Intra- and interspecific diversity in the response to waterlogging of two co-occurring white oak species (Quercus robur and Q. petraea)

Quercus robur L. and Quercus petraea (Matt.) Liebl. are sympatric oak species with different ecological requirements. Quercus robur is more tolerant to waterlogging than Q. petraea. This ecological divergence may play a role in the maintenance of the two species despite the absence of an insurmountable reproductive barrier between them. We predicted that the genetic architecture of traits related to waterlogging tolerance differs between the species. To gain insight into this architecture in the absence of genetic markers for waterlogging tolerance, we compared populations of seedlings of each species for diversity in the expression of quantitative phenotypic traits induced by severe hypoxia. To determine the capacity for hypertrophied lenticel formation, we applied gas-impermeable mastic to stems of seedlings. Two months after application, the mastic treatment had induced the formation of 3 (+/- 2) cm(-2) hypertrophied lenticels in the absence of root hypoxia. Leaf epinasty during root hypoxia was an early predictor of seedling mortality. Four weeks of waterlogging resulted in greater epinasty in Q. petraea than in Q. robur, but fewer hypertrophied lenticels (16 +/- 6 versus 21 +/- 9 cm(-2)) and adventitious roots (2.7 +/- 4.7 versus 5.2 +/- 5.9). Differences between species in these traits were associated with differences in the frequencies of extreme phenotypes rather than with a generally higher tolerance to waterlogging in Q. robur seedlings.     

Cause–effect relationship among morphological adaptations,growth, and gas exchange response of pedunculate oak seedlings to waterlogging

Context

In response to waterlogging, pedunculate oak is known to develop adventitious roots and hypertrophied lenticels. However, to date, a link between these adaptations and the ability to maintain net CO₂ assimilation rates and growth has not been demonstrated.

Aims

The aim of this study was to explore the cause–effect relationship between the ability to form morphological adaptations (hypertrophied lenticels and adventitious roots) and the capacity to maintain high assimilation rate and growth.

Methods

The occurrence of morphological adaptations and the parameters of photosynthesis were monitored over 20 days of waterlogging in 5-week-old pedunculate oak seedlings presenting similar morphological development.

Results

Based on the development or not of morphological adaptations, the following three categories of responses were identified: development of hypertrophied lenticels and adventitious roots, development of hypertrophied lenticels alone, and the lack of development of adaptive structures. These categories, ranked in the order given, corresponded to decreasing levels of initial net CO₂ assimilation rate growth and photosynthesis parameters observed during waterlogging.

Conclusion

We observed a two-way cause–effect relationship between the capacity to form adaptive structures and the assimilation rate. Indeed, the initial assimilation rate determined the occurrence of hypertrophied lenticels and growth during stress, and then the development of morphological adaptations enhanced the ability to maintain assimilation levels during the stress.     

Effects of acorn attack by curculio weevils on the germination and early growth of <Emphasis Type="Italic">Pasania edulis</Emphasis> (Makino) seedlings

We conducted field studies to evaluate the impact that curculio weevil attacks on Pasania edulis (Fagacea) acorns have on the regeneration of this tree. The germination ratio of weevil-attacked acorns was significantly lower than that of sound acorns. The number and position of the attacks on acorns affected the germination ratio. The seedlings from weevil-attacked acorns were shorter and had a smaller leaf area than those from sound acorns. The negative effects on seedling height lasted for at least three years after germination. We also studied the handling of the two types of acorns by granivorous Apodemus mice in a broad-leaved forest dominated by P. edulis. The mice picked up, transported, hoarded, and recovered sound and weevil-attacked acorns similarly. In the study site, the seedlings from weevil-attacked acorns were estimated to account for 1.5–20.4 % of the total seedlings for cohorts of mast years and 0–3.7 % for those of poor or medium acorn production. From these results, we conclude that acorns with the lower part of their cotyledons slightly damaged by weevil larvae might still be able to contribute to the regeneration of P. edulis in the field but that their contribution would be negligible or small even in mast years in this study site.     

Plastic response of four maritime pine (<Emphasis Type="Italic">Pinus pinaster</Emphasis> Aiton) families to controlled soil water deficit

Key message

Separating the internal (ontogenetic) and external (environmental) components of maritime pine development during controlled soil water deficit helps to highlight the plastic response. The adjusted measurements reveal significant differences between families for their plastic response for several physiology and growth traits.

