Exogenous phosphorus compounds interact with nitrogen availability to regulate dynamics of soil inorganic phosphorus fractions in a meadow steppe release_yr4kuyvrgrfyjh5b2ddneqzkeq

by Heyong Liu, Ruzhen Wang, Hongyi Wang, Yanzhuo Cao, Feike A. Dijkstra, Zhan Shi, Jiangping Cai, Zhengwen Wang, Hongtao Zou, Yong Jiang

Published in Biogeosciences Discussions by Copernicus GmbH.

2019   p1-36

Abstract

<strong>Abstract.</strong> Here we investigated the effects of P compounds (KH<sub>2</sub>PO<sub>4</sub> and Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>) with different addition rates of 0, 20, 40, 60, 80 and 100 kg P ha<sup>−1</sup> yr<sup>−1</sup> and NH<sub>4</sub>NO<sub>3</sub> addition (0 and 100 kg N ha<sup>−1</sup> yr<sup>−1</sup>) on soil labile (Olsen-P), moderate-cycling and recalcitrant inorganic phosphorus (IP) fractions in a calcareous grassland of northeastern China. Soil moderate-cycling IP, not readily available to plants but transforming into available P quickly, include variscite (Al-P), strengite (Fe-P), dicalcium phosphate (Ca<sub>2</sub>-P) and octacalcium phosphate (Ca<sub>8</sub>-P); recalcitrant fractions include hydroxylapatite (Ca<sub>10</sub>-P) and occluded P (O-P). Soil labile and moderate-cycling IP fractions and total P significantly increased with increasing P addition rates, with higher concentrations detected for KH<sub>2</sub>PO<sub>4</sub> than for Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub> addition. Combined N and P treatments showed lower moderate-cycling IP fractions compared to ambient N conditions due to enhanced plant productivity. Moderate-cycling IP was mainly regulated by aboveground plant biomass with KH<sub>2</sub>PO<sub>4</sub> addition, while by soil pH and plant biomass with addition of Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>. Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub> addition significantly increased the soil recalcitrant IP (Ca<sub>10</sub>-P) fraction, while KH<sub>2</sub>PO<sub>4</sub> addition showed no impact on it. A significant positive correlation was detected between soil moderate-cycling IP fractions and soil Olsen-P which illustrated that moderate-cycling IP fractions were important sources for available P. Our results suggest that moderate-cycling IP fractions are essential for grassland P biogeochemical cycling and chemical form of P fertilizer should be considered during fertilization management for maintaining soil available P.
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