We estimated quantitatively the effect of spatial scale magnification on land cover monitoring and landscape characteristics at regional scale, using different spatial remotely sensed data from RS (Remote Sensing), GIS (Geographic Information System) and GPS (Global Positioning System), and taking the west of the Northeast China Transect (NECT), one of the IGBP international transects in China, as the study area. A comparison study on land cover classification and landscape characteristics, using NOAA/AVHRR digital images of 3 different spatial resolutions, was performed in this paper in the study area. USGS EROS (Earth Resources Observation System) Data Center (EDC) provided the monthly remote sensing images as data resources, which were in uniform tempo and region at three different spatial resolutions: 1 km×1 km, 4 km×4 km and 8 km×8 km, spanning a 12-month period (April 1992-March 1993). Firstly, unsupervised classification algorithm ISODATA was employed to process 3 different spatial resolution images and obtained land classification information. Secondly, information transfer among different resolution images was calculated using a map algebraic algorithm. Finally, regional landscape characteristics of land cover types at different spatial scales were compared, taking landscape spatial structure indices such as fractal dimension, fragmentation, diversity and dominance as standards. Particular emphasis was put on the comparison of boundary consistency and spatial difference of classification result from remotely sensed data at 3 different spatial resolutions, and the difference of landscape pattern revealed by the images. The study results showed: 1) 9 land cover types obtained from remote sensing data were: temperate deciduous broadleaf forest, temperate upland deciduous leaflet forest, single crops + temperate typical steppe, temperate deciduous scrub and low forest, temperate meadow steppe, temperate typical steppe, temperate desert steppe, meadow + graminaceous swamp and water body; 2) the macro spatially pattern of regional land cover revealed by images of 3 different spatial resolutions was consistent, but the boundary of land cover type, the shape and the number of patches of each type differed greatly; 3) comparison of four indices (Fractal dimension, Fragmentation, Diversity, and Dominance) showed that the structure of the landscape changed greatly with change of spatial resolution as revealed by images. Fractal dimension of each cover type showed the most obvious variation, which indicated the change of spatial resolution contributed most to the patch complexity. This paper sets up a basis for further study at different scales on landscape change processes.

The effectiveness and accordance of four popular climate vegetation classification models (Penman model, Thornthwaite model, Holdridge Life Zone System and Kira model) for the geographic distribution of Chinese vegetation is compared using the KAPPA agreement statistic method. The results indicate that those four classification models work well in the first level of Chinese Vegetation Division. The KAPPA value of the Holdridge Life Zone System (0.57) is the largest among the four models. It showed that it is the best one among four models in simulating the geographical distribution of Chinese vegetation. However, regarding some specific regions, for example, the Tibetan plateau, all of the models need to be refined or to take new affecting factors into account in order to obtain a better simulation of the geographic distribution of vegetation. 1) The Penman model could simulate the geographic distribution of vegetation in temperate steppe and Tibetan plateau with a KAPPA value greater than 0.50. It is the best one for Tibetan plateau among the four models. 2) The Thornthwaite model could give the best simulation for tropical rain forests and seasonal rain forests with KAPPA value of 0.40. It might compensate for the ineffectiveness of the Holdridge Life Zone System in this area. 3) The Holdridge Life Zone System is the best one among the four models for simulating the geographical distribution of vegetation in China based on the first level of vegetation division in China, but it still fails to simulate west seasonal rain forests and rain forests (52), west temperate steppe (63), Tibetan plateau temperate desert (86) and Tibetan plateau temperate steppe (84). 4) The Kira model simulates the subtropical evergreen forest zone very well, and its KAPPA value in this zone is close to that of the Holdridge Life Zone System. Also it could simulate moderately well the geographical distribution of vegetation in low elevation and humid/semihumid area, but it was far from the ground truth when applied to the regions of temperate desert and Tibetan Plateau. This research also implies that it is urgent to develop better climate vegetati on classification model in order to provide better input to the general circulation models (GCMs) with the geographic distribution of vegetation and to accurately evaluate the possible effects of climate change on vegetation.

Crop growth modeling, which was developed very quickly in recent decades, is a forceful tool in scientific research. Many crop growth models, such aful tool iries, WOFOST and RZWQM and the like, have been developed and applied widely, but few of them have been introduced in China. This research was aimed at evaluating the suitability of WOFOST model for the North China Plain. WOFOST is a mechanistic crop growth model developed by Wageningen Agricultural University, the Netherlands. It was summarized briefly and then validated by using experimental data in North China Plain. This experiment was conducted in two successive years (2000-2001) in Yucheng Comprehensive Experiment Station, the Chinese Academy of Sciences (CAS), located at Yucheng, Shangdong Province of China. Water treatment pools have eight water treatments with two replicates: 1) treatments 1-5: water was supplied close to 40%, 50%, 60%, 70%, 80% of field water capacity; 2) treatment 6: water stress was set from turning green to shooting; 3) treatment 7: water stress was set from earring to filling; 4) treatment 8: water stress was set from filling to harvest. Each treatment was under a movable rain-shelter. Water content was measured using a neutron probe every five days; an additional measurement was taken before and after rainfall and irrigation. Crop growth was examined every five days, including tiller number, leaf area index, fresh and dry weight of all organs, filling rate and plant height. Leaf area was measured by LI-3100. The model was calibrated to get values of parameters using the experimental data in the year 2001, and then it was validated by data in 2000. The following crop growth simulation results (on a per-hectare basis) were examined: potential production, water limited production, potential total above-ground dry matter and water limited total above-ground dry matter, potential and water limited leaf area index, potential and water limited stem weight. Comparison between measured values and simulated results shows their correlation is close. The main conclusions of this study were as follows: 1) WOFOST model is suitable for similar research in North China Plain. It describes crop photosynthesis in detail and is good at simulating crop potential growth; 2) WOFOST treated some aspects simply and often uses a simple formula instead of a complex one to simplify input; 3) the potential production in North China Plain is about 8 100 kg·hm-2 and present production achieves only about 65% of this; 4) WOFOST has some problems that need to be improved. It disregards dry matter transportation from leaves and stems to seeds and describes dry matter partitioning too simply.

