Seasonal development of secondary xylem and phloem in <Emphasis Type="Italic">Schizolobium parahyba</Emphasis> (Vell.) Blake (Leguminosae: Caesalpinioideae)

The cambial activity and periodicity of secondary xylem and phloem formation have been less studied in tropical tree species than in temperate ones. This paper describes the relationship between seasonal cambial activity, xylem and phloem development, and phenology in Schizolobium parahyba, a fast growing semideciduous seasonal forest tree from southeastern Brazil. From 2002 to 2003, wood samples were collected periodically and phenology and climate were recorded monthly in the same period. S. parahyba forms annual growth increments in wood, delimited by narrow initial parenchyma bands. The reduction of the cambial activity to a minimum correlates to the dry season and leaf fall. The higher cambial activity correlates to the wet season and the presence of mature leaves. In phloem, a larger conductive region was observed in the wet season, when the trees were in full foliage. The secondary phloem did not exhibit any incremental zone marker; however, we found that the axial parenchyma tends to form irregular bands.     

Fluctuations of cambial activity in relation to precipitation result in annual rings and intra-annual growth zones of xylem and phloem in teak (Tectona grandis) in Ivory Coast

Background and Aims Teak forms xylem rings that potentially carry records of carbon sequestration and climate in the tropics. These records are only useful when the structural variations of tree rings and their periodicity of formation are known. Methods The seasonality of ring formation in mature teak trees was examined via correlative analysis of cambial activity, xylem and phloem formation, and climate throughout 1·5 years. Xylem and phloem differentiation were visualized by light microscopy and scanning electron microscopy. Key Results A 3 month dry season resulted in semi-deciduousness, cambial dormancy and formation of annual xylem growth rings (AXGRs). Intra-annual xylem and phloem growth was characterized by variable intensity. Morphometric features of cambium such as cambium thickness and differentiating xylem layers were positively correlated. Cambium thickness was strongly correlated with monthly rainfall (R(2) = 0·7535). In all sampled trees, xylem growth zones (XGZs) were formed within the AXGRs during the seasonal development of new foliage. When trees achieved full leaf, the xylem in the new XGZs appeared completely differentiated and functional for water transport. Two phloem growth rings were formed in one growing season. Conclusions The seasonal formation pattern and microstructure of teak xylem suggest that AXGRs and XGZs can be used as proxies for analyses of the tree history and climate at annual and intra-annual resolution.     

Potassium-dependent cambial growth in poplar

To study the involvement of potassium in wood formation, poplar plants ( Populus tremula L. x Populus tremuloides Michx.) were grown over a period of one growing season, under different potassium regimes. Seasonal changes in cambial potassium content, osmotic potential, and cambial activity correlated strongly throughout the season, increasing from spring to summer and decreasing from summer to autumn. Moreover, changing the potassium supply during the growing season affected the seasonal changes of these parameters in a similar way. Low potassium supply markedly reduced cambial activity, the number of expanding cambial cell derivatives, the seasonal rate of radial wood increment, and the vessel frequency. The possible effect of hormones on potassium-dependent cambial growth was investigated and revealed that abscisic acid (ABA) strongly decreased the potassium content within the cambial zone and reduced cambial activity, as well as the number of expanding cambial cell derivatives. In summary, our results indicate a key role for potassium in the regulation of cambial growth and wood formation due to its strong impact on osmoregulation in expanding cambial cells. They also demonstrate involvement of ABA in regulation of potassium-dependent cambial growth.     

Relating tree growth to rainfall in Bolivian rain forests: a test for six species using tree ring analysis

Many tropical regions show one distinct dry season. Often, this seasonality induces cambial dormancy of trees, particularly if these belong to deciduous species. This will often lead to the formation of annual rings. The aim of this study was to determine whether tree species in the Bolivian Amazon region form annual rings and to study the influence of the total amount and seasonal distribution of rainfall on diameter growth. Ring widths were measured on stem discs of a total of 154 trees belonging to six rain forest species. By correlating ring width and monthly rainfall data we proved the annual character of the tree rings for four of our study species. For two other species the annual character was proved by counting rings on trees of known age and by radiocarbon dating. The results of the climate–growth analysis show a positive relationship between tree growth and rainfall in certain periods of the year, indicating that rainfall plays a major role in tree growth. Three species showed a strong relationship with rainfall at the beginning of the rainy season, while one species is most sensitive to the rainfall at the end of the previous growing season. These results clearly demonstrate that tree ring analysis can be successfully applied in the tropics and that it is a promising method for various research disciplines.     

