Christopher Eagar

Mycorrhizal weathering of apatite as an important calcium source in base-poor forest ecosystems

The depletion of calcium in forest ecosystems of the northeastern USA is thought to be a consequence of acidic deposition and to be at present restricting the recovery of forest and aquatic systems now that acidic deposition itself is declining. This depletion of calcium has been inferred from studies showing that sources of calcium in forest ecosystems—namely, atmospheric deposition and mineral weathering of silicate rocks such as plagioclase, a calcium-sodium silicate—do not match calcium outputs observed in forest streams. It is therefore thought that calcium is being lost from exchangeable and organically bound calcium in forest soils. Here we investigate the sources of calcium in the Hubbard Brook experimental forest, through analysis of calcium and strontium abundances and strontium isotope ratios within various soil, vegetation and hydrological pools. We show that the dissolution of apatite (calcium phosphate) represents a source of calcium that is comparable in size to known inputs from atmospheric sources and silicate weathering. Moreover, apatite-derived calcium was utilized largely by ectomycorrhizal tree species, suggesting that mycorrhizae may weather apatite and absorb the released ions directly, without the ions entering the exchangeable soil pool. Therefore, it seems that apatite weathering can compensate for some of the calcium lost from base-poor ecosystems, and should be considered when estimating soil acidification impacts and calcium cycling.

RESPONSE OF SUGAR MAPLE TO CALCIUM ADDITION TO NORTHERN HARDWOOD FOREST

Watershed budget studies at the Hubbard Brook Experimental Forest (HBEF), New Hampshire, USA, have demonstrated high calcium depletion of soil during the 20th century due, in part, to acid deposition. Over the past 25 years, tree growth (especially for sugar maple) has declined on the experimental watersheds at the HBEF. In October 1999, 0.85 Mg Ca/ha was added to Watershed 1 (W1) at the HBEF in the form of wollastonite (CaSiO3), a treatment that, by summer 2002, had raised the pH in the Oie horizon from 3.8 to 5.0 and, in the Oa horizon, from 3.9 to 4.2. We measured the response of sugar maple to the calcium fertilization treatment on W1. Foliar calcium concentration of canopy sugar maples in W1 increased markedly beginning the second year after treatment, and foliar manganese declined in years four and five. By 2005, the crown condition of sugar maple was much healthier in the treated watershed as compared with the untreated reference watershed (W6). Following high seed production in 2000 and 2002, the density of sugar maple seedlings increased significantly on W1 in comparison with W6 in 2001 and 2003. Survivorship of the 2003 cohort through July 2005 was much higher on W1 (36.6%) than W6 (10.2%). In 2003, sugar maple germinants on W1 were approximately 50% larger than those in reference plots, and foliar chlorophyll concentrations were significantly greater (0.27 g/m2 vs. 0.23 g/m2 leaf area). Foliage and fine-root calcium concentrations were roughly twice as high, and manganese concentrations twice as low in the treated than the reference seedlings in 2003 and 2004. Mycorrhizal colonization of seedlings was also much greater in the treated (22.4% of root length) than the reference sites (4.4%). A similar, though less dramatic, difference was observed for mycorrhizal colonization of mature sugar maples (56% vs. 35%). These results reinforce and extend other regional observations that sugar maple decline in the northeastern United States and southern Canada is caused in part by anthropogenic effects on soil calcium status, but the causal interactions among inorganic nutrition, physiological stress, mycorrhizal colonization, and seedling growth and health remain to be established.

Ecology and decline of red spruce in the eastern United States.

This book focuses on the recent decline of red spruce and the role of acid rain and associated air pollutants in this decline. The purpose of the book is to summarize a large body of recent research on this important environmental issue. The book is divided into three sections: section one summarizes the features of spruce-fir forests in the eastern U.S. and examines the ecology of the forests, their soils, and the atmospheric conditions experienced by these forests. Section two looks at experimental results from many air pollution studies and evaluates mechanisms of air pollution effects on red spruce trees. Section three synthesizes the current state of knowledge regarding the widespread red spruce decline in forests of the eastern United States.

