Abstract
Soil microorganisms play key roles in biogeochemical cycling in forest ecosystems. However, whether the responses of microbial community with stand development differed in rhizosphere and bulk soils remains unknown. We collected rhizosphere and bulk soil in Chinese fir plantations with different stand ages (7a, 15a, 24a, and 34a) in subtropical China, and determined bacterial and fungal community variation via high-throughput sequencing. The results showed that soil bacterial, but not fungal, community diversity significantly differed among stand ages and between rhizosphere and bulk soils (p < 0.05). The differences in Shannon–Wiener and Simpson’s indices between rhizosphere and bulk soil varied with stand age, with significant higher soil bacterial diversity in rhizosphere than bulk soils in 7a and 34a plantations (p < 0.05), but there were no significant difference in soil bacterial diversity between rhizosphere and bulk soils in 15a and 24a plantations (p > 0.05). Soil microbial community composition varied significantly with stand age but not between the rhizosphere and bulk soil. The dominant bacterial phyla at all ages were Acidobacteria and Proteobacteria, while the dominant fungal phyla were Ascomycota and Basidiomycota in both rhizosphere and bulk soil. They showed inconsistent distribution patterns along stand age gradient (7–34a) in the rhizosphere and bulk soil, suggesting distinct ecological strategy (r-strategist vs. k-strategist) of different microbial taxa, as well as changes in the microenvironment (i.e., nutrient stoichiometry and root exudates). Moreover, bacterial and fungal community composition in rhizosphere and bulk soil were governed by distinct driving factors. TP and NH4+–N are the two most important factors regulating bacterial and fungal community structure in rhizosphere soil, while pH and NO3––N, DON, and TN were driving factors for bacterial and fungal community structure in bulk soil, respectively. Collectively, our results demonstrated that the changes in microbial diversity and composition were more obvious along stand age gradients than between sampling locations (rhizosphere vs. bulk soil) in Chinese fir plantations.
Highlights
Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] is an endemic, evergreen coniferous timber species and widely cultivated in southern China because of its high yield, rapid growth rate, and excellent wood quality
Plantation age significantly altered all measured soil parameters except for total C (TC), total N (TN), Dissolved organic N (DON), and available P (AP) (Table 1, p < 0.001), while significant differences were merely observed on soil pH, dissolved organic C (DOC), DON, and NH4+–N between rhizosphere and bulk soil (Table 1, p < 0.01)
Soil NO3−–N followed a decreasing trend from stand age 15a to 34a, which decreased by an average of 30.6, 51.2, and 24.8, 52.1%, respectively, for rhizosphere and bulk soil compared with the 15-year old stand soil
Summary
Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] is an endemic, evergreen coniferous timber species and widely cultivated in southern China because of its high yield, rapid growth rate, and excellent wood quality. A previous study reported that the growth of Chinese fir was limited by nitrogen (N) in subtropical China (Tong et al, 2020), and there was a shift from N limitation to phosphorus (P) limitation with the stand development of Chinese fir plantations (Wu et al, 2020) It seems that the reason for productivity decline in Chinese fir plantation is related to the converted nutrient cycling process, while the underlying microbial mechanism still remains unclear. Previous studies reported that changes in litter composition and soil nutrient stoichiometry were significant predictors for bulk microbial communities (Sun et al, 2016; Li et al, 2017), while rhizosphere microorganisms were strongly affected by tree species, root exudates, soil and root properties, and plant growth stages (Delgado-Baquerizo et al, 2017)
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