Growth characteristics ofNelumbo nucifera Gaertn. in response to water depth and flooding

Three experiments on the effects of water depth and flooding onNelumbo nucifera Gaertn. were made in the artificial environment of concrete ponds. First, plants were harvested in autumn after growing under seven different water levels ranging from 0.2–3 m The number of floating leaves, the total number of leaves and the leaf area index of emergent leaves were greatest in the tanks at 0.5 m depth. The petiole dry weight per unit length of emergent leaves and the ratio of aboveground to belowground biomass rose with increasing water depth up to 2 m. In contrast, that of floating leaves was constant at about 10 mg dry weight cm⁻¹. The proportion of biomass in tubers fell from 20% at 0.2 m to 6% at 2 m. Second, petiole elongation responses to the amplitude of flooding were investigated in early summer. The maximum rate of petiole elongation was 25 cm per day at 2.4 m water depth. This was the maximum depth at whichN. nucifera could grow. No petioles could elongate from 3 m to 5 m depth. Finally, the effects of timing of flooding on growth were investigated. At the end of growing season, the belowground biomass of plants in the flooding treatment in late summer was smallest among the flooding treatment plants (P<0.05), and was most severe when flooding occurred in this season. Based on the results of these experiments, the growth characteristics ofN. nucifera in relation to petiole elongation, biomass allocation, and flooding tolerance were discussed.     

Nutrient dynamics in a floating mat and pond system with special reference to its vegetation

Chemical properties of waters and their seasonal changes were studied in Mizorogaike Pond, a system of pond and floating mat. The following six sites including contrasting habitats and water conditions were monitored to assess nutrient dynamics in the system: 1) a pool on the mat, 2) margin of aSphagnum cuspidatum community, 3) an artificial ‘well’ (water layer beneath the floating mat), 4) aMenyanthes trifoliata community in a hollow, and 5) & 6) two sites in the open water. On the floating mat, the water around theSphagnum community had lower pH values, while that in theM. trifoliata community had higher pH values. This difference was related to the influence of flood water, the extent of which was determined by the microtopography. Seasonal changes in water chemistry on the mat suggested that pond water flooding the mat in late autumn and winter is important for the nutrient supply to the mat surface vegetation in this system. Water chemistry of the ‘well’ suggested that the diffusion of inorganic nitrogen occurs from beneath the peat layer. Two types of cluster analysis based on the mean values for chemical variables and the patterns of fluctuation in these variables were performed. The six sites were classified into similar groups which were identified by water type (pool, hollow, well and open water) by both types of analysis. The results showed that a common kind of perturbation should operate in determining the status of nutrient dynamics in the various water types.     

Seasonal change in the redox property of peat and its relation to vegetation in a system of floating mat and pond

A relationship was sought between species distribution and seasonal change in the redox property of peat in a floating mat in Mizorogaike Pond, central Japan. The mat surface experienced an annual submergence-emergence cycle due to its sinking-rising movement. Redox potential (Eh) of the surface peat showed little difference between communities in the mat in the submergence season (January–June) and early emergence season (July–August). However variation in Eh among communities was clear in the late emergence season (September–December). Among seven communities in the floating mat, theMenyanthes trifoliata-Rhynchospora fauriei, M. trifoliata-Eriocaulon sikokianum-E. bondoense f.pilosum, Sphagnum cuspidatum andM. trifoliata-Carex thunbergii communities had high Eh (400–600 mV) in the late emergence season, while theMenyanthes trifoliata andPhragmites australis-M. trifoliata communities had lower Eh (200–400 mV). TheM. trifoliata-Isachné globosa community was intermediate (300–500 mV). The earlier the emergence of the peat surface began, the higher the Eh became in the late emergence season.     

