A reconstruction of flood events using scarred trees in the Tatra Mountains, Poland

In this paper we reconstructed flood events in a small mountain stream (6.6 km long, elevation 1100–1950 m a.s.l.) in the Dolina Waksmundzka Valley in the Tatra Mountains in the Western Carpathians. This reconstruction was based on cross-dated flood scars found in Norway spruce trees growing along stream banks. The scars were most likely formed by woody debris and stones transported during flood events. Reconstructed flood years were then compared with climatic records collected at the nearest meteorological station.Fifty-eight scars were cross-dated indicating 17 years with flood events in the period between 1928 and 2005. The large number of reconstructed flood events proves that the Potok Waksmundzki stream discharge can be highly variable. The high mid-summer rainfall (approximately 300 mm or more per month) peaks in June, July, August and this period coincides with some of the flood scar formation. The high winter and spring precipitation (December–May) does not seem to induce floods. The rate of snow melting seems to be more important. The highest number of scars (33%) was formed in dormant season of 1957/1958. In April and May 1958 there was an unusually large difference between mean monthly temperatures, the highest recorded in the twentieth century. This probably led to an abnormally rapid snow melt. No one single climatic factor can be held responsible for all flood events. Intensive mid-summer rainfall as well as rapid snow melting may induce floods in the Dolina Waksmundzka Valley. Cross-dated scars have enabled past flood events to be detected, which are otherwise invisible from climatic data alone.     

The effects of a record flood on the aquatic vegetation of the Upper Mississippi River System: some preliminary findings

During 1993 the Upper Mississippi River System experienced floods of exceptional magnitude and duration, especially at its more downstream reaches. The flood had widespread effects on the vegetation. Submerged species such as Potamogeton pectinatus significantly decreased in abundance, especially at sites with more severe flooding. However, many species were able to regenerate in 1994 from seeds or storage organs. Emergent species such as Scirpus fluviatilis were similarly affected, but in the upstream reaches were able to regrow in the autumn following the flood and at many sites showed exceptionally high productivity in the following year, probably due to nutrient-rich sediment deposition by the flood. Many tree species were very severely impacted, although Acer saccharinum and Populus deltoides have shown some seedling regeneration on newly deposited sediment beneath stands of mature trees, which would have out-shaded the seedlings if they had not been killed by the flood.     

Patterns of forest succession and impacts of flood in the Upper Mississippi River floodplain ecosystem

The widespread loss of oak-hickory forests and the impacts of flood have been major issues of ecological interest concerning forest succession in the Upper Mississippi River (UMR) floodplain. The data analysis from two comprehensive field surveys indicated that Quercus was one of the dominant genera in the UMR floodplain ecosystem prior to the 1993 flood and constituted 14% of the total number of trees and 28% of the total basal area. During the post-flood recovery period through 2006, Quercus demonstrated slower recovery rates in both the number of trees (4%) and basal area (17%). In the same period, Carya recovered greatly from the 1993 flood in terms of the number of trees (11%) and basal area (2%), compared to its minor status before the flood. Further analyses suggested that different species responded to the 1993 flood with varying tolerance and different succession strategies. In this study, the relation of flood-caused mortality rates and DBH, f_m(d), can be expressed in negative exponential functions for each species. The results of this research also indicate that the growth functions are different for each species and might also be different between pre- and post-flood time periods. These functions indicate different survival strategies and emergent properties in responding to flood impacts. This research enhances our understanding of forest succession patterns in space and time in the UPR floodplain. And such understanding might be used to predict long-term impacts of floods on UMR floodplain forest dynamics in support of management and restoration.     

