Partial Submergence Research Articles

Dissecting lncRNA-mRNA networks underlying physiological alterations in Taxodium hybrid ‘Zhongshanshan’ leaves in acclimation to prolonged partial submergence

Long non-coding RNAs (lncRNAs) play essential roles in plant adaptation to various abiotic stresses. However, lncRNAs-mRNA networks underpinning physiological alterations in trees responding to long-term flooding remain unknown. Here, cuttings of Taxodium hybrid ‘Zhongshanshan 703’ (T. mucronatum × T. distichum; T. ‘Zhongshanshan’), which is highly tolerant to flooding, were irrigated to keep the field capacity (C) or partial-submerged (S) for two months. The leaves above (AL) and below (BL) flooding-water surface were separately harvested. In total, 294 and 975 lncRNAs (DELs) as well as 1503 and 6170 mRNAs (DEMs) were significantly differentially expressed in AL and BL of T. ‘Zhongshanshan’ treated with S than those exposed to C, respectively. 493 DELs were predicted to target 517 DEMs through co-location way, and 906 DEMs were identified as putative target genes of 314 DELs through co-expression way. Furthermore, co-expression networks of DELs and DEMs that are closely correlated with the changes in concentrations of organic acids, sugars, amino acids and phytohormones and activities of anaerobic respiratory enzymes and enzymatic antioxidants were established. For instance, the transcript levels of an lncRNA (TCONS_00030503) and its target gene ADH1 which is involved in alcoholic fermentation were elevated in the BL of T. ‘Zhongshanshan’ exposed to S. This is in line with increased ADH activity in BL due to flooding. Moreover, eight hub DELs and five hub DEMs that are related to photosynthesis, starch metabolism, glycolysis, amino acid metabolism and hormone metabolism were identified. Overall, these results suggest that lncRNA-mRNA networks play significant roles in regulating TCA cycle, fermentation, glycolysis, reactive oxygen species detoxification, and metabolism of carbohydrate, alanine and phytohormone in T. ‘Zhongshanshan’ leaves, and these processes play pivotal roles in acclimation to long-term submergence.

Response of endophyte‐infected and endophyte‐free tall fescue plants to partial submergence at two developmental stages

AbstractTall fescue (Festuca arundinacea Schreb.) is a perennial C3 grass species usually associated with the endophyte fungus Epichloë coenophiala that enhances tolerance to biotic and abiotic stresses. Given that the proportion of infected tall fescue plants in the grasslands of the Flooding Pampa (Argentina) has been progressively increasing, it is proposed that endophytes confer tolerance to the stresses characteristic of that environment, especially flooding. Plants from a naturalized population and a commercial cultivar were grown, both with and without endophyte (wild type and AR584 respectively). The plants were subjected to two submergence treatments (i.e., control and partial submergence) in two development stages (5‐leaf stage and beginning of the elongation of internodes). Plant performance (aerial and root biomass, root aerenchyma formation, total root length and root diameter, proportion of reproductive tillers, number of panicles and seeds produced) and endophyte transmission to progeny were evaluated. Endophytes did not alter the ecological fitness of plants under partial submergence. Independently of the water condition, the symbiosis was linked to low biomass in plants from the naturalized population, while the opposite occurred in plants from the cultivar. Partial submergence did not affect the germination of the seeds produced, nor the transmission of the endophyte to the seedlings that originated from them. Our work suggests that the invasion ability of tall fescue in the Flooding Pampa grasslands is not related to an endophyte‐mediated improvement of plants to tolerate water excess.

Grass pea (Lathyrus sativus) interesting panoply of mechanisms to cope with contrasting water stress conditions – a controlled study of sub populational differences in a worldwide collection of accessions