Seasonal changes in redox properties of peat, nutrition and phenology of Menyanthes trifoliata L. in a floating peat mat in Mizorogaike Pond, central Japan

Seasonal changes in leaf population per area, nutrient absorption rate and elemental concentration of Menyanthes trifoliata L. were studied in a floating peat mat in Mizorogaike Pond, central Japan, with reference to the peat redox potential. Leaf population of M. trifoliata showed a rapid increase in May, reached the maximum in June, and then decreased to 12% of the maximum density in July. The foliage density of M. trifoliata again increased and reached its second maximum in September, and then it decreased to zero in December. The decrease of the foliage density from June to July corresponded to the minimum of redox potential (Eh) of the surface peat. Low Eh in the rhizosphere of M. trifoliata relates to the temporary disappearance of the foliage of the plant from June to July. Nutrient concentration (K, Mg, Ca, Fe) in M. trifoliata roots showed minimum in June to August. The nutrient absorption rate of M. trifoliata evaluated from the rubidium absorption rate of excised root of M. trifoliata showed a minimum value in June and July. Peat redox properties would affect the nutrient absorption activity of the roots and the consequent foliage phenology of M. trifoliata in Mizorogaike Pond.     

洱海漂浮草垫的物种组成及分布

研究通过调查洱海2017年夏季和冬季漂浮草垫的物种组成及分布模式, 探究洱海在水位上升过程中, 哪些挺水植物更易形成漂浮草垫而存活下来。夏季共调查到漂浮草垫18个, 植物分属15科, 18属, 24种, 冬季共调查到漂浮草垫22个, 植物分属13科, 17属, 22种, 形成洱海漂浮草垫的植物共15科, 19属, 26个物种。草垫下水体中总氮(TN)、总磷(TP)、溶解性总磷(TDP)都明显高于开阔水域的(P<0.05), 而开阔水域的溶氧(DO)明显高于草垫下水体的(P<0.05)。结果表明在夏季和冬季漂浮草垫面积大小与其组成草垫的物种数和漂浮草垫生物量都呈显著正相关(P<0.01), 而在夏季和冬季漂浮草垫面积大小与漂浮草垫单位面积平均生物量相关性都不显著(P>0.05), 漂浮草垫面积大小与漂浮草垫下最长根在夏季相关性显著(P<0.01), 而在冬季相关性不显著(P>0.05)。漂浮草垫主要分布在离岸距离60 m以内以及水深不超过2 m的水域, 漂浮草垫面积大部分都小于600 m2(夏季占87%, 冬季占95%), 每个漂浮草垫的物种数都小于10个, 漂浮草垫下最长根主要分布在40—120 cm。组成漂浮草垫的物种中菰(Zizania latifolia)的频度和相对生物量在夏季和冬季(频度: 夏季-73.33%, 冬季-66.67%; 生物量: 夏季-43.38%, 冬季-41.91%)都是最高的, 说明菰相比其他挺水植物更容易形成漂浮草垫从而避免洱海水位上升对其生长和繁殖的影响, 这可能是菰成为洱海单优挺水植物的主要原因。而菰比其他挺水植物更容易形成漂浮草垫的机制则需要更进一步的研究。     

Sulfate Reduction in Peat from a New Jersey Pinelands Cedar Swamp

Microbial sulfate reduction rates in acidic peat from a New Jersey Pine Barrens cedar swamp in 1986 were similar to sulfate reduction rates in freshwater lake sediments. The rates ranged from a low of 1.0 nmol cm⁻³ day⁻¹ in February at 7.5- to 10.0-cm depth to 173.4 nmol cm⁻³ day⁻¹ in July at 5.0- to 7.5-cm depth. The presence of living Sphagnum moss at the surface generally resulted in reduced rates of sulfate reduction. Pore water sulfate concentrations and water table height also apparently affected the sulfate reduction rate. Concentrations of sulfate in pore water were nearly always higher than those in surface water and groundwater, ranging from 26 to 522 μM. The elevated pore water sulfate levels did not result from the evapotranspiratory concentration of infiltrating stream water or groundwater, but probably resulted from oxidation of reduced sulfur compounds, hydrolysis of ester sulfates present in the peat, or both. The total sulfur content of peat that had no living moss at the surface was 164.64 ± 1.5 and 195.8 ± 21.7 μmol g (dry weight)⁻¹ for peat collected from 2.5 to 5.0 and 7.5 to 10.0 cm, respectively. Organosulfur compounds accounted for 84 to 88% of the total sulfur that was present in the peat. C-bonded sulfur accounted for 91 to 94% of the organic sulfur, with ester sulfate being only a minor constituent. Reduced inorganic sulfur species in peat from 2.5 to 7.5 cm were dominated by H₂S-FeS (68%), while pyritic sulfide was the predominant inorganic sulfur species in the peat from depths of 7.5 to 10.0 cm (75%).     

