The biogeochemistry of sulfur at Hubbard Brook

A synthesis of the biogeochemistry of S was done during 34 yr(1964–1965 to 1997–1998) in reference and human-manipulated forestecosystems of the Hubbard Brook Experimental Forest (HBEF), NH. There have beensignificant declines in concentration (–0.44µmol/liter-yr) and input (–5.44mol/ha-yr)of SO₄ ^2– in atmospheric bulk wet deposition, and inconcentration(–0.64 µmol/liter-yr) an d output (–3.74mol/ha-yr) of SO₄ ^2– in stream water ofthe HBEF since 1964. These changes arestrongly correlated with concurrent decreases in emissions of SO₂from the source area for the HBEF. The concentration and input ofSO₄ ^2– in bulk deposition ranged from a low of 13.1µmol/liter (1983–1984) and 211 mol/ha-yr(1997–1998) to a high of 34.7 µmol/liter(1965–1966) and 479 mol/ha-yr (1967–1968), with along-term mean of 23.9 µmol/liter and 336mol/ha-yr during 1964–1965 to 1997–1998. Despiterecentdeclines in concentrations, SO₄ ^2– is the dominantanion in both bulk deposition and streamwater at HBEF. Dry deposition is difficult to measure, especially inmountainousterrain, but was estimated at 21% of bulk deposition. Thus, average totalatmospheric deposition was 491 and 323 mol/ha-yr during1964–1969 and 1993–1998, respectively. Based on the long-term³⁴S pattern associated with anthropogenic emissions,SO₄ ^2– deposition at HBEF is influenced by numerousSO₂sources, but biogenic sources appear to be small. Annual throughfall plusstemflow in 1993–1994 was estimated at 346 molSO₄ ^2–/ha. Aboveground litterfall, for thewatershed-ecosystemaveraged about 180 mol S/ha-yr, with highest inputs (190 molS/ha-yr) in the lower elevation, more deciduous forest zone. Weatheringrelease was calculated at a maximum of 50 mol S/ha-yr. Theconcentration and output of SO₄ ^2– in stream waterranged from a low of 42.3µmol/liter (1996–1997) and 309 mol/ha-yr(1964–1965), to a high of 66.1 µmol/liter(1970–1971) and 849 mol/ha-yr (1973–1974), with along-term mean of 55.5 µmol/liter and 496mol/ha-yr during the 34 yrs of study. Gross outputs ofSO₄ ^2– in stream water consistently exceeded inputsin bulkdeposition and were positively and significantly related to annualprecipitationand streamflow. The relation between gross SO₄ ^2–output and annual streamflow changed with time asatmospheric inputs declined. In contrast to the pattern for bulk depositionconcentration, there was no seasonal pattern for streamSO₄ ^2– concentration. Nevertheless, stream outputs ofSO₄ ^2– were highly seasonal, peaking during springsnowmelt, andproducing a monthly cross-over pattern where net hydrologic flux (NHF) ispositive during summer and negative during the remainder of the year. Nosignificant elevational pattern in streamwaterSO₄ ^2– concentration was observed. Mean annual,volume-weightedsoil water SO₄ ^2– concentrations were relativelyuniform by soil horizon andacross landscape position. Based upon isotopic evidence, much of theSO₄ ^2– entering HBEF in atmospheric depositioncycles throughvegetation and microbial biomass before being released to the soil solution andstream water. Gaseous emissions of S from watershed-ecosystems at HBEF areunquantified, but estimated to be very small. Organic S (carbon bonded andestersulfates) represents some 89% of the total S in soil at HBEF. Some 6% exists asphosphate extractable SO₄ ^2– (PSO₄).About 73% of the total S in the soilprofile at HBEF occurs in the Bs2 horizon, and some 9% occurs in the forestfloor. The residence time for S in the soil was calculated to be 9 yr, butonly a small portion of the total organic soil pool turns over relativelyquickly. The S content of above- and belowground biomass is about 2885mol/ha, of which some 3–5% is in standing dead trees. Yellowbirch, American beech and sugar maple accounted for 89% of the S in trees, with31% in branches, 27% in roots and 25% in the lightwood of boles. The pool of Sin living biomass increased from 1965 to 1982 due to biomass accretion, andremained relatively constant thereafter. Of current inputs to the availablenutrient compartment of the forest ecosystem, 50% is from atmospheric bulkdeposition, 24% from net soil release, 11% from dry deposition, 11% from rootexudates and 4% is from canopy leaching. Comparing ecosystem processes for Sfrom 1964–1969 to 1993–1998, atmospheric bulk deposition decreasedby 34%, stream output decreased by 10%, net annual biomass storage decreased by92%, and net soil release increased by 184% compared to the 1964–1969values. These changes are correlated with decreased emissions of SO₂from the source area for the HBEF. Average, annual bulk deposition inputsexceeded streamwater outputs by 160.0 ± 75.3 SD molS/ha-yr,but average annual net ecosystem fluxes (NEF) were much smaller, mostlynegativeand highly variable during the 34 yr period (–54.3 ± 72.9 SDmol S/ha-yr; NEF range, +86.8 to –229.5). While severalmechanisms may explain this small discrepancy, the most likely are netdesorption of S and net mineralization of organic S largely associated with theforest floor. Our best estimates indicate that additional S from dry depositionand weathering release is probably small and that desorption accounts for about37% of the NEF imbalance and net mineralization probably accounts for theremainder (60%). Additional inputs from dry deposition would result fromunmeasured inputs of gaseous and particulate deposition directly to the forestfloor. The source of any unmeasured S input has important implications for therecovery of soils and streams in response to decreases in inputs of acidicdeposition. Sulfate is a dominant contributor to acid deposition at HBEF,seriously degrading aquatic and terrestrial ecosystems. Because of the strongrelation between SO₂ emissions and concentrations ofSO₄ ^2– in both atmospheric deposition and streamwater at HBEF,further reductions in SO₂ emissions will be required to allowsignificant ecosystem recovery from the effects of acidic deposition. Thedestruction or removal of vegetation on experimental watershed-ecosystems atHBEF resulted in increased rates of organic matter decomposition andnitrification, a lowering of soil and streamwater pH, enhancedSO₄ ^2– adsorption on mineral soil and smallerconcentrations andlosses of SO₄ ^2– in stream water. With vegetationregrowth, this adsorbedSO₄ ^2– is released from the soil, increasingconcentrations andfluxes of SO₄ ^2– in drainage water. Streamwaterconcentration ofSO₄ ^2– and gross annual output ofSO₄ ^2–/ha are essentially the same throughout theHubbard BrookValley in watersheds varying in size by about 4 orders of magnitude, from 3 to3000 ha.     

