The current state of uncertainty reporting in ecosystem studies: a systematic evaluation of peer-... more The current state of uncertainty reporting in ecosystem studies: a systematic evaluation of peer-reviewed literature.
Increased Al mobilization and Ca and Mg leaching have been linked to nutritional imbalances in su... more Increased Al mobilization and Ca and Mg leaching have been linked to nutritional imbalances in sugar maple across the northeastern US and Canada. The susceptibility of sugar maple fine roots to Al stress is poorly understood, in part because roots respond to Al stress by altering the chemistry of the rhizosphere. AlCl 3 was applied to plots of sugar maple at the Hubbard Brook Experimental Forest, NH. After two years of treatment, we sampled fine roots of sugar maple, rhizosphere soil, and bulk soil in the Oa horizon and the upper 10 cm of the mineral soil. AlCl 3 treatments resulted in significantly less Ca (21%) and Mg (30%) in fine roots from the organic horizon, but had no significant effect on fine root Al. Fine root (Ca+Mg):Al ratios were 42% lower in AlCl 3 plots than in controls, though most roots had ratios above critical toxicity thresholds developed for hydroponically grown sugar maple seedlings. In the mineral horizon, roots differed only in Mg concentration, which was 22% lower in AlCl 3 plots. In the AlCl 3 treated plots, rhizosphere soil in the organic horizon had 47% greater Al and 29% less Mg than in controls. Combining data from both treatments we found significantly less Al and organically bound Al in rhizosphere soil than in bulk soil, possibly due to leaching of Al from the rhizosphere by organic acids released by roots. These results suggest that increased mobilization of Al in soil lowers (Ca+Mg):Al ratios in sugar maple fine roots, though roots may minimize Al stress by leaching Al from the rhizosphere.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Soil Science Society of America Journal, Nov 1, 1991
Forest harvest drastically alters nutrient cycling, yet stream water and mineral-soil solutions t... more Forest harvest drastically alters nutrient cycling, yet stream water and mineral-soil solutions typically show little change in P concentrations after forest disturbance. Changes in P availability and movement are more likely to be detected in forest-floor solutions, since P can be strongly sorbed in soil. Tension-free lysimeters were used to compare forest-floor and mineral-soil solution total-P concentrations in whole-tree-harvested and undisturbed forest sites for 2 yr after harvest in the Hubbard Brook Experimental Forest in New Hampshire. Mean total-P concentrations in solution in the forest floor (Oa horizon) were significantly higher in whole-tree-harvested sites (248 Mg P L" 1) than in undisturbed forest sites (67 Mg P L-'), presumably due to reduced plant uptake of P. Mean P concentrations in mineral-soil solution remained low after whole-tree harvest (32 Mg P L-1 in the Bh and 15 Mg P L" 1 in the Bs), consistent with the high P-sorption capacity of the mineral soil. Phosphorus flux in soil solution from the Oa to the B horizon, calculated from monthly mean P concentrations and monthly water flux simulated by a hydrologic model, was greater in whole-tree-harvested sites (1.0 kg P ha-1 yr-1) than in undisturbed forest sites (0.3 kg P ha-1 yr-1) in the first 2 yr after the disturbance. This redistribution of P from the forest floor to the mineral soil far exceeds stream-water export of dissolved P (0.02 kg P ha' 1 yr 1) but is small compared with forest-floor stores (85 kg P ha-1).
