刈割后两种不同体型植物的补偿式样对比研究

 对比了两种不同体型植物燕麦（Avena sativa）和油菜（Brassica campestris） 在不同施肥水平下的刈割反应特点。结果表明：对于燕麦而言,在不施肥条件下,3个时期的轻度刈割处理与对照相比,其生物量、总生物量、果重、果数等都有增加,但只有某些指标出现超补偿;在施肥条件下,各种刈割处理后均没有发生超补偿。并且无论施肥与否, 分蘖期与拔节期的补偿指数均高于抽穗期的补偿指数。可以认为,不施肥条件下营养期轻度刈割处理较有利于燕麦的补偿生长。对于油菜而言,花蕾期轻度刈割处理后植物补偿指数最大,且施肥条件下的补偿指数高于不施肥条件下的补偿指数。比较两种植物在不同资源下补偿反应的特点,可认为因休眠芽位置及其活动方式不同而所造成的体型差异对植物的补偿反应式样有很大影响。     

种群密度与施肥对垂穗披碱草刈割后补偿作用的影响

 以甘南亚高山草甸常见牧草垂穗披碱草(Elymus nutans)为对象,通过考察种群密度、施肥与刈割处理等对植物生长和生殖的影响效应,比较了垂穗披碱草在5个密度及2个施肥实验处理条件下对4种刈割处理的补偿性反应特点。结果表明,在所有密度及施肥处理条件下,早期轻度刈割处理 (分蘖期刈割,留茬4 cm) 都有利于植物的补偿作用,后期重度处理 (拔节期刈割,留茬2 cm) 可显著降低植物的地上部分生物量及生殖部分干重 (穗重)。在不施肥情况下,刈割对垂穗披碱草的影响程度随种群密度而加大,在低密度处理中早期轻度刈割的植物发生了超补偿。可以认为,低密度种群中植物具有较多的分蘖是植物在刈割后表现出较高补偿能力的一个重要生物学原因。实验还发现,施肥可提高植物个体的分蘖能力和秆叶再生能力,因而总体上可增强植物的补偿能力,并且在中等密度条件下垂穗披碱草的补偿能力较强,尽管没有发生超补偿现象。不过,施肥主要是有利于植物地上营养器官的补偿,生殖器官的补偿程度较小一些。试验结果对科学管理人工草场具有一定的指导意义。     

施肥和刈割对冷地早熟禾补偿生长的影响

以青藏高原东部高寒草甸常见牧草冷地早熟禾(Poa crymophila)为研究对象,比较研究了肥力和不同刈割处理对植物生长和生物量补偿的影响。实验采用随机设计,肥力分为施肥和不施肥,刈割处理为刈割时间、刈割频度和刈割强度3因子组合。结果表明:不刈割情况下,施肥显著促进冷地早熟禾的生长,而在刈割情况下,施肥对植物的生长没有明显的促进作用甚至有负作用。不施肥,刈割可促进冷地早熟禾地上生物量的增加并发生超补偿,但补偿程度因刈割强度、刈割频度和刈割时间而异;施肥时,刈割没有或很少促进植株发生超补偿。超补偿发生时,资源贫瘠的条件可能是必需的。冷地早熟禾发生超补偿可能是以损耗地下部分的资源为代价的,刈割刺激分蘖的增加对超补偿的发生也有一定的贡献。     

青藏高原东部高寒草甸群落生物量和补偿能力对施肥与刈割的响应

以青藏高原东部高寒草甸群落为研究对象,通过比较了不同施肥条件和不同刈割对群落地上生物量和多样性的影响。结果表明施肥可提高生物量且生物多样性降低,施肥和刈割处理后,施肥效应显著而刈割效应不显著,说明施肥是主效应。实验还发现施肥可提高群落的补偿能力;不同资源梯度的情况下植物群落对刈割处理后补偿作用也不相同,对刈割处理后植物群落补偿能力随资源的升高而增强。当未施肥和施肥30g/m^2时相同强度的1次刈割的补偿能力较相同强度的2次刈割的补偿能力大;当施肥60g/m^2和120g/m^2时相同强度的2次刈割的补偿能力较相同强度的1次刈割的补偿能力大。     

