Potential host plants of Corythucha arcuata (Het., Tingidae) in Europe: a laboratory study

Abstract:  The oak lace bug Corythucha arcuata (Say) (Het., Tingidae), native to North America, was found in Europe on Quercus robur L. and other oaks in the spring of 2000. The potential host plant range of this species in Europe and its development time were investigated in a laboratory study. An assay was performed on leaf cuts of different plant species. On the deciduous European oaks ( Q. robur , Quercus pubescens Willd, Quercus petraea (Mattuschka) Liebl., Quercus cerris L.), as well as Rubus ulmifolius Schott. and Rubus idaeus L., most of the lace bugs (>50%) reached the adult stage; on Castanea sativa Mill., Rubus caesius L. and Rosa canina L., a reduced number of individuals (<25%) reached the adult stage. No nymphs survived on Quercus rubra L. (mentioned in literature as a host plant), on the evergreen oaks Quercus suber L. and Quercus ilex L., on Malus domestica Borkh. and four tested maple species. On plant species where the lace bug reached the adult stage, the development time varied from 13 to 27 days. On European deciduous oak species, the development time was longer on leaves taken in late summer (September) than on those of late spring (June); on the contrary, such differences were not observed on Rubus species, and Castanea sativa .     

Nitric oxide is involved in dehydration/drought tolerance in Poncirus trifoliata seedlings through regulation of antioxidant systems and stomatal response

Nitric oxide (NO) is a component of the repertoire of signals implicated in plant responses to environmental stimuli. In the present study, we investigated the effects of exogenous application of NO-releasing donor sodium nitroprusside (SNP) and nitric oxide synthase inhibitor N ^G-nitro-l-arginine-methyl ester (l-NAME) on dehydration and drought tolerance of Poncirus trifoliata. The endogenous NO level was enhanced by SNP pretreatment, but decreased by l-NAME, in the hydroponic or potted plants with or without stresses. Under dehydration, leaves from the SNP-treated hydroponic seedlings displayed less water loss, lower electrolyte leakage and reactive oxygen species accumulation, higher antioxidant enzyme activities and smaller stomatal apertures as compared with the control (treated with water). In addition, pretreatment of the potted plants with SNP resulted in lower electrolyte leakage, higher chlorophyll content, smaller stomatal conductance and larger photosynthetic rate relative to the control. By contrast, the inhibitor treatment changed these physiological attributes or phenotypes in an opposite way. These results indicate that NO in the form of SNP enhanced dehydration and drought tolerance, whereas the inhibitor makes the leaves or plants more sensitive to the stresses. The stress tolerance by NO might be ascribed to a combinatory effect of modulation of stomatal response and activation of the antioxidant enzymes. Taken together, NO is involved in dehydration and drought tolerance of P. trifoliata, implying that manipulation of this signal molecule may provide a practical approach to combat the environmental stresses.     

Probability of tree seedling establishment changes across a forest-old field edge gradient

Forest edges affect many aspects of plant communities, causing changes in microclimate, species composition, and community structure. However, the direct role of edges in regulating forest regeneration is relatively unknown. The pattern of tree establishment across a forest-old field edge was experimentally examined to determine the response of three tree species to the edge gradient. We placed 100 1-m(2) plots in a 90 × 90 m grid that began 30 m inside the forest, extended across the edge, and ended at 60 m into the old field. Into each plot, we planted seeds of Acer rubrum, Acer saccharum, and Quercus palustris. Emergence increased with distance into the field for both A. saccharum and Q. palustris. Emergence for A. rubrum increased from forest to field, reaching a maximum near 20 m into the field, and then declined with further distance. Nearly all A. rubrum seedlings died shortly after emergence. Survival of A. saccharum increased with distance into the old field, while survivorship of Q. palustris did not respond to the edge gradient. Establishment probabilities increased with distance into the old field for both A. saccharum and Q. palustris. Growth of Q. palustris and allocation patterns of A. saccharum also varied across the edge gradient. These results suggest that edges have complex, species-specific effects on tree establishment and growth that can influence the spatial pattern and species composition of regenerating forests.     