Response of native Egeria najas Planch. and invasive Hydrilla verticillata (L.f.) Royle to altered hydroecological regime in a subtropical river

Egeria najas Planch. is the dominant native submersed macrophyte of the Upper Paraná River in Brazil, while Hydrilla verticillata (L.f.) Royle has recently invaded this area. From January 2006 to December 2007, comprising two annual flood cycles, we conducted monthly surveys at two river stations and two lakes connected to the river within this stretch of the Paraná River, aiming to understand how the hydrological regime influences the distribution and abundance of these native and invasive Hydrocharitaceae species. Hydrilla did not develop in the lakes, possibly due to the elevated proportion of organic matter in the sediment (∼10% DW). However, the exotic species dominated the river sites apparently suppressing E. najas. In the lakes E. najas reached a maximum biomass of 628 ± 82 g DW m⁻² but did not surpass 333 ± 83 g DW m⁻² in the river, where H. verticillata peaked at 1415 ± 255 g DW m⁻². Macrophyte biomass development was greatest during low-water periods, with transparent water and high temperatures. Floods probably affected submersed macrophytes (especially in 2007, when an extreme flood caused by an El Niño Southern Oscillation (ENSO) event occurred) via sediment movement and plant scouring (uprooting) effects, coupled with reduced water transparency. Macrophyte recovery started soon after the (less intense) 2006 flood but was delayed in 2007. In the river recovery started five months after the major flood, but in the lakes no significant plant regeneration was found even nine months after the disturbance. E. najas and H. verticillata started regeneration practically at the same time but H. verticillata had much higher rates of biomass increase.     

Dating lightning: Dendrochronological and magnetic analyses of lightning scars

Lightning impacts on forests and trees are still understudied from a tree-ring perspective. Lighting causes direct and indirect damages on forests and trees. Trees struck by lightning can show a growth reduction and lightning storms also trigger wildfires in seasonally dry areas such as Mediterranean mountains. Here we combined dendroecological and magnetic analyses to reconstruct and assess the impact of lightning on radial growth and the magnetic properties of wood in Scots pine (Pinus sylvestris) and Black pine (Pinus nigra) in two sites with a high density of lightning impacts located in eastern Spain. We dated several lightning scars, particularly in Scots pine, formed during 1982, when a wildfire was initiated by lightning during a dry summer storm. Growth was reduced during the year when the scar was formed in both pine species, albeit this effect could be masked or amplified by other disturbances (drought, outbreaks). However, despite that short-term growth reduction scarred trees showed higher growth rates than non-scarred trees in the case of Scots pine. The intensity of magnetization did not significantly differ in wood produced before and after the lightning scar was formed. This could be due to multiple lightning hits in the same or nearby stands affecting the magnetization of wood. Wood magnetic properties should be further explored as proxies of lightning impacts in sites where scars are not formed and tree-ring information is limited such as tropical forests. Further cross-disciplinary research is required to assess the impacts of lightning on tree growth and magnetism.     

Leaf nutrient concentration as an indicator of Populus and Tamarix response to flooding

Plants growing in infertile environments are able to produce more biomass per unit of nutrient taken up than plants of fertile habitats, and also to minimize nutrients loss by resorbing them from senescing leaves. The leaf nutrient concentration variability of two co-existing riparian tree genera (Populus and Tamarix) along a flood inundation gradient was examined to infer nutrient limitation and to compare nutrient use strategies in the two genera. To that end, seasonal and spatial variability in leaf nitrogen (N) and phosphorus (P) concentration (i.e., % dry mass of N and P) were analyzed in 720 samples of leaves (2 tree genera × 3 seasons × 12 sites × 10 tree replicates). Both Populus and Tamarix showed strong seasonal variability in leaf N and P concentrations, with values decreasing throughout the growing season. However, while N:P atomic ratio remained seasonally constant in Populus (N:P = 33), Tamarix shifted from N:P = 29 in spring to N:P = 36 and 37 in summer and fall. %N, %P and N:P atomic ratios were also spatially variable, but leaf litter N and P concentration (i.e., nutrient resorption proficiency) and leaf litter N:P generally followed the local flood inundation gradient as shown by linear mixed effects models. In particular, nutrient resorption was usually less proficient (higher terminal nutrient concentrations) at higher flood durations (in gravel bars and natural levees), whereas N:P increased in the drier sites (floodplain terrace). At floodplain level, a P-limitation that is higher than N-limitation seems to characterize the plant nutrient circulation in the riparian ecosystem studied. Tamarix was slightly more proficient in P resorption than Populus. The study shows that leaf nutrient concentration (e.g., N and P) derived from nutrient availability is partly controlled by the flood inundation regime and can be used as an indicator of nutrient limitation in forested floodplains. Subtle differences between tree genera provide an additional, novel explanation for the recent expansion of Tamarix in many arid and semi-arid rivers with altered hydrogeomorphic regimes.     

