Waterlogged Treatments Research Articles

Effects of Waterlogging on Rice Growth at Jointing–Booting Stage

The rice waterlogging stress test was conducted at the experimental base of the College of Agriculture, Yangtze University, using Yangxian You 418 as the test subject, in order to investigate the impact of waterlogging on rice growth during the period from July to August each year. Six waterlogging stress tests with different waterlogging depth (1/4 plant height (1/4PH), 2/4 PH, and 3/4 PH) and duration (5 d and 7 d) were set up at the jointing–booting stage of rice (T1: 1/4 PH, 7 d; T2: 2/4 PH, 7 d; T3: 3/4 PH, 7 d; T4: 1/4 PH, 5 d; T5: 2/4 PH, 5 d; T6: 3/4 PH, 5 d;) with shallow water irrigation (CK) as control. The plant height, population leaf area, above-ground dry matter, and the yield of rice were measured. The correlation between the waterlogging depth and rice yield reduction was analyzed, and the flood disaster threshold index of rice was established. The results showed that at the end of stress, the plant height of all waterlogged treatments exceeded CK, and the plant height of T3 and T6 treatments significantly increased by 31.90% and 15.93%, respectively. The leaf area of rice treated with T1, T3, T4, and T5 was higher than CK (p < 0.05), and the above-ground dry matter of rice treated with T2, T3, T4, T5, and T6 was higher than CK (p < 0.05). When normal irrigation was restored to the maturity stage, the plant height of all rice treated with waterlogging was still higher than CK (p < 0.05). However, as the degree of waterlogging increased, rice yield decreased significantly, with a notable reduction of 31.68% observed in the T3 treatment compared to CK. Assuming a drainage index based on a 20% decrease in rice yield, it is imperative that the ratio of flooded depth to plant height remains below 37% when waterlogging persists for 7 days in rice cultivation. These research findings offer crucial scientific insights for implementing effective drainage management measures during flood disasters in rice paddies.

Leaf formononetin content of Trifolium subterraneum increases in response to waterlogging but its proportion of total isoflavones is little changed.

The isoflavone formononetin (F) impacts livestock fertility and cultivars of the pasture legume Trifolium subterraneum L. (subclover) have been selected for F levels ≤0.2% of leaf dry weight. However, the impact of waterlogging (WL) on isoflavones is little studied. We investigated the response of isoflavones, biochanin A (BA), genistein (G) and F, to WL for: (1) Yarloop (high F) and eight low F cultivars each from subspecies subterraneum , brachycalycinum and yanninicum (Experiment 1); and (2) four cultivars and 12 ecotypes of ssp. yanninicum (Experiment 2). WL impacted F: estimated means increased from 0.19% (control) to 0.31% (WL) in Experiment 1 and from 0.61% to 0.97% in Experiment 2. Isoflavones under WL were highly heritable, particularly F (H 2 =95%). The proportions of BA, G and F were little changed by WL, with strong positive correlations between free-drained and waterlogged treatments. Isoflavone contents were not related to WL tolerance, as assessed by shoot relative growth rate. In conclusion, isoflavones varied among genotypes and increased with WL, but the proportion of individual isoflavones in each genotype was stable. High F under WL was unrelated with genotype tolerance to WL. Instead, it was a consequence of inherently high F for that particular genotype.

Effect of Plant Growth-Promoting Bacteria Azospirillum brasilense on the Physiology of Radish (Raphanus sativus L.) under Waterlogging Stress

Stress due to waterlogging is considered an abiotic factor that negatively affects crop production, which, together with the excessive fertilization of crops, reduces cost-effectiveness and generates the need to create sustainable alternatives economically and environmentally. The effect of inoculation with Azospirillum brasilense on the physiology of the Raphanus sativus var. Crimson Giant subjected to waterlogging, was evaluated. Stomatal conductance, chlorophyll concentration and chlorophyll a fluorescence were analyzed to establish this effect, corroborating the beneficial effect of inoculation with A. brasilense in radish under waterlogging stress. The stomatal conductance of inoculated and waterlogged treatments presented the same values as the control plants, and photosystem II efficiency was favored in inoculated and waterlogged treatments (0.6 Fv/Fm) compared to non-inoculated and waterlogged treatments (0.3 Fv/Fm). The results suggested that this increased efficiency was due to the preservation of photosynthetic pigments in the tissues, allowing the preservation of stomatal conductance and a reduction in the amount of energy dissipated in the form of heat (fluorescence) due to inoculation with A. brasilense. Therefore, plant growth-promoting bacteria are responsible for activating and improving some physiological mechanisms of the plant.

