Available Phosphorus in Forest Soil Increases with Soil Nitrogen but Not Total Phosphorus: Evidence from Subtropical Forests and a Pot Experiment

Xingzhao Liu,Kun Li,Junhua Yan,Weiqiang Xu,Guohua Liang,Liujing Huang,Wei Meng,Vishal Shah

doi:10.1371/journal.pone.0088070

Abstract

This paper aims to establish evidence for available phosphorous (AP) binding with total nitrogen (N) in subtropical forest soils. Soil organic carbon (SOC), total N, total phosphorous (P) and AP concentration were measured for three contrasting forest types in southern China: Masson pine forest (MPF), coniferous and broadleaved mixed forest (CBMF) and monsoon evergreen broadleaved forest (MEBF). A pot experiment with N addition was conducted to confirm the dominant factor to affect on soil AP concentration. The results showed that mean soil total N concentration in 0–10 cm soil layer was 440±50 for MPF, 840±80 for CBMF and 1020±50 mg kg−1 for MEBF, respectively. The mean soil AP concentration in 0–10 cm soil layer was 2.67±0.87 for MPF, 2.65±0.58 for CBMF, 4.10±0.29 mg kg−1 for MEBF, respectively. The soil total N concentration could explain about 70% of the variations in soil AP concentration in the top 20 cm soil layers in the three forest types. A pot experiment with N addition also showed an increase of AP concentration from 2.56 to 5.63 mg kg−1, when N addition increased from 5 g to 17 g NH4NO3. Our results therefore suggested that N addition significantly increased soil AP concentration, which might be beneficial for stabilizing the net primary production of subtropical forests that were limited by soil AP. This finding may provide a theory basis for tropical and subtropical forests management.

Highlights

Soil nitrogen (N) and phosphorus (P) are the most common macronutrients limiting plant growth under natural conditions
Mean Soil organic carbon (SOC) concentration in 0– 10 cm soil layer increased with the forest succession, being 1486862987 for Masson pine forest (MPF), 2850863175 for coniferous and broadleaved mixed forest (CBMF) and 3140663572 mg kg21 for monsoon evergreen broadleaved forest (MEBF)
Mean soil total N concentration in 0–10 cm soil layer increased with the forest succession, being 440650 for MPF, 840680 for CBMF to 1020650 mg kg21 for MEBF, respectively

Summary

Introduction

Soil nitrogen (N) and phosphorus (P) are the most common macronutrients limiting plant growth under natural conditions. Inventories of global soil P found that soil P amount is lowest in the tropical and subtropical regions [1,2] that account for about 40% of the global gross primary production and net carbon uptake over the past two decades [3,4]. Under global increasing atmospheric CO2 and N deposition in the future, P limitation of net primary production (NPP) in terrestrial ecosystems, tropical and subtropical forests, will likely exacerbate. A number of continuous eddy covariance measurements and long-term biomass inventories showed that old-growth forests can be significant carbon sinks, including tropical and subtropical forests [11,12,13,14,15]

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