Effects of drought and nitrogen addition on photosynthetic characteristics and resource allocation of Abies fabri seedlings in eastern Tibetan Plateau

Abies fabri (Mast.) Craib is an endemic and dominant species in typical sub-alpine dark coniferous forests distributed in mountainous regions of the eastern Tibetan Plateau, China. We investigated the ecophysiological responses of A. fabri seedlings to short-term artificially-applied drought, nitrogen addition alone, and the combination of these treatments. Drought was created by excluding natural precipitation with an automatically controlled plastic roof that covered the seedlings. Nitrogen fertilization was applied weekly by spraying over seedlings with ammonium nitrate solution. Experiment results showed that drought caused a reduction in photosynthetic nitrogen use efficiency and leaf mass per area. Nitrogen addition enhanced photosynthetic performance by increasing net photosynthetic rate. In the drought plots, nitrogen addition increased net photosynthetic rate and instantaneous water use efficiency. These results showed that applied nitrogen improved plant water use efficiency and N accumulation in plant organs under drought conditions. Especially under drought conditions more N was concentrated into needles by applied nitrogen as compared with other organs. In conclusion, our results indicated that the combination of nitrogen addition and drought may result in positive effects on A. fabri seedlings in the short-term.     

Effects of forest canopy gap on biomass of Abies faxoniana seedlings and its allocation in subalpine coniferous forests of western Sichuan

Using a strip transect sampling method, the density, height (≤ 100 cm), basal diameter and components of biomass of Abies faxoniana seedlings, living in a forest gap (FG) and under the forest canopy (FC) of subalpine natural coniferous forests in western Sichuan, were investigated and the relationships among different components of biomass analyzed. The results indicated that the density and average height (H) of A. faxoniana seedlings were significantly different in the FG and under the FC, with the values being 12903 and 2017 per hm², and 26.6 and 24.3 cm. No significant differences were found in the average basal diameter (D) and biomass. The biomass allocation in seedling components was significantly affected by forest gap. In the FG, the biomass ratio of branch to stem reached a maximum of 1.54 at age 12 and then declined and fluctuated around 0.69. Under the FC, the biomass ratio of branch to stem increased with seedling growth and exceeded 1.0 at about age 15. The total biomass and the biomass of leaves, stems, shoots and roots grown in the FG and under the FC were significantly correlated with D ² H. There were significant and positive correlations among the biomass of different components. __________ Translated from Chinese Journal of Applied Ecology, 2007, 18(4): 721–727 [译自: 应用生态学报]     

Environmental influences on the successful regeneration of pine-oak mixed forests in the Qinling Mountains,China

Understanding the factors that allow the successful regeneration of species is a key step toward the conservation and management of forests. In this study, canonical correspondence analysis was used to examine the relationships between the distribution of the regenerating species in pine-oak mixed forests and 18 environmental factors of topography, soil properties, and forest characteristics in seedlings and saplings in the Qinling Mountains in China. A generalized additive model was used to fit the response of the density of the regenerating species to the various environmental factors. Variation partitioning in both seedling and sapling stories indicated that the order of importance was soil properties?>?forest characteristics?>?topography. The distribution of seedlings and saplings was mainly influenced by slope gradient, shrub cover, and available phosphorus. Herb cover and total nitrogen level were major environmental factors affecting the density of the regenerating seedlings, but total potassium level and elevation were significant variables for saplings. Not all seedlings were able to establish successfully, perhaps due to stress from the external environment and the heterogeneity of the light availability in the understory as the forest developed. Appropriate thinning of stands with higher densities and closed canopies is expected to produce gaps and promote the natural regeneration of pine-oak mixed forests in the Qinling Mountains.     

四川卧龙岷江冷杉林分布规律及种群特征

通过典型抽样法,对四川省卧龙自然保护区邓生阴坡的的岷江冷杉原始林进行了分布以及种群特征的调查研究。结果表明,在卧龙自然保护区,岷江冷杉林主要分布在湿润的阴坡或半阴坡,常形成多种群落类型,并能从海拔2 700 m的坡底连绵成片分布到海拔3 800 m的林线;主要有6类群落,分别为岷江冷杉-华西箭竹林、岷江冷杉-峨眉玉山竹林、岷江冷杉-冷箭竹林、岷江冷杉-大叶金顶杜鹃林、岷江冷杉-星毛杜鹃林和岷江冷杉-无柄杜鹃林。研究区岷江冷杉相同径级的树高随着海拔的升高却逐渐变矮,在海拔2 700 m、2 900 m、3 100 m和3 300 m的岷江冷杉种群属于增长型的年龄结构,海拔3 600 m岷江冷杉种群属于稳定型的年龄结构;岷江冷杉林剧烈的种间竞争发生在森林底层或下层,海拔2 700 m~3 200 m间岷江冷杉种群的主要竞争对象是华西箭竹,海拔3 200 m~3 600 m的范围的主要竞争对象是大叶金顶杜鹃和无柄杜鹃,影响岷江冷杉种群繁殖与更新;岷江冷杉种群常遭受病虫兽害和风灾与雪灾,影响岷江冷杉种群生长发育和造成数量减小。     

