四种沙埋深度对羊草种子出苗和幼苗生长的影响

模拟羊草种子自然埋藏深度状况,设计了0、1、2和3cm共4种沙埋深度实验,研究了其出苗率及幼苗生长对沙埋深度的响应。结果表明,羊草种子出苗率随埋深的增加呈下降趋势,0cm时出苗率最高为89.3%,1和2cm时分别为81.5%和78.5%,3cm时最低(73.5%),与前三者具有显著差异。埋深对地上株高生长动态的影响主要表现在,播种后25d,0～2cm处理的羊草幼苗地上株高均高于3cm处理;播种后36d,4种处理的地上株高没有显著差异。此外,随着埋深的增加,羊草幼苗的根长、根数、根冠比呈先上升后下降趋势,叶片数呈下降趋势,绝对株高则呈上升趋势。表明1～2cm沙埋深度更适宜于羊草种子出苗及幼苗生长,而0或3cm埋深不利于其出苗和幼苗生长。     

沙埋和种子大小对柠条锦鸡儿种子萌发、出苗和幼苗生长的影响

研究了沙埋深度和种子大小对内蒙古毛乌素沙地植被群落中占优势的柠条锦鸡儿(Caragana korshinskii Kom.)种子萌发、出苗、幼苗存活和生长的影响.结果表明,沙埋深度显著影响柠条锦鸡儿的种子萌发率、休眠率、出苗率、幼苗存活率及生物量.在0.5-2cm的浅层沙埋下,种子萌发率、出苗率、幼苗存活率及生物量最高,休眠率最低;沙埋深度≥4 cm时,柠条锦鸡儿的种子萌发率、出苗率、幼苗存活率及生物量随着沙埋深度增加显著降低,而休眠率却显著升高;沙埋深度≥12 cm时,柠条锦鸡儿种子不能够出苗,幼苗也不能够存活.种子大小对柠条锦鸡儿种子萌发率没有显著影响,但对出苗率、幼苗存活率及生物量影响显著.在各个沙埋深度下,不同大小的柠条锦鸡儿种子间的萌发率没有显著差异.当沙埋深度≤6 cm时,不同大小的柠条锦鸡儿种子在同一沙埋深度下的出苗率间没有显著差异;但当沙埋深度≥8 cm时,在同一沙埋深度下,大种子的出苗率显著高于中种子和小种子的出苗率,而中种子和小种子出苗率间没有显著差异.0.5-10 cm的沙埋深度中,除6 cm和8 cm深度下中种子和小种子萌发幼苗的生物量间没有显著差异外,其余深度下,大种子萌发的幼苗的存活率及生物量显著高于同一沙埋深度下中种子萌发的幼苗的存活率及生物量,后者又显著高于小种子萌发的幼苗的存活率及生物量.可能正是种子萌发对沙埋环境的忍耐或响应能力以及种子的多态性提高了柠条锦鸡儿在毛乌素沙地的适合度,为其在流动或半流动沙丘环境中成功定居并形成优势群落奠定了基础.     

梭梭不同种源间种子性状和幼苗生长性状与地理和气候因子的关系

对6个种源区梭梭[Haloxylon ammodendron(C.A.Mey.)Bunge]的种子性状和幼苗生长性状进行比较,并对这些性状与地理气候因子的相关性进行了分析,通过聚类分析方法对不同种源进行了评价.结果显示,不同种源间梭梭种子性状和幼苗生长性状存在显著差异,种子的果翅长度、种子千粒重、单株种子质量和种子发芽率的变化范围分别为5.13～7.14 mm、2.21～3.75 g、2.49～53.17 g和24.45%～75.00%,幼苗株高、新生枝长度、幼苗地径和幼苗成活率的变化范围分别为16.67～56.67 cm、14.33～29.34 cm、4.04～8.06 mm和42.56%～84.45%.不同种源梭梭的种子及幼苗生长性状与地理分布有关;单株种子质量、种子发芽率、幼苗株高和幼苗成活率与经度极显著正相关,果翅长度、种子千粒重和幼苗株高与纬度极显著负相关,海拔仪与果翅长度有显著相关关系;单株种子质量、种子发芽率和幼苗成活率的直接影响因子为经度,果翅长度、种子千粒重和新生枝长度的直接影响因子为纬度.气候因子与种子性状紧密相关,而与幼苗生长性状的相关性较差,仅幼苗成活率与1月气温和相对湿度存在极显著相关性;1月气温对果翅长度、单株种子质量、种子发芽率、幼苗株高和新牛枝长度的直接作用最大;年降雨量对地径的直接作用最大,相对湿度对幼苗成活率的直接作用最强.通过聚类分析将6个梭梭种源分为3类,其中内蒙古磴口种源为优良梭梭种源,新疆乌苏种源为较差种源.     

