Evaluating Critical Soil Acidification Loads and Exceedances for a Deciduous Forest at the Turkey Lakes Watershed

Critical soil acidification loads (CL) and related exceedances, base cation leaching, N leaching, and forest biomass growth were evaluated for a well-studied deciduous forest site within the Turkey Lake Watershed (TLW). The assessment was done by way of steady-state mass balance considerations of primary inputs for N, Ca, Mg, and K. Critical soil acidification rates were found to be high at TLW. These rates amounted to about 900 or 1400 eq/(ha yr) depending on the forest harvesting regime (selective harvest or maintainence of old-growth condition, respectively). The TLW soil substrate (till derived from basaltic bedrock) appeared to weather well, thereby buffering against natural and anthropogenic soil acidification. As a consequence, soil acidification exceedances were estimated to be relatively low for both the selective harvest and old-growth scenarios. In comparing overall S and N input/output data (atmospheric deposition data vs soil leaching losses), we found that the TLW site was essentially near or at S and N saturation. We also found that atmospheric deposition and soil leaching rates have been declining since about 1980. The figures for CL and exceedance varied to some extent depending on the quality of input data and related uncertainties. Estimated exceedances were increased when dry- as well as wet-deposition rates were considered. They varied depending on the yearly sulfate/nitrate/base-cation mix, and the definition of “acceptable acid leaching.” In addition, they were dependent on whether the forest was considered old growth or not. Received 5 October 1999; Accepted 1 November 2000.     

Fifteen-year Change in Forest Floor Organic and Element Content and Cycling at the Turkey Lakes Watershed

To assess the long-term effects of atmospheric deposition on forest floor chemical composition, we took quantitative samplings of L-(Oi), F-(Oe), and H-(Oa) layers at an old-growth sugar maple–yellow birch stand on a till soil at the Turkey Lakes Watershed near Lake Superior, Ontario, Canada, in 1981 and 1996. We then assessed these samples for contents of organic matter (OM), total N, K, Ca, Mg, S, and Na, and exchangeable NH₄ ⁺, NO₃ ⁻, K⁺, Ca²⁺, Mg²⁺, SO₄ ²⁻, and Na⁺. Over the 15-year period, total OM and element contents remained unchanged, with the exception of N, which increased significantly from 61.3 kmol/ha in 1981 to 78.4 kmol/ha in 1996. On an area basis, there were significant increases in exchangeable Ca²⁺ (from 3.8 to 4.6 kmol/ha) and Na⁺ (from 0.05 to 0.08 kmol/ha) and decreases in exchangeable NH₄ ⁺-N (from 1.41 to 0.95 kmol/ha) and SO₄ ²⁻-S (from 1.29 to 0.96 kmol/ha). There were no significant differences in average annual litterfall OM, N, Ca, Mg, S or Na inputs between 1980 and 1985 and between 1992 and 1997. Average annual wet-only SO₄ ²⁻-S deposition during 1981–86 was 0.30; during 1992–97, it was 0.21 kmol/ha. Annual wet-only NO₃ ⁻-N averaged 0.33 kmol/ha during 1981–86 and was similar during 1992–97. Throughfall was less rich in SO₄ ²⁻ and Ca²⁺, Mg²⁺, and Na⁺ during 1992–97 than earlier. Throughfall NH₄ ⁺ and NO₃ ⁻ fluxes were unchanged. Efflux of cations from the forest floor reflected reduced throughput of SO₄ ²⁻. Overall, the results suggest that in spite of atmospheric inputs, active biological processes—including litter input, fine-root turnover, and tree uptake—serve to impart stability to the mineral composition of mature sugar maple forest floor. Received 5 October 1999; accepted 25 October 2000.     

Zinc distribution and speciation in roots of various genotypes of tobacco exposed to Zn

Cell walls of roots have a great reactivity towards metals, and may act as a barrier limiting the entry of metals, especially in non-hyperaccumulating species. The aim of this study was to determine the localization and speciation of Zn in roots of tobacco (Nicotiana tabacum) grown in Zn-contaminated substrates. Chemical extractions and EXAFS spectroscopy were applied on whole roots and on isolated cell walls of roots. Our results show that cell walls of roots exhibited a distribution of Zn affinity sites, from water-soluble to non-exchangeable Zn. In whole roots, Zn was bound with oxalate and other COOH/OH groups: the first species was probably intracellular while the second was attributed to Zn bound to the cell walls and, to a lesser extent, to intracellular organic acids. Moreover, Zn-phosphate was also identified, and this species was CuSO₄-extractable. It probably resulted from chemical precipitation in the apoplasm, and explained the steady increase in exchangeable root Zn observed in root of tobacco during the culture. This study shows the strength of combining EXAFS and chemical extractions for studying localization and speciation of metals in plants.     

