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1.
Three-week old soybean (Glycine max) plants were subjected to a factorial combination of four regimes of soil matric water potential (ψm=−0·03, −0·5, −1·0 and −1·5 MPa), two levels of supplementary Zn (O and 20 mgl−1) and two levels of foliar IAA application (O and 10 mgl−1). Under control conditions (no Zn, no IAA), increasing soil drying progressively retarded shoot and root growth (length and dry mass production), reduced leaf relative water content (RWC) and decreased the contents of chlorophyll (Chl) and shoot soluble sugars (SS), but increased soluble sugar content of roots and lowered osmotic water potential of shoots and roots (osmotic adjustment). Total free amino acid (TAA) content increased in shoots but decreased in roots whereas contents of soluble proteins (SP) decreased in shoots and roots. The effect of water stress was statistically significant (p<0·05) and had a major effect (as indicated by η2values) on leaf RWC, shoot and root dry masses and osmotic potential. Supplementary Zn improved root growth at all levels of stress and shoot growth under severe stress. Improvement of growth was positively correlated with the internal tissue Zn concentrations (r=0·91 and 0·86 for shoot and 0·94 and 0·82 for root length and dry mass respectively). Exogenous IAA raised (p<0·05) RWC, Chl, DM (slightly), root SS, and SP, whereas shoot TAA was lowered. Effects on root TAA and shoot SS were more complex: they were lowered at zero stress and raised under severe stress. IAA and Zn in combination had additive effects on Chl, growth and osmotic potential, but their combined effects on SP and TAA were more complex. It is concluded that the treatment of soybean plants grown under conditions of low soil water potentials and Zn deficiency with Zn and IAA solutions counteracted the deleterious effects of stress, especially at high stress levels, and helped stressed plants to grow successfully under these adverse unfavourable conditions.  相似文献   

2.
Soil salinity is a major abiotic stress influencing plant productivity worldwide. Schinopsis quebracho colorado is one of the most important woody species in the Gran Chaco, an arid and salt-prone subtropical biome of South America. To gain a better understanding of the physiological mechanisms that allow plant establishment under salt conditions, germination and seedling growth of S. quebracho colorado were examined under treatment with a range of NaCl solutions (germination: 0–300 mmol l−1 NaCl; seedling growth: 0–200 mmol l−1 NaCl). The aim was to test the hypothesis that S. quebracho colorado is a glycophite that shows different salt tolerance responses with development stage. Proline content, total soluble carbohydrates and Na+, K+ and Cl− concentrations in leaves and roots of seedlings, and the chlorophyll concentration and relative water content of leaves were measured. Germination was not affected by 100 mmol l−1 NaCl, but decreased at a concentration of 200 mmol l−1. At 300 mmol l−1 NaCl, germination did not occur. Seedling growth decreased drastically with increasing salinity. An increase in NaCl from 0 to 100 mmol l−1 also significantly reduced the leaf relative water content by 22% and increased the proline concentration by 60% in roots. In contrast, total soluble carbohydrates were not significantly affected by salinity. Seedlings showed a sodium exclusion capacity, and there was an inverse correlation between Cl− concentration and the total chlorophyll concentration. S. quebracho colorado was more tolerant to salinity during germination than in the seedling phase. The results suggest that this increased tolerance during germination might, in part, be the result of lower sensitivity to high tissue Na+ concentrations. The significant increment of proline in the roots suggests the positive role of this amino acid as a compatible solute in balancing the accumulation of Na+ and Cl− as a result of salinity. These results help clarify the physiological mechanisms that allow establishment of S. quebracho colorado on salt-affected soils in arid and semi-arid Gran Chaco.  相似文献   

3.
The distribution of Sarcocornia pillansii (Moss) A.J. Scott was determined by water-table depth and electrical conductivity (EC) of the groundwater. Where the groundwater was accessible (<1.5 m) and had a low EC (<80 mS cm−1), S. pillansii extended its roots down to the water-table where a suitable water potential gradient was shown to exist between the soil and roots. In areas where the groundwater was too deep and/or hypersaline, the plants grew on hummocks. The unconfined aquifer below the floodplain is linked to the estuary and although diurnal tidal waves were dampened, water-table level fluctuations were recorded between tidal events. The complex geomorphology of the floodplain influences groundwater flow, in turn affecting the distribution of the salt marsh vegetation.  相似文献   

