Intrinsic and extrinsic factors influencing Populus water use: A literature review.

Poplars (Populus L. spp.) are versatile, productive trees that are used in environmental systems worldwide to provide a variety of benefits. Though poplars are recognized for their elevated water use, summaries of existing data on poplar water use, its influencing factors, and the methodologies used to measure it, are lacking. We sought to 1) summarize the sap flow methodologies used to quantify poplar water use, 2) review sap flow-derived water use data reported in the literature for Populus hybrids and non-hybrids, and 3) assess the effects of different intrinsic factors (plant variables) and extrinsic factors (environmental variables) on poplar water use. We identified 133 articles containing information on the methodologies used to measure poplar sap flow. Of these, the thermal dissipation method was used in a majority (55%) of the studies. Poplar water use data were reported in 51 of the articles, with studies taking place in 13 countries, and representing the time period of 1992-2018. Hybrids were studied in 18 articles and included 17 genotypes, while non-hybrids were studied in 33 articles, and included eight species. Hybrid poplar water use ranged from 0.7 to 11.3 mm day-1, with an overall mean of 2.7 ± 0.3 mm day-1. Non-hybrid water use ranged from 0.2 to 19.5 mm day-1 with an average of 2.8 ± 0.4 mm day-1. Hybrid poplar water use differed significantly among hybrid types, tree age classes, and water availability classes, and non-hybrid water use was significantly different among species, experimental context, and water availability classes. While we focused on poplar water use measured by sap flow methodologies, this review builds the foundation for a comprehensive summary of available poplar water use information that has been reported in the literature. Our results on the factors influencing poplar water use can be used to aid in the decision-making process when designing poplar-based environmental systems such as remediation, bioenergy, and agroforestry systems.

Establishment of willows using the novel DeValix technique: ecological restoration mats designed for phytotechnologies.

Successful willow (Salix spp., hybrids and cultivars) establishment is a major determinant of their effectiveness when grown for phytotechnologies. Vertically-planted hardwood cuttings have been shown to produce adequate willow growth and survival, although site conditions at phytoremediation installations can make vertical planting methods unsuitable. The DeValix willow mat restoration technique was designed and tested as an alternative horizontal planting method that can be installed by hand in a variety of environmental applications. The DeValix technique was evaluated by testing five willow clones ("Millbrook"; "Sherburne"; "SX61"; "SX67"; "Tully Champion") grown at two phytoremediation sites (Ontonagon, MI; Manitowoc, WI) for the 2019 growing season. Differences in survival and growth were tested among sites, genotypes, and their interactions. Stem height, diameter, and number of stems per mat were compared to identify clones with greater establishment success and higher phytoremediation potential. Results demonstrated significant effects of site (p < 0.0001) and clone (p < 0.0001) on shoot number. Additionally, the site × clone interaction significantly affected stem height (p = 0.0045) and diameter (p = 0.0166). Stem density ranged from 95,000 to 212,000 stems per hectare, indicating the DeValix technique is a viable establishment method for environmental applications, including phytoremediation and shoreline stabilization.

This research analyzes the establishment success of the DeValix technique, a novel horizontal planting method for willow cultivars, and evaluates the DeValix technique as an alternative to other horizontal techniques and traditional vertical planting methods currently used in environmental applications. Results from this study add to the current knowledge of planting techniques and assesses the use of the DeValix technique for planting willow cultivars that are currently being tested in several phytotechnology systems.