Involvement of the ABA-and H_(2)O_(2)-Mediated Ascorbate-Glutathione Cycle in the Drought Stress Responses of Wheat Roots

Abscisic acid(ABA),hydrogen peroxide(H_(2)O_(2)) and ascorbate(AsA)–glutathione(GSH)cycle are widely known for their participation in various stresses.However,the relationship between ABA and H_(2)O_(2) levels and the AsA–GSH cycle under drought stress in wheat has not been studied.In this study,a hydroponic experiment was conducted in wheat seedlings subjected to 15%polyethylene glycol(PEG)6000–induced dehydration.Drought stress caused the rapid accumulation of endogenous ABA and H_(2)O_(2) and significantly decreased the number of root tips compared with the control.The application of ABA significantly increased the number of root tips,whereas the application of H_(2)O_(2) markedly reduced the number of root tips,compared with that under 15%PEG-6000.In addition,drought stress markedly increased the DHA,GSH and GSSG levels,but decreased the AsA levels,AsA/DHA and GSH/GSSG ratios compared with those in the control.The activities of the four enzymes in the AsA–GSH cycle were also markedly increased under drought stress,including glutathione reductase(GR),ascorbate peroxidase(APX),monodehydroascorbate reductase(MDHAR)and dehydroascorbate reductase(DHAR),compared with those in the control.However,the application of an ABA inhibitor significantly inhibited GR,DHAR and APX activities,whereas the application of an H_(2)O_(2) inhibitor significantly inhibited DHAR and MDHAR activities.Furthermore,the application of ABA inhibitor significantly promoted the increases of H_(2)O_(2) and the application of H_(2)O_(2) inhibitor significantly blocked the increases of ABA,compared with those under 15% PEG-6000.Taken together,the results indicated that ABA and H_(2)O_(2) probably interact under drought stress in wheat;and both of them can mediate drought stress by modulating the enzymes in AsA–GSH cycle,where ABA acts as the main regulator of GR,DHAR,and APX activities,and H_(2)O_(2) acts as the main regulator of DHAR and MDHAR activities.

THE KUROSHIO MEANDER/SOUTHERN OSCILLATION CONNECTION AND DROUGHT/FLOOD CYCLES IN THE CHANGJIANG RIVER

In response to a suggestion that the large meander of the Kuroshio is a good predictor of droughtsin the Changjiang River Valley, it is argued that more recent inceptions of the meander lend statisticalweigh to the belief that the large meander is itself a consequence of E1 Nino, and hence of the SouthernOscillation. The meander usually lags. Thus, if the meander reliably predicts droughts, the Tahiti componentof the Southern Oscillation will usually give six months’ extra warning.

Active Methyl Cycle and Transfer Related Gene Expression in Response to Drought Stress in Rice Leaves

Three rice varieties, Zhonghan 3, Shanyou 63 and Aizizhan, were used as materials in detecting differential active methyl cycle and transfer related gene expression in response to drought stress. The experiment was performed by gene chip and mRNA differential display technologies under the conditions of drought simulated with 10% PEG6000 solution. The results indicated that the methyl cycle could be activated in the leaves of Zhonghan 3 and Shanyou 63 but inhibited in the leaves of Aizizhan under drought stress. Furthermore, drought stress could induce the expression of a large number of methyltransferase genes, especially the transcription of Rubisco protein methylation related genes, which are beneficial for prevention of Rubisco protein oxidation and degradation, and drought stress could inhibit the transcription of DNA methyltransferase genes and histone methyltransferase genes. This result confirmed that the active methyl cycle and transfer related genes were involved in rice drought resistance.

Precipitation Cycles Relative to Storm Tracks, ENSO and PDO, and Drought—Continental Interior Central Western USA

Seventy-two years of central western United States precipitation data have been analyzed for storms originating 1000 to 3000 km away from four ocean moisture sources: Arctic, North Pacific, South Pacific, and Gulfs of California and Mexico. Precipitation trends were evaluated relative to precipitation phase, precipitation flux, storm track trajectory, and the sea surface temperature (SST) indices Oceanic Niño Index (ONI), and the Pacific Decadal Oscillation (PDO. The lack of correlation between SST indices with precipitation flux was evaluated. The relationships of meteorological, hydrological and snow droughts were evaluated relative to each other, to the climate change-induced temporal shifts in the timing of mountain snowpack decay, and the timing when North Pacific storm tracks shift from crossing to circumventing the Sierra Nevada Range.

