Weeks Of Flooding Research Articles

Effects of vegetation on methylmercury concentrations and loads in a mercury contaminated floodplain

The Yolo Bypass (YB) is a large flood conveyance system designed to protect the city of Sacramento, California, USA from flooding when the Sacramento River approaches flood stage. The Sacramento River watershed and YB are a source of methylmercury (MeHg) to downstream habitat as a result of historic mercury (Hg) and gold mining practices. In the dry season, the YB is extensively farmed and grazed. However, depending on the water year, the floodplain may remain inundated for months. Our experiments focused on the role of pasture land and decomposing vegetation as a source of MeHg during extensive periods of floodplain flooding. Decomposing vegetation, rather than sediment, was identified as the principal source of filter passing MeHg (fMeHg) within the floodplain. The decomposing vegetation provided a substrate for microbial methylation of inorganic Hg contained within the plants. In replicated flooded mesocosm experiments, MeHg concentrations increased from 2.78 to 31.0 ng g−1 dw and 3.41 to 56.8 ng g−1 dw in decomposing vegetation. In field collections, the concentrations of MeHg in vegetation increased from preflood levels of 2.78 to 45.4 ng g−1 dw after 17 weeks of flooding. The importance of vegetation was shown in laboratory experiments where there was a positive correlation between the amount of fMeHg in water and the amount of vegetation added. These results also provide Hg concentration data for an important functional type of vegetation, grasses, and fill a data gap that contributed to uncertainties with regards to the role of vegetation in Hg cycling.

Link between paddy soil mineral nitrogen release and iron and manganese reduction examined in a rice pot growth experiment

Paddy soil indigenous N supply is often poorly related to N status and our aim was to assess its linkage to reduction of Fe3+ and Mn4+, primary terminal electron acceptors in submerged soils. Transplanted rice was grown in the greenhouse in four Bangladeshi paddy soils with distinct SOC to Feox ratio (1.6 to 4.9) for 72 days firstly under continuous and then intermittent flooding. Solution buildup rates of Fe2+ and Mn2+ in the first 2–3 weeks of flooding correlated negatively with soil organic carbon (SOC) to NH4-oxalate extractable Fe (Feox) and Mn (Mnox) ratios (p < 0.01). Mössbauer analysis detected ferrihydrite and goethite in all soils and with Mn3O4 these are the likely source minerals. An electron (e−) balance calculated from soil C-emission rates suggested reductive Fe and Mn dissolution to relevant e−-accepting processes, probably responsible for no >50% of e− capture, though. Reduction of abundantly present octahedral Fe3+ in chlorites and vermiculite and their interstratified forms in these floodplain silty Inceptisols is hypothesized to also support microbial activity. Notwithstanding, a close temporal synergy existed between solution Fe and soil mineral N and their build-up rates were correlated (r: 0.77 to 0.90; p < 0.01) and with that of dissolved OC (DOC) (r: 0.84 to 0.96; p < 0.01), C emission rate (r: 0.99; p < 0.01) and SOC:Feox (r: −0.71; p < 0.01). These correlations suggest Fe3+ reduction to be a relevant intermediary step in soil N mineralization, possibly through release of associated DOC, N or both. After switching to intermittent flooding dissolution of Fe, Mn and DOC were decoupled from mineral N release but since Eh remained in the Fe3+-reduction range in three out of four soils, possibly clay-Fe3+ alternated with O2 as e−-acceptor. Most importantly, in all soils N release slowed or halted after only 2 weeks of flooding but recommenced with intermittent flooding. As a next step, field experiments could verify if indigenous soil N supply also benefits from non-continuous irrigation management. Lastly, experimental proof is pending for release of clay-bound N and interlayer NH4+ following reduction of octahedral Fe3+ with consequent increased negative charge or structural destabilization, possibly an important process in floodplain paddy soils in Bangladesh.