Longleaf pine (Pinus palustris Mill.) fire scars reveal new details of a frequent fire regime

Question: How frequent and variable were fire disturbances in longleaf pine ecosystems? Has the frequency and seasonality of fire events changed during the past few centuries? Location: Kisatchie National Forest, Western Gulf Coastal Plain, longleaf pine–bluestem ecosystem, in relatively rough topography adjacent to the Red River, Louisiana, USA. Methods: Cross‐sections of 19 remnant pines exhibiting 190 fire scars were collected from a 1.2‐km² area. Tree‐rings and fire scars were precisely dated and analysed for the purpose of characterizing past changes in fire and tree growth. Temporal variability in fire occurrence and seasonality was described for the pre‐ and post‐European settlement periods. Seasonality of historic fires was determined by the scar position within the rings. The relationship between fire and drought was investigated using correlation and superposed epoch analysis. Results: The mean fire return interval for the period 1650‐1905 was 2.2 years (range 0.5 to 12 yr). Significant new findings include: evidence for years of biannual burning, temporal variability in fire seasonality, an increase in fire frequency and percentage of trees scarred circa 1790, and synchronous growth suppression and subsequent release of trees coinciding with land‐use changes near the turn of the 20th century. Drought conditions appeared unrelated to the occurrence of fire events or fire seasonality. Conclusions: Multi‐century fire history records from longleaf pine ecosystems are difficult to obtain due to historic land‐use practices and the species high resistance to scarring; however, our results indicate potential for reconstructing detailed fire histories in this ecosystem. Fire scars quantitatively documented one of the most frequent fire regimes known. Fire regime information, such as the temporal variability in fire intervals, prevalence of late‐growing season fire events and biannual burning, provide a new perspective on the dynamics of longleaf pine fire regimes.     

Dating fire events in Pinus heldreichii forests by analysis of tree ring cores

Bosnian pine (Pinus heldreichii Christ, also known as Pinus leucodermis Antoine) is a relict species found in isolated locations in the mountains of the Balkan Peninsula and Southern Italy. The forests are of high conservational value because they are extremely rich in rare and endemic species of plants and fungi. Yet, the natural history and disturbance regime of P. heldreichii ecosystems is not well understood. Fire traces show that fires played a major role, but there is very limited historical data. Therefore proxy methods to reconstruct past events have to be used. The analysis of tree rings provides such an opportunity. To our knowledge, there have been no attempts to use tree ring cores from P. heldreichii trees to date fire events. Our aim was therefore to test if tree ring cores collected with an increment borer could successfully be used to date fires and verify other tree ring indicators caused by the fire events. We tested an approach that was based on extracting multiple cores from fire-scarred trees and nearby standing trees without injuries. A total of 136 cores from 99 trees were collected from which we dated all 34 cores with fire scars. We found the exact fire years for 29 of the samples, and the remaining 5 samples were approximately dated. Up to 83% of all sampled trees had additional growth reactions, mostly suppressions lasting 5–10 years after the fire years.     