4.
In the present study, growth and water relation parameters were analysed in drought-stressed Coriaria nepalensis Wall. seedlings. C. nepalensis seedlings were subjected to four drought cycles of 7, 14, 21, and 28-days, and to one control level (watered on alternate days) in a glasshouse. The seedlings failed to survive a 28-days drought during summer. Osmotic adjustment (defined as the decrease in osmotic potential at zero or full turgor in response to water deficit) was measured as the difference between the osmotic potential of seedlings watered on alternate days (control) and those subjected to 21-days drought cycle. Seedlings subjected to 21-days drought had a predawn water potential of −2.60 MPa, and showed an osmotic adjustment of −1.95 MPa at full turgor and −2.17 MPa at zero turgor. The growth of seedlings was positively related to moisture and with water potential. With decline in soil moisture the root:shoot ratio increased while leaf weight ratio decreased. Leaf characteristics, such as leaf number, leaf area, leaf area ratio, specific leaf area and leaf drop, were also affected by moisture stress. This study has indicated that osmotic adjustment is a major adaptive mechanism of C. nepalensis that aids successful regeneration of seedlings in degraded sites with inhospitable soil conditions.  相似文献   

5.
Matteo Tosi   《Geomorphology》2007,87(4):268-283
The role of root strength is important in stabilising steep hillslopes which are seasonally affected by storm-induced shallow landslides. In the Italian Apennines, steep (25–40°) slopes underlain by mudstone are generally stable if they are covered by shrubs whose roots anchor into the soil mantle. To quantify the mechanical reinforcement of roots to soil, the root tensile breaking force and the root tensile strength of three autochthonous shrub species commonly growing on stiff clay soils of the Northern Italian Apennines, Rosa canina (L.), Inula viscosa (L.) and Spartium junceum (L.), were measured by means of field and laboratory tests. For each test approximately 150 root specimens were used. The tensile force increases with increasing root diameter following a second-order polynomial regression curve. The tensile strength decreases with increasing root diameter following a power law curve. The field in situ tensile force required to break a root is always smaller than that obtained from laboratory tests for the same root diameter, although their difference becomes negligible if the root diameter is smaller than 5 mm. The influence of root tensile strength on soil shear strength was verified based on the infinite slope stability model. The root reinforcement was calculated using the number and mean diameter of roots. The factor of safety was calculated for three different soil thickness values (0.1, 0.3, and 0.6 m) and topographic slopes between 10° and 45°. The factor of safety for the combination of 0.6 m soil thickness, slopes smaller than 30°, and vegetation of I. viscosa (L.) or S. junceum (L.) is always larger than 1. If a slope is steeper, the factor of safety may be smaller than 1 for I. viscosa (L.), although it is still larger than 1 for S. junceum (L.). In the stiff clayey areas of the Northern Italian Apennines, I. viscosa (L.) mainly colonizes fan/cone/taluses and stabilises these zones up to a topographic gradient < 30° for a soil 0.6 m thick. S. junceum (L.) colonizes not only fan/cone/taluses but also headwalls and cliffs and, for a 0.6 m thick soil, it stabilises these areas up to 45°. The effectiveness of this reinforcement, however, depends strongly on the frequency of soil and seasonal grass vegetation removal due to shallow landsliding before the entrance of the shrub species.  相似文献   

6.
In vitro mass propagation of Acacia seyal Del. was achieved using seedling shoot tip explants on Murashige and Skoog (MS) medium supplemented with 6-benzyladenine (BA) or Thidiazuron (TDZ) with ∝-Naphtalene acetic acid (NAA). The best result was obtained with BA in the presence of NAA. The greatest shoot multiplication with long shoots was observed on media containing (mg l-1) 2·0 BA with 0·1 or 0·5 NAA and 4·0 BA with 0·1 NAA; with 6·4 and 6·7 mean number of shoots, respectively. TDZ also induced multiple shoots but most of the shoots were stunted. Microshoots were rooted better on half-MS salts supplemented with Indole-3-butyric acid (IBA). The highest rooting percentage (80%) and root number (4·9 roots/microshoot) were promoted by 4·0 mg IBA. The plantlets (90%) successfully survived acclimatization ex vitro.  相似文献   

