Flooding alleviates copper stress on Salix: Evidence from stoichiometric patterns among plant tissues

Background and aims The increasing flooding occurrence associated with climate change, results in soil becoming more vulnerable to heavy metal contamination. However, the mechanisms underlying the combined effects of flooding and metals on the stoichiometry of fast-growing trees (potential for bioremediation) remains poorly understood. Such information is vital to understand how Salix integra Thunb 'Yizhibi' (S. integra) alters the nutrient stoichiometry to cope with a single or combined stress of copper (Cu) and flooding. Methods S. integra seedlings were cultivated in four soil Cu treatments (control, 50, 150 and 450 mg.kg(-1)) and examined after a 90-day flooding period. The stoichiometric patterns of C:N:P among different tissues were analyzed upon single or co-exposure to Cu and flooding. Redundancy analysis (RDA) and partial least squares-path modeling (PLS-PM) were used to elucidate the relationship between the C:N:P stoichiometry of soil and plants. Results Leaf C concentration negatively correlated with leaf P concentration upon exposure to Cu stress. Flooding significantly increased the leaf C:N and C:P ratios, and leaf N:P increased (3.7-46.3%) with increasing soil Cu dose. The stoichiometric patterns of C:N:P in aboveground tissues were generally affected by flooding, and the ratios of C:N or C:P were in the order of cutting > stem > leaf. The PLS-PM result implied that flooding or Cu had a significantly positive effect on the nutrient stoichiometry (C:N and C:P) of stems and leaves. Moreover, flooding exhibited a stronger effect on C, N and P stoichiometry, with standardized path coefficients of 0.83 and 0.34 in stems and leaves, respectively. Conclusions Flooding is a primary factor that alters the C:N:P stoichiometry in tissues of S. integra under Cu induced stress. Flooding is likely to alleviate Cu induced stress via alterations in C:N:P stoichiometry patterns in Salix tissues. Thus, plants can regulate nutrient stoichiometric patterns to cope with single or combined stress, which might be used as an indicator of stress tolerance or ecological adaptation.

Automated summary

The study found that flooding significantly affected the C:N and C:P ratios of leaves in S. integra, and leaf N:P ratios were positively correlated with soil Cu levels. Flooding and Cu had a positive effect on the nutrient stoichiometry (C:N and C:P) of stems and leaves.