High Water Regimes Research Articles

High Water Regime Can Reduce Ammonia Volatilization from Soils under Potato Production

This research was conducted with Biscayne marl soil and Krome gravelly loam from Florida and Quincy fine sand and Warden silt loam from Washington to determine ammonia (NH3) volatilization at various temperature and soil water regimes. Potassium nitrate (KNO3), ammonium nitrate (NH4NO3), ammonium sulfate [(NH4)2SO4], or urea were applied to the soil at a rate of 75 kg N ha−1. Soil water regime was maintained at either 20% or 80% of field capacity (FC) and incubated at 11, 20, or 29°C, which represented the minimum, average, and maximum temperatures, respectively, during the potato growing season in Washington. Results indicated that the ammonia volatilization rate at 20% FC soil water regime was two‐ to three‐fold greater than that at 80% FC. The cumulative volatilization loss over 28 days was up to 25.7%. Results of this study demonstrated that ammonia volatilization was accelerated at low soil water regimes.

Effects of Water and Nutrient Availability in Pinus pinaster Ait. Open Pollinated Families at an Early Age: Growth, Gas Exchange and Water Relations

Growth and physiological responses of Pinus pinaster Ait. to water and nutrient availability were compared in four open pollinated families of Arenas de San Pedro provenance (Central Iberian Peninsula), looking for more useful parameters and growing conditions to be included in early selection programmes of forest trees. Young seedlings were grown in a greenhouse, subjected to high and low water and nutrient regimes, during 14 weeks. Interfamily differences were significant with regard to growth, nutrient content and water-use efficiency (WUE): differences in growth were higher under more favourable growing conditions; gas exchange differences were higher in the short term (9 weeks), indicating a faster reaction to water stress of the better adapted families to these conditions; the highest growth rates were found in the families with the largest plasticity, highest WUE and highest nutrient content. Water regime and nutrients had significant effects on growth, δ13C, gas exchange and water relation parameters. For these parameters the ranking of the families was kept regardless the water × nutrient supply combination and there was not a significant family × treatment interaction. In the long term (14 weeks) higher water supply and nutrient content significantly increased instantaneous WUE. The positive relationships between growth, intrinsic WUE (A/g wv) and δ13C demonstrate that it should be possible to use physiological parameters (e.g. g wv, δ13C) as a surrogate for the efficiency in the use of water, at least if short periods of water stress (up to 2 months long) were frequent, as it occurs in the Mediterranean basin. There was also some indication that the decrease in nitrogen or potassium supply led to increasing stomatal conductance and hence lower WUE.

Interactive effects of shade and irrigation on the performance of seedlings of three Mediterranean Quercus species

Shade and irrigation are frequently used to increase the success of Mediterranean Quercus spp. plantations. However, there is controversy about the combined effects of these treatments on plant performance. We assessed the effects of two irradiances (full sunlight and moderate shade) and two summer watering regimes (high (daily) and low (alternate days)) on leaf and whole-plant traits of 1-year-old seedlings of Quercus coccifera, Q. ilex subsp. ballota and Q. faginea grown outdoors for 8.5 months. Leaf traits included measures of morphology, nitrogen concentration, gas exchange and photochemical efficiency, and measures of whole-plant traits included biomass allocation patterns, growth phenology, across-summer leaf area change and relative growth rate (RGR). Moderate shade reduced leaf mass per area, increased photochemical efficiency, maximum carbon assimilation rate (Amax) and allocation to leaves, and prolonged the growing period in one or more of the species. Daily watering in summer increased Amax of Q. ilex and prolonged the growing period of Q. ilex and Q. faginea. Both treatments tended to increase RGR. The effect of shade was greater in the low-watering regime than in the high-watering regime for two of the 15 studied traits, with treatment effects being independent for the remaining 13 traits. Leaf nitrogen and the ability to maintain leaf area after the arid period, rather than biomass allocation traits, explained the variation in seedling RGR. Trait responsiveness to the treatments was low and similar among species and between study scales, being unexpectedly low in Q. faginea leaves. This may be because selective pressures on leaf plasticity act differently in deciduous and evergreen species. We conclude that moderate shade and daily summer watering enhance the performance of Mediterranean Quercus seedlings through species-specific mechanisms.