Differential accumulation of water stress-related proteins, sucrose synthase and soluble sugars in Populus species that differ in their water stress response

Proteins inducible by dehydration and abscisic acid (ABA), have been identified in a number of species and have been suggested to play a role in desiccation tolerance. Recently, we identified a novel boiling-stable protein (BspA) which accumulated in shoots of aspen ( Populus tremula L.) cultured in vitro, in response to gradual water stress and ABA application (Pelah et al. 1995. Tree Physiol. 15: 673–678.). Accumulation of BspA, and of the water stress-related protein dehydrin dsp- 16 and sucrose synthase from the resurrection plant. Craterostigma plantagineum , was examined in two greenhouse-grown Populus species to investigate the relationship between the presence of the proteins and water stress tolerance. Detached leaves of Populus tomentosa lost more water than Populus popularis , resulting in a significant decrease in leaf water potential. Using electrolyte leakage analysis, it was found that detached leaves of Populus popularis are more tolerant to water stress than those of Populus tomentosa . Using western blots with the corresponding antibodies, we have found in Populus popularis accumulation of BspA and sucrose synthase due to water stress, and the constitutive presence of a dehydrin-like protein. In contrast, a low expression of BspA was found in Populus tomentosa , but not of sucrose synthase and dehydrin-like proteins. Desiccation tolerance in many tissues can be partly attributed to soluble sugars. Analysis of the amount of soluble sugars did not reveal clear-cut differences between the two species, except for significant sucrose accumulation and glucose reduction in water-stressed Populus tomentosa and increase in glucose in water-stressed Populus popularis . The data obtained points to a positive correlation between increased water stress tolerance of one poplar species as compared with another and accumulation of water stress-related proteins and sucrose synthase.     

Carbon dioxide assimilation of hardwood seedlings in relation to community dynamics in central illinois

Summary Field measurements of net assimilation and respiration for seedlings of four hardwood species were made periodically over a growing season with soil moisture tension maintained between 0 and 0.75 bar. Total net assimilation per day was significantly greater for Acer saccharum than either Quercus rubra or Quercus alba and for Quercus macrocarpa as compared with Q. rubra, when measurements were made under natural shade conditions and light intensity varied from 80 to 120 ft-c. Mean light compensation points determined under canopy shade were 50.3, 53.5, 87.2, and 102.5 ft-c., respectively, for Acer saccharum, Quercus macrocarpa, Q. rubra, and Q. alba. In a 0.04-hectare canopy opening, total net assimilation per day was not significantly different between Q. rubra, Q. alba, and A. saccharum but was significantly greater for Q. macrocarpa than Q. alba and A. saccharum. Relationships between photosynthetic efficiency and successional characteristics of these species are inferred from the data.     

Foliar dehydration tolerance of twelve deciduous tree species

The potential for foliar dehydration tolerance and maximum capacity for osmotic adjustment were compared among 12 temperate, deciduous tree species, under standardized soil and atmospheric conditions. Dehydration tolerance was operationally defined as lethal leaf water potential (); the of the last remaining leaves surviving a continuous, lethal soil drying episode. Nyssa sylvatica Marsh., and Liriodendron tulipifera L. were most sensitive to dehydration, having lethal leaf of -2.04 and -2.38 MPa, respectively. Chionanthus virginicus L., Quercus prinus L., Acer saccharum Marsh., and Quercus acutissima Carruthers withstood the most dehydration, with leaves not drying until leaf dropped to -5.63 MPa or below. Lethal leaf (in MPa) of other, intermediate species were: Quercus rubra L. (-3.34), Oxydendrum arboreum (L.) D.C. (-3.98), Halesia carolina L. (-4.11), Acer rubrum L. (-4.43), Quercus alba L. (-4.60), and Cornus florida L. (-4.88). Decreasing lethal leaf was significantly correlated with increasing capacity for osmotic adjustment. C. virginicus and Q. acutissima showed the most osmotic adjustment during the lethal soil drying episode, with osmotic potential at full turgor declining by 1.73 and 1.44 MPa, respectively. Other species having reductions in osmotic potential at full turgor exceeding 0.50 MPa were (in MPa) Q. prinus (0.89), A. saccharum (0.71), Q. alba (0.68), H. carolina (0.67), Q. rubra (0.60), and C. florida (0.52).     

