Effects Of Prolonged Drought Research Articles

The effects of prolonged drought on vegetation dieback and megafires in southern California chaparral

AbstractDrought contributed to extensive dieback of southern California chaparral, and normalized difference vegetation index before drought and near the end of the drought was used to estimate this dieback, after accounting for other disturbances recorded in aerial photographs. Within the perimeters of two megafires that occurred after the drought, the 2017 Thomas Fire and the 2018 Woolsey Fire, there had been extensive areas of dieback. Comparing dieback with Monitoring Trends in Burn Severity measures of fire severity, there was a highly significant negative relationship between drought‐caused shrub dieback and fire‐caused dieback as measured by fire severity. We interpret this as further support for our remote sensing methodology for prefire dieback. Models of fire behavior suggest that one means by which dieback contributes to fire size is through increasing the density and distance of spot fires, particularly under extreme wind conditions. Lower elevation chaparral associations appear to be most vulnerable and are closer to urban environments, which should be a concern to fire managers in regions subjected to extended droughts.

Effects of prolonged drought on water quality after drying of a semiarid tropical reservoir, Brazil

In semiarid regions is recurrent water depletion of some reservoirs during periods of prolonged drought, intensifying eutrophication. After water depletion events, new waters arrival and the trophic state improvement is expected. Therefore, the aim of this study was to evaluate the change of the trophic state after the reservoir’s drying due to a prolonged drought in the Brazilian semiarid region. It is expected that the trophic state improves after the water renewal by decreasing nutrient concentrations and algal biomass. This study was performed in a tropical, semiarid reservoir (Cruzeta Reservoir, Brazil), and was carried out during two different periods: 2012 (beginning of the prolonged drought) and 2019 (after the drying and reflooding). Analyses of Wilcoxon test and principal components analysis (PCA) were used to identify significant changes and patterns between the periods studied. The studied periods differed significantly (p < 0.05) with regard to maximum depth, pH, dissolved oxygen, conductivity, turbidity, inorganic and organic suspended solids, total phosphorus, soluble reactive phosphorus, nitrate and chlorophyll a. The hydrological regime of the Brazilian semi-arid region, governed by the prolonged drought period (from 2012 to 2019), contributed to significant changes in the volume and water quality in Cruzeta reservoir, increasing nutrients and algal biomass, intensifying the symptoms of eutrophication. Thus, contrary to the hypothesis of this study, despite the reflooding after the drought period, a worsening in the trophic state of the reservoir from eutrophic to hypereutrophic was observed.

Effect of two organic fertilizers on some anatomical features of Pinus pinea L. seedlings grown in field and lathe house

Effect of two organic fertilizers on some anatomical features of Pinus pinea L. seedlings grown in field and lathe house

Effects of prolonged drought on stem non-structural carbohydrates content and post-drought hydraulic recovery in Laurus nobilis L.: The possible link between carbon starvation and hydraulic failure

Drought-induced tree decline is a complex event, and recent hypotheses suggest that hydraulic failure and carbon starvation are co-responsible for this process. We tested the possible role of non-structural carbohydrates (NSC) content on post-drought hydraulic recovery, to verify the hypothesis that embolism reversal represents a mechanistic link between carbon starvation and stem hydraulics. Measurements were performed in laurel plants subjected to similar water stress levels either over short or long term, to induce comparable embolism levels. Plants subjected to mild and prolonged water shortage (S) showed reduced growth, adjustment of turgor loss point driven by changes in both osmotic potential at full turgor and bulk modulus of elasticity, a lower content of soluble NSC and a higher content of starch with respect to control (C) plants. Moreover, S plants showed a lower ability to recover from xylem embolism than C plants, even after irrigation. Our data suggest that plant carbon status might indirectly influence plant performance during and after drought via effects on xylem hydraulic functioning, supporting the view of a possible mechanistic link between the two processes.

Lipidomics Unravels the Role of Leaf Lipids in Thyme Plant Response to Drought Stress.

