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

Background and aim

Root system activity is affected by abiotic stresses, which often creates spatial differences in root conditions. This is expected to influence plants ability to cope with suboptimal conditions.

Methods

Changes in root system activity were determined as ¹⁵N root uptake in top and bottom layers of potted tomato plants (Solanum lycopersicum L.), after waterlogging the bottom layer for 24 h or 5 d. The plants were grown in peat-based media; non-compacted or highly-compacted, resulting in differences in gas diffusion, air permeability and oxygen availability.

Results

The roots were affected by short-term waterlogging (24 h) by decreasing uptake in the bottom layer and increasing uptake in the pot top layer. Long-term waterlogging (5 d) decreased the ¹⁵N root uptake more in both layers. Root uptake recovered fast (within 6 h) after short-term waterlogging, whereas recovery of long-term waterlogged roots took more than 24 h, suggesting production of new root biomass. Despite affecting physical properties, medium compaction did not affect root uptake. Aboveground biomass was affected by waterlogging by increasing the dry matter percentage, decreasing nitrogen (N) percentage and increasing starch content.

Conclusions

The results confirmed that root uptake in different layers of small pots could be distinguished by the ¹⁵N technique, which was applicable under potentially denitrifying conditions. The results demonstrated that during short-term stress in part of the root system plants increased uptake from the non-affected parts of the root system, probably as compensation for suboptimal conditions.     

Biomechanics of nodal, seminal and lateral roots of barley: effects of diameter, waterlogging and mechanical impedance

Background and aims

Biomechanical properties of cereal root systems largely control both resistance to root lodging and their ability to stabilise soil. Abiotic stresses can greatly modify root system growth and form. In this paper the effect of waterlogging and moderate mechanical impedance on root biomechanics is studied for both lateral roots and the main axes of barley.

Methods

Barley (Hordeum vulgare) plants were subjected to transient water-logging and moderate mechanical impedance in repacked soil columns. Roots were excavated, separated into types (nodal, seminal or lateral) and tested in tension to measure strength and elastic modulus.

Results

Water-logging and mechanical impedance substantially changed root system growth whilst root biomechanical properties were affected by waterlogging. Root strength was generally greater in thin roots and depended on root type. For example, seminal roots 0.4–0.6 mm in diameter were approximately seven times stronger and five times stiffer than lateral roots of the same diameter when mechanically impeded. Root sample populations typically exhibited negative power-law relationships between root strength and diameter for all root types. Mechanical impedance slowed seminal root elongation by approximately 50 % and resulted in a 15 % and 11 % increase in the diameter of in nodal and seminal roots respectively. Power-law relationships between root diameter and root biomechanical properties corresponded to the different root types. Coefficients for between root diameter, strength and elastic modulus improved when separated by root type, with R² values increasing in some roots from 0.05 to 0.71 for root strength and 0.08 to 0.74 for elastic modulus.

Conclusions

Moderate mechanical impedance did not influence the tensile strength of roots, but, waterlogging diminished the relationship between root strength and diameter. Separation of root type improved predictions of root strength and elastic modulus using power-law regressions.     

First Report of <i>Fusarium striatum</i> Causing Root Rot Disease of <i>Panax notoginseng</i> in Yunnan,China

Panax notoginseng is a traditional Chinese medicinal plant. Root rot of P. notoginseng is one of the most serious diseases affecting P. notoginseng growth and causes wilted leaves, fewer lateral roots and rotten roots. Root rot is a soil-borne disease, and mainly occurs from June to August in Yunnan Province when the temperatures are high and the air is humid. In this study, the endophytic fungal genus Fusarium isolate E-2018.1.22-#3.2 was obtained from a P. notoginseng embryo. Fusarium isolate E-2018.1.22-#3.2 was identified as Fusarium striatum based on morphological characteristics and molecular analysis. The fungus was found to have conidiophores and macroconidia, and its ITS, LSU and TEF-1α genes shared 100%, 99.2% and 99% identities with the homologous genes of Fusarium striatum, respectively. Isolate F. striatum E-2018.1.22-#3.2 can cause root rot symptoms, including black, soft roots, fewer lateral roots and leaf wilt, in 93% of the experimental P. notoginseng plants, and could be re-isolated, fulfilling Koch’s postulates. When the P. notoginseng plants were treated with the fungicide pyraclostrobin, isolate F. striatum E-2018.1.22-#3.2 was unable to cause root rot. We have therefore demonstrated that F. striatum E-2018.1.22-#3.2 is able to cause root rot disease in P. notoginseng. This is the first report of root rot disease caused by F. striatum on P. notoginseng in China.     

