Changes in soil aggregation and microbial community structure control carbon sequestration after afforestation of semiarid shrublands

• Published in: Soil biology & biochemistry 2015-08, Vol.87, p.110-121
• Main Authors: Garcia-Franco, N., Martínez-Mena, M., Goberna, M., Albaladejo, J.
• Format: Article
• Language: English
• Subjects: Basal respiration; Microaggregates within macroaggregates; Microbial activity; Organic amendments; Priming effect; Soil C pools
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2015.04.012

Changes in plant cover after afforestation induce variations in litter inputs and soil microbial community structure and activity, which may promote the accrual and physical-chemical protection of soil organic carbon (SOC) within soil aggregates. In a long-term experiment (20 years) we have studied the effects, on soil aggregation and SOC stabilization, of two afforestation techniques: a) amended terraces with organic refuse (AT), and b) terraces without organic amendment (T). We used the adjacent shrubland (S) as control. Twenty years after stand establishment, aggregate distribution (including microaggregates within larger aggregates), sensitive and slow organic carbon (OC) fractions, basal respiration in macroaggregates, and microbial community structure were measured. The main changes occurred in the top layer (0–5 cm), where: i) both the sensitive and slow OC fractions were increased in AT compared to S and T, ii) the percentage and OC content of microaggregates within macroaggregates (Mm) were higher in AT than in S and T, iii) basal respiration in macroaggregates was also higher in AT, and iv) significant changes in the fungal (rather than bacterial) community structure were observed in the afforested soils (AT and T) – compared to the shrubland soil. These results suggest that the increase in OC pools linked to the changes in microbial activity and fungal community structure, after afforestation, promoted the formation of macroaggregates – which acted as the nucleus for the formation and stabilization of OC-enriched microaggregates. •Afforestation with Pinus halepensis promoted soil C sequestration.•Afforestation led to long-term changes in fungal but not in bacterial populations.•Changes in soil C pools and fungal taxa increased soil aggregation and C stocks.•Soil organic carbon was stabilized in microaggregates whithin macroaggregates.•Physical-chemical stabilization of OC is a key aspect to maintaining soil C stocks.