Thymus is one of the best known genera within the Labiatae (Lamiaceae) family, with more than 200 species and many medicinal and culinary uses. The effects of prolonged drought on lipid profile were investigated in tolerant and sensitive thyme plants (Thymus serpyllum L. and Thymus vulgaris L., respectively). Non-targeted non-polar metabolite profiling was carried out using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry with one-month-old plants exposed to drought stress, and their morpho-physiological parameters were also evaluated. Tolerant and sensitive plants exhibited clearly different responses at a physiological level. In addition, different trends for a number of non-polar metabolites were observed when comparing stressed and control samples, for both sensitive and tolerant plants. Sensitive plants showed the highest decrease (55%) in main lipid components such as galactolipids and phospholipids. In tolerant plants, the level of lipids involved in signaling increased, while intensities of those induced by stress (e.g., oxylipins) dramatically decreased (50–60%), in particular with respect to metabolites with m/z values of 519.3331, 521.3488, and 581.3709. Partial least square discriminant analysis separated all the samples into four groups: tolerant watered, tolerant stressed, sensitive watered and sensitive stressed. The combination of lipid profiling and physiological parameters represented a promising tool for investigating the mechanisms of plant response to drought stress at non-polar metabolome level.

Challenges to Water Security along the “Emerald Coast”: A Political Ecology of Local Water Governance in Nicaragua

Despite being a water-rich country, Nicaragua struggles to secure clean water access for many of its residents. In addition to distributional and water quality issues, a prolonged drought affecting all regions of the country has compounded preexisting governance challenges to ensuring rural water needs. This article focuses on a rural community along the southwest Pacific Coast of Tola, Nicaragua, where tourism development and drought converge to produce and exacerbate water insecurity. This article examines this water insecurity in the context of two recent national water laws in Nicaragua (passed in 2007 and 2010 respectively) that sought to provide a more comprehensive legal framework for freshwater water governance. Drawing upon semi-structured interviews and groundwater and meteorological data, we contend that water laws have not effectively mediated the hydrological effects of prolonged drought and tourism development, resulting in pronounced water insecurity for local populations in Tola. We cast the findings of this research as relevant to other water insecure areas in Latin America where industry development and weak policy implementation impact the creation and resolution of local water security—including insecurity compounded by increased climatic variability.

Demographic effects of prolonged drought on a nascent introduction of a semi-aquatic snake

Faced with a nascent introduction of a non-native species, conservationists need to quickly determine how a population performs in its new environment. Although correlative models can predict environmental suitability at a coarse scale, they often neglect short-term climatic variability, instead relying on long-term averages. Accurately projecting the fate of any particular introduction requires demographic data on how a population responds to a novel environment. The recent introduction of watersnakes (genus Nerodia) poses a risk to California’s already imperiled aquatic vertebrate fauna. Despite inhabiting a seemingly suitable climate, a non-native Nerodia sipedon population in central California is likely to have been affected by a prolonged extreme drought from 2012 to 2015. We studied the only known population of N. sipedon in California for 3 years from 2013 to 2015, and estimated its abundance and annual survival. Its abundance declined from a peak of 218 (95% Credible Interval 149–313) in August 2013 to 97 (80–119) in July 2015. Annual survival of N. sipedon from 2013 to 2014 (0.23, 0.13–0.39) and from 2014 to 2015 (0.29, 0.18–0.41) was lower than survival estimates reported from native populations. Snake body condition, the abundance of large adult females, and prey availability all declined throughout the study. We conclude that the population of N. sipedon declined from 2013 to 2015, likely due to decreasing habitat and prey availability from the prolonged regional drought. This study highlights the importance of the effect of climatic extremes on the trajectory of introduced populations in a novel environment.

Drying-Rewetting and Flooding Impact Denitrifier Activity Rather than Community Structure in a Moderately Acidic Fen.

