The role of carbohydrate reserves in the growth, resilience, and persistence of cabbage palm seedlings (Sabal palmetto)

Sabal palmetto (Walt.) Lodd. ex Schultes (cabbage palm) is an arborescent palm common in many plant communities throughout Florida, U.S.A., and the Caribbean. Although its seedlings grow very slowly in forest understories, they survive damage and defoliation well, and the species may increase in dominance following disturbances such as fire, logging, and hurricanes. We investigated the potential importance of total nonstructural carbohydrate (TNC) pools in the ability of cabbage palm seedlings to recover from the loss of aboveground tissue such as that caused by fire, grazing, or shallow burial by storm debris. TNC concentrations in belowground organs of seedlings from a forest understory were high, and TNC pools were sufficient to theoretically replace >50% of a seedling's canopy. The largest fraction of the belowground TNC pool was in stem tissue, where TNC in unclipped plants accounted for 26–54% of stem dry mass. Experimental reduction of TNC pools by repeated defoliation slowed seedling regrowth, and seedlings with inherently smaller pools (smaller seedlings) suffered higher mortality after repeated defoliation than did larger seedlings. Although regrowth and recovery after the loss of aboveground tissue was related to the size of the TNC pool in belowground organs, even the smallest seedlings with the smallest pools had sufficient stores to withstand at least two defoliations at frequent (7-week) intervals. Large belowground TNC pools in S. palmetto seedlings appear to enable them to survive all but the most frequent defoliations (e.g., frequent grazing or mowing). Allocation of resources to these stores, however, may contribute to the slow growth rates of S. palmetto seedlings in natural communities. Received: 13 April 1998 / Accepted: 28 August 1998     

Intra- and Extrabud Stages of Elementary Shoot Development in Ligneous Plants

Length of elementary shoots and the number of metamers in them have been compared in a number of ligneous plants. The shoot length varies to a greater extent than the number of metamers. The number of metamers with bud scales is the most invariable and species-specific. This indicates relative independence of the intrabud stage of the shoot development.     

Effects of neighbouring vegetation on eucalypt seedlings at two sites subject to different levels of abiotic stress

Abstract In spite of numerous studies on the effect of nutrient levels and/or standing crop on the intensity of resource competition the debate has not been resolved. Field studies that have used natural productivity gradients have generally supported the argument that competitive intensity and resource availability are positively correlated, whereas studies that have used artificial resource gradients have generally refuted the same argument. Here we report the results from study in which both approaches were used within the same system. We studied two species of eucalypt that occupy contrasting parts of the same landscape: Eucalyptus camaldulensis, found mostly along creek lines and in valleys with deep alluvial soils, and Eucalyptus microcarpa, found on hillsides and ridges with shallow soils. We studied the response of seedlings of the two species to the combined effects of competition and manipulated nutrient levels in a glasshouse experiment, and also investigated their responses to removal of neighbouring plants in the field. Eucalyptus microcarpa was less responsive to increased resource availability, which is consistent with one of the principal assumptions of Grime’s C‐S‐R model. In the glasshouse experiment both species of eucalypt responded in a qualitatively similar fashion to the combined effects of resource availability and competition: release from competition resulted in increased growth, but only in pots that received additional resources. In the field we found that neighbouring vegetation could severely limit the establishment of E. camaldulensis but the removal of neighbouring vegetation did not affect the performance of E. microcarpa seedlings. Eucalyptus camaldulensis seedlings suffered high levels of damage from herbivores. Our results thus generally support the predications of the C‐S‐R model, however, they indicate that the effects of competition and herbivory may be heavily confounded.     

Establishment of the neotropical predator Amblyseius idaeus (Acari: Phytoseiidae) in Benin,West Africa

Populations of the phytoseiid predator Amblyseius(=Neoseiulus) idaeus (Denmark & Muma) from northeastern Brazil, have been successfully introduced into Benin, West Africa, as part of a classical biological control campaign to control the exotic cassava green mite Mononychellus tanajoa (Bondar). Monthly follow‐up surveys revealed the presence of A. idaeus in most release sites. Some populations have persisted for at least 18 months, including two cycles of potentially limiting wet and dry season conditions. In some sites A. idaeus has been the numerically dominant phytoseiid predator on cassava Manihot esculenta, where it is associated with the tetranychids M. tanajoa and Oligonychus gossypii Zacher. During periods of low M. tanajoa densities A. idaeus disappeared from cassava, but were found on weeds with O. gossypii until prey densities on cassava increased.     

不同光环境对海南龙血树幼苗表型可塑性及生存策略的影响

为了解光照对海南龙血树(Dracaena cambodiana)幼苗生长的影响,研究了不同光照环境下海南龙血树幼苗形态、生理特性和生物量分配的变化,并分析了其生态适应性。结果表明,海南龙血树幼苗的形态、生理和生物量分配指标在不同光照强度间存在显著差异,各指标的可塑性指数为0.08~0.86,其中根茎叶及总生物量的可塑性指数普遍较高(0.67~0.86),表明海南龙血树幼苗有较好的光照适应性,其策略主要是通过调整根茎叶生物量的分配来适应光照的变化。随着光照强度的降低,海南龙血树幼苗的比叶面积、叶根比呈现显著增大趋势,表明幼苗可通过增加单株叶面积比例,扩大光合作用面积,有效调节自身生物量配置。37.3%自然光照(L2)是海南龙血树幼苗生长的最佳光照强度。现存海南龙血树生境改变,生境缺少林荫以致光照强度过大,不利于幼苗根系生长,难以度过干旱季节,可能是海南龙血树自然更新失败的重要原因之一。     

Are species photosynthetic characteristics good predictors of seedling post-hurricane demographic patterns and species spatiotemporal distribution in a hurricane impacted wet montane forest?

