Compensatory growth responses of seedlings of Pharbitis purpurea (Convulvulaceae) to tissue removal at different seeding depths of seeds

Tissue damage to seedlings can limit their later growth, and the further effects may be greater with increasing seedling age. Seedlings, however, can minimize the effect of damage through compensatory growth. Seedlings of Pharbitis purpurea grow in frequently disturbed habitats and generally tolerate damage to leaf tissues. We evaluated the compensatory responses of the cotyledon to different levels of defoliation and their effect on seedling growth and development. We also examined the relationship between seeding depth and compensatory growth. We tested seven defoliation treatments with one or both cotyledons and/or the apical meristem of seedlings removed from seeds buried at a seeding depth of either 2 or 5?cm. We then measured 12 growth traits of the seedlings to assess development and growth compensation. The area, thickness, biomass, and longevity of the remaining cotyledon were also measured to quantify increased growth as result of treatment effects at both seeding depths. The results showed that defoliation reduced seedling height, belowground length, and total biomass significantly in subsequent growth in all treatments. However, defoliation treatments had direct positive impacts on growth at 2?cm depth compared with 5?cm depth. In contrast, the compensation of cotyledon area (C _area), biomass (C _mass), and thickness (C _thickness) was greater at 5?cm depth than at 2?cm depth. The results thus indicate that P. purpurea seedlings adopted a compensatory growth strategy to resist leaf loss and minimize any adverse effects using the remaining cotyledon. Increasing seeding depth can aggravate the compensatory growth of remain cotyledon after partial defoliation.     

Effects of herbivory and herb interference on oak establishment in a semi-arid temperate savanna

Abstract. Early establishment of Quercus emoryi seedlings in the grassland phase of a semi-arid temperate savanna was evaluated in southern Arizona, USA. Controlled-environment experiments indicated that Quercus seedlings are tolerant of frequent clipping, but undipped seedlings produce more biomass than clipped seedlings. Seedlings were much less tolerant of clipping or defoliation in the field than in the growth chamber, and most seedlings died after being clipped or defoliated by herbivores. Invertebrate herbivory, which is rarely mentioned as an important factor limiting seedling establishment, was the leading cause of seedling mortality in the field study. Below-ground interference from herbs had a greater impact on seedling survival and growth than above-ground interference.     

Leaf compensatory growth as a tolerance strategy to resist herbivory in Pancratium sickenbergeri

We examined the effects of leaf herbivory by the dorcas gazelle, Gazella dorcas, on the compensatory growth of the geophyte Pancratium sickenbergeri (Amaryllidaceae) in the Negev desert, Israel. In three populations exposed to different levels of herbivory, we removed different amounts of photosynthetic leaf area from plants in five clipping treatments: 0, 25, 50%-dispersed over all leaves, 50%-entire area of half the leaves, 100%. The population with the lowest level of herbivory showed the lowest relative regrowth rate after clipping. In the population with a constantly high level of herbivory, plants in intermediate-clipping treatments overcompensated in leaf area after clipping. For all the populations, clipped plants produce more new leaves than unclipped plants. In the population with the highest level of herbivory, clipping treatments did not have a significant effect on the number of fruits per plant. In addition, we did not find a trade-off between investments in growth and reproduction in this population. Our results indicated that, in the desert lily, herbivores may select for plant mechanisms that compensate after damage as a tolerant strategy to maintain fitness.     

Compensatory growth responses to clipping defoliation in Leymus chinensis (Poaceae) under nutrient addition and water deficiency conditions

Compensatory growth responses of Leymus chinensis, a dominant species in Inner Mongolia steppe, to clipping defoliation were evaluated in a pot-cultivated experiment under different nutrient (N and P) and water availability conditions. Leymus chinensis exhibited over-compensatory growth at the light and moderate clipping intensities (20% and 40% aerial mass removed) with a greater accumulated aboveground biomass, higher relative growth rate (RGR), more rhizomatic tillers and a stimulation of compensatory photosynthesis to the remnant leaves as compared with those of the unclipped plants. Intense clipping (80% aerial mass removed), which removed most of the aboveground tissues, greatly reduced the growth of aboveground biomass in comparison with that of the unclipped plants. Nitrogen addition only slightly improved the biomass production and RGR in light and moderately clipped plants, and it did not allow plants in the intense clipping condition to over-compensate. Phosphorus addition had no obvious influences on the growth and physiological responses to clipping defoliation. These results indicated that nutrient addition could not compensate for the negative effects of severe clipping on the defoliated grass. On the other hand, there were no distinct positive responses under water deficiency condition for L. chinensis at all clipping intensities with a significant reduction of aboveground and belowground biomass, lower RGR, fewer rhizomatic tillers, and a lower net photosynthetic rate than other wet treatments. Additionally, the chlorophyll contents of remnant leaves gradually increased with the increase of clipping intensities in each treatment. In conclusion, although L. chinensis could compensate for tissues removal by some morphological and physiological responses, intense clipping and drought can result in a significant decrease of biomass and growth rate, even under enriched nutrition conditions.     

