Progress 08/01/05 to 07/31/09
Outputs
OUTPUTS: Understand the fate of anthropogenically-generated nitrogen (N) in forests is critical for the studies of soil biogeochemistry and terrestrial ecosystem function. Elevated N input can stimulate carbon sequestration, retained in soil and change soil fertility, or leached out of the forest and polluting aquatic ecosystems. We conducted three experiments to study the fate of externally added N. In the first experiment, soils were collected from a 60-year plantation site in south-central New York under different canopy tree species (red oak, sugar maple, Norway spruce, and red pine) and from different soil layers (0-5 cm soil or 5-15 cm soil). Soils had a wide range of organic matter (SOM) content and N mineralization and nitrification capacities. We used both 15NH4 and 15NO3 labels to trace the fate of N in a laboratory incubation experiment. 15N labels were partitioned into those immobilized into soil (retained) or extractable (not retained). We used a factorial statistical analysis to test the effects of N form (NH4 vs. NO3), stands where the soil was collected and the soil layer on N retention. Regression analyses were used to explore the relationships between N retention and SOM content and nitrification potential. In a greenhouse study, we examined the interactive effect of plant and SOM variation on the retention of 15NH4. Mesocosms filled with high-OM and low-OM soils were half planted with willow and half without. 15N retentions in plant biomass, soil or loss in leaching were quantified and a factorial two-way ANOVA was used to test the respective plant and soil effect on 15N retention and their interactive impacts. In the third experiment, soils collected from the same 60-year plantation site were used to study the fate of soil-immobilized N. After adding 15NH4 label to soils we performed a 20-week incubation-leaching experiment. Both the initial 15N retention in soil and the subsequent 15N loss in leaching were quantified. In the extension period of this grant (2008-09), the PI did a sabbatical leave at the Cary Institute of Ecosystem Studies, NY and conducted field studies at the Baltimore Urban Ecosystem Studies. Soils were collected from the Baltimore urban forests and tested to explore the urbanization effect on potential N retention. Results from these studies were reported in the Ecological Society of America Annual Meeting (2007), 5th International Symposium on Modern ecology, in Lanzhou, China (2009), and seminars in various institutions (Rutgers, 2008; University of Maryland Baltimore County, 2009). PARTICIPANTS: Weixing Zhu, PI, State University of New York, Binghamton, NY. Wenwen Wang, graduate student, Department of Biological Sciences, SUNY-Binghamton. Current address: Dept. Ecology and Evolutionary Biology, University of California, Irvine, CA. Ms. Wang finished her M.S. thesis (SUNY-Binghamton, 2007) under the scope of this grant. TARGET AUDIENCES: Information gathered under this grant is useful to the scientific community of soil biology and biochemistry, nitrogen and carbon biogeochemistry, and ecosystem ecology; as well as to the management professionals and policy makers interested in the nation's natural resource and environment. PROJECT MODIFICATIONS: During the extension period of the grant (2008-09), the PI did a sabbatical leave at the Cary Institute of Ecosystem Studies, NY and conducted field studies at the Baltimore Urban Ecosystem Studies. The impact of urbanization on soil C and N alteration and N retention is in line with the original objective of the grant.
Impacts
Global nitrogen (N) cycling has been fundamentally changed by human activities, leading to elevated N deposition in most parts of the world. The fate and transport of anthropogenic generated N in forests is critical to the fundamental researches of soil processes and terrestrial ecosystem function, and is directly related to the Nation's natural resource and environment management. Although both carbon and nitrogen cycling has been altered at global scales, their interactions at local scales are poorly known. This USDA NRI Seed Grant allows us to trace the fates of nitrogen in several experiments using 15N-labelling technique. In a laboratory experiment, we found substantial 15NH4 retention after a 7-day incubation in soils (20-70% of the input), and % retention was positively correlated to the soil organic matter content (P<0.001). The 15NO3 retention in soils was limited (<10%) and nitrification reduced soil retention of 15NH4. In the greenhouse experiment, we found that high-OM soils supported better plant growth but also lost more N in leaching. High-OM soils retained more 15NH4 input. Plant significantly increased 15NH4 retention in soils, in addition to retain 15NH4 directly in plant biomass. In the incubation-leaching experiment, we calculated the % 15N label recovery in leaching using a mass balance approach. Both initial 15N immobilization in soil and the stability of immobilized N during the 20-week incubation are soil specific. Our results suggested that soils differ in organic matter content and N cycling characteristics would immobilize N very differently, that plant-soil interactions are critical whether deposited N would increase plant growth, stay immobilized in soil, or lost in leaching. We propose that change of soil attributes (particularly its carbon content and nitrification potential) due to local and global environmental changes (for example, urbanization) would affect soil's capacity to retain N input, the effect of N on plant growth and C sequestration, and local and regional water quality.
