Late Drought Research Articles

Drought ecohydrology alters the structure and function of benthic invertebrate communities in mountain streams

AbstractWe studied benthic macroinvertebrate communities in 12 mid‐elevation mountain streams in the Sierra Nevada, California. Data were collected at nine times (seven springs and two autumns) over a 14‐year period of variable hydrological conditions, including years of flood and extreme unprecedented drought.The taxonomic and trait structures of communities were similar during wet and average springs but became increasingly different as drought continued and smaller streams became intermittent.The density of total invertebrates, primarily chironomids, increased during the drought years, but the richness and abundance of mayfly, stonefly, and caddisfly (EPT) taxa declined during the late drought. During the late drought, the proportions of rheophilic, semivoltine taxa with clinger or swimmer behavioural habits decreased, whereas small, stress‐tolerant taxa with burrower and climber habits increased. Collector–gatherers dominated in all periods, but during the severe drought the relative abundance of micropredators increased and filterers, shredders, and grazers decreased.We also found greater changes in community structure between spring runoff and autumn base flow conditions in an average than a wet year. However, spring to autumn population growth rates were much greater during the wet than average year.Invertebrate richness and EPT abundance decreased and community structure showed large changes when stream discharge fell below 1–10 L/s, but remained relatively constant across a range of higher flows. During the severe drought, there were significant declines in the densities of 40% of the common EPT taxa compared to average and wet years, but chironomid, mite, and other invertebrate taxa showed variable responses.Invertebrate diversity, community structure, and ecosystem functions in small, headwater streams are especially vulnerable to drought conditions, which are expected to increase in frequency and intensity with climate change in the Sierra Nevada and other mountainous regions.

A spatio-temporal analysis of trends in rainfall from long term satellite rainfall products in the Sudano Sahelian zone of Nigeria

Rainfall and its variability drive the rural economies across the Sudano-Sahelian zone of northern Nigeria, where drought strategies largely determine crop yields. The increasing scarcity of rain gauges in West Africa generally limits assessments of the degree and spatial extent of hardship arising from rainfall deficiency. However, the improved availability and robustness of satellite-based rainfall products since the early 1980s, offers an alternative source of rainfall data which is spatially, and often temporally, more complete than rain gauges. This research evaluates four satellite-based rainfall products for their ability to represent both long term rainfall trends such as recovery from decadal droughts, and trends in seasonal rainfall variables relevant to crop yield prediction. The Climate Hazards group Infrared Precipitation with Stations (CHIRPS) rainfall product at 5 km resolution, was observed to be consistently most representative of ground station rainfall across northern Nigeria over a 35-year period 1981–2015, followed by TARCAT. CHIRPS was found to give a good overall prediction of rainfall amounts at dekadal, monthly and seasonal time scales, and was therefore used in the study to represent the typical performance of satellite rainfall datasets. The CHIRPS-observed increase in growing season length since the 1970s and 80s drought decades, was accompanied by significant rainfall increases in the later part of the growing season, especially marked in northern and northeastern states. This is especially important for the main subsistence crops sorghum and millet as the risk of late drought impedes swelling of the grain, affecting dry weight production. The CHIRPS data also indicate a significant decrease in dry spells in the northwest and southern parts of the study area, which would have favourable outcomes for crop production in the densely populated rural hinterlands of the cities of Sokoto, Jos and Abuja. In view of the continued intra-and inter-annual rainfall variability across northern Nigeria, and amid rapid rural population growth recently, a return to the rainfall levels of the drought decades, would require informed response. The study suggests that satellite rainfall estimates can offer such information, especially since we observed high spatial variability in rainfall distributions and trends.

Effects of Drought on Nutrient Uptake and the Levels of Nutrient-Uptake Proteins in Roots of Drought-Sensitive and -Tolerant Grasses.

