The effects of fresh and rapid desiccated tissue on estimates of Ophiopogoneae genome size

Fresh plant material is usually used for genome size estimation by flow cytometry(FCM). Lack of fresh material is cited as one of the main reasons for the dearth of studies on plants from remote locations.Genome sizes in fresh versus desiccated tissue of 16 Ophiopogoneae species and five model plant species were estimated. Our results indicated that desiccated tissue was suitable for genome size estimation; this method enables broader geographic sampling of plants when fresh tissue collection is not feasible. To be useful, after dessication the Ophiopogoneae sample should be green without brown or yellow markings;it should be stored in deep freezer at à80C, and the storage time should be no more than 6 months.     

Comparison of tree sprouting in three regeneration stages of an evergreen broadleaved forest in a karst landscape, SW China

Little is known about the role of tree sprouting in the regeneration of karst forest communities. In Shilin Stone Forest Geographical Park, southwestern China, all genets with the largest stem ?3 cm DBH (diameter at breast height) and/or stumps ?3 cm BD (basal diameter) were identified and number of sprouts counted in 10 transects (10 m × 100 m) in each of three evergreen broadleaved forest stands representing three regeneration stages (about 10, 20, and 30 years old). Species with >10 genets accounted for 72.4% of the 76 species, and all of them showed evidence of sprouting. One-third to two-thirds of the genets in the three forests were sprouting, with an average of 4.0–5.7 sprouts per sprouting genet. Sprouting capability (sprouting genets/total genets) and intensity (sprouts per sprouting genet) differed significantly among the three forest stages. More than 90% of the damaged genets were sprouting. The number of sprouts in a non-damaged genet was determined by intrinsic sprouting ability, and the number of sprouts in damaged genets was determined by stump size. As the forest developed, percentage of damaged genets increased, the portion of shoots ≥3 cm DBH co-existing in a genet decreased, and the portion of shoots <3 cm DBH sprouted from damaged genet increased. Thus the role of sprouting changed from contributing recruitment in the young stage to persistence in the later stage.     

Comparison of tree sprouting in three regeneration stages of an evergreen broadleaved forest in a karst landscape, SW China

Little is known about the role of tree sprouting in the regeneration of karst forest communities. In Shilin Stone Forest Geographical Park, southwestern China, all genets with the largest stem ?3 cm DBH (diameter at breast height) and/or stumps ?3 cm BD (basal diameter) were identified and number of sprouts counted in 10 transects (10 m × 100 m) in each of three evergreen broadleaved forest stands representing three regeneration stages (about 10, 20, and 30 years old). Species with >10 genets accounted for 72.4% of the 76 species, and all of them showed evidence of sprouting. One-third to two-thirds of the genets in the three forests were sprouting, with an average of 4.0–5.7 sprouts per sprouting genet. Sprouting capability (sprouting genets/total genets) and intensity (sprouts per sprouting genet) differed significantly among the three forest stages. More than 90% of the damaged genets were sprouting. The number of sprouts in a non-damaged genet was determined by intrinsic sprouting ability, and the number of sprouts in damaged genets was determined by stump size. As the forest developed, percentage of damaged genets increased, the portion of shoots ≥3 cm DBH co-existing in a genet decreased, and the portion of shoots <3 cm DBH sprouted from damaged genet increased. Thus the role of sprouting changed from contributing recruitment in the young stage to persistence in the later stage.     