Context

Soil water deficit is and will be a growing problem in some regions. Pinus pinaster Ait. is a species of commercial interest and is recognized as a drought-avoiding species. It is thus of interest to evaluate the adaptation potential of P. pinaster to soil water deficit.

Aims

This paper aims to estimate the plastic response to the variation of water availability at the family level (half-sibs).

Methods

Two-year-old P. pinaster cuttings from four families were submitted during 6 weeks to two contrasting watering regimes. The experiment started in April 2011 shortly after sprouting. The photosynthesis and stomatal conductance to water vapor were measured on 1-year-old needles. Intrinsic water-use efficiency was calculated as the ratio of photosynthesis to stomatal conductance. Radial growth, length of terminal shoot, and total height were also measured. The ontogenetic component of tree development was estimated on the well-watered trees for all the traits. Then, this development effect was eliminated from the data collected on the trees submitted to the soil water deficit in order to keep only the effect of this soil water deficit.

Results

After 6 weeks of reduced watering, the value of all adjusted traits decreased. An average plastic response to the variation of water availability was found to be significant and variable at the family level for the six adjusted variables.

Conclusion

These results suggest that there is genetic variation of phenotypic plasticity to drought in P. pinaster for several traits, including stomatal conductance, which appears to be a promising variable for future selection for resistance to drought.

     

Interactive effects of irrigation and exponential fertilization on nutritional characteristics in <Emphasis Type="Italic">Populus</Emphasis> × <Emphasis Type="Italic">euramericana</Emphasis> cv. ‘74/76’ cuttings in an open-air nursery in Beijing,China

Nutritional characteristics determine tree stock quality to a considerable extent. Exponential fertilization can induce nutrient reserves within juvenile trees, but its validity on poplar is contingent on interaction with a scientific irrigation regime due to limited water resources under global warming. In the present study, we raised 3200 Populus × euramericana cv. ‘74/76’ cuttings under four irrigation regimes of 0 (I0), 60 % (I60), 80 % (I80), and 100 % (I100) of field capacity for soil moisture content with or without (control) the employment of nitrogen (N) addition delivered as exponential fertilization at the rate of 8 g N cutting^?1 (E8) in an open-air nursery in Beijing, China. Both height and diameter increased with the increment of soil moisture ratio or in response to exponential fertilization (EF) without any interactive effects. In general, concentrations of N, phosphorus (P), and potassium (K) declined with time in stem but foliar N concentration did not change. Under the I100 regime, EF increased foliar N concentration relative to the control but failed to affect N concentration in stem in September, when both N concentration and N content were increased by EF under the I80 regime. Stem-K content and concentration by EF under the I80 regime also increased in September, therefore EF-treated cuttings had a higher ratio of K content in stem to that in whole plant (%ANAR). Vector diagnosis for nutritional status indicated that EF resulted in dilution of K concentration but induced a steady-state P uptake in leaves under all irrigation regimes. Therefore, EF of N addition could promote N uptake to leaves of P. × euramericana cv. ‘74/76’ cuttings, but it had a null effect on N and P reserves in stem and impaired K reserves. In conclusion, the irrigation regime of 80 % field capacity of soil moisture content was suggested for the culture of juvenile P. × euramericana cv. ‘74/76’ cuttings. As the interactive meaning, EF was also suggested for its excellent promotion on both N and K uptakes.     

Effects of extreme soil water stress on photosynthetic efficiency and water consumption characteristics of <Emphasis Type="Italic">Tamarix chinensis</Emphasis> in China’s Yellow River Delta

