Processes regulating temporal and longitudinal variations in the chemistry of a low-order woodland stream in the Adirondack region of New York

Watershed processes influence the acid neutralizing capacity of surface waters by mediating changes in concentration of ionic solutes. Acidification of surface waters by atmospheric deposition of mineral acids and the extent to which ecosystem transformations neutralize this acidity are of particular concern. Seasonal variations in flow paths of water through soil and biological processes result in short-term changes in chemistry that may be critical to surface water ecology. In this study, we assessed longitudinal and temporal variations in the chemistry of a low-order stream, Pancake-Hall Creek, located in the west-central Adirondack region of New York. By quantifying changes in ionic solute concentration (e.g. Ca²⁺, Al^a+, SO ₄ ^2– , NO ₃ ^– ) we were able to evaluate processes responsible for short-term fluctuations in acid/base chemistry.In the headwater sites, stream water was acidic; changes in pH, acid neutralizing capacity (ANC) and Al were primarily due to seasonal variations in basic cation and NO ₃ ^– concentrations. At the downstream sites, water migrated through a large beaver impoundment and thick till resulting in higher pH, acid neutralizing capacity and basic cation concentrations, and lower concentrations of Al. Neutralization of acidity was particularly evident during the low flow summer period and coincided with retention of SO ₄ ^2– in the beaver impoundment. During the high flow non-summer (October to June) period, depressed pH and ANC, and elevated Al concentrations were observed in the downstream sites. Acidic conditions during the non-summer period were not due to the oxidation of reduced sulfur deposits (e.g. SO ₄ ^2– events) but rather the resumption of conservative SO ₄ ^2– transport through the beaver impoundment (e.g. minimal SO ₄ ^2– retention) coupled with increases in NO ₃ ^– .     

Hydrogeologic controls of surface-water chemistry in the Adirondack region of New York State

Relationships between surface-water discharge, water chemistry, and watershed geology were investigated to evaluate factors affecting the sensitivity of drainage waters in the Adirondack region of New York to acidification by atmospheric deposition. Instantaneous discharge per unit area was derived from relationships between flow and staff-gage readings at 10 drainage basins throughout the region. The average chemical composition of the waters was assessed from monthly samples collected from July 1982 through July 1984. The ratio of flow at the 50-percent exceedence level to the flow at the 95-percent exceedence level of flow duration was negatively correlated with mean values of alkalinity or acid-neutralizing capacity (ANC), sum of basic cations (SBC), and dissolved silica, for basins containing predominantly aluminosilicate minerals and little or no carbonate-bearing minerals. Low ratios are indicative of systems in which flow is predominately derived from surface- and ground-water storage, whereas high ratios are characteristic of watersheds with variable flow that is largely derived from surface runoff.In an evaluation of two representative surface-water sites, concentrations of ANC, SBC, and dissolved silica, derived primarily from soil mineral weathering reactions. decreased with increasing flow. Furthermore, the ANC was highest at low flow when the percentage of streamflow derived from ground water was maximum. As flow increased, the ANC decreased because the contribution of dilute surface runoff and lateral flow through the shallow acidic soil horizons to total flow increased. Basins having relatively high ground-water contributions to total flow, in general, have large deposits of thick till or stratified drift. A major factor controlling the sensitivity of these streams and lakes to acidification is the relative contribution of ground water to total discharge.     

Nitrogen biogeochemistry of three hardwood ecosystems in the Adirondack Region of New York

The biogeochemistry of nitrogen (N)was evaluated for three forest ecosystems[Woods Lake (WL), Pancake-Hall Creek (PHC) andHuntington Forest (HF)] in the Adirondackregion of New York, U.S.A. to evaluate theresponse of a range of N atmospheric inputsand experimental N additions. Bulk Ndeposition was higher at sites in the westthan those in the central and easternAdirondacks. These higher atmospheric N inputswere reflected in higher bulk throughfallfluxes of N (WL and PHC, 10.1 and 12.0 kg Nha^–1 yr^–1, respectively) in thewestern Adirondacks than at HF (4.6 kg Nha^–1 yr^–1) in the centralAdirondacks. Nitrogen was added to plots as(NH₄)₂SO₄ at 14 and 28 kg Nha^–1 yr^–1 or as HNO₃ at 14 kg Nha^–1 yr^–1. Litter decompositionrates of Fagus grandifolia and Acerrubrum were substantially higher at WL andPHC compared to HF but were not affected byexperimental N additions. Results usingmineral soil bags showed no effects of Naddition on N and C concentrations in soilorganic matter, but C and N concentrationincreases were less at WL and PHC compared toHF. Soil solution nitrate (NO₃ ^–)concentrations at 15-cm depth in the referenceplots were higher at PHC than at WL and HFwhile at 50-cm concentrations were higher atPHC and WL than at HF. The reference plots atthe two sites (WL and PHC) with the highestatmospheric inputs of N exhibited lower Nretention (53 and 33%, respectively) than HF(68%) in reference plots. The greatestincrease in NO₃ ^– loss in response tothe experimental treatments occurred at HFwhere the HNO₃ additions resulted in thehighest NO₃ ^– concentrations andlowest N retentions. In contrast, at WL andPHC increases in soil water NO₃ ^–were not evident in response to experimental Nadditions. The results suggest that the twosites (WL and PHC) in the western Adirondacksdid not respond to additional N inputsalthough they have experienced elevatedatmospheric N inputs and higher N drainagelosses in reference plots than the HF site inthe central Adirondacks. Some of thesedifferences in site response may have alsobeen a function of stand age of WL and PHCthat were younger (24 and 33 years,respectively) than the HF (age 70).Highest NO₃ ^– fluxes in thereference plots across the sites correspondedto higher ¹⁵N values in soil andplants. An experimental addition experimentat PHC found that the forest floor and themineral soil were the largest sinks forexperimentally added N.     

冬季雪被对青藏高原东缘高海拔森林凋落叶P元素释放的影响

雪被是影响高海拔森林凋落物分解的重要生态因子,其是否影响到生长季节与非生长季节凋落物中的P元素释放,尚未量化。为了量化季节性雪被对高海拔森林凋落物分解过程中P元素释放的影响,于2010年10月至2012年10月间,在青藏高原东缘川西高海拔森林不同厚度冬季雪被斑块下,设置凋落物分解袋实验。检测该地区代表性树种岷江冷杉(Abies faxoniana)、红桦(Betula albo-sinensis)、四川红杉(Larix mastersiana)和方枝柏(Sabina saltuaria)凋落叶在雪被覆盖不同关键时期(雪被形成前期、完全覆盖期和消融期)以及生长季节的P元素动态。结果表明,凋落物质量与雪被厚度均显著影响了P元素的释放过程。雪被覆盖时期凋落物P元素释放率表现为有雪被覆盖大于无雪被覆盖,而生长季节中除岷江冷杉外的其他3种凋落物P元素释放率均为无雪被覆盖下最大。相对于无雪被覆盖斑块,冬季雪被的存在提供了保护绝缘层,促进凋落物P元素释放,提高了各物种冬季P元素释放贡献率。这些结果表明,全球变化情景下的雪被减少可能减缓高海拔森林凋落物P元素的释放过程,改变森林土壤P元素水平。所以在研究高寒、高海拔地区全球气候变化下生态系统功能的工作中,应注重雪被这一异质性环境因子对生态系统功能的影响。     

壤中流和土壤解冻深度对黑土坡面融雪侵蚀的影响

融雪侵蚀是东北黑土区土壤流失的一种重要形式,而目前有关壤中流和土壤解冻深度对融雪径流侵蚀的影响研究较少.本研究采用室内模拟试验,设计两个融雪径流量(1和4 L·min-1)和两个土壤解冻深度(5和10 cm),以及有、无壤中流处理,分析壤中流和土壤解冻深度对黑土区坡面融雪侵蚀的影响.结果 表明:1)壤中流处理下坡面融雪...     

