Long-term Waterlogging Research Articles

Large-scale permafrost degradation as a primary factor in Larix sibirica forest dieback in the Khentii massif, northern Mongolia

The objective of this study is to investigate the potential causes of widespread Larix sibirica Ledeb. mortality observed in the Khentii massif of northern Mongolia. The ratio of deadwood to living trees in affected stands in the Goricho region, the southernmost study site situated close to the Gobi Desert, was as high as 3.6:1. Moisture fluctuations monitored over 2 years using electrical impedance spectrometry revealed that the Goricho study site had higher soil moisture levels than the two less affected sites Barun Bayan and Dzun Bayan. High soil moisture was recorded in an area characterized by highly skeletal soils, ones with more than 35% by volume of rock fragments, and comparatively shallow soil horizons, from valley to mountains. The layer of permafrost influencing hydrogeological processes is much deeper in the Goricho region compared to the undisturbed study sites. Redundancy analysis confirmed a significant number of dead L. sibirica on sites with developed soils. Live forest stands, however damaged, grow in this region on well-drained scree slopes or on rocky bastions. The mass mortality observed for L. sibirica may be directly linked to accelerated permafrost thaw in the area bordered by the Tuul and the Terelj Rivers. Our assumption is that L. sibirica root system necrosis occurred as a result of long-term waterlogging of developed soils with high spatial heterogeneity, normally able to absorb high quantities of groundwater. The areas unaffected were scree fields and rocky bastions characterized by adequate drainage. All of our findings support the primary stages of large-scale permafrost thaw, i.e., correlating increases in soil moisture with increasing permafrost active layer thickness.

Morphological assessments evidence that higher number of pneumatophores improves tolerance to long-term waterlogging in oil palm (Elaeis guineensis) seedlings

Oil palm (Elaeis guineensis Jacq.) apparently tolerates long-term waterlogging and numerous pneumatophores are evident morphological adaptation. The number of pneumatophores per plant is, however, quite variable. Thus we hypothesized that a higher number of pneumatophores may attenuate the stress effects on root system growth and induce higher tolerance to long-term waterlogging in oil palm seedlings. To test this hypothesis we compared morphological and physiological traits in well-watered (control) and waterlogged plants with 2–10, 30–40, 60–70, and 90–120 pneumatophores after ca. 77 days of waterlogging. Plant height was similar between control and waterlogged plants with 90–120 pneumatophores, but it was 21% lower in plants with 2–10 pneumatophores than in control. The stem diameter and bulb diameter and biomass were 16, 20 and 42% higher in waterlogged plants than in control, independent of number of pneumatophores. Similar number of leaves and leaflets were observed regardless of watering regime and pneumatophore number, but total leaflet area and leaflet biomass were higher in plants with 90–120 pneumatophores than in other plants. Root system biomass was remarkably decreased in waterlogged plants; however, such decreases were more expressive in plants with 2–10 pneumatophores. Leaf water potential, leaf gas exchange and chlorophyll fluorescence were unaffected by waterlogging. Thus, we conclude that waterlogging causes few changes in seedlings’ above-ground morphology but remarkably affects root system development, mainly in those plants with lower number of pneumatophores. Regardless of pneumatophores, the stressed oil palm seedlings were able to adjust their leaf water status and gas exchange to cope properly with the imposed waterlogging.

Elucidation of the molecular responses to waterlogging in Sesbania cannabina roots by transcriptome profiling

Sesbania cannabina, a multipurpose leguminous crop, is highly resistant to waterlogging stress. However, the scant genomic resources in the genus Sesbania have greatly hindered further exploration of the mechanisms underlying its waterlogging tolerance. Here, the genetic basis of flooding tolerance in S. cannabina was examined by transcriptome-wide gene expression changes using RNA-Seq in seedlings exposed to short-term (3 h) and long-term (27 h) waterlogging. After de- novo assembly, 213990 unigenes were identified, of which 145162 (79.6%) were annotated. Gene Ontology and pathway enrichment analyses revealed that the glycolysis and fermentation pathways were stimulated to produce ATP under hypoxic stress conditions. Energy-consuming biosynthetic processes were dramatically repressed by short and long term waterlogging, while amino acid metabolism was greatly induced to maintain ATP levels. The expression pattern of 10 unigenes involved in phenylpropanoid biosynthesis, glycolysis, and amino acid metabolism revealed by qRT-PCR confirmed the RNA-Seq data. The present study is a large-scale assessment of genomic resources of Sesbania and provides guidelines for probing the molecular mechanisms underlying S. cannabina waterlogging tolerance.