Tree growth in the aftermath of A flood: A tree-ring based reconstruction of the impacts of the 1996-Biescas catastrophe

Catastrophic floods and large debris flows are natural hazards common in mountain areas. They cause injuries and impact the radial growth of trees growing in the affected basins. Reconstructing how these catastrophic events impact trees by using dendrochronology improves our understanding of natural hazards. The 1996-Biescas (Central Spanish Pyrenees) flood was a catastrophic event causing the loss of many lives in a campsite located on an active alluvial fan. We investigated using tree rings how this catastrophic flood impacted planted trees (poplars, cedars) located in the campsite. Conspicuous scars in the stem were more abundant in cedar trees (75 %) than in poplar (36 %) trees. Scarred cedar trees formed traumatic resin ducts after the flood. In cedar tree perimeter influenced the size of the wound formed after the flood, but this was not observed in poplar. On average, 63 % of trees showing scars formed them in the side of the stem (N-NW) where the impact of the flood was assumed to be strongest. We also detected sharp reductions of tree-ring width after the flood (–56 % and –16 % in poplar and cedar, respectively). However, this was not found when using basal area increment, which suggests there was an age effect on the post-flood growth changes. The two species mean chronologies were also more coupled after the flood in agreement with an increased responsiveness to climate, particularly a higher dependence of growth on June precipitation. To adequately reconstruct responses to flood and to assess the actual vulnerability of forests to debris flow impacts tree features such as species, age, growth rate and responsiveness to climate must be considered.     

Riparian vegetation’s responses to the new hydrological regimes from the Three Gorges Project: Clues to revegetation in reservoir water-level-fluctuation zone

The new hydrological regime brought about by the Three Gorges Project is the absolute opposite of the natural flood rhythms of the Yangtze River. Flooding timing, duration, frequency, rate of change and magnitude in the Three Gorges Reservoir (TGR), as important factors in affecting riparian vegetation, are completely different from the natural Yangtze Rivers’. The riparian vegetation plays important roles in stabilizing riverbanks, maintaining local biodiversity and improving water quality. Pre-dam and postdam riparian vegetations along the Yangtze River basin in the Three Gorges Reservoir Area (TGRA) were investigated in 2001 and 2009, respectively. The investigation of pre-dam riparian vegetation in 2001 showed that about 405 vascular plant species belonging to 240 genera of 83 families were distributed in the natural water-level-fluctuation zone (WLFZ) of the Yangtze River. However, only 231 vascular plant species belonging to 169 genera of 61 families were found in the WFLZ of the TGR in 2009. The changes in riparian vegetation resulted in the formation of a bald WLFZ with a 30 m magnitude in the TGRA. Although certain perennial species could be repeatedly detected in both field surveys, these are unsuitable for revegetation in the WFLZ of the TGR. This unsuitability is due to their survival via seed germination, and death in subsequent winter flooding. We propose a list of local plants that may be used to recover and re-establish riparian vegetation in the WFLZ of the TGR. We suggest that numerous physiological experiments be performed to assess how the adaptable mechanisms of riparian plants from the TGRA will respond to winter flooding. Endangered wetland shrub species such as Rhamnus tzekweiensis and Buxus ichangensis, which are confined to the riverbanks of the Yangtze River in the TGRA, should be conserved.     

Assessing spatial variation in browsing history by means of fraying scars

Aim We used fraying scars to understand spatial variation in browsing history. Information on browsing history is an essential background in studies on the long‐term effect of deer browsing on the flora and fauna and of its variation in space. Location We focused on two small neighbouring islands of Haida Gwaii (British Columbia, Canada), Reef Island and South‐Skedans Island, colonized by introduced black‐tailed deer (Odocoileus hemionus sitkensis). Methods We searched for sites where trees with fraying scars were clustered. We studied the trees that deer selected (species, size) and the characteristics of scars (number, position, size). Using a cross‐dating procedure, we dated fraying scars with dendrochronology, obtaining an accurate estimate of the year the scar was formed. Results On Reef Island, Thuja plicata was the tree species chosen for fraying. On South‐Skedans Island, where Thuja plicata is missing, deer chose Salix sp. and Alnus rubra. Deer chose only trees with a circumference of less than 50 cm. About two to three fraying scars were recorded per tree. All of them extended between 30–40 and 70–80 cm from the ground and were between 5 and 6 cm in width. On Reef Island, 95% of the scars were formed during the last 50 years. On South‐Skedans Island, 95% were formed over the last 10 years. Age distribution of scars showed a constant increase of the number of scars over time. It indicated that deer had colonized Reef Island 53 years prior to this study but were absent or rare on South‐Skedans Island until 13 years prior to this study. Main conclusions These results indicate different colonization dates and thus different length of browsing histories for the islands studied and provide the historical background necessary to analyse the involvement of deer in the current differences in the flora and fauna observed between islands.     

