The impact of two gall-forming arthropods on the photosynthetic rates of their hosts

The impact of herbivores on host plant photosynthetic rates can range from negative to positive. While defoliation by chewing herbivores can result in increases in photosynthesis followed by compensatory growth, other herbivore guilds, such as mesophyll feeders which damage photosynthetic leaf tissues, almost always reduce photosynthetic rates. The impact of galling herbivores on host photosynthesis has rarely been examined, even though the limited tissue disruption and the strong metabolic sinks induced by gall-forming herbivores could potentially stimulate photosynthetic rates. I examined the hypothesis that gall-inducing herbivores could stimulate photosynthesis in neighboring leaves in response to increased sink-demand by the gall. To address this hypothesis, I measured photosynthetic rates of galled leaves or leaflets, neighboring ungalled leaves or leaflets, and ungalled leaves or leaflets on ungalled shoots on naturally growing Prunus serotina (wild cherry) and Rhus glabra (smooth sumac). The leaves of wild cherry were galled by an eriophyid mite, Phytoptus cerasicrumena; the leaves of smooth sumac by an aphid, Melaphis rhois. I found that both species reduced the photosynthetic rates of the leaves or leaflets they galled from 24 to 52% compared to ungalled leaves in ungalled areas of the plants. Contrary to my hypothesis, mite galls on wild cherry reduced photosynthesis of neighboring ungalled leaves within the same shoot by 24% compared to ungalled leaves on gall-free shoots. Aphid galls on sumac leaflets did not significantly alter the photosynthetic rates of neighboring leaflets relative to ungalled leaves on ungalled shoots. Although gall-formers would appear to have the potential to stimulate photosynthesis in the same manner as defoliating herbivores, i.e., by increasing sink demand relative to source supply, I found only negative impacts on photosynthesis. I suggest that sink competition for nutrients between developing leaves and growing gall tissue may account for the negative impacts of sink-inducing gallers on photosynthesis. Received: 17 October 1997 / Accepted: 2 February 1998     

Timing of deacclimation affects the ability to recover from simulated winter herbivory

The ability of Vaccinium myrtillus L. to recover from simulated winter herbivory has been investigated on different plants which had been exposed to three elevated temperatures (5 °C, 10 °C or 20 °C) for four weeks in a greenhouse environment. After herbivory, number and length of new aerial shoots and number of leaves/shoot increased faster in plants kept at 5 °C and 10 °C than in those kept at 20 °C. In the following autumn, however, only the shoot number differed between treatments, being greatest in plants of treatments at 5 °C and 10 °C and lowest at 20 °C and the outdoor control. Apparently the plants kept at 20 °C had already used their resources for growth before herbivory simulation, which reduced their recovery ability thereafter. In addition, the growing season was too short for the control plants to produce as many new shoots as the treatments. The results show that the recovery of V. myrtillus from winter herbivory is rapid if it occurs before growth has started. Hence the earlier onset of spring as a consequence of climate warming may not be fatal for the plant, unless the temperature increase triggers growth to start many months earlier than normal.     

Relationships between the effects of insect herbivory and sheep grazing on seasonal changes in an early successional plant community

Summary The effects of spring grazing by sheep and of natural levels of insect herbivory were studied in 1985 on a limestone field abandoned from arable land for four years. A split-plot design was adopted in which paddocks, arranged in Latin squares, were either left ungrazed or heavily grazed by sheep for ten days in April. Within each paddock plots were either sprayed regularly with Malathion-60 or untreated.Natural levels of insect herbivory, compared to the reduced levels in insecticide-treated plots, had effects of similar magnitude to those from the short burst of spring grazing. Many attributes of the grazed/insecticide-treated sward were either increased or decreased by a factor of two within a season. Both types of herbivore caused changes in the direction of plant succession as well as in its rate. Effects on early successional species were large and similar when caused by either type of herbivore. Effects on later successional species were often smaller, but also showed differences in the action of the two herbivore types, as did effects on sward height, species richness and total cover. The effects of sheep and insect herbivory were not always additive or in the same direction.The results suggest that manipulations of both mammal and insect herbivores may be powerful tools for directing changes in plant community composition.     

