牧食损害对伊乐藻(Elodea nuttallii)生长的影响

在室外实验条件下,研究了模拟牧食损害（动物牧食所造成的损害）对伊乐藻植株生长的影响。结果表明：3种人工损害方式（去除植株50%叶片,去除植株顶端,以及同时去除植物顶端与50%叶片）对伊乐藻的生长率、主枝与分枝长度的增长、植物的干物质、氮、磷含量等均有不同程度的影响。其中,去叶与去顶去叶损害显著抑制了伊乐藻的生长,相对生长率分别占未受损植株的62.8%与74.4%;去顶与去顶去叶损害使伊乐藻主枝生长几乎停止,却显著促进了植物分枝的生长;去叶损害对植株的生长率、主枝与分枝长度的生长无明显抑制并却显著地降低了分枝的重量。对受损伊乐藻生长的机理进行了分析,探讨了东太湖伊乐藻现存量近年来迅速增加的原因并认为植物残体是伊乐藻种群扩张的重要因素之一。     

切除顶技对加拿大伊乐藻生长的影响

切除5cm顶枝使加拿大伊乐藻生物量立即下降28%,净光合作用速率(Pn)和植株光合作用产量(PhP)与对照相比立即下降50%以上,去顶也对各种生长指标造成不同程度的即时损伤。经过随后28d的生长试验后,处理组与对照相比,生物量和总枝长(主枝+侧枝)增长率分别下降45%和53%,主枝伸长几乎停止;侧枝(分枝)数增长略有下降;水分含量明显增加;试验期间Pn平均下降了40%,PhP平均下降了51%.表明去顶对生物量增长、主枝伸长和冠层的发育有明显的抑制,对分枝数没有明显的影响。光合产量较生物量增长幅度的下降明显要大,其恢复去顶前水平的时间也比后者要长一倍。根据结果,讨论了去顶对沉水植物生长的影响机制、沉水植物的恢复能力并和其它收获试验进行了比较。       

螺类牧食对伊乐藻与苦草种间关系的影响

动物牧食可以调节植物种间的相对竞争能力,从而改变物种在群落中的竞争地位.外来植物伊乐藻生长迅速、具有较强的光竞争能力,土著种苦草根系发达、具有较强的地下资源竞争能力.选择这两种各具竞争特色的沉水植物为模式生物,通过室外受控实验研究了螺类牧食对两种沉水植物种间关系的影响.结果表明:不管有无螺类牧食,伊乐藻的相对生长率为苦草的2～5倍,伊乐藻具有明显的竞争优势.苦草低密度种植时,螺类牧食与种间竞争对其生长没有显著影响;高密度种植时,螺类牧食活动促进了苦草的生长,种间竞争则使苦草的生长率明显降低.无论伊乐藻种植密度如何,螺类牧食均使其生长率明显降低,混栽高密度的苦草也能抑制伊乐藻生长.探讨了螺类牧食对沉水植物的种间竞争关系的作用机理.     

不同遮光处理对猫须草生长及光合特性的影响

本文探讨全光照、遮光50%、遮光75%、遮光90%等4种处理对猫须草植株生长及光合特性的影响。结果表明,与全光照相比,3种遮光处理植株叶片净光合速率、蒸腾速率减少,叶片厚度及栅栏组织变薄,比叶鲜质量下降,植株分枝数减少,节间距、株高显著增加,植株根、茎、叶的生长量明显下降。从而表明,猫须草植株生长最适宜的光照条件为全光照。     