Climate change will increase drought in many regions of the world. Besides decreasing productivity, drought also decreases the concentration (%) of nitrogen (N) and phosphorous (P) in plants. We investigated if decreases in nutrient status during drought are correlated with decreases in levels of nutrient-uptake proteins in roots, which has not been quantified. Drought-sensitive (Hordeum vulgare, Zea mays) and -tolerant grasses (Andropogon gerardii) were harvested at mid and late drought, when we measured biomass, plant %N and P, root N- and P-uptake rates, and concentrations of major nutrient-uptake proteins in roots (NRT1 for NO3, AMT1 for NH4, and PHT1 for P). Drought reduced %N and P, indicating that it reduced nutrient acquisition more than growth. Decreases in P uptake with drought were correlated with decreases in both concentration and activity of P-uptake proteins, but decreases in N uptake were weakly correlated with levels of N-uptake proteins. Nutrient-uptake proteins per gram root decreased despite increases per gram total protein, because of the larger decreases in total protein per gram. Thus, drought-related decreases in nutrient concentration, especially %P, were likely caused, at least partly, by decreases in the concentration of root nutrient-uptake proteins in both drought-sensitive and -tolerant species.

Comparative kernel growth and yield components of two- and six-row barley (Hordeum vulgare) under terminal drought simulated by defoliation

Barley (Hordeum vulgare L.) is often grown in sites with low rainfall and high temperature during grain filling. Because spike architecture is one of basic footprints of barley domestication, the importance of spikes in adaptation to different environments or abiotic stresses can be hypothesised. In order to compare different barley spike types in terms of kernel growth and yield components, we tested 15 two-row and 10 six-row winter genotypes in eight environments where terminal drought was simulated by defoliation at 7 days after heading (7 DAH). Control plants were grown intact. On average, two-row genotypes outyielded six-row genotypes by 17% under control conditions and 33% under simulated late drought. Observations of kernel dry weights from 7 DAH through to harvest maturity at 5-day intervals were regressed onto a measure of thermal time. After preliminary evaluation of four nonlinear (S-shaped) models for kernel dry-weight accumulation, the ordinary logistic model was deemed the most appropriate in most cases and was finally applied to all plant-growth curves. Four parameters were estimated from the logistic model. Whereas two earliness estimators (inflection point and thermal time needed to reach maximum kernel weight) were similar for the two barley types, maximum kernel weight (Ymax) and mean rate of kernel growth (RG) were higher (P<0.05) in two-row than in six-row barleys. Differences in Ymax and RG among six-row barley genotypes were greater between control and defoliation treatments than between years, whereas among two-row barley genotypes, differences between years were greater, suggesting better stability of six-row types and better drought tolerance of two-row types in the tested barley set.

Linking gene regulation, physiology, and plant biomass allocation in Andropogon gerardii in response to drought

Plant responses to drought are often initiated at the molecular level and cascade upwards to affect physiology and growth. How plants respond to and recover from drought have consequences for their growth and survival in drier climates predicted with climate change. We studied four ecologically relevant genotypes of a common C4 grass, Andropogon gerardii. These genotypes had differential responses to a decade of more variable precipitation patterns in a field experiment in native tallgrass prairie. Here, we conducted a greenhouse experiment examining how these genotypes responded to repeated 10-day drought-recovery cycles when experiencing either a severe or moderate drought. We did this twice over the course of the experiment, early, after 5 weeks, and late, after 9 weeks of drought. We studied nine genes involved in water stress signaling and drought response in leaf tissue using real-time reverse-transcriptase polymerase chain reaction (qRT-PCR). We also measured photosynthesis, stomatal conductance, and biomass accumulation and allocation. In early drought, we found consistent differences among genotypes in gene expression, leaf-level physiology, and biomass accumulation and allocation. We found genes involved in ABA, proline synthesis, and mitigating oxidative stress were differentially expressed between genotypes, while genes that coded for aquaporins and chaperones were not. In late drought, we found fewer overall differences, and little regulation of drought responsive genes. Ultimately, we found genotypes either had greater phenotypic plasticity, suggesting an ability to avoid drought and maximize water resources when they were present, or genotypes were better at tolerating drought.

