黔西高原坡面次降雨产流产沙特征

利用野外径流小区径流泥沙观测数据与降雨特征资料,定量研究黔西高原地区降雨对坡面产流产沙的影响.结果表明:1)黔西高原地区年均侵蚀性降雨为22次,中、低降雨强度型降雨次数占降雨次数的93.0％;2)坡面产流产沙特征与降雨的年内分布密切相关,5-8月坡面产沙量占总产沙量的99.2％,产流量占总产流量的95.8％;3)坡面产沙量与降雨量存在显著的指数相关关系,其指数方程为M=0.346e0.109P;4)坡面产流产沙与中、高降雨强度型大雨和暴雨密切相关,4次暴雨事件产生的径流量占总径流量的57.3％,产沙量占总产沙量的91.5％.     

山东省药乡小流域侵蚀性降雨分布特征

为探究山东省药乡小流域侵蚀性降雨分布特征,本研究选择裸地坡面径流小区为研究对象,利用小区观测法得到的降雨、径流以及泥沙等资料,通过频率分析法拟定研究区侵蚀性降雨标准,并运用数理统计方法从时间、降雨强度、降雨侵蚀力角度分析侵蚀性降雨分布特征.结果表明:1)该研究区侵蚀性降雨标准为降雨量17.3 mm;2)7月份侵蚀性降雨场次、降雨量、径流量和产沙量占侵蚀性降雨比例为42.31％、45.71％、85.78％和97.97％,其他月份侵蚀性降雨分布较少;3)大雨、暴雨以上侵蚀性降雨,高降雨强度型降雨场次分别占相应雨量等级比例为60％和100％,其产沙量所占比例分别为75.07％、100％;4)降雨侵蚀力＞1000MJ·mm/(h·hm2)侵蚀性降雨产沙量占侵蚀性降雨比例为95.26％,其径流深是≤1 000 MJ·mm/(h·hm2)侵蚀性降雨3倍以上.以上研究表明,研究区侵蚀性降雨标准为17.3 mm,其主要分布在中雨以上雨量等级,造成严重土壤侵蚀的侵蚀性降雨多为高降雨强度型降雨或降雨侵蚀力＞1 000 MJ·mm/(h.hm2)的降雨,且其多分布于7月份.本文结果有助于研究区小流域侵蚀性降雨规律分析以及土壤侵蚀规律研究.     

贵州常态地貌区降雨侵蚀特征分析——以龙里县羊鸡冲小流域为例

为了解贵州常态地貌区降雨侵蚀力特征,以贵州省龙里县羊鸡冲小流域为研究区,根据小流域2009年6个标准径流小区的定位观测资料,利用统计分析方法,确定研究区侵蚀性降雨雨量标准,估算降雨侵蚀力,分析其年内分布规律及与侵蚀模数之间的关系。结果表明:研究区侵蚀性降雨雨量标准为23.6 mm;出现侵蚀性降雨的5个月(4、5、6、7、9月)中,6月份降雨侵蚀力最大,为2 589.10 MJ·mm/(hm~2·h),侵蚀模数也最大,为5 606.4 t/(km~2·a),4月份降雨侵蚀力最小,为818.49 MJ·mm/(hm~2·h),侵蚀模数也最小,为2 277.6 t/(km~2·a);拟合侵蚀模数与次降雨量的关系曲线为y=1 377.6ln x-3 849.1(R~2=0.607 2),两者相关性显著。     

