表层土壤湿度和pH值对胖大海幼树幼苗更新的影响

在越南同奈天然文化自然保护区设置150个样地,运用生态学理论,采用Logitic模型和生态学统计方法,分析表层土壤湿度和pH值对胖大海幼树幼苗更新出现频率的影响.结果表明,胖大海幼树幼苗在SL1、SL2和SL3三个阶段的天然更新出现频率均与各林分胖大海的优势度、表层土壤湿度和pH值有密切关系.适合胖大海幼树幼苗更新的表层土壤湿度:SL1阶段是57.7%~78.8%,最适度是68.2%;SL2阶段是64.8%~80.7%,最适度是72.8%;SL3阶段是65%~80%,最适度是73.3%.适合胖大海幼树幼苗更新的表层土壤pH值:SL1阶段是3.5~5.7,最适度是4.6;SL2阶段是4.4~5.9,最适度是5.1;SL3阶段是5.0~6.5,最适度是5.5.胖大海的丰富度变化受表层土壤湿度和pH值2个因素的影响,其关系能够用Logit Gauss模型来表征.表层土壤湿度和pH值受森林类型影响,胖大海高优势度林分或者高稳定性林分具有更适合胖大海幼树幼苗天然更新的环境.     

响应曲面法优化野蔷薇根多糖脱色工艺

[目的]优化野蔷薇根多糖的过氧化氢(H2O2)法脱色工艺条件,为野蔷薇根多糖的脱色纯化提供技术支持.[方法]以野蔷薇根为试验材料,以多糖脱色率和保留率为考察指标,利用响应曲面法对H2O2法脱色野蔷薇根多糖的工艺条件进行优化.[结果]通过响应曲面法建立野蔷薇根多糖脱色的回归模型为:Y=94.84+3.08A+1.83B+0.88C+0.17AB+0.23AC-0.055BC-3.17A2-1.31B2-0.87C2(Y为多糖脱色率,A为H2O2体积分数、B为溶液pH、C为脱色时间),该模型拟合度较好.H2O2法脱色野蔷薇根多糖的最佳工艺条件为:H2O2体积分数35.0%、溶液pH 9.00、脱色时间4.5 h,在此条件下多糖脱色率和保留率分别为95.48%和75.17%,脱色率与理论值96.55%的相对误差为1.11%.H2O2体积分数、溶液pH和脱色时间3个因素对野蔷薇根多糖脱色效果均有极显著影响(P<0.01).[结论]H2O2脱色法具有操作简便、脱色效果明显、成本低等优点,可对野蔷薇根多糖进行有效脱色.     

响应曲面优化丹参多糖提取工艺及抗氧化活性分析

【目的】优化丹参多糖提取的柔化工艺参数,并分析其抗氧化活性,为丹参多糖产品的研发提供参考依据。【方法】以液料比(A)、浸提温度(B)、浸提时间(C)为自变量,以丹参多糖提取率(Y)为响应值,采用3因素3水平的响应曲面分析法优化丹参多糖提取工艺,同时测定丹参多糖对羟基自由基的清除能力。【结果】建立的丹参多糖提取二次多项回归方程为:Y=1.94-0.041A-0.056B+0.022C-0.046AB+0.13AC-0.03BC-0.24A2-0.75B2-0.44C2,其中浸提温度与浸提时间的交互作用对丹参多糖提取率影响显著(P<0.05)。丹参多糖提取的最佳柔化工艺条件为:液料比25∶1(mL/g)、浸提温度75℃、浸提时间90 min,在此条件下多糖提取率为1.94%,与预测值1.97%接近。丹参多糖对羟基自由基有明显的清除能力,且随多糖质量浓度的增加而逐渐增强;丹参多糖质量浓度为4.5 mg/mL的清除率最高,为42%。【结论】采用响应曲面法优化的提取柔化工艺参数准确可靠,可用于丹参多糖提取;丹参多糖具有一定的体外抗氧化能力,可作为食品及医药行业的天然抗氧化剂资源进行开发利用。     

Controlling Properties and Cytotoxicity of Chitosan Nanocapsules by Chemical Grafting