The grain legume Lathyrus sativus L. (grass pea) is of high economic importance for food and feed in Asian and African developing countries and is part of cultural heritage of marginal areas in the Mediterranean region. Its outstanding robustness under adverse environmental conditions, when compared with other legume species, raises particular interest under the current climate change scenario. The aim of this work was to study the range, extent and mechanisms underlying this species’ reported tolerance to water stress. To achieve this, a worldwide representative collection of 194 grass pea accessions was subjected to specific well-watered, water deficit and waterlogging conditions. These conditions were defined previously to elicit differential physiologic responses among the collection on 21 days old plants as continuously kept at 95% field capacity, at 5 days without irrigation reaching 55% field capacity, and at 14 days of partial submergence, respectively. The assessment encompassed a comprehensive set of 20 traits, including gas exchange, chlorophyll a fluorescence, leaf photosynthetic pigments, leaf water status and biomass partitioning. This detailed phenotypic analysis demonstrated that leaf relative water content and gas-exchange related traits are particularly useful to differentiate accessions’ response to water treatments. We discovered that accessions with light and large seeds mostly of Mediterranean and East European origins produce plants with high total dry biomass, a trait that is mostly genetically determined and less affected by the water treatment. On the other hand, it is mainly dark and small seeded accessions that show advantageous physiological responses to water deficit and/or waterlogging, according to pigment contents, root to shoot ratio and water use efficiency traits. This integrative screening also allowed the identification of accessions displaying contrasting levels of tolerance and susceptibility to each stress (five tolerant and five susceptible to each stress), plus one multi-tolerant (PI283546) and one multi-susceptible (PTLS1001) accession. A comprehensive and deep understanding of grass pea’s water stress tolerance mechanisms is the first step for a more efficient exploitation of this grain legume as a model crop for multiple abiotic stress resistance studies and opens doors for further progresses on crop breeding efforts towards securing food and feed supplies.

Short Communication: Morphophysiological Response to Partial Submergence and Water Deficit in North Sulawesi Local Rice

Flood and drought are two disasters that resulted in crop failure, including rice production. The objective of this study was to evaluate the morphophysiological characteristics of North Sulawesi local rice (Oryza sativa L.) cultivars as response to partial submergence and water deficit at the vegetative phase based on plant height, number of leaves, root length and volume, and leaf total chlorophyll concentration. The factorial experiment in Completely Randomized Design consisted of four rice cultivars (Superwin, Ombong, Temo, and Burungan) and three treatments (well-watered, partial submerged, and water deficit). The treatments commenced at four-fully-expanded leaf stage for 14 days. Plant height and leaf number were recorded on day 0 (before the treatments commenced), 7, and 14 after treatments. The length and volume of roots as well as total chlorophyll were recorded at 14 days after treatment. Root length was potential indicator of partial submergence and water deficit as it was higher under partial submergence and water deficit than well-watered. Root volume was potential indicator of partial submergence as it was larger under partial submergence than water deficit and well-watered. The partial submergence and water deficit tolerance of North Sulawesi local rice should be further evaluated based on the other characteristics.AbstrakKebanjiran dan kekeringan merupakan bencana alam yang mengakibatkan kegagalan panen, termasuk produksi beras. Penelitian ini bertujuan untuk mengkaji karakterisitik morfofisiologis pada padi (Oryza sativa L.) lokal Sulawesi Utara sebagai respons terhadap kebanjiran dan kekeringan pada fase vegetatif berdasarkan tinggi tanaman, jumlah daun, panjang, dan volume akar serta kandungan klorofil daun. Percobaan faktorial dalam Rancangan Acak Lengkap ini menggunakan empat kultivar padi (Superwin, Ombong, Temo, dan Burungan) serta tiga perlakuan (diairi, digenangi, dan tidak diairi). Perlakuan dimulai pada saat tanaman mempunyai empat daun yang berkembang penuh selama 14 hari. Tinggi tanaman dan jumlah daun diamati pada hari ke-0 (sebelum perlakuan dimulai), hari ke-7, dan 14 setelah perlakuan. Panjang dan volume akar serta kandungan klorofil daun diukur pada 14 hari setelah perlakuan. Panjang akar merupakan indikator yang potensial untuk kebanjiran dan kekeringan karena panjang akar saat kebanjiran dan kekeringan lebih besar daripada diairi. Volume akar merupakan indikator yang potensial untuk kebanjiran karena volume akar saat kebanjiran lebih besar daripada saat kekeringan dan diairi. Toleransi padi lokal Sulawesi Utara terhadap kebanjiran dan kekeringan perlu dievaluasi lebih lanjut berdasarkan karakteristik lainnya.

Physiological and transcriptional regulation in Taxodium hybrid 'Zhongshanshan' leaves in acclimation to prolonged partial submergence.