EFFECT OF ISOLATION OF BARK ON CAMBIAL ACTIVITY AND DEVELOPMENT OF XYLEM AND PHLOEM IN TREMBLING ASPEN

Circular patches of bark were surgically isolated on the sides of trembling aspen (Populus tremuloides Michx.) trees at breast height at various times during the dormant and growing seasons. Subsequently, samples of wood and attached bark were taken from isolated and control sites to determine the effects of isolation of the bark on cambial activity and xylem and phloem development. In control trees cambial activity and xylem and phloem development occurred normally. Isolation of bark during the dormant season (in November, February, or March) did not prevent initiation of cambial activity and of phloem differentiation in spring but continued normal cambial activity and phloem developmented were prevent. Xylem differentiation was essentially prevented by isolation of tissues during the dormant season. The ultimate effect of isolation of the bark on the cambium, either during the dormant season or during the growing season, was subdivision of all fusiform cambial cells into strands of parenchymatous elements; the ultimate effect on the newly formed phloem was early death of the sieve elements. The most conspicuous effect of isolation of the bark after xylem differentiation had begun was the curtailment of secondary wall formation. Shortening of cells of the cambial region was reflected in the length of the vessel members which differentiated from such cells. These results indicate that normal cambial activity and xylem and phloem development require a supply of currently translocated regulatory substances from the shoots.     

Cambial growth dynamics and climatic control of different tree life forms in tropical mountain forest in Ethiopia

Munessa Forest is a mountain forest in south-eastern Ethiopia experiencing seasonal rainfall variation. We investigated seasonal cambial activity and dormancy from increment rates of four different tree species belonging to varying life forms, namely, evergreen native conifer (Podocarpus falcatus), evergreen introduced conifer (Pinus patula), evergreen broadleaved tree (Prunus africana) and deciduous broadleaved tree (Celtis africana). Measurements of stem radius fluctuations were registered with the help of high-resolution electronic dendrometers. Daily amplitudes of stem diameter variations and daily and monthly net growth rates were determined and related to climatic variables measured at local climate stations. Thin sections of wood collected with a microcorer every 3–6 weeks allowed a visual control of newly formed wood cells during consecutive time intervals. Lack of water availability during the long dry season induced cambial dormancy of 5–7 months depending on life forms. After the onset of the short rainy season, stem swelling started quite synchronously with a variation of only single days in all studied species. Evergreen tree species were able to initiate wood formation during the short rainy season, whereas growth in the deciduous broadleaved species started in the long rainy season. The acquired data provide a basis for delineating the species-specific growth boundaries and the duration of the cambial growing season.     

树木木质部生长动态及其调节机制研究进展

全球变化对树木木质部生长产生了深远影响,进而影响了森林生态系统的固碳功能以及全球生态系统能量和物质的循环过程。树木木质部生长动态主要包括形成层活动开始和结束的时间、生长季长度以及分裂速率等,其受到多种因素的共同调节,如植物激素、碳水化合物、氮素和气象因子等。通过在精细的时间尺度上对比研究树木木质部生长动态,揭示木质部形成的决定因子,可以加深对树木生长生理机制的理解,从而提高其对气候变化响应的预测精度。对近年来在木质部的形成动态及其调节机制方面取得的研究进展进行了综述,并对未来的研究方向进行了展望。     

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.     

Temporal dynamic of wood formation in Pinus cembra along the alpine treeline ecotone and the effect of climate variables

We determined the temporal dynamic of cambial activity and xylem development of stone pine (Pinus cembra L.) throughout the treeline ecotone. Repeated micro-sampling of the developing tree ring was carried out during the growing seasons 2006 and 2007 at the timberline (1,950 m a.s.l.), treeline (2,110 m a.s.l.) and within the krummholz belt (2,180 m a.s.l.) and the influence of climate variables on intra-annual wood formation was determined. At the beginning of both growing seasons, highest numbers of cambial and enlarging cells were observed at the treeline. Soil temperatures at time of initiation of cambial activity were c. 1.5°C higher at treeline (open canopy) compared to timberline (closed canopy), suggesting that a threshold root-zone temperature is involved in triggering onset of above ground stem growth. The rate of xylem cell production determined in two weekly intervals during June through August 2006–2007 was significantly correlated with air temperature (temperature sums expressed as degree-days and mean daily maximum temperature) at the timberline only. Lack of significant relationships between tracheid production and temperature variables at the treeline and within the krummholz belt support past dendroclimatological studies that more extreme environmental conditions (e.g., wind exposure, frost desiccation, late frost) increasingly control tree growth above timberline. Results of this study revealed that spatial and temporal (i.e., year-to-year) variability in timing and dynamic of wood formation of P. cembra is strongly influenced by local site factors within the treeline ecotone and the dynamics of seasonal temperature variation, respectively.     

