Irrigation with primary wastewater alters wood anatomy and composition in willow Salix miyabeana SX67

Abstract

Traditional treatment of wastewaters is a burden for local governments. Using short rotation coppice willow (SRCW) as vegetal filter has several environmental and economic benefits. Here, we investigated the effect of primary wastewater irrigation on wood structure and composition of the willow cultivar Salix miyabeana 'SX67' following two years of growth. Compared to unirrigated plants (UI), stem sections of plants irrigated with primary wastewater (WWD) showed an unexpected decrease of hydraulic conductance (K_S) associated with a decrease in vessel density but not vessel diameter. The majority (86%) of vessels had diameters range groups [20-30[, [30-40[and [40-50[µm and contributed to > 75% of theoretical K_S, while the group class [50-60[µm (less than 10% of vessels) still accounted for > 20% of total K_S regardless irrigation treatments. WWD significantly alters the chemical composition of wood with an increase of glucan content by 9 to 16.4% and a decrease of extractives by 35.3 to 36.4% when compared to UI or to plants irrigated with potable water (PW). The fertigation did also increase the proportion of the tension wood which highly correlated with glucan content. In the context of energetic transition and mitigation of climate change, such results are of high interest since WWD effectively permit the phytofiltration of large amounts of organic contaminated effluents without impairing SRCW physiology.

Keywords: cell wall composition; hydraulic conductance; phytofiltration; sustainable biomass; wastewater; willow.

Figure 1

Effects of nitrogen fertilization with primary municipal wastewater on the biomass, mechanical structure and willow wood composition. A–C) Trees with irrigation treatments UI, PW and WWD respectively. (E–G) Stem section from trees with irrigation treatments UI, PW and WWD respectively (scale bar = 1mm). (I–K) 100x magnification of stem section region from trees with irrigation treatments UI, PW and WWD respectively (scale bar = 200 µm). (M–O) 500x magnification of stem section region from trees with irrigation treatments UI, PW and WWD respectively (scale bar = 50 µm). (D) Above ground biomass (Mg ha^-1) of irrigation treatments UI, PW and WWD respectively (previously published results in Jerbi et al. (2020)). (H) Wood density (g cm^-3) of treatments UI, PW and WWD respectively. (L) Proportion of tension wood (%) of irrigation treatments UI, PW and WWD respectively. (P) Wood proportion of glucan (%) of treatments UI, PW and WWD respectively. The results represent the average values (mean ± standard error) for each irrigation treatment. Different letters indicate significant differences according to HSD-Tukey test for the irrigation treatments (p ≤ 0.05).

Figure 2

(A) Average vessel density (N mm^-2) per vessel lumen diameter class, (B) the theoretical sapwood area-specific hydraulic conductivity KS (Kg m^-1 pa^-1 s^-1) per vessel lumen diameter class, (C) the distributions of vessel diameters and their contribution to total hydraulic conductivity i.e. total K_S ( the histograms indicate vessel frequency per vessel diameter class and the lines indicate the contribution of each vessel lumen diameter class to total hydraulic conductivity K_S), (D) the cumulated theoretical sapwood area-specific hydraulic conductivity KS (Kg m^-1 pa^-1 s^-1) per vessel lumen diameter class . Results represent the average values (mean ± standard error) for each irrigation treatment. Different letters in the same column group indicate significant differences according to HSD-Tukey test for the irrigation treatments (p≤0.05).

Figure 3

Linear regression between the tension wood proportion and the biomass glucan proportion of the cultivar Salix miyabeana SX67. Black, blue and brown dots refers respectively to the data of UI, PW and WWD treatments.