The 1997/ 98 ENSO Cycle and Its Impact on Summer Climate Anomalies in East Asia

The observed data of the sea surface temperature (SST) anomalies and the sea temperature (ST) in the sub-layer of the equatorial Pacific, the NCEP/ NCAR reanalysis data and the data set of daily precipitation in China are used to analyze the characteristics of the 1997 / 98 ENSO cycle and its impact on summer climate anomalies in East Asia. The results show that the 1997/98 ENSO cycle, the strongest one in the 20th century, might be characterized by rapid development and decay and eastward propagation from the West Pacific warm pool. Influenced by the ENSO cycle, in 1997, the serious drought and hot summer occurred in North China, and in the summer of 1998, the severe floods occurred in the Yangtze River valley, especially in the Dongting Lake and Boyang Lake valleys, South Korea and Japan. The analysis also shows that: influenced by the 1997/98 ENSO cycle, the water vapor transportation by the Asian monsoon in the summer of 1997 was very different from that in the summer of 1998. In the summer of 1997, the water vapor transportation by the Asian summer monsoon was weak in North China and the northern part of the Korea Peninsula. Thus, it caused the drought and hot summer in North China. However, in the summer of 1998, the sea temperature in the sub-layer of the West Pacific warm pool dropped, the western Pacific subtropical high shifted southward. Thus, a large amount of water vapor was transported from the Bay of Bengal, the South China Sea and the tropical western Pacific into the Yangtze River valley of China, South Korea and Japan, and the severe flood occurred there. Key words ENSO cycle - Climate anomaly - Monsoon - Drought and flood This study was supported by the National Key Programme for Developing Basic Sciences under Grant No. G1998040900(I).

Litter quality and decomposer complexity co-drive effect of drought on decomposition

Litter decomposition is key to ecosystem carbon(C)and nutrient cycling,but this process is anticipated to weaken due to projected more extensive and prolonged drought.Yet how litter quality and decomposer community complexity regulate decomposition in response to drought is less understood.Here,in a five-year manipulative drought experiment in a Masson pine forest,leaf litter from four subtropical tree species(Quercus griffthii Hook.f.&Thomson ex Miq.,Acacia mangium Willd.,Pinus massoniana Lamb.,Castanopsis hystrix Miq.)representing different qualities was decomposed for 350 d in litterbags of three different mesh sizes(i.e.,0.05,1,and 5 mm),respectively,under natural conditions and a 50%throughfall rain exclusion treatment.Litterbags of increasing mesh sizes discriminate decomposer communities(i.e.,microorganisms,microorganisms and mesofauna,microorganisms and meso-and macrofauna)that access the litter and represent an increasing complexity.The amount of litter C and nitrogen(N)loss,and changes in their ratio(C/N_(loss)),as well as small and medium-sized decomposers including microorganisms,nematodes,and arthropods,were investigated.We found that drought did not affect C and N loss but decreased C/N_(loss)(i.e.,decomposer N use efficiency)of leaf litter irrespective of litter quality and decomposer complexity.However,changes in the C/N_(loss)and the drought effect on C loss were both dependent on litter quality,while drought and decomposer complexity interactively affected litter C and N loss.Increasing decomposer community complexity enhanced litter decomposition and allowing additional access of meso-and macro-fauna to litterbags mitigated the negative drought effect on the microbial-driven decomposition.Furthermore,both the increased diversity and altered trophic structure of nematode due to drought contributed to the mitigation effects via cascading interactions.Our results show that litter quality and soil decomposer community complexity co-drive the effect of drought on litter decomposition.This experimental finding provides a new insight into the mechanisms controlling forest floor C and nutrient cycling under future global change scenarios.

Unexpected Diversity in Ecosystem Nutrient Responses to Experimental Drought in Temperate Grasslands

The responses of ecosystem nitrogen (N) and phosphorus (P) to drought are an important component of globalchange studies. However, previous studies were more often based on site-specific experiments, introducing a significantuncertainty to synthesis and site comparisons. We investigated the responses of vegetation and soil nutrientsto drought using a network experiment of temperate grasslands in Northern China. Drought treatment (66%reduction in growing season precipitation) was imposed by erecting rainout shelters, respectively, at the driest,intermediate, and wettest sites. We found that vegetation nutrient concentrations increased but soil nutrient concentrationsdecreased along the aridity gradient. Differential responses were observed under experimentaldrought among the three grassland sites. Specifically, the experimental drought did not change vegetation andsoil nutrient status at the driest site, while strongly reduced vegetation but increased soil nutrient concentrationsat the site with intermediate precipitation. On the contrary, experimental drought increased vegetation N concentrationsbut did not change vegetation P and soil nutrient concentrations at the wettest site. In general, the differentialeffects of drought on ecosystem nutrients were observed between manipulative and observationalexperiments as well as between sites. Our research findings suggest that conducting large-scale, consistent, andcontrolled network experiments is essential to accurately evaluate the effects of global climate change on terrestrialecosystem bio-geochemistry.

