Chronosequence study of soil microbial communities from an olive orchard through PLFA profiling

In the Mediterranean region, olive plantations are often located on slopes. These sloping soils are typically less fertile for many crops due to high erosion and increased water drainage rates. However, olive trees, like vineyards and other fruit plantations, thrive in these conditions, making such sites common throughout the Mediterranean basin. Interrow spaces are frequently utilized to test various land management practices and study changes in soil organic matter, erosion, and microbial and molecular diversity. This approach is exemplified by the study plots in this work, located in an olive orchard in southern Spain.

We collected soil from an olive orchard with an 11% slope located in Southern Spain (Benacazón, Seville). The study aims to examine soil organic matter and microorganisms abundance along the slope under two soil management practices: conventional tillage (CT) and natural cover (NC). Additionally, soil from the tree line, treated with herbicide (TL-Herb.), is also included. To account for the effect of seasonality, four sampling campaigns were conducted between autumn 2022 and summer 2023. Phospholipid fatty acid (PLFA) and enzymatic activity analyses were performed to investigate microbial profiles and their relationship with organic matter content along the slope.

With increasing temperatures, we expect to observe a decrease in total microbial biomass and lower F/B ratios. Regarding differences due to land management, we anticipate that NC plots will exhibit the highest microbial biomass and greater total fungal biomass compared to CT and TL-Herb soils. Additionally, we expect stress indicators (saturated/monounsaturated fatty acid ratios) to increase during the driest season, coinciding with the lowest microbial biomass abundance. Our main hypothesis is that plots with natural cover will have higher organic matter (OM) content and total microbial biomass. We also expect to observe differences in the microbiome between the upper and lower parts of each plot, with higher microbial biomass in the lower areas due to the runoff of water and nutrients along the slope. These results will contribute to a better understanding of seasonal shifts in microbial profiles under these land management conditions.

Keywords: microbial profiling, soil management, sustainable agriculture