Wetlands represent sources or sinks of the greenhouse gas nitrous oxide (N2O). The acidic fen Schlöppnerbrunnen emits denitrification derived N2O and is also capable of N2O consumption. Global warming is predicted to cause more extreme weather events in future years, including prolonged drought periods as well as heavy rainfall events, which may result in flooding. Thus, the effects of prolonged drought and flooding events on the abundance, community composition, and activity of fen denitrifiers were investigated in manipulation experiments. The water table in the fen was experimentally lowered for 8 weeks in 2008 and raised for 5.5 months in 2009 on three treatment plots, while three plots were left untreated and served as controls. In situ N2O fluxes were rather unaffected by the drought treatment and were marginally increased by the flooding treatment. Samples were taken before and after treatment in both years. The structural gene markers narG and nosZ were used to assess possible changes in the nitrate reducer and denitrifier community in response to water table manipulations. Detected copy numbers of narG and nosZ were essentially unaffected by the experimental drought and flooding. Terminal restriction fragment length polymorphism (TRFLP) patterns of narG and nosZ were similar before and after experimental drought or experimental flooding, indicating a stable nitrate reducer and denitrifier community in the fen. However, certain TRFs of narG and nosZ transcripts responded to experimental drought or flooding. Nitrate-dependent Michaelis-Menten kinetics were assessed in anoxic microcosms with peat samples taken before and 6 months after the onset of experimental flooding. Maximal reaction velocities vmax were higher after than before flooding in samples from treament but not in those from control plots taken at the same time. The ratio of N2O to N2O + N2 was lower in soil from treatment plots after flooding than in soil from control plots, suggesting mitigation of N2O emissions by increased N2O-reduction rates after flooding. N2O was consumed to subatmospheric levels in all microcosms after flooding. The collective data indicate that water table manipulations had only minor effects on in situ N2O fluxes, denitrifier abundance, and denitrifier community composition of the acidic fen, while active subpopulations of denitrifiers changed in response to water table manipulations, suggesting functionally redundant subpopulations occupying distinct ecological niches in the fen.

Effects of prolonged drought on the anatomy of sun and shade needles in young Norway spruce trees.

Predicted increases in the frequency and duration of drought are expected to negatively affect tree vitality, but we know little about how water shortage will influence needle anatomy and thereby the trees' photosynthetic and hydraulic capacity. In this study, we evaluated anatomical changes in sun and shade needles of 20-year-old Norway spruce trees exposed to artificial drought stress. Canopy position was found to be important for needle structure, as sun needles had significantly higher values than shade needles for all anatomical traits (i.e., cross-sectional needle area, number of tracheids in needle, needle hydraulic conductivity, and tracheid lumen area), except proportion of xylem area per cross-sectional needle area. In sun needles, drought reduced all trait values by 10-40%, whereas in shade needles, only tracheid maximum diameter was reduced by drought. Due to the relatively weaker response of shade needles than sun needles in drought-stressed trees, the difference between the two needle types was reduced by 25% in the drought-stressed trees compared to the control trees. The observed changes in needle anatomy provide new understanding of how Norway spruce adapts to drought stress and may improve predictions of how forests will respond to global climate change.

Correlations between morpho-anatomical changes and radial hydraulic conductivity in roots of olive trees under water deficit and rewatering

The effects of prolonged drought were studied on olive (Olea europaea L.; drought-sensitive cultivar Biancolilla and drought-tolerant cultivar Coratina) to examine how morpho-anatomical modifications in roots impact on root radial hydraulic conductivity (Lpr). Two-year-old self-rooted plants were subjected to a gradual water depletion. The levels of drought stress were defined by pre-dawn leaf water potentials (Ψw) of -1.5, -3.5 and -6.5 MPa. After reaching the maximum level of drought, plants were rewatered for 23 days. Progressive drought stress, for both cultivars, caused a strong reduction in Lpr (from 1.2 to 1.3 × 10(-5) m MPa(-1) s(-1) in unstressed plants to 0.2-0.6 × 10(-5) m MPa(-1) s(-1) in plants at Ψw = -6.5 MPa), particularly evident in the more suberized (brown) roots, accompanied with decreases in stomatal conductance (gs). No significant differences in Lpr and gs between the two olive cultivars were observed. Epifluorescence microscopy and image analyses revealed a parallel increase of wall suberization that doubled in white stressed roots and tripled in brown ones when compared with unstressed plants. In drought-stressed plants, the number of suberized cellular layers from the endodermis towards the cortex increased from 1-2 to 6-7. Recovery in Lpr during rewatering was correlated to the physical disruption of hydrophobic barriers, while the time necessary to obtain new mature roots likely accounted for the observed delay in the complete recovery of gs. Radial hydraulic conductivity in olive roots was strongly influenced by soil and plant water availability and it was also modulated by structural root modifications, size, growth and anatomy. These findings could be important for maintaining an optimal water status in cultivated olive trees by scheduling efficient irrigation methods, saving irrigation water and obtaining yield of high quality.

