连续模拟降雨下岩溶区含砾石堆积体坡面径流产沙特征

为明确砾石含量对岩溶区石灰土质堆积体坡面径流产沙特征的影响,以土质坡面为对照,采用室内模拟降雨试验方法,研究了递增型降雨(0.5,1.0,2.0,2.5,3.0 mm/min)条件下偏土质(砾石含量30%)和偏石质(砾石含量70%)石灰土坡面的径流特性及侵蚀特征。结果表明:(1)随雨强增大,各坡面径流率呈稳定增长—波动的变化趋势,且土质坡面径流率整体小于2种含砾石坡面;偏土质、偏石质坡面累计产流量较土质坡面增加了0.49,0.37倍;(2)1.0~3.0 mm/min雨强下,土质坡面侵蚀速率在0.16~5.4 g/(m^2·s)范围内波动,整体呈稳定—波动增加的变化趋势;偏土质和偏石质坡面分别为0.16~5.4,0.06~0.74 g/(m^2·s),前者侵蚀速率变化范围大且波动剧烈,后者变化范围小且稳定;随砾石含量的增加,各坡面累计侵蚀量呈先增后减的变化趋势,偏土质坡面侵蚀量较土质坡面增加2.5倍,偏石质坡面较其减少了0.9倍;(3)土质、偏土质和偏石质坡面的侵蚀速率与径流率分别呈极显著正相关幂函数、线性函数和线性函数关系。研究结果可为桂西北岩溶区弃渣场水土流失治理提供一定的科学依据。     

镉和模拟酸雨胁迫对苦楝幼苗镉含量及叶片抗氧化系统的影响

为探讨苦楝在重金属Cd和酸雨的单一及复合胁迫下的生理响应特征,采用人工配置土壤盆栽试验,研究不同浓度Cd(0、30、60、90、120、150、180 mg·kg^-1)和3个梯度模拟酸雨(pH值5.6、4.5、3.5)单一及复合处理对苦楝幼苗生物量、Cd含量及叶片保护性酶[超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)]活性和抗坏血酸-谷胱甘肽循环(AsA-GSH)的影响。结果表明,除低浓度Cd(≤30 mg·kg^-1)单一及其与pH值4.5酸雨复合处理对幼苗地上部、地下部生物量有促进作用外,其他处理均表现出抑制作用,其中复合处理对苦楝幼苗的抑制作用更明显,表现为叠加效应;单一Cd处理时,随着Cd浓度的增加,幼苗根、茎、叶中Cd含量逐渐升高,且根系大于茎叶,复合处理抑制了植物对Cd的积累,对叶片的抑制作用最强;Cd和酸雨单一及复合处理下叶片SOD、CAT和POD活性均有所增加,分别在60 mg·kg^-1 Cd、pH值5.6,60 mg·kg^-1 Cd、pH值4.5和90 mg·kg^-1Cd、pH值4.5时出现阈值;在AsA-GSH循环中,单一Cd处理下,AsA、GSH含量和抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)活性均随着Cd浓度的增加呈先上升后下降的趋势,单一酸雨处理对上述4个指标的影响不尽一致,而复合处理下上述指标在Cd浓度≤60 mg·kg^-1、pH值≥4.5时均能保持较高值,且随着胁迫程度的加深均出现了阈值。综上所述,苦楝对重金属Cd和酸雨胁迫具有一定的耐性,可在Cd浓度≤60 mg·kg^-1和pH值≥4.5的酸雨双重污染区域正常生长。本研究结果为土壤Cd污染的酸雨区域的修复植物筛选提供了理论基础和参考依据。     

Italian ryegrass establishment by self-seeding in integrated crop-livestock systems: Effects of grazing management and crop rotation strategies

