亚热带阔叶林植物叶片虫食特征研究

植物与昆虫是森林生态系统的重要组成成分,两者通过长期的协同进化形成了密切的相互关系,在森林生态系统中发挥着承上启下的作用,连接了初级生产和高级消费,是森林生态系统中重要的动态中心。植物叶片的虫食特征是植物与昆虫相互作用关系的重要表征。选取福建梅花山和浙江天童两地76种常绿阔叶林植物为研究对象,采用野外调查与室内统计分析相结合的方式对植物叶片的虫食率和虫食频度进行了研究,以期了解亚热带常绿阔叶林植物叶片所面临的食叶昆虫取食压力。结果表明:76种植物平均虫食率为7.21%,虫食频度为32.95%。多数植物的叶片虫食率低于10%,叶片虫食频度主要分布在10%-60%之间。乔木种与灌木种、优势植物与伴生植物之间的叶片虫食率和虫食频度均不存在显著差异(P>0.05)。超过60%的叶片虫食率和虫食频度发生在展叶期。福建梅花山常绿阔叶林植物的叶片虫食率(P=0.012)和虫食频度(P=0.74)均高于浙江天童。植物幼叶的虫食率随着海拔的升高而下降。以上结果表明,常绿阔叶林植物的叶片虫食强度介于热带雨林(11.1%)和温带森林(7.1%)之间,展叶期是叶片虫食发生的主要阶段,表现出过渡性特征;叶片的虫食在不同生活型和优势程度的植物间存在差异;叶片虫食率随纬度的升高和海拔的上升而降低。     

常绿阔叶林林下6种木本植物叶片非结构性碳水化合物的动态特征

植物叶片非结构性碳水化合物(NSC)不仅为植物代谢提供重要能量,还能一定程度上反映植物对外界环境的适应策略.以亚热带常绿阔叶林林下6种植物:茶(Camellia sinesis)、细枝柃(Eurya loquaiana)、润楠(Machilus pingii)、短刺米储(Castanopsis carlesii)、大叶山矾(Symplocos grandis)和薄叶山矾(Symplocos anomala)为对象,研究各物种抽枝展叶进程中叶片大小、比叶重(LMA)、光合色素以非结构性碳水化合物及其组分含量的动态变化,分析NSC组分之间及与光合色素与LMA间的相互关系,探讨展叶过程中引起叶片NSC差异的原因.结果表明:(1)各物种单叶面积随叶片展开而增加直至8月下旬达到最大,为9.20 (茶)-40.81 cm2 (大叶山矾);而LMA在展叶初期下降后随叶片展开逐步升高,直到次年1月下旬还在持续缓慢增加,因各物种不同,最大值为82.90-152.10 g/m2;光合色素则在展叶进程中逐渐增加,6月下旬达到较高值后在整个夏秋季维持较高的含量,次年1月有所下降.(2)在整个当年生叶片生长进程中,6种植物叶片可溶性糖含量总体上由展叶初期逐渐增加,而淀粉含量随着叶片的生长成熟逐渐降低;各物种NSC含量为87.00 (薄叶山矾)-163.35 mg/g(细枝柃),除大叶山矾和薄叶山矾外,NSC含量随着叶片生长进程逐渐增加;(3)各物种可溶性糖含量随着淀粉含量的增加而降低,叶绿素含量随着LMA的增加而显著增加,可溶性糖与LMA具有显著的正相关关系,而淀粉与LMA呈显著负相关(R~2=0.51-0.86,P0.004),表明展叶后期部分淀粉转化为可溶性糖,这与展叶后期林内光资源的可利用性以及植物的生理活动相关.综上所述,随着展叶进程,非结构性碳水化合物及其组分具有不同的变化规律,一方面与叶片增大增厚进程中的生理活动有关,另一方面也反映了叶片功能属性间的权衡关系,研究结果可为阐明亚热带常绿阔叶林林下木本植物展叶期的碳代谢提供理论基础,亦丰富了森林植物生活史对策理论.(图6参53)     

