利用温度植被干旱指数（TVDI）方法反演杭州伏旱期土壤水分

利用MODIS资料构建了杭州地表温度（Ts）-增强植被指数（EVI）的特征空间,拟合了特征空间中的干、湿边方程,计算了温度植被干旱指数（TVDI）,并推导出利用TVDI和干、湿边土壤水分计算土壤含水量的方程。在计算TVDI的过程中,为了减少高程的影响,利用数字高程模型（DEM）对Ts进行了订正;利用同期野外实测土壤湿度数据计算了干边上的土壤水分值,从而反演杭州2006年伏旱期8月份每隔16d的平均土壤含水量。结果表明：①TVDI方法能反演杭州伏旱期土壤表层水分,实测值与预测值之间平均绝对误差在15个百分点左右。②高程校正后的TVDI能更好的反映土壤水分,与校正前相比,平均绝对误差减少5个百分点,基本满足业务需要。     

干旱遥感监测模型在中国冬小麦区的应用

温度植被干旱指数（TVDI）和植被供水指数（VSWI）由于其物理意义明确,且数据易于获取,因此成为近些年在遥感旱情监测中应用较多的两个模型。为更好地完成遥感监测任务,提高精度,以全国冬小麦主产区为研究区域,利用EOS/MODIS数据,构建两个干旱指数模型,对2009年冬小麦作物主要生长时期进行干旱监测应用,并将其与不同深度土壤湿度进行相关分析、线性拟合比较及应用验证,认为两指数与10 cm深度土壤湿度相关性较好,TVDI大部表现为极显著相关,VSWI的相关性表现差于TVDI。基于土壤湿度的遥感旱情监测,TVDI比VSWI更能体现区域旱情变化趋势,其优势更明显。     

藏北高原土壤湿度MODIS遥感监测研究

利用Terra与Aqua两颗卫星的MODIS地表温度和植被指数数据,分别构建LST-NDVI与LST-EVI共四种不同组合的Ts-VI特征空间,并依据该特征空间提取温度植被干旱指数(TVDI)作为反映土壤干湿状况的指标,探讨一种合适的遥感监测藏北高原土壤湿度的方案,并基于同步的实地土壤表层含水量采样数据进行验证评价。研究表明,四种数据组合方案提取的TVDI分布图均能较好反映藏北土壤湿度,且Terra MODIS LST-EVI构建的特征空间提取TVDI指标效果最佳。在此基础上获得的藏北高原土壤湿度分级图表明,从东南到西北土壤湿度逐渐降低,并呈现明显的空间分异规律。     

基于FY-3 VIRR的温度植被干旱指数在陕西省的应用及其IDL实现

以FY-3可见光红外扫描辐射计（VIRR）L1数据为信息源,对FY-3 VIRR L1数据在陕西省云检测、地表温度、温度植被干旱指数（TVDI）等反演方法进行本地化研究,同时使用IDL程序语言研制了FY-3 VIRR L1数据预处理、云检测、地表温度反演、TVDI指数法反演土壤干旱程度等应用程序,以实现利用温度植被干旱指数（TVDI）对陕西省土壤干旱程度的监测,并对检测结果进行数据反演。反演结果表明,利用FY-3 VIRR L1数据生成的TVDI与20cm土壤相对湿度具有良好的负相关性,相关系数在-0.535左右;TVDI能较好地反映陕西省土壤干旱状况,在延安、关中、陕南的TVDI反演结果与实际旱情一致性较好,但在植被覆盖较差的榆林部分地区,反演结果与实际旱情差异较大。     

植被指数—地表温度特征空间研究及其在旱情监测中的应用

植被指数—地表温度特征空间已被应用于多方面的研究。该文从区域旱情监测的角度分析了该特征空间的生态学内涵，指出地表温度是地表蒸散的函数，推导出了温度蒸散旱情指数(TEDI)的计算方法。利用NOAA数据，以河北省南部平原为研究区域，分别计算出了温度植被旱情指数(TVDI)与温度蒸散旱情指数(TEDI)，通过地面实测土壤相对湿度指数(SHI)验证，结果表明温度蒸散旱情指数(TEDI)可以更准确地反映下垫面的土壤墒情状况。     

利用改进温度植被干旱指数反演农田表层土壤水分的研究

土壤水分作为土壤的重要组成部分,是气候、农业和生态系统的关键组成要素。快速、大面积和实时地监测土壤含水量,对旱情预报、农田灌溉和作物估产有着十分重要的作用。本文主要结合Landsat 8光学影像数据对地表土壤含水量进行反演,在温度植被干旱指数（TVDI）的地表温度－植被指数特征空间基础上引入分形覆盖度,构建地表温度－分形覆盖度特征空间,从而计算得到改进温度植被干旱指数（ITVDI）,采用研究区实测土壤含水量数据对计算的结果进行对比分析。为了分析TVDI和ITVDI与土壤体积含水量的关系,分别制作TVDI、ITVDI与土壤体积含水量的散点图并分析相关性。研究结果表明:在小麦拔节期内,研究区域大部分地区处于干旱状态,轻旱地区主要分布在研究区西部、北部以及中部的高植被覆盖地区;重旱地区主要分布在城市中心及部分裸露地面和小麦种植地区。TVDI和ITVDI与地表土壤含水量线性相关显著,两者均可表征研究区干旱的实际情况。但ITVDI引入分形植被覆盖度参数,在一定程度上避免干旱指数受到地表覆盖类型的限制,使得ITVDI与实测土壤含水量的相关性和反演精度都高于TVDI。因此,ITVDI能够更好地反映研究区域土壤含水量的状况,更适合高植被覆盖度地区土壤含水量反演。     

基于多源数据的土壤水分反演及空间分异格局研究

温度植被干旱指数(TVDI)是一种通过反演土壤水分来反映土壤干旱状况的重要方法。在TVDI的基础上引入数字高程模型(DEM)数据对地表温度进行校正,能够减少地形起伏对能量二次分配的影响。用阈值将研究区分割成不同土地利用类型,结合野外同步实测数据,用分段反演模型反演渭-库绿洲土壤水分分布图,并对渭-库绿洲土壤水分的空间格局和分异规律进行分析。结果表明:(1)地形校正后的TVDI能够更好地反映土壤水分状况;(2)土壤水分总体上从西至东,由北向南降低,在绿洲内部较为稳定,在交错带变化较为剧烈,土壤水分垂直变异系数呈现幂函数递减的整体变化趋势;(3)针对研究区不同土地利用类型用分段反演模型进行反演,有效地实现优势互补,总体上提高了土壤水分的反演精度,在区域土壤水分研究中值得关注和应用。     

基于TVDI的沁水煤田地表土壤水分时空演变分析

温度植被干旱指数（Temperature Vegetation Dryness Index,TVDI）是表征地表干旱的有效指标,其时空格局分析是地表干旱与全球环境变化相互影响下的地表覆被变化的研究内容。以山西沁水煤田为研究区,结合2000—2010年MODND1M和MODLT1M数据,构建了NDVI-Ts特征空间并对干湿边拟合分析。结果表明:近11年来,沁水煤田年平均TDVI均大于0.4,且总体呈显著增加趋势,地表土壤湿度很低,部分区域处于中度和重度干旱之间。年度内,月平均TVDI处于0.5~0.7之间,且7月份TDVI存在明显波动。在空间上,研究区地表土壤湿度分布与地表植被分布基本一致。煤田南部和东部以干旱和极干旱为主,西北山区地带以正常或湿润为主,矿区密集区土壤湿度含量明显低于其他地区,矿井分布附近较其他区域地表干旱现象突出。     

河北省土壤干湿状况遥感监测指数比较

选用河北省2010年5月Terra/MODIS地表反射率产品MOD09A1计算得到了增强植被指数（EVI）,结合同期MOD11 A2地表温度LST数据,计算得到河北省TVDI（温度植被干旱指数）和VSWI（植被供水指数）,比较分析TVDI和VSWI监测河北省土壤干湿状况的适宜性.两种指数与同期8d平均降水量数据的定性分析表明TVDI与降水量数据间具有明显的相反趋势,VSWI与降水量数据间趋势关系不明显;定量的相关分析表明,TVDI与降水量数据间表现出较显著的负相关性（P＜0.05）,而VSWI与降水量数据间的相关不显著.可见,在所选取研究时段内,TVDI指数较VSWI指数监测河北省土壤湿度更为适宜.     

基于TVDI的山地平原过渡带土壤水分反演——以绵竹市为例

为了对生态脆弱的西部山地平原过渡带进行土壤水分监测研究。以绵竹市为例,利用Landsat8OLI/TIRS影像,获取了陆地表面温度(TS)和归一化植被指数(NDVI),通过温度植被干旱指数(TVDI)建立了土壤水分回归模型进行遥感水分反演,并通过野外采样数据对结果进行精度验证。结果表明:TVDI和土壤水分存在较强相关性(R=0.6553),能较好反映表层土壤湿度;土壤水分整体分布状况表现为西北山地地区高于东南平原地区,过渡带上山地向平原逐渐降低。因此,TVDI能较好反映过渡带土壤水分时空差异,对监测过渡带土壤干湿状况具有理论与现实意义。     

Plant canopy effects on litter accumulation and soil microbial biomass in two temperate forests

The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha⁻¹) compared to oak stands (15.7t ha⁻¹). Canopy leaf area was also significantly larger in mixed stands (1.96m² m⁻²) than in oak stands (1.73m² m⁻²). Soil organic carbon (C _org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C _mic), nitrogen (N _mic), and total soil nitrogen (N _tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C _org/N _tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C _mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.     

A simple gas chromatographic approach to evaluate CO2 release,N2O evolution,and O2 uptake from soil

Summary We have developed a simple method for the determination of gaseous compounds that reflect microbial activity in soil, as affected by factors such as the presence of an organic amendment (peat) or a variation in soil moisture. The method is based on a gas chromatographic analysis of the headspace of vials containing the soil under examination. A single gas chromatograph can detect up to 10 different gases. As expected, after peat was added to the soil, CO₂ evolution and O₂ uptake increased significantly. Positive relationships were found between the evolution of N₂O, and soil moisture and the amount of peat added to the soil. Both the these variables influenced the CO₂:O₂ ratio. The results given by this method show high reproducibility.     

Isotope 15N enrichment of soil-ammonium N as a reference to estimate N2 fixation by stem and root-inoculated S. rostrata

Summary A pot experiment in the greenhouse was conducted to compare the contribution of N derived from the atmosphere or from biological N₂ fixation by Sesbania rostrata inoculated with Azorhizobium caulinodans, applied either to roots or to roots and stems (single or multiple stem inoculation). Two subsequent crops were grown for 50 days under flooded conditions. N derived from air was estimated by ¹⁵N dilution using ¹⁵N enrichment of soil NH _inf4 ^sup+ -N and of Echinochloa crusgalli as the non-N₂-fixing reference datum and compared with estimates obtained by the N-difference method. The first crop was grown to stabilize the ¹⁵N into the soil organic N fraction. The ¹⁵N enrichment of soil NH _inf4 ^sup+ -N in the second crop declined slowly. The extractability ratio (¹⁵N enrichment of extractable soil N to ¹⁵N enrichment of total soil N) decreased from 4.8 to 4.1 50 days after planting. The enrichment of soil NH _inf4 ^sup+ -N was comparable to that of E. crus-galli, resulting in similar estimates of N derived from air when either soil NH _inf4 ^sup+ -N or enrichment of E. crus-galli was used as a non-fixing reference. The N-difference method did not always provide reliable estimates of N derived from air; percentages ranged from 75 to more than 80 by 50 days after planting in both crops and did not differ among treatments. The study demonstrates the potential of using ¹⁵N enrichment of soil NH _inf4 ^sup+ -N as a non-N₂-fixing reference for reliable BNF estimates of crops in lowland puddled soil.     

Abiotic drivers and their interactive effect on the flux and carbon isotope (C and δC) composition of peat-respired CO2

Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO₂ emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q₁₀ values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ¹³C analyses) subject to decomposition, changed depending on depth in the peat profile.     

Effect of nitrogen application on the A N value of soil

Pot experiments were conducted with two soils, from Rottenhaus and Seibersdorf in Austria, to ascertain whether the rate of fertilizer N application and the test crop would influence the amount of N available in the soil as assessed by the A-value method. ¹⁵N-labelled fertilizer was applied at rates of 10, 25, 40, 60, and 100 mg N kg^-1 soil, corresponding approximately to 20, 50, 80, 120 and 200 kg N ha^-1 respectively, and two crop species, barley (Hordeum vulgareL.) and non-nodulating soybean (Glycine max L.) were used to determine the soil A _N value under the various fertilizer regimes. The results showed that the Rottenhaus soil had a higher A _N value than the Seibersdorf soil, suggesting that the former was more fertile than the latter. The A _N values of both soils were significantly affected by the level of N application. When grown in the same soil, the two test crops showed significantly different fertilizer use efficiency and per cent N derived from fertilizer when the rate of N application exceeded 20 kg ha^-1. Thus, the A _N value as determined by the two test crops differed significantly for the same soil when the rate of N application was greater than 20 kg/ha. The difference was greater when the soil fertility level was high. The dependence of the A _N value on the level of N application and the species of crop seriously compromises the suitability of this method for determining plant-associated N₂ fixation. Hence, considerable caution is required when using this method to estimate plant-associated N₂ fixation.     

Estimating N2 fixation by Sesbania rostrata and S. cannabina (syn. S. aculeata) in lowland rice soil by the 15N dilution method

Summary A field experiment in concrete-based plots was conducted to estimate the contribution of N derived from air (Ndfa) or biological N₂ fixation in Sesbania rostrata and S. cannabina (syn. S. aculeata), using various references, by the ¹⁵N dilution method. The two Sesbania species as N₂-fixing reference plants and four aquatic weed species as non-N₂-fixing references were grown for 65 days after sowing in two consecutive crops, in the dry and the wet seasons, under flooded conditions. Soil previously labeled with ¹⁵N at 0.26 atom % ¹⁵N excess in mineralizable N was further labeled by ammonium sulfate with 3 and 6 atom % ¹⁵N excess. The results showed that ¹⁵N enrichment of soil NH ₄ ⁺ -N dropped exponentially in the first crop to half the original level in 50 days while in the second crop, it declined gradually to half the level in 130 days. The decline in ¹⁵N enrichment, in both N₂-fixing and non-fixing species, was also steeper in the first crop than in the second crop. Variations in ¹⁵N enrichment among non-fixing species were smaller in the second crop. The ratio of the uptake of soil N to that of fertilizer N in N₂-fixing and non-fixing species was estimated by the technique of varying the ¹⁵N level. In the second crop, this ratio in non-fixing species was higher than that in N₂-fixing species. Comparable estimates of % Ndfa were obtained by using ¹⁵N enrichment of various non-fixing species. There was also good agreement between the estimates obtained by using ¹⁵N enrichment of non-fixing species and those by using soil NH ₄ ⁺ -N, particularly in the second crop. By 25 days after sowing, the first crop of both Sesbania spp. had obtained 50% of total N from the atmosphere and the second crop had obtained 75%. The contribution from air increased with the age of the plant and ranged from 70% to 95% in 45–55 days. S. rostrata fixed substantially higher amounts of N₂ due to its higher biomass production compared with S. cannabina. Mathematical considerations in applying the ¹⁵N dilution method are discussed with reference to these results.     

Short-term dynamics of carbon and nitrogen after tillage in a freshwater marsh of northeast China

The Sanjiang Plain, one of the largest freshwater marshes in China, has experienced intensive cultivation over the past 50 years. However, there were few reports of short-term dynamics of soil carbon and nitrogen and CO₂ emission after tillage. In this paper, we studied the short-term dynamics of carbon and nitrogen after tillage in a freshwater marsh of northeast China. The results showed that response of carbon and nitrogen dynamic to tillage was different for intact wetland and soil cultivated for 10 years. Tillage was followed by immediate and significant increases in CO₂ efflux, which peaked at 0.25 h after tillage, four times higher than control in the wetland soils; while, only 2.5 times higher than control in the cultivated soils. Although, dissolved organic C (DOC) increased, the relative stability of microbial biomass C (MBC) pools together with the decreased respiration in the wetland soil suggested that the tillage did not lead to a burst in microbial activity and growth. Other factors such as moisture content before and after tillage may play an important role in determining microbial activity in the intact wetland. On the contrary, although dissolved organic C did not change, MBC pools, and soil respiration increase after tillage, suggesting tillage led to an increase in microbial activity and growth in the cultivated soil. Tillage initiated changes in soil aeration that was an important factor affecting soil microbiology in the long history of cultivation. Net N mineralization and nitrification occurred in both wetland and cultivated soils, but at different rates after tillage that in the intact wetland soil was higher than cultivated soil. Macroaggregates in the wetland soil would be expected to contain larger amounts of organic matter, and thus release a larger source of newly available substrate for microbes after tillage. In the intact wetland soil, ammonium, nitrate, and dissolved organic N (DON) concentrations were significantly negatively correlated to soil moisture (p < 0.01), suggesting high soil moisture in the natural wetland was not in favor of N mineralization.     

Competition and persistence of Rhizobium tropici and Rhizobium etli in tropical soil during successive bean (Phaseolus vulgaris L.) cultures

Strains of Rhizobium tropici IIB, CIAT899 and F98.5, both showing good N₂ fixation, and a R. etli strain W16.3SB were introduced into a field which had no history of bean culture. Plant dilution estimates showed that in the presence of its host (Phaseolus vulgaris cv. Carioca) during the cropping seasons and the subsequent fallow summer periods, the bean rhizobial populations increased from less than 30 to 10³ g^–1 dry soil after 1 year and to 10⁴ g^–1 dry soil after 2 years. In the 1st year crop, the inoculated strains occupied most of the nodules, which resulted in a higher nodulation and C₂H₂ reduction activity. Without reinoculation for the second and third crops, however, little R. tropici IIB was recovered from the nodules and the bean population consisted mainly of R. etli, R. leguminosarum bv. phaseoli, and R. tropici IIA. Reinoculation with our superior R. tropici IIB strains before the second crop resulted in R. tropici IIB occupying the main part of the nodules and a positive effect on nodulation and C₂H₂ reduction activity, but reintroduction of the inoculant strain in the third season did not have any effect.