Symbiotic nitrogen fixation and physiological performance of bean (Phaseolus vulgaris L.) plants as affected by Rhizobium inoculum position and bean rugose mosaic virus infection

Bean (Phaseolus vulgaris L. var. Tacarigua) plants were grownin sterilized Leonard jars under controlled conditions. Beforesowing, 1 g of gamma irradiated peat containing the Rhizobiumtropici strain CIAT899 was placed at either 2 or 10 cm belowthe sand surface. Mechanical infection of bean rugose mosaicvirus (BRMV) was carried out in 3-d-old seedlings. Thus, theearly events of nodulation occurred before the arrival of virusparticles to roots. Rhizobium inoculation at 2 cm deep resultedin the formation of nodule clusters close to the crown, in contrastto the homogeneous nodulation along the roots observed in plantsinoculated with Rhizobium at a depth of 10 cm. The uniform arrangementof nodules on the roots enhanced the plant shoot biomass, althoughthe total nodule mass per plant did not differ between Rhizobiuminoculation treatments. Nodules located on deeper roots resultedin higher ureide concentrations in shoots and leaves and inreduced carbohydrate concentrations in leaves. In healthy plants,nodules formed on deeper roots had higher allantoinase activityand a greater carbohydrate concentration when compared to thatof nodules located close to the crown. Deeper nodules had ureideconcentrations similar to those of upper nodules, probably asa consequence of increased translocation of N-compounds to aerialorgans. A similar pattern of nodule formation and response toinoculum position was observed in BRMV-infected plants at allharvests. However, virus infection resulted in reduced totalnodule mass, shoot biomass, total leaf area and induced transitoryalterations in the ureide, -amino-N and carbohydrate concentrationin the different plant compartments. The effect of BRMV infectionon plant parameters was more evident during the vegetative stagesof growth. Nevertheless, the magnitude of the effect was alwaysmore pronounced in plants inoculated with Rhizobium at a depthof 2 cm compared to those Inoculated at 10 cm due to a greateractivity of deeper nodules despite virus infection. Deeper nodulesin BRMV-infected plants showed higher carbohydrate concentrationas well as higher allantoinase and uricase activity than thosedeveloped close to the crown, at all harvests. This observationwas further supported by ultrastructural analysis of virus-infectednodules, since virus replication took place in cells containingbacteroids of upper and lower nodules, but only in the interstitialcells of the latter. BRMV infection did not hinder the allantoinaseactivity and the chlorophyll content of uppermost mature leavesregardless of inoculum position. At the flowering and fruitingstages, healthy and BRMV-infected plants did not differ withregard to any of the tested parameters. Only inoculum positionhad an effect. The nearly normal functioning of the symbioticprocess at these stages of growth was attributed to the formationof a new generation of nodules in BRMV-infected plants subjectedto each of the Rhlzobium inoculation treatments. Key words: Bean rugose mosaic virus, symbiotic nitrogen fixation, bean, Rhizobium inoculum position, nodule ultrastructure     

Sowing and transplantation of Adonis ramosa (Ranunculaceae) for the establishment of a new population in a seminatural broad-leaved deciduous forest floor

Adonis ramosa (Ranunculaceae) is a plant whose risk of extinction is increasing in Japan. In this study, we show that there is a significant possibility of establishing an A. ramosa population by sowing seeds or transplanting plants in a seminatural broad-leaved deciduous forest floor. Immediately after seed collection in early June, seeds were sown either in pots that were watered periodically or in a deciduous forest floor where the soil surface was prepared. In the following spring, 30–40% of the seeds germinated. Of the one-year-old plants buried at a depth of 2 cm and two-year-old plants buried at a depth of 2 or 8 cm in the fall, 96% sprouted leaves in the following spring. However, 79% of the one-year-old plants buried at a depth of 8 cm sprouted leaves. In spring, the number of leaves, the widths of individual plants, and the heights of the two-year-old plants were greater than those of the one-year-old plants. The dry weights of one- and two-year-old plants in fall after one spring growing season increased by 1.6–2.3 times and by 2.3–5.1 times, respectively, compared to the dry weight at the time of transplanting. Also, the dry weights of the plants transplanted at a depth of 8 cm were higher than those of plants transplanted at a depth of 2 cm for both one- and two-year-old plants. The results suggest that the growth conditions at a depth of 8 cm are more favorable than those at a depth of 2 cm.     

