Title: Evidence of Mineralogical Controls on C, N and P Reservoirs and Distributions in Natural Temperate Deciduous Forest and Exotic Pine Plantations Forests in Soils with Contrasting Mineralogy
Abstract: Soil organic carbon (SOC) in temperate forest ecosystems is a significant component of the terrestrial carbon pool. Management intensification in forest systems can significantly alter SOC inputs and dynamics having major implications for the long-term carbon stability and nutrient sustainability of these ecosystems. To understand how the intensification of forest cover and management modify the magnitude and distributions of C, N and P pools we selected 5 soils of contrasting mineralogy (crystalline to amorphous clays) under both remnants of secondary temperate oak forests and pine plantations in south-central Chile. In each of these sites two adjacent permanent plots were established, where a 2.4m soil pits were dug at the center of each plot and four 2.4m deep augers were sampled at each plot quadrant. The sites included volcanic soils formed from: recent volcanic ash (Vitrandic udortents), young ash deposits (Typic haploxerand) and old ash deposits (Typic rhodoxeralfs); and two residuals soils formed from granitic (Ultic palexeralfs) and slate (Rhodic paleudults). The recent ash-derived soils had clay mineralogy dominated by amorphous minerals, the young-ash by short range order SRO minerals and meta-halloysite, the old-ash soils has mineralogy dominated by halloysite, and goethite, while residuals soils had micaceous clays, kaolinite and iron oxyhydroxides clays. Soil types had a strong influence on the C, N and P pools. Soils formed in recent volcanic deposits have smallest total C,N,P pools followed by the young and old volcanic (e.g. 45 to 56 Mg C/ha), while the highest pool sizes were found in the residual palexeralf (e.g. 387 to 243 MgC /m2). For most sites plantation forest have lower total C and N pools and higher P pools, except for the soil from old-ash. d13C and d15N depth distribution were similar among forest types, however these were significantly different between soil types highlighting the influence of soil types in C and N dynamics. P availability was largest in the recent volcanic and slate-derived soils, followed by old ash and granitic, presenting its lowest in the young haploxerand. C and N pool sizes were correlated with leaf area index, litter production and litter decomposition rates, as well as with root biomass. Our preliminary results suggest that soil type and mineralogy are major control on SOC and nutrient reservoirs and dynamics and they emphasize the importance of including soil mineralogy in future carbon sequestration models as it is one of the main factors controlling SOC stabilization processes.