Herbivory pattern and induced responses to simulated herbivory inQuercus mongolica var.grosseserrata

Seasonal changes in leaf traits and the herbivory pattern ofQuercus mongolica var.grosseserrata were studied, and simulated herbivory experiments were carried out in order to evaluate leaf trait responses. Leaves ofQ. mongolica emerged simultaneously in spring and most were retained until autumn. Nitrogen concentration was highest when leaves first emerged and decreased rapidly with leaf age. Leaf mass per area (LMA) increased with leaf age. Herbivore attack was concentrated in the first 20 days after bud-break, which corresponded to the high nutritional value of the leaves for herbivores at this time. Simulated herbivory experiments indicated that LMA increased with artificial leaf damage, suggesting an increase in leaf toughness, and that nitrogen concentration decreased later in the season in comparison with intact leaves. As a result, herbivore attack following artificial leaf damage decreased with increasing initial leaf damage. However, leaf longevity was not affected by initial leaf damage. These responses were considered to be a strategy to disperse herbivory damage among leaves.     

Stand dynamics during a 12-year period in a second-growth stand in a cool temperature forest in northern Japan

In 1981 and 1993, trees over 2 m high were measured and mapped to clarify stand dynamics in two permanent plots of 0.1 ha in a secondary, cool temperate, mixed broadleaf/conifer forest after logging in the Tomakomai Experiment Forest, central Hokkaido, northern Japan. The species could be placed in two groups according to the change in basal area and density, and annual height growth:Quercus mongolica var.grosseserrata, Phellodendron amurense, Prunus sargentii andTilia japonica (Group I: GI) showed episodic regeneration and/or fast height growth;Acer mono, Acer palmatum var.matsumuae andSorbus alnifolia (Group II: GII) showed continuous regeneration and/or slow height growth. The age distribution of stems over 10 cm in d.b.h. suggests synchronous regeneration of GI and GII species. Vertical stratification was promoted during the 12-year period by the difference in annual height growth between the two species groups. Additional tree censuses in both remnant old-growth stands and second-growth stands after large scale blowdowns demonstrated thatQ. mongolica var.grosseserrata is most dominant in stands varying in the stages of development. Disturbance history and successional trends in dominant species implied that stand-devastating disturbances were responsible for the regeneration ofQ. mongolica var.grosseserrata in the study forest.     

Didymella fagi sp. nov. and its anamorphAscochyta fagi, causing the yellow leaf spot disease ofFagus crenata andQuercus mongolica var.grosseserrata in Japan

AnAscochyta fungus was obtained during a survey of leaf spot diseases ofFagus crenata in the mountains of Aomori prefecture in 1995. The pathogenicity of the fungus toF. crenata was confirmed by inoculation. Its teleomorph was first found on artificially infected leaves after the leaves were placed in an incubator at 5°C with a 12-h photoperiod (approximately 500lx, daylight strip lamps) for 4 mo. The fungus was found to be the causal agent of yellow leaf spots ofF. crenata andQuercus mongolica var.grosseserrata in the field. Comparison with similar fungi so far described from Fagaceae indicated that the anamorph isAscochyta fagi and the teleomorph is an undescribed species ofDidymella. The nameDidymella fagi is introduced for the teleomorph. Correlation between the two morphs has been proved by cultural, morphological and pathological studies.     

Isolation and characterization of microsatellite loci from Quercus mongolica var. crispula

Microsatellites were isolated and characterized for the Japanese oak species, Quercus mongolica var. crispula, distributed in temperate deciduous forests of Japan. Eleven of the 48 primer pairs designed successfully amplified unambiguous and polymorphic single loci among 67 Q. mongolica var. crispula individuals within a plot in southwestern Japan. The observed and expected heterozygosities of the 11 microsatellite markers ranged from 0.522 to 0.896 and from 0.536 to 0.882, respectively. These polymorphic microsatellite markers are useful for estimating pollen‐mediated gene flow in Q. mongolica var. crispula.     

