东北草原羊草种群单穗数量性状的生态可塑性

羊草（Leymus chinensis(Trin.)Tzvel.）是一种多年生禾本科优良牧草。经过对东北草原3个固定样地连续12a,分别随机取样100个穗状花序的调查和测定,将羊草种群单穗数量性状的生态可塑性进行了统计分析,并且分别与不同生长发育阶段气候因子进行了相关分析。结果表明,羊草种群的单穗长度、小穗数和小花数的生态可塑性变化在样地内和样地间,以及年度内和年度间均达到了极显著水平。其中,均表现为年度内大于年度间,样地内大于样地间,样地间大于年度间。羊草种群单穗数量性状均与形成性状的生育期,及其以前各生育期不同阶段的光照时间、积温、降水量有着一定程度的相关关系。在整个冬性枝条生长发育期,较多的降水、较少的光照时间和较低的积温将对翌年幼穗分化及其生长有一定的促进作用,而较少的降水、较多的光照时间和较高的积温则有不利影响;从拔节到抽穗阶段较多的降水对幼穗分化具有一定的促进作用,但从返青到抽穗不同阶段较高的积温和较多的光照、以及返青初期较多的降水量则有着一定的不利影响。气候因子对羊草种群幼穗分化滞后效应的生态时间差可长达10个月。     

温度和降水对蔬菜烟粉虱的影响

为了探讨温度胁迫和降水对蔬菜烟粉虱种群的影响,分别利用冬季零度以下的低温、夏季高温闷棚,以及降水量和降水程度与烟粉虱种群数量的关系,研究温度和降水对蔬菜烟粉虱的种群影响。结果发现,冬季低温强度和低温时间对翌年烟粉虱的种群数量有明显的影响,温度越低、低温时间越长,翌年春夏烟粉虱的种群数量越低。翌年春夏烟粉虱的种群数量和低温当量的相关关系符合下列方程:y=-63.16ln(x)+177.2(R~2=0.9102)。夏季高温闷棚后棚内温度迅速上升,闷棚1 d后,棚内地面以上10 cm的空气最高温度迅速上升到63.97℃,此后5 d闷棚期间最高温度一直保持在64℃以上;闷棚1 d后,辣椒上烟粉虱的虫口减退率达到60.41%,处理5 d后成虫全部死亡。闷棚后棚内土温迅速上升,闷棚1 d后,地下20 cm处的温度达到了39.53℃,随着闷棚时间的延长,土温一直保持在40℃以上。降雨量和降雨时间对烟粉虱种群数量有明显的影响,降雨量3.33 mm/12 h的烟粉虱的虫口减退率达到84.72%,11.67 mm/12 h的烟粉虱的虫口减退率达到96.32%。3.33 mm/12 h的降雨强度处理下,处理1.5 h、2.0 h后烟粉虱的虫口减退率分别为92.93%和95.42%。结果表明,冬季低温、夏季高温和降水对蔬菜烟粉虱种群数量有抑制作用。     

不同生态条件下羊草种群种子生产的探讨

本文以1982—1985年的野外定位调查为依据,定量分析了羊草种群种子生产的三个问题,即成穗率、结实器官性状及种子千粒重与生态条件的关系。放牧影响羊草种群的成穗率,但对籽粒的干物质生产过程有促进作用,停牧以后,即使经过数年割草,种群的种子生产仍有较强的恢复能力,与原放牧地有明显差异。长期割草对羊草种群的整个生殖生长过程均不利,停刈以后,经过数年休闲,种子生产能力仍很低,与原长期割草地几乎没有明显差异。由此反映出对种子生产的影响,长期割草较长期放牧更严重,并且自然恢复的速度缓慢。羊草种群各有性繁殖阶段的性状,均与光、温度和水分有比较密切的联系,但这些联系的密切程度,又因样地具体条件而有差异。     

松嫩平原不同生境条件下羊草无性系的生长规律

通过对栽培条件下实验无性系的跟踪调查和对羊草草甸水淹后恢复演替过程中天然无性系种群的随机取样调查,分析了不同生境条件下羊草无性系的生长规律.结果表明,在松嫩平原具有充分生长空间而没有种间竞争的风沙土上,两个实验羊草无性系的移植时间相差1个月,翌年生长季末期无性系的大小相差近1倍,整个生长季营养繁殖数量的增长规律均为指数函数.在羊草草甸水淹后恢复演替6年中,在羊草+杂类草群落、羊草+寸草苔群落,羊草无性系种群营养繁殖数量的增长规律均为幂函数.在具有种间竞争的碱化草甸土上,羊草无性系在水淹后恢复演替过程中仍可以通过指数形式迅速地增加无性系的子代数量,同时也迅速地扩展着无性系的生态位空间.     

