Trees

 Segments of standing beech stems (Fagus sylvatica) were put under mechanical pressure from the end of May, in order to investigate the influence of constant external pressure on the development of secondary vascular tissue. After 4 weeks, the new xylem increment was investigated anatomically in cross-sections. The first axial xylem derivatives of the new year’s increment had differentiated into normal vessel elements and fiber-tracheids. Application of the pressure girdle had no effect on fiber-tracheid development, but it inhibited vessel formation. Under pressure, changes in the two dimensional PAGE protein pattern were characterized by the appearance of two new protein species as well as by the absence of one species that occurs under regular growth.

Most of the plantations were planted with single species for economic reasons. Continuous planting of such single tree species over a longer period has led to a series of ecological problems including soil degradation, low stand productivity and ecosystem stability. Studies have suggested that mixed-species plantations have greater levels of ecosystem functions and services such as higher nutrient utilization and productivity than do monocultures. Chinese fir (Cunninghamia lanceolata), as an important tree species of fast-growing timber, has been widely planted in subtropical areas of China over 4 decades. The growth of Chinese fir is largely modified by soil nutrient dynamics. To better manage Chinese fir plantation and provide suitable tree species selection for mixed Chinese fir, the study aims to explore the effect of different neighboring species on nitrogen (N) uptake of Chinese fir because N is a major nutrient limiting plant growth. Three typical species (Schima superba, Michelia macclurei, and Pinus massoniana) were selected to plant with Chinese firs. Similar size of 1-year-old seedlings was planted in pots, each containing one C. lanceolata and one other tree species, with two C. lanceolata seedlings in one pot as the control. After 6 months, the soil was labeled with 15NH4+ or 15NO3− at 0–5 cm and 5–15 cm depths. The results showed that the neighbor species identity caused the changes of Chinese firs biomass. The above- and below-ground biomass of Chinese firs in monoculture was 8.7 g and 4.2 g, respectively, while P. massoniana increased it by 60% and 40%, respectively. M. macclurei did not change the biomass of Chinese firs, while S. superba decreased the above- and below-ground biomass by 28% and 33%, respectively. Neighboring tree species increased N uptake rates of Chinese firs from the 5- to 15-cm-deep layer, but not from the 0- to 5-cm-deep layer. Chinese firs preferred NO3− in the 5- to 15-cm-deep layer, while in the 0- to 5-cm-deep layer, it did not show preference between the two N forms. These findings demonstrated, under the pot-specific vertical distribution patterns of roots, species interaction between certain neighboring species promoted the growth and N uptake of Chinese firs as they had flexible uptake strategies to use inorganic N in different soil layers. This pot study provided insights into forest management to enhance ecosystem services through the selection of appropriate combinations of tree species.

Horse chestnut (Aesculus hyppocastanum L., Hyppocastanacea) is a relict species with a slow and complex reproductive cycle considered to have horticultural and medical importance. The cycle maybe circumvented via in vitro androgenesis. Androgenesis of horse chestnut was induced in microspores and anther culture on MS media. Some of the horse chestnut androgenic embryos were albinos. Addition of abscisic acid in media (in concentrations of 0.01, 0.1, 0.5, 1, 2, 5, 10, and 20 mg l−1) with horse chestnut androgenic embryos has circumvented the reproduction cycle barriers. The best results were achieved on medium with the lowest abscisic acid concentration (0.01 mg l−1) in microspore culture. The microspore culture proved to be a better model system for embryo production and albino embryo reduction than anther culture. Flow cytometry analysis after maturation treatments induced by ABA showed that 88 % of green embryos originating from microspore culture were haploid. However, 50 % of green embryos from anther culture were haploid. The remaining analyzed androgenic embryos, from both types of cultures were diploid.

Two members of the 48 laccase genes were highly expressed in peach endocarp and activated by the lignin biosynthesis-related MYB transcription factors, suggesting a role of them in lignification. Peach (P. persica) is an economically important fruit tree. Peach breeds drupe fruits with its seeds encased in an extremely hard lignified endocarp or stone. Laccases (LACs) are copper-containing glycoproteins that are involved in cell elongation processes and widely distributed in plant genomes. LACs are essential for lignin polymerization because laccase is the key enzyme responsible for monolignol polymerization. At present, the research on peach laccase is blank, and the members that play important roles in the polymerization of peach lignin are even unknown. In this study, we identified 48 laccase genes (PpLACs) in the peach genome. All 48 peach laccase genes were unevenly distributed on eight chromosomes and divided into six different phylogenetic groups (I–VI). Among them, 15 were predicted to be potential targets of miR397, a negative regulator of lignin biosynthesis. Phylogenetic analysis, sequence analysis and spatiotemporal expression profile analysis indicated that PpLAC7, 19, 20, 21, 27, 28 and 30 may be related to lignin synthesis and endocarp hardness in fruit. Through expression pattern analysis, PpLAC20 and PpLAC30 were finally screened as most likely important members involved in peach lignin biosynthesis. A peach MYB transcription factor PpMYB63, a homolog of AtMYB58 and AtMYB63, demonstrated the ability to activate the PpLAC20 and PpLAC30 promoters. Moreover, histochemical staining analysis of GUS activity in proPpLAC20::GUS transgenic Arabidopsis seedlings showed the tissue-specific expression pattern in limited tissues or organs, including siliques, inflorescence stems, cauline leaf main veins, and the outer coat of the seed. Our findings revealed that PpLAC20 and PpLAC30 are candidates involved in peach lignin biosynthesis and laid the foundation for subsequent researches on peach lignin synthesis and regulation.