Adaptation to Early-Season Soil Waterlogging Using Different Nitrogen Fertilizer Practices and Corn Hybrids

Excessive rainfall occurring in the early spring season in the Midwestern United States result in waterlogged soils contributing to corn production losses. The objective of our study is to evaluate the impact of soil waterlogging [non-waterlogged or waterlogged for 7 days when corn was at V3 growth stage (corn plant having three fully developed leaves with collar visible)], different pre-plant nitrogen (N) fertilizer sources and post-waterlogging rescue N fertilizer on grain and silage yield of two commercially available corn hybrids with different flood tolerance. Pre-plant N fertilizer was applied at 168 kg N ha−1. Nitrogen sources were a non-treated control (CO), polymer coated urea (PCU), urea (NCU), and urea plus Instinct (NCU + NI). A post-waterlogging rescue N fertilizer was applied at V7 as 0 or 83 kg N ha−1 of urea plus N-(n-butyl) thiophosphoric triamide (NBPT) (NCU + UI). Waterlogging decreased grain and silage yields in different years; however, significant interactions were observed among treatments. Rescue N applications increased grain yields by 6–46% in non-waterlogged treatments, but not in waterlogged treatments. The PCU and NCU + NI increased grain yields compared to the CO. Pre-plant N sources showed no significant differences in grain yield, probably due to existing environmental conditions or incorporation of fertilizer. The N source, application method, and timing for post-waterlogging rescue N application and flood-tolerant corn hybrids needs further investigation in poorly-drained claypan soils prone to waterlogging under a changing climate.

Spraying 6-BA could alleviate the harmful impacts of waterlogging on dry matter accumulation and grain yield of wheat.

BackgroundThe middle and lower reaches of the Yangtze River plain produce the second highest amount of wheat in China; however, waterlogging is an important environmental factor that substantially affects the yield production of wheat (Triticum aestivum L.) in this region.MethodsIn this study, seven treatments were implemented, including no waterlogging and exogenous 6-benzylaminopurine (6-BA) as a control (CK); waterlogging at booting (BW), anthesis (AW) and 15 days after anthesis (DAA, FW); and spraying 6-BA before waterlogging at booting (BW-6BA), anthesis (AW-6BA) and 15 DAA (FW-6BA), to determine the ability of 6-BA to alleviate the harmful impact of waterlogging on aboveground biomass production and grain yield. The widely cultivated wheat cultivar “Zhengmai 9023” was used.ResultsThe results showed that more than 190.0 mm of rainfall, which accounted for approximately 45.0% of the precipitation over the whole wheat growing season, was distributed after the booting stage (April and May). In all waterlogged treatments, the photosynthetic rate, aboveground biomass and grain yield decreased, but the differences between the CK and the FW treatment were not significant. The grain yield decreased by 18.38%, 41.79% and 5.67% in the BW, AW and FW treatments, respectively. Spraying 6-BA before waterlogging enhanced the root activities after anthesis and then decreased the malondialdehyde concentrations of the flag leaves and the third leaf, increased the photosynthetic rate of the flag leaves and enhanced aboveground biomass and grain yield. Among the increments between the treatments, the increments between the BW and BW-6BA treatments were the largest, but between the FW and FW-6BA were smallest. In comparison to the other waterlogging treatments, the grain yields from the FW and FW-6BA treatments were significantly higher because of the higher kernel numbers per spike. The results indicated that waterlogging after the booting stage restrained the dry matter production of winter wheat, but spraying 6-BA before waterlogging slowed the plant senescence rate and reduced grain yield loss.