Transformation and mineralization of soil organic nitrogen by the humivorous larva of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

In common bean (Phaseolus vulgaris L.), Fusarium root rot (caused by Fusarium solani f. sp. phaseoli) disease severity is increased by environmental factors that stress the plant. The current study used reciprocal grafting techniques with the resistant cultivar FR266 and the susceptible cultivar Montcalm to determine if the genetic control of resistance is conferred by the rootstock (root genotype) or the scion (shoot genotype) and if root vigor played a role in resistance. The influence of a compacted layer on root and shoot genotype response and root rot resistance was studied. Root rot resistance was found to be controlled by the root genotype, such that on a scale of 1 to 7 (severe disease) the FR266 root had an average score of 2.3 and the Montcalm root had an average score of 4.4. However, when grafted plants were grown in the presence of a compacted layer, the FR266 root and/or shoot genotype in any graft combination with the susceptible Montcalm had reduced root rot (score = 2.4 average) than the Montcalm self graft (score = 4.5). Root mass was shown to be controlled by the root genotype in the absence of compaction such that the FR266 root was 26% larger that the Montcalm root when grafted onto a FR266 shoot or a Montcalm shoot. When a compacted layer was present the root and shoot genotype both contributed to root mass. Average root diameter was controlled by the shoot genotype, as the FR266 shoot grafted to Montcalm or FR266 roots had thicker roots (average diameter 0.455 mm) than the Montcalm shoot (average diameter 0.418 mm). This study shows evidence that root vigor in the presence of Fusarium disease pressure should be evaluated to effectively develop common bean lines resistant to Fusarium root rot across a range of environments.     

Mechanisms for the increase in phosphorus uptake of waterlogged plants: soil phosphorus availability, root morphology and uptake kinetics

Waterlogging frequently reduces plant biomass allocation to roots. This response may result in a variety of alterations in mineral nutrition, which range from a proportional lowering of whole-plant nutrient concentration as a result of unchanged uptake per unit of root biomass, to a maintenance of nutrient concentration by means of an increase in uptake per unit of root biomass. The first objective of this paper was to test these two alternative hypothetical responses. In a pot experiment, we evaluated how plant P concentration of Paspalum dilatatum, (a waterlogging-tolerant grass from the Flooding Pampa, Argentina) was affected by waterlogging and P supply and how this related to changes in root-shoot ratio. Under both soil P levels waterlogging reduced root-shoot ratios, but did not reduce P concentration. Thus, uptake of P per unit of root biomass increased under waterlogging. Our second objective was to test three non-exclusive hypotheses about potential mechanisms for this increase in P uptake. We hypothesized that the greater P uptake per unit of root biomass was a consequence of: (1) an increase in soil P availability induced by waterlogging; (2) a change in root morphology, and/or (3) an increase in the intrinsic uptake capacity of each unit of root biomass. To test these hypotheses we evaluated (1) changes in P availability induced by waterlogging; (2) specific root length of waterlogged and control plants, and (3) P uptake kinetics in excised roots from waterlogged and control plants. The results supported the three hypotheses. Soil P avail-ability was higher during waterlogging periods, roots of waterlogged plants showed a morphology more favorable to nutrient uptake (finer roots) and these roots showed a higher physiological capacity to absorb P. The results suggest that both soil and plant mechanisms contributed to compensate, in terms of P nutrition, for the reduction in allocation to root growth. The rapid transformation of the P uptake system is likely an advantage for plants inhabiting frequently flooded environments with low P fertility, like the Flooding Pampa. This advantage would be one of the reasons for the increased relative abundance of P. dilatatum in the community after waterlogging periods. Received: 15 February 1997 / Accepted: 20 May 1997     

