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Table of Content
    Volume 28 Issue 6
    10 November 2004
      
    Research Articles
    THE STUDY OF A SPECIOUS INVASIVE PLANT, WATER HYACINTH (EICHHORNIA CRASSIPES): ACHIEVEMENTS AND CHALLENGES
    GAO Lei, LI Bo
    Chin J Plan Ecolo. 2004, 28 (6):  735-752.  doi:10.17521/cjpe.2004.0097
    Abstract ( 4591 )   PDF (664KB) ( 2073 )   Save
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    Water hyacinth (Eichhornia crassipes) originated in the state of Amazonas, Brazil, spread to other regions of South America, and was carried by humans throughout the tropics and sub-tropics. It is now widespread and recognized as one of the top ten weeds in the world. Water hyacinth has invaded Africa, Asia, North America and Oceania, occurs in at least 62 countries and causes extremely serious ecological, economic and social problems in regions between 40°N and 45°S. Water hyacinth forms dense monocultures and can threaten local native communities, reduce native species diversity, and change the physical and chemical aquatic environment, thus altering ecosystem structure and function by disrupting food chains and nutrient cycling. Water hyacinth has had a great impact on local economic development. The large, dense monoculture formed by this species covers lakes and rivers, thus blocking waterways and interfering with the water transport of agriculture products, tourism activities, water power and irrigation of agricultural fields. Dense mats of water hyacinth can lower dissolved oxygen levels in water bodies and reduce aquatic production, including fish production, thereby reducing fish catches. Annual global costs associated with water hyacinth have increased greatly in recent years. Also, the lifestyles of local people who use and depend on water bodies invaded by water hyacinth have been affected greatly. Water hyacinth is very efficient at taking up calcium, magnesium, sulfur, iron, manganese, aluminum, boron, copper, molybdenum zinc, nitrogen, phosphorus and potassium favoring its growth over other species. When water hyacinth dies, sinks and decomposes, the water becomes more eutrophic due to the large release of nutrients. Water quality can deteriorate, threaten clean drinking water and impact human health. At present, solutions for controlling the spread of water hyacinth are divided into three general categories: physical, chemical and biological control. Biological control has been promoted as the best means for controlling water hyacinth and currently is an important area of research. Biological control includes the utilization of natural enemies, pathogens and allelopaths; however, our knowledge and understanding of the biology and ecology of water hyacinth is limited. To effectively control water hyacinth through biological means, it will be necessary to study more thoroughly the physiology, population and community dynamics, and ecosystem ecology of this species as well as interspecific competition, predation and its evolution. In this paper, we review the costs and benefits associated with the different control methods. We suggest that water hyacinth populations can be reduced and controlled by using an integrated management approach that combines biological control with a watershed management strategy that minimizes pollution and promotes a long term sustainable approach for effective water management in a region.
    GEOGRAPHICAL VARIATION IN THE BREEDING SYSTEMS OF AN INVASIVE PLANT, EICHHORNIA CRASSIPES, WITHIN CHINA
    REN Ming-Xun, ZHANG Quan-Guo, ZHANG Da-Yong
    Chin J Plan Ecolo. 2004, 28 (6):  753-760.  doi:10.17521/cjpe.2004.0098
    Abstract ( 2665 )   PDF (403KB) ( 1162 )   Save
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    Knowledge about the breeding systems of invasive weeds is crucial for invasion management. Eichhornia crassipes, a noxious clonal plant, has a complex breeding system that includes clonal reproduction and a special sexual reproduction mode, tristyly, and a complex mating system that consists of three floral morphs that differ in the length of styly and stamens. In this paper, we compared the breeding systems of 40 Eichhornia crassipes populations in 24 localities throughout China by investigating the relative level of sexual and clonal reproduction, number of floral morphs and the variances in floral syndrome (especially the position of sexual organs) for each population. A Mann-Whitney test was used to detect whether the variation in the position of the sexual organs were significant among each other and the typical floral morphs. The seed-set ratio of each floral morph was investigated extensively in a Chongqing population that had a high number of floral morphs. All the populations were regenerated primarily by clonal propagation as a result of vigorous clonal growth. Sexual reproduction was presumably constrained because only one or two floral morphs existed in the populations. Sexual recruitment was further restricted by lack of suitable ecological conditions for seed germination and seedling establishment. Exposure to the sunlight and water temperature above 30 ℃ is generally necessary for seed germination, a condition not met in most populations. Most of the populations surveyed were monomorphic for the M floral morph, and only the populations in Chongqing (West China on the Yangtze River) and Nanning (Southwest China near the tropical zone) contained the L morph with the M morph still predominating the populations. No significant differences in the fecundity of the M and L morphs were found and only 4% of the individuals produced seeds for these two floral morphs. The number of seeds per capsule varied greatly in both morphs, from 13 to 296 in the L morph and from 20 to 230 in the M morph, which suggested that fecundity was greatly restricted by ecological conditions, such as pollination and weather conditions, rather than developmental deficiency. The variations in the position of the sexual organs in the M floral morph were not significantly different among each other and the typical flowers. But, populations in Chongqing, Nanning, Fuzhou and Haikou were found to have modified M morphs or L morphs with anthers and stigma adjacent to each other (namely semi-homostylous flowers). Semi-homostyly is thought to be controlled by modifier genes and is selected for since it can increase fecundity through autogamy in invaded regions that have unreliable and inefficient pollinators. Based on the relative levels of sexual reproduction and number of floral morphs in a population, our results showed that the breeding systems of populations in the southwestern region and on Hainan Island were much more diverse than in other regions. The evolutionary trend of the breeding systems that occurred in some E. crassipes populations is consistent with the Baker's law, which states that autogamy would be favored during an invasion event. These evolutionary changes of the breeding systems also have significant effects on the invasion process of this species.
