果表明:水生植物菖蒲的生长可大大提高沉积物中微生物的活性及多样性,菖蒲根际微生物总活性(AWCD)、微生物多样性指数(包括Shannon-Wiener 指数、丰富度指数及Pielou 均匀度指数)均显著高于非根际沉积物。菖蒲根际沉积物微生物主要是一些利用酯类及糖类作为碳源的微生物类群,而非根际沉积物微生物主要利用酯类及胺类碳源。菖蒲根际沉积物及非根际沉积物之间的代谢差异的碳源主要有D-纤维二糖、β-甲基D-葡萄糖苷、葡萄糖-1-磷酸、D-半乳糖醛酸及D-葡萄胺酸、苯乙基胺、N-乙酰基-D-葡萄胺、D-半乳糖内酯、D-甘露醇及D,L-a-甘油。根际及非根际微生物群落功能多样性差异可为揭示水生植物对水环境沉积物的根际效应机制提供一定的科学依据。     

Phosphorus,Nitrogen, and Silica as Controls on Phytoplankton Biomass and Species Composition in Lake Champlain (USA-Canada)

The long-standing assumption that the phytoplankton in Lake Champlain are phosphorus limited was tested through measurement of physiological indicators of phosphorus status (alkaline phosphatase activity and orthophosphate turnover time) and enrichment experiments conducted four times during the growth season. Phosphorus addition to experimental carboys incubated 4–5 days in situ substantially increased phytoplankton biomass relative to controls in June, but had only a mild impact in July and September, and no effect in May. Nitrogen addition augmented biomass in one of four experiments (in June), while silica had no impact at any time. In summer and fall, addition of N and P in combination always yielded more phytoplankton biomass than singular P addition. In spring, even combined addition of N, P, and Si failed to stimulate phytoplankton growth. The phytoplankton groups responding to fertilization were largely the same as those that flourished in controls (diatoms and green algae), suggesting that enclosure was a more powerful determinant of species composition than nutrient inputs. Orthophosphate turnover times and levels of alkaline phosphatase activity in the lake indicated spatial and temporal variability in phytoplantkon P status, with P sufficiency as common as P deficiency. We conclude that multiple interacting factors influence the abundance and species composition of phytoplankton in Lake Champlain. In spring, phytoplankton growth is not limited by N, Si, or P, but by some factor yet to be determined (perhaps light or temperature). In summer, P is the principal limiting nutrient, but N exerts an influence that deserves further investigation.     

Dynamics of the relative nitrogen and phosphorus concentrations in a reservoir situated in a semi-arid zone (Sahela,Morocco)

Fluctuations in total nitrogen and phosphorus concentrations and in the N/P ratio (i.e. in terms of mass) were measured at the entry and exit of the Sahela Reservoir (Morocco) throughout an annual cycle. Particulate N and P concentrations in sedimenting particles in the reservoir itself were also measured. The results obtained showed that the spring floods were a major source of N and P inputs, this being especially pronounced for phosphorus that was present mainly in particulate form. In all the compartments of the reservoir analysed, the N/P ratios were high (means between 81 and 314), especially in summer (the only season when the reservoir was emptied) when the supply of P was apparently limited by the drought. However, the values of this ratio in the sedimenting particles remained lower (mean = 21), at levels characteristic of natural communities. This implies that the reservoir's biological communities preferentially store phosphorus, no doubt to maximise their activity in an environment where a large proportion of this element is not bioavailable. Furthermore, it appeared that the quantity of particulate N and P sequestrated by the sediments and the total quantities of N and P leaving the reservoir were greater than the inputs of these nutrients, underlining the importance of lateral and internal nutrient supplies. One spot measurement, made in a single month, showed that nutrient release activity from the sediments was in fact quite considerable.     

Summer phytoplankton nutrient limitation in Maumee Bay of Lake Erie during high-flow and low-flow years

Algal production in Maumee Bay in western Lake Erie is highly affected by inputs of nitrogen (N) and phosphorus (P) from the Maumee River, which drains predominantly agricultural lands, leading to the formation of cyanobacterial blooms. In a 3-year study, precipitation and discharge ranged from relatively low (2012) to relatively high (2011) with corresponding changes in the size of the cyanobacterial bloom. This study aimed to quantify the relation between river discharge and algal nutrient limitation in Maumee Bay. During the summer growing seasons, 20 nutrient enrichment bioassays were performed to determine which nutrient (P or N) might limit phytoplankton growth; and ambient N and P concentrations were monitored. The bioassays suggested that phytoplankton growth shifted from P-limited to N-limited during summer of the low and intermediate discharge years (2012 and 2010, respectively), whereas during the high discharge year (2011) phytoplankton were nutrient-replete before becoming N-limited. Phosphorus-replete growth during the high discharge year likely was due to high P loads from the river and dissolved P concentrations greater than 1 μmol/L. Symptoms of N-limited growth occurred during August and September in all three years and during July of 2012 when NO₃⁻ plus NH₄⁺ concentration was less than 7.29 μmol/L suggesting low or no correspondence between N-limitation and size of the cyanobacterial bloom. Occurrence of a relatively small cyanobacterial bloom in 2012 following the record-breaking bloom in 2011 suggests the possibility of fast-reversal of eutrophication in Maumee Bay if P loading from the watershed could be decreased.     

