Mid-summer Drought Research Articles

The influence of water stress on non-structural carbohydrate concentration in Themeda triandra

The objective of this study was to determine the influence of four different watering treatments (T1 = 75-100%, T2 = 50-75%, T3 = 25-50% and T4= 0-25% of Field Water Capacity) on the concentration of total non-structural carbohydrates during three growth stages (vegetative, pipe and reproductive) and also in three plant parts (roots, stubble and leaves) of the indigenous C4 grass species Themeda triandra. The total non-structural carbohydrate concentration (TNCC) was higher in all the plant parts (P≤0.05) as well as all the growth stages (P≤0.05), in T4 than T1. The results confirm that total non-structural carbohydrates are allocated (as growth reserves) to certain plant parts with increased water stress, with the largest allocation to the stubble. Because a mid-summer drought is more the rule than the exception in semi-arid areas, severe defoliation of Themeda triandra in the pipe growth stage during these conditions will be extremely detrimental to the survival of this key forage plant.

Factors Controlling the Timing of Root Elongation Intensity in a Mature Upland Oak Stand

We examined the timing of root elongation intensity (REI) – the production of newly elongating roots measured in length per unit soil volume per unit time – in a mature white oak-chestnut oak forest in Tennessee, USA, over a 4-year period. We used a network of minirhizotrons to (1) examine environmental control of soil moisture and temperature over REI, (2) evaluate the control of phenology over REI (3) develop a multivariate regression equation using the variables of soil temperature, soil water potential and phenology to predict REI, and (4) delineate soil water potentials that were optimum for growth. Fifteen minirhizotron tubes were installed on the upper slope of an upland oak stand on Walker Branch Watershed in Oak Ridge, Tennessee. Measurements of REI were examined over three growing seasons in the upper 30 cm of the soil profile. Composited sets of data on REI, soil water potential, soil temperature and phenology were analyzed to determine the strength of relationships between the latter three variables and REI. There was no statistically significant relationship between REI and soil temperature during the growing season (March–November). The highly significant (p < 0.0001) relationship between soil water potential and REI was best described as log linear, using log10 (-Ψ) vs. log10 (REI). The correlation between a phenology index and REI was also highly significant (p < 0.0001), as the 24 highest REI levels occurred between late April and early August. Whereas soil water potential played a major role in controlling REI, our data indicate that at times phenologically related factors appeared to override environmental variables. The fact that REI generally peaked every year following completion of leaf expansion is congruent with the fixed shoot growth pattern of many temperate-zone deciduous tree species. In an attempt to explain the importance of phenology in controlling REI, we refer to the concept of `phenological programming'. This concept contrasts with more environmentally determinant explanations of the timing of root growth. Those theories cannot explain either our data or that of others, wherein, during late summer and early autumn, REI does not return to early summer rates, even though soil moisture and temperature conditions are equally, if not more, favorable. The particular type of `phenological programming' hypothesized in this study may be limited to mature deciduous trees exhibiting a fixed growth pattern of shoot expansion and growing in a temperate climate with a mid-summer drought period.

The Midsummer Drought over Mexico and Central America

The annual cycle of precipitation over the southern part of Mexico and Central America exhibits a bimodal distribution with maxima during June and September–October and a relative minimum during July and August, known as the midsummer drought (MSD). The MSD is not associated with the meridional migration of the intertropical convergence zone (ITCZ) and its double crossing over Central America but rather with fluctuations in the intensity and location of the eastern Pacific ITCZ. During the transition from intense to weak (weak to intense) convective activity, the trade winds over the Caribbean strengthen (weaken). Such acceleration in the trade winds is part of the dynamic response of the low-level atmosphere to the magnitude of the convective forcing in the ITCZ. The intensification of the trade winds during July and August and the orographic forcing of the mountains over most of Central America result in maximum precipitation along the Caribbean coast and minimum precipitation along the Pacific coast of Central America. Changes in the divergent (convergent) low-level winds over the “warm pool” off the west coast of southern Mexico and Central America determine the evolution of the MSD. Maximum deep convective activity over the northern equatorial eastern Pacific, during the onset of the summer rainy season, is reached when sea surface temperatures exceed 29°C (around May). After this, the SSTs over the eastern Pacific warm pool decrease around 1°C due to diminished downwelling solar radiation and stronger easterly winds (during July and August). Such SST changes near 28°C result in an substantial decrease in deep convective activity, associated with the nonlinear interaction between SST and deep tropical convection. Decreased deep tropical convection allows increased downwelling solar radiation and a slight increase in SSTs, which reach a second maximum (∼28.5°C) by the end of August and early September. This increase in SST results once again in stronger low-level convergence, enhanced deep convection, and, consequently, in a second maximum in precipitation. The MSD signal can also be detected in other variables such as minimum and maximum surface temperature and even in tropical cyclone activity over the eastern Pacific.

