Evergreen broad-leaved forest improves soil water status compared with tea tree plantation in Ailao Mountains,Southwest China

Abstract

In this paper, the spatial-temporal dynamics of soil moisture content was investigated in an evergreen broad-leaved forest and a tea tree plantation in Ailao Mountains, which was dominated by Fagaceae (Castanopsis wattii and Lithocarpus xylocarpus). Soil moisture content was studied between January 2005 and December 2006 at different depths (from 0–150 cm) with a neutron probe. The results showed that mean soil moisture content in the evergreen broad-leaved forest was usually higher than in the tea tree plantation in the dry season, whereas it was lower than the tea tree plantation in the rainy season. In addition, mean soil moisture content was depth dependent, and in the 10–50 cm layer the spatial variability was due to the active root zone within this depth area in two types of land use. From 50–150 cm, the spatial variability was slightly increasing in the evergreen broad-leaved forest or relatively stable in the tea tree plantation. Our study also showed that soil moisture content was higher and more stable under the evergreen broad-leaved forest than the tea tree plantation, hence we stress that evergreen broad-leaved forest plays an important role in holding soil moisture. It is suggested that the protection of evergreen broad-leaved forest should be strengthened.     

土壤空间变异研究现状及展望

阐述了应用地统计学方法，定量研究土壤空间变异的基本理论和基本方法以及国内外土壤空间变异的研究现状，探讨了该领域研究中存在的问题，展望了土壤空间变异研究前景。     

Assessment of Transmission Ability of Barley Yellow Dwarf Virus-PAV Isolates by Different Populations of Rhopalosiphum padi and Sitobion avenae

Populations of two aphid species from different geographic regions of Morocco were tested for their ability to transmit five barley yellow dwarf virus-PAV (BYDV-PAV) type isolates using Clintland 64 oat as the test plant. Transmission efficiencies were determined for 10 sub-populations of Rhopalosiphum padi and 12 sub-populations of Sitobion avenae. After a short acquisition access period (AAP) of 4h, all populations transmitted the virus but with different efficiencies. R. padi (Rp-S) and S. avenae (Sa-S) collected in the Settat region were the most efficient vectors, with transmission rates of 38% and 27%, respectively. R. padi (Rp-C) collected at Chaouen and S. avenae (Sa-B) at Berkane, were poor transmitters with respective vectoring abilities of 20% and 16%. These four sub-populations were chosen to study the acquisition of BYDV-PAV and the retention of virus within aphids in more detail. The transmission after two AAPs of 4h and 48h were compared. Starved aphids given a 4h AAP had significantly higher transmission efficiencies than non-starved aphids. However, after a 48h AAP, no difference was observed in the transmission between starved and non-starved aphids. Intraspecific variability was also detected by means of serial transfers of individual aphids after the given AAP. Following the first day of serial transfers, no differences were observed in transmission efficiency and virus titers for sub-populations within each species acquiring the virus during 48h, but there was significant variation when the virus was acquired in 4h. The levels of PAV antigen retained by aphids fed on healthy plants declined rapidly during the first day after acquisition, but remained fairly constant during the next 5–7 days depending on the length of the AAP. Virus antigen could be detected by ELISA in Rp-S and Sa-S for up to 11 days of serial transfer, but it was shown that aphids could retain and transmit BYDV-PAV for at least 3 weeks.     

潜蝇姬小蜂幼虫空间分布型研究

本文应用Iwao和Tayla’s回归模型以及6个聚集度指标(C、CA、M^*、M^8／m、I、K),对蚕豆田潜蝇姬小蜂幼虫的空间分布型进行了研究。测定结果属聚集分布,为田间调查及保护天敌提供了依据。     

