The Influence of Depth on Soil Chemical Properties and Microbial Respiration in the Upper Soil Horizons

Abstract

Soil microbial respiration is a biological process that converts soil organic matter into atmospheric CO2 via soil microorganisms. It reflects the overall metabolic activity of soil microbial populations and usually used as an indicator of soil health. Soil chemical properties, among others, have an influence on a catabolic capacity of the soil and greatly vary among different soil layers. In this study, we examined patterns of chemical soil properties and soil microbial respiration along 0–10 and 10–25 cm depths of the soil to investigate if soil depth had any effects on soil chemical properties and how these changes with depth could shift the soil microbial respiration. We employed basal respiration method to estimate the rate of soil microbial respiration and measured important chemical properties using standard protocols. The results showed differential effects of soil depth on chemical properties where available nitrogen ( $${\text{NH}}_{{\text{4}}}^{{\text{ + }}}$$ –N, $${\text{NO}}_{3}^{ - }$$ –N, and total N), cation exchange capacity, and Mg2+ were strongly influenced by soil depth. Soil microbial respiration greatly differed among the two soil depths (p = 0.0005) with a higher rate of soil microbial respiration in surface soils compared to subsurface soils. Soil microbial respiration had a significant positive correlation with total N, $${\text{NO}}_{3}^{ - }$$ –N, $${\text{NH}}_{{\text{4}}}^{{\text{ + }}}$$ –N, and soil organic matter (r = 0.98, 0.974, 0.9625, and 0.9455, respectively). The variation of soil microbial respiration was closely linked with the variation of soil organic matter and available nitrogen, implying that these variables were the key drivers of the variation of soil microbial respiration in the study area. Overall, the study highlighted that soil quality assessments and managements should include the depth effects to provide a better understanding of the dynamics of microbial respiration in the soil.