混播草地不同种群再生性的研究

在不同刈割频率和时间尺度下 ,对混播草地多年生黑麦草 (Lolium perenne)分蘖数和叶片生长、白三叶 (Trifoliumrepens)分枝数和匍匐茎生长及不同种群年产量和组分进行了连续 3年的监测研究 .结果表明 ,刈割能刺激黑麦草叶片、白三叶匍匐茎生长和分枝数发生 ,保持混播草地黑麦草和白三叶的适宜比和稳定共存 ,提高草地年生产力 ,但不同刈割频率和刈割时间对其影响差异不显著 (P >0 .0 5 ) .黑麦草叶片生长对 6月刈割效果比 8月明显 ,而白三叶匍匐茎生长则与之相反 ,黑麦草产量主要取决于叶片生长 ,白三叶产量主要取决于匍匐茎分枝数 .刈割的黑麦草、白三叶产量组分比分别为 5 0 %、15 % ,比试验前约低 10 %、5 % ,而CK为 39%、6 % .     

樟子松人工林分枝结构的分析

基于对6块樟子松(Pinus sylvestris var. mongolica)人工林固定标准地中的30株样木枝解析调查数据,通过分析不同林分、不同大小林木1级枝和2级枝的分枝概率、分枝格局和分枝角度,揭示了樟子松人工林树冠的分枝结构特点。研究结果表明：樟子松人工林1级枝和2级枝的平均分枝数量分别为3.84个和2.80个,两者分枝概率均呈正态分布;1级和2级枝条在光照条件好的几个区间（方位角46°～225°）分布较多,1级枝条的水平分布遵从均匀分布,而2级枝条则不遵从均匀分布;树冠上层枝条的分枝角度略小于树冠中、下层,上层平均分枝角度为45.6°,而中下层平均分枝角度都为49.4°。不同大小林木的1级枝分枝结构规律表明：Ⅰ级木和Ⅴ级木的每轮平均分枝数非常接近,分别为3.89和3.94个,比Ⅲ级木每轮分枝数大0.5个左右;1级枝水平分布在各区间内(45°间隔)相差在0.24%～2.81%之间,方差分析结果表明枝条水平分布与林木大小无关;不同大小林木的分枝角度有所差别,Ⅰ级木、Ⅲ级木和Ⅴ级木的平均分枝角度分别为48.5°、42.2°和50.7°。     

不同频次刈割对羊草草原主要植物种群能量现存量的影响

对内蒙古羊草草原主要植物种群能量现存量对刈割频次响应的研究表明,在17年不同频次刈割干扰影响下,植物种群能量现存量随刈割频次的变化表现出不同的变化趋势,据此可以划分出3个不同的刈割响应类群:受抑种、耐刈种和受益种.受抑种包括羊草、羽茅、黄囊苔草、葱属植物和直根型杂类草;耐刈种包括大针茅和冰草;受益种包括洽草和糙隐子草.对于种群相对能量现存量而言,除羊草随刈割频次的增加呈显著下降趋势外,其他受抑种均随刈割频次的增加保持相对稳定,而受益种和耐刈种的相对值则随刈割频次的增加而呈增加趋势.同时,刈割对植物能量现存量的影响还表现在植物热值变化上,但变化幅度小于10%.     

不同频次刈割对羊草草原主要植物种群能量现存量的影响

对内蒙古羊草草原主要植物种群能量现存量对刈割频次响应的研究表明,在17年不同频次刈割干扰影响下,植物种群能量现存量随刈割频次的变化表现出不同的变化趋势,据此可以划分出3个不同的刈割响应类群：受抑种、耐刈种和受益种。受抑种包括羊草、羽茅、黄囊苔草、葱属植物和直根型杂类草; 耐刈种包括大针茅和冰草; 受益种包括洽草和糙隐子草。对于种群相对能量现存量而言,除羊草随刈割频次的增加呈显著下降趋势外,其他受抑种均随刈割频次的增加保持相对稳定,而受益种和耐刈种的相对值则随刈割频次的增加而呈增加趋势。同时,刈割对植物能量现存量的影响还表现在植物热值变化上,但变化幅度小于10%。     

