Table of Content

25 March 1999, Volume 10 Issue 2

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Articles

Forest yield prediction with an artificial neural network and multiple regression

R. Pu, P. Gong, R. Yang

1999, 10(2):  129-134. 

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Use of traditional statistical techniques is often limited by shortage of observation samples and difference in data measurement scales. Neural network techniques have been extensively explored in many fields for prediction and classification as an alternative to statistical methods. In this paper, a feed forward neural network algorithm for predicting hardwood yield is introduced and evaluated. In addition, we report a data transformation method developed for converting qualitative variable data to quantitative data for use in multiple regression when relatively few samples are available for building prediction models. The method that converts qualitative data into quantitative data is helpful to improve hardwood yield prediction accuracy by multiple linear regression models. In this study, the best prediction results using the neural network technique are obtained.

Community analysis on secondary tropical vegetations in Xishuangbanna

Tang Jianwei, Zhang Jianhou, Song Qishi, Feng Zhili

1999, 10(2):  135-139. 

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Two secondary vegetations regenerated from the tropical rain forest in Menglun, Xishuangbanna after its. slash and burn cultivation were comparatively analyzed on their quantitative characteristics of community, population age structure, standing tree volume and stand volume. The results show that in a 900m² fixed plot, the natura secondary community had 73 species, 59 genera and 36 families of vascular plants. and the numbers of family, genus and species in it were 24.14%, 43.9% and 75.56% respectively higher than those of secondary community with artificial tending. The structure of the natural secondary community was also more complex than that of the artificial one, while the stand volume of the former was only 1/4 as much as that of the latter.

β diversity of forest communities in east Heilongjiang Province

Meng Qingfan, Hu Yinyue, Wang Qinggui, Zhang Fengbin

1999, 10(2):  140-142. 

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Using continuum index(CI) and collective habitat gradient(Gc) as quantitative indexes of plant community succession and habitat quality, this paper studied the β diversity of forest communities in east Heilongjiang Province. The β diversities of plant species(β_Z) and insect species(β_K) were increased with increasing of habitat gradient, i.e. the species turnover rate between communities declined as habitat quality increased, and β_K lagged behind β_Z. The relationships between β_Z and CIand between β_K and CI were close nonlinear. At initial succession stage, the species turnover rate between communities was higher, while at middle and end succession stages, it was the lowest. The peak value of β_K lagged behind β_Z, showing that the change of insect species diversity depended upon that of plant species.

Quantitative study on biomass accumulation of Paulownia elongata

Yang Xiu, Wu Gang, Huang Dongmei, Yang Changqun

1999, 10(2):  143-146. 

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The study on dry matter production, accumulation and return of Paulownia elongata in crop Paulownia intercropping system shows that the biomass of P.elongata increased with tree age, and its distribution in each organ followed the sequence: stem>branch>root>foliage>flower. The yearly dry matter production mainly occured from May to July, accounting for 77.3% of the whole yearly production. Defoliation accounted for 87.1% of the total litterfall. Litter fell throughout the whole yearly growth period, and showed two peaks annually. The yearly dry matter accumulation mainly occurred from May to July, accounting for 72.7% of the whole yearly accumulation, and the dry matter return ratio during its whole life period reached 33.73%.

Relationship between tree ring growth of Pinus taiwanensis and climatic factors

Wu Zemin, Huang Chenglin, Ma Qingshan

1999, 10(2):  147-150. 

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This paper dealt with the tree ring growth characteristics of Pinus taiwanensis on the top of Mt. Huangshan. Correlation functions of ring width index with climatic factors were obtained by step by step regression, which could provide a basis for studying the growth of Pinus taiwanensis and for constructing the historically climatic change of Huangshan region. Tree ring growth analysis shows that the pine had a wider range of mean sensitivity of tree ring growth. The tree ring growth model shows that the key factors affecting diameter growth were the solar radiation at the duration of>10℃ and the accumulated temperature in current year, with no relation to precipitation. The tree ring growth was strongly correlated with the climatic factors in current year, positively with the radiation in April and July, and negatively with the average temperature in April. There was no significant relationship with precipitation in current year.