Soil type and wetting intensity control the enhancement extent of N_(2)O efflux in soil with drought and rewetting cycles

Climate change alters the intensity and frequency of drought and rewetting(D/W)events;however,the influence patterns of D/W on soil N_(2)O efflux in the water-limited area were not fully understood.Therefore,the impacts of D/W cycles varying in different extent of rewetting and frequency to N_(2)O efflux in two kinds of soil on the Loess Plateau were investigated.The incubation conditions consisted of 1)D/W treatments with four 7-day cycles from 10%water holding capacity(WHC)to 60%WHC or 90%WHC,2)constant moisture of 60%WHC and 90%WHC.The pulse of N_(2)O efflux rate under 10-60%WHC treatment was higher than that under 10-90%WHC treatment in calcic cambisols,while opposite trend was observed in earth-cumuli-orthic anthrosols.Meanwhile,the pulse of N_(2)O efflux rate decreased as cycle number increased for different wetting intensities and soil types.The direct N_(2)O efflux under 10-60%WHC and 10-90%WHC treatments were 5.49 and 1.89μg N_(2)O-N g^(-1)soil in calcic cambisols,with those being 1.92 and 10.85μg N_(2)O-N g^(-1)soil in earth-cumuli-orthic anthrosols,respectively.The N loss in earth-cumuli-orthic anthrosols was approximately 5.74 times greater than that in calcic cambisols under 10-90%WHC treatment,whereas the N loss under 10-60%WHC treatment was about 2.86 times greater in calcic cambisols than that in earth-cumuli-orthic anthrosols.This study suggested that extreme rainfall events can enhance the N_(2)O efflux and N loss in agricultural soils on the Loess Plateau in terms of soil type and wetting intensity,which should not be ignored in the N fertilizer management.

Large-scale atmospheric singularities and summer long-cycle droughts-floods abrupt alternation in the middle and lower reaches of the Yangtze River

The daily precipitation data at 720 sta- tions over China for the 1957―2003 period during summer (May―August) are used to investigate the summer subseasonal long-cycle droughts-floods abrupt alternation (LDFA) phenomenon and a long-cycle droughts-floods abrupt alternation index (LDFAI) in the middle and lower reaches of the Yangtze River (MLYRV) is defined to quantify this phenomenon. The large-scale atmospheric circula- tion features in the anomalous LDFA years are ex- amined statistically. Results demonstrate that the summer droughts-to-floods (DTF) in the MLYRV usually accompany with the more southward western Pacific subtropical high (WPSH), negative vorticity, strong divergence, descending movements develop- ing and the weak moisture transport in the low level, the more southward position of the South Asia high (SAH) and the westerly jets in the high level during May―June, but during July―August it is in the other way, northward shift of the WPSH, positive vorticity, strong convergence, ascending movements and strong moisture transport in the low level, and the northward shift of the SAH and the westerly jets in the high level. While for the summer floods-to-droughts (FTD) in the MLYRV it often goes with the active coldair mass from the high latitude, positive vorticity, strong convergence, ascending movement develop- ing and the strong moisture transport in the low level, and the SAH over the Tibetan Plateau in the high level, but during July―August it is often connected with the negative vorticity, strong divergence, de- scending movements developing and the weak moisture transport in the low level, the remarkable northward shift of the WPSH, the SAH extending northeastward to North China and the easterly jets prevailing in the high level over the MLYRV. In addi- tion, the summer LDFA in the MLYRV is of significant relationship with the Southern Hemisphere annual mode and the Northern Hemisphere annual mode in the preceding February, which offers some predictive signals for the summer LDFA forecasting in the MLYRV.

