Northern Hardwood Forest Soil Research Articles

Phosphate additions have no effect on microbial biomass and activity in a northern hardwood forest

High rates of atmospheric nitrogen (N) deposition have raised questions about shifting patterns of nutrient limitation in northern hardwood forests. Of particular interest is the idea that increased supply of N may induce phosphorus (P) limitation of plant and microbial processes, especially in acid soils where P sorption by Al is high. In this study, we established field plots and plant-free laboratory mesocosms with P and Ca additions to test the hypotheses that 1) microbial biomass and activity are limited by P in the northern hardwood forest soils at the Hubbard Brook Experimental Forest in NH USA; 2) elevated Ca increases inherent P availability and therefore reduces any effects of added P and 3) P effects are more marked in the more carbon (C) rich Oie compared to the Oa horizon. Treatments included P addition (50 kg P ha −1), Ca addition (850 kg Ca ha −1) and Ca + P addition (850 kg Ca ha −1 and 50 kg P ha −1). The P treatments increased resin-available P levels and reduced phosphatase activity, but had no effect on microbial biomass C, microbial respiration, C metabolizing enzymes, potential net N mineralization and nitrification in the Oie or Oa horizon of either field plots or plant free mesocosms, in either the presence or absence of Ca. Total, prokaryote, and eukaryote PLFA were reduced by P addition, possibly due to reductions in mycorrhizal fungal biomass. These results suggest that increased N deposition and acidification have not created P limitation of microbial biomass and activity in these soils.

Earthworms increase the ratio of bacteria to fungi in northern hardwood forest soils, primarily by eliminating the organic horizon

The exotic earthworm invasion in hardwood forests of the northern United States is associated with many ecosystem-level changes. However, less is known about the effects of the invasion on the composition of the soil microbial community through which ecosystem-level changes are mediated. Further, earthworm effects on soil microbial community composition have not been well studied in the field. To evaluate changes in bacterial and fungal abundance associated with the earthworm invasion we quantified bacterial and fungal biomass by microscopic counts in paired earthworm-invaded (earthworm) and earthworm-free (reference) plots in five forest stands in central New York (USA). Earthworms significantly increased the ratio of bacteria to fungi on an area basis (per m 2), by more than two times in mid-summer and early autumn. While this effect was associated primarily with the lack of the fungal-dominated organic horizon in earthworm plots, a higher ratio of bacteria to fungi in the surface 5 cm mineral soil also contributed as it developed between spring and mid-summer. Earthworm reduction of fungal biomass was confirmed by substantially lower growth of fungal hyphae into mesh sand bags in earthworm compared to reference plots. Burrowing activity by the earthworm Lumbricus terrestris increased the ratio of bacteria to fungi over the short-term within earthworm plots, introducing small-scale spatial heterogeneity associated with burrows. Our study suggests that the exotic earthworm invasion in these northern hardwood forests markedly increased the ratio of bacteria to fungi by eliminating the fungal-rich organic horizon, and was associated localized increases in bacterial vs. fungal abundance in mineral soil, setting the stage for future research into linkages between the earthworm invasion, bacterial and fungal abundance, and ecosystem processes.

Effects of the invasive plant garlic mustard (Alliaria petiolata) on bacterial communities in a northern hardwood forest soil

We compared the effects of the invasive plant Alliaria petiolata (garlic mustard) and 2 native plants on soil bacterial communities in a mature mesophytic forest. Soil samples were collected from plant patches containing either Alliaria or the native plants Allium tricoccum (wild leek) and Gallium triflorum (bedstraw). Since Alliaria litter contains secondary compounds that have reported antimicrobial properties, soil was collected outside the root zone of the plants but within the plant patches such that the soil would have been influenced by the litter of the respective plant species but not by plant roots. DNA was extracted from the soil samples and used to amplify the 16S rRNA gene region using bacterial specific primers. Terminal restriction fragment length polymorphism (TRFLP) profiles of each bacterial community were used to examine differences in bacterial communities among the plant species and between August and April sampling. Bacterial richness, evenness, and diversity were not significantly affected by plant species. Non-metric multidimensional scaling (NMS) suggested that differences existed between August and April sampling, but that plant species litter exerted a much weaker effect on soil bacterial communities. Soil physiochemical conditions were significantly correlated with soil bacterial communities and may underlie the observed seasonal changes in bacterial communities.