Seasonal variation in native hydraulic conductivity between two deciduous oak species

植物抗旱性机制包括耐旱性和避旱性。耐旱性的特征主要是木质部易栓塞性和膨压损失点,而避旱性的特征则是叶片脱落和落叶性。虽然这些机制可以权衡物种连续性,但对于干旱引发的叶片脱落和持续时间的变化如何影响木质部和叶片耐受性之间的关系却知之甚少。在本研究中,我们研究两种具有不同叶片脱落叶行为的橡树(栎属)的耐旱性程度差异。我们预测了Quercus deserticola 在旱季结束时落叶(晚落叶)而面临更大的空化风险,导致其比Q. laeta更耐旱,对水分的利用也更加保守。Q. laeta 只在旱季中期很短的时间内落叶(短落叶)。本研究在墨西哥中部进行,两种橡树各具有单个种群,它们之间相距1.58公里,海拔差为191米。Q. deserticola (晚落叶)多出现在下坡,而Q. laeta (短落叶)多出现在沿坡度海拔较高的地方。我们评估了样地内茎干的水分传导率的季节差异(雨季和旱季),并检测了两个物种间木质部对空化的脆弱性、叶片水分利用和叶片膨松损失点的差异。两种橡树在耐旱性状方面没有显著差异,主要包括木质部易栓塞性、叶片膨松损失点和气孔导度。然而,两种植物在旱季都有不同的表现：短落叶植物对木质部功能的负面影响要比晚落叶植物低。综上所述,两种橡树在植物生理性能方面的季节变化取决于冠层叶面积的减少。     

Tradeoffs between functional strategies for resource-use and drought-survival in Mediterranean rangeland species

In environments where light is not a limiting resource such as rangelands and grasslands, there is much disagreement regarding the benefits provided by rapid light capture during the growing season and the species’ ability to withstand drought during the dry period. In this study, we selected four perennial herbaceous species with contrasting resource-use strategies (acquisitive versus conservative), which were transplanted as monocultures into PVC pots to evaluate their species-specific responses to drought. The two main strategies of drought-survival (avoidance versus tolerance) were driven by distinct underlying mechanisms that allow the plant to delay or tolerate water deficit in leaves. On the one hand, plants that produced reduced leaves with lower surface area:mass ratio (lower SLA) exhibited higher values of leaf water potential (LWP) and leaf relative water content (LRWC), which could be associated to a higher ability to delay tissue dehydration in enlarged leaves. Regarding the below-ground compartment, dehydration avoidance was promoted by prolonged elongation rates of thinner roots that allow the plant to increase water uptake and accessibility during the dry period. On the other hand, dehydration tolerance was positively related with progressive foliage senescence under water deficit, which probably favored a longer survival of meristematic basal tissues. The results presented in this study suggest the existence of a trade-off between the traits favoring rapid light-acquisition and those enhancing the ability to delay leaf dehydration. Thus, the species related most closely with a resource-acquisition strategy (Bromus erectus and Potentilla neumanniana) could be considered less efficient to delay leaf dehydration than the others (Carex humilis and Festuca christiani-bernardii), as indicated by their lower values of leaf water potential (LWP) and leaf relative water content (LRWC) under identical conditions of water deficit. Our findings support evidence that there is not a single strategy to effectively cope with drought and reveal the diversity of adaptive mechanisms among coexisting species.     

Patterns of intra- and interspecific association in leaf-mining insects on three oak host species

Abstract. 1. We determined mortality and distributional patterns of leaf miners on three oak host species (Quercus falcata, Q.nigra and Q.hemisphaerica) in northern Florida, U.S.A.
2. Patterns of intra- and interspecific occurrence within leaves, and mortality of five most abundant leaf miner species were analysed as a test of competition.
3. Miners co-occurred on leaves more often that expected by chance (P<0.05) in six of ten possible species combinations and log-linear model analysis showed no negative higher-order interactions.
4. All five miner species had highly clumped distributions between leaves (P<0.01).
5. Leaf miner survival was less than expected for four of five species when co-occurring on leaves with conspecifics than when mining with heterospecifics or alone (P<0.05).
6. We conclude that interspecific competition is unapparent within this leaf miner guild and that intraspecific competition occurs in four of the five major leaf miner species. We discuss leaf miner selection of common leaves, perhaps based on chemical/physical leaf characters, as a cause of intra- and interspecific aggregation.     

