Ovipositor length of threeApocrypta species: Effect on oviposition behavior and correlation with syconial thickness

We investigated oviposition behavior in three non-pollinating fig wasps: the sympatric speciesApocrypta bakeri Joseph onFicus hispida L.,A. westwoodi Grandi onF. racemosa L., andApocrypta sp. onF. semicordata Buch.-Ham. The oviposition behavior differs significantly between one pair of species (A. bakeri andA. westwoodi) and the other species (Apocrypta sp. onF. semicordata).A. bakeri andA. westwoodi were similar in the following aspects: the posture of the abdomen and the action of the hind legs before penetration, and the bending ovipositor sheath during penetration. In contrast, the oviposition behavior ofApocrypta sp. is quite different. This difference can be explained by the significant correlation between ovipositor length and syconial thickness.Apocrypta sp. has a shorter ovipositor than the two other species, which correlates with the thinner syconial wall of its host figF. semicordata. It is deduced that the ovipositor length adapts to the syconial thickness and induces the oviposition behavior in the different species to diverge. For all threeApocrypta species, the midleg length and hindleg length are significantly correlated with their ovipositor lengths. This may be explained as due to the fact that body movement adjusting the hindlegs and midlegs up and down, or forward and backward, is also influenced by the ovipositor length.     

高寒地区不同建植期人工草地群落垂直结构和生产力变化的研究

对高寒地区不同建植期人工草地群落垂直结构和生产力的变化研究结果表明：（1）随着人工草地建植时间的延长,人工草地群落垂穗披碱草高度异质性逐渐减小.（2） 不同建植期（1999、1998、1997年建植）人工草地垂穗披碱草和群落平均地上生物量均主要分布在0 ～20cm冠层中,约占平均地上生物量的61.03%、90.64%、84.55%和67.47%、92.54%、86.08%.（3） 不同建植期 （1999、1998、1997年建植）人工草地群落平均地下生物量均主要分布在0～10cm土层中,约占地下总生物量的85.97%、81.73%和78.47%.（4） 建植的人工草地如果其组分单一,即物种的丰富度很低时,均匀度增加,物种对环境资源的竞争力和利用率提高,导致土壤资源库中某些营养成分缺乏,草地群落初级生产力因此而降低。     

Two new diterpene derivatives from Euphorbia lunulata Bge and their anti-proliferative activities

A new ent-abietane-type diterpene lactone (1) and a new jatrophane-type diterpenoid (2), together with twelve known compounds including three diterpenes (3–5), five triterpenes (6–10) and four sterides (11–14) were isolated from the ethanol extract of the whole plant of Euphorbia lunulata Bge. The structure of compounds 1 and 2 was elucidated on the basis of 1D and 2D NMR spectra and the HR-ESI-MS data. The structure of compound 2 was further analyzed by an X-ray crystallographic study. The in vitro anti-proliferative activities against MCF-7 and NCI-H460 cell lines for compounds 1–5 (diterpene) were evaluated. The results showed marked activity for compound 1 against the two cell lines with the IC₅₀ values 19.5 (NCI-H460) and 18.6 (MCF-7) μM, while for cis-platinum (a positive cytotoxic control agent) 29.7 (NCI-H460) and 27.7 (MCF-7) μM. Compounds 2–5 exhibited moderate cytotoxic activities for the two cell lines with the IC₅₀ values ranging from 32.1 to 58.2 μM.     

Greater humification of belowground than aboveground biomass carbon into particulate soil organic matter in no-till corn and soybean crops

Quantifying the amount of carbon (C) incorporated from decomposing residues into soil organic carbon (C_S) requires knowing the rate of C stabilization (humification rate) into different soil organic matter pools. However, the differential humification rates of C derived from belowground and aboveground biomass into C_S pools has been poorly quantified. We estimated the contribution of aboveground and belowground biomass to the formation of C_S in four agricultural treatments by measuring changes in δ¹³C natural abundance in particulate organic matter (C_POM) associated with manipulations of C₃ and C₄ biomass. The treatments were (1) continuous corn cropping (C₄ plant), (2) continuous soybean cropping (C₃), and two stubble exchange treatments (3 and 4) where the aboveground biomass left after the grain harvest was exchanged between corn and soybean plots, allowing the separation of aboveground and belowground C inputs to C_S based on the different δ¹³C signatures. After two growing seasons, C_POM was primarily derived from belowground C inputs, even though they represented only ∼10% of the total plant C inputs as residues. Belowground biomass contributed from 60% to almost 80% of the total new C present in the C_POM in the top 10 cm of soil. The humification rate of belowground C inputs into C_POM was 24% and 10%, while that of aboveground C inputs was only 0.5% and 1.0% for soybean and corn, respectively. Our results indicate that roots can play a disproportionately important role in the C_POM budget in soils. Keywords Particulate organic matter; root carbon inputs; carbon isotopes; humification rate; corn; soybean.     

Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto,Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100 kg N ha⁻¹ for upland rice, and 0 and 20 kg N ha⁻¹ for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.     