Taxodium 703 leaves activate fermentation, amino acids metabolism and ROS detoxification, and reduce TCA cycle and ABA biosynthesis in acclimation to prolonged partial submergence stress. Taxodium hybrid 'Zhongshanshan 703' (T. mucronatum × T. distichum; Taxodium 703) is a highly flooding-tolerant woody plant. To investigate the physiological and transcriptional regulatory mechanisms underlying its leaves in acclimation to long-term flooding, we exposed cuttings of Taxodium 703 to either non-flooding (control) or partial submergence for 2months. The leaf tissues above (AL) and below (BL) flooding-water were separately harvested. Partial submergence decreased concentrations of chlorophyll (a + b) and dehydroascorbate (DHA) and lactate dehydrogenase (LDH) activity in AL, and reduced biomass, concentrations of succinic acid, fumaric acid and malic acid, and transcript levels of genes involved in tricarboxylic acid (TCA) cycle in BL. Under partial submergence, concentrations of starch, malondialdehyde and abscisic acid (ABA) decreased, and also mRNA levels of nine-cis-epoxycarotenoid dioxygenases that are involved in ABA biosynthesis in AL and BL of Taxodium 703. Partial submergence increased O2- content in AL, and improved concentrations of pyruvate and soluble sugars and activities of LDH and peroxidase in BL. In addition, partial submergence increased concentrations of ethanol, lactate, alanine, γ-aminobutyric acid, total amino acids and ascorbic acid (ASA), and ASA/DHA, activities of alcohol dehydrogenases (ADH) and ascorbate peroxidase, as well as transcript levels of ADH1A, ADH1B and genes involved in alanine biosynthesis and starch degradation in AL and BL of Taxodium 703. Overall, these results suggest that Taxodium 703 leaves activate fermentation, amino acids metabolism and reactive oxygen species detoxification, and maintain a steady supply of sugars, and reduce TCA cycle and ABA biosynthesis in acclimation to prolonged partial submergence stress.

Performance of young endophyte-free and endophyte-infected tall fescue (Festuca arundinacea) plants under partial and total submergence

Context Tall fescue (Festuca arundinacea Schreb.) is a valuable temperate forage grass. Tall fescue plants associated with Epichloë fungal endophytes are successfully spreading in grassland regions that are recurrently exposed to flooding. Aims We asked whether the association with fungal endophytes increases plant performance under water excess. Methods In a greenhouse experiment, we evaluated the differential performance of young endophyte-infected and endophyte-free tall fescue plants in response to 14 days of partial and total submergence. We included a wild local population and a cultivar, each with their respective fungal endophyte: the common endophyte and a safe (non-toxic) endophyte (AR584). Key results Relative to control (non-submerged) plants, and regardless of endophyte status, total submergence resulted in a significant growth reduction. At the end of the partial submergence period, the number of leaves per plant increased (21%) in the presence of the safe endophyte AR584 but decreased (18%) in the presence of the wild endophyte. Moreover, under partial submergence, the presence of wild endophyte decreased pseudostem dry weight by 10%. Conclusions Our results show that the presence of either the wild or the safe endophyte did not increase the performance of young tall fescue plants under submergence conditions. Implications Although all endophyte-free and endophyte-infected tall fescue plants survived submergence treatments, we cannot rule out that Epichloë endophytes might improve plant fitness under longer stressful submergence conditions. Future research should explore how endophytes modulate host performance under water excess, considering different phenological plant phases and/or co-occurrence with other stress factors (e.g. high temperatures).

Shaking off the blow: plant adjustments during submergence and post-stress growth in Lotus forage species.

Flooding significantly hampers global forage production. In flood-prone regions, Lotus tenuis and Lotus corniculatus are common forage legumes, yet little is known about their responses to partial or complete submergence. To address this, we evaluated 10 Lotus accessions subjected to 11days of either partial or complete submergence, analysing growth traits related to tolerance and recovery after de-submergence. Principal component analyses revealed that submergence associated growth parameters were linked to L. corniculatus accessions, whereas recovery was associated with L. tenuis accessions. Notably, in L. tenuis , recovery from complete submergence positively correlated with leaf mass fraction but negatively with root mass fraction, showing an opposite pattern than in L. corniculatus . Encouragingly, no trade-off was found between inherent growth capacity and submergence tolerance (both partial and complete) or recovery ability, suggesting genetic selection for increased tolerance would not compromise growth potential. L. tenuis exhibited accessions with both partial and complete submergence tolerance, making them versatile for flood-prone environments, whereas L. corniculatus accessions were better suited for partial submergence. These findings offer valuable insights to enhance forage production in flood-prone areas and guide the selection of appropriate Lotus accessions for specific flood conditions.

