Abstract
This study aimed to determine the microbial diversity at different soil depths (0–5 and 5–20 cm) in a subtropical orchard during different seasons (i.e., spring, summer and autumn) to advance knowledge of the roles of microbes in orchard ecosystem balance. In tracking experiments conducted in an orchard (established in 1996), the phospholipid fatty acid (PLFA) biomarker method was employed to determine the soil microbial system. The total PLFA concentration did not vary significantly between soil depths but changed between seasons. It peaked in the summer at 258.97 ± 23.48 μg g soil-1 from 0–5 cm and at 270.99 ± 58.94 μg g soil-1 from 5–20 cm. A total of 33 microbial fatty acid biomarkers were observed and identified in the sampled soil. The quantities of PLFAs for 29 microbial groups varied significantly between seasons, except for 15:0 iso 3OH, 15:1 iso G, 16:0 2OH, and 17:0 iso 3OH. The bacterial PLFAs and fungal and actinomycetic PLFAs in the orchard soil collected in summer were significantly more abundant than those collected in the spring or autumn (P < 0.01). The number of soil microorganism species (richness) and the Simpson and Shannon-Wiener indexes were all highest in summer. The total PLFAs, bacterial PLFAs, fungal PLFAs, actinomycetic PLFAs, richness, and Simpson and Shannon-Wiener indexes were all significantly negatively correlated with soil pH, total organic carbon (TOC), total nitrogen (TN) and the cation exchange capacity (CEC) (P < 0.05).
Highlights
The soil is alive in that hundreds of millions or even billions of microbes reproduce, grow and die in one gram of soil
Using the method of phospholipid fatty acid (PLFA) analysis to define the relationship between the live microbial community and soil chemical properties in the context of seasonality could help us learn more about soil microorganism functions
The results showed that the microbial quantities were significantly negatively correlated with the pH, total organic carbon (TOC), total nitrogen (TN) and cation exchange capacity (CEC), with Spearman correlation coefficients of -0.530 to -0.618 (P < 0.01), -0.572 to -0.642 (P < 0.01), -0.401 to -0.422 (P < 0.05) and -0.791 to -0.831 (P < 0.01), respectively (Table 5)
Summary
The soil is alive in that hundreds of millions or even billions of microbes reproduce, grow and die in one gram of soil. Using the method of phospholipid fatty acid (PLFA) analysis to define the relationship between the live microbial community and soil chemical properties in the context of seasonality could help us learn more about soil microorganism functions. This relationship is more difficult to make clear in agricultural ecosystems than in forest and grassland ecosystems because the soil-microbe interactions in the former related to management as well as seasonal moisture and temperature. It is urgently necessary to clarify agricultural soil-microbe interactions in order to maintain their delicate balance and reduce ecological problems, such as biodiversity decreases [1], soil erosion [2], and pollution [3,4]. Such clarification is very useful because soil microbes play a unique and indispensable role in the agricultural ecosystem balance [5]
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