在不同压力和干扰条件下黑麦草与其它6种植物的竞争研究

 对黑麦草(Lolium perenne)与白三叶(Trifolium repens)、鸭茅(Dactylis glomerata)、白茅(Imperata cylindrical)、芒(Miscanthus sinensis)、绣线菊(Spiraea japonica var. nepalensis)和地榆(Sanguisorba officinalis)等6种植物之间在不同压力和干扰条件下的竞争关系进行了试验研究,以便进一步探讨黑麦草草地群落退化演替的机理,为今后这种草地的有效管理提供科学依据。试验设置水分条件和土壤肥力两个压力因子处理及刈割频率和刈割强度两个干扰因子处理,其中,水分条件处理包括自然降水（1 800 mm）和自然降水＋浇水（2 300 mm）两个水平;土壤肥力处理包括施肥0 kg·hm-2·a-1、75 kg·hm-2·a-1和150 kg·hm-2·a-1 3个水平;刈割频率处理包括每年刈割1、3、6次3个水平;刈割强度处理包括刈割留茬2 cm和10 cm 两个水平。在专门设计的固定试验装置中,按各种植物单植和分别与黑麦草混植的方法以相同密度种植植物,通过对各处理植物产量的测定,运用de Wit提出的植物相对拥挤系数（RCC）,确定在不同压力和干扰条件下黑麦草对其它6种植物的竞争关系。试验表明,黑麦草对白三叶、鸭茅、地榆、白茅、芒、绣线菊的竞争力依次增强。同时,随着刈割次数的增加、水分条件和土壤肥力的提高,黑麦草的竞争力也明显增加,其中刈割次数对黑麦草竞争力变化的影响最大。另一方面,试验还表明,黑麦草等栽培牧草的生长速度和竞争力及耐刈割干扰程度均高于大部分野生杂草植物,但它们忍受环境压力的能力明显低于野生杂草植物,在环境压力大的地区,它们对杂类草的竞争力明显减弱,使得杂类草逐渐占优势。此外,分析表明,对于黑麦草来说,在试验的其它6种植物中绣线菊是压力忍耐（S）型植物;白三叶和鸭茅属于干扰忍耐（D）型植物;其它几种植物对压力和干扰的忍耐性处于中等水平。     

台湾相思林和芒草草丛中薇甘菊枝构件的分枝格局及其生物量

 外域杂草薇甘菊(Mikania micrantha)具有极强的分枝能力。在枝构件水平上,对生长在台湾相思(Acacia confusa)群落和芒草(Miscanthus sinensis)群落中的薇甘菊枝构件的分枝格局和生物量分配的比较分析得出：1）同芒草群落相比,台湾相思群落中薇甘菊各级枝的分枝数、分枝密度和分枝率都低,而分枝长度则较长;2）台湾相思群落中薇甘菊以第一级分枝为主,而在芒草群落中则以第二级分枝为主;3）台湾相思林中薇甘菊枝构件的叶面积率、比叶面积和比茎长及叶片生物量分配显著大于芒草草丛;4     

刈割对苜蓿主要害虫种群数量动态的影响

在甘肃省定西市九华沟系统研究了刈割对苜蓿主要害虫种群数量动态的影响.结果表明,刈割对害虫种群数量的影响在不同害虫种类之间存在明显差异.刈割对苜蓿斑蚜、豌豆蚜和蓟马的控制效果非常明显.6月初第1次刈割能极显著降低其季节平均数量,并使其保持较低的种群密度水平,7月中旬第2次刈割对其季节平均数量的影响小于第1次刈割.刈割对盲蝽种群的影响有所不同,虽然第1次刈割初期盲蝽的种群数量显著低于未刈割田,但刈割后盲蝽的种群数量回升较快,到8月上旬其种群数量显著高于未刈割田.第2次刈割对其季节平均数量的影响大于第1次刈割.     