Deepwater response in the African cultivated rice Oryza glaberrima

ABSTRACT Partial submergence of Oryza sativa deepwater rice elicits enhancement of internodal elongation, referred to as deepwater response, conferred by three types of genes, SNORKEL1/2 (SK1/2), SEMIDWARF1 (SD1), and ACCELERATOR OF INTERNODE ELONGATION 1 (ACE1). We investigated the presence and expression of these genes in the African cultivated rice Oryza glaberrima and the relationship between these genes and the deepwater response of O. glaberrima. In 49 of the 50 accessions tested, one or two SK genes were identified, which could be divided into three types of SK1 and four types of SK2. The accessions with the SK2 type whose expression was induced by submergence demonstrated rapid internodal elongation under submergence. In most of these accessions, submergence also increased the expression of SD1 and ACE1 genes. However, the accessions did not possess the haplotype of SD1 that is associated with high deepwater response in O. sativa. In contrast, they possessed the type of ACE1 gene similar to that in O. sativa deepwater rice. These results indicate that the molecular mechanisms underlying induction of deepwater response in O. glaberrima are similar to that found in deepwater rice of O. sativa and suggest that most O. glaberrima cultivars, including upland cultivars, can exhibit rapid internodal elongation under submergence.

An experimental study of wave-in-deck loading and its dependence on the properties of the topside structure

This paper concerns the largest and arguably the most threatening wave loading component experienced by a broad range of offshore structures. It arises when an incident wave crest exceeds the elevation of the underside of the deck structure, leading to direct wave-in-deck (WID) loading. The extent of this loading may be limited to the partial submergence of some of the lowermost deck beams, or could involve the large-scale inundation of the entire deck area. Either way, very large loads can arise which must be taken into account when assessing the reliability of the structure. In an earlier contribution Ma and Swan (2020) provided an extensive laboratory study exploring the variation of these loads with the properties of the incident wave. The present paper describes a second stage of this experimental study in which the variation of the WID loads with the properties of the topside structure is addressed. Specifically, it considers the porosity, position and orientation of the topside relative to the incident wave conditions, and seeks to explore both the variations in the maximum load and the loading time–history resulting from these changes.Given the highly transitory nature of a WID loading event, coupled with the fact that the problem is governed by flow conditions at, or very close to, the instantaneous water surface, the loading process is driven by an exchange of momentum from the wave crest to the topside structure. A recently developed WID load model, based on exactly these arguments (Ma and Swan 2020), is used alongside the laboratory data to provide a break-down of the load into its component parts. This provides an enhanced physical understanding of the resulting load time–history. The first part of the study is based upon an idealised generic topside structure, allowing a systematic variation in key parameters, particularly porosity. The second part addresses a realistic topside structure demonstrating the practical relevance of earlier work. Taken together, the analysis clearly establishes the importance of the topside porosity, clarifies the spatial effects associated with the evolution of a large ocean wave beneath the plan area of a structure and explains the unexpected occurrence of impact-type loading on topside structures having a high porosity. Most importantly, the paper highlights those properties of a topside structure which must be incorporated if the WID loads are to be accurately predicted.

Differential Growth Responses of Alternanthera philoxeroides as Affected by Submergence Depths.

Global climate change has resulted in an increase in intensity and frequency of flooding, plants living in lowlands, and shore areas have to confront submergence caused by flooding, submergence-tolerant plants usually respond by adopting either escape or quiescence strategies. While certain plants exhibit a changeover from escape strategy upon partial submergence to quiescence strategy under complete shallow submergence, it remains unknown whether plants completely submerged at different water depths would adjust their strategies to cope with the change in submergence depth. Alternanthera philoxeroides is an ideal species to explore this adjustment as it is widely distributed in flood-disturbed habitats and exhibits an escape strategy when completely submerged in shallow waters. We investigated the responses of A. philoxeroides in terms of morphology, anatomy, and non-structural carbohydrate metabolism by conducting experiments using a series of submergence depths (0, 2, 5, and 9 m). During the submergence treatment, environmental factors such as light, dissolved oxygen, and temperature for submerged plants were kept constant. The results showed that A. philoxeroides plants submerged at depth of 2 m presented an escape strategy via fast stem elongation, extensive pith cavity development, and small biomass loss. However, the retarded stem elongation, reduced pith cavity transverse area, and increased biomass loss along the water depth gradient indicated that A. philoxeroides altered its growth response as water depth increased from 2 to 9 m. It is found that the changeover of response strategies occurred at higher submergence depths (5–9 m). Based on the results of our experiments, we demonstrated that water depth played an important role in driving the change in strategy. The water-depth-dependent growth performance of A. philoxeroides would benefit the species in habit exploration and exploitation. Further studies should focus on the performances of plants when submerged at varied water depths with different light climates and dissolved oxygen content, and how water depths drive the response behaviors of the submerged plants.

