Using common mycorrhizal networks for controlled inoculation of Quercus spp. with Tuber melanosporum: the nurse plant method

The high cost and restricted availability of black truffle spore inoculum for controlled mycorrhiza formation of host trees produced for truffle orchards worldwide encourage the search for more efficient and sustainable inoculation methods that can be applied globally. In this study, we evaluated the potential of the nurse plant method for the controlled inoculation of Quercus cerris and Quercus robur with Tuber melanosporum by mycorrhizal networks in pot cultures. Pine bark compost, adjusted to pH?7.8 by liming, was used as substrate for all assays. Initially, Q. robur seedlings were inoculated with truffle spores and cultured for 12 months. After this period, the plants presenting 74 % mycorrhizal fine roots were transferred to larger containers. Nurse plants were used for two treatments of two different nursling species: five sterilized acorns or five 45-day-old, axenically grown Q. robur or Q. cerris seedlings, planted in containers around the nurse plant. After 6 months, colonized nursling plant root tips showed that mycorrhiza formation by T. melanosporum was higher than 45 % in the seedlings tested, with the most successful nursling combination being Q. cerris seedlings, reaching 81 % colonization. Bulk identification of T. melanosporum mycorrhizae was based on morphological and anatomical features and confirmed by sequencing of the internal transcribed spacer region of the ribosomal DNA of selected root tips. Our results show that the nurse plant method yields attractive rates of mycorrhiza formation by the Périgord black truffle and suggest that establishing and maintaining common mycorrhizal networks in pot cultures enables sustained use of the initial spore inoculum.     

The cultivation of oak seedlings inoculated with Tuber aestivum Vittad. in the boreal region of Finland

Despite recent findings, truffles are rarely found in Finland. In 2006, we began to explore the cultivation potential of Tuber aestivum/uncinatum in Finland. In 2006–2008, roughly 1,200 Quercus robur seedlings and 200 Q. pubescens seedlings were planted in 20 orchards. We aimed to challenge the Southern European (France) tree provenances of oak seedlings in a boreal climate. Additional winter coverings made up of fabric or plastic and twigs prevented the seedlings’ mortality even when the air temperature was below ?30 °C during the second winter. The results showed that the top soil temperature at 15 cm depth has to be above ?5 °C to guarantee the survival of seedlings. Q. pubescens was more sensitive to low soil temperatures than Q. robur. Morphological and PCR analysis of root samples collected over 2007–2010 confirmed the presence of T. aestivum in all orchards despite unfavorable temperatures during the winter time. The first T. aestivum sporocarps were found under Q. robur in October 2012 in the orchards established in 2006 on old agricultural land, showing truffle cultivation to be successful in the boreal climate.     

Sclerophylly in Quercus cerris L. var. cerris and Phillyrea latifolia L. and edaphic relations of these species

In this study foliar sclerophyll indexes, N %, P % and K % concentrations and correlations between sclerophyll index and these parameters were investigated in Quercus cerris L. var. cerris and Phillyrea latifolia L. In addition to this soil samples were collected and some physical and chemical analysis were carried out in these samples. Finally it has been determined that sclerophyll index was correlated with leaf N % concentrations in Q. cerris var. cerris and P. latifolia and leaf K % concentration in Q. cerris var. cerris.     

Leaf Water Potential and Peroxidase activity in Quercus cerris and Quercus pubescens after Inoculation with Diplodia mutila

Ten-year-old field-grown Quercus pubescens Willd. and Quercus cerris L. individuals were inoculated with Diplodia mutila (teleomorph Botryosphaeria stevensii Shoe-maker) to observe symptom evolution over 2 years. The experiments were carried out for the 3 years: 1991, 1992 and 1993. At the same time, the effect of D. mutila on leaf water potential and peroxidase activity was assessed on the leaves of 2-year-old seedlings from the same two species growing under controlled conditions (18 h day, relative humidity 75%), temperature 24/15°C day/night). Quercus pubescens was more susceptible than Q. cerris, and frequently exhibited dieback of the branch above the inoculation site. On the seedlings, the visible symptoms of infection were much more severe than on the older trees. The infected seedlings showed a lower leaf water potential than healthy seedlings, particularly those of Q. pubescens after the third week. The peroxidase activity was increased in infected Q. pubescens seedlings compared with both groups of control seedlings (wounded but not inoculated, and neither wounded nor inoculated) 14 and 21 days after inoculation. Leaf water potential and peroxidase activity are known indicators of stress which appear even before any visible symptoms; they could therefore serve as early indicators of D. mutila infection.     