The effect of Erwinia carotovora subsp. atroseptica (blackleg) on potato plants. II. Compensatory growth

In field experiments in 1981 and 1982, uninoculated seed tubers (cv. Désirée) and those inoculated with Erwinia carotovora subsp. atroseptica at the rose (apical) or heel (stolon attachment) ends were planted at normal (35 cm) or double spacing; in additional plots, inoculated and uninoculated tubers were planted alternately. Inoculation, especially at the rose end, decreased plant height and sometimes resulted in blackleg symptoms. Individual plant yields were recorded at the end of the season. In plots of uniform seed type at normal spacing, inoculation decreased total yield compared with uninoculated by 12–13% (heel-end inoculation) or 26–40% (rose-end inoculation). At double spacing, yields increased compared with normal spacing by 44–58% (uninoculated or heel-end inoculation) or 30–39% (rose-end inoculation). When rose-end-inoculated and uninoculated seed tubers were planted alternately, inoculated plants yielded less and uninoculated plants more than in plots planted throughout with the same seed treatment. The abilities of inoculated and uninoculated plants to compensate for weak or missing neighbours were combined using equations to predict the yields of crops with different proportions of diseased or missing plants.     

Effects of experimental stem burial on radial growth and wood anatomy of pedunculate oak

In dendrogeomorphology, abrupt changes in wood anatomy are frequently used to date the exact year of burial and exposure events. However, few studies have addressed the precision and underlying mechanisms of these changes. In a field experiment, performed in a drift-sand area in the Netherlands, we buried the stems of mature pedunculate oak trees (Quercus robur L.) up to a height of 50 cm and analysed the responses in ring width and earlywood-vessel characteristics, while monitoring the course of temperature above and below the soil surface.After 3 years of stem burial, we found no significant differences in ring width and earlywood-vessel characteristics between control and buried trees both above and below the burial level. Burial however strongly reduced temperature amplitude and the occurrence of sub-zero temperatures around the buried stems. All buried trees formed epitropic roots that grew upward into the new sediment layer, but no adventitious roots were formed on the buried stems. Irrespective of the burial treatments, we found that the mean ring width was largest at the original stem base and lowest at breast height. In contrast, vessel sizes were significantly larger at breast height compared with the stem base. Differences in vessel density barely differed between years and heights.In our field experiment on mature pedunculate oak trees, the burial of stems by 50 cm of drift sand did not induce any local growth suppression or detectable changes in wood anatomy. As wood-anatomical changes in response to burial have previously been reported for trees that had formed adventitious roots, we stress the role of adventitious-root formation as a possible trigger behind the local changes in wood anatomy, reflecting a functional change of a buried stem towards a root. Based on our field experiment, it seems unlikely that years of shallow or moderate burial events (≤50 cm) can be reconstructed using the wood structure of buried stems. As epitropic roots develop quickly after burial, dating such roots may potentially yield better estimates of burial events. Further research on the relation between adventitious root and changes in stem anatomy is needed to ascertain the precision of dating sand-burial events using tree rings.     