Effects of the Structure of Water Rights on Agricultural Production During Drought: A Spatiotemporal Analysis of California's Central Valley

AbstractCalifornia's Central Valley region has been called the “bread‐basket” of the United States. The region is home to one of the most productive agricultural systems on the planet. Such high levels of agricultural productivity require large amounts of fresh water for irrigation. However, the long‐term availability of water required to sustain high levels of agricultural production is being called into question following the latest drought in California. In this paper, we use Bayesian multilevel spatiotemporal modeling techniques to examine the influence of the structure of surface water rights in the Central Valley on agricultural production during the recent drought. California is an important place to study these dynamics as it is the only state to recognize the two dominant approaches to surface water management in the United States: riparian and appropriative rights. In this study, Bayesian spatiotemporal modeling is employed to account for spatial processes that have the potential to influence the effects of water right structures on agricultural production. Results suggest that, after accounting for spatiotemporal dependencies in the data, seniority in surface water access significantly improves crop health and productivity on cultivated lands but does not independently affect the ability to maintain cultivated extent. In addition, agricultural productivity in watersheds with more junior surface water rights shows less sensitivity to cumulative drought exposure than other watersheds, however the extent of cultivation in these same watersheds is relatively more sensitive to cumulative drought exposure.

Importance of Seasonality for the Response of a Mesic Temperate Grassland to Increased Precipitation Variability and Warming

Timing of precipitation events within the growing season and the non-uniformity of warming might be decisive for alterations in productivity and community composition, with consequences for ecosystem functioning. The responses of aboveground production, community composition, functional group and species evenness to altered intra-annual precipitation variability and their interactions with winter or summer warming were examined in European, mesic temperate grassland. Increased precipitation variability with an induced spring drought resulted in a 17% reduction in ANPP, and late drought reduced ANPP by 18% compared to regular rainfall patterns throughout the entire growing season. Winter warming increased ANPP by 12%, whereas summer warming showed no significant effect on biomass but decreased species richness. The effects of increased precipitation variability and warming on ANPP were independent of each other. Forbs benefited from high precipitation variability with spring drought events, likely due to reduced competitive pressure by decreasing, water stressed grasses. Increased precipitation variability coinciding with higher summer temperatures led to reduced species evenness and likely promoted the establishment of specialists and drought-tolerant species. Seasonality of climatic factors, here early versus late drought events in the high precipitation variability treatments, was important in driving shifts in community composition but not for decreases in ANPP. Non-uniform warming, here winter versus summer, affected the direction of response of both community composition and ANPP. Variability of resources is affecting ecosystem processes and species interactions. Recognition of seasonality and non-uniformity of climatic factors will improve predictions of plant performance and biotic interactions in response to climate change.

Impact of Grain Priming and Silicon Spraying on the Response of Barley to After Anthesis Drought Stress

Two field experiments were carried out in the experimental farm of Faculty of Desert and Environmental Agriculture, Fuka, Matrouh Branch, Alexandria University, Egypt, during two successive seasons 2012/2013 and 2013/2014 to study the effect of seed priming with Ascorbic and Salicylic Acids and spraying with silicon on drought tolerance of two barley cultivars, Giza 126 and Giza 2000. Six treatment were used as follows: Seed priming with Ascorbic acid (AA) and irrigation till heading (T1), seed priming with Salicylic acid (SA) and irrigation till heading (T2), seed priming with distilled water and irrigation till heading (T3), spraying with silicon and irrigation till heading (T4), dry seeds cultivation and irrigation till heading (T5) and dry seeds cultivation and all season irrigation (T6). The results indicated that post anthesis stress decreased grain yield by 17.1 % and 100-grain weight by 11.96 %, as an average of the two seasons. Hydropriming and osmopriming with salicylic acid, in addition to spraying with silicon, decreased the effect of drought and barley plants gave comparable grain yield to that of non-stress conditions. Barley cultivar Giza 126 was more tolerant to late drought compared to Giza 2000 cultivar with S values of 0.58 and 1.42, as an average of the two seasons, respectively.