    THE INFLUENCE OF TOPOGRAPHICAL FACTORS ON THE INVASION OF THE ALIEN SPECIES, EUPATORIUM ADENOPHORUM
    LU Zhi-Jun, MA Ke-Ping
    Chin J Plan Ecolo. 2004, 28 (6):  761-767.  doi:10.17521/cjpe.2004.0099
    Abstract ( 1942 )   PDF (354KB) ( 684 )   Save
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    To study the distribution of Eupatorium adenophorum in China and the relationship between its invasion and topographical factors, including elevation, aspect, slope and wind slope, 171 plots were established in 12 vegetation provinces within this species range. The results indicated that the invasion of E. adenophorum mostly occured in regions near 102° E and declined with latitude, but not significant (p > 0.05). The range of E. adenophorum in China was mainly on the Yungui Plateau, particularly the Yunnan Plateau. Based on climatic comparisons between the Yungui Plateau and this species native range in Mexico and Costa Rica, we concluded that the future range of E. adenophorum in China would be confined largely to the Yungui Plateau, although patches are likely to occur in other regions with suitable climatic conditions. The elevation range of this species was from 75 m to 2 330 m in our investigation. Using polynomial regressions, we concluded that the abundance and coverage of E. adenophorum increased with elevation (p < 0.05), but at about 2 000 m elevation, the line became horizontal, suggesting that E. adenophorum preferred elevations of about 2 000 m. An ANOVA analysis showed that the influence of aspect on the coverage of E. adenophorum was significant. Multiple comparison tests suggested that the coverage of E. adenophorum on north and south facing slopes was greater than that on east facing slopes, indicating a strong resistance of east facing slopes to the invasion of E. adenophorum. The difference between population coverage and abundance on north and south facing slopes was not significant (p>0.05), indicating that temperature and moisture were not the dominant factors influencing the invasion of E. adenophorum on different aspects. The influence of slope on the invasion of E. adenophorum was not significant (p>0.05). The results of the ANOVA analysis indicated that the influence of wind slope on the coverage of E. adenophorum was not significant (p>0.05) but significantly affected the abundance of E. adenophorum (p<0.05) with the abundance of E. adenophorum greater on the leeward than on the lateral side.
    PERSISTENT SOIL SEED BANK OF EUPATORIUM ADENOPHORUM
    SHEN You-Xin, LIU Wen-Yao
    Chin J Plan Ecolo. 2004, 28 (6):  768-772.  doi:10.17521/cjpe.2004.0100
    Abstract ( 3980 )   PDF (218KB) ( 961 )   Save
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    Plants with persistent soil seed banks have advantages in stress and harsh environments. Soil samples were collected from 19 different soil sites with different vegetation at 5 locations across Yunnan, Southern China, at different times from July to April after the germination season of Eupatorium adenophorum seeds. Germination research results showed that E. adenophorum had a persistent soil seed bank. Its seeds distributed widely across soils in Yunnan and seeds were found at all 19 sample sites. Seed density in the 0-10 cm soil layer varied between 47-13 806 ind.·m-2 with an average of 2 202 ind.·m-2. The density did not show a direct relationship with the mother plant of E. adenophorum, but did show strong relationships with standing vegetation types. The density increased from 47 ind.·m-2 in newly deposited material of a slide to 801 ind.·m-2 under grass cover, to 2 349 ind.·m-2 under shrub cover, and the highest density of 3 255 ind.·m-2 under forest cover. Frequency of seeds identified from soil samples across all 19 soil types varied between 60%-100%. Vertically, seed density in the 0-2 cm soil layer was the highest, followed by the 2-5 cm layer, and the 5-10 cm depth had the lowest seed density. E. adenophorum seeds accounted for 56.1%, 25.2% and 18.6% of the total seeds in the three soil layers, respectively. Although the total percentage of seeds in the 5-10 cm layer was low, the total density was high (270 seeds·m-2) and, although not in the position of germination, had the potential for germination and being environmentally harmful. The wide distribution and high density of E. adenophorum in the soil seed bank have significant implications for any prevention and control measures, and we suggest that a long-term, large-scale approach should be taken to deal with the spread of E. adenophorum.
