Abstract:It is to review the sources and contributions of anthropogenic nitrogen into water bodies, to summary the relationships between nitrogen concentrations in water bodies and human factors, and to highlight the general trends of the nitrogen levels in different times.

Abstract:Cessation of grazing is an important management practice in restoration of grassland ecosystem productivity and function. However, little is known about the effects of long-term exclusion of grazing on soil bacterial community structure and diversity in grassland ecosystems. This study utilized three grassland sites over two consecutive years (2004 and 2005) in a semi-arid Inner Mongolia steppe; there were a free grazing site (FG), fenced site since 1999 (UG99) and fenced site since 1979 (UG79). Soil moisture content, organic carbon (C) and nitrogen (N), NH₄⁺-N and NO₃^--N concentrations were measured across the treatments. Bacterial community structure and diversities were assessed with PCR amplification of genomic DNA extracted from soils and following denaturing gradient gel electrophoresis (DGGE) separation. Results showed that the UG99 soil had higher moisture, organic C, organic N and NH₄⁺-N concentrations than the other soils. Principal components analysis of DGGE patterns showed that soil bacterial community structure sampled in 2004 was different from that in 2005, and the UG99 soil was significantly different from the FG and UG79 soils across the two consecutive years. In addition, the UG99 soil had significantly higher bacterial diversity and evenness compared with the FG and UG79 soils. These results indicate that long-term exclusion of grazing decreases bacterial diversity, which has significant implication for grassland ecosystem management.

Abstract:Pomacea canaliculata (Lamarck) is an invasive snail species that has become a serious pest of rice and other hydrophytes. Usually it is aquatic but likes to lay its eggs higher than the waterline. In order to seek a feasible and efficient way to control the egg hatchling of this pest, here we systematically studied the effects of water spraying and submersion on its egg hatchling rates and durations. Our results demonstrated that water spraying and submersion could dramatically decrease the hatchling rates to maximal 5.8% and increase the hatchling duration up to 26.4 days on P. canaliculata. Not only the beginning time of water treatment, but also the frequencies of the water spraying is critical to control the hatchling rate and duration of P. canaliculata. Water submersion that began in 12 h after the eggs laid and lasted at least 48 h will significantly decrease the snails’ hatchling rates and extend the hatchling time. In addition, compared to spraying, the water submersion could achieve more remarkable effects. The capsule of the snail’s egg is able to withstand the water treatment. Based on our water spraying and submersion results, it can be inferred that 0–6 h after egg being laid, egg capsule precipitates are beginning to form, and this process will complete after 12–24 h. This special breeding characteristic of P. canaliculata makes the physical control by water treatment become feasible.

Abstract:The vertical biomass allocation patterns of roots grown under standardised conditions were determined for species representing the major New Zealand indigenous grass genera Chionochloa and Festuca. Ten ramets, each of 2–3 tillers from garden collections of each species were grown in irrigated vertical sand columns in a glasshouse, and harvested after 168 days. Chionochloa teretifolia, Chionochloa macra, and Chionochloa crassiusucula, characteristic of alpine environments failed to produce new roots and died. However, most of the Chionochloa taxa (Chionochloa beddiei, Chionochloa pallens, Chionochloa rigida ssp. rigida, Chionochloa rubra ssp. cuprea, Chionochloa vireta), developed extensive new roots that reached the base of the one metre sand column. Roots of Chionochloa cheesemanii and Chionochloa conspicua reached 80–90 cm depth. Two Festuca taxa (Festuca actae, Festuca luciarum) had roots to 1 m depth, and roots of Festuca coxii, Festuca matthewsii ssp. latifundii, Festuca matthewsii ssp. matthewsii, Festuca multinodis, and Festuca novae-zelandiae grew to 70–90 cm depth. The edaphic specialists (Festuca deflexa, Chionochloa spiralis, Chionochloa defracta) were all shallow rooting.
Species of Festuca maintained at least 40% of the root mass in the upper 10 cm of the column and most of the Chionochloa taxa had less than 40% of root mass in the upper zone. Genotype level variation in root mass less than 10 cm deep was greater in Chionochloa than in Festuca, and least in the edaphic specialist grasses.