Potential Yield and Climate Change Sensitivity of Groundnut in Cagayan Valley Using Simulation Models

This study aimed to determine yield and production constraints of peanut inCagayan Valley using Decision Support System for Agrotechnology Transfer; analyze yieldgaps between simulated and actual yield, and provide decision support to optimizeproduction. Simulation results using CSM-CROPGRO sub-model of DSSAT showed thathighest potential yield is 2,267 kgs. / Hectare when planted in October 15 under rainfedcondition. Under non-stressed conditions in the dry season, the potential yield is 4,805 kgs./hectare planted in December 15. From 10 years of yield data, gap between farmer’s yieldcompared with rainfed potential ranges from 153 to 2,116 kgs./ hectare. Low rates ofnitrogen application and pests and diseases were the factors causing yield gaps. The DSSATprogram also captured the effect of prolonged drought in the last quarter of 2009 whichresulted to underestimated yield, and the effect of warm weather in 2004 which showedlowering of potential yield by 50%. Regional analysis of peanut yields showed that centraleastern part is more productive for rainfed conditions during the dry season; whereassouthern part including Quirino and Ifugao is more suitable to producing peanut during thewet season due to cooler temperature.Keywords: Agriculture, groundnut, potential and actual yield, simulation, climate change,Decision Support System for Agrotechnology Transfer, Philippines

Effects of prolonged drought on the vegetation cover of sand dunes in the NW Negev Desert: Field survey, remote sensing and conceptual modeling

Luminescence dating of stable sand dunes in the large deserts of the world has shown several episodes of mobility during the last 30 k years. The logical explanation for the mobility of fixed dunes is severe drought. Though drought length can be estimated, the level of precipitation drop is unknown. The stabilized sand dunes of the northwestern Negev Desert, Israel have been under an unprecedented prolonged drought since 1995. This has resulted in a vast decrease of shrubs cover on the fixed sand dunes, which changes along the rainfall gradient. In the north, an average of 27% of the shrubs had wilted by 2009, and in the drier southern area, 68% of the shrubs had withered. This loss of shrubbery is not expected to induce dune remobilization because the existing bio-crust cover is not negatively affected by the drought. Eleven aerial photographs taken over the drier southern area from 1956 to 2005 show the change in shrub cover due to human impact and the recent severe drought.

Differences in desiccation tolerance do not explain altitudinal distribution patterns of tropical bryophytes

Bryophyte biomass and diversity vary strongly with altitude in the tropics. Low abundance and low species numbers in lowland rain forests are most likely due to reduced diurnal activity times combined with high nocturnal respiration rates at high temperatures. This may exclude many montane species from the warm lowlands. However, an alternative hypothesis explains the observed pattern, namely a limited desiccation tolerance of montane species, precipitation being more concentrated but less frequent in most lowland forests compared to montane cloud forests. To test this hypothesis, we studied the desiccation tolerance of four montane and four lowland bryophyte species. The effects of prolonged drought were quantified with chlorophyll fluorescence (Fv/Fm) and the extent of electrolyte leakage. Both montane and lowland species survived dry periods of ≧80 days, which far exceeds the duration of dry periods in the wet lowland tropics. We can thus exclude intolerance to long dry spells as an explaination for the absence of the tested montane species in the lowlands. We should continue to focus on other mechanisms to explain the altitudinal gradient of bryophyte abundance and diversity in the tropics, in order to understand this pattern, as well as to predict future trends under climatic warming.