Effects of flooding on phosphorus and iron mobilization in highly weathered soils under different land-use types: Short-term effects and mechanisms

The strong affinity of phosphorus (P) to iron (Fe) oxides and hydroxides in highly weathered tropical soils limits P availability and therefore plant productivity in tropics. In flooded soils, however, P fixed by Fe oxides and hydroxides can be released into more available forms because of Fe3+ reduction to Fe2+. These P dynamics in flooded soils are well documented for rice paddies. Such effects are much less studied in other land-use types influenced by seasonal flooding, especially in the tropics during heavy monsoon rains. The aim of this study was to investigate the P mobilization during flooding leading to anaerobic conditions in topsoil and subsoil depending on land-use type. Samples were collected in highly weathered Acrisols from four replicate sites under natural rainforest, jungle rubber, rubber and oil palm plantations in Sumatra, Indonesia. Topsoil and subsoil were taken to ensure a wide range of soil organic matter (SOM) and P contents. Soils were incubated under anaerobic, flooded conditions at 30±1°C for 60days. Our results confirmed the hypothesis that soil flooding mobilizes P and increases P availability. Two distinct and opposite periods were observed during the flooding. During the first three weeks of flooding, the dissolved P (DP) concentration peaked, simultaneously with the peak of dissolved Fe2+ (DFe2+) and dissolved organic carbon (DOC). After three weeks, P availability in soils decreased, although Fe-P (PNaOH) and available P (PNaHCO3) did not reach the initial, pre-flooding levels. The impacts of flooding on P and Fe forms was strong in the topsoil, where P dissolution and availability were generally higher under forest and, to a lesser extent, under jungle rubber. A positive correlation between DOC and DFe2+ (R2=0.42) in topsoil indicates that the intensity of microbially-mediated Fe3+ reduction is limited by the amount of available carbon (C) as an energy source for microorganisms and as electron donor. Microbial mineralization of organic P from SOM also increases P availability, and this process requires available C. This interpretation was supported by the strong correlation (R2=0.58) between available P and DOC, as well as between DP and DOC (R2=0.56) in topsoil. The increasing pH in topsoil and subsoil after flooding of all land-use types may also influence the P release over time. In summary, the increase of available P and DP during flooding is due to three main mechanisms: (1) P release via the microbially-mediated reductive dissolution of Fe3+ oxides; (2) P release during SOM mineralization and (3) solubility of Fe phosphate due to increasing pH. These mechanisms are relevant not only in riparian areas, where flooding occurs, but also in soils waterlogged after regular heavy rainfalls during the wet season. Therefore, we speculate that the P turnover is faster in compacted soils under plantations because of regular changes of oxic and anoxic conditions. Consequently, more P is pumped by the vegetation and then removed from plantations due to yield export.

Simulated storm surge effects on freshwater coastal wetland soil porewater salinity and extractable ammonium levels: Implications for marsh recovery after storm surge

Coastal wetland systems experience both short-term changes in salinity, such as those caused by wind-driven tides and storm surge, and long-term shifts caused by sea level rise. Salinity increases associated with storm surge are known to have significant effects on soil porewater chemistry, but there is little research on the effect of flooding length on salt penetration depth into coastal marsh soils. A simulated storm surge was imposed on intact soil columns collected from a non-vegetated mudflat and a vegetated marsh site in the Wax Lake Delta, LA. Triplicate intact cores were continuously exposed to a 35 salinity water column (practical salinity scale) for 1, 2, and 4 weeks and destructively sampled in order to measure porewater salinity and extractable NH4N at two cm depth intervals. Salinity was significantly higher in the top 8 cm for both the marsh and mudflat cores after one week of flooding. After four weeks of flooding, salinity was significantly higher in marsh and mudflat cores compared to the control (no salinity) cores throughout the profile for both sites. Extractable ammonium levels increased significantly in the marsh cores throughout the experiment, but there was only a marginally (p < 0.1) significant increase seen in the mudflat cores. Results indicate that porewater salinity levels can become significantly elevated within a coastal marsh soil in just one week. This vertical intrusion of salt can potentially negatively impact macrophytes and associated microbial communities for significantly longer term post-storm surge.

Survivorship of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae) in a Hypoxic Environment

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is a structural pest of major economic importance in the city of New Orleans, Louisiana. Hurricane Katrina made landfall along the United States Gulf coast on August 29, 2005, inundating approximately 80% of the city. Though termite colonies survived prolonged inundation, the survival mechanisms of colonies have yet to be fully understood. One hypothesis is that C. formosanus colonies survived within pockets of trapped air within their nesting system during times of flooding. This hypothesis was tested by measuring mortality of groups of 20, 40, and 60 termites in airtight environments maintained at three different temperatures. Groups of 20 termites maintained at 10, 21, and 32°C reached 100% mortality at 89.5, 52.0, and 3.5 days, respectively. Groups of 40 termites maintained at 10, 21, and 32°C reached 100% mortality at 89.5, 51.0, and 3.5 days, respectively. Groups of 60 termites maintained at 10, 21, and 32°C yielded 100% mortality at 57.5, 22.5, and 1.0 day, respectively. Field colonies of C. formosanus established before Hurricane Katrina survived up to three weeks of flooding, and our findings suggest that is possible for inundated colonies to survive this prolonged flooding by remaining within air pockets located in their nesting system until flood waters recede.