高寒草地狼毒枝-叶性状的坡度差异性

枝条与叶片的生长关系是植物形成不同冠层结构充分利用空间资源的一种策略, 有利于植株通过构型调整增强自身的光合效率和竞争力, 以适应不同的生境条件。在石羊河上游高寒退化草地, 利用ArcGIS建立研究区域的数字高程模型(DEM), 并提取样地坡度数据, 采用标准化主轴估计(SMA)方法, 研究了不同坡度狼毒(Stellera chamaejasme)种群枝与叶的生长。结果表明: 随着坡度增大, 狼毒叶大小、枝长度和分枝数均呈逐渐减小趋势; 狼毒分枝数与枝长度、叶片数与枝长度均呈异速生长关系, 枝长度增加的速度大于叶片数增加的速度, 分枝数增加的速度大于枝长度增加的速度; 不同坡度间的比较显示, 较大坡度上狼毒分枝数与枝长度、叶片数与枝长度的异速斜率均较大, 在枝长度一定的条件下, 较大坡度的狼毒具有更大的叶片数与枝长度的比值和分枝数与枝长度的比值。坡度差异造成环境因子和植被群落环境的变化, 进而影响狼毒的资源利用策略, 表现为枝条与叶片构型以及二者之间关系的变化, 反映了毒杂草较强表型可塑性的适应机制。     

不同养分水平对飞机草生长与生物量分配的影响

采用温室盆栽模拟实验研究了不同养分水平对外来入侵植物飞机草(Chromolaena odorata)的生长性状、生物量积累以及生物量分配格局的影响。实验共设置5 种养分浓度处理, 分别为Hoagland 标准营养液的10%、25%、50%、100%和200%溶液。结果表明: 养分水平对飞机草植株的生长性状以及生物量的积累、分配产生显著影响。随着养分水平的增加, 飞机草的总分枝数量、长度以及一级分枝数量、长度持续增加, 并且100%、200%处理还能促进二级分枝的萌发生长。飞机草的叶片数、总叶面积、总生物量以及茎、叶两器官生物量随养分水平的上升显著增加, 但株高、根生物量不受养分浓度变化的影响。根生物量比、根冠比随养分水平的提高显著下降, 叶生物量比则显著上升, 但茎生物量比在各养分浓度保持稳定。叶面积比、叶根比、RGR 亦随养分含量的上升显著增加。说明养分资源丰富的环境将促进飞机草的地上部生长, 而生物量分配格局的变化可能是其在入侵蔓延过程中适应养分异质性生境的重要生态策略。     

氮、磷养分对飞机草营养器官表型可塑性的影响

采用温室盆栽试验研究了不同氮、磷水平对入侵植物飞机草(Chromolaena odorata)营养器官表型可塑性的影响。结果表明:随着氮、磷水平的上升,飞机草的分枝数量、分枝长度、叶片数、总叶面积、总生物量以及茎、叶器官生物量显著增加。飞机草的根生物量比、根冠比随着氮、磷水平的升高显著下降;茎生物量比在供氮(磷)量达0.05 g·kg-1时显著增加,之后保持稳定;叶生物量比随氮水平的增加先降后升,但其受磷水平变化的影响较小。叶面积比、叶根比、比叶面积和平均相对生长速率随着氮、磷水平的上升显著增加,但叶面积比、叶根比和比叶面积在供磷量≥0.05 g·kg-1时的差异不明显。飞机草的分枝数量、分枝长度、叶片数、总叶面积、根生物量比、根冠比、叶根比以及茎、叶与植株总生物量等指标的可塑性指数较高,并且对氮素的响应更强。表明氮、磷水平能够显著影响飞机草的植株生长,飞机草亦能够通过植株形态、结构以及生物量积累与分配的调整来适应多变的养分环境,并表现出较高的可塑性。     

外界支持物直径对苦瓜生长和觅食行为的影响

采用实验生态学的方法研究了外界支持直径变化对苦瓜植株生长和觅食行为的影响。结果表明,支持物直径变化对主茎节间、叶片、叶柄和卷须的发育进程无明显影响。苦瓜植株的攀援生长显著受到支持物直径大小的影响,当支持物直径小于8mm时,植株能较好地自主攀援生长。生长于直径支持物上的植株比生长于小直径支持物上的植株表现出较高的分枝率、较短的主茎、较长的分枝、较大的比茎长和比叶柄长。相关分析表明,节间长度和叶柄长度同植株自主攀援程度成显著正相关关系,而单叶面积、分枝数量和比叶柄长同植株自主攀援程度成显著负相关关系。作为攀援植物的一种重要资源,外界支持物的特征和存在状况将对植物的生长和行为产生重要影响。     