The tunability of the properties of chitosan-based carriers opens new ways for the application of drugs with low water-stability or high adverse effects. In this work, the combination of a nanoemulsion with a chitosan hydrogel coating and the following poly (ethylene glycol) (PEG) grafting is proven to be a promising strategy to obtain a flexible and versatile nanocarrier with an improved stability. Thanks to chitosan amino groups, a new easy and reproducible method to obtain nanocapsule grafting with PEG has been developed in this work, allowing a very good control and tunability of the properties of nanocapsule surface. Two different PEG densities of coverage are studied and the nanocapsule systems obtained are characterized at all steps of the optimization in terms of diameter, Z potential and surface charge (amino group analysis). Results obtained are compatible with a conformation of PEG molecules laying adsorbed on nanoparticle surface after covalent linking through their amino terminal moiety. An improvement in nanocapsule stability in physiological medium is observed with the highest PEG coverage density obtained. Cytotoxicity tests also demonstrate that grafting with PEG is an effective strategy to modulate the cytotoxicity of developed nanocapsules. Such results indicate the suitability of chitosan as protective coating for future studies oriented toward drug delivery.     

Growth,Metabolism and Yield of Rice Cultivated in Soils Amended with Fly Ash and Cyanobacteria and Metal Loads in Plant Parts

Soil amendment with fly ash(FA) and combined supplementation with N_2-fixing cyanobacteria masses as biofertilizer were done in field experiments with rice. Amendments with FA levels, 0, 0.5, 1.0, 2.0, 4.0, 8.0 and 10.0 kg/m~2, caused increase in growth and yield of rice up to 8.0 kg/m~2, monitored with several parameters. Pigment contents and enzyme activities of leaves were enhanced by FA, with the maximum level of FA at 10.0 kg/m~2. Protein content of rice seeds was the highest in plants grown at FA level 4.0 kg/m~2. Basic soil properties, p H value, percentage of silt, percentage of clay, water-holding capacity, electrical conductivity, cation exchange capacity, and organic carbon content increased due to the FA amendment. Parallel supplementation of FA amended plots with 1.0 kg/m~2 N_2-fixing cyanobacteria mass caused further significant increments of the most soil properties, and rice growth and yield parameters. 1000-grain weight of rice plants grown at FA level 4.0 kg/m~2 along with cyanobacteria supplementation was the maximum. Cyanobacteria supplementation caused increase of important basic properties of soil including the total N-content. Estimations of elemental content in soils and plant parts(root and seed) were done by the atomic absorption spectrophotometry. Accumulations of K, P, Fe and several plant micronutrients(Mn, Ni, Co, Zn and Cu) and toxic elements(Pb, Cr and Cd) increased in soils and plant parts as a function of the FA gradation, but Na content remained almost unchanged in soils and seeds. Supplementation of cyanobacteria had ameliorating effect on toxic metal contents of soils and plant parts. The FA level 4.0 kg/m~2, with 1.0 kg/m~2 cyanobacteria mass supplementation, could be taken ideal, since there would be recharging of the soil with essential micronutrients as well as toxic chemicals in comparative lesser proportions, and cyanobacteria mass would cause lessening toxic metal loads with usual N_2-fixation.     

天津地区土壤环境中有机氯农药残留特征

通过对天津市辖区6种不同土地利用类型和2种灌溉类型的188个点位进行野外实地采样及定量分析,分析了天津市土壤环境中有机氯农药（OCPs）残留的空间分布特征及来源,系统研究了天津市六六六（HCHs）和滴滴涕（DDTs）各异构体单体在土壤中的残留水平、空间和剖面的分布特征,以及残留量今昔情况比较。结果表明：天津市土壤环境中HCHs和DDTs含量均可以达到国家一级标准。天津市HCHs污染空间分布特征为近郊区、滨海地区相对较重,市区次之,远郊区较轻;DDTs污染空间分布特征为近郊区、市区相对较重,远郊区次之,滨海地区较轻;不同的土壤利用类型中,城市绿地的OCPs残留量最高,清灌区和污灌区的OCPs残留量差异不大。剖面分析结果显示,有机氯农药的残留总量主要集中在0～30 cm的耕作层中。通过比较HCHs和DDTs的残留情况发现,DDTs的降解率高于HCHs,天津个别地区出现残留水平异常情况。     