Characteristics and underlying mechanisms of plant deep soil water uptake and utilization: Implication for the cultivation of plantation trees北大核心CSCD

Root water uptake is an essential part of tree water relations and plays a crucial role in tree physiological activities. Water resource in deep soil is relatively abundant and can provide plenty of water to trees to guarantee their survival and healthy growth during dry seasons. Thus, a good comprehension of the characteristics and underlying mechanisms of deep soil water uptake and utilization by trees will deepen the understanding of the interaction between trees and the environment, tree survival and growth strategies, coexistence and competition among different species, etc. This knowledge is important in establishing green cultivation schemes for plantations, which depend less on the external water resources input and avoid the adverse effects on the water ecological environment. From existing studies, the characteristics and underlying mechanisms of deep water uptake and utilization by trees are reviewed. Firstly, the definition of deep roots and deep soil is discussed, and 1 m depth is recommended as the average (reference) definition standard in main forest vegetation types except the boreal forest. The reasons for the formation of deep tree roots around the globe were also determined. Secondly, the observed deep soil water uptake characteristics of trees and their influencing factors are summarized. Then, from the aspects of the adjustment of deep root traits and the coordination of hydraulic traits of different organs, the mechanisms of deep water uptake by trees are discussed. For example, the spatial, temporal and efficiency adjustment strategies of deep roots can be used to facilitate the absorption of deep soil water. Finally, some implications of deep soil water uptake for the cultivation of plantations are proposed, such as “for water management in plantations, trees should be induced to moderately utilize some deep soil water and an appropriate irrigation frequency should be selected”, “appropriate mixed planting of different tree species can facilitate the buffering effect of deep soil water storage”, “developing techniques of selecting trees for thinning based on the water uptake depths of different species”, etc. Deficiencies of existing studies and some future research directions were also pointed out. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All Rights Reserved.     

Different Patterns of Changes in the Dry Season Diameter at Breast Height of Dominant and Evergreen Tree Species in a Mature Subtropical Forest in South China

Information on changes in diameter at breast height （DBH） is important for net primary production （NPP） estimates, timing of forest inventory, and forest management. In the present study, patterns of DBH change were measured under field conditions during the dry season for three dominant and native tree species in a monsoon evergreen broad-leaved forest in the Dinghushan Biosphere Reserve. For each tree species, different patterns of DBH change were observed. In the case of the fast-growing tree species Castanopsis chinensis Hance, large diurnal fluctuations occur, with a peak DBH in the early morning （around 05：00 h） that decreases to a minimum by about 14：00 h. Both Schima superba Gardn. et Chemp and Cryptocarya chinensis （Hance） Hemsh exhibited less diurnal swelling and shrinkage. Diurnal fluctuations for these species were observed on a few occasions over the period of observation. Graphical comparisons and statistical analysis of changes in DBH with meteorological variables indicate that for different trees, the different changes in DBH observed responded to different meteorological variables. Large stem changes were found to occur for Ca. chinensis trees that were associated with variations in solar radiation. However, both S. superba and Cr. chinensis were found to be less sensitive to solar radiation. Changes in the DBH of these two species were found to be controlled mainly by soil temperature and soil moisture. During the later dry season, with a lower soil temperature and soil moisture, all three tree species stopped growing and only negligible shrinkage, expansion, or fluctuation occurred, suggesting that the optimum time to measure tree growth in the Dinghushan Biosphere Reserve is the later dry season.     

Aboveground biomass dynamics of subalpine old-growth forest in the upper reach of the Minjiang River

Biomass estimation of old-growth forests in the upper Minjiang River (UMR) is important in quantifying carbon (C) sequestration and C sink size because majority of the natural forests in UMR are mature or over-mature. Based on the forest resource data from 27 fixed sampling plots that have been surveyed consecutively, the dynamics of the aboveground biomass density (AGBD) were characterized by the allometric relationships, and the space-time variations of the C sink size in the sub-alpine old-growth forests of UMR were explored. Our results showed that 1) the net increase in AGBD was (27.311 ± 15.580) Mg·hm^?2 and the mean annual growth rate and mean annual death rate were (1.930 ± 1.091) and (2.271 ± 1.424) Mg·hm^?2·a^?1 during 1988–2002, respectively. 2) The aboveground biomass (AGB) largely depended on the growth and death rates of the trees with different diameters at the breast height (DBH) classes and the recruitment rate from one DBH class to another as well. The largest increment component of AGB came from the DBH class of 20 to 40 cm, whereas the minimum increment component of AGB was above 80 cm in DBH. The net negative increment of AGB occurred at DBH classes of 40–60 and 60–80 cm. 3) There were space-time variations of AGB in the alpine old-growth forests, indicated by AGB changing over time in the same sampling plot and varying among the locations or plots during the same sampling period. These variations were not only reflected in numerical value but also in positive or negative biomass increment.     

