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Table of Content
    Volume 34 Issue 4
    01 April 2010

    A haloeremion landscape in southern periphery of Gurbantunggut Desert, Xinjiang, China, where Xu et al. investigated influence of solar radiation and groundwater table on carbon balance of scrub community dominated by Tamarix species (Pages 375–386 of this issue). (Photographed by XU Hao)

    Research Articles
    Transformation of vegetation structure in China’s Liaohe Delta during 1988-2006
    JI Yu-He, ZHOU Guang-Sheng
    Chin J Plant Ecol. 2010, 34 (4):  359-367.  doi:10.3773/j.issn.1005-264x.2010.04.001
    Abstract ( 2183 )   Full Text ( 3 )   PDF (644KB) ( 1693 )   Save
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    Aims An obvious transformation of vegetation structure in the Liaohe Delta has resulted from climatic fluctuation and human disturbance. We focus on the transformation of vegetation structure with the objective of contributing to management for maintaining a healthy ecosystem.

    Methods The study area included the entire Liaohe Delta, and data sources came from Landsat Thematic Mapper (TM) imagery in 1988 and 2006. The methods of digitizing, mapping vegetation and overlay analysis were used to explore structural characteristics, changed distributions and transformed areas of vegetation.

    Important findings The vegetation pattern consisted of a semi-ring of four main vegetation types (natural wetland, constructed wetland, constructed dryland and natural dryland vegetation) encircling the estuary of Shuangtaizi River. In terms of this macrostructure, the vegetation pattern did not change greatly, and the main vegetation types tended to aggregate rather than fragment as relatively large vegetation landscapes came into being from 1988 to 2006. However, almost all vegetation types changed in spatial distribution and area. In terms of vegetation area, the main vegetation types were rice (Oryza sativa) land, maize (Zea mays) land and coastal wetland reed. Rice land vegetation had the largest increase in area (977.1 km2), while maize land vegetation had the largest decrease (622.2 km2). The transforming percentages among vegetation types were 33.2%, -16.1% and -23.2% for rice land, maize land and coastal wetland reed, respectively. The meadow had the maximal decrease (-77.9%), while the community of salt meadow seepweed (Suaeda hetroptera) had the maximal increase (212.1%).

    Carbon and nitrogen release during decomposition of coarse woody debris for eleven temperate tree species in the eastern mountain region of northeast China
    ZHANG Li-Min, WANG Chuan-Kuan
    Chin J Plant Ecol. 2010, 34 (4):  368-374.  doi:10.3773/j.issn.1005-264x.2010.04.002
    Abstract ( 2464 )   Full Text ( 3 )   PDF (675KB) ( 1614 )   Save
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    Aims Our objectives were to quantify the loss of coarse woody debris (CWD) mass, carbon (C) and nitrogen (N) and main influencing factors during the first three years of CWD decomposition of 11 major tree species in Chinese temperate forests based on an in situ long-term experiment.

    Methods The experimental design was completely randomized blocking design of 11 species × 6 blocks × 4 sites. The species were white birch (Betula platyphylla), Amur linden (Tilia amurensis), Korean pine (Pinus koraiensis), Manchurian walnut (Juglans mandshurica), cork-tree (Phellodendron amurense), Mongolian oak (Quercus mongolica), Dahurian larch (Larix gmelinii), Mono maple (Acer mono), Manchurian ash (Fraxinus mandshurica), popular (Populus davidiana), and Japanese elm (Ulmus japonica). The four sites with various environmental conditions were Mongolian oak forest, hardwood forest, Korean pine plantation and open field. We randomly selected three CWD samples for each tree species in each site and cut a 5 cm-thick disc at the end of the CWD in October 2005 and October 2008, respectively, for measuring C concentration, C density, N concentration, N density, C/N ratio and CWD density.

    Important findings The C concentration of CWD did not change significantly during the early stage of CWD decomposition for all species (p > 0.05). The CWD mass, C density, N concentration and N density decreased during decomposition, whereas the C/N ratio increased. The differences in these parameters among the species were significant (p < 0.001). The coniferous species had significantly lower decomposition rates than the broad-leaved species. There was a negative correlation between size and decay rate. Loss of mass and release of C and N of the CWD were positively correlated with the initial N content, but negatively correlated with the initial C/N ratio. The changes of mass and C and N content of CWD had similar patterns at the four sites. Our results indicated that the CWD tended to be C and N sources during the first 3-year decomposition process.

