Biomass allocation and growth responses of Scots pine saplings to simulated herbivory depend on plant age and light availability

This study experimentally analyses the response to simulated herbivory of juvenile Scots pine of two different ages in contrasting abiotic scenarios, focusing on the potential dual role of browsing ungulates: negative, by removing aerial biomass, and positive, by stimulating compensation capacity and providing nutrients by depositing their excrement. Compensation against herbivory was investigated by experimentally clipping a set of Scots pine (Pinus sylvestris L. nevadensis) juveniles, grown under different levels of light and nutrient availability. The responses analysed were survival, trunk-diameter growth, leader-shoot growth, increment in number of meristems, RGR, biomass of needles, shoots, root and whole plant, and root-to-shoot ratio. Clipping consistently resulted in a worse survival and performance of pines with respect to unclipped ones. From the factors analysed, light availability was responsible mainly for the variations in plant performance, while the addition of nutrients was much less important. Age was also important, with older pines showing in general better performance after clipping. Overall, clipping invariably had a negative effect on Scots pine, since none of the combinations of abiotic factors used resulted in overcompensation. However, the intensity on this negative effect proved quite variable, from almost an exact compensation in clipped older pines under full sunlight availability to very poor performance and high death probability in younger pines in shade. Scots pine cannot overcompensate after clipping, but, depending of the environmental conditions, the negative result of clipping varies from severe undercompensation to almost exact compensation. Also, small differences in sapling age can promote significant differences in sapling response to clipping and light environment.     

Effects of endomycorrhizal infection,artificial herbivory,and parental cross on growth of Lotus corniculatus L.

Summary We examined how combinations of parentage, fungicide application, and artificial herbivory influence growth and shoot phosphorus content in pre-reproductive Lotus corniculatus, using young offspring arising from three parental crosses, two of which had one parent in common. Soil with vesicular-arbuscular mycorrhizal (VAM) fungi was treated with either water or benomyl, an anti-VAM fungicide, and added to trays containing groups of four full siblings. There were two experiments; in the first no plants were clipped while in the second two of the four plants were clipped to simulate herbivory. In both experiments plants of the two related crosses accumulated more biomass and total shoot P than did plants of the third cross. Plants inoculated with watertreated soil had greater shoot mass and P concentration than did fungicide-treated replicates but the extent of increase in P concentration varied among crosses. In Experiment 2, clipping reduced root mass and resulted in higher shoot P concentration. In this experiment there was a significant interaction of fungicide application and clipping: both unclipped and clipped plants grew better in soil not treated with fungicide, but the increase in shoot mass, total mass, and total P was greater in unclipped plants. Significant interaction of fungicide treatment and clipping is most likely due to reduced availability of carbon to the roots of clipped plants, resulting in poorer symbiotic functioning.     

Predicaments of endangered huemul deer, Hippocamelus bisulcus, in Argentina: a review

A total of 350–600 huemul (Hippocamelus bisulcus) remain as fragmented groups along 1,850 km of Argentine Andes. Their conservation depends on accurate knowledge of the species' requirements and the factors preventing their recovery. The Regional Delegation for Patagonian National Parks (RDP) erroneously alleged that huemul status is satisfactory, and current in situ efforts are sufficient to guarantee recovery. Therefore, conservation centers are regarded unnecessary and the associated risks too high, especially because previous attempts with manipulations have failed. No data support these claims, instead many subpopulations have disappeared recently even in national parks (NP) which hold <0.01 huemul/km². Causes preventing recovery or recolonization are unknown. Current pressures on huemul subpopulations include increased economic activities and alien species. Normal ranges for many biological parameters or population performance of huemul are unknown. Focus is on habitat studies using presence as surrogate for what should be studied on survival and reproduction. Factors important to small-sized populations or preventing recovery remain unstudied. RDPs insistence on indirect methodology prevents implementation of other potentially more promising research approaches. The lack of consensus regarding the necessity and feasibility of a conservation center prevented its establishment and related census flights in unprotected sites. RDP currently forecloses aerial census and capturing and thus prospects for a huemul conservation center, and the proposition of establishing such a center was neither discussed nor incorporated into the national recovery plan. Helicopter captures have been used successfully on deer in huemul habitat. Captures and translocation of huemul occurred since 1830; several zoos kept them successfully up to 10 years, and natural tameness facilitated husbandry. Recently, Chile successfully caught and transported huemul by helicopter to stock a private center. Unknowns can be addressed easily on semicaptive deer; other questions can be studied through reintroductions, employing adaptive management. RDP places faith in NP providing viable subpopulations. However, it remains doubtful whether some 220 huemul living in >22,000 km² of parks can guarantee species survival. For Argentine cervids, absence of studies and management plans due to lack of funds is typical. Considering the actual situation and future perspectives, it appears doubtful that recovery will be achieved based on strategies similar to those employed in the past.     

