Rodent acorn selection in a Mediterranean oak landscape

Quercus suber, Quercus ilex and Quercus coccifera (Cork, Holm and Kermes oaks, respectively) are common evergreen oak species that coexist in the landscapes of the western part of the Mediterranean basin. Rodents are the main acorn predators and thus one of the main factors for understanding recruitment patterns in oaks. In this paper we analyse to what extent mice prefer acorns from one oak species over another in three oak species studied using acorn removal experiments and video tape recordings. Twenty labelled acorns from each of the three Quercus species (60 acorns) were placed in 40 cm×40 cm quadrats on each plot. Because selection might vary as a result of the vegetation context, we performed the trials in the five main vegetation types within the study area (four replicates in each vegetation type) in order to control for habitat influences on rodent acorn preferences (a total of 20 plots). The removal of 1,200 acorns occurred within 68 days. Mice removed 98.7% of the acorns. Q. ilex acorns were preferred over Q. suber and Q. coccifera in all vegetation types except in pine forest, where no acorn preferences were detected. Acorn removal rates differed with vegetation type, correlating positively with shrub cover. The distance at which acorns were displaced by rodents (mean =4.6 m±5.1 SD) did not differ between acorn species, but varied among vegetation types. Bigger acorns of Q. coccifera were selected only after Q. ilex and Q. suber acorns were depleted, while no size selection was detected for the latter two species. Thus, we conclude that rodents show preference for some oak acorns and that landscape context contributes significantly to rodent activities and decisions.     

Hoarding behaviors of two wood mouse species: Different preference for acorns of two Fagaceae species

Two species of wood mouse, Apodemus argenteus and A. speciosus, were observed consuming and hoarding acorns of Quercus serrata and Castanopsis cuspidata. When each species of acorn was supplied individually, both species of mice used each species of acorn for eating and hoarding. When both species of acorn were supplied, A. argenteus consumed or hoarded only C. cuspidata, whereas A. speciosus tended to eat C. cuspidata acorns at the feeding site, and disperse or hoard Q. serrata acorns. Apodemus speciosus is unlikely to disperse C. cuspidata acorns (their utilization was biased towards consumption) when Q. serrata acorns are also available. Apodemus argenteus will make almost no contribution to the dispersal of Q. serrata when the two acorn species coexist.     

Quantitative analysis of acorn transportation by rodents using magnetic locator

Transported distance and mortality of acorns scattered by rodents were investigated with magnets inserted into acorns (40 of Quercus serrata and 20 of Quercus acutissima) and a magnetic locator in a natural forest stand. All the treated acorns were transported, and 60% of them were discovered again with a magnetic locator from autumn to the next spring. Most transported acorns suffered predation within one month after the start of the experiment. Several acorns were rehoarded at least two or three times. Average transported distance of scattered acorns was 22.1±8.9 m (max=38.5 m) and the survival rate was 3.0%. The magnet method is one of the most effective methods for tracking acorns through the winter.     

Prey distribution,foliage structure,and foraging behavior of insectivorous birds in two oak species (<Emphasis Type="Italic">Quercus serrata</Emphasis> and <Emphasis Type="Italic">Q. variabilis</Emphasis>)

We examined foraging behaviors of four insectivorous bird species (Great Tit Parus major, Varied Tit P. varius, Long-tailed Tit Aegithalos caudatus and Japanese White-eye Zosterops japonica) on the two oak species (Q. serrata and Q. variabilis) in relation to fine-scale foliage structures, abundance, and distribution of folivorous insects and physical and chemical characteristics of leaves. There was no difference in the mean number of insects for each oak species, but there was a significant difference in the mean biomass. The distance from twigs or branches to leaf tips or blade-petiole junctions showed that leaves of Q. variabilis were more dispersed than those of Q. serrata. The different size distribution of insects influenced insect sizes selected and foraging maneuvers used by each bird species. Parus major and P. varius fed on beetles (low energy gain) with perch-gleaning (the most energy-saving maneuver) from the upper side of leaves on Q. variabilis, whereas they fed on large lepidopteran larvae (high energy gain) from the lower side of leaves on Q. serrata using a variety of maneuvers (including energy-consuming ones). Both A. caudatus and Z. japonica fed on insects from the lower side of leaves by hang-gleaning and reach-gleaning, respectively. These species appeared to be morphologically adapted to the energy-consuming but more effective maneuvers used to take preys from the undersides of leaves. We hypothesize that differences in foliage structures between closely related species of trees have evolved as a balance between defense against folivorous insects and attraction of insectivorous birds.     