Measuring the impact of flooding on Amazonian trees: photosynthetic response models for ten species flooded by hydroelectric dams

Increasing areas of Amazonian forest are coming under flood stress due to dam construction and greater variability in river flood levels due to climate change. The physiological responses of Amazonian trees subjected to flooding are important to understand the consequences of these changes. Irradiance response curves for photosynthesis obtained from ten tropical tree species growing in flooded areas were used to fit three empirical models. The study was done in floodplains along the Uatumã River, both upstream and downstream of the Balbina Hydroelectric Dam in Brazil’s state of Amazonas (01°55′S; 59°28′W). Ten species were studied. Models compared were: non-rectangular hyperbola, rectangular hyperbola, and exponential. All models were quantitatively adequate for fitting the response of measured data on photosynthesis to irradiance for all ten species in the non-flooding and flooding periods. Considerable variation was found among the model estimates of maximum photosynthesis (P _nmax), dark respiration (R _d) and apparent quantum yield of photosynthesis (α). For photosynthesis, the two hyperbolas overestimated P _nmax while EXP presented more realistic values. For estimating R _d, RH presented the most realistic values. To avoid unrealistic value estimates of R _d, we recommend adding measured R _d values to the regressions. The results suggest that the EXP model presented the most realistic P _nmax and α values, and, in spite of less accuracy in fitting photosynthetic irradiance curves than the RH model, it can be recommended for accessing the information used in photosynthetic irradiance curves for the leaves of tropical trees growing in Amazonian floodplains or in areas that are artificially flooded by dams.     

Persistence of fishers in riparian forests in North Dakota,USA following a severe flood event

Historically, the distribution of fishers (Martes pennanti) in North America included portions of eastern North Dakota, USA; however, the population was reported to have become extirpated by the early 1900s. Verified reports, road-killed and incidentally trapped individuals, indicate that fishers have been re-establishing populations in riparian forests (the only areas with substantive forest cover in the region) over the last 10 years. During the summers of 2008 (16 Jun–1 Aug) and 2009 (1 Jun–18 Aug), we conducted presence–absence sampling using remote cameras and enclosed track-plates to determine the distribution of fishers along 237 km of the Red River of the North in North Dakota. Between sampling events, the Red River experienced an extreme flood with peak flooding above major flood stage, which inundated all riparian forests within the study area from approximately 23 Mar–22 May. Because of the severity of the flood, we anticipated that fishers could have perished or been displaced from much of the study area, resulting in lower detection rates in 2009 than 2008. However, fishers were detected throughout the study area during both years and, unexpectedly, detection rates were higher in 2009 than 2008 (28 out of 35 sites [80%] and 25 out of 57 sites [44%], respectively). Our study demonstrates that fishers existing in what traditionally would have been considered marginal habitat for the species were able to persist following a severe, multi-month flood that inundated >95% of the forest habitat.     

Isotopic and anatomical signals for interpreting fire-related responses in Pinus halepensis

Key message

Our study aims to define isotopic and anatomical responses to fires of P. halepensis . Main results: decrease in tree growth and relative conductivity and increase in water use efficiency.

