Pedogenesis Modulates the Effects of Vegetation on Organic Phosphorus Speciation Under Semi-Arid Climate.

Soil organic P (P_o) pool consists of a group of compounds differing in P bioavailability and behavior. Previous studies showed separately that both vegetation type and pedogenesis affect P_o speciation, but whether and how the impact of vegetation change during pedogenesis remains unknown. Here we used alkaline extraction and solution ³¹P nuclear magnetic resonance spectroscopy (NMR) to assess the soil P_o speciation in surface soils from the inter-canopy, under piňon pine canopy and under one-seed juniper canopy along a semi-arid chronosequence (1, 55, 750 and 3000 ka) at the San Francisco volcanic field, Arizona. As pedogenesis proceeds, the concentration of most P_o compounds in all types soils increased up to 750-ka and then declined, except that the corrected diesters in the under-canopy soils tended to increase, the total polyphosphate under juniper canopy and inter-canopy increased until 55-ka and declined while kept increasing under pine canopy, and DNA in all soils kept increasing. In terms of the proportions, the corrected monoesters and diesters in all under-canopy soils kept increasing while in the inter-canopy soils, their proportions increased until 750-ka and then declined; The DNA in the inter-canopy and under juniper canopy soils kept increasing while in the under pine canopy soils, it did not change consistently; The phytate kept increasing; Overall, the under-canopy soils have distinct P_o composition, and the difference for most P_o compounds except the total polyphosphate is greater at younger sites and disappears at the oldest site. However, these differences may be less related to tree species but more attributed to the distinct microbial community where ectomycorrhizal species are dominant under pine canopy, while endomyorrhizal in the other two types soils. Results indicate the P_o transformation in the semi-arid under-canopy soils is different to that under humid climate and the vegetation effects are strongly modulated by pedogenesis degree.