Beeches are important constructive species in humid temperate forests in the Northern Hemisphere. China contains rich species of genus Fagus, 5 out of the 11 distributed in the country. Although there were many reports about Fagus in China, most of them referred to the south of the Fagus distribution region, and specifically to F. lucida. In this paper, we examined the size class structure and distribution pattern of a deciduous and evergreen mixed beech forest dominated by F. engleriana and Cyclobalanopsis oxyodon to discuss the relationship of the two species, and the community dynamic. The research plot was located in Shennongjia area of Hubei province (31°19′04″ N, 110°29′44″ E), which was in the northern part of the Fagus distribution region. This area crosses the mid-subtropical and north-subtropical zones of China, and is also a transition area of landform. The unique geographic position causes its particular plant species diversity and antiquity. Beech community is an important type of mountain forest in the local vegetation. F. engleriana, F. long ipetiolata and F. lucida are all distributed there, and F. engleriana is the most common species. The 0.96 hm2 permanence plot was established in 2001, and was divided into 384 subplots. All the stems over 1 cm in DBH were identified, measured, tagged, and mapped.The community consisted of 46 woody plant species, belonging to 22 families and 27 genera. The dominant families were Fagaceae, Aceraceae, Ericaceae, Cornaceae and Rosaceae. The tree layer could be divided into three sub-layers. In the first layer, deciduous trees made up 80.7% of the layer, and evergreen species were 19.3%; dominant species were Fagus engleriana and Cyclobalanopsis oxyodon. In the second and third layers, evergreen species increased from 55.9% to 80.5%.C．oxyodon and Rhododendron hypoglaucum were dominant species. The size-class distribution of Fagus engleriana and Cyclobalanopsis oxyodon showed positive pyramidal type, which indicated that both species had rich sapling banks and regenerated well. Three hundred and fourteen stems including 289 sprouting ones were counted for Fagus engleriana in the 0.96 hm2 plot. The sprouting stems were 90.8% of the total stems, and some researches showed sprouting could be the major method of recruitment of the population. C.oxyodon had 1 576 stems, 74.6% sprouting. Although sprouting was a large part of the stems, C．oxyodon was mainly regenerated by seed. Distribution patterns were analyzed using David and Moore’s index, Lloyd’s index and Mosisita index in plot sizes of 1 m × 1 m, 3 m × 3 m, 5 m × 5 m, 7 m × 7 m, 9 m × 9 m, 11 m × 11 m, 13 m ×13 m, and 15 m × 15 m. The Cyclobalanopsis oxyodon population was divided into three size classes as DBH 1-4 cm, DBH 4－8 cm and DBH > 8 cm. The distributions of all of these classes were clumped. This may be because the life span of C．oxyodon was so short that no self-thinning happened during this period. The distribution pattern of F．engleriana was also clumped. The possible reasons were: 1) the recruitment of F. engleriana needed open canopies. The pattern in fact showed the disturbance history. 2) compared with other beech forests, this community had not reached maturity. In this stage of succession the distribution pattern was clumped. 3) the distribution could be influenced by topography. The slope of the plot is 49.5 degree on average. This could highly affect seed distribution, and so also affect the pattern of the population. The studied Fagus engleriana-Cyclobalanopsis oxyodon community had rich species diversity and clear structure. AlthoughC．oxyodon was the most important species in the community, it was not a canopy tree at this elevation. So F．engleriana was the constructive species and C．oxyodon was a co-dominator. The two species both had sufficient regeneration storage that the community could exist stably.