EFFECT OF OBSERVER VARIABILITY ON GLOMERULAR FILTRATION RATE MEASUREMENT BY RENAL SCINTIGRAPHY IN DOGS

Observer variation in kidney depth measurement for correction of soft-tissue attenuation and kidney region of interest (ROI) drawing was evaluated using 60 clinical dogs with a wide range of glomerular filtration rate (GFR) for their effect on the calculated percentage uptake of 99mTc-diethylenetriamine pentaacetic acid (DTPA) and individual kidney GFR by scintigraphy. Kidney depth was measured separately on the lateral image using two color tables: a threshold and a continuous red-green-blue. Within-observer variability of the semi-automatic ROI drawing of the estimated total GFR was up to 10% for the right kidney (RK) and 9% for the left kidney (LK). The variability was lower between observers, 6% for RK and 8% for LK. Manual ROI drawing caused more within observer variation than semi-automatic: up to 14% for RK and 11% for LK. Continuous red-green-blue table caused more variation within and between observers than threshold table. Average within-observer variability from both observers of kidney depth measurement on different color tables could vary up to 5.5% and 6.5% variation of the GFR of RK and LK, respectively. Most variation affecting the DTPA percentage uptake came from the ROI drawing technique. Variations of the method because of the effects of both kidney depth and kidney ROI drawing were up to 8% and 10% for RK and LK, respectively. To minimize these variations a threshold scale should be used for the kidney depth measurement and an automatic or semi-automatic ROI should be used whenever possible. In sequential examinations the same person should make all the measurements.     

A Severe Hellenic CMV Tomato Isolate: Symptom Variability in Tobacco, Characterization and Discrimination of Variants

A severe strain of Cucumber mosaic virus (CMV) originating from an infected tomato plant (Gastouni-Olympia, Greece) was isolated in tobacco (Nicotiana tabacum cv. Xanthi nc), after three serial local lesion passages in Chenopodium quinoa and designated CMV-G. CMV-G induces yellow mosaic (YM) symptoms in tobacco. When CMV-G was passed mechanically through C. quinoa, phenotypic variants inducing YM or green mild mosaic (MM) in tobacco were isolated. Aphid transmission, from different hosts, appears to be an effective approach for separating MM variants of CMV-G from YM variants. In particular, aphid transmission from zucchini proved to be very efficient in selecting for MM variants. In contrast, aphids transmitted only YM variants from tomato plants. Molecular characterization of CMV-G and its progeny resulted in their classification in the CMV subgroup IB, free of satellite RNA, being the first discovery of the subgroup IB in Greece. In the Solanaceae family (tobacco, tomato, pepper) YM variants induced more severe symptoms than the MM variants. YM and MM phenotype was stable in tobacco for all seven passages tried using the obtained YM and MM variants. Cross-protection experiments showed that an isolated MM variant was able to protect tobacco plants against a challenge infection by a YM variant.     

Spatial and temporal patterns of Lolium rigidum–Avena sterilis mixed populations in a cereal field

Through a detailed case study of a two‐species (Lolium rigidum and Avena sterilis) weed community at contrasting scales, this paper examined factors that affect weed distribution across space and time in a commercial wheat field in north‐east Spain. A. sterilis showed relatively stable spatial distribution and spatial structure of its population over time at large scale, with well‐defined patches, although weed density rose quickly. L. rigidum showed poorly defined patches that were not stable across time. Interaction between species could explain to some degree the spatial distribution at large scale: a negative relationship was detected between the spatial structures of both weed populations. At fine scale, both species showed a clear interaction effect from primary dispersal (more important in A. sterilis) and secondary dispersal from combine harvesting (more important in L. rigidum).     

禽流感病毒分子生物学的研究进展

禽流行性感冒(av ian in fluenza,A I,简称禽流感)是由A型禽流感病毒(av ian in fluenza v irus,A IV)引起的禽类烈性传染病。作为被世界动物卫生组织(O IE)定为A类的传染病,A I不仅给世界养禽业造成了巨大的经济损失,而且对人类健康和生命安全构成了严重威胁。因此,A I已经成为人们关注的焦点,国内外学者也对其进行了大量研究。作者从病原基因组及其编码的蛋白质、致病力、变异性以及对人类感染A IV的分子机制等角度就A IV的分子生物学研究作一综述,为防制A I提供理论基础,并在此基础上探讨了人类禽流感的防治措施,加深人们对A I的认识。     

Molecular systematics in Chrysanthemum × grandiflorum (Ramat.) Kitamura

An attempt was made to understand the molecular systematics and genetic differences between 10 original chrysanthemum cultivars and 11 mutants. The similarity among the cultivars and mutants varied from 0.17 to 0.90 using RAPD analyses, a simple but efficient method to distinguish cultivars and to assess parentage. Two distinct groups were found. Two cultivars were present as a separate group showing differences from all other cultivars. Mutants with different flower colour could be identified at the molecular level using RAPD technique holding promise to identify unique genes as SCAR markers. A high genetic distance among the different chrysanthemums showed that there exists a possibility of introgressing new and novel genes from the chrysanthemum gene pool.