Relationship between tree ring growth of Gordonia acuminata and climatic factors in Mt Jinyun

Sun Fan, Zhong Zhangcheng

1999, 10(2):  151-154. 

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With the methods of correlation analysis, stepwise regression, digital filtering and power spectrum, the dynamics of tree ring growth of Gordonia acuminata in Mt. Jinyun was analysed. After the genetic factors of tree growth were filtered by mathematical model, the chronological tables of Qinglongzhai and Xinglufeng were constructed, which showed a significant positive correlation with the precipitation in Chongqing. The mathematical model between tree ring growth and climatic elements was Y=-2.19+0.00747J₁+0.00612J₂+0.00140J₃+0.00384J₄+0.00371J₅+0.00731T₁+0.0564T₅. The power spectrum density was not evenly distributed with wave number,and the power spectrum cycle of tree ring width variation revealsed that the precipitation wave cycle of tree growth environment was about 2, 11～12 and 22 years. The construction and analysis of the chronological table of tree ring was one of the important ways to study the dynamics of ecosystem and the historical change of its environment.

Path analysis of morphological parameters of Convolvulus tragacuthoiedes population and individual biomass modeling of subshrubs

Sun Shucun, Qian Nengbin

1999, 10(2):  155-158. 

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Path analysis of four morphological parmeters of Convolvulus tragacuthoiedes shows that crown(C) contributed most to the population biomass,followed by branch number(BN), base diameter(BD)and height(H).Variable CH and D²H were used to build empirical models to compare the efficiency of biomass modeling,and the predicting equations for biomass of vegetative organs and individual plants were built.The result suggest that the models built on CHwere more appropriate than those on D²H, and the linear equation had the highest accuracy among the models.The optimum equation for predicting the individual biomass was: Y =12.10+0.0105 CH (R=0.983,P<0.01).

Disturbance of site preparation on chemical properties of calcic horizon in chestnut soil

Chen Lixin, Zhao Yuseng, Zhang Yan

1999, 10(2):  159-162. 

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This study comparatively analyzed the soil chemical properties of different aged poplar (Populus spp.) plantations with and without site preparation. After its calcic horizon was broken by ditch ploughing, the soil took about 10.7 yr for its chemical properties recovering to the state of no site preparation. After that, soil nutrients decreased rapidly, and even below to the level of no site preparation. Twenty years later, with the accumulation of organic matter,soil nutrients increased again, and ultimately higher than before site preparation. The successive order of soil nutrient recovery was organic matter, CaCO₃, available N, total P, total N, rapidly available K, and available P, with the recovery cycle of 6,7,7.5,9,10,17 and 17.5 yr, respectively; while the recovery cycle of soil nutrients in calcic horizon was 11.4 yr, and the successive order was available N, total P, organic matter, rapidly available K, CaCO₃,total N, and available P, with the recovery cycle of 5.5, 6, 6,8.5, 9.5, 10 and 34 yr, respectively.

Sensitivity analysis and grey forecast on the dynamics of desertification of Kerqin sandy land under humain activities

Zhang Jiahua, Wang Changyao

1999, 10(2):  163-166. 

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Using remote sensing pictures acquired by Landsat TM1◊250000 and 1◊500000 in 1990s and GISdata,combining with the results of remote sensing investigation from 1970s to 1980s, the types of land cover,potential dynamics of desertification and sensitive factors in six counties of Kerqin sandy land were analyzed.From 1980s to 1990s.the desertification area in the region increased from 53% to 70%,forested land decreased by 10.7%,and grassland area increased by 8.38%,with a major increase of lowly covered land.Due to the increase of human population density by 10 persons·km^-2 in recent ten years,the cultivated land was increased by 7% on average.Population increase and human activities were the sensitive factors affecting the change of land cover.The analysis of natural factors influencing desertification shows that climate change might result in the processing of desertification,and human activity is the direct cause aggravating the desertification of Kerqin sandy land at modern time.The grey forecast shows that the human population would increase,and the desertification tended to increase or decrease after the year of 2000.