荒漠一年生植物小画眉草的种群动态调节与模拟

以分布在沙波头沙漠试验研究站人工固沙植被中的一年生植物小画眉草为例,研究了荒漠一年生植物不同时间尺度上的种群动态与调节机制,试验结果表明：（1）一年生植物小画眉草种群的续存与其种子库中种子的分批萌发对策密切相关;（2）同一个生长季内,制约小画眉草种群数量变化的关键因子随降水条件的不同而变化,即当环境适宜度较小时（干旱胁迫）,非生物因子（降水）限制种群数量;当环境适宜度较大时,密度依赖的竞争作用调节种群大小;（3）在较长的生态时间尺度上土壤特性（结皮厚度,养分含量）也是影响小画眉草种群动态的一个重要因素;（4）小画眉草种群的存活曲线属于C型,说明该种是较为典型的r－对策者。     

羊草与大针茅根系构型对水分梯度响应的比较研究

羊草(Leymus chinensis)与大针茅(Stipa grandis)是内蒙古锡林郭勒典型草原的两大建群种,也是内蒙古草原的重要优良牧草。选取锡林郭勒草原以大针茅和羊草为优势种的围封草场为研究样地,通过原状土柱移栽,进行了两年的水分梯度控制实验(150、300、450、600 mm),分别模拟当地年降雨量由干旱年到是湿润年的变化情况,分析比较羊草种群和大针茅种群地上高度和根系构型对水分梯度的响应情况。结果表明:相比大针茅种群,羊草种群对水分梯度的响应更敏感,随着水分梯度的增加,羊草地上高度和根系直径显著增加,根系长度和根系深度显著减少;而大针茅的地上高度和根系特征各项指标均没有显出与水分梯度的相关性,显然大针茅比羊草更能适应干旱生境。在干旱条件(模拟年降雨量150 mm处理)下,大针茅种群地上高度达到峰值,生长状况良好;羊草种群则采用地上个体小型化,地下主根变细,分叉,向土壤深层扩展的生长策略。因此,在气候变化背景下,干旱化的气候将导致大针茅种群在群落中的优势地位逐渐增加,反之羊草种群则会随着气候湿润化而占据更大的优势。     

内蒙古锡林河流域典型草原狭翅雏蝗种群动态与气象关系的研究

狭翅雏蝗是我国西北草原的重要害虫之一。在内蒙古锡林河流域典型草原,其种群发生与气象因素有着密切关系。一般冬暖和6月干旱有利于其种群发生;7—8月多雨及7月平均最低温度较高有利于提高种群存活率。 在强度放牧条件下,在锡林河流域,狭翅雏蝗主要发生地冷蒿群落和羊草群落,由于小地形和下垫面性质不同,具有不同的小气候条件。1984年的小气候观测表明:在6月,冷蒿群落土壤含水率低于羊草群落,相应的前者狭翅雏蝗种群密度高于后者;在7—8月,冷蒿群落的温度、相对湿度以及温度和相对湿度的日变幅均低于羊草群落,冷蒿群落对小气候的调节能力较羊草群落强,冷蒿群落狭翅雏蝗蝻的存活率高于羊草群落。     