Synthesis and establishment of <Emphasis Type="Italic">Tuber melanosporum</Emphasis> Vitt. ectomycorrhizae on two <Emphasis Type="Italic">Nothofagus</Emphasis> species in Chile

Axenically germinated seedlings of two species of Southern beech (Nothofagus obliqua, N. glauca) from Chile were inoculated with spores of the Périgord black truffle (Tuber melanosporum). Ectomycorrhizal development was monitored for 6 months in the greenhouse and compared to the performance of the natural host species Quercus ilex and Quercus robur. Seedling survival and mycorrhization showed major differences in both Nothofagus species: T. melanosporum readily formed ectomycorrhizae with seedlings of N. obliqua, although at a lower rate than with Q. ilex but at a proportion very similar to Q. robur; survival and colonization rates were high, and seedling growth was not visibly affected by the high soil pH required by T. melanosporum. In contrast, more than 50% of N. glauca seedlings died after inoculation, and mycorrhiza formation was very sparse. In both species, no colonization by adventive ectomycorrhizal fungi could be observed, whereas both species of Quercus showed minor colonization by another fungus, probably Inocybe or Hebeloma. Our results show that it is possible to infect N. obliqua with the Périgord black truffle under greenhouse conditions, which opens up the possibility of cultivating this truffle as a secondary crop during reforestation with N. obliqua in Chile.     

Long-term radial growth and climate-growth relationships of Quercus petraea (Matt.) Liebl. and Quercus cerris L. in a xeric low elevation site from Hungary

Sessile oak (Quercus petraea [Matt.] Liebl.) and Turkey oak (Quercus cerris L.) dominated mixed forests are common in low montane and hilly regions in Hungary. Here, we aimed to describe the long-term pattern and climatic responses of the radial growth of Q. petraea and Q. cerris in a xeric low-elevation forest, using retrospective tree-ring analysis for the period 1910–2019. We performed separate analyses with time series of full tree-ring (TRW), earlywood (EW) and latewood (LW) widths. Our results showed that the radial growth of the two species was largely synchronous over time, but became transiently divergent for a 20-year period after a drought in 1968, due to the greater-than-expected growth of Q. cerris and the supressed growth of Q. petraea. Precipitation was the major growth-limiting factor for both species, with a strong positive influence on LW particularly during the current early growing season (March-June), on EW in the previous late summer (August-September) and in the current early spring (March), and on all tree-ring traits in the previous December. The radial growth of both species was negatively related to temperature in the spring (May) and late summer (August) of both current and previous years. The climate-growth relationships showed general instability over time: the most striking temporal change was a gradual shift of positive correlations with precipitation and SPEI during the growing season from spring (March-May) to summer (June-August) since the 1980s over the analysed period. The two species had similarly low growth resistance to droughts in four studied pointer years (1968, 1993, 2002 and 2012), but Q. cerris exhibited a greater capacity to recover over the four post-drought years, and thus higher growth resilience, particularly after the drought of 1968. Our results contribute to the better understanding of the role of climate variability and droughts in the growth of the two co-existing species in transitional locations between closed forests and forest-steppes.     

Impact of flooding and drought conditions on the emission of volatile organic compounds of Quercus robur and Prunus serotina

We conducted measurements with oak (Quercus robur L.) and black cherry (Prunus serotina Ehrh.) seedlings to investigate their volatile organic compound (VOC) emission behavior to flooding and drought conditions. A novel cuvette enclosure approach was applied on 18 individuals and emission rates were derived using proton transfer reaction-mass spectrometry (PTR-MS) and gas chromatography–mass spectrometry (GC–MS) techniques. Complementary chlorophyll fluorescence and CO₂ uptake measurements were performed for all of the samples. Q. robur seedlings remained unaffected by flood. On the contrary, P. serotina seedlings reduced their chlorophyll fluorescence yield by 34.5 ± 4.1 % and their CO₂ uptake by 67.5 ± 10.5 %. These observations along with the highest acetaldehyde emissions recorded indicate strong susceptibility to water stress. Drought had a similar impact on both species that reduced chlorophyll fluorescence yield, CO₂ uptake, and the emission rates of most VOC. Nevertheless, isoprene was found to be emitted more than 20 times stronger by Q. robur seedlings under all treatments. In general, most VOC emissions increased with soil water availability displaying an exponential trend for acetaldehyde and methanol and a linear one for the sum of mono- and sesquiterpenes. Only methyl salicylate was released about two times stronger from oaks under drought conditions in comparison to wet conditions. Considering their VOC emission behavior, Q. robur seedlings appear to tolerate flood much better than P. serotina and thus it is likely to have a competing advantage under these conditions.     