The Influence of Soil Fertility on Rhizosphere Effects in Northern Hardwood Forest Soils

Enhanced levels of microbial biomass and activity in the rhizosphere arise from labile C released from roots but the factors that mediate such “rhizosphere effects” are poorly understood. We hypothesized that the magnitude of rhizosphere effects would be reduced by increases in soil fertility, consistent with plant C allocation theory, which predicts decreased C flux to roots in fertile soils. Replicate plots of sugar maple (Acer saccharum Marshall) and northern red oak (Quercus rubra L.) at the Turkey Hill Plantations, New York, and yellow birch (Betula allenghaniensis Britton) at the Hubbard Brook Experimental Forest, New Hampshire, were fertilized from 2001 to 2003. In fall of 2003, rhizosphere and bulk soils were sampled from the organic horizon of control and fertilized plots and analyzed for microbial biomass and nutrient transformation rates. In general, fertilization reduced microbial biomass and activity in plots of all three species, and the magnitude of such effects was generally greater in rhizosphere than in bulk soil. In red oak soils, fertilization reduced rhizosphere effects on microbial biomass, net N mineralization rates, and phosphatase enzyme activity (P = 0.026, 0.091, and 0.061, respectively). In contrast, fertilization only reduced rhizosphere effects on microbial biomass in sugar maple soils (P = 0.019). In yellow birch soils, fertilization decreased rhizosphere effects on microbial biomass (P = 0.015). These results suggest that soil fertility may mediate the degree to which roots affect microbial activity in forest soils, possibly due to fertilizer‐induced shifts in belowground C supply.

Chronic experimental [formula omitted] deposition reduces the retention of leaf litter DOC in a northern hardwood forest soil

In forests of the Great Lakes region, experimental NO 3 − deposition has suppressed soil respiration and enhanced DOC export. Reasons for these responses are unknown, but they could arise via two alternatives: (i) direct suppression of microbial activity by NO 3 − or (ii) indirect suppression of the microbial community via changes in litter biochemistry in response to greater N availability. To test the second alternative, we conducted a controlled laboratory experiment to examine how chronic experimental NO 3 − deposition affects the contributions of fresh leaf litter to microbial respiration and DOC export. The study reported here used manipulations of mineral soil and fresh leaf litter from a previously studied northern hardwood forest stand in northern Lower Michigan that has received 9 years of ambient and experimental (three times ambient) atmospheric NO 3 − deposition. We found that cumulative microbial respiration over the 6-week incubation was substantially greater in fresh litter plus mineral soil (20.2–13.4 mg C) versus mineral soil alone (4.4–4.1 mg C); however, experimental NO 3 − deposition had no effect on microbial respiration across the litter–mineral soil manipulations. DOC production (∼75%) was primarily associated with leaching from fresh litter. In contrast, mineral soil was a significant sink for litter-derived DOC. Significantly, the mineral soil sink was less pronounced in soil receiving experimental NO 3 − deposition in which ∼30% more DOC was leached compared to the ambient NO 3 − deposition treatment. Furthermore, mineral soil was also both a source and sink for soluble phenolics; however, NO 3 − deposition suppressed a mineral–soil sink for phenolics derived from fresh leaf litter. These results suggest that increases in DOC export and declines in soil respiration in response to NO 3 − deposition in the field are not related to obvious changes in litter biochemistry or to the microbial metabolism of this material. Alternatively, these patterns may be linked to decreased abiotic sinks for litter-derived DOC in mineral soil, an unexpected ecosystem consequence of increased anthropogenic ( NO 3 − ) deposition.

Influence of nonnative earthworms on mycorrhizal colonization of sugar maple (Acer saccharum).

• Exotic earthworms can modify or eliminate surface organic (Oe/Oa) horizons in cold-temperate forest ecosystems and have profound effects on the forest soil environment, especially the rooting zone. • We examined the effects of earthworm colonization of northern hardwood forest soils on the abundance and morphology of mycorrhizal fungi associated with sugar maple ( Acer saccharum ). We compared mycorrhizal associations of areas of earthworm invasion with those of reference (no-worm) areas in Arnot Forest, central New York, USA. • The organic horizon in reference areas had higher mycorrhizal colonization rates and higher colonized root length than did surface layers in areas with active earthworm populations. Hyphal coils were more abundant and also formed a greater proportion of total fungal colonization in reference plots. Vesicles were more abundant and were a higher contribution to total colonization in earthworm plots, indicating a possible stress response to the presence of earthworms. • By affecting mycorrhizal colonization and morphology, earthworms may influence nutrient uptake capacity of dominant forest species. Our results suggest that a profound change in the mycorrhizal system will be one component of the potential ecosystem effects of invasion of new forest habitat by nonnative earthworms.