The major veins of mesomorphic leaves revisited: tests for conductive overload in Acer saccharum (Aceraceae) and Quercus rubra (Fagaceae)

Many leaves survive the severing of their major veins in apparently excellent health. According to the classical explanation, the leaf minor veins provide "conductive overload," an excess of parallel conductive paths, rendering the major veins hydraulically dispensable. Whether such an excess of conductive paths exists has important implications for vascular design and for leaf response to vascular damage. We subjected leaves of Acer saccharum and Quercus rubra to cutting treatments that disrupted the major vein system and determined leaf survival, stomatal conductance (g), quantum yield of photosystem II (Φ(PSII)), and leaf hydraulic conductance (K(leaf)). For A. saccharum, the cuts led to the death of distal lamina. For Q. rubra, however, the treated leaves typically remained apparently healthy. Despite their appearance, the treated Q. rubra leaves had a strongly reduced K(leaf), relative to control leaves, and g and Φ(PSII) were reduced distal to the cuts, respectively, by 75-97% and 48-76%. Gas exchange proximal to the cuts was unaffected, indicating the independence of lamina regions and their local stomata. Analogous results were obtained with excised Q. rubra leaves. These studies demonstrate an indispensable, vital role of the major veins in conducting water throughout the lamina.     

Stress resistance levels at the time of lifting affect post-planting performance of Quercus robur seedlings

The objective of this study was to describe the physiological condition of bare-root pedunculate oak (Quercus robur L.) seedlings at the time of lifting for cold storage or planting in 1996/1997 and 1997/1998. Dormancy intensity and other physiological measurements and field performance were assessed. Heat treatments were used to assess the taproot resistance to stress using root electrolyte leakage, but the results indicated that the plants were least resistant when mostdormant. Root electrolyte leakage and root growth potential were lowest during the deep dormancy stage and increased again as shoot dormancy was released, coinciding with the period that the plants were most resistant to storage stresses. Dry weight fraction of the shoots was a good indicator of storability, but the other measures were less useful. Despite good survival rates, shoot quality was poor for seedlings lifted early (October) or late (April, May) in the lifting season.     

Evidence for xylem embolism as a primary factor in dehydration-induced declines in leaf hydraulic conductance

Hydraulic conductance of leaves (K(leaf)) typically decreases with increasing water stress and recent studies have proposed different mechanisms responsible for decreasing K(leaf) . We measured K(leaf) concurrently with ultrasonic acoustic emissions (UAEs) in dehydrating leaves of several species to determine whether declining K(leaf) was associated with xylem embolism. In addition, we performed experiments in which the surface tension of water in the leaf xylem was reduced by using a surfactant solution. Finally, we compared the hydraulic vulnerability of entire leaves with the leaf lamina in three species. Leaf hydraulic vulnerability based on rehydration kinetics and UAE was very similar, except in Quercus garryana. However, water potentials corresponding to the initial decline in K(leaf) and the onset of UAE in Q. garryana were similar. In all species tested, reducing the surface tension of water caused K(leaf) to decline at less negative water potentials compared with leaves supplied with water. Microscopy revealed that as the fraction of embolized xylem increased, K(leaf) declined sharply in Q. garryana. Measurements on leaf discs revealed that reductions in lamina hydraulic conductance with dehydration were not as great as those observed in intact leaves, suggesting that embolism was the primary mechanism for reductions in K(leaf) during dehydration.     

Timing is everything? Phenological synchrony and population variability in leaf‐chewing herbivores of Quercus

