Subtropical Area Of China Research Articles

AFLP analysis and zebra disease resistance identification of 40 sisal genotypes in China

Sisal is the most important fiber crop in tropical and subtropical areas in China and the world. Zebra disease is a serious threat to the main cultivar Agave hybrid No.11648 (H.11648) worldwide. To select germplasm materials with zebra disease resistance for breeding, the fluorescent amplified fragment length polymorphism (AFLP) technique was used to make a cluster analysis of the genetic relationships of 40 sisal genotypes grown in China, and Phytophthora nicotianae was used to inoculate the 40 genotypes to identify their resistance to zebra disease. As a result, the similarity coefficient among 40 sisal genotypes was found to be 0.44-0.83 and the 40 genotypes show different levels of disease resistance. According to the AFLP analysis, the disease resistance and chromosomal ploidy, it can be reasoned that, A. attenuata var. marginata, Dong 109, Nan ya 1 and A. attenuata are suitable for hybridization with H.11648 to breed a new disease-resistant variety.

Summer Thermal Environment Measurement and Analysis of Subtropical Campus

In subtropical areas of China, air temperature and relative humidity were relatively high in summer, as well as the solar radiation. In the university campus, students are relatively concentrated and have more outdoor activities. Hot and humid weather conditions may cause students uncomfortable and even heat stroke. Therefore, the influences of landscape design on thermal environment should be taken into account in the process of campus planning. In this paper, the field measurement of outdoor air temperature, relative humidity, wind velocity, heat radiation and integrated hot environmental indicator namely wet bulb global temperature were carried out around the Dong Lake in South China University of Technology in typical summer days. The impacts of design methods of water, tree, grass and floor on thermal environment were analyzed.

Responses of Earthworms to Organic Matter at Different Stages of Decomposition

This study was conducted to examine the responses of earthworms to soil organic matter and litter at different decomposition stages and their contributions in litter decomposition processes in southern subtropical areas of China. Two plantations were selected as the study sites: Site I was dominated by the exotic endogeic earthworm species Ocnerodrilus occidentalis; Site II was dominated by epigeic species Amynthas corticis. After the fallen litter and earthworms were removed or expelled, four treatments were set up as: reserving the top soil (0–5 cm, equal to H layer) (H), removing the top soil and adding fresh litter (Le), removing the top soil and adding semi-decomposed litter (Li), and a control with no top soil nor any litter (CK). Five randomized blocks that were enclosed with nylon nets on the top were set up in each site, and then the four treatments were arranged randomly in each block. After 2–3 months, earthworms were collected using the formalin method. The results showed that Ocnerodrilus occidentalis preferred Treatment H though it was found in Treatments Le and Li as well; Amynthas corticis preferred Treatment Li though sometimes it also appeared in Treatment H; and Amynthas sp., another epigeic species, was mainly present under Treatment Le and only appeared in Treatment H occasionally. These findings confirmed that earthworm species belonging to different ecological groups had different responses to organic matter at different decomposition stages. The impacts of earthworm communities dominated by O. occidentalis mainly appeared at the later periods of litter decomposition.

Isolation and application of effective nitrogen fixation rhizobial strains on low-phosphorus acid soils in South China

Soybean (Glycine max L.) is a very important food and oil crop in China. Legume-rhizobium symbiotic nitrogen (N) fixation is an important biological character and also the base of improving soil fertility of soybean. However, soybean production and development is severely limited in tropical and subtropical areas in China due to a lack of effective rhizobial inoculants adapting to low-phosphorus (P) acid soils. In the present study, 12 soybean rhizobial strains were isolated and purified from the nodules of two soybean genotypes contrasting in P efficiency, which were grown on different low-P acid soils with different soybean cultivation histories. Results from 16S rDNA sequence analysis showed that these 12 rhizobial strains belonged to the genus of Bradyrhizobium, which had higher nitrogenase activities compared to the control strain, Bradyrhizboium japonicum USDA110. A field experiment was carried out by applying rhizobial inoculants, a mixture of three rhizobial strains that showed the highest nitrogenase activity, on a typical low-P acid soil in South China. The results showed that, without inoculation, no nodules were formed in the three soybean genotypes tested; with inoculation, the nodulation rates in all were 100%. Inoculation with rhizobial inoculants not only made many nodules formed, but also increased soybean shoot biomass and yield, and improved nitrogen (N) and P nutrient status. Among which, shoot dry weight, N and P content of a soybean genotype, Huachun 3, inoculated with rhizobium were increased 154.3%, 152.4% and 163.2% compared to that without inoculation, respectively. We concluded that: (i) The effective indigenous rhizobial strains isolated in this study from soybeans on low-P acid soils in South China have the characters of broad host range, high nodulation efficiency, efficient N fixation, great low pH and low P tolerance. (ii) Soil environment and host types are the key factors to screen the effective rhizobial strains. Considering soil pH values and P efficiency of the host genotypes might increase the screening efficiency. (iii) Improving N status and facilitating root growth might be the mechanisms of increasing the P uptake in soybean plants inoculated with the effective rhizobial strains on low-P acid soils. (iv) Inoculation with the effective rhizobial inoculants could significantly improve growth, N and P content of soybean on low-P acid soils, which might be an effective approach to enhance soybean cultivation and development in these areas. Therefore, application and extension of inoculation techniques with effective rhizobial inoculants in legumes would result in great economical, environmental and ecological benefits.