Characterization of organic matter in a northern hardwood forest soil by 13C NMR spectroscopy and chemical methods

Soil organic matter plays an important role in soil properties and influences ecosystem cycles of C, N, Al, Fe, and other major and trace elements. We examined spatial variations in the structure and chemistry of soil organic matter at the Hubbard Brook Experimental Forest in New Hampshire, USA. Humic substances were extracted and isolated chromatographically into humic acid, fulvic acid, and polysaccharide fractions. Chemical methods and solid-state 13C NMR spectroscopy were used to determine structural chemistry. On average, extractable humic substances accounted for nearly 50% of soil organic matter, with alkyl and O-alkyl C (carbohydrate) being the largest C fractions in whole soils and isolated humic substances. Alkyl C ranged from 33% to 56% of C, while O-alkyl C comprised 20–45% of C. Alkyl C increased, while O-alkyl C decreased with soil depth in whole soils, humin, and humic acid. Aromatic C increased with soil depth in whole soils and humin, while carbonyl C increased with depth in whole soils and fulvic acids. Fulvic acids were more acidic than humic acids, and were less phenolic and aliphatic than humic acids. Carboxylic acidity accounted for about 80% and 50% of total acidity in fulvic acid and humic acid, respectively. Soil from higher-elevation sites exhibited greater alkyl C and lower O-alkyl and aromatic C in the Oa horizon, suggesting a greater degree of decomposition of the organic matter in the Oa horizon of these conifer-rich sites. Mineral soils in conifer-rich sites contained organic matter that was more aromatic than in hardwood sites. Variations in humification processes, source materials, and transport of organic matter could account for variations in the structure and chemistry of organic matter in these forest soils.

Freezing Effects on Carbon and Nitrogen Cycling in Northern Hardwood Forest Soils

We evaluated the effects of freeze–thaw events on soil respiration, nitrogen mineralization, nitrification, and nitrous oxide production in soils from a northern hardwood‐dominated forest in New Hampshire, USA. Soil samples from three horizons (Oe, Oa, A) from nearly monospecific stands of sugar maple (Acer saccharumMarshall) and yellow birch (Betula alleghaniensisBritton) were placed in 200‐mL incubation vessels (microlysimeters), subjected to severe (−13°C) and mild (−3°C) freeze treatments for 10 d, and then incubated at laboratory temperature (20–25°C) for 3 wk. Evolution of CO2and N2O and concentrations of leachable NH+4and NO−3were measured at weekly intervals. Freezing increased rates of C and N cycling in these soils, but the effects varied with species, horizon, and freeze treatment. Whereas severe freezing stimulated respiration, N2O flux, and mineralization, mild freezing had very few effects. Nitrification did not appear to be affected by either freeze treatment, but increases in denitrification may have masked freeze effects on this process. Freeze effects were much more marked in maple than in birch soils and in the Oaand A horizons. Maple consistently had higher rates of nitrification and N2O production than did birch. The species and horizon differences were likely driven by higher levels of available C in the birch soils and Oehorizon at both sites. These results suggest that changes in climate and snow cover that influence soil freezing could increase N and C losses from northern hardwood forest ecosystems with potential effects on soil fertility and carbon storage, receiving water quality, and atmospheric chemistry.

Carbon additions increase nitrogen availability in northern hardwood forest soils

The effects of acetate additions to northern hardwood forest soils on microbial biomass carbon (C) and nitrogen (N) content, soil inorganic N levels, respirable C and potential net N mineralization and nitrification were evaluated. The experiment was relevant to a potential watershed-scale calcium (Ca) addition that aims to replace Ca depleted by long-term exposure to acid rain. One option for this addition is to use calcium-magnesium (Mg) acetate, a compound that is inexpensive and much more readily soluble than the Ca carbonate that is generally used for large-scale liming. Field plots were treated with sodium (NA) acetate, Na bicarbonate or water (control) and were sampled (forest floor – Oe and Oa combined) 2, 10 and 58 days following application. It was expected that the addition of C would lead to an increase in biomass C and N and a decrease in inorganic N. Instead, we observed no effect on biomass C, a decline in biomass N and an increase in N availability. One possible explanation for our surprising results is that the C addition stimulated microbial activity but not growth. A second, and more likely, explanation for our results is that the C addition did stimulate microbial growth and activity, but there was no increase in microbial biomass due to predation of the new biomass by soil fauna. The results confirm the emerging realization that the effects of increases in the flow of C to soils, either by deliberate addition or from changes in atmospheric CO2, are more complex than would be expected from a simple C : N ratio analysis. Evaluations of large-scale manipulations of forest soils to ameliorate effects of atmospheric deposition or to dispose of wastes should consider microbial and faunal dynamics in considerable detail.