FLOOD MANAGEMENT IN BOSNIA AND HERZEGOVINA: ROLE OF REMOTE SENSING AND GIS

The worst flooding that ever hit Bosnia was in May 2014. The official estimates indicate that over 1.5 million people were affected in Bosnia and Serbia after a week of flooding. The assessments of the damage in Bosnia go up to €2billion of euro. The loss in floods is estimated 5 to 10% of GDP (as per WorldBank estimate). The effective floodplain management is a combination of the corrective and preventative measures for reducing flood damage. These measures require integrating data from a variety of sources, including zoning, subdivision, or building requirements, and the special-purpose floodplain ordinances.There are varieties of tools to generate a flood forecasting model to identify the potentially affected zones, so as to prioritize for remediation or the damage assessment. Furthermore, it is possible to analyze the time-related data and to explore trends and phenomena, to conduct the historical analysis and ―what–if‖ scenarios, and to track and monitor events such as excessive rainfall, track water levels, etc. Bosnia is just starting to develop these tools and methods and this could be the way to improve capability to tackle such natural disasters. This paper describes some applications of Remote Sensing (RS) and Geographical Information Systems (GIS) in identifying flood hazard zones and flood shelters and are therefore important tools for planners and decision makers. The purpose is to describe a simple and efficient methodology to accurately delineate flood inundated areas, flood-hazard areas, and suitable areas for flood shelter to minimize flood impacts.

Mitigation of Iron Toxicity and Iron, Zinc, and Manganese Nutrition of Wetland Rice Cultivars (Oryza sativa L.) Grown in Iron‐Toxic Soil

AbstractWetland rice in many humid tropical regions of Asia, Africa, and South America are affected by iron toxicity, which mainly occur due to increase in Fe(II) concentration in soil solution resulting from drop of redox potential arising from anaerobic situations in submerged rice fields. The high quantity of ferrous ions in the soil solution upsets the mineral element balance in rice plants and affects its growth. A field experiment was carried out in acidic laterite soil (pH 5.1) having 400 mg kg−1 diethylene triamine pentaacetic acid extractable Fe for developing strategies to combat Fe toxicity and to study Fe, Zn, and Mn nutrition in rice. The treatments included four cultivars and six soil management options. Soil pH increased upon submergence and stabilized at 6.2 in compost treated plots and 6.8 in lime treated plots after eight weeks of flooding. Application of lime resulted significantly higher yields in all the four cultivars over control. Among the cultivars lowest Fe concentration both in grain and straw was recorded in tolerant as compared to susceptible cultivars. The ratio of Fe/Mn in rice plants was highest under control and reduced with Fe toxicity management treatments. It was further observed that Fe/Mn ratio of tolerant cultivars was lower as compared to susceptible cultivars irrespective of amendments. Similar relations were also recorded for Fe/Zn ratio under different Fe toxicity management interventions. Thus, the application of lime and limiting plant nutrients, such as K, Mn, and Zn along with tolerant cultivars could be important components of Fe toxicity management in Fe toxic acid lateritic soils.

Rice straw incorporated just before soil flooding increases acetic acid formation and decreases available nitrogen