Mercury (Hg) in the environment has been receiving considerable attention in recent years, but li... more Mercury (Hg) in the environment has been receiving considerable attention in recent years, but little is known about Hg accumulation in trees. We analyzed Hg in tree rings from four tree species at the Hubbard Brook Experimental Forest in New Hampshire to determine whether Hg concentrations are more influenced by soil Hg concentrations, which have been stable or increasing due to the cumulative retention of historical atmospheric Hg deposition, or by atmospheric Hg deposition, which has declined in recent decades. Declining concentrations from the top to the bottom of the bole (p < 0.001) and from older to newer tree rings (p = 0.001) suggest that foliar uptake of Hg is more important than root uptake. Ten sugar maple clones planted in six blocks at the Heiberg Forest in New York State showed significant genetic control of sap Hg concentration (p = 0.02), which was not related to soil Hg concentration differences across blocks. Clones could differ in stomatal uptake, root uptake, or translocation of Hg. Better understanding of the source of Hg in wood is needed to forecast future changes in Hg cycling in forested ecosystems.
Fertilization is essential to seedling production in nursery culture, but excessive fertilization... more Fertilization is essential to seedling production in nursery culture, but excessive fertilization can contaminate surface and ground water around the nursery. The optimal fertilization practice is that which maximizes seedling growth and minimizes nutrient loss. We tested three fertilization strategies: (1) constant fertilization (2) a three-stage rate, and (3) exponential fertilization on Liriodendron tulipifera and Larix leptolepis containerized seedlings. Growth performance, nutrient uptake, and nutrient loss in leaching were measured. Height, root collar diameter, and dry weight of both species were not significantly different among treatments even though the nutrient supply of the exponential treatment was half that of the constant and three-stage treatments. Generally, nutrient losses in leached solutions were higher in constant and three-stage than the exponential treatment. Nutrient use efficiency was calculated as the ratio of the nutrient content of the seedlings to the amount of nutrient applied to the containers. The nitrogen use efficiency in the constant, three-stage, and exponential treatments was 63, 61, and 85% for yellow poplar,
Soil Science Society of America Journal, Nov 1, 2014
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or b... more All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Page 368. Root life span, efficiency 339 13 Root Life Span, Efficiency, and Turnover David M. Eis... more Page 368. Root life span, efficiency 339 13 Root Life Span, Efficiency, and Turnover David M. Eissenstat The Pennsylvania State University, University Park, Pennsylvania Ruth D. Yanai State University of New York, Syracuse ...
Successional, second-growth forests dominate much of eastern North America, thus patterns of biom... more Successional, second-growth forests dominate much of eastern North America, thus patterns of biomass accumulation in standing trees and downed wood are of great interest for forest management and carbon accounting. The timing and magnitude of biomass accumulation in later stages of forest development are not fully understood. We applied a “chronosequence with resampling” approach to characterize live and dead biomass accumulation in sixteen northern hardwood stands in the White Mountains of New Hampshire. Live aboveground biomass increased rapidly and leveled off at about 350 Mg/ha by 145 years. Downed wood biomass fluctuated between 10 and 35 Mg/ha depending on disturbances. The species composition of downed wood varied predictably with overstory succession, and total mass of downed wood increased with stand age and the concomitant production of larger material. Fine woody debris peaked at 30-50 years during the self-thinning of early-successional species, notably pin cherry. Our d...
Accurate estimates of the retention of carbon in forest soils following forest disturbances are e... more Accurate estimates of the retention of carbon in forest soils following forest disturbances are essential to predictions of global carbon cycling. The belief that 50% of soil carbon is lost in the ®rst 20 years after clearcutting is largely based on a chronosequence study of forest¯oors in New Hampshire northern hardwoods (Covington, 1981). We resampled forest¯oors in 13 stands in a similar chronosequence after an interval of 15 years. The three youngest stands, which were predicted to lose organic matter over this time, did not exhibit the 40±50% losses predicted by the original chronosequence. The oldest stands had about twice as much organic mass in the forest¯oor as those cut recently, but this pattern could be explained equally well by historical changes in the nature of forest harvest as by the age of the stands. For example, mechanized logging probably causes more mechanical disturbance to the forest¯oor than horse logging, burying more organic matter into the mineral soil. Markets for forest products and the intensity of harvest removals have also changed over time, possibly contributing to lower organic matter in the forest¯oor in young stands. In any chronosequence study, effects of change in the nature of the treatment over time can easily be misinterpreted as change with time since treatment. Repeated sampling of the chronosequence provides controls for some of these effects. In the case of forest¯oor organic matter, however, high spatial variation makes it dif®cult to distinguish whether the observed variation is more likely due to changes in treatment over time or to differences in time since treatment. Because of the large amounts of carbon involved, small changes in rates of soil organic matter storage may be quite important in global climate change, but they will remain dif®cult to detect, even with very intensive sampling.