薰衣草枝叶性状关系的个体大小依赖

植物枝叶性状的个体大小差异,是植物适应异质性环境所形成的冠层构建策略,对于理解枝叶构建机制及光合生理代谢具有重要意义。于2017年7月下旬,在金水湖湿地公园选择一块薰衣草样地,根据体积将薰衣草(Lavandula angustifolia)分为3个大小等级[I级:植株体积的立方根(d)≤60 cm、II级(60 cmd≤90 cm)和III级(d90 cm)],采用一元线性回归方法,研究了薰衣草种群枝叶性状的个体大小依赖。结果表明:随着薰衣草植株大小等级增大,薰衣草的叶面积、枝长度、枝数量和枝横截面积逐渐增大,而叶数量、叶厚度和分枝角度逐渐减小。薰衣草叶面积、枝长度和枝数量与个体大小呈极显著的正相关(P0.01),枝横截面积与个体大小呈显著的正相关(P0.05),叶数量和叶厚度与个体大小呈极显著的负相关(P0.01),分枝角度与个体大小呈显著的负相关(P0.01)。为提高资源利用效率,大个体薰衣草选择生长少量大而薄的叶片以及分配更多的生物量用于小枝的生长;而小个体薰衣草选择生长多数小而厚的叶片以及短而细的枝条,体现了不同大小等级薰衣草枝叶表型可塑性。     

喜旱莲子草入侵群落土壤对植物生长的影响

分别以受喜旱莲子草(Alternanthera philoxeroides)入侵和未受喜旱莲子草入侵的当地植物群落土壤为生长基质,比较不同基质上入侵植物喜旱莲子草和同属的土著植物莲子草(A.sessilis)的生长指标,探讨喜旱莲子草入侵群落土壤对喜旱莲子草及莲子草生长的影响机制。结果表明,喜旱莲子草入侵群落土壤抑制了莲子草的生长,显著降低了根生物量、茎生物量和总生物;改变了形态特征,显著降低了分枝数量、茎长度、根长、根体积;减少了对根的生物量分配,显著抑制了根质量比与根冠比。喜旱莲子草入侵群落土壤对入侵植物喜旱莲子草的生物量、分枝数量、茎长度、根长、根体积没有显著的抑制作用,而显著增加了其叶片数量和叶质量比。这种效应将有利于喜旱莲子草在入侵地形成单优群落,表明土壤在喜旱莲子草成功入侵中起了重要作用。     

A comparison of artificial defoliation techniques using canola (<Emphasis Type="Italic">Brassica napus</Emphasis>)

We conducted two experiments that investigated how the method and location of artificial defoliation influenced growth, reproduction, and allocation in canola, Brassica napus. In one experiment, 0%, 25%, or 50% of leaf area was removed by cutting circular holes at three possible locations: concentrated at either the base of leaves or at their tips, or dispersed throughout leaf blades. Plants fully compensated for such damage; reproduction and allocation were unaffected by either defoliation intensity or wound location. In a second experiment, we again initiated three intensities of defoliation: non-damaged plants served as controls, while others had 25% or 50% of their leaf areas removed. The method of removal in the second experiment consisted of cutting either multiple, similar-sized, circular holes or single, contiguous patches of a leaf blade. At the highest defoliation intensity reproductive output and allocation were significantly less in plants treated with the former method than the latter, even though an equivalent initial amount of leaf area was removed in both treatments. We conclude that simulated herbivory studies must account for not only how much of the plant is damaged, but also the pattern of leaf damage itself, since both factors contribute to a plant’s physiological and ecological responses to grazing.     