Greenhouse gas fluxes from soils of different land-use types in a hilly area of South China

The magnitude, temporal, and spatial patterns of greenhouse gas (hereafter referred to as GHG) fluxes from soils of plantation in the subtropical area of China are still highly uncertain. To contribute towards an improvement of actual estimates, soil CO 2, CH 4, and N 2O fluxes were measured in two different land-use types in a hilly area of South China. This study showed 2 years continuous measurements (twice a week) of GHG fluxes from soils of a pine plantation and a longan orchard system. Impacts of environmental drivers (soil temperature and soil moisture), litter exclusion and land-use (vegetation versus orchard) were presented. Our results suggested that the plantation and orchard soils were weak sinks of atmospheric CH 4 and significant sources of atmospheric CO 2 and N 2O. Annual mean GHG fluxes from soils of plantation and orchard were: CO 2 fluxes of 4.70 and 14.72 Mg CO 2–C ha −1 year −1, CH 4 fluxes of −2.57 and −2.61 kg CH 4–C ha −1 year −1, N 2O fluxes of 3.03 and 8.64 kg N 2O–N ha −1 year −1, respectively. Land use types had great impact on CO 2 and N 2O emissions. Annual average CO 2 and N 2O emissions were higher in the orchard than in the plantation, while there were no clear differences in CH 4 emissions between two sites. Our results suggest that afforestation could be a potential mitigation strategy to reduce GHG emissions from agricultural soils if the observed results were representative at the regional scale. CO 2 and N 2O emissions were mainly affected by soil temperature and soil moisture. CH 4 uptakes showed significant correlation with soil moisture. The seasonal changes in soil CO 2 and N 2O fluxes followed the seasonal weather pattern, with high CO 2 and N 2O emission rates in the rainy period and low rates in the dry period. In contrast, seasonal patterns of CH 4 fluxes were not clear. Removal of surface litter reduced soil CO 2 effluxes by 17–25% and N 2O effluxes by 34–31% in the plantation and orchard in the second sampling year but not in the first sampling year which suggested micro-environmental heterogeneity in soils. Removal of surface litter had no significant effect on CH 4 absorption rates in both years. This suggests that microbial CH 4 uptake was mainly related to the mineral soil rather than in the surface litter layer.

Climatic Variables and the Transmission of Bacillary Dysentery: Any Differences Between Northern and Southern China?

TM4-O-05 Introduction: The impact of climate change on food-borne diseases is far from clear. Few relevant studies have been conducted in China. Using disease surveillance data, this paper examines the relationship between climate variables and bacillary dysentery in different climatic areas in China. Methods: Jinan city of Shandong Province in northern China, with a temperate climate, and Baoan district of Shenzhen in southern China, with a subtropical climate, were chosen as study areas. Monthly notified bacillary dysentery cases were obtained from local Centers for Diseases Prevention and Control. Monthly meteorologic data, including maximum temperature, minimum temperature, rainfall, relative humidity, and air pressure, were collected from the Chinese Meteorologic Bureau. Spearman correlation analysis and seasonal Autoregressive Integrated Moving Average (ARIMA) model were performed to investigate the association between climatic variables and the incidence of bacillary dysentery in the 2 study areas. The effect of seasonality was taken into account. The hockey stick model was used to explore the threshold of the effect of temperatures. Results: The incidence of dysentery positively correlated with maximum temperature, minimum temperature, rainfall, humidity, and related negatively to air pressure in both cities with the lag effects from zero to 2 months. In the ARIMA models, the only significantly included climatic variables are maximum and minimum temperatures. Additionally, an order-2 autoregressive variable and a seasonal variable were significant in the northern city, whereas an order-1 autoregressive variable and no seasonal variable were significant in the southern city. The thresholds for the effects of maximum and minimum temperatures were 17°C and 8°C, respectively, in the northern city. No thresholds were detected in the southern city. Conclusions: Although there are different seasonal patterns in the distribution of bacillary dysentery, maximum and minimum temperatures affect the transmission of bacillary dysentery in both temperate and subtropical areas in China. Threshold temperatures in the northern city were detected, which may have policy implications for the disease control and prevention. However, no threshold was identified in the southern city, which could be due to its subtropical climate with relevant higher temperatures throughout the year.

