Alteration of liver and muscle fatty acid composition in gilthead seabream (Sparus aurata) juveniles held at high stocking density and fed an essential fatty acid deficient diet

The aim of the present study was to determine the combined effect of both stress and EFA deficiency on several biological and biochemical parameters. Fish were fed during 15 weeks two isocaloric and isoproteic diets: a control diet based on fish oil and formulated to meet the n-3 HUFA requirements for this species (1.5% of n-3 HUFA) and a deficient diet containing beef tallow and formulated to be deficient in n-3 HUFA. Each experimental diet was evaluated both at high and low stocking densities (10 and 3.2 kg m^–3 of initial density, respectively).High stocking density produced a chronic stress situation with elevation of plasma cortisol levels. It also caused a reduction in hepatosomatic index and liver lipid contents, increasing the oleic acid/n-3 HUFA ratios in the polar lipids. Fish fed the EFA deficient diet at low stocking density showed common deficiency symptoms. High stocking density in fish fed the EFA deficient diet induced a higher degree of EFA deficiency symptoms leading to mortality, liver steatosis, liver lipid deposition, reduced muscle lipid and reduced n-3 HUFA contents, which particularly affected EPA, but not DHA, suggesting a preferential retention of the latter fatty acid, specially in the phosphoglycerides fraction.     

稀植栽培下春小麦旗叶光合性状的变化规律

试验选用适宜稀植栽培的三个春小麦品种,设三个处理A1:600万株.hm-2(三叶期开沟施肥),A2:450万株.hm-2(三叶期开沟施肥,花期叶面喷肥),A3:300万株.hm-2(花期叶面喷肥)。结果表明,三个品种旗叶叶绿素总量Chl(a+b)和叶绿素a/b值变化规律不同,东农122、龙麦26的Chl(a+b)最大值出现在300万株密度下,克丰6出现在450万株密度下。稀植栽培下比叶重也有不同程度提高,东农122、龙麦26在A1、A2处理下明显高于A3处理。     

不同退耕年限撂荒地植物多样性及生物量分析

退耕还林(草)作为黄土高原水土流失综合治理的主要生态建设措施,经过几十年的开展,黄土高原生态环境得到极大恢复,林草覆盖率明显增加。以安塞县纸坊沟流域为研究区,选取坡耕地(0a)为对照,研究了退耕年限(3～5,10,18,28,37a)对撂荒地植物多样性和生物量的影响。结果表明,随退耕年限的延长,物种丰富度指数、多样性指数、均匀度指数、相同土层根长密度都表现为增大—减小—增大的趋势;植被盖度和地上生物量表现为37a>28a>18a>3～5a>10a>0a;撂荒地植被根系生物量、根长密度均随土层深度增加而减少;不同退耕年限撂荒地,相同层根系生物量表现为28a>37a>18a>3～5a>10a>0a。     

Calibrating the self-thinning frontier

Calibration of the self-thinning frontier in even-aged monocultures is hampered by scarce data and by subjective decisions about the proximity of data to the frontier. We present a simple model that applies to observations of the full trajectory of stand mean diameter across a range of densities not necessarily close to the frontier. Development of the model is based on a consideration of the slope s = ln(N_t/N_t−1)/ln(D_t/D_t−1) of a log-transformed plot of stocking N_t and mean stem diameter D_t at time t. This avoids the need for subjective decisions about limiting density and allows the use of abundant data further from the self-thinning frontier. The model can be solved analytically and yields equations for the stocking and the stand basal area as an explicit function of stem diameter. It predicts that self-thinning may be regulated by the maximum basal area with a slope of −2. The significance of other predictor variables offers an effective test of competing self-thinning theories such Yoda's −3/2 power rule and Reineke's stand density index.     

有机肥质量分数对土壤导水率稳定性的影响

饱和导水率是水循环和土壤侵蚀模型中的重要参数,也是土壤结构改善的重要指标.通过室内土柱模拟实验研究有机肥添加量对风沙土和壤土导水率的影响.土壤添加有机肥的比例设置为0％、5％、10％、15％、20％、25％、30％7个水平,土壤密度设3个水平,各处理5个重复.结果表明：1）土壤饱和导水率随有机肥质量分数的增加呈降低趋势,风沙土的饱和导水率随有机肥质量分数的增加呈直线下降趋势,而壤土饱和导水率的降低趋势随有机肥质量分数的增加减缓;2）有机肥质量分数的增加对土壤密度的降低作用可以抵消有机肥增加导致的饱和导水率的降低;3）低土壤密度下土壤导水率随时间变化不稳定,土壤密度增大后随时间变化稳定.随着有机肥质量分数的增加,土壤导水率的测定过程趋于稳定,但是测定时间延长.     

