Acidification effects on larval striped bass,Morone saxatilis in Chesapeake Bay tributaries: A review

Reduced striped bass populations along the East Coast of the United States have prompted numerous studies to assess various factors contributing to the decline. Available data from in-situ, on-site and laboratory studies with striped bass in conjunction with water quality and contaminants data confirm that the eastern shore rivers of the Chesapeake Bay (Choptank, Nanticoke, and Pocomoke Rivers) are susceptible to acidic conditions. The Choptank and Nanticoke Rivers are significant striped bass spawning areas. Acidification conditions (low pH, Al, low hardness) were documented in these systems in 1984 at levels reported to cause high mortality to striped bass larvae. Striped bass populations in several western shore tributaries such as the Mattaponi, Pamunkey, Patuxent, and Rappahannock Rivers also appear to be vulnerable to acidic pH conditions. In-situ toxicity studies documenting actual striped bass larval mortality are lacking in these systems; however, based on laboratory data it appears that potentially toxic acidic conditions can exist. Although certain Chesapeake Bay spawning tributaries do exhibit acidic conditions during spawning periods, other systems are resistant to acidification. The Chesapeake and Delaware Canal (C & D Canal), Elk River and Susquehanna River of the Upper Chesapeake Bay and the Potomac River on the western shore appear to be resistant to reductions in pH. The upper Chesapeake Bay and Potomac River are major striped bass spawning areas. Therefore, reduced striped bass production in these systems may be related to factors other than acidification.     

TREATED EFFLUENT AND SALINE WATER IRRIGATION INFLUENCES SOIL PROPERTIES,YIELD, WATER PRODUCTIVITY AND SODIUM CONTENT OF SNOW PEAS AND CELERY

To determine the effects of irrigation water quality, plants were irrigated with normal potable water [0.25 dS m^?1 electrical conductivity (EC), 25 mg L^?1 sodium (Na), 55 mg L^?1 chloride (Cl)], treated effluent (0.94 dS m^?1 EC, 122 mg L^?1 Na, 143 mg L^?1 Cl) and saline water with low salinity (1.24 dS m^?1 EC, 144 mg L^?1 Na and 358 mg L^?1 Cl) and high salinity (2.19 dS m^?1 EC, 264 mg L ^?1Na and 662 mg L^?1 Cl) for snow peas, and high salinity (3.07 dS m^?1 EC, 383 mg L^?1 Na and 965 mg L^?1 Cl) and very high salinity (5.83 dS m^?1 EC, 741 mg L^?1 Na and 1876 mg L^?1 Cl) for celery. The greater salts build up in the soil and ion toxicity (Cl and Na) with saline water irrigation contributed to significantly greater reduction in root and shoot biomass, water use, yield and water productivity (yield kg kL^?1 of water used) of snow peas and celery compared with treated effluent and potable water irrigation. There was 8%, 56% and 74% reduction in celery yield respectively with treated effluent, high salinity and very high salinity saline water irrigation compared with potable water irrigation. The Na concentration in snow peas shoots increased by 54%, 234% and 501% with treated effluent, low and high salinity saline water irrigation. Similarly, the increases in Na concentration in celery shoots were 19%, 35% and 82%. The treated effluent irrigation also resulted in a significant increase in soil EC, nitrogen (N) and phosphorus (P) content compared with potable water irrigation. The heavy metals besides salts build up appears to have contributed to yield reductions with treated effluent irrigation. The study reveals strong implications for the use of saline water and treated effluent for irrigation of snow peas and celery. The salt build up within the root zone and soil environment would be critical in the long-run with the use of saline water and treated effluent for irrigation of crops. To minimize the salinity level in rhizosphere, an alternate irrigation of potable water with treated effluent or low salinity level water may be better option.     

Influence of pH on the toxicity of aluminium and other inorganic contaminants to East Coast striped bass

The toxicity of Al and a mixture of inorganic contaminants to young striped bass Morone saxatilis in soft fresh water was demonstrated to be age- and pH-dependent. Toxicity of the contaminants was increased with decreases of pH of the test waters. The interaction between low pH from acid deposition and inorganic contaminants should be considered as a possible factor contributing to the decline in abundance of east coast striped bass.     