7.
Hydraulic redistribution is the process of passive water movement from deeper moist soil to shallower dry soil layers using plant roots as conduits. Results from this study indicate that this phenomenon exists among two shrub species (Guiera senegalensis and Piliostigma reticulatum) that co-exist with annual food crops in Sahelian agro-ecosystems. Real-time measurements were conducted for soil water content, soil water potential and microclimate variables notably; air temperature, relative humidity, wind speed, precipitation and solar irradiance. Additionally, sap flow measurements were conducted in shrub roots using the thermal dissipation technique on intact and coppiced shrubs. Monthly predawn leaf water potential was measured using a portable pressure chamber. Soil water potential (Ψs) at the 20 cm depth declined significantly during the dry season with diel changes in Ψs of −0.6 to −1.1 MPa. These variations were attributed to passive water release from shrub roots resulting in overnight rewetting of drier upper soil layers. Sap flow measurements on tap and lateral shrub roots indicated daily reversals in the direction of flow. During the peak of the dry season, both positive (toward shrub) and negative (toward soil) flows were observed in lateral shrub roots with sap flow in the lateral roots frequently negative at night and rapidly becoming positive soon after sunrise. The negative sap flow at night in superficial lateral roots and the periodic positive flow in the descending tap roots were indicative of hydraulic redistribution. Hydraulic redistribution may be an important mechanism for drought stress avoidance while maintaining plant physiological functions in both shrubs and neighboring annuals in water-limited environments.  相似文献   

8.
The vascular vegetation of alpine talus slopes between 2035 and 3095 m altitude was studied at Lassen Volcanic National Park (California) in the Cascade Range. Taluses show a diverse flora, with 79 plant species; growth forms include coniferous trees, shrubs, suffrutices, herbs, graminoids, and ferns. Spatial patterns of plant distribution were studied along 40 point-intercept transects. Plant cover was low (0-32.7%) on all slopes, spatially variable, and showed no consistent trends. Sedimentological characteristics were determined by photosieving next to 1500 plants; this census indicated preferential plant growth on blocks and cobbles, with 43.2% and 23.3% of the plants growing on these stones, respectively; fewer specimens were rooted on pebbles (13%) or on stone-free gravel areas (20.5%). Growth forms displayed different substrate preferences: 92.5% of the shrubs and 83% of the suffrutices colonized blocks or cobbles, but only 57.2% of the herbs and 59.8% of the graminoids grew on large stones. Plants are associated with large clasts because (1) coarse talus is more stable than fine sediment areas, which are more frequently disturbed by various geomorphic processes, and (2) large stones help conserve substrate water beneath them while moisture quickly evaporates from fine debris.Root patterns were studied for 30 plant species; 10 specimens for each species were excavated and inspected, and several root growth ratios calculated. All species exhibited pronounced root asymmetry, as roots for most plants grew upslope from their shoot base. For 23 species, all specimens had 100% of their roots growing upslope; for the other 7 species, 92.2-99.3% of below-ground biomass extended uphill. This uneven root distribution is ascribed to continual substrate instability and resulting talus shift; as cascading debris progressively buries roots and stems, plants are gradually pushed and/or stretched downhill. Various disturbance events affect root development. Slope erosion following rubble removal often exposes plant roots. Debris deposition can completely bury plants; some may survive sedimentation, producing new shoots that grow through accumulated debris. Shrubs may propagate by layering, as adventitious roots develop along buried stems; or produce new clones along their roots. Slope processes may damage and transport plant pieces downhill; some species can sprout from severed, displaced root or stem fragments. Vegetation interacts with several geomorphic processes, including debris flows, grain flows, rockfall, snow avalanches, frost creep, and runoff. Larger plants may alter local patterns of debris movement and deposition, damming cascading debris on their upslope side and deflecting sediments laterally to plant margins, where they form narrow elongated stone stripes.  相似文献   

