黄土高原子午岭种子植物区系特征研究

黄土高原子午岭位于黄土高原中部半湿润半干旱过渡带(107°30′~109°40′E,33°50′~36°50′N)。其在植被分区上隶属于泛北极植物区、中国-日本森林植物亚区的华北地区黄土高原植物亚地区。区内共有种子植物94科361属689种,分别占黄土高原区种子植物总数的63.95%、41.78%和21.37%。其中大科、大属在区系组成中起着非常重要的作用。该区种子植物属包含15个分布区类型及12个变型,其中北温带分布、旧世界温带分布、泛热带分布、东亚分布等成分占有重要地位。其种子植物区系的基本特征是:植物种类相对丰富;多种地理成分交汇、过渡特征明显;区系组成以华北成分为主体,温带成分占优势;沿纬度梯度地理成分差异显著,垂直分布带谱不明显;区系成分新老并存,特有化程度低。     

Spatial patterns of foliar stable carbon isotope compositions of C<Subscript>3</Subscript> plant species in the Loess Plateau of China

The spatial pattern of foliar stable carbon isotope compositions (δ¹³C) of dominant species and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, was studied. The results showed that in the 121 C₃ plant samples collected from the Loess Plateau, the foliar δ¹³C value ranged from −22.66‰ to −30.70‰, averaging −27.04‰. The foliar δ¹³C value varied significantly (P<0.01) among the seven sites, and the average δ¹³C value increased by about 1.69‰ from Yangling in the south to Shenmu in the north as climatic drought increased. There was a significant difference in foliar δ¹³C value among three life-forms categorized from all the plant samples in the Loess Plateau (P<0.001). The trees (−26.74‰) and shrubs (−26.68‰) had similar mean δ¹³C values, both significantly (P<0.05) higher than the mean δ¹³C value of herbages (−27.69‰). It was shown that the trees and shrubs had higher WUEs and employed more conservative water-use patterns to survive drier habitats in the Loess Plateau. Of all the C₃ species in the Loess Plateau, the foliar δ¹³C values were significantly and negatively correlated with the mean annual rainfall (P<0.001) and mean annual temperature (P<0.05), while being significantly and positively correlated with the latitude (P<0.001) and the annual solar radiation (P<0.01). In general, the foliar δ¹³C values increased as the latitude and solar radiation increased and the rainfall and temperature decreased. The annual rainfall as the main influencing factor could explain 13.3% of the spatial variations in foliar δ¹³C value. A 100 mm increment in annual rainfall would result in a decrease by 0.88‰ in foliar δ¹³C values.     

山西绵山植被优势种群的分布格局与种间联结的研究

本文用方差/平均数比率的方法和通过2×2列联表进行X~2检验的方法,研究了山西绵山植被优势种的分布格局及种间联结性。结果表明:绵山优势种都服从集群分布;种间的正联结是物种对同质生境有相同适应性的反应;种问的负联结则是不同物种对异质生境适应性不同所致。在用X~2检验研究物种联结性的同时,用点相关系数来刻划种间的联结性强度,作为对种间联结的辅助说明是完全必要的。通过对种间联结的分析,还可以看出绵山植被的动态演替趋势。     

Quantification of methane emissions from Chinese rice fields (Zhejiang Province) as influenced by fertilizer treatment

Methane emissions from rice paddies were quantified by using an automatic field system stationed in Zhejiang Province, one of the centres for rice cultivation in China. The data set showed pronouned interannual variations over 5 consecutive vegetation periods; by computing average values of all experimental plots the annual emissions were 177 g CH₄ m⁻² yr⁻¹ in 1987, 50 g CH₄ m⁻² yr⁻¹ in 1988, and 187 g CH₄ m⁻² yr⁻¹ in 1989. The field preparations encompassed 4 different treatments: (1) no fertilizers, (2) mineral fertilizer (KCl, K₂SO₄), (3) organic manure (rape seeed cake, animal manure), (4) mineral fertilizer plus organic manure. The methane emission rates of the different fertilizer treatments did not show significant differences. The mean emission rates, calculated over the entire observation period of 5 seasons, were 30.4 mg CH₄ m⁻² h⁻¹ (non-fertilized plot) and 28.3 mg CH₄ m⁻² h⁻¹ (mineral fertilizers). These values indicate a high level of methane production even without additional input of organic material into the rice-soils. In the other plots, the organic fertilizers were added once per vegetation period at app. 1 t fresh weight per ha, a relatively low application rate by agronomical standards. The mean emission rates were 35.1 mg CH₄ m⁻² h⁻¹ when manure was applied as sole fertilizer and 27.5 mg CH₄ m⁻² h⁻¹ when applied jointly with potassium fertilizers. Based on the results of this study we estimate a range of 18–28 Tg CH₄ yr⁻¹ as the total methane emission from Chinese rice fields. However, more field data from representative sites in China are needed to reduce the uncertainties in this estimate.     