Short communication: Pattern of chlorophylls content declined during partial submergence for rice varieties cultivated in North Sulawesi at the vegetative stage

Abstract. Nio SA, Ludong DPM, Siahaan R. 2022. Short communication: Pattern of chlorophylls content declined during partial submergence for rice varieties cultivated in North Sulawesi at the vegetative stage. Biodiversitas 23: 2451-2456. Submergence or flooding stress limits plant growth in various physiological, anatomical, and morphological aspects. This study examined leaf chlorophyll content as a physiological response in some rice varieties cultivated in North Sulawesi during partial submergence imposed at the vegetative stage. Ten rice cultivars, i.e., Permata, Superwin, Cigeulis, Pulo Manado, TB, Ombong, Serayu, Temo, Burungan, and Inpari 31, were grown in plastic trays on planting media in the greenhouse, then watered to field capacity using a mixture of water and fertilizer every second day for two weeks. The plants were submerged 18 cm from the media's surface, and the content of leaf chlorophylls (total chlorophyll, chlorophyll a, and chlorophyll b) were measured using a spectrophotometer (? 649 and 665 nm) at 0, 3, 6 and 9 days of partial submergence. The chlorophylls (total, a, and b) content decreased during the 9 days of treatment. The highest chlorophylls contents were observed in rice cv. Superwin and the chlorophylls content at day 0 (before partial submergence commenced) were higher than at 3, 6, and 9 days after treatment (p<0.05). The data presented here supported that leaf chlorophylls content is a potential physiological indicator of partial submergence stress in rice, including the North Sulawesi local rice, at the vegetative phase.

Identification of QTLs for stagnant flooding tolerance in rice employing genotyping by sequencing of a RIL population derived from Swarna × Rashpanjor.

The online version contains supplementary material available at 10.1007/s12298-021-01107-x.

Development of waterlogging tolerant lines of pigeonpea for Eastern India

Pigeonpea is very sensitive to waterlogging. At pan India level, approximately 25-30 per cent area of pigeonpea is prone to excess moisture stress. Atotal of 63 germplasms/genotypes were evaluated along with IPAC-79 as the waterlogging tolerant check under controlled partial submergence condition and under waterlogged field condition for selection of waterlogging tolerant pigeonpea lines. Data were recorded for survivability, days to anthesis, per plant seed yield and maturity period. Pigeonpea genotypes ICARPP01, ICARPP02 and ICARPP03 were found promising. ICARPP01 produced highest biomass per plant (746.5g), pods/plant (924.6) and seed yield per plant (151g). The genotype ICARPP01 took minimum number of days for anthesis (124 days) and maturity (197days), whereas the check variety IPAC-79 recorded maximum number of days to anthesis (201 days) and maturity (255 days).

Preformed aerenchyma determines the differential tolerance response under partial submergence imposed by fresh and saline water flooding in rice.

Plant's response to fresh- and saline-water flooding and the resulting partial submergence, seems different due to the added complexities of element toxicity of salinity. We identified a few rice genotypes which can tolerate combined stresses of partial submergence and salinity during saline water flooding. To gain mechanistic insights, we compared two rice genotypes: Varshadhan (freshwater-flooding tolerant) and Rashpanjor (both fresh- and saline-water flooding tolerant). We found greater ethylene production and increased "respiratory burst oxidase homolog" (RBOH)-mediated reactive oxygen species (ROS) production led to well-developed constitutive aerenchyma formation in Rashpanjor, which makes it preadapted to withstand fresh- and saline-water flooding. On the contrary, an induced aerenchyma formation-dependent tolerance mechanism of Varshadhan worked well for freshwater flooding but failed to provide tolerance to saline-water flooding. Additional salt stress was found to significantly inhibit the induced aerenchyma formation process due to the dampening of ROS signaling by the action of metallothionein in Varshadhan. Besides, inconspicuous changes in ionic regulation processes in these two genotypes under saline-water flooding suggest preadapted constitutive aerenchyma formation plays a more significant role than elemental toxicity per se in tolerating combined stresses encountered during saline water flooding in rice. Overall, our study indicated that well-developed constitutive aerenchyma provide an adaptive advantage during partial submergence due to saline water flooding in rice as the key process of induced aerenchyma formation is hampered in the presence of salinity stress coupled with partial submergence.

