Unflooded Plants Research Articles

Photosynthesis and Survival of Young Carpotroche brasiliensis Endl. (Achariaceae) Plants Subjected to Flooding

Abstract Carpotroche brasiliensis is a native tree of the Brazilian Atlantic Forest with potential economic value for cultivation in agroforestry systems. We conducted an experiment to determine the photosynthetic and survival responses of young C. brasiliensis plants to electrochemical changes in flooded soils as an indication of their flood tolerance and potential for cultivation in flood-prone areas. Soil flooding decreases the reduction–oxidation potential (redox) potential (Eh), pH, and electrical conductivity (Ec) of the soil, with subsequent recovery of the pH and Ec. Decreases in Eh negatively affect net photosynthesis (A). In flooded soil, decreased A was associated with decreased stomatal conductance (gs) and after 21 days was also associated with decreases in the instantaneous carboxylation efficiency (A/Ci) and potential quantum yield of photosystem II (Fv/Fm). Although flooded C. brasiliensis seedlings developed morphological structures known to increase flood tolerance, this was not enough to prevent severe signs of flooding stress. After 21 days of flooding, flooded plants were unflooded, and 17 days after plants were removed from flood, 90 percent of the unflooded plants died. Our results demonstrate that young plants of C. brasiliensis are suitable for planting in agroforestry systems only in areas with well-drained soils.

Vascular Cavity Formation Enhances Oxygen Availability during Flooding in Root Tips of Phaseolus coccineus L. Primary Roots

Premise of research. Vascular cavities (VCs) form in the primary roots of many species of cool-season herbaceous legumes when the growing medium is saturated and relatively warm (>15°–20°C). Circumstantial evidence has suggested that VCs that rapidly form following flooding of these roots are a form of inducible aerenchyma that confers tolerance to waterlogging. This study was undertaken to directly confirm that, once formed, VCs improve internal and rhizosphere oxygen levels in and around tips of roots in which they occur.Methodology. Seedlings of Phaseolus coccineus were flooded after various periods of growth for 24 and 48 h and compared to unflooded plants. Some roots were freehand sectioned to confirm and locate VCs. Some root segments were embedded, sectioned, and photographed for image analysis of cortical intercellular porosity. An oxygen photomicroprobe was used to measure oxygen concentration in the rhizosphere at root surfaces and internally by penetration through roots.Pivotal results. Flooding rapidly depleted oxygen in the rhizosphere and within root-tip tissue. VCs formed within 24 h near root tips. Surface measurements showed that, after formation, VCs elevated rhizosphere oxygen levels at root tips compared to those measured 2 h after flooding. Internal measurements showed very low oxygen concentration in vascular tissue 2 h after flooding that significantly improved after VC formation 22 h later. In addition to VC formation, flooding induced an increase in cortical porosity along the root axis.Conclusions. VCs enhance internal and rhizosphere oxygen concentrations in P. coccineus primary roots within 24 h after flooding. VCs are therefore verified as a form of inducible aerenchyma.

Identification of Flooding-Response Genes in Eggplant Roots by Suppression Subtractive Hybridization

Roots of eggplant (Solanum melongena L.) cv. Pingtong Long Eggplant (EG117) were subjected to ten flooding treatments. Messenger RNAs from plants subjected to flooding periods for 0.25 to 1 and 3 to 12 h as well as unflooded plants (control) were used as the tester and driver samples, respectively. Following suppression subtractive hybridization, polymerase chain reaction (PCR) products were ligated into a cloned vector for Escherichia coli-competent cell transformation, followed by nested PCR screening of positive cDNA inserts. PCR products of these unique clones were digested with Sau3AI to identify any differentially displayed banding patterns. Recombinant cDNA clones were then picked for plasmid extraction and then sequenced. Using BLAST and Gene Ontology database searches, 25 of these unigenes were found to be involved in metabolism, regulation, stress, and development categories, whereas nine novel genes with unknown functions that may have potential roles in flooding stress in eggplant were also identified. Five differentially expressed gene transcripts with known functions were randomly selected for real-time reverse-transcription quantitative PCR to investigate plants subjected to flooding stress from 0 to 72 h. All genes were upregulated in flood treatments (15 min to 72 h) when compared to the control. These findings indicated that flood-induced genes were closely related to various metabolic pathways and involved in genetic regulation of flood stress response.