Phenotypic and phenological plasticity of an aquatic macrophyteMenyanthes trifoliata L.

Phenotypic and phenological properties ofMenyanthes trifoliata L. were investigated within and outside of aPhragmites australis (Cav.) Trin. ex. Steud. canopy in a floating peat mat in Mizorogaike Pond, Central Japan. Under theP. australis canopy,M. trifoliata adjusted its phenotypic properties to the conditions of decreased light by increasing leaf blade area, decreasing leaf blade thickness and elongating petioles. The earlier expansion of leaves ofM. trifoliata within theP. australis community than outside the community was advantageous in terms of allowing the plant in the mixed community to produce as much dry matter as possible before the foliage ofP. australis could overgrow it. Despite the harmful effect ofP. australis onM. trifoliata's vegetative growth and reproduction, the latter species can persist in aP. australis community by changing its phenotypic and phenological properties.     

Pore water phosphorus and iron concentrations in a shallow,eutrophic lake — indications of bacterial regulation

Peak pore water SRP and iron(II) concentrations were found during summer in surface sediments in the shallow and eutrophic L. Finjasjön, Sweden, and the concentrations generally increased with water depth. The SRP variation in surface sediments (0–2 cm) was correlated with temperature (R² = 0.82–0.95) and iron(II) showed a correlation with sedimentary carbon on all sites (R² = 0.42–0.96). In addition, sedimentary Chla, bacterial abundances and production rates in surface sediments (0–2 cm) varied seasonally, with peaks during spring and fall sedimentation. Bacterial production rates were correlated with phosphorus and carbon in the sediment (R² = 0.90–0.95 and R² = 0.31–0.95, respectively), indicating a coupling with algal sedimentation. A general increase in sediment Chla and bacterial abundances towards sediments at greater water depth was found. Further, data from 1988–90 reveal that TP and TFe concentrations in the lake were significantly correlated during summer (R² = 0.81 and 0.76, in the hypolimnion and epilimnion, respectively). The results indicate that the increase in pore water SRP and Fe(II) in surface sediments during summer is regulated by bacterial activity and the input of organic matter. In addition, spatial and temporal variations in pore water composition are mainly influenced by temperature and water depth and the significant correlation between TP and TFe in the water suggests a coupled release from the sediment. These findings support the theory of anoxic microlayer formation at the sediment-water interface.     

Mechanisms influencing changes in lake area in Alaskan boreal forest

During the past ～50 years, the number and area of lakes have declined in several regions in boreal forests. However, there has been substantial finer‐scale heterogeneity; some lakes decreased in area, some showed no trend, and others increased. The objective of this study was to identify the primary mechanisms underlying heterogeneous trends in closed‐basin lake area. Eight lake characteristics (δ¹⁸O, electrical conductivity, surface : volume index, bank slope, floating mat width, peat depth, thaw depth at shoreline, and thaw depth at the forest boundary) were compared for 15 lake pairs in Alaskan boreal forest where one lake had decreased in area since ～1950, and the other had not. Mean differences in characteristics between paired lakes were used to identify the most likely of nine mechanistic scenarios that combined three potential mechanisms for decreasing lake area (talik drainage, surface water evaporation, and terrestrialization) with three potential mechanisms for nondecreasing lake area (subpermafrost groundwater recharge through an open talik, stable permafrost, and thermokarst). A priori expectations of the direction of mean differences between decreasing and nondecreasing paired lakes were generated for each scenario. Decreasing lakes had significantly greater electrical conductivity, greater surface : volume indices, shallower bank slopes, wider floating mats, greater peat depths, and shallower thaw depths at the forest boundary. These results indicated that the most likely scenario was terrestrialization as the mechanism for lake area reduction combined with thermokarst as the mechanism for nondecreasing lake area. Terrestrialization and thermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthened the growing season, thereby increasing plant growth, floating mat encroachment, transpiration rates, and the accumulation of organic matter in lake basins. The transition to peatlands associated with terrestrialization may provide a transient increase in carbon storage enhancing the role of northern ecosystems as major stores of global carbon.     