Comparison of photosynthetic damage from arthropod herbivory and pathogen infection in understory hardwood saplings

Arthropods and pathogens damage leaves in natural ecosystems and may reduce photosynthesis at some distance away from directly injured tissue. We quantified the indirect effects of naturally occurring biotic damage on leaf-level photosystem II operating efficiency (Φ_PSII) of 11 understory hardwood tree species using chlorophyll fluorescence and thermal imaging. Maps of fluorescence parameters and leaf temperature were stacked for each leaf and analyzed using a multivariate method adapted from the field of quantitative remote sensing. Two tree species, Quercus velutina and Cercis canadensis, grew in plots exposed to ambient and elevated atmospheric CO₂ and were infected with Phyllosticta fungus, providing a limited opportunity to examine the potential interaction of this element of global change and biotic damage on photosynthesis. Areas surrounding damage had depressed Φ_PSII and increased down-regulation of PSII, and there was no evidence of compensation in the remaining tissue. The depression of Φ_PSII caused by fungal infections and galls extended >2.5 times further from the visible damage and was ∼40% more depressed than chewing damage. Areas of depressed Φ_PSII around fungal infections on oaks growing in elevated CO₂ were more than 5 times larger than those grown in ambient conditions, suggesting that this element of global change may influence the indirect effects of biotic damage on photosynthesis. For a single Q. velutina sapling, the area of reduced Φ_PSII was equal to the total area directly damaged by insects and fungi. Thus, estimates based only on the direct effect of biotic agents may greatly underestimate their actual impact on photosynthesis.     

长白山常绿针叶树越冬期间光合能力的抑制

在长白山地区以红皮云杉、樟子松为材料,研究其冬季光合能力的变化,探讨了除红松外的其它针叶树是否在冬季也存在光合抑制以及遮荫是否可减轻抑制等问题,结果表明,红皮云杉、樟子松有与红松相似的冬季光合抑制,但程度较轻;遮荫对减轻光合抑制非常有效,可以推测,在长白山地区或冬季气候与之相似的地区,常绿针叶树在冬季均可能表现光合抑制,遭受冬季光氧化伤害,并且其释放的ＣＯ２（光越强,释放量越大）是空气中ＣＯ２含量     

Relative herbivory tolerance and competitive ability in two dominant : subordinate pairs of perennial grasses in a native grassland

We evaluated herbivory tolerance and competitive ability within twodominant : subordinate pairs of C₄, perennial grasses at each of twosites to determine the contribution of these processes to herbivore-inducedspecies replacement. Herbivory tolerance was assessed by cumulative regrowthfrom defoliated plants of each species and competitive ability was evaluated byrelative uptake of a ¹⁵N isotope placed into the soil between pairedspecies in the field. Herbivory tolerance was similar for the dominant andsubordinate species in both plant pairs and defoliation intensity had a greaterinfluence on herbivory tolerance than did defoliation pattern. Both specieswithin the Sorghastrum nutans : Schizachyriumscoparium pairs exhibited comparable nitrogen acquisition from a¹⁵N enriched pulse with or without defoliation. In contrast,S. scoparium acquired more ¹⁵N than did itssubordinate neighbor, Bothriochloa laguroides when thisspecies pair was undefoliated. Uniform defoliation of this species pair at adefoliation intensity removing 70% of the shoot mass accentuated this responsefurther demonstrating the greater competitive ability of the dominant comparedto the subordinate species. Although the 90% defoliation intensity reducednitrogen acquisition by the dominant relative to the subordinate species,B. laguroides, it did not reduce nitrogen acquisition bythe dominant below that of the subordinate neighbor. The occurrence of similarherbivory tolerance among dominant and subordinate species indicates thatselective herbivory suppressed the greater competitive ability, rather than thegreater herbivory tolerance, of the dominant grasses in this experimentaldesign. These data suggest that interspecific competitive ability may be ofequal or greater importance than herbivory tolerance in mediatingherbivore-induced species replacement in mesic grasslands and savannas.     

Competitive ability of the bunchgrass Schizachyrium scoparium as affected by grazing history and defoliation

Herbivory by large animals is known to function as a selection pressure to increase herbivory resistance within plant populations by decreasing the frequency of genotypes possessing large, erect canopies. However, the increase in herbivory resistance of the remaining genotypes in the population may potentially involve a tradeoff with competitive ability. The perennial bunchgrass Schizachyrium scoparium was grown in a transplant garden to test the hypothesis that late successional plant populations with a history of grazing are at a competitive disadvantage relative to conspecific populations with no history of grazing were found to possess a greater competitive ability than plants with no grazing history in the absence of herbivory. This unexpected response resulted from the capacity of plants with a history of grazing to recruit a greater number of smaller tillers than did plants with no grazing history. This response was only significant when plants with a history of grazing were nondefoliated and grown with the weakest of the mid-successional competitors, indicating that both defoliation and intense interspecific competition can mask the architectural expression of herbivore-induced selection. Individual tillers did not display any architectural differences between plants with contrasting grazing histories other than mean tiller weight. These data confirm that herbivory by domestic cattle may function as a selection pressure to induce architectural variation in grass populations within an ecological time frame (ca <-25 yrs).     