This study would not have been possible without the assistance of my advisor Ruth Yanai who dilig... more This study would not have been possible without the assistance of my advisor Ruth Yanai who diligently worked with me and provided the opportunity to explore my own interest. My graduate committee members Chris Nowak, Colin Beier and Mike Farrell were always willing to provide assistance. Acknowledgement of Eric Randall for his advice on sap sampling is necessary along with Tim Wilmot, Tim Perkins, Steve Childs, Paul Schaberg, Heidi Asbjornsen, Adan Hernádez, and Sandy Wilmot for their many contributions. Mike Wild willing helped during the last sap sampling period which allowed for a shorter day in the field. Gas exchange measurements could not have been taken without Katherine Sinacore operating the portable photosynthesis system. Chris Costello was always willing to assist me with the snowmobile for sap sampling and ensure I came out of the woods safely. Melany Fisk was gracious in providing the soils data. Members of my lab, Craig See, Franklin Diggs, Yang Yang and Yi Dong were always willing to provide feedback on results. Foliage and tree growth sampling was completed by members of the MELNHE summer field crew including Eric MacPherson who assisted with the canopy assessment. Working with John View, Kevin Reynolds and members of the Mighty Oaks crosscountry and track team at ESF kept me sane by providing the opportunity to get away from my research and run.
Acid rain results in losses of exchangeable base cations from soils, but the mechanism of base ca... more Acid rain results in losses of exchangeable base cations from soils, but the mechanism of base cation displacement from the forest floor is not clear, and has been hypothesized to involve mobilization of aluminum from the mineral soil. We attempted to test the hypothesis that losses of calcium from the forest floor were balanced by increases in Al in New Hampshire northern hardwoods. We measured exchangeable (six stands) and acid extractable (13 stands) Ca and Al in horizons of the forest floor over an interval of 15 years. Our sampling scheme was quite intensive, involving 50 or 60 blocks per stand, composited in groups of 10 for chemical analysis. Even at this level of effort, few stands exhibited changes large enough to be significant. Because of high spatial variability, differences would have had to be greater than about 50% to be statistically detectable. Differences in Ca and Al concentrations between Oi, Oe, Oa, and A horizons, however, were readily detected. Acid-extractable Al increased with depth, while Ca concentrations decreased; Ca-to-Al ratios decreased from 8.3 (charge basis) in the Oi to 0.2 in the A horizon. Therefore, a small change in sampling depth, or the inclusion of more or less A horizon material in the forest floor, could cause large differences in measured Ca and Al concentrations. To detect small changes in exchangeable cations over time would require sampling very intensively with careful control for comparability of horizons.
TREGRO, a model of tree physiological response to environmental stress, was developed to examine ... more TREGRO, a model of tree physiological response to environmental stress, was developed to examine the details of tree response to the interaction between ozone stress and nutrient deficiency. TREGRO was used to test the hypothesis that the nutrient deficiency would exacerbate growth reductions caused by ozone. When TREGRO was applied to a range of multiple-stress scenarios involving these two stresses, the simulated effects of the combined stresses in reducing red spruce (Picea rubens Sara) tree growth were less than the sum of the effects simulated when each stress was acting alone. Red spruce, a species with a growth strategy involving low maximum potential growth rates and storage in C reserves, showed simulated patterns of allocation that minimized the added effect of ozone when Mg nutrient availability was low. In contrast, ponderosa pine (P/nus ponderosa Dougl.), a species that allocated C to the construction of new tissue preferentially, showed little ability to ameliorate ozone stress under low nutrient conditions. In neither case were the effects of ozone increased by nutrient deficiency. It is speculated that a species which maintains maximum C demand rates considerably below rates of C supply may be better able to adjust to conditions of multiple stresses.