Preference for plants damaged by conspecific larvae in ovipositing cabbage root flies: influence of stimuli from leaf surface and roots

In laboratory dual-choice assays females of the cabbage root fly, Delia radicum, prefer for oviposition plants with roots damaged by conspecific larvae to undamaged controls. Cauliflower and kale plants were inoculated with root fly eggs (25 per plant) and the hatching larvae were allowed to feed on the roots for various periods of time (1–17 days). After 4 (cauliflower) or 5 (kale) days of larval feeding the oviposition preference was most pronounced and flies laid between 64% and 68% of their eggs near plants with damaged roots. Later, with increasing damage but fewer surviving, and thus actively feeding, larvae, the magnitude of the preference declined. The preference for plants already damaged by conspecific larvae may contribute to the previously observed aggregated distribution of D. radicum eggs in Brassica crop fields.Further experiments revealed that the sensory cues inducing this oviposition preference originate from the complex consisting of the damaged roots, the surrounding substrate (soil) and associated microbes, rather than from the aerial plant parts. In choice assays using the root-substrate complex of damaged and control plants (aerial parts removed), the observed preference for damaged roots was similar to that found for the entire plant but was more pronounced. The damaged roots alone, compared to control roots, received up to 72% (cauliflower) and 75% (kale) of the eggs. By contrast, surrogate leaves sprayed with methanolic leaf surface extracts from the most preferred plants which had been damaged were not discriminated from surrogate leaved sprayed with extracts of the respective control plants. Analysis of glucosinolate levels in methanolic leaf surface extracts revealed that root damage resulted in enhanced concentrations of indole-glucosinolates on the leaf surface in kale but not in cauliflower. Although indole-glucosinolates are oviposition stimulants for the cabbage root fly, the induced changes were apparently too small to influence oviposition behaviour.     

Timing of root dormancy and tolerance to root waterlogging in clonal Sitka spruce

 Actively growing root tips of Picea sitchensis (Bong.) Carr. plants are highly susceptible to damage if waterlogged, but they are known to have some tolerance after they stop growing in the autumn. This paper describes the selection of clones on the basis of root dormancy timing and the corresponding responses of their roots to over-winter waterlogging. Sitka spruce transplants of Alaska, Queen Charlotte Islands (QCI), and Washington provenances were screened for early or late root dormancy over 2 successive years. Cuttings were propagated from the selected plants and after growing on for 2 years, they were planted in transparent acrylic tubes within outdoor ‘root observation chambers’. Extension of main roots and the timing of onset of root dormancy was recorded on the clonal plants. The tubes were flooded in November and maintained with a water table 280 mm below the soil surface until March of the next year. Waterlogging caused most main root tips to die back, but within 2 months of draining regeneration occurred on the main roots below the waterlogging level. This regeneration was most commonly the growth of existing lateral tips or production of new lateral roots. Roots of early-dormant Washington plants died back on average 129 mm less than late-dormant Washington plants, and early-dormant Alaska plants had 173 mm less dieback than late-dormant Alaska plants. Differences between the clones of the QCI provenance were not significant. The 40% and 52% increases in survival depth of roots in early-dormant Washington and Alaska clones respectively indicates a potential for improving the rooting depth of Sitka spruce on seasonally waterlogged soils by planting clones selected on the basis of root dormancy. Received: 14 July 1997 / Accepted: 15 September 1997     

The influence of soil drought and partial waterlogging on water relations of Gmelina arborea seedlings