排水对若尔盖高原泥炭地土壤有机碳储量的影响

泥炭地作为陆地上生态系统一个重要碳汇,存储了全球土壤有机碳储量的25%—43%。泥炭地排水与其他土地利用导致了大量的土壤有机碳损失。然而,有关排水对中国泥炭地土壤有机碳储量的影响研究报道较少,因此,为了获得更多可靠的泥炭地碳储量信息,以便减少它们估算的不确定性。选取了我国若尔盖高原未排水泥炭地和排水泥炭地进行土壤剖面取样,定量评价排水对泥炭地土壤有机碳储量的影响。研究表明:(1)未排水泥炭地土壤有机碳储量平均值为(923.71±107.18)t C/hm~2,为中国陆地和全球陆地土壤有机碳储量的8.1和9.4倍;而排水泥炭地土壤有机碳储量平均值为(574.01±66.86)t C/hm~2,为中国和全球陆地的5.1和5.8倍。(2)泥炭地排水后,导致表层(0—30 cm)土壤有机碳储量增加(59.11±9.31)t C/hm~2,可能源于土壤容重增加。(3)然而,完全考虑泥炭剖面深度后,排水泥炭地土壤有机碳储量较对照样地减少了349.7 t C/hm~2,这可能是由于泥炭地排水后,水位降低,加速了泥炭氧化,降低了泥炭厚度。     

Effect of flooding-drawdown cycle on vegetation in a system of floating peat mat and pond

The relationship between vegetation and seasonal changes in water level was examined in a system of terrestrializing floating peat mat and pond in a warm temperate zone. The duration of flooding, or drawdown period, is related to vegetation in the mat. The first process of terrestrialization would be the attenuation of floating-sinking movement of the mat and the consequent stabilization of water level. Water level at the time when the movement of the mat was attenuated determined the subsequent vegetation change at the site. Two series of succession according to terrestrialization were recognized, and started from initial conditions of low and high water levels respectively. Habitats in low initial water levels experienced short flooding and long drawdown periods. Species changes in the successional series were:Menyanthes trifoliata-Rhynchospora fauriei-Eriocaulon sikokianum-Sphagnum cuspidatum. Submerged peat was experimentally emerged, and the crowded community ofRhynchospora fauriei andEriocaulon sikokianum established within one or two years. Appearance of these species was controlled by the water level of the habitats in winter. Another series of species changes in terrestrialization process was:Menyanthes trifoliata-Phragmites australis-Carex thunbergii orIsachne globosa. Habitats of these types of vegetation were in the area with relatively high initial water level (long flooding and short drawdown) when the floating-sinking movement of the mat attenuated. After the temporal paludification, the water level was lowered by the accumulation of peat in the process of terrestrialization.     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

The distribution of phosphorus between soluble and particulate phases for seven Scottish East Coast rivers