Snowmelt and its role in the hydrologic and nutrient budgets of prairie streams

Small watersheds in the Canadian Prairies are characterized by seasonally disconnected hydrologic networks whereby stream channels are hydrologically connected during snowmelt but have disconnected reaches throughout the remainder of the year. Snowmelt is the most significant hydrological event in the Canadian Prairies, yet few studies have investigated the role of snowmelt in the nutrient budget of prairie streams. We quantified hydrologic and nutrient dynamics during snowmelt for ten agricultural subwatersheds distributed along a gradient of human activity in the Red River Valley, Canada, to evaluate the timing of nitrogen (N) and phosphorus (P) export. Elevated concentrations of total P (TP) and total N (TN) were observed during the snowmelt peak, with maximum concentrations reaching 3.23 mg TP L(-1) and 18.50 mg TN L(-1). Dissolved P and N dominated the total nutrient pool throughout snowmelt, likely due to reduced erosion and sediment transport resulting from the combination of the flat topography, frozen soil and stream banks, and gradual snow cover melt. Significant correlations were observed between snowmelt N load (r=0.91; p<0.05) and both agricultural land cover and fertilizer usage, with a weaker correlation between snowmelt P load (r=0.81; p<0.05) and agricultural area. Our results showed that snowmelt plays a key role in nutrient export to prairie aquatic ecosystems and this may have serious impacts on downstream ecosystems. Land use management practices need to consider the snowmelt period to control nutrient loads to Lake Winnipeg and other waterbodies in the Great Plains.     

Use of sediment elemental and isotopic compositions to record the eutrophication of a polymictic reservoir in central Texas, USA

Paleolimnological studies are rarely performed on reservoirs because of concern that sediments might not accurately chronicle reservoir history. Eutrophication indicators might behave differently in polymictic reservoirs and stratified natural lakes because of system and/or mixing regime differences. Particulate organic carbon (POC), particulate organic nitrogen (PON), and total phosphorus (TP) concentrations, carbon:nitrogen (C:N) and nitrogen:phosphorus (N:P) ratios, and carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotopes from a sediment core were measured to demonstrate that sufficient information can be derived from sediments to permit a historical reconstruction. The scattered POC data were likely biased by seasonal/annual variability in allochthonous organic matter (OM) loading. The upwardly increasing PON in the sediment core supported historic primary productivity (PP) data, suggesting PON could be a better PP indicator than POC. The upwardly increasing TP documented historic P enrichment. The upwardly decreasing C:N ratio identified an OM source shift from allochthonous to increasingly autochthonous sources with reservoir age. The upwardly increasing N:P ratio implied that N‐fixation rates have increased with reservoir age, to compensate for increasing N limitation as the P loading increased. The δ¹³C decreased as the PP increased with reservoir age producing an atypical relationship compared to stratified natural lakes. The OM source shifts likely biased the δ¹³C–PP relationship, and might weaken δ¹³C‐inferred PP reconstructions in similar reservoirs. The δ¹⁵N increased with reservoir age, likely resulting from dissolved inorganic N (DIN) source changes, rather than nitrate utilization. Watershed urban growth and dairy operation intensification potentially contributed greater loads of isotopically heavy DIN. This study demonstrated that paleolimnology has great potential to assist eutrophication assessment and management efforts in reservoirs.     

Paleolimnological evidence of the effects of recent cultural eutrophication during the last 200 years in Lake Malawi,East Africa

To assess the long-term water quality changes in Lake Malawi, paleolimnological reconstructions of four radiometrically dated sediment cores collected in 1997/98 along a longitudinal transect of the lake were based on preserved diatom assemblages, as well as stratigraphies of organic carbon, total nitrogen, total phosphorus and biogenic silica concentrations. Population growth, deforestation and intensive agriculture, especially in the southern catchments, have accelerated soil erosion causing rivers to transport greater sediment and nutrient loads into Lake Malawi. Southern cores contain evidence of nutrient enrichment starting around 1940, as indicated by increased silica, carbon and nitrogen influxes. By 1980, increased rates of sedimentation, phosphorus influx, diatom influx, and relative abundances of eutrophic diatom taxa are attributable to accelerated nutrient enrichment accompanying soil erosion. The succession of diatoms in southern Lake Malawi begins with dominance by Aulacoseira nyassensis and Fragilaria africana, followed by a shift in 1980 towards Stephanodiscus, Cyclostephanos and Nitzschia, diatom taxa that have reduced silica requirements. Paleoecological results indicate that patterns of diatom assemblage change are not uniform lake-wide. Evidence of eutrophication extends to central Lake Malawi, but is not observable in the paleo-record from the deeper northern basin. The recent cultural eutrophication of the southern lake has impacted the biogeochemical cycling of silica, the available silica to phosphorus ratios, and the diatom communities of a large portion of Lake Malawi. These results provide a warning that eutrophication of this great lake is underway and will continue unless changes are made to current land use practices within the lake's catchment.