THE THERMAL-STABILITY OF POLYETHYLENE BLENDS DURING HEAT-PROCESSING AND SHORT-TERM PHOTOOXIDATION

The melt flow behaviour of LDPE/HDPE blends with various compositions have been determined by melt flow index (MFI) measurement. The effects of stabilizers, photo-sensitizers, multiple extrusions and short-term photooxidation have been studied. The results show that there is no marked thermal stability difference between homopolymers and blends without multiple extrusions, no matter whether stabilizers or photo-sensitizers are added. Multiple extrusions or photo-sensitizers reduce their thermal stability, shown by the decrease in MFI. The decrease in MFI of photooxidized samples does not imply serious structural change and shows that the active species formed during photooxidation induce a crosslinking reaction in the melt indexer. Multiple extrusions increase the number of active species formed in LDPE or blends and lead to an obvious decrease in MFI. It is suggested that LDPE and LDPE-rich blends after short-term photooxidation can be characterized by MFI measurement. In contrast, HDPE cannot be characterized by this method due to its linear structure.

Studies on hybridization effects of different geographic populations of Chlamys farreri - II. The medium-term growth and development of Chlamys farreri populations from China and Russia and their reciprocal crosses

Based on the research of juvenile (2, 3, 4 months) growth and survival of three populations of two different geographic areas in Chlamys farreri from Russian and China and their F, hybrids derived from Chinese cultural population (CC) female x Russian population (RW) male, Chinese wild population (CW) female x Russian population (RW) male, Russian population (RW) female x Chinese wild population (CW) the study of the medium-term (6, 8, 10, 12 months) growth and development of Chlamys farreri was carried out. The four determined results indicated that there existed different extent heterosis (3% similar to 52 %) for the growth in three types of F-1 hybrids, and the offspring derived from CC female X Rmale had a stronger heterosis among the crosses at the medium-term; the uptrend among traits are wet weight > shell width > shell length > shell height, Chinese cultural population could be recognized as excellent parent, and seasonal variations influence very much on the daily increment and growth rate of each trait of Chlamys farreri and it is only able to survive and could barely grow in winter (6 similar to 8 months), but grows fast in temperate season (10similar to12 months).

Temperature tolerance of young sporophytes from two populations of Laminaria japonica revealed by chlorophyll fluorescence measurements and short-term growth and survival performances in tank culture

The cold-water subtidal brown alga Laminaria japonica has been commercially fanned in the Far East and has been on top of all marine-fanned species in terms of farming area and annual output worldwide. The successful trials of transplantation of young sporophytes from the north to the south in winter along the Chinese coast in the 1950s led to the spreading of cultivation activities down to a latitude of 25-26 degrees N. Up to today, nearly 50% of the annual output of this farmed alga, as a cold-water species, comes from the sub-tropical south in China. The demand to have high-temperature-tolerant strains/ecotypes in farming area calls for a practical method to judge and select the desired parental plants for breeding programs and for seedling production. In this paper, we report our results on using chlorophyll fluorescence measurement and short-term growth performance in tank culture to estimate the temperature tolerance of offspring from two populations, Fujian Farmed Population (FFP) sampled from Fujian province (latitude: 25-26 degrees N) in subtropical area and Qingdao Wild Population (QWP) sampled from Qingdao (latitude: 36 degrees N). Contrary to what has been usually thought, the results revealed that offspring from Qingdao wild population in the north showed better performance both in short-term growth and survival rates and in optimal quantum efficiency (F-v/F-m) when exposed to higher temperature (20-25 degrees C). This result was further confirmed by fluorescence quenching analysis. QWP distributed along the southern distribution limit at a latitude of 36 degrees N in the Pacific west coast is thus taken as a more ideal one than the fanned population in subtropical region as a source of parental plants for breeding high-temperature-tolerant varieties. (c) 2006 Elsevier B.V. All rights reserved.

Short-term morphological changes after sand-digging during a sand sculpture activity

The morphology of the beach backshore and foreshore at Huiquan Bay, Qingdao, China, is characterized by a single intertidal sandbar system with a spring tide range of 4.59 m. The beach was measured with a laser total station of Leica TPS402. Contours of the beach were generated using data collected in March and November 2005. The survey method provided 2 mm measuring accuracy and 4-10 m horizontal spacing. The net accretion volume of the foreshore was about 11, 215 m(3) from March to November. After sand sculpture activity, the axis of the sand trough migrated onshore from about 3.5 m to 17.5 m on the foreshore beach in November. At the same time, the axis of the sandbar crest migrated onshore no more than 42.25 m on the northwest foreshore; and it migrated offshore no more than 23.75 m on the southeast foreshore. On the northwest and southeast foreshore beach, two strips of erosion areas with a thickness of 0-0.2 m appeared on the sandbar crest. Accretion occurred at the bottom of the sand trough with a thickness of similar to 0.2-0.6 m. The sandbar height decreased after sand sculpture activity, and it was no more than 0.7 m in March and 0.6 m in November. Human activities, such as sand digging on the sandbar crest during sand sculpture activity, also can disturb the beach morphology of intertidal bar systems. This phenomenon also was validated by comparison of beach morphology, the results of a color artificial tracer experiment and a sediment transportation trend prediction.