Impact of simulated herbivory on Alliaria petiolata survival, growth, and reproduction

In weed biological control, insect damage to target weeds can be simulated in invaded habitats to study potential responses of the plant to introduced natural enemies. In the present study, we investigated the impact of two levels of manual flower-shoot damage (shoots cut at tip or base) on Alliaria petiolata (garlic mustard) survival, size, and reproduction. Experiments were conducted in 2002 and 2003 using invasive field populations of A. petiolata under naturally varying plant densities. Plant survival was recorded, and size and reproduction parameters were measured. Manual flower-shoot damage had a significant effect on plant survival. In both years, fewer plants survived in the basal-cut treatment than in either the control (un-cut) or tip-cut treatment. Plant size and reproductive output were likewise reduced in the basal-cut treatment. In both years, total seed production was significantly lower in the basal-cut treatment than either the control or tip-cut treatment. When combined, increased mortality and reduced seed production of basal-cut plants greatly reduced the contribution these plants made to the seed bank. Plant density did not affect reproduction or plant size. The impacts of cutting were consistent across years and sites with distinct biotic and abiotic conditions, and A. petiolata densities. We anticipate that herbivore damage to A. petiolata populations by introduced biological control agents will likewise remain consistent under varying biotic and abiotic conditions if the agents are equally adapted to these.     

Microsite variation in light availability and seedling growth ofQuercus serrata in a temperate pine forest

Spatial heterogeneity in light availability for tree seedlings under the canopy of a temperate pine forest was studied. Six-day measurements at 10-s intervals revealed a great variety in the temporal patterns of photosynthetic photon flux density (PPFD) and histograms among observation days and microsites; mean daily total PPFD relative to full sun varied from 1.5% to 10.4% depending on the microsites. The occurrence and duration of PPFD above 80 μmol m⁻² s⁻¹, which might reflect sunfleck activity, varied greatly among the microsites. However, several simple empirical relationships were found between some parameters characterizing microsite light availability and sunfleck activity; the diffuse site factor was correlated well with other parameters, including daily total PPFD, daily totals and daily summed durations of high PPFD above any examined threshold level, and its contribution to daily total PPFD. Diffuse site factors which were obtained for 700 microsites within an area of 28 m² on three different occasions during the growing season showed high correlations within the microsite. Based on the regressed relationship between the relative growth rate of current-year seedlings ofQuercus serrata and the microsite diffuse site factor and the results of area-survey measurement of the diffuse site factor, an estimation was made of the abundance of potential ‘safe-sites’ for seedling growth of the species; the ‘safe sites’ were estimated to cover 40% and 0% of the total area of the sunny and shady sites of the forest, respectively.     

Life history and demographic features of Astragalus nitidiflorus, a critically endangered species

Astragalus nitidiflorus is an endangered perennial, but short-lived legume of SE Spain, which has been re-found after 100 years. To identify possible weak points that might contribute to its rarity and hamper its conservation, this paper presents data concerning location, habitat, demographic features and reproductive biology of the species. Censuses of three cohorts of seedlings show that the seedling stage is the most critical in the life cycle. The adult plants show a long flowering season with a high degree of synchrony. Despite the low reproductive success of the species, the annual seed production is very high due to the high floral production. The data show that A. nitidiflorus is a facultative xenogamous species, but the presence of pollinators can enhance fruit set. The viability of the species is not limited by the flowering and fruiting process, however the maintenance of the habitat in the early successional stages seems to be the critical point for long-term survival of the species.     