光照，施肥及刈割对垂穗披碱草生长的影响

以甘南高寒草甸常见牧草垂穗披碱草（Elymus nutans）为研究对象，比较不同光照、肥力条件下，垂穗披碱草对刈割的生长和补偿反应。研究发现，光照和肥力存在交互作用。施肥、中度光照下，未刈割单株垂穗披碱草地上生物量最大，为3．239g。施肥、中度光照下，比较刈割植株地上生物量补偿发现：晚期刈割单株地上生物量的补偿大于早期刈割；刈割强度无显著影响；刈割两次单株地上生物量的补偿最大。施肥、中度光照、晚期、轻度、一次刈割时，单株垂穗披碱草地上生物量累积最大，为4．500g。全光照、未施肥条件下，刈割对单株地上生物量的补偿无影响。就补偿机制而言，植株地上生物量的增加以地下生物量为代价。     

刈割、施肥和浇水对垂穗披碱草补偿生长的影响

植物的补偿生长特性受放牧强度和生境资源获得性的影响。通过为期2年的野外控制实验,研究了刈割高度(留茬1cm、3cm及不刈割)、施肥(施、不施)和浇水(浇、不浇)处理对垂穗披碱草(Elymus natans)补偿生长的影响,并结合对各处理分株密度、比叶面积、净光合速率和相对生长率的变化研究,探讨了其补偿生长机制。结果表明:刈割后垂穗披碱草分株种群密度显著增加,补偿生长高度显著降低,比叶面积和相对生长率随刈割强度增加而呈上升趋势,叶片净光合速率变化不显著;施肥能显著增加垂穗披碱草的补偿生长高度、比叶面积、叶片净光合速率和相对生长率;浇水处理以及刈割、浇水、施肥处理之间的交互作用均不显著。可见,在刈割条件下,垂穗披碱草具有一定的密度补偿机制,但由于刈割抑制补偿性高生长,导致分株高度出现低补偿。因此,即使刈割后比叶面积和株高相对生长率显著增加,也不一定必然引起株高的超补偿;但施肥可显著提高垂穗披碱草的补偿能力,增加耐牧性,证实了改进后的限制资源模型的预测。     

刈割、施肥和浇水对矮嵩草补偿生长的影响

通过对青海海北高寒矮嵩草(Kobresia humilis)草甸进行为期3年的野外控制试验, 研究了刈割(留茬1 cm、3 cm及不刈割)、施肥(2.5 g·m^-2尿素+ 0.6 g·m^-2磷酸二胺、不施肥)和浇水(20.1 kg·m^-2、不浇水)处理对矮嵩草补偿生长(包括分株密度、株高和分株地上生物量)的影响, 及其比叶面积、叶片净光合速率和相对增长率的变化, 探讨矮嵩草补偿生长的机制。研究结果表明: 刈割后, 矮嵩草的补偿生长高度和比叶面积显著降低; 分株密度有增加的趋势, 但会随刈割强度的增加而下降; 株高和生物量的相对增长率随刈割强度的增加而呈上升趋势; 补偿地上生物量在重度刈割处理下最高。施肥能显著增加矮嵩草的补偿高度、分株密度、补偿地上生物量、株高相对增长率、生物量相对增长率、比叶面积和净光合速率; 与不浇水处理相比, 浇水处理对重度刈割处理下的分株地上生物量、密度相对增长率、比叶面积和净光合速率无影响, 而显著降低了中度刈割处理下的补偿高度和株高相对增长率, 提高了不刈割处理下的分株密度和重度刈割处理下的生物量相对增长率。刈割、施肥和浇水处理的交互作用也显示出刈割与施肥对矮嵩草补偿生长具有拮抗效应, 而刈割与浇水具有协同效应。上述结果说明, 矮嵩草在刈割后可通过增加分株密度和相对增长率等途径来提高补偿能力, 弥补在生长高度上出现的低补偿, 而施肥可显著抵消刈割的不利影响, 提高矮嵩草的补偿能力。     

施肥和刈割对青藏高原东部高寒草甸群落生物量补偿效应的影响

通过对青藏高原东部高寒草甸植物群落在4个施肥处理及7个刈割水平下的群落生物量、物种丰富度和补偿指数的比较,分析了该类草甸群落主要特征对施肥及刈割强度差异的响应.结果表明:施肥显著增加了群落生物量,并降低物种丰富度,而刈割处理虽然增加了物种丰富度,但对群落生物量无显著影响;随着施肥量的增加,高寒草甸由莎草科和杂草类物种占优势的群落构成逐渐向禾本科物种占优势的群落构成转变;施肥可提高群落的补偿能力,在不同施肥梯度中,刈割后植物群落补偿能力也不相同;随着施肥量的增加,增加刈割强度,减少刈割次数,发生超补偿的机率增大;可见,施肥是主效应,刈割对群落主要特征的影响随营养水平的不同而发生变化.     

