昆明西山滇青冈林内滇青冈种子库动态的研究

通过对昆明西山滇青冈林内滇青冈种子库的跟踪取样调查和种子埋藏试验,对滇青冈种子库的动态进行了研究。昆虫在种子成熟前侵入种子,经种子雨进入种子库时已有71．8％的种子失去萌发能力。种子雨输入种子库的绝大部分种子停留在表面种子库,其中48．55％的种子被虫害,25．36％被某些非生物或生物搬运,17．39％的腐烂,8．7％的被动物当场取食,没有种子萌发,影响种子库动态的各种因子的作用大小在时间上是变化。被搬运的种子中,有4．9％的由表面种子库转移到埋藏加。土层是滇青冈种子的安全生境,土壤种子库的存在时间超过250天。埋入土壤的试验种子一直处于静止状态,到6月雨季后有80％种子萌发,20％的腐烂。萌发种子数是当年产种子的0．26％。滇青冈林内的滇青冈种子库是季节性的,种子库对种群个体的补充作用是有限的。     

青冈种群的动态调节初探

本文通过调查统计和实验,对青冈种群动态进行了初步研究,包括种子库动态、种子萌发、无性繁殖以及密度调节等。研究表明,青冈种子量较大,但只有少数能发育成幼苗;有性繁殖和无性的克隆生长相互配合达到种群较高的繁殖效率;种群内个体的自疏定律说明,较成熟(40年左右)的青冈种群的增长速度已减慢。     

滇青冈幼苗的光合和生长对不同生长光强的适应

研究了3种光强(全日照的80%、20%和2%)下生长的滇青冈幼苗的光合-光强响应和生长状况。结果表明:3种光强生境滇青冈幼苗光饱和点和最大净光合速率没有显著差异,20%和2%生长光强下光补偿点显著低于80%生长光强。3种光强生境幼苗的光合饱和点在400~450μmol·m-2·s-1左右,光补偿点也很低(6~10μmol·m-2·s-1),表现出阴生植物的特征。但滇青冈幼苗较强的耐荫能力,是以牺牲生长为代价的。在2%的弱光生境中滇青冈幼苗比叶重显著降低,单位面积和单位干重叶绿素含量均显著增多,具有利用较强辐射的潜力,一旦林窗出现就可以利用增加的辐射提高光合速率,及时进入快速高生长。     

福建闽清福建青冈天然林种子雨和种子库

对福建闽清黄楮林自然保护区的福建青冈(Cyclobalanopsis chungii)天然林的种子雨和土壤种子库进行了观测和分析.结果表明,福建青冈种子雨持续2个月,其高峰期在11月下旬～12月上旬,总量为12.44个m~(-2),在种子散布过程中完好种子、虫蛀种子、败育种子、霉烂种子和萌发种子的比例差异明显,其中虫蛀种子是萌发种子的19.44倍.土壤种子库中虫蛀种子占53.79%,与种子雨相比,完好种子和萌发种子数量分别减少2.15个m~(-2)和0.20个m~(-2).土壤种子库种子存活率仅13.51%,动物捕食率达45.90%,说明动物的捕食和搬运是福建青冈种子缺失的原因之一.福建青冈天然林土壤种子库有69种植物种子,但种子数量较少,且分布不均匀,种子库中78.42%种子分布在2～5 cm土层中.福建青冈天然林中实生幼苗少与福建青冈种子本身特性及其生长环境密切相关,福建青冈种子发育成熟后因动物侵扰、虫蛀、霉烂和败育等情况发生,难以在土壤中长期保存,以致福建青冈林分天然更新严重受阻.     

沙坡头人工固沙区的种子库动态

沙坡头人工固沙区的土壤种子库中共有４６种植物的种子,属于１７个科。其中菊科植物最多,达１１种;其次为藜科,７种;禾本科７种;豆科４种。既是现有植被组分种,其种子又存在于种子库中的,占总种数的３３．３％ 。油蒿（Ａｒｔｅｍ ｉｓｉａ ｏｒｄｏｓｉｃａ）、花棒（Ｈｅｄｙｓａｒｕｍ ｓｃｏｐａｒｉｕｍ ）和柠条（Ｃａｒａｇａｎａ ｋｏｒｓｈｉｎｓｋｉｉ）的种子产量为５４５±６７６．７３粒／ｍ ２、６．６７±１３．７４粒／ｍ ２、０．０３２±２．４３×１０－ ３粒／ｍ ２。油蒿在植株上成熟时不受虫害,而花棒、柠条的种子受害比例分别为３１．９２％ 和８３．２９％ 。在最适埋藏深度下,油蒿、柠条、花棒种子的累积发芽率分别可达７８．３％ 、８５．０％ 和６６．７％ ;萌发速度：油蒿＞ 柠条＞ 花棒。根据种子库动态分析和植被调查结果可初步预测：沙坡头人工固沙植被的演替趋向将是灌木以油蒿为主,草本以雾冰藜（Ｂａｓｓｉａ ｄａｓｙｐｈｙｌｌａ）、小画眉草（Ｅｒａｇｒｏｓｔｉｓｐｏａｅｏｉｄｅｓ）为主的群落     