Acute and sub-chronic toxicity of lead to the early life stages of smallmouth bass (Micropterus Dolomieui)

The early life stages of smallmouth bass (Micropterus dolomieui) were exposed to Pb in acute (96 hr) and sub-chronic (90 day) bioassays (water hardness = 152 mg L^?1 as CaCO₃). After 96-hr static exposures at nominal Pb concentrations up to 15.9 mg L^?1, eggs and sac fry showed no increased mortality over that in controls. Swim-up fry (96-hr LC₅₀ = 2.8 mg Pb L^?1) were more sensitive to Pb exposure than were fingerlings (96-hr LC₅₀ of 29.0 mg Pb L^?1 ). The relation between dissolved Pb and mortality was non-significant for either swim-up fry or fingerlings. Fingerlings were exposed to Pb concentrations as high as 405 μg L^?1 for 90 day to evaluate effects on substrate selection, locomotor activity, hematology, and weight. Dark or light substrate selection (cover-seeking) and locomotor activity, weight and hemoglobin concentration in the blood were not significantly altered by any treatment. Hematocrit and leucocrit varied significantly but not in relation to Pb levels. Sub-chronic Pb exposure did not appear to represent a threat to smallmouth bass in waters of medium hardness and above-neutral pH (7.1 to 7.9).     

Growth and nutrient uptake of tomato in response to application of saline water,biological fertilizer,and surfactant

The importance of using low-quality water, such as saline waters, for food production has been increased in the recent decades. An experiment was conducted to evaluate the effect of diluted seawater (electrical conductivity (EC) of 6 dS m^?1) on growth and nutrient uptake of tomato. We examined if surfactant (0, 1, 2, 4 mg L^?1) and biological fertilizer (compost tea + arbuscular mycorrhizal fungi propagules) have potential to alleviate the adverse effects of salinity on tomato plant. Salinity stress significantly reduced all plant growth parameters. Under salinity stress, nitrogen (N) and potassium (K) contents in tomato shoot were lower, while phosphorus (P), sodium (Na), and calcium (Ca) contents were higher than non-salinized plants; showing ionic imbalance in this condition. Biological fertilizer improved root weight in saline condition. Under salinity stress surfactant application at the rate of 1 mg L^?1 helped tomato plants to maintain their ionic balance, especially declining Na uptake, and improved plant growth.     

Growth Response and Selenium and Boron Distribution in Broccoli Varieties Irrigated with Poor Quality Water

Abstract

Selenium (Se), and boron (B), and salinity contamination of agricultural drainage water is potentially hazardous for water reuse strategies in central California. This greenhouse study assessed tolerance and Se, B, and chloride (Cl^?) accumulation in different varieties (Emerald City, Samurai, Greenbelt, Marathon) of broccoli (Brassica oleracea L.) irrigated with water of the following different qualities: (1) non‐saline [electrical conductivity (EC) of <1 dS m^?1]; (2) Cl^?/sulfate salinity of ～5 dS m^?1, 250 µg Se L^?1, and 5 mg B L^?1; and (3) non‐saline and 250 µg Se L^?1. One hundred and ten days after transplanting, plants were harvested and dry weight (DW) yields and plant accumulation of Se, B, and Cl^? was evaluated in floret, leaf, and stem. Irrespective of treatments floret yields from var. Samurai were the lowest among all varieties, while floret yields from var. Marathon was the only variety to exhibit some sensitivity to treatments. For all varieties, plant Se concentrations were greatest in the floret (up to 51 mg kg^?1 DW) irrespective of treatment, and B and Cl^? concentrations were greatest in the leaves; 110 mg B kg^?1 DW and 5.4% Cl^?, respectively. At post harvest, treatment 2 (with salinity, B, and Se) increased soil salinity to almost 6 dS m^?1, total Se concentrations to a high of 0.64 mg kg^?1 DW soil, and water soluble B concentrations to a high of 2.3 mg B L^?1; soluble Se concentrations were insignificant. The results indicate that var. Emerald City, Greenbelt, and Marathon should be considered as recipients of moderately saline effluent enriched with Se and B under field conditions.     