Effect of Salinity on the Composition, Number and Size of Epidermal Cells along the Mature Blade of Wheat Leaves

Salinity inhibits leaf growth in association with changes in cell size. The objective of this study was to determine the spatial distributions of the composition, number and dimensions of epidermal cells in the mature blades of leaf four of wheat seedlings under saline conditions. Plants were grown in loamy soil either with or without 120 mmol/L NaCl in a growth chamber, and harvested after leaf four was fully developed. The results of the spatial distribution analyses of width along the blade showed that salinity not only reduced the width of the leaf blade, but that it also altered the distribution pattern of blade width along the leaf axis. The reduction in the final size of the leaf blade was associated with a reduction in the total number of epidermal cells and in their widths and lengths. This study also revealed the spatial effects of salinity on the blade and epidermal cell dimensions along the leaf axis. In particular, salinity inhibited the total cell number for interstomatal, sister and elongated cells, implying that cell division in wheat leaves is inhibited by salinity. However, the lengths of interstomatal cells were not affected by salinity （unlike those for the sister and elongated cells）, suggesting the relative contributions of cell length and numbers to the reduction in the final length of the blade under salinity is dependent on cell type.     

Effects of leaf shape plasticity on leaf surface temperature北大核心CSCD

Aims The shape plasticity of plant leaves is an important survival strategy to high temperature and drought in arid region, yet reliable evidences are insufficient to validate the fundamental concepts. Our objective was to demonstrate the specific effects of leaf morphology on leaf surface temperature. Methods Infrared thermal images were processed to determine the leaf temperature and shape parameters of simulated and actual leaf shape. Microclimatic conditions were recorded using a automatic weather station near the sampling plot, including wind speed, radiation and air temperature. Important findings Under the drought and high temperature, the plasticity of leaf shape appeared an important measure to regulate leaf temperature, except leaf transpiration. The exchange rates of matter and energy between leaves and the environment were enhanced by smaller leaves that effectively decreased leaf temperature. With low wind speed and high temperature, leaf surface temperature decreased 2.1 °C per 1 cm reduction in leaf width. However, leaf surface temperature of a simulated leaf decreased 0.60–0.86 °C per 1 cm reduction in leaf width. Results from this study will help us to understand plant adaptability and survival strategy in arid region. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

A new species of Leptocycas (Zamiaceae) from the Upper Triassic sediments of Liaoning Province,China

A new cycad,Leptocycas yangcaogouensis sp.nov.,was found in sediments from the Late Triassic in western Liaoning,China.The pinnately compound leaves(Pseudoctenis type)are screwed in a crown on the stem top.The leaflets are linear,with parallel veins and decurrent bases on the rachis.The leaf bases are persistent.The cataphylls intermix with the leaves.The female cone is ovoid in shape.The characteristics of the new plant are more similar to those of Leptocycas gracilis,a Triassic cycad from North America,but the new species differs from L.gracilis in the size of its stem(7–8 vs.3–5 cm in diameter,respectively),leaves(length×width 100×16 vs.30×7 cm,respectively)and leaf density along the stem(4–6 vs.1–2 bases/1 cm length,respectively).Both L.gracilis and L.yangcaogouensis,having leaves of the Pseudoctenis type,show a closer relationship to the extant Dioon of Zamiaceae.The present study provides evidence for the origin of the genus Dioon,which may have come from Leptocycas plants of the Triassic.It would be assumed that the extent cycads in Zamiaceae originate from the pteridosperms in the Late Paleozoic and have evolved through the stage of L.gracilis and L.yangcaogouensis in Late Triassic,and reaching the extant Dioon.     