Linking above-ground and below-ground effects in autotrophic microcosms: effects of shading and defoliation on plant and soil properties

Although factors affecting plant growth and plant carbon/nutrient balance – e.g., light availability and defoliation by herbivores – may also propagate changes in below‐ground food webs, few studies have aimed at linking the above‐ground and below‐ground effects. We established a 29‐week laboratory experiment (～one growing season) using autotrophic microcosms to study the effects of light and defoliation on plant growth, plant carbon/nutrient balance, soil inorganic N content, and microbial activity and biomass in soil. Each microcosm contained three substrate layers – mineral soil, humus and plant litter – and one Nothofagus solandri var. cliffortioides seedling. The experiment constituted of the presence or absence of two treatments in a full factorial design: shading (50% decrease in light) and artificial defoliation (approximately 50% decrease in leaf area in the beginning of the growing season). At the end of the experiment a range of above‐ground and below‐ground properties were measured. The shading treatment reduced root and shoot mass, root/shoot ratio and leaf production of the seedlings, while the defoliation treatment significantly decreased leaf mass only. Leaf C and N content were not affected by either treatment. Shading increased NO ₃–N concentration and decreased microbial biomass in humus, while defoliation did not significantly affect inorganic N or microbes in humus. The results show that plant responses to above‐ground treatments have effects which propagate below ground, and that rather straightforward mechanisms may link above‐ground and below‐ground effects. The shading treatment, which reduced overall seedling growth and thus below‐ground N use and C allocation, also led to changes in humus N content and microbial biomass, whereas defoliation, which did not affect overall growth, did not influence these below‐ground properties. The study also shows the carbon/nutrient balance of N. solandri var. cliffortioides seedlings to be highly invariant to both shading and defoliation.     

Flooding effects on rapid responses of the invasive plant Alternanthera philoxeroides to defoliation

In experiments under controlled growth conditions it was examined how flooding affected the responses of the invasive plant Alternanthera philoxeroides to defoliation. In drained and flooded conditions, plants were subjected to five defoliation levels: 0, 10, 50, 90% removal of leaf tissue and apex removal (90% leaf tissue plus apical bud removal). Plants were harvested weekly for five weeks. In drained conditions, plant biomasses including total biomass, shoot biomass and root biomass after 50% defoliation rapidly recovered to the control plant level. They were significantly lower for the 90% defoliation and apex removal treatments compared to control plants throughout the experiment. In flooded conditions, total biomass and shoot biomass after 50% defoliation, 90% defoliation, and apex removal treatments could return to control plant levels before the end of the experiment. In 90% defoliation and apex removal treatments root to shoot biomass ratios of both drained and flooded plants were initially much higher than in control plants, but the difference disappeared rapidly. The final biomasses decreased with increased defoliation intensity in drained conditions, but no significant difference was generally found in any of the defoliation treatments in flooded conditions. The rapid re-growth of A. philoxeroides plants after defoliation may partly be responsible for its invasion success. However, defoliation capable of removing 90% of the leaf tissue may be desirable in restricting the growth of this invasive species in drained conditions.     

Growth,chemical responses and herbivory after simulated leaf browsing in <Emphasis Type="Italic">Combretum apiculatum</Emphasis>

Vegetative and chemical responses to simulated leaf browsing during the growth season, and their subsequent effect on herbivory, were studied on Combretum apiculatum Sonder (Combretaceae) in Botswana. Treatments (50% and 100% leaf and shoot apex removal) were performed just before the shoot growth curve levelled out, and responses recorded 3 months later, just before leaf fall. Compared to controls, defoliation treatments, removing apical dominance, reduced growth in tree height and increased shoot mortality, although the production of lateral shoots increased. At the end of the trial, there was no difference in total length of annual shoots between treatment groups. Significant refoliation occurred only after 100% defoliation. Refoliated leaves were smaller and the 100% defoliated trees had a lower final leaf biomass. Total leaf biomass production was, however, equal for all treatment groups. Refoliated leaves contained higher levels of N, lower levels of acid-detergent fibre (ADF) and total phenolics, and showed a trend towards lower levels of condensed tannins, compared to leaves on control trees. Such chemical changes may be due to either carbon stress or to younger physiological age of new leaves. In spite of the observed potential increase in food quality, we found no evidence of increased levels of insect or ungulate herbivory on refoliated leaves, which, at least for insect herbivory, may be explained by the reduction in temporal availability of leaves. We conclude that the single severe defoliation was not detrimental to C. apiculatum in the short-term, although the resource loss and induced compensatory growth may produce negative effects during subsequent growth seasons.     

