Lithologic and Climatic Influences on Phosphorous in California.

Climate and lithology are master variables of pedogenesis. While the influence of climate and time on P fractions has been widely investigated the effect of lithology on the fate of P during pedogenesis remains understudied. In the classic Walker-Syers model, climate and time produce a trajectory of progressive P limitation and occlusion. Parent material effects are largely considered secondary, despite knowledge that the majority of terrestrial ecosystem P is ultimately lithologicaly derived. We hypothesize that differences in initial parent material composition will influence the outcome of P fractionation, in concert with climate and pedogenesis. Here, we investigate a unique climo-lithosequence to elucidate the influence of lithology and climate on P dynamics. Three climosequences (elevational transects) spanning four climatic zones (Blue-Oak, Ponderosa Pine, White fir and Red fir), and three bedrock lithologies (basalt, andesite and granite) were investigated across the Sierra Nevada and southern Cascades. Replicate soil samples were collected by genetic horizon at each of the twelve sites (4 climate zones x 3 lithologies) and characterized by a modified Hedley P fractionation method, to quantify P in operationally defined pools. 

Initial results from the fractionation of andesite and basalt transects (granite forthcoming) show large climatic and lithologic effects on soil P fractions, suggesting that the distribution of soil P and the trajectory of P transformations are significantly influenced by lithology as well as climate.  For example, in the climatic zone of least weathering (Red fir), all soil P fractions showed significant lithologic effects.  In contrast, with increased weathering, parent material effects on soil P become progressively muted, so that in the zone of most intense weathering (Ponderosa Pine), soil P fractions such as Ca-Pi (1 M HCl-Pi) and labile-Pi (Resin Pi + NaHCO3-Pi), no longer show an influence from lithology. Additionally, significant climatic effects were noted for labile-Pi, Ca-Pi and Fe/Al-Pi (0.1 M NaOH-Pi). Results suggest that P dynamics in soils are strongly influenced not only by climate and pedogenesis, but also lithology. Therefore, parent material and climate may interact more significantly than previously thought to regulate P biogeochemistry.