Clonal Variation in Survival and Growth of Hybrid Poplar and Willow in an IN SITU Trial on Soils Heavily Contaminated with Petroleum Hydrocarbons

Species and hybrids between species belonging to the genera Populus (poplar) and Salix (willow) have been used successfully for phytoremediation of contaminated soils. Our objectives were to: 1) evaluate the potential for establishing genotypes of poplar and willow on soils heavily contaminated with petroleum hydrocarbons and 2) identify promising genotypes for potential use in future systems. We evaluated height, diameter, and volume after first year budset by testing 20 poplar clones and two willow clones. Unrooted cuttings, 20 cm long, were planted in randomized complete blocks at 0.91- × 0.91-m spacing at Gary, IN, USA (41.5°N, 87.3°W). Four commercial poplar clones (NM6, DN5, DN34, and DN182) were planted as 20- and 60-cm cuttings. Sixty-cm cuttings exhibited greater height and diameter than 20-cm cuttings; however, we recommend continued use and testing of different combinations of genotype and cutting length. We identified promising genotypes for potential use in future systems and we recommend allocating the majority of resources into commercial poplar clones, given their generalist growth performance. However, further utilization and selection of experimental clones is needed. Specific clones rather than genomic groups should be selected based on the geographic location and soil conditions of the site.

KEYWORDS:

• phytoremediation
• plant-enhanced bioremediation
• phreatophytes
• Populus
• Salix
• oil

ACKNOWLEDGMENTS

In addition to the affiliations of the authors, this research was the result of cooperation from the following organizations: United States Environmental Protection Agency Office of Research and Development, Purdue University, United States Environmental Protection Agency Region V, United States Fish and Wildlife Service, Indiana Department of Environmental Monitoring, Roy F. Weston, Inc., and British Petroleum. We thank Steve Rock for conducting the controlled-environment treatability study that led to our planting methodology. We are grateful to the following people for review of earlier versions of this manuscript: Deahn DonnerWright, Rob Doudrick, Bill Headlee, Assibi Mahama, and Adam Wiese.

Notes

^a Selection of native Populus deltoides growing along the Indiana Harbors Canal. Note: Authorities for the aforementioned species of Populus and Salix are as follows: P. deltoides Bartr. ex Marsh; P. trichocarpa Torr. & Gray; P. maximowiczii A. Henry; P. nigra L.; S. × dasyclados Wimm.; S. sachalinensis F. Schmidt.

^a Reps 1 to 4 planted along the east shore of the Indiana Harbors Canal, rep 5 planted along the Lake George Branch of the canal (control site).

^b Cutting length in centimeters.

^c No trees planted.

^d Means followed by the same letter for each combination of genus and cutting length are not different; LSD_0.05 = 26, n = 5.

^e Means followed by the same letter within the row are not different; LSD_0.05 = 18, n = 25. Note: Twenty-cm and 60-cm poplar cuttings also were different (P = 0.0002) using a paired t-test according to Snedecor and Cochran (1989).

^a Restricted maximum likelihood (REML) estimates of variance components.

^b Variance attributed to additive, dominant, and epistatic genetic effects (combined genetic effects).

^c Variance attributed to phenotypic effects, where phenotype = genotype + environment + (genotype % environment).

^d Broad-sense heritability estimated on an individual-tree basis.

^a Coefficient of variation = ratio of standard deviation to the mean, with a mean height of 48 ± 2 cm and a mean diameter of 4.86 ± 1.27 mm.

^b Genotypic variation.

^c Phenotypic variation, where phenotype = genotype + environment + (genotype × environment).

^{a a} Mean estimated across all reps.

^b Clone-60 = 60-cm cuttings for designated clone; Clone-20 = 20-cm cuttings for designated clone.

^c No trees planted.

^d Lack of experimental trees due to mortality.

^e Mean estimated across all clones. Note: Overall means for clone and rep are not estimable from individual rep × clone interaction means shown in the table due to variable numbers of experimental units resulting from mortality.