In vitro embryonic axis and seedling shoot tip culture of Juglans nigra L.

Embryonic axes and seedling shoot tips of Juglans nitra L., Black walnut, were cultured in vitro. Significant variation existed among progeny from individual trees for growth of radicles and epicotyls and production of callus and axillary shoots from embryonic axes. The concentration of 6-benzyladenine influenced the growth of the radicle and epicotyl and production of callus and axillary shoots of axes. Axes generally initiated growth quicker on solidified woody plant medium than on Driver and Kuniyuki's walnut medium, but axillary shoot proliferation and elongation were eventually better on liquid Driver and Kuniyuki's walnut medium than on woody plant medium which required an etiolation treatment for microshoot elongation. The concentration of BA also influenced both callus growth and axillary shoot proliferation from seedling shoot tips. Axillary shoots which formed in Driver and Kuniyuki's walnut medium rooted best in sterile vermiculite following a 15 s dip in 10 mM indole-3-butyric acid. Micropropagated plants are growing in the greenhouse.     

Effect of defoliation intensity on aboveground and belowground relative growth rates

According to a simple growth model, grazed and ungrazed plants may have equal absolute growth rates provided that the relative growth rate (RGR) of grazed plants increases exponentially with grazing intensity (proportion of biomass removed). This paper reports results from an experiment designed to determine whether plants of two grass species subjected to a gradient of defoliation intensities, from 0 to 100% aboveground biomass removal, showed such a response. The relationship between aboveground RGR and defoliation intensity was exponential and closely matched the theoretical relationship of equal absolute growth rate. Thus, plants showed the same aboveground growth regardless of defoliation intensity thanks to an exponential stimulation of RGR by defoliation. Belowground RGR was depressed by defoliation of more than 20% of the above-ground biomass. In spite of the drastic modification imposed by the treatments on the relative proportions of different plant parts, after a 42-day recovery period basic allometric relationships, such as root:shoot and leafarea: weight ratios, were not affected by defoliation intensity. Exponential aboveground compensatory responses represent a key feedback process resulting in constant aboveground growth regardless of defoliation intensity and appear to be a simple consequence of strong commitments to certain allometric relationships.     

根茎克隆植物羊草体内可溶性碳水化合物的时间变异及其对去叶干扰的响应

该研究针对根茎型克隆植物羊草(Leymus chinensis)考察了以下内容:1)地上枝条和根茎中可溶性碳水化合物含量的时间动态及其对去叶干扰的响应;2)特定阶段植物体内一定部位的可溶性碳水化合物浓度差异;3)植物体各部分(地上部分、直立茎地下部分及根茎)间可溶性碳水化合物浓度变化之间的关联。基于上述研究结果,作者试图弄清碳水化合物对于羊草克隆分株和整个基株生长和存活的意义。实验共有4个处理:1个对照和3个不同频度(在整个实验进行期间分别去叶1次、3次和5次)的去叶处理。所有去叶处理都采取一个统一的强度,即留茬15 cm。地上枝条和根茎的取样频次为每10 d 1次。植物体各部分可溶性碳水化合物浓度以高效液相色谱法(HPLC)测定。对不同去叶频度处理间的碳水化合物含量差异显著性进行ANOVA分析。结果表明:不去叶对照处理在生长季盛期可溶性碳水化合物浓度的显著下降归因于植物体快速的生长而引起植物叶片旺盛的呼吸消耗,而去叶处理中植物的可溶性碳水化合物浓度并没有大的降低甚至在最频繁的去叶处理下还有所上升,主要是由于去叶处理减少叶片而造成地上部分总呼吸量下降所致。一次性去叶处理并没有影响植物地上部分最终的可溶性碳水化合物浓度,但是连续数次的去叶处理对地上部分可溶性碳水化合物浓度产生了一定的影响。在秋季气温下降时,碳水化合物自地上向地下的转移在去叶频度越大的处理下表现越为迅速。这表明当植物体接受到气温降低的信号后,去叶干扰加速碳水化合物自地上向地下的转移。可能由于地下枝条存在一定的贮藏功能,在实验过程中地下枝条中可溶性碳水化合物浓度比地上枝条中表现的更加稳定。根茎中的可溶性碳水化合物必要时会转移到地上以供应地上枝条的生长,而旺盛的生长会消耗可溶性碳水化合物,然而自未接受去叶处理的分株向接受去叶处理的分株的克隆整合(常常在较高频次的去叶处理中发生)可能会在一定程度上缓解这种消耗所造成的影响。     