Mechanistic models of nutrient uptake are essential to the study of plant-soil interactions. In t... more Mechanistic models of nutrient uptake are essential to the study of plant-soil interactions. In these models, uptake rates depend on the supply of the nutrient through the soil and the uptake capacity of the roots. The behaviour of the models is complex, although only six to ten parameters are used. Our goal was to demonstrate a comprehensive and efficient method of exploring a steady-state uptake model with variation in parameters across a range of values described in the literature. We employed two analytical techniques: the first a statistical analysis of variance, and the second a graphical representation of the simulated response surface. The quantitative statistical technique allows objective comparison of parameter and interaction sensitivity. The graphical technique uses a judicious arrangement of figures to present the shape of the response surface in five dimensions. We found that the most important parameters controlling uptake per unit length of root are the average dissolved nutrient concentration and the maximal rate of nutrient uptake. Root radius is influential if rates are expressed per unit root length; on a surface area basis, this parameter is less important. The next most important parameter is the effective diffusion coefficient, especially in the uptake of phosphorus. The interactions of parameters were extremely important and included three and four dimensional effects. For example, limitation by maximal nutrient influx rate is approached more rapidly with increasing nutrient solution concentration when the effective diffusion coefficient is high. We also note the ecological implications of the response surface. For example, in nutrient-limited conditions, the rate of uptake is best augmented by extending root length; when nutrients are plentiful increasing uptake kinetics will have greater effect.
The current state of uncertainty reporting in ecosystem studies: a systematic evaluation of peer-... more The current state of uncertainty reporting in ecosystem studies: a systematic evaluation of peer-reviewed literature.
Increased Al mobilization and Ca and Mg leaching have been linked to nutritional imbalances in su... more Increased Al mobilization and Ca and Mg leaching have been linked to nutritional imbalances in sugar maple across the northeastern US and Canada. The susceptibility of sugar maple fine roots to Al stress is poorly understood, in part because roots respond to Al stress by altering the chemistry of the rhizosphere. AlCl 3 was applied to plots of sugar maple at the Hubbard Brook Experimental Forest, NH. After two years of treatment, we sampled fine roots of sugar maple, rhizosphere soil, and bulk soil in the Oa horizon and the upper 10 cm of the mineral soil. AlCl 3 treatments resulted in significantly less Ca (21%) and Mg (30%) in fine roots from the organic horizon, but had no significant effect on fine root Al. Fine root (Ca+Mg):Al ratios were 42% lower in AlCl 3 plots than in controls, though most roots had ratios above critical toxicity thresholds developed for hydroponically grown sugar maple seedlings. In the mineral horizon, roots differed only in Mg concentration, which was 22% lower in AlCl 3 plots. In the AlCl 3 treated plots, rhizosphere soil in the organic horizon had 47% greater Al and 29% less Mg than in controls. Combining data from both treatments we found significantly less Al and organically bound Al in rhizosphere soil than in bulk soil, possibly due to leaching of Al from the rhizosphere by organic acids released by roots. These results suggest that increased mobilization of Al in soil lowers (Ca+Mg):Al ratios in sugar maple fine roots, though roots may minimize Al stress by leaching Al from the rhizosphere.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Soil Science Society of America Journal, Nov 1, 1991
