Search

1. Stream liming can alleviate the effects of anthropogenic acidification but itself constitutes a substantial ecosystem-level perturbation. Acidity in the humic streams of northern Sweden largely arises from natural causes but liming is extensively practised, with uncertain ecological outcomes. 2. We investigated macroinvertebrate assemblage structure and leaf-litter decomposition in seven humic Swedish streams, each of which is limed at a single point using a dosing tower. Grey alder Alnus incana leaves were enclosed in replicate fine (mesh size 0·5 mm) and coarse (10 mm) mesh bags at three locations in each stream: upstream of the dosing tower, in the transitional ‘mixing zone’ immediately downstream of the tower, and at a site further downstream where the lime powder is completely dissolved, with marked changes to water chemistry. Benthic macroinvertebrate assemblages were characterized from each site via five replicate Surber samples. 3. Alkalinity, pH, conductivity and calcium (Ca) concentrations increased following liming, whereas dissolved organic carbon and aluminium concentrations decreased. 4. Decomposition in fine mesh bags, primarily mediated by microbes, was positively associated with pH and Ca and was significantly elevated by liming, probably attributable to stimulation of fungal pectin-degrading enzymes that require Ca as a cofactor. 5. Decomposition attributable to detritivorous insects (shredders), assessed by subtracting decomposition observed in fine mesh bags from that observed in coarse bags, was reduced following liming, in concert with changes to shredder assemblages. Abundance of large caddisfly shredders declined in limed stream sections, whereas some smaller stoneflies increased in number. Shredder diversity declined following liming during spring. Species evenness fell overall, and richness was reduced in four of six streams. 6. Synthesis and applications. Water chemistry changes following stream liming in northern Sweden appear to overcompensate for the limited acid deposition observed in the region, with important ecosystem consequences. The potential deleterious impacts of liming need to be balanced against its desired outcomes in regions where acidity is largely attributable to natural causes. [ABSTRACT FROM AUTHOR]

• Background and Aims The present work aimed to study early stages of nodulation in a chronological sequence and to study phosphorus and nitrogen effects on early stages of nodulation in Alnus incana infected by Frankia. A method was developed to quantify early nodulation stages in intact root systems in the root hair-infected actinorhizal plant A. incana. Plant tissue responses were followed every 2 d until 14 d after inoculation. Cortical cell divisions were already seen 2 d after inoculation with Frankia. Cortical cell division areas, prenodules, nodule primordia and emerging nodules were quantified as host responses to infection.• Methods Seedlings were grown in pouches and received different levels of phosphorus and nitrogen. Four levels of phosphorus (from 0·03 to 1 mm P) and two levels of nitrogen (0·71 and 6·45 mm N) were used to study P and N effects on these early stages of nodule development.• Key Results P at a medium concentration (0·1 mm) stimulated cell divisions in the cortex and a number of prenodules, nodule primordia and emerging nodules as compared with higher or lower P levels. A high N level inhibited early cell divisions in the cortex, and this was particularly evident when the length of cell division areas and presence of the nodulation stages were related to root length.• Conclusions Extended cortical cell division areas were found that have not been previously shown in A. incana. The results show that effects of P and N are already expressed at the stage when the first cortical cell divisions are induced by Frankia. [ABSTRACT FROM AUTHOR]

Grey alder ( Alnus incana) and black alder ( Alnus glutinosa) stands on forest land, abandoned agricultural, and reclaimed oil-shale mining areas were investigated with the aim of analysing the functional diversity and activity of microbial communities in the soil–root interface and in the bulk soil in relation to fine-root parameters, alder species, and soil type. Biolog Ecoplates were used to determine community-level physiological profiles (CLPP) of culturable bacteria in soil–root interface and bulk soil samples. CLPP were summarized as AWCD (average well color development, OD 48 h−1) and by Shannon diversity index, which varied between 4.3 and 4.6 for soil–root interface. The soil–root interface/bulk soil ratio of AWCD was estimated. Substrate-induced respiration (SIR) and basal respiration (BAS) of bulk soil samples were measured and metabolic quotient ( Q = BAS/SIR) was calculated. SIR and Q varied from 0.24 to 2.89 mg C g−1 and from 0.12 to 0.51, respectively. Short-root morphological studies were carried out by WinRHIZOTM Pro 2003b; mean specific root area (SRA) varied for grey alder and black alder from 69 to 103 and from 54 to 155 m2 kg−1, respectively. The greatest differences between AWCD values of culturable bacterial communities in soil–root interface and bulk soil were found for the young alder stands on oil-shale mining spoil and on abandoned agricultural land. Soil–root interface/bulk soil AWCD ratio, ratio for Shannon diversity indices, and SRA were positively correlated. Foliar assimilation efficiency (FOE) was negatively correlated with soil–root interface/bulk soil AWCD ratio. The impact of soil and alder species on short-root morphology was significant; short-root tip volume and mass were greater for black alder than grey alder. For the investigated microbiological characteristics, no alder-species-related differences were revealed. [ABSTRACT FROM AUTHOR]