模拟增温和降水变化对北京东灵山辽东栎种子出苗和幼苗生长的影响

气候变化将增加地表平均气温、改变降水格局, 会影响到种子出苗和幼苗生长, 进而影响物种的更新动态。为探讨增温和降水变化对东灵山地区建群树种辽东栎(Quercus mongolica)种子出苗和一年生幼苗生长和适应状况的影响, 该文利用环境控制生长箱开展了温度和降水量的双因素控制实验, 温度设置3个梯度: 月平均气温(对照)、增温2 ℃和增温6 ℃; 降水量设置3个梯度: 月平均降水量(对照)、减水30%和加水30%。结果表明: 1)辽东栎的种子出苗率和一年生幼苗的生长对增温和降水变化的响应不一致, 种子出苗率主要受到降水及其与温度交互作用的影响, 幼苗生长仅受到温度和降水独立作用的影响; 2)春季增温2 ℃或降水量增加均使辽东栎种子出苗期提前; 增温6 ℃与降水量减少的水热组合延迟了种子出苗期并使其存活率和出苗率显著降低, 但在此温度下增加降水量则增加了出苗速率和出苗率。3)增温2 ℃对其生长无显著影响, 增温6 ℃则在不同水分条件下显著地增加了幼苗的比叶面积、抑制了叶的伸长生长, 同时也显著降低了各器官生物量积累, 并减少了幼苗生物量向根的分配; 降水量减少降低了幼苗根生物量, 但未影响总生物量和根冠比, 降水量增加显著促进了幼苗地上部分的生长, 特别是叶的生长。因此, 适当地增温或增加降水量将增加辽东栎幼苗的更新潜力, 但增温和降水量减少导致的干旱化将显著降低幼苗的更新潜力。     

紫花苜蓿和羊草种子出苗和幼苗生长对土壤含水量的响应

土壤含水量是种子萌发和幼苗生长阶段的关键环境因子。采用室内模拟方法,研究了不同土壤含水量(2.5%、5%、7.5%、10%、20%和30%)对紫花苜蓿和羊草种子出苗和幼苗生长的影响。结果表明:苜蓿和羊草种子的出苗率和幼苗的生长均显著受土壤含水量的影响;随着土壤含水量的增加,苜蓿和羊草的出苗率均呈先上升后下降的趋势;其中,苜蓿种子在土壤含水量为10%~20%时出苗率最高(93%),土壤含水量为30%时最低(2%);在5%土壤含水量时羊草出苗率最大(76%),在30%含水量时最低(9%);随着含水量增加,紫花苜蓿和羊草幼苗根苗长均表现为先上升后下降的趋势,土壤含水量7.5%~10%更适宜于紫花苜蓿种子出苗及幼苗生长,羊草种子的最适土壤含水量为5%~7.5%;综合出苗率和幼苗的生长情况,适宜苜蓿和羊草播种和幼苗生长的土壤水分含量分别为7.5%~10%和5%~7.5%。     

