EFFECTS OF NITROGEN SUPPLY ON THE DYNAMICS AND CONTROL OF JAPANESE BARBERRY AND JAPANESE STILTGRASS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: NRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 0192809
• Grant No.: 2002-35320-12416
• Proposal No.: 2002-00639
• Project Start Date: Sep 1, 2002
• Project End Date: Aug 31, 2005
• Grant Year: 2002
• Program Code: [51.9]- (N/A)

Recipient Organization
RUTGERS, THE STATE UNIVERSITY OF NEW JERSEY
3 RUTGERS PLZA
NEW BRUNSWICK,NJ 08901-8559

Performing Department
ECOLOGY, EVOLUTION AND NATURAL RESOURCES

Non Technical Summary
Eastern deciduous forests have been extensively invaded by two invasive exotic species, Japanese barberry (Berberis thunbergii) and Japanese stilt grass (Microstegium vimineum). Previous research has shown that soil properties, particularly the soil pH and the amounts of nitrate present in the soil solution, are markedly different in soils beneath these plants and beneath adjacent areas of native understory plants. It is possible that the exotics are modifying the soil properties in a way that promotes their growth more than that of the native species, thus allowing them to outcompete the native plants. I will use greenhouse studies to determine how the growth and reproductive capacity of these exotics and the two most common native species response to different amounts and chemical forms of nitrogen. I will also use a field experiment, implemented in two parks that are heavily invaded by these species, to test the applicability of the greenhouse results to field conditions and test the role of soil manipulations in both inhibiting the growth of the exotics and promoting the growth of re-introduced native species. The role of soil processes in promoting or retarding invasions into native ecosystems has been rarely examined; this project will provide an extensive test of the role soil processes in exotic invasions.

Animal Health Component

50%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	2300	1060	50%
213	2300	1070	50%

Knowledge Area
213 - Weeds Affecting Plants;

Subject Of Investigation
2300 - Weeds;

Field Of Science
1060 - Biology (whole systems); 1070 - Ecology;

Keywords

weeds

nitrogen cycle

nutrient cycling

invasive species

deciduous trees

nitrates

restoration

forest ecology

nitrogen

weed control

plant biology

forest soils

soil plant nutrient relations

berberis

microstegium vimineum

demography

seed production

plant growth

soil conditions

vaccinium

native plants

field testing

rate determination

viburnum

nutrient uptake (plants)

reductases

leaves

concentration

nitrification

Goals / Objectives
The goal of this project is to investigate the relationship between nitrogen cycling in forest soils and the invasibility of two common, widespread exotic species in eastern deciduous forests: Japanese barberry (Berberis thunbergii) and Japanese stilt grass (Microstegium vimineum). Although these two species are found in over the half the continental US and into Canada, very little is known of the demographic characteristics and the biological properties that enable them to be so highly invasive. My previous research on these species has provided strong evidence that both species are associated with soils that have a high rate of nitrate production, and that both species favor nitrate as a source of nitrogen. I hypothesize that high rates of N supply, particularly in the form of nitrate, promotes high rates of seed production, growth and vegetative spread, thus supporting high invasion rates. I further hypothesize that invasions can be managed by altering soil conditions to reduce nitrate production, which in turn should reduce sexual and asexual reproduction. The specific objectives of the research are: (1) to use greenhouse studies to define the growth and demographic responses of the two exotics and the two most common native understory plants (lowbush blueberry, Vaccinium pallidum, and maple-leaved viburnum, Viburnum acerifolium) to different amounts and chemical forms of nitrogen, (2) to test methods of manipulating nitrogen in field plots to test the applicability of the greenhouse results to methods of native plant restoration, and (3) to identify the growth and demographic responses of both invasive exotic and native species to soil manipulations of nitrogen, in order to identify the mechanisms of invasive spread. The project will thus both determine how soil nitrogen supply affects the invasibility of noxious plants in deciduous forests by identifying the specific growth and demographic mechanisms of response, and will determine whether practical methods of manipulating soils can be used in restoration projects to inhibit the growth of the invasives and promote the growth of the natives.