Summary Stomatal conductance of unstrossed, soil drought, and previously drought (predrought) Gmelina arborea seedlings increased in the morning and decreased before or immediately after midday. In the unstressed and predrought seedlings, leaf water potential decreased with increases in transpiration. In soil drought seedlings, there was some evidence of decreased hydraulic conductivity from soil to the plant, as indicated by the shape in the slope of the water potential/transpiration relationship. Root growth of drought plants was greater than in their unstressed counterparts at the lowest soil segment of a pot. The partial recovery of predrought seedlings was attributed to this subtantial root growth in the lowest soil segment.In the second experiment, Gmelina arborea seedlings were partially waterlogged, by flooding the polyethylene bag to half its length, for a period of 23 days. Waterlogging induced stomatal closure and reduction in leaf water potential but there was some evidence of tolerance to waterlogging towards the end of treatment. Root growth, shoot and root dry weights were slightly reduced below those of controls. After 9 days of waterlogging, adventitious roots began to form which correlated with depletion of soluble sugars in the shoot but with an increase in the roots.It is suggested that the tolerance of Gmelina plants to either soil drought or waterlogging may partly be due to partitioning of the soluble sugars from shoot to roots for production of roots and formation of adventitious roots respectively which are likely to enhance the flow of water from the soils to the plant. Therefore the plant response is very similar under conditions of increased deficits and surplus of soil water.     

A novel life cycle arising from leaf segments in plants regenerated from horseradish hairy roots

Summary Horseradish (Armoracia rusticana) hairy root clones were established from hairy roots which were transformed with the Ri plasmid in Agrobacterium rhizogenes 15834. The transformed plants, which were regenerated from hairy root clones, had thicker roots with extensive lateral branches and thicker stems, and grew faster compared with non-transformed horseradish plants. Small sections of leaves of the transformed plants generated adventitious roots in phytohormone-free G (modified Gamborg's) medium. Root proliferation was followed by adventitious shoot formation and plant regeneration. Approximately twenty plants were regenerated per square centimeter of leaf. The transformed plants were easily transferable from sterile conditions to soil. When leaf segments of the transformed plants were cultured in a liquid fertilizer under non-sterile conditions, adventitious roots were generated at the cut ends of the leaves. Adventitious shoots were generated at the boundary between the leaf and the adventitious roots and developed into complete plants. This novel life cycle arising from leaf segments is a unique property of the transformed plants derived from hairy root clones.     

Agrobacterium rhizogenes-mediated transformation of Taraxacum platycarpum and changes of morphological characters

Transformed hairy roots were efficiently induced from seedlings of Taraxacum platycarpum by infection with Agrobacterium rhizogenes 15834. Root explants produced transformed roots at a higher frequency (76.5±3.5%) as compared to stem (32.7±4.8%) or cotyledon (16.2±5.7%). Hairy roots exhibited active elongation with high branching of roots on growth regulator-free medium. The competence of plant regeneration from non-transformed adventitious roots and transformed hairy roots was compared. The frequency of adventitious shoot formation from transformed roots was much higher (88.5±9.8%) than that of non-transformed roots (31.7 ±9.5%) on hormone-free medium. Rooting of hairy root-derived adventitious shoots occurred easily on growth regulator-free medium but no rooting was observed on non-transformed shoots. The stable introduction of rol genes into Taraxacum plants was confirmed by PCR and Southern hybridization. Transgenic plantlets showed considerable differences in their morphology when compared to the corresponding wild-type (non-transgenic) plants. Plantlets formed from transformed roots had numerous fibrous roots with abundant lateral branches instead of the thickened taproots in non-transformed plants. The differences observed may reflect the modification of morphological root characters by introduction of rol genes.Communicated by M.R. Davey     

Growth responses to waterlogging and drainage of woody Hakea (Proteaceae) seedlings,originating from contrasting habitats in south-western Australia