Abstract: Riparian vegetation plays an integral role in the ecology of the streams it borders, and in many western US forests, is subjected to frequent wildfire disturbances. Many questions concerning the role of natural fire in the dynamics of riparian zone vegetation remain unanswered. This case study explores the relationships between wildfire burn patterns, stream channel topography, and the short-term response of riparian vegetation to fire along two creeks in the northern Sierra Nevada mixed-conifer forest. Post-fire sampling along 60, 3m wide transects across riparian zones was used to document the topography, species distribution, sprouting response, and seedling recruitment 1 year after the Lookout fire in the Plumas National Forest, CA. Our results indicate that larger riparian zones acted as natural fire breaks, limiting the progression of the predominantly backing fire downhill toward the stream. On Fourth Water creek''s steeper first terraces, where crown fires occurred, the percentage of burned plants that sprouted was higher than in the less-severely burned and more extensive first terraces of Third Water creek (93% versus 33%, P <0.05). Total seedling recruitment was higher along Fourth Water creek (69 versus 35 seedlings, P <0.05), while plant regeneration along Third Water creek was primarily vegetative. Along Fourth Water creek, the percent of burned hardwoods that sprouted increased with proximity to the water''s edge from 33% on the slope above the riparian zone to 95% on the gravel bar, suggesting that moisture content plays a role in riparian species response to fire. An influx of white fir (Abies concolor Gordon & Glend. (Lindl.)) seedlings on the second terraces of Third Water creek may indicate a shift in species composition if future fires are suppressed and regeneration trends do not change significantly in the next few years. These results contribute to the limited research on natural fire in riparian zones, and can inform management strategies designed to restore and maintain riparian vegetation in the fire-prone forests of the Sierra Nevada. [Copyright &y& Elsevier]

In the study 104 stands of Norway spruce [ Picea abies (L.) Karst.], silver birch ( Betula pendula Roth), downy birch ( Betula pubescens Ehrh.), common alder [ Alnus glutinosa (L.) Gaertner], grey alder ( Alnus incana Moench) and European aspen ( Populus tremula L.) were used for developing site index conversion equations by analysing stands where two or more species were growing close to each other. The stands were located at latitude 56–63° N in Sweden. In most localities paired comparisons were made between Norway spruce and one of the broadleaved species, but in some cases paired comparisons were made with two of the broadleaved species. In all, 46, 39, 37, 21 and 20 pairings of Norway spruce with European aspen, silver birch, downy birch, common alder and grey alder, respectively, were measured and analysed in the study. Coefficients of determination for predicted equations varied between 0.31 and 0.51 for pairs of Norway spruce and the broadleaved species. The presented site index conversion equations could be used as tools for choosing appropriate species for a site. The information provided by the site indicator(s) should be used as one factor when making final management decisions regarding future forest stands for the production of wood products or for maintaining desired levels of biodiversity. [ABSTRACT FROM AUTHOR]

Abstract: Speckled alder (Alnus incana ssp. rugosa) is a characteristic species of scrub-shrub 1-type wetlands, the second most common wetland type in major watersheds of the Adirondack Mountains in New York State. Speckled alder is an actinorhizal nitrogen fixer that relies heavily on N2 over soil N and fixes substantial amounts of nitrogen in wetlands, resulting in little vegetation processing of anthropogenic N between alder-shrub wetlands and streams. Phosphorus (P) is an element that limits nitrogen fixation and plant growth. However, studies testing this hypothesis in the field, especially for actinorhizal plants, are very few. The objectives of this study were to evaluate the potential limitation of N fixation and growth in speckled alder by P, and to determine interactions between P fertilization and nitrate levels in riparian alder stands in a region that receives elevated N in atmospheric deposition. P fertilization significantly increased specific nitrogenase activity during the seasonal peak in early August. Nitrate concentrations were greater in reference plots compared to treatment plots, and phosphate concentrations were lower in reference plots compared to treatment plots over a period of 6 weeks in the growing season. There was a significant twig and foliar biomass response to P fertilization in the second year after fertilization, but no significant change in individual biomass or relative numbers of different sized nodules. Response of nitrogen fixation to P appears limited to a brief but significant increase in specific activity of nitrogenase late in the growing season, but P stimulated growth of above ground tissues 1 year following fertilizer application, and decreased resin-captured nitrate beneath riparian speckled alder. These results suggest that growth of alder and growth or activity of soil microbes, rather than nitrogen fixation, is P limited in riparian wetlands dominated by speckled alder, and that P controls nitrate leaching in these near-stream systems. [Copyright &y& Elsevier]