    Influence of solar radiation and groundwater table on carbon balance of phreatophytic desert shrub Tamarix
    XU Hao, LI Yan, XIE Jing-Xia, CHENG Lei, ZHAO Yan, LIU Ran
    Chin J Plant Ecol. 2010, 34 (4):  375-386.  doi:10.3773/j.issn.1005-264x.2010.04.003
    Abstract ( 3065 )   Full Text ( 5 )   PDF (960KB) ( 1746 )   Save
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    Aims The groundwater table has changed and air pollution has been reducing solar radiation on the southern periphery of China’s Gurbantonggut Desert. Our objective was to investigate the response and adaptation of Tamarix ramosissima, a native dominant desert shrub in Central Asia, towards variation in groundwater and photosynthetically active radiation (PAR), in terms of ecophysiological activities, morphological characteristics and community carbon/water balances.

    Methods During the growing season from 2005 to 2007, we carried out experiments in the original habitat of T. ramosissima, where the groundwater table fluctuated from 2.9 to 4.5 m. Photosynthesis, transpiration, leaf water potential, water-use efficiency and root distribution were examined to reveal the water-use strategy of the species, and CO2 and H2O fluxes above an undisturbed T. ramosissima ecosystem were measured by eddy covariance method to evaluate net carbon assimilation, water loss and leaf area index (LAI).

    Important findings Physiological activity and community carbon uptake of T. ramosissima did not respond to sustained drought in upper soil or rainfall pulses, and its photosynthetic consistency is achieved by its water-use pattern. Special stomatal behavior and root distribution are two main mechanisms. Tamarix ramosissima tends to maximize its carbon gain at the cost of higher water consumption, attributable to its phreatophytic root system that ensures sufficient groundwater supply and avoids the effects of water deficiency in upper soil. Tamarix ramosissima can adapt to moderate fluctuation of groundwater table, but severe decline will threaten its survival, and hence the overexploitation of groundwater will cause severe degradation of Tamarix-dominated perennial vegetation and disturb the original ecohydrological processes in this arid region. PAR is another important environmental factor positively correlating with community carbon uptake. The LAI indicates that the seasonal pattern in community carbon assimilation represents the combined effects of groundwater table and PAR on the phenological photosynthesis capacity. It shows that the integrated study on different scales is an effective approach to further the understanding of desert shrub adaptive strategies and ecosystem processes under variable environmental conditions.

    Soil chemical properties and growth characteristics of mixed plantation of Pinus massoniana and Cinnamomum camphora in the acid rain region of Chongqing, China
    LI Zhi-Yong, WANG Yan-Hui, YU Peng-Tao, ZHANG Zhi-Jun, DU Shi-Cai, HE Ping, WANG Xiang, DUAN Jian, LI Zhen-Hua
    Chin J Plant Ecol. 2010, 34 (4):  387-395.  doi:10.3773/j.issn.1005-264x.2010.04.004
    Abstract ( 2850 )   Full Text ( 3 )   PDF (386KB) ( 1600 )   Save
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    Aims Acid rain has led to Pinus massoniana forest decline in Chongqing, Southwestern China. Cinnamomum camphora, an acid-resistant broadleaved tree species, has been widely distributed in the region. Cinnamomum camphora is thought to improve soil properties and health condition of P. massoniana; however, little information is available from mixed plantations of P. massoniana and C. camphora exposed to acid rain. Our objective was to examine soil chemical properties and growth traits of these two species in mixed plantations in the region.

    Methods We investigated soil chemical properties and above- and below-ground growth condition of a mixed plantation of P. massoniana and C. camphora in the Tieshanping Forest Farm of Chongqing City. We compared results with those from adjacent pure plantations of P. massoniana and C. camphora, which were planted at the same time as the mixed plantation.

    Important findings Compared with the pure P. massoniana plantation, pH values were greater in the humus and soil of the mixed plantation, contents of exchangeable Ca2+ and Mg2+ were higher, contents of exchangeable Al3+ and H+ were significantly lower (p < 0.05), the amount of fine roots of P. massoniana in the humus and soil was smaller (p < 0.05), height of dominant trees of P. massoniana was significantly lower (p < 0.05) and needle discoloration percentage of dominant trees of P. massoniana was higher (p < 0.05). Growth characteristics of C. camphora were similar to those of the pure C. camphora plantation. This study suggested that although C. camphora ameliorated soil chemical properties, health of P. massoniana of the mixed plantation worsened, which might be caused by stronger competitive abilities of C. camphora. Therefore, the competitive advantage of C. camphora against P. massoniana should be properly controlled when establishing mixed plantations of P. massoniana and C. camphora for improving the health of pure P. massoniana plantations in the region.