Seedling vigour and the early growth of transplanted rice (Oryza sativa)

Previous studies suggest that the positive response of transplanted rice (Oryza sativa L.) to nursery fertiliser application was due to increased seedling vigour or possibly to increased nutrient content. This paper presents results of two glasshouse experiments designed to test the hypothesis that seedling vigour was responsible for the response of transplanted seedlings to nursery treatments. The aim of the present study was to explore the concept of seedling vigour of transplanted rice and to determine what plant attributes conferred vigour on the seedlings. Seedling vigour treatments were established by subjecting seedlings to short-term submergence (0, 1 and 2 days/week) in one experiment and to leaf clipping or root pruning and water stress in another to determine their effect on plant growth after transplanting. Submerging seedlings increased plant height but depressed shoot and root dry matter and root:shoot ratio of the seedling at 28 days after sowing. After transplanting these seedlings, prior submergence depressed shoot dry matter at 40 days. Nursery nutrient application increased plant height, increased root and shoot dry matter, but generally decreased root:shoot ratio. Pruning up to 60% of the roots at transplanting decreased shoot and root dry matter, P concentration in leaves at panicle initiation (PI) and straw dry matter and grain yield at maturity. By contrast, pruning 30% of leaves depressed shoot and root dry matter by 30% at PI, and root dry matter and straw and grain yield by 20% at maturity. The combined effects of leaf clipping and root pruning on shoot, root and straw dry matter were largely additive. It is concluded that the response of rice yield to nursery treatments is largely due to increased seedling vigour and can be effected by a range of nutritional as well as non-nutritional treatments of seedlings that increase seedling dry matter, nutrient content, and nutrient concentration. Impairment of leaf growth and to a lesser extent root growth in the nursery depressed seedling vigour after transplanting. However, rather than increasing stress tolerance, seedling vigour was more beneficial when post transplant growth was not limited by nutrient or water stresses.     

Short feeding period of carrot psyllid (Trioza apicalis) females at early growth stages of carrot reduces yield and causes leaf discolouration

Overwintered adult carrot psyllids [Trioza apicalis Förster (Homoptera: Psylloidea: Triozidae)] damage carrot [(Daucus carota ssp. sativum L.) (Apiaceae)] seedlings by phloem feeding on the leaves. The aim of this study was to investigate the carrot root and shoot growth in relation to carrot psyllid density during early growth stages. One, two, or three carrot psyllids were allowed to feed on carrot seedlings for 3 days. Leaf damage was measured at the 8‐leaf stage, and root, leaf fresh weight, and number of true leaves were measured at harvest. Both the age of the carrot seedling at infestation and the psyllid density had a significant effect on leaf damage at the 8‐leaf stage: seedlings damaged at the cotyledon stage exhibited more leaf damage than seedlings damaged at the 1‐leaf stage. A higher psyllid density significantly reduced the carrot root weight at harvest. The significant interaction of psyllid density with seedling age indicates that differently aged carrot seedlings responded differently to feeding: one psyllid feeding for 3 days at the cotyledon stage caused a significant yield loss, whereas three psyllids were needed to cause the same impact at the 1‐leaf stage. Carrot leaf weight at harvest was not reduced by carrot psyllid feeding: leaves recovered from the damage but roots did not. Our results confirm the farmers’ observations that a trap replacement period of 1 week for carrot psyllid monitoring is too long, especially at the cotyledon stage. Severe leaf discolouration on damaged carrots was observed at harvest. The possible reasons for this discolouration, such as toxin excreted in psyllid saliva or plant pathogenic mycoplasma infection, are discussed.     