Differential effects of elevated CO2 on acorn density, weight, germination, and predation among three oak species in a scrub-oak forest

Much research on the effects of elevated CO₂ on forest trees has focused on quantitative changes in photosynthesis, secondary chemistry, and plant biomass. However, plant fitness responses to rising CO₂ should also include quantitative measures of reproduction, since most forest systems are recruitment limited. Until now, it has proved very difficult to grow forest trees to sexual maturity in a CO₂‐enriched environment. This paper is the first of its kind to address the effects of elevated CO₂ on the reproduction of hardwood trees in a natural forest. Beginning in 1996, scrub‐oak vegetation, predominantly three species of scrub‐oaks, Quercus myrtifolia, Q. chapmanii, and Q. geminata, were grown inside eight chambers with elevated CO₂ (704 parts per million (ppm)) and eight with ambient CO₂ (379 ppm) at Kennedy Space Center, Florida. In elevated CO₂, acorn production increased significantly for the dominant species Q. myrtifolia and for Q. chapmanii, but it did not increase for the subdominant, Q. geminata. Acorn weight, germination rate, and predation by weevils were unaffected by CO₂. Thus, recruitment of some forest tree species into the Florida scrub‐oak community is likely to be accelerated in an atmosphere of increased CO₂. However, because the acceleration of recruitment differs among species, over the long term, Q. myrtifolia and Q. chapmanii will be favored over Q. geminata and this is likely to change patterns of species diversity.     

Flooding effects on starch partitioning during early growth of two oak species

Pedunculate (Quercus robur L.) and sessile (Q. petraea [Matt.] Liebl.) oaks are the most common oak species in Western Europe. They are known to display different ecological requirements, particularly relative to root hypoxia induced by flooding: In a glasshouse study of seedlings, we quantified the effects of flooding on starch mobilization from cotyledons and starch partitioning. Growth and distribution of lateral roots were also measured. The above-ground growth of Q. robur was less affected by flooding than that of Q. petraea which failed to develop a second flush. Root growth was also severely inhibited, particularly in Q. petraea. In Q. robur, lateral root initiation as well as elongation was restricted to the soil surface layer. Flooding markedly reduced total growth and concentrations of in all components except stems. Starch mobilization from cotyledons was delayed by flooding, especially in Q. robur seedlings. Under flooding, the decrease of cotyledons dry mass and starch content in Q. robur was lower than in Q. petraea, whereas Q. robur displayed larger growth than Q. petraea. The features of carbohydrate management may be crucial in the observed differences in flooding tolerance of these species.     

A record of acorn eating by sika deer in western Japan

The rumen contents of 14 sika deer (Cervus nippon) collected in November 1996 in Yamaguchi Prefecture, the western end of Honshu, Japan, were analyzed by the point-frame method. The contents were composed of high-quality foods like deciduous and evergreen browse and acorns. The composition, which consisted of a significant amount of acorns (27.8 ± 22.5%, mean ± SD), was in contrast to that of northern sika deer populations which exclusively eat graminoid leaves including dwarf bamboos. This is the first record of acorns being a major contributor to diet for wild sika deer. By the point-frame method, acorns were underestimated, and the weight contribution was much greater.     

蒙古栎种子相对丰富度对小兴安岭5种木本植物种子扩散的影响

2009和2010年秋季,在黑龙江省伊春市带岭区东方红林场研究了蒙古栎结实量及啮齿动物密度变化对胡桃楸、红松、蒙古栎、毛榛和平榛5种木本植物种子扩散的影响.结果表明:在小兴安岭林区,啮齿动物种群数量具有年际变化,2009年小型啮齿动物的总捕获率(31.0％)显著高于2010年(16.7％);2009年蒙古栎种子雨密度(6.2±2.1粒·m-2)和种子相对丰富度(20.O)均显著低于2010年(26.7±10.2粒·m-2和160.0).2009年,除胡桃楸种子外,其他种子全部被扩散或者被原地取食,其中蒙古栎种子被分散埋藏的比例最高,且种子平均扩散距离最大;2010年,胡桃楸种子被分散埋藏的比例最高,且种子平均扩散距离最大.研究区蒙古栎种子相对丰富度是影响其他木本植物种子扩散的重要因素.     

