Abstract
Phosphorus (P) is one of the key limiting factors for the growth of forests and their net primary productivity in subtropical forest ecosystems. Phosphorus leaching of the forest soil to the catchment and groundwater in karst region is the main source of water eutrophication. Strong P sorption capacity of minerals is generally assumed to be a key driver of P leaching in subtropical ecosystems which varies among different soil types. Here, we estimated P adsorption capacity of the O/A and AB horizon in both limestone soil and red soil of subtropical forests by fitting the Langmuir and Freundlich isotherm to investigate the potential environmental risks of P. The maximum P sorption capacity ([Formula: see text]), P sorption constant ([Formula: see text]), P sorption index (PSI), degree of P saturation (DPS), and maximum buffer capacity (MBC) were calculated. The results indicate that [Formula: see text] of the O/A horizon in both soils were similar. Comparing these two soils, the red soil had a higher [Formula: see text] and MBC in the AB horizon; [Formula: see text] of limestone soil was larger but [Formula: see text] was lower, indicating that the adsorption capacity of limestone soil was weaker and MBC was lower. There was no significant difference in PSI between the two soils. The DPS values of both soils were below 1.1%, indicating that P saturation is low in both subtropical forest soils due to the lack of marked anthropogenic disturbance. In the O/A horizon, P saturation associated with available P (DPSM3 and DPSOlsen) and that associated with P in the Fe-Al bound state (DPScitrate) were higher in the red soil than in the limestone soil. DPS did not differ significantly in the AB horizon, except for higher DPSM3 and DPScitrate in the red soil. The findings highlight the influence of the soil types on P adsorption. The P adsorption and buffering of red soils were higher than those of limestone soils, indicating a lower risk of P leaching in red subtropical forest soils.
Highlights
Phosphorus is one of the key limiting factors for the growth of forest trees and their net primary productivity in natural forest ecosystems, and it exists mainly in the form of organic P (Po) and inorganic P (Pi) in primary and secondary minerals
We investigated the P adsorption and potential environmental risk in limestone and red soils which are the main soil types in subtropical forests of China
The study area is located in Guilin City, South China, which is located at low latitude and belongs to the subtropical monsoon climate zone with mild climate, abundant rainfall, and basically the same season of rain and heat; the average annual temperature is about 19.1°C, the average annual rainfall is about 1887.6 mm, the average annual relative humidity is about 76%, and the average annual sunshine duration is about 1447.1 hours
Summary
Phosphorus is one of the key limiting factors for the growth of forest trees and their net primary productivity in natural forest ecosystems, and it exists mainly in the form of organic P (Po) and inorganic P (Pi) in primary and secondary minerals. Due to the sorption and fixation of P by soil minerals, phosphate accounts for only a few fraction of the soil P pool, resulting in a generally low availability of P in soils [2, 3]. This is especially the case in subtropical forest ecosystems, due to a high degree of soil weathering and more pronounced fixation of P by iron and aluminum oxides. Most of P in soil is fixed in a stable form that is difficult to be absorbed and utilized by plants, so P limitation in subtropical forest ecosystems is more severe than in other ecosystems [4]. The input of P in forest ecosystems is mainly from slow weathering of the parent bedrock [5] and in a shorter time scale from the decomposition of litter and mineralization of organic
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