岷江干旱河谷5种乡土植物的出苗、存活和生长

为了阐明干旱河谷自然条件下乡土植物种子出苗与幼苗定居能力的空间差异性,选择环境适应能力较强的植被恢复物种,试验选择岷江上游干旱河谷水热条件具有明显差异的两个试验地点:四川省茂县撮箕山(南坡)和两河口(北坡),采用4因素随机区组设计,开展大量的野外播种对比试验,研究了微生境类型改变及不同播种处理方式对白刺花(Sophora davidi (Franch.) Skeels.)、小马鞍羊蹄甲(Bauhinia faberi var. microphylla)、岷谷木蓝(Indigofera lenticallata Craib)、落芒草(Oryzopsis munroi Stapf)和川芒(Miscamthus szechuanesis Keng)5种干旱河谷乡土植物种子出苗、幼苗存活及生长的影响.发现:(1)在干旱河谷自然气候条件下,播种后1个月是所有受试植物出苗的高峰期,但是种子出苗率都很低,达不到30%;幼苗存活能力也极低,在播种1个月后所有幼苗死亡数量增加而保存数明显下降;在播种2个后幼苗存活数均为0.相同条件下小马鞍羊蹄甲、岷谷木蓝与落芒草的出苗数量明显高于白刺花和川芒.这说明干旱河谷地区种子出苗与幼苗存活的限制是自然植被更新能力弱,并且恢复困难的主要原因.(2)种子出苗及幼苗存活能力在不同区域之间具有明显的差异,湿润地段种子出苗数量与幼苗保存数量都较大.但是,种子出苗及幼苗存活能力在同一地段灌丛、半灌丛与裸地等不同类型的微生境之间无明显变化.(3)小容器播种能够有效地增加种子出苗率与短期幼苗存活,但是未能提高幼苗最终的存活能力及生长速率;采用保水剂与腐殖质土壤改良措施对种子出苗数与幼苗保存数没有明显影响,因而这些措施不能解除干旱河谷地区极端环境胁迫对幼苗定居的阻碍.     

覆网保护和埋藏对坚果树种种子直播的影响

作者以都江堰林区6种代表性坚果树种为对象,研究了覆网保护和埋藏等措施对直播种子存活和幼苗建成的影响,同时调查了鼠类在春秋两季的数量变化。结果表明:秋季鼠类对种子的捕食压力大,使得种子在无保护的情况下很少存活到出苗;而秋季覆网保护(第二年春季解除覆网)和完全保护(覆网一直保留到第二年10月调查时为止)均增加了直播种子的存活和出苗率;将种子埋藏在土壤1–4cm也显著增加直播种子的存活率和出苗率,这与鼠类密度(12%)在秋季显著高于春季(2%)有直接关系。此外,坚果树种的种子存活和出苗与其种子特征有一定联系。因此,作者认为如果根据鼠类数量的季节波动规律而采取适当育林措施(如保护和埋藏等)能够增加森林种子直播的效率。     

沙埋对无芒雀麦种子萌发和幼苗生长的影响

研究了沙埋对浑善达克沙地植物群落中多年生禾草无芒雀麦种子萌发、出苗和幼苗生长的影响.结果表明:无芒雀麦种子能在深度≤12cm的沙埋中萌发,≤8cm的沙埋中出苗.在此范围内,随着沙埋深度的增加,无芒雀麦种子的萌发率和出苗率逐渐降低.沙埋深度在植株高度的33%时,无芒雀麦1周龄和2周龄幼苗均全部存活,且总生物量≥对照(未沙埋幼苗);当沙埋深度增至植株高度的66%时,1周龄和2周龄幼苗的存活率分别降至70%和25%,生长也受到抑制;而遭受全部沙埋时,1周龄和2周龄幼苗均不能存活.遭受沙埋后,无芒雀麦幼苗分配较多的生物量用于地上部分的生长,其生物量分配模式改变可能是无芒雀麦幼苗对沙埋环境的重要适应对策.     

不同地理种源紫茎泽兰的生态适应性比较

采用交互移植法,对移栽在6种不同生境中的5个不同种源紫茎泽兰幼苗的存活率、株高、分枝数、生物量、单株花序数、产种量和种子萌发率进行了为期1年的对比研究.结果表明：各种源紫茎泽兰的幼苗生长和繁殖特性对样地环境条件变化均表现出很强的可塑性.试验样地因素对幼苗株高、分枝数、生物量、单株花序数和产种量的影响均达到极显著水平(P＜0.001).随着样地纬度和海拔的升高,各种源的幼苗株高、分枝数量、单株生物量、每株花序数量和单株产种量均呈下降趋势,且各样地间的差异均达到显著水平(P＜0.05).但种源因素对幼苗株高、分枝数、生物量、单株花序数和产种量的影响均不显著（P＞0.05）.除单株产种量外,种源与试验样地的交互作用对上述各指标的影响均不显著.在各样地内,当地种源幼苗的存活率、生长能力和繁殖能力均未表现出显著的优势.说明紫茎泽兰在我国西南地区入侵成功主要依靠其较高的表型可塑性,而局域适应的作用相对较小.     