Chronic toxicity of tributyltin to Chesapeake bay biota

Chronic tributyltin toxicity experiments were conducted with the following Chesapeake Bay organisms: amphipod, Gammarus sp.; juvenile Atlantic menhaden, Brevoortia tyrannus and larval inland silverside, Menidia beryllina. TBT concentrations ranging from 29 to 579 ng L^?1 did not significantly affect survival of the benthic amphipod, Gammarus sp. after 24-d exposures. The weight of Gammarus exposed to control conditions was 2.8 times greater than the weight of these test organisms exposed to 579 ng L^?1 TBT. Twenty-eight day exposures to TBT concentrations of 93 and 490 ng L^?1 did not significantly affect survival of juvenile B. tyrannus or larval M. beryllina. Histological examinations of B. tyrannus did not demonstrate absolute effects resulting from TBT exposure due to extensive variation between individuals. Various morphometric measurements of M. beryllina after TBT exposure did not demonstrate significant effects. However, significant reductions in growth were reported for M. beryllina at both TBT concentrations. Environmental concentrations of TBT in Chesapeake Bay and possible effects on the above biota are discussed.     

咸水冻融灌溉对重度盐渍土壤水盐分布的影响

室内咸水冰融化试验设置2个处理:7.5 g L-1咸水冰(SIW(7.5))、15 g L-1咸水冰(SIW(15)),探究了咸水冰融化过程中的水量、水质以及离子组成的变化;土柱模拟试验设置同一灌水量(150mm),4个处理:淡水直接灌溉(FW)、7.5 g L-1咸水直接灌溉(SW)、7.5 g L-1咸水冻融灌溉(SIW(7.5))、15 g L-1咸水冻融灌溉(SIW(15)),对比分析两种灌溉水质(淡水、咸水)和两种灌水方式(直接灌溉、结冰灌溉)对土壤(粉砂壤土)水盐动态的影响。结果表明:咸水冰融化过程中,初期融出水量较大,但含盐量和钠吸附比(SAR)较高,后期融出水量较小,含盐量和SAR很低;融出水的离子含量变化与电导率(EC)变化表现相同的趋势;小于3 g L-1的水的融出率分别是SIW(7.5)=25.46%和SIW(15)=32.78%。FW处理下,土壤中水盐运动持续时间较其他3个处理长,土壤导水率降低最快,灌溉水入渗完成时表层土壤含水量达到33.88%,显著高于其他处理。四种处理下,0~15 cm土层土壤的含盐量平均值分别为FW=2.32 g kg-1、SIW(7.5)=2.80 g kg-1、SIW(15)=3.87 g kg-1、SW=4.31 g kg-1。同等灌水量下,SIW(15)处理下土壤脱盐深度最浅。离子分析表明:FW和SIW(7.5)处理下,0~25 cm土壤的钠吸附比(SAR)下降明显,显著小于SW、SIW(15);然而FW处理下,土壤碱化特征最为明显。综合而言,在淡水资源缺乏而咸水资源相对丰富的地区,中度矿化度咸水结冰融水灌溉可以有效降低根层土壤盐分,满足农业生产的要求。     