Plant responses to selective grazing by bison: interactions between light,herbivory and water stress

Two abundant tallgrass prairie forb species, Ambrosia psilostachya and Vernonia baldwinii, are commonly found intact in patches where the grasses have been selectively grazed by bison. Microclimatic patterns and physiological responses of these forbs were measured in grazed and ungrazed patches. These experiments demonstrated that bison herbivory indirectly enhanced water availability and productivity of forbs growing in grazed patches. This was due primarily to the reduction in transpiring grass leaf area in grazed patches and an increase in light availability. In grazed patches, incident light at forb mid-canopy height was 53% greater than ungrazed sites at midseason and soil temperatures were always warmer (e.g., 10°C at 5 cm), perhaps enabling forbs to initiate growth earlier in the spring. Enhanced leaf xylem pressure potential and stomatal conductance in plants in grazed areas were most evident when water availability was low (i.e., late in the growing season and over short-term dry periods characteristic of the tallgrass prairie environment). Relative to individuals in ungrazed areas, end-of-season biomass of A. psilostachya was 40% greater and reproductive biomass and head number of V. baldwinii was 45% and 40% greater, respectively, in plants in grazed patches. A favorable growing environment maintained in grazed patches during periods of water limitation enhances carbon gain in forbs leading to increased biomass and potential fitness.     

光照对蔺草生长和草茎开花率的影响

蔺草草茎长度和是否开过花是决定其品质的两个重要方面。试验表明,不同光周期及光照强度对蔺草的生长和草茎开花率会产生显著影响。生育前期,延长日照显著促进开花,遮光处理降低蔺草的分蘖、草茎长度、减少草茎开花率和每花序小花数。中后期对蔺草进行一定遮光处理后,草茎长度增加,开花率下降。试验表明,光照是造成蔺草开花逆转和影响草茎品质的重要生态因子之一。     

The influence of light on the growth of watercress (<Emphasis Type=Italic>Nasturtium officinale</Emphasis> R. Br.)

In stream ecosystems, the growth of aquatic primary producers is affected by spatial and temporal variations in the riparian canopy, which can influence the availability of light resources. Aquatic plants can acclimate to low light environments by employing a suite of morphological or physiological mechanisms to increase light capture or photosynthetic efficiency. Some species may also use alternate types of propagules to colonize environments with heterogeneous light environments. In a greenhouse experiment we examined the morphological and physiological response of watercress (Nasturtium officinale R. Br.) to a gradient of increasing light levels, which ranged from 7% ambient light to full sunlight. We also determined if watercress seedlings and vegetative fragments differed in their growth response to increasing light levels. Total biomass and root biomass of seedlings and vegetative fragments decreased with decreasing light levels. The difference in plant biomass across treatments was due to morphological changes in total canopy area and leaf area, both of which increased with decreasing light levels. Seedlings and vegetative fragments did not differ in their response to light availability, but vegetative fragments had higher final biomass as a result of higher initial biomass. Physiological acclimation to low light levels appears to be of secondary importance for watercress as the concentrations of total chlorophyll, chlorophyll a, chlorophyll b, and chlorophyll a:b did not differ among light levels or between seedlings and vegetative fragments. Seedlings and vegetative fragments grown under high light levels had a greater percentage of carbon and a lower percentage of nitrogen than plants grown under low light conditions. The results of this study indicate that watercress displays considerable morphological plasticity and acclimates to low light conditions primarily by increasing leaf area and canopy surface area. There is no evidence that the type of watercress propagule (seedling vs. vegetative fragment) imparts any growth advantage in low light environments and watercress grown from either type of propagule showed no differences in their morphological or physiological responses to varying light regimes. Handling editor: S. M. Thomaz     

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。     

CO2 and light effects on deciduous trees: growth, foliar chemistry, and insect performance

This study examined the effects of CO₂ and light availability on sapling growth and foliar chemistry, and consequences for insect performance. Quaking aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), and sugar maple (Acer saccharum Marsh.) were grown in controlled environment greenhouses under ambient or elevated CO₂ (38.7 and 69.6 Pa), and low or high light availability (375 and 855 μmol m⁻² s⁻¹). Because CO₂ and light are both required for carbon assimilation, the levels of these two resources are expected to have strong interactive effects on tree growth and secondary metabolism. Results from this study support that prediction, indicating that the relative effect of rising atmospheric CO₂ concentrations on the growth and secondary metabolism of deciduous trees may be dependent on light environment. Trees in ambient CO₂-low light environments had substantial levels of phytochemicals despite low growth rates; the concept of basal secondary metabolism is proposed to explain allocation to secondary metabolites under growth-limiting conditions. Differences between CO₂ and light effects on the responses of growth and secondary metabolite levels suggest that relative allocation is not dependent solely on the amount of carbon assimilated. The relative growth rates and indices of feeding efficiency for gypsy moth (Lymantria dispar L.) larvae fed foliage from the experimental treatments showed no significant interactive effects of light and CO₂, although some main effects and many host species interactions were significant. Gypsy moth performance was negatively correlated with CO₂- and light-induced increases in the phenolic glycoside content of aspen foliage. Insects were not strongly affected, however, by treatment differences in the nutritional and secondary chemical components of birch and maple. Received: 15 July 1998 / Accepted: 23 December 1998     