The chemistry and transport of mercury in a small wetland in the Adirondack region of New York, USA

The biogeochemistry of Hg was evaluated in a small wetland in the Adirondack region of New York. Concentrations of total Hg (Hg_T) in streamwater draining the wetland showed little temporal variation. The annual areal watershed flux of Hg_T (2.2 µg/m²-yr) was considerably smaller than regional inputs of atmospheric deposition of Hg_T, indicating that the terrestrial environment is a net sink for atmospheric deposition of Hg_T. Drainage inputs of Hg_T were conservatively transported through the beaver impoundment. The annual flux of total methyl mercury (CH₃Hg⁺ _T was greater than literature values of atmospheric deposition suggesting that the watershed is a net source of CH₃Hg⁺ _T . Stream concentrations of CH₃Hg⁺ _T increased during low-flow summer conditions in a riparian wetland, and particularly at the outlet of the beaver impoundment. Net production of CH₃Hg⁺ _T occurred in the beaver impoundment (0.45 µg/m²-yr). Rates of net methylation for the beaver impoundment were comparable to values reported in the literature for wetlands.     

Winter CO2 flux from soil and snow surfaces in a cool-temperate deciduous forest, Japan

We measured diurnal and wintertime changes in CO₂ fluxes from soil and snow surfaces in a Japanese cool-temperate Quercus/Betula forest between December 1994 and May 1995. To evaluate the relationship between these winter fluxes and temperature, flux measurements were made with the open-flow infrared gas analyzer (IRGA) method rather than with the more commonly used closed chamber method or the snow CO₂ profile method. The open-flow IRGA method proved to be more successful in measurements of winter CO₂ fluxes than the two standard methods. Despite colder air temperatures, soil temperature profiles were greater than 0°C because of the thermal insulation effect of deep snowpack. This reveals that soil temperature is satisfactory for microbial respiration throughout the winter. Unfrozen soils under the snowpack showed neither diurnal nor wintertime trends in CO₂ fluxes or in soil surface temperature, although there was a daily snow surface CO₂ flux of 0.18–0.32 g m^–2. By combining this with other reference data, Japanese cool-temperate forest soils in snowy regions can be estimated to emit < 100 g m^–2 carbon over an entire winter, and this value accounts for < 15% of the annual emission. In the present study, when data for all winter fluxes were taken together, fluxes were most highly correlated with deep soil temperatures rather than the soil surface temperature. Such a high correlation can be attributed to the relatively increased respiration of the deep soil where the temperature was higher than the soil surface temperature. Thus, deeper soil temperature is a better predictor of winter CO₂ fluxes in cold and snowy ecosystems.     

Evaluation of Shifts in White-Tailed Deer Winter Yards in the Adirondack Region of New York

ABSTRACT In the Adirondack region of northern New York, USA, severe weather and deep snow typically force white-tailed deer (Odocoileus virginianus) to congregate in areas of dense coniferous cover and along watercourses at lower elevations. We examined 16 yards in the Adirondacks and explored the observation that deer have changed their movement behavior to incorporate residential communities within their wintering areas. We compared locations of deer herds in 2003 and 2004 to deer wintering areas mapped during the 1960s and 1970s. Deer were predominantly absent in 9 of 16 historical yards but were present in residential communities within the same drainage. Yarding areas to which deer shifted contained more residential, deciduous, and mixed cover than yards where no shift occurred, indicating that deer in residential areas were using conifer and mixed cover at a finer scale than deer in nonresidential areas. Smaller winter ranges and core areas of marked deer in a residential winter yard further imply greater concentration of resources available in these areas. Marked deer demonstrated flexibility in core winter range fidelity, a behavior that allows for more permanent shifts as habitat and food resources change or as new areas with appropriate resources are encountered. Our study suggests that low-density residential areas in lowland conifer forests may provide an energetic advantage for deer during winter due to the assemblage of quality habitat interspersed with open areas and a variety of potential food sources in environments where movement is typically constrained by deep snow. Managers should consider the potential for changes in use of deer wintering areas prior to land conservation efforts and may need to adapt management strategies to reduce conflicts in communities occupied by deer during winter.     

