Effect of elevated CO2 on soil N dynamics in a temperate grassland soil

The response of terrestrial ecosystems to elevated atmospheric CO₂ is related to the availability of other nutrients and in particular to nitrogen (N). Here we present results on soil N transformation dynamics from a N-limited temperate grassland that had been under Free Air CO₂ Enrichment (FACE) for six years. A ¹⁵N labelling laboratory study (i.e. in absence of plant N uptake) was carried out to identify the effect of elevated CO₂ on gross soil N transformations. The simultaneous gross N transformation rates in the soil were analyzed with a ¹⁵N tracing model which considered mineralization of two soil organic matter (SOM) pools, included nitrification from NH₄⁺ and from organic-N to NO₃⁻ and analysed the rate of dissimilatory NO₃⁻ reduction to NH₄⁺ (DNRA). Results indicate that the mineralization of labile organic-N became more important under elevated CO₂. At the same time the gross rate of NH₄⁺ immobilization increased by 20%, while NH₄⁺ oxidation to NO₃⁻ was reduced by 25% under elevated CO₂. The NO₃⁻ dynamics under elevated CO₂ were characterized by a 52% increase in NO₃⁻ immobilization and a 141% increase in the DNRA rate, while NO₃⁻ production via heterotrophic nitrification was reduced to almost zero. The increased turnover of the NH₄⁺ pool, combined with the increased DNRA rate provided an indication that the available N in the grassland soil may gradually shift towards NH₄⁺ under elevated CO₂. The advantage of such a shift is that NH₄⁺ is less prone to N losses, which may increase the N retention and N use efficiency in the grassland ecosystem under elevated CO₂.     

中国农户信贷需求及其影响因素分析——基于Logistic模型的实证研究

本文基于来自中国12个省（市）3051户农户家庭的实地调查数据,运用Logistic模型实证研究了农户信贷需求及其影响因素。研究结果表明,样本农户的年龄与信贷需求之间成倒“u”型关系;农户家庭生命周期、受教育程度会在一定程度上影响信贷需求;农户的家庭收入、家庭规模、家庭负担率以及是否购买养老保险对农户的信贷需求有显著的正向影响。另外,农户从事的经济活动类型也会对农户的信贷需求产生影响,以兼业农户为参照,纯农业农户对信贷需求有显著的正向影响,而非农业农户对信贷需求有显著的负向影响。     

Sensitivity analysis and calibration of CN-SIM to simulate the mineralisation of liquid dairy manures

Scientific knowledge of carbon and nitrogen dynamics incorporated into soil organic matter (SOM) dynamic simulation models can be tested using experimental data from decomposition experiments. This possibility is particularly interesting for liquid animal manures, which are very heterogeneous materials. CN-SIM is a SOM model that was successfully applied for the short- and long-term simulation of C and N dynamics in the soil. The objective of this research was to test this model using results of a 180-d laboratory incubation of five liquid dairy manures in three soils. Initial sensitivity analysis indicated that model parameters that mostly impact net CO₂ and soil mineral nitrogen concentration (SMN) are those that allocate manure C and N to model pools, their decomposition constants and soil parameters that describe microbial biomass and its residues. Automatic parameter optimisation was carried out with the downhill simplex method separately for 15 manure by soil combinations. After optimisation, CO₂ respiration was well simulated for the entire period, while SMN was overestimated after day 40. Simulations overestimated the remineralisation of immobilised N in the first weeks. Simulated initial microbial immobilisation was the only possibility for the model to match the experimental decrease of SMN, while simulated N remineralisation after day 40 was necessary to enable a good simulation of respired CO₂. Further work is needed to test whether these simulations can be improved by adding SMN sinks (such as denitrified N and clay-fixed ammonium).     

Dependence of soil respiration on soil moisture, clay content, soil organic matter, and CO2 uptake in dry grasslands

The effects of abiotic and biotic drivers on soil respiration (R_s) were studied in four grassland and one forest sites in Hungary in field measurement campaigns (duration of studies by sites 2-7 years) between 2000 and 2008. The sites are within a 100 km distance of each other, with nearly the same climate, but with different soils and vegetation. Soil respiration model with soil temperature (T_s) and soil water content (SWC) as independent variables explained larger part of variance (range 0.47-0.81) than the Lloyd and Taylor model (explained variance: 0.31-0.76). Direct effect of SWC on R_s at much smaller temporal and spatial scale (1.5 h, and a few meters, respectively) was verified.Soil water content optimal for R_s (SWC_opt) was shown to significantly (positively) depend on soil clay content, while parameter related to activation energy (E₀) was significantly (negatively) correlated to the total organic carbon content (TOC) in the upper 10 cm soil layer. Dependence of model parameters on soil properties could easily be utilized in models of soil respiration. The effect of current (a few hours earlier) assimilation rates on soil respiration after removing the effect of abiotic covariates (i.e. temperature and water supply) is shown. The correlation maximum between the R_s residuals (R_{s_res}, from the R_s (SWC, T_s) model) and net ecosystem exchange (NEE) was found at 13.5 h time lag at the sandy grassland. Incorporating the time-lagged effect of NEE on R_s into the model of soil respiration improved the agreement between the simulated vs. measured R_s data. Use of SWC_opt and E₀ parameters and consideration of current assimilation in soil respiration models are proposed.     