Effect of larval ontogeny, turbulence and light on prey attack rate and swimming activity in herring larvae

The effects of ontogeny (larval size), light and turbulence on the attack rate and swimming activity (proportion of time swimming and duration of swimming bout) of herring larvae (15-28 mm TL) have been investigated. Emphasis was put on the experimental design in order to create a set-up where the turbulence intensity distribution could be accurately measured as well as controlled in the entire experimental tank.Both larval size (ontogeny) and light had a significant positive effect on prey attack rate. Likewise, an intermediate increase in turbulence had a positive effect on prey attack rate, but this effect was dependent of light intensity and larval size.At low light (1.5 μE m² s⁻¹) intermediate turbulence increased the prey attack rate significantly for larger larvae (26 and 28 mm), while at high light (18 μE m² s⁻¹) intermediate turbulence had only a significant positive effect on the attack rate of smaller larvae 20 and 23 mm.In general, our data show a dome-shaped response of turbulence on attack rate and a U-shaped response of turbulence on swimming activity.For herring larvae >20 mm, the maximum (attack rate) and minimum (swimming activity) response of turbulence were found at intermediate turbulence intensities (energy dissipation rates between 7∗10⁻⁸ and 1∗10⁻⁶ W/kg). The highest turbulence level tested (8∗10⁻⁶ W/kg) showed only negative effects, as attack rates where at the lowest and swimming activity at the highest.Swimming activity increased with larval size or light, and decreased at intermediate turbulence. Compared to turbulent intensities under natural conditions this implies that larger herring larvae at 10 m depth have to be exposed to wind speeds of more than 17 m/s before negative effects on attack rate and swimming activity occurs.     

Effects of nutrient supply,light availability and herbivory on the growth of heather and three competing grass species

Grasses are becoming more abundant in areas in NE Scotland which until recently were dominated by heather (Calluna vulgaris). However, it is not clear if grasses are aggressive competitors which are now able to outcompete the dwarf shrub due to changes in environmental factors (such as grazing pressure and increasing nutrient inputs), or just opportunistic invaders, occupying gaps in the canopy which occur when heather reaches the degenerate stage. Experiments in turves and in field plots were carried out in order to investigate the performance of three grass species, Nardus stricta, Deschampsia cespitosa and Deschampsia flexuosa growing in competition with heather. These three species were selected because they differ in their nutrient requirements, palatability to herbivores and tolerance of shading. The grasses were planted in heather canopies of different structure, either turves of heather of different height and age, or moorland plots with or without heavy grazing by sheep and deer. Fertiliser (NPK) was applied to half the experimental plants. The growth of the grass species and the heather in response to the fertiliser and grazing treatments was measured, together with the light levels penetrating the canopy and received by the grass plants.Results indicated that heather was likely to be outcompeted by grasses only when there are gaps in the canopy, resulting either from heavy grazing or from the heather being in the mature or degenerate phase. Fertiliser enhanced plant growth whereas fencing out herbivores led to strong competition for light as the heather canopy closed. It is concluded that grasses require gaps in the canopy to successfully invade heather moorland, or they tend to be shaded out. Thus better management of heather moorlands to maintain a dense canopy structure may help to preserve heather cover even under increasing nutrient inputs.     

光强梯度对羊草无性系分化与生长的影响

在温室内用透光率分别为 60 %、45%、30 %的遮阴网盖在花盆上遮阴 ,研究不同光照强度对羊草无性系分化与生长的影响 .结果表明 ,低光强影响羊草基株的生物量积累 ,抑制羊草无性系的分化和生长 .减少羊草地下根茎的数目 ( A=61 4个 ,D=2 31个 )和无性系分株数 ( A=70 4个 ,D=1 52个 ) .羊草根茎长度和节数、无性系分株干重等性状在不同的光强梯度之间存在显著差异 ( P<0 .0 1 ) ,这种差别在春季尤其显著 .     

