多源土地利用/覆被产品在黄土高原应用和精度评估

为准确掌握黄土高原土地利用/覆被的时空格局,基于6种不同来源的土地利用/覆盖数据产品,MCD12Q1,ESA-CCI-LC,GlobeLand30,GLASS,CAS-LUCC和ChinaCover,开展了黄土高原地区退耕还林(草)实施以来土地利用/地表覆被时空格局和转类特征的研究,对不同来源数据产品的精度进行了验证分析。结果表明：(1)分类特征和变化趋势上,MCD12Q1和GLASS产品与其他产品的差异最大,其次为ESA-CCI-LC产品,GlobeLand30,CAS-LUCC和ChinaCover产品的差异相对较小。(2)除MCD12Q1产品外,不同来源土地利用/覆被产品各类型面积随时间变化趋势基本一致。(3)空间转类上,GLASS产品与其他产品的差异最大,解译类型明显错误;其次为MCD12Q1产品,转林类和转草类也存在明显错误,退耕还林(草)特征表现不明显;ESA-CCI-LC和GlobeLand30在黄土丘陵沟壑区退耕还林(草)的转类特征表现不足;CAS-LUCC和ChinaCover退耕还林(草)特征明显。(4)抽样精度上,GlobeLand30,CAS-LUCC,Chin...     

基于时序NDVI图谱库提高土地覆盖分类精度的方法

为提高MODIS土地覆盖产品的分类精度,该文以河南省为试验区,首先将MODIS土地覆盖产品(MCD12Q1)分为高精度区域和低精度区域,然后通过构建时序NDVI图谱库并利用图谱曲线相似性测定方法,改进MCD12Q1低精度区域的分类精度。结果表明:1)时序NDVI是土地覆盖的重要分类特征,二者之间具有较强的关联性。2)利用时序NDVI图谱库能够明显提高MODIS土地覆盖产品的分类精度,改进后的MCD12Q1的总体分类精度分别由72.76%(比较评价)、64.52%(样本评价)提高到83.05%和81.72%。3)不同土地覆盖类别精度提高的程度不同,林地、草地、耕地、人工地表以及水体的生产者精度分别提高35.36%、29.51%、2.98%、6.96%和6.11%。4)对于判定时序NDVI曲线相似度的2种具体方法而言,最小距离法(minimum distance,MD)总体上优于光谱角度匹配法(spectral angle mapper,SAM)。综上,保留现有土地覆盖产品中分类精度较高的部分,基于时序NDVI图谱库改进分类精度较低的部分,是提高现有土地覆盖产品分类精度的有效方法。     

2001-2020年澜湄流域热带地区土地覆被变化对蒸散发的影响

准确量化土地覆被变化对蒸散发的影响是深刻理解全球变化背景下的水资源响应机理的重要前提。该研究基于土地覆被产品MCD12Q1、蒸散发产品MOD16及涡动相关等数据,通过构建剔除气候变化的动态分析方法,量化了2001-2020年间澜湄流域热带地区土地覆被变化对蒸散发耗水量的动态影响。结果表明：1）MCD12Q1与MOD16在该流域的精度较高,其中MCD12Q1的总体精度为82.3%,MOD16在8 d以及月尺度上的RMSE仅略大于1 mm/d;2）2001-2020年研究区植被整体退化明显,其中森林转变为灌木和灌木转变为农田约占流域变化面积的61.2%;3）2001-2020年期间主要土地覆被变化导致区域蒸散发耗水量减少约278.87亿m3,主要土地覆被变化区气候差异导致蒸散发耗水量增加190.96 亿m3。总体上,澜湄流热带地区植被整体呈现出退化的趋势,主要表现为森林转变为灌木和灌木转变为农田。该地区土地覆被变化区域也使得其近20年内蒸散发耗水量减少,改变了土地覆被变化区域水资源循环过程。以上研究结果可为澜湄流域热带地区水资源安全提供有效监测,对地区土水资源合理配置提供重要的科学参考依据。     

