Seasonal Rhythms of Structure and Behaviour of Vascular Cambium in Ficus rumphii

Cambial structure and activity of Ficus rumphii Blume vary withthe changes in local climate. The cambial cells start swellingearly in April prior to the onset of periclinal divisions whichare most frequent in August. Cell division stops in October.During the growth season, initiation as well as cessation ofthe phloem production precedes that of xylem. A moderately hightemperature is correlated with the cambial reactivation. Onceinitiated, the activity continues at relatively low temperatures.Hot and dry environment favours the phloem production, whereashot and moderately humid conditions induce xylogenesis. Thesize and relative proportion of cambial initials also changewith season. Fusiform initials are shorter and broader duringthe rainy season (July–September) than for the rest ofthe year. Multiseriate and triseriate rays, as also the tallrays, outnumber the other types of rays throughout the year. Ficus rumphii, vascular cambium, phenology, climatic variation     

近40年河北坝上地区杨树人工林径向生长对气候变化的响应差异

运用树木年轮气候学方法,研究近40年河北坝上地区健康和衰退小叶杨人工林径向生长对气候响应敏感性差异,揭示健康和衰退杨树生长与气候关系的时间变异规律。结果表明：（1）衰退杨树径向生长对温度、降水等气候因素响应较健康杨树敏感。衰退杨树年表中的气候信号较强,与当年生长季（4、8-10月）的气温因素呈显著负相关,与上一年休眠期（9月-当年1月）和当年生长季（7月）的降水和相对湿度呈显著正相关。健康杨树年表中气候信号较弱,主要与上一年冬季（12月）和当年生长季（4月）的气温因素呈显著负相关,与上一年生长末期（8-11月）降水和相对湿度呈显著正相关。（2）从各年表与帕默尔干旱指数（PDSI）的响应强度来看,衰退杨树生长更易受夏季干旱胁迫影响。衰退杨树年表与上一年9月-当年3月、6-10月的PDSI呈显著正相关,而健康杨树径向生长与PDSI呈弱的正相关。（3）1975-2017年间,随气温升高,健康和衰退杨树生长对温度的敏感性下降;健康杨树生长对降水和PDSI的敏感性较为稳定,适应能力强,而衰退杨树生长对降水和PDSI的敏感性增强,适应能力变弱。综上所述,干旱胁迫是限制衰退杨树生长的主要因素,而健康杨树生长受气候影响较弱,能适应当地气候条件。衰退杨树对气候变化响应较健康杨树明显,在气候变暖背景下,衰退杨树生长的气候限制因子由温度转变为水分,导致河北坝上地区遭受干旱灾害时发生退化的趋势更加明显。     

THE CAMBIUM AND SEASONAL DEVELOPMENT OF THE PHLOEM IN PYRUS MALUS

Evert , R. F. (U. Wisconsin, Madison.) The cambium and seasonal development of the phloem in Pyrus malus. Amer. Jour. Bot. 50(2): 149–159. Illus. 1963.—The cambium in apple consists of several layers of cells at all times, and practically all cambial cells divide periclinally one or more times before undergoing differentiation. The cambial initials do not seem to be in a uniform, uniseriate layer. Judged by collections made during 2 seasons (August, 1958–October, 1960), the seasonal cycle of phloem development is as follows. Early in April, cells in the outer margin of the cambial zone begin to differentiate into sieve elements. At approximately the same time, activity (division) commences throughout the cambial zone. By the end of July or early August, sieve-element differentiation is completed. Cessation of function begins in either late September or in October with the formation of definitive callose on the sieve areas of sieve elements in the outer margin of the functional phloem. By late November, all sieve elements are devoid of contents and most of their companion cells collapsed. Phloem differentiation precedes xylem differentiation by approximately a month and a half; xylem and phloem differentiation cease almost simultaneously; and fiber-sclereid development is coincident with the period of maximal xylem differentiation.     