Interactive effects of light environment and herbivory on growth and productivity of an invasive annual vine, Persicaria perfoliata

Plant populations often exist in spatially heterogeneous environments with varying light levels, which can affect plant growth directly through resource availability or indirectly by altering behavior or success of herbivores. The plant vigor hypothesis predicts that herbivores are more likely to attack vigorously growing plants than those that are suppressed, for example in more shaded conditions. Plant tolerance of herbivory can also vary under contrasting resource availability. Observations suggest that damage by Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae), introduced into the United States in 2004 as a biological control agent for mile-a-minute weed (Persicaria perfoliata [L.] H. Gross), is greater in the sun than in shade. We compared weevil densities and plant growth in paired plots in full sun or under shade cloth; a second experiment included insecticide-treated plots in sun and shade, to assess the ability of the plant to compensate for herbivore damage. Greater density of weevils and more node damage (indicating internal larval feeding) were found on P. perfoliata plants growing in sun than on those in shade. Nodes were 14% thicker in the sun, which may have provided better larval habitat. Biomass produced by plants without weevils in the sun was about twice that produced in any other treatment. Herbivory had a greater effect on plant growth in the high-light environment than in the shade, apparently because of movement into the sun and increased feeding there by the monophagous herbivore, R. latipes. Results support the plant vigor hypothesis and suggest that high weevil densities in the sunny habitats favored by P. perfoliata can suppress plant growth, negating the resource advantage to plants growing in the sun.     

Patch occupancy in the endangered butterfly Lycaena helle in a fragmented landscape: effects of habitat quality, patch size and isolation

While there is agreement that both habitat quality and habitat network characteristics (such as patch size and isolation) contribute to the occupancy of patches by any given species, the relative importance of these factors is under debate. This issue is of fundamental ecological importance, and moreover of special concern for conservation biologists aiming at preserving endangered species. Against this background we investigated patch occupancy in the violet copper Lycaena helle, one of the rarest butterfly species in Central Europe, in the Westerwald area (Rhineland-Palatinate, Western Germany). Occupied (n = 102) differed from vacant (n = 128) patches in altitude, size, connectivity, availability of wind shelter, in the abundance of the larval host-plant, in the abundance of a grass species indicating favorable habitat conditions and in the abundance of nitrophilous plants. Overall, patch occupancy was primarily determined by patch size, connectivity and the abundance of the larval host plant, while all other parameters of habitat quality were of subordinate importance. Therefore, our findings suggest that even for extremely sedentary species such as L. helle habitat networks are decisive and—next to the preservation of habitat quality—need to be an integral part of any conservation management for this species.     

Effect of light intensity on broiler behaviour and diurnal rhythms

Light intensity manipulation is an important management tool affecting broiler behaviour and physiology but still there is a debate regarding the optimum level to be used in confinement barns. Two experiments were completed to study the impact of light intensity (1, 10, 20 and 40 lx) on behaviour and diurnal rhythms of broilers raised to 35 d of age. For each experiment, 950 Ross × Ross 308 chicks were housed per room with replication of individual light intensity treatment in two environmentally controlled rooms. Within each large room, a small pen with 25 male and 25 female chicks was used for recording behaviour. Data were analyzed as a randomized complete block design with experiment acting as a block. All chicks were provided with 40 lx intensity and 23 h light until shifting to treatment light intensity and 17 h daylength at 7 d of age. For each replicate, behaviour was recorded for a 24 h period, starting at 16 or 17 d of age. At 23 d of age, three birds per room were bled at the start, middle and end of light and dark periods for melatonin estimation using RIA. When summarized over the 24 and 17 h observation periods, birds exposed to a light intensity of 1 lx rested more (P = 0.01) and preened (P < 0.05) and foraged (P < 0.05) less in comparison to other light intensities. Birds from all treatments exhibited diurnal rhythms for feeding, resting, drinking, walking, standing, foraging and preening behaviours with little or no activity during the 7 h dark phase. The serum melatonin levels at the start, middle and end of light and dark phases were unaffected by light intensity (P > 0.1). In conclusion, light intensity ranges from 1 to 40 lx did not affect melatonin levels or behavioural diurnal rhythms, but birds exposed to a light intensity of 1 lx rested more and preened less, potentially indicating a reduced welfare state.     