Calcium Additions and Microbial Nitrogen Cycle Processes in a Northern Hardwood Forest

Evaluating, and possibly ameliorating, the effects of base cation depletion in forest soils caused by acid deposition is an important topic in the northeastern United States. We added 850 kg Ca ha−1 as wollastonite (CaSiO3) to an 11.8-ha watershed at the Hubbard Brook Experimental Forest (HBEF), a northern hardwood forest in New Hampshire, USA, in fall 1999 to replace calcium (Ca) leached from the ecosystem by acid deposition over the past 6 decades. Soil microbial biomass carbon (C) and nitrogen (N) concentrations, gross and potential net N mineralization and nitrification rates, soil solution and stream chemistry, soil:atmosphere trace gas (CO2, N2O, CH4) fluxes, and foliar N concentrations have been monitored in the treated watershed and in reference areas at the HBEF before and since the Ca addition. We expected that rates of microbial C and N cycle processes would increase in response to the treatment. By 2000, soil pH was increased by a full unit in the Oie soil horizon, and by 2002 it was increased by nearly 0.5 units in the Oa soil horizon. However, there were declines in the N content of the microbial biomass, potential net and gross N mineralization rates, and soil inorganic N pools in the Oie horizon of the treated watershed. Stream, soil solution, and foliar concentrations of N showed no response to treatment. The lack of stimulation of N cycling by Ca addition suggests that microbes may not be stimulated by increased pH and Ca levels in the naturally acidic soils at the HBEF, or that other factors (for example, phosphorus, or Ca binding of labile organic matter) may constrain the capacity of microbes to respond to increased pH in the treated watershed. Possible fates for the approximately 10 kg N ha−1 decline in microbial and soil inorganic pools include components of the plant community that we did not measure (for example, seedlings, understory shrubs), increased fluxes of N2 and/or N storage in soil organic matter. These results raise questions about the factors regulating microbial biomass and activity in northern hardwood forests that should be considered in the context of proposals to mitigate the depletion of nutrient cations in soil.

Hydrometeorological database for Hubbard Brook Experimental Forest: 1955-2000

The 3,160-ha Hubbard Brook Experimental Forest (HBEF) in New Hampshire has been a prime area of research on forest and stream ecosystems since its establishment by the USDA Forest Service in 1955. Streamflow and precipitation have been measured continuously on the HBEF, and long-term datasets exist for air and soil temperature, snow cover, soil frost, solar radiation, windspeed and direction, and humidity. This information has provided the basis for hundreds of publications by Forest Service and cooperating scientists on numerous aspects of forest hydrology research as part of the ongoing Hubbard Brook Ecosystem Study. This report updates the tables, methods, watershed descriptions, and other pertinent data in ?Thirty Years of Hydrometeorological Data at the Hubbard Brook Experimental Forest, New Hampshire? (General Technical Report NE-141).

Nor Gloom of Night: A New Conceptual Model for the Hubbard Brook Ecosystem Study

Abstract The great challenge now facing forest ecosystem scientists and managers is to address the need for multiple ecosystem services over relatively large spatial and temporal scales (e.g., whole national forests over 50- to 100-year time frames). Here we present a new conceptual model for the study of forest ecosystems that aids in the analysis of factors that influence ecosystem structure, function, and services. We then go on to show how this model has been applied to the long-term Hubbard Brook Ecosystem Study. Our new model has three main components: (1) controllers, (2) ecosystem pattern and process, and (3) ecosystem functions and services. The controllers are the factors that drive ecosystem pattern and process; we split them into two groups, state factors and variable–stochastic factors. This new model will help to ensure a comprehensive approach to forest ecosystem analysis and will facilitate interactions of research with policy and management at many locations.

Analysis of Nitrogen Dynamics in the Lye Brook Wilderness Area, Vermont, USA

Nitrogen (N) deposition and its impact on terrestrial and aquatic ecosystems is a concern facing federal land managers at the Lye Brook Wilderness in Vermont and other protected aras throughout the northeastern United States. In this study, we compared N production in soils with N concentrations and outputs in leachates to determine how forest cover types differ in regulating N losses. Also, precipitation inputs and modeled estimates of streamwater outputs were used to calculate a watershed N budget. Most ammonium and nitrate were produced in organic soils with deciduous cover. Softwood stands had low net nitrification rates and minimal N leaching. A comparison of watershed inputs and outputs showed a net gain in total dissolved N (5.5 kg ha-1 yr-1) due to an accumulation of dissolved inorganic N. The Lye Brook Wilderness ecosystem has N budgets similar to other forested ecosystems in the region, and appears to be assimilating the accumulating N. However seasonal losses of nitrate observed in mineral soils and streamwater may be early warnings of the initial stages of N saturation.