EFFECTS OF HUMAN ACTIVITIES ON STRUCTURE AND COMPOSITION OF WOODY SPECIES OF THE NOKREK BIOSPHERE RESERVE OF MEGHALAYA,NORTHEAST INDIA

Aims Our study was conducted in the Nokrek Biosphere Reserve (NBR) in the Garo hills districts of Meghalaya, Northeast India. Our aim was to assess the effects of human activities on plant diversity,population structure and regeneration.Methods We selected a representative 1.2 hm2 stand in both the core and buffer zones of NBR. Structure and composition were determined by randomly sampling square quadrats, population structure was assessed by determining age structure, and regeneration was assessed by measuring densities of seedling, sapling and adult trees.Important findings More woody species were recorded from the core zone than the buffer zone (87 vs. 81 species), and there were a large number of tropical, temperate, and Sino-Himalayan, Burma-Malaysian and Malayan elements, primitive families and primitive genera. The trees were distributed in three distinct strata,canopy, subcanopy and sapling. Subcanopy and sapling layers had the highest species richness (81％ -88％ ). Lauraceae and Euphorbiaceae were the dominant families in terms of the number of species, and a large number of families were represented by single species. Most woody species (57 ％ - 79 ％ ) were contagiously distributed and had low frequency ( ＜ 20％ ). Although stand density was high in the buffer zone, its basal area was low compared to the stand in the core zone. Low similarity and high β-diversity indicate marked differences in species composition of the stands. Shannon diversity index was high in both the stands, while Simpson dominance index was low. The diameter-class distribution for dominant species revealed that the most had a large number of young individuals in their populations. Preponderance of tree seedlings, followed by a steep decline in population density of saplings and adult trees, indicated that the seedling to sapling stage was the most critical in the life cycle of the tree populations. Most species (42 ％ - 48 ％ ) had no regeneration,25 ％ - 35 ％ had good/fair regeneration, and the rest had poor regeneration or reoccurred as immigrants.     

Spatio-temporal dynamics of two alpine treeline ecotones and ecological characteristics of their dominate species at the eastern margin of Qinghai-Xizang Plateau北大核心CSCD

Aims Temperature limit is the main cause of alpine treeline formation. Therefore, it is important to understand the response mechanisms of alpine treeline as well as their tree species under the global climate change. The present study focused on the spatio-temporal dynamics of treeline and ecological characteristics of the tree species in two treeline ecotones. Methods Two vertical belt-transect plots were established in each treeline ecotone of the Zheduo Mountain and Jianziwan Mountain of the eastern Qinghai-Xizang Plateau. Top and bottom of each transects were lain between species line and forest line, respectively. Detailed information of each tree species treeline, including species name, latitude, longitude, height, age, base diameter, and coordinates, was recorded accordingly. Important findings The temperatures of the two research areas have increased during the past 58 years. The precipitation has decreased slightly in both the Zheduo Mountain and Jianziwan Mountain. The age structure of Abies fabri from the Zheduo Mountain and A. squamata from the Jianziwan Mountain showed a reversed “J” shape curve and a bimodal shape, respectively. Within the two transects, due to the limitation of seed diffusion, the dominate species showed aggregated distributions at the small scale. At the large scale, A. fabri was aggregated at the Zheduo Mountain, while A. squanmata of the Jianziwan Mountain was randomly distributed due to the impact of surrounding environmental factors. Both tree height and base diameter decreased with the increase of elevation. The fir trees (Abies spp.) at the upper part of the treeline ecotone presented an allometric growth, whose height growth rate was higher than that of base growth, while the relationships between height growth and base growth were isometric at almost mid and lower part of the treeline ecotone. Compared with 10 years ago, there was no significant change at the position of treeline and tree species line of the Zheduo Mountain and the Jianziwan Mountain, neither of the tree density in the Jianziwan Mountain. However, the number of trees in the Zheduo Mountain increased by about 25%. Compared with 20 years ago, tree species lines of the Zheduo Mountain and Jianziwan Mountain were shifted upwards by 50 and 30 m, respectively. Besides, their treeline positions were increased by 75 and 40 m, respectively. Furthermore, the number of trees also increased significantly by 220% and 100%, respectively. Therefore, the treeline and its constructive species are mainly affected by temperature at the large spatio-temporal scale, while influenced by temperature and ambient environment at the small spatio-temporal scale. © Chinese Journal of Plant Ecology.     