Morpholoical and enzymatic responses to waterlogging in three Prunus species

Anaerobic respiration is an important mechanism for plants to address energy deficiency under waterlogged (WL) conditions, when aerobic respiration is limited. Seedlings of three Prunus species—Prunus mira Koehne, Prunus persica (L.) Batsch, and Prunus amygdalus (L.)—were irrigated at 60% water (control) or waterlogged (100%) daily for 27 days, to investigate root morphological parameters and dynamics of anaerobic respiration enzymes. Both P. mira and P. persica had significantly increased the leaf number and plant height than P. amygdalus under WL. Additionally, WL decreased leaf chlorophyll content in P. mira and P. amygdalus significantly more than in P. persica. Root pyruvate carboxylase (PDC), alcohol dehydrogenase (ADH), and lactate dehydrogenase (LDH) activities first increased before decreasing under WL treatments. In P. persica, root PDC activity was significantly higher than in P. mira and P. amygdalus at 9 d and 21 d, whereas ADH activity was higher at 15 d, 21 d, and 27 d. Moreover, throughout the experiment, LDH activity was significantly higher in P. persica than in P. mira and P. amygdalus roots under WL treatments. The activities of all three measured enzymes were positively and significantly correlated. We suggest that, because of interspecific variation in root metabolic response to different environmental conditions, P. mira and P. persica may generate more energy anaerobically through EMP than through lactic-acid metabolism, whereas P. amygdalus was the reverse. We conclude that WL tolerance differed across the three Prunus, with P. persica being the most tolerant, followed by P. mira, and finally P. amygdalus.

Performance of Pongamia pinnata (L.) Pierre Seedlings in Nursery Under Salt and Water Stress Conditions

Pot culture experiments were conducted with twenty treatment combinations of salt and water stress following Randomized Complete Block Design in the nursery of Tropical Forest Research Institute, Jabalpur for one year. 4, 8 and 12 ds/m concentrations of salt in combination with moderate and severe drought & moderate and severe waterlogged treatments in the soil were applied. The amount of water equal to the field capacity of the soil was given to each treatment (24.86%). The drought conditions were maintained according to Permanent Wilting point (PWP), which was calculated on the basis of Cumulative Pan Evaporation (CPE) values measured through Open Pan Evaporimeter. It was observed that height and collar diameter of P. pinnata seedlings decreased with increase in drought conditions but increased with increase in severity of waterlogging. Growth characteristics significantly decreased with increase in concentration of salts in the soil. Cumulative effect of water and salt stress was found to be more pronounced than individual stress.

Effect of Waterlogging on Element Concentrations, Growth and Yield of Wheat Varieties Under Farmer’s Sodic Field Conditions

Six promising waterlogging tolerant varieties of wheat along with two local varieties were evaluated on farmer’s sodic field (pH, 8.9) under drained and waterlogged conditions. Waterlogging was imposed for 12 days at 25 days after sowing. The redox potential (Eh) value of the soil was reduced to +90 mV at 12 days of waterlogging and after removal of surface water, 16 days were taken to reach above the anoxic limit (≤+350 mV) of soil. Waterlogging reduced significantly the shoot dry weight of all varieties, but to a lesser extent for the tolerant varieties, KRL3–4, Kharchia65 and KRL99. Waterlogging caused many fold increase in leaf Fe, Al, Na and Na/K ratio and decrease in leaf K, P and S as compared to drained treatment; these increases or decreases in elements were above or below their critical toxicity or deficiency levels. The waterlogging tolerance of varieties based on relative shoot dry weight showed a significant negative correlation with leaf Na and Na/K ratio. As compared to drained condition, the reduction in grain yield ranged from 11 to 27 % in waterlogged treatments. KRL3–4 and NW1014 showed less yield loss and had significantly higher grain yield than local variety under waterlogging. Thus, these two varieties can be recommended for planting in study area. These results suggest for selecting a right tolerant variety for increasing wheat yield in a specific soil and waterlogging environment.

Waterlogging responses of Schoenoplectus scirpoides (Schrad) Browning (Cyperaceae)

AbstractWaterlogging responses of an emergent freshwater macrophyte, Schoenoplectus scirpoides, were investigated by carrying out laboratory and field experiments. Soil cores containing uniform plants of S. scirpoides were subjected to drained, 1/3 flooded, alternately flooded and drained at weekly intervals, and continuously flooded treatments for 6 months. Mean soil redox potential of the drained soil was 225 ± 29 mV and was significantly lower in the other treatments. Total dry biomass, above‐ground biomass and number of culms in the flooded/drained and flooded treatments were significantly higher than those in the drained and 1/3 flooded treatments. Below‐ground/above‐ground biomass ratios were highest in the drained treatment and significantly lower in the waterlogged treatments. Plant height and the growth rate of culms were least in the drained treatment and significantly higher in the other treatments. Culm specific gravity decreased significantly with increase in soil moisture. In the field study, soil redox potentials were moderately reduced in the inland and streamside sites, while culm elongation rate was significantly higher by 94% in the streamside compared with the inland site. Optimum growth occurred under flooded conditions, suggesting that the species could flourish with increasing water intrusion in estuarine areas, as predicted by global climate change.