基于青冈和滇青冈生态位模拟的湿润和半湿润常绿阔叶林替代分布及气候解释

为揭示湿润常绿阔叶林和半湿润常绿阔叶林替代分布的气候制约变量,该研究选择其代表性优势树种青冈(Cyclobalanopsis glauca)和滇青冈(C.glaucoides)为研究对象,收集两个物种的标本分布点数据和19个生物气候变量图层数据,运用MaxEnt模型,模拟其潜在分布区,通过判别分析(DFA)、方差分析(...     

滇青冈和高山栲种子昆虫寄生及其对种群更新的影响

对昆明西山地区滇青冈(Cyclobalanopsis glaucoides)和高山栲(Castanopsis delavayi)种子(坚果)虫蛀率在两个年份、整个落种期和山坡不同部位的变化情况进行研究,结果表明：① 寄生于滇青冈种子内的象甲为青冈象(Curculio megadens)和Curculio sp.,寄生于高山栲种子内的象甲是Curculio sp.和剪枝象(Cyllorhynchites sp.);② 滇青冈样地的虫蛀率为2484%~2760%,样地间无显著差异,两年间的平均虫蛀率亦无显著差异;高山栲样地间虫蛀率为1794%~2655%,有显著差异性,两年间的平均虫蛀率也有显著差异。③ 高山栲的下落种子虫蛀率随时间逐步下降,9月和10月中下旬出现两个虫蛀率的高峰期;高山栲种子内寄生的昆虫落地后即入土化蛹,滇青冈落地种子内的寄生昆虫在初期会滞留一段时间;④ 虫蛀率与林下实生苗数量无显著相关性,实生苗多集中在大树周围以及草本层植物较丰富的小生境。     

青冈常绿阔叶林的碳素动态

报道了浙江建德青冈林碳素的含量、现存量、存留量、归还量、释放量以及在生态系统中的动态过程。结果表明：植物群落中碳素含量的变化幅度不大,一般在１０％以下。其中,叶片（器官比较）、乔木层（层次比较）和春夏季（季节比较）的含量稍高,根系、草本层、秋冬季的含量稍低。群落的碳素现存量为６６．１１３ｔ／ｈｍ２,主要集中在乔木层或常绿树种内;群落的碳素存留量为５．６９１ｔ／ｍ２·ａ;每年通过凋落物归还至地表的量为２．２９６ｔ／ｍ２·ａ;死地被物中又有０．９１１ｔ／ｈｍ２·ａ的碳素释放至大气库中。     

黔西北喀斯特土壤种子库季节动态及种子库对策

采用野外样线取样与温室萌发相结合的方法,研究了贵州省西北部喀斯特区域处于不同演替阶段群落的土壤种子库季节动态与种子库对策.实验共检测出130个物种,种子库密度变动于541～11180粒·m-2,草本种子的密度和物种数远大于木本种子.采样时间和地点对土壤种子库平均物种数和密度有显著影响.各群落类型的土壤种子库平均物种数都在4月达到最高,除草地外在12月下降到最低,草地在8月下降到最低.各群落类型土壤种子库密度都在4月达到最高,8月、12月以及次年5月的密度差异不显著.至少两种种子仅存在于1年中某些时段的短暂性土壤种子库类型和两种种子在全年的土壤种子库中都存在的持久性土壤种子库类型.植物的种子库对策是物种本身固有的生活史对策,但某些物种的种子库对策可能受干扰历史及微环境因素的影响,使其在种子数量上表现出不同的季节动态.     

土壤种子库的结构与动态

土壤种子库的结构与动态班勇（中国林业科学院林业研究所,北京１０００９１）ＳｔｒｕｃｔｕｒｅａｎｄＤｙｎａｍｉｃｓｏｆＳｅｅｄｓＢａｎｋｓｉｎＳｏｉｌ．￥ＢａｎＹｏｎｇ（ＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅｏｆＦｏｒｅｓｔｒｙ,ＣｈｉｎｅｓｅＡｃａｄｅｍ...     