Forest landscape heterogeneity and its dynamics of Guandishan Mountain

Guo Jinping, Yang Hanxi, Xue Junjie, Wang Yimin and Wei Xin

1999, 10(2):  167-171. 

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Based on aerial images of four periods,the GIStechnique supported by ARC/INFOsoftware was used to analyze the forest landscape heterogeneity and its dynamics of Guandishan Mountain forested area since the end of 1950s,by selecting Landscape Element Dominance Index(LEDI), Landscape Diversity Index(LDI),Landscape Patch Density(LPD),Landscape Edge Density(LED),Landscape Patchness Index(LPI) and Landscape Contagion Index(LCI) as six indexes.Methods for data treatment and calculation were introduced, and the applicability of these indexes was analyzed.On the support of GIStechnique,the above mentioned indexes could reveal and describe the structural characteristics of landscape heterogeneity from different aspects,which was useful to study the dynamic process of landscape heterogeneity.The results show that since the end of 1950's,the forest landscape in studied area was controlled by the combination of environmental heterogeneity,natural vegetation succession and human's activities,and the whole landscape heterogeneity changed significantly with different dynamic characteristics in three periods.The basic patterns and regulation factors of dynamic changes of forest landscape heterogeneity in secondary forest area with frequent human's activities were also discussed.

Analysis of energy flow of rubber tea chicken agroforestry system in tropical area of China

Meng Qingyan, Wang Zhaoqian, Jiang Shuqian

1999, 10(2):  172-174. 

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The comparative analysies on the energy flow path, its input and output structure, and conversion efficiency of single rubber culture(R), rubber tea inter cropping(RT) and rubber tea chicken(RTC) gardens in Wenchang City, Hainan Province show that the utilization efficiency of solar energy increased gradually in the order of above mentioned three kinds of gardens. Their total energy output/input ratios were 1.50, 1.88 and 0.20, the organic energy input/total input ratios were 0.138, 0.119 and 0.997, and the inorganic energy input/total input ratios were 0.862, 0.881 and 0.023, respectively. In RTCsystem, the artificial subsidiary energy input decreased, and energy output increased.

Impact of soil erosion on soil fertility and land productivity

Yang Wude, Wang Zhaoqian

1999, 10(2):  175-178. 

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Studies on the spatial differentiation of soil fertility and land productivity of red soil slope fields under different land use patterns revealed that soil erosion had negative effects on soil fertility and land biological productivity,which mainly manifested in the decreasing contents of soil available N, P, K. and their relative poor on the top and rich at the bottom of the slope, the reduced soil organic matter content, the soil sandification, and the resultant reduction of land biological productivity.

Effect of Mn application depth on Mn deficiency of two wheat genotypes

Liu Xuejun, Lü Shihua, Zhang Fusuo, Mao Daru

1999, 10(2):  179-182. 

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Simulated Mn deficient soil column studies with wheat show that the Mn deficient symptom, grain yield, root system distribution and Mn content of two genotypes (Chuanmai 22 and genotype 3317) were greatly affected by Mn application depth. The yields of both genotypes were obviously increased with the application depth of Mn fertilizer, and the increment of Chuanmai 22 was higher than genotype 3317. It was suggested that the higher tolerance to Mn deficiency of genotype 3317 than Chuanmai 22 was related to the higher percentage of its roots distributing in the middle and lower soil layers and to the stronger capacity of absorbing Mn from soil. It was also found that the Mn deficient symptoms of wheat at seedling stage could be disappeared after Mn fertilizer was applied at mid late stage in the middle and lower soil layers, indicating that applying Mn fertilizer at mid late stage played an important role to the formation of wheat yields.

Effect of dicyandiamide on nitrogen transformation of ammonium bicarbonate in soil

Shang Zhaocong, Gao Ziqin

1999, 10(2):  183-185. 