Seasonal dynamic of plant phenophases in Beijing—A case study in Beijing Botanical Garden北大核心CSCD

Aims Seasonality is the typical characteristic of plant landscape in Beijing, including seasonal dynamics of plant phenology. We analyzed the seasonal changes in phenology of 120 deciduous trees in Beijing Botanical Garden, with additional efforts on an innovative methodology in studying plant phenology. Methods Based on the standards of the Chinese Phenological Observation Method, three-level Phenological Code (a, b, and c) was used to recode the phenology data. Our data analysis was performed with “pentad” (5-day period) in 24 Solar Terms. Analytical methods include a frequency distribution method to explore the division of phenophases and their dynamic constitution. The frequency distribution statistics in SPSS 20.0 were applied to explore the temporal dynamics in occurrence time and duration for different types of phenophases. Important findings We found that: The division of phenological seasons and their phenological constitution as: 6th–19th pentad for Spring, with 54.03% of the whole phenophases that are featured with sprouting, leaf spreading and flowering; 20th–45th pentad for Summer, with 12.95% of phenophases that include conclusions of leaf spreading for all trees, intensive fruiting, fewer flowering, and autumn-leaf scenery in late summer; 46th–59th pentad for Autumn, with 27.19% of the phenophases that are characterized with leaf discoloration and defoliation, some fruiting, and very few flowering; and 60th pentad for Winter, with 0.6% of phenophases that are all constituted with defoliation. The temporal distribution pattern of different kinds of phenophases is as follows. The leaf-unfolding phenophases span from 3rd to 23rd pentad and averagely last for 3.27 pentads, with Sorbaria kirilowii as one of the earliest leaf-unfolding species. The leaf coloration phenophases happen between 40th –63rd pentad, with Tilia mongolica and Armeniaca sibirica as the earliest species to show fall-color leaf. The autumn-leaf duration lasts for 8.2 pentads in average, with Euonymus alatus and Sambucus williamsii as the typical species that show longer leaf duration. The leaf period averagely lasts for 44.2 pentads, with Abelia chinensis, Salix matsudana and Kerria japonica holding the longest leaf time. The flowering-type phenophases happen during 1st–53rd pentad, with 8th–23rd pentad as the best ornamental period, and three species (Chimonanthus praecox, Jasminum nudiflorum and Ulmus pumila) as the earliest blooming species and Elsholtzia stauntoni as the last one to bloom. The flowering period lasts for 6.7 pentads in average, with Sorbaria kirilowii, Hibiscus syriacus and Lagerstroemia indica showing the longest flowering time. The fruiting-type phenophases happen between 8th–59th pentad, with Ulmus pumila and Lonicera fragrantissima as the earliest species for fruit maturation. The fruiting duration averagely lasts for 29.0 pentads, and those species that do not lose fruits during the winter and some other species with longer fruit holding period though falling fruits completely in winter such as Viburnum melanocarpum and Physocarpus opulifolius ‘Luteus’ have longer ornamental time of fruit scenery. Compared with a counterpart research in the 1980s, this study reveals that spring in 2017 came earlier by a pentad than that 30 years ago while autumn came later by 3 pentads; additionally, autumn duration shortened by 2 pentads while summer duration prolonged by 4 pentads, resulting in larger differences between the duration of the four seasons. © Chinese Journal of Plant Ecology.     

