Abstract
Field data about the effect of soil pH on phosphorus (P) cycling is limited. A promising tool to study P cycling under field conditions is the 18O:16O ratio of phosphate (δ18OP). In this study we investigate whether the δ18OP can be used to elucidate the effect of soil pH on P cycling in grasslands. Soils and plants were sampled from different fertilisation and lime treatments of the Park Grass long term experiment at Rothamsted Research, UK. The soils were sequentially extracted to isolate different soil P pools, including available P and corresponding δ18OP values were determined. We did not observe changes in plant δ18OP value, but soil P δ18OP values changed, and lower δ18OP values were associated with higher soil pH values. At sites where P was not limiting, available P δ18OP increased by up to 3‰ when lime was applied. We show that the δ18OP method is a useful tool to investigate the effect of pH on soil P cycling under field conditions as it highlights that different soil processes must govern P availability as pH shifts. The next challenge is now to identify these underlying processes, enabling better management of soil P at different pH.
Highlights
Field data about the effect of soil pH on phosphorus (P) cycling is limited
We investigate if shifts in available P δ18OP values in the soil are associated with changes in soil management strategies, changes in N applications and soil pH
Soil pH did not vary with depth while both Total carbon (TC) and total nitrogen (TN) concentrations decreased with depth
Summary
Field data about the effect of soil pH on phosphorus (P) cycling is limited. A promising tool to study P cycling under field conditions is the 18O:16O ratio of phosphate (δ18OP). We show that the δ18OP method is a useful tool to investigate the effect of pH on soil P cycling under field conditions as it highlights that different soil processes must govern P availability as pH shifts. As well as microorganisms, can adapt to P limitation by increasing the internal use efficiency of P or by increasing P availability in the soil This involves processes like replacing phospholipids by sulfo-galactolipids and exuding organic acids and phosphatases, respectively. Optimum pH values are a global problem due to soil acidification[9,10] and could further challenge the sustainable intensification of agriculture This pH optimum for P availability was questioned recently by Barrow[11], citing only laboratory studies for the determination of the pH optimum. The δ18OP values reported in the literature are often compared to this theoretical value, as it is considered to be an indication of P cycling through microorganisms[23]
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