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.

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.

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。

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.

Two Types of Flash Drought and Their Connections with Seasonal Drought

Flash drought is a rapidly intensifying drought with abnormally high temperature,which has greatly threatened crop yields and water supply,and aroused wide public concern in a warming climate.However,the preferable hydrometeorological conditions for flash drought and its association with conventional drought at longer time scales remain unclear.Here,we investigate two types of flash drought over China:one is high-temperature driven(Type Ⅰ),while the other is water-deficit driven(Type Ⅱ).Results show that the frequencies of the two types of flash drought averaged over China during the growing season are comparable.Type I flash drought tends to occur over southern China,where moisture supply is sufficient,while Type Ⅱ is more likely to occur over semi-arid regions such as northern China.Both types of flash drought increase significantly(p<0.01)during 1979–2010,with a doubled rise in Type Ⅰ as compared with Type Ⅱ.Composite analysis shows that high temperature quickly increases evapotranspiration(ET)and reduces soil moisture from two pentads before the onset of Type Ⅰ flash drought.In contrast,there are larger soil moisture deficits two pentads before the onset of Type Ⅱ flash drought,leading to a decrease in ET and increase in temperature.For flash drought associated with seasonal drought,there is a greater likelihood of occurrence during the onset and recovery phases of seasonal drought,suggesting perfect conditions for flash drought during transition periods.This study provides a basis for the early warning of flash drought by connecting multiscale drought phenomena.

The Monitoring Analysis for the Drought in China by Using an Improved MPI Method

MPI （microwave polarization index） method can use different frequencies at vertical polarization to retrieve soil moisture from TMI （tropical microwave imager） data, which is mainly suitable for bare soil. This paper makes an improvement for MPI method which makes it suitable for surface covered by vegetation. The MPI by using single frequency at different polarizations is used to discriminate the bare soil and vegetation which overcomes the difficulty in previous algorithms by using optical remote sensing data, and then the revision is made according to the different land surface types. The validation by using ground measurement data indicates that revision for different land surface types can improve the retrieval accuracy. The average error is about 24.5% by using the ground truth data obtained from ground observation stations, and the retrieval error is about 13.7% after making a revision by using ground measurement data from local observation stations for different surface types. The improved MPI method and precipitation are used to analyze the drought in Southwest China, and the analysis indicates the soil moisture retrieved by improved MPI method can be used to monitor the drought.

Analysis and Investigation on Drought Characteristics in Jinjiang City

The drought characteristics,the relationships between the drought and the meteorological factors,soil moisture content in Jinjiang City were analyzed.The results showed that Jinjiang belonged to the serious area which the drought occurred frequently.The summer drought occurrence frequency which was annual average 1.5 times was the highest.The droughts often occur in the continuous drought form,and the droughts which are above the great drought mainly occur in summer,fall and winter.Since 2000,the probabilities which spring drought and summer drought occurred in Jinjiang have reduced obviously.However,the probabilities which the continuous drought in summer,fall and fall,winter occurred have increased obviously.80% of droughts reached the special drought standard,and the drought disaster's times tended to aggravate and accelerate.The continuous drought days negatively correlated with the precipitation and positively correlated with the sunshine hours.The relativity was the highest.50% of meteorological droughts could cause the soil drought.However,the meteorological drought and the soil drought weren't synchronous.The soil moderate drought often happens in the meteorological drought's sunny and dry period,even the soil heavy drought can happen.It had the greatest influence on the agriculture.

Screening of Rice Cultivars for Morpho-Physiological Responses to Early-Season Soil Moisture Stress

The majority of rice(Oryza sativa L.) produced in the southern USA is drill-seeded and grown under upland-like conditions because permanent flooding is established after the four-leaf stage. Therefore, rice during the seedling growth stage will be subjected to variable soil moisture content. A greenhouse experiment was conducted to evaluate the performance of 15 rice cultivars commonly grown in Mississippi of USA under early-season soil moisture stress. Twenty morpho-physiological parameters of rice seedlings subjected to three different levels(100%, 66% and 33% field capacity) of soil moisture, from 10 to 30 d after sowing, were measured. Significant moisture stress × treatment interaction(P < 0.001) was observed for most of the parameters. Further, the total drought response index(TDRI) was developed to score the cultivars for drought tolerance with the variation from 26.88 to 36.21. Accordingly, the cultivars were classified into different groups of tolerance. The cultivars CL152 and CL142-AR were classified as the least and the most tolerant to drought based on TDRI and standard deviation, respectively. Even though both total root(R^2 = 0.98) or shoot(R^2 = 0.76) drought responses indices were positively correlated with TDRI, root traits were important in deriving the indices. Therefore, TDRI could be used to select cultivars for drought tolerance in a given environment and develop rice varieties with early-season drought tolerance. However, further research is needed to identify and characterize tolerance at other stages to assist breeding programs in rice.

Effects of soil-plant system change on ecohydrology during revegetation for mobile dune stabilization, Chinese arid desert

Soil-plant systems play an important role in sand fixing and surface protection in the arid desert of China. This study examines the ecohydrological responses after a soil-plant system change for mobile dune stabilization by using a series of soil hydrological experiments and ecological investigation. The study results showed that decades of succession of soil-plant system has endangered the stability of the protection system. With the accumulated water and nutrient, a bio-logical system develops in a thinner and thinner surface soil. Redistribution of precipitation has changed completely in the ecosystem. In 3–15 mm of soil, a high capacity of crust water retention ultimately limits most rainfall from infiltrating below 10–20 cm deep. When that takes place, lower plants begin to compete for water with grasses and shrubs. A drought horizon forms in 20–500 cm depth with shrub transpiration. Artificial shrubs with deep roots obtain hardly rainfall supply and are gradually eliminated from the protection system. All changes in water environment affect the structure and func-tion and stabilization of whole protection systems. It is necessary to establish a relatively stable water environment by managing the soil-plant system for constructing a sustainable protective system in arid desert.

