白皮松种子休眠特性的种源变异

对７个具有代表性种源的白皮松种子的休眠特性研究表明,白皮松种子种皮的透水性在种源间差异明显,表现出随地理纬度的增高而逐渐增大的趋势,分布越是偏北的种源透水性趋于加强。根据种皮的透水性,７个种源可被分为差异明显的２组,组间以秦岭为界。不同种源种子种皮的透气性以外种皮造成的差异为最大,内种皮次之。种子的透气性与透水性表现出的变化趋势相同。不同种源种子浸提液的抑制能力显著不同,而且这种差异随浸提液浓度的     

Diploid hybrid origin of Hippophaë gyantsensis (Elaeagnaceae) in the western Qinghai–Tibet Plateau

Homoploid hybrid speciation, the origin of a hybrid species without change in chromosome number, is currently considered to be a rare form of speciation. In the present study, we examined the phylogenetic origin of Hippophaë gyantsensis, a diploid species occurring in the western Qinghai–Tibet Plateau. Some of its morphological and molecular traits suggest a close relationship to H. rhamnoides ssp. yunnanensis while others indicate H. neurocarpa. We conducted phylogenetic analyses of sequence data of two maternally inherited chloroplast (cp) DNA fragments and the bi‐parentally inherited nuclear ribosomal internal transcribed spacer (ITS) from 17 populations of H. gyantsensis, 15 populations of H. rhamnoides ssp. yunnanensis and 27 populations of H. neurocarpa across their distributional ranges, and modelled the niche differentiation of the three taxa. Multiple lines of evidence suggested that H. gyantsensis is a morphologically stable, genetically independent and ecologically distinct species. The inconsistent phylogenetic placements of the H. gyantsensis clade that comprised the dominant cpDNA haplotypes and ITS ribotypes suggested a probable diploid hybrid origin from multiple crosses between H. rhamnoides ssp. yunnanensis and H. neurocarpa. This tentative hypothesis is more parsimonious than alternative explanations according to the data available, although more evidence based on further testing is needed.     

施氮水平和收获时期对夏玉米产量和籽粒品质的影响

为明确黄淮海夏玉米适宜的施肥量和最佳收获时期,设计了5个氮肥水平（不施肥、113、181、249和375 kg N·hm^-2）和2个收获时期（S₁：9月23日,农民习惯收获时间;S₂：9月29日,推迟6 d收获）,研究施氮量和收获时期对夏玉米产量和品质的影响.结果表明：随施肥量增加,夏玉米穗粒数、千粒重和产量均增加,但差异不显著,其中施肥量在113～181 kg N·hm^-2的玉米产量、氮素利用效率均相对较高;随施肥量增加,夏玉米蛋白质和赖氨酸含量增加,淀粉含量降低.与9月23日蜡熟期收获相比,9月29日完熟期收获的夏玉米籽粒千粒重、产量、淀粉和赖氨酸含量均增加,籽粒蛋白质和脂肪含量降低.依据产量水平,黄淮海高产夏玉米区适宜的施肥量在113～180 kg N·hm^-2,最佳收获时期应推迟至9月29日-10月5日.     

cDNA isolation,functional expression,and characterization of (+)-alpha-pinene synthase and (-)-alpha-pinene synthase from loblolly pine (Pinus taeda): stereocontrol in pinene biosynthesis

The complex mixture of monoterpenes, sesquiterpenes, and diterpenes that comprises oleoresin provides the primary defense of conifers against bark beetles and their associated fungal pathogens. Monoterpene synthases produce the turpentine fraction of oleoresin, which allows mobilization of the diterpene resin acid component (rosin) and is also toxic toward invading insects; this is particularly the case for alpha-pinene, a prominent bicyclic monoterpene of pine turpentine. The stereochemistry of alpha-pinene is a critical determinant of host defense capability and has implications for host selection, insect pheromone biosynthesis, and tritrophic-level interactions. Pines produce both enantiomers of alpha-pinene, which appear to arise through antipodal reaction mechanisms by distinct enzymes. Using a cDNA library constructed with mRNA from flushing needles of loblolly pine (Pinus taeda), we employed a homology-based cloning strategy to isolate, and confirm by functional expression, the genes encoding (+)-(3R:5R)-alpha-pinene synthase, (-)-(3S:5S)-alpha-pinene synthase, and several other terpene synthases. The pinene synthases, which produce mirror-image products, share only 66% amino acid identity (72% similarity) but are similar in general properties to other monoterpene synthases of gymnosperms. The stereochemical control of monoterpene cyclization reactions, the evolution of "antipodal" enzymes, and the implications of turpentine composition in ecological interactions are discussed.     