Trends in Summer Chemistry Linked to Productivity in Lakes Recovering from Acid Deposition in the Adirondack Region of New York

The US Environmental Protection Agency established the Adirondack Effects Assessment Program (AEAP) to evaluate and monitor the status of biological communities in lakes in the Adirondack region of New York that have been adversely affected by acid deposition. This program includes chemical analysis of 30 lakes, sampled two to three times each summer. Results of trends analysis for lake chemistry and chlorophyll a (chlor a) are presented for 1994 to 2003, and a general comparison is made with recent results of the Adirondack Long-Term Monitoring (ALTM) Program, which included chemical analysis of all but two of these lakes (plus an additional 24 lakes) monthly, year-round for 1992–2004. Increases in pH were found in 25 of the 30 AEAP lakes (P < 0.05) and increases in acid-neutralizing capacity (ANC) were found in 12 of the 30 lakes (P < 0.05). Concentrations of both SO ₄ ²⁻ and Mg²⁺ decreased in 11 lakes (P < 0.05), whereas concentrations of NO ₃ ⁻ decreased in 20 lakes (P < 0.05). Concentrations of NH ₄ ⁺ decreased in 10 lakes at a significance level of P < 0.05 and in three other lakes based on P < 0.1. Concentrations of inorganic and organic monomeric aluminum generally were below the reporting limit of 1.5 μmol L⁻¹, but decreases were detected in four and five lakes, respectively (P < 0.1). Concentrations of chlor a increased in seven lakes at a significance level of P < 0.05 and two lakes at a significance level of P < 0.1. A significant inverse correlation was also found between chlor a and NO ₃ ⁻ concentrations in nine lakes at a significance level of P < 0.05 and two lakes at a significance level of P < 0.1. Results of AEAP analysis of lake chemistry were similar to those of the ALTM Program, although decreases in SO ₄ ²⁻ concentrations were more evident in the year-round ALTM record. Overall, the results suggest (a) a degree of chemical recovery from acidification during the summer, (b) an increase in phytoplankton productivity, and (c) a decreasing trend in NO ₃ ⁻ concentrations resulting from the increased productivity.     

Stable sulfur isotopic distributions and sulfate reduction in lake sediments of the Adirondack Mountains,New York

Cores from five lakes of the Adirondack Mountains, New York, were analyzed for sedimentary sulfur concentrations and stable sulfur isotopic compositions. Isotopic values of total sedimentary sulfur were as much as 6 to 8 lower than isotopic values of sulfur sources (soils, tree leaves and lake water sulfate) which showed little isotopic variation in the Adirondacks. The low isotopic values of recent sediments indicate increased sulfate reduction, probably in response to increased sulfate loading and acid deposition. Detailed historical reconstruction of sulfate loading histories from sedimentary sulfur profiles is premature, however, since model calculations indicate that sulfur can be added to deeper older sediments by ongoing, contemporary sulfate reduction.     

Leaching of dissolved organic carbon,dissolved organic nitrogen,and other solutes from coarse woody debris and litter in a mixed forest in New York State

Coarse woody debris (CWD) may play a role in nutrient cycling in temperate forests through the leaching of solutes, including dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), to the underlying soil. These fluxes need to be considered in element budget calculations, and have the potential to influence microbial activity, soil development, and other processes in the underlying soil, but studies on leaching from CWD are rare. In this study, we collected throughfall, litter leachate, and CWD leachate in situ at a young mixed lowland forest in NY State, USA over one year. We measured the concentrations of DOC, DON, NH₄⁺, NO₃⁻, dissolved organic sulfur, SO₄²⁻, Cl⁻, Al, Ca, K, Mg, Na, and P, estimated the flux of these solutes in throughfall, and measured the cover of CWD to gain some insight into possible fluxes from CWD. Concentrations of DOC were much higher in CWD leachate than in throughfall or litter leachate (15 vs. 0.7 and 1.6 mM, respectively), and greater than reported values for other leachates from within forested ecosystems. Other solutes showed a similar pattern, with inorganic N being an exception. Our results suggest that microsite scale fluxes of DOC from CWD may be An high relative to throughfall and litter leaching fluxes, but since CWD covered a relatively small fraction (2%) of the forest floor in our study, ecosystem scale fluxes from CWD may be negligible for this site. Soil directly beneath CWD may be influenced by CWD leaching, in terms of soil organic matter, microbial activity, and N availability. Concentrations of some metals showed correlations to DOC concentrations, highlighting the possibility of complexation by DOM. Several solute concentrations in throughfall, including DOC, showed positive correlations to mean air temperature, and fewer showed positive correlations in litter leachate, while negative correlations were observed to precipitation, suggesting both biological and hydrologic control of solute concentrations.     

