Stochastic trajectories of succession initiated by extreme climatic events

Deterministic or rule-based succession is expected under homogeneous biotic and abiotic starting conditions. Effects of extreme climatic events such as drought, however, may alter these assembly rules by adding stochastic elements. We monitored the succession of species composition of 30 twin grassland communities with identical biotic and abiotic starting conditions in an initially sown diversity gradient between 1 and 16 species over 13 years. The stochasticity of succession, measured as the synchrony in the development of the species compositions of the twin plots, was strongly altered by the extreme warm and dry summer of 2003. Moreover, it was independent from past and present plant diversity and neighbourhood species compositions. Extreme climatic events can induce stochastic effects in community development and therefore impair predictability even under homogeneous abiotic conditions. Stochastic events may result in lasting shifts of community composition, as well as adverse and unforeseeable effects on the stability of ecological services.     

Polysome formation induced by light in Pinus thunbergii seed embryos

Ribosome patterns in embryos of light-requiring pine seeds duringprolonged dark imbibition and after red light irradiation werestudied. Ribosomes isolated from dry embryos were essentiallyhomogeneous monomer particles. During a dark imbibition periodas long as 42 days, no appreciable changes in ribosomal patternswere observed. However, a decrease in monomer ribosomes anddistinct polysome formation were detected within 24 hr aftera brief red light had been given at any point in the dark imbibitionperiod. (Received May 11, 1974; )     

Post-inoculation Population Dynamics of Bursaphelenchus xylophilus and Associated Bacteria in Pine Wilt Disease on Pinus thunbergii

Population dynamics of the pine wood nematode Bursaphelenchus xylophilus (PWN) and its accompanying bacteria in non-inoculated twigs along with the process of the disease was observed in Japanese black pine, Pinus thunbergii inoculated with PWN. In the non-inoculated twigs, bacteria could be detected when only a few pine needles became yellow. Once most needles had turned yellow or brown, the nematode began to appear and the bacterial populations increased. At the late stages of the disease when the inoculated pine was dying and the needles were totally wilted, the populations of both nematode and bacteria started to increase rapidly. Only a few bacterial species were found at the early stages. As the disease process advanced, the bacterial populations increased rapidly in both population size and variety of the species. However, Pseudomonas fluorescens , P. sp., Pantoea sp. and Sphimgomenas pancimobilis, remained dominant.     

Image measurements of leaf scorches on landscape trees subjected to extreme meteorological events

Trees grow in changing environments and are usually injured by many external factors including both abiotic and biotic. Leaf scorch is a main symptom for many landscape trees when they are stricken by meteorological extreme events, such as summer drought, strong typhoon and winter freezing and so on. In the study, the internal angle of injured area (IAIA) was defined in relation to vein lines and measured non-destructively for some landscape tree species. Meanwhile, the leaf scorch area percent (LSAP) and percent of scorched central vein (PSCV) were also determined from RGB images. Positive relationships between IAIA and LSAP and between PSCV and LSAP were found. The larger IAIA values for scorched leaves and smaller IAIA values for spot/anthracnose diseased leaves of the studied trees indicated that IAIA may be used as a diagnosing index of leaf scorch symptoms.     

Fingerprints of extreme climate events in Pinus sylvestris tree rings from Bulgaria

Tree-ring studies may help better understand climate variability and extreme climate event frequency and are especially useful in regions where detailed meteorological records lack. We studied the effect of droughts and unusually cold periods on Pinus sylvestris tree-ring width and wood anatomy. Study sites were selected along an altitudinal gradient on Vitosha Mountain, Bulgaria. Drought conditions caused the formation of narrow tree rings or light rings if the drought occurred in July–August at the lower altitude sites. In years with droughts in June and the first half of July, followed by precipitation in the middle of July, intra-annual density fluctuations (IADFs) were formed. Trees in the zone with optimal growth conditions produced fewer light rings and narrow rings in years with either strongest droughts or unusually cold summers. At the timberline zone, low summer temperature triggered narrow tree rings and light rings. Frost rings were formed when there was a drop in temperatures below the freezing point in the second half of May or at the beginning of June. Our findings show that studies of tree-ring anatomy may contribute to obtain further knowledge about extreme climatic events in the Balkan Peninsula and in other regions where meteorological data lack.     