Soil moisture is a major limiting factor for plant growth on shell ridge islands in the Yellow River Delta. However, it is difficult to carry out situ experiment to study dominant plant photosynthesis physiological on the shell ridge islands under extreme soil water stress. To evaluate the adaptability of plants to light and moisture variations under extreme soil moisture conditions present on these islands, we measured photosynthetic gas exchange process, chlorophyll fluorescence, and stem sap flow variables for 3-year-old trees of Tamarix chinensis Lour, a restoration species on these islands, subjected to three types of soil water levels: waterlogging stress (WS), alternating dry–wet (WD), and severe drought stress (SS) to inform decisions on its planting and management on shell ridge islands. Gas exchange, chlorophyll fluorescence, and stem sap flow in T. chinensis were then measured. Net photosynthetic rate (P _N), transpiration rate (E), and water use efficiency (W _UE) were similar under WS and alternating dry–wet conditions, but their mean E and W _UE differed significantly (P < 0.05). Under SS, the P _N, E and W _UE of T. chinensis leaves varied slightly, and mean P _N, E and W _UE were all low. Apparent quantum efficiency (A _QY), light compensation point (L _CP), light saturation point (L _SP), and maximum net photosynthetic rate (P _Nmax) of leaves were not significantly different (P > 0.05) under WS and dry–wet conditions; however, under extreme drought stress, compared with the dry–wet conditions, L _CP was higher, L _SP was lower, and A _QY and P _Nmax were both at the lowest level. Therefore, drought stress weakened light adaptability of leaves, and the efficiency of light transformation was poorer. (3) Maximum photochemical efficiency (F _v/F _m) and the actual photochemical efficiency (Φ _PSII) were similar under waterlogged stress and dry–wet conditions, indicating a similar healthy photosynthetic apparatus and photosynthetic reaction center activity, respectively. Under SS, F _v/F _m was 0.631, and the coefficient of non-photochemical quenching (N _PQ) was 0.814, which indicated that while the photosynthetic mechanism was damaged, the absorbed light energy was mainly dissipated in the form of heat, and the potential photosynthetic productivity was significantly reduced. The daily cumulants of sap flow of T. chinensis under dry–wet alternation and severe drought stress were 22.25 and 63.97% higher, respectively, than under waterlogging stress. Daily changes in sap flow velocity for T. chinensis differed under the three soil water levels. Stem sap flow was weak at night under severe drought stress. Under dry–wet alternation, daytime average stem sap flow velocity was the highest, and night stem flow accounted for 10.26% of the day cumulants, while under waterlogged stress, the average nightly stem flow velocity was the highest, accounting for 31.82% of the day cumulants. These results provide important information for regional vegetation restoration and ecological reconstruction.     

Assessing the roles of temperature,carbon inputs and airborne pollen as drivers of fructification in European temperate deciduous forests

We aimed at identifying which drivers control the spatio-temporal variability of fruit production in three major European temperate deciduous tree species: Quercus robur, Quercus petraea and Fagus sylvatica. We analysed the relations of fruit production with airborne pollen, carbon and water resources and meteorological data in 48 French forests over 14 years (1994–2007). In oak, acorn production was mainly related to temperature conditions during the pollen emission period, supporting the pollen synchrony hypothesis. In beech, a temperature signal over the two previous years eclipsed the airborne pollen load. Fruit production in Quercus and Fagus was related to climate drivers, carbon inputs and airborne pollen through strongly nonlinear, genus-specific relations. Quercus and Fagus also differed as regards the secondary growth versus fructification trade-off. While negative relationships were observed between secondary growth and fruit production in beech, more productive years benefited to both secondary growth and reproductive effort in oak.     

Acclimation of cuttings from different willow genotypes to flooding depth level

Climate change will increase the frequency of extreme rain events, causing more flooding episodes. Willows are usually planted in marginal lands like flood prone areas. For willow plantations developed from rootless cuttings, the establishment phase is crucial, because the cuttings are still developing a shoot and root system and have a higher vulnerability to stress. A flooding episode during this early period may have a negative effect upon plants. We analyzed the responses to flooding of eight willow genotypes, representing important species from the economic and ecological point of view (Salix alba, S. matsudana, S. amygdaloides and S. matsudana × S. nigra hybrids). The treatments started when the plants were 2 months old and lasted for 3 weeks. They were identified as: Control (watered to field capacity); F10 (plants submerged 10 cm above soil surface) and F50 (plants submerged 50 cm above soil surface). The F50 treatment showed a greater growth reduction than the F10 treatment in most clones, either measured in height, diameter or total biomass. Both flooding treatments reduced significantly the root-to-shoot ratio compared to control plants. The F50 treatment increased the leaf nitrogen content and specific leaf area in all genotypes. Both treatments changed plant and leaf traits in different ways according to the depth of the floodwater. These changes may have lasting effects on growth recovery in the post-flooding period. Willow clones with a fast initial growth will be the best option to minimize growth reduction in areas prone to experience flooding episodes.     