Impacts of elevated nitrogen inputs on oak reproductive and seed ecology

The effects of increased anthropogenic inputs of reactive nitrogen (N) have been studied at the Harvard Forest Chronic N Experiment, where NH₄NO₃ has been applied experimentally since 1988 to increase atmospheric deposition rates ～6‐ and ～18‐fold above ambient. This paper asks whether conditions favorable to primary production also resulted in plastic increases to flower, fruit, and seedling traits, and focuses primarily on the oaks that dominate the hardwood stands of the Harvard Forest experiment. Litterfall samples collected between 1996 and 2001 revealed that flowers and fruits were significantly more abundant in N‐treated plots, and an analysis of oak tree abundance found significant variation both among and within plots. Acorn samples collected during 2003 and 2004 (a mast and a postmast year) were therefore analyzed using ancova models that included an estimate of oak tree abundance. This tree abundance estimate was the only significant driver of increased acorn production during the mast year, and in both years it was a significant factor on plots receiving the highest levels of N. In the postmast year, acorn production was increased in direct response to N‐related factors other than tree abundance. Our comparisons of control and N‐treated plots for acorn quality traits (e.g. rates of acorn damage, germination percentage, seedling growth) revealed negligible or only transient differences. Shifts in overall acorn abundance – particularly disproportionate N‐mediated increases during nonmast years – could have a wide range of ecological consequences beyond the more frequently examined impacts of N deposition on primary production and carbon sequestration.     

Biomass and production of a naturally regenerated oak forest in southern Korea

Biomass and production of two stands with Quercus variabilis Bl. as the dominant species (stands 1 and 3) and one with Q. mongolica Fisch. as the dominant species (stand 2) were investigated in southern Korea. Stands 1 and 3 naturally occurred on sites with southerly aspects while stand 2 naturally occurred on northerly aspects; stand ages were similar for the three stands (36–38 years old). Total above- and belowground biomass including understory vegetation (Mg ha^–1) was 108.4 for stand 1, 115.6 for stand 2, and 132.0 for stand 3, respectively. Understory vegetation constituted 17.4% of the total biomass in stand 1 but only 3.7–4.5% in stand 2 and stand 3. Roots constituted 20.1–24.6% of the biomass of the overstory vegetation. Although stand 3 showed the highest total biomass, net production was highest in stand 2 at 12.6 (Mg ha^–1 year^–1); net production levels for stands 1 and 3 were 11.7 and 11.1 (Mg ha^–1 year^–1), respectively. It appeared that the differences in site conditions related to aspect influenced the distribution of naturally regenerated oak species within a relatively small area and resulted in differences in biomass and production among the stands.     

Application of radiotelemetry to the survey of acorn dispersal byApodemus mice

We examined the applicability of radiotelemetry to studies of acorn dispersal byApodemus mice and compared its efficiency with the of this spool-and-line method. Installation of a transmitter (2.2 g) onto acorns did not interfere with the transporting and feeding behavior of the mice. We were able to detect all transmitter-installed acorns and follow the daily changes in the sites in which they were hoarded, while we missed 59% of the spool-tied acorns due to mice breaking the threads. Mice carried transmitter-installed acorns farther than spool-tied ones. The radiotelemetry method is superior to the spool-and-line method and useful for the study of hoarding behavior in rodents.     

Tissue-water relations of two co-occurring evergreen Mediterranean species in response to seasonal and experimental drought conditions