Warming effect on growth and physiology of seedlings of Betula albo-sinensis and Abies faxoniana under two contrasting light conditions in subalpine coniferous forests of western Sichuan, China

The subalpine coniferous forests on the eastern Qinghai-Tibet Plateau provide a natural laboratory for studying the effect of climate warming on terrestrial ecosystems. Research on differences between tree species in their responses to experimental warming can provide insights into their regeneration behavior and community composition under a future warmer climate. We used open-top chamber (OTC) to determine the short-term effect of two levels of air temperature (ambient and warmed) and light (full light and ca. 10% of full-light regimes) on the early growth and physiology of Betula albo-sinensis and Abies faxoniana seedlings. The OTC manipulation increased mean air temperature and soil surface temperature by 0.51 and 0.34°C, respectively, in a 60-year-old plantation and 0.69 and 0.41°C in forest openings, respectively. Warming generally increased plant growth, biomass accumulation, and advanced physiological processes for seedlings of both species. In response to warming, both tree species allocated relatively more biomass to foliage and had significantly decreased root/shoot ratios (R/S), which might provide the two species with an adaptive advantage when other environmental factors were not limiting. Warming may enhance photosynthesis in the two seedlings by increasing efficiency of PSII in terms of increases in F _v/F _m, photosynthetic pigment concentrations, and apparent quantum yield (Φ). However, the effects of warming on seedling growth and physiological performance varied by light conditions and species. For B. albo-sinensis seedlings, the effects of warming were pronounced only under full-light conditions, while the growth and physiological responses of A. faxoniana seedlings to warming were found only under low-light conditions. Competitive and adaptive relationships between the two species may be altered as a result of response differences to warming manipulation. The shortterm beneficial impact of warming on the early growth and development of the two species suggests that global warming may lead to changes in regeneration dynamics and species composition in subalpine coniferous forest ecosystems.     

Shrub island effects on a high-altitude forest cutover in the eastern Tibetan Plateau

• Context  

The roles of woody-plant islands are well documented in low-altitude regions, but research related to such shrub effects in high-altitude regions is scant.     

王朗自然保护区岷江冷杉林(Abies faxoniana)更新及其种群结构分析

岷江冷杉(Abies faxoniana)林是四川王朗自然保护区主要群落类型,本文选择典型的亚高山针叶原始林设置标准样地,对其幼苗幼树查数轮生枝、大树钻取树轮样芯确定个体年龄,分别建立苗高-年龄、胸径-年龄的回归方程得到整个种群的年龄结构,通过编制生命表对其进行生存分析.结果表明,岷江冷杉存活曲线属于Deevey-Ⅲ型...     

川西亚高山岷江冷杉和铁杉年轮对气候因子的响应

研究四川卧龙亚高山森林岷江冷杉和铁杉树木年轮与气候因子的关系.结果表明:川西亚高山针叶林树木径向生长主要受气温的制约,卧龙地区岷江冷杉树轮宽度序列与当年2和4月月平均气温显著正相关(P≤0.05),而与多数月平均降水量和月平均相对湿度负相关;铁杉树轮宽度序列与上一年7月和当年2--4月月平均气温显著正相关(P≤0.05),与上一年10月和当年5月月平均降雨量显著正相关(P≤0.05),而与上一年7月及当年4和9月月平均相对湿度显著负相关(P≤0.05).     

Winter soil CO2 efflux in two contrasting forest ecosystems on the eastern Tibetan Plateau,China

Significant CO2 fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO...     

不同海拔岷江冷杉林凋落物量及其季节动态变化研究

本文对四川王朗国家自然保护区不同海拔岷江冷杉森林群落内的凋落物总量、各凋落物组分随海拔的变化及其季节动态进行了研究,结果显示,各凋落物组分和总凋落物的年产量在不同海拔间均无显著性差异,年总凋落物量在3 537.18~4 761.84 kg.hm-2.a-1,高于同一地区的相似群落,表明在该区域岷江冷杉林具有相对较高的生...     