刈割对苜蓿主要害虫种群数量动态的影响

在甘肃省定西市九华沟系统研究了刈割对苜蓿主要害虫种群数量动态的影响.结果表明,刈割对害虫种群数量的影响在不同害虫种类之间存在明显差异.刈割对苜蓿斑蚜、豌豆蚜和蓟马的控制效果非常明显.6月初第1次刈割能极显著降低其季节平均数量,并使其保持较低的种群密度水平,7月中旬第2次刈割对其季节平均数量的影响小于第1次刈割.刈割对盲蝽种群的影响有所不同,虽然第1次刈割初期盲蝽的种群数量显著低于未刈割田,但刈割后盲蝽的种群数量回升较快,到8月上旬其种群数量显著高于未刈割田.第2次刈割对其季节平均数量的影响大于第1次刈割.     

不同刈牧强度对冷蒿生长与资源分配的影响

利用野外实验与盆栽实验,对不同刈牧强度下冷蒿生长与资源分配影响的研究结果表明,按比例刈割冷篙的再生生长大于留茬高度刈割,在生长季前期,不刈割冷蒿净生长高于刈割处理,而进入生长季中后期(8月中旬以后),轻度刈割净生长高于不刈割处理,冷篙种群生物量分配的总体格局是根>叶>茎,刈牧明显影响冷蒿生物量分配格局,尤其是叶和花的分配,3／4刈割或留茬4cm刈割叶生物量分配显著高于其它各处理,而花的生物量及其分配显著低于其它处理,根、茎生物量分配各处理间差异不显著．冷蒿有性生殖分配随刈牧强度的增加而降低,繁殖方式发生了改变,优先将光合产物分配给再生茎以及繁殖方式转向营养繁殖,通过克隆生长维持和扩大种群是冷蒿对强度放牧的生态适应对策。     

刈割对外来入侵植物黄顶菊的生长、 气体交换和荧光的影响

为明确不同刈割处理对黄顶菊生长和生理特性的影响,本研究在田间条件下,对黄顶菊在生长季内不同时间进行刈割处理。结果表明,刈割降低了黄顶菊植株各部分的生物量积累,其中以刈割3次效果最为显著,使黄顶菊总生物量、根生物量、茎生物量、叶生物量分别较对照下降82.57%、44.53%、80.04%、91.76%;植株的高度和花序数随刈割次数的增加显著降低,其中刈割3次的花序数为0;刈割1次植株分枝数最大,出现超补偿现象,刈割3次分枝数显著低于其他处理;叶绿素含量除了刈割2次出现增高趋势外,随刈割次数的增加,叶绿素含量逐渐降低;刈割处理使黄顶菊净光合速率(Pn)、气孔导度(Cond)和蒸腾速率(Tr)均显著升高;刈割3次的PSⅡ的最大光化学效率(Fv/Fm)和PSⅡ的潜在活性(Fv/F0)显著低于其它各处理,而初始荧光(F0)则显著增加;生长指标的可塑性指数大于生理指标可塑性指数,表明前者在黄顶菊对刈割处理等物理措施适应方面起到了更为重要的作用。总之,刈割3次处理黄顶菊的各项生长和生理指标所受影响最大,对黄顶菊植株的再生和开花结实抑制效果最为理想。     

放牧对亚热带人工草地牧草构型及小格局的影响

对休牧后的亚热带人工草地及长期禁牧草地牧草种群的构型及小格局的研究结果表明。随着放牧强度的增加,鸭茅、红三叶株丛宽度逐渐变小．在对照及6只羊·hm^-2、7．5只羊·hm^-2、10只羊·hm^-2轮牧草地上,鸭茅基径的峰值分别介于6～8cm、2～4cm、0～2cm和0～2cm之间;红三叶则介于1～1．2cm、6～8cm、4～6cm和2～4cm之间;鸭茅丛密度分别为60、95．1、210．2和160丛·m^-1;单丛蘖数量分别为11．9、11．2、7．3、6．9蘖／丛．与禁牧草地相比,放牧草地鸭茅单丛蘖的数量明显减少,而丛密度则明显增加,白三叶节间长度因放牧强度增加而明显下降,为1．51～2．04cm,分枝角度则逐渐变大,介于46．5～77．3°,鸭茅、白三叶及红三叶在小格局水平上其格局规模均以1个样方(2cm×2cm)为主,并且随着放牧强度的提高,鸭茅、红三叶小格局规模进一步变小,白三叶构型及小格局的变化提高了牧草对环境资源的利用率。     