In order to evaluate the ecological safety and planting risk of insect resistant transgenic cotton, the composition and diversity of the weed community in transgenic Bt cotton (four Bollgard strains: ’109B’,’154’,’690’ and ’972’) fields were studied by means of the quantitative analysis method in Dafeng of Jiangsu coastal district and Rugao of Jiangsu Changjiang River bank district. There were marked differences in water content of soil due to differences in crop rotation systems (i.e. rotation with rice following dry-cropping) between cotton fields. The experimental design was as follows: five treatments include four Bollgard strains and traditional variety and four replicates in each location. Each plot area is about 60 m2. The traditional variety check was Simian-3 in Dafeng and Sumian-16 in Rugao respectively. All weed species and their number were investigated with the sampled method of five spots per plot and the spots area investigated per plot was 2.5 m2 in Dafeng and 1.25 m2 in Rugao respectively. The average of weed species and number per square meter for each treatment was calculated. The parameters and components analysis of weed community for each treatment and coefficients of weed species/community similarity between each of four Bollgard strains and traditional variety check were calculated and analyzed also. The results showed: 1) no significant difference in weed species was found between each of four transgenic Bollgard cotton strains and the traditional variety checked in the same location. The dominant species and their abundance were very similar among them.2) the parameters of weed community structure included species richness(S)，total number of individuals(N), community diversity (H′), evenness(J), and concentration(C) in each of the transgenic Bt cotton (four Bollgard strains) fluctuated similarly to the ones in the traditional variety in the same date and same location. The results of comprehensive analysis for two locations showed that the value of community diversity(H′) and evenness(J) in transgenic Bt cotton was a little higher than the ones in traditional cotton check, but the value of concentration(C) in transgenic Bt cotton was a little lower than the ones in traditional variety check. 3) the path analysis of diversity index(H′) with other parameters showed that it all was dominant concentration(C) and evenness(J) that mainly decided the change of diversity index(H′) for weed community in five treatments. Diversity index(H′) would be reduced with increasing of dominant concentration(C) and decreasing of evenness(J) for all treatments.4) the coefficient of weed species similarity(V1) and the coefficient of weed community similarity(V2) between each of four transgenic Bt Bollgard cotton strains and traditional variety check was determined by the Sorensen’s formula and all very high. The value of V 1 is 0.718 0－0.844 5 in Dafeng and 0.489 4-0.603 7 in Rugao，and V2 is 0.451 1-0.598 1 in Dafeng and 0.329 3-0.484 7 in Rugao respectively.From the above results, it is clear that the stability of weed community of transgenic Bt cotton field (four Bollgard cotton strains) is not different significantly than traditional cotton check and its weed risk increased by planting transgenic Bt cotton is not obvious. There was a close correlation among the structure of weed community, crop rotation system and geographical factors. The main factor that affected the weed occurrence and distribution pattern of weed infestation and community in the cotton fields was the difference of soil water content, which resulted from the different cropping system.

In order to investigate the differences in capacity of sunfleck utilization between species with different ecological characteristics, the photosynthetic characteristics and photosynthetic induction responses were examined with LI-6400 portable photosynthesis system in seedlings of six tropical rainforest species acclimated in simulated understory light environment for more than one and a half years. The species studied were Mallotus macrostachys, a pioneer species, Pometia tomentosa, Shorea chinensis, Barringtonia pendala, Linociera insignis, Lasianthus hookeri, four canopy species and an extremely shade-tolerant understory shrub. After leaves were shaded in darkness for 3 h, photosynthetic induction was measured under optimum temperature ((26±1.2) ℃) and humidity (75%±5%) and normal ambient CO2 ((400±0.5) μmol CO2·mol-1 air) in the morning. The time courses of induction varied from a sigmoidal to a hyperbolic increase in net photosynthesis. The time required to reach 90% of maximum net photosynthetic rate differed among species, and was short (4.4-12.5 min), which was consistent with induction times reported in other tropical shade-tolerant species. Seedlings of M. macrostachys and L. hookeri were induced two to three times more quickly than the other four canopy species. The response of attaining maximal stomatal conductance significantly lagged behind the increase in net photosynthetic rate during the induction course. When fully induced leaves were shaded in darkness for 20 min, loss of induction was moderate in all species. Among these species, seedlings of M. macrostachys had a relatively rapid induction loss, which was due to rapid loss of stomatal conductance and biochemical factors. The loss of B. pendala was mainly due to biochemical limitation as stomatal conductance decreased only slowly. Seedlings of L. hookeri showed the slowest loss of induction as a result of maintaining higher relative stomatal conductance and maximum carboxylation capacity. Thus this effective utilization of sunflecks is likely to be a critical determinant of growth and generation for understory species.

Acacia mangium is a fast growing tropical tree species with significant economic and ecological values. The diurnal variations of photosynthesis and daily-integrated photosynthetic CO2 assimilation over whole photoperiods of A. mangium phyllode were investigated. The results showed that the photosynthetic CO2 uptake of A. mangium phyllode exhibited a 14.5% decrease during midday. The PSII of the A. mangium phyllode was tolerant to high Photosynthetic photon flux density (PPFD) levels and high temperatures. The integrated daily carbon gain and nocturnal carbon loss of A. mangium phyllode was 502 mmol CO2·m-2·day-1 and 54 mmol CO2·m-2·day-1, respectively. All of these physiological traits allow A. mangium to take advantage of the high PPFD environment in the tropics and help this plant to realize rapid growth.