间伐对日本黑松海岸林更新的影响

为弄清间伐对海岸林内环境因子 ,进而对海岸林天然更新的影响 ,在黑松海岸林内进行了 4种不同强度的块状间伐试验 .林分间伐后 ,对更新状况和环境因子进行了连续观测 .结果表明 ,间伐可以改善林内光环境、提高土壤的含水量、加强空气流动、促进枯枝落叶的分解等 .4 0年生的黑松海岸林 5 0 %间伐处理后 (密度为 15 0 0株·hm-2 ,林冠开阔度 >30 % )不会对海岸林本身造成风害 ,也不会对防护功能产生较大影响 ,但却能为黑松海岸林天然更新提供良好的生态环境 .试验结果证实了间伐产生的林隙内日本黑松的更新规律 ,提出间伐可作为同龄黑松海岸林向复层、异龄海岸林演化的主要经营措施 .     

荧光假单胞菌鞭毛蛋白对黑松细胞的致死作用

采用细胞免疫荧光分析、细胞染色观察、电导率测定以及基因组DNA电泳分析技术,研究了松材线虫携带的荧光假单胞菌分泌的鞭毛蛋白对黑松愈伤组织细胞的作用及其致死方式。结果表明,鞭毛蛋白与黑松细胞之间存在直接的相互作用;鞭毛蛋白处理的细胞,细胞膜皱缩变形、细胞质浓缩、细胞核解体,形成若干小核,细胞质中的RNA降解;处理细胞的着色力增强,细胞培养液的电导率增加,说明鞭毛蛋白可增加处理细胞的细胞膜透性;基因组DNA的电泳分析证实,处理细胞的DNA发生了断裂,但无明显的梯子形成,推测鞭毛蛋白对黑松细胞的致死方式为非典型的细胞凋亡。     

福清黑松醇溶蛋白的群体遗传分析

采用聚丙烯酰胺凝胶电泳技术,对福清黑松群体进行醇溶蛋白的多样性分析,共获得40种图谱,9个等位基因位点。对这些位点的统计分析表明,福清黑松的多肽位点百分率P=55.56%, 等位基因平均数A=3.00,平均等位基因有效数目Ae=2.28,预期杂合度He=0.533,平均实际杂合度Ho=0.402,固定指数F仅为0.246>0。该群体表现出遗传多样性水平较高,但该群体偏离了Hardy-Weinberg平衡定律,原因可能是取样偏差、群体中个体密度分布不均和个体生长状况不好,不能产生充分的随机交配,出现遗传漂移导致的。     

Investigation on the Ontogeny of Pollen in Pinus thunbergii Parl

The microsporogenesis in Pinus thunbergii occurs in early to middle March, and the development of pollen in late March to early April. A mature pollen grain consists of four cells. The starch grains aggregate in the equators during meiosis Ⅰ to Ⅱ. The callose materials appear first in inner side of the wall of meiocyte and then in the equator. Sometimes the 3-or 4-sac- cate pollen grains have been found. In the ontogeny of pollen in Pinus thunbergii following events are noteworthy. (1) During meiosis the equatorial aggregation of starch grains in me iocyte becomes conspicuous. (2) During formation of tetrad the callose wall appears in regular activity. It is noteworthy that there is itself feature for the accumulation of callose in Pinus thunbergii. After formation of prothallial cells the callose appears mainly in the area between body and saccus. So the prominent symmetry of distribution of callose occurs in the pollen grains. But almost no callose accumulation takes place i,n tenuity in distal face of pollen grain. On the contrary, there are certain callose accumulation around the prothallial cells in the proximal face, forming the polar distribution of callose in pollen grains.     

林分结构对烟台黑松海岸防护林天然更新的影响

为阐明黑松(Pinusthunbergii)海岸防护林天然更新的影响机制,在对烟台2个典型样地6条样带共60个样方(10m×10m)调查的基础上,采用拟合模型和多重回归分析技术,探讨林分结构指标中,垂直结构(树冠指数、小树比例和大树比例)和密度因素(基面积、郁闭度和灌木盖度)对黑松种群天然更新的影响。结果表明在垂直结构变量中,树冠指数(CI)与幼龄植株个数之间存在典型的抛物线关系,在CI5-6范围内,幼龄植株个数达到最高;幼龄植株个数与小树比例关系较弱,但与大树比例表现出显著的正线性关系。在密度变量中,幼龄植株随着郁闭度的增加,个体数呈上升趋势,而随着灌木盖度的增加,则表现出显著的下降倾向;幼龄植株个数与基面积关系不明显。幼龄植株个体数变化取决于垂直结构变量CI和密度变量郁闭度和灌木盖度共同作用的影响。理解这些更新规律,是黑松海岸防护林可持续管理的前提。     

