INSTYTUT DENDROLOGII

Morphological, biochemical and molecular aspects of poplar and willow growth on tannery waste

Tannery industry is one of the main sources of emission of chromium to the environment. Treatment of tannery effluents generates large amounts of sludge (sediment) including concentrated doses of metals, other elements and organic matter. Presently, such waste is most commonly disposed by landfilling, however this method is likely to greatly endanger soil and water ecosystems and groundwaters due to Cr leaching. Afforestation of tannery waste disposal sites with poplars and willows, preventing contaminants from spreading into the environment, is a promising approach in reclamation and stabilization of landfill areas. The above-mentioned species are known to be metal-tolerant. Moreover, the fact that tannery sludge is usually abundant in nutrients (N, S, P etc.) provides an opportunity to combine phytoremediation with biomass production for energy purposes.

The aim of the presented project was to compare trees of the Salix and Populus genera considering their capability to grow on tannery waste, obtained from an active and closed tannery waste disposal site. Analysis of morphological traits, uptake of elements and ability to deal with oxidative stress after planting on Cr-rich sediment provided basis for the conclusion that poplars (particularly P. × canescens and P. alba ‘Villafranca’) show better growth in such conditions than S. viminalis. Proteins involved in metabolic adaptations of leaves and roots of particular species and cultivars were identified with the use of proteomic methods. These molecular results serve as a supplement to the available literature data on responses of plants to growth on tannery waste.

Sediment from the inactive landfill site appeared to be more toxic than one originating from the active area. This observation may result from different tanning procedures and treatment of effluents applied in the tanneries, however it also supports the concerns about long-term environmental impacts of such sites. Nevertheless, it was confirmed that tannery waste added in low concentration to soil may stimulate growth of saplings similarly as commercial fertilizers. High content of organic matter is likely to alleviate chromium toxicity to plants.

In both types of tannery waste, planting resulted in similar changes in carbohydrate and lipid metabolism in poplar and willow (e.g. caused an increase in lipid degradation and expression of glycolytic enzymes and proteins involved in synthesis of cell wall components), however had different effects on the level of proteins associated with photosynthesis, stress-related proteins, proteasome subunits as well as pyridoxal and methionine biosynthesis enzymes.

Additionally, it was found that rooting of willow cuttings directly in tannery waste is likely to induce higher tolerance of saplings to such conditions than rooting in control soil prior to planting in waste.