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

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

doi:10.5194/bg-16-4293-2019

Abstract

Abstract. Here we investigated the effects of P compounds (KH2PO4 and Ca(H2PO4)2) with different addition rates of 0, 20, 40, 60, 80, and 100 kg P ha−1 yr−1 and NH4NO3 addition (0 and 100 kg N ha−1 yr−1) on soil labile inorganic phosphorus (IP) (dicalcium phosphate, Ca2-P), moderate-cycling IP, and recalcitrant IP fractions in a calcareous grassland of northeastern China. Soil moderate-cycling IP fractions, not readily available to plants but transforming into soil-available P quickly, include variscite (Al-P), strengite (Fe-P) and octacalcium phosphate (Ca8-P); recalcitrant IP fractions include hydroxylapatite (Ca10-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 KH2PO4 than for Ca(H2PO4)2 addition. Combined N and P treatments showed lower soil labile IP and moderate-cycling IP fractions compared to ambient N conditions, due to enhanced plant productivity. Moderate-cycling IP was mainly regulated by P addition and plant P uptake to further enhance labile IP and total P concentrations with KH2PO4 and Ca(H2PO4)2 addition. Soil labile IP was also directly and negatively affected by soil pH and plant P uptake with Ca(H2PO4)2 addition. Ca(H2PO4)2 addition significantly increased the soil recalcitrant IP (Ca10-P) fraction, while KH2PO4 addition showed no impact on it. A significant positive correlation was detected between soil labile IP, moderate-cycling IP fractions and soil Olsen-P which illustrated that labile IP and moderate-cycling IP fractions were important sources for soil-available P. Our results suggest that moderate-cycling IP fractions are essential for grassland P biogeochemical cycling and the chemical form of P fertilizer should be considered during fertilization management for maintaining soil-available P.

Highlights

Phosphorus (P) is an essential nutrient affecting terrestrial plant productivity and ecosystem functions (Luo et al, 2015)
Aboveground biomass production did not show a clear trend in response to different levels of P addition, either as KH2PO4 or as Ca(H2PO4)2 (Fig. 1a, b)
Plant P uptake increased with increasing P addition rates with significantly higher overall KH2PO4 effect than Ca(H2PO4)2

Summary

Introduction

Phosphorus (P) is an essential nutrient affecting terrestrial plant productivity and ecosystem functions (Luo et al, 2015). The solubility of soil Ca-P fractions decreases in the order Ca2P > Ca8-P > Ca10-P (Jiang and Gu, 1989) These element-bound P fractions are not readily available to plants, soil Al-P, Fe-P, Ca2-P and Ca8-P can be converted to free phosphates, serving as important buffering pools for available P (Herlihy and McGrath, 2006; Zhao et al, 2019). Soil recalcitrant IP is relatively stable and unavailable for plants, which is mainly converted from the fixation of labile and moderate-cycling IP (Shen et al, 2004; Zhao et al, 2019). Soil IP transformation is crucial for nutrient cycling in terrestrial ecosystems

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