Adjustment Capacity of Maritime Pine Cambial Activity in Drought-Prone Environments

Intra-annual density fluctuations (IADFs) are anatomical features formed in response to changes in the environmental conditions within the growing season. These anatomical features are commonly observed in Mediterranean pines, being more frequent in younger and wider tree rings. However, the process behind IADF formation is still unknown. Weekly monitoring of cambial activity and wood formation would fill this void. Although studies describing cambial activity and wood formation have become frequent, this knowledge is still fragmentary in the Mediterranean region. Here we present data from the monitoring of cambial activity and wood formation in two diameter classes of maritime pine (Pinus pinaster Ait.), over two years, in order to test: (i) whether the differences in stem diameter in an even-aged stand were due to timings and/or rates of xylogenesis; (ii) if IADFs were more common in large trees; and (iii) if their formation is triggered by cambial resumption after the summer drought. Larger trees showed higher rates of cell production and longer growing seasons, due to an earlier start and later end of xylogenesis. When a drier winter occurs, larger trees were more affected, probably limiting xylogenesis in the summer months. In both diameter classes a latewood IADF was formed in 2012 in response to late-September precipitation, confirming that the timing of the precipitation event after the summer drought is crucial in determining the resumption of cambial activity and whether or not an IADF is formed. It was the first time that the formation of a latewood IADF was monitored at a weekly time scale in maritime pine. The capacity of maritime pine to adjust cambial activity to the current environmental conditions represents a valuable strategy under the future climate change conditions.     

Seasonal cambial activity of five tropical tree species in central Thailand

The seasonal cambial activity of five tropical tree species was investigated at Khao Yai National Park. The species studied were Tetrameles nudiflora, Magnolia baillonii, Canarium euphyllum Kur, Toona ciliata, and Spondias axillaris. Cambial activity was quantified by counting layers of undifferentiated cells in the cambium zone from wood anatomical micro sections prepared from wood samples collected in monthly intervals from July 2010 to June 2011. The relationship between cambial activity and climatic factors was investigated by using Pearson’s correlation. The growth dynamics of five studied species differed considerably. The cambium of Tetrameles nudiflora and Magnolia baillonii was most active when rainfall reached its maximum amount in June (mid rainy season), whereas the cambium of Canarium euphyllum, Toona ciliata, and Spondias axillaris was most active in March during the transition from the dry to the wet season.     

Tree-ring variation,wood formation and phenology of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>) from a representative site in Slovenia,SE Central Europe

Long-term variation in tree-ring widths (1873–2006) and intra-annual dynamics of cambial activity and tree-ring formation in 2006 were studied in mature beech (Fagus sylvatica L.) trees at a typical forest site near Ljubljana (46°N, 14°40′E, 400 m a.s.l.) and related to leaf phenology and climate data. Tree-ring widths were negatively affected by minimum March and maximum August temperatures and favoured by May and July precipitation. Precipitation of the previous August and temperature of the previous November also had a positive effect. Leaf unfolding was affected by March and April temperatures, occurring later if they were low. Leaf yellowing was positively affected by minimum July temperatures and negatively by September precipitation. In 2006, leaf unfolding occurred on 16 April and was immediately followed by reactivation of cambium at breast height of the trees. One week later, the cambium obtained its maximum width (around 11 cell layers) and the rate of division increased until the end of May/beginning of June. By the end of June, 75% of the tree-ring was formed. Cambial cell divisions stopped from the end of July to mid-August. The average time of cambial activity was 100 days. Leaf yellowing occurred at the end of October, i.e. nearly 2 months after the cessation of cambial cell division. We discuss the usefulness of a combination of long-term (tree-ring width and phenology) and short-term (wood formation at a cellular level) data to understand better the environmental signals registered by a tree during growth.     

The number of days on which increment occurs is the primary determinant of annual ring width in Callitris intratropica

Key message

The number of days on which a measureable increment occurred, and the average rate of stem growth, rather than the overall duration of the wet season, were the main determinants of ring width in young Callitris intratropica trees. These effects were amplified by competition.

