Characteristics of water relations in seedling of Machilus yunnanensis and Cinnamomum camphora under soil drought condition

The soil drought stress experiment in different durations (no watering within 3d, 6d, 9d, 11d individually) was conducted to study the drought-resistant capacity of one-year-old seedlings for the native tree species (Machilus yunnanensis) in Yunnan Province and the introduced tree species (Cinnamomum camphora). The leaf water potential, chlorophyll content, proline content and plasma membrane permeability for two species seedlings were measured in different soil drought conditions. The results showed that, on the 9th day of drought stress, the leaf water potential of two species decreased obviously, whereas the free proline content and plasma membrane permeability increased sharply. On the 11th day, the leaf water potential of C. camphora seedlings was lower than that of M. yunnanensis seedlings; the plasma membrane permeability in C. camphora seedling leaves increased much more than that in M. yunnanensis seedling leaves, which showed that the injury to the former by soil drought stress was more severe than that to the latter. The free proline content in M. yunnanensis seedling leaves continued to increase on the 11th day, but that in the C. camphora seedling leaves started to drop obviously, indicating that the reduction of osmotic regulation substance in C. camphora seedling leaves after the 11th day was unable to maintain the osmotic balance between the plasma system and its surroundings and the water loss occurred inevitably. Comprehensively, M. yunnanensis seedlings enhanced the drought-resistance in the course of soil drought stress by maintaining higher leaf water potential and by increasing osmotic regulation substance to promote cell plasma concentration and maintain membrane structure integrity so as to reduce water loss. The subordination function index evaluated with fuzzy mathematic theory also showed that the drought-resistant capacity of M. yunnanensis seedlings was stronger than that of C. camphora seedlings.

Effect of Soil Drought on C4 Photosynthetic Enzyme Activities of Flag Leaf and Ear in Wheat

The activities of RuBPC and C4 photosynthetic enzymes in ear and flag leaf blade were examined in wheat. The results showed that photosynthesis of ear was less sensitive to soil drought than that of flag leaf, and decrease of CO2 assimilation in flag leaf blade with water stress was more than that in ear. Compared with flag leaf, ear organs (awn, glume and lemma) had higher C4 enzyme activities and lower RuBPC activity. Under moderate water-stress, the increase of C4 enzyme activities was induced, and the increase was higher in ear than in flag leaf. Under severe water-stress, relatively higher C4 enzyme activities were still maintained in ear, rather than that in flag leaf. It suggests that high activities of C4 enzymes in ear may contribute to its high tolerance of photosynthesis to water-stress.

Photosynthesis of Digitaria ciliaris during repeated soil drought and rewatering

The ability of psammophyte photosynthesis to withstand and recover from severe droughts is crucial for vegetation sta- bility in semi-arid sandy lands. The responses of gas exchange and chlorophyll fluorescence of an annual grass, Digitaria ciliaris, were measured through three soil drought and rewatering cycles. Results showed that the net photosynthesis rate （P,） decreased by 92%, 95%, and 63% at end of the three drought periods, respectively, water use efficiency （WUE） decreased by 67%, 54%, and 48%, while the constant intercellular CO2 concentration （Ci） increased by 1.08, 0.88, and 0.45 times. During those three cycles, the trapping probability with no dark adaptation （Fv＇/Fm＇） decreased by 55%, 51%, and 9%, the electron transport per cross section （ET0＇/CS0＇） decreased by 63%0, 42%, and 18%, and the dissipation per cross section （DI0＇/CS0＇） increased by 97%, 96%, and 21%. These results indicated that D. ciliaris was subjected to photoinhi- bition and some non-stomatal limitation of photosynthesis under drought. However, after four days of rewatering, its photosynthetic characteristics were restored to control values. This capability to recover from drought may contribute to making the plant＇s use of water as efficient as possible. Furthermore, the photosynthesis decreased more slowly in the subsequent drought cycles than in the first cycle, allowing D. ciliaris to enhance its future drought tolerance after drought hardening. Thus, it acclimatizes itself to repeated soil drought.