Incorporation of rice straw into the soil just before flooding for water-seeded rice can immobilize mineral nitrogen (N) and lead to the production of acetic acid harmful to the rice seedlings, which negatively affects grain yield. This study aimed to evaluate the formation of organic acids and variation in pH and to quantify the mineral N concentration in the soil as a function of different times of incorporation of rice straw or of ashes from burning the straw before flooding. The experiment was carried out in a greenhouse using an Inceptisol (Typic Haplaquept) soil. The treatments were as follows: control (no straw or ash); incorporation of ashes from previous straw burning; rice straw incorporated to drained soil 60 days before flooding; straw incorporated 30 days before flooding; straw incorporated 15 days before flooding and straw incorporated on the day of flooding. Experimental units were plastic buckets with 6.0 kg of soil. The buckets remained flooded throughout the trial period without rice plants. Soil samples were collected every seven days, beginning one day before flooding until the 13th week of flooding for determination of mineral N- ammonium (NH4+) and nitrate (NO3-). Soil solution pH and concentration of organic acids (acetic, propionic and butyric) were determined. All NO3- there was before flooding was lost in approximately two weeks of flooding, in all treatments. There was sigmoidal behavior for NH4+ formation in all treatments, i.e., ammonium ion concentration began to rise shortly after soil flooding, slightly decreased and then went up again. On the 91st day of flooding, the NH4+ concentrations in soil was 56 mg kg-1 in the control treatment, 72 mg kg-1 for the 60-day treatment, 73 mg kg-1 for the 30-day treatment and 53 mg kg-1 for the ash incorporation treatment. These ammonium concentrations correspond to 84, 108, 110 and 80 kg ha-1 of N-NH4+, respectively. When the straw was incorporated on the day of flooding or 15 days before, the concentration of N-NH4+ in the soil was 28 and 54 mg kg-1, equivalent to an accumulation of 42 and 81 kg ha-1 of N-NH4+, respectively. There was formation of acetic acid in which toxic concentrations were reached (7.2 mmol L-1) on the 15th day of flooding only for the treatment with straw incorporated on the day of flooding. The pH of the soil solution of all the treatments increased after flooding and this increase was faster in the treatments with incorporation of straw, followed by the ash treatment and then the control. After 60 days of flooding, however, the pH values were around 6.5 for all treatments, except for the control, which reached a pH of 6.3. Rice straw should be incorporated into the soil at least 30 days before flooding; otherwise, it may immobilize part of the mineral N and produce acetic acid in concentrations toxic to rice seedlings.

Effect of flooding on the survival of Leptosphaeria spp. in canola stubble

This study used a versatile temperature‐control device to assess the effect of temperature (12–40°C) and duration (2–12 weeks) of flooding on the survival of Leptosphaeria spp. in canola (Brassica napus) stubble. Canola basal stems with blackleg symptoms were submerged in water in small glass jars containing 20 cm3 soil on a thermogradient plate capable of simultaneously maintaining up to 96 independent temperature regimes. Flooded stems were sampled at 2‐week intervals, surface‐sterilized, and incubated on V8‐juice agar for 10 days to recover the pathogen. Flooding for 2 weeks substantially reduced pathogen recovery relative to non‐flooded controls and the pathogen was not recovered after 6 weeks of flooding, irrespective of temperature. The pathogen was eliminated slightly more rapidly at flooding temperatures &gt;20°C than at 12–16°C. There was no difference between Leptosphaeria maculans and L. biglobosa in their ability to survive flooding. Stem tissues degraded most rapidly during the first 2 weeks of flooding, corresponding to a quick decline in pathogen survival during the same period. These results indicate that a paddy rice crop following winter rapeseed may minimize the impact of blackleg by eradicating the inoculum of Leptosphaeria spp. in stubble.

Effects of flooding on photosynthesis and root respiration in saltcedar (Tamarix ramosissima), an invasive riparian shrub

The introduced shrub Tamarix ramosissima invades riparian zones, but loses competitiveness under flooding. Metabolic effects of flooding could be important for T. ramosissima, but have not been previously investigated. Photosynthesis rates, stomatal conductance, internal (intercellular) CO2, transpiration, and root alcohol dehydrogenase (ADH) activity were compared in T. ramosissima across soil types and under drained and flooded conditions in a greenhouse. Photosynthesis at 1500μmolquantam−2s−1 (A1500) in flooded plants ranged from 2.3 to 6.2μmolCO2m−2s−1 during the first week, but A1500 increased to 6.4–12.7μmolCO2m−2s−1 by the third week of flooding. Stomatal conductance (gs) at 1500μmolquantam−2s−1 also decreased initially during flooding, where gs was 0.018 to 0.099mol H2O m−2 s−1 during the first week, but gs increased to 0.113–0.248molH2Om−2s−1 by the third week of flooding. However, photosynthesis in flooded plants was reduced by non-stomatal limitations, and subsequent increases indicate metabolic acclimation to flooding. Root ADH activities were higher in flooded plants compared to drained plants, indicating oxygen stress. Lower photosynthesis and greater oxygen stress could account for the susceptibility of T. ramosissima at the onset of flooding. Soil type had no effect on photosynthesis or on root ADH activity. In the field, stomatal conductance, leaf water potential, transpiration, and leaf δ13C were compared between T. ramosissima and other flooded species. T. ramosissima had lower stomatal conductance and water potential compared to Populus deltoides and Phragmites australis. Differences in physiological responses for T. ramosissima could become important for ecological concerns.