Abstract:Maintaining the stability of ecotone is a potential way to stop the expansion of arid areas, but little has known in many key arid ecotones. This study aimed to understand the responses of endemic species to drought conditions in an arid ecotone. A controlled experiment with different drought stress treatments (80%, 40% and 20% field water capacity (FC)) on two endemic species (Salix paraqplesia and Hippophae rhamnoides) was arranged in the ecotone between the Minjiang dry valley and mountain forest. Drought stress dramatically reduced the height, basal diameter, leaf number, biomass production and the accumulations of C, N and P of both species. An increase of belowground proportion was observed indicating higher root/shoot ratio under drought stress conditions, and drought further increased N and P use efficiencies and intrinsic water use efficiency (WUEi). Compared with S. paraqplesia under medium drought stress (40%FC), H. rhamnoides showed less change of morphology characteristics, higher P use efficiency, and WUEi due to better N sources. However, S. paraqplesia showed higher N use efficiency and WUEi under severe drought stress condition (20%FC) than H. rhamnoides. The results suggested that the expanding dry valley could seriously influence endemic species in the ecotone, and N-fixing plant such as H. rhamnoides could adapt to moderate drought stress better than non-N-fixing plant.

Abstract:An aeropalynological study was preformed in Chongwen district of Beijing, China during one year (from 21, March 2006 to 20, March 2007). A total of 1670 pollen grains from 37 taxa were identified. Two separate peaks of airborne pollen occurred during one year: one was related to the presence of the trees/shrubs pollen (Cupressus L., Pinus L., Populus L., Betula L., Corylus L., Salix L., Juglans regia L., Fraxinus L., Anacardiaceae and Livistona chinensis (Jacq.) R.Br.) in March, the other was attributed to herbaceous pollen (Artemisia L., Chenopodiaceae, Gramineae, Humulus L. and Labiatae) in September. Only a few pollen grains were found from December to next January. Results indicated that airborne pollen composition was consistent with the vegetation components and the pollination periods of the plants in the sampling site. The variations of pollen numbers were affected positively by temperature, negatively by relative humidity and precipitation. Stable wind speed seemed to have little effect on the fluctuation of the pollen number during the study period.

Abstract:The evaluation of microbial molecular diversity has been mainly based on the extraction of total DNA from environmental samples. The indirect extraction methods, which have been used for prokaryotes, have never been used to recover soil microeukaryotic DNA. We evaluated the efficiency of an improved indirect DNA extraction protocol developed herein and the direct lysis (the sodium dodecyl sulfate (SDS)-based method and commercial DNA extraction kit) on estimating the molecular diversity of soil microbial eukaryotes. DNA quality and quantity as well as denaturing gradient gel electrophoresis (DGGE) profiles were determined using three soil samples from different stations. The indirect method detected the highest DGGE bands in spite of the low DNA yield. The commercial kit detected a lower number of DGGE bands than the indirect method. The SDS-based method produced the lowest DGGE bands and DNA purity but the highest yield. Using the indirect method, we further evaluated the effect of freezing and air-dried preservations on estimating the microeukaryotic diversity. In spite of the low DNA yield obtained from the air-dried preservation, no significant differences were found in either the number of DGGE bands or the DNA purity between two manners. Our results indicate that the improved indirect method could obtain a high purity of intracellular DNA and high efficiency in the estimation of molecular diversity of soil microbial eukaryotes.

Abstract:Analyzing daily air temperature and precipitation observed during 48 years from 1958, we quantified changes in temperature and precipitation with year in Kherlon River Basin of semiarid northern China. In addition, the relationship between the dry biomass measured 23 years from 1983 at a grassland and the corresponding temperature accumulated for higher temperature than 5 °C (AET) and precipitation accumulated after 1 April (CP) was determined. It was estimated that the annual mean air temperatures during non-growing season (October to April) and growing season (May to September) had significantly risen during 50 years from 1958 by 2.38 °C and 1.83 °C, respectively. The year-to-year variation in the annual mean air temperature had a tendency to increase with year during the 48 years. Changes in annual precipitation and precipitation days for any of the entire year (January to December), growing and non-growing seasons with year were not significantly observed. Both the AET and CP (especially CP) during the growing season affected the biomass growth in the semiarid grassland. Prediction of seasonal changes in meteorological tendency as well as that of climate change is important to maintain the production in semiarid grassland and to conserve the plant community and landscape.