Managing invasive species in natural areas of high ecological value generally involves the selection of an appropriate control method that is cost effective while minimizing the secondary impacts of the control operation on the ecosystem. During the last decades, speckled alder (Alnus incana ssp. rugosa) has been invading wet sedge meadows of the Lac Saint-François National Wildlife Area (NWA), Québec, Canada. This invasion threatens the habitat of several bird and plant species considered rare at the national and provincial levels. We evaluated effectiveness and impacts of four methods for controlling alder invasion in the wetland. As a short-term control method, controlled fire appears to be ineffective in the context of the Lac Saint-François NWA, as suggested by the high survival of alders in a zone previously burnt on our study site. Double-cut of the shoots aims at killing the shrubs by depleting nutrient reserves in the roots using two successive cuts during the same growing season. This method was also shown to be ineffective: more than 80% of the treated alders resprouted vigorously the following year. Foliar application of herbicide with a rope-wick applicator to control smaller shrubs did kill all treated individuals. However, this method showed high risks of herbicide dripping and should be used with care. The most promising control method was the herbicide treatment of cut stumps. This method was efficient and cheap. It was also efficient at the end of winter, when the ground of the wetland was still frozen, which facilitated accessibility and limited damages to non-target species caused by trampling or herbicide dripping. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine whether symbiotic nitrogen-fixing bacteria and mycorrhizal fungi act synergistically to improve plant performance when grown on heavy metal mine tailings. Seedlings were inoculated with Frankia, Paxillus involutus (Batsch) Fr., or a combination of both and grown in 100% peat, a 1:1 mix of peat and tailings, or 100% tailings for 20 weeks. Mortality of plants grown on pure tailings (15.0%) and peat–tailings (17.9%) was significantly greater than mortality of plants grown on peat (3.5%). The rate of nodulation and mycorrhizae formation decreased from 90.0% and 66.7%, respectively, on the peat, to 11.9% and 2.6% on the tailings. Frankia-inoculated plants grown on peat–tailings showed twice the mortality rate (38.5%) of any other inoculation treatment. Plants grown on media containing tailings had greater root/shoot ratios than plants grown on peat. Inoculating plants grown in the presence of tailings with either Frankia and (or) P. involutus increased root thickness. Inoculating plants with both symbionts increased colonization rates and shoot yield on the peat and peat–tailings media, suggesting that these symbionts act synergistically to improve plant performance. However, inoculating plants with Frankia decreased shoot relative growth rate in the early part of the experiment when plants were not fixing nitrogen, which, coupled with the higher mortality effect, suggests that nodule development is a stress for plants. It may be advisable that plants have fully functioning nodules before transplanting if they are to be used in revegetation programs. [ABSTRACT FROM AUTHOR]

Abstract: Two methods of estimating the lateral migration of a river channel have been proposed. The first method is based on Coarse Woody Debris (CWD) dating. The terraces of the Mala Panew River are mainly covered with plantations of Pinus sylvestris where individual trees grow at equal distances to each other. During times of high discharges trees fall onto the riverbed providing information on the extent of flood plain erosion. The ages of CWD and the surface of the eroded flood plain provide an estimation of the rate of lateral migration. The erosion rates measured at two sites in the Mala Panew River were between 0.24 and 0.36 m/year. Another way of reconstructing the rate of lateral migration is by dating trees growing on different-aged sandy meander bars. These levels are primarily covered with Alnus glutinosa and Alnus incana. The oldest trees growing on each level give information about the minimum age of that level, which allows us to reconstruct the rate of lateral migration. The lateral migration of the channel has also been estimated dating the oldest trees growing on mid-channel islands separated from the lateral banks. The values obtained for 10 sites of the Mala Panew channel oscillate between 0.07 and 1.83m/year. Tree ring analyses also allow us to determine the impact of individual high discharges on the lateral migration rate of the Mała Panew channel. The lateral migration of the channel was most rapid in the years 1953–57 and 1966–68 as well as during the extraordinary flood in 1997. [Copyright &y& Elsevier]

The objective was to determine stem volume models for grey and common alders and, based on the models, stand volume for naturally regenerated grey and common alder stands was summarized. Basic density for grey and common alders and mean annual growth for stands was estimated. Net volume accretion data were collected from 24 stands of grey alder (Alnus incana (L.) Moench) and 31 stands of common alder (Alnus glutinosa (L.) Gaertner) in Sweden. The stands ranged in latitude from 58 to 64° N and from 56 to 62° N for grey and common alder, respectively. The mean age of grey and common alder stands was 41 years and 48 years, respectively, the mean stand density 1726 stems ha−1 and 1078 stems ha−1, and the mean diameter at breast height (over bark) was 20 cm and 21 cm. Stem volume equations were developed for grey and common alders. The adopted model for grey alder was based on diameter at breast height and height. For common alder, crown height was added to diameter and height. Mean standing volume (over bark) for grey and common alder stands was 428 and 374 m3 ha−1. Mean annual growth for grey and common alder stands was 12.0 m3 and 8.4 m3 a−1 ha−1, respectively. Basic density (under bark), for grey and common alder stems was 359 and 427 kg m−3, respectively. The basic density (under bark) for the lowest twigs in the crown and in the lateral part of the crown was 415 and 421 kg m−3 for grey alder and 423 and 423 kg m−3 for common alder. [ABSTRACT FROM AUTHOR]

The carbon cost of nitrogenase activity was investigated to determine symbiotic efficiency of the actinorhizal root nodule symbiosis between the woody perennialAlnus incanaand the soil bacteriumFrankia. Respiration (CO2 production) and nitrogenase activity (H2 production) by intact nodulated root systems were continuously recorded in short-term assays in an open-flow gas exchange system. The assays were conducted in N2:O2, thus under N2-fixing conditions, in all experiments except for one. This avoided the declines in nitrogenase activity and respiration due to N2 deprivation that occur in acetylene reduction assays and during extended Ar:O2 exposures in H2 assays. Two approaches were used: (i) direct estimation of root and nodule respiration by removing nodules, and (ii) decreasing the partial pressure of O2 from 21 to 15% to use the strong relationship between respiration and nitrogenase activity to calculate CO2/H2. The electron allocation of nitrogenase was determined to be 0.6 and used to convert the results into moles of CO2 produced per 2e- transferred by nitrogenase to reduction of N2. The results ranged from 2.6 to 3.4?mol CO2 produced per 2e-. Carbon cost expressed as g?C produced per g?N reduced ranged from 4.5 to 5.8. The result for this actinorhizal tree symbiosis is in the low range of estimates for N2-fixing actinorhizal symbioses and crop legumes. Methodology and comparisons of root nodule physiology among actinorhizal and legume plants are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The establishment and growth of trees can be compromised by soil contamination which can reduce populations of key microbial symbionts. We describe the colonisation of grey alder (Alnus incana) by Frankia from 10 urban soils with varying degrees of organic and inorganic pollution. Principal components analysis (PCA) of soil chemical profiles showed a separation of remediated and unremediated soils. A. incana seedlings were used as trap plants to capture the microsymbiont from soil. After 6 months growth, nodulation was lowest on trees grown with the most contaminated soils. Plant biomass was positively correlated with root nodule biomass and negatively correlated with PAH concentration. DNA was isolated from nodules for the analysis of Frankia genetic diversity. The polymerase chain reaction (PCR) was used to amplify the 16S–23S intergenic spacer (IGS) of Frankia ribosomal DNA. PCR products were subject to restriction digestion yielding 10 restriction fragment length polymorphism (RFLP) types from 72 nodules analysed. Our results demonstrate that each soil supports a distinct nodulating Frankia community. Partial 16S sequencing placed most strains in Frankia clusters 1a and 1b, which are typically Alnus-infecting, but sequences from several nodules obtained from a gasworks soil belonged to cluster 3, normally associated with Elaeagnus. These results show for the first time that polluted soils can be an effective source of Alnus-infective Frankia. Inoculation with site-adapted Frankia under greenhouse conditions could thus be an appropriate strategy to increase the symbiotic capacity of A. incana and to improve its chances of survival and growth when planted on polluted soils. [Copyright &y& Elsevier]

Goodyear Swamp Sanctuary, a wetland adjacent to Otsego Lake, Otsego County. New York, has been dominated by the invasive nonnative plant purple loosestrife (Lythrum salicaria L.) since 1975. In June 1997 a combined total of 100 adult Galerucella calmariensis (L.) and G. pusilla (Duft) were introduced into the Sanctuary in an attempt to control loosestrife. Since then, annual spring and fall monitoring has been conducted on 5/m² quadrats with the intention of evaluating the abundance of Galerucella spp. and their impact on loosestrife over time. Through 2000 Galerucella spp. populations increased, as did damage to loosestrife, though not to the extent of controlling its growth or seed production. During the summers of 2001 and 2002 loosestrife was decimated. Following those periods, ephemeral non-target feeding by Galerucella spp. was documented primarily on red osier (Cornus stolonifera) in 2001 and speckled alder (Alnus rugosa) in 2002 with three other species being grazed to a lesser degree. No non-target species were substantially impacted during these brief periods (<1 wk). Temporal variation in the population distribution suggests that a shortage of appropriate food may have initiated early aestivation. During the summer of 2002 Galerucella spp. were found 9 km off-site, believed to result from a single-season dispersal, suggesting a mobility of a greater extent than previously recorded. [ABSTRACT FROM AUTHOR]

We describe presence, abundance, and distribution of three sympatric nitrogen-fixing shrubs and their symbiotic diazatroph, Frankia, in a sand dune ecosystem differing in successional stage, vegetative cover, edaphic characteristics, and topography. Distribution of actinorhizal Myrica gale L., Alnus incana (L.) Moench subsp. rugosa (Du Roi) Clausen, and Shepherdia canadensis (L.) Nutt. was analyzed among 120 sampling locations representing a gradient of successional stages in a sand dune system along Lake Michigan. In a greenhouse study, seedlings of these species were employed to bioassay the presence and abundance of infective Frankia in soils. Shepherdia-infective Frankia was detected in 80% of the plots, while Alnus- and Myrica-infective Frankia were found in 65% and 64% of the plots, respectively, with no Frankia found in 18% of the plots. Only 14% of the plots supported actinorhizal host-plant species. Infective Frankia were present in soils of young dunes prior to the establishment of any actinorhizal hosts. Shepherdia-infective Frankia were more abundant in soils from drier, earlier successional sites, while Alnus- and Myrica-infective Frankia were more abundant in moister soils of later successional communities. A previous study had revealed that nodular Frankia strains at this site were host specific for Shepherdia and largely so for Myrica and Alnus, which had only a small proportion of shared strains (Huguet et al. 2001). The likelihood of host-plant nodulation by soilborne Frankia was increased by the presence of actinorhizal plants in general, but not by the presence of their respective specific host plants. Submerged soils had no infectious capacity, whereas soils with greater in situ moisture content and soils subject to intermittent saturation tended to have lower infectious capacities overall. Our results suggest that soilborne, infective Frankia genotypes are not only host specific, but are also associated with spatially and chronologically distinct sets of ecological conditions. [ABSTRACT FROM AUTHOR]

Phosphorus (P) and nitrogen (N) effects on nodulation, nitrogenase activity and plant growth were studied in the root‐hair‐infected actinorhizal plant Alnus incana (L.) Moench. A split‐root experiment, as well as a short‐term experiment with entire root systems and a broader range of P concentrations, showed that P effects were specific on nodulation and not a general stimulation via a plant growth effect. These results indicate that nodule initiation and nodule growth have a high P demand. The split‐root assay, comprising seven combinations of two N and two P levels, showed that P could counteract systemic N inhibition of nodulation, but did not counteract N inhibition of nitrogenase activity. [ABSTRACT FROM PUBLISHER]

The dynamics and annual rate of net nitrogen mineralization in a grey alder plantation growing on abandoned agricultural land was assessed in situ using the method of buried polyethylene bags. Nitrogen mineralization was assessed in the upper 0–10 and 10–20 cm soil layers, where 47.5 and 26.3% of the fine roots, respectively, were situated. Net nitrogen mineralization was the highest in May and September, 314 and 306 mg kg−1 N per day, respectively. Annual net nitrogen mineralization and net nitrification in the upper 0–10 cm soil layer were estimated as 84 and 87 kg ha−1 per year, respectively. Annual net nitrogen mineralization in the upper 0–20 cm soil layer was estimated as 141 kg ha−1, which accounted for 62% of the annual nitrogen used by trees and the understorey vegetation. Among various environmental factors related to mineralization, pH played a significant role. [Copyright &y& Elsevier]

Inhibition of nitrogenase (EC 1.18.6.1) activity by O2 has been suggested to be an early response to disturbance in carbon supply to root nodules in the Frankia‐Alnus incana symbiosis. Intact nodulated root systems of plants kept in prolonged darkness of 22 h were used to test responses to O2 and short‐term N2 deprivation (1h in Ar:O2). By using a Frankia lacking uptake hydrogenase it was possible to follow nitrogenase activity over time as H2 evolution in a gas exchange system. Respiration was simultaneously recorded as CO2 evolution. Dark‐treated plants had lower initial nitrogenase activity in N2:O2 (68% of controls), which declined further during a 1‐h period in the assay system in N2:O2 at 21 and 17% O2, but not at 13% O2. When dark‐treated plants were deprived of N2 at 21 and 17% O2 nitrogenase activity declined rapidly to 61 and 74%, respectively, after 20 min, compared with control plants continuously kept in their normal light regime. In contrast, there was no decline in dark‐treated plants at 13% O2, and only a smaller and temporary decline in control plants at 21% O2. When dark‐treated plants were kept at 21% O2 during 45 min prior to N2 deprivation at 17% O2 the decline was abolished. This supports the idea that the decline in nitrogenase activity observed in N2:O2 at 21% O2 and during N2 deprivation was caused by O2, which affected a sensitive nodule fraction. Nodule contents of the amino acids Gln and Cit decreased during N2 deprivation, suggesting decreased assimilation of NH4+. Contents of ATP and ADP in nodules were not affected by short‐term N2 deprivation. ATP/ADP ratios were about 5 indicating a highly aerobic metabolism in the root nodule. We conclude that nitrogenase activity of Alnus plants exposed to prolonged darkness becomes more sensitive to inactivation by O2. It seemed that dark‐treated plants could not adjust their nodule metabolism at higher perceived pO2 and during cessation of NH4+ production. [ABSTRACT FROM AUTHOR]

Positive effects of legumes and actinorhizal plants on N-poor soils have been observed in many studies but few have been done at high latitudes, which was the location of our study. We measured N2 fixation and several indices of soil N at a site near the Arctic Circle in northern Sweden. More than 20 years ago lupine (Lupinus nootkatensis Donn) and gray alder (Alnus incana L. Moench) were planted on this degraded forest site. We measured total soil N, net N mineralization and nitrification with a buried bag technique, and fluxes of NH+4 and NO-3 as collected on ion exchange membranes. We also estimated N2 fixation activity of the N2-fixing plants by the natural abundance of 15N of leaves with Betula pendula Roth. as reference species. Foliar nitrogen in the N2-fixing plants was almost totally derived from N2 fixation. Plots containing N2-fixing species generally had significantly higher soil N and N availability than a control plot without N2-fixing plants. Taken together, all measurements indicated that N2-fixing plants can be used to effectively improve soil fertility at high latitudes in northern Sweden. [ABSTRACT FROM AUTHOR]

Alteration of natural flooding regimes can expose lowlands to waterlogged soil conditions during any month of the year. The seasonality of flooding may have profound effects on the carbon and nitrogen budgets of N-fixing alders (Alnus spp.), and in turn, may impact the C and N economy of extensive alder-dominated, wetland ecosystems, including those dominated by speckled alder (Alnus incana ssp. rugosa). To better understand this process, two-year-old, nodulated seedlings of speckled alder were subjected to late spring (May 10 – July 10), summer (July 10 – September 8), and fall (September 8 – November 8) flooding treatments. Alders were root-flooded outdoors in tanks containing an N-free nutrient solution and compared with unflooded alders at the experimental site. Flooding arrested N fixation, photosynthesis, and growth of alders without recovery in all flooding treatments for the remainder of the growing season. Late spring and summer flooding resulted in complete mortality of alders while all seedlings survived flooding in the fall. Fall flooding increased foliar N resorption by 140% over unflooded seedlings. Eighty-seven percent of the total N fixed and 89% of biomass accumulation for the entire growing season occurred in unflooded alders after July 10. In unflooded alders, nitrogen fixation rates per unit mass declined by 63% for nodules, 28% for leaves, and 48% for whole seedlings during the fall, while total N fixed per plant in the fall was similar to that fixed in the summer. The majority of newly fixed N in unflooded alders was allocated to leaves before September 8 and to roots/nodules combined after September 8. In unflooded plants, the greatest proportion of new biomass was partitioned to leaves before July 10, to stems between July 10 and September 8, and equally to stems and roots/nodules after September 8. Fall-flooded alders did not increase root or nodule biomass. Proportional allocation of plant resources were such that the ratio of N fixed to seedling growth of unflooded alders decreased by 19% during summer before rebounding by 6% in fall. Seasonality of flooding alters seedling survival, growth, and resource allocation, and may be a critical determinant of speckled alder recruitment and occurrence in wetlands. [ABSTRACT FROM AUTHOR]

Summary 1. The root anchorage ability of saplings and vegetative propagules may be decisive for persistence of woody pioneers in the highly disturbed habitat of floodplains. 2. Vertical uprooting resistance was investigated in saplings of three floodplain pioneers of central Europe, Alnus incana , Populus nigra and Salix elaeagnos , at the near-natural River Tagliamento, north-east Italy. Uprooting resistance of planted cuttings of P. nigra and S. elaeagnos was studied at this site and in an experimental garden. 3. Uprooting resistance was lowest in saplings of A. incana , intermediate in P. nigra , and highest in S. elaeagnos . For cuttings, differences in uprooting resistance between species were evident only under floodplain conditions, where resistance was higher in P. nigra than in S. elaeagnos . This difference was related to better growth in P. nigra . 4. The anchorage ability of saplings may be one factor influencing the longitudinal and transverse zonation of species in floodplains, as S. elaeagnos is restricted to highly disturbed sites close to the main channel, whereas A. incana and P. nigra occupy more stabilized habitats. For vegetative propagules, in contrast, regeneration ability may be more important than uprooting resistance. [ABSTRACT FROM AUTHOR]

Root nodulation in actinorhizal plants, like Discaria trinervis and Alnus incana, is subject to feedback regulatory mechanisms that control infection by Frankia and nodule development. Nodule pattern in the root system is controlled by an autoregulatory process that is induced soon after inoculation with Frankia. The final number of nodules, as well as nodule biomass in relation to plant biomass, are both modulated by a second mechanism which seems to be related to the N status of the plant. Mature nodules are, in part, involved in the latter process, since nodule excision from the root system releases the inhibition of infection and nodule development. To study the effect of N2 fixation in this process, nodulated D. trinervis and A. incana plants were incubated under a N2‐free atmosphere. Discaria trinervis is an intercellularly infected species while A. incana is infected intracellularly, via root hairs. Both symbioses responded with an increment in nodule biomass, but with different strategies. Discaria trinervis increased the biomass of existing nodules without significant development of new nodules, while in A. incana nodule biomass increased due to the development of nodules from new infections, but also from the release of arrested infections. It appears that in D. trinervis nodules there is an additional source for inhibition of new infections and nodule development that is independent of N2 fixation and nitrogen assimilation. It is proposed here that the intercellular Frankia filaments commonly present in the D. trinervis nodule apex, is the origin for the autoregulatory signals that sustain the blockage of initiated nodule primordia and prevent new roots from infections. When turning to A. incana plants, it seems likely that this signal is related to the early autoregulation of nodulation in A. incana seedlings and is no longer present in mature nodules. Thus, actinorhizal symbioses belonging to relatively distant phylogenetic groups and displaying different infection pathways, show different feedback regulatory processes that control root nodulation by Frankia. [ABSTRACT FROM PUBLISHER]

Abstract: In many European rivers regulation measures have led to the decline of braided channel systems and associated pioneer ecosystems. Knowledge of their natural functioning is necessary to develop appropriate management and restoration strategies. We examine how woody vegetation within the active zone of the near-natural Tagliamento, NE-Italy, is impacted by environmental variables and patch age. Within 65 plots in 13 river segments the basal area of all woody species was determined, and minimal patch age (8.4 ± 1.6 years) obtained by counting annual rings of the largest trees. Canonical correspondence analyses suggested that the woody vegetation was mainly structured by the longitudinal gradient incorporating air temperature and altitude. Small-scale variables, such as patch age, distance from the nearest channel and elevation above water level, also had significant but smaller effects. All four variables together explained 38% of the variation in species composition. This suggests that additional processes might be important, e.g. specifics of plant dispersal or spatial separation of suitable regeneration sites. The low age of woody vegetation within the active zone of the Tagliamento suggests that hydroengineering measures for restoration of regulated rivers should allow frequent and severe disturbance. In den meisten europäischen Flussystemen haben Regulierungsmaßnahmen zu starken Verlusten an Pionierhabitaten der Auen geführt. Für die Entwicklung angemessener Renaturierungsstrategien ist eine gründliche Kenntnis der entsprechenden Vegetationstypen notwendig. Die vorliegende Studie beschreibt die Pionier-Gehölzvegetation der Sand- und Kiesbänke entlang des Tagliamento in NO-Italien und untersucht den Einfluss von Umweltvariablen und Bestandesalter auf die Zusammensetzung der Gehölzvegetation dieses weitgehend natürlichen Flusses. Auf insgesamt 65 Untersuchungsflächen in 13 Flussegmenten wurde die Basalfläche aller Gehölzarten erhoben. Das minimale Alter der Bestände (8.4 ± 1.6 Jahre) wurde durch Jahrringanalyse bestimmt. Kanonische Korrespondenzanalysen zeigten, dass die Gehölzvegetation überwiegend durch den longitudinalen Gradienten (Lufttemperatur und Meereshöhe) strukturiert wurde. Kleinräumige Variablen, wie Bestandesalter, Entfernung zum nächsten Gerinne und Höhe über dem Wasserspiegel, hatten ebenfalls signifikante, aber geringere Effekte auf die Artenzusammensetzung. Insgesamt konnte 38% der Variation der Artenzusammensetzung erklärt werden. Weitere entscheidende Prozesse sind vermutlich mit Unterschieden in der Regeneration der Gehölzarten verknüpft. Das geringe Alter der Gehölzbestände der aktiven Aue zeigt, dass für die Renaturierung von Pionierhabitaten in Auen solche wasserbaulichen Maßnahmen nötig sind, die eine hohe Störungsintensität erlauben. [Copyright &y& Elsevier]

Reports on population density fluctuations of the moth, Phyllonorycter stringulatella, around the coal fired power plant near Apatity, northwestern Russia, during 1991-2001. Development of larvae in leaves of Alnus incana; Absence of correlation with pollution; Mine distribution among individual leaves.

We investigated the changes in basal respiration (BASAL), microbial biomass as substrate-induced respiration (SIR) and their ratio (qCO2) in the organic layer along a primary successional transect (alder/rowan, birch, birch/spruce, spruce I and spruce II) typical of the land-uplift coast in western Finland. PLFA analysis was used to detect concurrent successional changes in microbial community structure. Along the transect the soil C/N ratio increased (from 16 to 37) and pH (H2O) decreased (from 5.11 to 3.98) substantially. Concurrently, BASAL and SIR remained mainly stable although, during the most favorable temperature and moisture conditions in the field, they tended to increase along the transect from the alder/rowan site to spruce I, and decreased again in spruce II. qCO2 showed no consistent trend along the transect. The soil of the birch site had the highest total PLFA and bacterial PLFA concentrations, while the soils of both spruce sites had the lowest. The ordination configuration of the PLFA data in non-metric multidimensional scaling was clearly related to the C/N ratio and pH, and separated the forest sites relatively well. It was possible, on the basis of the similarities in the variation pattern along the transect, to divide the PLFAs into six groups. [Copyright &y& Elsevier]

In 1999, the area of abandoned agricultural land in Estonia formed 223,000 ha which is partly perspective for afforestation with grey alder, the most rapidly growing indigenous tree species. The production and nutrient (NPK) accumulation of a grey alder short-rotation plantation on former agricultural land was investigated. The production of above-ground biomass was estimated during 5 years after the establishment of the stand. In the fifth year after planting, the biomass of the above-ground part of the plantation was 15.9 t DM ha−1 and above-ground biomass production was 6.4 t DM ha−1 per year. In the fourth year after planting, the biomass of the below-ground part was 2.7 t DM ha−1, which accounted for 18% of total biomass. The biomass of the nodules was estimated at 169±76 kg DM ha−1 and the biomass of fine roots (d<2 mm) at 550±105 kg DM ha−1. Of fine roots 73.8% and all nodules were located in the upper 0–20 cm soil layer. In the fourth year after establishment, the amount of nitrogen introduced in the soil through leaf litter was 59.6 kg ha−1. As the site represented abandoned farm land, the pool of total soil nitrogen was relatively large (2.64 t ha−1 in the 0–20 cm layer). However, concerning phosphorus, the positive effect of grey alders was significant. While in the first year after planting the concentration of lactate soluble phosphorus in the 0–20 cm layer was 22.53 mg kg−1, then in the following years it was more than twice as high, varying from 47.2 to 59.7 mg kg−1. After the fifth year the amount of nitrogen accumulated in above-ground biomass was 147.1 kg ha−1, that of phosphorus 21.3 kg ha−1 and that of potassium 42.6 kg ha−1. Most of accumulated nitrogen and potassium (38.9 and 37.6%, respectively) was located in the leaves and most of phosphorus (61.0%) in the wood. [Copyright &y& Elsevier]

We monitored net and gross N transformations in the organic layer along a primary successional transect (alder/rowan, birch, birch/spruce, spruce I and spruce II) typical for the land-uplift coast in Western Finland. The relationships between N transformations, vegetation succession and organic matter quality (i.e. concentration of dissolved forms of N, C/N ratio, moisture and acidity) were then evaluated. Net N mineralisation rates in the organic layer were estimated in 5-week incubation experiments in situ using intact soil cores, and in the laboratory on sieved, fresh organic layer samples. Microbial biomass N (fumigation–extraction) and gross N mineralisation (15N-isotope dilution method), were determined once in the laboratory. The C/N ratio increased and pH and net N mineralisation decreased in the organic layer along the succession transect. The alder/rowan site was the only site to show net nitrification. Microbial biomass N tended to increase along the transect from the alder/rowan site to spruce I, and decreased again in spruce II. Concurrently, gross N mineralisation showed a tentative increasing trend along the transect, although the differences between the sites were non-significant. The higher net N mineralisation rates in the alder/rowan site compared to the spruce sites were thus due to lower microbial immobilisation rather than to greater gross N mineralisation. Possible methodological reasons for the lack of response of gross N mineralisation rate to decreasing soil organic matter quality are discussed. [Copyright &y& Elsevier]

Discusses the diameter distribution, stem volume and stem quality models for grey alder in eastern Finland. Key issues of interest; Analysis of pertinent topics and relevant issues; Implications on forest conservation.

Tree stems play an important role in forest methane (CH4) and nitrous oxide (N2O) flux dynamics. Our paper aimed to determine the unknown diurnal variability of CH4 and N2O exchange in grey alder tree stems. The gas fluxes in tree stems and adjacent soil were measured using manual static and dynamic chamber systems with gas chromatographic and laser-spectroscopic analysis, respectively. The alder trees were predominant emitters of CH4 and N2O; however, N2O emission from stems was negligible. The soil mainly emitted N2O into the atmosphere and was both a source and sink of CH4, depending on environmental conditions. Neither the tree stems nor the riparian forest soil showed significant differences in their CH4 and N2O fluxes between the daytime and nighttime, independently of the exchange rates. In contrast to several previous studies revealing a diurnal variability of greenhouse gas fluxes from tree stems, our investigation did not show any clear daytime–nighttime differences. On the other hand, we found quite clear seasonal dynamics initiated by changing environmental conditions, such as temperature and soil water conditions and tree physiological activity. Our results imply a transport role of tree stems for soil-produced CH4 and N2O rather than the production of these gases in tree tissues, even though this cannot be excluded. [ABSTRACT FROM AUTHOR]