Determination of drought tolerance using root activities in Robinia pseudoacada 'Idaho' transformed with mtl-D gene

Idaho locust （Robinia pseudoacacia ‘Idaho＇） is an exotic multi-purpose tree used in landscaping, soil and water conserva- tion, fodder sources and others. To improve its drought tolerance for reclaiming arid land, five lines of transformed mtl-D gene, as osmotic regulator in plant cells, have been selected and managed to determine their drought tolerance under experimental conditions. Qualitative and quantitative variables of transformed plants were studied. The critical value of drought tolerance was determined by detecting the 2,3,5-triphenyl tetrazolium chloride （TTC） reductants in roots and soil water content （SWC）. The critical value for drought tolerance was SWC 6% while for the control plants the critical SWC was 8%; a moderate level of SWC is 13% and the highest SWC for plant endurance was 18%. The method proved to be reliable and sensitive in the evaluation of drought tolerance for forest trees.

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。

Research on Monitoring of Soil Humidity Based on AMSR-E Data

[Objective] The aim was to establish AMSR-E soil humidity monitoring model to realize the real-time monitoring of soil humidity.[Method] By dint of evaporation(small type) in Guangxi,daily precipitation,daily average maximum temperature,daily minimum relative humidity,≤ 5 mm precipitation day,as well as AMSR-E soil humidity data,with Stepwise regression method,soil humidity real-time monitoring was studied based on GIS technology,and monitoring result.[Result] The low soil humidity in Guangxi on September 23 in 2005 mainly distributed in northeast Guangxi and central Guangxi,including Guilin City,Liuzhou City,Laibin City,Hezhou City,Guigang City,Nanning City,Hechi City and Baise City.[Conclusion] The AMSR-E statistical model based on meteorological observation data can be applied in real-time monitoring of soil humidity.

Water infiltration and time to recharge the profile of three soils Rio Grande do Sul, Brazil

The Rio Grande do Sul-RS State, even with average annual rainfall of 1.721 mm, has shown a lack of water in the soil for crop production. The study aimed to determine the variation of annual and seasonal precipitation over the time;determine the year seasons that can provide the recharge of water into the soil profile and estimate the time needed to fulfill the soil pore space with water from effective rainfall with different scenarios of water infiltration. The soil uses were: oxisol;Red Yellow Podzolic and Planosolo Hydromorphic Eutrophic respectively in the North, Centre and South of RS State. We determined the total variation of annual rainfall, mean annual potential evapotranspiration and the time required to refill the soil profile for three infiltration scenarios: with fractions 1/2, 2/3 and 3/4 of effective rainfall. In the regions of Passo Fundo, Santa Maria and Santa Vitóriado Palmar, from 1914 to 2004 there was no reduction in the annual volume of rainfall. Considering that 50% of soil volume and water storage are met and that the fraction 1/2, 2/3 and 3/4 of the effective rainfall infiltrates into the soil, the recharging time profile varies from 3.7 to 16.6 years, infiltrating 2/3 range from 1.8 to 6.6 years and infiltrating 3/4 of effective precipitation range from 1.2 to 5.1 years, the time required to refill the entire soil porous space. The recovery of water storage in the soil profile must occur mainly during winter, followed by spring and fall.

Energy and Water Balance at Soil-Air Interface in a Sahelian Region

The aim of this work is an improvement of the parameterization of the soil moisture in the scheme of the Land Surface Process Model (LSPM) for applications over desert areas. In fact, in very dry conditions, the water vapour flux plays an important role in the evaporation processes and influences the underground profiles of humidity and temperature. The improved version of soil moisture parameterization in the LSPM scheme has been checked by using the data taken from the database of the field experiment HAPEX-Sahel (Hydrology-Atmosphere Pilot Experiment in the Sahel, 1990-1992). Model simulations refer to three dif- ferent stations located in Niger (Fallow, Millet and Tiger sites) where input data for LSPM and observations were simultaneously available. The results of simulations, taking into account the water vapour flux in the soil model LSPM, seem to compare better with the observed behaviour of soil moisture and turbulent heat fluxes than those overlooking the water vapour flux, confirming the great importance of the water vapour in such dry conditions.

Using Environmentally Friendly Hydrogels to Alleviate the Negative Impact of Drought on Plant

The use of natural hydrogels in agriculture provides solutions to many problems without threatening the environment. This study aims to evaluate the potential impact of environmentally friendly hydrogels (pectin, starch and pectin + starch) in reducing the negative effects of drought stress on tomato yield and quality. Two different peels (orange peel and banana peel) are used to prepare environmentally friendly hydrogels. The water retention efficiency of hydrogels has been studied. Greenhouse experiment for tomato under drought stress was conducted during 2019. These hydrogels were used under several level of irrigation (100%, 75%, and 50% FC), soil without hydrogel was used as a control. The results showed that the eco-friendly hydrogels (starch, pectin, and pectin + starch) had capacity retention of water for a long time. The obtained data from the greenhouse experiment showed that the eco-friendly hydrogel showed a positive effect on retention of water and increase the soil moisture content compared to control. The highest increase was observed at pectin + starch treatment. This increase reached to 2.8-, 2.4- and 2.0-fold for 100%, 75% and 50% FC compared to the control. Eco- friendly hydrogel application under different drought conditions led to improve yield and quality of tomato fruits. Moreover, conversion of agricultural wastes to hydrogels and the use of these eco-friendly materials instead of synthetic hydrogels are necessary to utilize the limited natural resources and decrease the harmful impact of agricultural wastes on the environment and pave the way for the transition to a sustainable agriculture system.