Lengthening of the duration of xylogenesis engenders disproportionate increases in xylem production

In cold climates, the expected global warming will lead to earlier cambial resumptions in spring, with a resultant lengthening of the growing season but unknown consequences on forest productivity. The phenological traits of cambium activity and xylem formation were analyzed at a short time scale along a thermal gradient represented by an alti‐latitudinal range from the 48th to 53rd parallels and covering the whole closed black‐spruce [Picea mariana (Mill.) BSP] forest in Quebec, Canada. A hypothesis was tested that warmer temperatures influence cambium phenology, allowing longer duration and higher intensity of growth, and resulting in proportionally increased xylem production. From April to October 2012, cell division in cambium and post‐cambial differentiation of xylem were observed on anatomical sections obtained from microcores collected weekly from the stem of fifty trees. The southern and warmer site was characterized by the highest radial growth, which corresponded to both the highest rates and longest durations of cell production. The differences in terms of xylem phenology and growth were marginal between the other sites. Xylem growth was positively correlated with rate and duration of cell production, with the latter explaining most variability in growth. Within the range analyzed, the relationship between temperature and most phenological phases of xylogenesis was linear. On the contrary, temperature was related with cell production according to an exponential pattern. Periods of xylogenesis of 14 days longer (+13.1%) corresponded to a massive increase in cell production (33 cells, +109%). This disproportionate change occurred at a May–September average temperature of ca. 14 °C and a snow‐free period of 210–235 days. At the lower boundary of the distribution of black spruce, small environmental changes allowing marginal lengthening of the period of cell division could potentially lead to disproportionate increases in xylem cell production, with substantial consequences for the productivity of this boreal species.     

芦芽山华北落叶松(Larix principis-rupprechtii)树轮宽度年表对气候因子的响应

在芦芽山地区采集3个不同海拔的华北落叶松(Larix principis-rupprechtii),在传统去趋势的基础上,采用"signal-free"方法对拟合曲线进行修正,避免了中等频率的气候信息引起的拟合偏差,最终建立3个不同海拔树轮宽度标准年表(STD)。同时以10a为界对上述年表进行滤波处理,得到3个低频年表。年表特征值表明,随着海拔升高,年轮平均轮宽变窄,敏感性和高频信息增强,低频信息减弱,这可能与逐渐恶劣的生境有关。中、低海拔年表的低频信息更一致,中、高海拔的高频信息更接近,而高、低海拔无论是标准年表还是高频、低频年表相似性均较差。树轮气候响应分析显示,低海拔STD年表与5月最低温负相关最为显著,STD和低频年表均与5、6月份土壤温度显著负相关,说明生境暖干,树木主要受生长季的干旱胁迫;中海拔STD年表与当年5月最高温正相关最为显著,STD和低频年表与土壤温度相关均不显著,说明生境逐渐变得冷湿,生长季的低温成为树木生长的限制因子;高海拔STD年表与气象要素相关不显著,低频年表与当年4月土壤温度正相关,说明高海拔最为冷湿,并有季节性冻土分布,生长季的土壤低温成为树木生长的限制因子。因此,全球变暖的趋势将更有利于高海拔树木的生长,而低海拔树木的干旱胁迫进一步加剧。     

How needle phenology indicates the changes of xylem cell formation during drought stress in Pinus sylvestris L.

Temperature, water availability and photoperiod are the primary drivers of tree phenological processes. However, there is lack of information how the spring temperature and summer drought affect phenology of both cambium and needles. We evaluated the interplay between xylem and needle development of mature Scots pine trees in three consecutive years differing in the spring temperatures and onset and duration of summer drought. Cambial activity began on the day of a year (DOY) 83–87, while the bud break occurred on DOY 113–119, when also the secondary cell wall of tracheids started its formation. While the timing of bud break correlated with the sum of effective temperatures, the beginning of cambial zone activity did not. The needles were fully unfolded around DOY 170, which corresponded to the transition between earlywood and latewood tracheids. Summer drought did not affect needle development, but it changed the rate of production and morphology of latewood tracheids. Latewood tracheids from the year 2015 when the drought was longest (i.e. until the second half of August in 2015 compared to the duration from June until the middle of July in the two other years) were 32% narrower and they had 34% thinner cell walls than in 2014 and 2016. The improvement of tree water status in July resulted in the formation of intra-annual density fluctuations (IADF). The interplay between needle and cambium phenology provided an insight into how the tree allocates the resources with varying temperature and soil water availability.     

Cambial reactivation in locally heated stems of the evergreen conifer Abies sachalinensis (Schmidt) Masters

A study was made of cambial activity, the localization of storage starch around the cambium, and the localization and occurrence of microtubules in cambial cells from dormancy to reactivation in locally heated (22–26 °C) stems of the evergreen conifer Abies sachalinensis. Heating induced localized reactivation of the cambium in the heated portions of the stem. Erect ray cambial cells resumed cell division 1 d prior to the reactivation of fusiform cambial cells and procumbent ray cambial cells. The re-initiation of the division of fusiform cambial cells occurred first on the phloem side. During the heat treatment, the amount of storage starch decreased in procumbent ray cambial cells and in the phloem parenchyma adjacent to the cambium but increased in fusiform cambial cells. Preprophase bands of microtubules, spindle microtubules and phragmoplast microtubules were observed both in erect ray cambial cells and in procumbent ray cambial cells. By contrast, no evidence of the presence of such preprophase bands of microtubules was detected in fusiform cambial cells. The results suggest that the localized heating of stems of evergreen conifers might provide a useful experimental model system for studies of the dynamics of cambial reactivation in intact trees. Received: 25 May 2000 / Accepted: 12 July 2000     

Cambial sensitivity to rising temperatures by natural condition and artificial heating from late winter to early spring in the evergreen conifer Cryptomeria japonica

Differences in the timing of cambial reactivation and the initiation of xylem differentiation in response to the sum of daily maximum temperatures were studied in two Cryptomeria japonica trees with cambium of different ages under natural and locally heated conditions. In addition, we observed the effects of low temperature on cambial activity. The timing of cambial reactivation and of the initiation of xylem differentiation differed between 55- and 80-year-old cambium under natural conditions. In the 55-year-old cambium, cambial reactivation occurred when the cambial reactivation index (CRI), calculated on the basis of daily maximum temperatures in excess of 10°C, was 94 and 97°C in 2007 and 2008, respectively. In 80-year-old cambium, cambial reactivation occurred when the CRI, calculated on the basis of daily maximum temperatures in excess of 11°C, was 69 and 71°C in 2007 and 2008, respectively. After cambial reactivation in 2007, normal cell division was evident in the cambium even though the minimum temperature had fallen between −2 and −3°C. Under natural conditions, xylem differentiation started 38–44 days after cambial reactivation. In heated stems, the time between cambial reactivation and the initiation of xylem differentiation ranged from 14 to 16 days, a much shorter time than under natural conditions, indicating that continuous exposure to an elevated temperature had induced earlier xylem differentiation. Our observations indicate that the sensitivity to reactivation inducing stimuli of the cambium depends on both the stage of dormancy and tree age of the cambium.     

中国北部不同地点樟子松人工林径向生长对气候响应的差异

通过树木年代学方法,测定了毛乌素和塞罕坝相同密度樟子松(Pinus sylvestris var.mongolica)全木(Ringwood,RW)、早材(Earlywood,EW)和晚材(Latewood,LW)宽度,计算胸高断面积增量(Basal area increment,BAI),并建立了樟子松年轮宽度年表,分析其对气候响应的差异。结果显示,毛乌素(Mu Us)樟子松轮宽随树龄呈"升-降"的曲线变化,塞罕坝(Saihanba)呈线性下降,两地樟子松BAI变化相似,呈"升-降"的曲线变化,EW占RW的65%—70%,表明EW对RW贡献较大。生长期间,毛乌素樟子松早晚材比例保持平稳,塞罕坝EW/RW值下降,LW/RW值上升,两地干旱事件均使LW/RW值下降,EW/RW值上升。差值年表(Residual chronology,RES)相关性分析显示,毛乌素樟子松径向生长主要与4、7月平均降雨,7月标准化降水蒸散发指数(Standardized precipitation evapotranspiration index,SPEI),3、8月平均温度及上年12月和当年3月最低温度呈正...     