Functional response of <Emphasis Type="Italic">Quercus robur</Emphasis> L. to taproot pruning: a 5-year case study

Key message

Quercus robur seedling mass was affected more by planting density than by taproot pruning. Root pruning enhanced stem biomass at the expense of roots in later growth stages. Alteration of biomass allocation due to nursery practices may result in greater susceptibility to injury and death of the seedlings under unfavorable environmental conditions.

Context

Plants adjust their growth and modulate the resource allocation in response to applied treatments and environmental conditions.

Aims

The aim was to examine how taproot pruning in seedlings grown at different densities affected long-term growth of Quercus robur.

Methods

Seedlings, sown as acorns at two planting densities, with or without pruned roots were harvested in the second, fourth, and fifth years of growth. The effect of root pruning on biomass allocation was determined by measuring leaf, stem, and root mass fractions; carbohydrate concentrations in the roots; and C/N ratios. Specific leaf area and root length were also determined to assess morphological adaptations to growth conditions.

Results

Total seedling mass was affected more by planting density than by taproot pruning. After 4 years of growth, root mass fractions were lower and stem mass fractions were greater in seedlings planted at a higher density. Five-year old root-pruned seedlings also had a lower root mass fraction and higher stem mass fractions than unpruned seedlings. Specific root length was not affected by root pruning or planting density.

Conclusion

Decrease of relative root biomass with simultaneous increase of stem biomass may be a long-term consequence of taproot pruning of Q. robur, and the effects may manifest years after the seedling stage.

     

Factors governing cesium adsorption of charcoals in aqueous solution

Cesium adsorption by commercial charcoals was examined to elucidate the mechanisms for capturing cesium ions in aqueous solution. Changes in the adsorption ability of charcoals due to water extraction (water washing) were investigated to develop practical cesium adsorptives based on charcoal. The commercial charcoals examined included mangrove charcoal (MC) and ubamegashi (Quercus phillyraeoides A. Gray) bincho charcoal (BC). Data from the two charcoals were compared with those of Japanese oak (Quercus serrata Thunb. and/or Quercus crispula Blume) charcoal (OC) reported previously. Aqueous cesium chloride solution (2.50 × 10^?5 mol/L) was used as a sample solution for the adsorption study. Charcoal powder was used as an adsorbent after passing through a 60-mesh sieve. The powders were characterized using methods, such as Raman spectroscopy, X-ray fluorescence spectrometry, and infrared photoacoustic spectroscopy. The results indicated that MC, which was manufactured at the lowest possible temperature and had the smallest specific surface area, possessed the greatest ability to adsorb cesium. The MC also had the great cesium-adsorption ability in weak acidic solution and maintained the ability even after lengthy extraction treatments.     

Flammability of some companion species in cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) forests

Key message

The high flammability of some companion species in Quercus suber forests, estimated in laboratory tests, could potentially generate an increase in fire vulnerability and in fire risk.

Context

Recurrent wildfire is one of the main causes of forest degradation, especially in the Mediterranean region. Increased fire frequency and severity due to global change could reduce the natural resilience of cork oak to wildfire in the future. Hence, it is important to evaluate the flammability of companion species in cork oak forests in the particularly dry bioclimatic conditions of North Africa.

Aims

This study aimed to assess and compare flammability parameters at laboratory scale among ten companion frequent species in cork oak forests.

Methods

Fuel samples were collected in a cork oak (Quercus suber L) forest in the southern part of the mountains of Tlemcen (Western Algeria). A series of flammability tests were carried out using a Mass Loss Calorimeter device (FTT ®). A cluster analysis to classify flammability of the selected species was conducted using the K-means algorithm.

Results

The results revealed differences in the four flammability parameters (ignitability, sustainability, combustibility and consumability), in both fresh and dried fine fuel samples from Quercus suber, Pinus halepensis, Quercus ilex, Quercus faginea, Erica arborea, Arbutus unedo, Pistacia lentiscus, Calicotome spinosa, Juniperus oxycedrus and Tetraclinis articulata. Application of the K-means clustering algorithm showed that C. spinosa, T. articulata, J. oxycedrus and P. halepensis are highly flammable because of their high combustibility and sustainability.

Conclusion

The findings identify species that could potentially increase the vulnerability of cork oak forests to forest fires.