Dwarf bamboos affect the regeneration of zoochorous trees by providing habitats to acorn-feeding rodents

The effects of dwarf bamboos (Sasa spp.) on the regeneration of trees in a natural hardwood forest were studied by analysing the spatial dispersion of seedlings and saplings of anemochores (Acer palmatum var. matsumurae, Fraxinus lanuginosa, and Carpinus laxiflora) and zoochores (Quercus mongolica var. grosseserrata and Q. serrata). Relative photosynthetic photon flux density at 10 cm above ground was significantly correlated with the coverage of dwarf bamboos (r=0.661, P<0.001). Seedlings were abundant and were randomly distributed in the anemochores, other than the shade-intolerant species C. laxiflora which was significantly more sparse in sites with dense Sasa than in sites where Sasa was rare. Distribution of saplings was also random in the shadetolerant anemochores A. palmatum var. matsumurae and F. lanuginosa but aggregated in sites with sparse Sasa in the shade-intolerant anemochore C. laxiflora. In contrast to the anemochores, seedlings of zoochores were very few and were distributed in sites with sparse Sasa. Saplings were also aggregated and negatively correlated with Sasa cover in the shade-intolerant species Q. serrata and the tolerant species Q. mongolica var. grosseserrata. The acorns put on the forest floor in a site with dense Sasa were quickly removed by small rodents such as Apodemus speciosus and A. argenteus. Trap census of rodents revealed that those mammals prefer the dense Sasa habitat to the sparse Sasa habitat. This suggests that the dwarf bamboos strongly affect the regeneration of zoochorous trees not only by shading the seedlings but also by providing habitats to acorn-feeding small mammals.     

Unveiling the origin of Quercus serrata subsp. mongolicoides found in Honshu,Japan, by using genetic and morphological analyses

Quercus mongolica is a tree found in temperate deciduous forests in east Asia. In Japan, Q. mongolica var. crispula is commonly found; moreover, an oak whose morphology is similar to that of Q. mongolica var. mongolica of the Asian continent has been found in certain areas of Honshu and Hokkaido. Recently, the oak found in Honshu was described as Q. serrata subsp. mongolicoides (QSM). However, genetic comparison between this oak and Q. mongolica var. mongolica of the Asian continent has not been performed; the origin of QSM is thus unknown. Therefore, we aimed to determine the origin of QSM by conducting nuclear microsatellite (nSSR), chloroplast DNA (cpDNA) and leaf morphology analyses for the three taxa, as well as other congeners. The cpDNA variation overlapped among the three taxa, suggesting low discrimination ability for these taxa. Although morphological congruency was found between QSM and Q. mongolica var. mongolica, results of nSSR analyses showed that QSM contained a genetic admixture of Q. mongolica var. mongolica of the Asian continent and Q. mongolica var. crispula of Japan, bolstering an admixture hypothesis. The nSSR and cpDNA analyses suggested that Q. mongolica var. crispula can be the progenitor of Q. mongolica var. mongolica and harbors the ancestral cpDNA haplotypes. Therefore, we concluded that QSM might have been created by an admixture that likely occurred within Japan between Q. mongolica var. crispula and putative relict Q. mongolica var. mongolica, which might have diverged in or around Japan from Q. mongolica var. crispula during the late Pleistocene.     

微地形对江西武夷山南方铁杉针阔混交林幼树更新的影响

为探讨江西武夷山南方铁杉针阔混交林内不同微地形中幼树更新特征的差异,明晰不同微地形生境对幼树天然更新的影响。以江西武夷山国家级自然保护区内海拔约1800m的南方铁杉针阔混交原始林为研究对象,基于在其中建立的中亚热带南方铁杉针阔混交林动态监测固定样地首次调查数据,将固定样地中160个20m×20m的样方根据其海拔、凹凸度和坡度3种地形参数通过C-均值模糊聚类划分成不同的微地形生境,比较这不同微地形下的更新幼树种类组成及幼树更新特征,包括幼树密度,幼树平均胸径、平均高、平均冠幅,空间分布格局,分析不同微地形下幼树更新特征与地形因子、林分因子之间的关系。结果显示：(1)通过聚类分析,最终将固定样地的微地形生境划分成4类,分别为陡坡、凹地、凸地、缓坡。(2)4类微地形更新幼树优势种组成类似,但优势程度存在差异。闽皖八角幼树在4类微地形中的重要值皆为第一,均大于43%。建群种南方铁杉的幼树在凸地的重要值为9.09%,具有一定优势;在陡坡的重要值为0.62%,优势程度较差。(3)陡坡的更新幼树密度最高,为399株/hm~2,高于凹地,凸地和缓坡;幼树平均胸径和平均高的大小表现为：缓坡>凸地&...     