Long- and short-term changes in sulfate deposition: Effects of the 1990 Clean Air Act Amendments

Annual, volume-weighted concentrations ofSO₄ ^2– in bulk precipitation have declinedsteadily (–0.44 mol/liter-yr) since 1965 atthe Hubbard Brook Experimental Forest (HBEF), NH inresponse to decreases in regional SO₂ emissions(r ² = 0.74). Similar declines in concentrationshave occurred in wet-only precipitation at HBEF and atnearby sites since 1978. However, decreases inSO₄ ^2– concentrations following passage ofthe U.S. Clean Air Act Amendments in 1990, were notunusual from the perspective of long-term data fromthe HBEF. Statistically significant declines (–5.6mol/ha-yr) in bulk deposition of SO₄ ^2– also have occurred since 1965 in relation to decreases inSO₂ emissions (r ² = 0.58), but annualvariations in deposition also are strongly related toamount of precipitation and other factors.     

Biomass,production and nutrient distribution of a natural oak forest in central Korea

Biomass, production, and nutrient distribution of a pure Quercus variabilis Bl. stand (stand 1) and two mixed Q. variabilis–Q. mongolica Fisch. stands (stand 2 and 3) were investigated in central Korea. Stand 1 naturally occurred on a site with a southern aspect while stand 2 and stand 3 occurred on sites with a northern aspect. Total (overstory+understory vegetation) biomass (tha^-1) and annual production (tha^–1year^–1) were 137.8 and 11.1 for stand 1, 216.2 and 16.6 for stand 2, and 253.3 and 19.7 for stand 3. Nutrient contents (kgha^–1) in the vegetation were distributed as follows: K, 478–860; N, 471–839; Ca, 428–791; Mg, 72–125; Na, 77–141; and P, 37–71, and were greatest in stand 3 followed by stand 2, and stand 1. Stand density influenced the differences in biomass, annual production and nutrient contents in the vegetation. Forest floor dry mass and N content (kgha^–1) were 13400 and 169 for stand 1, 10400 and 133 for stand 2, and 11200 and 127 for stand 3. Total amounts of N, P and Na in the ecosystem were greatest in the upper 40cm of mineral soil followed by the vegetation and forest floor. However, the vegetation contained a greater amount of K than the mineral soil. It appeared that microenvironments, such as, aspect influenced the distribution of natural oak species within a relatively small area and resulted in differences in biomass, production and nutrient distribution among the stands.     

