Progress 09/15/04 to 09/14/07
Outputs
OUTPUTS: Objective 1. Characterization of a gorse-infested landscape for symbiotic and edaphic properties that contribute to its dominant nature. We studied the gorse infestations, located at an altitude of 6000 ft on the slopes of Mauna Kea, Hawaii. We observed that all gorse plants, including young seedlings were nodulated on surface roots within the crown of the taproot. The nodules of gorse were occupied by Bradyrhizobium, which is also the symbiont of Acacia koa. Bradyrhizobium strains isolated from the nodules of gorse and Acacia koa plants in Humuula had similar DNA fingerprint profiles, suggesting that the same group of Bradyrhizobium isolates nodulate both plants. Inoculation of A. koa seedlings grown in controlled growth chamber were nodulated by Bradyrhizobium isolated from gorse. Gorse plant samples had significantly higher nitrogen contents than the kikuyu grass samples collected from the same location. The soils collected within the epicenters of the gorse infestation
were significantly more acidic than the periphery soils where kikuyu grass occupied the soil surface. Objective 2. Risk assessment of non-infested locations by identifying symbiotic and edaphic properties conducive to gorse establishment. Gorse is competitive in degraded soils with low fertility where other plants generally do not grow well. Due to its nitrogen-fixing ability in symbiosis with Bradyrhizobium, gorse can grow even in degraded soils. Sequence analyses of PCR amplified 16 rDNA from total DNA isolated from soils samples collected from Palaau State Park forest areas on the island of Molokai and forests and grazing areas in the slope of Mauna Kea on the island of Hawaii, show presence Bradyrhizobium in these soils. These results indicate that forest soils in Hawaii have Bradyrhizobium to support nitrogen-fixing symbiosis with gorse. Objective 3. Developing gorse eradication methods. To develop an improved strategy to control gorse, we used fertilizer to enhance kikuyu grass
and thereby suppress gorse. An experiment was set up within a cleared area of 1000 m2 in Haleakala Ranch that contained experimental units consisting of a 2x2 factorial treatment design with five replications to compare the interactions between fertilizer inputs (f+, f-) and herbicide applications (h+, h-). After one year, all plots that received fertilizer treatments (h+f+ and h-f+), were fully covered with kikuyu grass, and therefore no other vegetations could grow and establish in these plots. The plots that did not receive fertilizer (h-f- and h+f-) were also covered kikuyu grass, although their growth was less than half of those in the f+ plots. These f- plots also showed emergence of other weed that are generally common in that area. These observations suggest that a heavy dose of fertilizer application following land clearing by mechanical scarification followed by fertilizer application can promote fast growth of kikuyu grass, which effectively suppresses gorse
reestablishment. It is expected that by maintaining thick kikuyu grass vegetation for 3-5 years, the gorse seed bank in the area will be exhausted.
PARTICIPANTS: Participants 1. James Leary (Graduate student) 2. Sandro Jube (Graduate Student) 3. Rudolph Fredua-Agyeman (Graduate Student) 4. Paul Scowcroft, US Forest Service, Hilo 5. Nguyen V. Hue, Professor, Department of Tropical Soil and Plant Sciences, University of Hawaii at Manoa 6. Paul Singleton, Professor, Department of Tropical Soil and Plant Sciences, University of Hawaii at Manoa 7. Nick Dudley, Forest Scientist, Hawaii Agriculture Research Center 8. Dulal Borthakur, Professor, Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa Collaborators Richard Hill, Landcare Research, New Zealand (contact: HillR@crop.cri.nz) Mike Robinson, Department of Hawaiian Home Lands (contact: Tel: 1-888-943-4335; email: merobi@hilo.net) Richard Wass, U.S. Fish and Wildlife Service, (Contact: Tel: 808-933-6915 ext. 23; email: richard_wass@fws.gov) Training and Professional Development 1. James Leary completed his PhD on this work 2. Other two graduate
students Rudolph Fredua-Agyeman and Sandro Jube participated in this project and were trained in soil biology research 3. Undergraduate student Richard Liao received training in soil microbiology and molecular biology methods through this project.
TARGET AUDIENCES: Ranchers, conservationists, and land managers from the islands of Maui and Hawaii who have to deal with gorse infestations are the target audience of this project. Results obtained from this project will also be useful for ranchers and weed scientists in New Zealand, Australia, Tasmania, Chile, Spain, U.K., British Columbia, Oregon, and California where gorse infestation is a problem.
PROJECT MODIFICATIONS: There were minor modifications related to methodology to characterize soil microbial populations and the experimental design of the field experiment to adjust to the available field situations.