Electrophoretic Analysis of Genetic Variation within and between Populations of Quercus cerris,Q. pubescens,Q. petraea and Q. robur (Fagaceae) from Eastern Austria

Allozyme variation at 14 loci was studied electrophoretically in 19 population samples of Quercus cerris, Q. pubescens, Q. petraea, and Q. robur. Genetic variation, measured as mean heterozygosity, was found to be high within populations but low among populations. A significant deficit of heterozygotes was observed in most of the populations of Q. pubescens, Q. petraea, and Q. robur. At the species level, Q. cerris (sect. Cerris) appears to be clearly separated from the rest (sect. Quercus). Q. pubescens, Q. petraea, and Q. robur form a cluster of closely-related species. The degree of genetic differentiation among these species is low, i.e. in the range normally found among con-specific populations. Nevertheless, allozyme data allow the elaboration of a dendrogram which is in reasonable accordance with the taxonomic classification, but also supports the importance of hybridization and introgression. This is also underlined by the fact that the allelic differentiation at the Got-2 locus corresponds with the phenotypic classification (petraea-like, hybrids, and robur-like) in samples from mixed populations.     

Molecular evidence for hybrid origin of Quercus crenata Lam. (Fagaceae) from Q. cerris L. and Q. suber L.

Abstract

Random Amplified Polymorphic DNA (RAPD) and Inter-Simple Sequence Repeats (ISSR) markers were employed to examine samples from Quercus cerris, Q. suber and Q. crenata in order to test the hypothesis of the hybrid origin of Q. crenata from Q. cerris and Q. suber in a part of its distribution area where the two putative parents do not overlap at present. Leaves from 21 Q. crenata and 37 Q. cerris individual trees were collected at natural sites in northern Italy, where Q. suber is currently lacking; 21 Q. suber and six Q. crenata plants from central Italy were also analysed. Results from Unweighted Pair Group Method with Arithmetic mean (UPGMA) analysis and principal component analysis (PCA) implied that exchange of neutral markers has been considerable between the three species, while differences in morphological characters have remained comparatively stable. The Mantel test indicated low correlation between RAPD- and ISSR-based similarity matrices, showing that the two screening techniques reveal unrelated estimates of genetic relationships. Hybrid indices computed for both markers displayed an intermediate position of Q. crenata individuals between the two putative parents shifted toward Q. cerris. Results from the present study corroborate the hypothesis of a hybrid origin for Q. crenata occurring in northern Italy, and suggest asymmetrical backcrossing with Q. cerris acting as the recurrent parent.     

Morphological and physiological reactions of young deciduous trees (Quercus robur L., Q. petraea [Matt.] Liebl., Fagus sylvatica L.) to waterlogging

One-year-old seedlings of Quercus robur L., Q. petraea (Matt.) Liebl. and Fagus sylvatica L. were cultivated in lysimeters and subjected to waterlogging for 17 weeks, interrupted by a five-week drainage period during summer. The growth of Q. robur was less affected by waterlogging than that of Q. petraea and Fagus. Waterlogging resulted in the formation of adventitious roots in Q. robur and Q. petraea, but not in Fagus. In contrast to Fagus, Q. robur and, to a lesser extent, Q. petraea were able to generate roots even below the water table. The hydraulic conductance of the excised root systems, the stomatal conductance and, in Fagus, the leaf water potential and the leaf-mass related hydraulic conductance were decreased by waterlogging. The decrease in the hydraulic conductance was largest in Fagus, and smallest in Q. robur. The roots of Fagus responded to anaerobic conditions with an increase in ethanol concentration. The measurements of nitrate reductase activities in roots and leaves provided no indications of a persistent contribution of NO₃ ⁻ metabolism to the alleviation of waterlogging-induced stress. It is concluded that Q. robur and, to a lesser extent, Q. petraea can tolerate waterlogging periods better than Fagus due to a different pattern of root formation, and to a better adjustment of leaf biomass production to the hydraulic conductivity of the root system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Regeneration of oaks (Quercus robur/Q. petraea) and three other tree species during long-term succession after catastrophic disturbance (windthrow)