    RELATIONSHIPS BETWEEN ALLELOPATHY AND INVASIVENESS BY EUPATORIUM ADENOPHORUM AT DIFFERENT SITES
    YU Xing-Jun, YU Dan, MA Ke-Ping
    Chin J Plan Ecolo. 2004, 28 (6):  773-780.  doi:10.17521/cjpe.2004.0101
    Abstract ( 3624 )   PDF (365KB) ( 1311 )   Save
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    With an increase in the abundance and cover of Eupatorium adenophorum, there is a concurrent decrease in the abundance and cover of native species; however, this decrease varies at different sites and in different forests. The relative abundance and cover of E. adenophorum in deciduous broad-leaved forests and along the roadside were 3-5 times greater than in evergreen broad-leaved forests. The composition, relative abundance and cover of native plants in deciduous broad-leaved forests and along the roadside decreased by 30%, 50% and 70%, respectively, as compared to the evergreen broad-leaved forest. By bioassay, we investigated the allelopathy of aquatic extract from E. adenophorum that grew under evergreen broad-leaved forests, deciduous broad-leaved forests and along the roadside. We found that allelopathy of aquatic extract of E. adenophorum was different among sites, viz. roadside > deciduous broad-leaved forests > evergreen broad-leaved forests. Correlation analysis showed that allelopathy of E. adenophorum was significantly correlated to the relative abundance of native species at each of the sites. These results showed that differences in invasiveness among sites are due to differences in allelopathy at the different sites. The cabbage biomass showed that the allelopathy of aquatic extract from E. adenophorum shoots was greater among sites than its roots. This suggests that the allelopathy of aquatic extract from E. adenophorum shoots contributes to different levels of invasiveness among sites more than its roots. The growth of E. adenophorum is hearty and the biomass per unit area is great along roadsides and under deciduous broad-leaved forests, so the allelopathy of E. adenophorum populations per unit area along roadsides and under deciduous broad-leaved forests must be much more than in evergreen broad-leaved forests. Hence, the affects of E. adenophorum will be greater on these communities accelerating their decline.
    THE EFFECT OF LIGHT INTENSITY ON BIOMASS ALLOCATION, LEAF MORPHOLOGY AND RELATIVE GROWTH RATE OF TWO INVASIVE PLANTS
    WANG Jun-Feng, FENG Yu-Long
    Chin J Plan Ecolo. 2004, 28 (6):  781-786.  doi:10.17521/cjpe.2004.0102
    Abstract ( 2712 )   PDF (305KB) ( 1858 )   Save
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    The high biodiversity and economic costs associated with invasive plants have promoted research to identify traits associated with invasiveness. At present, most research has been based on comparisons between invasive and native species but, in this paper, two invasive species with different levels of invasiveness, Eupatorium adenophorum and Gynura sp., were studied. Both species were grown under four different relative irradiances (RI 12.5%, 36%, 50%, 100%) for 50 days, and we then measured their biomass allocation, leaf morphology and growth properties to compare their light acclimation abilities and growth strategies.The two species exhibited typical leaf morphological responses to different light conditions. At low light levels, plants enhanced light interception by means of increased biomass allocation to leaves and formation of large, thin leaves with high specific leaf area (SLA), leading to a high leaf area ratio (LAR). At high light levels, plants reduced transpiration losses and increased carbon gain by making small-sized, thick leaves with a low SLA, leading to a low LAR and leaf area to root mass ratio. Under most light regimes, E. adenophorum was higher in leaf mass ratio (LMR), leaf mass fraction (LMF), LAR, root mass ratio (RMR) and root mass to crown mass ratio (R/C), but lower in supporting organ biomass ratio (SBR), MLA and branch number as compared to Gynura sp. Leaf mass ratio, LMF, and leaf area index of E. adenophorum were the highest under 100% irradiance than under other light regimes and higher than for Gynura sp.; however, for SBR, these patterns were reversed. Under 100% irradiance, leaves were much more self-shaded in E. adenophorum than in Gynura sp. This might be an adaptive strategy that supports the vigorous invasiveness of this species because a high-shaded canopy could prevent other plant species from surviving and competing. The number of branches of Gynura sp. was greater under 100% irradiance than under other light regimes and significantly more than for E. adenophorum. This might be an adaptive strategy for Gynura sp. because a greater number of branches can produce more flowers and thus more seeds. For both species, an increase in light intensity resulted in an increase in net assimilation rates (NAR) and growth response coefficient of NAR (GRCNAR), whereas mean leaf area ratio (LARm) and growth response coefficient of LARm (GRCLARm) decreased. GRCLARm was higher than GRCNAR at all times. The relative growth rate (RGR) of E. adenophorum increased with an increase in light intensity but decreased in Gynura sp. With a decrease in light intensity, both E. adenophorum and Gynura sp. grew taller and produced more branches to intercept more light energy. The biomass allocation strategy differed between the two species: RMR decreased and SBR increased in E. adenophorum, while RMR increased, and SBR decreased in Gynura sp. All of the results presented above indicate that E. adenophorum was able to acclimate better to different light conditions, especially to low light regimes, than Gynura sp., and its better ability to acclimate might explain its greater invasiveness.