Impact of herbivory and pollination on performance and competitive ability of oilseed rape transformed for pollen beetle resistance

Competitive ability of transgenic oilseed rape transformed with a pea lectin gene was estimated by comparisons of its performance when grown in a mixture with its non-transgenic counterpart and when grown singly, with and without pollen beetles present. The experiments were carried out in cages, once with bumblebees as pollinators and once without. In the absence of herbivory but with the presence of bumblebees, singly grown plant lines without lectin generally performed better than lines with lectin. Pollen beetles affected plant growth and reproduction, but there were no consistent differences between the lectin and non-lectin plant lines indicating that the transgenic trait did not protect plants from pest attack. Herbivory reduced the number of seeds when bumblebees were present. In the absence of bumblebees, however, plants produced more seeds with pollen beetles than without, indicating that some pollination was carried out by the beetles. Efficient pollination affected the competitive abilities of the lines; lectin lines were more competitive with bumblebees present and the reverse was true when bumblebees were absent. In the presence of bumblebees, lectin lines gained from being grown mixed with its non-transgenic counterpart. Because the transgenic plants expressed pea lectin in developing pollen it is possible that pollen quality in those plants was reduced, which may explain why the lectin lines had an advantage over non-lectin lines when exchange of pollen between the two plant types was facilitated by bumblebees.     

Variation in Cnidoscolus texanus in relation to herbivory

Summary Twelve Oklahoma populations of Cnidoscolus texanus were investigated for morphological variation between and within populations, and between site classes with contrasting histories of use by domesticated livestock. Characters scored were numbers of stinging hairs on petioles and midribs, and depth of leaf lobing. Leaf lobing was not significantly variable within or among populations or grazing categories. Stinging hair numbers showed significant differences within and among populations. Petiole stinging hairs were more numberous in heavily grazed sites, suggesting population differentiation in response to the selective pressures of herbivory.     

Interactions between herbivory and resource availability on grazing tolerance of Leymus chinensis

Herbivory and resource interact to influence plant regrowth following grazing, but few detailed investigations on grazing tolerance at population levels are available. We conducted two pot experiments along a simulated grazing gradient (0%, 25%, 50% and 75% of shoot removal) at three water or nutrient levels to determine the interaction of resource and herbivory on Leymus chinensis, a perennial, dominant species in the eastern Eurasian steppes. Interactions between water availability and clipping intensity on the relative height growth rate (RHGR) and bud number were significant. Significant interactions between nutrient and clipping on RHGR, total biomass and specific leaf area (SLA) were also found. Total biomass and bud number, showing a unimodal curve along the clipping gradient in resource-rich environments, were highest at light clipping level, suggesting that this species has the plastic compensatory responses from under- to overcompensation. Interactions between herbivory and water or nutrient were opposite to each other. The “cooperative” interactions between water and herbivory magnified the difference in grazing tolerance of L. chinensis between high and low water treatments. The “antagonistic” interactions between nutrient and herbivory, on the other hand, were reflected in the lower tolerance to heavy clipping in the high nutrient than low nutrient treatments. Results partly support the limiting resource model (LRM). A modified and simplified graphic model of the LRM was proposed based on our results. The new LRM clearly demonstrated that “cooperative” interactions between varying water levels and clipping intensities aggravate the detrimental impacts of herbivores on plant growth and reproduction, whereas “antagonistic” interactions between nutrient and grazing alleviate the negative effects of herbivores. Biomass compensation and density compensation were identified as main mechanisms of herbivory tolerance in this clonal species.     