浙江天童亚热带常绿阔叶林栲树叶片发育动态

于2008年3-6月,定期记录了浙江天童亚热带常绿阔叶林栲树(Castanopsis fargesii)的展叶情况,包括标记枝的叶长、叶宽、叶面积、叶干重、叶鲜重和叶绿素含量等指标.结果表明,所调查的栲树叶面积增加持续时间为34 d,展叶速率最高达40.5%·d-1;成熟叶面积越大,其展叶速率越快;比叶重随叶面积增加呈波动变化,含水量在叶片发育过程中呈先增加后降低的变化趋势,叶绿素含量则随叶面积的增加而逐渐增高.对栲树展叶速率、叶面积和叶属性之间的相关分析结果显示,展叶速率分别与叶面积、叶绿素含量在α=0.01水平上呈显著正相关,叶面积分别与含水量、叶绿素含量在α=0.01水平上呈显著正相关;叶绿素含量与含水量在α=0.01水平上呈显著正相关.     

PEG模拟干旱条件下尾叶桉和枫香苗木的生理响应

以尾叶桉(Eucalyptus urophylla)和枫香(Liquidambar formosana)幼苗为试验材料,利用聚乙二醇6000(PEG-6000)人工模拟水分胁迫环境,设置三个胁迫强度处理(轻度胁迫、中度胁迫、重度胁迫)和三个胁迫持续时间处理(持续12h、24 h、36 h),研究幼苗叶片相对含水量、相对电导率、脯氨酸质量分数、叶绿素质量分数、超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量和可溶性糖质量分数的变化,结果表明:经水分胁迫处理后,6种树种幼苗叶片相对含水量皆显现下降的趋势,水分胁迫处理12 h的尾叶桉叶片相对含水量下降幅度小于枫香;随着水分胁迫强度的加深及持续时间的延长,2种树种幼苗叶片内相对电导率呈波动性上升的趋势;脯氨酸质量分数都有明显的增加,枫香叶片内脯氨酸质量分数的变化幅度大于尾叶桉叶片;苗木叶片叶绿素质量分数出现不规则波动;尾叶桉的SOD活性胁迫12 h和24 h时在中度胁迫达到最大,胁迫36 h在轻度胁迫时达到高峰,而枫香的SOD活性经不同胁迫时间的胁迫处理后,在轻度胁迫时达到高峰;随胁迫强度的增加及胁迫时间的延长,尾叶桉叶片MDA含量有逐渐上升的趋势,枫香叶片MDA含量变化趋势表现为增加、下降、再增加;经水分胁迫处理12 h时,随着水分胁迫强度的加剧,尾叶桉的可溶性糖质量分数显著增加.而枫香的可溶性糖质量分数在中度时下降,水分胁迫处理24 h时2种苗木的可溶性糖质量分数波动,处理36 h时轻度胁迫后下降.结果表明,叶片相对含水量、SOD活性和可溶性糖质量分数可以作为评价苗木抗旱性的依据,尾叶桉的抗旱能力大于枫香.     