可获得种子量和种子出苗对草地裸沙斑植被恢复的相对制约

以科尔沁沙化草地的裸斑为研究对象,布设种子捕捉器监测生长季传播到裸斑的种子数量、物种组成,并人工播种监测裸斑中出苗情况,研究可获得种子数量和出苗对裸斑植被恢复的制约.结果表明:沙生植物3种,种子数为71 ～623粒·m-2,非沙生植物9种,种子数为73 ～410粒·m-2;裸斑中沙生植物的出苗数(9.3 ～22.3株·m-2)高于非沙生植物(0 ～3.4株·m-2);沙生植物在裸斑的出苗率最高为沙蓬(12.2％ ～34.1％),其次是乌丹蒿(4.5％ ～10.3％),小叶锦鸡儿(0～0.5％),非沙生植物狗尾草出苗率为0～6％,蒲公英为0 ～0.4％,其余植物种出苗率为0;沙生植物裸斑出苗数(9.3 ～22.3株·m-2)高于植被区(7.7株·m-2),而非沙生植物在裸斑的出苗数(0～3.4株·m-2)低于植被区(4.5株·m-2).可见,裸斑植被恢复中,沙生植物的可获得种子量制约高于出苗制约;非沙生植物的可获得种子量制约与出苗制约相当.     

The chemical nature of P accumulation in agricultural soils��implications for fertiliser management and design: an Australian perspective

Sand burial, persistent seed bank and soil water content (SWC) are three factors that potentially can affect regeneration in sand dune plant populations. To evaluate the effects of these three factors on population regeneration of Eremosparton songoricum, a rare and endangered legume, we investigated seed germination, seedling emergence and seedling survival in greenhouse and controlled field experiments in different sand dunes microsites. Freshly matured seeds are physically dormant, and the highest germination was only 9.3?±?5.8% at 25/10°C. Seed germination occurred at burial depths from 0 to 10 cm, but the maximum depth from which seedlings emerged was 6 cm; from 1 to 6 cm, the deeper the burial, the lower the percentage of seedling emergence. Only 36.2% of the total soil seed banks occurred at depths of 0?C6 cm. For artificially sown seeds at different dune microsites, mean seedling emergence percentage was 6.8%. Of 150 seedlings that emerged in the field investigation at the study site, only those germinating in flat sandy areas survived, and mean survival percentage was only 2.0%. Thus, the proportion of non-dormant seeds in soil seed banks that developed into seedlings and survived to the end of the growing season was only 0.2%. Minimum SWC for seed germination, seedling emergence and seedling survival was 2.0%. During monitoring of emergent seedlings in the field, low seedling recruitment was at least partly due to the rate of root extension (1.6?±?0.3 cm day^?1) into the sandy soil, which was slower than that of the downward movement of plant-available moisture (2.8?±?0.6 cm day^?1). Thus, population regeneration under natural conditions rarely occurred via sexual reproduction, owing to the limited water resources available for seedling establishment. Rational field seeding practices, including manually scarified or dry stored seeds before sowing, sowing the seeds at right time and suitable place, are suggested for ecological restoration of endangered E. songoricum populations.     

辽东山区长白落叶松人工林天然更新障碍分析

通过对辽东山区不同间伐强度下长白落叶松林内种子库,种子萌发,幼苗出现、成活与生长的观测,分析了长白落叶松天然更新的主要影响因素.结果表明:40年生落叶松人工林的种子雨中,有30%的种子有活力,可以满足天然更新的需要;土壤种子库的种子主要分布在枯枝落叶层,4月下旬林内种子开始萌发,6月幼苗数量达到最大,幼苗累计出现率与间伐强度(光照)之间无显著相关,只受到地被物的影响;随间伐强度的增加,幼苗平均存活率提高,但林下幼苗生长缓慢,苗高均不超过6 cm;林内当年幼苗9月全部消失,没有超过1年生的幼苗,但皆伐迹地的更新幼苗存活较多、生长良好.初步确定地被物和光照是辽东山区长白落叶松天然更新的主要障碍因子.     