年际尺度上土地覆盖类型时空分异及其对气候和地形的响应

为了更加深刻地理解气候和地形条件对土地覆盖的作用机理,该研究以2001年-2009年逐年的MODIS Land Cover(MCD12Q1)为主要数据源,参考中国土地覆盖分类体系整合国际上通用的5种(IGBP、UMD、LAI-fPAR、NPP和PFT)土地覆盖分类体系,分析年际尺度上中国西北干旱半干旱地区的土地覆盖时空分异及其对气候和地形的响应。研究结果表明:IGBP较其他4种更适合年际尺度上干旱半干旱地区土地覆盖的时空分异研究。2001年-2009年,5种分类体系中农田和草地增加,水体湿地和荒漠减少,聚落保持不变,森林有增有减,并且土地覆盖类型间相互发生转换,其在空间上的转移与干旱半干旱地区的自然条件变化和人类活动相适应。6种土地覆盖类型对自然条件的响应与光、热、水在时空格局上的分配以及人类活动作用的强弱相一致。研究结果可为区域或全球土地利用和土地覆盖研究提供参考。     

田间作物杂草识别的最优遥感测量尺度

遥感分类识别精度受测量尺度的制约。为克服现有最优测量尺度选择方法存在的问题,该文提出一种基于光谱角匹配的最优测量尺度选择方法。该方法将每个像元的光谱看作其所属地物类别参考光谱叠加混合像元与光谱变异性的净效应的总和,计算不同空间分辨率下像元光谱与其所属地物类别参考光谱的光谱角,用以衡量混合像元与光谱变异性净效应的大小,当光谱角最小时说明混合像元与光谱变异性的净效应最小,此时的遥感测量尺度即为最优尺度,并在1幅实例数据中实现了该方法,利用基于光谱角匹配的尺度选择方法得到了最优遥感测量尺度,通过试验证明在该尺度下进行分类识别时精度优于比其更大或更小的尺度,验证了本研究提出的最优空间分辨率选择方法的可靠性。将该实例数据中的目标地理实体对象化,从理论上分析了目标对象的面积和形状指数与最优遥感测量尺度之间的关系。该研究为田间作物杂草遥感识别提供了一种有效的最优测量尺度选择方法,可为当前变量作业中田间数据获取工作提供参考,对于推动遥感测量尺度选择研究也具有积极意义。     

基于MODIS数据的内蒙古野火时空变化特征

野火是陆地生态系统的重要干扰因子,影响生态系统的演替和更新。研究基于MCD45A1火烧迹地和MCD12Q1土地利用数据,提取2002—2014年内蒙古不同生态分区、土地利用类型的过火面积及火点分布,分析该区域野火的时空分布格局,同时结合降水数据,探讨野火年际变化对降水的响应特性。结果表明:1)2002—2014年内蒙古野火火点空间分布格局表现为由东北向西南逐渐减少,高密度火点主要分布在中蒙边境区域、森林-草原区以及平原典型农耕区。2)内蒙古野火过火面积2003年最大,2006年次之,2010年最小,分析表明过火面积的年际变动与火灾高发月降水异常有关。过火面积的季节变化表现为春秋多,冬夏少,尤其是3月、4月、5月和9月灾情严重。在7大生态分区中,90%的过火面积集中在兴安岭山地丘陵区、呼伦贝尔高平原丘陵区和锡林郭勒高平原区,过火面积占比分别为52%、28%和10%。3)野火干扰最严重的土地利用类型为草地,火点主要集中分布于草甸草原和典型草原,其次为农业用地和林地,对其他类型干扰程度最小。充分认识野火时空分布格局有利于深入了解其发生规律,为区域火灾预警监测提供科学依据。     

冬小麦面积遥感识别精度与空间分辨率的关系

不同空间分辨率农作物面积识别精度是农情遥感监测数据源选择的依据。该文采用WFV(wide field view)、MODIS(moderate-resolution imaging spectroradiometer)、OLI(operational land imager)、Google Earth影像,在天津市武清区选择了12 km×14 km的冬小麦种植区作为研究区域,采用目视识别的方法,分析了2、5、10、15、30、100、250 m共7个空间分辨率尺度下冬小麦面积识别精度与遥感数据分辨率、农田景观破碎度之间的关系。结果表明,随着空间分辨率由2 m变化到250 m,冬小麦面积识别的总体精度逐步由98.6%降低到70.1%,精度降低28.5%;面积数量比例由5.5%扩大到110.6%,误差增加105.1个百分点;面积精度呈明显下降趋势,数量误差呈明显增加趋势,数量误差的增加速度高于精度下降的趋势。高、中、低3个景观破碎度条件下,随着分辨率由2 m降低到250 m,作物识别精度分别降低了72.8、63.2和47.0个百分点,破碎度的增加导致面积识别精度下降速度更快;同等分辨率下,破碎度越高的地区面积识别精度越低。像元内冬小麦占比与可识别能力密切相关,像元占比达到45.0%以上时才能够被正确识别为冬小麦类型,像元尺度降低导致细小斑块丢失是造成面积识别与数量精度降低的主要原因。像元空间分辨率越高,冬小麦像元的光谱一致性越强,越有利于冬小麦分类精度的提高。针对农情遥感监测业务运行的需要,上述研究结果可以作为区域范围不同用户精度要求前提下遥感数据源选择的依据。     