Calcium addition at the Hubbard Brook Experimental Forest increases the capacity for stress tolerance and carbon capture in red spruce (Picea rubens) trees during the cold season

Red spruce (Picea rubens Sarg.) trees are uniquely vulnerable to foliar freezing injury during the cold season (fall and winter), but are also capable of photosynthetic activity if temperatures moderate. To evaluate the influence of calcium (Ca) addition on the physiology of red spruce during the cold season, we measured concentrations of foliar polyamines and free amino acids (putative stress-protection compounds), chlorophyll (a key photosystem component), and sapwood area (a proxy for foliar biomass), for trees in Ca-addition (CaSiO3 added) and Ca-depleted (reference) watersheds at the Hubbard Brook Experimental Forest (NH, USA). Ca-addition increased concentrations of the amino acids alanine and γ-aminobutyric acid (GABA) and the polyamines putrescine (Put) and spermidine (Spd) in November, and Put in February relative to foliage from the reference watershed. Consistent with increased stress protection, foliage from the Ca-addition watershed had higher total chlorophyll and chlorophyll a concentrations in February than foliage from the reference watershed. In contrast, foliage from the reference watershed had significantly lower glutamic acid (Glu) and higher alanine (Ala) concentrations in February than foliage from the Ca-addition watershed. Imbalances in Ala:Glu have been attributed to cold sensitivity or damage in other species. In addition to concentration-based differences in foliar compounds, trees from the Ca-addition watershed had higher estimated levels of foliar biomass than trees from the reference watershed. Our findings suggest that Ca-addition increased the stress tolerance and productive capacity of red spruce foliage during the cold season, and resulted in greater crown mass compared to trees growing on untreated soils.

Impacts of acidic deposition on high-elevation spruce-fir forests: results from the Spruce-Fir Research Cooperative

Abstract Large numbers of standing dead red spruce trees in high-elevation spruce-fir forests of the northeastern US, coupled with nearly synchronous decreases in radial growth, have caused much concern and have been linked with elevated levels of air pollutants. These high-elevation forests, frequently immersed in clouds, receive a significant amount of sulfate and nitrate from cloudwater deposition. The Spruce-Fir Research Cooperative, (SFRC), an integrated multi-institutional research program, is investigating a number of hypothesized effects of acidic deposition on the spruce-fir forests including: (1) soil-mediated effects: (2) altered physiological processes: (3) increased foliar injury: (4) increased susceptibility to winter injury. Major conclusions of the SFRC research will be presented in this paper. In the northeastern US, spruce-fir forests are experiencing visible decline, with large numbers of standing dead trees (> 50% on some mountains). Results from a number of research projects suggest red spruce is particularly sensitive to winter injury, that cloudwater inputs increase that susceptibility, and that repeated winter injury may play a role in red spruce decline in the northeastern US. Increased rates of dark respiration, reduced photosynthesis, and reduced foliar chlorophyll levels have been measured for red spruce at sites receiving high cloudwater deposition in the southern Appalachians relative to trees receiving lower deposition, and these physiological changes may be contributing to reduced growth of red spruce saplings. Effects of acid anion deposition on soil aluminum levels could have important implications for soil and tissue cation levels. The relative role of the particular mechanisms associated with acidic deposition may vary with natural biotic and abiotic factors.

Response from driscoll and colleagues

Author(s): CHARLES T. DRISCOLL, GREGORY B. LAWRENCE, ARTHUR J. BULGER, THOMAS J. BUTLER, CHRISTOPHER S. CRONAN, CHRISTOPHER EAGAR, KATHLEEN F. LAMBERT, GENE E. LIKENS, JOHN L. STODDARD, and KATHLEEN C. WEATHERS Source: BioScience, Vol. 52, No. 1 (January 2002), p. 6 Published by: University of California Press on behalf of the American Institute of Biological Sciences Stable URL: http://www.jstor.org/stable/10.1641/00063568%282002%29052%5B0006%3ARFDAC%5D2.0.CO%3B2 . Accessed: 10/12/2013 12:32