We evaluated the re-establishment of an Italian ryegrass pasture by self-seeding on a no-till integrated crop-livestock systems (ICLS) in the southern region of Brazil. This work is part of a long-term experimental protocol initiated in 2003. We tested the effects of various management practices, such as summer crop systems (soybean vs. maize–soybean rotation), stocking methods (continuous vs. rotational) and grazing intensities (low vs. moderate), on Italian ryegrass pasture establishment. In addition, we tested resilience of the system by testing pasture's ability to re-establish following a year without seed head production. The experiment consisted in the rotation, on the same area, of Italian ryegrass pasture grazed by sheep during the winter and up to the end of the grass production cycle, and soybean or soybean-maize grain crops rotation cultivated during the summer. The pasture established itself by self-seeding since 2005. Data were collected in 2011 and 2012 stocking season. The soybean summer crop, continuous stocking and low grazing intensity, all positively affected the production of reproductive tillers in 2011. Grazing intensity in 2011 strongly influenced early vegetative tiller densities (before crop harvest) in 2012. However, none of the grazing intensity or the stocking method treatments affected herbage mass at the end of pasture establishment in 2011 or 2012. On the other hand, the soybean summer crop positively affected pasture establishment, both in term of tiller densities and herbage mass at the end of pasture establishment. The removal of all seed heads in 2011 (preventing seed production) resulted in the total failure of pasture establishment in 2012. Overall, Italian ryegrass establishment by self-seeding relies on the annual replacement of the soil seed bank. This experiment demonstrated that under various stocking methods, moderate grazing intensity and maize or soybean summer crop, Italian ryegrass pasture establishment by self-seeding remains successful even when the stocking periods extended up to the end of the grass production cycle. Self-seeding with moderate grazing intensity ensures successful pasture establishment, reduces labour and costs and allows to increase the stocking period and so animal live weight gain over the grazing season.     

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

Aeolian-fluvial interplay erosion regions are subject to intense soil erosion and are of particular concern in loess areas of northwestern China.Understanding the composition,distribution,and transport processes of eroded sediments in these regions is of considerable scientific significance for controlling soil erosion.In this study,based on laboratory rainfall simulation experiments,we analyzed rainfall-induced erosion processes on sand-covered loess slopes(SS)with different sand cover patterns(including length and thickness)and uncovered loess slopes(LS)to investigate the influences of sand cover on erosion processes of loess slopes in case regions of aeolian-fluvial erosion.The grain-size curves of eroded sediments were fitted using the Weibull function.Compositions of eroded sediments under different sand cover patterns and rainfall intensities were analyzed to explore sediment transport modes of SS.The influences of sand cover amount and pattern on erosion processes of loess slopes were also discussed.The results show that sand cover on loess slopes influences the proportion of loess erosion and that the compositions of eroded sediments vary between SS and LS.Sand cover on loess slopes transforms silt erosion into sand erosion by reducing splash erosion and changing the rainfall-induced erosion processes.The percentage of eroded sand from SS in the early stage of runoff and sediment generation is always higher than that in the late stage.Sand cover on loess slopes aggravates loess erosion,not only by adding sand as additional eroded sediments but also by increasing the amount of eroded loess,compared with the loess slopes without sand cover.The influence of sand cover pattern on runoff yield and the amount of eroded sediments is larger than that of sand cover amount.Furthermore,given the same sand cover pattern,a thicker sand cover could increase sand erosion while a thinner sand cover could aggravate loess erosion.This difference explains the existence of intense erosion on slopes that are thinly covered with sand in regions where aeolian erosion and fluvial erosion interact.     

Effects of Grazing Intensity on Soil and Vegetation Properties in a Mediterranean Rangeland

Grazing modifies the aboveground soil and plants of rangeland ecosystems. This study was conducted to determine the effects of various grazing intensity levels on soil bulk density, soil pH, soil electrical conductivity (EC), soil total organic carbon (TOC), aboveground biomass production, plant community richness (N), and vegetation diversity (H) in Gian Rangeland, Hamedan Province, Iran. Soil and vegetation samplings were conducted based on the randomized systematic method. Soil and vegetation samplings were carried out along 100-m-long transects placed at 100, 200, 400, 800, and 1600 m running perpendicular to six sheep corrals. The effects of various grazing intensities on studied parameters were detected by analysis of variance (ANOVA) (at α = 0.05). Results of this study indicated the soil bulk density, EC, TOC, aboveground biomass production, plant community richness, and vegetation diversity values were altered significantly at different distances from the sheep corrals. However, soil pH was not significantly affected by various grazing intensities.     

