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• 1. [Article] Temporal Variation in Nutrient Uptake Capacity by Intact Roots of Mature Loblolly Pine

  Nutrient uptake is generally thought to exhibit a simple seasonal pattern, but few studies have measured temporal variation of nutrient uptake capacity in mature trees. We measured net uptake capacity ...

  Citation × Citation Citation Abstract Copy Title: Temporal Variation in Nutrient Uptake Capacity by Intact Roots of Mature Loblolly Pine Author: Lucash, Melissa S., Joslin, J. Devereux, Yanai, Ruth D. Year: 2005 Nutrient uptake is generally thought to exhibit a simple seasonal pattern, but few studies have measured temporal variation of nutrient uptake capacity in mature trees. We measured net uptake capacity of K, NH+ 4, NO 3 −, Mg and Ca across a range of solution concentrations by roots of mature loblolly pine at Calhoun Experimental Forest in October 2001, July 2001, and April 2002. Uptake capacity was generally lowest in July; rates in October were similar to those in April. Across a range of concentrations, antecedent nutrient solution concentrations affected the temporal patterns in uptake in July but not in October or April. In July, uptake of NH+ 4, Mg and Ca was positively correlated with concentration when roots were exposed to successively lower concentrations, but negatively correlated with concentration when exposed to successively higher concentrations. In contrast, uptake in October was constant across the range of concentrations, while uptake increased with concentration in April. As in studies of other species, we found greater uptake of NH+ 4 than NO 3 −. Temporal patterns of uptake capacity are difficult to predict, and our results indicate that experimental conditions, such as experiment duration, antecedent root conditions and nutrient solution concentration, affect measured rates of nutrient uptake. Title: Temporal Variation in Nutrient Uptake Capacity by Intact Roots of Mature Loblolly Pine Author: Lucash, Melissa S., Joslin, J. Devereux, Yanai, Ruth D. Year: 2005 Nutrient uptake is generally thought to exhibit a simple seasonal pattern, but few studies have measured temporal variation of nutrient uptake capacity in mature trees. We measured net uptake capacity of K, NH+ 4, NO 3 −, Mg and Ca across a range of solution concentrations by roots of mature loblolly pine at Calhoun Experimental Forest in October 2001, July 2001, and April 2002. Uptake capacity was generally lowest in July; rates in October were similar to those in April. Across a range of concentrations, antecedent nutrient solution concentrations affected the temporal patterns in uptake in July but not in October or April. In July, uptake of NH+ 4, Mg and Ca was positively correlated with concentration when roots were exposed to successively lower concentrations, but negatively correlated with concentration when exposed to successively higher concentrations. In contrast, uptake in October was constant across the range of concentrations, while uptake increased with concentration in April. As in studies of other species, we found greater uptake of NH+ 4 than NO 3 −. Temporal patterns of uptake capacity are difficult to predict, and our results indicate that experimental conditions, such as experiment duration, antecedent root conditions and nutrient solution concentration, affect measured rates of nutrient uptake. Close

• 2. [Article] Estimating Nutrient Uptake by Mature Tree Roots Under Field Conditions: Challenges and Opportunities

  Nutrient uptake by roots of mature trees is difficult to measure accurately under field conditions using existing methods. In this review, we discuss current techniques for measuring uptake at the root ...

  Citation × Citation Citation Abstract Copy Title: Estimating Nutrient Uptake by Mature Tree Roots Under Field Conditions: Challenges and Opportunities Author: Lucash, Melissa S., Eissenstat, Dave M., Joslin, J. Devereux, McFarlane, Karis J., Yanai, Ruth D. Year: 2007 Nutrient uptake by roots of mature trees is difficult to measure accurately under field conditions using existing methods. In this review, we discuss current techniques for measuring uptake at the root surface including excised roots, isotopic tracers, autoradiography, depletion, and lysimeters. Although these methods have provided many insights, each has drawbacks. Estimates of uptake are affected by the sampling scheme, experimental conditions, whether roots are excised or not, concentrations of ions, and the rate of efflux of ions. Microbes and mycorrhizas can also affect estimates of uptake. A greater focus on methods development is critical to advancing our understanding of nutrient uptake of mature trees under conditions representative of those in the field. Title: Estimating Nutrient Uptake by Mature Tree Roots Under Field Conditions: Challenges and Opportunities Author: Lucash, Melissa S., Eissenstat, Dave M., Joslin, J. Devereux, McFarlane, Karis J., Yanai, Ruth D. Year: 2007 Nutrient uptake by roots of mature trees is difficult to measure accurately under field conditions using existing methods. In this review, we discuss current techniques for measuring uptake at the root surface including excised roots, isotopic tracers, autoradiography, depletion, and lysimeters. Although these methods have provided many insights, each has drawbacks. Estimates of uptake are affected by the sampling scheme, experimental conditions, whether roots are excised or not, concentrations of ions, and the rate of efflux of ions. Microbes and mycorrhizas can also affect estimates of uptake. A greater focus on methods development is critical to advancing our understanding of nutrient uptake of mature trees under conditions representative of those in the field. Close