河北坝上樟子松人工林径向生长及其对气候因素的响应

利用树木年轮学方法测定了河北坝上地区樟子松逐年树轮宽度和胸高断面积增量,建立了樟子松树轮宽度差值年表并分析其对气候因素的响应以及生态弹性,为河北坝上地区利用樟子松开展退化杨树防护林更新建设的适宜性提供理论参考。研究结果表明,河北坝上地区樟子松树龄在28 a左右,其生长阶段可划分为快速生长期(0—10 a),生长下降期(11—20 a)和生长平稳期(21—28 a);樟子松树轮宽度在1992—2000年期间为快速增长期((4.49±1.15)mm/a),在2001—2010年期间呈现下降趋势((3.62±1.39)mm/a),而在2011—2019年期间樟子松生长呈平稳特征((2.21±0.68)mm/a),约为快速增长期增长速度的一半;樟子松BAI在1992—2000年间一直呈上升趋势((5.09±2.26)cm~2/a),2001—2019年期间呈平稳特征((10.46±0.67)cm~2/a),表现出稳定且持续的生长能力。樟子松差值年表与气候因素的相关性显示：樟子松径向生长主要与上一年生长季末期(9、10月)、休眠期(12月)及当年生长季(7月)平均温度和最高温度呈显著负相关,其中...     

A newOphiostoma species isolated from Japanese oak infested byPlatypus quercivorus

A newOphiostoma species was isolated from the sapwood ofQuercus mongolica var.grosseserrata and described asOphiostoma longicollum sp. nov. The species is characterized by a long perithecial neck with a gelatinous cap at the apex and a constricted base, orange-section-shaped ascospores that accumulate in a yellow-orange drop at the apex of the neck, and itsSporothrix anamorph. Contribution No. 137, Laboratory of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

樟子松幼苗生长及光合特性对强风沙流吹袭的响应

为了解樟子松幼苗对不同时间强风沙流吹袭的生理生态响应,2013年春季在内蒙古科尔沁沙地研究了8级大风风沙流(风速18m·s-1,风沙流强度173g·cm-1·min-1)吹袭10、20和30min下樟子松幼苗生长与光合特性的变化。结果显示:(1)随着风吹时间的增加,樟子松的株高生长量减少、茎粗生长加快,落叶数量增加,其中30min处理与CK相比的株高生长量下降52.63%,茎粗生长量增加233.30%,落叶指数增加466.70%。(2)风沙流吹袭没有改变樟子松幼苗的净光合速率、蒸腾速率、气孔导度和胞间CO2浓度的日变化规律,但日光合峰值下降,日最大蒸腾速率增加;与CK相比,30min处理的日最大光合速率下降22.69%,日最大蒸腾速率增加11.89%。(3)随风吹时间增加,其叶片温度、叶片相对含水量、日均光合速率、水分利用效率下降,30min处理较CK依次下降0.60%、4.37%、28.57%和31.58%,且日均蒸腾速率、气孔导度和胞间CO2浓度增加,30min处理较CK依次增加6.25%、6.67%和12.60%。研究表明,在持续风沙流胁迫下,樟子松幼苗光合作用受到抑制,蒸腾耗水增加,水分利用效率降低;樟子松幼苗生长速率降低主要源于光合面积减少和光合作用受到抑制,而其光合速率下降主要因幼苗叶片叶温和叶片含水量下降所致,蒸腾速率的增加主要源于气孔导度的增加;为了适应风沙流持续吹袭的胁迫,樟子松幼苗采取了降低株高生长速率,加快茎粗生长速率的适应策略。     

Detection and features of wetwood in Quercus mongolica var. grosseserrata

To elucidate the location of water in wetwood, variations in moisture content within a tree of Quercus mongolica var. grosseserrata were observed macroscopically by determination of moisture content and by soft x-ray photography. Then the typical wetwood, which had been precisely located by such macroscopic analysis, was examined further by cryo-scanning electron microscopy. The moisture content varied considerably within the tree trunk, and typical wetwood was detected in limited regions of the heartwood. The distribution of the wetwood did not always correspond to the discoloration of the wood. In the wetwood, almost all the lumina of vessels and fibers were filled with water, while the lumina of ray and axial parenchyma cells were often cavitated. Intercellular spaces produced by deformation of cell walls and radial shakes were filled with water. In addition, tyloses were collapsed and torn in the wetwood, and they did not block the vessel lumina. These results suggest the possibility that vessels and fibers might serve as effective pathways for the accumulation of water in the wetwood.     