Forest harvest drastically alters nutrient cycling, yet stream water and mineral-soil solutions t... more Forest harvest drastically alters nutrient cycling, yet stream water and mineral-soil solutions typically show little change in P concentrations after forest disturbance. Changes in P availability and movement are more likely to be detected in forest-floor solutions, since P can be strongly sorbed in soil. Tension-free lysimeters were used to compare forest-floor and mineral-soil solution total-P concentrations in whole-tree-harvested and undisturbed forest sites for 2 yr after harvest in the Hubbard Brook Experimental Forest in New Hampshire. Mean total-P concentrations in solution in the forest floor (Oa horizon) were significantly higher in whole-tree-harvested sites (248 Mg P L" 1) than in undisturbed forest sites (67 Mg P L-'), presumably due to reduced plant uptake of P. Mean P concentrations in mineral-soil solution remained low after whole-tree harvest (32 Mg P L-1 in the Bh and 15 Mg P L" 1 in the Bs), consistent with the high P-sorption capacity of the mineral soil. Phosphorus flux in soil solution from the Oa to the B horizon, calculated from monthly mean P concentrations and monthly water flux simulated by a hydrologic model, was greater in whole-tree-harvested sites (1.0 kg P ha-1 yr-1) than in undisturbed forest sites (0.3 kg P ha-1 yr-1) in the first 2 yr after the disturbance. This redistribution of P from the forest floor to the mineral soil far exceeds stream-water export of dissolved P (0.02 kg P ha' 1 yr 1) but is small compared with forest-floor stores (85 kg P ha-1).
Mercury (Hg) in the environment has been receiving considerable attention in recent years, but li... more Mercury (Hg) in the environment has been receiving considerable attention in recent years, but little is known about Hg accumulation in trees. We analyzed Hg in tree rings from four tree species at the Hubbard Brook Experimental Forest in New Hampshire to determine whether Hg concentrations are more influenced by soil Hg concentrations, which have been stable or increasing due to the cumulative retention of historical atmospheric Hg deposition, or by atmospheric Hg deposition, which has declined in recent decades. Declining concentrations from the top to the bottom of the bole (p < 0.001) and from older to newer tree rings (p = 0.001) suggest that foliar uptake of Hg is more important than root uptake. Ten sugar maple clones planted in six blocks at the Heiberg Forest in New York State showed significant genetic control of sap Hg concentration (p = 0.02), which was not related to soil Hg concentration differences across blocks. Clones could differ in stomatal uptake, root uptake, or translocation of Hg. Better understanding of the source of Hg in wood is needed to forecast future changes in Hg cycling in forested ecosystems.
Fertilization is essential to seedling production in nursery culture, but excessive fertilization... more Fertilization is essential to seedling production in nursery culture, but excessive fertilization can contaminate surface and ground water around the nursery. The optimal fertilization practice is that which maximizes seedling growth and minimizes nutrient loss. We tested three fertilization strategies: (1) constant fertilization (2) a three-stage rate, and (3) exponential fertilization on Liriodendron tulipifera and Larix leptolepis containerized seedlings. Growth performance, nutrient uptake, and nutrient loss in leaching were measured. Height, root collar diameter, and dry weight of both species were not significantly different among treatments even though the nutrient supply of the exponential treatment was half that of the constant and three-stage treatments. Generally, nutrient losses in leached solutions were higher in constant and three-stage than the exponential treatment. Nutrient use efficiency was calculated as the ratio of the nutrient content of the seedlings to the amount of nutrient applied to the containers. The nitrogen use efficiency in the constant, three-stage, and exponential treatments was 63, 61, and 85% for yellow poplar,
Soil Science Society of America Journal, Nov 1, 2014
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or b... more All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Page 368. Root life span, efficiency 339 13 Root Life Span, Efficiency, and Turnover David M. Eis... more Page 368. Root life span, efficiency 339 13 Root Life Span, Efficiency, and Turnover David M. Eissenstat The Pennsylvania State University, University Park, Pennsylvania Ruth D. Yanai State University of New York, Syracuse ...