Root submergence enhances respiration and sugar accumulation in the stem of flooded tomato plants.

Flooding is a major environmental constraint that obliges plants to adopt plastic responses in order to cope with it. When partially submerged, tomato plants undergo profound changes involving rearrangements in their morphology and metabolism. In this work, we observed that partial submergence markedly dampens root respiration and halts root growth. However, the flooded hypocotyl surprisingly enhances oxygen consumption. Previous results demonstrated that aerenchyma formation in the submerged tomato stem re-establishes internal oxygen tension, making aerobic respiration possible. Indeed, potassium cyanide abruptly stops oxygen uptake, indicating that the cytochrome c pathway is likely to be engaged. Furthermore, we found out that leaf-derived sugars accumulate in large amounts in hypocotyls of flooded plants. Girdling and feeding experiments point to sucrose as the main carbon source for respiration. Consistently, submerged hypocotyls are characterized by high sucrose synthase activity, indicating that sucrose is cleaved and channelled into respiration. Since inhibition of hypocotyl respiration significantly prevents sugar build-up, it is suggested that a high respiration rate is required for sucrose unloading from phloem. As substrate availability increases, respiration is fuelled even more, leading to a maintained allocation of sugars to flooded hypocotyls.

Experimental comparison of two methods to study barley responses to partial submergence

BackgroundCrop yield is dependent on climate conditions, which are becoming both more variable and extreme in some areas of the world as a consequence of global climate change. Increased precipitation and flooding events are the cause of important yield losses due to waterlogging or (partial) submergence of crops in the field. Our ability to screen efficiently and quickly for varieties that have increased tolerance to waterlogging or (partial) submergence is important. Barley, a staple crop worldwide, is particularly sensitive to waterlogging. Screening for waterlogging tolerant barley varieties has been ongoing for many years, but methods used to screen vary greatly, from the type of soil used to the time at which the treatment is applied. This variation makes it difficult to cross-compare results.ResultsHere, we have devised a scoring system to assess barley tolerance to waterlogging and compare two different methods when partial submergence is applied with either water or a starch solution at an early developmental stage, which is particularly sensitive to waterlogging or partial submergence. The use of a starch solution has been previously shown to result in more reducing soil conditions and has been used to screen for waterlogging tolerance.ConclusionsOur results show that the two methods provide similar results to qualitatively rank varieties as tolerant or sensitive, while also affecting plants differently, in that application of a starch solution results in stronger and earlier symptoms than applying partial submergence with water.

Geological and seafloor investigations of the cause of partial submergence of Yokoshima Island, Nagasaki, Japan

Between 1950 and 1980, about half of Yokoshima Island disappeared beneath the East China Sea. The island lies about 1 km off the coast of Nagasaki and was mined for coal during the late 19th and early 20th centuries. We analyzed the geology of the island and surrounding seafloor to investigate how it became submerged. Two low-cost techniques were used to view underwater structures: a commercial drone fitted with a video camera in waters shallower than 5 m and an echo sounder and side-scan sonar system designed for amateur fishers in waters deeper than 5 m. We showed that the partial submergence of the island could be interpreted as a result of subsidence. Subsidence and northward tilting of sedimentary rocks north of the island, probably caused by collapse of abandoned subsea mine workings, created an extensional regime south of the island that led to the formation of steep cliffs and collapse of the southern side of the island. Our study also shows that low-cost commercially available technology can be used for rapid scientific investigations in shallow water areas. • Submergence of half of an island in a 30 year period was investigated. • Low-cost shallow seafloor investigation techniques helped geological analysis. • Subsidence was associated with uneven settlement into abandoned coal mine workings.

Thermal treatment using microwave irradiation for the phytosanitation of Xylella fastidiosa in pecan graftwood.