SOYBEAN RESPONSE AND ION ACCUMULATION UNDER SPRINKLER IRRIGATION WITH SODIUM-RICH SALINE WATER

The magnitude of crop growth and yield depends on the salinity level, the toxic ions present, and the irrigation system used. In order to study the effect of saline sprinkler irrigation on soybean growth and ionic accumulation in plant tissues a pot experiment was set up. There were three irrigation water quality treatments [electrical conductivity (EC) 0, 2, and 4 dS m^?1]. Soybean aerial biomass was 25% lower than the Control when irrigation salinity was 4 dS m^?1. Clearly salinity entering via leaves affected the grain filling stage and severely reduced soybean grain production (80% reduction) when salinity in irrigation water surpassed 2 dS m^?1. Sprinkler irrigation aggravates soybean's low salinity tolerance and restricts its cropping in such conditions. For early stages two linear relationships between leaf chloride (Cl^?) concentration (Y = 14.2–2x) or potassium (K⁺)/ sodium (Na⁺) ratio (Y = 5.3x?3.4) and soybean grain yield were found. Both relationships may be used as diagnostic tools for soybean growing under saline sprinkler irrigation.     

Occurrence of Emerging Contaminants in Brazilian Drinking Waters: A Sewage-To-Tap Issue

The goal of this work was to investigate the occurrence of emerging contaminants in drinking water of the city of Campinas, Brazil. Tap water samples were analyzed using SPE-GC-MS for 11 contaminants of recent environmental concern. Six emerging contaminants (stigmasterol, cholesterol, bisphenol A, caffeine, estrone, and 17β-estradiol) were found in the samples. The latter two were detected only during the dry season, with concentrations below quantification limits. Stigmasterol showed the highest average concentration (0.34?±?0.13?µg L^?1), followed by cholesterol (0.27?±?0.07?µg L^?1), caffeine (0.22?±?0.06?µg L^?1), and bisphenol A (0.16?±?0.03?µg L^?1). In Campinas, where surface drinking water supplies receive large amounts of raw sewage inputs, the emerging contaminants levels in drinking waters were higher than median values compiled for drinking and finished water samples around the world.     

Volume regulation and accumulation of copper in whole and decapitated Hediste (Nereis) diversicolor under varying salinity — Copper regimes

Volume regulation (weight change) correlates with varying salinity — Cu regimes in whole worms. Decapitation removed this correlation. Regulation of volume and Cu ion uptake are not coupled. Whole worms when exposed to Cu levels of 0.15 to 0.45 mg L^?1 accumulated Cu which ranged from 48.9 to 145 μg g^?1 dry weight within four days. Decapitated worms exposed to similar doses of Cu accumulated from 77.3 to 405.4 μg g^?1 dry weight Cu within three days. Volume regulation appears to be both passive and active processes mediated by the nervous system.     

Dynamics of Soil Moisture and Salt Content After Infiltration of Saline Ice Meltwater in Saline-Sodic Soil Columns

Saline ice meltwater can be used for irrigation and leaching of salts in salt-affected soil regions.A laboratory experiment was conducted using soil columns to investigate the redistribution of soil moisture, salt and sodium adsorption ratio(SAR) in saline-sodic soil under the infiltration of saline ice meltwater.Soils were treated using saline water of three irrigation volumes(1 600, 2 400 and 3 200 mL) at four salinity levels.These four salinity levels included salt free(0 g L~(-1)), low salinity level(1.4 g L~(-1)), moderate salinity level(2.7 g L~(-1)) and high salinity level(4.1 g L~(-1)).The prepared saline water was frozen into ice, and then the ice was put on the surface of soil columns.After 96 h, the infiltration rate and soil moisture content of saline ice treatments were greater than those of salt-free ice treatments, increasing with the increase of ice salinity.Infiltration of saline ice meltwater increased soil moisture content in the upper layers for all treatments.Both salt contents and SAR values in the upper soil layers decreased in all saline ice treatments and were lower than those in salt-free ice treatment.However, this trend was reversed in the deeper(below 20 cm) soil layers.The highest desalting rate and lowest SAR were observed in high-salinity treatment under three irrigation volumes in the 0–15 cm soil layer,especially under irrigation volume of 2 400 mL.These results indicate that saline ice(0–20 cm) meltwater irrigation is beneficial to saline-sodic soil reclamation, and the best improvement effect would be achieved when using high-salinity ice under optimal irrigation volume.     