Phosphorus (P) fractions were quantified in water samples collected on four occasions from sites at the lower tidal limit of seven Scottish East Coast rivers. Individual catchment characteristics ranged from those dominated by semi-natural land use to those where agriculture predominated. Together the rivers displayed attributes ranging from nearly pristine to those impacted by point and diffuse sources of pollutants. Sampling times were chosen to coincide with periods of low river flows where conditions should result in low concentrations of suspended particulate matter (SPM) but favourable for phytoplankton growth. Total phosphorus (TP) concentrations were < 0.004 mg l^–1, 0.005–0.048 mg l^–1 and 0.28–2.2 mg l^–1 for pristine, agricultural and point source impacted rivers respectively. Soluble reactive phosphorus (SRP) represented from < 5% to > 90% of TP and dissolved P dominated all samples. The total phosphorus content (TPC) of SMP ranged from 0.1 to 1.1% and was significantly related to SRP. Organic matter was a significant component of SPM and organically bound phosphorus was the dominant form of particulate P. The C/P ratio of organic matter was wide, between 500–1200 for the more pristine systems which narrowed to < 400 for heavily impacted rivers. Exchangeable P increased during the summer but was generally a minor component of TP and therefore likely to be a significant source of SRP only in pristine rivers. Phytoplankton constituted between 5 and 46% of organic matter and concentrations of chlorophyll-a were significantly correlated with both TP and SRP.     

陕西榆林春玉米高产田土壤理化性状及根系分布

调查分析了陕西榆林2块19500 kg·hm^-2以上超高产春玉米田的产量构成、干物质分配和0～100 cm土层根系分布及土壤理化性状指标.结果表明：其种植密度为105000～123000株·hm^-2、成穗率97.7%～102.2%、千粒重320 g以上,果穗干物质积累量占整株干物质积累量的60.2%～65.5%.0～100 cm土壤平均容重为1.28～1.33 g·cm^-3,层间（每层20 cm）土壤容重、孔隙度和田间持水量均呈“M”型变化.玉米根系主要分布在0～60 cm,0～20 cm土层根系量占根系总量的64.8%～72.1%,20～60 cm土层根系量占根系总量的23.30%～28.17%.根系分布与土壤理化性状关系密切,0～20 cm土层玉米的根系量与土壤有机质、全氮和全磷含量呈显著正相关,20～60 cm土层根系量与土壤容重和田间持水量显著相关.因此,选择通透性和保水保肥能力良好的土壤,实行宽窄行双株密植栽培是获得玉米高产的关键.     

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。     

Phosphorus and light colimit periphyton growth at subsaturating irradiances

1. This study investigated the combined effects of light and phosphorus on the growth and phosphorus content of periphyton. To investigate the potential for colimitation of algal growth by these two resources, diatom‐dominated periphyton communities in large flow‐through laboratory streams were exposed under controlled conditions to simultaneous gradients of light and phosphorus. 2. Periphyton growth rate was predictably light‐limited by the subsaturating irradiances (12–88 μmol photons m^?2 s^?1) used in this experiment. However, phosphorus concentration also limited growth rate: growth increased hyperbolically with increasing soluble reactive phosphorus (SRP), reaching a threshold of growth saturation between 22 and 82 μg L^?1. 3. Periphyton phosphorus content was strongly and nonlinearly related with SRP, reaching a maximum at 82 μg L^?1 SRP. Contrary to the Light : Nutrient Hypothesis, periphyton phosphorus content did not decrease with increasing light, even at the lowest concentrations of SRP. Periphyton phosphorus was highly correlated with periphyton growth rate (Spearman's ρ = 0.63, P < 0.005). 4. Multiple regression analysis reinforced evidence of simultaneous light and phosphorus limitation. Both light and periphyton phosphorus content were significant variables in multiple regressions with growth parameters as dependent variables. Light alone accounted for 67% of the variance in periphyton biomass, and the addition of periphyton phosphorus as an additional independent variable increased the total amount of variance explained to 81%. 5. Our results did not support the hypothesis that extra phosphorus is required for photoacclimation to low light levels. Rather, the effect of additional phosphorus may have been to accommodate increased requirements for P‐rich ribosomal RNA when growth was stimulated by increased light. The potential colimitation of periphyton growth by phosphorus and light at subsaturating irradiances has important implications in both theoretical and applied aquatic ecology.     