Drought changes phosphorus and potassium accumulation patterns in an evergreen Mediterranean forest

Summary Climate models predict more extreme weather in Mediterranean ecosystems, with more frequent drought periods and torrential rainfall. These expected changes may affect major process in ecosystems such as mineral cycling. However, there is a lack of experimental data regarding the effects of prolonged drought on nutrient cycling and content in Mediterranean ecosystems. A 6‐year drought manipulation experiment was conducted in a Quercus ilex Mediterranean forest. The aim was to investigate the effects of drought conditions expected to occur over the coming decades, on the contents and concentrations of phosphorus (P) and potassium (K) in stand biomass, and P and K content and availability in soils. Drought (an average reduction of 15% in soil moisture) increased P leaf concentration by 18·2% and reduced P wood and root concentrations (30·9% and 39·8%, respectively) in the dominant tree species Quercus ilex, suggesting a process of mobilization of P from wood towards leaves. The decrease in P wood concentrations in Quercus ilex, together with a decrease in forest biomass growth, led to an overall decrease (by approximately one‐third) of the total P content in above‐ground biomass. In control plots, the total P content in the above‐ground biomass increased 54 kg ha−1 from 1999 to 2005, whereas in drought plots there was no increase in P levels in above‐ground biomass. Drought had no effects on either K above‐ground contents or concentrations. Drought increased total soil soluble P by increasing soil soluble organic P, which is the soil soluble P not directly available to plant capture. Drought reduced the ratio of soil soluble inorganic P : soil soluble organic P by 50% showing a decrease of inorganic P release from P bound to organic matter. Drought increased by 10% the total K content in the soil, but reduced the soil soluble K by 20·4%. Drought led to diminished plant uptake of mineral nutrients and to greater recalcitrance of minerals in soil. This will lead to a reduction in P and K in the ecosystem, due to losses in P and K through leaching and erosion, if the heavy rainfalls predicted by IPCC (Intergovernmental Panel on Climate Change) models occur. As P is currently a limiting factor in many Mediterranean terrestrial ecosystems, and given that P and K are necessary for high water‐use efficiency and stomata control, the negative effects of drought on P and K content in the ecosystem may well have additional indirect negative effects on plant fitness.

The Effects of Prolonged Drought and Nitrogen Fertilizer on Root and Shoot Growth and Water Uptake by Winter Wheat

AbstractWinter wheat growing on a silty clay loam soil was protected from rainfall by a mobile shelter for 100 days from tillering to maturity. During this time the crop was either irrigated according to demand or grew on stored soil water. The effects of this high and low water supply, in combination with a high and low N supply, on root and shoot growth and water uptake were studied.The crop given both N and water yielded 9.7 t/ha of grain (85 % DM), drought reduced this to 7.9 t/ha, low N to 4.3 t/ha and drought and low N to 3.8 t/ha. Yield reductions were mainly due to fewer grains being produced.Little root growth occurred in the topsoil during the drought but there was compensatory growth in the subsoil provided that N fertilizer was given. The droughted crops rooted to 160 cm, about 20 cm deeper than the irrigated crops, but the amount of root in the deep subsoil was very small, less than 0.1 cm/cm3 ai 140–160 cm, compared with 5–9 cm/cm3 in the topsoil.The crop demand for water at any given time was partitioned throughout the root system but atmospheric demand was only met whilst the topsoil was wet. The fertilized, droughted crop extracted all of the potentially available water to a depth of 80 cm and a mean rooting density of 1 cm/cm3 was necessary to achieve this. Uptake from below this depth was limited by root growth.The limiting value of the potential soil water deficit was 170 mm, and weather records showed that this would be exceeded one year in ten, on average. The likelihood of yield reduction due to drought could be reduced on this soil by improving root growth below 80 cm depth, although the chances of achieving this are low as root growth was probably limited by poor soil structure.