Response of two prairie forbs to repeated vole herbivory

Vertebrate herbivores as diverse as ungulates, geese, and rabbits preferentially feed on plants that have previously experienced herbivory. Here, we ask whether smaller grassland “cryptic consumers” such as voles (Microtus ochrogaster and M. pennsylvanicus) preferentially clip (cut stems for access to leaves or seeds) or avoid previously clipped individuals of two tallgrass prairie species (Desmanthus illinoensis and Echinacea purpurea) within a growing season. Further, we ask how these plants respond to repeated clipping within a growing season, and whether the effects of this herbivory last into the subsequent growing season. Voles preferentially clipped stems of D. illinoensis and E. purpurea plants that had been previously clipped. The exception was indiscriminant clipping of stems of E. purpurea late in the growing season when its achenes, a favorite vole food, ripened. For D. illinoensis, repeated clipping resulted in a 59% reduction in biomass, 42% lower ratio of reproductive to vegetative biomass, and 57% fewer seeds produced per plant compared with unclipped plants. These effects lasted into the following growing season in which plants were protected from voles. In contrast, the only effect of repeated clipping for E. purpurea was that the number of achenes per plant was substantially reduced by three episodes of clipping. This effect did not carry over to the next growing season. Such differences in D. illinoensis and E. purpurea response to repeated stem clipping by voles offer insights into how these small rodents can effect major changes in composition and dominance in grassland communities.     

Impact of Cotyledon and Leaf Removal on Seedling Survival in Three Tree Species with Contrasting Cotyledon Functions1

The relative importance of cotyledons and leaves for seedling survival was evaluated using a factorial field experiment on three neotropical tree species with contrasting cotyledon functional morphologies (photosynthetic, epigeal reserve vs. hypogeal reserve). In all species, cotyledon and leaf removal shortly after leaf expansion had additive negative effects on seedling survival over 7 weeks. Carbon supplies from cotyledons and other carbohydrate reserves apparently enhanced ability of seedlings to cope with herbivory and disease.     

MYCORRHIZAL AND CLIPPING EFFECTS ON ANDROPOGON GERARDII PHOTOSYNTHESIS

Mature Andropogon gerardii (Vitman) plants were placed in a 2 × 2 factorial treatment regime with clipping soil fumigation as main treatment effects. Plants were grown in a greenhouse using a Latin square design; pots were watered daily, and fertilized weekly with a low phosphorus nutrient solution. Photosynthesis and conductance were measured prior to and after a clipping which removed about 23% of the total leaf length of clipped plants. Fumigation reduced mycorrhizal colonization levels from 34.3 to 7.4%. Conductance was not affected by either treatment. Fumigated, clipped plants had significantly lower photosynthetic rates than their nonfumigated counterparts. However, there were no significant differences between fumigated and nonfumigated unclipped plants. The initial slope of the photosynthetic light response curve was significantly greater for the nonfumigated plants. Greater mycorrhizal development in nonfumigated plants appeared to be beneficial only when the host plants were under defoliation stress.     

Responses of an African graminoid (Themeda triandra Forsk.) to frequent defoliation,nitrogen, and water: a limit of adaptation to herbivory

Summary Themeda triandra Forsk., a medium height perennial grass common in semi-arid Africa, was collected from Serengeti National Park in Tanzania, propagated vegetatively and grown in controlled environments simulating native conditions. The experiment demonstrated mechanisms that result in inability to withstand frequent defoliation, and thus how plant-herbivore interactions are affected by plant morpho-physiology. Clipping reduced most plant yield components. After two months leaf elongation rate was greater in clipped plants, but over the whole experiment aboveground yield was unaffected by clipping. Since clipping did not stimulate growth, residual leaf area was less in clipped plants. Tillering was not stimulated by clipping so there was no mechanism to increase leaf area below the clipping height. The resulting reduced leaf area accounted for reduced root and crown production by clipped plants.     

Morphological and physiological responses of <Emphasis Type="Italic">Vitex negundo</Emphasis> L. var. <Emphasis Type="Italic">heterophylla</Emphasis> (Franch.) Rehd. to drought stress