IDENTIFICATION OF GROUNDNUT (ARACHIS HYPOGAEA L.) CULTIVARS TOLERANT OF SOIL SALINITY

Field screening of 83 groundnut cultivars was undertaken for two seasons to assess their tolerance of salinity based on plant mortality and yield attributes. During the dry season, soil salinity of 4 dS m^?1 at sowing and 6–7 dS m^?1 21–98 days after sowing (DAS) caused high mortality without seed formation in any cultivars, however, at salinity 4.5 dS m^?1 during sowing and 3.5–3.0 dS m^?1 15–80 DAS during wet season, 61 cultivars produced seed. The cultivars ‘VRI 3’, ‘UF 70–103’, ‘TKG 19A’, ‘S 206’, ‘Tirupati 4’, ‘M 522’, ‘Punjab 1’, ‘BG 3’, ‘Somnath’ and ‘ICGV 86590’, with high plant stand during both the seasons and over 75 g m^?2 seed yield during wet season, were identified salinity tolerant. However, 15 cultivars with more than 50 g m^?2 seed yield were moderately tolerant and 28 cultivars with less than 25 g m^?2 seed yield were sensitive to salinity.     

咸水灌溉对麦—玉两熟制农田土壤水稳性团聚体的影响

为探明咸水灌溉对麦—玉两熟轮作农田土壤团聚体的影响效应,在长期定位咸水灌溉试验(始于2006年)的基础上,研究了不同矿化度咸水连续灌溉第13~14年农田土壤盐分(EC e)及水稳性团聚体分布和稳定性指标的变化规律。试验设置5个灌溉水矿化度处理,分别为1,2,4,6,8 g/L。结果表明,0—40 cm土层土壤EC e随灌溉水矿化度增加而增大,4,6,8 g/L灌水处理与1 g/L处理间差异达显著水平。咸水灌溉改变土壤水稳性团聚体的粒级分布,灌溉水矿化度≤4 g/L时,0—40 cm土壤水稳性团聚体以大团聚体(>0.25 mm)为优势粒级,随灌溉水矿化度增加,大团聚体质量分数降低,微团聚体(0.053~0.25 mm)和粉+黏团聚体(<0.053 mm)质量分数增大,当灌溉水矿化度达到6 g/L时,粉+黏团聚体占比最大。咸水灌溉降低土壤水稳性团聚体的稳定性,随灌溉水矿化度的增加,土壤团聚体平均重量直径和几何平均直径减小,分形维数增大,但2 g/L与1 g/L灌水处理间无显著差异。在该研究灌溉制度下,≥4 g/L咸水灌溉显著增加土壤盐分,破坏土壤团粒结构,应谨慎使用。     

Effect of Magnesium Chloride–Induced Salinity on Carbon Dioxide Evolution and Nitrogen Mineralization in a Silty Clay Loam Soil

A laboratory incubation experiment was conducted to evaluate the effect of magnesium chloride–induced salinity on carbon dioxide (CO₂) evolution and nitrogen (N) mineralization in a silty loam nonsaline alkaline soil. Magnesium chloride (MgCl₂) salinity was induced at 0, 4, 8, 12, 16, 20, 30, and 40.0 dS m^?1 and measured CO₂ evolution and N mineralization during 30 days of incubation. Both CO₂ evolution and N mineralization decreased significantly with increasing salinity. The cumulative CO₂ evolution decreased from 235 mg kg^?1 soil at electrical conductivity (EC) 0.65 dS m^?1 to 11.9 mg kg^?1 soil at 40 dS m^?1 during 30 days of incubation. Similarly, N mineralization decreased from 185.4 mg kg^?1 at EC 0.65 dS m^?1 to 34.45 mg kg^?1 at EC 40.0 dS m^?1 during the same period. These results suggested that increasing magnesium chloride salinity from 4 dS m^?1 adversely affect microbial activity in terms of carbon dioxide evolution and N mineralization.     