The Environment of Chamaecyparis lawsoniana

The environment of Chamae'cyparis lawsoniana (A. Murr.) Parl. was measured at 10 or more sites in Oregon and California which represent six different plant communities. Water is probably the factor most limiting the species' distribution. Most populations have late summer predawn xylem pressure potentials above -11 bars. The eastern range boundary coincides with a rapid decrease in the ratio of precipitation to evaporation. The species is usually confined to wet ultramafic parent materials except at high elevations and in the N. Its southern limit may coincide with absence of consistently wet ultramafics. Success of Chamaecyparis on ultramafics may result from failure of Pseudotsuga and other competitors to cope with the chemical composition and saturation of these substrates. Foliar nutrient concentrations of C. lawsoniana are lower on ultramafics than on other soils, but have a high Ca:Mg ratio. Mycorrhizae show no differences associated with soil type. Despite a large temperature range in the habitat of C. lawsoniana, temperature does not seem to limit the species directly. Mean annual air temperatures range from 4.4-10.9 C. Especially at the northern end of the range, temperatures decrease more slowly in late summer than outside the range. Soils are cool, with little annual variation in areas with seepage. Chamaecyparis lawsoniana seems to be restricted by different aspects of the environment than are most dominant species with which it grows. Variations in temperature and parent material within its range are responsible for large changes in vegetation type without excluding the Chamaecyparis. Yet the changes in water availability which limit C. lawsoniana, often do not produce discontinuities in the other vegetation present. INTRODUCTION Chamaecyparis lawsoniana (A. Murr.) Parl. (Cupressaceae), Port Orford cedar, is endemic to the Klamath Mountain region of Oregon and California. It is of interest because: (1) It has a paradoxical distribution, being restricted to a limited geographic range but occurring on many diverse habitats (Fowells, 1965); (2) exploitation and a nonendemic root rot are rapidly decimating the natural forests; (3) the wood is very valuable; and (4) as Chama,ecyparis also grows in temperate habitats in Japan and Taiwan, comparison with studies of those species may clarify the meaning of our results. The distribution. vegetation, topographic and geologic relationships of Chamaecyp,aris lawsoniana, forests are known in some detail (Whittaker, 1960; Griffin and Critchfield, 1972; Hawk, 1977). Other ecological descriptions of this species (Fowells, 1965). are mostly general. This study sampled several aspects of the environment of C. lawsoniana. Sampling sites included extreme as well as typical conditions for the species. Air and soil temperatures, humidity, depth to water table, degree of shading of tree reproduction, effects of prolonged drought, and xylem pressure potential and foliar nutrient concentrations of the plants 'were measured. Our results cara help define reasons for the range restriction of C. lawsoniana, as well as the environment where it may be best managed. GENERAL ENVIRONMENT OF THE SPECIES' RANGE Chamaecyparis lawsoniana receives moderately high precipitation. In southernmost Oregon, the eastern range boundary coincides approximately with the 1000mm (40-inch) isohyet (U.S. Dep. Agric., 1964), and in California most stands receive at least 1500 mm (Rantz, 1968). East of its range, rainfall is less and evaporative stress is greater, as shown by the flora (Waring, 1969) and by moisture 1 Present address: Forestry Sciences Laboratory, U. S. Forest Service, 3200 Jefferson Way, Corvallis, Oregon 97331.

Seasonality of Nesting by Zebra Finches at Armidale, NSW

Nests of Zebra Finches were surveyed from 1961 to 1965 at Saumarez Pond near Armidale. About 200 birds used 220 trees for nesting within an area of five square kilometres. Two types of nest (breeding and roosting) varied in number according to the season from eighteen (January 1964) to ninety-eight (October 1961). The number of breeding nests built in a season varied between eighty-one (1963 - 64) and 154 (1961-62). Nesting success (young fledged from eggs laid) varied little, averaging about forty-four percent (n=382). No laying occurred in June or July (except once), when temperatures were often below freezing. At least two birds born in spring bred in the autumn of the same breeding season. In contrast to the breeding regime in arid areas, nesting activities of Zebra Finches at Armidale were not directly affected by drought; during the autumn of 1965 the peak of breeding activity was reached in March (19 breeding nests) when no rain had fallen for six weeks and the effect of prolonged drought on the vegetation was apparent. The results may be interpreted in several ways: that low temperatures (but not drought) inhibit breeding or that changes of photoperiods or increased availability of food itself stimulate many individuals to breed in this population. From a review of relevant literature, it is concluded that, if there is a proximate factor for the breeding of Zebra Finches, it must be different in different parts of the range of the species. It is suggested that individual differences exist in response to various proximate factors for reproduction and that the populations in the intermediate climatic zone are more polymorphic with respect to types of response than the populations that occur where the causal relations of environmental factors are predictable, if not periodic, in occurrence.