Physiological characterization of Turkish bread wheat genotypes for resistance to late drought stress

A number of physiological traits have been proposed as selection criteria for late drought resistance and grain yield improvement in wheat. To characterize them in terms of late drought resistance, 64 bread wheat genotypes were evaluated for canopy temperature difference (CTD), leaf senescence rate (LSR), SPAD chlorophyll value, initial fluorescence (Fo), maximum fluorescence (Fm), variable fluorescence (Fv), maximum quantum efficiency of PSII (Fv/Fm), leaf ash content, and grain ash content in two field experiments conducted in irrigated and late drought conditions during the 2011-12 and 2012-13 seasons in Erzurum, Turkey. The experiments were conducted in an 8 x 8 lattice design with two replicates. Significant variation was observed among the genotypes for all the traits. Late drought decreased the grain yield, CTD, SPAD, Fm, Fv, Fv/Fm, and leaf ash content but increased LSR and grain ash content. The drought sensitivity of the genotypes was determined by a ranking method based on 25 traits measured in the late drought conditions. According to the rank-sum (RS) values of the genotypes, four genotypes were defined as resistant, 15 genotypes as medium resistant, 34 genotypes as medium sensitive, and 11 genotypes as sensitive. Resistant genotypes M?fitbey and Dağdaş 94 produced the highest grain yields in late drought conditions and appeared to be promising parents for the breeding of resistant cultivars. RS was negatively correlated with CTD, SPAD, Fm, Fv, and Fv/Fm, while it was positively correlated with LSR. For screening late drought-resistant genotypes, 15 days post anthesis (15DPA) is the optimum time for Fv, CTD, and SPAD measurements. The stepwise multiple linear regression analysis indicated that the Fv15DPA, Fv25DPA, CTD15DPA, and SPAD15DPA could explain 75.2% of the total variation in RS. Therefore, the Fv15DPA, Fv25DPA, CTD15DPA, and SPAD15DPA traits can be used as selection criteria as a combination for the classifying of wheat genotypes in terms of late drought resistance.

Experience of inundation or drought alters the responses of plants to subsequent water conditions

Summary The availability of water is often highly variable over the life of a plant in nature, and most plants experience episodic extremes in water scarcity and abundance. The importance of plant plasticity in coping with such experiences is widely recognized, but little is known about how plastic responses to current conditions are affected by prior environmental experiences. Our objectives were to investigate the effects of early inundation or drought on the subsequent responses of plant species to the same, opposite or more favourable conditions. To address these questions, we subjected four invasive and four native herbaceous perennial species from different habitats (xeric, mesic, hydric) to two rounds of hydrological treatments (drought, moderate water, inundation) and analysed the effects of the early treatments on survival and performance (total biomass and relative growth) of individuals in the later treatments. In general, (i) early drought reduced the performance of more species than did early inundation, and decreased the final total mass of all species; (ii) early inundation and early drought did not lead to lower survival immediately or later, but improved the relative growth of survivors across all late conditions; (iii) late drought resulted in the highest mortality and lowest performance after any early treatment. With respect to habitat of origin: (i) early inundation was more beneficial for species from wet habitats than for other species; (ii) species from xeric habitats had the strongest drought tolerance after early drought; (iii) mesic species were more likely to suffer reduced later growth after either inundation or drought experience. Invasive species benefitted more from early inundation than did native species, but native species grew better after experiencing early drought. Results indicate that early exposure to inundation or drought conditions alters how plants respond to later conditions and suggest that exposure to extreme events can induce physiological or morphological changes that improve tolerance for either extreme conditions later. This increased tolerance can be at the cost of poorer performance under more benign conditions. Synthesis. Early inundation or drought experience may be harmful immediately, but can be beneficial for the later growth of plants. The ability of species to utilize early hydrological experiences was associated with the water range of their habitats and whether the species is invasive or native. The ability to modulate future plastic responses may be as important as short‐term plasticity in adapting to temporal environmental heterogeneity. Such ‘metaplasticity’ can optimize current performance, while avoiding the potential costs of maintaining a high degree of plasticity throughout life.