Water is a main factor limiting plant growth. Integrative responses of leaf traits and whole plant growth to drought will provide implications to vegetation restoration. This study investigated the drought responses of Vitex negundo L. var. heterophylla (Franch.) Rehd. with a focus on leaf morphology and physiology, seedling growth and biomass partitioning. Potted 1-year-old seedlings were subjected to four water supply regimes [75, 55, 35 and 15% field capacity (FC)], served as control, mild water stress, moderate water stress and severe water stress. Leaf morphological traits varied to reduce the distance of water transfer under water stress and leaflets were dispersed with drought. Net photosynthetic rate decreased significantly under water stress: stomatal closure was the dominant limitation at mild and moderate drought, while metabolic impairment was dominant at severe drought. The physiological impairment at severe drought could also be detected from the relative lower water use efficiency and non-photochemical quenching to moderate water stress. Total biomass of well-watered plants was more than twice that at moderate water deficit and nearly ten times that at severe water deficit. In summary, V. negundo var. heterophylla had adaptation mechanism to water deficit even in the most serious condition, but different strategies were adopted. Seedlings invested more photosynthate to roots at mild and moderate drought while more photosynthate to leaves at severe drought. A nearly stagnant seedling growth and a sharp decline of total biomass were the survival strategy at severe water stress, which was not favorable to vegetation restoration. Water supply above 15% FC is recommended for the seedlings to vegetation restoration.     

辽东栎幼苗生长对种子大小和子叶去除处理的响应

该文在温室内盆播条件下,设置不去除子叶(对照)、去除1/4子叶(轻度子叶去除)、1/2子叶(中度子叶去除)和3/4子叶(重度子叶去除) 4个处理,研究了种子大小和子叶去除处理对辽东栎幼苗生长及其形态学可塑性的影响。结果表明:(1)大种子幼苗株高、基茎、叶片数、单株叶面积、总干质量和根冠比在所有处理均大于小种子幼苗,除株高外,上述其他参数在轻度子叶去除处理的不同大小种子幼苗间均差异显著(P0.05),前者总干质量在中度子叶去除处理与后者差异也显著(P0.05)。大种子幼苗比叶面积和比根长在各处理均大于小种子幼苗,比枝长则相反。(2)随着子叶去除强度增大,大、小种子幼苗株高、基茎、叶片数、单株叶面积和总干质量等均呈减小趋势,株高、基径、叶片数和单株叶面积在重度子叶去除处理均显著小于对照和轻度子叶去除处理;小种子幼苗对子叶损失反应更为敏感,其株高、叶片数、单株叶面积和总干质量在中度子叶去除处理也显著小于对照(P0.05);小种子幼苗根冠比随子叶去除强度增大而增大,在中度和重度子叶去除处理显著大于对照和轻度子叶去除处理(P0.05)。(3)随着子叶去除强度增大,大小种子幼苗的比叶面积和比根长均逐渐增大,但大种子幼苗比枝长持续减小,轻度子叶去除处理的小种子幼苗比枝长最大。     

A test of compensatory photosynthesis in the field: Implications for herbivory tolerance

Summary The occurrence of compensatory photosynthesis was examined in the field for all foliage elements on two Agropyron bunchgrass species that differ in their evolutionary history of grazing pressure. This is the first reported field study of compensatory photosynthesis in individual foliage elements of graminoids. Compensatory photosynthesis was defined as an increase in the photosynthetic rates of foliage on partially defoliated plants relative to foliage of the same age on undefoliated plants. Compensatory photosynthesis did occur in many individual foliage elements during at least part of their ontogeny. For both species, compensatory photosynthesis was related primarily to delayed leaf senescence and increased soluble protein concentrations, but not to an improvement in the water status of clipped plants. Soluble protein concentration increased in all foliage elements. A delay in senescence on clipped plants was documented for the two oldest, fully-expanded leaves that were present when the plants were initially clipped, but the initiation and senescence of all other foliage elements were not affected by the clipping treatments. Photosynthetic water use efficiency and photosynthetic rates per unit soluble protein of foliage on partially defoliated plants were not increased following the clipping treatments. Although A. desertorum and A. spicatum were exposed to different levels of grazing pressure during their evolutionary history, the phenology, water status, and gas exchange rates of foliage were very similar both for undefoliated as well as partially defoliated plants. Thus, we conclude that compensatory photosynthesis does not appear to be an important ecological component of herbivory tolerance for these species.     

Survivorship and Spatial Development of Spartina alterniflora Loisel. (Gramineae) Seedlings in a New England Salt Marsh