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Incubation studies on the effect of dicyandiamide (DCD) on NH₄⁺-N dynamics of ammonium bicarbonate (AB) in soil show that whether mechanical mixed with AB or being a component of slow releasing AB,DCDinhibits the nitrification of NH₄⁺-N and decreased the ammonium volatilization, which made soil preserve more NH₄⁺-N in a longer period and buffered the intensity of soil acidification or alkalization after ABapplication.Adding DCDcould increase the utility efficiency of AB,and decrease its nitrogen losses.

Effect of soil water regime and chemical N fertilizers application on N₂O emission from paddy field

Xu Hua, Xing Guangxi, Cai Zucong, H.Tsuruta

1999, 10(2):  186-188. 

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The mean N₂O emission from paddy field under continuously flooding, alternately flooding and soil draining, and drying was 1.02, 23.87 and 47.99μg·m^-2·h^-1,respectively. Application of chemical N fertilizers could increase N₂O emission, and ammonium sulphate seemed to emit more N₂O than urea. The fertilizer induced N₂O Nloss from ammonium sulfate was 0.04% at the application rate of 100kg·hm^-2, and 0.26% at the rate of 300kg·hm^-2. The corresponding loss was 0.03% and 0.15% from urea.

Effect of hydroquinone and dicyandiamide on N₂O and CH₄ emissions from lowland rice soil

Zhou Likai, Xu Xingkai, Chen Lijun, Li Ronghua, Oswald Van Cleemput

1999, 10(2):  189-192. 

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Through pot experiments, this paper studied the effect of urease inhibitor hydroquinone (HQ), nitrification inhibitor dicyandiamide (DCD) and their combination (HQ+DCD) on the N₂O and CH₄ emissions from a lowland rice soil. The results show that with no wheat straw powder amended, all treatments with inhibitors significantly reduced the N₂O and CH₄ emissions during rice growth, as compared with the treatment only urea applied. Especially for treatment HQ+DCD, its total amount of N₂Oand of CH₄ emission was about 1/3 and 1/2 of the control, respectively; while with wheat straw powder amended, the total N₂O emission of this treatment was 1/2 of the control, but that of CH₄ emission had less difference. Wheat straw powder amendment induced one times and more emissions of N₂O and CH₄ than no its application, and hence, even only from the standpoint of diminishing soil source greenhouse gases emission, applying unmatured composted organic materials with urea is an inappropriate fertilization system. The N₂O flux from this soil had a significant positive exponential relationship with the NO₃^--N content of rice plant and a significant positive linear relationship with the mineral Ncontent in soil surface waterlayer, while CH₄ flux had a significant negative linear relationship both with the growth rate of rice plant and with the mineral Ncontent in soil surface waterlayer. There existed a quantitative trade off between N₂O and CH₄ emission in case of no wheat straw powder incorporated, while with its amendment, the trade off still existed, but hard to quantify.

Effect of shading on growth, development and yield formation of rice

Cai Kunzheng, Luo Shiming

1999, 10(2):  193-196. 

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Field experiments under 45% shading at different stages(early, middle 1, middle 2 and later stages) of rice growth show that regardless of different stages, shading decreased the accumulation rate of dry matter and the uptake of nutrients, but increased the nutrient content in rice plant, and affected its yield in varying degrees. Shading at early growth stage mainly decreased tiller number, effective panicle number and leaf area index, and reduced yield by 11.56%, but increased plant height. At middle 1 stage, shading showed no significant influence on rice growth, and the yield was reduced by only 5.46%. At middle 2 stage, shading mainly decreased grains per panicle and 1000 grain weight, and the yield was reduced markedly by 30.80%. At later stage, shading decreased the percentage of filled grains and 1000 grain weight, and the yield was the lowest, reduced by 55.40%. Suggestions on the way of regulating sowing and transplanting dates and making fertilization decision under low light intensity also put forward in this paper.

Interspecific competition and facilitation in wheat/soybean intercropping system

Li Long, Yang Sicun, Sun Jianhao, Li Xiaolin and Zhang Fusuo

1999, 10(2):  197-200. 