美国红枫和元宝枫幼叶春季转色期生理特性研究

为了探索美国红枫(Acer×freemanii‘Autumn Blaze’)和元宝枫(Acer truncatum)在春季转色期的生理特性,测定其春季转色期内幼叶叶绿素含量、类胡萝卜素含量、花青素含量、可溶性糖含量,以及叶绿素荧光、叶片含水率等生理指标,分析各生理指标变化及相关性。结果表明,(1)美国红枫和元宝枫转色期叶绿素a和叶绿素b的含量都呈现逐步上升趋势,总叶绿素含量(Chl)增幅分别为85.3%和235.5%,类胡萝卜素变化不明显。美国红枫花青素含量(Ant)稳步下降,降幅为33.3%,而元宝枫呈现波动状态,整个试验期前者花青素含量都高于后者,树种间差异显著(F=68.69,P0.01)。二者可溶性糖含量均呈波动性变化,树种间差异显著(F=36.54,P0.01);叶片含水率都呈缓慢下降趋势。F_v/F_m树种间差异不显著(F=0.11,P=0.736),都随叶片成熟而逐渐升高,美国红枫最小值为0.53,最大值为0.72;元宝枫最小值为0.49,最大值为0.75。(2)花青素与叶绿素的比例决定了叶片颜色。当两树种的Ant/Chl比值大于2.5时,叶绿素的主导作用减弱,叶片呈现花青素的颜色——红色;当比值小于2.5时,花青素的主导作用减弱,叶片呈现叶绿素的颜色——绿色。(3)相关性研究表明,美国红枫花青素与质体色素表现为显著负相关,而元宝枫表现为显著正相关(P0.01)。两树种在花青素和可溶性糖之间都没有表现出显著相关性;F_v/F_m与各色素间均存在显著相关性(P0.01)。研究美国红枫和元宝枫叶色变化的生理特性,可为园林树种叶色改良或调控观赏期提供理论依据。     

热带次生林两种林下植物叶片生理特性对氮磷添加的响应

为探究热带次生林林下植物叶片对长期氮(N)、磷(P)添加的响应,阐明热带森林植物对土壤低磷环境适应的生理生态机制,基于华南热带次生林长达9年的氮、磷添加实验,测定两种分布较广的林下乡土树种大青(Clerodendrum cyrtophyllum)和紫玉盘(Uvaria microcarpa)的叶片基本属性、叶绿素含量及氮磷元素含量等指标.结果显示:(1)两种植物叶片的基本属性及光合色素存在显著的种间差异(P 0.05);氮和磷添加提高了大青叶片的比叶面积(35%-38%),对两个树种叶片的叶长、叶宽、叶面积等无显著影响;(2)氮添加显著影响两种植物叶片叶绿素a和总叶绿素含量(P=0.036和P=0.043),而磷添加对光合色素含量无显著影响;(3)对照处理下,大青和紫玉盘叶片的N:P分别为28.71与21.75,大于16,表明两个树种仍受到较强的磷限制;磷添加显著提高了两种植物叶片的磷含量,并降低N:P值;(4)相关性分析表明叶片基本属性、光合色素与氮磷元素含量三者之间的相关性关系较弱.综上,热带森林植物叶片氮和磷元素含量对氮磷添加的响应较敏感,叶绿素a和总叶绿素对氮添加的响应较敏感,而其他属性对氮磷添加的响应较小;因此,在热带森林土壤磷长期缺乏的情况下,植物叶片的生理功能对环境变化具有较好的适应性,其蕴含的生物学机制仍需要进一步的探讨.(图3表2参31)     

计划烧除攀枝花苏铁林区地面覆盖物对苏铁生长和土壤理化性质的影响

选择攀枝花苏铁林下计划烧除试验后苏铁及其根系周围土壤(0~15 cm)为对象,研究火烧对攀枝花苏铁植株生长、叶片生理和苏铁根系周围土壤理化性质的影响,以期为区域攀枝花苏铁种群恢复和生态环境保护提供理论依据.结果表明:计划烧除区域苏铁成年树的株数及株高没有显著变化,新生叶片数目和幼苗株数相对未烧除区域显著增加,增幅分别达201.66%和317.7%;烧除区域苏铁植株新生叶片叶绿素a、叶绿素b、叶绿素a+b,可溶性糖、蛋白质含量,硝酸还原酶(NR)、谷氨酰胺合成酶(GS)活性,叶片碳(C)、氮(N)、磷(P)、钾(K)含量,C/N、N/P比与对照区域新生叶片相比无显著性差异,只有类胡萝卜素含量显著降低.计划烧除改变了苏铁根围土壤(0~15 cm)的理化性质,表现在烧除后的土壤含水量、pH值及总N、P、K含量显著降低;但是,火烧显著提高了土壤有机碳(TOC)、硝态氮(NO3--N)、铵态氮(NH4+-N)含量,微生物量C、N含量也略有升高;这说明火烧有利于增加苏铁林下土壤养分(N)的有效性,为烧除后苏铁快速恢复生长提供有利条件.     