水分胁迫和复水对紫花苜蓿幼苗叶绿素荧光特性的影响

利用PEG-6000模拟水分胁迫(ψs=-0.2MPa,胁迫时间:48 h,复水48 h),研究了紫花苜蓿(Medicago sativa L)品种陇东苜蓿和阿尔冈金叶片叶绿素荧光特性和光合色素含量的变化,旨在探讨紫花苜蓿水分胁迫条件下的光合反应机制.结果表明:光化学淬灭系数(qP)和PSII线性电子传递的有效量子产额(YIELD)以及非光化学淬灭系数(qN)和表观光合电子传递效率(ETR)在胁迫前后随光合有效辐射(PAR)的变化规律分别可用公式:Y=aLn(X) b(Y:qP或YIELD,X:PAR,X≠0)和Y=aX2 bX c(Y:qN或ETR,X:PAR)来表示;在受到干旱胁迫后,PSII最大光能转化效率(Fv/Fm)、PSII潜在活性(Fv/Fo)和光合色素含量均明显低于对照,在任意光强下的qP、YIELD和ETR值也极显著低于对照的相应值,qN值则极显著高于对照的相应值;同时,和对照相比,qN和ETR光响应曲线顶点所对应的光强值在受到胁迫后亦明显下降,表明光抑制初始点的降低和最大光保护能力的减弱,甚至光抑制的提前到来.干旱胁迫使得PSⅡ反应中心结构和功能遭到破坏而部分关闭,光合电子传递受阻,光能利用与光化学转化与能力下降,吸收的光能更多的以热能形式耗散.复水后,虽然有光保护机制的存在,但除陇东苜蓿光合色素含量及阿尔冈金类胡萝卜素外,各参数均未能恢复到对照水平,因此旱后复水不能完全解除干旱对PSII反应中心所带来的伤害.紫花苜蓿幼苗对干旱胁迫较为敏感.供试品种相比,陇东苜蓿耐旱性优于阿尔冈金.     

Induction of antiviral resistance and stimulary effect by oligochitosan in tobacco

Oligochitosan was applied by spraying it on tobacco leaves for inhibition of tobacco mosaic virus (TMV). The maximum inhibition of TMV by oligochitosan was observed when inoculation occurred at 24 h after spraying 50 μg ml⁻¹ oligochitosan. The production of H₂O₂ and NO in epidermal tobacco cells induced by oligochitosan was investigated by epidermal strip bioassay and LSCM, using cell permeable fluorophore diaminofluorescein diacetate (DAF-2D) and 2′,7′-dichlorofluorescin diacetate (H₂DCF-DA), respectively. Epidermal tobacco cells treated with oligochitosan resulted in a strong increase of intracellular NO and H₂O₂. Oligochitosan and NO donor sodium nitroprusside (SNP) induced the defense reaction against tobacco mosaic virus (TMV), and increased phenylalanine ammonia-lyase (PAL) activity. Co-treatment of the tobacco cells with oligochitosan and NO scavenger CPTIO blocked the inducing resistance. The results indicated that the defense response induced by oligochitosan was connected with NO pathway.     

Simulated rain addition modifies diurnal patterns and temperature sensitivities of autotrophic and heterotrophic soil respiration in an arid desert ecosystem

The timing and magnitude of rainfall events in arid and semiarid regions are expected to change dramatically in future decades, which will likely greatly affect regional carbon cycles. To understand how increases in rainfall affect the diurnal patterns and temperature sensitivities (Q₁₀) of soil respiration (R_S) and its key components (i.e. heterotrophic respiration (R_H) and autotrophic respiration (R_A)), we conducted a manipulative field experiment in a desert ecosystem of Northwest China. We simulated five different scenarios of future rain regimes (0%, 25%, 50%, 75% and 100% increase over local annual mean precipitation) each month from May to September in 2009. We measured R_S and R_H every three hours on 6 and 16 days after the rain addition, and estimated R_A by calculating the difference between R_S and R_H. We found that rain addition significantly increased the daily mean R_S and its components on the two measurement days during the growing season. However, the diurnal pattern was different between the two respiration components. Rain addition significantly increased the daily Q₁₀ value of R_H but suppressed that of R_A on Day 6. Rain addition had no influence on daily Q₁₀ value of both respiration components on Day 16 when soil moisture was lower. In addition, we observed significantly higher daily Q₁₀ of R_H than R_A under all five rain addition treatments, indicating that microbial respiration is more temperature sensitive than root respiration in a short-time scale in this desert ecosystem. Thus, partitioning soil respiration into its two components, and analyzing the differential responses of R_H and R_A to future climate changes should be considered for more accurate predictions of soil respiration and regional carbon cycle in these arid and semiarid regions.     

玉米籽粒的特征选择算法——基于支持向量机与遗传算法

在基于数字图像的玉米品种自动识别的研究中,寻找对识别贡献大的新特征项,对玉米品种识别率的提高具有十分重大的意义.把遗传算法和支持向量机算法相结合,设计了具体的基于支持向量机和遗传算法的玉米籽粒特征选择算法,利用这种算法优选提取出的玉米籽粒特征,从玉米籽粒的胚部和冠部的颜色特征与形状特征中找出了对玉米品种识别贡献较大的新特征.     

Inversely estimating temperature sensitivity of soil carbon decomposition by assimilating a turnover model and long-term field data

Change in temperature sensitivity of soil organic carbon (SOC) decomposition with change in soil qualities (i.e. decomposability or lability) is one of the most important issues to be evaluated for projection of future CO₂ emissions from soils. We inversely estimated the temperature sensitivity of SOC decomposition rate by applying a hybrid of the Metropolis-Hasting algorithm and the particle filter method to the extended Rothamsted carbon model (RothC), together with long-term (9 years) experimental data on SOC obtained at five sites in Japanese upland soils. Contrary to the prediction of the Arrhenius kinetics theory, we found no significant differences in temperature sensitivity among soils with different qualities (represented as soil compartments in the RothC model). We also confirmed that there was a positive correlation between the relative temperature sensitivity of the humus compartment and future total CO₂ emissions. The RothC model with default parameterization tended to overestimate future total CO₂ emissions relative to the calibrated model, and the degree of overestimation was larger than that of underestimation.