Evergreen Oak Tree Research Articles

Changes in leaf lifespan, nitrogen resorption, and mean residence time of leaf nitrogen along a soil fertility gradient in an evergreen oak tree.

The ability of plants to retain nitrogen (N) for a long period of time is critical to their N use efficiency, growth, and fitness, particularly in infertile environments. The mean residence time of leaf N (MRTL) and its two determinants, leaf lifespan and N resorption efficiency (rN, the fraction of the total leaf N pool that is resorbed during leaf senescence), have been hypothesized to increase plastically with decreasing soil N fertility but this remains to be fully tested. To avoid confusion by random changes in these characteristics in a relatively narrow N fertility range, MRTL, leaf lifespan, and N resorption efficiency were measured in Quercus glauca over a broad N fertility range. In the high to moderate N fertility range, leaf lifespan and rN increased with decreasing N addition rate, and thus the MRTL increased. However, in the moderate to low N fertility range, leaf lifespan increased but rN decreased significantly, so MRTL decreased. The decrease in rN occurred because the senesced leaf N concentration was almost constant at the lower limit while the green leaf N concentration decreased in this range. The hump-shaped quadratic responses of MRTL and rN along the N fertility gradient suggest that incorrect conclusions about the response of these traits to N fertility variation may be drawn from experiments that include only a few fertility levels, and N recycling within leaf canopy alone cannot achieve efficient N use in infertile environments.

Revealing early Neolithic vegetation and environmental changes in the Lower Yangtze Valley, eastern China: Pollen insights

The Lower Yangtze Valley, a key region in understanding early Neolithic human activities, presents an unsolved question regarding the early occurrence of such impact before 8.0 cal ka BP. The elusive details around the specific time and the environmental background underscore the need for more investigation. In addition, regional vegetation is obscurely known in this region mainly attributed to variable pollen sources resulting from highly unstable deposition environment in this widespread marine-flood interaction plains. This paper reconstructs the vegetation-environmental history in the Lower Yangtze Valley during 10.1–7.2 cal ka BP and identifies regional forests and potential signals of human activities through analyses of AMS 14C dates, pollen data, and grain size. The results show that during the period from 10,100 to 8270 cal a BP, a stable deciduous oak forest as the regional forest dominated the region in a monotonous vegetation pattern. After 8270 cal a BP, deciduous oak trees receded, while evergreen oak trees and other woody types expanded, resulting in the regional vegetation transitioning to a regional mixed evergreen-deciduous broad-leaved forest up to 7230 cal a BP. Moreover, early indications of human activity were detected by high abundance of Poaceae including rice (Oryza sativa) type. Together with a previously reported rice phytolith record from neighboring areas, this research provides compelling pollen evidence suggesting that human activities in the Lower Yangtze Valley likely at least dated back to 8200 cal a BP, around 2000 years earlier than current archeological records.

Estimation of Oak Leaf Functional Traits for California Woodland Savannas and Mixed Forests: Comparison between Statistical, Physical, and Hybrid Methods Using Spectroscopy