Specific leaf area estimation model building based on leaf dry matter content of Cunninghamia lanceolata北大核心CSCD

Aims With progresses of leaf functional traits study, there is an increasing demand to explore the life history strategy and trade-offs in plants, as well as estimate stand productivity, by employing easy and simple leaf parameters. For instance, the interconversion between leaf dry matter content (LDMC) and specific leaf area (SLA) just fit the bill. Cunninghamia lanceolata serves as one of the most important afforestation evergreen needle species in subtropical zone. Building the SLA estimation model based on LDMC could provide a new approach to estimate SLA, and establish a connection path between mechanism explanation and productivity evaluation. Moreover, it could also build a bridge between individual level and large-scale, as well as between actuarial and estimation. Methods Leaf samples were collected from two sampling sites located in C. lanceolata growing region: Huitong County of Hunan Province and Xinyang City of Henan Province. The samples covered fundamentally different niches (aspect, slope position, and canopy depth), and different life history (stand age and leaf age). SLA and LDMC were determined along leaf age gradients, and their value distributions in linkage to different factors were discussed. A general model based on LDMC of C. lanceolata was built to estimate SLA, and the impact of leaf age on the model was explored. Important findings The SLA of C. lanceolata was (103.15 ± 69.54) cm2·g–1, while LDMC was 0.39 ± 0.11. The LDMC and SLA of C. lanceolata can be estimated by nonlinear model (R2 = 0.718 4, p < 0.001), which meets the estimation requirements. One-year-old leaves showed the best fitting model (R2 = 0.889, p < 0.001), while old leaves (more than 2-year-old) showed the worst (R2 = 0.100 1, p < 0.001). Old leaves with a lower SLA (52.28–75.74 cm2·g–1) might imply the relative independence among the variation of LDMC. The model based on LDMC to evaluate SLA is credible and effective. The effects on LDMC and SLA along leaf age gradients indicate leaf sensitivity, life history strategies and trade-offs. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Identification of a delayed leaf greening gene from a mutation of pummelo

Delayed greening of young leaves is an unusual phenomenon of plants in nature. Citrus are mostly evergreen tree species. Here, a natural mutant of “Guanxi” pummelo(Citrus maxima), which shows yellow leaves at the young stage, was characterized to identify the genes underlying the trait of delayed leaf greening in plants. A segregating population with this mutant as the seed parent and a normal genotype as the pollen parent was generated. Two DNA pools respectively from the leaves of segregating seedlings with extreme phenotypes of normal leaf greening and delayed leaf greening were collected for sequencing. Bulked segregant analysis(BSA) and In Del marker analysis demonstrated that the delayed leaf greening trait is governed by a 0.3 Mb candidate region on chromosome 6. Gene expression analysis further identified a key candidate gene(Citrus Delayed Greening gene 1, CDG1) in the 0.3 Mb region, which showed significantly differential expression between the genotypes with delayed and normal leaf greening phenotypes. There was a 67 bp In Del region difference in the CDG1 promoter and the In Del region contains a TATA-box element. Confocal laser-scanning microscopy revealed that the CDG1-GFP fusion protein signals were co-localized with the chloroplast signals in the protoplasts. Overexpression of CDG1 in tobacco and Arabidopsis led to the phenotype of delayed leaf greening. These results suggest that the CDG1 gene is involved in controlling the delayed leaf greening phenotype with important functions in chloroplast development.     

