模拟增温对川西亚高山人工林土壤有机碳含量和土壤呼吸的影响

采用原位OTCs模拟增温方法，研究了川西亚高山人工云杉林下土壤有机碳含量、土壤呼吸速率及土壤酶活性对温度升高的响应.结果表明：在2005年11月—2007年7月的模拟增温试验期间，林下空气平均温度和土壤平均温度分别比对照提高了042 ℃和025 ℃.增温1年和2年后的0～10 cm和10～20 cm层土壤有机碳、C/N均比对照有所降低：增温1年后，在0～10 cm层分别降低了869%和852%；增温2年后的降低幅度比增温1年后有所缓解.与对照相比，增温1年后土壤呼吸速率显著提高；2年后，土壤呼吸没有明显差异，表现出对温度升高的适应性.增温1年后，蔗糖酶、过氧化氢酶、蛋白酶、脲酶和多酚氧化酶活性均增强，其中0～10 cm土层的蔗糖酶和多酚氧化酶活性与对照的差异达到显著水平；增温2年后，蔗糖酶、蛋白酶和脲酶活性仍有所增强，但过氧化氢酶和多酚氧化酶活性与对照相比则呈下降趋势.     

Investigation of PVA/ws-chitosan hydrogels prepared by combined γ-irradiation and freeze-thawing

γ-Irradiation combined with freeze-thawing, i.e. irradiation followed by freeze-thawing and freeze-thawing followed by irradiation, was applied to prepare poly(vinyl alcohol) (PVA)/water soluble chitosan (ws-chitosan) hydrogels for wound dressing. The properties of these hydrogels were investigated and compared to those prepared by freeze-thawing and by irradiation, respectively. Hydrogels made by irradiation followed by freeze-thawing show larger swelling capacity and mechanical strength, higher thermal stability, lower water evaporation rate, and are less turbid than those made by pure freeze-thawing and freeze-thawing followed by irradiation. Hydrogels made by irradiation alone cannot be used as wound dressing due to their poor mechanical strength. SEM results show that the final structure of hydrogels made by combined irradiation and freeze-thawing is mainly determined by the first processing step. It is found that the appropriate amount of ws-chitosan can endow hydrogels with large swelling capacity and mechanical strength. The presence of ws-chitosan provides the hydrogels with good antibacterial activity against Escherichia coli (E. coli).     

近20年来江苏省土壤pH值时空变化及其驱动力

通过比较1980年和2003年江苏省土壤pH空间分布图,发现虽然两个时期土壤pH空间分布的基本格局仍然相似,表现为南酸北碱,但局部地区也存在较大的变化,主要表现为酸化.沂沭岗地浅洼平原土区、里下河浅洼地土区、宁镇扬低山丘陵土区和太湖平原土区均有较严重的酸化出现.分析发现前两者主要受不合理施肥、田间管理和土地利用及种植类型变化的影响,后两者除以上的影响因素外还包括工业化和城市化.另外在后两者和宜溧洞庭山地土区由于土地利用和种植方式的变化、建筑和道路的兴建,还导致了局部地区土壤pH有所上升.土类中潮土酸缓冲性能强、pH变化不大,水稻土pH下降严重,特别是里下河浅洼地土区水稻土,在现有的管理利用方式下,继续下降的可能性很大.     

波动和静止水文情势下小叶章(Calamagrostis angustifolia)的生理生态特征

通过野外调查与控制试验相结合的方法,比较研究了波动和静止两种水文情势下,沼泽化草甸植物--小叶章(Calamagrostis angustifolia)某些生理生态特征(种群密度与高度、叶长、叶宽、茎长、节长以及叶绿素含量)对不同水分条件的响应.结果表明,不同水文情势对小叶章生理生态特征具有明显的影响.波动水文情势下,小叶章种群、形态指标及叶绿素含量总体随水分的增加而减小或下降,但是由于特定水文情势下形成的群落竞争格局的影响,小叶章单优群落分布带上小叶章各指标值明显大于其它水分带;静止水文情势下,小叶章各指标值呈波动变化,30 cm积水处理下的种群密度、高度、叶宽和茎长以及叶绿素含量与其它处理差别显著.波动水文情势下小叶章各指标测定值均大于静止水文情势下的,同一生活史阶段要较静止水文情势下的提前,生长能力较强.湿地水分条件不仅直接影响植物特性,还通过影响植物定植的土壤环境特征及群落内的竞争格局间接作用于植物.不同水分条件下,小叶章的生理生态特征是水分条件直接与间接作用的综合结果.     