Project Methods
The study will incorporate both greenhouse studies of growth responses to different amounts and forms of nitrogen by the exotics and the most common native species, and field studies using soil manipulations of available N to determine the relative rates of spread of these species. The field studies will be conducted in a national park and a state park, both of which are currently heavily invaded by these species. In the greenhouse studies, plants will be grown from seed (Microstegium) and cuttings (Berberis, Vaccinium, Viburnum), with five levels of N supplied, in one set of pots as nitrate and in another set of pots as ammonium. Response variables will include aboveground growth rates, seed set, vegetative spread (measured repeatedly during growth), above- and below-ground biomass at harvest, leaf tissue concentrations of N and nitrate reductase enzyme, and rate of N uptake by roots (using 15N techniques). Multivariate statistical analyses will be used to determine the responsiveness of each species to added N of each chemical form. In the two parks, experimental plots will be established and to which soil manipulations are applied. Using a latin square/split plot design, each plot will include a subplot from which the exotics are removed, a suplot from which the exotics are removed and in which the native understory plants are re-introduced, and a subplot in which the exotics are not removed. The eoxtics-removal subplots will be used to test hypotheses concerning the role of N forms and amounts in the rates of re-invasion by the exotics, and the competition interactions between the natives and the exotics; these experiments will directly inform restoration efforts. The unweeded plots will test hypotheses concerning the efficacy of soil manipulations on the population dynamics of the exotics; the results will be useful in evaluating the value of such manipulations in exotic control strategies. Response variables will include the same growth and demographic variables as in the greenhouse studies, plus documentation of soil conditions and N cycling rates. Two-way analyses of variance using appropriate models for the split-plot latin square design will be used to test the hypotheses that soil manipulations, native plant reintroductions, and/or their interaction affect reinvasion rates and the growth and spread within the plots of any reinvading stems. Similar analyses will be used to test the long-term (over the course of the experiment) efficacy of the soil treatments (in terms of percentage reduction of nitrification and NO3 concentrations between treatments and the controls); these analyses will determine whether the native plant reintroductions augments the effects of the soil manipulations.

Progress 09/01/02 to 08/31/05

Outputs
This project was a large-scale field manipulative experiment that explored the potential effectiveness of soil manipulations to control the spread of two noxious invasive species that in previous research had been found to be associated with elevated pH and high rates of nitrification and nitrate availability. Fifty plots, each 5 x 7 m, were established in which the exotics were cleared from two-thirds of the plot and soil manipulations (management of pH, removal of surface organic matter, and additions of carbon via wood chips) were applied to the entire plot. We have monitored growth, spread, and success of the remaining exotics and of native species planted into the plots for two years following plot establishment. This experiment has just concluded, and data analysis is still in progress. In addition, a large greenhouse study was conducted to test the relative responsiveness of exotic and native species to the amount and form of nitrogen nutrition. The field experiment resulted in small but significant changes to soil properties. In particular, removal of the organic horizon and addition of wood chiops reduced N availability, as originally hypothesized. However, the effects were smaller than expected, and there were no significant changes in the growth of the exotics, as measured by stem counts, stem lengths (barberry) or biomass (stilt grass), nor in the growth, survivorship or recruitment of native species. It was concluded from this experiment that manipulation of forest soils is not a practical method of controlling exotic growth and promoting native species; the amount of manipulation necessary to achieve a large change in soil conditions is prohibitive for most management agencies. The experimental analysis of growth with respect to N additions showed that both Microstegium and Berberis responded strongly to both nitrate and ammonium additions with increased growth, whereas the native species (Vaccinium angustifolium and Viburnum dentatum) were inhibited by high concentrations of N. These results support the initial hypothesis of the study, showing that N availability is a strong determinant of exotic invasion. The overal results suggest that further research to develop practical methods of reducing N availability in forest soils is urgently needed to promote the growth of native species and reduce exotic invasions

Impacts
The results of this study have been presented at numerous meetings, both scientific meetings and meetings of land managers. The work is being used to design control and management strategies for enhancing forest health.

Publications

• Ehrenfeld, J. G., B. Ravit and K. Elgersma. 2005. Feedback in the Plant-Soil System. Annual Review of Environment and Resources 30:75-115
• Ehrenfeld, J. G. 2004. Implications of invasive species for below-ground community and nutrient processes. Weed Technology 18:1232-1235.
• Ehrenfeld, J. G., K. R. Ross and M. Patel. 2006. Soils and the management of invasive plant species: a case study of the challenges of soil restoration. Annual Meeting, Ecological Society of America, Memphis TN
• Ross, K., J. G. Ehrenfeld and M. Patel. 2006. Effects of soil amendments on the nitrogen dynamics of Japanese barberry (Berberis thunbergii) and Japanese stiltgrass (Microstegium vimineum) in New Jersey forests. Ecology in an Era of Globalization: Challenges and Opportunities for Environmental Scientist in the Americas, January 8-12, 2006, Merida, Mexico, sponsored by the Ecological Society of America
• Ehrenfeld, J. University of Pennsylvania, Morris Arboretum and the Mid-Atlantic Plant Pest Council. Exotic invasions in deciduous forests - can managing soil help? August 2005.
• Ehrenfeld, J. Yale University, Invasive Species and the Public Good lecture series: Ecological consequences and Management Innovations. New Haven, CT. Jan. 24, 2005.
• Patel, M. V., K. A. Ross and J. G. Ehrenfeld. 2005. Growth responses of exotic and native forest understory species to different forms of nitrogen nutrition. Ecological Society of America Annual Meeting, Montreal, Canada. Abstracts p. 493.
• Ross, K. A., M. V. Patel and J. G. Ehrenfeld. 2005. Effects of soil amendments on nitrogen dynamics of Berberis thunbergii and Microstegium vimineum in New Jersey forests. Ecological Society of America Annual Meeting, Montreal, Canada. Abstracts p. 547.
• Ehrenfeld, J. G. 2003. Challenges in restoring soils altered by exotic plant invasions. Invasive Plants in Natural and Managed Systems. 7th International Conference on the Ecology and Management of Alien Plant Invasions., Ft. Lauderdale, FL. (invited presentation)
• Ehrenfeld, J. G. 2003. Implications of invasive species for below-ground community and nutrient processes. Invasive Plants in Natural and Managed Systems. 7th International Conference on the Ecology and Management of Alien Plant Invasions., Ft. Lauderdale, FL. (invited presentation)
• Ross, K. A. and J. G. Ehrenfeld. 2003. Effects of nitrogen supply on the dynamics and control of Japanese barberry (Berberis thunbergii) and Japanese stiltgrass (Microstegium vimineum). 7th International Conference on the Ecology and Management of Alien Plant Invasions., Ft. Lauderdale, FL.