春小麦对刈割伤害的补偿作用研究

通过１９９５年大田试验研究了黄土高原半干旱区春小麦受刈割伤害（模拟动物采食）后的补偿作用。结果表明,在大田实验条件下,刈割处理一般会使小麦生长受阻且减产,即不足补偿。在刈割一半叶片的处理中,拔节期的减产效应重于苗期的减产效应;在苗期处理中,重度伤害（刈割全部叶片的减产效应大于轻度刈割（刈割一半叶片）的减产效应,而拔节期刈割前三位叶片的处理不仅未造成减产,还出现产量的超越补偿,是由于此时小麦早期生长     

苗期刈割伤害对春小麦生长及产量的影响

通过1996年大田试验研究了黄土高原半干旱区春小麦苗期（三叶－心期）受到不同强度刈割伤害（模拟动物的采食）后的补偿作用,结果,在大田试验条件下,受轻度刈割（刈割一半叶面积,H0,H1）,春小麦的补偿效应大于受重度刈割（刈割全部叶面积T0,T1）春小麦的补偿效应,且都低于未受刈割处理（对照,CK0,CK1）,即CK0＞H0＞T0;CK1＞H1＞T1,刈割处理后,灌溉一次水（CK1,H1,T1）虽可增强其补偿能力,促进小麦的生长,但仍为低补偿。     

Experimental clipping of sagebrush inhibits seed germination of neighbours

Current views of plant communities emphasize the importance of competition for resources and colonization ability in determining seedling establishment and plant distributions. Many desert shrubs are surrounded by bare zones that lack other plants or have different suites of species beneath them compared with the open desert surrounding them. Releases of biochemicals as volatiles from leaves, leachates from litter, or exudates from roots have been proposed as mechanisms for this pattern, but such phytotoxicity has been controversial. I tested the hypothesis that experimental clipping of sagebrush foliage enhances its effect as a germination inhibitor. Germination of native forbs and grasses was reduced in association with clipped, compared with unclipped, sagebrush foliage in lath house and field experiments. Sagebrush seeds were not significantly affected. Air contact was required for this inhibition of germination. Soil contact and leaf litter were not required and added little inhibition of germination. These results suggest a potentially large, indirect, and previously overlooked role for interactions between herbivory and germination that could affect plant community structure.     

The effect of clipping on methane emissions from Carex

The purpose of this study was to estimate theresistance to methane release of the above-groundportion of Carex, a wetland sedge, and todetermine the locus of methane release from the plant. Measurements conducted on plants clipped to differentheights above the water level revealed that themethane flux from clipped plants was on the order of97% to 111% of control (unclipped) values. Thegreatest increase was observed in the initial fluxmeasurement after the plants had been clipped to aheight of 10 cm. Subsequent measurements on the 10 cmhigh stubble were similar to control values. When theends of plants which had been clipped to 10 cm weresealed, the methane flux was reduced to 65% ofcontrol values. However, sealing had no effect on theflux from plants which were clipped at 15 cm andhigher, indicating that virtually all methane wasreleased on the lower 15 cm of the plants as theyemerged from the water. The results indicate that theabove-ground portions of Carex at our studysite offered only slight resistance to the passage ofmethane, and that the main sites limiting methaneemission are below-ground, at either theporewater-root or root-shoot boundary. We hypothesizethat the transitory increase in flux associated withclipping was due to the episodic release of methaneheld within the plant lacunae. The buildup ofCH₄ partial pressure within lacunal spacesovercomes the resistance to gas transport offered byaboveground parts.     