Effects of sand burial on purple sandgrass (Triplasis purpurea): the significance of seed heteromorphism

The effects of sand burial on seedling emergence, growth, and reproduction of the annual dune grass Triplasis purpurea (Walt.) Chapm. were examined. This species matures heteromorphic seeds on panicles enclosed by leaf sheaths along tiller nodes in a characteristic pattern: seeds at the lower nodes are heaviest, whilst those at the upper nodes are lightest. Field excavation of seedlings revealed that seedlings can emerge from seeds buried to 4 cm.In one experiment in an incubator, seeds collected from the upper and lower tiller nodes of glasshouse-grown parental plants were buried in sand at depths of 0, 3, and 6 cm. As expected, the effects of seed depth on seedling growth were due to delayed emergence for seedlings from buried seeds. However, seedlings from the larger seeds from the lower nodes of parental plants had significantly greater dry mass than those from the lighter seeds from upper nodes. Because lower node seeds are the most likely to become buried by sand in nature, the seed heteromorphism may be adaptive in the coastal environment.A second experiment involved the burial of seedlings to 0, 50, or 100% of their height. Although most seedlings did not survive complete burial (100% height), for partially buried seedlings (50% height) there was high survival and a marked stimulation of growth and eventual reproduction compared to unburied seedlings. This stimulation could be linked to increased root growth for seedlings that had been buried. The ability to respond positively to sand accumulation may represent an adaptation to the dynamic dune environment.     

Survival and Growth of Planted Uniola paniculata and Dune Building Using Surrogate Wrack on Perdido Key Florida,U.S.A.

The increasing number of stresses on coastal dune ecosystems requires the use of more effective restoration strategies to enhance dune‐building and increase vegetation reestablishment. In this study, the use of a wheat straw as a surrogate wrack was an effective method to improve growth of spring planted Uniola paniculata (sea oats). Approximately 1,000 U. paniculata plugs were planted within 21 × 4 m plots at six replicate sites. Two weeks later, plantings were divided into 11 × 4 m subplots with half of the subplots receiving five bales of wheat straw and the remaining subplots receiving no wheat straw. This surrogate wrack layer measured approximately 10 cm in depth. Mean aboveground biomass of U. paniculata 6 months after planting with surrogate wrack was 9.25 ± 1.00 g compared with 2.18 ± 0.24 g without surrogate wrack. Number of tillers, tiller height, and basal width were also greater at the end of the first growing season for plants treated with surrogate wrack (p < 0.05). Two years after planting, significantly more inflorescences occurred and aboveground biomass (g/m²) was greater with than without surrogate wrack. Sand accumulation was notably greater with surrogate wrack (11.16 cm) than without wrack (7.78 cm) 8 months after planting (p = 0.1093). However, relative sand accumulation was significantly greater with than without surrogate wrack 2 years after planting. Increased sand accumulation suggests surrogate wrack either directly or indirectly traps more sand by creating an additional obstacle or promoting the growth of dune grasses.     

沙埋和种子大小对固沙禾草沙鞭的种子萌发与幼苗出土的影响

该文研究了野外条件下不同深度的沙埋对沙鞭(Psammochloa villosa)种子萌发和幼苗出土的影响,以及温室条件下种子大小对不同深度沙埋后的种子萌发和幼苗出土的影响。结果表明,沙埋深度显著影响沙鞭的种子萌发率、幼苗出土率和种子休眠率。沙子表面的种子不能萌发。2 cm的浅层沙埋时的种子萌发率和幼苗出土率最高,1 cm 沙埋的种子萌发率和幼苗出土率次之。沙埋深度超过2 cm之后,沙鞭的种子萌发率和幼苗出土率与沙埋深度呈负相关。2 cm的种子休眠率最低。从2 ~12 cm,种子休眠率随着沙埋深度的增加而增加。在幼苗能够出土的深度(1~6 cm),幼苗首次出土所需的时间随着沙埋深度的增加而延长。种子大小对沙鞭的种子萌发率没有显著影响。但是在深层沙埋(6 cm)时,与小种子相比,大种子产生的幼苗的出土率较高。从2~6 cm,大种子形成的幼苗的茎长度都较长。     

Seed size and seedling emergence: an allometric relationship and some ecological implications