不同LED光质对迭鞘石斛生理及品质的影响

设置6种光质,自然光(对照,N5)、100%红光+0%蓝光(R5)、100%蓝光+0%红光(B5)、80%红光+20%蓝光[RB(4:1)]、60%红光+40%蓝光[RB(3:2)]、40%红光+60%蓝光[RB(2:3)],测定不同处理时间迭鞘石斛的生理指标以及多糖、黄酮的含量.结果显示光质对迭鞘石斛生理及品质有较为明显的影响.B5处理组的超氧化物歧化酶含量最高;R5处理组的丙二醛含量最高.RB(3:2)处理组的叶绿素含量最高,RB(2:3)处理组的可溶性糖、可溶性蛋白、多糖含量都最高;N5处理组的黄酮含量最高.R5处理组的叶绿素、可溶性糖、可溶性蛋白、多糖和黄酮含量都较低,说明纯红光并不利于迭鞘石斛生长.此外,不同处理天数下丙二醛、可溶性蛋白、可溶性糖、多糖和黄酮含量整体上呈现上升趋势;超氧化物歧化酶活力整体下降趋势;叶绿素含量整体上呈现先下降后上升的趋势.本研究说明红蓝光配比有利于迭鞘石斛生长发育和次生代谢物质积累,对迭鞘石斛组培苗的光控培养和品质改良具有生产上的指导意义.     

大气CO2浓度和温度升高对岷江冷杉（Abies faxoniana）幼苗针叶化学特性的影响

以6年生岷江冷杉(Abies faxoniana)幼苗为研究对象,利用控制环境生长室进行了2个生长季的大气CO2浓度倍增和增温(+2.2℃)处理,旨在探讨岷江冷杉幼苗针叶化学特性对CO2浓度倍增和增温的响应.结果表明:大气CO2浓度倍增对岷江冷杉幼苗针叶的叶绿素含量无显著影响,但降低了针叶N、P和纤维素含量,并增加了针叶可溶性糖和淀粉含量.增温显著降低了1年生针叶的叶绿素b含量,同时降低了当年生和1年生针叶的N、P和纤维素含量;显著提高了针叶的可溶性糖和淀粉含量.CO2浓度倍增和增温同时作用显著增加了针叶叶绿素含量,但降低了针叶N、P和纤维素含量,而对针叶可溶性糖和淀粉含量无显著影响.大气CO2浓度倍增和增温对针叶的叶绿素、N和碳水化合物含量有显著的交互作用.在大气CO2浓度倍增和增温条件下,岷江冷杉针叶化学性质将发生改变,可能影响针叶的生物化学过程和凋落物分解.     

土壤栽培和无土栽培菜心中内生细菌比较及分离鉴定

菜心(Brassica parachinensis)是华南地区的一种特色蔬菜.为探究无土栽培和土壤栽培菜心内生细菌的差异,以这两种栽培方式的菜心为材料,分离内生细菌.根据插入序列指纹图谱(IS-PCR)结果进行聚类,对代表性菌株的16S rRNA基因序列进行系统发育分析,并将菌株加入无土栽培营养液中,收获后测定菜心的的相对叶绿素含量(SPAD)和可溶性糖含量.结果显示,从两种菜心中共分离到31株内生细菌,IS-PCR结果将其聚为9个类群,16S rRNA基因鉴定其分别属于Bacillus sp.(芽孢杆菌属)、Rhizobium sp.(根瘤菌属)、Microbacterium sp.(微杆菌属)、Leifsonia sp.(雷夫松氏菌属)、Sphingomonassp.(鞘氨醇单胞菌属)、Alcaligenessp.(产碱菌属)和Agrobacteriumsp.(农杆菌属).土壤栽培菜心中可培养细菌数目多于无土栽培菜心,且土壤栽培菜心中内生细菌的碳代谢更多样化.生理生化实验显示,部分菌株能分泌生长素和铁载体.加入土壤栽培菜心中分离得到的菌株SCG14和SCG0802后,无土栽培菜心的相对叶绿素含量和可溶性糖含量比对照显著提高.本研究表明无土栽培和土壤栽培的菜心中的内生细菌在种类、数目、分布部位和碳源利用能力上有差异;此外,分离得到的菌株能提高无土栽培菜心的相对叶绿素以及可溶性糖含量,有开发为微生物制剂的潜力.(图4表6参35)     