Water availability drives signatures of local adaptation in whitebark pine (Pinus albicaulis Engelm.) across fine spatial scales of the Lake Tahoe Basin,USA

Patterns of local adaptation at fine spatial scales are central to understanding how evolution proceeds, and are essential to the effective management of economically and ecologically important forest tree species. Here, we employ single and multilocus analyses of genetic data (n = 116 231 SNPs) to describe signatures of fine‐scale adaptation within eight whitebark pine (Pinus albicaulis Engelm.) populations across the local extent of the environmentally heterogeneous Lake Tahoe Basin, USA. We show that despite highly shared genetic variation (F_ST = 0.0069), there is strong evidence for adaptation to the rain shadow experienced across the eastern Sierra Nevada. Specifically, we build upon evidence from a common garden study and find that allele frequencies of loci associated with four phenotypes (mean = 236 SNPs), 18 environmental variables (mean = 99 SNPs), and those detected through genetic differentiation (n = 110 SNPs) exhibit significantly higher signals of selection (covariance of allele frequencies) than could be expected to arise, given the data. We also provide evidence that this covariance tracks environmental measures related to soil water availability through subtle allele frequency shifts across populations. Our results replicate empirical support for theoretical expectations of local adaptation for populations exhibiting strong gene flow and high selective pressures and suggest that ongoing adaptation of many P. albicaulis populations within the Lake Tahoe Basin will not be constrained by the lack of genetic variation. Even so, some populations exhibit low levels of heritability for the traits presumed to be related to fitness. These instances could be used to prioritize management to maintain adaptive potential. Overall, we suggest that established practices regarding whitebark pine conservation be maintained, with the additional context of fine‐scale adaptation.     

Ethephon and auxin induce mycorrhiza-like changes in the morphology of root organ cultures of Mugo pine

The effects of ethylene and auxin on the morphology and anatomy of root organ cultures of Pinus mugo Turra var. mugo were investigated to test the hypothesis that changes in root morphology associated with formation of ectomycorrhizae may be related to ethylene produced by ectomycorrhizal fungi or by host plant roots in response to fungus-produced auxin. Morphological changes characteristic of mycorrhizal infection include dichotomous branching of lateral roots, inhibition of root hair formation and enlargement of cortical cells. Lateral roots on non-mycorrhizal root organ cultures, grown in a defined medium, underwent dichtotomous branching while root hair formation was inhibited in response to the ethylene released by 50 and 100 μ M ethephon (2-chloroethylphosphonic acid), but no effect on cortical cell dimensions was observed. The auxin, naphthaleneacetic acid (1 and 10 μ M ) also stimulated dichotomous branching and inhibited root hair formation, but to a lesser extent and with a greater lag time than ethephon. Auxin-stimulated ethylene production by root organ cultures was demonstrated. This appeared to be responsible, at least in part, for the auxin-induced dichotomous branching since the ethylene action inhibitor, silver thiosulfate (0.1 m M ) inhibited the response to auxin by 35%.     