The effect of boron tolerance, deep ripping with gypsum, and water supply on subsoil water extraction of cereals on an alkaline soil

Crop adaptation to edaphic constraints has focussed largely on increasing boron (B) tolerance in cereals, targeted to alkaline soils with high boron content. However, recent studies have implicated several other physicochemical constraints, such as salinity and sodicity, in reduced grain yields of cereals by restricting water extraction in the subsoil. Consequently, the value of B-tolerance may be limited on soils where multiple constraints exist. To test the contribution of B-tolerance where multiple constraints exist, near-isogenic lines of wheat and barley differing in B-tolerance were used, where growth and water extraction by crops in large intact cores, extracted from a Calcarosol profile, were measured. The effect of subsoil disturbance (deep ripping) and growing-season water supply was also investigated. Use of B-tolerant crops did not increase use of subsoil water or grain yield. Wheat and barley extracted soil water down to 0.6 m depth but not below 0.8 m. The soil B concentration of these 2 layers was equivalent (29 ν. 31 mg/kg), whereas salinity [(ECe) 7.2 ν. 8.1 dS/m] and sodicity [(ESP) 22 ν. 29%] both increased significantly with depth, implying that these 2 latter properties had a greater effect than B. Deep ripping with gypsum had no effect on grain yield. Wheat and barley grown under high water supply outyielded their counterparts grown under low water supply, although grain yield per unit of applied water for the crops under low water was 1.5 times that of the crops under high water regime. The results suggest that high salinity and sodicity, rather than B, were exerting the major effects on water extraction of wheat and barley from the deep subsoil, thus negating the effect of crop B-tolerance where multiple constraints exist. This highlights the need to breed cultivars with increased sodium tolerance, pyramided with current B-tolerance, for those crops targeted to many alkaline soils.

Burning, watering, litter quality and time effects on N, P, and K uptake by pitch pine (Pinusrigida) seedlings in a greenhouse study

Young pitch pine seedlings are frequently subjected to prescribed burns in the New Jersey pine barrens as part of the management to eliminate fuel load in these forests, thereby reducing the risk of wildfire. The burns are relatively cool and release nutrients without killing the vegetation. Not all nutrients mineralized are immediately available to the plants, however. To determine factors that may contribute to nutrient release and to link this to availability of nutrients to plants following a fire in the pine barrens, a greenhouse study was conducted. The experimental design was a 3×2×2×3 factorial with three types of litter, high and low watering regime, burned and unburned litter, and three sample dates. Nitrogen, phosphorus, and potassium (through a rubidium analog) uptake rates were measured using natural isotope or radioisotope root bioassays. Though in the short time the experiment ran, neither an overall burned litter nor a litter quality effect was seen, high watering made P less available and K more available. N and K were the most available immediately following application of treatments, whereas P was not available until after 6 weeks following treatment application. Net mineralization of nitrogen, phosphorus, and potassium occurred in burned litter, whereas net immobilization of N and P occurred in highly watered, unburned litter. Since watering and timing were most influential in making nutrients available to seedlings following application of treatments in this greenhouse study, these factors may also be important in making nutrients available to mature trees in the New Jersey pine barrens.