呼伦贝尔沙地樟子松林净初级生产力对气候变化的响应

以呼伦贝尔沙地樟子松人工林为研究对象，利用树木年轮学和解析木法，推算过去41年樟子松林的生物量和年净初级生产力，并分析年净初级生产力与气温、降水、湿度等气象因子的关系。研究表明：随着林龄的增加，樟子松林生物量变化符合逻辑斯蒂生长方程；樟子松林生物量从1977年的4.83 t/hm²到2017年的167.95 t/hm²。樟子松林净初级生产力年际差异较大，呈先增加后减小、最后趋于稳定的趋势，多年平均净初级生产力为4.08 t hm^-2 a^-1，最高达到6.13 t hm^-2 a^-1，最低为2.63 t hm^-2 a^-1。气候因子与樟子松林净初级生产力关系较为密切，并具有一定的"滞后效应"；樟子松林净初级生产力与上一年8月、12月和当年3月的降水量显著相关；净初级生产力与上一年和当年8-9月的月均湿度极显著正相关；净初级生产力与各月温度均呈不同程度的负相关，尤其是上一年和当年的6-9月温度显著影响着净初级生产力。研究表明，樟子松林净初级生产力受温度和降水的综合影响，净初级生产力与气候因子的关系属于温度敏感型，未来该地区持续升温的条件下樟子松林净初级生产力可能会降低。     

Importance of seed size for the establishment of seedlings of five deciduous broad-leaved tree species

Effects of seed size and phenology on the establishment of five deciduous broad-leaved tree species were examined in deciduous woodland. Treatments included absence and presence of litter in the forest understory, a small gap, and a large gap. Seedling emergence of large-seeded speciesQuercus mongolica var.grosseserrata andAcer mono was not reduced by accumulation of litter in the forest understory, but was promoted in the large gap where litter was less. Seedling emergence of small-seeded species,Alnus hirsuta, Cercidiphyllum japonicum andBetula platyphylla var.japonica, was reduced by the litter in almost all of the sites. Seedlings of large-seeded species avoid shade stress phenologically by unfolding all of their large leaves in a short period before canopy closure in the forest understory. These species had little mortality after seedling emergence. In contrast, small-seeded species have a longer duration of leaf emergence, shorter leaf longevity, and rapid leaf turnover in all the sites. These seedlings attained similar height to those of the large-seeded species at the end of the second year in the large gap, but survival and height growth rate decreased after canopy closure in the forest understory. We suggest that the importance of seed size in determining seedling establishment largely depends on the relationships between seasonal changes of environmental conditions and phenological traits of seedlings, which are related to seed size.Abbreviations Ah Alnus hirsuta - Am Acer mono - Cj Cercidiphyllum japonicum - Bp Betula platyphylla var.japonica - Qm Quercus mongolica var.grosseserrata     

沙质草地营造樟子松林后土壤容重的变化及其影响因子

采用野外调查和室内试验相结合,以辽宁省章古台地区不同生长阶段(包括幼龄林、中龄林、成熟林和过熟林)的20块樟子松人工固沙林样地(以临近的7块天然草地为对照)为研究对象,研究了沙质草地营造樟子松人工林后不同生长阶段0—100 cm土层土壤容重的变化及其影响因子。结果表明:天然沙质草地营造樟子松人工固沙林后,不同生长阶段樟子松林在0—10 cm土层土壤容重变化的变异系数为78%,其他土层变异系数范围为1.08%—4.35%。随着樟子松人工林林龄的增加,土壤容重变化量在0—20 cm和60—100 cm层逐渐降低,在20—60 cm层先降低,到37年左右后逐渐升高,过熟林较成熟林显著增大。林龄对不同土层容重变化的决定系数由大到小依次为40—60、60—80、20—40、10—20、0—10、80—100 cm层。土壤容重变化在60—80 cm层与土壤粗颗粒(粒径0.05 mm)含量、在0—10、20—40 cm和60—80 cm层与土壤全氮含量、在0—10、20—60 cm和80—100 cm层与土壤全磷含量、在20—40 cm和80—100 cm层与土壤全钾含量显著负相关,且土壤全氮和全磷含量对土壤容重的影响效果随土层深度的增加逐渐降低,土壤容重变化在10—20 cm层与土壤含水率、在20—40 cm层与土壤有机碳含量呈显著的正相关。总体上,沙质草地营造樟子松人工林可以改善土壤结构,提高土壤质量,建议采取封育禁牧等营林措施增加樟子松林下枯落物积累,提高土壤养分含量,同时对37年樟子松人工林逐渐进行更新。     