Impacts
Heavy gorse infestations occur on the islands of Maui and Hawaii and occupy thousands of acres of important high-elevation rangelands. These rangelands provide natural resources that are vital to conservation and agriculture. Rangeland operations (cattle and forestry) are important to Hawaii because they occupy the largest area of agricultural land. Yet these operations provide much smaller returns on investment, relative to other agricultural operations. Thus, opportunities to implement effective gorse control strategies are limited. Current strategies implemented by land managers are inadequate for controlling gorse infestations. We observed that treatment of herbicide garlon can effectively desiccate a koa stand, but this cannot prevent the growth of new gorse seedlings from the seed bank in the soil. Repeated herbicide application will be expensive. We have developed a practical strategy for effective growth control, in which a heavy dose of fertilizer is applied
following land clearing in gorse infested areas. The fertilizer application promotes fast growth of kikuyu grass that forms a thick mat over the land within a few months and thus suppresses the reestablishment of gorse. As a nitrogen-fixing legume, gorse is competitive only under low fertility condition where grasses cannot grow well. However, when fertilizer is applied, kikuyu grass becomes competitive and suppresses reemergence of growth.
Publications
- Leary JK (2007) Diversity and distributions of indigenous bradyrhizobia populations associated with Acacia koa. PhD dissertation submitted to the University of Hawaii in May 2007, 125p.
- Leary JK, Scowcroft P., (2007) Control of invasive shrub, restoration/establishment of desirable trees. Pacific Islands Forestry Short Course, August 15-17, 2007, organized by the U.S. Forest Service at the Hakalau Forest National Wildlife Refuge, HI.
- Jube S, Borthakur D (2007) Expression of bacterial genes in transgenic tobacco: methods, applications and future prospects. Electronic J Biotechnology. 10 (3)452-467. DOI: 10.2225/vol10-issue3-fulltext-4 ; http://www.ejbiotechnology.info/content/vol10/issue3/full/4/4.pdf
- Leary JK, Peltzer DA, Hue NV, Borthakur D (2007) Gorse (Ulex europaeus) infestations in Hawaii and New Zealand display similar patterns of resource exploitation from altered landscapes. The 47th Annual Conference of the Weed Science Society of America, held on February 4-7, 2007 in San Antonio, CA.
- Leary JK, Peltzer DA, Hue NV, Borthakur D (2005) Gorse (Ulex europaeus) infestations in Hawaii and New Zealand display similar patterns of resource exploitation from altered landscapes. Report to the Pacific-Hawaii Conservation Exchange Program. http://www.hawaiiconservation.org/exchangeprogram.asp
- Leary JK, Hue NV, Singleton PW, D. Borthakur (2006) Soil acidification, nutrient depletion, and symbiotic nitrogen fixation are the major features of gorse (Ulex europaeus) infestation on volcanic soils in Hawaii. Biol. Fertility Soils. 42:215-223.
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Progress 10/01/05 to 09/30/06
Outputs
Gorse is a woody leguminous shrub that is endemic to Western Europe and the Mediterranean, but has become a major cosmopolitan weed with infestations existing in at least 10 countries. To determine the effects of gorse infestations in different geographical locations, separate field analyses were conducted on Mauna Kea, Hawaii and Bank's Peninsula, New Zealand. At both sites, three experimental units were identified and consisted of a high-density gorse population (HD) zone and an adjacent low-density gorse population (LD) zone. Furthermore, the LD zones in Hawaii were areas with young pioneer gorse individuals in early succession, while the LD zones of New Zealand were former infestations in late succession. Soil, plant, and bacterial samples were collected from all zones at both locations. Soil nutrient status was the best indicator of gorse impacts on the landscape. Soil pH was significantly lower in the HD zones for both sites. Concentrations of Ca and Mg were
also significantly higher in the LD zones for both sites, while Al concentrations were significantly higher in the HD zones. Plant Al concentration was significantly higher only in the LD zone in New Zealand, but not in Hawaii. This was the only significant difference for all tissue nutrients for both sites. This suggests that changes to the soil are dependent on gorse plant densities (i.e. infestation) and reversion of soil nutritional status may be a successional trait of the landscape. This work also suggests that Al accumulation by gorse in late succession may be an indicator of decline. Bradyrhizobium isolates from Hawaii and New Zealand do not share the same Box-PCR marker profiles, while gorse and koa (Acacia koa) Bradyrhizobium isolates do. This indicates that gorse does not require specific host-symbiont relationships for symbiosis and is compatible with a wide range of indigenous Bradyrhizobium for effective nitrogen fixation. The lack of specificity for root mutualists
(Bradyrhizobium) may play a major role in the cosmopolitan success of gorse invasion. Regardless of the geographic location, soil nutrition and symbiosis appear to be important factors to consider when developing preventative or responsive control strategies.