Effect of temperature on below-ground N-dynamics in a weedy model ecosystem at ambient and elevated atmospheric CO 2 levels

Model multispecies terrestrial communities composed of four trophic levels (plants, herbivores, parasitoids, decomposers) were established in the Ecotron controlled environment facility. Two experimental runs enabled us to investigate the effects of enhanced temperature on below-ground microbial processes (N-mineralisation, urease, arginine deaminase, protease activity and potential denitrification) in both ambient and elevated (ambient +200 ppm) CO 2 atmospheres. The enzyme activities involved in nitrogen cycling showed weak responses to elevated temperature in both experimental runs. In the Ambient CO 2 Run, protease and arginine deaminase values tended to be lower in elevated temperature; on the other hand, N-mineralisation, urease and denitrification enzyme activity (DEA) were higher. In the Elevated CO 2 Run, all microbial variables showed higher activities at elevated temperature, although only the results for DEA and arginine deaminase were statistically significant. The interaction between higher temperature and elevated CO 2 weakly affected root growth and tissue C:N ratio, limiting feedbacks into the microbial community. Besides temperature and CO 2, substrate availability, water stress and successional development regulated the response of the soil microbes. The supply of organic carbon and nitrogen in the soil allowed plant growth and maintenance of the microbial population. Nitrogen competition between vegetation and microbes restricted net microbial growth. The increase of dissolved organic carbon (DOC) at higher CO 2 and temperature levels significantly favoured DEA. The high water regime in the soil also favoured DEA and inhibited oxidation of organic compounds, as indicated by low levels of enzyme activity. Additionally, water stress decreased rooting density in the soil; this resulted in negative feedback into microbial processes. We conclude that water stress and soil nitrogen deficiency caused an early levelling-off of both microbial population growth and activity rates during the early part of the model ecosystem's development.

Preference–performance linkage in the neotropical spittlebug Deois flavopicta, and its relation to the Phylogenetic Constraints Hypothesis

Summary1. Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in a tropical system using the pasture pest Deois flavopicta Stal, which oviposits into the ground and not into plant tissues. The prediction that there is no oviposition preference–larval performance linkage was supported. The absence of such a link provides an evolutionary basis for eruptive population dynamics.2. The effects of host species and host plant quality on the preference of ovipositing females of D. flavopicta and performance of their offspring on the selected host plants were tested at the population level.3. Female oviposition behaviour was affected by the presence of the host plant. Females of D. flavopicta showed a strong preference to oviposit close to host plants. The number of eggs was higher in pots containing Brachiaria ruziziensis (121.88 ± 13.70) than in pots containing only the wet oviposition substrate (5.2 ± 1.98) or dry oviposition substrate (0.067 ± 0.067). Ovipositing females did not, however, discriminate between plants of Brachiaria decumbens and Axonopus marginatus and did not show a strong oviposition preference in relation to differences in plant quality (protein and fibre content). They did show oviposition preference for plants under the high watering regime. The mean number of eggs collected from pots with non water‐stressed plants was 60% higher than the mean number of eggs collected on pots with water‐stressed plants.4. Although females did not show ovipositional preference, spittlebug larval performance, measured as percentage survival and duration of nymphal period, was better on plants of high protein and low fibre content. These results indicate that there is not a linkage between female oviposition preference and subsequent nymphal performance in relation to differences in protein and fibre content in the host plants. There was, however, a limited linkage between oviposition preference and nymphal performance in relation to plant water content. Females showed preference for moist sites that have high survival of newly hatched nymphs.5. Evidence indicates that for D. flavopicta, the influences of natality and female oviposition behaviour in response to plant quality are not the major factors driving population outbreaks, which is in accordance with the Phylogenetic Constraints Hypothesis.

Photosynthesis, water and nitrogen use efficiencies of four paper birch ( Betula papyrifera) populations grown under different soil moisture and nutrient regimes

