Carbon dioxide enrichment affected flower numbers transiently and increased successful post-pollination development stably but without altering final acorn production in mature pedunculate oak (Quercus robur L.)

Acorn production in oak(Quercus spp.)shows considerable inter-annual variation,known as masting,which provides a natural defence against seed predators but a highly-variable supply of acorns for uses such as in commercial tree planting each year.Anthropogenic emissions of greenhouse gases have been very widely reported to influence plant growth and seed or fruit size and quantity via the‘fertilisation effect’that leads to enhanced photosynthesis.To examine if acorn production in mature woodland communities will be affected by further increase in CO_(2),the contents of litter traps from a Free Air Carbon Enrichment(FACE)experiment in deciduous woodland in central England were analysed for numbers of flowers and acorns of pedunculate oak(Quercus robur L.)at different stages of development and their predation levels under ambient and elevated CO_(2) concentrations.Inter-annual variation in acorn numbers was considerable and cyclical between 2015 and 2021,with the greatest numbers of mature acorns in 2015,2017 and 2020 but almost none in 2018.The numbers of flowers,enlarged cups,immature acorns,empty acorn cups,and galls in the litter traps also varied amongst years;comparatively high numbers of enlarged cups were recorded in 2018,suggesting Q.robur at this site is a fruit maturation masting species(i.e.,the extent of abortion of pollinated flowers during acorn development affects mature acorn numbers greatly).Raising the atmospheric CO_(2) concentration by 150μL L^(−1),from early 2017,increased the numbers of immature acorns,and all acorn evidence(empty cups+immature acorns+mature acorns)detected in the litter traps compared to ambient controls by 2021,but did not consistently affect the numbers of flowers,enlarged cups,empty cups,or mature acorns.The number of flowers in the elevated CO_(2) plots’litter traps was greater in 2018 than 2017,one year after CO_(2) enrichment began,whereas numbers declined in ambient plots.Enrichment with CO_(2) also increased the number of oak knopper galls(Andricus quercuscalicis Burgsdorf).We conclude that elevated CO_(2) increased the occurrence of acorns developing from flowers,but the putative benefit to mature acorn numbers may have been hidden by excessive pre-and/or post-dispersal predation.There was no evidence that elevated CO_(2) altered masting behaviour.

Success factors for high-quality oak forest(Quercus robur, Q. petraea) regeneration

Background: Within the framework of close-to-nature forestry, oak forest(Quercus robur, Q. petraea) regeneration techniques that consider both silvicultural and nature conservation demands have become a very important issue.While there are many experimental and local studies that aim at disentangling the relationships between different environmental and silvicultural factors and the success of oak regeneration, systematic supra-regional studies at the greater landscape level are missing so far.Against this background, the first objective(a) of this study was to present an efficient and sufficiently accurate sampling scheme for supra-regional forest regrowth inventories, which we applied to young oaks stands. The second, and major, objective(b) was to identify the crucial success factors for high-quality oak forest regeneration in northwest Germany.Results: Objective(a): Factors that have been identified as potentially crucial for the success or failure of oak regeneration were either included in a field inventory procedure or extracted from forest inventory databases. We found that the collected data were suitable to be analyzed in a three-step success model, which was aimed at identifying the crucial success factors for high-quality oak forest regeneration.Objective(b): Our modeling procedure, which included a Bayesian estimation approach with spike-and-slab priors,revealed that competitive pressure from the secondary tree species was the most decisive success factor;no competition, or low competition by secondary tree species appeared to be particularly beneficial for the success of high-quality oak regeneration. Also fencing and the absence of competitive vegetation(weeds, grass, bracken)seemed to be beneficial factors for the success of oak regeneration.Conclusions: Trusting in biological automation was found to be mostly useless regarding economically viable oak forest regeneration. To efficiently organize oak regeneration planning and silvicultural decision-making within a forest enterprise, it is strongly recommended to initially evaluate the annual financial and personnel capacities for carrying out young growth tending or pre-commercial thinning and only then to decide on the extent of regenerated oak stands. Careful and adaptive regeneration planning is also indispensable to secure the long-term ecological continuity in oak forests. Oak regeneration should therefore preferably take place within the close vicinity of old oak stands or directly in them. The retention of habitat trees is urgently advised.