Sera from patients with type 2 diabetes and neuropathy induce autophagy and colocalization with mitochondria in SY5Y cells

The etiology of diabetic neuropathy is multifactorial and not fully elucidated, although oxidative stress and mitochondrial dysfunction are major factors. We reported previously that complement-inactivated sera from type 2 diabetic patients with neuropathy induce apoptosis in cultured neuronal cells, possibly through an autoimmune immunoglobulin-mediated pathway. Recent evidence supports an emerging role for autophagy in a variety of diseases. Here we report that exposure of human neuroblastoma SH-SY5Y cells to sera from type 2 diabetic patients with neuropathy is associated with increased levels of autophagosomes that is likely mediated by increased titers of IgM or IgG autoimmune immunoglobulins. The increased presence of macroautophagic vesicles was monitored using a specific immunohistochemical marker for autophagosomes, anti-LC3-II immunoreactivity, as well as the immunohistochemical signal for beclin-1, and was associated with increased co-localization with mitochondria in the cells exposed to diabetic neuropathic sera. We also report that dorsal root ganglia removed from streptozotocin-induced diabetic rats exhibit increased levels of autophagosomes and co-localization with mitochondria in neuronal soma, concurrent with enhanced binding of IgG and IgM autoimmune immunoglobulins. To our knowledge, this is the first evidence that the presence of autophagosomes is increased by a serum factor, likely autoantibody(ies) in a pathological condition. Stimulation of autophagy by an autoantibody-mediated pathway can provide a critical link between the immune system and the loss of function and eventual demise of neuronal tissue in type 2 diabetes.     

山西云蒙山油松种群的年龄结构和动态特征

本文用样方法研究了山西云蒙山油松种群的年龄结构、存活曲线和数量动态规律,并且讨论了油松种群数量动态和群落演替的关系,结果表明:油松种群具有增长型和衰退型的动态特征,影响油松种群数量的内在机制主要是种内光资源的竞争。尽管大多数油松种群处于不断衰减状态,但其群落结构及性质在较长时期内将不会发生显著的变化。     

黄土区次降雨条件下林地径流和侵蚀产沙形成机制——以人工油松林和次生山杨林为例

以黄土区两种常见森林植被(次生山杨林和人工油松林)长期定位观测试验为基础,从水量平衡和径流产沙机理出发,分析了次降雨条件下两种林地和荒地坡面产流产沙过程.结果表明,次降雨量在5.0～50.0 mm范围内,油松林和山杨林的林冠和枯枝落叶层总截留率分别为15.45%～56.80%和20.56%～47.81%,且随降雨量的增大而减小.与荒坡地相比,林地土壤入渗性能显著增强,尤其是0～20cm土层.分析表明,在一般降水条件下林地无径流产生;而在降雨雨强为2.5 mm·min^-1和历时30 min条件下,山杨林地无地表径流产生,荒坡地的径流流速和径流挟沙浓度均为油松林地的23.5倍,而其径流剪切力和径流能量均为后者的8倍;油松林地的径流量和产沙量比荒地分别减少了87.6%和99.4%,与径流小区多年(1988～2000)观测平均值(分别为87.0%和99.9%)相近.     

A mammary repopulating cell population characterized in mammary anlagen reveals essential mammary stroma for morphogenesis

The cells with mammary repopulating capability can achieve mammary gland morphogenesis in a suitable cellular microenvironment. Using cell surface markers of CD24, CD29 and CD49f, mouse mammary repopulating unit (MRU) has been identified in adult mammary epithelium and late embryonic mammary bud epithelium. However, embryonic MRU remains to be fully characterized at earlier mammary anlagen stage. Here we isolated discrete populations of E14.5 mouse mammary anlagen cells. Only Lin⁻CD24^medCD29⁺ cell population was predicted as E14.5 MRU by examining their capacities of forming mammosphere and repopulating cleared mammary fat pad in vivo. However, when we characterized gene expressions of this E14.5 cell population by comparing with adult mouse MRU (Lin⁻CD24⁺CD29^hi), the gene profiling of these two cell populations exhibited great differences. Real-time PCR and immunostaining assays uncovered that E14.5 Lin⁻CD24^medCD29⁺ cell population was a heterogeneous stroma-enriched cell population. Then, limiting dilutions and single-cell assays also confirmed that E14.5 Lin⁻CD24^medCD29⁺ cell population possessed low proportion of stem cells. In summary, heterogeneous Lin⁻CD24^medCD29⁺ cell population exhibited mammary repopulating ability in E14.5 mammary anlagen, implying that only suitable mammary stroma could enable mammary gland morphogenesis, which relied on the interaction between rare stem cells and microenvironment.