放牧对草甸草原土壤水热状况和地上生物量的影响

本文以呼伦贝尔草甸草原为对象,研究了不同放牧强度对草原群落土壤水热状况和地上生物量的影响,旨在揭示二者之间的相互关系。研究结果表明,随着放牧强度的增加,生长季平均土壤温度呈逐渐上升的趋势;放牧对群落3个组份[羊草（Leymus chinensis）、贝加尔针茅（Stipa baicalensis）、杂类草]生物量和相对优势度产生影响。其中,羊草地上生物量和优势度随着放牧强度的增加显著线性降低,而贝加尔针茅和杂类草的生物量与优势度均在中度放牧处理下最高。土壤含水量与羊草生物量显著正相关,与杂类草生物量负相关,而与贝加尔针茅生物量间的关系极弱。本研究为完善放牧优化理论,揭示放牧在草地生态系统功能过程中的梯度效应提供了一个较为重要的研究线索,为草地放牧优化管理制度的确立提供了一定的科学依据。     

荒漠草原主导种群与植物群落地上现存量的关系

以内蒙古锡林郭勒盟苏尼特右旗短花针茅荒漠草原为对象,采用随机区组放牧试验设计,结合对比分析、线性回归分析以及结构方程模型等数据分析方法,探讨荒漠草原主要种群与植物群落地上现存量的关系及在放牧条件下的变化特点。结果表明:随放牧强度增大,短花针茅、无芒隐子草和碱韭主导种群地上现存量占植物群落地上现存量的比例下降,且主导种群与植物群落地上现存量的线性关系减弱;不同年度间主导种群占植物群落地上现存量比例以及线性关系会产生变动;短花针茅种群对荒漠草原植物群落的影响强于无芒隐子草种群和碱韭种群,但无芒隐子草种群在降雨较好年份具有补偿作用。     

A longitudinal study of oestrous characteristics and conception in tie-stalled and loose-housed Swedish dairy cows

The presence and importance of visual oestrous symptoms and the relation to conception, breed, housing system and milk yield were studied. Data were collected from a Swedish research herd during a 16-year period. Local, secondary and primary oestrous symptoms and an overall oestrus intensity score (OI) were studied. Decreasing trends in oestrous expression and conception rates (CR), and an increase in CR with more intensive oestrus, from 24% at OI score one (very week) to 54% at OI score five (very strong) were observed. The mean interval from first to last observed oestrus symptom was long with a large variation (54?±?SD?=?32?h). Generally, irrespectively of housing system, Swedish Red cows had higher CR, more intensive oestruses and longer oestrus durations compared to Swedish Holstein cows. Local oestrous symptoms, with CR of 24–28%, were most frequently detected, which is why more attention should be paid to local oestrous symptoms.     

刈割强度对大针茅草原植物群落特征和土壤理化性质的影响

探究不同刈割强度对大针茅典型草原植物群落特征以及土壤理化性质的影响,可为大针茅草原制定合理科学的刈割制度提供理论依据。本研究以大针茅典型草原为对象,于2020年在内蒙古锡林浩特市毛登牧场刈割实验平台进行野外植被调查和取样。该实验平台于2014年建立,以不刈割为对照（CK）,设置轻度（LM）、中度（MM）及重度刈割（HM）3个处理。本研究通过计算物种重要值和多样性指数,测定植物群落地上、地下生物量以及土壤理化性质,探究群落特征与土壤理化性质的关系。结果表明：1）与不刈割相比,不同刈割强度均增加了新物种,且中度刈割的物种数最多;与不刈割相比,不同刈割强度均显著增加了群落的丰富度和Shannon-Wiener指数,且轻度刈割显著增加了优势度和均匀度指数,表明轻度刈割最有利于群落多样性的维持;不同刈割强度对大针茅草原的生产力均无显著影响;2）土壤全碳、全氮和pH均在中度刈割时最高,且显著高于不刈割,表明中度刈割对土壤养分有积极影响;3）硝态氮是影响草地生产力的主要土壤因子,土壤含水量是影响草地群落多样性的主要土壤因子。本研究可为大针茅典型草原群落结构、物种多样性以及生产力等方面的研究提供重要参...     

应用GOMPERTZ模型预测交通生成量

应用GOMPERTZ模型预测了出行强度，并通过实际数据对GOMPERTZ模型参数进行了标定，采用实例对模型进行了比较分析。结果证明了GOMPERTZ模型用于小区居民出行强度预测的可行性，以及具有一定的优越性。再根据小区预测年的的人口便可以得到小区的交通生成量。