Protein synthesis in the embryo of Pinus thunbergii seed II. An induction by light

¹⁴C-Amino acid incorporating activity in the absence of exogenousmRNA was found in a cell-free system from embryos of light-germinatedPinus thunbergii seeds, but not in that from dark-imbibed seedembryos. Template activity in the cell-free system from thelight-germinated seed embryos was observed in the ribosome fraction,especially the polyribosome fraction, but not in the 100,000?gsupernatant fraction (s100). These facts suggest that the natureof the block in protein synthesis during the imbibition of seedsin the dark is due to the lack or inactivity of mRNA. The s100from light-germinated seed embryos was found to be less activein amino acid incorporation than that from dark-imbibed seedembryos. (Received November 29, 1976; )     

Development and seasonal variations of Lophodermium populations on Pinus thunbergii needle litter

A quantitative method was developed to describe Lophodermium (Rhytismataceae, Ascomycetes) populations on Pinus thunbergii needle litter, and seasonal patterns of population variation were examined based on this method. We focused on the formation of black zone lines across needles and the production of Lophodermium ascocarps on needle portions delimitated by zone lines. The study was carried out at a soil erosion control site on a mountain slope and at a coastal sand dune site. Most Lophodermium spp. on needle litter were identified as L. pinastri according to morphological characteristics of ascocarps and ascospores and DNA analysis. Zone lines were produced on needles when isolates of L. pinastri were in contact with other isolates of L. pinastri or with isolates of other species in dual culture tests. This observation provided a rationale to consider that individual colonies with ascocarps and delimitated by zone lines were occupied by a single Lophodermium isolate. Frequency of occurrence of Lophodermium colonies, total colony length, and mean colony number per needle were higher at the coastal sand dune site than at the soil erosion control site. Total colony length and mean colony number also varied with season. Mean colony length and mean ascocarp number per colony were not different between sites or seasons.     

沙质海岸黑松分枝格局特征及其抗风折能力分析

沙质海岸空间梯度上环境差异较大, 黑松(Pinus thunbergii)在长期的适应过程中树冠结构变化也很大。为揭示黑松树冠结构与环境间的适应机制, 在山东省胶南市灵山湾国家森林公园距海岸线0-50、200-250和400-450 m梯度内各设置1个样带, 记为带I、带II、带III, 采用枝构型的理论和方法, 对黑松的分枝格局进行了研究, 并采用模拟自然风法测定了黑松枝条的抗风折能力。结果表明: 1)在海岸梯度上黑松分枝格局差异较大, 随着距离海岸越来越远, 黑松各级枝的分枝长度、总体分枝率均逐渐增大, 而枝径比和逐步分枝率逐渐减小, 各级分枝角度表现为带I >带III >带II。2)带I树冠背风面与迎风面相比, 分枝长度、分枝角度、分枝数量、枝条干枯率分别是迎风面的1.62、1.38、2.65和0.59倍, 随着距离海岸越来越远, 这种不对称性逐渐减弱, 至带III树冠基本对称。3)海风是影响带I分枝角度偏转、枝条干枯和冠型不对称现象的主要原因。4)带III枝条的抗风折能力高于带I, 且两个样带模拟风速与枝条所承受的拉力之间的关系均符合逻辑斯蒂方程, 相关系数R²均达0.97以上。该研究揭示了不同海岸梯度上黑松分枝格局的形成机制及其抗风折能力, 可为沿海黑松防护林的合理经营提供科学依据。     