Abstract.  1. Specialization on ephemeral resources (e.g. new leaves) should produce large annual variation in herbivore population size when the timing of availability of those resources is unpredictable. Despite considerable evidence for impacts of synchrony with budburst on survival of larval Lepidoptera, previous studies of adult Geometridae and Noctuidae found no correlations between insect phenology and population variability.
2. We surveyed larval Lepidoptera feeding on Quercus alba and Q. velutina in Missouri from 1993 to 2003 and examined population variability, measured as the coefficient of variation of population density (CV), in a subset of abundant species. We compared CV values among species whose larvae feed only in spring, early summer, mid-summer, late summer, or all season. We predicted that univoltine species whose larvae eclose and complete development in spring during leaf expansion would have higher variability than species feeding later in the season, having multiple generations, or having longer development times.
3. As predicted and consistent with hypotheses, spring-feeding species had CV values 32% higher than species feeding in summer months. Coefficients of variation were also 34% higher in leaf-rolling and mining guilds compared with free-feeders, suggesting that mobile species may compensate for asynchrony with budburst by dispersing to higher quality plants or plant parts. Multivoltine species, however, did not differ from univoltine species in population variability.
4. Our results suggest that asynchrony with plant phenology and factors that might exacerbate it, such as climate change, will have the largest impacts on the dynamics of spring-feeding Lepidoptera, particularly species with limited mobility.     

Ecological studies on the plants of fagaceae V. Growth in the sapling stage and minimal participation of reserve materials in the formation of annual new shoots of the evergreenQuercus glauca thunb

The growth in the sapling stage and participation of reserve materials in the formation of annual new shoots were studied in the evergreen treeQuercus glauca. The growth and some allometric relationship were analyzed for 1-to 4-year-oldQ. glauca plants. Each individual was felled at the foot, or all the leaves were removed at the end of the growth season (December). Sprouts were formed on the remaining stump and new shoots were formed from winter buds under dark or light conditions. The dry weight of each plant part was measured before and afte,, the formation of these new shoots. The amount of reserve materials in each plant part was estimated from the difference in allometric relatationships before and after the formation of new shoots. Although the results showed that a small amount of reserve material existed in roots, the participation of reserve materials in the formation of annual new shoots was negligible inQ. glauca growing under usual conditions, and substrates for the formation of new shoots were derived from the products of photosynthesis in old leaves and developing new leaves. Some of the growth characteristics ofQ. glauca were compared with those of the deciduous speciesQuercus variabilis to explain ecological behavior of the two species in warmtemperate secondary forests.     

北美东部8种温带树种向北分布的限制气候因子

利用分布于北美东部的 8种温带落叶树种为研究材料 ,应用反映热量和降水状况的 11个变量为气候指标 ,用标准差分析方法分析了这 8个树种的分布北界与气候因子之间的关系。结果表明 ,在所使用的气候指标中 ,同一树种不同地点的温暖指数或年生物温度的标准差最小 ,说明积温是限制这些树种向北分布的主要气候因子 ;温暖指数和寒冷指数随着年降水量的增大而减小 ,寒冷指数随着年较差的增加而增加 ,温暖指数随着水热综合指数的增加表现出减小的趋势。表明 ,除了生长季节的积温之外 ,降水和大陆性等气候条件对温带树种向北分布也起着重要作用     

Effects of winter cold stress on photosynthesis and photochemical efficiency of PSII of the Mediterranean <Emphasis Type="Italic">Cistus albidus</Emphasis> L. and <Emphasis Type="Italic">Quercus ilex</Emphasis> L.

This study examined the photosynthetic and growth performances of potted plants of Cistus albidus L. and Quercus ilex L. submitted either to natural Mediterranean winter conditions or to mild greenhouse conditions. Plants grown outdoors exhibited lower light and CO₂-saturated CO₂ assimilation rates (A_sat) and apparent quantum yield (_i) than those indoors. Until mid-winter, C. albidus had higher A_sat than Q. ilex, but differences disappeared after a period of severe cold. Maximal photochemical efficiency of PSII (Fv/Fm) measured predawn was higher in C. albidus than in Q. ilex, and decreased throughout the season in outdoor plants. Fv/Fm also decreased at light saturation (A_sat) in both species. Fv/Fm was correlated with photosynthetic capacity and efficiency (quantum yield), but the resulting regression slopes were different between the two species. At the physiological level, C. albidus seemed to cope better with cold stress than Q. ilex. However, winter stress induced reduction of leaf absorptance, increased leaf mass per area, extensive leaf damage and high plant mortality in C. albidus. This suggests that the high performance of C. albidus leaves is not likely to be maintained for long periods of cold stress, and may therefore depend on continuous leaf replacement. Quercus ilex showed a conservative behaviour, with low net assimilation rates but greater leaf and plant survival than C. albidus.     