Toxicity of Nerium oleander leaf extract in mice

Non-lethal dose of 70% ethanol extract of the Nerium oleander dry leaves (1000 mg/kg body weight) was subcutaneously injected into male and female mice once a week for 9 weeks (total 10 doses). One day after the last injection, final body weight gain (relative percentage to the initial body weight) had a tendency, in both males and females, towards depression suggesting a metabolic insult at other sites than those involved in myocardial function. Multiple exposure of the mice to the specified dose failed to express a significant influence on blood parameters (WBC, RBC, Hb, HCT, PLT) as well as myocardium. On the other hand, a lethal dose (4000 mg/kg body weight) was capable of inducing progressive changes in myocardial electrical activity ending up in cardiac arrest. The electrocardiogram abnormalities could be brought about by the expected Na+, K(+)-ATPase inhibition by the cardiac glycosides (cardenolides) content of the lethal dose.     

Determinants of paternity in the milkweed leaf beetle

Summary Males and females of the milkweed leaf beetle mate for up to 2.5 d in the field; copulation is interspersed with mounted courtship behavior and periods of passive riding on the female's back. In 1985, females mated with up to 10 different males in Bridgeport, New York, and matings averaged 0.75±0.04 (SE) d in duration. Sperm utilization patterns are complex in the milkweed leaf beetle. In the laboratory, mating duration, mating order and the duration of the gap between matings affected paternity. The second male's sperm predominated when a female's two consecutive matings were of equal duration (but were long: 45 h each) or when they were intermediate in duration (15 h each) with a 5 day gap between the two matings. The mechanism of sperm predominance appears to be one of time-dependent sperm removal and replacement. Neither relative nor absolute size of males affected the extent to which they superceded the sperm of rivals. Electrophoretic analysis of paternity at 6 polymorphic loci showed that offspring of at least eight out of 11 mating pairs pairs collected in the field at the end of the 1984 breeding season were sired by more than one male. At least seven of the 11 families produced some offspring that were sired by the female's most recent mate in the field and in no case was the collected male completely excluded from paternity. In a greenhouse plot, males climbed off females' backs a mean of 1.1±0.3 h before oviposition. Females did not oviposit with males on their backs and did not oviposit sooner when males were removed than when males were allowed to remain mounted, indicating that males don't keep females from ovipositing until they can achieve sperm predominance. The close concordance between male disembarkment and oviposition suggests that males remain with females beyond the time when they have superceded the sperm of their prior mates, possibly to guard them from rival males. Although the prolonged mating association of the milkweed leaf beetle cannot be separated into discrete copulatory and guarding phases, the results of this study suggest that prolonged mating enables males both to remove and replace the sperm of the females' prior mates with their own sperm and to prevent females from remating prior to oviposition.     