化肥配施生物炭对稻田田面水氮磷流失风险影响

在控制外源氮输入相同的前提下,通过大田试验研究生物炭部分替代化肥作为底肥,不同生物炭施用量(5、10、20 t·hm~(-2))对水稻生长期内稻田田面水氮磷迁移转化特征的影响。研究结果表明:各处理的田面水总氮、硝氮、铵氮浓度在施肥后第3 d达到最高,然后迅速下降,并逐渐稳定;田面水总磷浓度在施肥后2~4 d内增幅较小,而后迅速下降至稳定,施加生物炭对田面水总磷的影响不大;可溶性磷浓度在施肥后2~4 d内处于平稳下降的状态,之后迅速下降至稳定。稻田施肥后10 d内是控制氮磷流失的最佳时段。采用生物炭代替部分化肥的施肥方式,在一定范围内能降低稻田田面水的氮磷浓度,稻田退水氮、磷的输出负荷分别减少了39%~50%和38%~50%,显著提高了水稻生态效益。通过综合效益评估可知,施加5 t生物炭代替化肥是综合效益最高的施肥方法,该施肥方式下氮、磷的年输出负荷分别为16.83、1.89 kg·hm~(-2)。     

不同生物质炭对铅污染淡灰钙土的性质与铅形态变化的影响

通过盆栽试验研究了Pb污染淡灰钙土中施加不同量鸡粪衍生生物质炭(CBC)和油菜秸秆衍生生物质炭(RBC)后,土壤性质变化及基于BCR 4步连续提取法的土壤Pb形态转化特征,并通过逐步回归分析探讨了土壤性质变化与Pb形态转化间的相关性。结果显示:随生物质炭施加量的增加,Pb污染淡灰钙土中Pb形态向更稳定态转化,CBC(RBC)施加量为15%时,酸可提取态Pb百分含量分别下降17.04%(12.3%)。当生物质炭处理水平在10%以下时,RBC施入Pb污染淡灰钙土后对Pb的固定作用更加明显;施加量10%以上时,CBC施加后对Pb的固定效果更占优势。随CBC施加量的增加,土壤p H值、碳酸盐含量、有机质含量显著增加(最大增幅分别为11.36%、6.7%、419.13%),并与Pb形态转化相关性显著(P0.05);随RBC施加量的增加,土壤p H值显著增加(最大增幅10.99%)是影响酸可提取态Pb转化的重要因素,而有机质含量显著增加(最大增幅1 334.56%)对铁锰氧化物结合态、有机结合态和残留态Pb的转化影响显著。由于土壤p H过大会降低土壤质量,建议RBC施加量在10%以内,而CBC的施加量应小于5%。     

响应面法优化海洋沉积物微生物总DNA提取方法

海洋沉积物中的微生物是自然界生态系统中不可或缺的组分,在维持环境与海洋生态平衡方面发挥着重要作用.在海洋沉积物微生物的研究中,细胞裂解率低、片段不够完整等问题导致无法高效地提取微生物的总DNA片段.本实验采用响应面分析法对CTAB-SDS-冻融DNA提取法进行优化.根据单因素的实验结果,选取溶菌酶含量、65℃水浴时间、蛋白酶K含量作为影响因子,利用Box-Behnken进行实验设计,将DNA浓度作为响应值,进行DNA提取方法的响应面优化实验.结果发现:当溶菌酶含量为1.13 mg/mL、65℃水浴时间为100 min、蛋白酶K含量为0.21 mg/mL时,DNA提取效果达到最好.验证实验表明:优化后提取DNA的实际值与理论值相近,具有可行性,优化后提取的DNA片段在纯度、浓度方面高于优化之前.     

农村土地产权收益与投资

本文从代际公共品理论的角度时我国的农村土地制度改革进行分析,既为我国的土地制度改革研究开辟了独特的理论分析视角,又从现实上对农村土地制度改革的目标和办法做出分析,具有重要的理论与现实意义。