In situ measurements of leaf level photosynthetic response to light were collected from seedlings of ten tree species from a tropical montane wet forest, the John Crow Mountains, Jamaica. A model-based recursive partitioning ('mob') algorithm was then used to identify species associations based on their fitted photosynthetic response curves. Leaf area dark respiration (R_D) and light saturated maximum photosynthetic (A_max) rates were also used as 'mob' partitioning variables, to identify species associations based on seedling demographic patterns (from June 2007 to May 2010) following a hurricane (Aug. 2007) and the spatiotemporal distribution patterns of stems in 2006 and 2012. R_D and A_max rates ranged from 1.14 to 2.02 μmol (CO₂) m⁻²s⁻¹ and 2.97–5.87 μmol (CO₂) m⁻²s⁻¹, respectively, placing the ten species in the range of intermediate shade tolerance. Several parsimonious species 'mob' groups were formed based on 1) interspecific differences among species response curves, 2) variations in post-hurricane seedling demographic trends and 3) R_D rates and species spatiotemporal distribution patterns at aspects that are more or less exposed to hurricanes. The composition of parsimonious groupings based on photosynthetic curves was not concordant with the groups based on demographic trends but was partially concordant with the R_D - species spatiotemporal distribution groups. Our results indicated that the influence of photosynthetic characteristics on demographic traits and species distributions was not straightforward. Rather, there was a complex pattern of interaction between ecophysiological and demographic traits, which determined species successional status, post-hurricane response and ultimately, species distribution at our study site.     

滇重楼种子水浸液对三种植物种子萌发和幼苗生长的影响

利用滇重楼(Paris polyphylla Smith var.yunnanensis(Franch.)Hand.-Mazz.)种子外种皮和胚乳的水浸液对白菜(Brassica pekinensis(Lour.)Rupr.)、绿豆(Vigna radiata(Linn.)Wilczak)、小麦(Triticum aestivum L.)种子进行处理,研究滇重楼种子水浸液对3种植物种子萌发、幼苗生长和保护酶活性的影响,并利用GC-MS方法对滇重楼种子内源抑制物的成分进行分析。结果显示,不同浓度滇重楼外种皮、胚乳水浸液对上述3种受体植物的发芽率、苗高、根长及鲜重均产生影响,其作用强度和水浸液的浓度有关,总体上表现出低促高抑的双重浓度效应。滇重楼种子水浸液对白菜的影响作用最强,对绿豆的影响作用最弱,且胚乳水浸液的影响较外种皮强。不同浓度滇重楼种子外种皮和胚乳水浸液均能影响3种植物幼苗体内保护酶的活性,随着水浸液浓度的升高,叶片中超氧化物歧化酶(SOD)、过氧化物酶(POD)活性总体增加,与对照相比差异显著。白菜、小麦过氧化氢酶(CAT)活性减少,与对照相比差异显著;绿豆过氧化氢酶(CAT)活性增加,但与对照相比无显著差异。利用GC-MS方法从胚乳和外种皮水浸液中分别检出8种和2种物质。研究结果表明滇重楼种子中存在内源抑制物质,可能是导致种子休眠的原因;种子水浸液可能通过影响植物幼苗保护酶的活性进而影响其正常生长;有机酸类物质可能是滇重楼种子内源抑制物之一。     

小径竹密度对雷公鹅耳枥幼苗早期更新的影响

通过去除法控制竹丛密度,人为设置4种竹丛密度梯度[密度1:(3.83±0.53)株/m~2;密度2:(16±1.80)株/m~2;密度3:(39±1.69)株/m~2;密度4:(69±2.15)株/m~2],测定不同密度竹丛下的微环境(包括土壤温度、湿度、电导率、凋落物厚度),研究竹丛密度及微环境对雷公鹅耳枥(Carpinus viminea Wall.)幼苗数量、存活动态、生长情况的影响。结果显示,竹丛密度对环境有显著影响,随着竹丛密度的增加,竹丛盖度、凋落物厚度、土壤温度升高明显;雷公鹅耳枥幼苗萌生量显著减少,4组密度梯度中幼苗数量分布依次排序为:密度1(28.53±3.14)株/m~2密度2(17.36±1.45)株/m~2密度3(12.36±0.93)株/m~2密度4(8.92±0.93)株/m~2,表明随着小径竹密度增加,其对雷公鹅耳枥幼苗萌发的抑制作用越强;小径竹的密集生长可对雷公鹅耳枥幼苗的存活率产生影响,且对幼苗的生长具有一定抑制作用。研究结果表明小径竹密集生长的环境不仅抑制了雷公鹅耳枥新生幼苗的分布和幼苗生长,还对种群的更新以及森林群落的演替产生一定的负面影响。