铅笔柏与小意杨混交效果测定

铅笔柏可与意杨、泡桐等砍伐周期短的树种混交。混交的铅笔柏品种以选鳞叶,冠幅小的圆锥形或圆柱形类型为好,密度可为2×3米或2×2米,并以阔叶树造林2～3年再栽植铅笔柏为宜。混交12年后可逐渐对阔叶树进行间伐。     

四川卧龙岷江冷杉林小流域土壤水分的时空分布特征及变异性

本文应用CNC503DR型中子土壤水分仪,在四川卧龙亚高山暗针叶林生态系统定位站,研究了林分和小流域尺度上岷江冷杉林土壤水分的时空分布特征及变异性。结果表明：研究期间,小流域土壤平均容积含水量在0.59~0.66之间,不同群落类型之间,差异比较明显,且随时间的变化规律不同;小流域内土壤剖面的平均容积含水量在0.52~0.77之间,平均值为0.60,土壤表层最高,45 cm深度最低;随着海拔升高,土壤含水量增加,但超过3 700 m则减少;不同坡向,土壤含水量在0~30 cm土层半阴坡高于半阳坡,30 cm以下土层则相反;不同坡位,土壤含水量下坡最高,其次是中坡,上坡最低;小流域土壤水分变异系数在0.217 6~0.409 8之间,不同群落类型之间差异显著,随着土层剖面深度增加而减小,随着海拔升高而减小,半阴坡高于半阳坡,下坡大于中坡和上坡。     

Short-term effects of nitrogen deposition on soil respiration components in two alpine coniferous forests,southeastern Tibetan Plateau

Nitrogen (N) deposition to alpine forest ecosystems is increasing gradually, yet previous studies have seldom reported the effects of N inputs on soil CO2 flux in these ecosystems. Evaluating the effects of soil respiration on N addition is of great significance for understanding soil carbon (C) budgets along N gradients in forest ecosystems. In this study, four levels of N (0, 50, 100, 150 kg N ha^-1 a^-1) were added to soil in a Picea baifouriana and an Abies georgei natural forest on the Tibetan Plateau to investigate the effect of the N inputs on soil respiration. N addition stimulated total soil respiration (Rt) and its components including heterotrophic respiration (Rh) and autotrophic respiration (Ra);however, the promoted effects declined with an increase in N application in two coniferous forests. Soil respiration rate was a little greater in the spruce forest (1.05 μmol CO2 m^-2 s^-1) than that in the fir forest (0.97 μmol CO2 m^-2 s^-1). A repeated measures ANOVA indicated that N fertilization had significant effects on Rt and its components in the spruce forest and Rt in the fir forest, but had no obvious effect on Rh or Ra in the fir forest. Rt and its components had significant exponential relationships with soil temperature in both forests. N addition also increased temperature sensitivity (Q10) of Rt and its components in the two coniferous forests, but the promotion declined as N in put increased. Important, soil moisture had great effects on Rt and its components in the spruce forest (P<0.05), but no obvious impacts were observed in the fir forest (P>0.05). Following N fertilization, Ra was significantly and positively related to fine root biomass, while Rh was related to soil enzymatic activities in both forests. The mechanisms underlying the effect of simulated N deposition on soil respiration and its components in this study may help in forecasting C cycling in alpine forests under future levels of reactive N deposition.     

川西亚高山森林岷江冷杉树轮碳稳定同位素对气候要素的响应

利用四川卧龙亚高山暗针叶林岷江冷杉树木年轮样本资料,建立树轮宽度年表,对比宽度年表,提取树木年轮(简称树轮)碳稳定同位素(δ13C)序列和去趋势序列(DS),研究岷江冷杉树轮碳稳定同位素序列对气候要素的响应关系.结果表明:岷江冷杉(1904-2009年)树轮碳稳定同位素变化范围为-23.33‰～-26.31％‰,平均值为-24.91‰,变异系数为-0.025;相关分析表明,岷江冷杉δ13C序列(DS)与前一年11月和当年1月的月平均气温显著正相关(P≤0.05),与前一年1月和当年2,11月的月平均气温极显著正相关(P≤0.01),冬季平均气温对岷江冷杉树轮碳稳定同位素的响应最为敏感,是研究过去环境变化的良好载体,与当年1月降水量显著正相关(P≤0.05),与全年的月平均相对湿度相关性不显著(P≥0.05).     