    Diversity and distribution of epiphytic orchids in different types of old-growth tropical forests in Bawangling National Nature Reserve, Hainan Island, China
    LIU Guang-Fu, ZANG Run-Guo, DING Yi, WANG Wen-Yi, LI Ru-Cai, CHEN Shao-Wei, ZHOU Zhao-Li
    Chin J Plant Ecol. 2010, 34 (4):  396-408.  doi:10.3773/j.issn.1005-264x.2010.04.005
    Abstract ( 3657 )   Full Text ( 3 )   PDF (685KB) ( 2580 )   Save
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    Aims Epiphytic orchids are a major group of epiphytes and vital to maintaining biodiversity and ecosystem functioning in tropical forests. Our objective was to explore diversity and distribution of epiphytic orchids among six different types of old-growth tropical forests (tropical monsoon forest, SF; tropical lowland rain forest, LF; tropical coniferous forest, CF; tropical montane rain forest, MF; tropical mountain evergreen forest, ME; and tropical elfin forest, EF) in Bawangling National Nature Reserve, Hainan Island, China.

    Methods We established twelve 0.05 hm2 (10 m × 50 m) plots in each type of old-growth forest and recorded species, individuals and position of epiphytic orchids on each tree and liana with diameter at breast height (DBH) ≥ 5 cm in each plot.

    Important findings We recorded a total of 9 634 epiphytic orchids belonging to 60 species and 26 genera in the total sample of 3.6 hm2. Detrended Correspondence Analysis based on the presence-absence and abundance showed that the epiphytic orchids of the six types of forests were divided into five groups (epiphytic orchids in ME and EF were clustered into one group). There was high similarity between neighboring altitudinal forest types, with the highest value (88.9%) between the ME and EF. Species richness and abundance of epiphytic orchids in the high altitude forest types were greater than in the low altitude forest types, with highest value in the ME. Differences in abundance of epiphytic orchids between in the trunk and the crown were crown > trunk in the SF, LF, CF and MF, no difference in ME and trunk > crown in EF. The ratio of the epiphytic orchids phorophytes to the total investigated plants was higher in the high altitude forest types than in the low altitude forest types. Epiphytic orchid abundance and species richness were both significant positive correlated with phorophyte size (DBH) in each forest type.

    A comparison of selecting data points and fitting coefficients methods for estimating self-thinning boundary line
    SUN Hong-Gang, ZHANG Jian-Guo, DUAN Ai-Guo
    Chin J Plant Ecol. 2010, 34 (4):  409-417.  doi:10.3773/j.issn.1005-264x.2010.04.006
    Abstract ( 2460 )   Full Text ( 1 )   PDF (554KB) ( 1602 )   Save
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    Aims The self-thinning boundary line represents the upper boundary of possible yield-density combinations in crowded stands. Our aim was to elucidate how to objectively select data points and the most appropriate regression method for estimating the self-thinning boundary line.

    Methods We compare alternatives for selecting data points and fitting coefficients that have been or can be used to estimate the self-thinning boundary line. The selecting data point methods include visualized inspection, mortality criterion, equal intervals method and relative density method; the fitting coefficients methods include ordinary least squares regression, reduced major axis method, quantile regression and stochastic frontier function. We used data from an even-aged Cunninghamia lanceolata stand as example.

    Important findings Visualized inspection is subjective. Mortality criterion can precisely determine onset of the self-thinning without the independent-density stand. The equal intervals method has the potential to reduce independent-density mortality effect and the selected data points may adequately reflect stand self-thinning dynamics. The relative density method can avoid influence of independent-density mortality and ensure stand density threshold value. Stand self-thinning span is a limiting factor with equal intervals and relative density. The slope and intercept estimates used in ordinary least squares regression and reduced major axis differ from the stand self-thinning upper boundary line. Both the quantile regression technique and stochastic frontier function produce the self-thinning boundary line because the method can easily perform that there are no significant departures based on the adequate selection of quantile value and residual converge to zero with underlying distributional assumptions.