放牧影响下羊草草地主要植物种群生态位宽度与生态位重叠的研究

本文采用Shannon—Wiener和Pianka公式,在土壤水分、土壤含盐量和土壤有机质含量三维生态因子梯度上测定了松嫩草原碱化羊草草地放牧演替系列12种主要植物种群的生态位宽度和生态位重叠。结果表明,植物种群长期适应由放牧引起的群落和土壤环境因子梯度变化是种群生态位分化的主要原因。优势种羊草种群生态位宽度最大,三维上生态位宽度分别为0.910、0.869和0.930。五脉山黧豆和湿生植物生态位宽度均很窄。增加种表现出较强的适应环境能力,生态位宽度都较大。在放牧演替的先锋植物中,只有虎尾草生态位宽度较大(三维上平均0.707),角碱蓬和星星草种群生态位宽度均很窄。生态位宽度较大的物种与其它种群间生态位重叠较大。分布于相同或相邻放牧阶段及具有相同或相似环境要求的物种间生态位重叠较大。放牧条件下,羊草群落的演替过程也就是种群生态位分化的过程。     

东北草原羊草种群结实特性与气候年变化的关系

对３个固定样地的羊草（Ｌｅｙｍｕｓ ｃｈｉｎｅｎｓｉｓ（Ｔｒｉｎ．）Ｔｚｖｅｌ．）种群连续１２￣１６年的调查和测定及其与不同生长发育阶段气候因子的相关分析,表明羊草种群结实数量和籽实重量均与形成这些性状的生育期内,及其以前各生育期不同阶段的光照时间、积温、降水量有着一定程度的相关关系。从分蘖株的营养生长到生殖生长,包括开花、授粉、受精、胚珠发育为种子形成的整个过程中,较低的温度和生长季前期较多的光     

喀什霸王的结实和种子萌发特性

喀什霸王(Zygophyllum kaschgaricum)是生长于中国新疆南部荒漠环境的稀有种及二级保护植物。当前, 该物种在自然种群中呈分散式及片段化分布, 且种群密度低, 种群老龄化较严重。因此, 为了了解该物种种子萌发特性及其对荒漠环境的响应, 该文采用室内控制实验方法, 对该物种的自然坐果率、结籽率、种子吸水特性、种子休眠和萌发特性及对干旱胁迫的响应进行了比较研究。结果表明: 喀什霸王在自然种群中的坐果率及结籽率较低, 且种子的败育率较高。不同干藏时间种子的吸水速率间存在显著差异; 随着干藏时间的延长, 种子的吸水率逐步增强。刚成熟的种子在不同温度及光周期下均可萌发; 其中高温(10/20 ℃, 20/30 ℃)及黑暗条件下的萌发率比低温(10/5 ℃, 5/2 ℃)及光照条件下的萌发率高。不同干藏时间的种子在不同浓度赤霉素(GA₃)下的萌发率均较高; 但低温储藏时间对该物种种子的打破休眠及萌发率没有促进作用。以上结果说明该物种存在非深度生理休眠; 而干藏时间、高温且黑暗及高浓度(50 mmoloL ^-1) GA₃是打破休眠及促进种子萌发的最合适条件。高温条件下的干旱胁迫对喀什霸王种子萌发具有抑制作用; 春季和秋季降水量决定种子的萌发率。总之, 喀什霸王种子在物候上表现出的春秋季萌动及非深度生理休眠以提高幼苗存活力及保障种群稳定性, 是一种对新疆南部干旱及高温胁迫荒漠环境的适应策略。     

东北草原羊草种群结实特性与气候年变化的关系

Leymus chinensis（Trin.）Tzvel. is a fine herbage, which is a perennial rhizome grass species with high potentiality of vegetative propagation. The quantitative characters of fruit-bearing and grain weight of the population were successively investigated in three fixed stands from 1983 to 1998,analyzing the relationship between these characters and the climatic factors in different growing and developing stages. Certain degree of correlations were found between the number of seeds and grain weight of the population and different time of sunshine, temperature and rainfall accumulation before and during the growing and developing stages. From vegetative to reproductive growth of the tiller, including flowering, pollination, fertilization, and ovule development and seed formation, lower accumulated temperature and longer day light during the early growth season promoted fruit-bearing of the population, and vice versa. From turning green to fruit-ripening stage, longer sunshine duration benefited while higher accumulated temperature inhibitted nutrient deposition in the grain. Furthermore rainfall was also good to nutrient collection in the grain from turning green to milky stage,not from milky stage to mature stage. Growth and development of the winter tillers would affect the flowering, fruit-bearing, as well as the quality and quantity of seed production in the following year. Therefore, the number of fruit-bearing and the grain weight of the population could be predicted by the length of sunshine duration from August to September of the previous year and amount of rainfall in May of the present year,but the quantitative variation that estimated by simple climatic factor model was only 29.27%-35.76%.     