基于水循环全过程的旱涝级联效应研究框架

气候变化与人类活动影响加剧背景下,亟须实现旱涝灾害风险精准防控。从孕育机理、传播机制、事件评价、风险评估、影响效应等方面回顾了旱涝事件研究现状,明晰了当前在旱涝事件演变机理和评价指标构建方面存在的不足。从水循环全过程视角,分析了干旱和洪涝事件在坡面、河道、流域和区域4个尺度与水量和效应2个层面的本质内涵、影响效应及评价方式。基于地表-土壤-地下、坡面-河道、支流-干流及水网工程间的水力联系,分别从水量和效应层面分析了不同空间尺度上干旱和洪涝的内在联系,明确了干旱、洪涝及旱涝级联过程本质上受流域调蓄作用的影响。从旱涝级联效应的内涵、类型、表现形式和关键技术等方面,提出了旱涝级联效应的研究框架。未来应从流域调蓄作用的视角量化不同空间尺度各要素调蓄能力变化,分层调蓄防范化解旱涝风险。

不同土壤湿度产品对长江中下游极端气候事件响应过程分析

评估了5种常用的土壤湿度产品(SMOS、SMAP、ESA CCI、ERA5、SMCI)在长江中下游地区的适用性,并结合气象数据分析了各产品在极端降水、干旱事件期间的时空变化特征。结果表明:5种产品都能较好地反映长江中下游地区土壤湿度空间分布特征,SMOS与其他产品相比存在普遍低估,时空变化特征与其他几种产品有一定差异。在反映土壤湿度对极端降水响应方面,SMAP、SMCI和ERA5都能反映出与异常降水变化相匹配的土壤湿度空间变化特征,而SMOS在空间上没能准确反映对降水的响应过程。在反映土壤湿度对极端干旱响应方面,SMOS和ESA CCI对极端干旱事件的响应与其他几种产品差异较大,ERA5和SMCI土壤湿度对干旱在空间上的响应较为准确。

基于索周法的辽宁省干旱周期演变特征研究

为探究辽宁省不同气候特征区域年、季干旱周期性规律,基于辽宁省22个国家地面气象观测站1961~2020年逐日降水数据,首先采用旋转经验正交函数对研究区进行降水分区,再计算不同时间尺度的标准化降水指数,利用索周法分析各分区不同尺度标准化降水指数周期特征,并与Morlet小波周期分析的结果进行对比。研究表明,索周法可以很好地应用于干旱周期分析。年尺度上,Ⅰ、Ⅱ区存在7年左右的显著周期规律,Ⅲ区周期规律以5年为主。季尺度上,Ⅰ、Ⅱ区各季节的周期规律以4~7年为主,而Ⅲ区周期尺度稍长,各季节主要表现为6~9年,各分区不同时间尺度周期演变特征存在一定的差异。

我国夏季降水的年代际变化及华北干旱化趋势

利用１９５１ ～１９９４ 年全国３３６ 个测站夏季（６～８ 月） 降水和太平洋海表面温度资料来分析我国夏季降水的年代际变化及华北地区干旱化趋势。分析结果表明：我国夏季降水在１９６５ 年前后发生了一次气候跃变，华北地区从１９６５ 年后夏季降水明显减少，干旱化的趋势明显，这种趋势与西非萨赫尔地区干旱化的趋势相似； 分析结果还表明我国８０ 年代的气候与７０年代的气候有较大差别，这种差别表现在长江、淮河流域从７０ 年代末起降水增多，涝灾明显增多，而华南和华北在８０ 年代降水明显比７０ 年代少， 干旱趋势加重。然而，从９０ 年代中期开始，华北地区北部的降水有增多的趋势。上述所发生的气候变化可能主要是由于６０ 年代中期和从８０ 年代到９０ 年代初赤道东、中太平洋海表温度明显增加，而在７０ 年代明显降低所造成。这种现象似如年代际的“ＥＮＳＯ 循环”现象，它对全球和我国气候变化有较大影响，特别对华北地区干旱化趋势有很大影响。然而从９０ 年代中期开始，赤道中、东太平洋海温有下降的趋势，这有利于华北降水的增多。

干旱胁迫对苹果叶片抗坏血酸含量及其代谢相关酶活性的影响

【目的】研究干旱胁迫对苹果叶片抗坏血酸(ASA)含量及其代谢相关酶活性的影响,探讨干旱胁迫与抗坏血酸-谷胱甘肽(ASA-GSH)循环的关系,为植物抗旱研究提供理论依据。【方法】以2年生嘎拉苹果(MalusdomesticaBorkh.)盆栽苗为试验材料,分别在轻度、中度和重度干旱胁迫及复水条件下,检测其叶片相对膜透性、丙二醛(MDA)、过氧化氢(H2O2)和ASA-GSH循环各组分(ASA、脱氢抗坏血酸(DHA)、GSH、氧化型谷胱甘肽(GSSG)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶(MDHAR)、脱氢抗坏血酸还原酶(DHAR)和谷胱甘肽还原酶(GR))含量或活性的变化。【结果】苹果叶片相对膜透性、MDA、H2O2含量随胁迫程度的加剧而上升,复水后下降。ASA-GSH循环各组分,除ASA含量在轻度干旱胁迫时上升之后略有下降、GSSG含量持续增加外,DHA和GSH含量,APX、DHAR、MDHAR和GR活性均在中度胁迫时达最大值,之后下降;ASA/DHA、GSH/GSSG比值均随胁迫程度的加剧而下降,复水后上升。【结论】随着干旱胁迫程度的加剧,苹果叶片ASA-GSH循环系统的防御能力在达到最大防御机能后下降。