Publications
- Zhu, W., W. Wang, J. Mo, Y. Fang, and S. Fu. 2009. Nitrogen biogeochemistry and its alterations in terrestrial ecosystems under the global dominance of human activities. In Jianguo Wu and Jie Yang (eds) Lectures in Modern Ecology (IV): Theory and Applications. Advanced Education Publications, Beijing, China.
- Zhu, W., and W. Wang. 2010. Soil attributes affect the retention of 15NH4+ and 15NO3- in forest ecosystems. Soil Biology and Biochemistry: in review.
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Progress 08/01/07 to 07/31/08
Outputs
OUTPUTS: Understand the fate of anthropogenically-generated nitrogen (N) in forest ecosystems is critical for the studies of soil biogeochemistry and terrestrial ecosystem function in a changing world. Elevated N input can stimulate carbon sequestration, retained in soil and change soil fertility, or leach out of the forest polluting aquatic ecosystems. We collected soils from a 60-year plantation site in the south-central New York from monoculture plots including two plots of red oak (ROI and ROII), sugar maple (SMI and SMII), Norway spruce (NSI and NSII), and red pine (RPI and RPII). Soils had a wide range of organic matter (SOM) contents and N mineralization and nitrification potentials. In this 3rd project of the proposal, we added 15NH4 label to all soils and then measure the stability of immobilized 15N through a 20-week incubation-leaching experiment. Enrichment of 15N in leaching declined linearly with time; average 15N enrichment ranged from 10.9 - 35.4% in L0 (initial leaching after the labeling - indicating 15N not immobilized) and 1.2-2.1% in LIV (leaching combination from Week 16-20). We calculated the % label recovery in leaching using a mass balance approach. There was a wide range of initial 15N immobilization. Recovery of the initial 15N label in L0 ranged from 2.9-57.5%. After 20-weeks of incubation-leaching, another 3.7-19.4% of the original label was released, making total recovery in leaching ranged from 22.3-69.7%. Both initial 15N immobilization and the stability of immobilized N during the 20-week incubation are soil specific. We are currently in the process of quantifying 15N content in residue soils, and to use density-fractionation to further separate 15N immobilization in fast-turnover pool (light fraction) and slow-turnover pool (heavy fraction). PARTICIPANTS: Weixing Zhu - PI Wenwen Wang - Graduate student Both Zhu and Wang presented results from this project to the 92nd Ecological Society of America (ESA) Annual Meeting, San Jose, California, Aug 5-10, 2007. Wang finished her M.S. degree at the Binghamton University and moved to the Ph.D. program at the UC-Irvine. TARGET AUDIENCES: Scientists and policy makers interested in evaluating the impact of elevated atmospheric nitrogen deposition on forest ecosystems, including effects on carbon sequestration and local/regional water quality. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Understand the fate of anthropogenically-generated nitrogen in forest ecosystems is important to evaluate both the direct and indirect impacts of human activities on terrestrial ecosystem function. Both carbon and nitrogen cycling has been altered at global scales yet their interactions at local scales are poorly known. Our results showed that soils differ in organic matter content and N cycling characteristics would immobilize newly deposited atmospheric N very differently. We suggest that the change of soil (particularly its carbon content) due to local and global environmental changes would affect soil's capacity to retain new N input, the effect of N on plant growth and C sequestration, and local and regional water quality.