结瘤因子的研究进展

结瘤因子是由根瘤菌产生的一类信号分子,它们在结瘤的起始阶段发挥着十分重要的作用。新近的研究结果证明结瘤因子大分子骨架上的不同侧链基团是决定细菌与宿主植物间相互识别的关键因素,根瘤菌细胞中一系列结瘤基因编码能够合成Lipo-chio-oligosaccharides(LCOs)的各种酶类,进而确定结瘤信号分子的特定结构。目前,一系列令人兴奋的实验结果表明：LCOs不仅可促进豆科作物的生物固氮作用,对一些非豆科作物的细胞分裂作用等同样具有刺激作用。对根瘤菌结瘤因子的研究显然有助于进一步了解细菌与植物的相互作用机理,并进而为农业生产为直接利益。本文在综述这方面的研究进展同时,还就瘤菌,豆科作用和结瘤信号分子之间的相互作用机理,以及根际促生细菌,水杨酸和结瘤信号分子之间的可能关系进行了理论分析。     

根瘤菌NOD因子的感知与信号传导

根瘤菌是一类引起豆科植物结瘤固氮的土壤细菌。根瘤中的类菌体固定空气中的氮气为宿主植物提供充足的氮源。共生体系的建立始于细菌与宿主植物间复杂的信号交换过程。植物产生类黄酮诱导相应的根瘤菌合成分泌结瘤因子 ,后者进而诱导宿主植物根系形态变化以及早期根瘤素基因表达。以下将就宿主植物结瘤因子的特异识别和早期信号传导进行讨论。     

LysM domains of Medicago truncatula NFP protein involved in Nod factor perception. Glycosylation state, molecular modeling and docking of chitooligosaccharides and Nod factors

The establishment of the symbiosis between legume plants and rhizobial bacteria depends on the production of rhizobial lipo-chitooligosaccharidic signals (the Nod factors) that are specifically recognized by roots of the host plant. In Medicago truncatula, specific recognition of Sinorhizobium meliloti and its Nod factors requires the NFP (Nod factor perception) gene, which encodes a putative serine/threonine receptor-like kinase (RLK). The extracellular region of this protein contains three tandem lysin motifs (LysMs), a short peptide domain that is implicated in peptidoglycan or chitin binding in various bacterial or eukaryotic proteins, respectively. We report here the homology modeling of the three LysM domains of M. truncatula NFP based on the structure of a LysM domain of the Escherichia coli membrane-bound lytic murein transglycosidase D (MltD). Expression of NFP in a homologous system (M. truncatula roots) revealed that the protein is highly N-glycosylated, probably with both high-mannose and complex glycans. Surface analysis and docking calculations performed on the models of the three domains were used to predict the most favored binding modes for chitooligosaccharides and Nod factors. A convergent model can be proposed where the sulfated, O-acetylated lipo-chitooligosaccharidic Nod factor of S. meliloti binds in similar orientation to the three LysM domains of M. truncatula NFP. N-glycosylation is not expected to interfere with Nod factor binding in this orientation.     

Gas exchange characteristics and dry matter accumulation of soybean treated with Nod factors

The effect of Nod factors on gas exchange characteristics and growth of soybean plants was studied. Soybean responded positively to some concentrations of Nod factors. Photosynthesis was increased up to 13% over the control, and this was accompanied by increases in stomatal conductance; plant dry weight was also increased. Near-fully expanded leaves responded more strongly to Nod factors than fully expanded leaves. Only Nod factor NodBj-V (C18:1, MeFuc) had significant effects on soybean. The finding suggests that Nod factors can affect photosynthesis, possibly indirectly, by stimulating sink strength.     

Nod factor [Nod Bj V (C(18:1), MeFuc)] and lumichrome enhance photosynthesis and growth of corn and soybean

The foliar application of Nod factor [Nod Bj V (C(18:1), MeFuc)] enhanced (P<0.05) the photosynthetic rate of corn; the increases were 36%, 23% and 12% for 10(-6), 10(-8) and 10(-10)M treated plants, respectively. Similarly, lumichrome at 10(-5) and 10(-6)M stimulated the photosynthetic rate of corn plants 1 and 2 days after application. Lumichrome (10(-5) and 10(-6)M) also increased the photosynthetic rates of soybean plants 3 days after treatment. Foliar applications of LCO (10(-6)M) to corn and soybean and of lumichrome (10(-5)M) to soybean increased leaf area, shoot dry mass and total dry mass relative to control plants. However, lumichrome treatments did not affect any growth variable of corn. Results of this study indicate that this signal compound can enhance the photosynthetic rate and growth of plants.     

