3.1 Ecosystem functioning and microbial community richness
Both land use types and seasons significantly influenced ecosystem functioning including the mSR, NR and PNR (all P < 0.05; Fig. 1). Afforestation significantly promoted the mSR irrespective of season (F = 8.8, P < 0.01), with decrease in the order of woodland (3.03 ug/(g*day)-1) > shrubland (2.36 ug/(g*day)-1) > cropland (1.27 ug/(g*day)-1). The NR did not significantly differ among different land use types irrespective of season, whereas woodland significantly inhibited the PNR compared to the shrubland and cropland (F = 9.5, P < 0.05) (Fig. 1). For seasonal pattern, the mSR was higher in summer than in winter in all land use types. However, the seasonal pattern of the NR and PNR varied with different land use types, with higher levels in summer than in winter in the cropland, and inconsistent trends in the afforested land (Fig. 1).
The microbial community diversity was based on the biomarker of PLFAs. The richness of microbial richness was significantly higher in summer than in winter with 73.4%, 44.4% and 53.4% higher level in the cropland, shrubland and woodland, respectively (Fig. 2a). There was no significant difference between land use types (F = 0.18, P = 0.84; Fig. 2a). Meanwhile, the 858, 591 and 1, 135, 240 high quality sequences of AOA and AOB were obtained from the 18 soil samples totally. After uniformed sequences (10,900 and 25,798) per sample, 1, 528 and 8,484 OTUs was identified of archaeal and bacterial communities, respectively. Land use types and seasons did not significantly interactively affect the alpha diversity of the microbial community and functional genes (Fig 2a, c, e). The alpha diversity indices of microbial communities of AOA and AOB including richness, Shannon index and chao1 index did not vary with different land use types, but the alpha diversity of microbial community was higher in summer compared to winter (Fig. 2 & S1). Furthermore, the ordination analysis revealed a less consistent pattern of the total microbial and amoA gene communities (Fig. 2b, d, f). The clustering effects of land use types ( ANOSIM; R = 0.19, P < 0.001) and seasons (R = 0.63,P < 0.001) on the pattern of microbial communities were significant, whereas only the significant effect of afforestation were detected in the AOA (R = 0 .22, P < 0.001) and AOB (R = 0.25, P < 0.001) communities composition (Fig. 2b, d, f).