Genetic diversity and differentiation among populations of the pedunculate oak(Quercus robur)at the eastern margin of its range based on a new set of 95 SNP loci

The aim of this study is to determine the genetic variability and differentiation among populations of pedunculate oak(Quercus robur)at the eastern margin of the species distribution range.We applied new set of 95 geographically informative nuclear SNP(single nucleotide polymorphism)loci developed using Double Digest Restriction Site Associated DNA(ddRAD),a new generation DNA sequencing technology.The study area is located in the basins of the Volga River and its two main tributaries,Kama and Belaya.Despite the strong reduction and fragmentation of pedunculate oak forests over the last several centuries and comparatively small sizes of present stands,a relatively similar genetic diversity of seven populations was observed(on average,allelic diversity v_(a)=1.472-1.603,observed heterozygosity H_(O)=0.305-0.358,expected heterozygosity H_(E)=0.272-0.343).The genetic distances between populations vary between 0.102 and 0.170(on average,d_(0)=0.128).We have identified the absence of a spatial genetic structure and the existence of genetically peculiar populations in the territory studied.The genetic distances of Gregorius between populations vary between 0.102 and 0.170(on average,d_(0)=0.128).Genetic differentiation among populations was statistically significant with a mean of the fixation index FST of 0.075.Populations from the Privolzhye Upplands and from northern parts of the study area make the most contribution to overall inter-population differentiation(d_(0)=0.137).No significant differences exist among the samples at lowlands along the Volga river(d_(0)=0.110).It was concluded that the multiplicity and different ages of local populations and the complexity of migration routes of the pedunculate oak from Pleistocene refugia and secondary Holocene shelters can cause this phenomenon.

Increased Drying Rate Lowers the Critical Water Content for Survival in Embryonic Axes of English Oak (Quercus robur L.) Seeds

The potential to cryopreserve embryonic axes of desiccation-sensitive（recalcitrant） seeds is limited by damage during the desiccation necessary for low temperature survival,but the basis of this injury and how to reduce it is not well understood.The effects of drying rate on the viability,respiratory metabolism and free radical-mediated processes were therefore investigated during dehydration of Quercus robur L embryonic axes.Viability,assessed by evidence of germination and tetrazolium staining,showed a sharp decline at 0.27 and 0.8 g/g during rapid（〈12 h） or slow（3d） dehydration,respectively.Rapid dehydration therefore lowered the critical water content for survival.At any given water content rapid dehydration was associated with higher activities of the free radical processing enzymes,superoxide dismutase,catalase and glutathione reductase and lower levels of hydroperoxide and membrane damage.Rapid dehydration was also associated with lower malate dehydrogenase activity,and a reduced decline in phosphofructokinase activity and in levels of the oxidized form of nicotinamide dinucleotide.Ageing may have contributed to increased damage during slow dehydration,since viability declined even in hydrated storage after 3 d.The results presented are consistent with rapid dehydration reducing the accumulation of damage resulting from desiccation induced aqueous-based deleterious reactions.

Response of photosynthesis,growth,and acorn mass of pedunculate oak to diff erent levels of nitrogen in wet and dry growing seasons

The objective was to examine the effects of optimal leaf nitrogen levels>2.0%and suboptimal levels<2.0%,nitrogen nutrition on net photo synthetic rate,stem diameter increment,height growth increment and acorn mass of pedunculate oak during 2010 in the absence of drought stress and during 2011 under the impact of moderate drought stress.According to the results,moderate drought stress significantly reduced net photo synthetic rate,stem diameter increment and height growth increment,while acorn mass was not affected.Suboptimal nitrogen nutrition significantly reduced the net photo synthetic rate and stem diameter increment only in the wet year,acorn mass in both wet and dry years,while height growth increment was not significantly reduced by suboptimal nitrogen nutrition in either year.The results indicate that optimal nitrogen levels can stimulate photo synthetic rate and stem diameter increment of pedunculate oak only in the absence of moderate drought stress.Moreover,the results show that moderate drought stress is a more dominant stressor for photosynthesis and growth of pedunculate oak than suboptimal nitrogen nutrition,while for acorn development,it is the more dominant stressor.

Production of micro-cuttings from acorns to test the plasticity of response to contrasting soil water regimes

We collected acorns from selected Quercus robur and Quercus petraea mother trees growing at sta- tions with different depths to the water table. We produced pairs of micro-cuttings from these single acorns. The obtained pairs of cuttings represented phenotypes of high similarity according to photosynthetic parameters. These pairs of cuttings were used to test the plasticity of response to contrasting water regimes. For each pair, one cutting was submitted to drought and the other was submitted to waterlogging. Drought response was recorded according to gas exchange traits （stomatal closure and water use effi- ciency）. The response to waterlogging was recorded according to the capacity to form hypertrophied lenticels and to maintain the CO2 assimilation rate. Intermediary phenotypes presenting both high water use efficiency and the capacity to develop hypertrophied lenticels were expected.