Key leaf functional traits, such as chlorophyll and carotenoids content (Cab and Cxc), equivalent water thickness (EWT), and leaf mass per area (LMA), are essential to the characterization and monitoring of ecosystem function. Spectroscopy provides access to these four leaf traits by relying on their specific spectral absorptions over the 0.4–2.5 µm domain. In this study, we compare the performance of three categories of estimation methods to retrieve these four leaf traits from laboratory directional-hemispherical leaf reflectance and transmittance measurements: statistical, physical, and hybrid methods. To this aim, a dataset pooling samples from 114 deciduous and evergreen oak trees was collected on four sites in California (woodland savannas and mixed forests) over three seasons (spring, summer and fall) and was used to assess the performance of each method. Physical and hybrid methods were based on the PROSPECT leaf radiative transfer model. Physical methods included inversion of PROSPECT from iterative algorithms and look-up table (LUT)-based inversion. For LUT-based methods, two distance functions and two sampling schemes were tested. For statistical and hybrid methods, four distinct machine learning regression algorithms were compared: ridge, partial least squares regression (PLSR), Gaussian process regression (GPR), and random forest regression (RFR). In addition, we evaluated the transferability of statistical methods using an independent dataset (ANGERS Leaf optical properties database) to train the regression algorithms. Thus, a total of 17 estimations were compared. Firstly, we studied the PROSPECT leaf structural parameter N retrieved by iterative inversions and its distribution over our oak-specific dataset. N showed a more pronounced seasonal dependency for the deciduous species than for the evergreen species. For the four traits, the statistical methods trained on our dataset outperformed the PROSPECT-based methods. More particularly, statistical methods using GPR yielded the most accurate estimates (RMSE = 5.0 µg·cm−2; 1.3 µg·cm−2; 0.0009 cm; and 0.0009 g·cm−2 for Cab, Cxc, EWT, and LMA, respectively). Among the PROSPECT-based methods, the iterative inversion of this model led to the most accurate results for Cab, Cxc, and EWT (RMSE = 7.8 µg·cm−2; 2.0 µg·cm−2; and 0.0035 cm, respectively), while for LMA, a hybrid method with RFR (RMSE = 0.0030 g·cm−2) was the most accurate. These results showed that estimation accuracy is independent of the season. Considering the transferability of statistical methods, for the four leaf traits, estimation performance was inferior for estimators built on the ANGERS database compared to estimators built exclusively on our dataset. However, for EWT and LMA, we demonstrated that these types of statistical methods lead to better estimation accuracy than PROSPECT-based methods (RMSE = 0.0016 cm and 0.0013 g·cm−2 respectively). Finally, our results showed that more differences were observed between plant functional types than between species or seasons.

Characterization of the complete chloroplast genome of Quercus acrodonta (Fagaceae)

Quercus acrodonta Seemen is an East Asian evergreen oak tree species belonging to the Quercus section Ilex. Here, we assembled and annotated the complete chloroplast (cp) genome of the species. The circular genome is 161,105 bp in size, presenting a typical quadripartite structure including two copies of inverted repeat (IR) regions (25,864 bp), one large single-copy (LSC) region (90,357 bp), and one small single-copy (SSC) region (19,020 bp). A total of 131 genes are encoded, including 85 protein-coding genes (PCGs), 38 tRNAs, and eight rRNAs. Phylogenetic analysis based on cp genome sequences of 18 Quercus species indicated that Q. acrodonta was more closely related to Q. phillyraeoides.

BEST-WR: An adapted algorithm for the hydraulic characterization of hydrophilic and water-repellent soils

Water-repellent soils usually experience water flow impedance during the early stage of a wetting process followed by progressive increase of infiltration rate. Current infiltration models are not formulated to describe this peculiar process. Similarly, simplified methods of soil hydraulic characterization (e.g., BEST) are not equipped to handle water-repellent soils. Here, we present an adaptation of the BEST method, named BEST-WR, for the hydraulic characterization of soils at any stage of water-repellency. We modified the Haverkamp explicit transient infiltration model, included in BEST for modeling infiltration data, by embedding a scaling factor describing the rate of attenuation of infiltration rate due to water repellency. The new model was validated using analytically generated data, involving soils with different texture and a dataset that included data from 60 single-ring infiltration tests. The scaling factor was used as a new index to assess soil water repellency in a Mediterranean wooded grassland, where the scattered evergreen oak trees induced more noticeable water repellency under the canopies as compared to the open spaces. The new index produced results in line with those obtained using the water drop penetration time test, which is one of the most widely test applied for quantifying soil water repellency persistence. Finally, we used BEST-WR to determine the hydraulic characteristic curves under both hydrophilic and hydrophobic conditions.