9.
Cactus seedlings often establish under nurse plants which modify environmental conditions by increasing moisture and decreasing solar radiation, which may cause beneficial and detrimental effects, respectively, on seedling growth. Three soil moisture treatments (5%, 25% and 60%) and two solar radiation levels (100% exposure=243 μmol m−2 s−1, and 40%=102 μmol m−2 s−1) were used in a factorial design to analyze seedling growth response of three rare cactus species (Mammillaria pectinifera, Obregonia denegrii and Coryphantha werdermannii). The variables evaluated were relative growth rate (RGR), root/shoot ratio (R/S), and K (RGRroots/RGRshoot), obtained from an initial seedling harvest (6-month-old seedlings) and a final harvest 6 months after treatment application. All three species had slow RGRs (0.002–0.012 g g−1 day−1). O. denegrii had the lowest RGR values, but was the only species for which R/S and K varied with soil moisture. While all seedlings responded markedly to soil moisture, no response was observed to radiation treatments. The latter might have been related to the relatively low solar radiation levels present in the greenhouse. Yet, our results suggest that the main benefit nurse plants offer to seedlings is the increase in soil moisture.  相似文献   

10.
Changes in dry matter accumulation and allocation, gas exchange, abscisic acid content (ABA) and water use efficiency (WUE) of three contrasting Populus davidiana ecotypes were recorded after exposure to five different soil water contents. The ecotypes used were from dry, middle and wet climate regions, respectively. In the controlled environment study, five different soil water contents which were watered to 100%, 80%, 60%, 40% and 20% field capacity were used, respectively. Significant differences in height growth (HT), total biomass (TB), total leaf area (LA), total leaf number (TLN), specific leaf area (SLA), root/shoot ratio (RS), net photosynthesis (A), transpiration (E), stomatal conductance (C), transpiration efficiency (WUET) and instantaneous water use efficiency (WUEi) between the ecotypes were detected under all soil water contents. Ecotypic differences in ABA and carbon isotope composition (δ13C) were also detected under low soil water contents, but these differences were not significant under high soil water content. Compared with the wet climate ecotype, the dry climate ecotype had lower HT, TB, LA, TLN, SLA, A, E and C, and higher RS, WUET and WUEi under all soil water contents. On the other hand, the dry climate ecotype also exhibited higher ABA and δ13C as affected by low soil water contents than the wet climate ecotype. These morphological and physiological responses to water availability showed that the different ecotypes may employ different survival strategies under drought at the initial phase of seedling growth and establishment. The wet climate ecotype possesses a prodigal water use strategy and quick growth, while the dry climate ecotype exhibits a conservative water use strategies and slow growth.  相似文献   

11.
The germination response of Denmoza rhodacantha (Salm-Dyck) Britton & Rose to seed scarification and different calcium concentrations was analysed. Both scarified and unscarified seeds were treated with two different calcium concentrations (1.74 or 6.36 meq l−1 calcium sulfate in distilled water). All treatments were conducted under a constant temperature (30 °C), and a photoperiodic regime of 12 h light and 12 h dark. Germination was initiated significantly sooner (3.6 days), and the rate of final germination was significantly higher (90.8%), for scarified seeds treated with a solution of 6.36 meq l−1 Ca compared with all other treatments (9.0–11.4 days and 3.6–6.8%, respectively). There were no significant differences among the treatments for the time in which 50% of final germination occurred (6.9–13.6 days). The results suggest that both factors, scarification and calcium concentration, favor germination of Denmoza seeds.  相似文献   