     

Effects of water stress on emission of volatile organic compounds by <Emphasis Type="Italic">Vicia faba</Emphasis>, and consequences for attraction of the egg parasitoid <Emphasis Type="Italic">Trissolcus basalis</Emphasis>

When plants are damaged by herbivorous insects, blends of volatile organic compounds (VOCs) are induced and released and can also be used by parasitoids to locate hosts. The aim was to determine whether VOCs induced by water stress affect the plant–herbivore–parasitoid system represented by broad bean (Vicia faba; Fabales: Fabaceae) stink bug (Nezara viridula; Heteroptera: Pentatomidae) egg parasitoid (Trissolcus basalis; Hymenoptera: Platygastridae). The effects of water stress (expressed as the percentage fraction of transpirable soil water [FTSW] supplied) alone and in combination with N. viridula damage (feeding plus oviposition) were determined according to: (1) the behavioural response of the egg parasitoid in a Y-tube olfactometer and (2) the plant VOCs collected and analysed by thermal desorption–gas chromatography–mass spectrometry. With pot water capacity as FTSW₁₀₀, water stress was applied as mild (FTSW₈₀), moderate (FTSW₅₀) and severe (FTSW₁₀). Bioassays with plants under abiotic stress alone showed that egg parasitoids are more attracted by FTSW₁₀ plants than by well-watered plants. When plants were under abiotic and biotic stress interactions, the egg parasitoids are more attracted by FTSW₁₀ and FTSW₅₀ plants than by well-watered plants infested with N. viridula. Considering VOCs emissions, projection to latent structures discriminant analysis (PLS-DA) separated treatments according to egg parasitoid responses. Water stress alone and in combination with biotic stress induced changes in VOC emissions of V. faba plants that attract egg parasitoids. These findings contribute to our understanding of how water stress affects the interactions between plants, insect pests and egg parasitoids.     

Physiological regulation of poplar species to experimental warming differs between species with contrasting elevation ranges

Climate warming has resulted in rapid range shifts of plant species, but it is not well known how species with different natural distribution ranges adapt to increase in temperature through physiological adjustment. We experimentally imposed a 1.8 °C increase of air temperature to the cuttings of two common poplar species Populus yunnanensis and Populus szechuanica naturally growing in southwest China using open-top chambers. Populus yunnanensis is distributed along a narrower elevation range compared with P. szechuanica. We determined some key physiological parameters and plant growth regulator activities during the growing season without soil water limitation. Our results showed that a 1.8 °C increase in air temperature increased shoot growth of P. szechuanica through an extension of its growth period but did not affect the growth of P. yunnanensis. Malondialdehyde content, guaiacol peroxidase activities and abscisic acid content increased while indoleacetic acid content decreased in P. yunnanensis. Our results suggest that the two common poplar species in southwest China should be able to adapt to the moderate increase in temperature projected for future climate. The growth of P. szechuanica may benefit through phenological adjustment but a further increase in temperature may inhibit the growth of P. yunnanensis. For poplar plantation management, selecting species with a wide natural distribution range could provide an adaptive alternative for buffering anthropogenic induced increase in temperature and help in sustaining productivity for the long term.     

Photosynthetic acclimation to long-term high temperature and soil drought stress in two spruce species (<Emphasis Type="Italic">Picea crassifolia</Emphasis> and <Emphasis Type="Italic">P. wilsonii</Emphasis>) used for afforestation

Picea crassifolia and P. wilsonii, commonly used for afforestation in northern China, are increasingly likely to be subjected to high temperatures and soil drought stress as a result of global warming. However, little is known about the effects of these stresses on foliar photosynthesis in the two species. To investigate how photosynthetic characteristics and sensitivity respond to prolonged high temperatures and soil drought, foliar gas exchange and other closely related parameters were recorded from four-year-old seedlings of both species. Seedlings were grown under two temperature treatments (25/15 and 35/25 °C) and four soil water regimes [80, 60, 40 and 20% of maximum field capacity (FC)] for 4 months. Although all treatments significantly reduced photosynthetic rates (P _n) of both species, P. crassifolia exhibited greater photosynthetic acclimation than P. wilsonii. Differences in photosynthetic acclimation were mainly related to variations in stomatal conductance (Cond) and the maximum quantum yield of PSII (F _v/F _m) between treatments. Indeed, higher Cond and F _v/F _m in all treatments were shown for P. crassifolia than for P. wilsonii. Moreover, photosynthesis in P. crassifolia exhibited inherently lower temperature sensitivities (broader span for the temperature response curves; lower b) and higher thermostability (invariable b between treatments). Further, severe drought stress (20% FC) limited the survival of P. wilsonii. Our results indicate that P. wilsonii is more susceptible to high temperatures and soil drought stress. Planting P. crassifolia would be more expected to survive these conditions and hence be of greater benefit to forest stability if predicted increases in drought and temperature in northern China occur.     