In broadleaved temperate forests in Europe, oak (Quercus robur/Q. petraea) regeneration is reported to be weak or absent. However, most work concern seedlings or saplings, studied relatively few years. We studied a Picea abies stand in Sweden, windthrown and logged (all stems harvested) in 1969, testing the hypothesis that oaks regenerate in the long term among competing tree species after catastrophic disturbance. In 2011, after 40 years/growth seasons, we recorded live and dead trees in the new stand and investigated the surroundings, competition, and succession. The following trees, up to 26 m tall, colonized: Sorbus aucuparia, Betula pendula/B. pubescens, Fagus sylvatica, Q. robur/Q. petraea, and Corylus avellana (a shrub). Betula dominated, and only Fagus was regenerating in 2011. Sorbus had produced most of the dead trees, mainly or partly through intraspecific competition. In the stand, compared to the surroundings, Quercus, Picea, and Alnus glutinosa were under-represented, and Sorbus, Betula, and Fagus were over-represented. Yet, the density of Quercus was far from negligible; 48 large trees/ha. Most of the oaks (74 %) were co-dominant trees and many grew near Sorbus. Thus, oaks can survive and grow fast among pioneer trees and browsing animals, a conclusion which is supported by the literature (nine studies identified). High mortality of Sorbus is part of a long-term succession, where Fagus might come to dominate. However, Quercus likely will persist, in low density. We propose three key traits contributing to long-term persistence of Q. robur/Q. petraea in European temperate forests: long life span, ecological plasticity, and resistance to disturbances.     

Cytosolic ascorbate peroxidase in some species of the Quercus genus

ABSTRACT

Six species of the Quercus genus (Quercus ilex L., Q. coccifera L., Q. suber L., Q. trojana Webb, Q. macrolepis Kotschy, Q. cerris L.) have been screened for cytosolic ascorbate peroxidase (APX) by means of native polyacrylamide gel electrophoresis (PAGE). A single isozyme was found in five species (Q. trojana, Q. suber, Q. cerris, Q. macrolepis and Q. coccifera), while Q. ilex shows two different APX proteins. The data showed marked similarities among Q. trojana, Q. suber, Q. cerris and Q. macrolepis with respect to the electrophoretic mobility. The validity of APX electrophoretic patterns in systematic studies is discussed.     

Root hydraulic conductance,gas exchange and leaf water potential in seedlings of Pistacia lentiscus L. and Quercus suber L. grown under different fertilization and light regimes

Differences in morphology, biomass allocations and physiological responses were investigated in seedlings of Mastic tree (Pistacia lentiscus L.) and Cork oak (Quercus suber L.) submitted to contrasting fertilization and light regimes during early growth. These species are two evergreen sclerophyllous Mediterranean species frequently used in Mediterranean reforestation programmes. Fertilization was the treatment that affected most of the morphological and physiological variables evaluated in P. lentiscus and Q. suber seedlings. Leaf area and specific leaf area (SLA) were affected by shading treatment in both species, showing higher values in seedlings grown under shade. P. lentiscus seedlings showed a high capacity to modify root morphological variables and root hydraulic conductance (K_R) with the fertilization treatment. In contrast, Q. suber showed low to moderate root system changes with the treatments applied, although the fertilization level affected biomass allocation (i.e., root to shoot ratio) in both species. Under high water demand, P. lentiscus seedlings with high K_R allowed transpiration (E) to increase without increasing the water potential gradient between soil and leaves. In Q. suber, high fertilization induced significant increases in photosynthesis (A), as well as a tendency to increase E with significantly lower leaf water potential (ψ_L).     

Different ability of three Mediterranean oak species to tolerate progressive water stress

Inter-comparisons in the gas exchange patterns and root characteristics under both well-watered and drought conditions were done in three-years-old seedlings of three oak species (Quercus cerris L., Q. frainetto Ten., and Q. ilex L.) growing in controlled environment. Well-watered Q. cerris had greater physiological performances than other oaks, but under drought it was not able to face the water stress showing also structural modifications such as reduction of root length and average diameter. On the other hand, Q. ilex maintained root growth both in drought or well-watered soils. Moreover, it was able to keep open stomata also under water stress, although stomatal conductance (g _s) was low. Q. frainetto had an intermediate position in regard to its physiological and root structural characteristics between Q. cerris and Q. ilex under drought stress. For all oaks the relationship between g _s and the ratio of sub-stomatal and ambient CO₂ concentration (C _i/C _a) highlighted the dynamic adaptation of g _s to the increase of hydraulic resistances of leaf, stem, and roots portions, more evident during the air humidity change and progressive soil dehydration. This suggests a well-triggered above-and under-ground mechanism to endure the drought stress.     