Injured and uninjured leaf photosynthetic responses after mechanical injury on <Emphasis Type="Italic">Nerium oleander</Emphasis> leaves,and <Emphasis Type="Italic">Danaus plexippus</Emphasis> herbivory on <Emphasis Type="Italic">Asclepias curassavica</Emphasis> leaves

Insect herbivory has variable effects on plant physiology; so greater understanding is needed about how injury alters photosynthesis on individual injured and uninjured leaves. Gas exchange and light-adapted leaf chlorophyll fluorescence measurements were collected from uninjured and mechanical partial leaf defoliation in two experiments with Nerium oleander (Apocynaceae) leaves, and one experiment with Danaus plexippus herbivory on Asclepias curassavica (Asclepiadaceae) leaves. Gas exchange impairment (lower photosynthetic rate (P _n ), stomatal conductance (g _s)) indicates water stress in a leaf, suggests stomatal limitations causing injury P _n impairment. The same pattern of gas exchange impairment also occurred on uninjured leaves opposite from injured leaves in both N. oleander experiments. This is an interesting result because photosynthetic impairment is rarely reported on injured leaves near injured leaves. No photosynthetic changes occurred in uninjured A. curassavica leaves opposite from D. plexippus-fed leaves. Partially defoliated leaves that had P _n and g _s reductions lacked any significant changes in intercellular leaf [CO₂], C _i. These results neither support, nor are sufficient to reject, stomatal limitations to photosynthesis. Manually imposed midrib vein severance in N. oleander experiment #1 significantly increased leaf C _i, indicating mesophyll limitations to photosynthesis. Maximal light-adapted leaf photochemical efficiency () and also non-photochemical quenching (q _N) were reduced by mechanical or insect herbivory to both study species, suggesting leaf trouble handling excess light energy not used for photochemistry. Midrib injury on N. oleander leaves and D. plexippus herbivory on A. curassavica leaves also reduced effective quantum yield (ΦPSII) and photochemical quenching (q _P); so reduced plastoquinone pools could lead to additional PSII reaction center closure.     

Phenology and photosynthetic activity in sterile and fertile sporophytes of Dryopteris filix-mas (L.) Schott

Summary This study describes the phenology of sporophytes of the fern Dryopteris filix-mas in relation to whole plant development. Sterile and fertile potted sporophytes were set out at an exposed site and the seasonal development of the fronds was measured from the commencement of unfolding, through the phase of increasing length, up to discoloration. The physiological activity of the fronds was determined by measuring photosynthetic gas exchange. The fronds of sterile sporophytes unfolded in April, about a week earlier than those of fertile plants, but the colour had already begun to turn in September and their life span was 1–2 months shorter. However, between mid-June and the end of August the sterile sporophytes put out several sets of new fronds: these overwintered without changing color and were still photosynthetically active in the following spring. All types of fronds were fully expanded 1–2 months from the beginning of unfolding and, with a natural supply of CO₂, had similar maximum net photosynthetic rates of 8–9 mol/m² · s. The decline in photosynthetic performance began before symptoms of senescence were visible and was due to decreased efficiency of the mesophyll. It is concluded that the phenology of D. filix-mas changes with transition from the sterile to the fertile phase. Whereas fertile sporophytes are genuinely summergreen, the sterile sporophytes with their summer fronds remain green throughout the winter and should therefore be termed semi-evergreen. The formation of overwintering summer shoots clearly extends the period of photosynthetic productivity of sterile sporophytes.     

Timing of reproduction in a prairie legume: seasonal impacts of insects consuming flowers and seeds

Summary Seasonal patterns of insect damage to reproductive tissue of the legume Baptisia australis were studied for three years in native tallgrass priairie. Contrasting seasonal patterns of damage were associated with the major species of insect consumers. The moth Grapholitha tristegana (Olethreutidae) and the weevil Tychius sordidus (Curculionidae), which together infested 80–100% of developing fruits (pods), consistently damaged more seeds on average in early than in late maturing pods. But while late opening flowers were less subject to attack from moths and weevils, they were more subject to attack from chewing insects, particularly blister beetles (Epicauta fabricii, Meloidae), which destroyed >80% of all flowers and developing young pods (including moth and weevil larval inhabitants). The blister beetles arrived late in the flowering season and fed particularly on young reproductive tissue, allowing larger, older pods that had developed from early opening flowers to escape destruction. The relative abundances and impacts of blister beetles, moths, and weevils varied from year to year. Adding to the uncertainty of reproductive success of the host plant were the large and variable amounts of damage to immature buds inflicted by insects (including the blister beetles and weevil adults) and late killing frosts. Thus, timing of flowering is critical to success in seed production for B. australis. The heavy impacts of insects and weather can result in a very narrow window in time (which shifts from year to year) during which B. australis can flower with any success. The opposing pressures exerted by insects and weather on floral reproductive success may act in concert with other features of the plant's biology to foster the maintenance of considerable diversity in flowering times among individuals in local populations of B. australis.     