12.
Microcoleus vaginatus isolated from a desert algal crust of Shapotou was cultured in BG-11 medium containing 0.2 mol l−1 NaCl or 0.2 mol l−1 NaCl plus 100 mg l−1 sucrose, extracellular polymeric substances (EPS) or hot water-soluble polysaccharides (HWP), respectively. Photosynthetic oxygen evolution rates, photosystem II activity (Fv/Fm) and dark respiration of NaCl-stressed cells were enhanced significantly by the added sucrose or EPS under salt stress conditions (0.2 mol l−1 NaCl). Compared with cells treated with salt alone, sodium contents in cells reduced significantly; the content of cellular total carbohydrate did not change, and intracellular sucrose, water-soluble sugar increased significantly following the addition of exogenous carbohydrates. Sucrose synthase (SS) activity of NaCl-stressed cells increased following the addition of sucrose, and sucrose phosphate synthase (SPS) activity of NaCl-stressed cells increased following the addition of exogenous sucrose, EPS or HWP compared with cells stressed with NaCl only. The results suggested that the extruded EPS might be re-absorbed by cells of M. vaginatus as carbon source, they could increase salt tolerance of M. vaginatus through the changes of carbohydrate metabolism and the selective uptake of sodium ions.  相似文献   

13.
We measured and compared the δ13C values and nitrogen concentrations within the photosynthetic parts (Np) of phototrophs growing in different successional stages and different soil conditions at Ny-Ålesund, Svalbard, Norway. At all study sites, the Np value of vascular plants ranged from 1.0 to 2.2%. The Np value for most moss species was less than 1.0%; values for lichens were about 0.5%. No significant correlation was detected between Np and δ13C; however, different plant species occupied distinct fields on a δ13C–Np plot, with minimal overlap between species. The Np value of Saxifraga oppositifolia, which grew at all of the study sites, ranged from 1.1 to 1.5%. Differences in growth form had no effect on Np. The Np and δ13C values obtained for S. oppositifolia were confined to within a narrow range regardless of site conditions.  相似文献   

14.
霸王(Zygophyllum xanthoxylum)是荒漠区广为分布的一种多浆旱生植物。采用盆栽育苗的方法,初步评价了干旱胁迫下Na+对霸王根系生长的贡献,探讨了一种新型钠复合肥对霸王根系形态、生理学指标的影响。结果显示,钠复合肥能显著促进霸王根系的生长并提高其抗旱性:(1)正常浇水时,钠复合肥对霸王的促进作用主要体现在株高的增加和侧根的增长上,根系活力显著增强;(2)自然干旱15d后,钠复合肥使得霸王根系活跃吸收面积显著提高24%,促进主根的加粗和伸长以吸收更多的水分和矿质养分;(3)干旱胁迫下,钠复合肥处理使霸王根部Na+浓度保持较高水平,K+浓度下降42%。因此认为,干旱前钠复合肥显著促进了霸王侧根的生长和根系活力的提高,干旱后钠复合肥通过促进根系活跃吸收面积的扩大和主根的生长以提高霸王的抗旱性,其主要原因是根和叶中积累了较多的Na+、而非K+。  相似文献   

15.
Salinization and alkalinization are increasing problems in the world. Some land has been degraded to bare saline-alkaline soil where vegetation restoration is difficult because high toxic ionic content and pH are harmful to the survival of introduced plants. We grew Leymus chinensis with and without arbuscular mycorrhizal fungi (Glomus mosseae and G. geosporum) in either pots filled with soil from bare saline-alkaline land, or transplanted seedlings into field plots, to determine the influence of AM fungi on the reestablishment of this dominant grass species in bare degraded land. Association with AM fungi increased the absorption of N, P, K+, Ca2+, but decreased Mg2+, Na+ and Cl− uptake under saline-alkaline stress. Therefore, higher K/Na, Ca/Na, P/Na, and P/Cl ratios were found in the inoculated plants. Plants inoculated with AM fungi accumulated significantly higher biomass, root/shoot ratio and tiller number than non-inoculated plants. AM fungi also significantly increased the survival of seedlings when they were transplanted into a bare saline-alkaline land in the field. The improvement of survival, growth and asexual reproduction of inoculated plants indicated that the plant-AM fungi mutualism could improve the reestablishment of vegetation in bare saline-alkaline soil, drive the vegetation restoration to a community dominated by original species.  相似文献   