Abstract

We investigated the ecophysiological responses of a Pinus halepensis Mill. stand surviving two wildfires in southern France. Basal area, isotope composition and anatomical traits were analysed before and after fires, using tree rings to assess the ecological responses of trees to heat-related damage. The years were determined based on the presence of fire scars. Stable isotopes (δ¹³C and δ¹⁸O) were measured in tree rings before and after the “fire years”. Anatomical observations allowed qualitative analysis of the scar region and quantification of tracheid size in tree rings before and after the fire years. Relative and percentage conductivity of earlywood and latewood far from the woundwood were estimated. Results showed a decrease in tree growth after the fire events accompanied by an increase in ¹³C-derived water use efficiency (WUE_i) and a decrease in relative conductivity. The positive relationship between δ¹³C and δ¹⁸O suggested that both isotopic variations are mostly driven by changes in stomatal conductance following fire events. P. halepensis proved to be a strong isohydric species, able to survive frequent fires with temporary ecophysiological modifications and anatomical adaptations. Our findings afford new insights into post-fire survival strategies of this species in an environment where fires are predicted to increase in frequency during the twenty-first century.     

Autofluorescence imaging for recurrence detection in skin cancer postoperative scars

This clinical study is a first attempt to use autofluorescence for recurrence diagnosis of skin cancer in postoperative scars. The proposed diagnostic parameter is based on a reduction in scar autofluorescence, evaluated in the green spectral channel. The validity of the method has been tested on 110 postoperative scars from 56 patients suspected of non‐melanoma skin cancer, with eight patients (13 scars) available for the repeated examination. The recurrence diagnosis within a scar has been made after two subsequent autofluorescence check‐ups, representing the temporal difference between the scar autofluorescence amplitudes as a vector. The recognition of recurrence has been discussed to represent the significant deviations from the value of vector angle θ. This new autofluorescence‐based method can be easily integrated into the postoperative monitoring of surgical scars and can help diagnose the recurrence of skin cancer from the early stage of scar development.     

Matrix metalloproteinase‐2 and ‐9 activities in human keloids,hypertrophic and atrophic scars: a pilot study

Proteolytic degradation of extracellular matrix is one of the principal features of cutaneous wound healing but little is known about the activities of gelatinases; matrix metalloproteinase‐2 (MMP‐2) and matrix metalloproteinase‐9 (MMP‐9) on abnormal scar formation. The aim of this study is to determine collagen levels and the gelatinase activities in tissue from hypertrophic scars, atrophic scars, keloids and donor skin in 36 patients and 14 donors. Gelatinase levels (proenzyme + active enzyme) were determined by ELISA and their activities by gelatin zymography. MMP‐9 activity was undetectable in gelatin zymography analysis. Pro‐MMP‐2 levels (median) were highest in normal skin group 53.58 (36.40–75.11) OD µg^?1 protein, while active MMP‐2 levels were highest in keloid group 52.53 (42.47–61.51) OD µg^?1 protein. The active/pro ratio was the highest in keloid group 0.97 followed by hypertrophic scar, normal skin and atrophic scar groups 0.69 > 0.54 > 0.48, respectively. According to results of our study, the two‐phase theory of the duration of hypertrophic scar and keloid formation can be supported by the data of tissue collagen and gelatinase analysis. This study is the first to relate scar formation relationship in regard to gelatinase activation ratio in a keloid, hypertrophic and atrophic scar patient group which is chosen appropriate in age and sex. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of the Changjiang River Flood on Synechococcus Ecology in the Surface Waters of the East China Sea