A greenhouse experiment was conducted to determine how four populations of paper birch ( Betula papyrifera Marsh.), adapted to particular temperature, water and photoperiod regimes responded physiologically to different soil water and nutrient regimes. Seedlings of each of the four populations (Eaglet, LeeCreek, Porcupine and Skeena) from British Columbia were planted in pots and subjected to high and low water and nitrogen regimes for 4 months. Net photosynthesis ( A), stomatal conductance ( g s), water use efficiency (WUE) and nitrogen use efficiency (NUE) were measured and compared among treatments. Trade-offs between WUE and NUE were examined. Soil moisture was the major factor affecting A for all the populations. All populations showed relatively high A in the high-water and high-nitrogen (HWHN) treatment, ranging from 8.5 to 9.9 μmol CO 2 m −2 s −1. Photosynthesis of trees in the low-water and high-nitrogen (LWHN) treatment was about 45% of that in the HWHN treatment. There was a linear increase in A as g s increased in all populations. A decreased with increasing vapor pressure deficit (VPD). The populations demonstrated significantly different relationships between A and g s, and VPD, with the LeeCreek population being the most conservative. This may provide a physiological basis for provenance selection and seed transfer. Eaglet and LeeCreek populations had lower WUE at the same level of NUE compared with Porcupine and Skeena populations. Porcupine and Skeena populations may be more suitable for moist sites due to their greater capacity to sequester water quickly, while the LeeCreek and Eaglet populations may be more suitable for drier interior sites where long drought periods can occur.

Branching and percolation in lecithin wormlike micelles studied by dielectric spectroscopy

Lecithin water-in-oil microemulsions have been shown to form long polymerlike micelles. Dielectric spectra of this system are characterized by two dispersions. The high frequency dispersion, related to the head-group rotation of the lecithin molecule, displays a different dependence on water addition in the same two regimes that show up differently in the dynamics measured with several other techniques. The low frequency dispersion is due to a polymeric Rouse/Zimm type mode, which above a certain concentration starts to decrease and shows the characteristics of percolation. In the high water regime the decrease of the relaxation time is accompanied by an increase in conductivity, whereas in the low water regime the conductivity decreases. These data are interpreted in terms of concentration induced percolation and water induced coalescence into a connected network.

Ecophysiology of five Mediterranean perennial grasses: I) Effects of shade, water stress and defoliation on growth and allocation

ABSTRACT Five perennial grasses from different Mediterranean environments (Ampelodesmos mauritanicus (Poiret) Dur et Sch., Brachypodium ramosutn (L.) R. et S., Festuca drymeia M. et K., Brachypodium sylvaticum (Hudson) Beauv., Festuca heterophylla Lam.) were pot cultivated and subjected to shading, water stress and defoliation in a factorial experiment. Growth, root/shoot ratio and reproductive allocation were measured during 7 months. Drought conditions determined a growth reduction in all species, though A. mauritanicus and F. heterophylla showed a relatively higher tolerance. Shade effects were evident under high watering regime, but they were not significant for droughted plants. Highest compensatory growth after defoliation was shown by B. ramosum under full light and by B. sylvaticum under shade. The effects of the experimental treatments are discussed in this paper in relation to the different ecological behaviour of the five grasses.

Observed and Simulated Solute Transport Under Varying Water Regimes: II. 2,6‐Difluorobenzoic Acid and Dicamba

AbstractSignificant interest in the fate of agrichemicals in soils has prompted the development of several transport simulation models. Our primary objective was to evaluate the simulation model LEACHM for predicting the fate of dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) and a nonreactive tracer, 2,6‐difluorobenzoic acid (2,6‐DFBA) in fallow and cropped (barley, Hordeum vulgare L.) systems under different water application levels. A field study (1992) was conducted using in situ soil columns on a Borollic Calciorthid (Brocko silt loam, Gallatin Co., MT). Dicamba (14C‐labeled) and 2,6‐DFBA were surface applied at rates of 0.26 and 112 kg ha−1, respectively. Solute concentrations were measured at three depths (0.36, 0.66, and 0.96 m) using porous cup lysimeters for 70 d following chemical application. Time‐moment analysis of observed solute breakthrough curves (BTCs) generally showed increasing travel times with increasing soil depth and decreasing water application. Dicamba transport was similar to 2,6‐DFBA, with the exception that 40 to 60% of applied dicamba was degraded during transport. The distribution of 14C remaining in the soil columns showed that the primary degradate of dicamba, 3,6‐dichlorosalicylic acid (DCSA), was confined primarily to surface samples (0–0.2 while dicamba was found only at lower depths. This is consistent with a much higher sorption coefficient (Koc) determined for DCSA relative to dicamba. Comparison of observed and predicted (LEACHM) solute BTCs suggested that preferential solute transport occurred especially under high and medium water regimes. Finally, data from three field seasons at the same site suggest that the timing of chemical application relative to initial soil water content and plant stage, the presence of root channels, and temporal changes in soil hydraulic properties in the absence of tillage may significantly affect the degree of preferential flow and subsequent agreement between predicted and observed BTCs.