Host-plant leaf surface compounds influencing oviposition in Delia antiqua

Summary. Delia antiqua (Diptera: Anthomyiidae) females lay eggs between the leaves of onion plants or in the soil around the base of the plants, then the maggots feed on the onion bulb and roots causing rapid secondary infection by fungi and bacteria. It is well known that the first sensory modality used by the onion fly is vision, therefore the shape (vertical narrow cylinders) and colour (yellow) of the plant play a crucial role in the recognition of a potential host plant. In the past it has been shown that n-dipropyl disulfide (Pr₂S₂), a typical component of onion volatiles, is an important chemical host plant cue. We extracted host leaf surface to verify if Pr₂S₂ is the major chemical oviposition stimulant and to determine if other as yet unknown substances may play a role in host-plant selection. We confirmed that the females laid more eggs around onion plants with leaves than when only the onion bulb was present and that the odour of chopped onion stimulates oviposition. Extraction of the surface of onion leaves revealed that only the apolar fraction contained substances that stimulate egg-laying in D. antiqua. GC-EAD analysis indicated that a minor constituent, Pr₂S₂, is perceived by the olfactory receptor on the antennae of the onion fly females. This confirmed the importance of Pr₂S₂ as oviposition stimulant. Contact with the polar fraction did not stimulate egg-laying behaviour in this Delia species. We discuss the oviposition strategy of D. antiqua in comparison with its closely related species, D. radicum, in which the oviposition behaviour is stimulated mainly through contact with the cabbage leaf surface and only partially by the host volatiles.     

Phototransformation of chlorimuron-ethyl on leaf surface

Chlorimuron-ethyl, a post-emergent herbicide selectively used in soybean and maize, degrades mainly through chemical hydrolysis. Photolysis has also an important role in the degradation of this compound. Phototransformation of chlorimuron-ethyl takes place through the cleavage of the sulfonylurea bridge, dechlorination, de-esterification and cyclization. Enzymatic de-esterification usually takes place in plant system to liberate the free acid, chlorimuron, which, in fact, inhibits the acetolactate synthase enzyme. In the non-enzymatic environment, de-esterification generally does not occur at normal pH and in moisture-free medium. But on the leaf surface of maize crop de-esterification of chlorimuron-ethyl takes place. The moisture deposited on leaf surfaces by virtue of evapo-transpirational loss of water may cause the de-esterification of chlorimuron-ethyl to the free acid, chlorimuron.     

Preferences of six leaf beetle species among qualitatively different leaf age classes of three Salicaceous host species

Summary. As Salicaceous plants produce new leaves for a prolonged period of time, they expose a wide range of differentially aged leaves to herbivores during the growing season. In this work, I show that young leaves of three Salicaceous species, Populus tremula L., Salix phylicifolia L. and S. pentandra L., contain more nitrogen than conspecific old leaves. In P. tremula and S. pentandra young leaves also contained more low-molecular weight secondary compounds, phenolic glucosides. Leaves of S. phylicifolia did not contain phenolic glucosides in detectable amounts. Furthermore, in P. tremula and S. pentandra young leaves contained less polymeric digestability-reducing phenolics, condensed tannins, than old leaves. In S. phylicifolia, higher concentrations of condensed tannins were found in young leaves. In laboratory feeding trials with six leaf beetle species, young leaves of the studied plants were invariably preferred in all tested herbivore × host species combinations. In particular, it is remarkable that three leaf beetle species with known different overall relationships to phenolic glucosides equally preferred more glucoside-containing young S. pentandra leaves over conspecific old ones. Four beetle species were found to prefer young leaves of S. phylicifolia despite the higher content of condensed tannins in young leaves. These results indicate that the general preference of leaf beetles for young leaves of Salicaceous plants probably does not primarily result from variable distribution of secondary compounds. Apparently, the preference for young leaves is fundamentally due to variation in leaf nutritive traits, such as nitrogen content. Received 9 February 2001.     