Progress 01/01/04 to 12/31/04

Outputs
The purpose of this project is to explore the use of soil manipulations to reduce the growth of two noxious invasive species, Microstegium vimineum and Berberis thunbergii, and promote the growth of the native species that they are replacing. During the past year, a large field-based experiment has been implemented at two sites, and a greenhouse study of nitrogen nutrition of these species has been initiated. The field experiment has been established in densely infested areas in Morristown National Historical Park and the Delaware Gap National Recreation Area. In each site, 25 plots, each 5m x 7m, were established on similar west-facing slopes. After an initial census of the vegetation, two-thirds of each plot was cleared of all exotics. The barberry stems were cut at ground level, and spot-treated with herbicide (glyphosate) to prevent re-growth. Stilt grass was gently scraped from the soil. Initial soil samples were taken to characterize soil organic matter, pH, and nitrogen fractions. Soil treatments were assigned to plots using a Latin square design. These included application of (1) elemental sulfur and aluminum sulfate to lower pH, (2) hardwood wood chips, and(3) nitropyrin as a nitrification inhibitor. The fourth treatment involved removing the surface 5 cm of organic-rich soil from the plot. Following the implementation of the soil treatments, the plots (one of the cleared thirds) were planted with nursery-grown seedlings of native shrub species (two plants of Vaccinium pallidum, one plant of Lindera benzoin, one plant of Hamamelis virginiana). All plants were fenced to prevent deer browse. Planting was conducted in the late fall in Morristown, and due to an unusually early freeze, in early spring in the Delaware Gap site. During the second year of the project, we monitored plant growth, survival and recruitment, soil pH, organic matter, and nitrogen dynamics (in each third of each plot, 3 x 50 = 150 samples per sampling time), three times during the growing season (May, August, October). The same program of monitoring of the plots will be conducted during the coming growing season. A greenhouse study designed to test the relative response of the two exotics and two native species (Vaccinium pallidum and Viburnum acerifolium) to nitrate and ammonium as sources of nitrogen was also carried out. Plants were grown in sand culture, and amended weekly with Hoaglands solution with three levels of nitrogen. Pots intended to have only NH4 as an N source were also amended periodically with nitropyrin to reduce or eliminate nitrification. The experiment was completed in November, and all plants were harvested, separated into above- and below-ground poprtions, and the dry masses determined. Data analysis of the results is on-going. Preliminary assessment of the data suggests that the Microstegium is indeed more responsive to nitrate than the other species. We also are planning studies of mycorrhizal mutualisms in the target exotic species on the treated and untreated soils.

Impacts
The experiment has been described and discussed in several presentations at the IPINAMS conference on exotic invasive species, the Northeast Ecology Conference this year, and abstracts have been submitted for the Ecological Society of America meeting this coming summer. The results have also been used in discussions of management policies as part of the work of the New Jersey Invasive Species Council, of which the PI is a member.

Publications

• Ehrenfeld, J. G. 2004. Implications of invasive species for below-ground community and nutrient processes. Weed Technology 18:1232-1235.