Effects of organic horizon removal, ash, watering regime, and shading on red pine seedling emergence

Soil monoliths were used to determine the effects of organic horizon removal, ash, water regime, and shading on red pine (Pinusresinosa Ait.) seedling emergence. Soil monoliths were collected from a jack pine (Pinusbanksiana Lamb.) stand and taken to the laboratory for prescribed burning, leading to 25%, 50%, 75%, and 100% organic horizon removal. One half of each monolith contained ash generated from burning, while the other half was kept ash-free. Each half of every monolith was sown with red pine seeds. The monoliths were then placed in a greenhouse and, in separate experiments, were exposed to different water regimes and shade regimes. Red pine seedling emergence was highest under high water regimes, increased shade regimes, and increased organic horizon removal. Seedling emergence was reduced by the presence of ash.

Soil moisture and potassium affect the performance of symbiotic nitrogen fixation in faba bean and common bean

Potassium (K) is reported to improve plant's resistance against environmental stress. A frequently experienced stress for plants in the tropics is water shortage. It is not known if sufficient K supply would help plants to partially overcome the effects of water stress, especially that of symbiotic nitrogen fixation which is often rather low in the tropics when compared to that of temperate regions. Thus, the impact of three levels of fertilizer potassium (0.1, 0.8 and 3.0 mM K) on symbiotic nitrogen fixation was evaluated with two legumes under high (field capacity to 25% depletion) and low (less than 50% of field capacity) water regimes. Plants were grown in single pots in silica sand under controlled conditions with 1.5 mM N (15N enriched NH4NO3). The species were faba bean (Vicia faba L.), a temperate, amide producing legume and common bean (Phaseolus vulgaris L.), a tropical, ureide producing species. In both species, 0.1 mM K was insufficient for nodulation at both moisture regimes, although plant growth was observed. The supply of 0.8 or 3.0 mM K allowed nodulation and subsequent nitrogen fixation which appeared to be adequate for respective plant growth. High potassium supply had a positive effect on nitrogen fixation, on shoot and root growth and on water potential in both water regimes. Where nodulation occurred, variations caused by either K or water supply had no consequences on the percentage of nitrogen derived from the symbiosis. The present data indicate that K can apparently alleviate water shortage to a certain extent. Moreover it is shown that the symbiotic system in both faba bean and common bean is less tolerant to limiting K supply than plants themselves. However, as long as nodulation occurs, N assimilation from the symbiotic source is not selectively affected by K as opposed to N assimilation from fertilizer.

Observed and Simulated Transport of a Conservative Tracer under Line‐Source Irrigation