Calibration of CERES3 (Maize) to improve silking date prediction values for South Africa

Silking which coincides with the mid-summer drought in South Africa, could have a significant negative effect on maize yield. Errors in the prediction of silking date could contribute to errors in kernel number simulation, and consequently to errors in yield simulation. A field trial, comprising 21 planting dates and three cultivars representing short, medium and long growing season requirements was used to modify the crop growth model CERES3 (Maize) to improve its accuracy in the simulation of silking date by four days. The results were verified against a historical data set and showed an improvement in the simulation of silking date by two days.

Effect of Irrigation on Crabapple Growth and Water Relations During Field Production with In-Ground Fabric Containers

Abstract Growth and water relations of irrigated and non-irrigated Malus sieboldii var. zumi produced with and without in-ground fabric containers in a field-nursery setting were investigated. Predawn and midday leaf water potential and midday stomatal conductance were measured periodically through the season, and trunk increment, leaf area, root growth, and osmotic potential were measured in late season. Water potential became more negative and stomatal conductance decreased in non-irrigated treatments during an extended mid-summer drought that resulted in less trunk diameter growth and leaf area. Trees grown in fabric-containers, both irrigated and non-irrigated, exhibited no detectable differences in water relations over the season. These trees did have fewer roots and less leaf area than the trees grown without fabric containers, indicating that in-ground fabric containers can limit growth even when irrigated. Non-irrigated trees in fabric containers were nonetheless affected by water stress as they had the least trunk growth and most negative osmotic potential of all treatments. Careful management practices would suggest increased irrigation frequency during production with in-ground fabric containers to avoid water stress.

Drought Effects on Yield and Quality of Perennial Grasses in the North Central United States

Drought frequently limits perennial grass productivity during midsummer in the North Central States, yet the relative drought tolerance of perennial grasses grown in this region is unknown. We determined the effect of water deficit (drought) on the forage yield, forage quality, and stand persistence of reed canarygrass (Phalaris arundinacea L.), smooth bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), and timothy (Phleum pratense L.). Grasses were grown on a Hubbard loamy sand (sandy, mixed, Udorthentic Haploboroll) and subjected to two soil-water regimes simulating ‘droughted’ and ‘well-watered’ (control) plant growth. When drought occurred throughout the regrowth cycle, forage yields of droughted reed canarygrass, orchardgrass, smooth bromegrass, and timothy were 33, 37, 24, and 34%, respectively, of the controls. Reed canarygrass yields under drought were similar to those of orchardgrass but greater than those of timothy and smooth bromegrass. Total season yields of reed canarygrass, orchardgrass, smooth bromegrass, and timothy exposed to periods of drought followed by well-watered conditions were 54, 60, 81, and 62%, respectively, of the irrigated controls, which suggests that smooth bromegrass may be capable of compensatory growth following drought. Drought consistently enhanced the leafiness of reed canarygrass, smooth bromegrass, and timothy, which have a culmed growth habit (i.e., stem elongation during all regrowths). When drought occurred throughout growth, crude protein concentration of leaf, stem, and total forage of all species was greater than the controls. Drought decreased neutral and acid detergent fiber (NDF and ADF) concentrations in total forage of reed canarygrass and smooth bromegrass at all harvests and of orchardgrass and timothy at two of three harvests. Enhanced forage quality was associated with increased forage leafiness and enhanced stem and leaf quality. Drought reduced the persistence of reed canarygrass and timothy compared with the control, but had no effect on smooth bromegrass or orchardgrass persistence. Smooth bromegrass was the most persistent and orchardgrass was the least persistent grass. Our results indicate that reed canarygrass is among the most productive cool-season grasses during drought. Smooth bromegrass, however, may have greater long-term yield and persistence than other cool-season grasses under the typical pattern of favorable spring moisture and midsummer drought in the North Central States.