Effects of enhanced nitrogen deposition and phosphorus limitation on nitrogen budgets of semi-natural grasslands

Increased reactive atmospheric N deposition has been implicated in floristic changes in species‐rich acidic and calcareous grasslands, but the fate of this pollutant N in these ecosystems is unknown. This paper reports the first analysis of N budgets and N fluxes for two grasslands in the White Peak area of Derbyshire, one of the most heavily N‐polluted locations in the UK. N fluxes were monitored in lysimeter cores (retaining the original turfs) taken from field plots of unimproved acidic and calcareous grasslands that had received (in addition to ambient N deposition) simulated enhanced N deposition treatments of 3.5 and 14 g N m^?2 yr^?1 for 6 years. The influence of reducing phosphorus limitation was assessed by factorial additions of P. Seasonal leached losses of nitrate, ammonia and organic N were monitored in detail along with estimates of N removal through simulated grazing and gaseous losses through denitrification and volatilization. The rates of N fluxes by these pathways were used to create N budgets for the grasslands. Both grasslands were found to be accumulating much of the simulated additional N deposition: up to 89% accumulated in the calcareous grassland and up to 38% accumulated in the acidic grassland. The major fluxes of N loss from these grasslands were by simulated grazing and leaching of soluble organic N (constituting 90% of leached N under ambient conditions). Leached inorganic N (mainly nitrate) contributed significantly to the output flux of N under the highest N treatment only. Loss of N through ammonia volatilization accounted for less than 6% of the N added as simulated deposition, while denitrification contributed significantly to output fluxes only in the acidic grassland during winter. The implications of the results for ecosystem N balances and the likely consequences of N accumulation on these grasslands are discussed.     

Environmental impacts of bioenergy wood production from poplar short‐rotation coppice grown at a marginal agricultural site in Germany

For avoiding competition with food production, marginal land is economically and environmentally highly attractive for biomass production with short‐rotation coppices (SRCs) of fast‐growing tree species such as poplars. Herein, we evaluated the environmental impacts of technological, agronomic, and environmental aspects of bioenergy production from hybrid poplar SRC cultivation on marginal land in southern Germany. For this purpose, different management regimes were considered within a 21‐year lifetime (combining measurements and modeling approaches) by means of a holistic Life Cycle Assessment (LCA). We analyzed two coppicing rotation lengths (7 × 3 and 3 × 7 years) and seven nitrogen fertilization rates and included all processes starting from site preparation, planting and coppicing, wood chipping, and heat production up to final stump removal. The 7‐year rotation cycles clearly resulted in higher biomass yields and reduced environmental impacts such as nitrate (NO₃) leaching and soil nitrous oxide (N₂O) emissions. Fertilization rates were positively related to enhanced biomass accumulation, but these benefits did not counterbalance the negative impacts on the environment due to increased nitrate leaching and N₂O emissions. Greenhouse gas (GHG) emissions associated with the heat production from poplar SRC on marginal land ranged between 8 and 46 kg CO₂‐eq. GJ^?1 (or 11–57 Mg CO₂‐eq. ha^?1). However, if the produced wood chips substitute oil heating, up to 123 Mg CO₂‐eq. ha^?1 can be saved, if produced in a 7‐year rotation without fertilization. Dissecting the entire bioenergy production chain, our study shows that environmental impacts occurred mainly during combustion and storage of wood chips, while technological aspects of establishment, harvesting, and transportation played a negligible role.     

Response of soil microbial activity to temperature,moisture, and litter leaching on a wetland transect during seasonal refilling

In nutrient impoverished landscapes in southwest Australia, terrestrial litter appears to be important in phosphorus (P) turnover and in the gradual accumulation of P in wetland systems. Little is known about the fate of P leached from litter during the wet season and the associated effects of soil microclimate on microbial activity. The effects of temperature, moisture, and litter leaching on soil microbial activity were studied on a transect across a seasonal wetland in southwestern Australia, after the onset of the wet season. Heterotrophic respiration (CO₂ efflux) was higher in the dried lakebed and riparian areas than in upland soils, and higher during the day than at night. There were significant variations in CO₂ efflux with time of sampling, largely caused by the effect of temperature. The addition of litter leachate significantly increased CO₂ efflux, more significantly in soils from upland sites, which had lower moisture and nutrient contents. There was a difference in response of microbial respiration between upland soils and wetland sediments to litter leachate and wetter, warmer conditions. In general, the litter leachate enhanced heterotrophic microbial respiration, and more significantly at warmer conditions (31 °C). The relative fungal to bacterial ratio was 2.9 – 3.2 for surface litter and 0.7–1.0 for soils, suggesting a fungal dominance in heterotrophic respiration of surface litter, but increased bacterial dominance in soils, especially in exposed sediments in the lakebed.     