AbstractAlthough a number of solute transport models are currently available to predict the transport of agrichemicals in the vadose zone, validation of these models under field conditions has been limited. This study monitored the transport of a conservative tracer (Br−) under three water regimes (high, medium, and low) imposed by a line‐source irrigation system and tested the validity of the simulation model, LEACHM, to predict Br− transport. In July 1990, RbBr was surface applied to 12 uncropped columns at 56 kg Br− ha−1. Four columns (0.203‐m diam., 1.2‐m length) were positioned in each water regime and equipped with soil solution samplers at 0.36‐, 0.66‐, and 0.96‐m depths. Soil solution samples were taken 20 times over 80 d to monitor Br− transport. Cumulative water applied to each water regime, by irrigation and precipitation, ranged between 251 and 458 mm. Results indicated dramatic differences in Br− transport among water regimes. Complete Br− breakthrough curves (with apex concentrations of approximately 60 mg Br− L−1) were observed under high water regime at all depths whereas the majority of Br− applied to the low water regime remained at or near the 0.36‐m depth. Inputs used to predict Br− transport in LEACHM simulations were either measured directly or estimated from experimental conditions. To simulate Br− transport for each water regime, we used three LEACHM input files, which reflected the variability of the soil profile water release retention coefficients. Results indicated that LEACHM's predictions of Br− concentration (at all depths and under all water regimes) differed from observed means by an average (n = 180) of 9.0 to 9.4 mg Br− L−1 (approximately 15–16% of the average apex concentrations). These results indicate that under the experimental system studied, LEACHM adequately predicted the transport of a conservative tracer in the vadose zone.

The molecular biology of disease resistance.

Plants have evolved with pathogens and insect pests for millions of years. It is therefore not surprising that a particular plant is resistant to most of them. When certain environmental conditions exist, however, virulent pathogens can cause damage to plant tissues both in the field and in storage. Indeed, modern intensive agriculture has often exacerbated the occurrence of disease outbreaks by presenting the pest with an intense monoculture of genetically identical plants grown in close proximity under high water and fertilizer regimes. Plant pathologists and entomologists are faced with the job of preventing economic losses in these contrived situations. Historically, the most desirable and effective strategy has been the incorporation of disease resistance genes into commercially acceptable cultivars. In the past ten years, the tools of molecular biology have been applied to the study of the mechanisms accounting for disease resistance.

Flooding and the decomposition of litter of four emergent plant species in a prairie wetland

Changes in mass, N, and P for old and new litter of four emergent plant species (Scolochloa festucacea (Willdl.) Link,Phragmites australis (Cav.) Trin ex Steud.,Typha ×glauca Godr., andScirpus lacustris L. spp.glaucus (Sm.) Hartm.) were studied under two water-level regimes in a 10-cell experimental marsh complex in the Delta Marsh, Manitoba, Canada. In the normal regime, water levels were kept at the regulated water level for Lake Manitoba until the fall of 1981, while in the flooded or high-water regime, they were raised 1 m above the regulated level in the fall of 1980. In the spring of 1980, old litter (i.e., litter from the previous growing season) was placed in all ten cells of the complex, and in the fall of 1980, new litter (i.e., litter from the 1980 growing season) was placed in the same 10 cells. Litter ofS. festucacea had the highest mean decomposition rate (k=0.00171), followed byT. ×glauca (0.0131),S.l. glaucus (0.00126), andP. australis (0.00050). Mean decomposition rates were higher in the flooded treatment than in the normal treatment forP. australis andS. festucacea. Within water-level treatments, mass loss depended on initial litter age. The amount of N and P lost or gained by the end of 1981 varied with species, litter age, and water-level treatment.Scolochloa festucacea old and new litter had a lower percent N and P remaining in the flooded than in the normal water-level treatment. The percent N and P remaining in old litter ofP. australis andS.l. glaucus at the end of the study was higher than that in new litter regardless of water-level treatment. ForT. ×glauca, however, new litter had a higher percent of N and P remaining than old litter at the end of the study in both water-level treatments. Litter with lower initial N and P levels accumulated more N and P than did that with higher initial levels.