WATER STRESS DETECTION WITH FOLIAGE TEMPERATURE FOR IRRIGATION SCHEDULING IN NURSERY PRODUCTION

Changes in foliage temperature with environmental conditions were investigated for use in detecting water stress and scheduling irrigations of woody nursery plants. Midday leaf-minus-air temperature (Tl-Ta) and vapor pressure deficit (VPD) were monitored seasonally for container-grown shrubs--prostrate juniper, upright juniper and dwarf red-stem dogwood--at open and closed spacings. There was an inverse relationship between Tl-Ta and VPD for all species and spacings but with substantial scatter. Slopes for openand closed-spaced shrubs were not significantly different for any species. As container moisture and predawn leaf water potential declined during a dry-down cycle Tl-Ta increased significantly over well-watered levels for open-spaced plants and closed-spaced dogwood. In a field experiment Tl-Ta and VPD were monitored in young London plane, flowering pear, and redbud with-and-without irrigation. Only irrigated London plane Tl-Ta was inversely related to VPD. Leaves coated with petroleum jelly, however, had Tl-Ta levels consistently greater than uncoated leaves in all species, and non-irrigated Tl-Ta rose to those levels during a mid-summer drought. These results suggest that irrigation of container shrubs can be timed to increases in Tl-Ta with VPD, while comparing coated and non-coated Tl-Ta may be more successful for irrigated field production.

IRRIGATION, WATER RELATIONS, AND CRABAPPLE GROWTH IN ROOT-CONTROL BAGS IN A FIELD NURSERY

Limited root development of nursery stock in root-control bags facilitates harvest but without irrigation may predispose stock to water stress. The effect of bags and irrigation on growth and water relations of field-grown Malus sieboldii var. zumi were investigated following transplanting as large liners into a silty-clay soil. Predawn leaf water potential (ψ), and midday stomatal conductance (gs) and ψ, were measured periodically through the season. Late-season osmotic potential (ψπ), caliper, leaf area, and root growth were also measured. Non-irrigated treatments exhibited water stress during an extended mid-summer drought, as predawn ψ and particularly gs were less than irrigated treatments, resulting in lower vegetative growth and ψπ. For combined bagged treatments water relations did not differ, but leaf area, root growth, and ψπ, but not caliper, were less than non-bagged trees. Growth measurements and ψπ of non-irrigated bagged trees, however, were consistently lower but nonsignificant than the other treatments. Bag-induced root reduction can limit some top growth even with optimum soil water. Moreover, in terms of potential Type-II errors extrapolated over a conventional production cycle, trees grown in root-control bags in normally non-irrigated soils may be more susceptible to water stress and subjected to further cumulative growth limitation.

Juvenile survival and population structure of blue wildebeest and warthogs in the Central Region of the Kruger National Park during the mid-summer drought of 1988/89

The survey was undertaken to investigate juvenile survival and population structure of blue wildebeest and warthogs during a mid-summer drought, and to gain sup- plementary data for a longer-term population monitoring programme. The per- centage of adult wildebeest cows with juveniles was lower than normal for the time, but was not commensurate with a sharp decline in the population. Warthogs did not tolerate the drought as well as wildebeest and experienced a larger reduction in juvenile recruitment, albeit much less than the 80-90 losses of piglets recorded in the more severe drought of late 1982.

Above-Ground Phytomass Dynamics in a Grassland Steppe of Patagonia, Argentina

Aerial phytomass and litter dynamics of a grassland steppe in Patagonia, Argentina, were studied at either monthly or bimonthly intervals for 2 years. This area is characterized by a cold and wet winter (June to September) and a warm and dry summer (December to March). The growing season extends from September to April, with moist spring and fall periods interrupted by a midsummer drought. Festuca pallescens (St. Yves) Parodi produced about 95% of the total annual phytomass. Peaks of green phytomass were recorded in spring-summer of the first growing season (33.6 +/- 2.9 g . m-2) and in early spring (35.0 +/- 2.4 g . m-2) and fall (32.7 +/- 2.7 g . m-2) of the second growing season. Less abundant forage grasses were Poa ligularis Nees ap Steudel, Bromus setifolius Presl., Hordeum comosum Presl., and Rytidosperma virescens (Desvaux) Nicors. Shrubs and forbs represented less than 2% of the total annual phytomass of this grassland. The relationships between phytomass production of the main species and some environmental variables are discussed. These results contribute to the knowledge of above-ground phytomass dynamics and forage availability throughout seasons of this grassland in Patagonia, and are part of the data necessary for proper range management planning. This information will permit the designing of appropriate grazing schedules by balancing the number of grazing animals to the forage resources available.