• 3. [Article] Improving the Representation of Roots in Terrestrial Models

  Root biomass, root production and lifespan, and root-mycorrhizal interactions govern soil carbon fluxes and resource uptake and are critical components of terrestrial models. However, limitations in data ...

  Citation × Citation Citation Abstract Copy Title: Improving the Representation of Roots in Terrestrial Models Author: Smithwick, Erica A.H., Lucash, Melissa S., McCormack, M. Luke, Sivandran, Gajan Year: 2014 Root biomass, root production and lifespan, and root-mycorrhizal interactions govern soil carbon fluxes and resource uptake and are critical components of terrestrial models. However, limitations in data and confusions over terminology, together with a strong dependence on a small set of conceptual frameworks, have limited the exploration of root function in terrestrial models. We review the key root processes of interest to both field ecologists and modelers including root classification, production, turnover, biomass, resource uptake, and depth distribution to ask (1) what are contemporary approaches for modeling roots in terrestrial models? and (2) can these approaches be improved via recent advancements in field research methods? We isolate several emerging themes that are ready for collaboration among field scientists and modelers: (1) alternatives to size-class based root classifications based on function and the inclusion of fungal symbioses, (2) dynamic root allocation and phenology as a function of root environment, rather than leaf demand alone, (3) improved understanding of the treatment of root turnover in models, including the role of root tissue chemistry on root lifespan, (4) better estimates of root stocks across sites and species to parameterize or validate models, and (5) dynamic interplay among rooting depth, resource availability and resource uptake. Greater attention to model parameterization and structural representation of roots will lead to greater appreciation for belowground processes in terrestrial models and improve estimates of ecosystem resilience to global change drivers. Title: Improving the Representation of Roots in Terrestrial Models Author: Smithwick, Erica A.H., Lucash, Melissa S., McCormack, M. Luke, Sivandran, Gajan Year: 2014 Root biomass, root production and lifespan, and root-mycorrhizal interactions govern soil carbon fluxes and resource uptake and are critical components of terrestrial models. However, limitations in data and confusions over terminology, together with a strong dependence on a small set of conceptual frameworks, have limited the exploration of root function in terrestrial models. We review the key root processes of interest to both field ecologists and modelers including root classification, production, turnover, biomass, resource uptake, and depth distribution to ask (1) what are contemporary approaches for modeling roots in terrestrial models? and (2) can these approaches be improved via recent advancements in field research methods? We isolate several emerging themes that are ready for collaboration among field scientists and modelers: (1) alternatives to size-class based root classifications based on function and the inclusion of fungal symbioses, (2) dynamic root allocation and phenology as a function of root environment, rather than leaf demand alone, (3) improved understanding of the treatment of root turnover in models, including the role of root tissue chemistry on root lifespan, (4) better estimates of root stocks across sites and species to parameterize or validate models, and (5) dynamic interplay among rooting depth, resource availability and resource uptake. Greater attention to model parameterization and structural representation of roots will lead to greater appreciation for belowground processes in terrestrial models and improve estimates of ecosystem resilience to global change drivers. Close

• 4. [Article] Similarity of Nutrient Uptake and Root Dimensions of Engelmann Spruce and Subalpine Fir at Two Contrasting Sites in Colorado

  Nutrient uptake capacity is an important parameter in modeling nutrient uptake by plants. Researchers commonly assume that uptake capacity measured for a species can be used across sites. We tested this ...

  Citation × Citation Citation Abstract Copy Title: Similarity of Nutrient Uptake and Root Dimensions of Engelmann Spruce and Subalpine Fir at Two Contrasting Sites in Colorado Author: Lucash, Melissa S., Yanai, Ruth D., McFarlane, Karis J., Kulpa, Sarah E., Wood, Dustin M. Year: 2009 Nutrient uptake capacity is an important parameter in modeling nutrient uptake by plants. Researchers commonly assume that uptake capacity measured for a species can be used across sites. We tested this assumption by measuring the nutrient uptake capacity of intact roots of Engelmann spruce (Picea engelmanni Parry) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) at Loch Vale Watershed and Fraser Experimental Forest in the Rocky Mountains of central Colorado. Roots still attached to the tree were exposed to one of three concentrations of nutrient solutions for time periods ranging from 1 to 96h, and solutions were analyzed for ammonium, nitrate, calcium, magnesium, and potassium. Surprisingly, the two species were indistinguishable in nutrient uptake within site for all nutrients (P >0.25), but uptake rates differed by site. In general, nutrient uptake was higher at Fraser (P =0.01, 0.15, 0.03, and 0.18 for NH4+, NO3−, Ca2+, and K+, respectively), which is west of the Continental Divide and has lower atmospheric deposition of N than Loch Vale. Mean uptake rates by site for ambient solution concentrations were , , , and at Loch Vale, and , , , and at Fraser. The importance of site conditions in determining uptake capacity should not be overlooked when parameterizing nutrient uptake models. We also characterized the root morphology of these two species and compared them to other tree species we have measured at various sites in the northeastern USA. Engelmann spruce and subalpine fir were indistinguishable in specific root length and diameter distribution, while most of the other 10 species had statistically distinct diameter distributions across five diameter classes. Title: Similarity of Nutrient Uptake and Root Dimensions of Engelmann Spruce and Subalpine Fir at Two Contrasting Sites in Colorado Author: Lucash, Melissa S., Yanai, Ruth D., McFarlane, Karis J., Kulpa, Sarah E., Wood, Dustin M. Year: 2009 Nutrient uptake capacity is an important parameter in modeling nutrient uptake by plants. Researchers commonly assume that uptake capacity measured for a species can be used across sites. We tested this assumption by measuring the nutrient uptake capacity of intact roots of Engelmann spruce (Picea engelmanni Parry) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) at Loch Vale Watershed and Fraser Experimental Forest in the Rocky Mountains of central Colorado. Roots still attached to the tree were exposed to one of three concentrations of nutrient solutions for time periods ranging from 1 to 96h, and solutions were analyzed for ammonium, nitrate, calcium, magnesium, and potassium. Surprisingly, the two species were indistinguishable in nutrient uptake within site for all nutrients (P >0.25), but uptake rates differed by site. In general, nutrient uptake was higher at Fraser (P =0.01, 0.15, 0.03, and 0.18 for NH4+, NO3−, Ca2+, and K+, respectively), which is west of the Continental Divide and has lower atmospheric deposition of N than Loch Vale. Mean uptake rates by site for ambient solution concentrations were , , , and at Loch Vale, and , , , and at Fraser. The importance of site conditions in determining uptake capacity should not be overlooked when parameterizing nutrient uptake models. We also characterized the root morphology of these two species and compared them to other tree species we have measured at various sites in the northeastern USA. Engelmann spruce and subalpine fir were indistinguishable in specific root length and diameter distribution, while most of the other 10 species had statistically distinct diameter distributions across five diameter classes. Close

• 5. [Article] Foliar Nutrient Concentrations Related to Soil Sources Across a Range of Sites in the Northeastern United States

  Understanding the supply of nutrients from various soil sources and the sensitivity of tree species to soil nutrient availability is critical for predicting the effects of declines in base cations due ...

  Citation × Citation Citation Abstract Copy Title: Foliar Nutrient Concentrations Related to Soil Sources Across a Range of Sites in the Northeastern United States Author: Lucash, Melissa S., Yanai, Ruth D., Blum, Joel D., Park, B. B. Year: 2011 Understanding the supply of nutrients from various soil sources and the sensitivity of tree species to soil nutrient availability is critical for predicting the effects of declines in base cations due to acid rain and forest harvesting on forest health and productivity. We collected soil samples from 19 sites in the northeastern United States, chemically analyzed them using a sequential extraction procedure, and compared them to the chemical composition of foliage of the dominant tree species. Concentrations of Ca and Mg in foliage were correlated with exchangeable Ca and Mg concentrations in the upper mineral soil; for most tree species they were also correlated to acid-extractable Ca and Mg in the parent material (C horizon). Foliar P was better correlated with soil P in the upper mineral soil than in the C horizon, while foliar AI was insensitive to soil AI concentrations. In five sites in New Hampshire, the Ca/Sr of foliage was consistent with that of the Oie horizon, after taking the reported discrimination of Ca over Sr into account. In sites in New York, without an Oie horizon, the Ca/Sr of foliage was too high to be explained by any of the soil pools. A comparison of Ca/Sr ratios of foliage among species at common sites showed oak (Quercus spp.) to have higher Ca/Sr ratios than sugar maple (Acer saccharum Marsh.), birch (Betula spp.), red maple (A. rubrum L.) and beech (Fagus spp.). The interpretation of soil Ca sources from Ca/Sr ratios is complicated at sites where a single horizon does not dominate the source. Title: Foliar Nutrient Concentrations Related to Soil Sources Across a Range of Sites in the Northeastern United States Author: Lucash, Melissa S., Yanai, Ruth D., Blum, Joel D., Park, B. B. Year: 2011 Understanding the supply of nutrients from various soil sources and the sensitivity of tree species to soil nutrient availability is critical for predicting the effects of declines in base cations due to acid rain and forest harvesting on forest health and productivity. We collected soil samples from 19 sites in the northeastern United States, chemically analyzed them using a sequential extraction procedure, and compared them to the chemical composition of foliage of the dominant tree species. Concentrations of Ca and Mg in foliage were correlated with exchangeable Ca and Mg concentrations in the upper mineral soil; for most tree species they were also correlated to acid-extractable Ca and Mg in the parent material (C horizon). Foliar P was better correlated with soil P in the upper mineral soil than in the C horizon, while foliar AI was insensitive to soil AI concentrations. In five sites in New Hampshire, the Ca/Sr of foliage was consistent with that of the Oie horizon, after taking the reported discrimination of Ca over Sr into account. In sites in New York, without an Oie horizon, the Ca/Sr of foliage was too high to be explained by any of the soil pools. A comparison of Ca/Sr ratios of foliage among species at common sites showed oak (Quercus spp.) to have higher Ca/Sr ratios than sugar maple (Acer saccharum Marsh.), birch (Betula spp.), red maple (A. rubrum L.) and beech (Fagus spp.). The interpretation of soil Ca sources from Ca/Sr ratios is complicated at sites where a single horizon does not dominate the source. Close

• 6. [Article] Nutrient Uptake by Intact and Disturbed Roots of Loblolly Pine Seedlings

  Most measurements of nutrient uptake use either hydroponic systems or soil-grown roots that have been disturbed by excavation. The first objective of this study was to test how root excavation affects ...

  Citation × Citation Citation Abstract Copy Title: Nutrient Uptake by Intact and Disturbed Roots of Loblolly Pine Seedlings Author: Lucash, Melissa S., Yanai, Ruth D., Joslin, J. Devereux Year: 2008 Most measurements of nutrient uptake use either hydroponic systems or soil-grown roots that have been disturbed by excavation. The first objective of this study was to test how root excavation affects nitrate uptake. Rates of NO3− uptake by mycorrhizal loblolly pine (Pinus taeda L.) seedlings were measured in intact sand-filled columns, hydroponics, and disturbed sand-filled columns. Total nitrate uptake in intact sand-filled columns was higher than in disturbed columns, indicating that disturbance lowers uptake. Transferring plants from the sand-filled columns to hydroponics had little effect on NO3− uptake beyond delaying uptake for an hour. The second objective of this study was to determine whether NH4+, Ca2+, Mg2+ and K+ uptake could be studied using sand-filled columns, since previous studies had tested this method only for nitrate uptake. Uptake rates of NH4+ and K+ were positive, while Ca2+ and Mg2+ uptake rates were negative in intact sand-filled columns, indicating that net efflux may occur even without physical disturbance to the root system. The sand-filled column approach has some limitations, but holds promise for conducting nutrient uptake studies with minimal disturbance to the root system. Title: Nutrient Uptake by Intact and Disturbed Roots of Loblolly Pine Seedlings Author: Lucash, Melissa S., Yanai, Ruth D., Joslin, J. Devereux Year: 2008 Most measurements of nutrient uptake use either hydroponic systems or soil-grown roots that have been disturbed by excavation. The first objective of this study was to test how root excavation affects nitrate uptake. Rates of NO3− uptake by mycorrhizal loblolly pine (Pinus taeda L.) seedlings were measured in intact sand-filled columns, hydroponics, and disturbed sand-filled columns. Total nitrate uptake in intact sand-filled columns was higher than in disturbed columns, indicating that disturbance lowers uptake. Transferring plants from the sand-filled columns to hydroponics had little effect on NO3− uptake beyond delaying uptake for an hour. The second objective of this study was to determine whether NH4+, Ca2+, Mg2+ and K+ uptake could be studied using sand-filled columns, since previous studies had tested this method only for nitrate uptake. Uptake rates of NH4+ and K+ were positive, while Ca2+ and Mg2+ uptake rates were negative in intact sand-filled columns, indicating that net efflux may occur even without physical disturbance to the root system. The sand-filled column approach has some limitations, but holds promise for conducting nutrient uptake studies with minimal disturbance to the root system. Close

• 7. [Article] Disequilibrium of Fire-prone Forests Sets the Stage for a Rapid Decline in Conifer Dominance during the 21st Century

  As trees are long-lived organisms, the impacts of climate change on forest communities may not be apparent on the time scale of years to decades. While lagged responses to environmental change are common ...

  Citation × Citation Citation Abstract Copy Title: Disequilibrium of Fire-prone Forests Sets the Stage for a Rapid Decline in Conifer Dominance during the 21st Century Author: Serra-Diaz, Josep M., Maxwell, Charles, Lucash, Melissa S., Scheller, Robert M., Laflower, Danelle M., Miller, Adam D., Tepley, Alan J., Epstein, Howard E., Anderson-Teixeira, Kristina J., Thompson, Jonathan R. Year: 2017 As trees are long-lived organisms, the impacts of climate change on forest communities may not be apparent on the time scale of years to decades. While lagged responses to environmental change are common in forested systems, potential for abrupt transitions under climate change may occur in environments where alternative vegetation states are influenced by disturbances, such as fire. The Klamath mountains (northern California and southwest Oregon, USA) are currently dominated by carbon rich and hyper-diverse temperate conifer forests, but climate change could disrupt the mechanisms promoting forest stability– regeneration and fire tolerance— via shifts in the fire regime in conjunction with lower fitness of conifers under a hotter climate. Understanding how this landscape will respond to near-term climate change (before 2100) is critical for predicting potential climate change feedbacks and to developing sound forest conservation and management plans. Using a landscape simulation model, we estimate that 1/3 of the Klamath could transition from conifer forest to shrub/hardwood chaparral, triggered by an enhanced fire activity coupled with lower post-fire conifer establishment. Such shifts were more prevalent under higher climate change forcing (RCP 8.5) but were also simulated under the climate of 1950-2000, reflecting the joint influences of early warming trends and historical forest legacies. Our results demonstrate that there is a large potential for loss of conifer forest dominance—and associated carbon stocks and biodiversity-- in the Klamath before the end of the century, and that some losses would likely occur even without the influence of climate change. Thus, in the Klamath and other forested landscapes subject to similar feedback dynamics, major ecosystem shifts should be expected when climate change disrupts key stabilizing feedbacks that maintain the dominance of long-lived, slowly regenerating trees. Title: Disequilibrium of Fire-prone Forests Sets the Stage for a Rapid Decline in Conifer Dominance during the 21st Century Author: Serra-Diaz, Josep M., Maxwell, Charles, Lucash, Melissa S., Scheller, Robert M., Laflower, Danelle M., Miller, Adam D., Tepley, Alan J., Epstein, Howard E., Anderson-Teixeira, Kristina J., Thompson, Jonathan R. Year: 2017 As trees are long-lived organisms, the impacts of climate change on forest communities may not be apparent on the time scale of years to decades. While lagged responses to environmental change are common in forested systems, potential for abrupt transitions under climate change may occur in environments where alternative vegetation states are influenced by disturbances, such as fire. The Klamath mountains (northern California and southwest Oregon, USA) are currently dominated by carbon rich and hyper-diverse temperate conifer forests, but climate change could disrupt the mechanisms promoting forest stability– regeneration and fire tolerance— via shifts in the fire regime in conjunction with lower fitness of conifers under a hotter climate. Understanding how this landscape will respond to near-term climate change (before 2100) is critical for predicting potential climate change feedbacks and to developing sound forest conservation and management plans. Using a landscape simulation model, we estimate that 1/3 of the Klamath could transition from conifer forest to shrub/hardwood chaparral, triggered by an enhanced fire activity coupled with lower post-fire conifer establishment. Such shifts were more prevalent under higher climate change forcing (RCP 8.5) but were also simulated under the climate of 1950-2000, reflecting the joint influences of early warming trends and historical forest legacies. Our results demonstrate that there is a large potential for loss of conifer forest dominance—and associated carbon stocks and biodiversity-- in the Klamath before the end of the century, and that some losses would likely occur even without the influence of climate change. Thus, in the Klamath and other forested landscapes subject to similar feedback dynamics, major ecosystem shifts should be expected when climate change disrupts key stabilizing feedbacks that maintain the dominance of long-lived, slowly regenerating trees. Close