We develop a geometric model predicting that maximum seedling emergence depth should scale as the cube root of seed weight. We tested the prediction by planting seeds from 17 species ranging in weight from 0.1 to 100 mg at a variety of depths in a sand medium. The species were spread across 16 genera and 13 families, all occurring in fire-prone fynbos shrublands of South Africa. Maximum emergence depth was found to scale allometrically with seed weight with an exponent of 0.334, close to the predicted value. We used the allometry to predict recruitment response to experimentally simulated variation in fire intensity. Five species with small (<2 mg) seeds and five with large (>10 mg) seeds were planted at ≤20-mm and 40-mm depths and exposed to low and high heat treatments and a control. The allometric equation predicted that species with large seeds would be able to emerge from a depth of 40 mm but those with small seeds would not. Only 1% of 481 seedlings from small-seeded species emerged from the 40-mm planting compared with 40% of 626 seedlings from the large-seeded group. The simulated fire treatments killed seeds in shallow, but not deeper, soil layers. At simulated high fire intensities, seedling emergence was poor in small-seeded species but good in large-seeded species, with most seedlings emerging from the 40-mm planting depth. Seed size could be a useful general predictor of recruitment success under different fire intensities in this system. We suggest that allometric relationships in plants deserve wider attention as predictive tools. Received: 28 September 1998 / Accepted: 3 March 1999     

Burial of canopy-stored seeds in the annual psammophyte Agriophyllum squarrosum Moq. (Chenopodiaceae) and its ecological significance

Agriophyllum squarrosum Moq. is a dominant annual on sand dunes in the arid regions of central Asia. A high percentage of seeds is retained on dead plants which become covered by moving sand, but little is known about the ecological significance of burial of canopy-stored seeds. We investigated the size and dynamics of the buried canopy-stored seed bank and effects of burial on seed germination. In March (during the windy season), May (beginning of the germination season), and July (middle of the growing season), the number of seeds per square meter in sample plots in the dunes was 623, 223 and 22, respectively, with 54.6, 30.6 and 12.9% of the total seeds retained on buried plant canopies. In a controlled experiment, more seedlings emerged from released (dispersed) than from canopy-stored seeds when burial depth was the same. No viable ungerminated released seeds were found, but 45–80% of the ungerminated canopy-stored seeds were viable. In general, with an increase in applied water germination of released seeds buried at a depth of 1 or 2 cm and of canopy-stored seeds buried at 1 cm increased, but regardless of watering regime few or no released seeds at 4 cm or canopy-stored seeds at 2 or 4 cm germinated. Significantly more seedlings emerged from plants buried in a horizontal than in a vertical position. Seedlings originating from buried canopy-stored seeds on an active dune accounted for only 5.4% of the total seedlings emerging, and most of them emerged later than those from released seeds. Thus, seed release is more effectively postponed in buried than in exposed canopies, and burial of canopy-stored seeds is a mechanism that helps regulate seed germination and seedling emergence of A. squarrosum on active dunes.     

Effects of sand burial depth on seed germination and seedling emergence of Cirsium pitcheri

A greenhouse study was conducted to determine the effects of sand burial on seed germination and seedling emergence of Cirsium pitcheri, a threatened species along Lake Huron sand dunes. In October 1996, seeds of C. pitcheri were sorted into three groups (small, medium and large) and artificially buried at 2, 4, 6, 8, 10 and 12 cm depths in plastic pots filled with unsterilized sand from Lake Huron sand dunes. These pots were placed outside in sand boxes for natural stratification. In early February, the pots were brought into the greenhouse for germination of seeds. Data showed that percent seed germination and emergence of seedlings were not related to seed size. However, both variables were negatively correlated with depth. Seedling emergence occurred from a maximum depth of 6 cm with most seedlings emerging from 2 cm depth. Only one seedling emerged from 8 cm depth. Seedlings from large seeds produced longer roots than those of small seeds. Larger root system would probably enhance seedling establishment.     