Tissue-water relations were used to characterize the responses of two Mediterranean co-occurring woody species (Quercus ilex L. and Phillyrea latifolia L.) to seasonal and experimental drought conditions. Soil water availability was reduced 15% by partially excluding rain throughfall and lateral flow (water runoff). Seasonal and experimental drought elicited physiological and morphological adaptations other than osmotic adjustment: both species showed large increases in cell-wall elasticity and decreased saturated-to-dry-mass ratio. Increased elasticity (lower elastic modulus) resulted in concurrent decreases in relative water content at turgor loss. In addition, P. latifolia showed significant increases in apoplastic water fraction. Decreased saturated-to-dry-mass ratio and increased apoplastic water fraction were accompanied by an increased range of turgor maintenance, which indicates that leaf sclerophyllous traits might be advantageous in drier scenarios. In contrast, the degree of sclerophylly (as assessed by the leaf mass-to-area ratio) was not related to tissue elasticity. An 15% reduction in soil water availability resulted in significant reductions in diameter growth when compared to control plants in both species. Moreover, although P. latifolia underwent larger changes in tissue water-related traits than Q. ilex in response to decreasing water availability, growth was more sensitive to water stress in P. latifolia than in Q. ilex. Differences in diameter growth between species might be partially linked to the effects of cell-wall elasticity and turgor pressure on growth, since Q. ilex showed higher tissue elasticity and higher intrinsic tolerance to water deficit (as indicated by lower relative water content at turgor loss) than P. latifolia.     

Effects of microsite light availability on the survival and growth of oak seedlings within a grassland

Effects of microsite light availability on the growth and survival of transplantedQuercus serrata Thunb. seedlings in aMiscanthus sinensis Anderss. grass canopy were investigated by a “plant's eye view” approach. Diffuse site factors, i.e., the fractional transmissions of diffuse photosynthetic photon flux density, were estimated at 15 cm aboveground in 108 microsites where the seedlings grew. Microsite diffuse site factors were significantly different between surviving and dead seedlings during the experiment period from April to October (F_[1,14]=10.9, P<0.01). Relative growth rate of dry weight for individual seedlings positively depended on the diffuse site factors (r²=0.482, P<0.001 in May; r²=0.312, P<0.001 in October). Only 16 seedlings produced their second stem flush within the grass canopy. The ratio of height to dry weight of the second stem flush was significantly higher for the seedlings grew in shady microsites than for those in less shady microsites (r²=0,471, P<0.01 in May). This study suggests that the microsite heterogeneity of light availability is one of the important factors affecting the establishment of tree seedlings in patchy grasslands.     

PEG模拟干旱胁迫对栓皮栎种子萌发及生长生理的影响

为了阐明栓皮栎种子萌发期对水分胁迫的耐受性,以当年采集的栓皮栎种子为材料,采用培养皿滤纸萌发的方法研究了不同浓度（0%、5%、10%、20%、30%）PEG-6000溶液对其种子萌发、生长、保护酶活性和有机渗透调节物质的影响,并对种子萌发率、胚根生长速率等与PEG浓度进行了回归分析。结果表明:（1）随着干旱胁迫程度的加剧,栓皮栎种子的发芽率、发芽指数、胚根长度、胚根生长速率和活力指数均呈先升高后下降趋势,说明低浓度（5%、10%）PEG胁迫可以促进栓皮栎种子萌发及生长,而高浓度（20%、30%）则具有抑制作用。（2）建立水分胁迫条件下种子萌发率、胚根生长速率等与PEG浓度的回归方程发现,栓皮栎种子在PEG胁迫下的萌发临界值和极限值分别为32.01%和36.99%,胚根生长速率的临界值和极限值分别为30.1%和33.35%。（3）随着PEG浓度的升高,栓皮栎种子中3种保护酶（SOD、POD、CAT）活性和3种有机渗透调节物质（可溶性蛋白、脯氨酸、可溶性糖）含量呈现不同的变化,但均有不同程度升高趋势。由此可见,栓皮栎种子可通过增加保护酶活性和体内渗透调节物质来适应水分胁迫环境,使自身萌发和生长受抑制程度降到最低。     

A newOphiostoma species isolated from Japanese oak infested byPlatypus quercivorus

A newOphiostoma species was isolated from the sapwood ofQuercus mongolica var.grosseserrata and described asOphiostoma longicollum sp. nov. The species is characterized by a long perithecial neck with a gelatinous cap at the apex and a constricted base, orange-section-shaped ascospores that accumulate in a yellow-orange drop at the apex of the neck, and itsSporothrix anamorph. Contribution No. 137, Laboratory of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Estimation of the retention times and distances of seed dispersed by two monkey species, Alouatta seniculus and Lagothrix lagotricha, in a Colombian forest