长白山北坡不同年龄红松年表及其对气候的响应

运用树木年轮气候学方法,研究了长白山北坡红松(Pinus koraiensis)不同年龄年表特征及其与气候因子间的关系,以期揭示年龄因素对年表的潜在影响。结果表明,平均年龄为63a的红松低龄年表与平均年龄为184a的高龄年表对气候的响应明显不同:低龄红松径向生长与当年1、2月月平均温度负相关(P<0.05),同时也受到上年及当年多个月份的月平均最高温度或最低温度的影响,但与降水的相关性未达到显著水平;高龄红松径向生长则与月平均温度间的关系不明显,而与当年1、2、4、6、7、9月的月平均最高温度正相关,与当年4月、9月的月平均最低温度负相关,同时受到上年5月及当年5月月总降水量的影响。因此,年龄因素对红松年表的气候响应方面存在一定影响,且高龄年表对气候响应的敏感性更高,包含有更多的气候信息。     

贺兰山地区植被冠层物候与树干形成层物候的关系

基于贺兰山地区98棵油松树轮样本的宽度数据、植被归一化指数(NDVI)数据以及土地覆被数据,采用VS-oscilloscope模型模拟的油松径向生长过程,研究植被冠层与树干形成层物候之间的联系.结果表明:林地冠层与油松形成层生长结束期(EOS)显著相关,且高于草地与形成层之间的相关.油松生长开始期(SOS)和EOS分别...     

Age-dependent xylogenesis in timberline conifers

Neither anatomical change nor physiological abnormalities have been observed in the cambia of older trees. However, different sensitivity and period of significant responses to climate suggest the existence of some age-related change in the patterns of cambial activity and/or wood cell formation. Here, weekly cambial activity and timing and duration of xylem cell enlargement and wall thickening were compared in adult (50-80 yr) and old (200-350 yr) trees of Larix decidua, Pinus cembra and Picea abies at the Alpine timberline during 2004 and 2005. Timings and durations of xylogenesis differed between adult and old trees, with 2-3 wk shorter cambial activity found in the latter. The delayed onset of cambium division and lower cell production in old trees, with respect to adult trees, led to reductions of 15-20% in the overall duration of xylem differentiation. These results demonstrate that cambial dynamics change during the tree lifespan and that the time window of tree-ring production shortens with age. Variations in the period of xylem growth may be the cause of age-dependent responses to climate. The observed shorter xylogenesis in older plants at the Alpine timberline could be related to a size effect and not just to age per se.     

Cambial activity and annual rhythm of xylem production of elephant apple tree (<Emphasis Type="Italic">Dillenia indica</Emphasis> Linn.) in relation to phenology and climatic factor growing in sub-tropical wet forest of northeast India

The interrelationship between phenological events, climatic factors, periodicity of cambial activity and seasonal production of xylem was examined in Dillenia indica L. (Dilleniaceae) growing in sub-tropical wet forest of Meghalaya state, India. The reactivation of cambial activity was seen in the first week of May, 15 days after sprouting of new leaves and buds. The activity of cambium and xylem production gradually declined toward December and ceased from January to April end. There was correlation between leaf fall and cambial dormancy. It was evident from the correlation and regression analysis, the relationship between cambial activity, xylem production with climatic factors, the monthly mean minimum temperature plays an important role for the cambial activity and xylem production rather than influence by rainfall and relative humidity in D. indica L. The data were discussed in the light of cambial activity, xylem production and phenological events.     

Seasonal variations in the cambial anatomy of Tectona grandis (Verbenaceae)

A study of seasonal activity of the cambium in Tectona grandis L. f. has shown that the activity initiates in the first week of June, reaches a peak in July and then slowly declines. The length of fusiform cambial initials undergo considerable variations during the activity and dormancy of the cambium. The initiation of cambial activity is closely associated with the opening of the dormant foliar buds in the first week of May. Cambium is more active with high numbers of immature xylem and phloem elements from July to September when the trees are with mature foliage and flowers and dormant from January to April when leaves dry and defoliation takes place. The differentiation of xylem and phloem starts simultaneously and the number of their immature elements reach the maximum in July.     