Long-term ecological interactions between nutrient and phytoplankton community in the Changjiang estuary

Both nitrate (NO (3) (-) ) and soluble reactive phosphate (PO (4) (3-) ) concentration in the freshwater end-member at the mouth of the Changjiang River have increased dramatically since the 1960s. Within the same period in the sea area, with surface salinity > 30, NO (3) (-) concentration has shown an obvious increase, PO (4) (3-) has not changed greatly and dissolved reactive silica (SiO (3) (2-) ) has deceased dramatically. An examination of the elemental ratio of NO (3) (-) to PO (4) (3-) at the mouth of the Changjiang River did not show a systematic trend from the 1960s to 2000s largely because both nutrients increased simultaneously. In comparison, the elemental ratio of dissolved inorganic nitrogen (DIN) to PO (4) (3-) in surface seawater, with salinity > 22, has shown a clearly increasing trend. Furthermore, an overall historical change of the SiO (3) (2-) :PO (4) (3-) ratio has undergone a reverse trend in this area. Based on the changes of SiO (3) (2-) :PO (4) (3-) and DIN:PO (4) (3-) ratios, we can conclude that an overall historical change of SiO (3) (2-) :DIN ratio has decreased in this area from the 1950-1960s to 2000s. The argument that phytoplankton productivity in the Changjiang estuary has been enhanced by increasing nutrient input from the riverine transport was supported by these results. A comparative study analyzing the shift of phytoplankton composition from the mid-1980s to 2000s was also made. The results indicated that the average yearly percentage of diatom species in the Changjiang estuary has decreased from 84.6% during 1985-1986 to 69.8% during 2004-2005. Furthermore, the average yearly percentage of diatom abundance in the Changjiang estuary decreased from 99.5% during to 75.5% over the same time period, while the abundance of dinoflagellates has increased dramatically, from 0.7% to 25.4%.

Extension of life span and improvement of vitality of Drosophila melanogaster by long-term supplementation with different molecular weight polysaccharides from Porphyra haitanensis

Polysaccharides isolated from Porphyra (porphyran) have been known to have diverse biological activities, including immunomodulatory and antioxidant activities. The molecular weight-antiaging activity relationship of degraded porphyrans was examined in this study. Natural porphyran was extracted from P. haitanensis, and then was degraded into different molecular weight fractions, P1 molecular weight 49 kDa, P2 molecular weight 30 kDa, P3 molecular weight 8.2 kDa, by free radical. The influence on life span and vitality of porphyrans were carried out on Drosophila melanogaster. We found that all the degraded porphyrans and natural porphyran (P), added daily to the diet, can significantly increase the life span of D. melanogaster, except for P3. Among them, P1 exhibited the most prolonging life span activity. Furthermore, vitality of middle-aged flies (assessed by measuring their mating capacity) receiving porphyrans was increased considerably in comparison with the controls. Finally, in the heat-stress test, we observed a remarkable increase in survival time, especially in P3-diet groups. These results suggest that porphyrans may be effective in reducing the rate of the aging process and molecular weight has important influence on the effects. It seems that P1 and P2, possessed higher molecular weight, may be more useful in normal metabolic condition and P3, possessed the lowest molecular weight, may be more beneficial for D. melanogaster in stress condition. (C) 2007 Elsevier Ltd. All rights reserved.

Effect of long-term cryopreservation on physiological characteristics, antioxidant activities and lipid peroxidation of red seabream (Pagrus major) sperm

The aim of this study was to determine the effect of long-term cryopreservation on physiological characteristics, the antioxidant activities and lipid peroxidation of red seabream sperm which were respectively cryopreserved with 15% dimethylsulfoxide (Me2SO) for 1 month, 13 months, 26 months, 48 months and 73 months. The motility and fertility of post-thaw sperm decreased with the storage time going on. The highest motility (87.67 +/- 2.52%) was obtained in sperm cryopreserved for 1 month and the lowest (50.67 +/- 5.31%) was in sperm for 73 months. There were no significant differences (p < 0.05) in fertilization rates of sperm cryopreserved for 1 month (71.33 +/- 8.84%), 13 months (69.22 +/- 1.02%) and 26 months (60.33 +/- 2.33%); however, the sperm fertility decreased significantly for 48 months (47.22 +/- 3.89%) and 73 months (39.56 +/- 0.69%) storage. In addition, superoxide dismutase (SOD) activities of sperm were at a stable level for less than 26 months storage, then, decreased significantly after 48 months storage. Catalase (CAT) activities of sperm cryopreserved for 13 months, 26 months, 48 months and 73 months were significantly lower than that for 1 month. There were no significant differences in the malondialdehyde (MDA) level of sperm for less than 13 months storage. After 26 months storage, the concentration of MDA increased significantly, and the highest concentration (3.22 +/- 0.05 nmol/mgprot) was obtained in 73 months storage sperm. (C) 2010 Elsevier Inc. All rights reserved.