    STUDIES ON THE REPRODUCTION AND PHOTOSYNTHETIC ECOPHYSIOLOGY OF THE EXOTIC INVASIVE PLANT, PLANTAGO VIRGINICA
    GUO Shui-Liang, FANG Fang, HUANG Hua, QIANG Sheng
    Chin J Plan Ecolo. 2004, 28 (6):  787-793.  doi:10.17521/cjpe.2004.0103
    Abstract ( 3705 )   PDF (333KB) ( 1196 )   Save
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    Plantago virginica, an annual weed species originating from North America, was introduced into Eastern China during the 1950's. The populations of this invasive species have spread rapidly during recent years in Zhejiang, Jiangsu, Jiangxi, Guangdong and Hunan provinces. In the present paper, reproductive indices of Plantago virginica, including spike weight per individual, flower number per spike, reproductive biomass per vegetative biomass and Gini coefficient, which indicates individual size inequality, were obtained from populations growing at different densities. The photosynthetic indices of Plantago virginica and its companion species were determined using a LCA-4 portable photosynthesis and transpiration system (ADC, England). The companion species included Erigeron annuus, Conyza canadensis, Conyza bonarinsis, Lantana camara, Mirabilis jalapa, Alternathera philoxeroides, Ricinus communis, Chenopodium album, Rumex japonicus, Plantago asiatica, Sonchus oleraceus and Helianthus tuberoses. Their net photosynthetic rates (Y) and leaf photosynthetic active radiation (X) were modeled using the equation Y=aX2+bX+c. The main experimental results are summarized below. 1) During the reproductive phase, the relationships of the population density (X) with spike weight per individual (Y1), flower number (Y2), reproductive effort (Y3) and seed numbers per vegetative biomass (Y4) were as follows: Y1 = 0.138 2+15.959 8/X, Y2 = 46.306 9+6 914.07/X, Y3 = 0.046 9 + 0.000 2X and Y4 = 130.24 + 0.023 9X. 2) With an increase in the population density of P. virginica, the individual size inequality (Gini coefficient, Y5) declined by the following relationship: Y5 = 0.374 8 - 0.000 02X. 3) The individual size inequality (Y5) was negatively related to reproductive effort (X), following Y5 = 0.379 3 - 0.106 6X, which indicated that the population reproductive effort declined with an increase in individual size inequality. 4) The photosynthesis (Y) - light (X) response curve followed: Y = -7E-06X2+0.022 3X-0.831 2. The light compensation point, light saturation point and the maximum net photosynthetic rate of P. virginica were 37.32 μmol·m-2·s-1, 1 593 μmol·m-2·s-1 and 16.93 μmol CO2·m-2·s-1, respectively, indicating that P. virginica is a typical heliophyte. The shade-tolerant ability of P. virgincia was lower than that of Plantago asiatica, Youngia japonica, Conyza canadensis, Erigeron annuus, Conyza bonarinsis, Ricinus communis, Solidago canadensis, Sonchus oleraceus, Rumex japonicus and Lantana camara, its net photosynthetic rate was lower than that of Erigeron annuus, Conyza canadensis, Conyza bonarinsis and Solidago canadensis, but higher than that of Chenopodium album, Sonchus oleraceus, Ricinus communis and similar to that of Plantago asiatica. 5) During the last ten-day period of May, the photosynthetic “midday-depression” was not apparent in the three typical weedy species (Erigeron annuus, Conyza canadensis and Alternathera philoxeroides) but obvious in P. virginica and the escaped species, Mirabilis jalapa. Plantago virginica is an early-spring weedy species, and the high temperature and intensive light were not suitable for its growth during the last ten-day period of May. We drew the following conclusions based on the experimental results. 1) The high population density of P. virginica resulted in self-thinning, which reduced the individual size inequality. Because of environmental stress resulting from high densities, the high-density population of P. virginica switched to an r-strategy to increase its reproductive output by producing more seeds in order to maintain large numbers of offspring. Obviously, Plantago virgincia had the flexibility to adapt its reproductive strategy to environmental conditions. 2) If there was no human disturbance to the recipient environments, the populations of P. virginica would rapidly decline in the community over five successive years due to their higher light compensation point and their mucilage seeds. 3) Our suggestions for controlling Plantago virginica include protection of vegetation, planting horticultural plants with higher stalks and reducing disturbance to the recipient environments.
    SOME PHOTOSYNTHETIC CHARACTERISTICS OF FRAXINUS MANDSHURICA SEEDLINGS GROWN UNDER DIFFERENT SOIL WATER POTENTIALS
    CUI Xiao-Yang, SONG Jin-Feng, ZHANG Yan-Hua
    Chin J Plan Ecolo. 2004, 28 (6):  794-802.  doi:10.17521/cjpe.2004.0104
    Abstract ( 2763 )   PDF (516KB) ( 1129 )   Save
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    Manchurian ash, (Fraxinus mandshurica), typically distributed along lower streams and regenerated under the canopy of natural forests, is an important hardwood silvicultural species in the temperate forest regions of northeast China. On most reforestation sites, however, Manchurian ash plantations exhibit very restricted growth. Therefore, the main objectives of this study were to gain an insight into the physio-ecological mechanisms responsible for the poor growth and low productivity of Manchurian ash in plantations and to analyze the environmental limitations of soil water on photosynthetic activity. Two-year old Manchurian ash seedlings were planted in rainproof soil pots (8 m length × 0.5 m width × 0.3 m depth). When seedlings had restored vigor, soil water potentials were maintained at five treatment levels in the different pots: 0 - -0.02 MPa (W1), -0.02 - -0.04 MPa (W2), -0.04 - -0.06 MPa (W3), -0.06 - -0.08 MPa (W4) and -0.08 - -0.16 MPa (W5). Soil water potential was controlled using a specially designed root-sphere osmotic irrigation technique. After 3 months of soil water conditioning, the diurnal course of gas exchange, PSⅡ photochemical efficiency (Fv/Fm) and rubisco carboxylation activity of Manchurian ash seedlings grown under the different soil water conditions were investigated. All treatments showed a maximum net photosynthetic rate (Pn) in the early morning (approx. 6∶00) and a noontime depression of photosynthesis that was the greatest in the low soil water treatment. The cumulative values of diurnal photosynthesis (mmol CO2·m-2·d-1) from W1 to W5 were in the proportion of 100∶96∶64∶60∶52. The initial depression of Pn in the early morning for all the treatments was caused primarily by lowered stomatal conductance, but the strong inhibition of photosynthesis that occurred from 10∶00 to 14∶00 for W3, W4, and W5 treatments was due predominately to non-stomatal limitations. Simultaneous with the morning-to-noon or soil-water-ordered depression of Pn, there was a corresponding decrease in PSII photochemical efficiency (Fv/Fm) and in rubisco carboxylation activity, particularly for the W3, W4 and W5 treatments. There were no significant differences in diurnal average water use efficiency (WUE) among treatments with the exception of a pronounced lower WUE in W1. The morning to noon depression of Pn observed in the well-watered treatments (W1 and W2) indicated that climatic conditions (e.g. high light levels, high temperature, and low humidity) of the experiment differed from the species natural environment and caused physiological stress on the wet-adapted and shade-tolerant Manchurian ash seedlings. This stress was intensified as soil water deficiency increased from W3 to W5 treatments.