Effects of acid anion additions (trifluoroacetate and bromide) on soil solution chemistry of a northern hardwood forest soil

Experimental plots within the Hubbard Brook Experimental Forest, NH, were treated with sodium trifluoroacetate (TFA) and lithium bromide (Br), to study the impact of TFA alone and in the presence of increased anion concentrations (e.g. acid deposition) on the soil solution chemistry of a northern hardwood forest soil. Trifluoroacetate is a major atmospheric degradation product of replacement compounds of chlorofluorocarbons (CFC) and Br is widely used as a hydrologic tracer. Calculated drainage losses via soil water flow were less than 60% of inputs, added during the summer, and TFA and Br were temporarily retained in the soil until fall. The initial indication of an acid input of the treatments (HTFA, HBr) in the Bs2 horizon, which reflects stream water chemistry as well, was an increase of base cations in the soil solution, decreasing the soil's acid neutralizing capacity. Thereafter, trifluoroacetate and Br concentrations peaked after the peak in base cations, synchronous with peaks in H+ and Al concentrations. Organic anions, nitrate and chloride played the major role in accompaning base cations out of the solum. Sulfate retention at soil adsorption sites was increased by the presence of TFA and Br, reducing its role as a mobile anion of base cations in this experiment. Relative retention of anions for the whole profile of this northern hardwood forest soil was estimated by correlation analyses and input-output balances in decreasing order on an equivalant basis: SO4 > TFA = Br ≥ Cl > NO3 > organic anions. Recovery from acid additions were recorded within several weeks after the treatments were stopped. Evaluating the impact of added chemical compounds to soils must be considered within the context of linkages among element cycles and pools.

Trifluoroacetate Retention in a Northern Hardwood Forest Soil

Chlorofluorocarbons (CFCs) catalyze the breakdown of stratospheric ozone. As a result, international agreements now require the use of CFCs to be discontinued. Trifluoroacetate (TFA) is formed as a...

Soil disturbance and elemental dynamics in a Northern Hardwood forest soil, USA

Loss of soil nutrients due to disturbance may serve as an index of the homeostasis of biogeochemical cycling and ecosystem stability. Soil and the surrounding root system were disturbed during the installation of Soil Containment Systems (SCSs) in the hill slope at the Bear Brook Watershed in Maine (BBWM). The SCSs were constructed from high density PVC pipe (24 cm i.d. and 30 cm height) implanted at field. Leachate cations and anions, soil organic matter and exchangeable cations were analyzed. Leachate NO3− was higher by an order of magnitude compared to undisturbed soils from the same research site and other hardwood forest soils in the northeast U.S. The concentrations of cations in the leachate from SCSs were also higher and loss of NO3− was positively correlated with the loss of most cations. Calcium was the dominant cation representing 55% of the base cation composition of soil leachate. Monthly losses of Ca2+, Mg2+ and K+ were 1.8, 1.6 and 1.2% of total exchangeable pools, respectively. Disturbance of the BBWM soil ecosystem caused high rates of NO3− leaching which markedly changed the soil biogeochemistry. These results and other supporting data from watershed mass balances and experimental chemical additions suggest that BBWM may be N saturated.

Nitrogen Retention Capacity of a Northern Hardwood Forest Soil Under Ammonium Sulfate Additions

To determine the N‐retaining capacity of a beech‐dominated stand in the Hubbard Brook Experimental Forest, we added (NH4)2SO4 at three levels (40, 160 and 520 kg N°ha‐1°yr‐1) to replicate plots in monthly increments for two years, and measured NH4+ and NO3‐ concentrations in monthly samples from zero‐tension lysimeters. The two lower treatment levels failed to increase N loss through the deepest soils horizon when compared to controls. Plots under the highest treatment level retained >95% of the added N; NH4+ accounted for 77% of the leaching loss. The treatments caused an accumulation of exchangeable NH4+ in the soil, but concentrations of exchangeable NO3‐ remained small, even after samples were incubated at room temperature. Leaching, uptake by plants, and the increase exchangeable NH4+ accounted for 3‐25% of the added N. Accumulation of available N without nitrification contradicts common expectations concerning N saturation. It was not clear why excess N was not nitrified.