The Optimal <i>In Vitro</i> Culture Condition for Shoot Multiplication of Evergreen Oak Tree, <i>Quercus myrsinaefolia</i> Blume

The evergreen oak tree, Quercus myrsinaefolia Blume, is not only economically important for wood, medicine, landscape trees, etc., but also becoming more important in terms of ecology due to climate change. However, asexual reproduction was difficult, so this study was conducted to establish the optimum conditions for micropropagation by shoot multiplication. The surface sterilized seeds of Q. myrsinaefolia were successfully germinated in WPM basal medium. BAP (1.0 mg/L) treatment was most effective for inducing multiple shoots. The highest induction rates of adventitious roots from the multiple shoots was shown in the treatment of 1.0 mg/L NAA. Both MS and WPM medium were most effective for growth of multiplied plantlets. For ex vitro acclimatization, the survival rates of multiplied plantlets were 100% in vermiculite and commercial soil. The results of this study can be used for proliferation and supply, and establishment of ex situ conservation of Q. myrsinaefolia elite trees.

‘Emplaced Transcendence’ as Ecologising Education in Michael Bonnett's Environmental Philosophy

At the 2019 Annual Conference of the Philosophy of Education Society of Great Britain, Michael Bonnett was an invited speaker, giving a paper entitled ‘Transcendent nature, sustainability, and ‘ecologising’ education’. In this keynote, Bonnett shared portions of his forthcoming book, Environmental Consciousness, Nature, and Philosophy of Education: Ecologizing Education (London, Routledge). A day earlier at the conference Jeff Stickney gave a paper entitled ‘Informal place-based learning in environmental sustainability education: Seeing anew the Cloister oak tree at New College through Heidegger & Wittgenstein's Philosophies.’ Here we offer a section of Stickney's paper discussing Bonnett's environmental philosophy, focusing on a central aspect of his work: aesthetic and place-based education as a way of connecting more deeply with ‘nature’. Instead of delivering his paper at the conference, Stickney led participants on a walk across the Oxford campus, talking about the place and seeking to enhance appreciation of the evergreen oak tree in the cloister by entertaining different philosophical perspectives while those gathered drew the tree. The exercise was meant to illustrate what aesthetic, emplaced transcendence might actually look and feel like, in practice. Bonnett humbly agreed to write a brief response for this Special Issue.

The complete chloroplast genome sequence of Quercus stewardiana (Fagaceae)

Quercus stewardiana A.Camus is an East Asian evergreen oak tree species belonging to Quercus section Cyclobalanopsis. In this study, we assembled and annotated the complete chloroplast (cp) genome of the species. The circular genome is 160,842 bp in size, presenting a typical quadripartite structure including two copies of inverted repeat (IR) regions (25,823 bp), one large single-copy (LSC) region (90,294 bp), and one small single-copy (SSC) region (18,902 bp). It encodes a total of 114 unique genes, including 80 protein-coding genes, 30 tRNA genes, and four rRNA genes. Phylogenetic analysis based on cp genome sequences of 35 Fagaceae species indicated that Q. stewardiana was more closely related to Q. myrsinifolia.

The complete chloroplast genome sequence of Quercus myrsinifolia (Fagaceae)

Quercus myrsinifolia Blume is an evergreen oak tree species native to East Asia, and is also one of the dominant trees of subtropical evergreen broad-leaved forests. In this study, we sequenced and analysed the complete chloroplast (cp) genome of the species. The circular genome is 160,803 bp in size, consisting of two copies of inverted repeat (IR) regions of 25,840 bp, one large single-copy (LSC) region of 90,223 bp, and one small single-copy (SSC) region of 18,900 bp. It encodes a total of 114 unique genes, including 80 protein-coding genes, 30 tRNA genes, and four rRNA genes. Phylogenetic analysis based on 30 cp genome sequences indicated that Q. myrsinifolia was among the members of section Cyclobalanopsis, and was most closely related to Q. sichourensis.

Diversity of fungal endophytic community in Quercus suber L. under different climate scenarios

Cork oak (Quercus suber L.) is an evergreen oak tree species, typically found throughout the Mediterranean Basin, which presents a great ecological and economic importance for Portugal. An increase of cork oak decline due to biotic and abiotic stresses has been reported, which could damage the ecosystem and lower cork production. The attack of some fungal pathogens seems to increase when trees are under several environmental stresses, such as increased temperatures or drought. In this work, fungal endophytic species of cork oak were collected from forest stands in different sites of Portugal. The community of fungal endophytes of young and old twigs was studied by obtaining fungal isolates from plant material and grouping them into morphotypes. This study allowed the comparison of fungal endophytic communities living in cork oak trees from different forests, displaying distinct climates and water availability levels. The results revealed that endophyte communities are better discriminated when considering different plant tissues than cork oak stand location or climate.

