Soil phosphorus fractions and tree phosphorus resorption in pine forests along an urban-to-rural gradient in Nanchang, China

Abstract

Urbanization has been rapid across the world but the responses of phosphorus (P) cycling to urbanization have not been well-investigated. This study was to understand the influences of rapid urbanization on forest P cycling in a developing country. Soil P fractions and P resportion were determined for nine slash pine (Pinus elliottii Engelm.) forests along a 30-km long urban-suburban-rural gradient in Nanchang City, southern China. The total P stocks in the surface soils in urban and suburban forests were 317% and 182% higher, respectively, than levels found in rural forests. The concentrations of soil available P, labile P, slow P, occluded P and total extractable P were also much higher in urban and suburban forests than in rural forests (P<0.05). Soil weathered P concentrations were highest in urban forests. Annual mean foliar P concentrations were enhanced in urban and suburban forests compared to rural forests. The P resorption efficiency (PRE) was higher in rural forests than in suburban and urban forests, while the P resorption proficiency (PRP) was lower in rural forests than in suburban and urban forests. Urbanization associated with high extraneous P inputs has altered soil P status and plant P uptake. Foliar P concentration, PRE and PRP were largely dependent on soil P availability in our study forests.

Does Plant Size Influence Leaf Elements in an Arborescent Cycad?

“…Soil nutrition status is one site factor that is closely related to the concentration of leaf nutrients [39,40], a concept that justifies fertilization in managed systems. Moreover, nutrient resorption [38,41,42] and stoichiometry [43,44,45] are also responsive to fertilization and soil nutrient levels. With the exception of Ca, our habitat differences in concentration of leaf elements did not follow the same direction as the differences in concentration of corresponding soil elements.…”

Mixed Broadleaved Tree Species Increases Soil Phosphorus Availability but Decreases the Coniferous Tree Nutrient Concentration in Subtropical China

“…For the determination of extractable P, we employed improved Hedely P fractionation methods to quantify soil P functional fractions [28,29]. Air-dried soil samples were processed to follow the soil P fractionation sequential procedure [15]. The corresponding supernatants sequentially exacted with anion exchange resin (weak base), 0.5 M NaHCO 3 , 0.1 M NaOH, 0.1 M NaOH with sonication, 1.0 M HCl were collected by centrifuge at 1.7 × 10 4 m•s −1 (3200 rpm) for five minutes, followed by filtering samples through a 0.45-µm micropore filter.…”

“…Phosphorus concentration in each supernatant was determined by the phosphomolybdic acid blue color method. The extractable P, including Resin-P, NaHCO 3 -P, NaOH-P, sonication-P, and HCl-P, are defined as available P, soluble P, slowly released P, occluded P, and weathered mineral P, respectively, based on their functions in soils [15]. The residual P is the difference between total P and extractable P.…”

“…Unfortunately, the difference of nutrient transformation and availability between the rhizosphere and bulk soil is less understood especially in forest ecosystems [14]. The modified P functional fractionation method in acidic soils provides an effective tool to explore the P supply process in the rhizosphere soil of subtropical forests [15].…”

Inserting cycads into global nutrient relations data sets

“…Leaf P resorption has been studied in relation to soil P availability, and resorption tends to increase as background soil P decreases. 48 However, resorption does not always track soil nutrient status, making determination of the effectors and effects on nutrient resorption complex. The only publication comparing leaf nutrient resorption among more than one soil type included a comparison of four soil types for Cycas nitida.…”