Vegetation Responses to A Long-term Grazing Intensity Experiment in Alpine Shrub Grassland on Qinghai-Tibet Plateau

在青藏高原中国科学院海北高寒草甸生态系统定位研究站对金露梅高寒灌丛草场植被开展了长期不同放 牧强度试验,分别在短期(4 年) 、中期(11 年) 和长期(18 年) 放牧阶段研究不同放牧干扰强度对草地植物物种多样 性、群落结构、地上生物量和草场质量的影响。研究表明,在不同放牧阶段,随着放牧强度增加植物群落的高度和 盖度都降低。在中期放牧干扰阶段,物种多样性指数和均匀度指数随着放牧强度增加呈现典型的单峰曲线模式; 在长期放牧干扰阶段,随着放牧强度增加,占优势地位的灌木和禾草被典型杂类草替代,其中的重度放牧干扰简化 了高寒灌丛植被群落结构,减少了地上现存生物量,特别是可食优良牧草生物量。植被对放牧的响应除了与放牧 强度和放牧时间阶段密切相关外,还与该地区水热条件的变化有一定的相关性。针对长期放牧干扰的反应特性可 将金露梅灌丛草场中植物划分为增加型、敏感型、忍耐型和无反应型4 种类型。除了丰富度指数、多样性指数和均 匀度指数外,其它一些特征参数并不支持著名的中度干扰假说。本研究发现,长期重度放牧促进了青藏高原高寒 草地退化,适度放牧有利于高寒灌丛草场的生物多样性保护和牧草利用;“取半留半”的放牧原则在青藏高原草场 放牧管理实践中值得推荐,它将有利于防止草场退化,提高牧草利用率和维持较高的生物多样性。

Response of Polygonum viviparum species and community level to long-term livestock grazing in alpine shrub meadow in Qinghai-Tibet Plateau

Grazing by domestic herbivores is generally recognized as a major ecological factor and an important evolutionary force in grasslands. Grazing has both extensive and profound effects on individual plants and communities. We investigated the response patterns of Polygonum viviparum species and the species diversity of an alpine shrub meadow in response to long-term livestock grazing by a field manipulative experiment controlling livestock numbers on the Qinghai-Tibet Plateau in China. Here, we hypothesize that within a range of grazing pressure, grazing can alter relative allocation to different plant parts without changing total biomass for some plant species if there is life history trade-offs between plant traits. The same type of communities exposed to different grazing pressures may only alter relative species' abundances or species composition and not vary species diversity because plant species differ in resistant capability to herbivory. The results show that plant height and biomass of different organs differed among grazing treatments but total biomass remained constant. Biomass allocation and absolute investments to both reproduction and growth decreased and to belowground storage increased with increased grazing pressure, indicating the increasing in storage function was attained at a cost of reducing reproduction of bulbils and represented an optimal allocation and an adaptive response of the species to long-term aboveground damage. Moreover, our results showed multiform response types for either species groups or single species along the gradient of grazing intensity. Heavy grazing caused a 13.2% increase in species richness. There was difference in species composition of about 18%-20% among grazing treatment. Shannon-Wiener (H') diversity index and species evenness (E) index did not differ among grazing treatments. These results support our hypothesis.

Short-term effect of targeted placements of sheep excrement on grassland in inner mongolia on soil and plant parameters

Grazing animal excrement plays an important role in nutrient cycling and redistribution in grazing ecosystems, due to grazing in large areas and return in small areas. To elucidate the changes to the soil and pasture caused by sheep urine, fresh dung, and compost patches, a short- term field experiment using artificially placed pats was set up in the autumn of 2003 in the Inner Mongolian steppe. Urine application significantly increased soil pH during the first 32 days in soil layers at depths of both 0 - 5 cm and 5 - 15 cm. Rapid hydrolysis of urea gave large amounts of urine- nitrogen ( N) as ammonium ( NH4+) in soil extracts and was followed by apparent nitrification from day 2. Higher inorganic N content in the urine- treated soil was found throughout the experiment compared with the control. No significant effects of sheep excrement on soil microbial carbon ( C) and soil microbial N was found, but microbial activities significantly increased compared with the control after application of sheep excrement. Forty- six percent of dung- N and 27% of compost- N were transferred into vegetation after the experiment. The results from this study suggest that large amounts of nutrients have been lost from the returned excrement patches in the degraded grassland of Inner Mongolia, especially from sheep urine- N.