Accounting for California Water

Understanding California’s water balance sheet—how much there is, who has claims to it, and what is actually being “spent”—is key to effectively managing the state’s limited water supply in support of a healthy economy and environment. The latest drought has spotlighted serious gaps in California’s water accounting system. California is a large, geographically diverse state, and its water systems are physically interconnected and institutionally fragmented. Water infrastructure connects the state’s northern watersheds to its southernmost communities, Sierra Nevada rivers to coastal cities, and surface water to groundwater. Additional complexity arises from having hundreds of independently governed water systems, each with its own water accounts; from the widespread practice of managing linked surface water and groundwater as separate systems; and from a lack of clarity on how much water is reserved for environmental purposes. The combination of physical interconnectedness, institutional fragmentation, and water scarcity heightens the need for more effective accounting at the statewide and river-basin levels. We identify gaps in California’s water information systems and recommend that the state modernize its water accounting, and that key state agencies—supported by an oversight committee of key stakeholders and independent experts—develop and adopt a common accounting framework.

Accounting for California Water

Understanding California’s water balance sheet—how much there is, who has claims to it, and what is actually being “spent”—is key to effectively managing the state’s limited water supply in support of a healthy economy and environment. The latest drought has spotlighted serious gaps in California’s water accounting system. California is a large, geographically diverse state, and its water systems are physically interconnected and institutionally fragmented. Water infrastructure connects the state’s northern watersheds to its southernmost communities, Sierra Nevada rivers to coastal cities, and surface water to groundwater. Additional complexity arises from having hundreds of independently governed water systems, each with its own water accounts; from the widespread practice of managing linked surface water and groundwater as separate systems; and from a lack of clarity on how much water is reserved for environmental purposes. The combination of physical interconnectedness, institutional fragmentation, and water scarcity heightens the need for more effective accounting at the statewide and river-basin levels. We identify gaps in California’s water information systems and recommend that the state modernize its water accounting, and that key state agencies—supported by an oversight committee of key stakeholders and independent experts—develop and adopt a common accounting framework.

Effects of Recent Instability on Cultivated Area Along the Euphrates River in Iraq

We used MODIS NDVI data to determine whether there was a significant change in cultivated area along the Euphrates River in Iraq after the Iraq War compared to before and during the war. Results revealed that mean cultivated area was largest during the pre–Iraq War period (2000–2003) with 99,115 Mha, reduced some during the early Iraq War period (2003–2006) to 83,480 Mha, reduced even further during the late Iraq War period (2007–2011) to 53,813 Mha due to drought, and increased slightly during the post–Iraq War period (2012–2015) to 69,161 Mha, although not returning to previous highs of the pre–Iraq War or early Iraq War periods. Statistical analysis with the Kruskal–Wallis test revealed that the small cultivated area during the post–Iraq War period was more closely related to the late Iraq War and drought period than previous periods, indicating that recent instability, such as political turmoil following the departure of U.S. troops, violent militant extremism, lack of economic investment, and environmental degradation, has had a similar effect on cultivated area as a devastating drought.

Association of Characters and Selection Parameters for Quality Traits in Maize (Zea mays L.) as Influenced by Late Sown and Drought Conditions

An experiment consisting of twenty-one maize hybrids was conducted during kharif 2012 at Oilseeds Research Farm, Kalyanpur, Kanpur. Each genotype was sown in two rows each of 4 meter long spaced at 60x25 cm between rows and plants respectively in a randomized complete block design in three replications. The observations were recorded on five randomly selected plants for chlorophyll intensity at 30 and 60 DAS, Proline content (mm) at 60 DAS, Dry weight/plant at the intervals of 30, 60 and 90 DAS, cob weight per plant (g) and protein content. The statistical and biometrical analysis was carried out using standard formula. The results showed high heritability coupled with high genetic advance for total dry weight at maturity followed by cob yield per plant, dry weight at 60 DAS and proline content at 60 DAS reflecting the role of additive gene action. High heritability and low genetic advance was observed for chlorophyll intensity at 30 and 60 DAS and plant dry weight at 30 DAS indicating the presence of both additive and non-additive genes for controlling the characters. Cob yield per plant showed positive and significant correlation with plant dry weight at maturity. Its association with plant dry weight at 60 DAS was negatively significant.