Pecan bacterial leaf scorch caused by Xylella fastidiosa is an emerging disease for the U.S. and international pecan industries and can be transmitted from scion to rootstock via grafting. With the expanse of global transportation and trade networks, phytosanitation is critical for reducing the spread of economically significant pathogens, such as X. fastidiosa. We developed and evaluated thermal treatments using microwave irradiation and microwave absorbers [sterile deionized water (dH2O) and carbon nanotubes (CNTs)] as novel disinfectant methods for remediating X. fastidiosa in pecan scions. Partial submergence of scions in dH2O or CNT dispersions resulted in the transport of microwave absorbers in the xylem tissue via transpiration but did not compromise plant health. The microwave absorbers effectively transferred heat to the scion wood to reach an average temperature range of 55–65°C. Microwave radiation exposure for 6 sec (3 sec for two iterations) of CNT- or dH2O-treated scions reduced the frequency of X. fastidiosa-positive in pecan scions without negatively affecting plant viability when compared to the control group (dH2O-treated with no microwave). The efficacy of the new thermal treatments based on microwave irradiation was comparable to the conventional hot-water treatment (HWT) method, in which scions were submerged in 46°C water for 30 min. Microwave irradiation can be employed to treat X. fastidiosa-infected scions where the conventional HWT treatment is not feasible. This study is the first report to demonstrate novel thermal treatment methods based on the microwave irradiation and microwave absorbers of dH2O and CNT as an application for the phytosanitation of xylem-inhabiting bacteria in graftwood.

Partial submergence: An undescribed behavioral adjustment for thermoregulation at high ambient temperature in Aeshnidae

Many insects including odonates thermoregulate using a combination of behavioral and physiological mechanisms. At high ambient temperature (Ta), these mechanisms include decreased heat production and increased heat loss. Heat production can be reduced by decreasing activity. Heat loss can be enhanced by perching in a shaded microhabitat where temperature is cooler than in the surrounding environment. Aeshnids, which are intermittent endotherms, increase heat loss at high Ta; also by increasing hemolymph circulation from the thorax, where most metabolic heat is produced, to the abdomen, where it dissipates to the environment by convection. While studying two aeshnid species (Anax junius and Rhionaeschna multicolor) at a Sonoran Desert (Arizona, USA) stream, I observed partially submerged mature individuals of both sexes of these species. This heretofore undescribed behavior was seen only at Ta; ≥ 43 °C and almost exclusively during the hottest part of the day (15:00–17:00 hr), when the daily difference between Ta; and water temperature (Tw) was, on average, largest. A cooling effect of partial submergence behavior on body temperature would, therefore, presumably be most effective also during this period. Several percher species of libellulids were present at the study site. These dragonflies are not known to use endothermy for thermoregulation or to increase hemolymph circulation to the abdomen to dissipate heat at high Ta;, and none was ever observed to partially submerge. It is suggested in aeshnids that partial submergence at high Ta; serves a thermoregulatory function by facilitating body heat dissipation from the abdomen.

Hydraulics of sharp-crested weir culverts with downstream ramps in free-flow, partially, and fully submerged-flow conditions

Laboratory experiments were conducted to investigate the hydraulics and discharge characteristics of sharp-crested weir culverts with downstream ramps for hydraulically smooth wall boundary and for free, partially submerged, and fully submerged-flow conditions. Four weir-culvert models were tested with different weir heights, ramp lengths, and culvert heights. The partially submerged-flow conditions were created when a slight increase in tailwater caused the headwater to rise due to partial submergence of the culvert. In this flow regime, supercritical flow over the ramp interacted with culvert outflow and this flow regime was classified as Supercritical Jet Interaction Regime or SJIR. Once tailwater reached the weir crest, the weir flow regime became submerged indicating fully submerged-flow condition. Based on the variations of water surface profiles, submerged flows were further classified into Surface Jump Regime (SJR), Surface Wave Regime (SWR), and Deeply Submerged Regime (DSR) and the boundaries between each flow regime were defined by regime plots. To predict discharge of weir culverts with downstream ramps, variations of discharge coefficient with weir geometry and flow regimes were studied and empirical formulations were developed. In addition, free and partially submerged flow discharges were predicted by implementing the interaction factor. It was found that the interaction factor was independent of the Froude number in SJR, while it correlated with the Froude number in SJIR. Under submerged-flow conditions, evaluation of the discharge characteristics of the proposed weir-culvert model showed correlations with water surface flow regimes and a three-stage prediction formula was proposed for estimation of submerged flow. The energy losses over weir-culvert models were also calculated and it decreased with submergence.