Impacts
his research initiative will promote the revitalization of degraded gorse-infested lands from an environmental burden to an economic engine that will advance agriculture and watershed conservation in Hawaii.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
The aim of this investigation is to identify ecological features associated with the invasive weed gorse (Ulex europaeus) by comparing the gorse-infested areas to the surrounding uninfested areas of this landscape. The soils within the gorse infestation are more acidic, resulting in higher levels of KCl-extractable Al and lower levels of Mehlich III-extractable Ca, Mg, Mn, and Zn. Yet, gorse accumulates higher concentrations of Ca, Zn and, Cu than the kikuyu grass (Pennesitum clandestinum), which is ubiquitous throughout the site. The Ca:Al and Mg:Al molar charge ratios of the soils are lowest within the epicenter of the gorse infestation, while the molar ratios are highest in the gorse apical stem tissues. All gorse plants are nodulated and have higher nitrogen contents than the surrounding kikuyu grass. Furthermore, the delta15N of the gorse stem tissues approaches 0, suggesting that nitrogen is being symbiotically fixed from the atmosphere. Characterization of the
Bradyrhizobium isolated from gorse nodules shows similarities and distinctions to Bradyrhizobium isolated from the endemic legume koa (Acacia koa) within the same location. Population densities of the indigenous Bradyrhizobium are higher within the gorse rhizosphere than the kikuyu grass. Soil acidification, nutrient depletion, and symbiotic nitrogen fixation distinguish gorse-infested areas from the surrounding uninfested areas. These observations suggest that gorse has a competitive advantage over kikuyu grass in conditions of soil nutrient deficiency.
Impacts
This research initiative will promote the revitalization of degraded gorse-infested lands from an environmental burden to an economic engine that will advance agriculture and watershed conservation in Hawaii.
Publications
- Leary, J.K., Hue, N.V., Singleton, P.W. and Borthakur, D. 2005. Soil acidification, nutrient depletion, and symbiotic nitrogen fixation are the major features of gorse (Ulex europaeus) infestation on volcanic soils in Hawaii. Biol. Fertility Soils (Published online: 28 June 2005)
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Progress 10/01/03 to 09/30/04
Outputs
Gorse (Ulex europaeus) infestation occupies over 4,000 ha of agricultural and conservation lands on the southeastern slope of Mauna Kea on the Island of Hawaii. The aim of this investigation is to identify ecological features associated with gorse infestation by comparing the gorse-infested areas to the surrounding uninfested areas of this landscape. The soils within the gorse infestation are more acidic, resulting in higher levels of extractable Al. Gorse-infested soils are also more deficient in Ca, Mg, Mn, and Zn. Gorse accumulates higher amounts of Ca, Zn and Cu than the kikuyu grass (Pennesitum clandestinum), which is ubiquitous throughout the site. The Ca:Al and Mg:Al ratios of the soils are lowest within the epicenter of the gorse infestation. In contrast, these same ratios are high in all gorse stem tissues. All gorse plants are nodulated and have higher nitrogen contents than the surrounding kikuyu grass. The natural abundance of 15N approaches zero in the
gorse stem tissues, suggesting that nitrogen is being symbiotically fixed from the atmosphere. Characterization of the Bradyrhizobium isolated from gorse nodules shows similarities to koa bradyrhizobia of the same location and population densities of these indigenous bradyrhizobia are higher within the rhizosphere of gorse than kikuyu grass. Soil acidification, nutrient depletion, and symbiotic nitrogen fixation distinguish gorse-infested areas from the surrounding uninfested areas. These observations may be useful in designing a gorse control strategy that incorporates techniques in soil fertility management.
Impacts
This research initiative will promote the revitalization of degraded gorse-infested lands from an environmental burden to an economic engine that will advance agriculture and watershed conservation in Hawaii.
Publications
- Leary, J., Hue, N.V., Singleton, P.W. and Borthakur, D. 2004. Soil acidification, aluminum exclusion, and symbiotic nitrogen fixation are the major features of gorse (Ulex europaeus) infestation on young volcanic soils in Hawaii. Abstract of poster presentation at the 19th North American Symbiotic Nitrogen Fixation Conference, held at Montana State University, Bozeman, Montana, June 27-July 1, 2004. p72.
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