Hydrogeochemical variation of carbonate aquifer,Al-Sulaibiya,Kuwait

A study of the hydrochemical facies, zonation, genesis and the trend in ground water quality of Al-Sulaibiya field was conducted. The study area is located 120 km south of Kuwait Bay. It comprises the oldest and largest water well field which produces brackish ground water from the Dammam limestone aquifer. > 1000 ground watger samples in the period 1980–1990 were analysed. The study revealed the dominance of two major water types and two genetic water types of continental and marine origin: NaCl and CaSO₄ and SO₄-Na and Cl-Mg respectively. It also revealed that the water is mainly of chloride-sulphate and calcium-sodium facies. The aquifer salinity which increases in the NE direction, ranges from 3500 to 8000 mg L^?1. The water is very hard. The total hardness as CaCO₃ ranges between 1500–3500 mg L^?1. Thus, the only new finding was that the salinity and the total hardness of the aquifer have increased slightly and steadily over the period under investigation.     

Physiological response of brown trout (Salmo trutta) spawners and postspawners to acidic alminum-rich stream water

High immediate postspawning mortality due to inferior autumn water quality has been hypothesized to cause juvenilization in some brown trout populations in acidified areas. We exposed male and female spawners and female postspawners from a juvenile-dominated brown trout population to acidic streamwater (pH = 4.83, Al_i = 240 μg L^?1) and a limed control (pH = 5.70, Al_i = 55 μg L^?1) for 28 days in November and December, 1984. Water chemistry was monitored at least bi-daily, and physiological stress was assessed by analysis of plasma chloride, osmolality and haematocrit. Neither pronounced physiological stress nor mortality was observed at the control site. At the exposure site trout showed significant but moderate stress responses and 15 % died. The results are discussed in terms of potential population effects and physiological mechanisms, e.g., plasma volume reduction.     

Gas exchange,water relations,and Ion concentrations of salt‐stressed tomato and melon plants

Abstract

Tomato and melon plants were grown in a greenhouse and irrigated with nutrient solution having an EC of 2 dS m^?1 (control treatment) and 4, 6, and 8 dS m^?1, produced by adding NaCl to the control nutrient solution. After 84 days, leaf water relations, gas exchange parameters, and ion concentrations, as well as plant growth, were measured. Melon plants showed a greater reduction in shoot weight and leaf area than tomato at the two highest salinity levels used (6 and 8 dS m^?1). Net photosynthesis (Pn) in melon plants tended to be lower than in tomato, for all saline treatments tested. Pn was reduced by 32% in melon plants grown in nutrient solution having an EC of 4 dS m^?1, relative to control plants, and no further decline occurred at higher EC levels. In tomato plants, the Pn decline occurred at EC of 6 dS m^?1, and no further reduction was detected at EC of 8 dS m^?1. The significant reductions in Pn corresponded to similar leaf Cl^? concentrations (around 409 mmol kg^?1 dry weight) in both plant species. Net Pn and stomatal conductance were linearly correlated in both tomato and melon plants, Pn being more sensitive to changes in stomatal conductance (g_s) in melon than in tomato leaves. The decline in the growth parameters caused by salinity in melon and tomato plants was influenced by other factors in addition to reduction in Pn rates. Melon leaves accumulated larger amounts of Cl^? than tomato, which caused a greater reduction in growth and a reduction in Pn at lower salinity levels than in tomato plants. These facts indicate that tomato is more salt‐tolerant than melon.     