Sulfur speciation, vertical distribution, and seasonal variation in a northern hardwood forest soil, U.S.A

Sulfur biogeochemistry of a northern hardwood forest soil in Bear Brook Watershed, Maine, was studied utilizing 35S in situ. The objectives of study were to characterize different S pools, their vertical distribution, and seasonal variation. Soil cores were used at the field and treated with 35SO42−. The distribution of total and C-bonded S followed a typical pattern of decreasing concentration with soil depth. More than 86% of total 35S added was retained by the soil. Most of the 35S activity was in the organic S pool (up to 73 and 20% of total 35S in C-bonded S and ester-sulfate forms, respectively) in both the forest floor and the mineral soil horizons. Ester sulfate increased with depth from 5.3 to 25.5% of total S. During the summer the relative importance of mineralization to immobilization decreased. Inorganic sulfate was the smallest S pool. However, higher specific activity and turnover rate of the inorganic 35SO42− pool than organic 35S pool indicated that S concentration and solution flux were more regulated by abiotic (adsorption and desorption) than biotic (mineralization and immobilization) processes.

Harvesting Causes Only Minor Changes in Physical Properties of an Upland Vermont Soil

Abstract Bulk density, oxygen, and temperature of a northern hardwood forest soil in Vermont were measured immediately before and for 2 years following harvesting using conventional clear-cut and whole-tree removal methods. Bulk density increased (P ≤0.10) as a result of harvesting, but there was no difference between the two harvest methods. Increases were relatively small, and essentially disappeared within 2 years. Soil oxygen was never significantly affected by treatment. Soils in uncut (control) plots were warmer in winter and cooler in summer than those of either harvest area, but these differences appear to be diminishing with establishment of vegetation cover on the harvested plots.

Harvesting Causes Only Minor Changes in Physical Properties of an Upland Vermont Soil

Abstract Bulk density, oxygen, and temperature of a northern hardwood forest soil in Vermont were measured immediately before and for 2 years following harvesting using conventional clearcut and whole-tree removal methods. Bulk density increased (P ≤ 0.10) as a result of harvesting, but there was no difference between the two harvest methods. Increases were relatively small, and essentially disappeared within 2 years. Soil oxygen was never significantly affected by treatment. Soils in uncut (control) plots were warmer in winter and cooler in summer than those of either harvest area, but these differences appear to be diminishing with establishment of vegetation cover on the harvested plots. North. J. Appl. For 8(1):33-36.

Estimating Soil Nitrogen and Carbon Pools in a Northern Hardwood Forest Ecosystem

AbstractAn intensive soil sampling design was evaluated to determine what resolution could be obtained in N and C pool size estimates in a northern hardwood forest soil. Pits of measured volume were excavated by horizon in the forest floor and in three depth strata in the mineral soil. Future comparisons should be able to detect differences in N and C pool sizes ranging from 8 to 25% of the observed mean values depending upon the element and depth strata. Future sampling should detect changes of 230 and 130 kg N ha−1 in the forest floor (combined O horizons) and 0‐ to 10‐cm stratum in the mineral soil respectively. Similarly, changes of 5.9 and 2.4 Mg C ha−1 should be detectable for forest floor and 0 to 10 cm pools respectively. Soil N content for the forest floor was 1300 kg N ha−1. For the mineral soil depth strata (0–10 cm, 10–20 cm, 20 cm to the bottom of the B horizon), N contents were 1600, 1200 and 3100 kg N ha−1 respectively. Total solum N content was estimated to be 7200 kg N ha−1. Soil C contents for the combined O horizons, 0‐ to 10‐, 10‐ to 20‐ and ≥ 20‐cm strata were 30, 32, 27 and 73 Mg C ha−1 respectively. The total solum C content was estimated to be 160 Mg C ha−1. Concentrations of soil N and C were positively correlated with elevation over the 240 m range studied, but soil pools of N and C were not correlated with elevation or soil mapping unit.