Responses of ABA and CTK to soil drought in leafless and leafy apple tree

The authors tested the contents of ABA (abscisic acid), ZR (zeatin riboside), DHZR (dihydrozeatin riboside) and iPA (isopentenyl adenosine) in leafless and leafy apple trees (\%Red Fuji/Malus micromalus Makino\%) during soil drought stress. ABA concentration in drought stressed leafless trees increased significantly compared to the controls. ABA both in roots and xylem rose steadily in the earlier drought stage, reaching a maximum of 1.46±0.35 nmol g\+\{ 1\}FW and 117 nmol l\+\{-1\} after the 8th day. Similar change patterns of ABA concentration was observed in the leafy trees during soil drought stress; ABA concentrations in roots and xylem sap increased and reached the maximum in the first three days; after 8th day , it decreased slightly, whereas leaf ABA concentration increased steadily in drought stressed plants throughout the duration of the experiment. Between drought stressed and control trees, no significant differences were observed in concentration of ZR and DHZR in both leafless and leafy trees; whereas iPA concentration of the drought stressed leafless and leafy plants decreased markedly in the later stage of drought. These results showed that endogenous ABA originated mainly from the roots in the earlier drought stage, and mainly from the leaves in the later drought stage. Total CTK showed no reduction in the earlier drought stage and decreased in the later drought stage.

An overview of soil moisture drought research in China:Progress and perspective

论文回顾了中国土壤湿度干旱(SMD)历史重建和季节预测研究进展,并对未来研究进行了展望,自1950s年代以来,全国整体干旱频率增加,持续时间延长,且有明显区域特征.SMD预测多是利用土壤湿度与气候变量之间的统计关系,而少量基于动力学方法的干旱预测研究强调了初始条件和大气强迫数据对季节尺度干旱预测的重要性,本论文提出:1)加强多时间尺度,跨区域的SMD研究;2)联合气候预测系统,陆面模式和多源土壤湿度数据研制SMD预测系统。

Spatiotemporal Analysis of Soil Moisture Drought over China during 2008-2016

Drought has been analyzed by various indices based on rainfall, temperature, evapotranspiration or soil moisture data. Remoste-sensing based data has spatial continuity with certain resolution and is useful for drought monitor. The purpose of this study was to investigate quality used of grid relative soil moisture, the spatial and temporal variation of soi moisture, and soil moisture drought based on relative soil moisture over China during 2008-2016. The results show that the relative soil moisture data set can reflect the spatial characteristics of the development of drought in China during 2008-2016. From the spatial distribution analysis, the northwest to northeast, south part of China, and other major arid areas, the performance is particularly evident. The results show that the use of CLDAS V1.0 real-time products, access to time and space continuous soil relative humidity products, can achieve the drought in China real-time

Response of soil respiration to a severe drought in Chinese Eucalyptus plantations

Extreme droughts can adversely affect the dynamics of soil respiration in tree plantations. We used a severe drought in southwestern China as a case study to estimate the effects of drought on temporal variations in soil respiration in a plantation of Eucalyptus globulus. We documented a clear seasonal pattern in soil respiration with the highest values (100.9 mg C-CO2 m(-2) h(-1)) recorded in June and the lowest values (28.7 mg C-CO2 m(-2) h(-1)) in January. The variation in soil respiration was closely associated with the dynamics of soil water driven by the drought. Soil respiration was nearly twice as great in the wet seasons as in the dry seasons. Soil water content accounted for 83-91% of variation in soil respiration, while a combined soil water and soil temperature model explained 90-99% of the variation in soil respiration. Soil water had pronounced effects on soil respiration at the moisture threshold of 6-10%. Soil water was strongly related to changes in soil parameters (i.e., bulk density, pH, soil organic carbon, and available nitrogen). These strongly influenced seasonal variation in soil respiration. We found that soil respiration was strongly suppressed by severe drought. Drought resulted in a shortage of soil water which reduced formation of soil organic carbon, impacted soil acid-base properties and soil texture, and affected soil nutrient availability.