Peat and solution chemistry responses to CaCO3 application in wetlands next to Woods Lake,New York

We studied the effect of a calcite (CaCO₃) treatment on peat and pore water chemistry in poor fen and conifer swamp wetlands next to Woods Lake and its tributaries to evaluate the role of wetlands in an Experimental Watershed Liming Study (EWLS). Peat was characteristically organic rich and nutrient poor, with exchangeable Ca concentrations of < 13 cmol_ckg^–1. We estimated that between 0.4 to 4 Mg (CaCO₃) ha^–1 fell directly on three study sites; however, one year after the treatment the increase in Ca concentration (0–8 cm depth) was equivalent to a (CaCO₃) dosage of 3 Mg ha^–1 with an additional 2–4 Mg ha^–1 of undissolved (CaCO₃) still present, suggesting the peat retained Ca supplied from uplands. Most aspects of peat chemistry including microbial respiration and SO₄ reduction did not respond to the treatment.Peat pore water (5 and 20 cm depths) had a mean pH of 4.82 before treatment with high concentrations of dissolved organic carbon (DOC mean of 790 mol C/l) and low Ca²⁺ concentration (mean of 32 mol/l). The (CaCO₃) treatment increased concentrations of Ca²⁺ to a mean of 87 mol/l and dissolved inorganic carbon (DIC) from 205 to a mean of 411 mol/l, whereas it decreased monomeric Al concentration from 19 to 10 mol/l. Otherwise, pore water chemistry showed little response to the treatment, at least within natural spatial and temporal variation of solute concentrations. The results suggest that liming watersheds with the relatively low (CaCO₃) dosage applied in this study can benefit acidic waters downstream by exporting more Ca and DIC and less monomeric Al, with otherwise little effect on the peat itself.     

Inactivation of calcium currents in the soma of spinal ganglia by removing the membrane potential depolarization shift

Kinetic and voltage-dependent characteristics of the inactivating action of incoming calcium currents were investigated in the somatic membrane of rat spinal ganglia neurons using an intracellular dialysis technique. It was shown that the "tail" of low-threshold calcium current could be reliably described by one exponent with a time constant of =1.2–1.8 msec at a repolarization potential of –90 mV. The "tail" of the high-threshold calcium current represented the sum of several exponents. The time constant of the main component which expressed inactivation of the high threshold calcium current was ^h=250–350 µsec. It was also shown that and ^h remained virtually unchanged for repolarization potentials in the subthreshold region; they increase, however, if the repolarizing potential is close to those potentials at which the corresponding component of calcium current is initially activated. A dependence was observed between the levels and ^h and duration of the depolarizing shift. Findings are discussed in the context of a three-tier model of calcium channels.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 682–691, September–October, 1985.     

5-Fluorotryptophan-Containing N-Terminal Domain of the α-Subunit of the Torpedo californica Acetylcholine Receptor: Preparation in Escherichia coli and 19F NMR Study

A protein corresponding to the extracellular 1–209 domain of the -subunit of the nicotine acetylcholine receptor from the electric organ of Torpedo californica was prepared using the corresponding cDNA domain by culturing Escherichia coli cells on a synthetic medium supplemented with 5-fluoro-L-tryptophan. The presence of a (His)₆ fragment preceding the 1–209 sequence allowed purification of the protein isolated from inclusion bodies by affinity chromatography on Ni-NTA Agarose. The incorporation of 5-fluorotryptophan residues was found by ¹⁹F NMR to be 50%. The spectrum of the protein reduced in the denaturing conditions and subsequently reoxidized in a dilute solution under denaturing conditions in the presence of 0.05% SDS was sufficiently resolved, which allowed partial assignment of ¹⁹F resonances using the Trp60Phe mutant protein. The ability of the prepared domains to specifically bind snake -neurotoxins was demonstrated with the use of radioiodinated -bungarotoxin and trifluoroacetylated -cobratoxin.     