Land use designation and vegetation community structure in the Adirondack uplands (New York,USA)

Question: Does forest vegetation community structure reflect legislative land use designations? Location: Adirondack Park, New York, USA. Methods: The Adirondack Park, located in northern New York State, is a mixture of public and private lands, with state‐owned Forest Preserve lands comprising ca. 42% of the 2.4 million ha, on which timber harvesting and many other forms of anthropogenic disturbance are prohibited. A survey of vegetation communities was conducted in eighteen upland catchments with differing land use history (managed and Forest Preserve), including overstory, understory, and dead wood (snags and downed woody debris) using randomly placed plots. Results: Mean overstory density and basal area were not significantly different between land uses, although mean overstory tree size was greater in Preserve catchments. Sapling densities were greater in managed catchments, while mean herb/shrub coverage was not affected by land use. Densities of 25% of common species were affected by land use, determined by GIS coverages constructed using an Inverse Distance Weighted estimation procedure. Discriminant Analysis of per‐plot plant community data correctly classified 89% of both managed and Preserve plots. Conclusion: The success of the Discriminant Analysis in classifying land uses based on vegetation communities indicates its potential utility of this method in comparing forest vegetation to a reference condition in this and other areas. The analysis suggests that at least 85 years is required for Adirondack up‐land catchments to recover following harvesting. Uncertainty in classification was related to heterogenous management and disturbance patterns within catchments.     

Leaf litter fall and soil acidity during half a century of secondary succession in a temperate deciduous forest

Vegetation, leaf litter fall and soil pH were sampled repeatedly within semipermanent plots in a South-Swedish deciduous forest, 1935–1983. Leaf litter fall was summarized in a litter quality index. Vegetation types were differentiated along similar gradients in soil pH and leaf litter quality. The greatest shifts in dominance among field layer species were found in those plots where the quality of the leaf litter had improved. These plots also showed a halt in the general tendency towards a decreasing pH in the top soil.     

Litterflow chemistry and nutrient uptake from the forest floor in northwest Amazonian forest ecosystems

Samples of the fraction of net rainfall passing through the forest floor collected at monthly intervals in four pristine forests in Colombian Amazonia, during the period between 1995–1997 were analysed for solute concentrations to estimate the element fluxes from the forest floor into the mineral soil and root nutrient uptake from these forest floors. Results were compared with inputs by throughfall, stemflow, litterfall and fine root decay. Element concentrations were tested for their relationship with litterflow amounts, rainfall intensity and length of the antecedent dry period and differences in element fluxes between ecosystems were assessed. Concentrations of elements in litterflow followed a similar pattern as those in throughfall, which indicates that element outputs from the forest floor are strongly related to those inputs in throughfall. In the forests studied, the average concentrations of elements as K, Mg, orthoP and the pH of the litterflow decreased relative to that in throughfall in most events, while the concentration of elements such as dissolved organic carbon, H, SO₄ and Si increased in litterflow from these forests. Element concentrations in litterflow showed a poor correlation with variables such as litterflow amounts, rainfall intensity and antecedent dry period, except for K which showed a significant correlation (p>0.95) with analysed variables in all forests. Outputs were significantly different between forests (p>0.95); these fluxes, which particularly concerned cations, being the largest in the flood plain, while for anions outputs increased from the flood plain to the sedimentary plain. After adding the nutrient contributed by litter decomposition and fine root decay, the net outputs of main elements from the forest floors were still smaller than inputs by net precipitation (throughfall+stemflow) indicating that the litter layers clearly acted as a sink for most nutrients. Accordingly, the element balances confirm that the forest floors acted as a sink for nutrients coming in by throughfall, stemflow, litterfall and fine root decomposition. P, Mg and N appeared to be the most limiting nutrients and the forests studied efficiently recycled these nutrients.     