土壤不同水分条件对长春花(Catharanthus roseus)生活史型的影响

为了研究土壤中不同水分条件对长春花生活史型形成及生理代谢的影响,设置对照、轻度干旱、中度干旱和重度干旱等土壤水分梯度,对长春花(Catharanthus roseus(L.)G.Don)幼苗进行处理。对长春花形态指标进行聚类分析发现选择的20个聚类实体被分为2组,第1组为对照(CK)和轻度干旱(LD)处理的植株,第2组为中度干旱(MD)和重度干旱(HD)处理的植株。运用主成分分析(Principal component analysis,PCA)方法对不同土壤水分条件下长春花营养生长(Vegetative growth,V)、有性生殖(Sexual reproduction,S)和无性繁殖(Clone reproduction,C)等3类15种性状进行统计。结果显示,长春花在对照条件下生活史型为V0.39S0.54C0.07,轻度干旱为V0.36S0.50C0.14,中度干旱为V0.53S0.27C0.20,重度干旱为V0.45S0.09C0.46,干旱程度加强显著提高了无性繁殖的比重,降低了有性生殖的比例。同时,对长春花中文朵灵、长春质碱和脱水长春碱等生物碱的含量进行了动态测定,发现重度干旱下的文朵灵、长春质碱和脱水长春碱的含量在16d时分别是对照水平的1.5倍、2.3倍和3.1倍,表明干旱胁迫诱导生物碱积累,为长春花高效栽培提供了理论依据。

关于中国重大气候灾害与东亚气候系统之间关系的研究

在总结中国国旱涝等重大气候灾害的种类、时空分布特征及其形成机理研究的基础上,分析东亚气候系统对东亚地区水分循环和中国旱涝等重大气候灾害发生的影响;并且,从东亚气候系统各成员,特别是从大气圈中的东亚季风、西太平洋副热带高压、中纬度扰动,海洋圈中的ENSO循环、热带西太平洋暖池和印度洋的热力状态,以及从青藏高原的动力、热力作用、高原积雪等来分析和讨论中国重大气候灾害的形成机理。此外,还结合1998年夏季长江流域的特大洪涝以及从20世纪70年代末迄今华北地区的持续干旱所发生的具体实际,进一步分析了东亚气候系统异常对东亚地区水分循环和我国重大气候灾害影响的过程。

外源MeJA对花后干旱胁迫下小麦光合特性的影响

为给外源茉莉酸甲酯(Me JA)在小麦抗旱栽培中的合理利用提供依据,以大面积推广的小麦品种周麦18为试验材料,用盆栽控水的方法模拟干旱胁迫,研究了外源Me JA对花后干旱胁迫下小麦光合特性的影响。结果表明,干旱胁迫显著降低了小麦旗叶叶绿素a、叶绿素b、叶黄素含量及气孔导度和蒸腾速率,提高了PSⅡ初始荧光(F_o)和非光化学淬灭系数(NPQ)及叶黄素循环组分(V+A+Z)含量和(A+Z)/(V+A+Z)值,导致光合速率(P_n)及PSⅡ潜在活性(F_v/F_o)、最大光化学效率(F_v/F_m)、实际光化学效率(Φ_(PSⅡ))受到显著抑制,最终表现为叶片瞬时水分利用效率(WUE)和光能利用率(LUE)显著降低。干旱胁迫下喷施Me JA显著增加了叶黄素、β-胡萝卜素、(V+A+Z)含量及(A+Z)/(V+A+Z)值,从而使F_o和NPQ显著增大,缓解了干旱胁迫下强光对叶绿素产生的氧化破坏,而较低的叶绿素a/b也增强了小麦对弱光的利用效率。喷施Me JA能诱导叶片气孔适当关闭,减少了水分的散失,因而显著提高了灌浆中后期叶片P_n、F_v/F_o、F_v/F_m、Φ_(PSⅡ),最终表现为WUE和LUE显著提高。这表明外源Me JA能增强小麦叶片光合系统在干旱胁迫下的稳定性,改善小麦光合作用。

近50年鄱阳湖流域入湖总水量变化与旱涝急转规律分析

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