Effects of litter accumulation and water table on morphology and productivity of Phragmites australis

Phragmites australis (Common reed) occurs in the interface between water and land. The water depth gradient from deep water to dry land is inversely related to litter accumulation. Eutrophication can result in an excessive production of litter, which may have a large impact on the occurrence of P. australis in this gradient. In an outdoor pot experiment, it was investigated how water tables in combination with substrates containing variable amounts of litter affect morphology and productivity of P. australis. Vegetatively propagated P. australis was grown in pots filled with river sand, litter, and different mixtures of sand and litter (25, 50 and 75% by volume). Four water table treatments were applied; drained (–12 cm), waterlogged (0 cm), flooded (+12 cm), and weekly fluctuating drained and flooded conditions (–12/+12 cm of water relative to substrate level). When drained, no differences between substrate treatments were present. Waterlogging, flooding fluctuating water table treatments caused growth reduction in substrate containing litter. The plants formed short shoots and thin rhizomes. With increasing water table, allocation of dry matter to stems increased at the expense of leaves and rhizomes. At intermediate levels of litter in the substrate, allocation to leaves was lowest. In both instances a lower leaf weight ratio (LWR) was (partly) compensated for by a higher specific leaf area (SLA), resulting in less pronounced differences in leaf area ratio (LAR). Aquatic roots developed when plants were waterlogged or flooded, and increased when litter was present in the substrate. Aquatic roots were formed in the top soil layer when waterlogged. The percentage of aquatic roots increased with increasing amount of litter in the substrate when plants were flooded. It was concluded that the morphological responses of P. australis to litter strongly constrain its ability to maintain itself in deep water when the substrate contains litter. This might one of the explanations for the disappearance of P. australis along the waterward side of littoral zones.     

风蚀和沙埋对塔克拉玛干沙漠南缘骆驼刺水分和光合作用的影响

塔克拉玛干沙漠南缘风沙活动十分频繁, 风蚀和沙埋是该地区自然植被生长发育的重要影响因子。该文以塔克拉玛干沙漠南缘策勒绿洲-沙漠过渡带为研究区, 以该区域主要建群种植物骆驼刺(Alhagi sparsifolia)为研究对象, 对一次强沙尘天气过后沙丘表面5种不同风蚀沙埋状况的骆驼刺植物进行标定(包括10 cm风蚀、5 cm风蚀、不蚀不积、10 cm沙埋、30 cm沙埋), 天晴后测定其叶水势、叶片含水量、光合参数和叶绿素荧光等参数, 分析研究自然环境条件下风蚀和沙埋对骆驼刺水分和光合作用的影响。结果表明: (1)风蚀显著降低了骆驼刺叶水势和叶片含水量, 进而导致植物气孔导度降低, 并引起植物光合速率和蒸腾速率的下降。风蚀的植物水分利用效率低于沙埋, 特别是在10 cm风蚀深度明显降低。 (2)沙埋增加了骆驼刺的叶水势、叶片含水量和气孔导度, 并引起植物光合速率和蒸腾速率的上升, 水分利用效率也得到提升。(3)风蚀条件下骆驼刺所受胁迫增加, 但可以通过增加活性反应中心的数量和光化学效率来抵消胁迫造成的不利影响。沙埋条件下骆驼刺受胁迫减轻, 反应中心吸收的光能和用于光化学反应的能量随着沙埋程度增加而减小, 这是骆驼刺适应风沙环境的一种生存策略。(4)与5 cm风蚀以及10 cm沙埋相比, 10 cm风蚀显著抑制骆驼刺的生长, 30 cm沙埋则会显著促进骆驼刺的生长。     

Effects of wind erosion and sand burial on water relations and photosynthesis in Alhagi sparsifolia in the southern edge of the Taklimakan Desert