Subsidies promote use of drought tolerant maize varieties despite variable yield performance under smallholder environments in Malawi

This study used a three-year panel dataset for 350 Malawian farm households to examine the potential for widespread adoption of drought tolerant (DT) maize varieties, a technology that holds considerable promise for helping smallholder farmers in Sub-Saharan Africa (SSA) adapt to drought risk. Regression results revealed that DT maize cultivation increased substantially from 2006 to 2012, with the main driver being the Malawi Farm Input Subsidy Program. Recently experienced drought and farmer risk aversion stimulated adoption of DT maize. In yield performance, improved maize varieties performed significantly better than local maize during the 2011/12 drought year. However, DT maize did not perform significantly better than other improved maize varieties used in Malawi, which is in contradiction to results obtained from on-station and on-farm trials. A plausible explanation is that the severe drought in Malawi in the 2011/12 season occurred early in the rainy season and DT maize primarily provides an advantage in the case of late droughts during the silking/grain filling stage of the crop. Preliminary results herein suggest that it was lack of rainfall in December 2011 that constrained maize yield while rainfall in January and February was less limiting. Additionally, the length of the longest dry spells in December and February further strengthens the evidence in favor of this explanation, but further research is needed to reach a conclusion.

The late Holocene drought: A persistent dry period between 2800 and 1800 cal yr BP across the central Great Basin

The late Holocene drought: A persistent dry period between 2800 and 1800 cal yr BP across the central Great Basin

Investigating Correlation among NDVI Index Derived by Unmanned Aerial Vehicle Photography and Grain Yield under Late Drought Stress Conditions

Normalized Difference Vegetation Index (NDVI) has been related with grain yield and other important agronomic traits of rainfed cereal crops grown under Mediterranean conditions. In most studies, spectral measurements were carried out using portable spectroradiometers; however, Unmanned Aerial Vehicles (UAVs) carrying conventional digital cameras equipped with spectral filters have been recently used as an alternative. The main scope of this work was to investigate whether grain yield and yield-related traits under late drought stress conditions are correlated with NDVI Index derived by low height combined photography obtained by UAVs.Experiments were sown at the Athalassa experimental station for two consecutive growing seasons. Twenty durum wheat varieties were sown in a Randomized Complete Block Design with four and six replications in the 1st and 2nd growing season, respectively. In the 1st growing season, plants received 270mm of rainfall and extra 30mm irrigation during booting. In the 2nd growing season, plants received 140mm of rainfall, 50mm irrigation during tillering and 50mm irrigation during booting. In both growing seasons, plants received no rainfall or irrigation from booting to maturity.Conventional and near infra red photography were taken by a CanonIS200 camera mounted on a UAV. Geo-processing of the imagery and orthorectification was applied on the data to become compatible. After that proper samples were masked from the orthoimagery and processed for NDVI index calculation. Two flights were carried out during the 1st growing season when most varieties were at booting and milk stage respectively. Four flights were carried out during the 2nd growing season when most varieties were at booting, heading, milk and dough stages respectively.In our study there was significant correlation between yield and NDVI in both growing seasons with the correlation been stronger during the 2nd season. Correlations were stronger when estimated during the milk and dough stages.