Genetic diversity, seed traits and salinity tolerance of Millettia pinnata (L.) Panigrahi, a biodiesel tree

The leguminous tree, Millettia pinnata (pongamia) produces oilseed suitable for biodiesel production. Assessment of oil production and genetic, morphological and physiological traits are required. Collections from the Forest Products Commission in Kununurra, Western Australia were compared with accessions from India, Indonesia, Queensland and the Northern Territory in Australia. Molecular diversity, examined using the internal transcribed spacer region, indicated distinctiveness of genotypes from Java, Indonesia. Seed traits varied across trees with the smallest seeds from Indonesia and the largest from Kununurra. Oil content varied across trees with a minimum of 28 % in an Indonesian accession and the highest of 45 % from Kununurra. Major fatty acids across trees were oleic (51 %), linoleic (19 %), palmitic (11 %) stearic (6 %), linolenic (4.5 %) and behenic (4.5 %) acids. Seed weight and oil content per seed of developing seeds increased with a sigmoid pattern and oleic acid was the major fatty acid throughout seed development. Waterlogging and salinity tolerance were assessed. Four month-old seedlings from Kununurra, Western Australia and India were exposed to: non-saline drained control, saline drained, non-saline waterlogged and saline waterlogged treatments. Seedlings were waterlogging tolerant. Salt, applied in weekly increments of 50 mM, led to reduced survival, height growth rate, leaf number and stomatal conductance and increased concentrations of leaf Na+ and Cl−. Salinity tolerance was 200 mM NaCl under saline drained and 150 mM NaCl under waterlogged conditions. Milletia pinnata diversity could be exploited for selection of superior genotypes for oil production on marginal land.

Tracing Si–N–P ecosystem-pathways: is relative uptake in riparian vegetation influenced by soil waterlogging, mowing management and species diversity?

Despite the growing concern about the importance of silicon (Si) in controlling ecological processes in aquatic ecosystems, little is known about its processing in riparian vegetation, especially compared to nitrogen (N) and phosphorus (P). We present experimental evidence that relative plant uptake of N and P compared to Si in riparian vegetation is dependent on mowing practices, water-logging and species composition. Results are obtained from a controlled and replicated mesocosm experiment, with a full-factorial design of soil water logging and mowing management. In our experiments, the Si excluding species Plantago lanceolata was dominant in the mown and non-waterlogged treatments, while Si accumulating meadow grasses and Phalaris arundinacea dominated the waterlogged treatments. Although species composition, management and soil moisture interacted strongly in their effect on relative Si:N and Si:P uptake ratios, the uptake of N to P remained virtually unchanged over the different treatments. Our study sheds new light on the impact of riparian wetland ecosystems on nutrient transport to rivers. It indicates that it is essential to include Si in future studies of the impact of riparian vegetation on nutrient transport, as these are often implemented as a measure to moderate excessive N and P inputs.

Preliminary Evidence that Copper and Zinc Inhibits the Dissipation of Synthetic Pyrethroid in Red Soil

Extensive use of synthetic pyrethroids has resulted in concerns regarding their potential effects on human health and ecosystems. In the present study, we evaluated the influence of coexisting Cu2+, Zn2+, soil water contents (15%, 25%, 40% by weight and waterlogged) and temperature levels (15°C, 25°C, 35°C, and 45°C) on the dissipation of cypermethrin, fenvalerate and deltamethrin in red soil. To further clarify the influence of Cu2+ and Zn2+ on biological and chemical dissipation processes, serial concentrations of the synthetic pyrethroids containing Cu2+ (21.3, 50, 100, and 400 mg kg−1) and Zn2+ (35.8, 100, 250, and 500 mg kg−1) were used to spike the soil and then incubated at 25°C in the dark at 25% moisture. The results revealed a very severe inhibitory effect on the dissipation rates with increasing Cu2+ and Zn2+ levels. Conversely, there were no significant decreases in dissipation rates in response to exposure to 50 mg kg−1 Cu2+ or 100 mg kg−1 Zn2+, and the dissipation rates decreased significantly (p < 0.05) when the Cu2+ and Zn2+ concentration increased to 100 and 250 mg kg−1, respectively, which were the respective maximum field recommended rates. When compared with unsterilized batch treatments, the t 1/2 in sterilized (chemical dissipation) batch treatments increased by 1.0–4.8-fold. Additionally, there was a highly significant difference in the dissipation of pyrethroids in the 15% water content treatments and waterlogged treatments (p < 0.05). Finally, the difference in the dissipation rates at 15°C and 25°C was significant (p < 0.05).

