Table 3.

Effects of latitude, cover treatment and heavy metal on the content of resistance substances and nutrients in the second year of P. americana leaves. To make the data conform to a normal distribution before analysis, the following conversions were performed on data that were not normally distributed: log₁₀ conversion: total flavonoids, starch, soluble sugar; Box–Cox conversion: total saponins. Bold type means P<0.05.

		Tannin		Total phenols		Total flavonoids		Total saponins
Effect	Degrees of freedom	F	P	F	P	F	P	F	P
Latitude	5105	5.3906	0.0223	3.4909	0.0646	0.4369	0.5101	0.9086	0.3428
Heavy metal	1105	0.0116	0.9145	0.1508	0.6986	1.1299	0.2903	0.6713	0.4145
Cover	1105	16.1877	0.0001	28.4431	<0.0001	70.3434	<0.0001	9.0724	0.0033
Latitude: heavy metal	1105	1.3069	0.2577	0.0090	0.9246	0.330	0.8563	0.7045	0.4032
Latitude: cover	1105	0.0576	0.8108	0.0764	0.7828	2.4820	0.1183	2.9110	0.0911
Heavy metal: cover	1105	0.6624	0.4176	0.2681	0.6057	0.4526	0.5027	1.9933	0.1611
Latitude: Heavy metal: cover	1105	0.3910	0.5332	1.5836	0.2112	0.0461	0.8303	4.6536	0.0344

		Starch		Soluble sugar
Effect		F	P	F	P
Latitude		0.4167	0.5201	0.4114	0.5227
Heavy metal		11.5427	0.0010	11.5833	0.0010
Cover		19.6654	0.0002	19.6416	0.0002
Latitude: Heavy metal		1.1422	0.2877	1.1447	0.2872
Latitude: cover		1.6369	0.2037	1.6494	0.2020
Heavy metal: cover		0.5292	0.4686	0.5401	0.4641
Latitude: heavy metal: cover		0.0161	0.8992	0.0204	0.8868