Phenothiazine radicals inactivate Trypanosoma cruzi dihydrolipoamide dehydrogenase: enzyme protection by radical scavengers

Phenothiazine cation radicals (PTZ + •) irreversibly inactivated Trypanosoma cruzi dihydrolipoamide dehydrogenase (LADH). These radicals were obtained by phenothiazine (PTZ) peroxidation with myeloperoxidase (MPO) or horseradish peroxidase (HRP/H 2 O 2 ) systems. LADH inactivation depended on PTZ structure and incubation time. After 10 min incubation of LADH with the MPO-dependent systems, promazine, trimeprazine and thioridazine were the most effective; after 30 min incubation, chlorpromazine, prochlorperazine and promethazine were similarly effective. HRP-dependent systems were equally or more effective than the corresponding MPO-dependent ones. Chloro, trifluoro, propionyl and nitrile groups at position 2 of the PTZ ring significantly decreased molecular activity, specially with the MPO/H 2 O 2 systems. Comparison of inactivation values for LADH and T. cruzi trypanothione reductase demonstrated a greater sensitivity of LADH to chlorpromazine and perphenazine and a 10-fold lower sensitivity to promazine, thioridazine and trimeprazine. Alkyl-amino, alkyl-piperidinyl or alkyl-piperazinyl groups at position 10 modulated PTZ activity to a limited degree. Production of PTZ + • radicals was demonstrated by optical and ESR spectroscopy methods. PTZ + • radicals stability depended on their structure as demonstrated by promazine and thioridazine radicals. Thiol compounds such as GSH and N -acetylcysteine, l -tyrosine, l -tryptophan, the corresponding peptides, ascorbate and Trolox, prevented LADH inactivation by the MPO/H 2 O 2 /thioridazine system, in close agreement with their action as PTZ + • scavengers. NADH (not NAD + ) produced transient protection of LADH against thioridazine and promazine radicals, the protection kinetics being affected by the relatively fast rate of NADH oxidation by these radicals. The role of the observed effects of PTZ radicals for PTZ cytotoxicity is discussed.     

The venerable inveterate invertebrate TRP channels

The transient receptor potential (TRP) superfamily is subdivided into four main classes of cation channels, TRPC, TRPV, TRPM and TRPN, each of which includes members in worms, flies, mice and humans. While the biophysical features of many of the mammalian channels have been described, relatively little is known concerning the biological roles of these channels. Forward genetic screens in Drosophila melanogaster and Caenorhabditis elegans have led to the identification of the founding members of each of these four subfamilies. Moreover, phenotypic analyses of invertebrate mutants have contributed greatly to our understanding of the roles of TRP proteins. A recurring theme is that many of these proteins function in sensory signaling processes ranging from vision to olfaction, osmosensation, light touch, social feeding, and temperature- and mechanically-induced nociception. In addition, at least one invertebrate TRP protein is required for cell division. As many of these functions may be conserved among the mammalian TRPs, the invertebrate TRPs offer valuable genetic handles for characterizing the functions of these cation channels in vivo.     

The requirement of ammonium or other cations linked with p-cresol sulfate for cross-reactivity with a peptide of myelin basic protein

Urinary myelin basic protein-like material (MBPLM), so designated because of its immunoreactivity with a polyclonal antibody directed against a cryptic epitope located in residues 83-89 of myelin basic protein (MBP), exists in humans normally but increases in concentration in patients with multiple sclerosis who have progressive disease. Given its possible role in reflecting events of neural tissue destruction occurring in multiple sclerosis, urinary MBPLM is a candidate surrogate marker for this phase of the disease. Previously, it has been demonstrated that p-cresol sulfate (PCS) is the dominant component of MBPLM; however, another component(s) was essential in enabling p-cresol sulfate to have molecular mimicry with MBP peptide 83-89 detected by immunoreactivity. In the present investigation, this remaining component(s) was characterized by a combination of high performance size exclusion chromatography followed by nuclear magnetic resonance spectroscopy and shown to be ammonium. The monovalent cation ammonium could be substituted in vitro by several different monovalent and divalent cations, most notably zinc, in restoring to deprotonated p-cresol sulfate its immunoreactivity as MBPLM. These findings indicate the basis for the unexpected molecular mimicry between an epitope of an encephalitogenic protein and a complex containing a small organic molecule, p-cresol sulfate. Furthermore, the reaction of either ammonium or other cations with p-cresol sulfate may represent an in vivo process directly related to damage of axonal membranes.     

Direct NMR detection of the "invisible" alkali metal cations tightly bound to G-quadruplex structures

We report the first direct solution NMR detection of the alkali metal cations (²³Na⁺, ³⁹K⁺, and ⁸⁷Rb⁺) residing inside G-quadruplex channel structures formed by guanosine 5′-monophosphate and a DNA oligomer, d(TG₄T). In solution, these channel alkali metal cations are tightly bound to the G-quadruplex structure and have been considered to be “invisible” to NMR spectroscopy for many years. Our finding that it is possible to directly observe these alkali metal cations by NMR spectroscopy provides a new tool for studying cation binding affinity and dynamics in G-quadruplex DNA.