三峡库区典型农业小流域次降雨产沙过程及其影响因素

为探究引起三峡库区农业小流域土壤侵蚀的主要次降雨因子,通过天然降雨观测资料,分析忠县石盘丘小流域2019年侵蚀性降雨年内分布特征和典型次降雨条件下A和B 2个集水区产沙过程的变化规律,采用相关性分析方法,揭示次降雨产沙的主要影响因素。结果表明:(1)全年119场降雨资料中,有19场为侵蚀性降雨。全年侵蚀性中雨共发生10次,是侵蚀性降雨中最常见的降雨类型。暴雨及以上降雨是造成研究区产沙量最大的降雨类型。(2)在典型中雨、大雨和暴雨产沙事件中,B集水区产沙量分别是A集水区的5.13,1.66,7.56倍。对3场典型次降雨产沙过程进行分析发现,B集水区产沙过程线随降雨历时的延长,变化程度更剧烈。(3)各PIn因子与研究区产沙量的相关性系数大小排序为PI30>PI10>PI15>PI60>PI5>PI90>PI。对各类降雨因子与研究区的产沙量进行相关性分析,系数大小排序为P>PIn>In>I>T。A、B集水区产沙量与次降雨量P和PI30均存在极显著正相关性。总之,在三峡库区开展水土保持工作时,要加强对暴雨及以上降雨造成农业小流域水土流失的监测与预警响应能力;P和PI30能较好地反映三峡库区天然次降雨对农业小流域侵蚀产沙的影响;对天然降雨条件下的次降雨侵蚀力进行估算时,可将PI30作为主要参考因子;农林水复合生态系统与结构简单的传统农耕模式相比,具有更丰富多元的层次结构,不仅能全面开发利用小流域的农业资源,更有利于保持水土,且其对降雨环境变化的适应性也更强。     

西部黄土丘陵区不同草地土壤侵蚀对侵蚀性降雨的响应

[目的]研究西部黄土丘陵区人工和天然草地对不同类型侵蚀性降雨的响应,为该区植被建设和水土流失防治提供指导。[方法]利用甘肃省定西市安家沟径流场2007—2015年的观测数据,分析侵蚀性降雨因素对坡度为20°的人工草地和天然草地土壤侵蚀的影响。[结果]西部黄土丘陵区的侵蚀性降雨分布在5—9月,其中7—8月的侵蚀性雨量较大,其侵蚀量占年均侵蚀的70%以上。两种不同类型的草地侵蚀量均与PI10相关性最好。该区域侵蚀性降雨主要是中雨和大雨,造成的草地侵蚀量占年均侵蚀的86%。中、高雨强型降雨的侵蚀量分别占人工、天然草地总量的90.8%和91.2%,其侵蚀量与PI10,PI30呈较好的幂函数关系。大于300 MJ·mm/(hm2·h)的高侵蚀力型降雨引起的侵蚀量最大,分别占人工、天然草地总侵蚀量的32.3%和33.4%;50~100MJ·mm/(hm2·h)的中侵蚀力型降雨次数最多,而引起人工、天然草地的侵蚀占相应总量的26.0%和29.1%。[结论]人工草地(盖度75%~82%)和天然草地(盖度80%)的侵蚀性降雨量标准分别为11.3和11.9mm,最大I10标准分别为10.4和11.7mm/h。天然草地比人工草地具有更好的水土保持效果。     

黔西高原地区降雨侵蚀力的简易算法

[目的]对黔西高原地区侵蚀性降雨特性进行分析并探索降雨侵蚀力的简易算法,为该区土壤侵蚀预报模型的建立提供理论依据。[方法]利用径流小区观测法,基于毕节小区2012—2014年53次降雨过程资料进行分析。[结果](1)降雨量(P)和最大60min降雨动能(E60)是影响坡面产流、产沙的两个主要因子。坡面产流、产沙与最大60min雨强(I_(60))显著相关;(2)坡面产流产沙与二元复合因子的相关系数显示,EI_(60),PI_(60)和I30I_(60)是影响坡面产流、产沙的3类主要降雨复合指标,EI30和EI_(60)与坡面产流产沙的相关系数间相差较小;(3)基于坡面产流、产沙与降雨单指标和降雨复合指标的相关关系,确定了简易算法的参数。[结论]基于可比性,以R=EI30作为参照值对3种简易算法的结果进行决定系数和偏差率比较后,得到研究区便捷、快速的降雨侵蚀力简易算法为:R=0.344(PI_(60))。     

坡度对黔西北地区坡面产流产沙的影响

利用野外径流小区观测获得的径流泥沙数据与降雨资料,分析了黔西北地区坡面产流产沙随坡面坡度变化产生的变化规律。结果表明:(1)坡面产流量与产沙量随坡度的增加呈先增大后减小再增大的变化趋势。(2)坡面产流量和产沙量与大雨和暴雨存在显著性相关关系,这2类降雨条件下产流量占总产流量的71.3%~76.5%;产沙量占总产沙量的75.9%~93.8%。(3)坡面产流量与中雨强型侵蚀性降雨显著相关;坡面产沙量与高雨强型侵蚀性降雨显著相关,该类降雨条件下产沙量占总产沙量的46.6%~76.4%。(4)坡面产流产沙与降雨复合因子PI30在不同坡度条件下呈幂函数关系。     