    CHANGES IN BIOMASS ALLOCATION AND GAS EXCHANGE CHARACTERISTICS OF LEYMUS CHINENSIS IN RESPONSE TO SOIL WATER STRESS
    WANG Yun-Long, XU Zhen-Zhu, ZHOU Guang-Sheng
    Chin J Plan Ecolo. 2004, 28 (6):  803-809.  doi:10.17521/cjpe.2004.0105
    Abstract ( 2470 )   PDF (362KB) ( 1000 )   Save
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    Global environmental change has already been and will continue to reallocate water and heat resources at a global scale, and, as a result, will affect the structure and function of terrestrial ecosystems. For temperate zone steppe ecosystems, aridification currently is the most significant environmental problem and this may be intensified due to global warming. The responses of the dominant species of these ecosystems to water stress will be important for understanding how terrestrial ecosystems will respond to global change and how species will adapt to the aridification under the backdrop of global warming as well as the impact on the global carbon budget. The response of leaf relative water content, leaf photosynthetic rate, biomass allocation and net population CO2 exchange rate of Leymus chinensis to soil water stress were studied using a pond cultivation experiment from May to July 2002. Five soil water treatment levels were used: 75%-80% (control), 60%-65%, 50%-55%, 35%-40% and 25%-30% of soil water holding capacity. The results are summarized below. 1) The relationship between leaf relative water content of L. chinensis and soil water stress could be expressed as a single peak curve with its maximum value appearing in the 50%-55% soil water treatment. 2) Leaf photosynthetic rates decreased with an increase in soil water stress, and the diurnal pattern of leaf photosynthetic rates in the soil water treatments of 75%-80%, 60%-65% and 50%-55% were different than that under the drier conditions of 35%-40% and 25%-30%. 3) The total biomass, root biomass, sheath biomass and leaf biomass of L. chinensis decreased with an increase in soil water stress. 4) Soil water stress promoted the allocation of carbon to roots and increased the root to shoot ratio of L. chinensis at the early growth stage but not at late growth stages. These results imply that increasing the root to shoot ratio is an adaptive strategy for tolerating drought conditions. The relationship between the biomass of roots and sheaths and the percent of carbon allocation to soil water stress could also be expressed as a single peak curve with the maximum value of root and sheath biomass (1.28 g·plant-1) appearing at the 50%-55% soil water treatment and the maximum allocation to root and sheaths (48.5%) at 35%-40% soil water content. 5) The net population CO2 exchange of L. chinensis decreased with an increase in soil water stress. The relationship between daily net population CO2 exchange of L. chinensis and soil water stress showed a single peak with the maximum value occurring at 60%-65%. Negative values of daily net population CO2 exchange of L. chinensis occurred at 25%-30% soil water content. Moreover, the results indicated that 40% soil water holding capacity might be the tolerance threshold for L. chinensis below which this species is not able to survive.
    NUTRIENT DYNAMICS IN RESPONSE TO HARVESTING PRACTICES IN A PINE FOREST OF SUBTROPICAL CHINA
    MO Jiang-Ming, PENG Shao-Lin, Sandra BROWN, FANG Yun-Ting, KONG Guo-Hui
    Chin J Plan Ecolo. 2004, 28 (6):  810-822.  doi:10.17521/cjpe.2004.0106
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    Over the past two decades, society has become increasingly aware of problems of forest degradation. The effects of forest degradation transcend individual countries and now impact global processes. Research on the restoration of degraded forests has become a key issue in global ecology. Of particular concern are the effects of human activities on forest productivity and site fertility, especially as the demands for fuel and timber from tropical forests increase. Removal and burning of biomass causes nutrient losses and changes to the soil’s physical and chemical characteristics. The amount of nutrient loss depends on the intensity of the activities, local environmental factors, and the type and successional state of the forest. If nutrient losses cannot be recovered during regrowth, forests often become degraded through time. Thus, it is important that the nutrient dynamics of human-impacted forests are well understood in order to develop plans for restoration of degraded forests and for sustainable forest management. Most of the primary tropical forests in southern China have been degraded by human activities during the past several hundred years. Factors leading to their degradation include: timber harvesting, unsustainable agriculture, overgrazing by domestic animals, and intensive harvesting for fuel. In extreme cases, the land has become completely denuded. Attempts to reverse this process of land degradation have been initiated in this region of southern China. Over the last few decades, large areas have been reforested with a native pine species, Pinus massoniana, to prevent further degradation to the landscape. Cutting of trees is now prohibited, but harvesting of the understory and collection of litter is still allowed to satisfy local fuel needs. Compared with whole-tree harvests, this practice removes less biomass from the forests; however, as the understory and litter are relatively nutrient-rich, this practice may slow or prevent the recovery of soil fertility and productivity of these forest ecosystems. The objective of this study was to determine the effects of harvesting understory plant species and litter on nutrient accumulation dynamics in a Pinus massoniana forest of subtropical China. The results are used to address the following questions: 1) How are nutrients distributed in plants of this pine forest; 2) What quantity of nutrients are removed annually from the ecosystem by the practice; 3) Is this harvesting practice sustainable or not; 4) What alternative management options are available for continued use to meet fuel needs while at the same time improving site fertility, productivity and regeneration processes; and, 5) How do stressed ecosystems respond when the stressors are removed, that is, how would the forest respond if the harvesting practice was stopped.