Effect of soil flooding on photosynthesis, carbohydrate partitioning and nutrient uptake in the invasive exotic Lepidium latifolium

Lepidium latifolium L. is an invasive exotic crucifer that has spread explosively in wetlands and riparian areas of the western United States. To understand the ecophysiological characteristics of L. latifolium that affect its ability to invade riparian areas and wetlands, we examined photosynthesis, chlorophyll concentration, carbohydrate partitioning and nutrient uptake in L. latifolium in response to soil flooding. Photosynthesis of flooded plants was about 60–70% of the rate of unflooded controls. Chlorophyll concentrations of flooded plants were about 60–70% of the unflooded plants during 15–50 days of flooding. Flooding resulted in an increase in leaf starch concentration, but root starch concentration was not significantly affected. However, concentrations of soluble sugar were significantly higher in both leaves and roots of flooded plants than unflooded controls. On day 50 after initial flooding, the concentrations of N, P, K and Zn in leaves of flooded plants were lower than in control plants. The concentrations of Mn and Fe in leaves of flooded plants were eight and two times those of control plants, respectively. In contrast, N, P, K and Zn concentrations of roots of flooded plants were slightly higher than in unflooded plants. The concentrations of Fe and Mn in roots of flooded plants were 15 and 150 times those of the control plants, respectively. The transport of P, K, and Zn to shoots decreased and that of Mn increased under flooding. The accumulation of N, K and Zn in roots decreased and that of Mn increased in response to flooding. The results suggested that the maintenance of relatively high photosynthesis and the accumulation of soluble sugar in roots of flooded plants are important adaptations for this species in flooded environments. Despite a reduction in photosynthesis and disruption in nutrient and photosynthate allocation in response to flooding, L. latifolium was able to survive 50 days of flooding stress. Overall, L. latifolium performed like a facultative hydrophyte species under flooding.

Different patterns of aerenchyma formation in two hygrophytic species of Paspalum (Poaceae) as response to flooding

Paspalum modestum and P. wrightii are perennial grasses growing in permanent and seasonally flooded areas, respectively. The former produces short rhizomes and floating culms, the latter forms long rhizomes and erect culms. Variations in percentage aerenchymatous space (PAS) in different organs as a response to flooding was analysed using a clone of each species. Eighteen plantlets of each clone were cultivated during 7 months under flooded vs. unflooded conditions. After this period, roots, rhizomes, culms, and leaf sheaths were collected and prepared. PAS was measured using an image analysis device, and data were analysed using ANOVA. Production of aerenchyma took place in both species within the cortical parenchyma of roots, rhizomes and culms, and the mesophyll of leaf sheaths, both in flooded and unflooded plants. Under flooding conditions PAS increased in both species, although the individual response of organs differed: whereas in P. modestum PAS increased primarily in substratum-fixed roots, in P. wrightii all organs produced additional aerenchyma uniformly. Contrasting responses are understood as adaptations to permanent and seasonal flooding, respectively.

Seasonal flooding regimes influence survival, nitrogen fixation, and the partitioning of nitrogen and biomass in Alnus incana ssp. rugosa

Alteration of natural flooding regimes can expose lowlands to waterlogged soil conditions during any month of the year. The seasonality of flooding may have profound effects on the carbon and nitrogen budgets of N-fixing alders (Alnus spp.), and in turn, may impact the C and N economy of extensive alder-dominated, wetland ecosystems, including those dominated by speckled alder (Alnus incana ssp. rugosa). To better understand this process, two-year-old, nodulated seedlings of speckled alder were subjected to late spring (May 10 – July 10), summer (July 10 – September 8), and fall (September 8 – November 8) flooding treatments. Alders were root-flooded outdoors in tanks containing an N-free nutrient solution and compared with unflooded alders at the experimental site. Flooding arrested N fixation, photosynthesis, and growth of alders without recovery in all flooding treatments for the remainder of the growing season. Late spring and summer flooding resulted in complete mortality of alders while all seedlings survived flooding in the fall. Fall flooding increased foliar N resorption by 140% over unflooded seedlings. Eighty-seven percent of the total N fixed and 89% of biomass accumulation for the entire growing season occurred in unflooded alders after July 10. In unflooded alders, nitrogen fixation rates per unit mass declined by 63% for nodules, 28% for leaves, and 48% for whole seedlings during the fall, while total N fixed per plant in the fall was similar to that fixed in the summer. The majority of newly fixed N in unflooded alders was allocated to leaves before September 8 and to roots/nodules combined after September 8. In unflooded plants, the greatest proportion of new biomass was partitioned to leaves before July 10, to stems between July 10 and September 8, and equally to stems and roots/nodules after September 8. Fall-flooded alders did not increase root or nodule biomass. Proportional allocation of plant resources were such that the ratio of N fixed to seedling growth of unflooded alders decreased by 19% during summer before rebounding by 6% in fall. Seasonality of flooding alters seedling survival, growth, and resource allocation, and may be a critical determinant of speckled alder recruitment and occurrence in wetlands.