Dynamics of long-leaved sundew Drosera intermedia populations at two extremes of a hydrological gradient

Densities of Drosera intermedia were low in two studied habitats (10–25 ramets m⁻¹), a path through a wet heath (short inundation in spring, low soil moisture in summer) and a pool edge (longlasting inundation, high soil moisture in summer). The low densities could be explained by the observed low recruitment and high adult mortality.
The low recruitment resulted from: (1) a high first year mortality of the large number of seedlings that emerged each year in the path population, caused by summer drought and cover with algae after heavy rainfall; (2) the absence in two years out of three of seedling emergence at the pool edge, due to the longlasting inundation. In neither population any seedlings survived to flower; (3) low vegetative reproduction rate.
Adult mortality during the growing season was caused by drought, which did not occur at the pool edge. Rapid senescence in autumn, caused by summer drought on the path and by a rapid submersion after heavy rainfall at the pool edge, was associated with a high winter mortality.     

Pollen grain viability in Parietaria judaica L. during the long blooming period and correlation with meteorological conditions and allergic diseases

Abstract

Pollen grain viability and starch presence in pollen were followed during the long blooming period (May-November) of Parietaria judaica, the most widespread pellitory in Italy, responsible for many cases of allergic diseases. Observations were carried out near Siena (Tuscany), in the years 1978 and 1979.

Viability is high in late spring and early autumn, and pollen grains are starchy. The presence of starchless grains is always related to low viability: a production of pollen with a low viability occurs at the beginning and end of blooming, and also in summer, during drought periods. Pollen grain viability varies widely during the blooming period, and its variations are correlated to meteorological conditions, mainly rainfall and temperature.

Allergic diseases due to pellitory, however, are mainly reported between April and July, and on the other hand a small amount of patients states that they suffer all the year round. The discrepancies between the periods of viable pollen production and of declared symptoms by patients, are discussed.     

Seed size and response to rainfall patterns in annual grasslands: 16 years of permanent plot data

Question: Are seed size and plant size linked to species responses to inter‐annual variations in rainfall and rainfall distribution during the growing season in annual grasslands? Location: A 16‐year data set on species abundance in permanent plots 15 km north of Madrid in a Quercus ilex subsp. ballota dehesa. Methods: At species level, a GLM was used to analyse the effects of various rainfall indices (total autumn rainfall, early autumn rainfall and spring drought) on species abundance residuals with respect to time and topography. We also assessed the importance of seed size and plant size in the species responses at community level using species as data points. Seed mass and maximum stem length were used as surrogates for seed size and plant size, respectively. Results: Seed mass and plant size may explain some of the fluctuations in the floristic composition of annual species associated with autumn rainfall patterns. Species that are more abundant in dry autumns have greater seed mass than those species that are more abundant in wet autumns. Early autumn rainfall seems to favour larger plants. Conclusions: Our empirical results support the hypothesis that autumn rainfall patterns affect the relative establishment capacity of small and large seedlings in annual species.     

Tiller dynamics and assimilate partitioning in Lolium perenne with particular reference to flowering