Effects of Overland Flow on Plant Water Relations, Erosion, and Soil Water Percolation on a Mojave Desert Landscape

AbstractPrevious work in the Mojave Desert of California has shown that diversion of overland flow from alluvial piedmonts results in lower shrub density and biomass compared to that in adjacent areas that receive overland flow. In this study, measurements of predawn xylem pressure potential of creosotebush (Larrea tridentata) on three areas that were deprived of overland flow and three adjacent areas indicated that shrubs in areas of drainage‐diversion maintained higher water potentials during midsummer drought, suggesting a greater availability of soil moisture in those areas. There were no differences in the distribution of 137Cs between these areas, suggesting that drainage‐diversion has not affected erosion of surficial deposits. Mean depth of wetting of the soil profile, as indicated by the depth distribution of mobile ions (Na+, Cl−, and SO2−4) in the soil, was not significantly different between areas, although the depth to the first peak in concentration of these ions was consistently shallower in areas of drainage‐diversion, suggesting reduced percolation of soil moisture. We conclude that the higher water potential of shrubs in areas of drainage‐diversion is due to lower competitive exploitation of soil moisture than is found among the high biomass of shrubs in undisturbed areas. In contrast, soil properties have not been greatly affected by the diversion of overland flow for the past 50 yr.

モモ及びニホンナシ生産と雨量の変動との関係

Correlations between total rainfall variation in growing seasons and yields (kg/10a) of Peach and Japanese Pear at 3 typical production Prefectures were examined, and approximate quadratic equations were derived for Japanese Pear.Rainfall variations in Baiu seasons (much rain in June and July) and midsummer (little rain in August), which were closely related to fruits culture distribution and management, were analysed using the Quintile Grouping of rainfall data. Ratios of rainfall/potential evapotranspiration were derived and compared by distribution maps with fruits culture regions in normal year, more rainy year (once in 5 years level) and less rainy year (same above).From the prospect of climatic change in near future, the author appointed that warmer temperature and activiation or going north of Baiu Front might cause earlier outburst of pests and diseases and intensification of midsummer drought, which necessitated sufficient irrigation fascilities and water.

Seasonal Changes in Smooth Bromegrass Top and Root Growth and Fate of Fertilizer Nitrogen

AbstractWhile information is available at the end of the growing season on the fate of fertilizer N applied to perennial grasslands, little detailed information is available on the transformations and translocation of N during a growing season. The purpose of this research was to measure the effect of N fertilization on time, quantities, and rates of dry‐matter accumulation by smooth bromegrass (Bromus inermis L.) tops and roots, water use, and fertilizer N transformations and uptake. Ammonium nitrate was surface broadcast at 0, 90, and 270 kg N ha−1 on established smooth bromegrass at Mandan, ND. At approximately 3‐wk intervals, top and root (0–900 mm) dry weights were measured, N uptake calculated, soil inorganic N concentrations determined, and apparent fertilizer N in tops, roots, and as soil inorganic N was calculated (fertilized minus check). Growth and N uptake of tops increased until physiological maturity in July, decreased during a midsummer drought, and increased after August rains. Fertilization greatly increased growth rate. For roots, growth stopped or even declined slightly at time of floral emergence in June, resumed until physiological maturity, remained constant or decreased slightly through the summer drought (when soil water reserves were depleted), then increased rapidly in September after fall rains. Dry matter accumulated at rates in excess of 300 kg ha−1 d−1 in May and September, when N uptake rates exceeded 4 kg ha−1 d−1. Over 40% of the fertilizer N at the 270 kg N rate was immobilized in organic forms other than root growth within 10 d after application, but by physiological maturity, 51% was in tops, 27% in roots, 3% as soil inorganic N, and only 19% was immobilized in other organic forms or lost by gaseous means (no leaching occurred). Results suggest that gaseous losses were no more than 10%. Nitrogen fertilization appeared to enhance three labile N pools—readily available (inorganic), highly labile (probably including microbial biomass), and moderately labile (possibly primarily grass roots).

Grazing effects on shoot and root dynamics and above‐ and below‐ground non‐structural carbohydrate in Caucasian bluestem

AbstractThe objective of this study was to characterize changes in morphology and shoot/root total nonstructural carbohydrate (TNC) relationships in Caucasian bluestem (Bothriochloa caucasica) under grazing. Pastures were continuously grazed by steers weighing about 225 kg from mid‐May to late September of 1983 and 1984. Heavily grazed (H) swards produced more tillers m−1 than lightly grazed (L) swards. Number of tillers declined in both treatments during the midsummer drought period; however, the reduction was much less in H than in L swards. Above normal precipitation in August 1983 allowed number of tillers to rapidly recover (by approximately 4000 and 8000 m−1 for L and H treatments, respectively) reaching 10 700 and 17 800 tillers m−1 respectively, in late September. After 2 years of grazing, H swards initiated twice as many roots on an area basis; however, ability to penetrate soil to lower depths may have been reduced. Heavily grazed Caucasian bluestem had lower concentrations of total non‐structural carbohydrate (TNC) in shoots (P &lt; 0.04) in both years, but had higher (28% at the end of 1984) TNC concentration in roots compared to lightly grazed (P= 001) plants. Greater root mass was found in lightly grazed swards; therefore, we suggest that root growth and TNC concentration tend to be inversely related. Total amount of TNC was higher in L swards, but during the course of the study total above and below‐ground TNC in H swards remained stable. Total above‐ground TNC pools are subject to short‐term variation and dilution from senescent herbage, thus TNC pools in individual plant parts may be a better indication of plant response.