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Wheat and soybean intercropping is a high yield planting system widely distributed in one crop a year irrigation area of northwest China. Field plot and microplot root partition experiments show that under wheat/soybean intercropping, the land equivalent ratio was 1.23～1.26,and wheat was the dominant species with more competitive ability relative to soybean and possessing obvious edge row advantages, in which, 1/3 of the contribution came from its underground part. There was a recovery to soybean growth after wheat harvesting, which was considered as one of the mechanisms of interspecific facilitation. The harvesting index of intercropped species was significantly higher than that of sole species, indicating another mechanism of facilitation in the intercropping.

Introduction of large ear wheat variety Xianyang84(Jia)79 31

Liu Siheng, Liu Wenbing

1999, 10(2):  201-205. 

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Three years studies on the introduction of large ear wheat variety Xianyang84(Jia)79 31 in different ecological areas of Fujian Province show that the variety belonged to springiness type which was similar to the local cultivars of Fujian Province in differentiation procedure of young ear and growing period. The variety had normal heading and maturity, and had dwarfed stems and large ears, with a 80～88cm of plant height and 18～20cm of ear length. There were 22～23 spikelets and 46～48 grains per spike, and 55～60g per 1000 grains. The spikelets had a low density, top spikelets were easy to degrade, and the plant had a weaker tillering capacity and less productive ears. The plants had a stronger tolerance to fertilization, and the yield could attain6000 kg per hectare, about 20% more than that of check cultivar under fertile condition. The tolerance to moisture and drought was weak, and strong to rust, medium to powdery mildew and seriously susceptible to scab. Xianyang84(Jia)79 31 could be planted in high-yield fields of coastal area in Fujian Province, and be applied in breeding as large ear parent.

Allelopathy of Pisolithus tinctorius fruitbodies and isolation and identification of allelochemicals

Zeng Rensen, Luo Shiming, Shi Mubiao, Tu Congyong, Zeng Qiang, Tan Huifen

1999, 10(2):  206-208. 

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Pisolithus tinctorius can form ectomycorrhizae with pine and eucalyptus.The aqueous,ethanol and acetone extracts from its fruitbodies significantly inhibited the seedling growth of Echinochloa crusgalli and Oryza sativa, and acetone extract at concentration of 0.0125g·ml^-1 inhibited the seedling growth of Pennisetum alopecuroides and Brassica campastris. Two pure compounds were isolated from the fruitbodies of P.tinctorius by silica gel column chromatography, and were identified as pisolactone and ergosterol. Ergosterol significantly inhibited the root growth of E.crusgalli seedlings at concentration of 400μg·ml^-1,and pisolactone could do it at concentration of 100μg·ml^-1.

Simulations of allelopathy in continuous cropping of soybean

Du Yingjun, Jin Yuehua

1999, 10(2):  209-212. 

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Tissue culture methods were used to simulate the allelopathy effect of root exudates and plant aqueous extracts of continuously cropped soybean under sterilized conditions. The results show that the exudates and extracts both apparently affect the growth and physiological activities of second-batch seedlings, which may be related to the disturbance in the metabolism of plant hormones. The known allelochemicals as vanillic acid, vanillin and p-hydroxybenzoic acid were detected from both the exudate and the extract, and the continuous cropping obstacle of soybean may be related to their deleterious effect.

Analysis on structure and function of agro ecolomic system in oasis—taking Zhangye oasis as an example

Meng Jijun, Long Hualou, Liu Song

1999, 10(2):  213-217. 

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In this paper, through analyzing the structure and function of agro ecolomic system of Zhangye oasis, it was found that the unitary population structure, irrational industrial composition and weak spatial structure, led to the bad function and low productivity of the oasis. From the viewpoint of sustainable development, strategies and suggestions for improving the structure of the agro ecolomic system and enhancing its function were put forward.

Optimal ecological conditions for strawberry storage and fresh keeping

Cai Yongping, Yan Jinghua, Ge Huimin, Li Wenzhong, Chu Mingjie

1999, 10(2):  218-220. 