Long‐term impacts of nitrogen and sulphur deposition on forest floor vegetation in the Northern limestone Alps,Austria

Question: Are there effects of long‐term deposition of airborne nitrogen and sulphur on the forest floor vegetation from permanent plots collected in 1993 compared to 2005. Location: Northern limestone Alps in Austria. Methods: Single species responses were analysed by correlating trends in cover‐abundance values, as derived from marginal models, with Ellenberg indicator values. Changes in the species composition of plots were analysed by correlating changes in mean Ellenberg indicator values with the displacement of plots within a multidimensional scaling ordination. Results: Trends in single species abundance were positively correlated with indicator values of soil pH but were independent of nutrient availability. A general trend towards the homogenisation of vegetation, due to convergent time vectors of the relevés, became obvious. Oligotrophic sites previously situated at the distal ends of ordination axes shifted towards the centre since they were enriched by species preferring mesotrophic conditions. The bulk of plots with intermediate site conditions hardly showed any trends. A concomitant analysis demonstrated that temporal changes in species composition exceed the variation in cover abundance estimates among different field botanists. Conclusions: N deposition can lead to a homogenisation of forest floor vegetation. Larger limestone areas with diverse soil conditions, such as the Northern limestone Alps in Austria, as a whole are thus negatively affected by airborne N deposition. Nevertheless, the vegetation was at least as strongly affected by an increase of basiphilous species as a result of decreasing S deposition.     

Effects of spring acid episodes on macroinvertebrates revealed by population data and in situ toxicity tests

1. While streams in Europe and North America are now recovering chemically from chronic acidification, severe episodic acidification continues to threaten sensitive biota. To appraise further the biological importance of episodic acidification, we surveyed the distribution of the mayfly Baetis alpinus in streams in the Southern Alps (Canton Ticino, Switzerland) in relation to runoff acidity during spring floods. Moreover, to improve mechanistic understanding, in situ toxicity assays were carried out on nymphal B. alpinus during low flows and spring floods, both in streams prone to acid episodes and in well‐buffered controls. 2. Streams surveyed for invertebrates represented three groups which contrasted in susceptibility to episodic acidity. Group one included streams that were acid (alkalinity <0) in spring; group two streams were susceptible to acid episodes because of low base‐flow alkalinity (<200 μeq L^?1); and group three streams were well‐buffered and unlikely ever to be acid. The abundance of B. alpinus was similar among groups during stable flows in winter and summer, but was significantly lower in groups one and two following spring snowmelt. 3. During the bioassays, control streams remained circumneutral to alkaline (pH >6.4). By contrast, episodic streams were circumneutral at low flows, but became acid (pH 4.5–5.6 and total dissolved aluminium to 276 μg L^?1) during intense spring snowmelt. After 15‐day exposures, nymphal B. alpinus survival in the circumneutral control streams exceeded 92% irrespective of flow. In the episodic streams, survival matched the controls during low flows, but declined significantly to 10–20% during acid episodes in spring. Shorter exposure (2–4 days) to pH 5.5–5.7 did not cause significant mortality either during the exposure or over the following 7 days, indicating that B. alpinus might recover from short acid episodes. 4. Our data suggest that the spring distribution of B. alpinus in acid sensitive parts of the Alps directly reflects the toxicity of acid runoff during snowmelt. Our study illustrates that even mild episodic acidification can have significant consequences in Alpine streams for one of the most important invertebrate indicators of acidity.     