Vertical seed distribution in the soil constrains regeneration of Bromus pictus in a Patagonian steppe

Question: What is the effect of vertical seed distribution (i.e. seeds on soil surface or buried) and the relative importance of vertical and horizontal seed distribution (i.e. seeds near established vegetation or near bare soil) for seedling emergence? Location: Patagonian arid steppe. Methods: To evaluate the effect of vertical seed distribution on seedling emergence, four sowing treatments were used in field and greenhouse experiments. Vertical vs. horizontal seed distribution and the occurrence of seedlings were analysed in the field. Effects of trampling and mechanical drilling on seedling emergence were investigated experimentally in the field. Results: In field and glasshouse experiments buried seeds showed a higher emergence and larger seedling size than seeds lying on the soil surface. The observational field study indicated that natural emergence was not associated with particular microsites or plant cover (horizontal distribution), but that most seedlings emerged from buried positions (vertical distribution). Buried seeds represented less than 10% of the sampled seed cohort but account for almost 60% of the seedlings. The trampling/drilling experiment showed that sheep trampling and mechanical drilling increased seedling emergence compared to non‐treated controls. Conclusions: The population dynamics of Bromus pictus is strongly constrained by the vertical position of seeds, which largely affects emergence, and seed horizontal distribution, which largely affects seedling survival. Our results showed that sheep trampling after seed dispersal may be a low‐input technique for increasing grass recruitment.     

The performance of carrot seeds in relation to their viability

The germination and emergence characteristics, and early seedling growth, of carrot seeds cv. Chantenay red-cored from different sources with a range of germination from 54–94%, was compared. Seeds from protected crops (mean temperature of growth 21°C, r.h. 45–70%) gave higher percentage germination than those from crops grown outdoors (mean temperature 15°C, 70–100% r.h.). Germination was also higher from mature (seed moisture content at harvest 20% or lower) than immature seed (seed moisture content at harvest between 20 and 60%). High percentage germination (>90%) was associated with low mean germination times and low spreads of germination times whilst the reverse was true for low percentage germination. Similar relationships were found for seedling emergence characters in the field although a lower proportion of the viable seeds produced seedlings from slowly than rapidly germinating seed lots. In general, seed lots having a low percentage germination gave greater variability in plant weight than those of higher percentage germination. There was no effect of seed source on radicle or shoot relative growth rates or on post-emergence seedling growth rates.     

<Emphasis Type="Italic">Pinus nigra</Emphasis> Arn. ssp <Emphasis Type="Italic">salzmannii</Emphasis> early recruitment and initial seedling growth in warmer and drier locations: the role of seed and soil provenance

Current decreasing precipitation and increasing temperatures promote the likelihood of extreme drought events and may alter the recruitment capacities of tree species. Spanish black pine (Pinus nigra ssp. salzmannii) initial recruitment is being one of the most affected pine species by changing conditions with alterations in the future species distribution. In this context, a cross-exchange experiment was implemented using an outdoor nursery located in a warmer and drier location for testing different Spanish Black pine seeds and soil provenance combinations in relation to early recruitment and initial seedling growth. Soil and seeds were collected at a high (HA, 1641 m.a.s.l.) and low (LA, 1099 m.a.s.l.) altitude in Cuenca Mountains (Spain). Then, a cross-sown experiment using HA and LA soils and seeds was set up in an outdoor nursery, which is located in Albacete (704 m.a.s.l.). Soil quality, seedling emergence, seedling survival, initial seedling growth and total seedling dry mass were measured after one year. We found higher seed emergence and seedling survival by combining LA soil with LA seeds or HA soil with HA seeds. Seedlings from LA seeds with both soil origins and seedlings from HA seeds with LA soils allocated more biomass to roots than seedlings from HA sites growing in HA soils under drier and warmer conditions. These results support the idea that autochthonous provenances have the potential to adapt to changing climatic conditions in their habitats.     