Cortical oleoresin composition of lateral shoots (mono- and sesquiterpenes) was analysed by gas chromatography on 18 Mediterranean fir populations grown in experimental fields in southern France: 13 Abies cephalonica Loudon provenances and one A. borisii regis Mattfeld provenance from Greece, 2 A. alba Miller provenances from Romania and Bulgaria, 1 Abies bornmuelleriana Mattfeld provenance and 1 A. equi trojani Ascherson and Sintenis provenances from Turkey. Terpenes with the highest between-provenance variability were limonene, β-pinene, longifolene, δ-cadinene and α-humulene. Both similarity in terpene composition of all the firs studied and paleogeographical data demonstrated the possible existence of a unique Eastern Mediterranean tertiary ancestor for present-day Aegean species. The Pliocene marine transgression of the Aegean basin could have caused this geographical disjunction. According to this hypothesis, A. alba would have appeared in the Northern part of the Aegean and then colonized all of Europe while A. bornmuelleriana would have appeared in its Eastern part. Frequent Pleistocene contacts between the two species could have contributed to the individualization of A. equi trojani and given rise to the particular morphology of the south-eastern ecotypes of A. alba. In the western part of the basin, A. cephalonica populations would have appeared. Southern migrations of A. alba during the Ice Age and contact with A. cephalonica in refugia probably led to the development of A. borisii regis hybrid populations. Evidence for an A. alba gene flow can be found in the southernmost A. cephalonica populations.

Chemical elicitors and mechanical treatments simulating real insect herbivory have been increasingly used to study induced defensive responses in woody plants. However, simultaneous quantitative comparisons of plant chemical defences elicited by real and simulated herbivory have received little attention. In this paper we compared the effects of real herbivory, simulated herbivory using two chemical elicitors, and mechanical damage treatments on the quantitative secondary chemistry of Pinus pinaster juveniles (namely on non-volatile resin in the stem and total phenolics in the needles). The real herbivory involved phloem wounding by Hylobius abietis and defoliation by Brachyderes lusitanicus (two pine weevils); the chemical elicitors to simulate herbivory induction were 40 mM methyl jasmonate (MJ) and 20 μM benzothiadiazole (BTH); and the mechanical treatments included phloem wounding and needle clipping. We also performed an additional experiment for assessing at what extent insect extracts could increase plant responses over mechanical damage. Chemical induction with MJ, mechanical wounding and real phloem herbivory by H. abietis all produced quantitatively similar results, increasing the concentration of resin in the stem and total phenolics in the needles by equivalent magnitudes. Exogenous application of BTH increased the concentration of phenolic compounds in pine needles, but did not show the same effect on stem resin. Contrastingly, we did not find significant changes in the concentration of resin in the stem or phenolics in the needles after needle clipping and B. lusitanicus feeding. Mechanical damage followed by the application of extracts from the insects B. lusitanicus and H. abietis on the injured tissues did not increase the responses in comparison to mechanical damage alone. The fact that strong induced responses elicited by phloem wounding insects are equally elicited by phloem injuries suggests that defences in pine trees are raised with low specificity regarding biotic enemies. Results from this paper support future methodological approaches using chemical elicitors and mechanical damage as simulated herbivory treatments for the experimental induction of conifer defences.

Across their natural distributions, tropical tree species are regularly exposed to seasonal droughts of varying intensities. Their ability to tolerate drought stress plays a vital role in determining growth and mortality rates, as well as shaping the functional composition of tropical forests. In order to assess the ability of species to acclimate to contrasting levels of drought stress, physiological and structural traits involved in drought adaptation—wood C isotope discrimination (δ13C), wood specific gravity, and wood C content—of 2-year-old saplings of nine tropical tree species were evaluated in common garden experiments at two study sites in Panama with contrasting seasonality. We assessed co-variation in wood traits with relative growth rates (RGRBD), aboveground biomass, and basal diameter and the plasticity of wood traits across study sites. Overall, species responded to lower water availability by increasing intrinsic water-use efficiency, i.e., less negative wood δ13C, but did not exhibit a uniform, directional response for wood specific gravity or wood C content. Trait plasticity for all wood traits was independent of RGRBD and tree size. We found that the adaptive value of intrinsic water-use efficiency varied with water availability. Intrinsic water-use efficiency increased with decreasing RGRBD at the more seasonal site, facilitating higher survival of slower growing species. Conversely, intrinsic water-use efficiency increased with tree size at the less seasonal site, which conferred a competitive advantage to larger individuals at the cost of greater susceptibility to drought-induced mortality. Our results illustrate that acclimation to water availability has negligible impacts on tree growth over short periods, but eventually could favor slow-growing species with conservative water-use strategies in tropical regions experiencing increasingly frequent and severe droughts.

We investigated the physiological responses of Tibetan juniper (Sabina tibetica) to changes in the atmospheric CO2 concentration (C a) and climate on the northeastern Tibetan Plateau based on annual tree-ring δ13C values since 1850. Intrinsic water-use efficiency (iWUE) increased, and the internal to ambient CO2 ratio (C i /C a) showed no significant trend from 1895 to 1974 in the study region, indicating an active response to changing C a. The long-term trends in iWUE in the naturally occurring trees were mainly caused by the anthropogenic increase in C a. However, from 1975 to 2002, iWUE increased rapidly at the study site (by 12.4 % compared with the overall mean from 1850 to 2002), which is greater than the expected increase due only to an active response to C a. Our analysis showed that decreased water availability caused by greater evaporation due to decreased precipitation and a warming growth environment from 1975 to 2002 may have reduced stomatal conductance, leading to a higher iWUE. The warming climate and increased C a accounted for 83.6 % of the variance in iWUE of Tibetan juniper on the northeastern Tibetan Plateau from 1975 to 2002.