Ecophysiological and morphological adaption to soil flooding of two poplar clones differing in flood-tolerance

Responses to soil flooding of two poplar clones differing in flood-tolerance were studied to elucidate ecophysiological and morphological adaptation to hypoxia. Results showed that Populus deltoides cv. Lux ex. I-69/55 (Lux) was flood-tolerant, whereas P. simonii was flood-susceptible, based on structural and functional differences. They differed in morphological, ecophysiological, and anatomical characteristics when subjected to flooding. The difference between cv. Lux and P. simonii became particular obvious with increased length of the flooding period (8–22 days), but responses to flooding differed already during the first week of flooding. Ecophysiologically, in the beginning of flooding cv. Lux kept a high level of photosynthesis, showed a high free water content and water use efficiency at reduced leaf conductances and leaf water potentials. Chlorophyll content of cv. Lux was reduced so that sunlight absorption was lower as well and destruction of the photosynthesis system by photooxidation was avoided. Free protein content of Lux under flooding was also low, probably in favor of synthesis of other substances that enforce flood tolerance. On the contrary, in P. simonii transpiration only slowly decreased due to slow stomatal closure of leaves in the first day of flooding, and water potential decreased slowly, accompanied with high transformation rate of free water into bound water and low water use efficiency. Slow decomposition of chlorophyll of P. simonii resulted in overabundant light energy absorption and serious destruction of photosynthesis system II (PSII). Net photosynthesis of P. simonii seriously decreased under flooding. At the morphological level, cv. Lux developed many small and obviously functional hypertrophied lenticels throughout the flooding treatment. Bigger hypertrophied lenticels of P. simonii inclined to become rotten. Under complete submergency, cv. Lux could keep an intact leaf structure, whereas epidermis and structure of leaves of P. simonii were destroyed severely. Anatomically, the ultrastructures of leaves of cv. Lux were still intact at the end of flooding, whereas those of P. simonii were destroyed seriously, and many organelles were decomposed.The flood-tolerant poplar clone showed better mechanisms of avoiding oxygen scarcity and tolerating oxygen scarcity. By contrast, the flood-susceptible poplar clone possessed such mechanisms to an insufficient degree. Under soil flooding, rapid formation and maintenance of fine hypertrophied lenticels, a quick decrease of water potential and stomatal closure, keeping for some days still a high level of photosynthesis and water use efficiency, and maintaining intact structures of leaves and roots, etc. were critical traits to survival and growth of the flooding-tolerant poplar clone.

Effects of flooding on grafted annona plants of different scion/rootstock combinations

Annona atemoya Hort cv. African Pride (AP) is highly valued due to its high quality and unique flavor, but highly susceptible to water-logging. Prevalence of root diseases in saturated soils is one of the main problems in production, which restricts the development of AP in south China, where flooding frequently occurs in rainy seasons. However, some annona species, e.g. A. montana, A. glabra and A. muricata, are relatively tolerant to continuous flooding and periodic water-logging conditions, but of limited commercial value. Yet, the potential may exist to increase flood tolerance of commercial annona varieties by the use of flood tolerant rootstocks. An experiment was conducted with the aim to study the effects of continuous or periodical soil flooding on tree performances of four different annona scion/rootstock combinations: AP/AR/G (scion/interstock/rootstock), AR/G (scion/rootstock), AP/AR/M and AR/M, where AP stands for Annona atemoya Hort cv. African Pride, AR for the hybrid of “AP” atemoya × A. reticulata, used as an interstock, G for pond apple (A. glabra), and M for mountain soursop (A. montana). Plant growth, leaf net photosynthetic rates and chlorophyll fluorescence parameters were measured regularly after flooding treatments were applied. Flooding treatments reduced shoot extension, leaf production, net photosynthetic rates and maximum quantum efficiency of photosystem II (Fv/Fm) in plants of AP/AR/M and AR/M, which displayed wilting within 2 weeks of flooding, with a higher wilting percentage in AP/AR/M than in AR/M. The wilted plants shed all leaves but remained alive and sprouted new but weak shoots after 16 weeks of flooding. Long term flooding did not suppress but enhanced photosynthesis as well as tree growth in AP/AR/G and AR/G, with vigorous growth of adventitious roots. Thus, we suggest the use A. glabra instead of A. montana as a rootstock and AR as an interstock to increase flood tolerance of commercial annona varieties.

