Using Microbial Indicators to Assess Soil Ecosystem Restoration

Abstract

Soil microbial communities play a crucial role in maintaining ecosystem health and sustainable integrity. The objective of this study was to determine the progress of ecosystem recovery in soils under a federal conservation reserve program (CRP) by examining several key microbial community-related soil health indicators. Three adjacent soil ecosystems were evaluated, including conventional crop production, undisturbed (>20 years post tillage), and marginal land that was formally cultivated and has been under CRP for five years. The latter two ecosystems contained mixed perennial vegetation, whereas the former was cultivated with winter wheat, Triticum aestivum L for at least 20 years. Soils were taken from these three ecosystems at two different locations twice a year for two consecutive years. Five replicate samples were taken from each ecosystem at each location during each sampling event. Soils were evaluated for water-stable aggregation and composition and structure of the soil microbial communities using fatty acid methyl ester analysis. Roots isolated from soils were evaluated for arbuscular mycorrhizal intraradical colonization. Results show that AMF abundance was high in CRP plots compared to both Wheat and Native systems. Microbial indicators suggest that the level of disturbance and nutritional stress remained significantly higher in CRP than Native plots during the 1st and 3rd samplings, indicating less resistance against heat or drought stress. Total microbial abundance and geometric mean diameter, which were highly correlated with each other, were found to be significantly lower in CRP than Native systems. Soil organic carbon and total nitrogen in CRP was not significantly different from the wheat fields, suggesting a much greater amount of time would be needed to reach pre-cultivation levels. Because of significant differences between the two Native plots at different locations, using this study's selected indicators for soil ecosystem recovery, we were able to ascertain based on a combined value for measured indicators that the CRP at one location had recovered approximately 50% compared to the Native system, but that the other only recovered about 10% after 5-6 years in the program. The Native plot at the former location was possibly more degraded before being abandoned, or was less disturbed than the latter. Because a typical contract with the CRP typically lasts 10-15 years, more time may be required for full recovery of the soil properties measured in this study than what is currently allotted.