The patterns of CO2 exchange were studied in leaves of Dendrobium officinale during 24 hour periods in sunny, rainy and cloudy days to identify its photosynthetic pathway, and the response of CO2exchange rate to light intensity and temperature was studied. The results showed that there were differences in patterns of CO2 exchange among sunny, rainy and cloudy days. In sunny days CO2 was assimilated by D. officinale in daytime and at night, with the exception of midday, where no net CO 2 was taken up. The maximum rate of CO2 uptake in daytime and at night was at 9∶00 and 23∶00, respectively, which showed that the pattern of CO2 exchange was typical of Crassulacean Acid Metabolism (CAM) with four phases of CO2 assimilation during a 24 hour period. On rainy days CO2 uptake appeared only in daytime, and the CO2 exchange pattern was typical of C3 photosynthesis. On cloudy days, CO2 uptake occurred in daytime and continued to 21∶00, then CO2 was released from 23∶00 to dawn, showing a pattern intermediate between CAM and C3 photosynthesis. Under 500 μmol·m-2·s-1 light intensity CO2 uptake rate was the highest, (4.55±0.17) μmol·m-2·s-1, at 20 ℃; it decreased with temperature increase or decrease. The net rate of photosynthesis was near zero at 35 ℃. The stomatal conductance ecreased from 10 ℃ to 35 ℃, the lowest internal CO2 concentration and the highest stomatal limiting value both occurred at 25 ℃. The temperature-dependent reduction of CO2 uptake rate was due to stomatal limitation at 20-25 ℃, but not at the low temperature (<20 ℃) and high temperature (>25 ℃). However, the nocturnal CO2 uptake rate was the highest, (1.01±0.03) μmol·m-2·s-1, at a temperature of 25 ℃, and it showed a negative value at 35 ℃. Stomatal conductance was the highest at 25 ℃, and both the lowest internal CO2 concentration and the highest stomatal limiting value were at 30℃. The temperature-dependent reduction of nocturnal CO2 uptake rate was due to stomatal limitation at 20-30 ℃, but not at the low temperature (<20 ℃) and high temperature (>30 ℃) .Apparent quantum yield, light compensation point and saturated light intensity in the morning was 0.035, 2.9 μmol·m-2·s-1 and approximately 500 μmol·m-2·s-1, respectively. Photoinhibition of photosynthesis was induced by light intensity over 500 μmol·m-2·s-1. When leaves were pre-exposed to high-light for 20 min, light compensation point increased, while apparent quantum yield and CO2 uptake rate decreased. After leaves were pre-exposed to high-light of 2 000 μmol·m-2·s-1, apparent quantum yield decreased to 0.018, and the light compensation point was increased to 69 μmol·m-2·s-1. This indicated that photoinhibition remained while light intensity decreased. Based on the results above, D. officinale should be a facultative CAM plant. The pathway of photosynthesis could change between CAM and C3 pathway with variations of environmental factors. The difference of CO2 exchange patterns in D. officinale among sunny, cloudy and rainy days depended mainly on changes in light intensity, humidity and air temperature.

The seasonal changes of soil urease activity appeared to produce single-peaked curves in Leymus chinensis, Puccinellia tenuiflora and Chloris virgata communities in the Songnen meadow. The activity became gradually lower with increasing depth of soil layers. Soil urease activity of the 0-10 cm layer had a power-function correlation to rainfall (monthly mean value) and an exponential correlation to soil temperature, which showed that urease activity was deeply influenced by water and heat factors. Path analysis between urease activity and soil physical-chemical factors showed that urease activity was the result of interactions among soil physical-chemical factors, and each factor acted differently in the three communities. In the L. chinensis community, soil physical-chemicalfactors affecting urease activity decreased in the order of pH > organic matter > available N > C/N ratio > soil bulk density > total N > available P. In the P． tenuiflora community, the order was organic matter > C/N ratio > total N > soil bulk density > available P > available N > pH. In the C． virgata community, the order was total N >organic matter> available N > pH > C/N ratio > available P > soil bulk density. The dominant influencing factors were also found in the three communities through stepping multi-regression. They were organic matter and pH in L． chinensis community, organic matter and soil bulk density in P．tenuiflora community and total N in C．virgata community, which showed that organic matter was the base of soil urease activity. Principal component analysis of the soil fertility indicated that the contribution of or ganic matter, total N, available N, C/N ratio and soil bulk density accounted for the most part, while the contribution of urease activity was low. That is why the soil urease activity of the C．virgata community, which grew in the barren region, was higher than that of the L．chinensis community, which grew in the fertile region in the Songnen meadow. Although the soil urease activity was remarkably correlated with most of the soil physical-chemical factors, it only dealt with the nitrogen transformation among many soil nutritional element transformations. Therefore, soil urease activity does not completely reflect the conditions of soil fertility but is only an assistant index for evaluation.