Carbon accumulation and distribution in Pinus massoniana and Cunninghamia lanceolata mixed forest ecosystem in Daqingshan, Guangxi, China

Carbon accumulation and distribution were studied at three sampling plots in a 13-year-old mixed planatation of Pinus massoniana and Cunninghamia lanceolata in Daqingshan, Guangxi, China. The results showed that carbon content varied with tissues and tree species, but the total carbon content of Pinus massoniana was higher than that of Cunninghamia lanceolata. The average tissue carbon contents of Pinus massoniana were: wood (58.6%) > root (56.3%) > branch (51.2%) > bark (49.8%) > leaf (46.8%), while those of Cunninghamia lanceolata were: bark (52.2%) > leaf (51.8%) > wood (50.2%) > root (47.5%) > branch (46.7%). The carbon contents of the soil (at a depth of 60cm) ranged from 1.45% to 1.84% with an average of 1.70%. Carbon contents were higher in the surface soil (0–20cm) than in the deep layer (below 20cm). The average carbon contents were the highest for trees (51.1%), followed by litter (48.3%), shrubs (44.1%), and herbs (33.0%). The biomass of the trees in the three plots ranged from 85.35 t hm?2 to 101.35 t hm?2 with an average of 93.83 t hm^?2, in which 75.7%–82.6% was Pinus massoniana. The biomass of the understory was 2.10–3.95 t hm^?2 with an average of 2.72 t hm^?2, while the standing stock of ground litter was 5.49–7.91 t hm^?2 with an average of 6.75 t hm^?2. The carbon storage in the mixed plantation reached the maximum in the soil layer (69.02%), followed by vegetation (29.03%), and standing litter (1.82%). The carbon storage in the tree layer occupied 23.90% of the total ecosystem and 97.7% of the vegetation layer. Pinus massoniana accounted for 65.39% of the total carbon storage in the tree layer. Tissue carbon storage was directly related to the corresponding amount of biomass. Trunks had the highest carbon storage, accounting for 53.23% of the trees in Pinus massoniana and 55.57% in Cunninghamia lanceolata, respectively. Roots accounted for about 19.22% of the total tree carbon. The annual net productivity of the mixed plantation was 11.46 t hm?2a?1, and that of sequestered carbon was 5.96 t hm?2a?1, which was equivalent to fixing CO2 of 21.88 t hm?2a?1. The plantation was found to be an important sink of atmospheric CO₂.     

How does tree age influence damage and recovery in forests impacted by freezing rain and snow?

The response and recovery mechanisms of forests to damage from freezing rain and snow events are a key topic in forest research and management. However, the relationship between the degree of damage and tree age, i.e., whether seedlings, young trees, or adult trees are most vulnerable, remains unclear and is rarely reported. We investigated the effect of tree age on the degrees of vegetation damage and subsequent recovery in three subtropical forest types-coniferous, mixed, and broad-leaved —in the Tianjing Mountains, South China, after a series of rare icy rain and freezing snow events in 2008. The results showed that damage and recovery rates were both dependent on tree age, with the proportion of damaged vegetation increasing with age(estimated by diameter at breast height, DBH) in all three forest types and gradually plateauing. Significant variation occurred among forest types. Young trees in the coniferous forest were more vulnerable than those in the broad-leaved forest. The type of damage also varied with tree age in different ways in the three forest types. The proportion of young seedlings that were uprooted(the most severe type of damage) was highest in the coniferous forest. In the mixed forest, young trees were significantly more likely to be uprooted than seedlings and adult trees, while in the broad-leaved forest, the proportion of uprooted adult trees was significantly higher than that of seedlings and young trees. There were also differences among forest types in how tree age affected damage recovery. In the coniferous forest, the recovery rate of trees with broken trunks or crowns(DBH 2.5 cm) increased with tree age. However, in the mixed and broad-leaved forests, no obvious correlation between the recovery rate of trees with broken trunks or crowns and tree age was observed. Trees with severe root damage did not recover; they were uprooted and died. In these forests, vegetation damage and recovery showed tree age dependencies, which varied with tree shape, forest type, and damage type. Understanding this dependency will guide restoration after freezing rain and snow disturbances.     