Variation in Arundo donax stem and leaf strength: Implications for herbivory

We determined leaf and stem strength for Arundo donax from plants grown in different geographic areas and at different times within their growing cycle. Mean leaf strength for plants collected within California was 1.72 Newtons (N) and ranged from 0.36 to 6.32 N, based on 1170 individual determinations. For leaves collected from 30 plants within four states between July 11 and 20, 2007, mean leaf strength was 1.58 N based on 936 determinations. Values ranged from 0.24 to 4.90 N. Overall, leaf strength showed statistically significant changes depending on the sampling date, sampling location, type of leaf sampled, and position within the leaf where the measurement was taken. In general leaf strength was greater near the base of the leaf and decreased with distance away from the base; leaf strength changed as the growing season progressed; and first year leaves had leaf strength values about 25% greater than leaves produced on stems >1-year old. This represents two of the three age categories of leaves which may be present on giant reed at any one time. Stem strength and stem wall thickness were strongly correlated (Kendall's Tau b = 0.92, P < 0.0001, N = 26). Linear regression indicated that mean stem strength decreased by approximately 6.8% (95% confidence limits 5.8-7.7%) from one node to the successive node progressing from the stem base to the shoot tip. These results imply that the ability of biological control agents to damage A. donax leaves may not be the same across the locations this plant occurs or at all times during the growing season within a given location.     

Denitrification in a semi-arid grazing ecosystem

The effect of large herbivores on gaseous N loss from grasslands, particularly via denitrification, is poorly understood. In this study, we examined the influence of native migratory ungulates on denitrification in grasslands of Yellowstone National Park in two ways, by (1) examining the effect of artificial urine application on denitrification, and (2) comparing rates inside and outside long-term exclosures at topographically diverse locations. Artificial urine did not influence denitrification 3 and 12 days after application at hilltop, mid-slope, and slope-bottom sites. Likewise, grazers had no effect on community-level denitrification at dry exclosure sites, where rates were low. At mesic sites, however, ungulates enhanced denitrification by as much as 4 kg N ha⁻¹ year⁻¹, which was double atmospheric N inputs to this ecosystem. Denitrification enzyme activity (DEA, a measure of denitrification potential) was positively associated with soil moisture at exclosure sites, and herbivores stimulated DEA when accounting for the soil moisture effect. Glucose additons to soils increased denitrification and nitrate additions had no influence, suggesting that denitrification was limited by the amount of labile soil carbon, which previously has been shown to be enhanced by ungulates in Yellowstone. These results indicate that denitrification can be an ecologically important flux in portions of semi-arid landscapes, and that there is a previously unsuspected regulation of this process by herbivores. Received: 6 March 1998 / Accepted: 28 August 1998     

Spiny east Mediterranean plant species flower later and in a drier season than non-spiny species

We compared the flowering phenology of spiny and non-spiny native species belonging to three families (Asteraceae, Fabaceae and Lamiaceae), which include the highest number of spiny species in the flora of Israel. We found that the peak of flowering (when the highest number of species flowered) was 4–8 weeks later for spiny species than for non-spiny species. The flowering peak of non-spiny species was in late March, while that of spiny species was at the beginning of May. The seasonal shift in flowering time from the main season, when most Mediterranean plants bloom, to the end of the flowering season, when fewer species bloom, might be the evolutionary result of a change in phenology reducing the competition for pollinators. Our results clearly indicate that spinescence of plants in the semi-arid east Mediterranean region is associated with a delayed flowering season at the beginning of the dry summer when most of the herbaceous vegetation is already dry. During this season, mammalian grazers consume any edible herbaceous vegetation, selecting for late flowering species that allocate more resources for anti-herbivore defenses than early flowering species. There is a well-known global geographical trend where the occurrence of spiny plants is higher in arid regions than in humid ones. In parallel to the global trend, we show a seasonal one, that non-spiny plants grow and flower in the spring, which is the main flowering season in the Mediterranean basin, while spiny plants flower later, in the hot and dry summer. Under the current trend of global warming, there are prospects of future increase in the dominance of spiny species in the Mediterranean region.     

