EFFECTS OF CLIMATE AND DUST INPUTS ON PHOSPHORUS AVAILABILITY AND SPECIATION IN FOREST SOIL PROFILES

Phosphorus (P) availability in soils controls critical functions and properties of terrestrial ecosystems. However, the effects of climate and dust inputs on P availability and speciation in soils remain not fully understood. We determined P availability and speciation in soil profiles of contrasting climate using a combination of P K-edge X-ray absorption near edge spectroscopy and chemical extractions. The major features of the vertical distributions of P concentration and speciation persist under the contrasting climates and can be predicted by combinations of weathering, leaching, biolifting and dust inputs. Warmer/wetter climate results in decreases in the proportions of both calcium-bound P (Ca-P) and non-occluded P (P_n‑occ), but increases in the P loss and the proportions of organic P (P_o), Fe- and Al-bound P [(Fe+Al)‑P] and occluded P (P_occ). Regardless of soil depth and climate, the inorganic P (P_i) speciation, i.e., the relative proportions of Ca-P and (Fe+Al)‑P over total P_i, correlates well with soil pH and weathering degree (Chemical Index of Alteration, CIA), and P_o concentration with pedogenic Fe and Al and organic carbon concentration, which suggest that P_i speciation is primarily controlled by soil geochemistry/mineralogy, and P_o concentration by both soil geochemistry/mineralogy and biological activities. P_occ correlates with CIA, and thus is mainly controlled by soil mineralogy; but P_n-occ correlates weakly with soil properties, probably due to its susceptibility to combined influences of dust inputs, leaching, biological activities, and sorption. Furthermore, we evaluated the effects of dust inputs on P transformation in sub-humid ecosystems. Continuous dust inputs increase the concentration of total P in the acidic surface soils and maintain relatively high Ca-P levels there although acidic dissolution constantly transforms the Ca-P to other forms. The dust-borne Ca-P in soils is likely the main source of soil labile P as suggested by a positive correlation between them. On the other hand, dust inputs bring iron-rich materials and enhance formation of large amounts of (Fe+Al)-P and P_occ in soils. In addition, C horizon shows a relatively high weathering degree, likely caused by dust inputs that increase soil moisture and microbial activities. This study provides an integration and synthesis of controls of climate, dust inputs and edaphic variables on P dynamics in forest soils.