Publications
- No publications reported this period
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Progress 08/01/06 to 07/31/07
Outputs
Human activities have greatly altered global nitrogen (N) biogeochemical cycling, and for terrestrial ecosystems, increased the level of atmospheric N deposition. Understand the fate of atmospheric deposited N in forests is important for studies of soil biogeochemistry and terrestrial ecosystem function. In a lab incubation study, we collected soils from a 60-year plantation site in south-central New York under different canopy tree species (red oak, sugar maple, Norway spruce, and red pine) with a wide range of soil organic matter (SOM) content and N mineralization and nitrification capacities. Labeled 15NH4 and 15NO3 were separately injected into soils, and after 7-days incubation, separated into extractable pool (not-retained) and residue soil pool (retained). We found substantial 15NH4 retention in residue soils (20-70% of the input), and the % retention was positively correlated to %SOM (P<0.001). The 15NO3 retention in soils was limited (<10%). The percentage of
15NH4 label that was recovered as extractable 15NO3 was quite variable (0-60%). We proposed that both the variations of SOM and nitrification capacity affect the retention of NH4-N deposited into the forest, while the NO3-N deposited will be poorly retained. In a greenhouse mesocosm study, we examined the interactive effect of plant and SOM variation on the retention of labeled 15NH4-N. High-OM soils supported better plant growth but also lost more N in leaching. High-OM soils also retained more 15NH4 input. Plant significantly increased 15NH4 retention in soils, in addition to retain 15NH4-N in plant biomass. We found the amount of 15N recovered in plant biomass was lower when plant grew in high-OM soils than in low-OM soils. Our results suggest that the retention of atmospheric deposited N, as well as the impact on plant growth, are strongly affected by the plant-soil interactions in terrestrial ecosystems. A third lab study is also underway, to examine the long-term fate of 15N
retained in forest soils.
Impacts
Understand the fate of atmospherically deposited nitrogen from human activities is important for evaluating terrestrial ecosystem dynamics. The complex plant-soil interactions in terrestrial ecosystems, including the formation of soil organic matter with different quantity and quality, have been found in our study affecting the retention of atmospherically deposited N and the level of deposited N that was incorporated into plant biomass. Our project also showed very different fate of ammonium-N and nitrate-N in forest soils, suggesting different ecosystem consequences of elevated N deposition depending on the source and form of N pollution.
Publications
- No publications reported this period
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Progress 08/01/05 to 07/31/06
Outputs
Understand the fate of atmospheric nitrogen deposition input from human activities is important for soil biogeochemistry studies and terrestrial ecosystem dynamics. We hypothesized that inorganic N immobilizations (both microbial assimilation and abiotic-chemical immobilization) are positively correlated with SOM quantity; are higher in SOM-rich organic soils than in SOM-poor mineral soils, and higher in forest stands with higher SOM quantity than in forests with lower SOM quantity. Soils were collected from a 60-year plantation site in south-central New York with different canopy tree species (red oak, sugar maple, Norway spruce, and red pine, two 1-acre stands per tree species) and a wide range of %SOM. Labeled 15NH4 and 15NO3 were separately injected into soils and half the soils were immediately extracted with cold 0.5M K2SO4 (T0) and another half incubated in the lab and extracted with K2SO4 7 days later (T7). The T0 15N recovery in residue soils (not extracted
by K2SO4 solution) was less than 10%, and 15NO3 immobilized into soils was very low (< 2%). The 15NH4 immobilization after 7-days incubation ranged from 20-70%, and the % Recovery in residue soils were positively correlated to soil organic matter concentration. The 15NO3 immobilization remained much lower than the 15NH4 immobilization. SOM-rich surface soils (0-5 cm) generally had much higher 15N immobilization capacity than mineral-rich sub-surface soils (5-15 cm). Our preliminary results did not support the notion that significant nitrate immobilization occurred in this plantation forest soils and demonstrated that SOM variation played a major role in retaining atmospheric deposited N. We have also initiated a greenhouse study in which shrub willow was planted to test the relative contribution of live plant and dead SOM on N retention.
Impacts
Understand the fate of atmospherically deposited nitrogen from human activities is important for evaluating terrestrial ecosystem dynamics. If pants are the dominating sink of deposited N, that could stimulate plant growth and the increased assimilation of atmospheric carbon. On the other hand, if most N was retained in soils, that could stimulate a wide range of biogeochemical processes, with some affecting N loss to surface- and ground water and causing aquatic eutrophication. This project will study the mechanisms controlling N retention in forest soils and the fate of atmospherically deposited N using stable isotope 15N labeling.
Publications
- No publications reported this period
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