We investigated the responses of seven woody Hakea (Proteaceae) species (two populations of each), to two months of waterlogging and subsequent drainage, in a controlled glasshouse experiment. The species originated from contrasting environments (winter-wetland versus non-wetland habitats), and differed in abundance (endangered ironstone species versus common species). Waterlogging arrested growth of the main root system, and stimulated the formation of superficial adventitious roots just below the root/shoot junction in all species. Wetland species produced at least twice the amount of adventitious root dry mass of that of non-wetland species, due to differences in number, length or degree of branching. Their adventitious roots also tended to have higher porosities (7–10% versus 5–6% gas spaces). The relative amount of adventitious roots formed was strongly, positively correlated with the maintenance of shoot growth, and only the non-wetland species showed significant shoot growth reductions (19%) upon waterlogging. Dry mass percentage of stems and leaves, and leaf dry mass per area (LMA) increased considerably during waterlogging in all species (averages of 15, 29 and 27%, respectively), returning to the values of continuously drained control plants after drainage. Similarly, upon drainage, a suppression of shoot growth (average 35%) and a stimulation of root growth (average 50%) restored the root mass ratios to those of control plants. We found a negative correlation between the maintenance of growth during waterlogging versus that after waterlogging, suggesting a trade-off in functioning of the superficial adventitious roots between waterlogged and drained conditions. The rare winter-wet ironstone endemics resembled the common winter-wet species in most of their responses to waterlogging and drainage. Therefore, the results presented here cannot offer an explanation for their different distribution patterns. Our results suggest that non-wetland species may be disadvantaged in a wetland environment, due to their lower capacity to form adventitious roots resulting in stronger growth reductions.     

Effect of pruning or removal of in vitro formed roots on ex vitro root regeneration and growth in micropropagated grapes

Pruning or total removal of in vitro formed roots of grape (Vitis vinifera L.) plantlets at planting offered considerable ease and time economy compared to control plantlets with intact roots. The ex vitro establishment was unaffected by the practice with 90% or higher establishment in each treatment. When observed at 4 weeks from planting, growth was slightly affected by root pruning and significantly by root removal. However, both these treatments showed better adventitious root regeneration at the base compared to control plants, which showed elongation of in vitro formed roots with fewer new roots. Root pruning and root removal treatments reduced the influence of the number of in vitro formed roots on vigour of ex vitro plants since the number of new roots formed was independent of the roots initially present. Consequently, these plants showed more uniformity compared to control plants. With a better root system, root pruned plants showed faster subsequent growth. Root pruning at planting is recommended for easier handling and more uniform plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Waterlogging responses in dune,swale and marsh populations of Spartina patens under field conditions

Summary Soil waterlogging responses were examined in three Spartina patens populations along a steep flooding gradient in coastal Louisiana. Root anatomy and physiological indicators of anaerobic metabolism were examined to identify and compare flooding responses in dune, swale and marsh populations, while soil physicochemical factors were measured to characterize the three habitats. Soil waterlogging increased along the gradient from dune to marsh habitats and was accompanied by increases in root porosity (aerenchyma). Aerenchyma in marsh roots was apparently insufficient to provide enough oxygen for aerobic respiratory demand, as indicated by high root alcohol dehydrogenase activities and low energy charge ratios. Patterns of root metabolic indicators suggest that dune and swale roots generally respired aerobically, while anaerobic metabolism was important in marsh roots. However, in each population, relatively greater soil waterloging was accompanied by differences in enzyme activities leading to malate accumulation. In dune and swale roots under these circumstances, depressed adenylate energy charge ratios may have been the result of an absence of increased ethanol fermentation. These trends suggest that: 1) Aerenchyma formation was an important, albeit incomplete, long-term adaptation to the prevalent degree of soil waterlogging. 2) All populations adjusted root metabolism in response to a relative (short-term) increase in soil waterlogging.     

Selection for Fusarium root rot resistance in red clover

Intercrossing red clover plants, selected for reaction to Fusarium root rot (F. avenaceum), produced progenies with lower root rot scores than the parental cultivar Hermes II. Eleven percent of the progenies had less than 2 mm root rot after two cycles of selection, compared to less than 1% in the parental cultivar. Root rot severity in two old local strains of red clover, as well as in two populations of wild red clover, was lower than in cv. Hermes II. This could indicate that a natural selection for root rot resistance can occur in red clover.     