    Effects of inflorescence position on seed production and seedling establishment in Ligularia virgaurea
    XIE Tian-Peng, DU Gou-Zhen, ZHANG Ge-Fei, ZHAO Zhi-Gang
    Chin J Plant Ecol. 2010, 34 (4):  418-426.  doi:10.3773/j.issn.1005-264x.2010.04.007
    Abstract ( 2735 )   Full Text ( 4 )   PDF (1179KB) ( 2230 )   Save
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    Aims Position-effect of seeds within inflorescences of flowering plants is a common phenomenon, but its influence on seedling establishment is not well known. Our objective was to determine: 1) the pattern of seed production within inflorescences in Ligularia virgaurea (top, middle and bottom of inflorescences) and 2) if position-effect exists, whether it affects seed germination and seedling establishment.

    Methods We surveyed seed production of L. virgaurea in the field, seed germination under an alternating temperature regime (15 °C / 5 °C; 12 h light/dark) in the laboratory and seedling establishment under 25% shade by potted plants in the field. One-way ANOVA was used to determine the effects of seed position on seed set, seed weight, ovule number, seed number, germination percentage, initial germination time, emergence percentage, survival percentage, root-shoot ratio (R/S), total biomass (TB) and net photosynthetic rate (Pn). Tukey’s test was used to determine the difference between average values.

    Important findings Seed production of L. virgaurea is affected significantly by position within an inflorescence: seed set and seed mean weight are greatest at the top, mean number of ovules is highest at the bottom, and the middle position has the most seeds. Initial germination time is earlier for seeds from the bottom than top, germination percentage and emergence percentage are not significantly different among different positions, and survival percentage among three positions is nearly consistent. R/S and Pn are top > bottom, but TB is not significantly different. Seedling traits are consistent under two different rates of fertilizer application. Results imply that the seeds from different positions have inherently different germination and seedling growth strategies. Top seeds can disperse further and have stronger seedling establishment ability than bottom seeds. Therefore, top seeds have greater ecological significance for sexual recruitment, regeneration and colonizing new habitats.

    Effects of simulated sulfur-rich, nitric-rich and mixed acid rain on the physiology, growth and yield of rape (Brassica napus)
    MAI Bo-Ru, ZHENG You-Fei, WU Rong-Jun, LIANG Jun, LIU Xia
    Chin J Plant Ecol. 2010, 34 (4):  427-437.  doi:10.3773/j.issn.1005-264x.2010.04.008
    Abstract ( 2953 )   Full Text ( 3 )   PDF (1031KB) ( 2053 )   Save
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    Aims Our objective was to investigate the effect of sulfur acid rain (SAR), nitric acid rain (NAR) and their mixture (MAR) on the physiology, growth and yield of the crop rape (Brassica napus).

    Methods Fifteen 4 m × 5 m plots were distributed stochastically for exploring SAR, NAR and MAR stress, with a roughly 0.6 m spacing between plots to avoid interference. We used three replicate treatments of pH = 7.0, 1.5, 3.1, 4.1 and 5.1 and examined growth and development at 5-day intervals from budding to the end of flowering (March 10 to April 25, 2006). On April 12 for the peak period of flowering, we measured leaf cell membrane permeability, contents of malondialdehyde (MDA) and photosynthesis pigment in leaves, photosynthesis speed, leaf injury rate and leaf area as physiological and growth parameters. On May 10, we measured the yield index during the ripening stage.

    Important findings These kinds of acid rains can inhibit physiology, growth and yield with effects differing among treatments. At pH ≤ 4.1, SAR, NAR and MAR damage the membrane of rape leaves, decreasing photosynthetic pigment content and photosynthetic speed, thereby diminishing photosynthesis of the crop. For pH ≤3.1, leaf area is decreased and the leaf injury rate increases greatly. The value of pH = 4.1 can be used as the threshold for impact on rape yield. Over the range of pH = 1.5-7.0, leaf membrane permeability, MDA content and leaf injury rate follow the pattern of NAR > MAR > SAR and for the photosynthetic speed, content of photosynthesis pigment, leaf area and yield the order is SAR > MAR > NAR. At pH > 4.1, the differences between these treatments of acid rain are insignificant. For pH ≤ 3.1, the stress differences become large (p < 0.05), with greater differences at stronger acidities, following the pattern NAR > MAR > SAR. This indicates the first two treatments have stronger inhibiting effects on the physiology, growth and yield of rape.