Progress 01/01/03 to 12/31/03

Outputs
The purpose of this project is to explore the use of soil manipulations to reduce the growth of two noxious invasive species, Microstegium vimineum and Berberis thunbergii, and promote the growth of the native species that they are replacing. During the past year, a large field-based experiment has been implemented at two sites, and a greenhouse study of nitrogen nutrition of these species has been initiated. The field experiment has been established in densely infested areas in Morristown National Historical Park and the Delaware Gap National Recreation Area. In each site, 25 plots, each 5m x 7m, were established on similar west-facing slopes. Each site was censussed to determine initial population densities of the Berberis and cover of Microstegium. Following the census, two-thirds of each plot was cleared of all exotics. The barberry (Berberis) stems were cut at ground level, and spot-treated with herbicide (glyphosate) to prevent re-growth. Stilt grass was gently scraped from the soil. Initial soil samples were taken to characterize soil organic matter, pH, and nitrogen fractions. Following this, soil treatments were assigned to plots using a Latin square design, and were then applied in the field. These included application of (1) elemental sulfur and aluminum sulfate to lower pH, (2) hardwood wood chips, and(3) nitropyrin as a nitrification inhibitor. Preliminary studies were conducted to determine the amounts of amendment necessary to lower soil pH and reduce nitrification. The fourth treatment involved removing the surface 5 cm of organic-rich soil from the plot. Following the implementation of the soil treatments, the plots (one of the cleared thirds) were planted with nursery-grown seedlings of native shrub species (two plants of Vaccinium pallidum, one plant of Lindera benzoin, one plant of Hamamelis virginiana). All plants were fenced to prevent deer browse. Planting was conducted in the late fall in Morristown, and due to an unusually early freeze, in early spring in the Delaware Gap site. We are now following nitrogen dynamics, plant growth of exotics in the uncleared third and of natives in the cleared and planted third, and recruitment of exotics and natives in the cleared and unplanted plot thirds. A preliminary greenhouse study designed to test the relative response of the two exotics and two native species (Vaccinium pallidum and Viburnum acerifolium) to nitrate and ammonium as sources of nitrogen was carried out. Unanticipated problems with growth in sand culture and sensitivity to drought occurred. A revised experimental design has been implemented for the experiment this growing season.

Impacts
The experiment has been described and discussed in several presentations at the IPINAMS conference on exotic invasive species, and the Northeast Ecology Conference last year. These presentations have generated considerable discussion about the feasibility and novelty of approaching invasive species management through soil manipulation. We anticipate that the continued presentation of the approach and results will open up a new avenue of approach to exotic species management.

Publications

• Ehrenfeld, J. G. 2003. Implications of invasive species for below-ground community and nutrient processes. Invasive Plants in Natural and Managed Systems. Ft. Lauderdale, FL.
• Ehrenfeld, J. G. 2003. Challenges in Restoring Forest Soils Altered by Exotic Plant Invasions . Invasive Plants in Natural and Managed Systems. Ft. Lauderdale, FL.
• Ross, K. and J. G. Ehrenfeld. 2003. Effects of nitrogen supply on the control of Berberis thunbergii and Microstegium vimineum. Invasive Plants in Natural and Managed Systems. Ft. Lauderdale, FL.
• Ross, K. 2003. Effects of nitrogen supply on the control of Berberis thunbergii and Microstegium vimineum. Northeast Ecology Conference, Rutgers University, New Brunswick, NJ.

Progress 01/01/02 to 12/31/02

Outputs
The purpose of this project is to determine whether manipulations of soil conditions, particularly the inhibition of nitrification, will inhibit the growth of two widespread exotic species found in eastern deciduous forests (Japanese barberry, Berberis thunbergii, and Japanese stiltgrass, Microstegium vimineum). In previous research, we have found that both species are associated with decreased soil acidity and increased availability of nitrate in the soil. We hypothesize that these species can grow better (faster growth rates, higher reproductive rates) with nitrate as a nitrogen source, whereas the native species perform better with ammonium as a nitrogen source. We are in the process of setting up field plots in two natural areas in New Jersey, as described in the project proposal, and will be implementing the experimental protocols this summer. In each park (Morristown National Historical Park and Delaware Water Gap National Recreation Area), a set of 25 plots, each 5 x 7.5 m, have been delimited within an area of the forest invaded by both species. Each plot has been divided into three strips (5 x 2.5m), and two strips cleared of the exotics. Preliminary testing of soil conditions (pH, organic matter, extractable nitrate and ammonium, total Kjeldahl nitrogen) is being carried out (samples collected, laboratory processing in progress). In addition, preliminary studies to determine the level of application of the projected soil treatments (bark chips and sawdust to reduce nitrogen availability, aluminum sulfate to reduce pH, and N-serve to reduce nitrification rates) have been conducted. We expect to apply the treatments to the plots in spring 2003. We are also setting up a greenhouse experiment to determine the responsiveness of the exotics and two native species to different levels of nitrate and ammonium. This portion of the study will also be established in early spring.

Impacts
This study is expected to show whether soil nitrogen dynamics are an important determinant of exotic invasions in forested ecosystems, and whether it is feasible and useful to manipulate soil N processes as part of restoration efforts. Because the two study species are widely distributed throughout the eastern and midwestern United States, and are often associated with other noxious invasive species in these ecosystems, the results may have considerable impact on efforts to control these species and restore native species.

Publications

• No publications reported this period