Rhizobial Nod factors stimulate somatic embryo development in Picea abies

 Nod factors are lipochitooligosaccharides (LCOs) secreted by rhizobia. Nod factors trigger the nodulation programme in a compatible host. A bioassay was set up to test how crude (NGR234) and purified (NodS) Nod factors influence cell division and somatic embryogenesis in a conifer, Norway spruce (Picea abies). The Nod factors promoted cell division in the absence of auxin and cytokinin. More detailed studies showed that NodS stimulates development of proembryogenic masses from small cell aggregates and further embryo development. However, stimulation was only observed in low-density cell cultures. Our data suggest that rhizobial Nod factors substitute for conditioning factors in embryogenic cultures of Norway spruce. Received: 20 January 1999 / Revision received: 26 March 1999 / Accepted: 27 April 1999     

Nod factor enhances calcium uptake by soybean

Inoculation with rhizobia or application of Nod factors (lipo-chitooligosaccharides, LCOs) causes transient increases in cytosolic calcium concentration in root hairs of legume plants. We conducted experiments to evaluate whether application of LCO and inoculation with rhizobia improved (45)CaCl(2) uptake into soybean (Glycine max [L.] Merr.) leaves. Roots of soybean seedlings with one developing trifoliolate were immersed in Murashige and Skoog (MS) basal liquid medium containing treatment solutions and (45)CaCl(2), and the plants were incubated under continuous light. After 24 h, leaf samples were taken, and their radioactivity levels were determined. Addition of NodBj-V (C18:1 MeFuc) at a concentration of 10(-7) M increased (45)Ca(2+) uptake. Inoculation with genistein-induced Bradyrhizobium japonicum strain 532C and USDA3 also increased (45)Ca(2+) uptake; whereas, inoculation with strain Bj-168, a nodC-mutant incapable of producing LCO, did not. Rhizobia that do not normally nodulate soybean, i.e. Rhizobium leguminosarum, and Sinorhizobium meliloti did not affect calcium uptake, nor did the tetramer or pentamer of chitosan, or lumichrome. Surprisingly, Rhizobium sp. NGR234, which can nodulate some types of soybean, although without effective N(2)-fixation, also did not affect calcium uptake. This work suggests that the rhizobial symbiosis, in addition to its known role in provision of nitrogen fixation, also improves early calcium uptake into soybean plants.     

Different and new Nod factors produced by Rhizobium tropici CIAT899 following Na+ stress

The root nodule bacterium Rhizobium tropici strain CIAT899 is highly stress resistant. It grows under acid conditions, in large amounts of salt, and at high osmotic pressure. An earlier study reported a substantial qualitative and quantitative effect of acid stress on the biosynthesis of Nod factors. The aim of the present work was to investigate the effect of high salt (NaCl) concentrations, another common stress factor, on Nod factor production. For this purpose, thin-layer chromatography, HPLC and MS analyses were carried out. The expression of nodulation genes was also studied using a nodP ∷ lacZ fusion. High concentrations of sodium enhanced nod gene expression and Nod factor biosynthesis. The effect is sodium specific because high potassium or chloride concentrations did not have this effect. Under salt stress conditions, 46 different Nod factors were identified in a CIAT899 culture, compared with 29 different Nod factors under control conditions. Only 15 Nod factor structures were common to both conditions. Under salt stress conditions, 14 different new Nod factor structures were identified that were not observed as being produced under neutral or acid conditions. The implications of our results are that stress has a great influence on Nod factor biosynthesis and that new, very interesting regulatory mechanisms, worth investigating, are involved in controlling Nod factor biosynthesis.     

Rhizobial Nod factors are required for cortical cell division in the nodule morphogenetic programme of the Aeschynomeneae legume Arachis

Nod factors are among the best-studied molecules implicated in the signal exchange that leads to legume-rhizobia symbiosis. The role of these molecules in symbiosis development has been primarily studied in legumes invaded through infection threads. In these plants, Nod factors generate several responses required for nodulation, including the induction of cortical cell division to form the nodule primordium. Arachis hypogaea L. (peanut) exhibits a specific mode of rhizobial infection and nodule morphogenetic programme in which infection threads are never formed. The role of Nod factors in this particular mechanism is unknown. In this work, a peanut symbiont mutant strain unable to produce Nod factors was obtained and characterised. The strain Bradyrhizobium (Arachis) sp. SEMIA 6144 V2 is altered in the nodC gene, which encodes an N-acetylglucosaminyl transferase involved in the first step of the Nod factor biosynthetic pathway. Further research revealed that, although its ability to colonise peanut roots was unaffected, it is not capable of inducing the division of cortical cells. The results obtained indicate that rhizobial Nod factors are essential for the induction of cortical cell division that leads to nodule primordium formation.