Root morphology is related to the phenotypic variation in waterlogging tolerance of two populations of Suaeda salsa under salinity

The effects of waterlogging and salinity on seedling emergence, seedling growth and ion accumulation in a euhalophyte Suaeda salsa in an intertidal zone and on saline inland soil were investigated. Seedlings of S. salsa from the intertidal zone emerged more rapidly than those of the inland population under both waterlogged and drained conditions. Waterlogging and salinity had no adverse effects on seedling emergence of S. salsa from the intertidal zone, but markedly inhibited this parameter in the inland population. Waterlogging did not affect the seedling survival, shoot dry mass, and shoot height in high salinity in S. salsa from the intertidal zone, while the opposite trend was shown in the inland population. The root dry mass was higher in S. salsa from the intertidal zone as compared to the inland population, in waterlogged treatments by 1.9, 1.3, and 1.5 times in 1, 200, and 600 mM NaCl, respectively, and in drained treatments by 1.8, 2.3, and 3.0 times in 1, 200, and 600 mM NaCl, respectively. Waterlogging increased Na+ and K+ concentrations in high salinity, but waterlogging had no effect on Cl- concentration in shoots of S. salsa from the intertidal zone. In all NaCl treatments, waterlogging had no effect on concentrations of these ions in shoots of S. salsa from the saline inland site. In a field investigation, the fresh mass of shoots and roots were lower, whereas the root/shoot ratio was 1.5 times higher in S. salsa from the intertidal zone, compared with the inland population. These findings indicate that S. salsa population from the intertidal zone is more waterlogging tolerant than the inland population. S. salsa from the intertidal zone produced relatively more root biomass and this might help anchor plants against tidal action in the intertidal zone. The physiological and morphological characteristics may determine the natural distributions of the two S. salsa populations in their different saline environments.

Short‐term waterlogging has long‐term effects on the growth and physiology of wheat

Summary The effect of different durations of waterlogging and subsequent drainage is described for 3‐wk‐old wheat (Triticum aestivum) plants. In a pot experiment, plants were subjected to waterlogging to the soil surface for 0, 3, 7, 14, 21 or 28 d, and then drained to allow recovery for up to 25 d. During waterlogging, the seminal root system stopped growing. Adventitious roots grew to a maximum length of c. 150 mm. Leaf nitrogen concentration was severely decreased by waterlogging. When waterlogged pots were drained, seminal root mass did not recover to control values, even when waterlogging lasted only 3 or 7 d, due to death of existing apices and no initiation of new lateral roots. By contrast, adventitious roots resumed elongation after drainage. By the end of the experiment, shoot mass remained two‐ to threefold lower in plants from all waterlogged treatments compared with continuously drained controls, due to lower tiller numbers and shorter final leaf lengths in previously waterlogged plants. The results demonstrate that even short periods (as little as 3 d) of waterlogging have considerable long‐term effects on the growth of young wheat plants.

