淹水胁迫对铺地黍几种保护酶活性的影响

目的:探讨淹水胁迫对铺地黍几种保护酶活性的影响.方法:通过模拟试验,研究不同淹水时间对铺地黍体内超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)及多酚氧化酶(PPO)活性的影响.结果:在淹水胁迫前期,铺地黍体内SOD、CAT和PPO活性总体表现为升高的变化特征.之后,随着胁迫时间的延长,3种酶活性均逐渐降低,在淹水5w时,SOD、CAT和PPO活性分别为对照的38.7%、50.3%和178.2%.而在整个淹水期间POD活性则一直呈升高的趋势.结论:几种保护酶对淹水胁迫的响应能力有差异,其中SOD、CAT活性的变化可作为铺地黍对淹水反应的生理指标.     

Higher treefall rates on slopes and waterlogged soils result in lower stand biomass and productivity in a tropical rain forest

1.  Relationships between tropical rain forest biomass and environmental factors have been determined at regional scales, e.g. the Amazon Basin, but the reasons for the high variability in forest biomass at local scales are poorly understood. Interactions between topography, soil properties, tree growth and mortality rates, and treefalls are a likely reason for this variability.
2.  We used repeated measurements of permanent plots in lowland rain forest in French Guiana to evaluate these relationships. The plots sampled topographic gradients from hilltops to slopes to bottomlands, with accompanying variation in soil waterlogging along these gradients. Biomass was calculated for >175 tree species in the plots, along with biomass productivity and recruitment rates. Mortality was determined as standing dead and treefalls.
3.  Treefall rates were twice as high in bottomlands as on hilltops, and tree recruitment rates, radial growth rates and the abundance of light-demanding tree species were also higher.
4.  In the bottomlands, the mean wood density was 10% lower than on hilltops, the basal area 29% lower and the height:diameter ratio of trees was lower, collectively resulting in a total woody biomass that was 43% lower in bottomlands than on hilltops.
5.  Biomass productivity was 9% lower in bottomlands than on hilltops, even though soil Olsen P concentrations were higher in bottomlands.
6.   Synthesis . Along a topographic gradient from hilltops to bottomlands there were higher rates of treefall, which decreased the stand basal area and favoured lower allocation to height growth and recruitment of light-demanding species with low wood density. The resultant large variation in tree biomass along the gradient shows the importance of determining site characteristics and including these characteristics when scaling up biomass estimates from stand to local or regional scales.     

Impacts of Boron Application on Maize Plants Growing under Flooded and Unflooded Conditions

Plants of maize (Zea mays L.) were waterlogged for 7 d and irrigated (root application) or sprayed (foliar application) with 0, 1, 3 and 6 mg dm-3 of boron. The stability of leaf membranes was assessed by determining leakage of electrolytes from leaf discs exposed to heat (51 °C) and dehydration (40 % PEG). Leaf membranes were more stable to heat than to dehydration. The membranes of waterlogged plants were more injured than those of control plants. Waterlogging reduced contents of dry mass, chlorophyll, soluble proteins, total free amino acids and soluble sugars and leaf relative water content (RWC). Application of boron increased the stability of leaf membranes, chlorophyll, soluble sugars, soluble proteins, amino acids contents, leaf RWC and dry mass accumulation. Foliar boron application was more effective. Application of boron alleviated the deleterious effect of waterlogging. This revised version was published online in July 2006 with corrections to the Cover Date.     

The possible consequences for herbage growth of waterlogging compacted pasture soils