Simulation of Winter Wheat Yield in Response to Irrigation Level at Critical Growing Stages in the Huang-Huai-Hai Plain

Water deficiency is recognized as a major problem in winter wheat production in the Huang-Huai-Hai Plain. This study aimed to assess the impact of drought stress on winter wheat yield and raise irrigation proposals for water-saving production in this area. With reference to the fact of water deficits in major growth stages of wheat and the local irrigation practice, we input different irrigation levels(volumes) required by the DSSAT crop model to simulate yield variations in response to irrigation levels at critical growing stages in four typical sites during the past three decades. The cumulative probability for yield reduction was concluded based on irrigation at jointing–heading and filling stages. The greatest yield reduction was found under jointing–heading drought stress, and the relative change rate in yield was two folds to that under drought stress at filling stage. This relative yield change was primarily attributed to the relative change in grain number per square meter caused by water deficiency during jointing–heading stage. Under high-strength drought stress, medium yield reduction dominantly resulted from water deficiency during jointing–heading, with a two-fold probability to that under drought stress at filling stage(except for Yanzhou site); whereas, slight and severe yield reductions at Shijiazhuang and Tianjin sites resulted from early(jointing–heading) drought stress and those at Yanzhou and Xinxiang sites were attributed to either early(jointing–heading) or late(filling stage) drought stress. At Yanzhou and Xinxiang sites, the probabilities of slight yield reduction were similar under early and later drought stressed; however, water deficiency at filling stage resulted in severe yield reduction. These results indicate that irrigation is important not only from jointing to heading but also at filling stage of winter wheat in the southern area of the Huang-Huai-Hai Plain.

The Influence of Atlantic Tropical Cyclones on Drought over the Eastern United States (1980–2007)

Abstract To assess the influence of Atlantic tropical cyclones (TCs) on the eastern U.S. drought regime, the Variable Infiltration Capacity (VIC) land surface hydrologic model was run over the eastern United States forced by the North American Land Data Assimilation System phase 2 (NLDAS-2) analysis with and without TC-related precipitation for the period 1980–2007. A drought was defined in terms of soil moisture as a prolonged period below a percentile threshold. Different duration droughts were analyzed—short term (longer than 30 days) and long term (longer than 90 days)—as well as different drought severities corresponding to the 10th, 15th, and 20th percentiles of soil moisture depth. With TCs, droughts are shorter in duration and of a lesser spatial extent. Tropical cyclones variously impact soil moisture droughts via late drought initiation, weakened drought intensity, and early drought recovery. At regional scales, TCs decreased the average duration of moderately severe short-term and long-term droughts by less than 4 (10% of average drought duration per year) and more than 5 (15%) days yr−1, respectively. Also, they removed at least two short-term and one long-term drought events over 50% of the study region. Despite the damage inflicted directly by TCs, they play a crucial role in the alleviation and removal of drought for some years and seasons, with important implications for water resources and agriculture.

Shoot growth, root growth and resource capture under limiting water and N supply for two cultivars of lettuce (Lactuca sativa L.)

Background and aims To improve vegetable crops adapted to low input and variable resource availability, better understanding is needed of root system functioning, including nitrogen and water capture. Methods This study quantified shoot and root development and patterns of water and nitrate capture of two lettuce cultivars subjected to temporary drought at two development stages (Trial 1) or to continuous, localized drought and/or nitrate shortage (Trial 2). Results In Trial 1, early drought slowed down shoot and root growth, whereas late drought enhanced root proliferation in the top 0.1 m. Nitrate capture during drought was sustained by increased nitrate inflow from deeper layers. Plants did not recover fully from drought after re-watering. In Trial 2, root proliferation was stimulated in the drier soil compartment partially compensating reduced water availability and nitrate mobility. Under nitrate shortage, root proliferation was enhanced in the compartment where nitrate was more abundant, irrespective of water availability. Conclusions Changes observed in the root system are ‘feed-forward’ mechanisms to sustain resource capture in a limiting growing environment. The type of stress (drought or nitrate shortage) affects coping strategies; nitrate concentration in the soil solution, combined with the nutritional status of the plant will determine the stress response.