Seasonal variation of leaf wax n-alkane production and δ2H values from the evergreen oak tree, Quercus agrifolia

In order to understand the timing of leaf wax synthesis in higher plants, we analysed the variability in leaf wax n-alkane concentration, composition (expressed as average chain length (ACL)), and δ2Hwax values as well as plant source water δ2H values (xylem and leaf water) in the evergreen tree Quercus agrifolia over a period of 9 months, beginning with leaf flush. We identified three distinct periods of leaf development with the first month following leaf flush being characterized by de novo synthesis and possibly removal of n-alkanes. During the following 3 months, n-alkane concentrations increased sevenfold and δ2Hwax and ACL values increased, suggesting this period was the major leaf wax n-alkane formation period. During the remaining 4 months of the experiment, stable values suggest cessation of leaf wax n-alkane formation. We find that n-alkane synthesis in Q. agrifolia takes place over 4 months, substantially longer than that observed for deciduous trees.

Persistence and detection of black truffle ectomycorrhizas in plantations: comparison between two field detection methods

Owners of black truffle (Tuber melanosporum) plantations are concerned about the persistence of its mycorrhizas and mycelium in the soil, especially until the appearance of the "truffle burn" areas and the triggering of sporocarp production, at least 5-7 years after planting truffle-inoculated seedlings. During this period, the farmer does not know whether his management is promoting black truffle development. To study the presence and abundance of T. melanosporum ectomycorrhizas in plantations, two sampling methods, direct sampling of root tips and soil core collection, are compared by analyzing 48 evergreen oak trees (Quercus ilex) inoculated with truffle. Those trees are grouped by age (<6, 6-9, >9 years old) and presence or absence of truffle production. T. melanosporum was present in 46 out of the 48 studied trees, and its ectomycorrhizas appeared in 65% of the ectomycorrhizal tips. Its abundance is significantly higher with productive trees and young trees. Direct sampling of root tips and soil core collection were equally effective in detecting this species, although soil core collection proved a better method to also evaluate ectomycorrhizal fungal diversity. To detect the presence of T. melanosporum in a given plantation, three samples suffice, with a single sample per random tree. Although the presence of mycorrhizas is not a sure sign of the future success of a black truffle plantation, its absence influences managers as to whether to continue culturing truffles in a plantation.

Thermal dissipation probe measurements of sap flow in the xylem of trees documenting dynamic relations to variable transpiration given by instantaneous weather changes and the activities of a mistletoe xylem parasite

The thermal dissipation probe was described in the early 1930s for the demonstration of a volume and mass flow of sap in the conductive elements of the xylem in trees. It was subsequently developed further and is now widely used in physiological ecology including measurements in the field. Thermal dissipation demonstrates the occurrence of sap flow and allows determination of its velocity. Here we report simultaneous continuous measurements of sap flow using the thermal dissipation technique and of transpiration by infrared gas analysis for diurnal and annual cycles in a deciduous and an evergreen oak tree, Quercus robur L. and Quercus turneri Willd., respectively, in a deciduous and an evergreen conifer, Larix decidua Mill. and Pinus griffithii McClell., respectively, and the host/mistletoe consortium of the deciduous linden Tilia mandschurica Rupr. & Max. and the evergreen Viscum album L. We show (1) that in diurnal cycles sap flow closely follows dynamic changes of the rate of transpiration elicited by daily fluctuations of weather parameters (sunshine, cloudiness, air temperature and humidity), (2) that in annual cycles sap flow reflects autumnal yellowing and shedding of leaves of the deciduous trees. We report for the first time comparative measurements of sap flow towards mistletoe shoots and host branches in a parasite/host consortium. This demonstrates (3) that mistletoes maintain considerably larger sap flow rates in their xylem conduits than the adjacent host branches dragging the transpiration stream of their host towards their own shoots. We also show (4) that even after the deciduous host has shed its leaves and itself does not transpire any more the evergreen mistletoe towards its shoots can maintain the persistence of a continuous sap flow via the stem and branches of the host as long as frost does not prevent that. The work presented underlines the contention that transpiration is the driving force for sap flow with continuous files of water in the xylem. It shows for the first time that mistletoes direct the flow of water through host roots and stems towards its own shoots by not only performing stronger transpiration as it is known from the literature but also by maintaining larger sap flow rates in the xylem conduits of its stems.