Influence of Fusarium solani on citrus root rot caused by Phytophthora parasitica and Phytophthora citrophthora

Interactions between Fusarium solani and Phytophthora parasitica or F. solani and P. citrophthora influenced the development of root rot of citrus but depended on the temporal order of inoculation with F. solani or the two Phytophthora spp. Inoculation of citrus with either Fusarium solani and Phytophthora parasitica or Phytophthora citrophthora increased root rot compared to inoculation with P. parasitica or P. citrophthora alone when plants were inoculated with Phytophthora by dipping their roots in zoospore suspensions and subsequently transplanted into soil infested with F. solani. However, root rot was not increased by simultaneous co-inoculation of P. parasitica and F. solani or when plants were inoculated with F. solani first. Root rot was not increased when heat-stressed or non-stressed plants were inoculated with P. parasitica 30 days after transplanting into soil infested with F. solani. In most but not all experiments, F. solani alone reduced growth of tops or roots a small but significant amount.Co-inoculation of citrus by root-dipping into zoospore suspensions of P. parasitica and transplanting into soil infested with F. solani reduced feeder root length by 62% and root weight by 61% but did not significantly reduce the percentage of living roots when compared to inoculation with P. parasitica alone. When citrus roots were immersed in zoospore suspensions of P. citrophthora and transplanted into soil infested with F. solani, feeder root length was reduced by 68%, but feeder root weight and the percentage of living roots were not significantly reduced when compared to plants inoculated with P. citrophthora alone.Propagule densities of both P. parasitica and P. citrophthora in the rhizosphere of plants inoculated by root-immersion and then transplanting into soil infested with F. solani were not significantly different than propagule densities from plants transplanted into non-infested soil. Propagule densities of P. parasitica were suppressed an average of 41% when citrus was inoculated with P. parasitica 30 days after transplanting into soil infested with F. solani and by 41% when citrus was co-inoculated by transplanting into soil infested with both F. solani and P. parasitica.     

Comparison of Screening Methods for Resistance to Fusarium Root Rot in Common Beans (Phaseolus vulgaris L.)

Root rot, caused by Fusarium solani f. sp. phaseoli, is one of the main root diseases impacting production of common beans throughout the world. Because resistance of common beans to root rot is a quantitative trait that is strongly influenced by environmental factors, reproducible methods to screen bean plants for resistance to root rot are critical to the selection process. In this study, we adapted the inoculum layer method (ILM) developed for screening soybeans for resistance to Phytophthora rot and compared it with the traditional liquid inoculum method (LIM) for screening common beans for resistance to Fusarium root rot. In addition, two methods of evaluating resistance using the ILM were compared. The most significant Pearson correlation coefficient between trials involving 80 recombinant inbred lines was achieved with the ILM and counting discoloured vascular bundles in the lower stem (r_p = 0.7113***) compared to rating the discoloration on root and hypocotyl (r_p = 0.5555***). The traditional (LIM) screening method and rating the discolouration on roots resulted in a non‐significant correlation between trials (r_p = 0.1084).     

Plant growth, nutrient acquisition and mycorrhizal symbioses of a waterlogging tolerant legume (Lotus glaber Mill.) in a saline-sodic soil

Seedlings of Lotus glaberMill., were grown in a native saline-sodic soil in a greenhouse for 50 days and then subjected to waterlogging for an additional period of 40 days. The effect of soil waterlogging was evaluated by measuring plant growth allocation, mineral nutrition and soil chemical properties. Rhizobiumnodules and mycorrhizal colonisation in L. glaberroots were measured before and after waterlogging. Compared to control plants, waterlogged plants had decreased root/shoot ratio, lower number of stems per plant, lower specific root length and less allocation of P and N to roots. Waterlogged plants showed increased N and P concentrations in plant tissues, larger root crown diameter and longer internodes. Available N and P and organic P, pH and amorphous iron increased in waterlogged soil, but total N, EC and exchangeable sodium were not changed. Soil waterlogging decreased root length colonised by arbuscular mycorrhizal (AM) fungi, arbuscular colonisation and number of entry points per unit of root length colonised. Waterlogging also increased vesicle colonisation and Rhizobium nodules on roots. AM fungal spore density was lower at the end of the experiment in non-waterlogged soil but was not reduced under waterlogging. The results indicate that L. glaber can grow, become nodulated by Rhizobium and colonised by mycorrhizas under waterlogged condition. The responses of L. glaber may be related its ability to form aerenchyma.     