    EFFECTS OF ISO-OSMOTIC SALT AND WATER STRESSES ON GROWTH AND IONIC DISTRIBUTION IN ALOE SEEDLINGS
    ZHENG Qing-Song, LIU Zhao-Pu, LIU You-Liang, LIU Ling
    Chin J Plan Ecolo. 2004, 28 (6):  823-827.  doi:10.17521/cjpe.2004.0107
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    Among many kinds of stresses, drought and salinity are the most serious ones that limit plant growth and crop productivity in agriculture with their damage exceeding the sum of that attributed to all other natural disasters. Plant responses to drought and salinity have much in common: Water stress in its broadest sense encompasses both drought and salt stress; Salt stress occurs from both osmotic stress due to low water potentials and salt-specific effects. However, studies on the comparative physiology of plants to water and salt stress are few. Aloe is a typical xerophyte with important economic and social value, but is not a halophyte. Little information was available on its response to salt and its mechanisms of tolerance. In this paper, dry matter accumulation of seedlings, growth rates, water content, electrolytic leakage of leaves and ionic absorption and distribution of organ and tissue levels in six-leaf Aloe vera seedlings exposed to iso-osmotic conditions of -0.44 Mpa and -0.88 Mpa using NaCl, and compared to exposure to polyethylene glycol 6000 (PEG 6000) concentrations to understand the responses of plants to water and salt stress. The results showed that leaf elongation was inhibited, plant dry matter accumulation rates decreased significantly, water content in leaves decreased, and leaf electrolytic leakage increased 10 days after treatments using NaCl and PEG. Growth inhibition of salt-treated Aloe seedlings greatly exceeded that of PEG-treated seedlings. Ion content analysis in different organs and X-ray microanalysis of root and leaf cross sections indicated that Na+、Cl- content increased significantly and K+、Ca2+ absorption in the roots and transport to leaves were inhibited in seedlings exposed to NaCl stress. Maintenance of better ion homeostasis under the PEG treatment was a primary reason for the greater adaptation to water stress than to iso-osmotic salt stress in Aloe. However, Aloe seedlings also showed some specific adaptations to -0.44--0.88 NaCl stress in Aloe seedlings: 1) Ionic selective absorption and transport were high in Aloe roots under salt stress and increased with increasing salt stress; 2) Salt accumulation in aqueous tissues was significantly higher than that in the other tissues of Aloe leaves. Also, as a CAM (Crassulacean acid metabolism) plant, the transpiration rate in Aloe seedlings was very low and the rate of salt accumulation in the shoots was also slow.

    SIMULATION OF AUTOTOXICITY OF STRAWBERRY ROOT EXUDATES UNDER CONTINUOUS CROPPING
    ZHEN Wen-Chao, CAO Ke-Qiang, DAI Li, ZHANG Xue-Ying
    Chin J Plan Ecolo. 2004, 28 (6):  828-832.  doi:10.17521/cjpe.2004.0108
    Abstract ( 2476 )   PDF (211KB) ( 1370 )   Save
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    Replant disease is a serious problem for the development of sustainable cropping systems of strawberry, Fragaria ananassa. Previous studies have shown that auto-toxicoids secreted from roots play an important role in replant disease of some crops, and autotoxicity of root exudates is a very important aspect of understanding replant disease mechanisms. In this paper, root exudates were extracted and their autotoxicity was studied by using tissue culture methods in order to avoid interferences from external factors. Root tissue culture mediums (MS+BA 0.2 mg·L-1), in which one generation of seedlings had been cultivated, were collected in a bio-clean cabinet and mixed with a new culture medium. Five treatments were set up in which the volume proportion of the new culture medium to the used culture medium were 10∶30, 15∶25, 20∶20, 25∶15 and 30∶10. Tissue culture seedlings of the same age and with the same appearance were chosen and inoculated in the five culture medium treatments. Our results showed that on the 40th day after inoculation, development and growth of roots were inhibited in mixed tissue culture mediums, and the inhibitory effects were greater as the proportion of the used culture medium increased. As a result, increments of plant height and leaves, number of roots, length of roots, and weight of plants were reduced in mixed culture mediums as compared to the pure new culture medium treatment. The vermiculite in which strawberry tissue culture seedlings had been cultivated for 60 days was collected and placed into 500 ml erlenmeyer flasks. The same quantity of distilled water was added to each flask and then shaken on a shaker for 48 hours. After centrifuging (2 670×g) for 20 minutes, the supernatant was collected and evaporated on a rotary vaporizer at 42 ℃ to 1/10 volume, and then filtered through qualitative filter paper. The extract was diluted in a series of density solutions of 50%, 40%, 30%, 20% and 10% (V%). Strawberry seedlings were treated once every 5 days with 10 ml of the different solutions and the growth of seedlings measured after 40 days. Control seedlings were treated with distilled water. Results showed that root exudates of strawberry could inhibit the growth of strawberry, and the inhibitory effect became stronger with increasing concentrations of root exudates. Physiological disease occurred in treatments treated by root exudates, and the disease index was greater as the concentration of root exudates increased. At the same time, strawberry root activity was also restrained by root exudates. Physiological analysis showed that activities of 2,3,5-Tripheyl Tetrazolium Chloride (TTC) reduced and superoxide-dismutase (SOD) decreased, and root relative conductivity and malondialdelyole (MDA) contents increased. The greater the concentration of root exudates, the more significant the effect on all of these physiological factors. Our results showed that when root exudates accumulated in their growing medium, the growth and metabolism of strawberry roots were inhibited, which resulted in an increase in the percentage of electrolytes in cells, a decrease in the free radical scavenging activity of roots, and an increase in root lipid peroxidation. Hence, the growth and development of strawberry seedlings showed reduced vigor, which could lead to declines in root resistance to soil-borne disease, and replant disease of strawberry could become increasingly serious.
