3.3 The relationship of NEP and biophysical climate factors
The influence of annual temperature on NEP, Re, and GEP is negligible (Figure 6a), and precipitation has a significant effect on Re only (Figure 6b). DCUP had a strong correlation with NEP and GEP, but no statistically significant relationship with Re (Figure 6c). This reveals that the increase in DCUP leads to an increase in NEP and GEP, but has no significant effect on Re.
The relationship between NEP and biophysical climate factors varied within the seasons. Spring temperature and the advanced SCUP led to an increase in spring NEP (Figure 7a, b), but spring precipitation had no significant influence on spring NEP (Figure S3). In summer, NEP was mainly influenced by summer precipitation, which explained 48% of the variation (R2 = 0.48, Figure 7c) and was not correlated to temperature (Figure S3). Summer precipitation also has a significant influence on autumn NEP, with precipitation explaining 49% of the variation of NEP in autumn (R2 = 0.49, Figure 7d). NEP in autumn did not correlate with autumn temperature, precipitation, or ECUP (Figure S3).