Soil Phosphate Stable Oxygen Isotopes across Rainfall and Bedrock Gradients

The stable oxygen isotope compositions of soil phosphate (δ¹⁸O_p) were suggested recently to be a tracer of phosphorus cycling in soils and plants. Here we present a survey of bioavailable (resin-extractable or resin-P) inorganic phosphate δ¹⁸O_p across natural and experimental rainfall gradients, and across soil formed on sedimentary and igneous bedrock. In addition, we analyzed the soil HCl-extractable inorganic δ¹⁸O_p, which mainly represents calcium-bound inorganic phosphate. The resin-P values were in the range 14.5–21.2‰. A similar range, 15.6–21.3‰, was found for the HCl-extractable inorganic δ¹⁸O_p, with the exception of samples from a soil of igneous origin that show lower values, 8.2–10.9‰, which indicate that a large fraction of the inorganic phosphate in this soil is still in the form of a primary mineral. The available-P δ¹⁸O_p values are considerably higher than the values we calculated for extracellular hydrolysis of organic phosphate, based on the known fractionation from lab experiments. However, these values are close to the values expected for enzymatic-mediated phosphate equilibration with soil–water. The possible processes that can explain this observation are (1) extracellular equilibration of the inorganic phosphate in the soil; (2) fractionations in the soil are different than the ones measured at the lab; (3) effect of fractionation during uptake; and (4) a flux of intercellular-equilibrated inorganic phosphate from the soil microbiota, which is considerably larger than the flux of hydrolyzed organic-P

Wild barley (<i>Hordeum spontaneum</i>).

<p>(A) Wild barley field in Yakum Park (32° 14′ 50.28″ N, 34° 50′ 33″ E. March 18, 2013). It grows here with other species such as <i>Galium aparine</i>, <i>Chrysanthemum coronarium</i>, <i>Notobasis syriaca</i>, and <i>Anthemis</i> sp. (B) Same field, showing wild barley at three ripening stages – green, green-yellow and yellow.</p

Proto-weed species from Ohalo II: current weeds in cultivated fields.

<p>^aThe taxa identified as two closely related species in this table are both weeds. Some of these plants are edible.</p><p>Proto-weed species from Ohalo II: current weeds in cultivated fields.</p

Wild-type (left) and domestic-type (right) scars in rachises of wild barley (<i>Hordeum spontaneum</i>) from Ohalo II.

<p>Wild-type (left) and domestic-type (right) scars in rachises of wild barley (<i>Hordeum spontaneum</i>) from Ohalo II.</p

Location map of Ohalo II and central area of excavation at the site.

<p>Location map of Ohalo II and central area of excavation at the site.</p

biomass_1.2

biomass per mesocosm and harvest and species (or community if no species-specific values available

NDVI

NDVI data per mesocosm and dat

Appendix D. Patterning of factor relationships with litter decomposability fitted within individual sites in relation to the range of factor variation and sample size at the study sites.

Patterning of factor relationships with litter decomposability fitted within individual sites in relation to the range of factor variation and sample size at the study sites

Appendix B. Near-infrared reflectance spectroscopy calibrations between initial litter spectral properties and (a) litter decomposability and (b) litter quality.

Near-infrared reflectance spectroscopy calibrations between initial litter spectral properties and (a) litter decomposability and (b) litter quality

Appendix A. List of selected treatments at each site.

List of selected treatments at each site