四川卧龙岷江冷杉天然林生物多样性随海拔梯度的响应

采用典型样带调查法,在卧龙自然保护区邓生阴坡的岷江冷杉天然林内设置不同海拔梯度的样带,分析岷江冷杉天然林的生物多样性随海拔梯度的响应规律。研究结果表明:岷江冷杉天然林乔木和草本植物的物种丰富度、Shannon-Wiener多样性指数、Pielou均匀度指数和均优丰多样性指数随着海拔升高呈下降趋势,而生态优势度指数呈上升趋势;灌木种随着海拔梯度上升物种丰富度下降,Shannon-Wiener多样性指数、Pielou均匀度指数和均优丰多样性指数则呈现出先降低后升高的趋势,生态优势度指数的变化与之相反;群落所有植物的α多样性随海拔梯度的变化规律与乔木层一致。从β多样性变化来看:随着海拔上升,岷江冷杉林内乔木、草本和所有群落所有植物的相异系数CD和Cody指数均呈下降趋势;而灌木层因为物种数和优势种的改变形成β多样性的双峰变化,这与灌木植物的实际分布是相符的。群落整体的物种差异和更替速率受物种数较多的植被类型影响较大,随海拔升高呈逐渐减小趋势。     

Growth rate of mosses and their environmental determinants in subalpine coniferous forests and clear-cuts at the eastern edge of the Qinghai-Tibetan Plateau, China

Mosses cover most of the forest floor of subalpine forests at the eastern edge of the Qinghai-Tibetan Plateau, the origin of many important rivers in China. They play a crucial role in preventing soil erosion and conserving large amounts of water thereby regulating the water budget of local ecosystems. This area has a harsh climate due to low temperatures and low air pressure at high elevations. But the temperature varies considerably during the growing season, which does not favor the regeneration of spruce seedlings on clear-cuts after logging. Leaves of mosses have a single layer of cells and are thus sensitive to environmental changes. This attribute may be useful for monitoring environmental conditions and guide artificial regeneration. The growth of mosses has never been studied in this area and the variables indicating their growth in the subalpine forest ecosystems still needs investigation. Growth rates of mosses have been rarely studied worldwide because the methods are time consuming and often inaccurate. A more simple and accurate method for measuring moss growth would help and encourage relevant research. We have found a method that will promote the efficiency in field measurements. Because of the special growth properties of mosses, the apical cell of branches initiates growth and the preceding leaves will stay where they were as the tips grow. Once mosses are marked with red oil at the tip of branches surrounded by young leaves, that portion of the branch above the marked leaves represents growth after labeling. Two plots, one in an old-growth spruce forest and another in a nearby clear-cut, were selected to label mosses in a subalpine area of western Sichuan Province during the growing season in 2001. The labeling was done on May 7 and measurements were made on August 7. Microclimate measurements on both sites were simultaneously carried out. Of the six mosses, five species were present in both the forest and on the clear-cut. One species, Entodon conncinus, was found only on the clear-cut. The growth rates of mosses varied among species and habitats. Hylocomium splendens grew the fastest while Dicranum assamicum had the slowest growth rate. Habitat conditions have a distinct effect on the growth of Hylocomium splendens, Dicranum assamicum and Thuidium lepidoziaceum and their growth rates were higher in forests than on clear-cuts. The growth rates of these mosses increased as their habitat approached the forest. Actinothuidium hookeri and Rhytidiadelphus triquetrus have moderate growth rates and is almost entirely independent of the type of habitat. The mosses can therefore be classified into habitat-sensitive and habitat-insensitive types. Analysis of microclimate characteristics shows that from May to July, the solar radiation level is lower and the environment is drier in the forest than those on the clear-cut. But a vapor pressure deficit (VPD) regime shows that the VPD in the morning is almost always lower in the forest than that on the clear-cut. With lower radiation and VPD, forests are more favorable to moss growth. For habitat-insensitive species, favorable micro-topographic factors might have offset the effect of habitat type. VPD is strongly correlated with the growth of mosses. Eco-physiological characteristics, such as poikilohydry, play an important role in the survival and growth of mosses under harsh climatic conditions. Temperature and humidity are two factors critical for seedling establishment in artificial regeneration processes in the subalpine areas of western Sichuan. Since the growth of mosses is a function of the two factors, moss growth rates can be used to indicate the more favorable habitats. Therefore, the status of moss growth can be used to indicate habitats potentially favorable to the growth of tree seedlings. __________ Translated from Journal of Plant Ecology, 2007, 31(3): 464–469 [译自: 植物生态学报]     