Cryopreservation of embryogenic cultures of Scots pine

The aim of the study was to develop an effective cryopreservation method for Scots pine (Pinus sylvestris L.) embryogenic cultures. Altogether nine cell lines derived from three mother trees were cryopreserved after cold hardening using dimethylsulfoxide or two different mixtures of polyethyleneglycol 6000, glucose and dimethylsulfoxide as cryoprotectants. Seventy-eight percent of the cell lines remained viable after cryostorage, the best cryoprotectant treatment being 10% polyethyleneglycol 6000, 10% glucose, and 10% dimethylsulfoxide in water. This treatment resulted in significantly better regrowth of the embryogenic cultures than with the other cryoprotectants or with the controls. According to microscopical observations, the cells that retained their viability and regrowth ability after cryopreservation were the embryonal head cells, as well as some elliptic suspensor cells close to the embryonal head cell area. When proliferation growth of the frozen cultures had started, their morphological appearance was the same as the non-frozen cultures. In addition, the RAPD assays suggested that the cryostorage treatment used here preserved the genetic fidelity of the Scots pine embryogenic cultures. This revised version was published online in June 2006 with corrections to the Cover Date.     

Interactions among moths, crossbills, squirrels, and lodgepole pine in a geographic selection mosaic

Repeated patterns among biological communities suggest similar evolutionary and ecological forces are acting on the communities. Conversely, the lack of such patterns suggests that similar forces are absent or additional ones are present. Coevolution between a seed predator, the red crossbill (Loxia curvirostra complex), and lodgepole pine (Pinus contorta var. latifolia) exemplifies the ecological and evolutionary predictions for coevolving systems. In the absence of another seed predator and preemptive competitor (pine squirrels Tamiasciurus hudsonicus), natural selection by crossbills results in the evolution of larger cones with thicker distal scales, while relaxation of selection by squirrels results in the evolution of cones with more seeds and a greater ratio of seed mass to cone mass. However, in one range, the Little Rocky Mountains, distal scale thickness has diverged as expected but cone size has not. In these mountains seed predation by lodgepole pine cone borer moths (Eucosma recissoriana) was about 10 times greater than in other ranges lacking squirrels. We quantified moth predation and cone traits and found that moths select for smaller cones with fewer seeds. Thus, selection by moths in the Little Rocky Mountains counters both selection by crossbills for large cone size and relaxation of selection by squirrels favoring more seeds per cone and accounts for the relatively small and few-seeded cones in these mountains. It is also apparent that selection by crossbills changes seed defenses in a manner that favors seed predation by moths, whereas selection by squirrels likely reduces such predation. These results demonstrate the importance of considering the evolutionary consequences of community context in locally evolved (coevolved) traits and interactions.     

Aerenchyma and lenticel formation in pine seedlings: A possible avoidance mechanism to anaerobic growth conditions

Seedlings of pond pine ( Pinus serotina Michx.), sand pine [ P. clausa (Engelm.) Sarg.], and loblolly pine ( P. taeda L., wet-site and drought-hardy seed sources) were grown in hydroponic solution culture using a non-circulating, continuously flowing design under anaerobic or aerobic conditions to determine whether flooding tolerance was correlated with enhanced internal root aeration. Transport of atmospheric O₂ from the shoot to the root of anaerobically grown loblolly and pond pine seedlings was demonstrated via rhizosphere oxidation, using both reduced indigo-carmine solution and a polarographic, ensheathing Pt-electrode. Stem and root collar lenticels were the major sites of atmospheric O₂ entry for submerged roots in these seedlings. No O₂ leakage was detected from roots of aerobically grown pine seedlings. Longitudinal and radial pathways for gaseous diffusion via intercellular air spaces in the pericycle and between ray parenchyma cells, respectively, were demonstrated histo-logically in anaerobically grown loblolly and pond pines. Rhizosphere oxidation, and lenticel and aerenchyma development in roots of flood-intolerant sand pine seedlings grown in anaerobic solutions were minimal. Only 15 days of anaerobic growth conditions were necessary to increase internal root porosities of loblolly and pond pine seedlings – although not to the extent found in seedlings treated for 30 or 75 days. Histological results indicated that root tissue in the secondary stage of growth was capable of forming intercellular air spaces, demonstrating a degree of internal plasticity – at least in the more flood-tolerant loblolly and pond pine seedlings.