The influence of soil moisture on water potential,transpiration and photosynthesis of conifer seedlings

Summary The influence of soil moisture content and soil water potential on plant water potential, transpiration and net-photosynthesis of potted larch (Larix decidua), spruce (Picea abies) and pine (Pinus cembra) was studied under constant and close to optimum conditions in a laboratory.The equilibrium plant water potential measured under non-transpiring conditions came close to soil water potential, but in moist soil the equilibrium potential was slightly lower, particularly in larch where transpiration was not fully arrested. In very dry soil, plants had higher water potential than soil, presumably due to roots exploiting the wettest points within the soil.Pine, spruce and larch utilised a large part of soil moisture (down to 25wt.% soil water content or –1.5 bars potential) while maintaining plant water potential near –8, –9.5 and –12.5 bars respectively. A similar pattern occurred in dry soil. The differences between species are explained by differing stomatal sensitivity to water potential.Pine began a gradual reduction in gas-exchange below a soil water potential of –0.4 bars. Larch showed no marked reduction until the soil potential fell to –3.5 bars but below this the shut-down in gas-exchange was rapid. Spruce lay in between.In spite of the early and sensitive gas-exchange reduction with decreasing soil moisture, pine maintained the highest net photosynthesis/transpiration ratio and thus used limited soil water more slowly and economically than the other species.Seedlings maintained a higher rate of gas-exchange in strong light than in weak light, especially at low soil water potentials.     

Nitrate reduction activity in a continuous flow-through system in marine sediments

Nitrate reduction in a non-polluted, coastal marine sediment was measured with an open flow-through system. The recorded rates depended upon nitrate concentration but were largely independent of the weight of sediment (14–35 g) and the dilution rate (0.7–5 h^–1). Rate of nitrate uptake followed classical Michaelis-Menten kinetics, and km and V_max values were equal to 78M and 0.168m mol g^–1 hour^–1, respectively. These values are in good agreement with those found by the other authors for the same biotope but by different methods. This technique of the open flow-through system is fast, simple, and inexpensive and involves small quantities of sediment (10 g).     

Spatial and temporal variation in soil CO2 efflux in an old-growth neotropical rain forest, La Selva, Costa Rica

Our objectives were to quantify and compare soil CO₂ efflux of two dominant soil types in an old-growth neotropical rain forest in the Atlantic zone of Costa Rica, and to evaluate the control of environmental factors on CO₂ release. We measured soil CO₂ efflux from eight permanent soil chambers on six Oxisol sites. Three sites were developed on old river terraces (old alluvium) and the other three were developed on old lava flows (residual). At the same time we measured soil CO₂ concentrations, soil water content and soil temperature at various depths in 6 soil shafts (3 m deep). Between old alluvium sites, the two-year average CO₂ flux rates ranged from 117.3 to 128.9 mg C m^–2 h^–1. Significantly higher soil CO₂ flux occurred on the residual sites (141.1 to 184.2 mg C m^–2 h^–1). Spatial differences in CO₂ efflux were related to fine root biomass, soil carbon and phosphorus concentration but also to soil water content. Spatial variability in CO₂ storage was high and the amount of CO₂ stored in the upper and lower soil profile was different between old alluvial and residual sites. The major factor identified for explaining temporal variations in soil CO₂ efflux was soil water content. During periods of high soil water content CO₂ emission decreased, probably due to lower diffusion and CO₂ production rates. During the 2-year study period inter-annual variation in soil CO₂ efflux was not detected.     

On the dependence of salt tolerance of beans (Phaseolus vulgaris L.) on soil water matric potentials

Summary Bean plants (Kora cv) were grown in potted soil artificially salinized by adding NaCl and CaCl₂ to the irrigation water to obtain an electrical conductivity of the soil saturation extract (EC_e) thirty days after emergence of 0.1, 0.3, 0.5 and 0.7 S/m at 25°C and a sodium adsorption ratio (SAR) of 4 (mmol/l)². Thereafter, plants were irrigated when soil water matric potential (_M) was in the range of –20 to –30 kPa (wet treatment) and when _M was in the range of –40 to –60 kPa (dry treatment).Transpiration rates (Tr) and leaf extension rates (LER) per plant or per unit of leaf area were decreased by increasing soil salinity and by decreasing soil moisture. However, a given decrement of _M produced a considerable larger decrement in Tr of LER than an equivalent decrement of soil water osmotic potential (₀). Absolute yields of green pods under wet treatments were from twice to one and a half time as large under the wet than under the dry treatment at equivalent values of ₀. Relative yields were reduced by 25% when EC_e were about 0.5 S/m and 0.7 S/m in the dry and wet treatment respectively. Salt tolerance data of crops may not have a quantitative interest when soil irrigation regimes under which they were obtained are not specified.