水淹和恢复对凤丹光合特性和根系活力的影响

选用3年生油用牡丹凤丹(Paeonia ostii)实生苗为试验材料,以常规供水管理的凤丹苗为对照,测定凤丹光合特性以及根系活力和形态随着水淹和水淹恢复处理时间的变化,探究牡丹的耐湿机制。结果表明:(1)水淹后,凤丹叶片净光合速率、蒸腾速率、气孔导度及根系活力均较对照组显著下降,且下降幅度随着水淹时间的延长而增大;在持续水淹过程中,叶片胞间CO_2浓度则呈先下降后上升的变化趋势;水淹168h时,根系活力在所测定指标中下降幅度最大,仅为对照组的2.34%,此时根系变黑且腐烂,大部分根系脱落。(2)凤丹叶片净光合效率的下降在水淹120h过程中与气孔限制性调节密切相关,而到水淹168h时非气孔限制性成为光合作用的限制因子。(3)水淹72h后进行恢复处理120h后,叶片净光合速率、蒸腾速率、胞间CO_2浓度和根系活力均显著上升;恢复处理168h后,净光合速率和胞间CO_2浓度恢复到正常的生长水平,同时绝大部分根尖呈现白色且发育良好,根系生长向正常的生命状态恢复。研究表明,油用牡丹凤丹对水淹胁迫的应答迅速且灵敏,虽不耐水淹,但恢复能力强,这为其栽培管理以及在相对湿润地区推广种植提供了理论依据。     

Fungicidal drenches for control of root rot in subterranean clover

Fungicide drenches of benomyl, metalaxyl, iprodione, propamocarb, or thiram were applied to intact soil cores taken from known root rot affected fields in Western Australia, to control subterranean clover root rot. Metalaxyl was the most effective in reducing seedling damping-off. The most effective fungicide for reducing the level of rotting of both tap and lateral root systems of survixing plants varied from season to season at one site and varied between different sites in any one season with each fungicide giving a significant reduction in root disease on at least one occasion. Results suggest that different individuals or complexes of root pathogens were operative between seasons in any one site, and between sites for any one season. In some instances it appears that different individual root pathogens or pathogen complexes were operative on tap roots compared to lateral roots.     

Physiological responses of cotton to a single waterlogging at high and low N-levels

Surface-irrigated cotton (Gossypium hirsutum L.) grown on slowly draining clay soil is subjected to short-term periods of waterlogging at each irrigation which generally results in reduced productivity. The sequence of above- and below-ground plant responses to transient waterlogging and the role of N availability in modifying the immediate responses were studied. Lysimeters of Marah clay loam (a Natrustalf) were instrumented to monitor soil and plant responses to a 7-day waterlogging event beginning 67 days after sowing. Cotton (‘Deltapine 61’) plants (8 per lysimeter) were grown with two levels of added N (300 kg ha⁻¹ and 30 kg ha⁻¹) and two irrigation treatments (flooded and control). Measured soil-O₂ levels decreased rapidly upon surface flooding because water displaced air and root zone respiration consumed O₂. The rate of O₂ consumption was 2.7 times greater in the high-N treatment than the low-N treatment. This difference was associated with a 1.8 fold difference in numbers of observed roots. Root growth was only slightly affected by flooding. Leaf growth decreased by 28%, foliage temperature increased 2.3% and apparent photosynthesis decreased by 16%. It is suggested that flooding reduced photosynthetic activity within 2 days while other stress symptoms became apparent after about 6 days. Although this stress was reflected in a trend for decreased plant productivity, the effect of flooding on boll dry mass at harvest was not significant at the level of replication used. The single waterlogging did not cause yield reductions comparable to those observed elsewhere when several waterlogging events were imposed. Contribution from the CSIRO, Centre for Irrigation Research, Griffith, NSW, Australia and USDA-ARS, Morris, MI, USA, in cooperation with the univ. of Minnesota.