The carbon cycle of restoring steppe in degraded land is one of the important parts of the global terrestrial carbon cycle. The study of soil respiration in restoring steppe plays a very important role in accurately evaluating the carbon budget of restoring steppe and its function in the global carbon budget. As we know, temperature and soil water content are two important environmental factors in understanding the soil respiration process in terrestrial ecosystems. To quantify their allocation and the relationship between soil respiration and temperature and soil moisture, we conducted field experiments to investigate soil respiration from June to September 2001. The effects of heat and water factors on soil respiration of restoring Leymus chinensis steppe in degraded land was studied at Baiyinxile pasture (43°55′N, 116°31′E, with an altitude of about 1 200 m) in Inner Mongolia. This region, un-grazed in June, has a typical temperate and semi-arid climate and the community structure of the vegetation consisted mainly of two species, Leymus chinensis and Stipa grandis; the soil type was classified as chestnut. Daily variation was investigated by taking measurements once an hour from 6∶00 to 19∶00 every ten days during the whole growing season using an enclosed chamber method. The results indicated that environmental factors affecting soil respiration ranged as soil water content > temperature, and the soil water content in the upper 10 cm of the soil was of real significance in all of the environmental factors. We analyzed the relationship between daily average soil respiration rate (6∶00-19∶00) and daily average soil water content (%) using the partial correlation analysis of the SPSS and the coefficients showed that soil water content of 7.5% and 18.4% were two thresholds affecting the soil respiration rate. Soil water content could be divided into three levels: <7.5%, 7.5%-18.4% and >18.4% based on their effects on soil respiration. When soil water content was less than 7.5%, soil temperature was the dominant factor of soil respiration. Soil respiration (Rs) could be expressed as an exponential relationship with soil temperature (t) at the depth of 5 cm and their relationship was Rs=4.07t1.098 (w<7.5%, R2=0.49, n=80, p<[KG-*2]<0.01). When soil water content was more than 7.5%, soil respiration was affected by soil temperature (t), soil moisture (w)and the interaction of the two, and their relationship was Rs=-147.693+5.11w+6.012t+1.214wt (w>7.5%, R2=0.81, n=69,<[KG-*2]<0.01). When soil water content was close to the water wilting coefficient, about 6.0%, plant root respiration had few contributions to soil respiration. When soil water content was more than 7.5%, soil respiration mainly comes from the metabolism and other living activities of the plants and microbes. Thus, the contributions of soil and plants respectively to soil respiration might be explained from environmental factors. This research will help to develop soil respiration models and to understand accurately the carbon budget of terrestrial ecosystems. Our research implied that drought in the growing season in the year of 2001 tended to reduce the soil respiration rate but temperature did not. There were only three times when the soil water content was more than 18.4%, and so, because of the limitation of the data, the threshold of soil water content of 7.5% must be verified in future of experiments.

The practicability of edge effect research with FTIR (Fourier transform infrared spectroscopy) was investigated by two experiments. In the first, Davidia involucrata seedlings were treated with nitrogen fertilizer and nitrogen content of both tip and middle parts of seedling leaves was detected with FTIR and the method of Kjeldahl. The results showed that there were significant differences in nitrogen content among five treatment levels, either between tips or between middle parts of leaves. The nutritional status could be well estimated by leaf tips in terms of nitrogen content compared with that of middle parts of leaves according to correlation analysis. Spectral index （A1653-A3400）/（A1653+A3400） was revealed to be raised with the increase in availability and of leaf content of nitrogen, which suggested that it is possible to detect the nutritional status of D. involucrata seedlings in terms of nitrogen content by FTIR. In the second, D. involucrata leaves were collected from four aspects in Bainigang, Wolong National Nature Reserve. Tips of the leaves were analyzed with FTIR. The edge effects of nitrogen status of D. involucrata in Bainigang in terms of FTIR showed that the nitrogen levels rose from border to core areas of the forest within certain distance and the average nitrogen levels varied among different aspects and distances to different extents. It suggested that the nitrogen status of D. involucrata was significantly affected by aspect. The D. involucrate fragmentation of forest would impact the regular physiology of internal trees growing at least 30 to 40 meters away from the fragmented border. The impacts were at least 90 to 100 meters from the edge. It suggested that the growth of remaining D. involucrata was impacted seriously by human activities in the east of the forest. The results were consistent with those of previous studies of nitrogen distribution and plant nitrogen absorption at the forest edge. It showed that studying edge-effect of D. involucrata with FTIR is practicable. In our experiments, we discovered that accurate results require that the sample must be kept dry and flat.