    A STUDY ON PLANT DIVERSITY OF TROPICAL MONTANE RAIN FORESTS IN XISHUANGBANNA, YUNNAN
    LI Zong-Shan, TANG Jian-Wei, ZHENG Zheng, LI Qing-Jun, LUO Cheng-Kun, LIU Zheng-An, LI Zi-Neng, DUAN Wen-Yong, GUO Xian-Ming
    Chin J Plan Ecolo. 2004, 28 (6):  833-843.  doi:10.17521/cjpe.2004.0109
    Abstract ( 2614 )   PDF (390KB) ( 904 )   Save
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    Tropical montane rain forest (TMRF), one of the primary forest vegetation types in Xishuangbanna, occurs at lower altitude in the north (TMRF I) and higher altitude in the south (TMRF II). In order to understand the plant diversity characteristics of tropical montane rain forests in different zones, six permanent plots (50 m×50 m) of tropical montane rain forest communities at different sites in Xishuangbanna were established, two of which were in the TMRF I and four in the TMRF II. The grid method (10 m×10 m) was used to record all individuals with a DBH greater than 2.0 cm in each plot. Shrub and herb species were investigated in nine 5 m×5 m and 2 m×2 m sub-quadrats, respectively. Plant diversity indices of trees, shrubs, herbs, and three sub-tree layers, and changes in plant diversity indices of communities along the altitudinal gradient were analyzed. The results showed that the total number of plant species in the TMRF communities were 99-181, tree species richness (S) was 54-113, Shannon-Wiener diversity (H′) was 1.648 7-4.049 1, Simpson index (λ) was 0.503 5-0.969 5 and Pielou's evenness index (Jsw) was 0.413 3-0.854 9. For shrubs, S was 35-89, H′ was 2.413 2-3.716 2, λ was 0.762 7-0.958 2, and Jsw was 0.678 8-0.859 3. For the herbs, S was 31-65, H′ was 2.792 1-3.499 2, λ was 0.902 0-0.938 2, and Jsw was 0.729 3-0.838 2. The diversity indices, H′, λ, and Jsw, were greatest in the herb layer followed by shrubs and then trees, whereas species richness showed no obvious differences in the TMRF I. For TMRF II, the species richness and diversity indices, H′ and λ, were greatest in the tree layer followed by the shrub layer and then the herb layer, but the evenness index (Jsw) was not different among the three layers. The species richness, diversity indices and evenness index of the tree layer and shrub layer in TMRF II communities were higher than those in TMRF I communities, most likely due to the superior habitat of the TMRF II communities. Along the altitudinal gradient, all indices (S, H′, λ, Jsw) were greatest at the mid-altitudinal zone (about 1 200-1 220 m) for trees. This can be attributed to the fact that TMRF communities in the mid-altitudinal zone are situated in a ravine area and have the most favorable growing conditions among the six plots. Furthermore, these communities are very near to the seasonal rain forest at lower altitudes, and thus the tropical rain forest plants are very abundant at these altitudes.

