Plant residue chemical quality modulates the soil microbial response related to decomposition and soil organic carbon and nitrogen stabilization in a rainfed Mediterranean agroecosystem

Soils play a major role in the global carbon cycle and are crucial to the management of climate change. Changes in plant cover derived from different agricultural practices induce variations in the quality of plant residue inputs and in the soil microbial community structure and activity, which may enhance the storage and protection of organic carbon (OC) and nitrogen (N) within aggregates. The aim of this study was to assess how differences in the chemical composition of plant residues in combination with tillage management practices affect the local microbial community activity and structure, and subsequent soil aggregation and OC and N dynamics in an organic, rainfed almond (Prunus dulcis Mill.) orchard. In the laboratory, three types of plant residue (shoots, roots, and the combination of both) coming from different species belonging to each agricultural practice (reduced tillage, reduced tillage plus green manure, reduced tillage plus organic manure, and no-tillage) were mixed with their respective soils and the CO₂ released was measured over 243 days at 60% WHC and 28 °C. Water-stable aggregates (including microaggregates within macroaggregates), enzymatic activities related to carbon (dehydrogenase and β-glucosidase) and N (urease) cycling, and the microbial biomass and community structure through phospholipid fatty acid analysis, were measured at the end of the incubation period. Our results indicate that the chemical composition of plant residues controls the microbial community response, mediating decomposition and the incorporation of OC and N in stable aggregates. Therefore, the incorporation of labile and N-rich plant residues into the soil by reduced tillage is recommended since mixing roots and shoots from green manure increased the formation of free micro-aggregates and improved OC and N stabilization in our semiarid agroecosystem.