Flooding influences ovipositional and feeding behavior of the rice water weevil (Coleoptera: Curculionidae).

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the United States. As part of an effort to develop strategies to manage this pest, the ovipositional and feeding habits of L. oryzophilus on rice plants subjected to different flooding treatments were characterized in greenhouse studies. Presence and depth of flood had a direct influence on the ovipositional behavior of weevils in no-choice studies. More eggs were found in flooded plants than in unflooded plants. Moreover, plants flooded to a depth of 5.1 cm received more eggs than plants flooded to depths of 1.3 or 10.2 cm. Presence and depth of flood influenced both the proportion of females that oviposited in plants and the number of eggs laid by those females that did oviposit. In choice studies, female weevils showed a marked ovipositional preference for plants flooded to a depth of 10.2 cm over unflooded plants and plants flooded to a depth of 1.3 cm. In separate choice experiments, adult rice water weevils fed more on flooded plants than on unflooded plants. In a third set of experiments, flooded plants were taller and had higher concentrations of 10 of 13 plant nutrients than unflooded plants. Thus, flooding may influence rice water weevil behavior both directly, by acting as a stimulus for feeding or oviposition, and indirectly, by inducing changes in the suitability of rice plants for feeding or oviposition. These data suggest that it may be possible to manipulate populations of weevils in rice by changing water management practices.

Flooding induces a suite of adaptive plastic responses in the grass Paspalum dilatatum

Summary We studied individual responses to flooding in the perennial grass Paspalum dilatatum, a widespread species in the Flooding Pampa of Argentina, using plants established in species‐diverse grassland microcosms. Flooding effects were evaluated on root and leaf sheath anatomy and shoot morphological traits. Leaf water status and CO2 exchange rates were monitored in flooded and unflooded plants under changing, natural and controlled atmospheric conditions. Root porosity and leaf sheath aerenchyma increased with flooding. Leaf extension rates and tiller height were also higher in flooded plants, which resulted in a large fraction of the shoot architecture emerging above the water surface. Flooding enhanced stomatal conductance, leaf water potential and net photosynthesis, especially under conditions leading to high air‐vapour pressure deficits. Therefore, flooded plants experienced fewer water deficits during periods of high atmospheric evaporative demand. P. dilatatum showed tight regulation of water and carbon relations under severe soil‐oxygen deficiency, even in the presence of natural competitors. The suite of adaptive responses documented here might help to explain the observed increase in abundance of this species during extensive floods.

Responses to flooding intensity in Leontodon taraxacoides

Natural flooding is one of the major factors affecting vegetation dynamics in many regions of the world. The Flooding Pampa Grasslands (Argentina) are frequently exposed to flooding events of diverse intensity and duration, some of which Leontodon taraxacoides, an exotic dicot. frequent in these grasslands, seems to survive. Its responses to four different water depths (0, 1, 7 and 13 cm) were studied. The results indicate that plants in conditions of total submergence (depth of 13 cm) did not survive. In less severe flood conditions, increases in the leaf insertion angle resulted in the maintenance of a large proportion of the total leaf area above the water. Differences in leaf length and a decrease in the width and the proportion of lobes per leaf were also found under partial submergence conditions (depth of 7 cm). Root and leaf aerenchyma, present in unflooded plants, showed a significant increase in flood conditions. In spite of the anatomical and morphological responses, total biomass and leaf area were severely affected by water depth. Control plants allocated more biomass to reproductive organs, while partly submerged plants allocated more to leaves and less to reproductive organs. Mature L. taraxacoides plants presented a wide range of plastic adjustment as a survival strategy in soil anaerobiosis, and appear to be able to survive short spring floods in a vegetative state; in contrast, they might not tolerate total submergence conditions imposed by more intense and long‐lasting floods.

Can early wilting of old leaves account for much of the ABA accumulation in flooded pea plants?