MORFOANATOMIA FOLIAR EM MUDAS DE Schinus terebinthifolius SOB DIFERENTES NÍVEIS DE SATURAÇÃO HÍDRICA

As características morfológicas e anatômicas foliares de espécies vegetais são importantes indicadores de sua ecologia e de seus hábitats. Objetivou-se caracterizar a plasticidade fenotípica de Schinus terebinthifolius Raddi em diferentes condições de saturação hídrica. As mudas foram produzidas em tubetes plásticos, permanecendo em estufa por quatro meses, sendo irrigadas normalmente. Em seguida foram submetidas aos tratamentos: T1- testemunha, T2- alagamento parcial e T3- alagamento total. Após três semanas sob alagamento, foram realizadas descrições anatômicas foliares comparativas e avaliadas as características morfológicas área foliar, área específica foliar, espessura foliar, teor de água e densidade estomática. Durante 10 semanas foram observadas as modificações fenotípicas adaptativas. Foi observado aumento da espessura da base do caule, clorose e abscisão foliar, surgimento de lenticelas e raízes adventícias. Após três semanas de alagamento, não foram verificadas grandes modificações na morfologia das folhas, principalmente para a AF e AEF. Em T3, o teor de água foi maior e a espessura foliar menor. Não houve diferença entre os tratamentos para DE. Quanto aos aspectos anatômicos, observou-se uma redução na espessura do mesofilo e das nervuras, assim como a produção de compostos fenólicos por alguns tipos celulares. Os espaços intercelulares são progressivamente mais amplos nas plantas submetidas ao alagamento.Palavras-chave: Morfometria; alagamento; plasticidade fenotípica; descrição anatômica. AbstractLeaf morphoanatomy in seedlings of Schinus terebinthifolius, under different levels of water saturation. The morphological and anatomical leaf characteristics plant species are important indicators of their ecology and habitat The purpose of this work was to characterize the phenotypic plasticity of Schinus terebinthifolius Raddi in different conditions of water saturation. The seedlings were grown in plastic tubets, kept in a greenhouse for four months, and irrigated normally. Then they were treated: T1-control, T2-partial flooding and T3- total flooding. After three weeks under flooding leaf comparative anatomical descriptions were done and the following morphological characteristics were assessed: leaf area, specific leaf area, leaf thickness, water content and stomatal density. Over 10 weeks, were observed the adaptive phenotypic changes. We observed an increase in thickness of the base of the stem, leaf chlorosis and abscission, and the appearance of lenticels and adventitious roots. After three weeks of flooding, there were no major changes in the morphology of the leaves, mainly to AF and AEF. In T3, the water content was higher and leaf thickness. There was no difference between treatments for DE. Concerning the anatomy, we noticed that there was a reduction in the thickness of the mesophyll and vein as well as the production of phenolic compounds by some cell types. The intercellular spaces are progressively larger in plants subjected to flooding. Keywords:Morphometry; flooding; phenotypic plasticity; anatomical description.

Stress responses of Salix gracilistyla and Salix subfragilis cuttings to repeated flooding and drought

To compare the responses to repeated flooding and drought of Salix gracilistyla, which grows on coarse gravel substrates, and Salix subfragilis, which grows on fine silt or clay substrates, we measured pre-dawn leaf water potential (ψwpd), osmotic adjustment (ψwtlp, ψosat), and biomass production of cuttings under greenhouse conditions. The experimental design involved a control and four treatments that crossed 1 or 3-week flooding (F) with 1 or 2-week droughts (D). ψwpd was reduced after 2 weeks of drought when preceded by 1 week of flooding. Neither species increased osmotic adjustment in response to increased duration of drought between repeated 3-week flooding. Moreover, a decrease in the ratio of leaf biomass to total biomass or an increase in the ratio of root biomass to total biomass with longer drought repetitions was not observed for either species. The root ratio of S. gracilistyla was more strongly inhibited by flooding than that of S. subfragilis. The shoot-to-root ratio of S. subfragilis was higher than that of S. gracilistyla in all F combinations. The hypertrophied lenticel ratio of S. gracilistyla after 1 week of flooding was nearly the same as that after 3 weeks of flooding, whereas values for S. subfragilis after 1 week of flooding were lower than those after 3 weeks of flooding. The low allocation to roots and the generation of hypertrophied lenticels by S. gracilistyla in response to flooding, as compared with S. subfragilis, seem to be related to the different habitat substrate conditions of the two species.