Effect of defoliation on tracheid production and the level of indole-3-acetic acid in Abies balsamea shoots

To simulate feeding by the spruce budworm ( Choristoneura fumiferana Clem.), the apical current-year shoots on 1-year-old branches in the uppermost whorl of 6-year-old balsam fir [ Abies balsamea (L.) Mill.] trees were either removed completely by debudding before the start of the growing season or defoliated 0, 50, 90 or 100% shortly after budbreak. Debudded branches were treated at the apical end with 0, 0.1 or 1.0 mg of indole-3-acetic acid (IAA) (g lanolin)⁻¹. Ninety % of the 1-year-old needles were also removed from some of the experimental branches. After ca 4 weeks of growth, the radial width of new xylem and the level of IAA were determined in the 1-year-old internode. The IAA content was measured by radioimmunoassay.
The removal or defoliation of current-year shoots inhibited tracheid production and decreased the IAA level. Exogenous IAA stimulated tracheid production and increased the IAA level in debudded branches. Current-year shoot defoliation also inhibited current-year shoot elongation. The inhibitory effect of current-year needle removal on all parameters generally increased with increasing intensity of defoliation. The removal of 1-year-old needles did not affect the IAA level or current-year shoot elongation, nor did it influence tracheid production in branches with current-year shoots. However, removal of 1-year-old needles inhibited tracheid production in debudded branches supplied with exogenous IAA. The results indicate that (1) IAA is involved in the control of tracheid production in the 1-year-old internode, (2) IAA is supplied primarily by current-year shoots, and (3) defoliation by the spruce budworm inhibits tracheid production partly by decreasing the supply of IAA.     

How do water depth and harvest intensity affect the growth and reproduction of Elodea nuttallii (Planch.) St. John?

Aims Both high and low densities of macrophyte vegetation can impair its ecosystem service function. Harvesting is often applied to macrophyte vegetation to maintain an appropriate density. Vegetation harvesting has occasionally gone awry and caused catastrophes, such as vegetation disappearance and cyanobacterial dominance in waterways and lakes. Because water depth influences macrophyte density at all life stages, the simultaneous influences of harvesting and water depth should be carefully examined. Thus, this study aims to quantify the effects of differently harvesting Elodea nuttallii on its growth and reproduction at different water depths in field experiments.Methods Four harvest intensities (harvesting E. nuttallii plant heights equal to 25%, 50%, 75% and 100% of the water depth) were applied to E. nuttallii growing at four different water depths (60, 90, 120 and 150cm). Plant length and root length were measured. The node number, root number of each plant and number of floating plants were counted before harvesting. The harvested plant were dried to a constant weight for dry weight determination.Important findings The rate of increase in the length and shoot number of E. nuttallii varied from ?0.012 to 0.440 day^-1 and from ?0.020 to 0.639 day^-1, respectively. Water depth>150cm would limit E. nuttallii growth. Elodea nuttallii responded to increasing water depths and low-intensity harvesting by increasing internodal length and decreasing shoot number. The larger internodal length of E. nuttallii observed in relatively deeper water was also induced by the physical strain generated by its buoyancy as its specific gravity was less than water's. The physical mechanism of removing the plant canopy by harvesting decreased E. nuttallii buoyancy and prevented floating. Harvesting increased plant production in shallow waters <90cm deep. Moreover, it is also necessary to perform three medium-intensity harvests at a water depth of 120cm and one low-intensity harvest or no harvesting at a water depth of 150cm to achieve longer lifetimes and less biomass near the water surface when the plants reach or approach the water surface.