Sprout recruitment and self-thinning of Erica multiflora after clipping

Regrowth after clipping and the effect of local competition were studied in a natural population of Erica multiflora in a Mediterranean shrubland, by removing neighbours at 1 and 2 m around the target plants during four growing seasons. Removal of surrounding natural vegetation increased the number, the density (number of sprouts per stump area) and the biomass of the sprouts growing from clipped plants. Target plants ònly interacted with their near neighbours. Target plants had a negative relative increment in the number of sprouts per stump during the 18 months immediately following treatment, but a positive increment thereafter, which suggests that there was a constant or episodic recruitment of sprouts within the stump after clipping. Competition treatment had a non-significant effect on the negative increment of sprouts per stump. The self-thinning trajectory was different for the different competition treatments: there was an allometric negative relationship between density of sprouts and mean biomass of survivors during all sampling periods in genets without neighbours in a 1-m radius; the self-thinning trajectory of sprouts in genets without neighbours in a 2-m radius was short, a net increase in sprouts per stump area was accompanied by an increase in mean sprout biomass 30 months after clipping. During the same period, however, plants with neighbours showed a decline in both the sprout biomass and density.     

The effect of clipping on self-thinning in Trifolium pratense

The self-thinning rule describes mortality in a crowded even-aged stand as a function only of biomass accumulation. We tested this prediction by stopping biomass accumulation with clipping treatments in Trifolium pratense. Moderate levels of clipping slowed thinning mortality considerably, but did not stop it entirely.     

Lignotuber reserves support regrowth following clipping of two Mediterranean shrubs

1. We investigated whether reserves stored in the lignotubers of two Mediterranean shrubs, Arbutus unedo and Erica arborea , were significantly mobilized to support the demands of regrowth and respiration after clipping the tops at different frequencies.
2. After a single clipping, Arbutus showed a 29% decrease of phosphorus concentration by the end of the first growing season. Two years after recovery from clipping, the starch levels remained lower than those of unclipped plants. Similarly, Erica showed depletion of starch, but no nutrient reserves were depleted significantly.
3. Regrowth after multiple clippings mobilized a large fraction of the starch and nutrients stored in the lignotuber. Mean starch concentrations were depleted by 87–93% after multiple clippings and concentrations of nitrogen, phosphorus, potassium and magnesium were depleted by 10–45%, 27–41%, 19–39% and 23–31%, respectively.
4. An average-sized lignotuber produced 288 resprouts for Arbutus and 1990 resprouts for Erica during a 27 month period of multiple clippings, at the end of which the first plants died.
5. Plant mortality after multiple clipping was 10% for Arbutus and 30% for Erica , and was primarily attributed to exhaustion of carbon reserves because starch concentrations decreased by 96% in dead plants.     

Effect of local competition on resprouting of Arbutus unedo after clipping

Abstract. To evaluate the effects of local competition on the growth and size variability of sprouts following disturbance in a natural population of Arbutus unedo in Catalonia, plants were cut at the base and a neighbor removal experiment was performed. Removal of neighbors resulted in an increase in the number and biomass of sprouts at 2 and 7.5 months after clipping. Number and biomass of sprouts was also correlated with initial plant size (stump area). Inter-genet competition appeared to be symmetric, and acted to delay the onset of interference among sprouts within a genet. Size variability of sprouts on an individual was positively correlated with their density on the stump, supporting the hypothesis that competition among ramets (sprouts) within a genet is asymmetric. Reduced inter-genet competition from neighbor removal resulted in an increase in the number and biomass of sprouts growing from a stump. This resulted in an increase in the asymmetry of competition among sprouts, and therefore an increase in the size variability of these sprouts.     

Growth responses of a woody species to clipping and goat saliva

Studies on the role of mammalian herbivore saliva in plant–animal interactions have mostly focused on graminoid species and bovine saliva. A trial was performed in Botswana with clipping treatments to simulate browsing of shoots and the application of goat saliva on the woody species Combretum apiculatum Sonder (Combretaceae). Treatments were performed during early growing season while shoot growth was rapid, and responses of trees were recorded later in the same season. Clipped shoots with saliva had significantly enhanced shoot growth (tripled in length) and leaf production (2.7 times more leaves) compared to clipped shoots without saliva. However, unclipped shoots still grew more than clipped shoots, with or without saliva treatment.