Changes in leaf photosynthetic characteristics and water use efficiency along with tree height of 4 tree species

As main photosynthetic organs, leaves are very sensitive to exterior environments. Water deficiency obviously affects the biological and physiological characteristics of leaves. Xylem pathways increase when trees grow tall, which results in the increase in water gravity as well as pathway resistance. Accordingly, the physiological characteristics of leaves change along with tree height. In this research, the photosynthetic characteristics and carbon isotope ratio (δ¹³C) in the leaves of 4 tree species, Platanus hispanica, Robinia pseudoacacia, Fraxinus chinensis and Ginkgo biloba, were measured. The results showed that the leaf photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Cond) and internal CO₂ concentration (Ci) reduced along with tree height, while the leaf δ¹³C increased along with tree height. The One Way ANOVA and LSD tests showed that the leaf photosynthetic characteristics and δ¹³C varied significantly at different tree heights (P < 0.05). The decrease in leaf photosynthetic capability and the increase in δ¹³C along with tree height indicate that the leaves at the tree tops suffer from water stress. These results support the hydraulic limitation hypothesis.     

Community characteristics and population structure of Ferrocalamus strictus,a rare species in Mojiang,Yunnan, China北大核心CSCD

Aims As an endangered wild species with extremely small populations, Ferrocalamus strictus is narrowly distributed in South Yunnan with a small number of individuals. The survey of population structure and community characteristics of the wild population of F. strictus can facilitate understanding its endangered system and mechanisms and provide preliminary research basis for its protection. Methods We investigated the community and population structure of F. strictus, including species composition, population density, population survivorship curve and death factors by plot surveying and sampling. Important findings The community in which population of F. strictus is located in Mojiang has some characteristics of mountain rainforests in terms of appearance and species composition. The population density of F. strictus was 2.04 ind.·m–2. The survivorship curve of F. strictus was between Deevey-I and Deevey-II. The net proliferation rate (R0) of F. strictus population was 1.10, which indicates an expanding population of F. strictus. The death of F. strictus is caused by human logging, natural death, shoot degradation and insects feeding. Among them, artificial cutting accounts for the largest proportion. Ferrocalamus strictus is a species of forest bamboos distributed in the South Asian subtropics, which is a medium-sized bamboo species. Its internode length change suddenly from the base 3–4 nodes. The longest ones exceed 1 m, which ranks at the top of all bamboo species and is closely related to its adaptation to the tropical mountain rainforest environment. © Chinese Journal of Plant Ecology.     

Effects of Logging on the Genetic Diversity of Quercus tiaoloshanica Chun et Ko in a Tropical Montane Forest of Hainan Island, Southern China

Quercus tiaoloshanica Chun et Ko, which has a narrow range of distribution, is one of the important endemic species of the tropical montane rain forest on Hainan Island, southern China. Long-term logging and habitat destruction have resulted in population decline and distribution retreat of Q. tiaoloshanica. To determine the impact of logging on the genetic diversity of Q. tiaoloshanica, the authors investigated the genetic structures using amplified fragment length polymorphism markers in four regenerated stands after logging and in one unlogged stand. Compared with the unlogged stand, the effective number of alleles per locus dropped by 1.0% in selective logging stands and by 2.0% in clear logging stands, corresponding to reductions of 3.8% and 5.2%, respectively, in mean Nei＇s gene diversity and 2.9% and 3.5%, respectively, in mean Shannon diversity index. No substantial genetic erosion was detected in any of the regenerated stands owing to the high tree density and high heterogeneity of the Q. tiaoloshanica stands investigated. Meanwhile, there was no natural regeneration of the species observed in a Dacrydium pierrei Hickel plantation 700 m away from the regenerated stands, suggesting the limited ability of seed dispersal of Q. tiaoloshanica. Clear logging should be undertaken cautiously because the total number of plant species dropped by 15.2% in the clear-logged stands compared with the unlogged stand. To conserve the genetic diversity of this species, as well as the plant biodiversity of tropical forests, the habitats of Q. tiaoloshanica should be protected against exploitation in terms of agricultural or other forms of land use, and some mature trees should be preserved as seed sources to maintain an adequate regeneration base for this species in the management of logging.