Critical temperatures for xylogenesis in conifers of cold climates

Aim To identify temperatures at which cell division and differentiation are active in order to verify the existence of a common critical temperature determining growth in conifers of cold climates. Location Ten European and Canadian sites at different latitudes and altitudes. Methods The periods of cambial activity and cell differentiation were assessed on a weekly time‐scale on histological sections of cambium and wood tissue collected over 2 to 5 years per site from 1998 to 2005 from the stems of seven conifer species. All data were compared with daily air temperatures recorded from weather stations located close to the sites. Logistic regressions were used to calculate the probability of xylogenesis and of cambium being active at a given temperature. Results Xylogenesis lasted from May to October, with a growing period varying from 3 to 5 months depending on location and elevation. Despite the wide geographical range of the monitored sites, temperatures for onset and ending of xylogenesis converged towards narrow ranges with average values around 4–5, 8–9 and 13–14 °C for daily minimum, mean and maximum temperature, respectively. On the contrary, cell division in the cambium stopped in July?August, when temperatures were still high. Main conclusions Wood formation in conifers occurred when specific critical temperatures were reached. Although the timing and duration of xylogenesis varied among species, sites and years, the estimated temperatures were stable for all trees studied. These results provide biologically based evidence that temperature is a critical factor limiting production and differentiation of xylem cells in cold climates. Although daily temperatures below 4?5 °C are still favourable for photosynthesis, thermal conditions below these values could inhibit the allocation of assimilated carbon to structural investment, i.e. xylem growth.     

Comparative anatomy and ultrastructure of active and dormant vascular cambium in rhizome ofBotrychium ternatum

Vascular cambium ofBotrychium ternatum rhizome varied according to age, position and season was studied by light and electron microscopy. Cambium at the 6th internode (6-year-old cambium) had the greatest number of active cambial cells in August and September, thus it was in the most active stage. The active cells were characterized by the presence of a large vacuole, few storage materials such as starch grains within plastids or lipid droplets, a thin tangential wall; and various cell organelles in the thin peripheral layer of cytoplasm. When the 6-year-old cambium reached its dormant season after November, the dormant cells were filled with numerous storage materials and had few cell organelles. Our observations suggested that the initiation and cessation of cambial activity may be correlated with the annual life cycle of this plant: the vegetative and reproductive leaves began to emerge in June and July, respectively, and the sporophyll withered in November after the spore dispersal. Most cambial cells at the 10th internode, which remained in a dormant state throughout the year, were filled with numerous storage materials. Our results indicated that the activity of vascular cambium in the 10th internode was determinate.     

Periodicity of cambial activity in Abies balsamea. I. Effects of temperature and photoperiod on cambial dormancy and frost hardiness