不同光照条件下聚花过路黄的克隆构型和分株种群特征

以都江堰灵岩山常绿阔叶林林下、林缘和林缘旷地3种不同光照环境中匍匐茎草本聚花过路黄(Lysimachla congestiflora)为对象,对其匍匐茎节间长、分枝强度、分枝角度、分株种群密度、分株种群生物量等指标进行了测定和分析．结果表明,聚花过路黄的匍匐茎节间长、分枝强度、分株种群密度和分株种群生物量在3种生境间差异显著．Kruskal Wallis检验表明,匍匐茎节间长度和分枝角度的频次分布在3种生境间差异显著．3种生境中匍匐茎节间长度分布偏斜度(skewness)的大小分别为：林缘旷地>林缘>林下．林缘旷地与林缘和林下生境在分枝角度、分株种群高度和分株种群根冠比差异显著,而且林缘旷地生境中分枝角度分布偏斜度最小．林缘和林下生境在分枝角度、分株种群高度和分株种群根冠比差异不显著．从林缘旷地、林缘到林下,聚花过路黄的克隆构型和分株种群特征发生了相应改变．结合克隆植物对资源的利用对策,讨论了不同生境中聚花过路黄克隆构型和分株种群特征可塑性的生态适应意义．     

Seasonal pattern of accumulation and effects of low temperatures on storage compounds in Trifolium repens

The seasonal pattern of concentrations of nitrogen, starch and vegetative storage protein (VSP) in stolons of Trifolium repens L. grown in the field were studied. Two different genotypes, cv. Aran and cv. Rivendel, differing in their morphology (stolon thickness and branching rate) but with similar growth rates, were used. Maximum concentrations of starch were found in summer whereas hydrolysis of starch took place throughout winter, suggesting that C storage is more important for winter survival than for promotion of early spring growth. On the other hand, VSP and nitrogen accumulated in autumn and early winter and then decreased when growth was resumed during early spring. For both cultivars, an inverse relationship was found between VSP concentration in stolons and mean air temperature, suggesting that VSP accumulation may be triggered by low temperature. Further experiments with plants grown under different regimes of temperature and daylength, suggested that VSP synthesis is stimulated by low root temperatures, with a slight synergistic effect of short daylength.
The effects of root temperature on growth, N₂ fixation, NH₄⁺ uptake and N allocation within Trifolium repens L., were studied under controlled conditions. The shoot growth rate was greatly reduced when root temperatures were lowered from 12 to 6°C, while the rate of stolon growth was less affected. Low root temperatures inhibited N2 fixation more than it did NH₄⁺ uptake, but the relative allocation of N to stolons was increased. Lowering root temperature also increased the accumulation of VSP in stolons. These results are discussed in terms of the mechanism associated with low temperature stimulation of VSP accumulation and its coupling with changes in the source/sink relations for allocation of N, between growth and storage.     

Density and the commitment of apical meristems to clonal growth and reproduction in Hieracium pilosella