川西亚高山岷江冷杉和紫果云杉径向生长对气候因子的响应

【目的】探讨川西亚高山地区各海拔生境处岷江冷杉和紫果云杉径向生长对气候因子的响应,为进一步揭示当地森林对气候变化的响应机制提供依据。【方法】分别获取王朗自然保护区中海拔与高海拔生境处岷江冷杉和紫果云杉的标准年表,分析年表同气候因子间的关系。【结果】中海拔生境处岷江冷杉生长在1990年后与年均气温存在一定程度的“分离效应”;中海拔生境处岷江冷杉和紫果云杉生长与上年生长季(上年7月和8月)气温和上年生长季末(上年10月)降水量显著负相关( P <0.05),岷江冷杉生长与当年9月气温和降水量显著负相关( P <0.05),紫果云杉生长与当年2、6月月均最低气温显著正相关( P <0.05);高海拔生境处岷江冷杉和紫果云杉生长均与当年生长季前(上年11月、当年1月、当年2月)、当年生长季(当年7月)和上年生长季(上年6月)气温显著正相关( P <0.05),岷江冷杉生长还与当年6月份的降水量及上年8月份的气温显著负相关( P <0.05);滑动相关分析和年表特征年气候分析结果充分印证了各年表对月气候因子响应的可靠性。【结论】上年生长季气温的“滞后效应”对中海拔生境处的岷江冷杉、紫果云杉以及高海拔生境处的岷江冷杉生长均有显著影响;近几十年来,上年生长季末降水对中海拔生境处的岷江冷杉、紫果云杉以及高海拔生境处的紫果云杉生长都具有稳定而显著的抑制作用。     

Climate,plant organs and species control dissolved nitrogen and phosphorus in fresh litter in a subalpine forest on the eastern Tibetan Plateau

Key message

Fresh litter contains a higher concentration of dissolved phosphorus (DP) than dissolved nitrogen (DN), which implies a more efficient DN transformation or reabsorption in the subalpine forest on the eastern Tibetan Plateau. Both DN and DP concentrations increased with the increase of mean monthly temperature, although the concentrations were also regulated by plant organs and species.

Context

The dissolved nitrogen (DN) and dissolved phosphorus (DP) released from fresh litter are important pathways by which total nitrogen and phosphorus are transferred from the vegetation to soil in forest ecosystems. However, few studies have paid attention to the DN and DP in fresh litter, which affects our understanding of the nitrogen and phosphorus cycles.

Aims

The objectives of this study were to elucidate the dynamic characteristics of the concentrations and storage of DN and DP, and to analyze how DN and DP are affected by different plant species and organs, and climate factors.

Methods

Fresh litter was collected in three plots in a spruce-fir forest and classified by different plant species and organs. Concentration and storage of DN and DP in fresh litter were determined and related to the climatic variables that were monthly recorded.

Results

The concentration of DP was higher than that of DN in fresh litter, and the concentrations of both elements were determined by plant organs and species. Moreover, The DN and DP concentration was positively related to mean monthly temperature, while DN and DP storage was negatively correlated with mean monthly temperature and monthly precipitation. The storage of DN and DP was determined by litter biomass, which the order in litter from different plant organs was leaves>twigs>miscellaneous>flowers and fruits. The storage of DN and DP in leaves showed two peaks in April and October, but that in twigs and the miscellaneous showed only one peak in October.

Conclusion

Our results indicated that dissolved nitrogen (DN) is transferred and reabsorbed more than dissolved phosphorus (DP) before plant leaf senescence and other organs fall. Furthermore, DN and DP were associated with climate, plant organs and species in a subalpine forest on the eastern Tibetan Plateau.

     

Landscape pattern and fragmentation of natural secondary forests in the eastern mountainous region, northeast China: A case study of Mao'ershan forests in Heilongjiang Province

Mao'ershan region is a representative natural secondary forested region in the eastern mountainous region, northeast of China. Under the support of ARC/INFO and GIS technology, the landscape shape and fragment indices of Mao'ershan experimental plantation were studied by combining the forest type map (1∶10000), which was drawn from the aerial photographs (1999), field investigation (1999) and soil utilized map (1∶10000). The results showed that the shape index and shape fragment index of natural landscape were higher than those of artificial landscapes and landscape patch fragment index depended on the number of patches. The natural forest had complex shape, suffering little jamming, and its shape index was higher than that of artificial forest. The manual controlled landscape (e.g. nursery, cropland and cutting blank) had regular shape, and its shape index was smaller. The fragment index of patches in natural forest was higher than that of artificial forest. The soft broad-leaved had the highest fragment index of patch amount. Foundation item: This paper was supported by National Key Technologies P&D Program of China during the 10^th Five-Year Plan Period (2002BA515B040). Biography: LI Shu-juan (1977-), female, Lecturer in Ocean University of China, Qingdao 266003, P. R. China. Responsible editor: Zhu Hong