The Influence of Climate and Soils on the Distribution of Four African Grasses

Around 1900 temperate and semidesert grassland productivity declined, soil erosion increased, and drought destabilized the livestock industry in the northern and southern hemispheres. As government leaders throughout the world began to recognize the importance of grassland productivity and soil conservation, a massive experiment began to evolve. Government and private individuals collected seed from every continent, and planted seed at experimental stations and ranches in their respective countries. Hundreds of individuals who conducted thousands of seeding trials observed that buffelgrass (Cenchrus ciliaris L.), weeping lovegrass [Eragrostis curvula (Schrad.) Nees], kleingrass (Panicum coloratum L.), and Lehmann lovegrass (Eragrostis lehmanniana Nees) plants from seed collected in Africa were easier to establish and persisted longer than other grasses. Between 1930 and 1986 scientists in many countries evaluated the establishment and persistence of these grasses, but no attempt was made to synthesize the data base and determine the effects of climate and soil on plant establishment and persistence. Our objective was to: (1) determine the climatic and edaphic characteristics of areas where the seed of each grass was collected in Africa, and where each grass has been successfully established in both hemispheres, and (2) identify characteristics which influence long-term persistence. Where buffelgrass predominates and spreads, summer rainfall varies from 150 to 550 mm, winter rainfall is less than 400 mm, mean miminum winter temperatures rarely fall below 5? C, and soil texture is loamy. Weeping lovegrass can be established and plants persist when spring, summer, and fall rainfall varies from 400 to 1,000 mm on deep sandy soil and mean minimum winter temperatures rarely fall below -5? C. The invasion of adjacent nonplanted sites occurs only in Africa where growing season rainfall infrequently cycles between 750 and 1,000 mm and soils remain wet in mid-summer. Kleingrass can be established where mean maximum daily summer temperatures are above 30? C, mean minimum daily winter temperatures rarely fall below 0 C, summer growing season rainfall varies from 400 to 990 mm, and soils are clayey or silty. Kleingrass, like weeping lovegrass, spreads to nonplanted sites only in Africa where a mid-summer drought does not occur. Lehmann lovegrass predominates and spreads only in southern Africa, southeastern Arizona, and northern Mexico when summer rainfall in 30 to 40 days exceeds 150 mm, and soil textures are sandy or

Long-term effects of smelter pollution at Sudbury, Ontario, on forest community composition

Forest communities were quantitatively analyzed along a south-southeast transect from a large, 70- to 80-year-old smelter complex near Sudbury, Ontario. None currently exist within 3 km SSE of this smelter. At distances of up to 8 km, pockets of remnant forest communities of various sizes occur, mainly on protected slopes and in valley bottoms. Most hilltops are bare of vegetation, denuded of soil, and blackened from the effects of sulfur dioxide fumigations. Beyond this distance, the forests are more or less continuous, although there are still some bare hilltops as far as 15 km from the smelter. The forests which do occur are relatively depauperate in terms of tree diversity and biomass at the closer sites. Similar effects on the ground flora are also documented, although the forest canopy appears to be more greatly affected than the ground flora. Certain species are widely distributed in the inner polluted areas, while others, notably conifers and such ground flora components as bracken fern and most lichens and bryophytes, are absent from sites closer to the smelter.Some changes in the plant communities close to the Copper Cliff smelter have occurred subsequent to the building of a tall (380 m) smokestack in 1972. These have mainly occurred at sites where soils remain, where residual soil toxicity is not excessive, and where midsummer drought is not severe. Colonization has largely involved the spread of such pioneer grasses as Agrostis hyemalis var. tenuis, A. stolonifera var. major, and Deschampsia caespitosa, and more vigorous growth of certain surviving woody species. The recovery of denuded, blackened hilltops, essentially a primary succession on naked Precambrian bedrock, will be a much slower process.