修枝截干对二球悬铃木叶片光合特性的影响

采用Li-6400便携式光合作用测定系统对修枝截干和自然生长的二球悬铃木中部当年向南枝顶的完全展开叶进行单叶光合特性测定.结果表明,修枝截干和自然生长的二球悬铃木叶片的净光合速率(Pn)日变化均呈双峰曲线,有明显的"午休"现象,最高峰发生在11:00,次高峰在15:00,光强最大时(13:00) Pn最低,即两种生长状态下都受到光抑制.修枝截干二球悬铃木Pn[μmol(CO2)·m-2·s-1]的最高峰为12.16,次高峰为9.21,最低谷为6.47,分别比自然生长高27.06%、69.93%和159.84%,这暗示修枝截干可促进光合作用,减轻光抑制.修枝截干的Pn-光量子通量密度(PPFD)响应可拟合为Pn=12.30(1-1.135 3e-0.030 2PPFD/12.30)(R2 =0.989 1**),自然生长的为Pn=10.92(1-1.130 7e-0.030 5PPFD/10.92)(R2 =0.984 9**),修枝截干的最大光合速率(Pmax)、光补偿点、光饱和点及光合幅度的估算值分别为12.30 μmol(CO2)·m-2·s-1、51.67 μmol·m-2·s-1、1 927.32 μmol·m-2·s-1和1 875.65 μmol·m-2·s-1,分别比自然生长提高12.64%、17.33%、13.85%和13.76%,这意味着修枝截干可提高单叶对光能的利用.修枝截干的Pn-CO2浓度(Ci)响应可拟合为Pn=11.96(1-1.471 6e-0.028 7Ci/11.96)(R2=0.982 4**),自然生长的为Pn=10.70(1-1.465 7e-0.029 2Ci/10.70)(R2 = 0.981 0**),修枝截干的Pmax、CO2补偿点、CO2饱和点及CO2幅度估算值分别为11.96 μmol(CO2)·m-2·s-1、67.54 μmol·mol-1、872.02 μmol·mol-1和804.48 μmol·mol-1,分别比自然生长提高11.78%、-27.44%、0.39%和3.73%,说明修枝截干可增强叶片对低浓度CO2的同化能力.     

沟壑密度调查应采取水文网络法

沟壑密度是评价小流域沟蚀程度的指标,具体地反映了小流域沟蚀轮廓。目前,对于沟壑密度调查,尚无统一规定,有方格网法,小斑号法等。这些方法虽能描述小流域沟蚀现状但不能为沟壑治理的工程设计提供前期资料。水文网络法,从沟道发育入手,将大流域依沟道分布划分为若干小流域,结合工程布局进行调查,计算结果与其它方法相同,结论相同,而基础资料均为以后的工程设计提供了必要的准备,可随时调用。     

辣椒-玉米的不同间作密度对作物产量的影响

[目的]找出辣椒产量最高的辣椒-玉米的最佳间作密度。[方法]研究辣椒-玉米不同面积比下辣椒产量(值)、玉米产量(值)和净增产值,并采用插值分析近似获得玉米-辣椒其他占地面积比值间作密度下辣椒的产量情况。[结果]辣椒-玉米的不同间作密度其产量和产值有显著的区别,间作模式的总产值大小顺序依次为:辣椒-玉米(10∶2)、辣椒-玉米(15∶5)、辣椒-玉米(8∶4)、辣椒-玉米(8∶1)、辣椒单作。[结论]采用合理的间作密度可以有效地提高辣椒的产量和产值。     

Emission of N2O, N2 and CO2 from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting

Soil compaction and soil moisture are important factors influencing denitrification and N₂O emission from fertilized soils. We analyzed the combined effects of these factors on the emission of N₂O, N₂ and CO₂ from undisturbed soil cores fertilized with (150 kg N ha⁻¹) in a laboratory experiment. The soil cores were collected from differently compacted areas in a potato field, i.e. the ridges (ρ_D=1.03 g cm⁻³), the interrow area (ρ_D=1.24 g cm⁻³), and the tractor compacted interrow area (ρ_D=1.64 g cm⁻³), and adjusted to constant soil moisture levels between 40 and 98% water-filled pore space (WFPS).High N₂O emissions were a result of denitrification and occurred at a WFPS≥70% in all compaction treatments. N₂ production occurred only at the highest soil moisture level (≥90% WFPS) but it was considerably smaller than the N₂O-N emission in most cases. There was no soil moisture effect on CO₂ emission from the differently compacted soils with the exception of the highest soil moisture level (98% WFPS) of the tractor-compacted soil in which soil respiration was significantly reduced. The maximum N₂O emission rates from all treatments occurred after rewetting of dry soil. This rewetting effect increased with the amount of water added. The results show the importance of increased carbon availability and associated respiratory O₂ consumption induced by soil drying and rewetting for the emissions of N₂O.     

不同种植方式对红壤旱地土壤水分及抗旱能力的影响

通过3年田间小区试验,研究不同种植方式对红壤旱地土壤水分及抗旱能力的影响.结果表明：1）与种植花生相比,种植苎麻可显著提高土壤有机质质量分数（28.44％）、田间持水量（10.06％）和总孔隙度（5.65％）,土壤密度则显著降低7.20％;2）监测期内,花生地各层土壤以及整个0～ 100 cm土体水分变异系数普遍高于苎麻地,苎麻地0 ～ 100 cm土体水分的时间稳定性和空间协调性优于花生地;3）苎麻地0～ 40 cm土壤较花生地延长抗旱时间7d以上,但随着土层的加深,差异越来越小;4）红壤坡耕地种植苎麻有利于提高红壤旱地土壤抗旱能力,特别是中、上层土壤.从扩充土壤水库的角度考虑,红壤旱地种植苎麻优于种植花生,该研究结果可为挖掘红壤区深层土壤水分提供参考.