Changes in physiological and morphological traits of roots and shoots of wheat in response to different depths of waterlogging

The growth reduction of wheat (Triticum aestivum L.) during and after waterlogging stress depends on the depth of water from the soil surface. In a pot experiment with 3-week-old plants, soil was waterlogged for 14 d at the surface, or at 100 or 200 mm below the surface, and pots were then drained to assess recovery. A fully drained treatment kept at field capacity served as control. During waterlogging, the relative growth rate of roots decreased more than that of shoots (by 6–27% for shoots, by 15–74% for roots), and plant growth was reduced proportionally as the water level was increased. Light-saturated net photosynthesis was reduced by 70–80% for the two most severe waterlogging treatments, but was little affected for plants in soil waterlogged at 200 mm below the surface. The number of adventitious roots formed per stem in plants grown in waterlogged soil increased up to 1.5 times, but the number of tillers per plant was reduced by 24–62%. The adventitious roots only penetrated 85–116 mm below the water level in all waterlogging treatments. Adventitious root porosity was enhanced up to 10-fold for plants grown in waterlogged soil, depending on water level and position along the roots. Porosity also increased in basal zones of roots above the water level when the younger tissues had penetrated the waterlogged zone. Fourteen days after draining the pots, growth rates of plants where the soil had been waterlogged at 200 mm below the surface had recovered, while those of plants in the more severely waterlogged treatments had only partially recovered. These findings show that the depth of waterlogging has a large impact on the response of wheat both during and after a waterlogging event so that assessment of recovery is essential in evaluating waterlogging tolerance in crops.

N 2O and CH 4 emission and CH 4 consumption in a sugarcane soil after variation in nitrogen and water application

Nitrous oxide (N 2O) and methane (CH 4) exchanges between the soil and the atmosphere are influenced by management practices currently used in agriculture. This study was conducted to determine whether N 2O and CH 4 emission and CH 4 consumption in a trash blanketed sugarcane soil could be influenced by changed N fertiliser practice and variation in soil water content. Microplots were placed in rows of sugarcane and urea and ammonium sulphate (both 99 atom % 15N excess) applied to the soil surface, urea as both a split application of 80 kg N ha −1 and a full rate of 160 kg N ha −1 and ammonium sulphate at 160 kg N ha −1. Sugarcane trash (15 t ha −1) was applied to the surface of all microplots. Water was then added to all microplots to achieve water contents of 80% water-filled pore space (WFPS) in half the plots and saturation in the other half. Initially, the application of urea at 160 kg N ha −1 to microplots at 80% WFPS resulted in greater emission of ( 14N+ 15N)–N 2O than was recorded from the split urea and the ammonium sulphate treatments at both moisture regimes. A mean value of 47 g N 2O–N ha −1 d −1 was measured for this treatment compared with 18.5 and 15.2 g and 4.9 and 7.7 g N 2O–N ha −1 d −1 for the split urea and ammonium sulphate waterlogged and 80% WFPS treatments respectively. Greater emissions of ( 14N+ 15N)–N 2O were measured following 132 mm rainfall in February, with mean values of 214 and 143 g N 2O–N ha −1 d −1 being recorded for the waterlogged treatments of the split urea and ammonium sulphate treatments respectively. A decrease in the 15N–N 2O emission from the split urea treatment was the only difference recorded when comparing the initial ( 14N+ 15N)–N 2O and 15N–N 2O emissions from all treatments. 14N–N 2O appeared to be the major gaseous N product from this treatment initially. Total emission of 15N–N 2O ranged from 105 to 453 g N 2O–N ha −1, which represented between 25.3 and 23.4% of the total amount of N 2O evolved. CH 4 emission occurred from all microplots fertilised with urea whereas CH 4 consumption was measured in plots fertilised with ammonium sulphate only. CH 4 emission ranged from 297 to 1005 g CH 4–C ha −1 while CH 4 consumption ranged from 442 to 467 g CH 4–C ha −1. The application of ammonium sulphate and using a split application of urea initially decreased N 2O emissions but the delay in nitrification obtained from changing the type and rate of application of these fertilisers resulted in greater N 2O emissions later in the season when the soil moisture regime had changed. CH 4 emission and consumption were not affected by these management changes.

The role of limited oxygen supply and soil microorganisms on germination and survival of lupin seeds (Lupinus angustifolius L. cv. Gungurru) in waterlogged soil

The role of limited oxygen supply and soil microorganisms in the germination and survival of lupin seeds was studied in waterlogged soil and in solution culture at low oxygen pressures. Oxygen pressures in soil solutions decreased with time in all waterlogged soil treatments and in stagnant solution culture containing seeds. No seeds germinated in unsterilised waterlogged soil, but up to 95% of seeds germinated after 6 days in sterilised waterlogged soil. Germination and survival of seeds decreased significantly with time in solution cultures at 0 or 2 kPa O2, but remained high at 21 kPa O2. These solution culture studies confirmed that low oxygen supply in soil during waterlogging, which resulted mainly from activity of micro-oganisms, was the major factor causing the reduction in survival of lupin seed in waterlogged soil.