Patterns of survival and spatial arrangement of tillers of Spartinaalterniflora were examined in natural and in artificially producedbare areas, and in pure stands of adult S. alterniflora in aNew England salt marsh. Seedling growth and survival were highin naturally occurring bare patches and in artificial patches,whether created by continual clipping of adult plants to groundlevel throughout the growing season or by providing bare substrateafter removal of adult plants. Seedling growth and survivorshipincreased with increasing size of bare area. S. alternifloraseedlings were also common in areas dominated by adult plants,but no seedlings survived a whole first growing season underthe mature canopy, probably because of competition from adultplants. In large bare areas, S. alterniflora seedlings grew non-directionally,reaching heights of 0.5 m, and producing as many as 36 tillersin one growing season. Examination of leaf area ratios suggestedthat the production of tillers increased photosynthetic capacityin seedlings with several tillers in contrast to seedlings withouttillers. Thus, seedlings can apparently tiller and colonizefree space radially without a loss of photosynthetic capacity. These results suggest that while seedling success is generallylimited by adult plants in monocultures of S. alterniflora,in disturbed spaces seedling success is high and results ina rapid non-directional proliferation of sexually generatedclones that ultimately preclude the successful invasion of futureseedlings. Clones, directional growth, leaf area ratio, salt marsh cordgrass, seedling survivorship, Spartina alterniflora Loisel     

Photosynthetic Responses to Light for Rainforest Seedlings Planted in Abandoned Pasture, Costa Rica

Efforts to reforest tropical pasture with native tree species have increased in recent years, yet little is known about the physiology of most tropical trees. The goal of this study was to assess the effect of habitat on photosynthetic responses to light for seedlings of four native rainforest species (Calophyllum brasiliense, Ocotea glaucosericea, Ocotea whitei, and Sideroxylon portoricense) planted to facilitate tropical rainforest recovery in southern Costa Rica. Seedlings were planted in primary forest, in open abandoned pasture, and in the shade of remnant trees within the pasture. Growth, morphology, photosynthetic gas exchange responses to light, and chlorophyll fluorescence (an indication of the integrity of photosynthetic processes) were measured in the three habitats. Height and leaf area were generally greater for seedlings in tree shade compared to those in the forest and open pasture. Photosynthetic rates were higher for plants in open pasture and tree shade compared to those in the forest for two of the four species. Chlorophyll fluorescence results indicated flexibility in the photosynthetic processing of light energy that may help plants tolerate the bright light of the pasture. This study demonstrates that, for certain species, seedlings under remnant pasture trees do not exhibit the level of photosynthetic stress experienced in open abandoned pasture. Seedling responses to light, in combination with other factors such as increased nutrient input through litterfall, help explain the enhanced growth of seedlings under remnant pasture trees. Planting seedlings under remnant trees may increase the success of future efforts to restore tropical forest in abandoned agricultural land.     

不同密度下辽东栎幼苗子叶丢失及其对幼苗存活和生长的影响

在宁夏六盘山区龙潭林区华北落叶松(Larix principis-rupprechtii )人工林的不同样带, 按6个密度梯度(3.24、2.56、1.96、1.44、1.00和0.64株·m^-2)移栽萌发生根的辽东栎(Quercus wutaishanica)幼苗, 研究了啮齿动物对幼苗子叶取食的密度效应及其对幼苗存活与生长的影响。结果表明, 辽东栎幼苗的子叶留存率随着幼苗密度的增大而减小。2个高密度处理(3.24和2.56株·m^-2)的幼苗子叶留存率分别在移栽6周和5周后稳定在最低水平, 分别为8.64%和7.81%; 而2个较低密度处理(1.44和0.64株·m^-2)的幼苗在最后一次观测时子叶留存率仍很高, 分别为44.44%和31.25%, 且二者均显著高于其他密度处理(p < 0.05)。受啮齿动物取食的影响, 在从高到低的不同密度处理下, 幼苗的主根留存率分别为64.16%、80.46%、87.23%、80.25%、69.84%和69.84%; 在1.44株·m^-2处理下, 顶芽留存率最高(25.23%), 显著大于3.24株·m^-2处理(4.19%) (p < 0.05), 其他密度处理的顶芽留存率均不足20%。子叶被动物取食的幼苗和子叶完整幼苗的最终留存率基本一致, 仅在个别密度处理的某一观测时期差异显著; 顶芽被动物取食的幼苗留存率略低于顶芽完整幼苗的留存率, 但个别密度处理完全相反; 不同类型幼苗的留存率随时间推移而上下波动, 可能与幼苗顶芽被动物取食后萌生形成新芽有关。幼苗的株高、基径、叶片数和单株叶面积均随密度的减小而略有增大, 但除株高外, 其他3个生长参数均在1.44株·m^-2处理时最大, 与子叶是否被动物取食有一定的对应关系, 即高密度下更多的幼苗丢失了供应其生长所需营养物质的子叶, 从而影响了幼苗的早期生长。研究结果不仅丰富了“负密度效应”理论和种群更新的“增补限制”理论, 也可为六盘山区退化辽东栎灌丛和辽东栎次生林的恢复及生态系统管理提供 参考。     