Gnawing damage by rodents to the seedlings ofFagus crenata andQuercus mongolica var.grosseserrata in a temperateSasa grassland-deciduous forest series in southwestern Japan

The effects of dwarf bamboo,Sasa, cover on the initial morrality of hardwood seedlings were investigated by transplanting 1-year-old beech (Fagus crenata) and current-year oak (Quercus mongolica var.grosseserrata) seedling to three different stands; old-growth beech and secondary oak forests withSasa undergrowth, and aSasa grassland in a grassland-forest series near the top of Mt Jippo, southwestern Japan. The most frequent cause of seedling morrality was gnawing of the stems by rodents. In the beech forest, the gnawing was more likely to occur underSasa cover, suggesting that it provides a good habitat for rodents on the beech forest floor. TheSasa under growth may thus play an imporrant role in regeneration of beech forest. In the oak floor, mortality of both species was low and only a little gnawing occurred during a year. However, no natural oak seedling were found in the forest even after a mast year. This may be because most of the acorns disappeated before establishment. The early-stage demography of hardwood seedling as oak may thus play an imporrant role in regeneration of oak forest. In theSasa grassland where the seed supply is small, almost all of the seedlings died fromo gnawing regardless of the presence ofSasa cover. These factors prevent the recruitment of a sizable seedling bank. Rodents may thus play an imporrant role in maintenance of theSasa grassland.     

樟子松人工林营建对土壤颗粒组成变化的影响

植被恢复是退化生态系统的主要恢复措施,也是人类改善区域生态环境较为重要和直接的活动。目前,针对不同植被恢复方式对干旱半干旱地区土壤理化性质及生物特征开展了大量研究。然而,关于科尔沁沙地樟子松人工林营建对土壤颗粒组成变化的影响却鲜有报道。因此,以辽宁省章古台地区不同生长阶段(包括幼龄林、中龄林、成熟林和过熟林)的20块樟子松人工林样地为研究对象(以临近的7块天然草地为对照),研究了沙地樟子松人工林营建对0—100 cm土层土壤颗粒组成变化的影响。结果表明:沙质草地营建樟子松人工林后,不同土层土壤细颗粒(0.05 mm)含量均呈增加趋势,并且在0—10 cm层增加趋势明显,随土层深度增加土壤细颗粒增加量逐渐降低(除幼龄林外),但樟子松林地土壤颗粒组成仍以砂粒为主,土壤粘粒和粉粒含量极低(仅占5%左右)。随着樟子松人工林林龄的增加,土壤细颗粒变化量在0—10 cm层逐渐升高,而在10—100 cm层并无显著变化趋势。土壤细颗粒含量的变化在10—100 cm层与土壤含水量呈显著正相关,在0—10、20—40 cm和80—100 cm层与土壤全钾极显著负相关,在20—60 cm层与土壤有机碳呈显著正相关,在10—40 cm和80—100 cm层分别与土壤全磷呈显著正相关和负相关。综上所述,樟子松人工林营建可有效提高土壤细颗粒含量且在土壤表层效果明显,但短期内并不会使土壤颗粒组成发生显著变化,樟子松林改善土壤颗粒组成的同时也会使其他土壤因子发生相应的变化。     

Differential anatomical responses to elevated CO2 in saplings of four hardwood species