Successional, second-growth forests dominate much of eastern North America, thus patterns of biom... more Successional, second-growth forests dominate much of eastern North America, thus patterns of biomass accumulation in standing trees and downed wood are of great interest for forest management and carbon accounting. The timing and magnitude of biomass accumulation in later stages of forest development are not fully understood. We applied a “chronosequence with resampling” approach to characterize live and dead biomass accumulation in sixteen northern hardwood stands in the White Mountains of New Hampshire. Live aboveground biomass increased rapidly and leveled off at about 350 Mg/ha by 145 years. Downed wood biomass fluctuated between 10 and 35 Mg/ha depending on disturbances. The species composition of downed wood varied predictably with overstory succession, and total mass of downed wood increased with stand age and the concomitant production of larger material. Fine woody debris peaked at 30-50 years during the self-thinning of early-successional species, notably pin cherry. Our d...
Accurate estimates of the retention of carbon in forest soils following forest disturbances are e... more Accurate estimates of the retention of carbon in forest soils following forest disturbances are essential to predictions of global carbon cycling. The belief that 50% of soil carbon is lost in the ®rst 20 years after clearcutting is largely based on a chronosequence study of forest¯oors in New Hampshire northern hardwoods (Covington, 1981). We resampled forest¯oors in 13 stands in a similar chronosequence after an interval of 15 years. The three youngest stands, which were predicted to lose organic matter over this time, did not exhibit the 40±50% losses predicted by the original chronosequence. The oldest stands had about twice as much organic mass in the forest¯oor as those cut recently, but this pattern could be explained equally well by historical changes in the nature of forest harvest as by the age of the stands. For example, mechanized logging probably causes more mechanical disturbance to the forest¯oor than horse logging, burying more organic matter into the mineral soil. Markets for forest products and the intensity of harvest removals have also changed over time, possibly contributing to lower organic matter in the forest¯oor in young stands. In any chronosequence study, effects of change in the nature of the treatment over time can easily be misinterpreted as change with time since treatment. Repeated sampling of the chronosequence provides controls for some of these effects. In the case of forest¯oor organic matter, however, high spatial variation makes it dif®cult to distinguish whether the observed variation is more likely due to changes in treatment over time or to differences in time since treatment. Because of the large amounts of carbon involved, small changes in rates of soil organic matter storage may be quite important in global climate change, but they will remain dif®cult to detect, even with very intensive sampling.
This study would not have been possible without the assistance of my advisor Ruth Yanai who dilig... more This study would not have been possible without the assistance of my advisor Ruth Yanai who diligently worked with me and provided the opportunity to explore my own interest. My graduate committee members Chris Nowak, Colin Beier and Mike Farrell were always willing to provide assistance. Acknowledgement of Eric Randall for his advice on sap sampling is necessary along with Tim Wilmot, Tim Perkins, Steve Childs, Paul Schaberg, Heidi Asbjornsen, Adan Hernádez, and Sandy Wilmot for their many contributions. Mike Wild willing helped during the last sap sampling period which allowed for a shorter day in the field. Gas exchange measurements could not have been taken without Katherine Sinacore operating the portable photosynthesis system. Chris Costello was always willing to assist me with the snowmobile for sap sampling and ensure I came out of the woods safely. Melany Fisk was gracious in providing the soils data. Members of my lab, Craig See, Franklin Diggs, Yang Yang and Yi Dong were always willing to provide feedback on results. Foliage and tree growth sampling was completed by members of the MELNHE summer field crew including Eric MacPherson who assisted with the canopy assessment. Working with John View, Kevin Reynolds and members of the Mighty Oaks crosscountry and track team at ESF kept me sane by providing the opportunity to get away from my research and run.
