Drought differently destabilizes soil structure in a chronosequence of abandoned agricultural lands

Climate change is causing an increase in the frequency and severity of drought, and this has a significant influence on the global C cycle as soils are the main sink for C in terrestrial ecosystems. Drought can have serious consequences for the structural stability of the soil, which influences the protection of the organic matter stored in the soils and hence its mineralization. In this work we study the effects of an extreme drought event on the structural stability of the soil in Mediterranean annual grasslands developed after the abandonment of agricultural activity. This was done by building a chronosequence of abandoned vineyards and determining the changes in the stability of the soil aggregates and organic matter by monitoring these parameters for three consecutive years in permanent plots with different ages of abandonment. This period of time included an extreme drought event in the second year with a strong positive thermal anomaly, which caused a serious structural destabilization of the soil and had a major impact on the soil C and N cycles. The breakdown of the soil aggregates left unprotected a large amount of organic substrates that were rapidly mineralized when the environmental conditions were favourable for soil biological activity. This had significant repercussions on the functioning of these abandoned ecosystems, which became sources of atmospheric CO 2, when under normal conditions they act as C sinks. Furthermore, the effects of this extreme event were more severe in the plots with longer periods of abandonment, which have the highest amount of C accumulated in the soil.