南亚热带水土流失地区人工加速植被演替过程

水土流失地区植被在自然条件下从阳生草本到乔灌草复合植被的演替过程常常需要很长的时间,选取适当树种人工造林可以省略先锋物种强阳生草本的发育时间,提早诱发灌木和草本植物发育,大大加速植被恢复演替过程。通过对广东惠州市惠阳区上杨试验站等南亚热带典型水土流失地区的研究发现：自然封育状态下,水土流失地区植被恢复和演替缓慢,25。后植被覆盖度只有35％,且主要以阳生性耐贫瘠的灌木及草本为主,土壤侵蚀仍然比较严重。选择大叶相思树人工造林加速了植被演替进程,控制了水土流失,12a左右植被覆盖度就达90％左右。造林23a左右,林地遮蔽涵养水分和控制侵蚀作用下迅速生长多种当地物种,形成了乔、灌、草、藤、竹多层复合植被。在南亚热带季风气候地区,自然封育状态下严重水土流失区植被恢复至较稳定的次生林阶段需要60a左右的时间;人工造林加速植被演替只需要20a。植树造林是该地区植被恢复发育及控制水土流失的有效措施。     

Preformed mRNA and Light-induced Germination of Pine (Pinus thunbergii) Seed

The mRNAs were isolated from dry, dark-imbibed and light-imbibedpine (Pinus thunbergii) seeds, in which germination is inducedupon exposure to light, and their translational activities ina wheat embryo cell-free system were examined. A portion ofthe mRNA extracted from each type of seed appeared to be poly(A)⁺RNA.A significant translational activity was already present inthe RNA fraction isolated from the dry pine seeds. The preformedmRNA seems not to be translated in vivo during the dark-imbibition,since most of the in vivo protein synthesis did not occur untilthe seeds were exposed to light. The SDS polyacrylamide gelelectrophoregrams of the polypeptides synthesized in vitro inresponse to either the preformed mRNA or the mRNAs from thedark-imbibed or light-imbibed seeds were qualitatively identical;thus it seems that the preformed mRNA is conserved during darkimbibition, and that its translation is initiated after theexposure of the imbibed seeds to light. (Received August 10, 1981; Accepted May 15, 1982)     

海岸梯度上黑松针叶形态与解剖结构性状的变化规律

风对树木形态、生理和生长的影响一直是生态学研究的热点和难点问题,目前主要采用模拟风速或机械刺激的方式来研究树木对风胁迫的响应与适应变化,无法准确反映出树木在风环境下的长期适应机制。本文以海岸60年生黑松林（Pinus thunbergii）为对象,分析了海岸距离梯度上黑松迎风面和背风面针叶长度、宽度、面积、比叶面积、角质层厚度、表皮厚度等形态和解剖结构特征的变化规律。结果表明：黑松迎风面针叶长度、宽度、周长、面积、厚度和比叶面积随着离海岸距离的减小逐渐减小（P<0.05）;而表皮厚度、角质层厚度和导管孔径则随着离海岸距离的减小逐渐增加（P<0.05）;背风面各指标均无明显变化规律。黑松迎风面与背风面针叶性状（比叶面积除外）主要在海岸500 m内存在显著差异（P<0.05）。可以看出,随着海风胁迫的增加,黑松通过降低针叶长、宽等形态指标,有效减少了风胁迫下黑松的受力面积,是一种躲避策略;而增加针叶表皮、角质层厚度和导管孔径等解剖结构指标,则增强了针叶坚韧性和保证针叶的水分供应,是一种忍受策略,这些策略有利于该树种在大风环境中得以更好的生存。     

Spreading of Nuclear Degradation in Pinus thunbergii Parl. Cuttings under Water Stress

The killing of suspension-cultured tobacco cells and stem cellsof Japanese black pine (Pinus thunbergii Parl.) by drying, autoclaving,hypertonic treatment or freezing caused the disappearance ordeformation of nuclei, as monitored by staining with 4',6-diamidino-2-phenylindole(DAPI). This observation suggests that disappearance or deformationof the nucleus can be taken as an index of cell death. Usingthis index, we examined the spreading of the cell death in water-stressedcuttings of Japanese black pine. Various portions of the cuttingswere examined over time and DAPI-stained nuclei were seen todisappear more rapidly in the upper than in the lower portionsof water-stressed cuttings. In every portion, undeformed, DAPI-stainednuclei disappeared sequentially from the cortex and the pith,from the periderm, from the xylem and finally from the cambium,indicating that cell death caused by water stress spreads fromthe cortex and the pith to the periderm, then to the xylem,and finally to the cambium. Water conduction was ex amined byimmersing the cut ends of cuttings in a red solution of acidfuchsin. Under water stress, water conduction was reduced andthe height of the upper limit of the sucked solution above thecut end was reduced. Just below this upper limit, water conductionwas inhibited in some regions of the xylem. However, undeformed,DAPI-stained nuclei were distributed homogeneously over bothconductive and non-conductive regions of the xylem, indicatingthat there is no direct relationship between cell death andwater conductivity of the xylem. Undeformed, DAPI-stained nucleidisappeared in regions around the upper limit of suction ofthe dye, and the sequence of disappearance was again from thecortex and the pith, from the periderm, from the xylem and,finally, from the cambium. (Received January 16, 1992; Accepted July 14, 1992)     