Effects of Irrigation on Soil and Wheat Yield under Drought Conditions in Sichuan

In order to study the effective water-saving cultivation of wheat in Sichuan under drought conditions to reduce grain loss,the effects of different irrigation methods（ natural rainfall,artificial irrigation,and infiltrating irrigation） on soil physical characteristics and main agronomic characters and yield of wheat were analyzed. The results showed that different irrigation treatments at different growth stages had different effects on soil physical characteristics and agronomic characters of wheat. At the seedling and jointing stage,there were small differences between the treatments in soil compactness,soil bulk density,and soil water content. At the flowering and maturation stage,different irrigation treatments had great impacts on soil compactness,soil bulk density,soil water content,and agronomic characters of wheat. In the hilly areas of Sichuan Basin,infiltrating irrigation at the jointing stage was the best,and wheat yield increased significantly,2 113. 46 kg/hm^2 higher than that in the control.

Detection of a Real Time Remote Sensing Indices and Soil Moisture for Drought Monitoring and Assessment in Jordan

Drought monitoring represents a challenge for water and agricultural sector as this natural hazard accelerates water deficiency and leads to adverse environmental and socioeconomic impacts. The use of remote sensing data and geospatial techniques to monitor and map drought severity expanded in the last decades with progressive developments in data sources and processing. This study investigates the correlations among drought indices derived with soil moisture stress (K) obtained from ground data collected from fields cultivated with barley. The study, carried out in Yarmouk basin in the north of Jordan, includes NDVI, PDI, MPDI and PVI derived from Landsat 8-OLI and Sentinel 2-MSI. Results showed different behavior among the indices and throughout the 2016/2017 growing season, with maximum correlation between PDI and MPDI followed by NDVI with PVI. Correlations among the remote sensing indices and K for different soil depths during March-April were significant for most indices with a maximum (R2) of 0.82 for K30-50 and MPDI, followed by K30-50 with NDVI. Drought severity maps for the month of March showed different trends for the different indices, with similarities between MPDI and PDI. The map of drought severity combined from the remote sensing indices and K showed that PDI and soil moisture could significantly explain 56% of variations in spatial patterns of drought, while the combination of MPDI, PDI and NDVI could significantly explain up to 59% of variations in drought severity map. Therefore, the study recommends the adoption of these remotely sensed indices for monitoring and mapping of agricultural droughts.

黑果腺肋花楸苗木对土壤干旱的光合及生理响应

【目的】探究黑果腺肋花楸在自然土壤干旱条件下的光合及其生理生化特性。【方法】以3年生的黑果腺肋花楸盆栽苗木为试材,通过持续干旱处理,观测苗木叶片的水分参数、光合及叶绿素荧光参数、保护酶活性和渗透调节物质含量等指标的动态变化规律,并对这些生理参数进行相关性和主成分分析。【结果】在自然干旱的过程中,叶片相对含水量(RWC)显著降低,而水分饱和亏(WSD)显著增加;光合色素包括Chl a、Car和总叶绿素含量随着土壤含水量的降低呈先上升后下降的趋势。在初期阶段,当土壤含水量由田间持水量80%~75%(CK)下降至40%~35%(T3)时,黑果腺肋花楸苗叶片的净光合速率(P_(n))、气孔导度(G_(s))和蒸腾速率(Tr)呈逐渐降低的趋势;而水分利用效率(WUE)则显著提高;PSⅡ最大光化学效率(F_(v)/F_(m))与对照组无显著差异。随着土壤干旱程度加剧,P_(n)、G_(s)、T_(r)和F_(v)/F_(m)下降幅度越大,而C_(i)上升显著。通过观察叶片P_(n)、G_(s)、C_(i)和F_(v)/F_(m)的变化趋势和相关性分析,在干旱前、中期影响黑果腺肋花楸光合特性的主要因素是气孔限制,在后期则出现非气孔限制。随着干旱的加剧,叶片的质膜受损,电解质外渗率显著增加;丙二醛和H2O2含量以及超氧化物歧化酶、过氧化物酶和过氧化氢酶活性呈先上升后下降的趋势;同时,渗透调节物质含量也逐渐增加。综合分析各指标之间的相关性发现,不仅各个参数内部存在显著相关性,而且水分、光合参数、保护酶活性和渗透调节物质指标之间也存在重要关联。【结论】综合考虑测定指标的主成分分析和评价结果,黑果腺肋花楸在面临持续干旱胁迫时,会迅速降低气孔导度以减少水分散失并提高水分利用效率,会通过提高部分光合色素含量维持光合结构PSⅡ的正常功能以应对干旱环境。同时,在干旱胁迫下,它能通过调节自身保护酶活性及增加渗透调节物质含量来缓解干旱胁迫造成的伤害,表现出较强的适应干旱逆境的能力。

土壤水分对不同抗旱性春小麦品种叶片保护性酶活性及产量的影响

【目的】研究土壤水分对不同抗旱性春小麦品种叶片保护性酶活性及产量的影响,为选育春小麦抗旱品种及制定节水高产措施提供理论依据。【方法】在大田条件下,以抗旱性较强的品种新春46号、抗旱性中等的品种新春37号、抗旱性较弱的品种新春26号为材料,设置3种水分处理,研究土壤水分对不同抗旱性春小麦品种旗叶超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性、丙二醛(MDA)含量及产量的影响。【结果】随着水分亏缺程度的加剧,春小麦旗叶SOD、CAT活性在扬花期呈升高的趋势,而在灌浆期则呈先升高后降低的趋势;POD活性在扬花期呈先升高后降低的趋势,灌浆期则呈升高的趋势;MDA含量呈升高的趋势;SOD、POD活性表现为抗旱性较强的品种新春46号>抗旱性中等的品种新春37号>抗旱性较弱的品种新春26号,MDA活性在春小麦品种间则呈相反的趋势。收获穗数、穗粒数和产量均随着水分亏缺程度的加剧而降低,抗旱性较强的品种新春46号在有限灌溉和亏缺灌溉处理下,其收获穗数和穗粒数降低幅度小于新春37号和新春26号,且产量高于新春37号和新春26号。【结论】抗旱性较强的品种新春46号在有限灌溉和亏缺灌溉条件下,旗叶SOD、POD酶活性较高,MDA含量较低,活性氧清除能力较强,有效延缓了小麦植株的衰老,收获穗数和穗粒数较抗旱性中等的新春37号和抗旱性较弱的新春26号下降幅度低,在水分亏缺条件下有利于获得较高的产量。

基于CLDAS土壤相对湿度的云南农业干旱监测

选取2016-2020年云南37个土壤水分观测站逐日0-10cm土层相对湿度观测数据和逐日降水、气温观测资料,采用线性插值法,将CLDAS格点数据插值到观测站点上,用于与站点观测数据对比分析。利用回归订正法对插值后的CLDAS土壤相对湿度产品进行订正。采用相对误差、平均偏差、相关系数、标准差和均方根误差统计指标,定量评估CLDAS土壤相对湿度在云南的适用性。结果表明:云南土壤水分观测站相对湿度数据观测有效率不高,选用陆面融合数据开展农业干旱监测十分必要;云南地区近80%的CLDAS土壤相对湿度与土壤水分观测站观测值的相对误差绝对值<30%,数据可信度高;在干旱发生频率高的云南中部地区,CLDAS土壤相对湿度与土壤水分观测站观测值的相关系数均在0.8以上,平均偏差小于10%。从农业干旱监测效果来看,基于CLDAS土壤相对湿度的干旱监测指标能很好地描述由气温和降水异常导致的土壤墒情变化,当日降水量接近或超过5.0mm时,能快速响应轻旱站点数的减少;当连续有效降水发生后,监测指标可反映中等及以上等级农业干旱的缓解。综合来看,CLDAS土壤相对湿度在云南农业干旱监测的适用性好。

黄河流域植被总初级生产力对持续性干旱水分亏缺的响应

利用植被总初级生产力和高精度分层土壤含水量数据分析了2001—2020年黄河流域生长季总初级生产力时空分布和变化特征,量化了流域不同深度土壤湿度之间的相关关系,探究了不同植被类型在生长季的总初级生产力对土壤连续水分亏缺事件的响应关系。结果表明:黄河流域总初级生产力空间上呈东高西低、南高北低的分布特征,生长季耕地累积总初级生产力最大、林地次之、草地最小,研究期内流域总初级生产力整体呈上升趋势,耕地相对增速最大、草地次之、林地最小;流域土壤湿度在空间和时间上均有显著差异,表层土壤含水量波动对深层土壤含水量的影响随深度增加而减小,林地和耕地表层与深层土壤含水量的相关性远高于草地;流域草地和耕地总初级生产力对土壤水分的深度敏感区间为0~40 cm,林地的深度敏感区间为0~100 cm,在深度敏感区间内,随着土壤连续水分亏缺天数的增加,草地和耕地总初级生产力依次经历短暂平稳、加速下降、降速趋缓的变化过程,而林地总初级生产力则表现出短暂下挫、长时间平稳、加速下降的变化特征。

长沙城市绿地森林与草地土壤呼吸及温度敏感性变化特征

城市绿地在减缓城市碳排放和温室效应中发挥着巨大作用。土壤呼吸是城市绿地碳循环的重要环节,决定着生态系统碳汇功能的强弱。以湖南省长沙市远大城园区内森林和草地生态系统为研究对象,于2021年11月—2022年12月对土壤呼吸速率及土壤环境进行监测,并结合2022年发生的极端干旱事件,分析城市绿地森林与草地生态系统土壤呼吸特征及其对极端干旱的响应。结果表明:森林和草地生态系统土壤呼吸速率总体呈现出夏秋季(231.98、239.33 mg·m^(-2)·h^(-1))>冬春季(179.28、91.15 mg·m^(-2)·h^(-1))(以C计);极端干旱下土壤呼吸变化显著,在森林生态系统中更加明显;年尺度下,森林和草地生态系统土壤碳排放量分别为681.55、564.66 g·m^(-2)·a-1(以C计);森林和草地生态系统土壤呼吸温度敏感性系数(Q 10值)的范围分别为0.81~1.06、1.19~1.80,草地生态系统对温度变化的响应更敏感,在极端干旱气候条件下可能会导致更多的土壤碳流失。研究结果可以为城市绿地建设和城市“碳中和”目标的实现提供科学依据。

基于温度植被干旱指数(TVDI)的甘肃省农业干旱监测方法研究

改进温度植被干旱指数(Temperature Vegetation Dryness Index,TVDI)并明确TVDI的农业干旱等级阈值,对提高TVDI指数监测农业干旱能力有重要意义。利用近19 a的MODIS(Moderate Resolu⁃tion Imaging Spectro-radiometer,MODIS)遥感数据,基于单时次和多时次方法构建NDVI(Normalized Difference Vegetation Index,NDVI)-LST(Land Surface Temperature,LST)、EVI(Enhanced Vegetation In⁃dex,EVI)-LST、RVI(Ratio Vegetation Index,RVI)-LST、SAVI(Soil-Adjusted Vegetation Index,SAVI)-LST等几种特征空间,讨论TVDI计算方法,分析TVDI在甘肃省农业干旱监测中的适用性,并明确甘肃省夏季TVDI农业干旱分级标准。结果表明:(1)基于多时次方法构建的SAVI-LST特征空间TVDI更适合甘肃省农业干旱监测,其对土壤相对湿度(Relative Soil Moisture,RSM)拟合的均方根误差(Root Mean Squared Error,RMSE)和平均绝对误差(Mean Absolute Error,MAE)比NDVI-LST特征空间TVDI对RSM拟合的RMSE和MAE下降1%~5%;(2)TVDI适用于夏季甘肃省半干旱区、半湿润区、湿润区等非干旱区浅层10、20 cm土壤深度的农业干旱监测,RMSE和MAE约15.6%和12.6%,拟合误差湿润区<半湿润区<半干旱区;(3)利用TVDI与RSM线性关系确定的TVDI农业干旱等级更有利于提高TVDI监测农业干旱的准确性。