1951-2018年韶关不同量级降雨侵蚀力变化

降雨是引起土壤水蚀的主要动力因子之一,为探讨韶关市不同量级降雨对土壤水蚀特征造成的影响,选取1951—2018年韶关市逐日降雨量数据,采用日降雨侵蚀力模型计算降雨侵蚀力,利用变异系数、趋势系数分析不同时间尺度各量级降雨侵蚀力的变化。结果表明:(1)68年来韶关市年均降雨侵蚀力为9 314(MJ·mm)/(hm~2·h·a),变异系数为0.29,属于中等变异;(2)年降雨量、降雨日数、侵蚀性降雨量和降雨日数均呈上升趋势,而非侵蚀性降雨量和降雨日数则呈下降趋势,且暴雨量和暴雨侵蚀力呈较明显上升趋势,说明韶关市降雨更为集中,降雨侵蚀力增加;(3)大雨以上量级的降雨日数和降雨量占总降雨日数和总降雨量的比例分别为43.91%,51.15%,而其引起的降雨侵蚀力占总降雨侵蚀力比例却高达77.05%。研究结果为韶关市的土壤侵蚀的监测和水土保持工作提供参考。     

紫色丘陵区侵蚀性降雨与降雨侵蚀力特征

降雨侵蚀力（R值）的空间分布反映了区域气候对土壤侵蚀的作用。利用四川盆地紫色丘陵区多年实测降雨资料,应用频率分析法,推求该地区侵蚀性降雨的一般雨量标准,揭示该地区侵蚀性降雨及其侵蚀特征,进而运用降雨侵蚀力日降雨量计算方法,分析紫色丘陵区降雨侵蚀力时空分布特征。结果表明：1）紫色丘陵区顺坡休闲农耕地的侵蚀性降雨的一般雨量标准为11．3mm;2）紫色丘陵区多年平均总降雨量中有60％以上属于侵蚀性降雨,侵蚀性降雨主要集中于5—9月,其中7、8月年均侵蚀性降雨量和土壤侵蚀量最大,空间分布上表现为丘陵区边缘地区大于中部地区;3）紫色丘陵区年均R值介于5000～6500MJ／（mm·hm^2·h）之间,由丘陵区周边向中心逐渐减小,研究区北部的巴中、达县、阆中3站的年均降雨侵蚀力形成高值区,中部的遂宁站形成低值中心,北部大于南部,西部大于东部;4）紫色丘陵区R值主要由≥15mm的降雨构成,占76．9％-82．1％,年内集中度较高,主要分布在汛期5—10月份,占年R值的89％以上;5）R值的年际变化较大,达到中等程度变异,不同地区的R值年际变化差异较大,但并未表现出明显的随时间变化的增减趋势。     

重庆涪陵区降雨侵蚀力时间分布特征

降雨侵蚀力反映降雨引起土壤侵蚀的潜在能力.利用涪陵区49 a气象资料,对该地区降雨侵蚀力的年内分布和年际变化特征进行研究.结果表明: (1)涪陵区多年平均降雨侵蚀力为3571.07 MJ·mm·hm-2·h-1·a-1,最大年为4039.07MJ·mm·hm-2·h-1·a-1,最小年为1193.76 MJ·mm·hm-2·h·a-1,年际差异非常显著且明显大于降雨量和侵蚀性降雨量的年际变化.(2)该区降雨侵蚀力季节分布为单峰型,可分为高值期、中值期、低值期和无侵蚀期4个不同的时期;4～10月的降雨侵蚀力可占全年年降雨侵蚀力(尺)值的94.06%,6月最大为670.94 MJ·mm·hm-2·h-1·a-1,其次7月为664-26MJ·mm·hm-2·h-1·a-1,最小月为0;降雨侵蚀力的季节变化与降雨量和侵蚀性降雨总体变化趋势一致. (3)降雨侵蚀力时间变化与地表状况的配合可对实际土壤侵蚀的发生产生较大影响,在该地区5、6、7月降雨量在147.4 mm和176.0 mm范围内变化,4月、8、9、10月降雨量在101.9ranl和115.7mm范围变化,年降雨量大于1090.6mm的年份,是当地水土流失极易发生的侵蚀敏感期.(4)该地区小流域综合治理中应充分重视每年5、6、7三个月内坡耕地覆盖情况,开发建设活动不仅应避开这3个月,同时在雨季开始前应注意裸露开挖面及弃土弃渣堆放地的水土保持措施布置和完善,以最大程度地减少人为水土流失.     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications     