Clonal propagation of mastic tree (<Emphasis Type="Italic">Pistacia lentiscus</Emphasis> var. <Emphasis Type="Italic">chia</Emphasis> Duham.) in outdoor beds using different rootstock and grafting techniques

We assessed different rootstocks and grafting techniques to clonally propagate mastic tree (Pistacia lentiscus var. chia). Mastic tree is a dioecious tree but the quantity and quality of the resin secreted by female trees are very low; therefore, male trees that are clonally propagated are used to establish commercial plantations for mastic production. Conventional long branch cuttings for clonal production requires too much materials and has a very low rooting rate. Rooting with tissue culture and green cuttings has also failed outdoors. Grafting of mastic on other Pistacia species has not been tried so far; therefore, this study was aimed at developing grafting methods for the clonal propagation of mastic. P. atlantica and P. lentiscus rootstocks were grafted from 15 February to 15 October every 15 days using three grafting methods and a two-factor randomized block trial design. Early spring (15 February–15 March) proved to be the best time for grafting using either of the rootstocks. The highest grafting success was attained using the scions grafted on P. atlantica from 15 February to 15 March. The best bud-burst percentage was obtained using P. atlantica and P. lentiscus rootstocks.     

Field attraction of Cerambyx welensii to fermentation odors and host monoterpenes

Cerambyx welensii Küster is one of the greatest threats to Quercus suber L. and Quercus ilex L. in Spain. Efficient control methods for this species are currently being tested, and the use of traps baited with food-related products for their monitoring and control has been proposed. Cerambyx welensii adults prefer to colonize old or decayed trees, in which cortical exudates frequently release fermentation odors. Fermentation-related compounds, such as ethanol, have been cited as attractants to various hardwood woodborers (as Cerambyx cerdo L.), used either alone or sometimes in combination with other host odors. In this work, we conducted field experiments to ascertain whether chemical blends mimicking fermentation odors were attractive for C. welensii. To this end, we used three types of traps (multiple funnel, cross-vane and single-funnel) baited with six synthetic blends including one or more fermentation-related chemicals (ethanol, ethyl acetate, 3-methyl-1-butanol, acetaldehyde, 2-methyl-1-propanol and 2-methyl-1-butanol), various food-related products (beer, melon and red wine mixed with peach juice) and host monoterpenes (α-pinene, β-pinene, limonene, α-phellandrene and camphene). At high release rates (5–11 g/day), various synthetic blends proved attractive irrespective of trap type. Our results contribute to understand the impact of volatile organic compounds in host selection by woodborers infesting deciduous trees. The results hold promise for optimizing trapping strategies to control C. welensii within an integrated pest management framework.     

A dwarf bamboo (<Emphasis Type="Italic">Pleioblastus chino</Emphasis>) and winter browsing by Japanese hare (<Emphasis Type="Italic">Lepus brachyurus</Emphasis>) combine to limit establishment of transplanted native tree seedlings in an abandoned agricultural field

Natural forest recovery on abandoned farmland is hindered by a variety of factors and active restoration plays an important role when quick afforestation is desired. We investigated seedling survival of four transplanted native tree species (Quercus myrsinifolia, Quercus serrata, Aphananthe aspera, and Rhus sylvestris) by experimentally manipulating the vegetation cover, which was mainly dominated by dwarf bamboo (Pleioblastus chino), and herbivore access to the planting sites on farmland that had been abandoned for 15 years at the start of the study. Few transplanted seedlings of any species survived under intact vegetation cover, irrespective of herbivore presence. In gaps in the vegetation cover, winter browsing by Japanese hare (Lepus brachyurus) damaged all species. However, lower browsing frequency and higher resprouting ability after grazing of the seedlings enabled both Quercus species to survive better than the other species. These results indicate that dwarf bamboo and the hare jointly limit the establishment of native trees in old fields. If active afforestation by transplanting seedlings at sites dominated by dwarf bamboo is planned, a combination of vegetation removal, selection of suitable species, and temporary seedling protection will be most effective.     