When pea plants (Pisum sativum L.) were subjected to flooding, abscisic acid (ABA) content in shoots and roots increased up to 8-fold in the following days and stomatal conductance significantly decreased. Although young leaves of flooded plants had a slightly higher water potential than those of the unflooded plants, old leaves had lower water potential and lost turgor at the time when a substantial ABA increase was detected. In plants where the old leaves were clipped off, flooding did not cause any ABA increase during 7 d of the experimental period, except under conditions of higher transpiration demand, when the increase in ABA content was both delayed and small in scale (only I-fold). When intact plants were flooded and ABA was assayed separately in both old and young leaves, the ABA increase in old leaves preceded that in young leaves. Evidence here suggests that the flooding-induced ABA increase mainly results from the wilting of old leaves. This suggests that young leaves may be protected from wilting by ABA originating in old leaves under unfavourable environmental conditions.

Flooding, Hydraulic Conductivity, and Root Electrolyte Leakage of Rabbiteye Blueberry Plants

Abstract The relationship of root (RLp) and stem hydraulic conductivity (SLp), root electrolyte leakage (EL), and stomatal conductance (gs) to flooding was investigated using 2-year-old ‘Tifblue’ and ‘Woodard’ rabbiteye blueberry (Vaccinium ashei Reade) plants. Soil redox potentials (Eh) decreased to about — 225 mV within 4 to 10 days of flooding, whereas Eh of unflooded soils were always > 400 mV. Root hydraulic conductivity decreased by 44% to 60%, compared to that of unflooded plants after 4 to 6 days of flooding in two of three experiments, decreasing by 29% to 81% by the end of 2 to 3 weeks. Root electrolyte leakage increased and SLp decreased after 6 to 10 days of flooding. Stomatal conductance decreased by 49% to 93% compared with that of unflooded plants after 4 to 6 days of flooding. Decreases in RLp and gs for flooded plants occurred concomitantly and are two of the earliest physiological responses of rabbiteye blueberry plants to flooding.

Flooding, gas exchange and hydraulic root conductivity of highbush blueberry

Highbush blueberry plants (Vaccinium corymbosum L. cv. Bluecrop) growing in containers were flooded in the laboratory for various durations to determine the effect of flooding on carbon assimilation, photosynthetic response to varying CO2 and O2 concentrations and apparent quantum yield as measured in an open flow gas analysis system. Hydraulic conductivity of the root was also measured using a pressure chamber. Root conductivity was lower and the effect of increasing CO2 levels on carbon assimilation less for flooded than unflooded plants after short‐(i‐2 days), intermediate‐(10–14 days) and long‐term (35–40 days) flooding. A reduction in O2 levels surrounding the leaves from 21 to 2% for unflooded plants increased carbon assimilation by 33% and carboxylation efficiency from 0.012 to 0.021 mol CO2 fixed (mol CO2)−1. Carboxylation efficiency of flooded plants, however, was unaffected by a decrease in percentage O2, averaging 0.005 mol CO2 fixed (mol CO2)−1. Apparent quantum yield decreased from 2.2 × 10−1 mol of CO2 fixed (mol light)−1 for unflooded plants to 2.0 × 10−3 and 9.0 × 10−4 for intermediate‐ and long‐term flooding durations, respectively. Shortterm flooding reduced carbon assimilation via a decrease in stomatal conductance, while longer flooding durations also decreased the carboxylation efficiency of the leaf.

Gas Exchange and Flooding Stress of Highbush and Rabbiteye Blueberries

Abstract Highbush (Vaccinium corymbosum L. ‘Bluecrop’) and rabbiteye (V. ashei Reade ‘Woodard’) blueberry plants were flooded in the greenhouse to determine how transpiration, stomatal conductance to water and CO2, residual conductance, and C assimilation are affected during flooding and recovery. Carbon assimilation was measured using a portable CO2 analyzer and stomatal conductance using a steady-state porometer. Stomatal conductance and transpiration decreased significantly after 4 to 5 days of flooding, and responses were similar for highbush and rabbiteye blueberries. Carbon assimilation decreased for both species within 9 days and became negative in 11 to 19 days due to decreased photosynthesis, stomatal conductance to CO2, and high leaf temperatures, which increased respiration. Recovery after 24 days of flooding to preflood stomatal conductance values required 18 days for ‘Woodard’ and more than 18 days for ‘Bluecrop’. In laboratory experiments flooded plants were less responsive to changes in ambient CO2 and vapor pressure deficits than unflooded plants, and flooding durations of greater than 9 days significantly decreased residual conductance of the leaves.