    Effect of media and light on asymbiotic germination of Malaxis monophyllos seeds
    WANG Rui-Xia, HE Ming-Gao, SONG Song-Quan
    Chin J Plant Ecol. 2010, 34 (4):  438-443.  doi:10.3773/j.issn.1005-264x.2010.04.009
    Abstract ( 2992 )   Full Text ( 4 )   PDF (757KB) ( 1396 )   Save
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    Aims Extensive collection, environmental deterioration, slow seed germination and low germination percentage have seriously degraded the natural resources of Malaxis monophyllos, resulting in a vulnerable situation for the species. Our objective is to establish an asymbiotic germination system of M. monophyllos seeds to protect and propagate the species.

    Methods Seed morphology was investigated by optical microscope and scanning electron microscope. We used Knudson C medium supplemented with 2% sucrose, 3% activated charcoal and 0.8% agar as the basic medium to investigate the effects of α-naphthalene acetic acid (NAA), 6-benzylaminopurine (6-BA), coconut milk, meshed banana, meshed potato and light on seed germination via the orthogonal test.

    Important findings Periclinal walls of testa cells were smooth and had no veins, but anticlinal walls were thick and had clear surface patterns. Through the orthogonal test and redundancy analysis, an optimal formula for asymbiotic seed germination was determined: the medium supplemented with 4.5 mg·L-1 NAA, 10 mg·L-1 6-BA, 8% meshed banana and 3% meshed potato in the light (12 h light/12 h dark at 20 μmol·m-2·s-1 of light intensity). Seed germination was > 90% with this formula.

    Evolvement of harvest index and water-use efficiency in diploid, tetraploid and hexaploid wheats during grain-filling stage under different water treatments
    ZHAO Zi-Ping, DENG Xi-Ping, WANG Zheng-Hong, LIU Bin-Bin
    Chin J Plant Ecol. 2010, 34 (4):  444-451.  doi:10.3773/j.issn.1005-264x.2010.04.010
    Abstract ( 2554 )   Full Text ( 1 )   PDF (201KB) ( 1529 )   Save
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    Aim Our objective was to understand differences in grain yield and water-use efficiency among wheats of different ploidy.

    Methods We conducted experiments on six wheat varieties: diploid species (Triticum boeoticum, T. monococcum), tetraploid species (T. dicoccoides, T. dicoccon) and hexaploid species (T. aestivum Changwu 134 and Shaan 253). These were treated with different water conditions in the grain-filling stage, and we determined root biomaSD, aboveground biomaSD, grain yield, water consumption for transpiration and water-use efficiency.

    Important findings There were significant differences in biomaSD, grain yield and water-use efficiency among different wheat varieties with different diploid chromosomes under each water treatment. In the evolution of wheat from diploid to hexaploid, dry weight of root system increased first and then decreased; aboveground biomaSD, 1 000-kernel weight, grain number per spike, grain yield, harvest index and water-use efficiency increased gradually. With the aggravation of drought, harvest index of wheat increased first and then decreased; values of harvest index were 41.26%, 42.28% and 38.19%, respectively. Water-use efficiency for biomaSD gradually increased; values were 2.39, 2.43 and 2.53 g·kg-1, respectively. Values for water-use efficiency for grain yield were 1.05, 1.10 and 1.04 g·kg-1, respectively. Therefore, water condition was a key factor influencing harvest index and water-use efficiency during grain-filling stage, and moderate water streSD is helpful to improve water-use efficiency for crops. Water deficit during the grain-filling stage could improve the harvest index of hexaploid wheat as well as biomaSD water-use efficiency of tetraploid wheat, and moderate water deficit may increase yield water-use efficiency of both tetraploid and hexaploid wheat.

    Review of advances in measurements and effects of diffuse radiation on terrestrial ecosystem productivity
    SUN Jing-Song, ZHOU Guang-Sheng
    Chin J Plant Ecol. 2010, 34 (4):  452-461.  doi:10.3773/j.issn.1005-264x.2010.04.011
    Abstract ( 2496 )   Full Text ( 4 )   PDF (386KB) ( 2876 )   Save
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    Changes of diffuse radiation resulting from global changes, especially atmospheric composition changes, influence terrestrial ecosystem productivity and the carbon budget. We review the effects of diffuse radiation on terrestrial ecosystem productivity and carbon budget, including controls and methods of estimating diffuse radiation, processes and mechanisms of diffuse radiation effects on canopy light-use efficiency (LUE), terrestrial ecosystem productivity and carbon budget. Suggested future research tasks are study of 1) responses of leaf photosynthesis to diffuse radiation at different temporal and spatial scales; 2) effects of diffuse radiation and its interaction with other environmental factors on photosynthesis and modeling; 3) effects of diffuse radiation and its interaction with other environmental factors on soil respiration; 4) adaptation of plants and terrestrial ecosystems to diffuse radiation and its interaction with other environmental factors; and 5) response processes and mechanisms of terrestrial ecosystem productivity and carbon budget to diffuse radiation and its interaction with other environmental factors.