Characterization of responses to flooding and post – flooding recovery in two Populus deltoidesclones: physiological and biochemical aspects

Background In Argentina, most poplar plantations are located at the Parana River Delta. Climate change models indicate an increase of flooding events for the next decades in this area. Therefore, poplar genotypes with a higher flooding tolerance will be needed for the forest activity. Whether this aim is achieved through traditional breeding or biotechnological developments, it will be important to gain a better understanding of poplar responses to flooding at physiological, biochemical and molecular levels. In a previous work, we characterized the growth and morphological responses of several poplar clones to 35 days of flooding of the root system [1]. From this group, we selected two Populus deltoides clones with different growth responses to flooding: Alton and Stoneville 67. In clone Alton, above ground growth is not affected by flooding, while in Stoneville 67 growth is reduced after the second week of flooding. In the present work, our aim was to identify mechanisms underlying the differences in growth responses to flooding between the two clones. We characterized physiological and biochemical responses in roots and leaves, during a flooding period of 28 days, followed by an after flooding period of three weeks.

Root signalling and modulation of stomatal closure in flooded citrus seedlings

In this work, we studied the sequence of responses induced by flooding in citrus plants, with the aim of identifying the signals that lead to stomatal closure. One-year-old seedlings of Carrizo citrange, grown in sand under greenhouse conditions, were waterlogged for 35 d and compared with normally watered well-drained plants. Significant decreases in stomatal conductance and transpiration were detected between flooded and control seedlings from a week after the beginning of the experiment. However ABA concentration in leaves only started to increase after three weeks of flooding, suggesting that stomata closed in the absence of a rise in foliar ABA. Therefore, stomatal closure in waterlogged seedlings does not appear to be induced by ABA, at least during the early stages of flood-stress. The low levels of ABA detected in roots and xylem sap from flooded seedlings indicated that it is very unlikely that the ABA increase in the leaves of these plants is due to ABA translocation from roots to shoots. We propose that ABA is produced in old leaves and transported to younger leaves. Flooding had no effect on water potential or the relative water content of leaves. Soil flooding reduced root hydraulic conductance in citrus seedlings. This effect was already evident after a week of waterlogging, and at the end of the experiment, flood-stressed seedlings reached values of root hydraulic conductance below 12% of that of control plants. This reduction was related to down-regulation of the expression of PIP aquaporins. In addition, whole plant transpiration was reduced by 56% after 35 d under flooding conditions. Flood-stress also decreased the pH of sap extracted from citrus roots. Evidence is presented suggesting that acidosis induced by anoxic stress in roots causes gating of aquaporins, thereby decreasing hydraulic conductance. Additionally, stomatal closure finely balances-out low pH-mediated losses of root hydraulic conductance therefore maintaining stable leaf hydration.

Nutrient Release from a Recently Flooded Delta Wetland: Comparison of Field Measurements to Laboratory Results

Wetland restoration is expected to reduce external phosphorous (P) loading to hypereutrophic Upper Klamath Lake in Oregon, USA, where P was identified as the primary driver of lake productivity. However, previous laboratory experiments showed that a large P release could occur when former agricultural land is re-flooded for restoration, thus presenting an initial challenge for wetland restoration projects. We tested whether results from those experiments were supported during the initial phase of restoration at the Williamson River Delta adjacent to Upper Klamath Lake. Our objectives were to document post-flood surface water nutrient concentrations, estimate the P mass released from the newly flooded wetlands, and compare these results to the laboratory experiments. Phosphorus concentrations in the wetlands ranged from 0.1 to 0.63 mg P/L and were up to six times greater than in the lakes, corroborating that the wetlands released P upon flooding. However, we estimated 2 Mg P released within three weeks of flooding, which is much lower than the anticipated 64-Mg release from these wetlands, and a fraction of the annual 21–25 Mg load from the Delta before reconnection. This pulse is expected to be short-term; longer term studies will address the role of these wetlands in retaining nutrients.