Effect Of Soil Waterlogging Stress On The Physiological Performance Of Seeds And On The Productivity Of Rye Plants

The objectives of this study were to evaluate the effect of waterlogging on seed physiological performance and plant productivity in rye. Our study consisted of three treatments: 1) no waterlogging, 2) a single waterlogging period, and 3) double waterlogging period. Plant productivity was evaluated from the number of spikes per plant, the number of seeds per plant, the number of seeds per spike, and seed yield. Seeds were exposed to a germination test and seed physiological quality was evaluated from the seed germination rate, initial germination rate, germination speed index, electric conductivity, shoot length, primary root length, shoot dry matter and primary root dry matter, and weight per 1000 seeds. The seeds derived from plants not exposed to waterlogging showed a higher germination rate in a shorter period of time and higher germination speed index than those derived from plants that were exposed to waterlogging; however, the weight per 1000 seeds was lower and seedlings had longer shoots and primary roots. The plants that were not exposed to waterlogging had a higher number of spikes per plant, higher number of seeds per plant, higher number of seeds per spike, and better seed yield per plant. Therefore, it was concluded that waterlogging has a negative effect on seed physiological performance in rye and that plant productivity is reduced under long-term waterlogging.

Analysis and prediction of selected mechanical/dynamic properties of wood after short and long-term waterlogging

Wood is one of the oldest building materials and, thanks to its favorable mechanical and technological properties, one of the most versatile. Due to its biological nature, wooden artefacts can undergo some alteration during their service life that can be caused by mechanical, environmental or biological agents.Waterlogged and buried wood elements, present in wetlands and aquatic environments, are subject to modifications at the chemical and anatomical level, which also affect physical and related mechanical properties of the material.The possibility to predict long-term performance and the rate of modification of mechanical/physical properties of the wood material in specific environmental conditions is crucial for proper design and optimal maintenance of submerged load-bearing timber structures. Therefore, prediction models to estimate selected material properties were developed within this study. For this purpose Fourier Transform near-infrared (FT-NIR) spectroscopy and multivariate analysis based on partial least-squares (PLS) were used. The models proved to be effective to predict selected dynamic and physical parameters of waterlogged samples. However, in order to include the effect of water saturation in the material on site further research is indispensable.The possible detrimental effect on wood mechanical properties of waterlogging in differing environmental conditions is also discussed in this paper. Dynamic tests were performed on samples of two species, Quercus robur L. and Pinus sylvestris L., after 8years of deposition in two differing sites. Additionally, the results obtained from fresh and archaeological samples were compared.No significant effects have been observed due to the depositional environment after short-term waterlogging. A more remarkable difference in the rate of the modification of dynamic and physical (density) properties can be attributed to differing natural features of the tested wooden species. It may be concluded that, in order to ensure a longer service-life of waterlogged timber structures, original wooden material should be properly selected, with regard to species, growth conditions, and log characteristics.

Molecular and physiological responses of trees to waterlogging stress

One major effect of global climate change will be altered precipitation patterns in many regions of the world. This will cause a higher probability of long-term waterlogging in winter/spring and flash floods in summer because of extreme rainfall events. Particularly, trees not adapted at their natural site to such waterlogging stress can be impaired. Despite the enormous economic, ecological and social importance of forest ecosystems, the effect of waterlogging on trees is far less understood than the effect on many crops or the model plant Arabidopsis. There is only a handful of studies available investigating the transcriptome and metabolome of waterlogged trees. Main physiological responses of trees to waterlogging include the stimulation of fermentative pathways and an accelerated glycolytic flux. Many energy-consuming, anabolic processes are slowed down to overcome the energy crisis mediated by waterlogging. A crucial feature of waterlogging tolerance is the steady supply of glycolysis with carbohydrates, particularly in the roots; stress-sensitive trees fail to maintain sufficient carbohydrate availability resulting in the dieback of the stressed tissues. The present review summarizes physiological and molecular features of waterlogging tolerance of trees; the focus is on carbon metabolism in both, leaves and roots of trees.

Spatial variation in root system activity of tomato (Solanum lycopersicum L.) in response to short and long-term waterlogging as determined by 15N uptake

Root system activity is affected by abiotic stresses, which often creates spatial differences in root conditions. This is expected to influence plants ability to cope with suboptimal conditions. Changes in root system activity were determined as 15N root uptake in top and bottom layers of potted tomato plants (Solanum lycopersicum L.), after waterlogging the bottom layer for 24 h or 5 d. The plants were grown in peat-based media; non-compacted or highly-compacted, resulting in differences in gas diffusion, air permeability and oxygen availability. The roots were affected by short-term waterlogging (24 h) by decreasing uptake in the bottom layer and increasing uptake in the pot top layer. Long-term waterlogging (5 d) decreased the 15N root uptake more in both layers. Root uptake recovered fast (within 6 h) after short-term waterlogging, whereas recovery of long-term waterlogged roots took more than 24 h, suggesting production of new root biomass. Despite affecting physical properties, medium compaction did not affect root uptake. Aboveground biomass was affected by waterlogging by increasing the dry matter percentage, decreasing nitrogen (N) percentage and increasing starch content. The results confirmed that root uptake in different layers of small pots could be distinguished by the 15N technique, which was applicable under potentially denitrifying conditions. The results demonstrated that during short-term stress in part of the root system plants increased uptake from the non-affected parts of the root system, probably as compensation for suboptimal conditions.