Canola seed germination and seedling emergence from pre-hydrated and re-dried seeds subjected to salt and water stresses at low temperatures

Low soil temperatures and low water potentials reduce and delay the seed germination of canola (Brassica rapa L., B. napus L.) in western Canada. Germination is also very sensitive to the salinity effects of nitrogen fertiliser placed with the seed, especially when the seed bed is relatively dry. The effects of pre-hydration and re-drying treatment on canola (Brassica rapa L. cv. Tobin) seed germination and seedling emergence at 10°C subjected to either a water or salt stress were determined. Low water potentials, induced by polyethylene glycol (PEG 8000), low soil moisture, or high concentrations of salts, reduced both germination and seedling emergence, and increased the time to 50% germination and emergence of seeds at 10°C. At equal osmotic potentials, Na₂SO₄ was less inhibitory on low temperature germination than either NaCl or PEG, suggesting that the sulphate ion partially alleviated the inhibitory effects of low water potential. Solutions of NaCI produced more abnormal seedlings compared to Na₂SO₄, suggesting that NaCl was more toxic than Na₂SO₄ during seedling development. Pre-hydration and re-drying partially overcame the inhibitory effects of both low water potential and salts on seed germination and seedling emergence at 10°C. The seed treatment increased the germination rate in Petri dishes and seedling emergence from a sandy loam soil. Water potentials or soil water contents required to inhibit 50% germination or emergence at 10°C were lower for treated seeds compared to control seeds. Salt concentrations inhibiting 50% emergence were higher for treated seeds than control seeds. Neither treated nor control seeds produced seedlings which emerged if the soil water content was lower than 9% or when the soil was continuously irrigated with salt solutions of 100 mmol kg^-1 of NaCl or 50 mmol kg^-1 of Na₂SO₄. These results suggest that the pre-hydration and re-drying treatment did not lower the base water potentials at which seedling emergence could occur. Abnormal seedlings were observed in both treated and control seeds, particularly if the soil was watered with NaCl solutions; however, the seed treatment reduced the number of abnormal seedlings.     

六盘山区辽东栎的实生苗更新及其影响因子

研究了六盘山区辽东栎(Quercus liaotungensis)灌丛的种子产量、土壤种子库组成、湿沙和风干贮藏对种子寿命的影响以及动物取食子叶对种子萌发和幼苗建立的影响。结果表明, 辽东栎灌丛种子的完好率为27.51%, 被动物取食或搬运种子的比例(41.51%)显著高于其他类型种子(p < 0.01); 辽东栎次生林土壤种子库中萌发和虫蛀种子分别占35.16%和38.29%, 完好种子仅占13.65%, 捕食动物主要通过贮藏或搬运而影响土壤种子库中的种子密度。湿沙贮藏60天的辽东栎种子自动萌发率高达96.67%, 短期贮藏可加快种子的萌发进程, 提高萌发率和萌发指数, 但随着贮藏时间的延长, 种子萌发进程延迟, 萌发率、萌发指数和活力指数均不同程度地降低。排除动物取食处理的幼苗在林窗和林下生境的存活率分别为80%和83%, 而不排除动物取食幼苗在2种生境中分别仅有25%和31%能够存活, 表明子叶在幼苗建立中具有重要作用。林窗中幼苗子叶的动物取食率(85.00%)高于林下(71.00%), 子叶留存的幼苗在林窗中的存活率(6.00%)低于林下(15.50%), 而子叶被取食幼苗的存活率在两种环境中基本相等(分别为18.50%和18.00%)。     

Multivariate path analysis of the relationships between seedling regeneration and environmental factors beneath a dwarf bamboo understory

