Table 1 Eigenvalues and cumulative contribution rates of principal components.

Ecological factors	Principal components	Eigenvalues	Contribution rates (%)	Cumulative contribution rates (%)
X_N	F₁	8.95	54.782	54.782
X_P	F₂	7.784	39.974	94.756
X_K	F₃	3.339	1.111	95.867
X_OM	F₄	1.734	0.915	96.782
X_TN	F₅	0.423	0.807	97.589
X_TP	F₆	1.725	0.613	98.202
X_TK	F₇	0.68	0.572	98.774
X_pH	F₈	0.437	0.4105	99.184
X_AMT	F₉	0.342	0.377	99.561
X₁	F₁₀	0. 175	0.3135	99.875
X₇	F₁₁	0.072	0.1065	99.981
X_AAT	F₁₂	0.057	0.0065	99.988
X_AHT	F₁₃	0.041	0.004	99.992
X_ALT	F₁₄	0.033	0.0024	99.994
X_AAP	F₁₅	0.024	0.0021	99.996
X_ASD	F₁₆	0.022	0.0015	99.998
X_FFP	F₁₇	0.018	0.001	99.999
X_ALTI	F₁₈	0.011	0.001	100

X_N(mg/kg), rapidly available nitrogen; X_P(mg/kg), rapidly available phosphorus; X_K(mg/kg), rapidly available potassium; X_OM(%), organic matter; X_TN(%), total nitrogen; X_TP(%), total phosphorus; X_TK(%), total potassium; X_pH, pH; X_AMT(°C), annual mean temperature; X₁(°C), january average temperature; X₇(°C), july average temperature; X_AAT(°C), annual accumulated temperature(≥10 °C); X_AHT(°C), annual highest temperature; X_ALT(°C), annual lowest temperature; X_AAP(mm), annual average precipitation; X_ASD(h), annual sunshine duration; X_FFP(d), frost free period; X_ALTI(m), altitude.

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