Hydrologic,vegetation, and substrate characteristics of floating marshes in sediment-rich wetlands of the Mississippi river delta plain,Louisiana, USA

Floating marshes occur over 70% of the western Terrebonne Basin, Louisiana, USA, freshwater coastal wetlands. They are of several types: A free-floating thick-mat (45–60 cm) marsh dominated by Panicum hemitomon and Sagittaria lancifolia; a thick mat marsh dominated by Panicum hemitomon and Sagittaria lancifolia that floats part of the year, but whose vertical floating range is damped compared to adjacent water; and an irregularly-floating thin mat (< 30 cm) dominated by Eleocharis spp. in the spring and Ludwigia leptocarpa and Bidens laevis in the summer and fall. Floating mats must be almost entirely organic in order to be buoyant enough to float. The western Terrebonne wetlands receive large winter/spring supplies of suspended sediments from the Atchafalaya River. Even though sediment concentrations in the adjacent bayou are as high as 100 mg l^–1, the Panicum hemitomon/Sagittaria lancifolia free-floating marsh probably receives no over-surface sediments since it floats continuously. The bulk density data of the damped-floating marsh, however, suggest some mineral sediment input, probably during winter when this marsh is submerged. These two types of floating marsh could not have developed in the present sediment regime of the Atchafalaya River, but as long as they remain floating can continue to exist. Thin floating mats are found in areas receiving the least sediment (<20 mg 1^–1 suspended sediment concentration in adjacent bayous). This low sediment environment probably made possible their formation within the past 20 years. They may represent a transitional stage in mat succession from (1) existing thick-mat floating marsh to a degrading floating marsh, or (2) a floating marsh developing in shallow open water.Corresponding editor: D. Whigham     

Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm^-3 throughout the growing season and decreased with depth to about 2 cm cm^-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study. Published with permission of the Arkansas Agricultural Experiment Station.     

13C natural abundance variations in carbonates and organic carbon from boreal forest wetlands

¹³C natural abundance variations were measured in peat soil and vegetation from two contrasting boreal forest wetlands: an upland watershed basin and a permanently saturated lowland mire. Evidence of methane oxidation was shown in the permanently saturated wetland with δ¹³C values as low as -97 ‰ in carbonate minerals found in floating peat mats. It is postulated that¹³C depleted CH₄ is oxidized in the mat and reacts with calcium ions to form calcite (identified through x-ray diffraction). Methane flux measurements during the summer of 1992 showed much lower fluxes in areas with floating peat mats relative to open water. Secondary carbonates in the basin peat have isotope compositions close to the δ¹³C values of the peat organic carbon (-25 ‰), indicating their origin from fermentation and possibly from sulfate-reduction. In the upland basin peat deposits, the δ¹³C_PDB values of organic C were constant with depth, while the permanently saturated mire had localities of¹³C enrichment in deeper layers of the peat. The¹³C enrichment may reflect areas of intense CH₄ production in which¹³C enriched residual substrate is left behind during the production of highly¹³C depleted CH₄.     

Phragmites australis makes valuable floating mat biotopes under oligotrophic conditions

To understand the mechanism of how Phragmites australis makes valuable floating mat biotopes under oligotrophic conditions, we investigated the environmental (water chemistry) and vegetational characteristics (growth, plant species richness, and floristic composition) of a floating mat consisting of three main mat-forming species with a zonal distribution (P. australis on the land side of the floating mat, Zizania latifolia on the middle area, and Typha angustifolia on the water side). Although they showed relatively low growth in the floating mat, compared to those in land-based wetlands, P. australis grew better than other mat-forming species in terms of shoot height and biomass production. Specifically, P. australis made more below-ground parts (593?±?38 g/m²) than other mat-forming species (Z. latifolia, 100?±?10 g/m²; T. angustifolia, 167?±?8 g/m²) and more companion species were found in P. australis-dominated plots (8.5?±?1.0 species/m²) than other plots (Z. latifolia-dominated plots, 2.7?±?0.6 species/m²; T. angustifolia-dominated plots, 1.0?±?0.0 species/m²). The larger amount of below-ground P. australis parts could contribute to thicker and denser mat structures, possibly providing more favorable habitats for neighboring plant species, thus facilitating more companion species within the P. australis-dominated area of the mat.