Acid rain results in losses of exchangeable base cations from soils, but the mechanism of base ca... more Acid rain results in losses of exchangeable base cations from soils, but the mechanism of base cation displacement from the forest floor is not clear, and has been hypothesized to involve mobilization of aluminum from the mineral soil. We attempted to test the hypothesis that losses of calcium from the forest floor were balanced by increases in Al in New Hampshire northern hardwoods. We measured exchangeable (six stands) and acid extractable (13 stands) Ca and Al in horizons of the forest floor over an interval of 15 years. Our sampling scheme was quite intensive, involving 50 or 60 blocks per stand, composited in groups of 10 for chemical analysis. Even at this level of effort, few stands exhibited changes large enough to be significant. Because of high spatial variability, differences would have had to be greater than about 50% to be statistically detectable. Differences in Ca and Al concentrations between Oi, Oe, Oa, and A horizons, however, were readily detected. Acid-extractable Al increased with depth, while Ca concentrations decreased; Ca-to-Al ratios decreased from 8.3 (charge basis) in the Oi to 0.2 in the A horizon. Therefore, a small change in sampling depth, or the inclusion of more or less A horizon material in the forest floor, could cause large differences in measured Ca and Al concentrations. To detect small changes in exchangeable cations over time would require sampling very intensively with careful control for comparability of horizons.
TREGRO, a model of tree physiological response to environmental stress, was developed to examine ... more TREGRO, a model of tree physiological response to environmental stress, was developed to examine the details of tree response to the interaction between ozone stress and nutrient deficiency. TREGRO was used to test the hypothesis that the nutrient deficiency would exacerbate growth reductions caused by ozone. When TREGRO was applied to a range of multiple-stress scenarios involving these two stresses, the simulated effects of the combined stresses in reducing red spruce (Picea rubens Sara) tree growth were less than the sum of the effects simulated when each stress was acting alone. Red spruce, a species with a growth strategy involving low maximum potential growth rates and storage in C reserves, showed simulated patterns of allocation that minimized the added effect of ozone when Mg nutrient availability was low. In contrast, ponderosa pine (P/nus ponderosa Dougl.), a species that allocated C to the construction of new tissue preferentially, showed little ability to ameliorate ozone stress under low nutrient conditions. In neither case were the effects of ozone increased by nutrient deficiency. It is speculated that a species which maintains maximum C demand rates considerably below rates of C supply may be better able to adjust to conditions of multiple stresses.
Mechanistic models of nutrient uptake are essential to the study of plant-soil interactions. In t... more Mechanistic models of nutrient uptake are essential to the study of plant-soil interactions. In these models, uptake rates depend on the supply of the nutrient through the soil and the uptake capacity of the roots. The behaviour of the models is complex, although only six to ten parameters are used. Our goal was to demonstrate a comprehensive and efficient method of exploring a steady-state uptake model with variation in parameters across a range of values described in the literature. We employed two analytical techniques: the first a statistical analysis of variance, and the second a graphical representation of the simulated response surface. The quantitative statistical technique allows objective comparison of parameter and interaction sensitivity. The graphical technique uses a judicious arrangement of figures to present the shape of the response surface in five dimensions. We found that the most important parameters controlling uptake per unit length of root are the average dissolved nutrient concentration and the maximal rate of nutrient uptake. Root radius is influential if rates are expressed per unit root length; on a surface area basis, this parameter is less important. The next most important parameter is the effective diffusion coefficient, especially in the uptake of phosphorus. The interactions of parameters were extremely important and included three and four dimensional effects. For example, limitation by maximal nutrient influx rate is approached more rapidly with increasing nutrient solution concentration when the effective diffusion coefficient is high. We also note the ecological implications of the response surface. For example, in nutrient-limited conditions, the rate of uptake is best augmented by extending root length; when nutrients are plentiful increasing uptake kinetics will have greater effect.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.
well as accurate, nutrient-uptake models must be combined with detailed whole plant carbon alloca... more well as accurate, nutrient-uptake models must be combined with detailed whole plant carbon allocation models so that interactions between the two models can occur and the results can describe verifiable changes in key parameters. l , 304
Uploads
Papers by Ruth Yanai