塔克拉玛干沙漠南缘风沙活动十分频繁, 风蚀和沙埋是该地区自然植被生长发育的重要影响因子。该文以塔克拉玛干沙漠南缘策勒绿洲-沙漠过渡带为研究区, 以该区域主要建群种植物骆驼刺(Alhagi sparsifolia)为研究对象, 对一次强沙尘天气过后沙丘表面5种不同风蚀沙埋状况的骆驼刺植物进行标定(包括10 cm风蚀、5 cm风蚀、不蚀不积、10 cm沙埋、30 cm沙埋), 天晴后测定其叶水势、叶片含水量、光合参数和叶绿素荧光等参数, 分析研究自然环境条件下风蚀和沙埋对骆驼刺水分和光合作用的影响。结果表明: (1)风蚀显著降低了骆驼刺叶水势和叶片含水量, 进而导致植物气孔导度降低, 并引起植物光合速率和蒸腾速率的下降。风蚀的植物水分利用效率低于沙埋, 特别是在10 cm风蚀深度明显降低。 (2)沙埋增加了骆驼刺的叶水势、叶片含水量和气孔导度, 并引起植物光合速率和蒸腾速率的上升, 水分利用效率也得到提升。(3)风蚀条件下骆驼刺所受胁迫增加, 但可以通过增加活性反应中心的数量和光化学效率来抵消胁迫造成的不利影响。沙埋条件下骆驼刺受胁迫减轻, 反应中心吸收的光能和用于光化学反应的能量随着沙埋程度增加而减小, 这是骆驼刺适应风沙环境的一种生存策略。(4)与5 cm风蚀以及10 cm沙埋相比, 10 cm风蚀显著抑制骆驼刺的生长, 30 cm沙埋则会显著促进骆驼刺的生长。     

The role of seed depth,litter, and fire in the seedling establishment of amphicarpic peanutgrass (Amphicarpum purshii)

Summary Amphicarpum purshii is an annual grass which mostly grows in disturbed areas of the New Jersey Pine Barrens, USA. It is amphicarpic, producing spikelets (and seeds) both above and below the soil surface. Previous research has shown that subterranean seed production ensures reproduction in the event of a major disturbance such as fire and results in rapid post-burn colonization of these sandy habitats. The effects of fire, litter, and seed depth were further examined by planting subterranean seeds at four depths in 16 litter-covered flats buried at ground level and comparing plants arising from burned flats with those in undisturbed litter-covered flats. At 0 and 1 cm depth, rates of seedling emergence were lowest in burned flats. Surface-sown seeds produced seedlings more likely to desiccate. Sowing depth had a greater influence on most measured characters than burning treatments. The mean depth of subterranean seed placement by Amphicarpum is 3.5 cm and this coincides with the seed depth from which plants showed the greatest height growth, shoot biomass, and reproductive output. In a second experiment, subterranean seeds on the bare soil surface in clay pots were more likely to lose viability and less likely to germinate than seeds protected by litter or burial in soil. In addition to providing protection from fire, placement of seeds below ground in the sandy habitat of peanutgrass provides conditions more suitable for seed survival and subsequent seedling establishment.     

柠条人工林细根不同分枝根序寿命估计

植物细根在发育结构上表现的形态特征和生理功能异质性影响细根寿命的准确估计,因此了解分枝根序细根寿命差异对于深入认识细根的周转过程和陆地生态系统碳分配具有重要意义。采用微根管(Minirhizotron)技术对晋西北黄土区的五年生柠条(Caragana Korshinskii Kom.)人工林细根的生长过程进行了为期3a(2007—2009年)的追踪观测,分析了不同因素(土层深度、季节变化、空间位置)对一级根和高级根寿命的影响。结果表明:(1)在各土层深度处,一级根的中值寿命均低于高级根中值寿命,其中一级根中值寿命表现随土层深度增加而增加趋势,而高级根除表层0—20 cm中值寿命较短外,各土层间变化趋势不明显,40—60 cm、80—100 cm土层高级根在观测期结束时其累积存活率仍在50%以上;(2)不同季节出生一级根和高级根的中值寿命季节性表现为:秋季夏季春季,并且在各个季节均表现,高级根寿命显著大于一级根寿命(P0.01);一级根仅夏季与秋季差异性不显著(P0.05),而高级根仅春季与秋季存在极显著差异(P0.01);(3)一级根和高级根距树干基部0 cm处细根中值寿命均大于50 cm处一级根和高级根细根的中值寿命。同一位置处高级根寿命要大于一级根寿命。在距树干基部0 cm处和50 cm处,一级根和高级根的寿命均存在极显著差异(P0.01),但高级根却在距树干基部0 cm和50 cm处差异不明显,而一级根却表现极显著差异(P0.01)。     