基于主被动遥感数据和面向对象的大蒜识别

针对开封市大蒜种植破碎化程度高,光学数据难以高精度、快速提取问题。该研究基于谷歌地球引擎（Google Earth Engine,GEE）云平台、随机森林算法（Random Forest,RF）和面向对象方法,选择融合Sentinel-1卫星的后向散射系数与Sentinel-2卫星的光谱、光谱指数及纹理特征,分别应用10 m与加入植被红边波段的20 m空间分辨率遥感数据,探究不同特征组合对改善大蒜识别精度的性能。试验结果表明：应用10 m空间分辨率的Sentinel主被动遥感数据,在简单非迭代聚类（Simple Non-iterative Clustering,SNIC）分割尺度为5,灰度共生矩阵（Gray-level Co-occurrence Matrix,GLCM）邻域值为4,7个纹理特征选择第一、二主成分时,分类总体精度和Kappa系数最高,为94.54%、0.93,大蒜的制图精度和用户精度为97.83%、96.38%。应用加入植被红边波段的20m空间分辨率Sentinel主被动遥感数据,在SNIC分割尺度为3,GLCM邻域值为4,7个纹理特征选择第一、二主成分时,分类总体精度和Kappa系数最高,为94.14%、0.92,大蒜的制图精度和用户精度为95.72%、98.81%。单独使用Sentinel-2光学数据,加入植被红边波段的20m分辨率数据相对10 m分辨率数据,大蒜制图精度和用户精度分别提高0.49%和4.38%。单独使用时序Sentinel-1 SAR数据,10 m空间分辨率数据的大蒜制图精度和用户精度优于20 m分辨率数据0.66%和2.07%。本研究为遥感数据识别生长周期相同或重叠的大宗、小宗经济作物提供技术参考。     

基于空间Logistic的黑龙江省林火风险模型与火险区划

林火风险分析和森林火险区划是林火管理的重要组成部分。该文利用黑龙江省2000-2010年MODIS火烧迹地遥感数据集MCD45A1,在RS和GIS技术支持下构建林火空间分布与林火影响因子间的空间Logistic林火风险模型,在较大时间尺度和省域空间尺度上进行了森林火险区划研究,结果表明:通过空间采样构建的Logistic林火风险模型拟合效果很好,在显著性水平为0.05的情况下,通过模型系数的混合检验和Wald检验;相对运行特征(relative operating characteristic,ROC)值为0.753;经图层运算得到森林火险概率分布图,并将黑龙江省分为无火险区、低火险区、中火险区、高火险区和极高火险区。大兴安岭山地集中了极高火险区和高火险区;小兴安岭基本上属于高火险区和中火险区;东部山地小部分地区属于中火险区;其它地区属于低火险区和无火险区。黑龙江省森林火险的定量定位评价可为林火的预防、扑救以及防火指挥员进行防火规划和部署扑火力量、指导森林防火工作提供科学依据。     

九龙江流域生态需水量时空变化趋势分析

为了维持和保护流域生态系统健康,避免流域生态环境退化,进行流域生态需水量的确定和研究是有必要的。根据九龙江2000—2018年2个水文站实测数据,结合Tennant法确定河道内生态基流,选择面积定额法,利用流域内土壤质地分布状况,以及基于遥感开发的MCD12Q1土地利用产品和MOD16A2蒸散发产品估算植被生态需水量,并对区域生态环境需水量进行时间变化趋势分析和空间分布分析。结果表明：(1)在2000—2018年,九龙江流域有林地、草地面积整体呈现增加趋势,农田、疏林地面积呈现下降趋势;(2)九龙江流域内北溪、西溪河道内多年平均生态需水量分别为22.68亿m³,10.67亿m³,植被多年平均生态需水量为105.27亿m³;(3)有林地、草地的生态需水量呈显著上升趋势,疏林地、农田生态需水量呈下降趋势,前者显著,后者不显著。受人类活动影响,九龙江流域土地覆盖/利用类型年际变化剧烈,因此在区域生态需水量变化中其作用不可忽略,随着遥感/GIS技术的发展,对土地覆盖/利用类型以及植被蒸发量的高时空分辨率观测变得可能,有助于准确预...     

“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.