Drought Avoidance in Sand Dune Populations of Dactylis Glomerata

(1) Seed was collected from populations of Dactylis glomerata growing at three sites on a transect across sand dunes at Druridge Bay, Northumberland. It is known that when grown under water stress the net assimilation rate of seedlings from these sites is inversely related to water retention at the sites. (2) Transpiration rate and relative water content at high and low water regimes, leaf dimensions, stomatal frequencies and the density of cuticular waxes on leaves were determined for the different populations. (3) Compared with the population from the wettest site, one of the two populations from the drier sites had a lower stomatal frequency, and the other had a larger density of leaf cuticular waxes. Both had lower transpiration rates, which were associated with higher relative water contents at the low water regime and with smaller leaf dimensions. (4) It was concluded that these populations exhibited features associated with drought avoidance, and were at least partially adapted to conditions in a sand-dune habitat.

Effect of Water Regime on the Sucrose-Enzyme Relationships of Sugarcane Desiccated with Paraquat

Immature sugarcane was given variable-water regimes in sand culture and subsequently treated with a powerful desiccant, the bipyridylium herbicide Paraquat, applied as a 0.05-percent aqueous foliar spray. There were two objectives: (a) To evaluate the effects of water regime on sucroseenzyme relationships in desiccating sugarcane; and (b) to determine whether controlled water regimes could effectively modify Paraquat activity in sugarcane. Tissue samples were harvested for moisture, sugar and enzyme analyses at 1,3 and 9 days after Paraquat application. Low water supply (1 liter per day) reduced total fresh weights and stalk weights, and increased sucrose content of immature storage tissue. Paraquat significantly lowered total fresh weights, stalk weights, sheath moisture and leaf sucrose by the 9-day harvest. Desiccant action was generally more rapid within the low-water regime. High- and intermediate-water regimes tended to modify Paraquat activity at 1 or 3 days, but its ultimate effects were comparable regardless of water regime. No evidence was found to support the theory that desiccating cane accumulates water as a function of continued water absorption when transpiration has ceased. Acid invertase was suppressed by Paraquat, an effect consistent with earlier findings. The suppression was most severe in the low-water regime. Low-water supply significantly lowered invertase level but the response was not consistent at all harvests. Acid phosphatase and ATP-ase were severely repressed by Paraquat in leaves but not in immature storage tissue. An explanation was offered in terms of distinct chloroplast and mitochondrial enzymes rather than localized Paraquat action. For both enzymes the desiccant repression was significantly more severe in the high-water regime at 1 or 3 days, but water regime showed no effect at 9 days. Paraquat significantly increased ß-amylase in leaves (consistent with earlier studies), particularly within the high-water regime. In immature stem tissue ß-amylase was repressed by high water in Paraquat-free plants. Paraquat eliminated the water effect. Peroxidase was increased in storage tissue by Paraquat. This response was statistically significant only under conditions of low-water supply. It is concluded that variable water regimes can modify the rate of initial Paraquat activity in sugarcane; however, the ultimate effects of Paraquat will not be changed under conditions of thorough chemical application. Under field conditions of marginal chemical penetration, the plant's moisture status might play a more decisive role in determining the desiccant's effectiveness.

Physiology of Sugarcane Under Water Stress: Invertase, ATP-ase and Amylase Behavior in Plants Experiencing Water Deficiency, Night Flooding and Continuous Flooding