Genetic diversity and population structure of Swertia tetraptera (Gentianaceae), an endemic species of Qinghai-Tibetan Plateau

Swertia tetraptera Maxim is an annual alpine herb endemic to the Qinghai-Tibetan Plateau (QTP). Its populations are locally scattered as isolated patches throughout this region. Genetic variation within and among thirty-four populations of this species was assessed using ISSR fingerprinting with 10 primers. High levels of genetic diversity exist within species (P = 98.9%, I = 0.3475; He = 0.2227), while the within-population diversity is low (P = 32.7%, I = 0.177; He = 0.12). High levels of genetic differentiation were detected among populations based on various statistics, including Nei’s genetic diversity analysis (G_ST = 0.4608), Bayesian analysis (θ^B = 0.476) and AMOVA (F_ST = 0.57). That is, populations shared low levels of genetic identity (I = 0.2622–0.0966). This genetic structure was probably due to severe genetic drift, breeding system and limited gene flow. The observed genetic structure of the populations implies that different populations across the distribution range of the species should be sampled to maintain high genetic diversity when a conservation strategy is implemented.     

Potential refugium on the Qinghai–Tibet Plateau revealed by the chloroplast DNA phylogeography of the alpine species Metagentiana striata (Gentianaceae)

Metagentiana striata is an alpine annual herbaceous plant endemic to the east of the Qinghai–Tibet (Q–T) Plateau and adjacent areas. The phylogeography of M. striata was studied by sequencing the chloroplast DNA (cpDNA) trn S– trn G intergenic spacer. Ten haplotypes were identified from an investigation of 232 individuals of M. striata from 14 populations covering the entire geographical range of this species. The level of differentiation amongst populations was very high ( G _ST = 0.746; N _ST = 0.774) and a significant phylogeographical structure was observed ( P  < 0.05). An analysis of molecular variance found a high variation amongst populations (76%), with F _ST = 0.762 (highly significant, P  < 0.001), indicating that little gene flow occurred amongst the different regions; this was explained by the isolation of populations by high mountains along the Q–T Plateau and adjacent areas ( N _m = 0.156). Only one ancestral haplotype (A) was common and widespread throughout the distributional range of M. striata. The populations of the Hengduan Mountains region of the south-eastern Q–T Plateau showed high diversity and uniqueness of haplotypes. It is suggested that this region was the potential refugium of M. striata during the Quaternary glaciation, and that interglacial and postglacial range expansion occurred from this refugium. This scenario was in good agreement with the results of nested clade analysis, which inferred that the current spatial distribution of cpDNA haplotypes and populations resulted from range expansion, together with past allopatric fragmentation events.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 125–140.     

不同地域卵黄萤荧光素酶基因的克隆与序列分析

为了比较不同地域萤火虫荧光素酶基因的进化关系，通过GenBank中已知的荧光素酶基因保守区段设计引物，利用5′ RACE（rapid amplification of cDNA ends）和3′ RACE技术克隆了来自云南省文山州和西双版纳州的同种卵黄萤荧光素酶基因cDNA和全基因序列.来自不同地域的2种卵黄萤荧光素酶在基因序列上存在3个不同碱基位点，但是它们编码的荧光素酶只存在1个不同的氨基酸.卵黄萤荧光素酶基因全长（从起始密码子到终止密码子）1998 bp，包含7个外显子,6个内含子，其cDNA序列共1976 bp，包含102 bp 5′ UTR (untranslated region)、1635 bp的荧光素酶基因开放阅读框和239 bp的3′ UTR序列.卵黄萤荧光素酶基因的开放阅读框编码1个544个氨基酸的蛋白质，比同属的其它几种荧光素酶少4个氨基酸. 来自2个不同地域的卵黄萤荧光素酶在进化上是比较保守的，它们与北美萤火虫Photinus pyralis荧光素酶在碱基序列上分别有629%和63%相似性.     

Facile purification of mono-PEGylated interleukin-1 receptor antagonist and its characterization with multi-angle laser light scattering

Recombinant human interleukin-1 receptor antagonist (rhIL-1ra) was chemically conjugated with succinimidyl carbonate monomethoxyl polyethylene glycols of 5 kDa (SC-PEG_5k) and 10 kDa (SC-PEG_10k) molecular weight. A facile purification of the conjugates was achieved by one-step cationic exchange chromatography. The purity of mono-PEGylated protein was greater than 95%. The purified conjugate was characterized by multi-angle laser light scattering (MALLS) for determining the apparent gyration radius (r_g) and hydrodynamic radius (r_h). MALLS results showed that the conjugation of PEG markedly enhanced r_g and r_h of parent protein (r_g: from 15.7 to 48.2 nm for the PEG_5k and 81.9 nm for the PEG_10k; r_h: from 4.2 to 58.4 nm for the PEG_5k and 102.3 nm for the PEG_10k). The PEGylated rhIL-1ra retained 44.6% of binding activities to the cell receptor for PEG_5k and 40.2% for PEG_10k, compared to the original protein.     

Size-dependent mortality in a Neotropical savanna tree: the role of height-related adjustments in hydraulic architecture and carbon allocation

Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than ∼6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO₂ assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance ( K _leaf) than small trees and all tree sizes exhibited lower K _leaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits.