The objectives of the workshop were to (1) develop a conceptual model of ecosystem response to gl... more The objectives of the workshop were to (1) develop a conceptual model of ecosystem response to global warming, and (2) use meta-analysis to evaluate the response of soil respiration, N mineralization, and plant growth to experimental increases in temperature at 25 independent research sites. These sites represented six biomes, including broadleaf deciduous forests, needleleaf evergreen forests, perennial grasslands, tundra , polar deserts, and peatlands. Warming technologies included ground cables, closed chambers, open-top chambers, infra-red heaters, night warming, Final Report: 9730110 and natural gradients. The workshop was attended by forty-two participants representing twelve countries (
Inferring regional patterns and responses in N and Hg biogeochemistry using two sets of gauged pa... more Inferring regional patterns and responses in N and Hg biogeochemistry using two sets of gauged paired-watersheds ... University of Maine Investigators: Steve Kahl, Director, Water Research Institute ([email protected]) Ivan Fernandez, Professor of Soil Science Stephen Norton, ...
Page 1. Ecologv, 75(4), 1994, pp. 867-879 fc) 1994 by the Ecological Society of America ELEMENT D... more Page 1. Ecologv, 75(4), 1994, pp. 867-879 fc) 1994 by the Ecological Society of America ELEMENT DYNAMICS ALONG A DECAY CONTINUUM IN A RED SPRUCE ECOSYSTEM IN MAINE, USA' LINDSEY E. RUSTAD Department ...
Bulletin of the American Meteorological Society, Jul 1, 2023
Freezing rain scientists and stakeholders generated a road map of risk-relevant knowledge gaps in... more Freezing rain scientists and stakeholders generated a road map of risk-relevant knowledge gaps in freezing rain science and critical avenues to fill those gaps.
3. The superlattice structure appears to enhance the transport of currentcarrying electrons (and ... more 3. The superlattice structure appears to enhance the transport of currentcarrying electrons (and holes) while inhibiting transport of heat-carrying phonons (quantized vibrations of the crystal lattice). Both effects boost ZT. When the modern era of thermoelectric science and technology began to emerge in the late 1950s, it seemed possible that thermoelectrics might approach the efficiency of mechanical refrigerators and power generators. By the 1970s, given the lack of progress, few thought it likely. There was even speculation that a ZT of 1 represented some sort of thermoelectric barrier. Certainly it was an empirical limit that nearly halted research and development. But in the early 1990s Rudolph Buser, then associated with the United States Army Night and Electro-Optics Directorate, called on scientists to reexamine thermoelectrics. A basic science programme to increase ZT was soon underway, with support principally from the US Navy's Office of Naval Research and DARPA (Defense Advanced Research Projects Agency). By the late 1990s there was some progress, but even then you had to be an optimist to believe the barrier had been broken 2 .
Tissue concentrations of A1 in red and Norway spruce trees were compared across 5 sites in North ... more Tissue concentrations of A1 in red and Norway spruce trees were compared across 5 sites in North America and Europe as part of an investigation of A1 biogeochemistry in forested ecosystems (ALBIOS). Fine roots and foliage were sampled and analyzed for A1, Ca, Mg, and P, and the chemistry of soil and soil solutions was characterized at each plot by horizon. Sites exhibited a wide range in soil AI saturation and in concentrations of A1 and sulfate in lysimeter solutions. Aluminium concentrations in roots were two orders of magnitude higher than those in foliage. Fine roots (< 1.0 mm) from B horizons had the highest A1 concentrations and appeared to be the best phytoindicators of plant-available A1. Aluminium concentrations in free roots from B horizons were highly correlated with soil solution monomeric A1, and with A1 in 0.01 M SrC12 soil extracts. Stronger soil A1 extractants were generally poor predictors of concentrations of A1 in plant tissue. Sites with higher levels of plant-available A1 supported spruce trees with correspondingly lower foliar levels of Ca and Mg. As such, these field sites provided circumstantial evidence that AI may be interfering with Ca and Mg uptake and transport. No evidence was found of A1 interference with P uptake or transport at these sites.
Accumulating evidence points to an anthropogenic 'fingerprint' on the global climate change that ... more Accumulating evidence points to an anthropogenic 'fingerprint' on the global climate change that has occurred in the last century. Climate change has, and will continue to have, profound effects on the structure and function of terrestrial ecosystems. As such, there is a critical need to continue to develop a sound scientific basis for national and international policies regulating carbon sequestration and greenhouse gas emissions. This paper reflects on the nature of current global change experiments, and provides recommendations for a unified multidisciplinary approach to future research in this dynamic field. These recommendations include: (1) better integration between experiments and models, and amongst experimental, monitoring, and space-for-time studies; (2) stable and increased support for long-term studies and multi-factor experiments; (3) explicit inclusion of biodiversity, disturbance, and extreme events in experiments and models; (4) consideration of timing vs intensity of global change factors in experiments and models; (5) evaluation of potential thresholds or ecosystem 'tipping points'; and (6) increased support for model-model and model-experiment comparisons. These recommendations, which reflect discussions within the TERACC international network of global change scientists, will facilitate the unraveling of the complex direct and indirect effects of global climate change on terrestrial ecosystems and their components.
Forest and Rangeland Soils of the United States Under Changing Conditions, 2020
Box Fig. 9.2 Outline of the development of Ecological Classification System (ECS) land type phase... more Box Fig. 9.2 Outline of the development of Ecological Classification System (ECS) land type phase (LTP) concepts and modeling data used for mapping these concepts. Soil maps are a key component in this process Box 9.1 (continued)
Frontiers in forests and global change, Feb 26, 2021
Large-scale disturbances such as ice storms may increase in frequency and intensity as climate ch... more Large-scale disturbances such as ice storms may increase in frequency and intensity as climate changes. While disturbances are a natural component of forest ecosystems, climatically driven alteration to historical patterns may impart fundamental change to ecosystem function. At Hubbard Brook Experimental Forest, NH, experimental ice storms of varying severity were applied to replicate plots of mature northern hardwoods to quantify their effects on forested ecosystems. We assessed ice storm treatment effects on insectivorous foliage-gleaning birds and evaluated insectivore predation on model caterpillars in the understory vegetation. These birds are charismatic, of conservation concern, and are major predators of caterpillars. In turn, lepidopterans are the dominant herbivores in temperate forests and are integral to ecosystem function. We predicted that avian abundance would increase due to additional structural heterogeneity caused by ice treatments, with a concomitant increase in caterpillar predation. Point counts were used to measure insectivorous bird activity in the ice storm experiment plots and additional control plots before and after treatments. We deployed and retrieved plasticine model caterpillars and estimated predation from characteristic marks to these surrogates. Abundance of foliage-gleaning birds was higher in the ice storm plots and birds responded to treatments as a single diffuse disturbance rather than on an individual plot level. All species except one were observed both before and after the ice treatments. Surprisingly, predation on caterpillar models was unaffected by ice storm treatments but rather was a function of caterpillar density. The increase in avian abundance in the ice storm treatment plots corroborates other studies of bird responses to relatively small-scale disturbances in forests and the limited change in species composition was expected given the plot size. We conclude that ice storms may provide beneficial changes for foliage-gleaning birds in the growing season following the disturbance.
In the Northeastern U.S., drought is expected to increase in frequency over the next century, and... more In the Northeastern U.S., drought is expected to increase in frequency over the next century, and therefore, the responses of trees to drought are important to understand. There is recent debate about whether land-use change or moisture availability is the primary driver of changes in forest species composition in this region. Some argue that fire suppression from the early twentieth century to present has resulted in an increase in shade-tolerant and pyrophobic tree species that are drought intolerant, while others suggest precipitation variability as a major driver of species composition. From this debate, an emerging hypothesis is that mesophication and increases in the abundance of mesophytic genera (e.g., Acer, Betula, and Fagus) resulted in forests that are more vulnerable to drought. This review examines the published literature and factors that contribute to drought vulnerability of Northeastern U.S. forests. We assessed two key concepts related to drought vulnerability, including drought tolerance (ability to survive drought) and sensitivity (short-term responses to drought), with a focus on Northeastern U.S. species. We assessed drought-tolerance classifications for species, which revealed both consistencies and inconsistencies, as well as contradictions when compared to actual observations, such as higher mortality for drought-tolerant species. Related to drought sensitivity, recent work has focused on isohydric/ anisohydric regulation of leaf water potential. However, based on the review of the literature, we conclude that drought sensitivity should be viewed in terms of multiple variables, including leaf abscission, stomatal sensitivity, turgor pressure, and dynamics of non-structural carbohydrates. Genera considered drought sensitive (e.g., Acer, Betula, and Liriodendron) may actually be less prone to drought-induced mortality and dieback than previously considered because stomatal regulation and leaf abscission in these species are effective at preventing water potential from reaching critical thresholds during extreme drought. Independent of drought-tolerance classification, trees are prone to dieback and mortality when additional stressors are involved such as insect defoliation, calcium and magnesium deficiency, nitrogen saturation, and freeze-thaw events. Overall, our literature review shows that multiple traits associated with drought sensitivity and tolerance are important as species may rely on different mechanisms to prevent hydraulic failure and depleted carbon reserves that may lead to mortality.
Nitrogen (N) deposition is impacting the services that ecosystems provide to humanity. However, t... more Nitrogen (N) deposition is impacting the services that ecosystems provide to humanity. However, the mechanisms determining impacts on the N cycle are not fully understood. To explore the mechanistic underpinnings of N impacts on N cycle processes, we reviewed and synthesised recent progress in ecosystem N research through empirical studies, conceptual analysis and model simulations. Experimental and observational studies have revealed that the stimulation of plant N uptake and soil retention generally diminishes as N loading increases, while dissolved and gaseous losses of N occur at low N availability but increase exponentially and become the dominant fate of N at high loading rates. The original N saturation hypothesis emphasises sequential N saturation from plant uptake to soil retention before N losses occur. However, biogeochemical models that simulate simultaneous competition for soil N substrates by multiple processes match the observed patterns of N losses better than models based on sequential competition. To enable better prediction of terrestrial N cycle responses to N loading, we recommend that future research identifies the response functions of different N processes to substrate availability using manipulative experiments, and incorporates the measured N saturation response functions into conceptual, theoretical and quantitative analyses.
Climate models project an increase in mean annual air temperatures and a reduction in the depth a... more Climate models project an increase in mean annual air temperatures and a reduction in the depth and duration of winter snowpack for many mid and high latitude and high elevation seasonally snow-covered ecosystems over the next century. The combined effects of these changes in climate will lead to warmer soils in the growing season and increased frequency of soil freeze-thaw cycles (FTCs) in winter due to the loss of a continuous, insulating snowpack. Previous experiments have warmed soils or removed snow via shoveling or with shelters to mimic projected declines in the winter snowpack. To our knowledge, no experiment has examined the interactive effects of declining snowpack and increased frequency of soil FTCs, combined with soil warming in the snow-free season on terrestrial ecosystems. In addition, none have mimicked directly the projected increase in soil FTC frequency in tall statured forests that is expected as a result of a loss of insulating snow in winter. We established the Climate Change Across Seasons Experiment (CCASE) at Hubbard Brook Experimental Forest in the White Mountains of New Hampshire in 2012 to assess the combined effects of these changes in climate on a variety of pedoclimate conditions, biogeochemical processes, and ecology of northern hardwood forests. This paper demonstrates the feasibility of creating soil FTC events in a tall statured ecosystem in winter to simulate the projected increase in soil FTC frequency over the next century and combines this projected change in winter climate with ecosystem warming throughout the snow-free season. Together, this experiment provides a new and more comprehensive approach for climate change experiments that can be adopted in other seasonally snow-covered ecosystems to simulate expected changes resulting from global air temperature rise.
Litter decay in a Maine red spruce ecosystem was examined to determine the importance of decompos... more Litter decay in a Maine red spruce ecosystem was examined to determine the importance of decomposition as a recycling pathway for the trace metals Al, Mn, and Fe versus the major nutrients N, P, Ca, and Mg. The experimental design included litterbags containing the following species: red spruce (Picearubens Sarg.), red maple (Acerrubrum L.), white pine (Pinusstrobus L.), and mixtures of all three. Although decomposing litter was an important source of P, Mg, and Mn, the litter acted as a sink for Al, Fe, and N. Calcium showed a variable, species-dependent pattern. During the 2-year study, there was no net mineralization of Al, Fe, or N. The estimated net accumulations of Al and Fe during the first 24 months of litter decomposition were 0.58 and 0.50 kg ha−1, respectively. By comparison, the net accumulation of N during the same period was approximately 3.43 kg ha−1. Evidence suggests that Al and Fe accumulation are controlled by abiotic adsorption on humified litter, whereas N retention is controlled by microbial immobilization.
The objectives of the workshop were to (1) develop a conceptual model of ecosystem response to gl... more The objectives of the workshop were to (1) develop a conceptual model of ecosystem response to global warming, and (2) use meta-analysis to evaluate the response of soil respiration, N mineralization, and plant growth to experimental increases in temperature at 25 independent research sites. These sites represented six biomes, including broadleaf deciduous forests, needleleaf evergreen forests, perennial grasslands, tundra , polar deserts, and peatlands. Warming technologies included ground cables, closed chambers, open-top chambers, infra-red heaters, night warming, Final Report: 9730110 and natural gradients. The workshop was attended by forty-two participants representing twelve countries (
Inferring regional patterns and responses in N and Hg biogeochemistry using two sets of gauged pa... more Inferring regional patterns and responses in N and Hg biogeochemistry using two sets of gauged paired-watersheds ... University of Maine Investigators: Steve Kahl, Director, Water Research Institute ([email protected]) Ivan Fernandez, Professor of Soil Science Stephen Norton, ...
Page 1. Ecologv, 75(4), 1994, pp. 867-879 fc) 1994 by the Ecological Society of America ELEMENT D... more Page 1. Ecologv, 75(4), 1994, pp. 867-879 fc) 1994 by the Ecological Society of America ELEMENT DYNAMICS ALONG A DECAY CONTINUUM IN A RED SPRUCE ECOSYSTEM IN MAINE, USA&#x27; LINDSEY E. RUSTAD Department ...
Bulletin of the American Meteorological Society, Jul 1, 2023
Freezing rain scientists and stakeholders generated a road map of risk-relevant knowledge gaps in... more Freezing rain scientists and stakeholders generated a road map of risk-relevant knowledge gaps in freezing rain science and critical avenues to fill those gaps.
3. The superlattice structure appears to enhance the transport of currentcarrying electrons (and ... more 3. The superlattice structure appears to enhance the transport of currentcarrying electrons (and holes) while inhibiting transport of heat-carrying phonons (quantized vibrations of the crystal lattice). Both effects boost ZT. When the modern era of thermoelectric science and technology began to emerge in the late 1950s, it seemed possible that thermoelectrics might approach the efficiency of mechanical refrigerators and power generators. By the 1970s, given the lack of progress, few thought it likely. There was even speculation that a ZT of 1 represented some sort of thermoelectric barrier. Certainly it was an empirical limit that nearly halted research and development. But in the early 1990s Rudolph Buser, then associated with the United States Army Night and Electro-Optics Directorate, called on scientists to reexamine thermoelectrics. A basic science programme to increase ZT was soon underway, with support principally from the US Navy's Office of Naval Research and DARPA (Defense Advanced Research Projects Agency). By the late 1990s there was some progress, but even then you had to be an optimist to believe the barrier had been broken 2 .
Tissue concentrations of A1 in red and Norway spruce trees were compared across 5 sites in North ... more Tissue concentrations of A1 in red and Norway spruce trees were compared across 5 sites in North America and Europe as part of an investigation of A1 biogeochemistry in forested ecosystems (ALBIOS). Fine roots and foliage were sampled and analyzed for A1, Ca, Mg, and P, and the chemistry of soil and soil solutions was characterized at each plot by horizon. Sites exhibited a wide range in soil AI saturation and in concentrations of A1 and sulfate in lysimeter solutions. Aluminium concentrations in roots were two orders of magnitude higher than those in foliage. Fine roots (< 1.0 mm) from B horizons had the highest A1 concentrations and appeared to be the best phytoindicators of plant-available A1. Aluminium concentrations in free roots from B horizons were highly correlated with soil solution monomeric A1, and with A1 in 0.01 M SrC12 soil extracts. Stronger soil A1 extractants were generally poor predictors of concentrations of A1 in plant tissue. Sites with higher levels of plant-available A1 supported spruce trees with correspondingly lower foliar levels of Ca and Mg. As such, these field sites provided circumstantial evidence that AI may be interfering with Ca and Mg uptake and transport. No evidence was found of A1 interference with P uptake or transport at these sites.
Accumulating evidence points to an anthropogenic 'fingerprint' on the global climate change that ... more Accumulating evidence points to an anthropogenic 'fingerprint' on the global climate change that has occurred in the last century. Climate change has, and will continue to have, profound effects on the structure and function of terrestrial ecosystems. As such, there is a critical need to continue to develop a sound scientific basis for national and international policies regulating carbon sequestration and greenhouse gas emissions. This paper reflects on the nature of current global change experiments, and provides recommendations for a unified multidisciplinary approach to future research in this dynamic field. These recommendations include: (1) better integration between experiments and models, and amongst experimental, monitoring, and space-for-time studies; (2) stable and increased support for long-term studies and multi-factor experiments; (3) explicit inclusion of biodiversity, disturbance, and extreme events in experiments and models; (4) consideration of timing vs intensity of global change factors in experiments and models; (5) evaluation of potential thresholds or ecosystem 'tipping points'; and (6) increased support for model-model and model-experiment comparisons. These recommendations, which reflect discussions within the TERACC international network of global change scientists, will facilitate the unraveling of the complex direct and indirect effects of global climate change on terrestrial ecosystems and their components.
Forest and Rangeland Soils of the United States Under Changing Conditions, 2020
Box Fig. 9.2 Outline of the development of Ecological Classification System (ECS) land type phase... more Box Fig. 9.2 Outline of the development of Ecological Classification System (ECS) land type phase (LTP) concepts and modeling data used for mapping these concepts. Soil maps are a key component in this process Box 9.1 (continued)
Frontiers in forests and global change, Feb 26, 2021
Large-scale disturbances such as ice storms may increase in frequency and intensity as climate ch... more Large-scale disturbances such as ice storms may increase in frequency and intensity as climate changes. While disturbances are a natural component of forest ecosystems, climatically driven alteration to historical patterns may impart fundamental change to ecosystem function. At Hubbard Brook Experimental Forest, NH, experimental ice storms of varying severity were applied to replicate plots of mature northern hardwoods to quantify their effects on forested ecosystems. We assessed ice storm treatment effects on insectivorous foliage-gleaning birds and evaluated insectivore predation on model caterpillars in the understory vegetation. These birds are charismatic, of conservation concern, and are major predators of caterpillars. In turn, lepidopterans are the dominant herbivores in temperate forests and are integral to ecosystem function. We predicted that avian abundance would increase due to additional structural heterogeneity caused by ice treatments, with a concomitant increase in caterpillar predation. Point counts were used to measure insectivorous bird activity in the ice storm experiment plots and additional control plots before and after treatments. We deployed and retrieved plasticine model caterpillars and estimated predation from characteristic marks to these surrogates. Abundance of foliage-gleaning birds was higher in the ice storm plots and birds responded to treatments as a single diffuse disturbance rather than on an individual plot level. All species except one were observed both before and after the ice treatments. Surprisingly, predation on caterpillar models was unaffected by ice storm treatments but rather was a function of caterpillar density. The increase in avian abundance in the ice storm treatment plots corroborates other studies of bird responses to relatively small-scale disturbances in forests and the limited change in species composition was expected given the plot size. We conclude that ice storms may provide beneficial changes for foliage-gleaning birds in the growing season following the disturbance.
In the Northeastern U.S., drought is expected to increase in frequency over the next century, and... more In the Northeastern U.S., drought is expected to increase in frequency over the next century, and therefore, the responses of trees to drought are important to understand. There is recent debate about whether land-use change or moisture availability is the primary driver of changes in forest species composition in this region. Some argue that fire suppression from the early twentieth century to present has resulted in an increase in shade-tolerant and pyrophobic tree species that are drought intolerant, while others suggest precipitation variability as a major driver of species composition. From this debate, an emerging hypothesis is that mesophication and increases in the abundance of mesophytic genera (e.g., Acer, Betula, and Fagus) resulted in forests that are more vulnerable to drought. This review examines the published literature and factors that contribute to drought vulnerability of Northeastern U.S. forests. We assessed two key concepts related to drought vulnerability, including drought tolerance (ability to survive drought) and sensitivity (short-term responses to drought), with a focus on Northeastern U.S. species. We assessed drought-tolerance classifications for species, which revealed both consistencies and inconsistencies, as well as contradictions when compared to actual observations, such as higher mortality for drought-tolerant species. Related to drought sensitivity, recent work has focused on isohydric/ anisohydric regulation of leaf water potential. However, based on the review of the literature, we conclude that drought sensitivity should be viewed in terms of multiple variables, including leaf abscission, stomatal sensitivity, turgor pressure, and dynamics of non-structural carbohydrates. Genera considered drought sensitive (e.g., Acer, Betula, and Liriodendron) may actually be less prone to drought-induced mortality and dieback than previously considered because stomatal regulation and leaf abscission in these species are effective at preventing water potential from reaching critical thresholds during extreme drought. Independent of drought-tolerance classification, trees are prone to dieback and mortality when additional stressors are involved such as insect defoliation, calcium and magnesium deficiency, nitrogen saturation, and freeze-thaw events. Overall, our literature review shows that multiple traits associated with drought sensitivity and tolerance are important as species may rely on different mechanisms to prevent hydraulic failure and depleted carbon reserves that may lead to mortality.
Nitrogen (N) deposition is impacting the services that ecosystems provide to humanity. However, t... more Nitrogen (N) deposition is impacting the services that ecosystems provide to humanity. However, the mechanisms determining impacts on the N cycle are not fully understood. To explore the mechanistic underpinnings of N impacts on N cycle processes, we reviewed and synthesised recent progress in ecosystem N research through empirical studies, conceptual analysis and model simulations. Experimental and observational studies have revealed that the stimulation of plant N uptake and soil retention generally diminishes as N loading increases, while dissolved and gaseous losses of N occur at low N availability but increase exponentially and become the dominant fate of N at high loading rates. The original N saturation hypothesis emphasises sequential N saturation from plant uptake to soil retention before N losses occur. However, biogeochemical models that simulate simultaneous competition for soil N substrates by multiple processes match the observed patterns of N losses better than models based on sequential competition. To enable better prediction of terrestrial N cycle responses to N loading, we recommend that future research identifies the response functions of different N processes to substrate availability using manipulative experiments, and incorporates the measured N saturation response functions into conceptual, theoretical and quantitative analyses.
Climate models project an increase in mean annual air temperatures and a reduction in the depth a... more Climate models project an increase in mean annual air temperatures and a reduction in the depth and duration of winter snowpack for many mid and high latitude and high elevation seasonally snow-covered ecosystems over the next century. The combined effects of these changes in climate will lead to warmer soils in the growing season and increased frequency of soil freeze-thaw cycles (FTCs) in winter due to the loss of a continuous, insulating snowpack. Previous experiments have warmed soils or removed snow via shoveling or with shelters to mimic projected declines in the winter snowpack. To our knowledge, no experiment has examined the interactive effects of declining snowpack and increased frequency of soil FTCs, combined with soil warming in the snow-free season on terrestrial ecosystems. In addition, none have mimicked directly the projected increase in soil FTC frequency in tall statured forests that is expected as a result of a loss of insulating snow in winter. We established the Climate Change Across Seasons Experiment (CCASE) at Hubbard Brook Experimental Forest in the White Mountains of New Hampshire in 2012 to assess the combined effects of these changes in climate on a variety of pedoclimate conditions, biogeochemical processes, and ecology of northern hardwood forests. This paper demonstrates the feasibility of creating soil FTC events in a tall statured ecosystem in winter to simulate the projected increase in soil FTC frequency over the next century and combines this projected change in winter climate with ecosystem warming throughout the snow-free season. Together, this experiment provides a new and more comprehensive approach for climate change experiments that can be adopted in other seasonally snow-covered ecosystems to simulate expected changes resulting from global air temperature rise.
Litter decay in a Maine red spruce ecosystem was examined to determine the importance of decompos... more Litter decay in a Maine red spruce ecosystem was examined to determine the importance of decomposition as a recycling pathway for the trace metals Al, Mn, and Fe versus the major nutrients N, P, Ca, and Mg. The experimental design included litterbags containing the following species: red spruce (Picearubens Sarg.), red maple (Acerrubrum L.), white pine (Pinusstrobus L.), and mixtures of all three. Although decomposing litter was an important source of P, Mg, and Mn, the litter acted as a sink for Al, Fe, and N. Calcium showed a variable, species-dependent pattern. During the 2-year study, there was no net mineralization of Al, Fe, or N. The estimated net accumulations of Al and Fe during the first 24 months of litter decomposition were 0.58 and 0.50 kg ha−1, respectively. By comparison, the net accumulation of N during the same period was approximately 3.43 kg ha−1. Evidence suggests that Al and Fe accumulation are controlled by abiotic adsorption on humified litter, whereas N retention is controlled by microbial immobilization.
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