Summary We examined responses to population density in the commitment of apical meristems to reproduction and clonal growth in a rosette-forming, stoloniferous herb (Hieracium pilosella). Despite close physiological coupling between the evocation of the terminal inflorescence bud and the development of one or more axillary buds into stolons, the allocation of meristems was extremely plastic.Genets at the higher sowing densities showed density-dependent mortality consistent with self-thinning along a-3/2 trajectory. The probability of inflorescence evocation and associated stolon development was negatively dependent on surviving density. The proportinal distribution of primary stolons amongst genets became strikingly more unequal (expressed as the Gini coefficient) with increasing density. Clonal growth was resolved into the number of primary stolons per stoloniferous genet and the extent of stolon branching (i.e. number of apices per primary stolon); both showed strongly negative density-dependence. Reproduction, expressed as the mean number of flowering capitula per stoloniferous genet, declined 15-fold with increasing density; although theoretically expected to be unity, greater values resulted from capitulum production by attached secondary rosettes and lower values reflected the increasing abortion rate of inflorescence buds with increasing density.Both the total number of apices produced per unit area and the corresponding number of reproductive apices were maximal at intermediate surviving densities (700–1,000 m^-2). The balance between reproductive and clonal growth may be expressed as the probability of an apical meristem producing a capitulum, that also peaked sharply at intermediate density. This finding does not conform with linear models that predict a shift from vegetative growth to sexual reproduction with increasing population density.     

The Growth and Carbon Allocation Patterns of White Clover (Trifolium repens L.) Plants of Contrasting Branching Structure

The growth, morphology and carbon allocation patterns of F1progeny white clover (Trifolium repens L.) plants selected foreither low (‘LBF’) or high (‘HBF’) frequencyof stolon branching were compared in two controlled-environmentexperiments. Selections from within both a small-leaved (‘GrasslandsTahora’) and a large-leaved (‘Grasslands Kopu’)clover cultivar were compared, and plants were grown under arelatively lenient defoliation treatment (expt 1) or under threelevels of defoliation seventy (expt 2). Carbon allocation patternswere measured by ¹⁴CO₂ pulse-chase labelling using fully unfoldedleaves on the main (parent) stolon. LBF and HBF displayed consistent differences in the selectedcharacter though, within cultivars, the difference between selectionswas most pronounced for Kopu. The selections developed fundamentallydifferent branching structures resulting from differences inbranching frequency, with total branch weight per plant averaging122 mg for LBF and 399 mg for HBF (mean of both experiments).More C moved from parent stolon leaves to branches in HBF thanin LBF (mean 22.6% vs. 15.1% respectively of the ¹⁴C exportedfrom source leaves). More C also moved to stolon tissue in HBF,but, counterbalancing this and the difference in allocationto branches, less moved to developing leaves and roots on theparent stolon itself compared to LBF. However, the total weightof developing leaves and roots per parent stolon was generallygreater in HBF than in LBF, probably reflecting greater C importby these sinks from the higher number of branches present perplant in the former selection. HBF plants were consistentlylarger at harvest than LBF plants. There were no defoliationtreatment x selection interactions in C allocation patternsin expt 2. The implications of the results for plant performancein grazed pastures are discussed. Branching, carbon translocation, defoliation, growth, morphology, Trifolium repens, white clover     

Relationships among shoot sinks for resources exported from nodal roots regulate branch development of distal non-rooted portions of Trifolium repens L

Two manipulative experiments tested hypotheses pertaining to the correlative control exerted by nodal roots on branch development of the distal non-rooted portion of Trifolium repens growing clonally under near-optimal conditions. The two experiments, differing in their pattern of excision to manipulate the number of branches formed at the first 9-10 phytomers distal to the youngest nodal root, each found that after 20 phytomers of growth the total number of lateral branches formed on the primary stolon remained between five and seven regardless of where the branches formed along the stolon. Additional treatments established that nodal roots influenced branch development via relationships among shoot sinks for the root-supplied resources rather than through variation in the supply of such resources induced by fluctuations in photosynthate supply to roots from branches. Regression analysis of data pooled from treatments of both experiments confirmed that shoot-sink relationships for root- supplied resources controlled the branching processes on the non-rooted portion of plants. A disbudding treatment, which removed all the apical and axillary buds present on basal branches, but left other branch tissues intact, increased branch development of the apical region in the same way as did complete excision of the basal lateral branches. The apical buds and the elongation processes occurring immediately proximal to the buds were thus identified as strong sinks for the root-supplied resources. Such results suggest that branch development on the non-rooted shoot portion distal to the youngest nodal root is regulated by competition among sinks for root-derived resources, of limited availability, necessary for the processes of elongation of axillary buds and the primary stolon apical bud.     