Short-Term Flooding Effects on Gas Exchange and Quantum Yield of Rabbiteye Blueberry (Vaccinium ashei Reade)

Roots of 1.5-year-old ;Woodard' rabbiteye blueberry plants (Vaccinium ashei Reade) were flooded in containers or maintained at container capacity over a 5-day period. Carbon assimilation, and stomatal and residual conductances were monitored on one fully expanded shoot/plant using an open flow gas analysis system. Quantum yield was calculated from light response curves. Carbon assimilation and quantum yield of flooded plants decreased to 64 and 41% of control values, respectively, after 1 day of flooding and continued decreasing to 38 and 27% after 4 days. Stomatal and residual conductances to CO(2) also decreased after 1 day of flooding compared with those of unflooded plants with residual conductance severely limiting carbon assimilation after 4 days of flooding. Stomatal opening occurred in 75 to 90 minutes and rate of opening was unaffected by flooding.

Comparative Studies of Plant Growth and Distribution in Relation to Waterlogging: X. Differential Formation of Adventitious Roots and their Experimental Excision in Epilobium Hirsutum and Chamerion Angustifolium

(1) Response to soil waterlogging was experimentally compared in two closely related species. Epilobium hirsutum was almost unaffected but Chamerion angustifolium was seriously harmed by 31 days of waterlogging which reduced dry weight production and total leaf area of adult plants. (2) The first symptom of damage in C. angustifolium was total wilting which occurred within 12 hours of flooding; it was followed by the slow recovery of the upper leaves and death of the lower leaves. (3) Within a few days of flooding, E. hirsutum commenced adventitious root formation from primordia already present near the stem base. (4) Once the first adventitious roots appeared, the stem base swelled consequent on callus formation in the cortex, medulla and probably vascular ray parenchyma. Later-formed adventitious roots arose from this callus which became so massive as to produce vertical, callus-filled cracks on the stem base. Both adventitious roots and stolon buds emerged from these cracks. (5) C. angustifolium produced no adventitious roots and showed no stem base hypertrophy. (6) A few lateral roots of C. angustifolium and many more of E. hirsutum emerged from the soil surface and floated in the floodwater. (7) Wild E. hirsutum formed adventitious roots and showed stem hypertrophy in wet sites but this was never observed in C. angustifolium. (8) Neither species showed significant accumulation of iron or manganese in leaf tissue during 31 days of waterlogging; this contrasted with many plants previously described in this series. (9) Pruning of adventitious roots limited growth of waterlogged plants but had no effect on unflooded plants in which adventitious rooting was stimulated by burial of the stem base. (10) Waterlogged plants with pruned adventitious roots were unstable and easily felled by wind or flooding. (11) Pruning of superficial adventitious roots limited the depth of the primary root system.

Nitrogen Fixation by Nodulated Roots of Viminaria juncea (Schrad. & Wendl.) Hoffmans, (Fabaceae) When Submerged in Water

Nodulated seedlings of Viminaria juncea were raised in free-draining or flooded sand culture. Unflooded seedlings developed limited amounts of aerenchyma in lower stem, root and nodules, and responded to flooding by accelerated aerenchyma production and, after 10 days, by formation of pneumatophores from their near-surface lateral roots. Continuously flooded seedlings showed earlier and greater development of aerenchyma and pneumatophores, and had their nodules and roots restricted to the upper 10 cm of the rooting medium. Aerenchyma was developed from an inner cambium, distinct from the outer phellogen which subsequently developed on older parts of stem, root and nodules. Gas contents of plant parts varied from 4-8% for organs with little aerenchyma to over 30% for the aerenchyma-invested basal stem and root of continuously flooded seedlings. A role of the sheaths of aerenchyma in gaseous exchange between aerial environment and nodulated root was demonstrated by gas injection experiments, in situ C2H2 reduction assays and 15N2 feeding experiments on intact plants with flooded roots. Samples of gas removed from the aerenchyma of plants exposed to C2H2 contained up to 14 times the amount of C2H2 and 4 times the amount of CO2 than in the atmosphere of the assay chamber, indicating that gas exchange for both N2 fixation and respiration occurred via the aerenchyma. Previously unflooded, 12-week seedlings exposed to 14 days flooding gained as much dry matter and total N in the 2-week treatment as did control unflooded plants, but 21-week continuously flooded seedlings showed only half the dry matter and nitrogen gains of similarly aged unflooded seedlings. Observations on the seasonal growth, nodulation and pneumatophore development of natural populations of the species were discussed in relation to the above findings.