Soil compaction through intensive stocking with cattle has been found to cause a reduction in herbage production which could be ameliorated by soil aeration. Depression in yield was evident under wet soil conditions suggesting that problems were created by poor aeration. The objectives were to identify and quantify the reduction processes in waterlogged pasture soil and to establish the sensitivity of herbage species to some potentially toxic products. Topsoil passed through a 5 mm mesh sieve and intact soil cores with surface vegetation were incubated anaerobically with or without added mineral-N. Also perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) were grown hydroponically to examine their sensitivity to high concentrations of Mn. Nitrate-N at the rate of 200 mg kg^–1 acted as a redox buffer in soil until it was denitrified. It delayed an increase in exchangeable Mn for around one day and exchangeable Re for at least 3 days. Almost all the water extractable Mn was cationic but most of the Fe was non-cationic. Ethylene reached a maximum concentration of around 5 µL L^–1 in 3 days and then decreased. Only very small concentrations of acetic acid were produced. Net mineralization of NH₄-N occurred during anaerobic incubation at about one eighth of the rate of denitrification and the process was not affected by added NO₃-N. Ryegrass was more tolerant than clover of high concentrations of Mn. Depletion of available nitrate through denitrification appeared to be the main reason for a decrease in growth of grass on waterlogged intact cores, but in field conditions where anaerobiosis is probably more severe there may be an additional effect of Mn toxicity to clover although ethylene is unlikely to cause physiological damage.     

Nutrient accumulation and translocation in maturing wheat plants grown on waterlogged soil

Wheat plants (Triticum aestivum L., cv. Arina) growing in large pots (perforated at the bottom for controls, intact for flooding) were embedded in the field in spring. Waterlogging was initiated at anthesis and was maintained throughout the maturation period. Grain yield as well as potassium, phosphorus and magnesium contents in the shoot were decreased on flooded soil, while manganese and iron contents increased considerably. Total calcium and zinc contents per shoot remained comparable to those in controls. The reduction of potassium, phosphorus and magnesium contents by waterlogging was greatest in the grains, while manganese and iron accumulated mostly in the vegetative parts and the glumes. Zinc contents were also lowered in the grains during waterlogging due to an inhibited redistribution from the vegetative parts to the grains. Our results indicate that flooding caused not only an accumulation of manganese and iron in the shoot, but also affected the redistribution of macro- and micronutrients to the maturing gains.     

Root porosity and oxygen movement in waterlogging-tolerant Trifolium tomentosum and -intolerant Trifolium glomeratum

Trifolium tomentosum and T. glomeratum are small (< 0·5 mg) seeded pasture legumes which are considered to be waterlogging tolerant and intolerant, respectively. The root porosity of the two species was compared for plants raised for 10 d in aerated nutrient solution and then transferred to either aerated (0·25 mol O₂ m^–3) or ‘hypoxic’ (0·031–0·069 mol O₂ m^–3) solutions for a further 7 and 21 d. After 21 d, T. tomentosum developed a root porosity of 11·2% in ‘hypoxic’ solution, which was significantly higher than the 6·1% developed by T. glomeratum. When grown in aerated solution, T. tomentosum also had a larger constitutive porosity (6·7%) than T. glomeratum (3·9%). Cylindrical root-sleeving O₂ electrodes were used to measure the rates of radial O₂ loss (ROL) from roots of the two species when in an O₂-free medium. In general, roots previously grown in ‘hypoxic’ solution had higher rates of ROL than roots grown in aerated solution. Moreover, the rates of ROL along the main root of T. tomentosum were ≈ 5-fold faster than from equivalent locations along roots of T. glomeratum. Manipulations of the shoot O₂ concentration resulted in rapid changes in ROL near the root tip of T. tomentosum plants raised in aerated or ‘hypoxic’ solutions, whereas for T. glomeratum ROL only increased for roots of plants raised in ‘hypoxic’ solution. Thus, the cortical air spaces in roots of both species raised in ‘hypoxic’ solution formed a continuous, low resistance pathway for O₂ diffusion from the shoots to the roots. ROL from the lateral roots was also evaluated and it was 3-fold faster from T. tomentosum than from T. glomeratum. Moreover, ROL from lateral roots of T. tomentosum was 10–20-fold higher than from a position on the primary root axis the same distance from the root/shoot junction. Relatively, high rates of ROL were also recorded for young (40 mm in length) lateral roots of T. glomeratum which were previously grown in ‘hypoxic’ solution, but the ROL was low for the older lateral roots of this species. The substantial amounts of ROL from the lateral roots may limit O₂ supply to the lower parts of the primary root axis, so that the laterals probably become the main functional root system in waterlogged soils.     