在旱化土壤条件下来自不同生境的20种植物幼苗根系的形态反应的比较(英文)

在浇水和未浇水的塑料管中栽培了 2 0个植物种 ,测量了其幼苗的根深、根重和茎重。这些种的原始生境含水状况差异较大 ,是从沼泽到沙漠的系列。植物种原始生境的水分状况用Ellenberg水分序数定量。幼苗首先在湿沙中生长 2 1d ,然后进入为期也是 2 1d的处理阶段 (浇水和不浇水 )。浇水植株的根深与Ellenberg水分序数无关。在旱化的沙层中 ,源于干旱生境的植物的根深趋向于增加 ,来自湿润生境的则减少。根深塑性 (即未浇水的根深 /浇水的根深 )与Ellenberg水分序数显著相关 (R2 =0 .5 6 ) ,茎 /根比值塑性也与Ellenberg水分序数相关 ,但不如根深塑性的关系明显。根深塑性表现最为明显的植物种具有在未浇水沙层中维持茎生长的最大能力。有迹象表明 ,在浇水处理时 ,来自很干旱生境的植物生长减弱。研究结果表明 :幼苗利用深层水分的能力是植物对干旱生境的主要适应。     

在旱化土壤条件下来自不同生境的20种植物幼苗 根系的形态反应的比较

Rooting depth and root and shoot biomass were measured for seedlings of 20 species in both watered and unwatered sand columns. The species were from habitats of widely varying moisture status, ranging from marsh to desert. Moisture status of the species' habitats was quantified as Ellenberg moisture number. Seedlings were allowed to grow in moist sand for 21 days and were then exposed to the treatments (watered and unwatered) for a further 21 days. Rooting depth of control plants was not correlated with Ellenberg number. Riit depth of plants from dry habitats tended to increase in drying sand, while roots of plants from wet habitats decreased in depth. Plasticity of rooting depth (depth in unwatered/depth in watered sand) was significantly correlated with Ellenberg number (r2=0.56). Plasticity of shoot/root ratio was also correlated with Ellenberg number, but the relationship was weaker than for rooting depth plasticity. Species that showed the greatest pasticity in rooting depth also showed the greatest ability to sustain shoot growth in unwatered sand. There was some evidence that growth of plants from very dry habitats was reduced in the watered treatment. Results of this study suggest that a major, although not the only, adaptation of plants of dry habitats is the ability of their seedlings to exploit deeply buried water resources.     

泥沙掩埋和干旱对三峡库区消落带狗牙根生长恢复的影响

三峡库区消落带植物恢复不仅面临长期淹水逆境,还面临泥沙、干旱等环境因素的胁迫。蓄水期后引种三峡库区消落带狗牙根,掩埋于不同粒径和埋深的沉降泥沙,探讨泥沙掩埋、干旱对反季节淹水后狗牙根出苗和生长恢复的影响。结果表明:在埋深≥8cm和粒径1.25 mm条件下消落带狗牙根萌发苗不能穿透覆盖层出苗。泥沙掩埋导致狗牙根出苗率显著降低,随着埋深增加狗牙根出苗率迅速下降;并且在埋深相同的条件下随着粒径减小狗牙根出苗速率呈增大趋势。随着埋深增加和粒径减小处理组株高、叶长的增长显著被抑制,处理组的株高、叶片数、叶长显著低于对照组。随着干旱、泥沙掩埋复合胁迫时间延长狗牙根分株株高、叶片数、叶长、叶宽的生长发育显著被抑制,且随着泥沙粒径减小和埋深增加其光合电子传递速率呈显著降低趋势,热耗散量显著增大。同时,干旱、泥沙掩埋复合胁迫导致处理组分株光合电子传递速率和热耗散能力显著低于对照组,光合作用能力显著降低,易受到夏季高光伤害。因此,三峡库区周年淹水导致狗牙根对泥沙掩埋以及干旱复合胁迫的耐受能力显著降低,在泥沙掩埋以及干旱复合胁迫下消落带狗牙根的生长恢复能力随粒径减小和埋深增加呈显著降低趋势,会导致库区消落带狗牙根种群衰退演替加快。     