Polyamine (PA) plays an important role in the regulation of senescence and stress-resistance of plants. It has been reported that PA accumulated, and the activities of PA-associated enzymes, involving polyamine oxidase (PAO), increased rapidly in leaves under drought stress. However, little is known about the effect of drought stress on PA metabolism of roots. In the present experiment, two wheat cultivar seedlings with different drought-resistances (Triticum aestivum L. cv. Jinmai 33 and Wenmai 8) under sand-cultivation were used to study the relationship between PA metabolism and drought-resistance. The results showed that the relative water content (RWC) of leaves declined gradually during drought stress (without water supply) compared with controls (with water supply during treatment), and the cv. Wenmai 8 (drought-resistant cultivar) could maintain more leaf RWC than cv. Jinmai 33 (drought-susceptible cultivar) after 48 h of drought stress. The PA (Put, Spd, Spm) content and PAO activity in roots and leaves of seedlings increased quickly during drought stress for 12 h. At this time, the contents of putrescine (Put), spermidine (Spd), spermine (Spm) in drought-treated seedlings of cv. Jinmai 33 were 86%, 69%, 50% higher than control in roots, and 71%, 18%, 11% higher in leaves, while in cv. Wenmai 8 these were 91%, 103%, 85% higher in roots, and 78%, 55%, 53% higher in leaves than control, respectively. The change of PAO activity between two cultivars differed, PAO activity in roots and leaves of drought treated seedlings were 47%, 40% in cv. Jinmai 33, and 26%, 10% in cv. Wenmai 8 higher than their control, respectively. Afterwards, the PA (Put, Spd, Spm) content and PAO activity in roots and leaves of seedlings in two cultivars all decreased, which PA did in a slower rate in cv. Wenmai 8. The Put content and PAO activity in roots and leaves of both cultivars, and the contents of Spd and Spm in cv. Jinmai 33 under drought stress, were significantly lower than their control, whereas the Spm and Spd contents in cv. Wenmai 8 were similar with control during drought stress for 48 h. The changing trends of PA content and PAO activity in roots and leaves were similar. A significant positive relationship in PA content and PAO activity was found between roots and leaves. It is suggested that the rapid accumulation of PA might be a signal responding to drought stress at first, and then the higher contents of Spm and Spd in roots and leaves could enhance drought-resistance in wheat seedlings.

Abies chensiensis, an endangered plant mainly distributed in Qinling Mountains and Dabashan Mountains, was listed as one of national protected plants at second category in China. There have been no reports about the study of seed germinating characteristics of A. chensiensis until now. The objectives of this study were to 1) identify whether cold stratification was effective for breaking the dormancy of A. chensiensis seeds and find out the optimum duration of cold stratification; 2) determine the optimal temperature for germination and whether alternating temperatures affected germination; 3) test whether germination was affected by light; 4) choose the better germination texture between silver sand and filter paper.The 1 000-seed weight of A. chensiensis was (33.92±1.01) g, which was higher than other fir seeds. The viability of seedlot was tested by TTC (1.0 %). The results of seed dissection, reflecting the high seed abortion, showed that the percentages of viable seeds, empty seeds and shrunken seeds were 26.00%, 20.50% and 33.75%, respectively. Germination tests were performed to determine the effects of cold stratification (4 ℃ for 0, 14, 21 and 28 days), temperatures (two constant temperatures 20 ℃, 25 ℃ and an alternating 20-30 ℃), light (in light of 8 h·d-1, 100μmol·m-2·s-1 and in darkness) and germination textures (filter paper and silver sand) on germination rate. The results showed that cold stratification could increase seed germination percentage and germination energy; the longer the duration of cold stratification, the higher the germination rate; but the percentages of germination energy did not increase if the duration was longer than 21 days. 25 ℃ was not better for the seed germination percentage, but was better for germination energy than the other two temperature regimes, because a 9-day treatment showed 90% of the biggest germination percentage in 25 ℃; and the alternating 20-30 ℃ did not increase the germination percentages of the seeds of A. chensiensis. Compared with those in darkness, light (8 h·d-1, 100μmol·m-2·s-1) did not increase germination percentages, although it did increase germination energy; light was not indispensable for germination of A. chensiensis seeds, but did accelerate the process of germination. Great differences were found for germination percentage and germination energy in two germination textures; the percentages of germination and germination energy on silver sand were 19.75% and 16.75% respectively, but 8.00% and 6.00% on filter paper. The result showed that the silver sand was a better germination texture for A. chensiensis seeds than filter paper, perhaps because silver sand could offer more sufficient water for the germination of bigger seeds such as A. chensiensis than filter paper.

The influences of different concentrations of ASP and SMZ-TMP on seed germination of soybean (Glycine max) were studied. The results indicated that the germination percentages, vigor index and root development were increased by presoaking the seeds in ASP and SMZ-TMP solutions. The optimal concentrations of ASP and SMZ-TMP soaking solutions are 50 mg·L-1 (24 h) and 62.5 mg·L-1 (12 h), respectively. The results also showed that the relative conductivity of soybean seedlings was decreased by ASP soaking pretreatment, while scavenger enzymes were increased. Seed protein and amino acid content were increased by SMZ-TMP soaking pretreatment.

Potamogeton pectinatus is a perennial submerged aquatic macrophyte with a parvopotamid growth form. It inhabits many different environments from the south to the north in China. According to observation in Dianchi Lake, P. pectinatus is a tolerant species with wide ecological amplitude and can survive in heavy polluted waters. Presently, Dianchi Lake has been seriously polluted. Cyanobacteria blooms were serious, which led to a low transparency. While the other submerged aquatic macrophytes have disappeared, this species still occurs in Dianchi Lake. This suggests that P. pectinatus must possess various survival strategies being worthy of further research. Reproduction is a key factor influencing survival, distribution and dynamic variation of community structure. In this paper, reproduction diversity of P. pectinatus was studied through experiment and observation in situ. The results showed that pollination of P. pectinatus is by way of bubble enveloping for flowers that are underwater and pollen floating when flowers are at the water surface in sexual reproduction. The fruit-set efficiency in P. pectinatus that are underwater was low, being only 6.41%, compared to 24.38% of flowers reaching the surface. Seed number of P. pectinatus in exposed, and sheltered or pond sites is 794, 1 627 and 2 140 per square meter, respectively. Seed germination rate of P. pectinatus was under 6% in Dianchi Lake. As a result, sexual reproduction is not important to regenerate populations of P. pectinatus. This species also possesses an extensive and effective system of asexual reproduction, through shoot fragments, rhizomes, stem tubers, root tubers and axillary shoot regeneration. The populations of this species are mainly produced from the root tubers and rhizomes. Asexual reproduction has a large contribution to population restoration during the next growth season. The main function of the seeds appears to be dispersal and long-term survival of the species. In addition, some suggestions for aquatic vegetation restoration by this species were put forward according to the results of experiment and observation.