森林流域坡地壤中流模型与模拟研究

本文以水量平衡原理、动力学假设以及饱和导水率与有效孔隙度的对数递减模型为基础,提出了一个形式简单的森林流域坡地壤中流模型（以下称为改进模型）。并以二道白河森林流域内阔叶红松林土壤为背景制作模拟坡面,在模拟坡面上用两场不同强度的降雨对该模型进行了验证;同时,本文也分别用Ｓｌｏａｎ所提出的贮水泄流模型（以下称Ｓｌｏａｎ模型）与Ｒｏｂｉｎｓｏｎ所修改后的贮水泄流模型（以下称Ｒｏｂｉｎｓｏｎ模型）对这两场降雨进行了预测,并将这３个模型预测的结果与实测结果进行了比较。结果表明,改进模型精度比其它两个模型高。     

火锅蘸酱常温贮存过程中微生物的变化研究

为预测和制定火锅蘸酱在常温贮存条件下的货架期,研究常温下火锅蘸酱中微生物生长趋势的变化,利用DPS软件,建立Gompertz模型,然后用生产日期相近的2个组蘸酱的微生物变化验证所建立的生长模型的准确度。研究结果表明,试验中所建立的Gompertz模型能有效地拟合火锅蘸酱在常温下菌落总数的动态变化,准确度较高,能准确预测不同贮藏时间内火锅蘸酱的菌落总数,为快速、可靠地实时预测火锅蘸酱的货架期和微生物学品质,提供了一个方便有效的方法;利用该模型可以预测火锅蘸酱12个月的保质期内菌落总数小于105cfu/g。     

肉鸡氨基酸需要动态预测模型的评价

选用初出壳爱拔益加健康雏鸡480只,分别按氨基酸模型预测值的90%、100%、110%以及中国饲养标准配制饲粮,进行饲养和屠宰试验,以评价肉鸡氨基酸需要动态模型预测值在商业饲养条件下的应用效果.结果表明,模型用于预测肉鸡的氨基酸需要量有很好的精确度.将模型预测值降低10%配制饲粮,虽然没有影响到肉鸡的增质量(P>0.05),但显著提高了肉鸡采食量(P＜0.05),导致耗料增质量比和肉鸡腹脂率显著增加(P＜0.05).而将模型预测值提高10%,没有表现生长性能和胴体品质以及其他方面的持续改善.按模型100%预测值配制的饲粮饲养效果良好,与按中国饲养标准配制的饲粮相比,肉鸡生长性能无显著差异(P>0.05),但血清中IGF-Ⅰ 水平显著提高(P＜0.05),腹脂率显著降低(P＜0.05),总经济效益显著增加(P＜0.05).     

模拟技术在水库防洪预案中的应用(英文)

[目的]探讨模拟技术在水库防洪预案中的应用。[方法]在研究河流系统模拟相关理论的基础上,采用InfoWorks RS系统建立了河流系统洪水演进模拟数字化模型,并对校核标准洪水下泄进行了仿真模拟分析。[结果]利用基于InfoWorks RS软件的洪灾信息系统对校核标准下洪水下泄对下游的淹没情况进行模拟,得出了各断面最大流量时的各水力参数、各控制断面流量与流速度随时间的变化图、各断面水力要素随时间的变化图以及下游水库控制流域最大淹没面积风险分析图。[结论]为减少洪涝灾害造成的严重损失、制定防洪预案提供了参考。     

不同贮藏条件下小麦和玉米种子的水分变化规律及其建模验证

种子平衡水分(EMC)是评价种子吸湿或解吸动态变化的重要指标。本研究以不同初始水分(IMC)小麦和玉米种子为试材,研究了不同贮藏条件下的吸湿解吸规律,并建模验证。结果表明,玉米种子在8.0%IMC、15℃、相对湿度(RH)<18.8%, 25°C或40℃和RH<48.1%条件下; 以及在13.5%IMC或18.0%IMC、15°C、25°C或40℃、RH<48.1%条件下呈解吸变化; 而在其他条件下均呈吸湿变化。小麦种子在贮温15、25和40℃时,8.0%IMC在RH≤18.8%、18.0%IMC在RH≤48.1%时解吸,其他条件下吸湿; 13.5%IMC在15℃和RH<48.1%以及25、40℃和RH<18.8%时解吸,其他条件下吸湿。小麦种子在15℃和RH=53.0%、25℃和RH=48.0%以及40℃和RH=43.0%时的安全水分(SWC)依次为13%、11%和9%; 玉米种子在15℃和RH=55.0%、25℃和RH=50.0%以及40℃和RH=40.0%时,其SWC依次为14%、12%和9%。小麦种子EMC在15℃和RH>50.0%、25℃和RH>50.0%、40℃和RH>48.0%时超过其对应条件下的SWC; 玉米种子EMC在15℃和RH>50.0%、25℃和RH>47.0%以及40℃和RH>47.0%时超过其对应条件下的SWC。玉米郑单958的平衡时间(d)与IMC(x)、RH(y)和温度(z)的预测模型为d = 35.34 + 4.32x - 0.28y - 0.35z - 0.031xy - 0.012xz - 0.0011yz + 0.003y²,农大108为d = 39.76 + 2.35x - 0.39y - 0.27z - 0.022xy - 0.014xz - 0.0057yz + 0.008y²,小麦山农15为d = 25.69 + 7.65x - 0.27y - 0.89z - 0.12xy - 0.07xz - 0.007yz + 0.006y²+ 0.04z²,泰农18为d = 46.67 + 0.39x - 0.28y - 1.72z - 0.006yz + 0.006y²+ 0.017z²。模型经验证,预测性良好。