Effect of Habitat Modification on the Distribution of the Endangered Aquatic Fern Ceratopteris thalictroides (Parkeriaceae) in China

ABSTRACT Progressive decline in natural populations of Ceratopteris thalictroides has resulted from the deterioration or complete loss of its primary habitat. We surveyed 22 tropical and subtropical areas in China where C. thalictroides occurred based on historical records and/or from observations during preliminary field surveys. Ten previously recorded populations have been extirpated, and human activity was identified as the most important cause of destruction and loss of the primary habitat of C. thalictroides. The distribution and occurrence of C. thalictroides were closely associated with water chemistry, with pH and conductivity being the most important factors.

Changes in Freezing Tolerance and its Relationship with the Contents of Carbohydrates and Proline in Overwintering Centipedegrass (Eremochloa ophiuroides (Munro) Hack.)

The objective of this study was to clarify the changes in the contents of endogenous carbohydrates and proline in the stolons and leaves of centipedegrass (Eremochloa ophiuroides (Munro) Hack.), during the natural cold acclimation (hardening) and de-acclimation (dehardening) in relation to freezing tolerance in the field at the transition zone between temperate and subtropical areas in China. The contents of carbohydrates and proline, and freezing tolerance estimated by LT50, which is the temperature at which 50% of the electrolytes in the organ was measured in the leachate, were determined at 10-day intervals from October 1, 2001 to April 18, 2002. It was indicated that the freezing tolerance of stolons increased (LT50 of stolons decreased) quickly, as temperature dropped before winter, but that of leaves which senesced along with the drop in temperature did not. The freezing tolerance of stolons decreased gradually along with the rise in temperature above 5 °C in spring, when the overwintered plants started to grow. The contents of proline and soluble carbohydrates, including sucrose, fructose and glucose, increased as LT50 decreased when temperature dropped below 5 °C before winter, and decreased as LT50 increased in early spring. Correlation analysis revealed that the freezing tolerance of stolons of centipedegrass significantly and positively correlated with the contents of proline and soluble carbohydrates, and the ratio of the soluble carbohydrates to starch. Thus, the freezing tolerance of stolons, which are critical organs that determine the winter surviving ability, largely depended on the content of soluble carbohydrates and the ratio of soluble carbohydrates to starch in centipedegrass. The possible relationship between freezing tolerance and carbohydrate metabolism was also discussed.

Rain Attenuation Ratios on Short Microwave and Millimeter Wave Bands Earth-Space Paths

The knowledge of the ratio of rain attenuation at one frequency to that at another on slant paths is useful for the design of satellite-to-Earth communication links and up-link power control systems. It is well known that the rain attenuation is influenced by parameters of precipitation along the slant path such as DSD (raindrop size distribution), raindrop temperature, rainfall rate, and so on. In this paper, based on several DSDs applied to various climate zones, at short microwave and long millimeter wave bands, the attenuation ratios are estimated on Earth-space paths. A comparison of the prediction results with the experiment data in Boston and Kashima areas is carried out. It is shown that the M-P and Weibull DSD applied to rain attenuation ratios estimation are better DSD at higher latitude regions. The Guangzhou DSD applied to rain attenuation ratios prediction is better in tropical and subtropical areas in China. The lognormal DSD may be a appropriate DSD applied to predict rain attenuation ratios in tropical areas at Adown>1dB or R>15mm/h. However, the attenuation ratios predicted by the Guangzhou DSD disagree with by the lognormal DSD, it requires that the DSD applied to predict rain attenuation ratios are further studied in tropical areas.