Ligularia virgaurea has become a dominant weed in degraded rangeland of alpine meadow because of over-grazing and the selective feeding habit of livestock. Its coverage has risen from 5%-20% in the 1970s to 20%-50% at present. Since knowledge of the growth, development, reproduction and dispersal characteristics is lacking, we have no good ways to prevent its spread and eradicate it. Therefore, researching the features of seed production of L. virgaurea in natural populations, the principles of sexual reproduction in this species, and the variation in degree and reason of seed size within habitats, individuals and different positions of capitulum intra-inflorescence has important applicable value and theoretical implications. The material we studied was collected from Nima (101°53′E, 35°58′N, altitude 3 500 m) in Maqu county, Gansu province, North-east region of Qingzang Plateau. The plot is in an area with different degrees of degradation. This region belongs to the alpine meadow rangeland type. L. virgaurea is a perennial herb of Compositae: its common inflorescence lies at the top of stem and it consists of capitula that bloom from top to bottom. It can also clone through rhizomes. After maturation of L. virgaurea seed, 10-16 quadrats per plot were set up, from which 1-3 seed producing ramets per quadrat were sampled, and brought to the laboratory. The vegetative structure and reproductive structure were separated, heated for 24 hours at 75 ℃ for drying over, and weighed with an electronic balance (g/10 000). The biomass of ramets, common inflorescence, seeds and capitula of different positions of the common inflorescence were measured; the numbers of capitulum and seed per common inflorescence, and capitate seed numbers of different positions in the common inflorescence were amounted. The data were analyzed through ANOVA and linear regression. The measurements taken were: the size of ramet and common inflorescence represented by their dry weight of biomass (common inflorescence biomass means the dry weight of section from the first available capitulum in the bottom to the top of common inflorescence); the available capitulum of the top, middle and bottom representing separately the first of the top, the 1/2 position of common inflorescence and the last of the bottom; the percentage produced seed of the common inflorescence in every plot (setting percentage per plant); capitulum percentage (setting percentage per inflorescence); mean seed weight (seed weight of common inflorescence per plant/ its number that amplified 100 times). Mean seed number is the number of seeds per common inflorescence per plant. Capitula number and mean seed number per capitulum were also calculated.The results show: 1) the seed production of L. virgaurea was affected by habitats not only at a population level but at the capitulum level of the same position (such as top or middle or bottom) within common inflorescence, and shows definite trends; for example, floodland＞lowland＞hillside, and in the same habitat, lower population densities＞higher one, lower vegetational coverage＞higher one except for lowlands. 2) except for the seed mean weight, there was a highly positive correlation between the seed number or seed weight and common inflorescence size or capitate number or individual size, but there was no correlation with individual densities. 3) the trend (top＞bottom) of seed production among the different positional capitula within the common inflorescence was not influenced by the factors of habitats and population densities. 4) position-based seed production may be caused by blooming time series of the different positional capitula within the common inflorescence. This inherent mechanism may ensure early developing capitula can gain more resources from the resource pool than later developing ones.

Artemisia halodendron an important semi-shrub used for preventing drift-sand and sand storms, degraded significantly in the desert succession series from shifting sandy land to fixed sandy land in the Horqin Sandy Land. In order to find one of the vital reasons of its degradation, growth and distribution of absorbent roots (fine roots, diameter<1 mm) of A. halodendron in relation to soil moisture were studied in shifting sandy land and fixed sandy land with trench and root augur methods. Differences between distribution (0-90 cm depth) of its absorbent roots before a raining period and that after the raining period were compared. 1) In the dry season, soil moisture in the rhizosphere increased with depth. It increased much more in shifting sandy land than in fixed sandy land. Soil moisture in the rhizosphere decreased with depth after the raining period. It decreased more rapidly in fixed sandy land than in shifting sandy land. 2) There was more dry weight of main roots in the 0-15 cm layer than in the other layers. This phenomenon was more obvious in shifting sandy land than in fixed sandy land. 3) In the dry season, there was a larger proportion of fine roots dry weight in 0-45 cm in fixed sandy land (84.9%) than in shifting sandy land (61.9%). In the rainy period, the dry weight of the fine roots of A. halodendron in 0-15 cm layer mounted up more rapidly than in the other layers. Furthermore, the fine roots of A. halodendron in shifting sandy land grew more rapidly than the ones in fixed sandy land. The reaction of the fine roots of A. halodendron to precipitation was less sensitive in fixed sandy land than in shifting sandyland, which was a disadvantage of amending of root’s distribution and sucking up of soil moisture.