Evaporation of intercepted rainfall from isolated evergreen oak trees: Do the crowns behave as wet bulbs?

A new approach is suggested for estimating evaporation of intercepted rainfall from single trees in sparse forests. It is shown that, theoretically, the surface temperature of a wet tree crown will depend on the available energy and windspeed. But for a fully saturated canopy under rainy conditions, surface temperature will approach the wet bulb temperature when available energy tends to zero. This was confirmed experimentally from measurements of the radiation balance, aerodynamic conductance for water vapour and surface temperature on an isolated tree crown. Net radiation over a virtual cylindrical surface, enclosing the tree crown, was monitored by a set of radiometers positioned around that surface. Aerodynamic conductance for the tree crown was derived by scaling up measurements of leaf boundary layer conductance using the heated leaf replica method. Thermocouples were used to measure the average leaf surface temperature. Results showed that a fully wet single tree crown behaves like a wet bulb, allowing evaporation of intercepted rainfall to be estimated by a simple diffusion equation for water vapour, which is not restricted by the assumptions of one-dimensional transfer models usually used at the stand scale. Using this approach, mean evaporation rate from wet, saturated tree crowns was 0.27 or 0.30 mm h −1, when surface temperature was taken equal to the air wet bulb temperature or estimated accounting for the available energy, respectively.

Spatial variations in xylem sap flux density in evergreen oak trees with radial-porous wood: comparisons with anatomical observations

To estimate whole-tree water use when employing sap flow measurements, integration of the sap flux density (F d) over the sapwood area is needed. Accordingly, it is necessary to obtain information on the characteristics of stem water transportation such as spatial variations in F d and the active xylem area in the stem cross-section. Although evergreen oak trees with radial-porous wood represent a major component of secondary forests in western Japan, detailed information on their stem water transportation characteristics remains unclear. In the present study, we used the heat dissipation method (Granier method) to conduct measurements of azimuthal and radial variations in the F d of Quercus glauca Thunb. ex Murray, a representative evergreen broad-leaved tree in western Japan. Further, by analyzing the anatomy of the xylem structure, we examined why F d varies spatially in the stem cross-section. By using a dye solution injected into a radial hole bored into the tree trunk, we confirmed that the entire stem is hydroactive. We also compared the spatial variations in F d and water conductivity per xylem area (K s) which were estimated by using the observed vessel diameters and their density over the stem cross-section and Hagen–Poiseuille’s law. Azimuthal and radial variations in F d reached about 60 and 50% of the maximum values, respectively, and could be explained by spatial variation in K s. As a result, we obtained statistical parameters describing the spatial variation in F d in Q. glauca and determined that whole-tree water use estimated from measurements in one direction had at most ±20% potential errors for studied trees.