Effects of simulated root herbivory and fertilizer application on growth and biomass allocation in the clonal perennialSolidago canadensis

Summary Compensatory growth in response to simulated belowground herbivory was studied in the old-field clonal perennialSolidago canadensis. We grew rootpruned plants and plants with intact root systems in soil with or without fertilizer. For individual current shoots (aerial shoot with rhizome and roots) and for whole clones the following predictions were tested: a) root removal is compensated by increased root growth, b) fertilizer application leads to increased allocation to aboveground plant organs and increased leaf turnover, c) effects of fertilizer application are reduced in rootpruned plants. When most roots (90%) were removed current shoots quickly restored equilibrium between above-and belowground parts by compensatory belowground growth whereas the whole clone responded with reduced aboveground growth. This suggests that parts of a clone which are shared by actively growing shoots act as a buffer that can be used as source of material for compensatory growth in response to herbivory. Current shoots increased aboveground mass and whole clones reduced belowground mass in response to fertilizer application, both leading to increased allocation to aboverground parts. Also with fertilizer application both root-pruned and not root-pruned plants increased leaf and shoot turnover. Unfertilized plants, whether rootpruned or not, showed practically no aboveground growth and very little leaf and shoot turnover. Effects of root removal were as severe or more severe under conditions of high as under conditions of low nutrients, suggesting that negative effects of belowground herbivory are not ameliorated by abundant nutrients. Root removal may negate some effects of fertilizer application on the growth of current shoots and whole clones.     

Impact of growth form and carbohydrate reserves on tolerance to simulated deer herbivory and subsequent recovery in Liliaceae

? Premise of the study: Over-browsing of the understory vegetation by white-tailed deer has been a cause of decline in many plant populations. Liliaceae are particularly sensitive, yet individual species differ in their tolerance to deer herbivory. In this paper, we examine whether differences in clonal habit, carbon allocation patterns, and phenology influence the capacity of a species to tolerate and recover from repeated herbivory. ? Methods: Flowering ramets of Clintonia borealis, Maianthemum canadense, and Trillium erectum were subjected to total defoliation for one or two springs. ? Key results: Survival was highest in the nonclonal species, T. erectum, most probably due to its very large carbohydrate reserves. Nutrient reserves were less affected than carbohydrate reserves by defoliation, confirming the importance of carbohydrate reserves for survival. However, faster recovery following episodes of defoliation was observed not in the species that sprouted the earliest, T. erectum, but in the clonal species, M. canadense, which had the smallest carbohydrate reserves but also a lower shoot to root ratio than the other clonal species, C. borealis. All plants that were defoliated for 2 years only partially recovered in terms of leaf area, plant biomass, and carbohydrate and nutrient reserves, confirming the overall sensitivity of these species to simulated deer herbivory. ? Conclusions: High carbohydrate reserves and consequently low shoot to root ratios appear to increase tolerance to herbivory, whereas clonal species recover faster than nonclonal species. The role played by carbohydrates reserves suggests that these species could benefit from slightly higher light conditions in areas subjected to high deer pressure.     

Environmental influences on growth and defence responses of the invasive shrub,Lonicera maackii,to simulated and real herbivory in the juvenile stage

Background and Aims

Tolerance and defence against herbivory are among the many mechanisms attributed to the success of invasive plants in their novel ranges. Because tolerance and defence against herbivory differ with the ontogeny of a plant, the effects of herbivore damage on plant fitness vary with ontogenetic stage and are compounded throughout a plant''s lifetime. Environmental stresses such as light and nutrient limitations can further influence the response of the plant. Much is known about the response of plants in the seedling and reproductive adult stages, but less attention has been given to the pre-reproductive juvenile stage.

Methods

Juvenile plants of the North American invasive Lonicera maackii were exposed to simulated herbivory under high and low light and nitrogen availability and growth, allocation patterns and foliar defensive chemistry were measured. In a second experiment, complete nutrient availability and damage type (generalist caterpillar or simulated) were manipulated.

Key Results

Juvenile plants receiving 50 % defoliation had lower total biomass and a higher root^:^shoot ratio than controls for all treatment combinations except low nitrogen/low light. Low light and defoliation increased root^:^shoot ratio. Light, fertilization and defoliation had little impact on foliar defensive chemistry. In the second experiment, there was a reduction in total biomass when caterpillar damage was applied. The root^:^shoot ratio increased under low soil fertility and was not affected by defoliation. Stem-diameter growth rates and specific leaf area did not vary by damage type or fertilization. Foliar protein increased through time, and more strongly in defoliated plants than in controls, while peroxidase activity and total flavonoids decreased with time. Overall, resource limitations were more influential than damage in the growth of juvenile L. maackii plants.

Conclusions

The findings illustrate that even when resources are limited, the tolerance and defence against herbivory of a woody invasive plant in the juvenile stage may contribute to the establishment and persistence of some species in a variety of habitats.