    Research Communications
    Analysis of main volatile organic compounds and study of aboveground structures in Artemisia frigida
    ZUO Zhao-Jiang, ZHANG Ru-Min, WANG Yong, HOU Ping, WEN Guo-Sheng, GAO Yan
    Chin J Plant Ecol. 2010, 34 (4):  462-468.  doi:10.3773/j.issn.1005-264x.2010.04.012
    Abstract ( 2588 )   Full Text ( 1 )   PDF (1097KB) ( 1960 )   Save
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    Aims Special volatile organic compounds (VOCs) are released from Artemisia frigida in its growth, and the smell of VOCs is stronger when it is damaged. Our objective was to determine the VOCs from A. frigida and the relationship between the VOCs release and organization structure of A. frigida.

    Methods VOCs were collected using the dynamic headspace air-circulation method and analyzed with the thermal-desorption cold trap/gas chromatography/mass spectrum (TCT/GC/MS). The coat hairs of A. frigida were observed with scanning electron microscope, and the paraffin section of aboveground structures was observed with microscope.

    Important findings Twenty-two main compounds were identified in undamaged A. frigida: camphene (14.27%), (E)-3-hexen-1-ol,acetate (10.85%), p-cymene (9.05%), eucalyptol (39.80%), α-terpineol (10.04%), β-terpineol (2.48%), camphor (5.66%) and (R)-(-)-p-menth-1-en-4-ol (3.84%). Twelve kinds of VOCs increased with damage; those with a relative content > 1% were cis-3-Hexenal (1.15%), 2-Pentenal (1.34%), cis-Geraniol (2.66%), Borneol (4.47%), (1R,4R)-(+)-p-Mentha-2,8-diene (9.15%), Bornyl acetate (1.37%) and Eudesma-4(14),11-diene (1.30%). There were many palisade tissues in A. frigida blades, 2-3 palisade tissues in petioles, and many air chambers in palisade tissue connected with stoma. The kinds and relative content of damaged A. frigida VOCs were more than the undamaged, possibly because A. frigida VOCs were stored in air chambers, which were released when A. frigida was damaged, and some new VOCs were composed and released. Therefore, the kinds and content of VOCs were increased in damaged A. frigida.

    Growing season sap-flow dynamics of Robinia pseudoacacia plantation in the semi-arid region of Loess Plateau, China
    WU Fang, CHEN Yun-Ming, YU Zhan-Hui
    Chin J Plant Ecol. 2010, 34 (4):  469-476.  doi:10.3773/j.issn.1005-264x.2010.04.013
    Abstract ( 2589 )   Full Text ( 2 )   PDF (993KB) ( 1787 )   Save
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    Aim We studied the relationship between sap-flow velocity and meteorological factors to quantitatively correlate tree growth and transpirational water-consumption, determine the dynamic change of water use of Robinia pseudoacacia in a semi-arid region, reveal its mechanism to adapt to environmental factors and provide the theoretical basis for local ecological reconstruction of the environment.

    Methods A thermal dissipation probe (TDP) was used to measure the sap-flow dynamics of R. pseudoacacia in Ansai County in the semi-arid region of the Loess Plateau of China during July 1-26, 2008. Soil water content, photosynthetic active radiation (PAR), air temperature, relative humidity, water vapor pressure deficit (VPD) and wind speed were measured at the same time.

    Important findings Diurnal variation of sap flow displayed a broadly peaked curve during the season of rapid growth. The average value was 0.001 33 cm·s-1. Sap-flow velocity per unit sapwood area was significantly correlated with PAR, air temperature and VPD and was negatively correlated with atmospheric relative humidity. The ranking of correlation coefficients was PAR > air temperature > VPD > relative humidity > wind speed. Sapwood area and diameter at breast height (DBH) were significantly correlated (r = 0.878), and sap-flow velocity per unit sapwood area decreased with increased stem diameter.

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