16.
A greenhouse experiment was conducted to explore whether additional nitrogen (N) supply could enhance carbon (C) accumulation, and phosphorus (P) use efficiency (NUEP) of Sophora davidii seedlings under dry conditions. Two-month-old seedlings were subjected to a completely randomized design with three water (80, 40 and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg−1 soil) regimes. Water stress decreased C, N and P accumulation, NUEP, N and P uptake efficiency (NUtEN and NUtEP) regardless of N supply. The S. davidii seedlings exhibited strong responses to N supply, but the responses were not consistent with the various N supply levels. Nl increased C, N and P accumulation, and improved NUEP, NUtEN and NUtEP in the same water treatment. In contrast, Nh did few or even depress effects on C, N and P accumulation, and NUEP, although NUtEN and NUtEP increased with Nh in the same water treatment. Even so, NUEN decreased with increase of N supply in the same water treatment. The results suggested that appropriate or low N supply should be recommended for S. davidii seedling establishment in dry environment by improving C accumulation and NUEP.  相似文献   

17.
The effects of temperature, water stress, hydration–dehydration cycles and seed priming on the germination of Callitris verrucosa and Callitris preissii, two Australian semi-arid coniferous tree species, were investigated. Optimum germination occurred at 18°C, with a minimum germination time of 8–9 days for both species. At this temperature, germination was inhibited at osmotic potentials lower than −1·0 MPa, but the capacity to germinate at low osmotic stress increased as the temperature decreased. Seed priming and hydration–dehydration cycles did not reduce seed viability, and Callitris seeds appear to retain the physiological changes induced by short-term hydration, as the time to the onset of germination was decreased to about 3 days. The capacity of Callitris seeds for incremental germination is likely to increase overall germination success in a low rainfall environment.  相似文献   

18.
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19.
The increased shear resistance of soil due to root-reinforcement by four common Australian riparian trees, Casuarina glauca, Eucalyptus amplifolia, Eucalyptus elata and Acacia floribunda, was determined in-situ with a field shear-box. Root pull-out strengths and root tensile-strengths were also measured and used to evaluate the utility of the root-reinforcement estimation models that assume simultaneous failure of all roots at the shear plane. Field shear-box results indicate that tree roots fail progressively rather than simultaneously. Shear-strengths calculated for root-reinforced soil assuming simultaneous root failure, yielded values between 50% and 215% higher than directly measured shear-strengths. The magnitude of the overestimate varies among species and probably results from differences in both the geometry of the root-system and tensile strengths of the root material. Soil blocks under A. floribunda which presents many, well-spread, highly-branched fine roots with relatively higher tensile strength, conformed most closely with root model estimates; whereas E. amplifolia, which presents a few, large, unbranched vertical roots, concentrated directly beneath the tree stem and of relatively low tensile strength, deviated furthest from model-estimated shear-strengths. These results suggest that considerable caution be exercised when applying estimates of increased shear-strength due to root-reinforcement in riverbank stability modelling. Nevertheless, increased soil shear strength provided by tree roots can be calculated by knowledge of the Root Area Ratio (RAR) at the shear plane. At equivalent RAR values, A. floribunda demonstrated the greatest earth reinforcement potential of the four species studied.  相似文献   

20.
The Mu Us Sandland is basically characterized by water shortage and high wind. Thus, wind-induced mechanical perturbation (MP) and soil water availability are likely to interact to affect plant growth. Since high water availability and MP can induce responses that are in the opposite direction, we hypothesized that MP effects on perennial grasses might be mitigated by increased soil water availability in the Mu Us Sandland. We counducted an experiment in which seedlings of Psammochloa villosa were subjected to two levels of MP (non-MP vs. MP 1 min d−1) and two levels of water availability (200 ml d−1vs. 400 ml d−1) and measured three plant traits. MP significantly decreased plant height, total biomass, and root/shoot ratio. There were significant interactions between MP and soil water availability on plant height and root/shoot ratio. These findings imply that MP alone is a stressful factor for P. villosa and MP effects on its growth can be partially mitigated by increased soil water availability, and also suggest that P. villosa may respond to MP in a way that allows plants to survive in the windy semiarid environments.  相似文献   

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