Isolated-bout method to estimate the retention times and dispersal distances was applied to the seed dispersal by red howler monkeys (Alouatta seniculus) and Humboldts woolly monkeys (Lagothrix lagotricha) in a lowland tropical forest at La Macarena, on the border of the Macarena and Tinigua National Parks, the Department of Meta, Colombia. Continuous observations were made on the feeding and ranging behavior of well-habituated troops of howler monkeys and woolly monkeys as well as continuous collection of monkeys feces. We selected out the isolated-bout as a feeding bout on the specific species that was only once recorded within 48 h before the seeds of that species appeared in the feces of monkeys. In that case, the seeds were strongly suggested to come from that isolated bout. Then retention times, route seed dispersal distances and direct seed dispersal distances were estimated. Howler monkeys, which are regarded as generalist herbivores, showed longer retention times and dispersal distances along monkeys route than did woolly monkeys, which are specialist frugivores. However, the direct distances that seeds were carried from the mother tree were not significantly greater for howler monkeys than for woolly monkeys. This shows that both retention time and movement patterns by the monkeys, especially the total ranging area, influence the direct distance that seeds are carried from the mother tree.     

Ectomycorrhizal responses to organic and inorganic nitrogen sources when associating with two host species

While it is established that increasing atmospheric inorganic nitrogen (N) deposition reduces ectomycorrhizal fungal biomass and shifts the relative abundances of fungal species, little is known about effects of organic N deposition. The effects of organic and inorganic N deposition on ectomycorrhizal fungi may differ because responses to inorganic N deposition may reflect C-limitation. To compare the effects of organic and inorganic N additions on ectomycorrhizal fungi, and to assess whether host species may influence the response of ectomycorrhizal fungi to N additions, we conducted an N addition experiment at a field site in the New Jersey pine barrens. Seedlings of two host species, Quercus velutina (black oak) and Pinus rigida (pitch pine), were planted at the base of randomly-selected mature pitch pine trees. Nitrogen was added as glutamic acid, ammonium, or nitrate at a rate equivalent to 227.5 kg ha⁻¹ y⁻¹ for eight weeks, to achieve a total application of 35 kg ha⁻¹ during the 10-week study period. Organic and inorganic N additions differed in their effects on total ectomycorrhizal root tip abundance across hosts, and these effects differed for individual morphotypes between oak and pine seedlings. Mycorrhizal root tip abundance across hosts was 90 % higher on seedlings receiving organic N compared to seedlings in the control treatment, while abundances were similar among seedlings receiving the inorganic N treatments and seedlings in the control. On oak, 33–83 % of the most-common morphotypes exhibited increased root tip abundances in response to the three forms of N, relative to the control. On pine, 33–66 % of the most-common morphotypes exhibited decreased root tip abundance in response to inorganic N, while responses to organic N were mixed. Plant chemistry and regression analyses suggested that, on oak seedlings, mycorrhizal colonization increased in response to N limitation. In contrast, pine root and shoot N and C contents did not vary in response to any form of N added, and mycorrhizal root tip abundance was not associated with seedling N or C status, indicating that pine received sufficient N. These results suggest that in situ organic and inorganic N additions differentially affect ectomycorrhizal root tip abundance and that ectomycorrhizal fungal responses to N addition may be mediated by host tree species.     

Proteins in development and germination of a desiccation sensitive (recalcitrant) seed species

In the recalcitrant seeds of Avicennia marina, protein content and the rates of protein synthesis increase during histodifferentiation. This is similar to the situation in desiccation tolerant seeds. During the stage of reserve accumulation the protein content and rates of synthesis remain constant and there is no de novo synthesis of proteins which might qualify as storage proteins. There is also no change in the nature of proteins present in either axis or cotyledonary tissues during development or germination. Similarly, fluorographs of axis proteins show only very limited changes in the patterns of protein synthesis during development and germination, at least until the onset of root growth. Heat-stable proteins are present from an early developmental stage. However, no late embryogenic abundant (LEA) proteins are synthesised during the late stages of development, indicating that seedling establishment is independent of such maturation proteins. It is suggested that the lack of desiccation tolerance of A. marina seeds might be related to the absence of desiccation-related LEAs. Although the rate of protein synthesis increases during germination, protein metabolism appears to remain qualitatively the same as that occurring during development. The present results suggest that in these desiccation sensitive seeds, protein metabolism characterising development changes imperceptibly into that of germination.