Both interspecific association and interspecific segregation can be used to study the spatial affinity between different species. They are connected but different. Interspecific association is more related to habitat, while interspecific segregation more to small-scale effects and intra-/inter-specific interactions. Association is measured by plot sampling while segregation is measured by plotless nearest neighbor methods. Compared with interspecific association, few studies on pairwise segregation in a multi-species community have been reported. Meanwhile, clarifying the segregation relationship between different species pairs will be helpful for revealing the phenomena of the species interactions, community structure and community dynamics.With the aid of GIS software (ArcView), a distribution map of all trees with DBH ≥1cm from a tropical rain forest community at Bawangling National Nature Reserve in Hainan Island was drawn. The nearest neighbors of each individual and the distances between every indivi

Diagnosis of degradation degree of ecosystems is the basis and the precondition of ecological restoration. Currently, the diagnosis of degradation degree of ecosystems is at the qualitative level. It is an urgent and key issue in the field of restoration ecology theory and ecological restoration practice to diagnose the degradation degree of ecosystems quantitatively. A series of questions about diagnosis of degradation degree of ecosystems was discussed systematically in this paper by summarizing former studies, and a conceptual model of the degradation degree of ecosystems was pictured. The conceptual model is the basis of diagnosis of degradation degree of the ecosystem and upholds the viewpoint that many thresholds determined by the comprehensive effects of different factors may be involved in the process of ecosystem degradation. To certain extent, the scale of understanding of the process of ecosystem degradation with this model is less than that with previous models. “Natural ecosystem” characterized by little disturbance from human beings or nature was suggested to be a reference ecosystem of diagnosis of the degradation degree of the ecosystem; we provided a transformation model of ecosystem structure and function followed over time, modified from Bradshaw (1997).The ways of expression of degradation degree of ecosystems were classified into three types, the third type of expression was encouraged in the relative study and practice because the third bridges the relationship between the degradation degree of ecosystem and ecosystem succession. Diagnostic approaches were presented as follows: biological approach, habitat approach, eco-process approach, ecosystem function/service approach, landscape approach. Diagnostic methods were classified into single approach and single factor diagnostic methods, single approach and multi-factorial diagnostic methods, and multi-approach comprehensive diagnostic methods. The possible indices (system) about diagnosis on degradation degree of ecosystem were analyzed. The strategies and steps for diagnosis of degradation degree of an ecosystem were provided by a case analysis. Some critical points during diagnosis of the degradation degree of an ecosystem and ecological restoration were discussed. We suggest that the study of comprehensive diagnosis of degradation degree of ecosystems should be strengthened.

Environmental pollution has become more and more serious in recent years, and much attention has been paid to its effects in soil-plant systems. Phytoremediation, a technique using plants to remove contaminants from soil and water, has become a hot topic in the last decade due to its environmental safety and potential cheapness. It can clean up heavy metals and organic contaminants in the environment in four major ways: phytoextraction, rhizofiltration, phytostabilization and phytovolatilization. Numerous studies and several reviews have been made on phytoremediation of contaminated environments, but reviews on the role and the mechanism of root exudates in phytoremediation of contaminants are few. Here we sum up the varieties of root exudates and discuss the internal and external factors influencing the exudation of plant roots. These factors include plant species, nutrient and heavy metal stresses, rhizosphere, soil microbes and others. The roles of root exudates in phytoremediation of heavy metals and organic pollutants are also reviewed and illustrated by some case-study examples. In general, root exudates can affect metal absorption by plants through changing the physical and chemical characters of rhizospheres. The modes of root exudates in removing heavy metals vary in a broad range, for example, by modifying the pH of the rhizosphere, chelating, complexting and depositing with heavy metals, altering the numbers and the activity of rhizospheric microbes. Through these ways, root exudates can change the chemical existence of heavy metals, increase their bio-availability, activate soil microbes and reduce the environmental dangers. While removing organic contaminants in the soil, the ecotoenzymes in the root exudates may degrade pollutants directly, or degrade them indirectly by stimulating the activity of rhizospheric microbes (which is considered to be the dominant process). Root exudates do play a key role in phytoremediation on contaminated sites. Future research should focus on seeking and screening certain specific plants with high bioproduction and excellent efficacy, especially developing hyper-accumulators, and testing their efficiency in removing heavy metals or organic pollutants by lab and/or field trials. Emphasis should also be laid on process-oriented correlations between contaminants and root exudates of these plants. If so, more effective approaches to ecological restoration of polluted soils can be developed and put into practice. For instance, we can attempt to plant various kinds of plants, especially already-known hyper-accumulators on a large scale on contaminated sites, and supplement treatment with additional forestry practices such as coppicing, to enhance the efficiency of phytoremediation by speeding up the processes of bioremediation. The important ecological contribution and wide perspectives in field application of root exudates provides an entirely new research area. A combined and integrated study of pollution ecology and chemical ecology, and new findings and breakthroughs, are to be expected.