Effects of water stress on growth, sugar production and enzymology of sugarcane were evaluated in two greenhouse experiments in which sugarcane of the variety P.R. 980 was grown in sand culture with controlled nutrient supply. At 14 weeks of age, four water regimes were created for each of the two experiments: No water, normal water (2 liters daily), normal water plus night flooding, and continuous flooding. One experiment was pretreated with a 0.01-percent solution of active gibberellic acid (GA) 10 days before water variables were initiated. Samples of leaf, leaf sheath, immature storage tissue and stalk tissue were harvested at 0, 2, 5, and 9 days. Enzyme assays were conducted with leaf and immature storage tissue preparations for acid invertase, adenosine triphosphatase (ATP-ase), and ß-amylase. The following results were obtained: 1. Foliar symptoms appeared between the fifth and ninth day among the low-water and continuous flooding regimes. Wilting of leaves and leaf sheaths, yellowing of leaf tips, extensive yellowing of older leaves and leaf sheaths, and severe curling of spindle tissues was general among both treatments. Symptoms were delayed but not prevented by GA pretreatment. Normal water and night flooding produced no visible effects. Whorls of adventitious roots grew from submerged nodes of continuously flooded plants. 2. Sheath moisture values ultimately declined in water-deficient and water-toxic plants regardless of GA treatment. Continuously flooded plants increased total fresh weight, regardless of leaf and sheath desiccation, when pretreated with GA. A GA role in promoting water uptake is suggested. 3. Leaf sucrose declined in water-deficient and continuously flooded sugarcane but increased in immature storage tissues. This was taken as evidence of continued sucrose transport under moisture conditions restrictive against sugar synthesis. Polarization values for milled juice indicated that GA pretreatment caused a decline of storage sucrose under a normal water regime, but GA prevented storage sucrose losses under a regime of continuous flooding. The former GA effect is interpreted in terms of growth stimulation, the latter in terms of GA involvement in sugar accumulation processes effective in transport of sucrose to storage areas. 4. Invertase was suppressed both by deficient and excessive water regimes and by GA pretreatment. Night flooding produced little effect. 5. ATP-ase was strongly suppressed by night flooding but no consistent effects were produced by the other water regimes. The ATP-ase suppression by excessive night water was interpreted as a perturbation of normal diurnal-nocturnal rhythms rather than a sensitivity of synthesis mechanisms to flooding per se. GA pretreatment suppressed ATP-ase among all water regimes. Assuming that foliar ATP-ase is a functional entity of photosynthetic phosphorylation, the GA effect was taken as further evidence of a GA influence upon sugarcane photosynthesis. 6. Foliar amylase remained at a constant level in water-deficient cane, while other water regimes tended to increase the enzyme. Amylase was less sensitive to water regime than invertase and appeared to be synthesized under flood conditions highly repressive for invertase. It is concluded that low- and high-water regimes tend to produce common effects upon the overall synthesis and utilization of sugar in the cane plant. Hormone level may affect the rate of sugar utilization within high and low water regimes without altering the outward manifestations of these regimes. Hydrolytic enzyme level is apparently affected indirectly by prolonged water stress or by perturbation of endogenous day-night rhythms. However, the enzymes measured were not sufficiently sensitive to changing water supply to serve as indicators of water status.

Digestion and nitrogen metabolism in sheep and red deer given large or small amounts of water and protein.

1. The interaction between nitrogen and water intake was studied in two ewes and two red deer hinds. They were given pelleted diets, at maintenance level, containing equal amounts of roughage but either rich or poor in nitrogen. The deer received 50 % more food than the sheep. Water was given either in large amounts (sheep 5.01, deer 7.0 1 daily) or in small amounts (sheep 1.1 l, deer 2.4 l daily).2. Nearly three-quarters of the nitrogen of the high-nitrogen rations but less than half of that of the low-nitrogen rations was excreted in the urine. Restriction of water intake reduced urinary nitrogen excretion by only about 1 g daily, mainly as a result of decreases in the excretion of urea and ammonia, but did not affect the excretion of nitrogen in the faeces.3. The urinary excretions of creatinine, creatine, hippuric acid, uric acid and allantoin were also examined. The excretion of creatinine was not related to either nitrogen or water intake. The excretion of uric acid and of allantoin was greater in the sheep than in the deer.4. The concentrations of urea in the plasma and of ammonia in the rumen fluid were measured before and after feeding. The plasma urea value was related to dietary nitrogen intake and was higher on the low- than on the high-water regime. The rumen ammonia value also was related to the nitrogen intake but, while it generally increased after feeding when the high-nitrogen diet was given, it fell almost to zero 2 h after feeding when the low-nitrogen diet was given.5. The sheep digested dry matter, cellulose and nitrogen a little more fully than the deer. The high-water regime slightly increased the digestibility of dry matter and cellulose but did not affect the digestibility of nitrogen.