Oxygen insensitivity of photosynthesis by waterlogged Apios americana

Apios americana, a tuber-producing viny legume, occurs naturally in areas which experience episodic soil waterlogging. In a 2-year study, plants were grown under well-drained or waterlogged soil conditions. Tuber production did occur in the waterlogged situation, but yield was substantially depressed. Specific leaf weight increased by a factor of 40% compared to the well-drained controls. Likewise, increases in soluble carbohydrate and starch were observed in leaf tissue under waterlogged conditions. Because of the increase in carbohydrate content in the foliage with waterlogging, plants were probed for feedback limitations on photosynthesis. Net assimilation rates of single leaves measured under ambient conditions were not different between well-drained and waterlogged treatments. However, oxygen insensitivity of photosynthesis was observed under waterlogged conditions, particularly in one genetic line which had high mortality in the waterlogged treatment. Well-drained plants demonstrated similar stimulations of photosynthesis by 2% oxygen regardless of genetic background. No interaction was observed between drainage and oxygen content of the assay gas in determining stomatal conductance values. Oxygen insensitivity of photosynthesis may be an indication of poor adaptation to rootzone waterlogging.

Response to Salt and Waterlogging Stress of Ten Taxa of Acacia Selected From Naturally Saline Areas of Western Australia

Ten taxa of Acacia were selected from areas of moderate to high soil salinity (electrical conductivities of saturated soil paste extracts (ECe) between 1000 mS m--1 and 4800 mS m-1 at 50-600 mm depth) and sodicity to test the tolerance of young, symbiotic plants to increasing levels of salinity both with and without waterlogging. Nodulated plants, 3 months old, were grown in glasshouse experiments which consisted of four treatments: non-saline drained control (12 weeks); saline drained (12 weeks); non-saline waterlogged (5 weeks); and saline waterlogged (5 weeks). Acacia cyclops, A. brumalis, A. redolens (Ravensthorpe) and A. aff. lineolata had 100% survival after 12 weeks irrigation with saline solution (final ECw = 9500 mS m-1). Generally, the species tested were sensitive to waterlogging with A. patagiata, A. cyclops and A. brumalis being the most sensitive, having 19-44% mortality with no salt in the solution. The combined treatment of salt and waterlogging greatly increased the mortality of plants, with four species having &gt; 70% dead after 5 weeks treatment (ECw = 3900 mS m-1). A. aff. lineolata and A. mutabilis subsp. ,stipulifera were highly tolerant of salt plus waterlogging, with 100% and 96% survival respectively. In salt plus waterlogged treatments, Na+ concentration in phyllodes of all taxa exceeded (0.37-2.13 mmol g-1 dry wt) that taken up by plants in freely drained salt treatments (0.03-0.42 mmol g-1 dry wt). Taxa with the slowest rates of growth tended to accumulate the highest concentrations of Na+ in the uppermost phyllodes. Provenances of A. redolens and A. patagiata collected from sites of high soil salinity (ECe &gt; 2200 mS m-1) had less than half the Na+ concentration in uppermost phyllodes (0.22 mmol -1 dry wt) at the termination of the salt treatment, compared with provenances of the same species collected from moderately saline areas (ECe = 1100 mS m-1). This indicates that Acacia provenances collected from the most saline sites had greater potential to survive high levels of external salinity in the longer term than those from less saline sites.

Nitrogen transformations in soil and rhizosphere of rice plants

Summary Different nitrogen forms (ammoniacal, nitrite and nitrate nitrogen) were determined in a pot experiment during 14 weeks to detect the nitrogen transformations in the soil and rhizosphere of rice plants. The results showed that ammoniacal nitrogen generally increased up to the 6th week after flooding and decreased thereafter in organic manured and unmanured treatments. High nitrate figures were recorded throughout the experiment in organic manured treatments, while nitrite figures showed no considerable amounts throughout the experiment. The amount of Jiitrate-N continuously decreased in both planted and unplanted waterlogged treatments, but the rate of decrease was slower in planted than in unplanted treatments. The results also showed that nitrate content of normally irrigated soil was much higher than that detected in waterlogged soils.