Collection and preliminary evaluation of native turfgrass accessions in Italy

Despite a raising interest on turfs in Italy, all theavailable varieties of this kind in the Country are of foreign origin, and areoften poorly adapted to the prevailing climatic conditions. This prompted tobegin a collection activity of indigenous turfgrass species, with the ultimategoal of identifying promising materials for future breeding based on localgenetic resources. The collection was carried out in three areas of Italy, viz.the northern Po Plain, the coastal region of Liguria, and the island of Sardiniathat are characterised, respectively, by subcontinental, warm temperate, andtypical Mediterranean climate. Altogether, 141 sites were visited, yielding 226accessions belonging to eight species of potential interest for turfs:Poa pratensis, Poa trivialis,Festuca rubra, Festuca arundinacea,Lolium perenne, Agrostis stolonifera,Agrostis tenuis, and Cynodon dactylon,this last being a warm-season grass. Poa pratensis andCynodon dactylon were mostly collected in northern Italyand Sardinia, respectively, whereas Festuca arundinacea andLolium perenne were rather ubiquitous. The collection sitesranged from 0 to 1040 m asl, but sites over 750 m wereonly visited in the inner part of Sardinia. All the accessions, collected aswhole plants, were transplanted at Lodi, northern Italy, where they are beingevaluated. Their preliminary evaluation for traits of importance for turf use,such as sward colour and overall quality, highlighted the great variation andthe occurrence of interesting accessions in all species. Other characters wererecorded, bearing specific importance in individual species, and in all casespromising accessions were identified. The germplasm of Festucarubra, Festuca arundinacea, and Loliumperenne proved highly infected by endophytic (symbiotic) fungi of thegenus Neotyphodium.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.     

Short-term variation in the concentration of selected ions within individual tropical rainstorms

Rainwater was collected at the campus of the University of Brunei Darussalam in Bandar Seri Begawan, Brunei Darussalam, using a funnel-in-bottle sampler. Polypropylene bottles were changed at intervals during rainstorm events. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5°C for subsequent chemical analysis. Analyses for Na, Mg, Ca, Zn and Fe were carried out by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES); Cu and Mn were analysed by graphite furnace atomic absorption spectroscopy (GFAAS); K was analysed using flame atomic emission spectroscopy (FAES); and Cl^–, NO₃ ^– and SO₄ ^2– were analysed by ion chromatography (IC). Concentration versus time profiles are reported for three rainstorm events. All ions exhibited a decrease in concentration during the rainstorm. The first sample contained the highest concentration of ions, consistent with a first-flush effect. The contribution of the initial stages of the shower to the total quantity of ion deposited during the entire rainstorm is quite overwhelming; in many cases 20 to 30% of the mass was deposited in less than 5% of rainstorm duration. On the other hand, the pH and conductivity variation during rainstorms did not exhibit a consistent pattern.     

The 5S rRNA gene diversity in the genus <Emphasis Type="Italic">Secale</Emphasis> and determination of its closest haplomes

We analyzed 127 rDNA sequences (5S DNA units) obtained from 23 seed accession samples from more or less 10 taxa in wild and cultivated rye, genus Secale L. The sequences fell into two known groups, here assigned to two unit classes, viz. long R1 and short R1 (designations to reflect on R haplome of rye). The different taxa could not be fully differentiated based on the 5S DNA units. We searched for 5S DNA sequences from known unit classes most closely similar to the long R1 and the short R1. One set with the long R1 unit class contained sequences of the long P1 unit class from Agropyron (P haplome) and from Kengyilia (StYP haplome), long J1 from Thinopyrum (J haplome), whereas the set with the short R1 included the long S1 from Pseudoroegneria (St haplome) and Kengyilia (StYP haplome), the short J1 from Thinopyrum (J haplome) and the short V1 from Dasypyrum (V haplome). Each of the two sets was analyzed separately by maximum likelihood (ML) phylogenetic analysis from which we were able to infer that the 5S DNA units of Secale differentiated in a non-clock fashion and followed the HKY substitution model in the gene tree with the long R1 unit class and the HKY + G in the gene tree with the short R1 unit class. A complementary Bayesian analysis yielded identical tree topologies to the ML ones for each of the two sequence sets. In the tree with the long R1 units the long P1 and long J1 unit classes were closest to the long R1 unit class, whereas in the tree with the short R1 units the long S1 and short J1 unit classes were closest to the short R1 unit class, indicating possibly a close relationship between the St, J and R haplomes.     