Abstract

Dendroclimatology of tropical tree species is an important tool for understanding past climatic variability at low latitudes where long-term weather records are often absent. Despite the growing number of published tropical tree-ring chronologies, however, still little is known of the factors that control annual ring formation in tropical tree species. In this paper we used an endemic Australian conifer, Callitris intratropica, to study the intra-annual dynamics of seasonal growth and xylem formation, and the effects of environmental conditions and competition, on growth ring formation. We combined high-resolution growth and climate monitoring (every 15 min for 2 years) with less frequent cambial sampling. Trees exhibited marked reductions in growth during certain periods within the rainy season when rainfall was not as regular and VPD was high. Overall, we found that ring width was most influenced by the number of days when increment occurred; regardless of how early the growing season began or ended, and by the rates of tracheid production. The effect of competition was also important. Trees growing in dense groves had narrower annual rings (4.6 mm) than trees that were growing in the open (6.7 mm), due to less active cambia, slower rates of xylem production and expansion and more increment days, although the overall growing season duration was also shorter in grove trees.     

Effects of a 20-day-long dry period on cambial and apical meristem growth in Abies balsamea seedlings

There is general agreement that in many regions additional precipitation with climate change will not be able to balance the increased evaporation rate induced by higher air temperatures, causing periods of intense drought. Although seedlings of Abies balsamea growing in the boreal forest are known for their resistance to harsh environmental conditions, the impact of water stress on their growth still remains largely unexamined. The aim of this study was to investigate growth responses of this species during and after a dry period by monitoring cambial and apical meristem activity at short time scale. Meristem growth was studied from May to October 2005 on seedlings of A. balsamea submitted to a 20-day-long dry period in June–July. Lower rates of shoot lengthening were observed in non-irrigated seedlings only in the first part of the growing season. Irrigated and non-irrigated trees showed the same trend of xylem formation and timings of cell differentiation. Cell production during cambial activity was estimated at about one xylem cell per day thus achieving in 100 days 108 tracheids in the tree ring and a width of 2 mm, with thinner tree rings observed in non-irrigated plants. A reduction of up to 50% in lumen area and cell diameter was observed for the cells produced during the dry period. Response of A. balsamea seedlings to a 20-day-long dry period consisted of good resistance of the cambial meristems during and after water stress, high sensitivity and rapid recovery of cell sizes during water depletion and slow but effective recovery of shoot growth after treatment.     

Cambial activity,annual rhythm of xylem production in relation to phenology and climatic factors and lignification pattern during xylogenesis in drum-stick tree (Moringa oleifera)

The interrelationship among seasonality of cambium, wood formation, cell size variation, lignification, tree phenology and climatic factors has been examined in Moringa oleifera, a tropical evergreen tree. The vascular cambium in Moringa is a storied with a distinct seasonal variation in its structure due to dimensional changes in rays. Though cambium remains active throughout the year it is sensitive to water availability. Peak cambial cell division and rate of xylem differentiation are influenced by average rainfall during the monsoon period. Cambial cell division reaches higher up in the tree trunk when it is supporting a high number of branches and leaves. Statistical analysis of cell size variation and climate factors revealed that xylem cell development is greatly influenced by rainfall and rarely by temperature. Lengths of fusiform initials and vessel elements are positively correlated. The pattern of lignification during xylogenesis shows that the vessels are the first element to develop lignified walls and ray cells are the last elements to become lignified. Fiber cell walls show more syringyl lignin, while the cell walls of other xylem elements are characterized by relatively more guaiacyl lignin units.     

Cambial activity of Pinus elliottii var. densa reveals influence of seasonal insolation on growth dynamics in the Florida Keys

We determined the temporal and seasonal dynamics of intra-annual cell formation of south Florida slash pine (Pinus elliottii Engelm. var. densa Little & Dor.), the southernmost native pine in the United States and the foundation species of globally endangered pine rockland ecosystems. To assess intra-annual cambial activity and identify possible relationships between cell production and climatic factors, wood micro-cores were extracted monthly from six trees during the period March 2010 to March 2011. The results confirmed annual growth ring formation in P. elliottii var. densa and indicated that its growing season extends from February to December, with a short period of dormancy that varied little between individuals. Within the growing season, earlywood cells were produced from February to July, latewood cells produced from July to December, and intra-annual density fluctuations (IADFs) occurred in the growth rings of four of six trees between July and August. A principal component analysis indicated a homogeneous response of cambial activity among trees to site-specific climatic factors. The first principal component axis explained 71?% of the total variance in cell production during the study period. Our results indicated that the dynamics of seasonal cambial activity of P. elliottii var. densa are controlled by solar radiation (r?=?0.51, p?<?0.10) in the Florida Keys. The nature of our data allow us to only speculate on the ecophysiological processes responsible for IADFs in P. elliottii var. densa, and additional research is needed to better understand the relationship between their formation and the environment in the Lower Florida Keys.     