海滨沙地单叶蔓荆匍匐茎对沙埋适应的生长对策

单叶蔓荆(Vitex trifolia var.simplicifoli)是一种耐盐、耐旱固沙地被植物。依据海滨沙地自然沙埋特点对单叶蔓荆匍匐茎进行了不同厚度(半埋和全埋)和不同长度交叉沙埋处理,研究探讨了单叶蔓荆沙埋适应生长对策,为其开发利用、科学管理和海滨环境修复提供指导。结果表明,正常情况下,单叶蔓荆匍匐茎基部和中部生长缓慢,顶部生长快。轻度(沙埋匍匐茎基部)和中度(沙埋匍匐茎基部和中部)半埋和全埋使匍匐茎顶部生长加速,茎长增长量较对照高出1.5到3.1倍;但重度(沙埋整个匍匐茎)半埋和全埋使匍匐茎顶部净增长量减少12%和13%。在20d沙埋中,对照整个匍匐茎各段均无不定根长出,但不同程度半埋和全埋沙埋处理下沙下匍匐茎上均长出不定根,重度半埋使不定根生长受抑;同时匍匐茎上各段茎生物量上升,枝叶生物量下降,且随着沙埋程度的增加而增减幅度提高,在重度半埋和全埋达到最大。在轻度和中度半埋和全埋下,匍匐茎上未沙埋部位枝条生长加速。研究表明,在自然环境中,单叶蔓荆匍匐茎顶端是一个对环境变化反应敏感的部位,并与沙埋后单叶蔓荆茎延伸生长和植株能否生存密切相关。当匍匐茎顶部没被沙埋时,沙埋促进沙埋部位匍匐茎和枝叶中物质转移,加速匍匐茎顶部快速生长和物质积累以弥补沙埋带来的损伤维持物质和能量的代谢平衡。沙埋后,单叶蔓荆以茎顶端快速生长、形成不定根、枝条生长维持茎水分平衡和能量和物质代谢平衡,以快速生长摆脱沙埋影响的生长方式为其对沙埋环境的重要适应对策。因此,在海岸沙地单叶蔓荆种群管理和维护中,在强风移沙引起的重度沙埋后,及时剥离匍匐茎顶部沙子对维护单叶蔓荆种群的延续生存和扩散均有重要作用。     

The effect of granular nematicide incorporation depth and potato planting depth on potatoes grown in land infested with the potato cyst nematodes Globodera rostochiensis and G. pallida

Field experiments at Harper Adams, Shropshire and Wisbech, Cambridgeshire investigated the effect of nematicide incorporation and seed tuber planting depth on the yield of the potato (Solamum tuberosum L.) cultivars Estima and Maris Piper and the population control of the potato cyst nematodes Globodera rostochiensis Woll. (Skarbilovich) and G. pallida (Stone). The nematicide fosthiazate was applied at 3 kg^?1 ha and either not incorporated, or incorporated to 20 cm or 35 cm. Potatoes were mechanically planted to three depths; approximately 10 cm, 15 cm and 25 cm. Incorporation to 20 cm with tubers planted at a depth of 10 cm or 15 cm, reduced root invasion compared with the other treatments. Incorporating nematicide to 20 cm also gave consistently higher ware yields and better nematode control than the other incorporation methods, which were not significantly different to the control. However, ware yield and nematode multiplication rate were not significantly affected by planting depth.