Leaf litter selection by detritivore and geophagous earthworms

Summary Litterbag experiments with 10 different kinds of leaf litter showed that detritivore (Lumbricus species) and geophagous (Aporrectodea species) earthworms prefer certain litter types over others, since different numbers of worms were found below the litter after 50–52 days of exposure in a pasture. The detritivores preferred Fraxinus, Tilia, and predecomposed Ulmus and Fagus litter to Fagus litter and paper, while geophages preferred Tilia litter to Alnus and Ulmus litter, so that the two groups of earthworms showed different preferences. The detritivores seemed to be more selective than the geophages. The palatability of the litter was examined in relation to the C: N ratio, the lignin concentration and the initial and final polyphenol concentration. The numbers of detritivores were significantly correlated with the C: N ratio and the final polyphenol concentration, so that selection of litter seems to be related to palatability. The numbers of geophages were not significantly correlated with any of the parameters for palatability. The disappearance of litter after 50–52 days appeared to be due to detritivore activity, since the numbers found below the litter were positively and significantly correlated with the litter disappearance. There was no significant correlation with geophage activity. This indicates that detritivores use litter as food, and therefore influence the composition of the litter layer.     

Nematode succession and microfauna-microorganism interactions during root residue decomposition

The quality of plant material affects the vigor of the decomposition process and composition of the decomposer biota. Root residues from hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and vetch+rye, packed in litterbags were placed in pots of soil at 15 C and the content of the bags was analyzed after 2, 4, 8 and 12 weeks. Bacterial biomass did not differ between residues with contrasting composition. Among bacterivores groups of nematodes that require high bacterial production dominated in fast decomposing resources whereas flagellates with smaller requirements prevail in slower decomposing resources. Biomass of bacterial feeding nematodes correlated positively with early phase (0-2 wk) decomposition that increased in the order: rye< vetch+rye<vetch. Bacterial biomass therefore seems to be under top-down (predation) control during early decomposition. In contrast, the fungal biomass differed between resources with highest values for rye. Moreover, this increase in fungal biomass occurred later during succession and was correlated with decomposition activity for rye in that period. Fungal biomass therefore seems to be under bottom-up (resource) control. The composition of the nematode assemblages (composed of 25 taxa) showed a clear relationship to initial plant resource quality as well as decomposition phase. Early successional microbivorous nematodes vary according to resource quality with demanding bacterivores+predators (Neodiplogasteridae) dominating in vetch and less demanding bacterivores (Rhabditidae) and fungivores (Aphelenchus) being equally common in vetch and rye. Later in the succession (2-4 wk) bacterivorous Cephalobidae and fungivorous Aphelenchoides prevailed similarly on the different root materials whereas bacterivorous protozoa and the amoebal fraction thereof dominated in rye. At week 12 no species dominated the nematode assemblages that were similar between the resources. The differences between nematode assemblages among plant resources at 2 week were similar to the results of a field study sampled after 6 weeks with the same soil and plant resources. This lends support to the relevance of the successional patterns observed in this incubation study.     

Cycling of extracellular DNA in the soil environment

Upon entering the soil environment, extracellular DNA is subjected to dynamic biological, physical, and chemical factors that determine its fate. This review concerns the fate of both recombinant and non-recombinant sources of DNA. A schematic of DNA cycling coupled with genetic transformation is presented to understand its behavior in soil. Extracellular DNA may persist through cation bridging onto soil minerals and humic substances, be enzymatically degraded and restricted by DNases of microbial origin, and/or enter the microbial DNA cycle through natural transformation of competent bacteria. Lateral gene transfer may disseminate DNA through the microbial community. An understanding of DNA cycling is fundamental to elucidating the fate of extracellular DNA in the soil environment.