Seedling emergence and establishment are fragile processes that determine the direction and structure of forest succession and regeneration. However, seedling emergence and establishment are easily affected by biotic and abiotic (environmental) factors. A dense and expanding understory of dwarf bamboo is one such important factor that can seriously hinder the seedling regeneration. We conducted a field experiment to investigate the emergence and establishment of canopy tree seedlings under artificially controlled densities of dwarf bamboo. We found that understory dwarf bamboo obstructed seedling emergence but reduced the death of seedlings. Although understory dwarf bamboo reduced the median retention time of seedlings, dense bamboo increased the mean survival time of seedlings. Our results suggest that understory dwarf bamboo has multiple selectivities for tree seedling emergence and establishment: high‐density dwarf bamboo was beneficial to evergreen species but lower‐density of bamboo was conducive to the survival of deciduous species, it means the dwarf bamboo potentially alters successional trajectories of forest communities. Path analysis revealed that the most important factors affecting tree seedling emergence and death were the abundance of seeds in the seed bank and the density of emerged seedlings, and that the soil temperature promoted seedling emergence but increased seedling death, the thickness of litter limited seedling emergence, and the leaf area index of the bamboo canopy limited seedling death. The present study suggests that dwarf bamboo can directly alter the microenvironment, significantly reducing light levels and soil temperature but increasing the thickness of litter and soil humus, thereby indirectly impacting the regeneration of tree seedlings. Our results indicate that various factors affected seedling emergence, and there were complex indirect relationships among these factors. In general, biological factors had a stronger influence on tree seedling regeneration than environmental factors.     

矮沙冬青种子特性和萌发影响因素的研究

 对矮沙冬青(Ammopiptanthus nanus)种子的特性和萌发影响因素进行了初步研究,结果表明：种子不易传播;虫蛀率高,室温贮藏60 d的种子虫害率为38%;易形成硬实,含水量为7.68%的种子在30 ℃温水中浸泡90 h,只有33.33%能吸水膨胀。种子萌发时不需光,在15～30 ℃和室温（18～32 ℃）条件下,经9 d的萌发,发芽率均可达80%以上,30℃时萌发最快;在1～2 cm深的沙壤中,种子出苗率可达75%以上,超过3 cm显著降低,超过6 cm则低于20%;种子在沙壤中萌发时,沙壤的适宜湿度为19.35%～28.75%,高于32.43%或低于3.85%,很少有种子萌发;含水量分别为19.36%、10.64% 和7.68%的种子发芽率无显著差异,在-10 ℃和5 ℃下贮藏7个月,发芽率也无显著降低,但在室温和35 ℃下贮藏7个月则显著下降,发芽率下降的速度与种子本身的含水量和贮藏温度正相关;在湿度分别为7.41%、13.79%和28.57%的沙壤中播种育苗,幼苗死亡率高达77.49%、81.25%和89.49%,即使用三唑酮拌种,死亡率亦高达50.27%、69.53%和76.03%,幼苗死亡率与沙壤湿度正相关。     

Effects of Planting Depth,Sediment Grain Size,and Nutrients on Ruppia maritima and Potamogeton perfoliatus Seedling Emergence and Growth

Protocols are now available for seed harvest, storage and germination of several mesohaline and polyhaline species; however, low seedling survival rates point to the need for an increased understanding of factors affecting seedling establishment. Depth of seed burial in sediments and initial seedling growth rates are shown to be limiting factors for photosynthetic competency of Ruppia maritima and Potamogeton perfoliatus. Seedling emergence is inversely proportional to planting depth on sediments ranging in grain size from coarse sands (850 μm) to silt (63 μm). Less than 6% of the seeds of either species emerged when buried to a depth of 3 cm in test sediments. Germination was greatest for seeds placed on the surface of sediments; however, these seedlings were subject to displacement because of the weak and fragile roots produced during early growth. Fine sediments may be more favorable for R. maritima seedling establishment, because seedling emergence and height decreased with increasing sediment grain size. Potamogeton perfoliatus seedlings seem to be more tolerant of a wider range of sediment grain sizes than R. maritima as indicated by the lack of an effect of sediment grain size on P. perfoliatus seed emergence, seedling height, and biomass. Increasing nutrients stimulated seedlings of both species; however, even at the highest concentrations tested, growth, as determined by shoot elongation and leaf and root formation, slowed within 7–10 days. This suggests factors other than mineral nutrients and light limit growth or that growth shifts from aboveground biomass production to belowground vegetative spread.