Are stoloniferous plants able to avoid neighbours in response to low R: FR ratios in reflected light?

An experiment was set up to test whether stoloniferous plants are able to avoid neighbours by means of asymmetric growth in response to low red:far-red (R:FR) ratios in light that is reflected by neighbouring plants. Neighbours were simulated by green mirrors that were placed on the north-side of the plants while spectrally neutral mirrors served as a control. Six stoloniferous species (Trifolium repens L., Hydrocotyle vulgaris L., Lysimachia nummularia L., Glechoma hederacea L., Lysimachia nemorum L. and Lamium galeobdolon L.) were included in the experiment. Measurements were made on branching frequency, timing of branching, stolon growth rate, internode length, growth direction and biomass distribution. Although differences between treatments were found in some of these parameters, they were too small to lead to the avoidance of the simulated neighbours. Only L. galeobdolon produced lower biomass in response to the green-mirror treatment compared to the control one.     

Competitive Performance of Nymphoides Peltata (Gmel.) O. Kuntze Growing in Microcosm

Two experiments were conducted to investigate the effects of competition on growth and performance of Nymphoides peltata (Gmel.) O. Kuntze in microcosm. Part of the research on growth and biomass allocation of N. peltata in response to competition had been reported early (Wu, Z. & D. Yu, 2004, Hydrobiologia 527: 241–250). This paper focuses on the morphological variations of N. peltata under competitive pressure. First, competition between N. peltata and Zizania latifolia (Griseb.) Turcz. ex Stapf. was assigned with the densities of N. peltata to Z. latifolia ratios of 4:0, 4:2, 4:4 and 4:8. Water surface coverage, surface area per leaf blade and number of leaves per plant of N. peltata all declined significantly with increasing density of competitor. Similar results were also found for petiole length and density of branching. However, the variations of planting density did not significantly affect the number of ramets per plant and the stolon length of N. peltata. Second, competitions between N. peltata and emerged Z. latifolia, floating-leaved Trapa bispinosa Roxb. and submerged Myriophyllum spicatum L. were also studied simultaneously. The results showed that significant difference was only found for the water surface coverage of N. peltata. No other significant differences were found for the number of ramets per plant, number of leaves per plant, density of branching, surface area per leaf blade, petiole length, and stolon length of N. peltata. Our studies indicate that N. peltata presents morphological variations when it is growing with Z. latifolia, such that the growth of above-ground parts decrease (i.e., leaf number, petiole length, branching density) and the growth of below-ground parts remains stable (i.e., stolons length). However, N. peltata does not show apparent differences in morphology when it is growing with T. bispinosa or M. spicatum. Accordingly, we conclude that the growth of N. peltata may be apparently inhibited by the presence of Z. latifolia, while T. bispinosa and M. spicatum may have little impact on the growth and performance of N. peltata.     

Response of Trifolium repens to UV-B radiation: morphological links to plant productivity and water availability

This study used nine populations of Trifolium repens L. (white clover) to investigate possible relationships between plant morphological attributes and responses to ultraviolet-B (UV-B) radiation. Plants were exposed to 0 or 13.3 kJ·m(-2) ·day(-1) UV-B for 12 weeks. Drought was applied in parallel to these treatments during the last 4 weeks of the experiment to test whether limited moisture availability would alter morphological UV-B responses. UV-B affected plant morphology under well-watered conditions, reducing leaf size by 15%, leaf number by 5% and stolon elongation by 19%. The number of leaf primordia in the apical bud was decreased by 4% under UV-B, and by 12% under drought. In drought-exposed plants, leaf size was reduced by 50%, leaf number by 30% and stolon elongation by 60%. In addition, drought reduced specific leaf area (SLA) by 33% and increased leaf percentage dry mass (PDM) by 40%. UV-B-induced reduction in plant biomass in the T. repens populations was associated with higher plant productivity and this was further linked to larger leaf size as well as to lower PDM. In conclusion, the findings suggest that morphological attributes conferring fast potential growth under productive conditions carry a cost in the form of lower biomass accumulation under UV-B.