Parasitic wasps orient to green leaf volatiles

Summary Undamaged plants emit low levels of green leaf volatiles (GLVs), while caterpillar-damaged and artificially damaged plants emit relatively higher levels of certain GLVs. Female braconid parasitoids,Microplitis croceipes, oriented to both damaged plants and to individual GLVs in no-choice tests in a wind tunnel, but seldom oriented to undamaged plants. Female ichneumonid parasitoids,Netelia heroica, also oriented to individual GLVs in a wind tunnel. Males of both wasp species failed to orient to the GLVs. These data show that leaf-feeding caterpillars can cause the release of GLVs, and that parasitic wasps can respond to these odors by flying upwind (chemoanemotactic response), which brings the wasps to their caterpillar hosts. This supports the hypothesis that plants communicate with members of the third trophic level,i.e., plants under herbivore attack emit chemical signals that guide natural enemies of herbivores to sites of plant damage. In this interaction, the GLVs serve as tritrophic plant-to-parasitoid synomones. That parasitoids from two different wasp families oriented to GLVs suggests that the response may be widespread among the Hymenoptera.Mention of a commercial or proprietary product does not constitute an endorsement by the U.S. Department of Agriculture     

Thalassia testudinum leaf dynamics in a Mexican Caribbean coral reef lagoon

Shoot density, leaf growth, initiation, biomass and primary production in Thalassia testudinum (Banks ex König) were monitored at monthly intervals from August 1990 until January 1992 at three stations in the tropical coral reef of Puerto Morelos lagoon, Mexico. Leaf growth decreased with increasing leaf length, declining rapidly once the tips of leaves had started to decay; however, the leaves continued to grow until complete senescence. Maximum potential leaf age was>90 d. Leaf growth, biomass and primary production were highest at the station in the vicinity of mangrove discharges, intermediate at the nearshore fringe of the seagrass meadow, and lowest at the back-reef station. Leaf growth, leaf initiation, biomass and primary production were minimum in the winter months and maximum in the summer. Leaf growth and primary production were significantly correlated with water temperature or/and the hours of daylight. This is the first report of temperature-or/and hours of daylight-related seasonal variability in T. testudinum production from the tropical Caribbean.     

Search behavior of the checker-throated antwren foraging in aerial leaf litter

Summary Checker-throated antwrens (Formicariidae: Myrmotherula fulviventris) live in lowland neotropical forests and forage from dead curled leaves in the understory. Because they search each leaf individually they provide an opportunity to study the use of potential visual cues by an insectivorous bird. Long and highly curled leaves contain the most arthropods and checker-throated antwrens were more successful when foraging at those leaves. Yet, they used leaves at random with respect to these potential cues. Antwrens spent longer searching for arthropods in each highly curled leaf than in less curled leaves. Because of this additional search time, prey capture success per unit foraging time was only slightly greater for highly curled leaves than at the average dead leaf in the aerial leaf litter. Thus, the cues that antwrens could use to locate richer leaves are those features that obscure the prey from avian predators. Unlike other foraging systems, the antwrens appear to have no reliable cues indicating more profitable foraging sites.Address for correspondence     

Modeling leaf dispersal in mixed hardwood forests using a ballistic approach

In mixed-species stands, modeling leaf litter dispersal is important to predict the physical and chemical characteristics of the forest floor, which plays a major role in nutrient cycling and in plant population dynamics. In this study, a spatially explicit model of leaf litterfall was developed and compared with two other models. These three models were calibrated for a mixed forest of oak and beech using litterfall data from mapped forest plots. All models assumed that an allometric equation described individual leaf litter production, but they strongly differed in the modeling of the probability density of leaf shedding with distance from source trees. Two models used a negative exponential function to account for leaf dispersal with distance, and this function was allowed to vary according to wind direction in one of them. In contrast, our approach was based on a simple ballistic equation considering release height, wind speed, wind direction, and leaf fall velocity; the distributions of wind speeds and wind directions were modeled according to a Weibull and a Von Mises distribution, respectively. Using an independent validation data set, all three models provided predictions well correlated to measurements (r > 0.83); however, the two models with a direction-dependent component were slightly more accurate. In addition, parameter estimates of the ballistic model were in close agreement with a foliar litter production equation derived from the literature for beech and with wind characteristics measured during leaf litterfall for both species. Because of its mechanistic background, such a spatially explicit model might be incorporated as a litterfall module in larger models (nutrient cycling, plant population dynamics) or used to determine the manner in which patch size in mixed-species stands influences litter mixture.