基于分布于全省的8637个耕层（0-20 cm）土壤样品有机碳含量和土壤、气象以及农田分布等空间数据，本研究采用随机森林模型的方法绘制了云南省农田1 km分辨率的土壤有机碳分布图，并估算了土壤有机碳总储量。结果表明，云南省农田平均土壤有机碳密度和总储量分别为4.86 kg m^-2和337.5 Mt。从空间分布来看，西北与东北地区的土壤有机碳密度相对较高。海拔高度、大气温度、年降水量以及地形湿度指数是影响土壤有机碳密度空间分布最主要的因素，其预测重要性指数分别达19.5%、17.3%、14.5%和9.9%。改善农田管理措施，如推广秸秆还田、优化肥料运筹等，可为提高作物产量、增加土壤固碳、实现云南省农田可持续生产提供有效保障。

Received  14 August, 2017    Accepted  20 December, 2017

In order to understand molecular characterization of Citrus tatter leaf virus (CTLV) isolated from China, full-length cDNAs of CTLV-MTH and CTLV-XHC from Citrus reticulata and Citrus sinensis were cloned and sequenced based on whole-genome amplification by RT-PCR. The complete nucleotide sequences of CTLV-MTH and CTLV-XHC were determined to be 6 497 nucleotides in length and shared 79.9–91.0% and 78.8–98.0% nucleotide sequence identity, respectively, with other Apple stem grooving virus (ASGV) or CTLV strains available in GenBank. Unexpectedly, CTLV-MTH showed the highest nucleotide sequence identity (91%) with an apple isolate of ASGV, followed by 86.5% with ASGV-HH and 85.7% with ASGV-CHN. Furthermore, CTLV-MTH and three ASGV strains were grouped to a separate cluster in the phylogenetic tree, suggesting it has a closer relationship to ASGV than to CTLV. Therefore, it can be concluded roughly that CTLV may be not a distinct strains of ASGV. We proposed that Citrus tatter leaf virus should be renamed Apple stem grooving virus.

The complete nucleotide sequence of an isolate of Citrus vein enation virus (CVEV-XZG) from China has been determined for the first time. The genome consisted of 5 983 nucleotides, coding for five open reading frames (ORFs), had a similar genomic organization features with Pea enation mosaic virus (PEMV). Nucleotide and deduced amino acid sequence identity of the five ORFs compared to isolate CVEV VE-1 range from 97.1 to 99.0% and 97.4 to 100.0%, these values compared to isolate PEMV-1 range from 45.2 to 51.6% and 31.1 to 45.2%. Phylogenetic analysis based on the complete genome sequence showed that the isolate CVEV-XZG had close relationship with Pea enation mosaic virus. The results supports CVEV may be a new member of genus Enamovirus. The full sequence of CVEV-XZG presented here may serve as a basis for future study of CVEV in China.

Changes in the soil nematode community induced by global warming may have a considerable influence on agro-ecosystem functioning. However, the impacts of predicted warming on nematode community in farmland (e.g., winter wheat field) have not been well documented. Therefore, a field experiment with free air temperature increase (FATI) was conducted to investigate the responses of the soil nematode community to nighttime warming in a winter wheat field of Yangtze Delta Plain, China, during 2007 to 2009. Nighttime warming (NW) by 1.8°C at 5-cm soil depth had no significant impact on the total nematode abundance compared to un-warmed control (CK). However, NW significantly affected the nematode community structure. Warming favored the bacterivores and fungivores, such as Acrobeles, Monhystera, Rhabditis, and Rhabdontolaimus in bacterivores, and Filenchus in fungivores, while the plant-parasites were hindered, such as Helicotylenchus and Psilenchus. Interestingly, the carnivores/ omnivores remained almost unchanged. Hence, the abundances of bacterivores and fungivores were significantly higher under NW than those under CK. Similarly, the abundances of plant-parasites were significantly lower under NW than under CK. Furthermore, Wasilewska index of the nematode community was significantly higher under NW than those under CK, indicating beneficial effect to the plant in the soil. Our results suggest that nighttime warming may improve soil fertility and decrease soil- borne diseases in winter wheat field through affecting the soil nematode community. It is also indicated that nighttime warming may promote the sustainability of the nematode community by altering genera-specific habitat suitability for soil biota.