Synechococcus spp. have been suggested as the primary component of picophytoplankton in the East China Sea (ECS). However, the influences of sudden environmental changes on Synechococcus assemblage composition have not yet been investigated. In the summer of 2010, a disastrous flood occurred in the Changjiang River basin. To improve our understanding of how this flood affected the Synechococcus ecology on the ECS surface, their assemblages and distributions have been described using two-laser flow cytometry and phylogenetic analysis of the phycocyanin operon. During the nonflooding summer of 2009, phycoerythrin-rich (PE-rich) Synechococcus thrived near the outer boundary of the Changjiang River diluted water (CDW) coverage, while phycocyanin-rich (PC-rich) Synechococcus predominated inside the turbid CDW with a transparency of <80 %. During the 2010 summer, flooding expanded the CDW coverage area to over half of the ECS. PE-rich cells showed a homogeneous distribution and a decline in abundance, while the spatial pattern of the PC-rich Synechococcus resembled the pattern from 2009. Based on the phycocyanin operon phylogeny, the Synechococcus in the ECS were categorized into five groups, ECS-1 to ECS-4 and ECS-PE, comprising a total of 19 operational taxonomic units. In the summer of 2009, ECS-2 dominated in the coast, and the ECS-3 and ECS-PE clades prevailed in the offshore waters. However, during the summer of 2010, ECS-4 and ECS-PE became the dominant strains. The injection of abundant anthropogenic pollutants and the enhancement of transparency within the CDW expansion area appear to be the factors needed to transiently alter the ecology of Synechococcus after flooding.     

Tree-ring analysis of traditional native bark-stripping at Ship Island, Southeast Alaska, USA

Tree-ring analyses of 23 bark-stripped trees, mostly Thuja plicata (western red cedar) but also Chamaecyparis nootkatensis (yellow cedar) and Picea sitchensis (Sitka spruce), help describe traditional Native tree-bark exploitation at a site north of Ketchikan in southeast Alaska, USA. Tree-ring samples exposed 36 cultural scars dating from between a.d. 1718 and 1912, showing that Natives landed on this hazardous stretch of Clarence Strait to take tree bark in 29 (about 15%) of the 195 years spanned by the sample. One-third of these culturally modified trees had multiple scars indicating repeated use of individual trees. The most intensive forest use occurred between 1852 and 1895, while the lack of bark scars after 1912 marks a decline in traditional Native craft. A burst of bark-stripping between 1779 and 1787 may be associated with the legendary last battle between the Stikine Tlingit of Alaska and the Tsimshian of British Columbia. The sample is compared with dated samples from British Columbia (Canada) and Washington State, USA.     

浑太流域洪涝灾害及其治理方略

抚顺、鞍山、辽阳等在内的中部城市群提供年用水量７．０×１０９ｍ３的７０％［５］,对辽宁经济发展与生态环境建设具有至关重要的作用．本文试图剖析浑河、太子河洪涝灾害问题,找出其成因与特点,从生态与工程结合角度提出治理方略,为防洪减灾,振兴经济服务．２　洪涝灾害成因分析２．１　洪涝灾害的一般分析　　洪涝灾害是天降暴雨和下垫面综合作用的结果．它通常依赖气象、水文地理和生态环境三方面因素．气象因素主要指暴雨,包括雨量、雨强和降雨落区．暴雨主要受大气环境制约,目前人类难以左右．然而,通过人工控制增减局地降雨…     

Variation of cytosine methylation in response to water availability in two contrasting growth types of an amphibious plant Alternanthera philoxeroides

We used methylation-sensitive amplified polymorphisms (MSAP) to examine the alterations of cytosine methylation in two contrasting growth types of an amphibious plant Alternanthera philoxeroides in response to change of water availability. Using 34 pairs of selective primer combinations, we amplified 1026 and 1128 clear and reproducible bands in root and leaf of A. philoxeroides, respectively. When the aquatic types of plants were transplanted into drought culture, we found a decrease in the overall DNA methylation. When the terrestrial types of plants were transferred into flood culture, we detected a higher frequency of methylation than demethylation events. Alterations of DNA methylation were more evident in root than in leaf in response to change of water availability. When the confounding effects of variable environmental factors were removed, differences of cytosine methylation profiles were observed between two growth types of plants under common growth conditions.