GROWTH,YIELD, AND ION RELATIONS OF STRAWBERRY IN RESPONSE TO IRRIGATION WITH CHLORIDE-DOMINATED WATERS

Strawberry is listed as the most salt sensitive fruit crop in comprehensive salt tolerance data bases. Recently, concerns have arisen regarding declining quality of irrigation waters available to coastal strawberry growers in southern and central California. Over time, the waters have become more saline, with increasing sodium (Na⁺) and chloride (Cl^?). Due to the apparent extreme Cl^? sensitivity of strawberry, the rising Cl^? levels in the irrigation waters are of particular importance. In order to establish the specific ion causing yield reduction in strawberry, cultivars ‘Ventana’ and ‘Camarosa’ were grown in twenty-four outdoor sand tanks at the ARS-USDA U. S. Salinity Laboratory in Riverside, CA and irrigated with waters containing a complete nutrient solution plus Cl^? salts of calcium (Ca²⁺), magnesium (Mg²⁺), Na⁺, and potassium (K⁺). Six salinity treatments were imposed with electric conductivities (EC) = 0.835, 1.05, 1.28, 1.48, 1.71, and 2.24 dS m^?1, and were replicated four times. Fresh and dry weights of ‘Camarosa’ shoots and roots were significantly higher than those of ‘Ventana’ at all salinity levels. Marketable yield of ‘Camarosa’ fruit decreased from 770 to 360 g/plant as salinity increased and was lower at all salinity levels than the yield from the less vigorous ‘Ventana’ plants. ‘Ventana’ berry yield decreased from 925 to 705 g/plant as salinity increased from 0.835 to 2.24 dS m^?1. Relative yield of ‘Camarosa’ decreased 43% for each unit increase in salinity once irrigation water salinity exceeded 0.80 dS m^?1. Relative ‘Ventana’ yield was unaffected by irrigation water salinity up to 1.71 dS m^?1, and thereafter, for each additional unit increase in salinity, yield was reduced 61%. Both cultivars appeared to possess an exclusion mechanism whereby Na⁺ was sequestered in the roots, and Na⁺ transport to blade, petiole and fruit tissues was limited. Chloride content of the plant organs increased as salinity increased to 2.24 dS m^?1 and substrate Cl increased from 0.1 to13 mmol_cL^?1. Chloride was highest in the roots, followed by the leaves, petioles and fruit. Based on plant ion relations and relative fruit yield, we determined that, over the range of salinity levels studied, specific ion toxicity exists with respect to Cl^?, rather than to Na⁺ ions, and, further, that the salt tolerance threshold is lower for ‘Camarosa’ than for ‘Ventana’.     

The extent of drying influences the flush of respiration after rewetting in non-saline and saline soils

Drying and rewetting are common events in soils during summer, particularly in Mediterranean climate where soil microbes may be further challenged by salinity. Previous studies in non-saline soils have shown that rewetting induces a flush of soil respiration, but little is known about how the extent of drying affects the size of the respiration flush or how drying and rewetting affects soil respiration in saline soils. Five sandy loam soils, ranging in electrical conductivity of the saturated soil extract (ECe) from 2 to 48 dS m⁻¹ (EC2, EC9, EC19, EC33 and EC48), were kept at soil water content optimal for respiration or dried for 1, 2, 3, 4 or 5 days (referred to 1D, 2D, 3D, 4D and 5D) and maintained at the achieved water content for 4 days. Then the soils were rewet to optimal water content and incubated moist for 5 days. Water potential decreased with increasing drying time; in the 5D treatment, the water potential ranged between −15 and −30 MPa, with the lowest potentials in soil EC33. In moist and dry conditions, respiration rates per unit soil organic C (SOC) were highest in soil EC19. Respiration rates decreased with increasing time of drying; when expressed relative to constantly moist soil, the decline was similar in all soils. Rewetting of soils only induced a flush of respiration compared to constantly moist soil when the soils were dried for 3 or more days. The flush in respiration was greatest in 5D and smallest in 3D, and greater in EC2 than in the saline soils. Cumulative respiration per unit SOC was highest in soil EC19 and lowest in soil EC2 Cumulative respiration decreased with increasing time of drying, but in a given soil, the relationship between water potential during the dry phase and cumulative respiration at the end of the experiment was weaker than that between respiration rate during drying and water potential. In conclusion, rewetting induced a flush in respiration only if the water potential of the soils was previously decreased at least 3-fold compared to the constantly moist soil. Hence, only marked increases in water potential induce a flush in respiration upon rewetting. The smaller flush in respiration upon rewetting of saline soils suggests that these soils may be less prone to lose C when exposed to drying and rewetting compared to non-saline soils.