The fate of 100 seedling plants of Lolium perenne L. was studied over a period of 2 years in a field plot. The birth and death of tillers and the production of inflorescences was followed, and the components of seed yield were recorded in detail in the first year. The pattern of distribution of ¹⁴CO₂ assimilated by the main shoot was examined at monthly intervals and during the first flowering season the distribution of ¹⁴C-assimilate from individual leaves and from the inflorescence was also studied. The capacity of individual tillers to assimilate ¹⁴CO₂ prior to flowering and the re-distribution of previously accumulated assimilate during seed growth were also assessed. Plants died at a more or less constant rate with time and only 54 survived to the end of the 2–yr period. First year mortality was associated with severe grazing or cutting but in the second year the death of ungrazed plants was observed. There was great variability in the production of tillers by surviving plants. In both years the number of live tillers per plant increased from July to the end of April with particularly rapid tillering in March and April establishing the maximum value for each year. There was a similar phase of rapid tillering after flowering in July. The number of live tillers per plant declined by 50% during stem elongation and inflorescence emergence and the majority of dead tillers were young secondary (in the first year) and tertiary (in the second year) tillers with a mean age of 40 days. Such tillers had poor assimilatory capacity prior to the onset of death and were not supplied with assimilate from the main shoot. Most of the plants surviving at the end of the experiment flowered in both years and one quarter of the maximum number of live tillers per plant recorded in April of each year produced inflorescences. The earlier a tiller was produced the greater was its chance of flowering and the greater its production of seed. The greater weight of seed produced was associated with the development of more seed-bearing florets per spikelet. There was relatively little export of “C-assimilate from the flowering main shoot, and the lower internodes formed the major sink for post-anthesis assimilate. The growth of seeds appeared to be relatively independent of the leaves for current assimilate. There was some evidence that assimilate accumulated in lower internodes was remobilised and utilised in the growth of seeds and new tillers. Overall, the results confirm the view that the grass plant is a dynamic population of short-lived tillers and indicate that increasing competition for assimilate at flowering exerts a major influence on the production and survival of tillers.     

Inter-annual variability of seed rain and seedling establishment of two woody Mediterranean species under field-induced drought and warming

We aimed to assess the impact of warmer and drier climate change conditions on the seed rain and seedling establishment of Globularia alypum L. and Erica multiflora L., two dominant species in Western coastal Mediterranean shrublands. We performed a non-intrusive field experiment in which we increased the night-time temperatures and excluded spring and autumn rainfall. We monitored the seed rain over 5 years and the seedling recruitment over 9 years on these experimental plots. Seed rain of E. multiflora was enhanced by warming treatment in relation to control, and higher annual rainfall, while seed rain of G. alypum was increased by drought treatment in relation to control, dry years and higher minimum annual temperature. Annual rainfall enhanced the seedling emergence of both species, which also positively correlated with annual mean temperatures. Drought treatment significantly decreased seedling emergence for both species, which was higher in open areas than below vegetation cover. The seedling survival of both species diminished at closer distances to competing neighbours, and in G. alypum seedling survival was higher with lower annual mean temperatures and higher annual rainfall, but also in drought treatment, which have experienced vegetation cover decline. The study confirms that the increasing aridity in Mediterranean ecosystems would constrain the early stages of development in typical co-occurring shrubs. However, there are contrasting responses to climatic conditions between species recruitment, which might favour changes in vegetation through modification of species relative abundance.     

Physiological responses of lupin genotypes to terminal drought in a Mediterranean-type environment

Field experiments concerning lupin grown in a low‐rainfall environment of the Mediterranean climatic region of Western Australia were conducted over three seasons to identify and evaluate the characteristics that maximise yield per unit of rainfall. The characteristics of early flowering and podding, high pod retention, fast rates of seed filling, osmotic adjustment and the degree of dry matter transfer from stem to the seed were studied in 12 lupin genotypes differing in seed yield under conditions of terminal drought. To allow recently released cultivars and advanced breeding lines to be evaluated, five to six genotypes were included in the first and the third year and nine in the second year. The genotypes were grown rainfed until pod set and then under a rainout shelter. Flowering and podding dates, pod retention, seed growth rate and osmotic adjustment were measured in detail, together with leaf water potential, seed yield and its components. The timing and intensity of development of the terminal drought varied from average in 1998 and 1999 to extreme in 2000. In each year, the seed yield under terminal drought showed genotypic differences, which appeared consistent with the timing and intensity of the development of terminal drought. Early flowering and podding were significantly correlated with seed yield. Fast rates of seed growth were highly and significantly correlated with high yields regardless of the intensity of development of terminal drought. Pod retention was highly correlated with yield in seasons in which the intensity of the development of terminal drought was average but not under extreme conditions of terminal drought. This was because the seed number per pod was markedly reduced to compensate for the high number of pods retained. Osmotic adjustment did not occur during the development of terminal drought in any of the genotypes. Dry matter transfer from stems to seeds was insignificant and not related to seed yield, suggesting that it is not a useful characteristic in screening for high yield under terminal drought.