Table 4. Calculated EC50 toxicity thresholds, models, R and P. for roots and the aboveground tissues (combined wood, new shoots and leaves) of three willow varieties exposed to increasing levels of lead.

S. integra varieties	Model	R	P	EC50 (µM)
Roots
Yizhibi	y = 0.091727*e −0.002786x	0.8925	0.0416	242.6
Weishanhu	y = 0.123656*e −0.002779x	0.9566	0.0108	258.5
Dahogntou	y = 0.095516*e −0.003416x	0.9897	0.0013	204.5
Aboveground tissue
Yizhibi	y = 1.7132*e −0.001531x	0.8685	0.0561	481.3
Weishanhu	y = 1.8468*e −0.001252x	0.9132	0.0303	537.5
Dahogntou	y = 1.8086*e −0.001921x	0.9298	0.0221	335.9