Mistletoes: a hypothesis concerning morphological and chemical avoidance of herbivory

Summary Leaves from many misletoe species in Australia strongly resemble those of their hosts. This cryptic mimicry has been hypothesized to be a means of reducing the likelihood of mistletoe herbivory by vertebrates. Leaf Kjeldahl nitrogen contents (a measure of reduced nitrogen and thus amines, amino acids and protein levels) of mistletoes and their hosts were measured on 48 mimetic and nonmimetic host-parasite pairs to evaluate hypotheses concerning the significance of crysis versus noncrypsis. The hypothesis that mistletoes mimicking host leaves should have higher leaf nitrogen levels than their hosts is supported; they may be gaining a selective advantage through crypsis (reduced herbivory). The second hypothesis that mistletoes which do not mimic their hosts should have lower leaf nitrogen levels than their hosts is also supported; they may be gaining a selective advantage through noncrypsis (reduced herbivory resulting from visual advertisement of their reduced nutritional status).     

Some observations of phenology and ecophysiology ofDaphne kamtschatica Maxim.var.jezoensis (Maxim.) Ohwi, a shade deciduous shrub, in the forest of northern Japan

The phenology and leaf traits ofDaphne kamtschatica Maxim. var.jezoensis (Maxim.) Ohwi, the only summer deciduous shrub (20–40 cm) in the temperate forest of northern Japan, are examined. This plant carries through the winter mature leaves and well formed flower buds. It flowers in early spring during snowmelt and begins photosynthesis under relatively high irradiance under an open forest canopy. Our results show that there is significant carbon gain during the period when new leaves and fruit maturation also take place. Beginning in June, as the forest canopy closes, leaves onDaphne shoots senesce acropetally and the plants become completely bare in mid-July. After a period of 20-day dormancy, the shoots begin to resprout. Leaves become mature in early October and remain on the stem over winter. Leaf traits and photosynthesis measurements suggest as follows. 1) By becoming summer deciduous,D. kamtschatica avoids the cost of maintaining leaves inefficient under deep shade. 2) The onset and breaking of the summer dormancy is triggered by photoperiod since plants at the forest edge also become dormant even when light remained relatively high. However, the decreased duration of dormancy with higher light levels suggests that there is a tendency towards shorter dormancy where summer shade is absent and this could eventually lead to an evergreen habit such as that found in the alpine speciesDaphne miyabeana.     

Seasonality of herbivory and communication between individuals of sagebrush

Seasonal changes in herbivore numbers and in plant defenses are well known to influence plant–herbivore interactions. Some plant defenses are induced in response to herbivore attack or cues correlated with risk of attack although seasonal variation in these defenses is relatively poorly known. We previously reported that sagebrush becomes more resistant to its herbivores when neighboring plants have been experimentally clipped with scissors. In this study we asked whether herbivory to leaves of sagebrush varied seasonally and whether there was seasonal variation in natural levels of damage when neighbors were clipped. We found that sagebrush accumulated most chewing damage early in the season, soon after the spring flush of new leaves. This damage was caused by generalist grasshoppers, deer, specialist caterpillars, beetles, gall makers, and other less common herbivores. Sagebrush showed no evidence of preferentially abscising leaves that had been experimentally clipped. Experimental clipping by Trirhabda pilosa beetle larvae caused neighbors to accumulate less herbivore damage later that season, similar to results in which clipping was done with scissors. Induced resistance caused by experimentally clipping a neighbor was affected by season; plants with neighbors clipped in May accumulated less damage throughout the season relative to plants with unclipped neighbors or neighbors clipped later in the summer. We found a correlation between seasonal herbivore pressure, damage accumulated by plants, and induced responses to experimentally clipping neighbors. The causal mechanisms responsible for this correlation are unknown although a strong seasonal effect was clear.     

Phenolics,nutrition and insect herbivory in some garrigue and maquis plant species

Summary Garrigue plant species growing on a calcareous substrate in southern France had higher foliar N levels than the same species growing on a relatively lower nutrient siliceous substrate (maquis). However maquis species had significantly higher foliar levels of P, more water, higher phenolic concentrations and larger leaf areas. The cumulative amount of insect damage on garrigue and maquis plants was similar, presumably due to different nutritional advantages in each case. Soil fertilization signifincantly elevated N levels in Q. coccifera, increased total leaf areas, decreased condensed tannin levels, and these leaves showed significantly more insect damage. Some effects of burning on Q. coccifera are also described. In these shrublands, fertilization may render leaf material more nutritional for herbivores by increasing nitrogen content and decreasing condensed tannin concentration, although very heavy grazing pressure may increase levels of leaf phenolics.