Photoinhibition and drought in Mediterranean woody saplings: scaling effects and interactions in sun and shade phenotypes

Interacting effects of high light and drought on the performance of sun and shade phenotypes were experimentally undertaken following survival, chlorophyll fluorescence and gas exchange in 2-year-old saplings of four Mediterranean trees (Quercus ilex and Q. coccifera as water-saving species, and Pistacia lentiscus and P. terebinthus as water-spending species). Half of the saplings were grown in full sunlight and the other half in the shade (6% sunlight). Half of each combination of species-phenotype was exposed to high light during a simulated late-summer drought. Light absorptance and gas exchange were scaled up to the whole plant with the 3-D geometrical model, Y-Plant. Quercus species were more plastic and tolerated high light and water stress better than Pistacia species, surviving longer and in drier soils, and exhibiting a less pronounced photoinhibition. There was no evidence of disadvantage for shade phenotypes under high light with increasing drought. By contrast, shade phenotypes survived longer despite larger initial decreases in photochemical efficiency and higher sensitivity to drought than sun phenotypes. The enhanced control of transpiration during drought in water-saving versus water-spending species (and also in shade versus sun phenotypes in three out of the four species) allowed extended survival. Photoinhibition reduced whole crown carbon gain in high light by c. 3% and affected significantly more the shaded leaves of a given plant (reducing their carbon gain by up to 7%) than those exposed to direct sunlight. Despite this apparently minor impact, whole plant carbon gain reduction by photoinhibition negatively correlated with survival and drought tolerance. The implications for succession and forest regeneration in arid environments, particularly under a global change scenario, are discussed.     

Physiological and morphological acclimation of shade-grown tree seedlings to late-season canopy gap formation

Because acclimation to canopy gaps may involve coordination of new leaf production with morphological or physiological changes in existing, shade-developed leaves, we examined both new leaf production and photosynthesis of existing leaves on shade-grown seedlings after exposure to a late-season canopy gap. Midway through the summer, we transferred potted, shade-grown seedlings of four co-occurring temperate deciduous tree species representing a range of shade-tolerance categories and leaf production strategies to gaps. Shade-tolerant Acer saccharum was the least responsive to gap conditions. It produced few new, high-light acclimated leaves and increases in photosynthetic rates of shade-developed leaves appeared stomatally limited. Intermediately shade-tolerant Fraxinus americana and Quercus rubra responded most, by producing new leaves and increasing photosynthetic rates of existing shade-developed leaves to levels not significantly different from gap-grown controls within four weeks of gap exposure. Shade-intolerant Liriodendron tulipifera was intermediate in response. In these species, the degree of shoot-level morphological acclimation (new leaf production) and leaf-level physiological acclimation (photosynthetic increases in existing leaves) appear coupled. Mechanisms of acclimation also appear related to intrinsic patterns of nitrogen use and mobilization, the ability to adjust stomatal conductance, and shade tolerance.     

VARIATION IN THE NUTRIENT CONTENT OF LEAVES OF QUERCUS ALBA,QUERCUS COCCINEA,AND PINUS RIGIDA IN THE BROOKHAVEN FOREST FROM BUD-BREAK TO ABSCISSION

Leaves of Quercus coccinea, Q. alba, and Pinus rigida were collected at six dates during the growing season and analyzed for N, P, K, Ca, Mg, Fe, S, and Na. Leaf weights per unit of leaf area (or length) were determined for the same period. Quercus coccinea and Q. alba leaves increased in weight per unit area by about 30 % and 50 %, respectively. First-year pine leaves increased in weight per unit length by about 65 %. During the second year the weight of pine leaves changed little. Two broad patterns in the nutrient content of leaves were apparent when nutrient content was expressed on the basis of leaf area rather than leaf weight. N, P, and K concentrations increased to a peak in mid- or late summer and declined abruptly just prior to abscission. Concentrations of other elements tended to rise slowly throughout the life of the leaves in all three species. The differences among nutrients and among species support the hypothesis that differential partitioning of the nutrient pool occurs as a result of evolutionary adaptation. The changes in weight of leaves per unit area and in nutrient content during the growing season are important for studies of net primary production and in appraisals of the cycling of nutrients. Least distortion of nutrient relationships occurs when area or length of leaf is used as the basis for expression of nutrient content.