Wood formation in urban Norway maple trees studied by the micro-coring method

Intra-annual wood formation in healthy and affected Norway maple (Acer platanoides L.) street trees in the City of Ljubljana, Slovenia, was studied by the micro-coring method. Samples were taken with a Trephor instrument at weekly intervals during the 2005 growing season. The beginning of wood formation corresponded to the initiation of cambial activity in the middle of April in all investigated Norway maple trees. In healthy trees, the period of wood formation was finished in mid-September, persisting 7 weeks longer than in affected ones. Small destructivity and sufficient quality of micro-cores confirmed that sampling with a Trephor is a convenient method for the study of wood formation in diffuse-porous hardwoods, growing in the harsh conditions of an urban environment.     

祁连山中部祁连圆柏年内径向生长对气候因子的响应

通过对祁连山中部葫芦沟流域的祁连圆柏连续采集微树芯,对其形成层活动和径向生长动态进行了连续两年的监测研究。结果表明,2012年细胞壁加厚和细胞成熟阶段开始时间分别发生在6月26日和7月24日,比2013年细胞壁加厚（6月22日）和细胞成熟阶段（6月26日）开始时间分别晚5 d和28 d。2012年细胞扩大、细胞壁加厚和细胞成熟阶段结束时间分别为7月16日、8月9日和9月8日,比2013年各阶段结束时间分别晚7、28 d和24 d。2012年最大细胞分裂速率为0.33细胞/d,共形成20.9个细胞,细胞分裂速率和木质部细胞总数均高于2013年。通过与附近气象站记录的气象数据进行对比,发现祁连圆柏生长开始时间在温暖年份显著早于寒冷年份,说明祁连圆柏的径向生长开始时间与温度有关。但2013年春季和夏初的高温导致区域干旱程度加剧,使祁连圆柏生长结束时间显著早于2012年,并导致2013年的木质部细胞总量和生长速率都小于2012年。研究表明,在寒冷干旱地区,尽管升温会使生长季提前,但升温导致的干旱胁迫可能对树木的生长速率和木质部细胞总量产生重要影响。     

INFLUENCE OF PHLOEM BLOCKAGE ON CAMBIAL GROWTH OF SUGAR MAPLE

Circular patches of bark were surgically isolated on the sides of sugar maple (Acer saccharum Marsh.) trees at breast height at various times during the dormant and growing seasons. Subsequently, samples of wood and attached bark were taken from isolated and control sites to determine the effects of isolation of the bark on cambial activity and xylem and phloem development. In control sites cambial activity and xylem and phloem development occurred normally. Isolation of bark during the dormant season (in November, February, or March) prevented initiation of cambial activity and xylem and phloem development in isolated areas of half of the trees. Varying degrees of cambial activity (periclinal divisions) occurred in the remaining isolated areas, but normal cambial activity and xylem and phloem development were prevented. Isolation of bark after initiation of cambial activity and phloem differentiation, but prior to initiation of xylem differentiation, resulted in the formation of very narrow xylem and phloem increments with atypically short vessel members and sieve-tube members, respectively. The xylem increments consisted primarily of parenchyma cells. Isolation of bark after initiation of xylem differentiation resulted in curtailment of secondary wall formation in the last-formed part of many increments. The last-formed vessel members of all these xylem increments were atypically short. Similarly, the last formed sieve-tube members of corresponding phloem increments were atypically short. The atypically short cells in the xylem and phloem of isolated areas reflected the effect of isolation on the cambial region, viz., the subdivision of all fusiform cells into strands of cells. Ultimately, the strands of short fusiform cells lapsed into maturity, leaving only strands of parenchymatous elements between xylem and phloem.     

Radial stem variations of Tabebuia chrysantha (Bignoniaceae) in different tropical forest ecosystems of southern Ecuador

Stem diameter increments of the broadleaved deciduous tree species Tabebuia chrysantha were measured with high-resolution dendrometers in a tropical lower montane forest and in a dry forest in southern Ecuador, the latter showing a distinct dry season. Those analyses were complemented by wood anatomical studies on regularly collected microcores to determine the season of active cambial growth and the time of formation of annual growth boundaries. The length of the cambial active period varied between 3 and 7 months at the tropical lower montane forest and 2 and 4 months in the dry forest, respectively. During dry days, amplitudes of daily stem diameter variations correlated with vapour pressure deficit. During October and November, inter-annual climate variations may lead to dry and sunny conditions in the tropical lower montane forest, causing water deficit and stem diameter shrinkage in T. chrysantha. The results of the climate–growth analysis show a positive relationship between tree growth and rainfall as well as vapour pressure deficit in certain periods of the year, indicating that rainfall plays a major role for tree growth.