Stress responses in Salix gracilistyla cuttings subjected to repetitive alternate flooding and drought

To determine the tolerance of Salix gracilistyla to repetitive alternate flooding and drought, we measured leaf stomatal conductance, pre-dawn water potential, osmotic adjustment, and biomass production under greenhouse conditions. We used a control and nine crossed treatments (F1-D1–F3-D3) in which we combined 1-, 2-, or 3-week floodings (F) and droughts (D). Leaf stomatal conductance was lowest in 3 weeks of flooding or drought when the preceding event (flood or drought) was also of a 3-week duration. Leaf pre-dawn water potential was reduced in 3 weeks of drought when preceded by 2 or 3 weeks of flooding. Cuttings had slight osmotic adjustments in repetitions of long floodings and droughts. During longer durations of drought in crossed experiments, plants had low root and shoot mass, few hypertrophic lenticels, and reduced leaf mass; when flooding duration increased in crossed experiments, root mass was reduced, there were more hypertrophic lenticels, and the leaf area was reduced. Cuttings achieved stress tolerance by inhibition of transpiration, osmotic adjustment, reduction of transpiration area, and development of hypertrophic lenticels. Stress tolerance was weak when repetitive 2- or 3-week floodings were combined with 3-week droughts. The duration of flooding and drought periods under which S. gracilistyla achieves stress tolerance may be critical in determining distributions along riverbanks.

Effects of Green Manure and Clay on the Soil Characteristics, Growth and Yield of Peanut at the Coastal Sandy Soil

The Properties of Humic Acids Extracted from Four Sources of Organic Matters and Their Ability to Bind Fe2+ at New Established Rice Field (Herviyanti, TB Prasetyo, F Ahmad and Darmawan): In order to identify the properties of humic acid extracted from four kinds of organic matters (a peat soil, a stable manure, a compost of rice straw and a municipal waste) and their potentiality to bind Fe2+ at new established rice field, a series of experiment was done in Soil Laboratory Faculty of Agriculture, Andalas University Padang. First step was characterization of functional groups and other chemical properties of humic acids, and their reaction with Fe2+. The second step was to examine the ability of humic acids to bind Fe2+ solution at new established rice field by conducting incubation experiments. The experiment used a completely randomized design with three replications. The 450 ppm Fe solution was treated with 0, 50, 100, 150, 200, 250, 300, 350, 400, and 450 ppm humic acids and incubated for 24 hours. While top soil samples taken from Sitiung, West Sumatera were treated with 0,100, 200, 300, and 400 ppm humic acids, flooded with deionized water, and incubated for 6 weeks. The result showed that the functional group and other chemical characteristic of humic acid from rice straw compost and peat soil were better than those of manure and municipal waste compost. Functional group of both humic acids was dominated by COO-. High reactivity of the humic acid had been found when humic acids were added to Fe solution with ratio 1 : 1. Use of humic acid extracted from peat soil with the levels from 0 to 100, 200, 300, and 400 ppm decreased the Fe2+ concentration from 1.361 ppm to 910, 860, 831, and 776 ppm, respectively at new established rice field. While the use of humic acid extracted from rice straw compost with the same levels as above decreased the Fe2+ concentration from 1361 to 770, 701, 612, and 600 ppm, respectively, after four weeks of flooding.

Geomicrobiological Changes in Two Ephemeral Desert Playa Lakes in the Western United States

The geochemistry and microbiology of two ephemeral playa lakes in the Western United States, Surprise Valley Alkali Lake (SVAL) and Eldorado Playa (EP), were examined over one wetting cycle, revealing dramatic temporal changes in suspended mineralogy, aqueous chemistry, and bacterial populations. In SVAL the predominant suspended mineral changed from smectite to vermiculite and clinoptilolite, which led to a depletion of soluble Mg2+. Nitrate became depleted in both playas as a result of biological nitrogen demand imparted by unusually dense microbial communities reaching ∼1 × 108 cultivable heterotrophs per ml of water. One hundred eighty eight bacterial isolates were obtained, representing sixty phylotypes and four phyla: Actinobacteria, Bacteroidetes, Proteobacteria, and Firmicutes. Phylogenetic analyses suggested that the microbial communities reflected different phases of succession, with SVAL changing from a diverse community with abundant Yonghaparkia to a less diverse late summer community with abundant Bacteroidetes and Proteobacteria such as Loktanella, Rhodobaca, Saccharospirillum, Flexibacter, and phylogenetically novel members of the Flexibacteriaceae. In EP, a diverse assemblage of bacteria often associated with soils was replaced very quickly by a much less even community dominated by Yonghaparkia, Sandarakinorhabdus, and relatives of Belliella baltica. Strikingly, the early summer microbial community from SVAL was not significantly different from the EP community that developed within one week of flooding, even though these playas are almost 1000 km apart, whereas sympatric communities in different phases of succession were different. To our knowledge, this is one of the first geomicrobiological studies of a recharge playa, the dominant playa type worldwide.