Effects of soil drought stress on photosynthetic gas exchange traits and chlorophyll fluorescence in <Emphasis Type="Italic">Forsythia suspensa</Emphasis>

To clarify the changes in plant photosynthesis and mechanisms underlying those responses to gradually increasing soil drought stress and reveal quantitative relationships between photosynthesis and soil moisture, soil water conditions were controlled in greenhouse pot experiments using 2-year-old seedlings of Forsythia suspensa (Thunb.) Vahl. Photosynthetic gas exchange and chlorophyll fluorescence variables were measured and analyzed under 13 gradients of soil water content. Net photosynthetic rate (P _N), stomatal conductance (g _s), and water-use efficiency (W _UE) in the seedlings exhibited a clear threshold response to the relative soil water content (R _SWC). The highest P _N and W _UE occurred at R _SWC of 51.84 and 64.10%, respectively. Both P _N and W _UE were higher than the average levels at 39.79% ≤ R _SWC ≤ 73.04%. When R _SWC decreased from 51.84 to 37.52%, P _N, g _s, and the intercellular CO₂ concentration (C _i) markedly decreased with increasing drought stress; the corresponding stomatal limitation (L _s) substantially increased, and nonphotochemical quenching (N _PQ) also tended to increase, indicating that within this range of soil water content, excessive excitation energy was dispersed from photosystem II (PSII) in the form of heat, and the reduction in P _N was primarily due to stomatal limitation. While R _SWC decreased below 37.52%, there were significant decreases in the maximal quantum yield of PSII photochemistry (F _v/F _m) and the effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching (q _P), and N _PQ; in contrast, minimal fluorescence yield of the dark-adapted state (F ₀) increased markedly. Thus, the major limiting factor for the P _N reduction changed to a nonstomatal limitation due to PSII damage. Therefore, an R _SWC of 37.52% is the maximum allowable water deficit for the normal growth of seedlings of F. suspensa, and a water content lower than this level should be avoided in field soil water management. Water contents should be maintained in the range of 39.79% ≤ R _SWC ≤ 73.04% to ensure normal function of the photosynthetic apparatus and high levels of photosynthesis and efficiency in F. suspensa.     

Electrophysiological responses of <Emphasis Type="Italic">Thaumetopoea pityocampa</Emphasis> females to host volatiles: implications for host selection of active and inactive terpenes

Volatiles from newly cut branches with needles of Pinus sylvestris L. were collected with headspace sampling technique, and then identified and quantified by combined gas chromatographic-mass spectrometry (GC-MS). The response of antennae of the female pine processionary moth, Thaumetopoea pityocampa, to these volatiles was recorded by coupled gas chromatographic-electroantennographic detection (GC-EAD). Surprisingly, the most common and major monoterpene hydrocarbons (MT), α-pinene, 3-carene, and β-pinene were antennally inactive. Female antennae responded strongly only to four minor MT components, myrcene, β-phellandrene, trans-β-ocimene, and terpinolene. Weaker, but repeatable responses were also found to limonene, cis-β-ocimene, and γ-terpinene. Further EAD recordings with two synthetic MT mixtures supported our findings from the natural material. When separating the two enantiomers of limonene by running different synthetic MT mixtures, the EAD response was found only to the(?)-enantiomer, but not to the opposite (+)-enantiomer. EAD-responses were also found to some less volatile compounds, such as sesquiterpenes (SqT), active at ng-levels. The sensitivity and specificity of the antenna to a select number of active host MTs and SqTs suggest that these play a role in the host selection process of T. pityocampa females.     

Comparison of the responses to flooding of seedlings and cuttings of Gmelina

The effects of flooding on Gmelina arborea Roxb. seedlings and cuttings of the same parent stock were compared to determine their suitability as transplanting stock. Flooding caused reductions in stomatal conductance, xylem pressure potential and dry matter accumulation in both groups of plants. In seedlings, flooding induced formation of hypertrophied lenticels, stem hypertrophy and production of short, thick, adventitious roots in seedlings, whereas in cuttings, only thin roots and numerous smaller lenticels were induced. For 8 days after the flooding treatment ended, the flooded seedlings grew faster than control seedlings, whereas in cuttings, post-flooding growth was similar to that of control plants. It is suggested that seedlings may perform better than cuttings in very wet or saturated soil.