Changes in Cell Wall Architecture of Differentiating Tracheids of Pinus thunbergii during Lignification

The cell wall architecture, before and after lignification,of differentiating tracheids in Pinus thunbergii has been examinedusing a rapid-freeze deep-etching technique combined with transmissionelectron microscopy. Replicas of cells from the cambial zoneshowed that the unlignified primary cell wall was highly porouswith microfibrils extensively interconnected by crosslinks.The unlignified secondary cell wall has unidirectional microfibrils,more or less associated in bundles, forming a wavy pattern aroundpores of characteristic slit-like shape with narrowing ends.As the lignification progresses, the cell wall structure becomesdense, with no detectable pores. Delignification of wood samplesleads to the reappearance of crosslinks, individual microfibrilsand pores in the secondary cell wall, although in a somewhataltered shape. In addition, cellulose-synthesizing enzyme complexes(rosettes) have for the first time been detected on the plasmamembrane of differentiating xylem cells of softwood. (Received August 28, 1998; Accepted March 10, 1999)     

Effect of meteorological events on ragweed pollen count

Hourly and daily counts of air-borne ragweed pollen, AMBROSIA SPP, taken with a volumetric sampler during the 1961 season at Ottawa, Canada, were compared with meteorological events. The time of daily peak concentration of pollen coincided with the time of decreasing relative humidity and development of a super-adiabatic lapse rate in the first 200 ft of atmosphere. Daily variations in pollen count were virtually completely dominated by the local ragweed population and microclimate but could be explained to a limited extent by variations in air mass.On occasions, gravity slide counts using a Durham type apparatus varied qualitatively with volumetric counts, but it was not possible to obtain a constant factor to convert gravity to volumetric counts.

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Zusammenfassung Die stündliche und tÄgliche Anzahl von Pollen des Jakobskreuzkrauts(AMBROSIA SPP.) in der Luft (mit einem volumeterischen Sammler bestimmt) wÄhrend der Saison 1961 in Ottawa, Kanada, wurde mit meteorologischen Daten korreliert. Die höchste Pollenzahl in der Luft fiel mit dem Abfall der rel. Feuchte zusammen und der Entwicklung eines überadiabatischen Gradienten in den ersten 65 m Höhe der AtmosphÄre. Die tÄglichen Schwankungen der Pollenzahl wurden tatsÄchlich vollstÄndig von der lokalen Verteilung der Ambrosia spp. und dem Mikroklima bestimmt und konnten nur in geringem Masse mit den Schwankungen der Luftmassen in Zusammenhang gebracht werden.Die Zahl der Pollen in durch Schwerkraft gewonnen Proben fiel gelegentlich qualitativ mit den volumetrisch gewonnen Proben zusammen; es war jedoch nicht möglich, einen konstanten Faktor zu berechnen, um gravimetrisch gewonnene Werte in volumetrische umzuwandeln.

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Résumé Le nombre par heure et par jour, des grains de pollen de AMBROSIA SPP. dans l'air, mesuré par un collecteur volumétrique pendant la saison 1961 à Ottawa (Canada)a été comparé avec les données météorologiques.Le nombre le plus élevé correspondait à une chute de l'humidité relative et à un gradient superadiabatique s'élevant jusqu'à 65m d'altitude. La cause des variations quotidienne du nombre des grains de pollen correspondait pratiquement à la distribution locale de Ambrosia spp. et au microclimat, et ne correspondait que dans une faible mesure avec les déplacement des masses d'air. Le nombre des grains de pollen obtenus par gravitation au moyen d'un appareil du type Durham coincidait parfois qualitativement aux valeurs obtenues par un collecteur volumétrique, mars il n'a pas été possible d'établir un facteur constant,qui permÎt de transformer les valeurs gravimétriques en valeurs volumétriques.