广西沿海红海榄造林的宜林临界线

2004年8月—2005年8月,在广西英罗湾滩涂上建造8个高程梯度(320~390cm,相邻梯级间高度差10cm)的试验平台,研究全日潮海区潮汐淹水胁迫对红海榄幼苗生长和生理指标的影响.结果表明:小高程(320~330cm)生境对红海榄幼苗茎高生长有微弱促进作用,340cm以上高程组幼苗茎高随滩涂高程增加而增大.中等高程(350~370cm)有利于幼苗茎节数的增长.滩涂高程越低,幼苗叶数、叶面积和叶保存率越低.小高程组幼苗叶片叶绿素a受损明显,叶绿素b则受损相对较轻;叶绿素a/b值随滩涂高程降低而减少.长时间淹水诱导使根系中SOD活性上升,叶片中则表现为中等高程组酶活性较低.叶片和根系中POD活性均随高程降低而增加.淹水胁迫使红海榄幼苗各器官及全株的生物量降低;随着淹水程度加大,新生器官生物量分配比例由叶向茎转移.随着高程降低,幼苗存活率从88.9%降至40.0%,但370cm以上高程组存活率均在80%以上.建议将当地平均海面线作为广西沿海红海榄胚轴造林的宜林临界线.     

Morphological and physiological reactions of young deciduous trees (Quercus robur L., Q. petraea [Matt.] Liebl., Fagus sylvatica L.) to waterlogging

One-year-old seedlings of Quercus robur L., Q. petraea (Matt.) Liebl. and Fagus sylvatica L. were cultivated in lysimeters and subjected to waterlogging for 17 weeks, interrupted by a five-week drainage period during summer. The growth of Q. robur was less affected by waterlogging than that of Q. petraea and Fagus. Waterlogging resulted in the formation of adventitious roots in Q. robur and Q. petraea, but not in Fagus. In contrast to Fagus, Q. robur and, to a lesser extent, Q. petraea were able to generate roots even below the water table. The hydraulic conductance of the excised root systems, the stomatal conductance and, in Fagus, the leaf water potential and the leaf-mass related hydraulic conductance were decreased by waterlogging. The decrease in the hydraulic conductance was largest in Fagus, and smallest in Q. robur. The roots of Fagus responded to anaerobic conditions with an increase in ethanol concentration. The measurements of nitrate reductase activities in roots and leaves provided no indications of a persistent contribution of NO₃ ⁻ metabolism to the alleviation of waterlogging-induced stress. It is concluded that Q. robur and, to a lesser extent, Q. petraea can tolerate waterlogging periods better than Fagus due to a different pattern of root formation, and to a better adjustment of leaf biomass production to the hydraulic conductivity of the root system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Flooding tolerance of Carex species in relation to field distribution and aerenchyma formation

The flooding tolerance of Carex species was studied in relation to their field distribution and their capacity to form root aerenchyma under controlled conditions. In an alpine meadow, six Carex species were selected which were distributed in a clear zonation correlating with water content of the soil. Carex sempervirens and C. ferruginea were only found on nonflooded soil, the latter species preferring moister conditions. Carex davalliana and C. nigra were both associated with water-saturated soil, whereas C. limosa and C. rostrata preferred partially submerged conditions. Carex davalliana and C. limosa were bound to flooded soils with a relatively high redox potential and horizontally flowing groundwater. Carex rostrata and C. nigra grew in stagnant soil-flooded conditions with low soil redox potentials. The amount of aerenchyma in the roots of all species increased when grown in oxygen-deficient stagnant agar. This increase in root porosity, combined with increased root diameter, presumably improved internal aeration of the roots. Although all species survived experimental soil flooding, partial submergence was lethal to C. sempervirens and, surprisingly, also to the wetland species C. davalliana. Carex ferruginea showed a reduced growth rate during partial submergence. The three other species, all wetland plants, reached highest biomass production under soil-flooded and partially submerged conditions, with slower growth on free-draining soil. It is concluded that aerenchyma is not constitutive in the Carex species under study, and is best developed in Carex species from wetlands. Species with less aerenchyma perform poorly when soil-flooded, but conditions of partial submergence could even affect species with a considerable amount of root aerenchyma.