2022年长江流域农业干旱发展过程及气象成因

2022年长江流域发生了大面积的干旱,此次干旱涉及范围广,持续时间长,对于农业、生态等方面都造成了较大影响。降水量相比同期减少,气温增加,导致土壤含水量降低,农业干旱同步发生。复演长江流域此次农业干旱的发展过程,探寻其气象成因,对于完善干旱发生机理的认识,实现干旱的有效应对具有重要意义。研究基于ERA5数据,对比2022年土壤含水量与多年同期均值,从时空维度揭示了2022年农业干旱的主要土壤含水量特征;采用标准化土壤湿度指数值,通过与往期干旱事件对比,阐明此次农业干旱的严重性;最后,从大气环流角度与外强迫场海温角度,分析了此次干旱的气象成因。分析表明,2022年,6-9月全流域的农业干旱程度分别为:无旱、极旱、极旱、极旱。流域遭受长达3个月的农业极端干旱,其中依据数值判断,8月干旱程度最深。就干旱气象成因而言,西太副高2022年6-9月较往年同期影响面积增大、强度增强,且西太副高位置异常偏西,近乎包括流域整个范围,导致流域整体处于单纯西太副高控制之下;同时,长江流域夏季降水与前一年秋冬季大西洋北部、太平洋北部的海温,以及同年春夏季太平洋东部、大西洋及印度洋海温关系较为密切,高相关性时段内的海温与往期均值存在差异性,引起相关干旱。

施用生物有机肥对旱地红壤保水性与细菌群落的影响

土壤干旱是制约我国农业生产的重要瓶颈。施用生物有机肥可有效提高土壤有机质含量,改善土壤理化性质,促进作物生长;然而,其对旱地红壤保水性与细菌群落的影响还鲜见报道。通过室内土培试验,持续观测生物有机肥不同施加量处理的土壤含水量动态变化,并利用高通量测序技术,对细菌群落进行定量分析。结果表明,施用生物有机肥对土壤保水性的影响因施肥量与模拟干旱时间的不同而存在显著差异;施加量为1%、模拟干旱为31d时,土壤含水量是对照组(CK)的1.8倍。施用生物有机肥显著提高了土壤有机质与铵态氮、硝态氮、有效磷、速效钾含量,且其随施加量的增加而升高。此外,施加生物有机肥显著影响了土壤细菌群落组成与多样性;与CK相比,施加生物有机肥的土壤中变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、酸杆菌门(Acidobacteria)和放线菌门(Actinobacteria)相对丰度较高,厚壁菌门(Firmicutes)相对丰度较低,且细菌群落多样性显著增加(P<0.05)。施用生物有机肥显著提高了干旱环境下土壤中溶杆菌属(Lysobacter)、Ramlibacter和鞘氨醇单胞菌属(Sphingomonas)的相对丰度,降低了芽孢杆菌属的相对丰度,与施肥导致的细菌生境变化有关。因此,施用生物有机肥不仅能有效提高土壤有机质与速效养分含量,还能在持续干旱环境下显著提升土壤保水性与细菌多样性,是应对季节性土壤干旱、调节细菌群落的有效措施。