The relationship between from hardiness and growth potential, and their dependence on temperature and photoperiod, was investigated in the one-year-old cambium of balsam fir [Abies balsamea (L.) Mill.]. Six-year-old trees were exposed for 9 weeks to either the natural environment or one of 4 controlled environments in the fall (18 September-18 November), spring (12 April–14 June) and summer (19 July – 19 September). The 4 controlled environments were (1) WS, warm temperature (24/20°C in day/night) + short day (8 h). (2) WL. warm temperature (24/20°C) + long day (8 h + 1 h night break), (3) CS. cold temperature (9/5°C) + short day (8 h) and (4) CL, cold temperature (9/5°C) + long day (8 h + 1 h night break). At the beginning and end of each exposure, cambial activity was measured by recording the number of xylem, cambium and phloem cells, frost hardiness was estimated from the cambium's ability to survive freezing to –40°C, and cambial growth potential was deduced from the duration of the cell cycle and the production of xylem, cambium and phloem cells in cuttings cultured for 4 weeks with exogenous indole-3-acetic acid (IAA) under environmental conditions favourable for cambial activity. In the natural environment, frost hardening began in September and was completed in November, while dehardening occurred when the cambium reactivated. CL, CS, and to a lesser extent WS, promoted hardening in the summer and fall, but did not prevent dehardening in the spring. The cambial growth potential in the natural environment declined from a maximum in April to a low level in June, reached a minimum in September, then increased to a high level in November. This potential was promoted by CL and CS on all dates by WL in the summer and fall. The ratio of xylem to phloem induced by IAA treatment was greatest in June and least in September in cuttings from trees exposed to the natural environment, and was increased by CL and CS in the fall. The cambium in intact branches of trees protected from chilling during the fall and winter resumed cell cycling after less than 9 weeks of dormancy, but produced mostly or only phloem in the subsequent growing period. It is concluded that the frost hardiness of the cambium, the IAA-induced cycling of cambial cells, and IAA-induced xylem to phloem ratio vary independently with season, temperature and photoperiod, and that the periodicity of these processes is regulated endogenously.     

Induction of cambial reactivation by localized heating in a deciduous hardwood hybrid poplar (Populus sieboldii x P. grandidentata)

BACKGROUND AND AIMS: The timing of cambial reactivation plays an important role in the control of both the quantity and the quality of wood. The effect of localized heating on cambial reactivation in the main stem of a deciduous hardwood hybrid poplar (Populus sieboldii x P. grandidentata) was investigated. METHODS: Electric heating tape (20-22 degrees C) was wrapped at one side of the main stem of cloned hybrid poplar trees at breast height in winter. Small blocks were collected from both heated and non-heated control portions of the stem for sequential observations of cambial activity and for studies of the localization of storage starch around the cambium from dormancy to reactivation by light microscopy. KEY RESULTS: Cell division in phloem began earlier than cambial reactivation in locally heated portions of stems. Moreover, the cambial reactivation induced by localized heating occurred earlier than natural cambial reactivation. In heated stems, well-developed secondary xylem was produced that had almost the same structure as the natural xylem. When cambial reactivation was induced by heating, the buds of trees had not yet burst, indicating that there was no close temporal relationship between bud burst and cambial reactivation. In heated stems, the amount of storage starch decreased near the cambium upon reactivation of the cambium. After cambial reactivation, storage starch disappeared completely. Storage starch appeared again, near the cambium, during xylem differentiation in heated stems. CONCLUSIONS: The results suggest that, in deciduous diffuse-porous hardwood poplar growing in a temperate zone, the temperature in the stem is a limiting factor for reactivation of phloem and cambium. An increase in temperature might induce the conversion of storage starch to sucrose for the activation of cambial cell division and secondary xylem. Localized heating in poplar stems provides a useful experimental system for studies of cambial biology.     

Changes of Peroxidase and Estease Isozymes During Periodicity of Cambial Activity in Broussonetia papyrifera (L.) Vent.

Methods of sampling and sections preparaction were the same as reported previously. Except that sampling was made at monthly intervals between May 20 and July 30, then at 7–14 day-intervals between July 30 and October 14, and then at monthly intervals between October 14 and March 25 in the next year. The stored starch in various tissues was stained with PAS reaction. During active period of cambium in Broussonetia papyrifera after July 30, the cell layers of immature xylem and phloem decreased progressively, and the formation of mature xylem and phloem increased rapidly. The formation of late wood started early in August, formation of xylem ceased after September 5, followed by ceasation of phloem formation about 1.5 months later. Increasing and decreasing of stored starch were closely related to the periodicity of cambial activity during the year. Starch grains decreased progressively after cambial activity was resumed in early spring until they disappeared in all the stem tissues. Then, starch accumulated progressively again after cambial activity slowed down, particularly after the ceasation of xylem formation. However, after the formation of phloem had ceased, the stored starch once again disappeared progressively until the end of December, and accumulated again. Such changes might be related to the transition of cambium activity involving two periods of dormancy.