Ultrastructure changes of seedlings of Kosteletzkya virginica under waterlogging conditions

The changes in ultrastructure of leaf cell in waterlogged Kosteletzkya virginica seedlings were observed by transmission electron microscope. During waterlogging, the chloroplasts turned into a round shape and their volume was gradually reduced. Furthermore, the lamellae of thylakoids swelled, and the inclusions in chloroplast decreased. The shape of starch grains slightly changed, but their number and volume decreased, and they even disappeared in the end. On the other hand, plastoglobules enlarged and their amount enhanced gradually. The membrane and inner cristea of mitochondria gradually became unclear, while the mitochondria firstly enlarged but disappeared at the end. Similar to chloroplast, cell nucleus dwindled gradually, concentrated and tended to a round shape. Additionally, the annulate lamellae and multivesicular body occurred on the 20th day of experiment, and the cell wall distorted and twisted at the late stage of waterlogging. Consequently, these changes of organelles are the typical characteristics of the complete cell disintegration or death for Kosteletzkya virginica under long-term waterlogging.

Effect of flooding on survival and initial growth of Ocotea pulchella (Nees) Mez. seedlings in semi-controlled light conditions

Taking into account the occurrence of Ocotea pulchella in areas subjected to periodic flooding, this work aimed to evaluate the survival and initial development of Ocotea pulchella seedlings (2 months old) and juveniles (9 months old) in response to waterlogging under different light regimes by varying both light quantity and light quality, in order to test for possible flood tolerance of the species as affected by light conditions. Three levels of soil moisture (field capacity, mean flooding - only for seedlings - and full flooding) and four light treatments (full sun, neutral shade, far red enriched shading and neutral plus far red) were tested. The survival of seedlings and juveniles during one year was relatively high, whereas growth was negatively affected by full sun and flooding. Seedling growth was inhibited by soil waterlogging whatever the light condition, whereas plant growth at field capacity and mean fl ooding was similar. Flooding also inhibited the growth of juveniles, and that response was practically not affected by the light regimes. The results suggest that Ocotea pulchella seedlings can survive in the understory, even in areas subject to fl ooding, forming a slow-growth seedling bank. The species seems to tolerate relatively long-term soil waterlogging when kept out of direct sunlight. Otherwise, responses of waterlogged plants to shading seem to be aff ected by irradiance and light quality.

The application of cutting plus waterlogging to control Spartina alterniflora on saltmarshes in the Yangtze Estuary, China

Control and eradication of the exotic and invasive plant Spartina alterniflora within the Chongming Dongtan nature reserve, Shanghai, China, is vital for the management and conservation of the saltmarshes. A demonstration project was established using waterlogging and cutting to control this invasive species. Results from 2007 to 2008 showed that, although the managed waterlogging significantly reduced biomass and seed production of S. alterniflora at an early stage, the species subsequently showed rapid adaptation to the long-term waterlogging stress. Thus, managed waterlogging alone was insufficient for the effective eradication of S. alterniflora. However, managed waterlogging for around 3 months, combined with cutting the above-ground part of S. alterniflora at a key stage (flowering period in July), controlled and eradicated the plant successfully. Both the above-ground and below-ground parts of S. alterniflora were killed and the plants began to decompose after 3 months. Furthermore, there was no re-growth of the emergent part of S. alterniflora in the following years. However, once the impounded water was released restoring the natural hydrodynamic regime of the saltmarshes, the seeds and seedlings of S. alterniflora reinvaded the controlled site from the neighboring areas and the S. alterniflora community was re-established. Thus, after eradication of S. alterniflora, control measures should be maintained to prevent the re-establishment of S. alterniflora. The results of this demonstration project indicate a potentially useful and effective approach for the control and management of large-scale invasion by S. alterniflora on saltmarshes in the Yangtze Estuary, China.