    ADVANCES IN ECOLOGICAL STUDIES ON LEAF LIFESPAN AND ASSOCIATED LEAF TRAITS
    ZHANG Lin, LUO Tian-Xiang
    Chin J Plan Ecolo. 2004, 28 (6):  844-852.  doi:10.17521/cjpe.2004.0110
    Abstract ( 2986 )   PDF (338KB) ( 1470 )   Save
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    Over the past two decades, society has become increasingly aware of problems of forest degradation. The effects of forest degradation transcend individual countries and now impact global processes. Research on the restoration of degraded forests has become a key issue in global ecology. Of particular concern are the effects of human activities on forest productivity and site fertility, especially as the demands for fuel and timber from tropical forests increase. Removal and burning of biomass causes nutrient losses and changes to the soil’s physical and chemical characteristics. The amount of nutrient loss depends on the intensity of the activities, local environmental factors, and the type and successional state of the forest. If nutrient losses cannot be recovered during regrowth, forests often become degraded through time. Thus, it is important that the nutrient dynamics of human-impacted forests are well understood in order to develop plans for restoration of degraded forests and for sustainable forest management. Most of the primary tropical forests in southern China have been degraded by human activities during the past several hundred years. Factors leading to their degradation include: timber harvesting, unsustainable agriculture, overgrazing by domestic animals, and intensive harvesting for fuel. In extreme cases, the land has become completely denuded. Attempts to reverse this process of land degradation have been initiated in this region of southern China. Over the last few decades, large areas have been reforested with a native pine species, Pinus massoniana, to prevent further degradation to the landscape. Cutting of trees is now prohibited, but harvesting of the understory and collection of litter is still allowed to satisfy local fuel needs. Compared with whole-tree harvests, this practice removes less biomass from the forests; however, as the understory and litter are relatively nutrient-rich, this practice may slow or prevent the recovery of soil fertility and productivity of these forest ecosystems. The objective of this study was to determine the effects of harvesting understory plant species and litter on nutrient accumulation dynamics in a Pinus massoniana forest of subtropical China. The results are used to address the following questions: 1) How are nutrients distributed in plants of this pine forest; 2) What quantity of nutrients are removed annually from the ecosystem by the practice; 3) Is this harvesting practice sustainable or not; 4) What alternative management options are available for continued use to meet fuel needs while at the same time improving site fertility, productivity and regeneration processes; and, 5) How do stressed ecosystems respond when the stressors are removed, that is, how would the forest respond if the harvesting practice was stopped. In order to achieve the objectives above, an experiment was established in a MAB reserve of subtropical China in May 1990. The experiment was a paired-plot design with 20 replicates. Each pair consisted of a treatment (continued harvest) and control (no harvest) plot, 10 m×10 m in size and surrounded by a 10 m wide buffer strip. In the treatment plots, local people continued to harvest litter and understory plants according to local practice (about 2-3 times a year) from the beginning of the experiment in May 1990. The harvesting according to local practice occurred during the period of 1990 to 1995 and was stopped after this time. Control plots were protected from any harvesting. Each set of paired plots was similar in soil, slope, aspect, and elevation. In this paper we report only the results of nutrient dynamics and its responses to human impacts over a ten-year period from 1990 to 2000.
    ARIDITY INDEX AND ITS APPLICATIONS IN GEO-ECOLOGICAL STUDY
    MENG Meng, NI Jian, ZHANG Zhi-Guo
    Chin J Plan Ecolo. 2004, 28 (6):  853-861.  doi:10.17521/cjpe.2004.0111
    Abstract ( 2876 )   PDF (315KB) ( 2494 )   Save
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    The aridity Index (AI, here defined as the climatic aridity) is an index that describes the dry and wet conditions of a site. Historically, the AI has been often used in long-term studies of geography and ecology. Recently it has became one of the most frequently used climatic factors in studies of global change, especially in studies of climate change, ariditification and desertification. A total of 22 AIs used worldwide were briefly introduced in this paper, and of these eight of the more commonly used AIs were evaluated. We discussed their principles, calculation methods, their applications in ecological and geographical studies, and the advantages and shortcomings of each indice were analyzed based on their applications and practice in China. Our analyses indicated that three AIs, the modified Selianinov AI, the de Martonne AI and the Holdridge potential evapotranspiration ratio (another AI to some extent) have clear applicability and significance for physics and ecology. These AIs are suitable for characterizing the physical environment of China and can be used in future studies of climate change, aridification and desertification in China.
    CORRELATION ANALYSIS OF LANDSAT TM DATA AND ITS DERIVED DATA, METEOROLOGICAL DATA AND TOPOGRAPHIC DATA WITH THE BIOMASS OF DIFFERENT AGED TROPICAL FORESTS
    YANG Cun-Jian, LIU Ji-Yuan, LUO Jian-Cheng
    Chin J Plan Ecolo. 2004, 28 (6):  862-867.  doi:10.17521/cjpe.2004.0112
    Abstract ( 2562 )   PDF (219KB) ( 829 )   Save
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    Correlation analysis of LANDSAT TM data and its derived data, meteorological data and topographic data with the biomass of tropical forest vegetation of different ages (Young, middle-aged, near mature, mature and over mature forests) were explored in Xishuangbanna, Yunnan Province, China. The analysis included four steps. First, the biomass of each forest was determined from field inventory data and a GIS database based on the geo-coordinates of each forest sample site. Second, the LANDSAT TM images were geometrically corrected using topographic maps. The derived data were derived from the LANDSAT TM images using principal component analysis, tasseled cap transform and vegetation index analysis. Third, the data, including LANDSAT TM data and its derived data, topographic data, such as DEM and aspect, and climatic data, such as annual average temperature, annual average accumulative temperature above zero degree, annual average precipitation and humidity, were referenced to the same projection and coordinate system and interpolated across a grid at a resolution of 30 meter. The LANDSAT TM data and its derived data, the topographic data and the climatic data for the samples were achieved by using overlay analysis. Fourth, all of the data were overlaid onto the different-aged forests. Finally, correlations among the LANDSAT TM and its derived data, meteorological data, topographical data and forest biomass were analyzed for each forest type. Our results are as follows: 1) Correlations between the biomass of the young forest and LANDSAT TM1 and LANDSAT TM6 were significant at the 0.05 level and both correlations reached -0.33. 2) The correlation between the biomass of the middle-aged forest and precipitation was significant at the 0.05 level and reached 0.33. 3) The correlations between the biomass of the near mature forest and VI3, TM4 and Bright Index were significant at the level 0.05 and were 0.50, -0.45 and -0.45, respectively. 4) Correlations of the biomass of mature and over mature forest and the second principal component, which were significant at the 0.05 level, reached -0.46. 5) The highest correlation existed between the near mature forest biomass and VI3.

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