中南半岛野火变化特征及其与土壤水分的相互作用

[目的]分析野火变化特征并探讨火点数与不同深度土壤水分的关联性,为评价生态文明建设和人类生产生活提供科学依据。[方法]基于SNPP/ⅦRS卫星火点监测、火烧迹地和SMAP土壤水分等数据,使用统计方法多角度对2016—2021年中南半岛野火变化特征进行分析,探讨不同干湿条件下火点数与0—5cm和0—100cm2个不同深度土壤水分的相互作用。[结果]①中南半岛火点数和火烧迹地年内主要出现在2—4月,二者在时空分布上具有较高的一致性,多集中在缅甸西部与印度接壤区域、缅甸中部以东和老挝北部。②2—4月火点主要出现在林地、灌木地和耕地,而易发生在归一化植被指数(NDVI)为如下3个等级的区域:0.2<NDVI≤0.4,0.4<NDVI≤0.6,0.6<NDVI≤0.8,但其所占比例随地表覆盖类型和月份的不同存在一定差异。③特旱和重旱条件下火点区明显较无火点区广,火点数集中程度更高;土壤水分随火点数的增加整体呈减少趋势,但极端干湿条件下,土壤水分随火点数变化存在由减转增的“拐点”,且“拐点”值随时间延后而减小。④滞后1~2个月的火点数与土壤水分相关程度最高;日时间尺度上土壤水分对火点数变化同期响应快,且土壤水分和NDVI高的区域关联性更强。[结论]土壤水分亏缺是中南半岛火点高发的重要驱动力。火点数与土壤水分之间相互作用,二者之间存在显著负向关联性。

干旱条件下苔藓层对祁连山青海云杉林土壤水分变化的缓冲作用

【目的】探讨干旱条件下苔藓层对青海云杉林土壤水分变化的影响,为理解气候变化背景下旱区土壤水分的变化规律及森林可持续管理提供依据。【方法】通过对干旱年和常水年有、无苔藓样地土壤水分的连续观测,分析不同干旱条件下苔藓层对土壤水分的影响。【结果】年际尺度上,常水年有、无苔藓样地平均土壤含水量分别为(29.5±6.1)%、(29.6±7.1)%,干旱年有、无苔藓样地平均土壤含水量分别为(22.3±4.7)%、(27.7±4.2)%;常水年苔藓层对青海云杉林土壤水分无显著影响(P>0.05),干旱年苔藓层会显著增加土壤含水量(P<0.05)。年内尺度上,不同月份苔藓层对土壤水分的作用存在差异,表现为生长季早期苔藓层对青海云杉林土壤水分的作用不显著(P>0.05),生长季中后期作用显著(P<0.05)。不同降雨条件下苔藓层对土壤水分的影响显著。晴天或小雨条件下,苔藓层对土壤水分作用不明显(P>0.05),中大雨条件下,苔藓层会显著增加土壤含水量(P<0.05)。【结论】苔藓通过增加入渗和抑制土壤蒸发,从而在干旱条件下对土壤水分变化起到缓冲作用。

基于Copula函数的千米尺度综合干旱指数构建与应用——以重庆市为例

干旱是影响农业生产最大的自然灾害之一,开发综合干旱指数对于评估干旱具有现实意义。该文耦合XGBoost算法降尺度后的土壤水分和降水Z指数数据,在空间上以重庆市行政区县边界分区,时间上以旬为单位分段,基于Copula函数构建千米尺度网格化的综合干旱指数(meteorology-agriculture composite standardized dranght index,CSDI M-A),评估干旱的时空特征。结果表明,降尺度提高了遥感产品的空间连续性,为后续构建千米尺度的CSDI M-A提供支持;广义极值分布和t位置尺度分布分别适用于拟合重庆市大多数区县土壤水分和降水变量数据分布,Frank-copula函数适用于拟合旬尺度下二元变量的联合分布;基于土壤墒情数据验证构建的CSDI M-A比降水Z指数能更好地反映干旱信息,基于各区县得到CSDI M-A的空间分布与实际旱情资料相符,说明所构建的CSDI M-A可为干旱评估提供参考。