Distribution of seedlings and saplings of Quercus robur in a grazed deciduous forest

Seedling and sapling distribution of the deciduous tree Quercus robur was, studied in a grazed, partly open forest, ca. 20 km S of Linkoping, Sweden. Numbers of seedlings and saplings were compared between open and shaded parts of the forest. Cover values for the shrub and tree layers, proportion of bare ground and of stones and soil water content were determined. Q. robur was shown to germinate equally well in open and shaded parts of the forest; however, most saplings were found in the shade. No correlation was found between seedlings or saplings and cover of shrub layer or proportion of stones in the soil surface or with soil water content.     

Mycorrhization of Quercus spp. with Tuber huidongense and T. himalayense Collected in Korea

Fungi of the genus Tuber are ectomycorrhizal fungi that form a symbiotic relationship mainly with oak and hazel trees. Tuber spp. exhibit a highly selective host plant preference; thus, for cultivation purposes it is important to select an appropriate host plant for successful mycorrhization. In addition, as mycorrhizal characteristics differ according to Tuber spp., it is necessary to understand the differences in mycorrhizae according to the fungal species. Tuber huidongense and Tuber himalayense were recently discovered in Korea; therefore, we used spore suspensions from these two species to inoculate two species of oak trees, Quercus acutissima and Quercus dentata, to compare colonization rates and morphologies of the mycorrhizae. The colonization rates demonstrated that the different Tuber spp. favored different host plant species. In addition, unique morphological and anatomical characteristics were observed for T. huidongense and T. himalayense depending on the host species. These findings can lead to new economically important agricultural activities related to truffle cultivation in Korea.     

Seasonal variations of gas exchange, photosynthetic pigments, and antioxidants in Turkey oak (Quercus cerris L.) and Hungarian oak (Quercus frainetto Ten.) of different age

Seasonal changes in physiological and biochemical parameters were studied in 35-, 55- and 140-year-old trees of Turkey oak (Quercus cerris L.) and Hungarian oak (Q. frainetto Ten.), growing in natural stands in Eastern Balkan Mountains (Bulgaria). During the seasonal drought period (August), assimilation activity, transpiration rate, stomatal conductance and water potential had a seasonal minimum in all the studied tree ages and species. The foliar concentrations of glutathione, ascorbate, α-tocopherol, as well as photosynthetic pigments in oak leaves were significantly affected by season. With the increasing age of the studied trees, we observed a decrease of the physiological activity and an increase of the antioxidants’ accumulation. Both the species were drought tolerant and anisohydric, where Q. frainetto exhibited higher rates of gas exchange than Q. cerris. Moreover, they differed in the extent of increase in the foliar antioxidants and carotenoids.     

DNA methylation of Quercus robur L. plumules following cryo-pretreatment and cryopreservation

Pedunculate oak (Quercus robur) is an ecologically and economically important forest tree species which produces seeds that are classified as recalcitrant. Thus, cryopreservation of seed meristems is a method for long-term preservation of this germplasm in gene banks. During cryopreservation, many factors, such as desiccation, cryoprotection and cooling/rewarming, can induce stress in the frozen meristems. In this study, in vitro survival and the global DNA methylation level of plumules after cryoprotection, desiccation and cryostorage was evaluated. Results indicated that both desiccation and storage in liquid nitrogen have negligible influence on DNA methylation status of Q. robur plumules. These findings support the cryopreservation of plumules as an appropriate method for conservation of Q. robur germplasm.     

Root hydraulic conductivity and vessel structure modification with increasing soil depth of two oak species: Quercus pubescens and Quercus robur

There are numerous studies on water transport characteristics of trees from the base to tops, but only few deal with the variation in xylem conduit diameters from shallow to deep roots. This study compares variation in root conduit properties as a function of increasing soil depths for two oak species (Quercus pubescens Willd and Quercus robur L.) growing on two different plots. We measured root vessel characteristics at three soil depths including 0, 50 and 100 cm, and calculated the associated root-specific hydraulic conductivities. Vessel diameter and specific hydraulic conductivity increased with increasing soil depth from 0 to 50 cm, but did not change in the deeper soil layer in both species. We conclude that freeze–thaw events in upper soil layer limit vessel diameters and thus hydraulic conductivity of roots.