苗圃氮加载及水分胁迫对栓皮栎苗木叶片光合氮分配及生物量积累的影响

苗圃科学施氮(N)作为提高苗木N贮存水平与质量的核心手段,能否提高干旱立地苗木造林效果仍存在争议;N贮存水平与干旱如何协同作用影响叶片光合N分配及苗木生物量积累尚不明确。阐明上述问题,能够为干旱立地下的森林植被恢复以及造林苗木科学精准施N提供科学依据。选择栓皮栎(Quercus variabilis Blume)为研究对象,对一年生苗木设置2个苗圃木质化期N加载水平(0、24 mg N/株),翌年春苗木移栽后设置2个灌溉水平(85%、40%田间持水量),取样测定苗木生物量、叶片N、叶绿素与脯氨酸水平、以及气体交换参数,计算光合N分配及光合N利用效率(PNUE)。结果表明,叶片发育完成后,干旱抑制N向光合系统分配,但N加载处理提高了干旱下的光合N含量,从而在一定程度上抵消干旱对生物量积累的抑制;无N加载苗木则向光合系统投入更少的N,而提高脯氨酸水平,生物量积累受抑制更为显著。无N加载苗木在遭受干旱后将N向羧化组分分配,而N加载苗木遭遇干旱后则显著抑制叶片将N向羧化系统以及电子传递系统分配,捕光组分N的分配则不受植物体内N贮存或外部水分状况的影响,栓皮栎苗木通过调整不同功能组分光合N含量和...     

Plant regeneration from leaf petioles in <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

Summary Camptothecin, produced by Camptotheca acuminata, is a pharmaceutically important compound. Transgenic technology has potential uses for the enhancement of camptothecin production; however, an efficient plant regeneration protocol for C. acuminata is not currently available. Factors that affected successful seedling germination were evaluated. The regeneration potential of various parts of seedlings was tested. Camptothecin production in regenerated plants was compared to its production in calluses and the original seedlings. Dark incubation and seed coat removal led to a higher germination rate and a higher survival rate after germination. The best shoot induction medium was found to be Gamborg's B5 medium+8.9 μM benzyladenine. Among the calluses induced from various parts of seedlings, leaf petiole calluses, leaf dise calluses, and cotyledon calluses regenerated shoots, but internode calluses did not. Furthermore, leaf petiole calluses and leaf dise calluses regenerated normal shoots, while cotyledon calluses regenerated hyperhydric shoots. Moreover, leaf petiole calluses had a higher shoot regeneration rate, 50% versus 9%, and a higher shoot number, 6.2±0.5 versus 2.0±0.3, than did leaf dise calluses on the best shoot induction medium. It took 4–6 wk to regenerate shoots after transfer into shoot induction media. Camptothecin concentration in the regenerated plants was significantly higher than that in the calluses and similar to that in the original seedlings. In conclusion, leaf petioles provide efficient plant regeneration of C. acuminata.     

香果树实生苗的光合特性及其与环境因子的关系

为确定香果树实生苗的适生环境并为其自然更新提出有针对性策略,研究了不同生境(冠下、冠缘、林窗和林缘)中2年生香果树实生苗的净光合速率、水分利用效率、叶绿素含量、苗高、基径、生物量等的变化及其与生态因子之间的关系.结果表明: 4种生境中的光合有效辐射最大值为50～1380 μmol·m^-2·s^-1,冠下和冠缘中香果树实生苗的净光合速率日变化呈单峰型,而林窗和林缘实生苗的净光合速率日变化呈双峰型;香果树实生苗为耐阴植物,但耐阴能力较弱,其功能叶的光饱和点、补偿点和暗呼吸在4种生境中大小顺序为: 林缘>林窗>冠缘>冠下,表观量子效率的变化规律与之相反;林窗和冠缘2种生境中香果树实生苗的适应能力较强,叶片的蒸腾速率、气孔导度、水分利用效率和净光合速率较高;林窗中香果树实生苗叶片的叶绿素含量较低,但实生苗的生长速度最快,生物量最大;香果树实生苗的净光合速率与光合有效辐射和气孔导度呈显著正相关.对于冠下生境,需降低林冠层密度,增加透光率,以利于香果树实生苗的光合作用;对于林缘生境,则需要增加植被盖度,降低光照强度,以利于其快速生长.     

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.