Some physiological and morphological responses of Quercusmacrocarpa seedlings to flooding

Flooding for 30 days induced several changes in Quercusmacrocarpa Michx. seedlings, with stomatal closure among the earliest responses. Stomata remained more closed in flooded than in unflooded plants during the entire experimental period. Leaf water potential was consistently higher in flooded than in unflooded plants. Other responses to flooding included acceleration of ethylene production by stems; formation of hypertrophied lenticels on submerged portions of stems; growth inhibition, with greatest reduction in roots; and formation of a few adventitious roots on submerged portions of the stem above the soil line. Some of the morphological responses to flooding, especially formation of hypertrophied lenticels, appeared to be associated with increased ethylene production. Quercusmacrocarpa seedlings adapted poorly to flooding as shown by failure of stomata to reopen after an early period of flooding and low capacity for production of adventitious roots. The much greater inhibition of root growth than shoot growth by flooding will reduce drought tolerance after floodwaters recede.

Growth Responses and Adaptations of Fraxinus pennsylvanica Seedlings to Flooding

Flooding induced several physiological and morphological changes in Fraxinus pennsylvanica seedlings, with stomatal closure among the earliest responses. Subsequent changes included: reduction in dry weight increment of roots, stems, and leaves; formation of hypertrophied lenticels and production of adventitious roots on submerged portions of the stem above the soil line; leaf necrosis; and leaf abscission. After 15 days of stomatal closure as a result of flooding, stomata began to reopen progressively until stomatal aperture was similar in flooded and unflooded plants. Adventitious roots began to form at about the time stomatal reopening began. As more adventitious roots formed, elongated, and branched, the stomata opened further. The formation of adventitious roots was an important adaptation for flooding tolerance as shown by the high efficiency of adventitious roots in absorption of water and in high correlation between the production of adventitious roots and stomatal reopening.

Flue‐Cured Tobacco Yield and Oxygen Content of Soil in Lysimeters Flooded for Various Periods1

AbstractTobacco (Nicotiana tabacum L. var. ‘Coker 298’) plants grown in lysimeters were flooded for 0, 12, 24, 48, 96, and 120 hours to define more clearly 02‐depletion rates in soil and effects of flooding on growth. The 02 content of air entrapped in soil pores was monitored with membrane‐covered galvanic‐type probes before, during, and after a 96‐hour flooding. Oxygen decreased from 16 to less than 4% in the soil atmosphere within 24 hours after flooding. Upon drainage, 02 increased within 48 hours to the original concentration.Growth and yield differences between the control and 12‐ and 24‐hour flooding treatments were not significant. Flooding for longer than 48 hours significantly reduced yield to less than 40% of that of the unflooded plants. Plants were more susceptible to flood damage at the 12‐ leaf stage of development than at the 17‐leaf stage. Reducing sugars increased from 11.8 to 14.8% and total alkaloids decreased from 1.26 to 0.76% in tobacco leaves flooded for 24 hours.

Flooding tolerance of some Western Australian pasture legumes

The effect of flooding on several varieties of clover was studied in three separate experiments. In experiment 1 ten cultivars of subterranean clover (Trifolium subterraneum), two of strawberry clover (T. fragiferum), two of white clover (T. repens) and Serradella (Ornithopus sativa) were subjected to two flooding treatments 77 days after planting. With the water table at ground level, herbage yields were not significantly less than those of unflooded plants in Yarloop, N2254, Yabba North, Wenijup, Palestine, and Salina and New Zealand white clovers, hut there were significant decreases in yield in N2167, N2168, Clare, Geraldton, Mt. Barker, Morocco, Ladino, and Serradella. When the water table was raised to three inches above ground level, all the cultivars had significantly lower herbage and root yields than the control plants. Overall, Yarloop appeared to be the most productive under both of the flooding treatments. In experiment 2 Yarloop and Geraldton clovers were flooded at three different stages of growth (one third eleven days after planting, one third sixty days after planting, and one third 86 days after planting). Flooding lasted 21 days then half of each group was harvested and the other half allowed to grow for a further 14 days under free drainage before harvesting. Both Geraldton and Yarloop were affected most by flooding sixty days after planting. Nodulation was delayed in the plants that were flooded eleven days after planting, but commenced once the soil was allowed to drain freely. In experiment 3, eight Yarloop crosses were flooded three inches above ground level for 21 days, 80 days after planting. The crosses were subdivided on seed colour. Flooding reduced yield in all crosses except Yarloop x Yabba Noah brown seed and Yarloop x Mt. Barker brown seed. The data suggest that breeding for greater tolerance to flooding may be practicable.