Simultaneous pituitary–gonadal recrudescence in two Corsican populations of male blue tits with asynchronous breeding dates

Animal populations living in geographically variable environments respond to different selection pressures. The adaptive character of the responses to environmental information determines the degree of synchrony of the breeding period with local optimal conditions. An example is provided by two populations of Mediterranean blue tits ( Parus caeruleus) in Corsica, breeding in different habitats, with a 1-month difference in the onset of egg laying. This difference in the onset of lay is supposed to be adaptive because, although chicks from both populations are raised mostly on caterpillars, the timing of the appearance of caterpillars is earlier for populations of tits associated with deciduous oak trees than those associated with evergreen oak trees. Here, we show that, despite the difference in the timing of egg laying, males from these two populations start seasonal hypothalamo–hypophysial–testicular development at approximately the same time, in late winter. Specifically, the vernal recrudescence of brain GnRH-I perikarya and fibers, testes volume and song activity began around the same dates and proceeded at the same pace in late winter in both populations. Plasma testosterone and LH levels displayed seasonal variations that were shifted by less than 2 weeks compared to the 1-month difference in egg laying periods. We hypothesize that the strong selection pressures on these two populations to adapt the timing of their breeding seasons to their local environment may have acted mostly on the female egg laying dates, and not so much on the initiation and rate of seasonal recrudescence of the hypothalamo–hypophysial–testicular activity in males.

Rainfall interception by an isolated evergreen oak tree in a Mediterranean savannah

AbstractRedistribution of ground‐level rainfall and interception loss by an isolated Quercus ilex tree were measured over 2 years in a Mediterranean oak savannah. Stemflow, meteorological variables and sap flow were also monitored. Rainfall at ground level was measured by a set of rain‐gauges located in a radial layout centred on the tree trunk and extending beyond the crown limits. Interception loss was computed as the difference between the volume of rainwater that would reach the ground in the absence of the tree and the volume of water that actually fell on the ground sampling area (stemflow included). This procedure provided correct interception loss estimates, irrespective of rainfall inclination. Results have shown a clear non‐random spatial distribution of ground‐level rainfall, with rainwater concentrations upwind beneath the crown and rain‐shadows downwind. Interception loss amounted to 22% of gross rainfall, per unit of crown‐projected area. Stand interception loss, per unit of ground area, was only 8% of gross rainfall and 28% of tree evapotranspiration. These values reflect the low crown cover fraction of the stand (0·39) and the specific features of the Mediterranean rainfall regime (predominantly with few large storms). Nevertheless, it still is an important component of the water balance of these Mediterranean ecosystems. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Early seasonal development of brain song control nuclei in male blue tits

In songbirds, the seasonal growth of the song system is generally thought to be controlled by the spring increase in plasma levels of testosterone and/or related changes in singing activity. Here we report an extremely early seasonal growth (before February) of the song control nuclei HVC and RA in Corsican blue tits ( Parus caeruleus) indicating that the vernal development of these nuclei occurs well before the vernal increase in plasma testosterone, testes size and song activity. The development of HVC and RA occurred simultaneously in two populations that are known to breed consistently 1 month apart as an adaptation to heterogeneous landscapes (predominance of broad-leaved deciduous versus evergreen oak trees). The unidentified environmental and/or physiological cues controlling the plasticity in the song system must therefore differ, at least in part, from those affecting other morphological and physiological traits controlling reproduction.

温暖化環境下での樹林の炭素循環・収支研究のためのオープントップチャンバー（OTC）の環境条件の制御

温暖化環境下での樹林の炭素循環・収支研究のためのオープントップチャンバー（OTC）の環境条件の制御

Constraints on transpiration from an evergreen oak tree in southern Portugal

The experiment took place at a sparse evergreen oak woodland in southern Portugal. Seasonal courses of sap flow, measured in eight points of the stem of a Quercus rotundifolia tree, were monitored during a 2-year period. Plant water relations (predawn and midday leaf water potential, canopy conductance and whole-plant hydraulic conductance) as well as meteorological variables were also measured during the experimental period (May 1996–August 1998). All evidence showed that the plants remained well watered throughout the observation period. The highest transpiration rates occurred during the summer, when only vestigial amounts of rain fell on the shallow soil with a low water storage capacity. This could only be explained by the direct access of the root system to a 13 m deep water table. Although there was no increase in water stress during the summer drought, the transpiration rates showed an upper limit well below the atmospheric evaporative demand. This was consistent with the occurrence of a maximum limit for the root water uptake capacity determined by the summer value of whole-plant hydraulic conductance and by stomatal control, which prevented leaf water potential from falling below a cavitation threshold.