To determine whether an elevated carbon dioxide concentration ([CO₂]) can induce changes in the wood structure and stem radial growth in forest trees, we investigated the anatomical features of conduit cells and cambial activity in 4‐year‐old saplings of four deciduous broadleaved tree species – two ring‐porous (Quercus mongolica and Kalopanax septemlobus) and two diffuse‐porous species (Betula maximowicziana and Acer mono) – grown for three growing seasons in a free‐air CO₂ enrichment system. Elevated [CO₂] had no effects on vessels, growth and physiological traits of Q. mongolica, whereas tree height, photosynthesis and vessel area tended to increase in K. septemlobus. No effects of [CO₂] on growth, physiological traits and vessels were seen in the two diffuse‐porous woods. Elevated [CO₂] increased larger vessels in all species, except B. maximowicziana and number of cambial cells in two ring‐porous species. Our results showed that the vessel anatomy and radial stem growth of Q. mongolica, B. maximowicziana and A. mono were not affected by elevated [CO₂], although vessel size frequency and cambial activity in Q. mongolica were altered. In contrast, changes in vessel anatomy and cambial activity were induced by elevated [CO₂] in K. septemlobus. The different responses to elevated [CO₂] suggest that the sensitivity of forest trees to CO₂ is species dependent.     

Photosynthetic responses of birch and alder saplings grown in a free air CO2 enrichment system in northern Japan

Though birch and alder are the common pioneer tree species which dominate in northeast Asia, little is known about the effects of the predicted increase in atmospheric CO₂ concentrations ([CO₂]) upon their photosynthesis in field conditions. To investigate this, we grew 2-year-old saplings of three Betulaceae species (Betula platyphylla var. japonica Hara, Betula maximowicziana Regel, and Alnus hirsuta Turcz) for 2 years in a free air CO₂ enrichment system in northern Japan. Since the effect of high [CO₂] is known to depend on soil conditions, we evaluated the responses in two soils which are widely distributed in northern Japan: infertile and immature volcanic ash (VA) soil, and fertile brown forest (BF) soil. For B. platyphylla, photosynthetic down-regulation occurred in both soils, but for B. maximowicziana, down-regulation occurred only in VA soil. The explanation is reduced nitrogen and Rubisco content in the leaf. For A. hirsuta, down-regulation occurred only in BF soil because of the accumulation of starch in foliage, which restricts CO₂ diffusion inside the chloroplast. The higher photosynthetic rate of A. hirsuta in infertile VA soil could be due to the sink for photosynthates in the N₂-fixing symbiont. These three species are all able to down-regulate at high [CO₂]. However, it is possible that A. hirsuta would dominate in VA soil and B. maximowicziana in BF soil in the early stages of forest succession in a CO₂-enhanced world.     

樟子松幼树株高及其逆境生理指标对沙埋的响应特征

以3龄樟子松幼树为材料,2013年在科尔沁沙地研究了不同沙埋深度下其株高、叶片膜透性、渗透调节物质含量及保护酶活性变化,以揭示沙埋条件下樟子松幼树生长及其对逆境的生理响应特征。结果显示:(1)在沙埋深度低于株高以上2cm时被埋樟子松幼树能够正常生长,其株高和芽长均明显高于非沙埋对照,并以沙埋深度为株高的50%时增长幅度最大;当沙埋深度超过株高2cm以上时,虽然植株高度和芽长也较埋前有一定增长,但均低于对照,且所有处理植株均未破土,后来全部死亡。(2)所有沙埋处理的叶片可溶性糖含量均显著低于对照,而POD活性显著高于对照,可溶性蛋白质和脯氨酸含量也高于对照。(3)随沙埋深度增加,叶片相对含水量总体呈增加趋势,但大多数处理与对照差异不显著;丙二醛含量基本呈显著下降趋势,可溶性蛋白和脯氨酸含量先增加后下降,而大多数处理的膜透性与对照差异不显著;随着沙埋深度增加,叶片可溶性糖含量显著下降,SOD和POD活性均先增加后下降。(4)相关分析显示,樟子松幼树叶片膜透性变化与MDA含量变化相关性几乎为零,可溶性蛋白与脯氨酸含量呈显著正相关关系,可溶性糖含量与脯氨酸含量呈显著负相关关系。研究表明,沙埋深度低于樟子松株高以上2cm能够促进其幼树生长;沙埋并没有导致樟子松幼树体内的膜脂过氧化,也没有引起细胞膜的损伤,在受到沙埋胁迫时,樟子松幼树体内SOD、POD以及可溶性蛋白和脯氨酸分别在防止其膜脂过氧化和维持细胞膨压中起到重要作用,而可溶性糖含量在沙埋过程中没有起到渗透调节作用。