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This paper studied the optimal environmental factors for strawberry storage and fresh keeping at normal temperature and the physio biochemical changes of strawberry during its storage. The results indicate that it was important to improve environmental factors, keep the temperature and moisture stable (about RH 80%, T 20℃) in storage room and make it sterilize, and put the strawberrys in a covered small box, which could make the storage extended to 2 days. With fresh keeping membrane, the duration of storage could be extended to 5 days. Among the test, fresh keeping membranes, LF₁ and LF₃ could keep the rate of good fruits by 69.27% and 69.94% after storing5 days. Fresh keeping membrane could inhibit the respiration and metabolism of strawberry, increase its SODactivity and ASAcontent, delay strawberry from decaying, and increase the rate of good fruits.

Intensive production of housefly larva—a preliminary study

Sun Gang, Wang Zhentang, Song Yujun

1999, 10(2):  221-224. 

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This paper studied the intensive production of housefly larva under artificial conditions. In an area of 240m² (daily production unit 60m²), the maximum yield of fresh maggot was more than 200kg·d^-1, with an average of 150kg·d^-1. The second day after hatching was the key stage for maggot growth and development, and thus, the environmental conditions and food quality should be controlled strictly. Three days after same aged housefly cohort oviposition, the oviposition climax emerged and maintained 3～4 days. Female individuals oviposited 10～14 times in their life span, 100～200 ovums in average, and 900 ovums in maximum per time. It took one day and 4～5 days respectively to make the ovum become larva and adult. The increasing process of maggot weight could be simulated by Logistic curve. The ratio of maggot/feeding was 0.4～0.5, and that of economic output/input 2.1～3.3. In our experiment, the practical multiplication of housefly population size after one generation was 25.5% of theoretical one. Making use of agricultural by-products and waste materials to rear maggot was an available approach to gain high-quality animal protein and forage.

Plant bioremediation of PAHs and mineral oil contaminated soil

Sun Tieheng, Song Yufang, Xu Huaxia, Zhang Hairong, Yang Guifen

1999, 10(2):  225-229. 

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Taking alfalfa(Medicago sativa) as test plant and with pollutant content level,specific bacteria,fungi and organic fertilizer as control factors,the plant bioremediation of polycyclic aromatic hydrocarbons (PAHs) and mineral oil contaminated soil was conducted.The degradation rate of PAHs and mineral oil was positively correlated with the content of organic fertilizer in soil.Increasing the content of organic fertilizer by 5% would increase the degradation rate of mineral oil by 176～256%,PAHs by 9%.On the presence of plants,the degradation ability of soil microbes was enhanced,with the average degradation rate of total PAHs 20～47%higher than that of control.The applied fungi improved in some degree the degradation of PAHs and mineral oil.Fungi obviously enhanced the degradation rate of fluoranthrene,pyrene and benzo(a)anthracene/chrysene,while bacteria obviously increased the degradation rate of acenathene/fluorene,anthracene and benzo(a)fluoranthene/benzo(k)fluoranthrene.

Effect of surfactant TW80 on biodegradation of PAHs in soil

Song Yufang, Sun Tieheng, Xu Huaxia

1999, 10(2):  230-232. 

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An experiment was conducted on the effect of surfactant TW 80 on biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil for 150 days. Samples were collected in the intermittence of 30, 60 and 150 days to monitor the degradation rate of PAHs. The results indicate that after 30 days, the degradation rate reached 90%, approximately 30% higher than that of control. After 60 days, the degradation rate with a concentration of TW 80 at 1000mg·kg^-1 and the control reached from 65.1% and 60.0% to 93.8% and 79.2%, respectively; but the average degradation of PAHs in other treatements increased only by 4%, compared with results of 30 days. One hundred and fifty days later, the degradation rate in all treatments was over 90%. It is suggested that surfactant can improve the bioavailability of PAHs and speed up the degradation rate, therefore, reduce the exposure time of pollutants. But, surfactant at high concentration can inhibit the activity of microbes. It was also found that the soil with surfactant TW-80 contained dominant fungi which were identified as Penicillium freguentant, P.vermiculatum, P.lilacinum and Cephalosporium acremonium, indicating that these fungi were the driving force for rapid degradation of PAHs in soil.

Ecosystem services: the biological conditions and ecological supports necessary for the development of human societies

Dong Quan

1999, 10(2):  233-240. 