Uptake of inorganic ions and compatible solutes in cultured mangrove cells during salt stress

Summary Callus of the mangrove plant, Sonneratia alba J. Smith, established from pistils of flower buds were cultured on solid Murashige and Skoog medium supplemented with 0 to 500 mM NaCl. Maximum growth was observed with 50 mM NaCl, and net growth of callus occurred for concentrations up to 200 mM NaCl. At 500 mM NaCl, growth of callus was completely inhibited, although a part of the tissue was still alive after 30 d. Cellular levels of Na⁺ and Cl⁻ were greatly increased by the treatment with NaCl. Uptake of K⁺ was also enhanced and was accompanied by increasing levels of Na⁺ and Cl⁻ so that the Na⁺/K⁺ ratio was almost constant (4.1–4.2) in callus grown with 50–200 mM NaCl. Levels of Mg²⁺ and Ca²⁺ were not changed significantly with 50–200 mM NaCl, whereas levels of free NH ₄ ⁺ , NO ₃ ⁻ and SO ₄ ²⁻ ions, which are convertible to organic compounds, were lowest in callus grown with 50 mM NaCl. The rate of conversion of ¹⁵NH ₄ ⁺ into macromolecules during 30 d culture with 0–100 mM NaCl did not vary greatly, but 200 mM NaCl reduced the biosynthesis of macromolecules from this ion. The highest rate of conversion of ¹⁵NO ₃ ⁻ into macromolecules was observed at 50 mM NaCl. Identification of compatible solutes with NMR-spectroscopy indicated that mannitol is the compatible solute for intact plants of Sonneratia alba, but no accumulation of mannitol was found in calluses, not even in those grown at high concentrations of NaCl.     

Mineralization of soil nitrogen in three forest communities from the New England region of New South Wales

Nitrogen (N) mineralization rates and the temperature response patterns of mineral N production in surface (0–7.6 cm) soils were compared in laboratory incubation studies based on disturbed, composite samples. Seasonal variation in the field levels of mineral N, and mineralization potential of intact (7.6 × 5.6 cm diameter) soil cores, were also investigated. Ammonification proceeded rapidly in each soil. Nitrification did not occur in grassy forest (GF) soil but was active in both layered forest (LF) and mossy forest (MF) soils, especially the former. Total mineral N production was greatest in MF and least in LF. Ammonification in disturbed samples was maximal at 50°C in all three soils with a secondary peak at 10°C in LF soil. Nitrification in LF and MF soils was most rapid at 25°C. Several species of ammonifying bacteria with different temperature optima were isolated, indicating that the process of ammonification is a composite of the activities of a variety of decomposer microbes. Mean field levels of mineral N and NH₄–N throughout the year were greatest in MF and least in LF. Seasonal fluctuations in NH₄–N were evident, concentrations being universally low in mid-winter (about 1.5 μgg^-1), increasing to a maximum in late summer (about 5 μg g^-1 in LF: 16–18 μg g^-1 in GF and MF). Field levels of NO₃–N were more constant and never more than 5 μg g^-1 in any community. Both total mineralization and ammonification in intact cores were greatest in MF and least in LF while nitrification was greatest in LF and almost negligible in GF, thus confirming the results obtained with disturbed samples. The potential for mineralization was large in mid-winter when the amount of mineral N was very low, and small in late summer when field levels were higher: this is interpreted as indicating that seasonal climatic factors regulate the availability of substrates for decomposers. Spatial variability in field levels of mineral N and mineral N production in the laboratory was evidenced by significant ‘sampling site’ effects in each community: however, at the sampling intensity used, the presence of bark mounds around Eucalyptus saligna trees could not be shown to affect these attributes. The inability of GF soil to nitrify when incubated in the laboratory could not be ascribed to a high C/N ratio, low pH, lack of substrate ammonium, or a low population of autotrophic nitrifying bacteria. No attempt was made to investigate the presence of allelopathic nitrification inhibitors. No evidence was obtained to support the view that nitrification is atypical of climax communities in situ. The most productive forest (LF) had the greatest capacity to nitrify and the least productive community (GF) the smallest capacity to do so.