Stem anatomical variations in seedlings of the mangrove Bruguiera gymnorrhiza grown under periodical waterlogging

The purpose of this study was to investigate the stem anatomical adaptations of the mangrove Bruguiera gymnorrhiza seedlings under experimental conditions that simulated semidiurnal tides. The inundation periods in these treatments were 0, 2, 4, 6, 8, 10 and 12 h. In the 0–6 h treatments, cortex thickness, pith radius and stem radius increased, but then declined when inundation period exceeded 6 h. Significant negative linear correlations were found between waterlogging duration and vessel element length, bar number per perforation plate and gelatinous fibre ratio. Whereas vessel density and fibre diameter showed only slight fluctuations, fibre cell wall thickness declined dramatically from 2 h treatments onwards, in contrast, vessel wall thickness increased under long-term waterlogging conditions (>6 h). Tangential vessel diameter and fibre length exhibited similar tendencies, first decreasing significantly with prolonged inundation, and then increasing under long-term waterlogging duration up to 6 h. These results indicated that the internal structure of B. gymnorrhiza seedlings was affected by periodical waterlogging. The distinct structural changes with short (<6 h) or long (> 6 h) term inundation suggest distinct strategies for maintaining a balance between growth, conductive capacity, conductive safety and mechanical strength.

Submergence research using Rumex palustris as a model; looking back and going forward

Flooding is a phenomenon that destroys many crops worldwide. During evolution several plant species evolved specialized mechanisms to survive short- or long-term waterlogging and even complete submergence. One of the plant species that evolved such a mechanism is Rumex palustris. When flooded, this plant species is capable to elongate its petioles to reach the surface of the water. Thereby it restores normal gas exchange which leads to a better survival rate. Enhanced levels of ethylene, due to physical entrapment, is the key signal for the plant that its environment has changed from air to water. Subsequently, a signal transduction cascade involving at least four (classical) plant hormones, ethylene, auxin, abscisic acid, and gibberellic acid, is activated. This results in hyponastic growth of the leaves accompanied by a strongly enhanced elongation rate of the petioles enabling them to reach the surface. Other factors, among them cell wall loosening enzymes have been shown to play a role as well.

Interactive effects of nitrate and long-term waterlogging on growth, water relations, and gaseous exchange properties of maize (Zea mays L.)

The interactive effect of additional amount of NO3-N and long-term waterlogging on maize was studied in glasshouse conditions. Forty-two-day-old plants were subjected to continuous flooding for 21 days at three different NO3-N regimes (196, 294 and 392 mg N kg−1 soil). Shoot fresh mass and leaf area of waterlogged plants reduced significantly at two higher NO3 regimes. Leaf water potential was generally decreased, whereas osmotic potential increased in all waterlogged plants but much reduction in leaf water potential was found at the highest external NO3 regime. Leaf turgor potential decreased due to waterlogging but this decrease progressed with increase in external NO3 concentration. Chlorophylls ‘a’ and ‘b’ increased in non-waterlogged plants with increase in NO3 concentration of the growth medium, but these two pigments decreased significantly due to waterlogging particularly at the two higher NO3 regimes. Chlorophyll a/b ratio increased linearly in non-waterlogged plants with increase in external NO3 regimes but the ratio remained almost unchanged due to waterlogging. Waterlogging caused a reduction in net photosynthesis and stomatal conductance but no effect of additional amount of NO3 was observed on these two variables. Transpiration was also decreased as a result of waterlogging but a marked reduction in this variable was observed at the highest external NO3 concentration. Water-use efficiency increased with increase in external NO3 concentration in both waterlogged and non-waterlogged plants. Although waterlogging caused a reduction in substomatal CO2 concentration, it generally increased in both waterlogged and non-waterlogged plants due to supplementary NO3, particularly at its highest concentration. From these results, it is clear that supplementary NO3 in the growth medium of maize plants experiencing long-term waterlogging had injurious effect on growth.

The effect of waterlogging on nitrogen fixation and nodule morphology in soil-grown white clover (Trifolium repensL.)

Nodulated, pot-grown plants of white clover (Trifolium repens cv. Katrina) were subjected to different soil moisture regimes and the effect of these treatments on dry matter production, nitrogenase activity, aerenchyma formation, and bacteroid distribution was determined. In the first experiment, after 9 weeks growth shoots were significantly (P<0.01) heavier for clover plants which were flooded from germination compared with those subjected to normal watering, indicating that clover can adapt to long-term waterlogging. In the second experiment, time-courses of acetylene reduction showed a lag phase of only 10 min for waterlogged plants, suggesting that gas exchange was occurring through aeration pathways rather than the water. Flooded plants that were drained 24 h prior to acetylene reduction assays had substantially greater nitrogenase activity than normally watered or continually flooded plants. However, there was a marked decrease in nitrogenase activity when plants which had been watered normally were flooded, suggesting a sensitivity of white clover to sudden changes in moisture conditions. Morphological studies of nodules from plants grown in normally watered and continually flooded soil showed increased aerenchyma production around roots and nodules of waterlogged plants. In addition, the infected cells of submerged nodules were larger and had larger vacuoles than those from nodules of normally watered plants. This increase in vacuole volume to protoplast volume in infected cells may play a role in the tolerance of white clover nodules to waterlogging.