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atural ecosystems support life, contribute to human welfare, and provide essential conditions and services for civilization. The contributions and benefits from natural ecological systems to human societies are ecosystem services, which include: production of natural goods, biodiversity maintenance, climate regulation, regulation of hydrological flows and water supply, mitigation of droughts and floods, cycling and moving nutrients, generation and preservation of soils and renewal of their fertility, detoxification and decomposition of wastes, pollination and seed dispersal, pest control, maintenance of conditions for both mental and physical health and healing of human beings, provision of aesthetic, intellectual, and spiritual stimulation. The services flowing from natural ecosystems are enormous and indispensable for economy and welfare, but have been greatly undervalued by society, partly because they are not traded in markets and people are rarely ware of the role and importance of these services. In market-driven societies, the valuation of ecosystem services is useful to support more ecologically conscious decision-making. Identification and monitoring of ecological processes that generate ecosystem services are much needed. Human activities already have altered physical, chemical, biological and geographic attributes of the Earth profoundly and have been impairing the flow of ecosystem services on a large scale. We are facing a great challenge to maintain a sustainable society that is ecologically sound, economically feasible, socially just and peaceful. Ecologists should work closely with public and policy-makers to answer this challenge.

Effect of soil plant underlying surface on microecological environment

Li Quansheng, Wu Jianjun, Ye Xujun, Wang Zhaoqian

1999, 10(2):  241-244. 

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This paper summarized the effect of soil plant underlying surface on such microecological environment as radiation balance, heat condition, soil erosion, soil fertility, utilization rate of solar radiation, etc.. The solar reflection rate, effective radiation, daily change of soil heat flux, and turbulence heat flux in the underlying surface covered by vegetation were smaller than those in the uncovered land. On slope land, planting grass and reducing the times of ploughing would be beneficial to soil and water conservation, while growing forage grass on underlying surface would increase soil fertility and utilization rate of solar radiation.

Effect of plant diversity in agroecosystems on insect pest populations

Hou Maolin, Sheng Chengfa

1999, 10(2):  245-250. 

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In this paper, the ecological mechanism about the effect of plant diversity on insect pest development and its population dynamics was analyzed. Natural enemy hypothesis and food source concentration hypothesis, the two main prevailing hypotheses concerning this ecological mechanism, were reviewed, and the advantages and disadvantages of plant diversity for insect pest control were summarized. Empirical data show that increased plant diversity in agroecosystems may, at many cases, reduce the populations of certain insect pests, but at present, it is difficult to draw a general conclusion about the effect of plant diversity on populations for all types of insect pests in different habitats.

Bio availability of aluminum and its ecological effect—a review on related studies

Liu Wenxin, Luan Zhaokun, Hongxiao Tang

1999, 10(2):  251-254. 

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Serious acid rain and large acidic wastewater discharge can cause the release and mobilization of aluminum from soil and sediment, which latently imperils many kinds of organisms. Meanwhile, the utilization of coagulants, additives and aluminumware may increase the possibility of human being's exposure to aluminum. With the profound researches on the environmental geochemistry and biological toxicology of aluminum, the publics concentrate their attentions more and more on its ecological effect. Based on latest literatures, this paper discusses the recent advance on the study of bio availability of various chemical forms of aluminum and their toxicology, and the focus and tendency of this research in future are put forward.

Phytoalexins in Dracaena cochinchinensis resin

Wang Jinliang, Ruan Dechun, Cheng Zhiying, Zhou Ligang

1999, 10(2):  255-256. 

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After the trunk of Dracaena cochinchinensis was separately inoculated with Fusarium graminum var. dracaena, F. graminum var. yunnanensis and Cladosporium carpophilum for 5～15 days, small red circles emerged around its inoculated positions and gradually enlarged with increasing days, and the redness also gradually became deep. Antifungal experiment and HPLC analysis confirmed that 7,4'-dihydroxyflavan, 7-hydroxy-4'-methoxyflavan and Loureirin Awere the three phytoalexins which were extracted and identified from the red xylems.