危害夏橡的病虫害及防治

通过对夏橡(Quercus robur L.)病虫害的调查,总结出目前危害夏橡的2种病害及3种虫害的危害状,并针对病害和虫害危害特点采取相应的防治措施,为夏橡育苗及造林病虫害防治提供参考。

夏栎叶片体细胞胚胎发生技术

为完善夏栎(Quercus robur L.)体细胞胚胎发生体系,以夏栎新鲜叶片为外植体,分析不同消毒方式、基本培养基的种类、不同激素组合方式和浓度配比以及其他一些培养条件对愈伤组织诱导的影响,筛选出诱导愈伤组织以及体细胞胚胎发生的最佳条件。结果表明:1)最佳消毒方式为:75%酒精30 s+0.1%升汞2 min;2)叶片愈伤组织诱导最佳培养基配方为:MS+4.0 mg/L NAA+0.5 mg/L 6-BA;3)正向接种的诱导率均会比反向接种的诱导率高,且生长速度快;4)无光条件更适合叶片愈伤组织诱导;5)叶片体胚诱导最佳培养基配方为:MS+0.1 mg/L NAA+0.01mg/L 6-BA。

Distribution and effects of tree leaf litter on vegetation composition and biomass in a forest–grassland ecotone

Aims After abandonment of grasslands,secondary succession leads to the invasion by woody species.This process begins with the accumulation of tree litter in the forest–grassland ecotone.Our objectives were to determine the relationships between litter amounts and vegetation composition and cover along natural forest–grassland ecotones and to experimentally study the initial effects of tree litter accumulation on grassland vegetation and on microsite conditions.Methods We established 11 transects varying from 12 to 15 m in length in different forest–grassland ecotones in the Lahn-Dill highlands,Germany,and measured the mass and cover of tree litter and the cover and composition of vegetation at five sequential positions along each transect by using 1 m2 plots with five replications.In a field experiment,we established plots subjected to different litter amounts(0,200 and 600g m^(−2))and evaluated changes in grassland vegetation,soil temperature and soil nutrient availability below the litter layer.Important Findings Tree litter amounts decrease from 650 to 65g m^(−2) across the forest–grassland ecotone.Vegetation changed from shrubs and annual species(adapted to more stressful conditions)in the forests edge to grasses,rosettes and hemirosette species(with higher competitive abilities)in the grassland.These anthropogenic forest–grassland ecotones showed abrupt edges,and the two adjacent ecosystems were characterized by different species pools and functional groups.In the field experiment,the presence of a litter layer reduced vegetation biomass and cover;the species richness was only reduced in the treatment with high litter(600g m^(−2)).Additionally,adding litter on top of vegetation also reduced thermal amplitude and the number of frost days,while increasing the availability of some nutrients,such as nitrogen and aluminium,the latter being an indicator of soil acidification.Adding a tree litter layer of 600g m^(−2) in grassland areas had strong effects on the composition and diversity of grassland vegetation by reducing the cover of several key grassland species.In,or near,forest edges,litter accumulation rapidly changes established vegetation,microsite conditions and soil nutrients.

夏橡高效育苗技术试验

针对夏橡(Quercus robur L.)种子发芽难、出苗率低、苗木质量差、苗木移栽成活率低等问题,进行种子处理、容器选择、基质配置、移栽等试验。结果表明:夏橡用沙藏催芽效果较好,发芽率达到92%。夏橡在设施条件下采用轻基质穴盘育苗的高生长量、地径分别比直播苗高62.3%、19.3%,同时穴盘育苗的单位面积出苗量是大田育苗出苗量的2.3倍。

Climate variation, reproductive frequency and acorn yield in English Oaks

Aims Annually variable but synchronous production of large seed crops(‘masting’)is a widespread phenomenon in temperate trees.Mounting concerns about the impacts of anthropogenic climate change(ACC)on plant reproduction gives urgency to our need to understand better the role of climate on tree reproduction,and in particular,mast events.Unlike our understanding of reproductive phenology however,there is little consensus regarding how climate affects plant reproductive effort or indeed the actual environmental triggers that underpin masting behaviour.Methods We used a 27-year record of acorn yield from a population of 12 Quercus robur trees located in southern England to compare mast-ing frequency and post-dispersal acorn yield each year for each tree,with long-term weather data over the same period.We focussed on discrete or sequential climate cues(temperature,precipitation and frost days)as likely predictors of oak reproduction.Important Findings Annual post-dispersal acorn crop varied greatly;i.e.no acorns in 14 of the 27 years,but there was no sequential pattern of crop ver-sus non-crop years indicating that weather,rather than resource limitation alone,dictated the timing of reproduction.Crop years were instead most closely associated with relatively cool late sum-mer conditions in the preceding year,followed by anomalous sum-mer warmth within crop year.Acorn yield increased following dry April and above-average May and June temperatures within crop year.Although our results support a general association between warm late spring and summer conditions,and crop frequency and yield,respectively,the influence of cooler later summer conditions in the year prior to masting highlights how a combination of weather cues may dictate the occurrence of mast years.Consequently,our results corroborate not only the hypothesis that temperature differ-entials between consecutive years,not absolute temperatures,may be the better predictor of mast seeding events but lend support also to the suggestion that reproductive failure and resource accumu-lation resulting from a climate-linked environmental veto,drives future reproductive synchronization in temperate tree species.