Phosphorus (P) is one of the limiting nutrients for most terrestrial ecosystems. Unlike nitrogen (N), which is derived from atmospheric deposition, the ultimate source of P is the weathering of primary mineral phosphate. The biogeochemical processes of P in soil after the P in primary minerals has been weathered and released have been extensively studied. However, the processes and rates of weathering of primary mineral phosphate remain poorly understood.
Based on the Hailuogou glacier chronosequene in Mt. Gongga, SW China, Dr. ZHOU Jun of Institute of Mountain Hazards and Environment of Chinese Academy of Sciences (IMHE) and his co-workers collected soil samples with six lengths of exposure (0, 30, 40, 52, 80 and 120 years). Soil samples were analysed using the sequential extraction procedure. The specific aims of this study were to (i) clarify the weathering processes of primary mineral phosphate and evaluate its rate of weathering in the initial stage of ecosystem development and (ii) identify the factors controlling the rate of weathering of primary mineral phosphate on both short and long time scales from the data in this study and data in the literature, respectively.
Their results revealed that the weathering processes of apatite in the Hailuogou chronosequence were divided into two stages (Figure 1): the first was observed at the 30-, 40- and 52-year-old sites, where the average rate of weathering of primary mineral phosphate (RLP) increased from 2.6 to 8.7 mmol m-2 year-1, and the second was observed at the 80- and 120-year-old sites, where the average RLP increased markedly to 26.0 mmol m-2 year-1. The RLP at the 120-year-old site was significantly larger than at sites with similar ages in temperate and subtropical zones, mainly because of differences in climate, vegetation type and initial P content of the parent material. The rapid increase in RLP with age in the Hailuogou chronosequence was fitted well by a power function (RLP=0.012×Age1.66) and was affected mainly by the rapid decrease in soil pH and rapid development of vegetation. By compiling the data in this study and from the literature, we propose that changes in the RLP with age (100–12 000 years) can be described by a decreasing power function and can be divided roughly into three stages (Figure 2): (i) the RLP is more than 10 mmol m-2 year-1 in soil of ≤ 260 years age, (ii) the RLP ranges from 1 to 10 mmol m-2 year-1 in soil of 260–2200 years in age and (iii) the RLP decreases to less than 1 mmol m-2 year-1 in soil of > 2200 years in age. This information can help to predict soil P status and source of available P in the long-term development of ecosystems. In addition, these results provide quantitative information to explain the marked decrease in primary mineral phosphate during the initial stage of pedogenesis described in the Walker & Syers (1976) conceptual model. The average RLP (14.1 mmol m-2 year-1) in the Hailuogou chronosequence is ~47 times larger than the global rate of P release, thus indicating the importance of glacier forelands in global P cycling.
This study has been supported by the National Natural Science Foundation of China (Grant No. 41630751 and No. 41401253), the 135 Strategic Program of the Institute of Mountain Hazards and Environment of Chinese Academy of Sciences (Grant No. SDS-135-1702) and the Chinese Academy of Sciences “Light of West China” Program.
The study entitled Weathering of primary mineral phosphate in the early stages of ecosystem development in the Hailuogou Glacier foreland chronosequence has been published online in European Journal of Soil Science.
Figure 1. Changes in rate of weathering of primary mineral phosphate (RLP) with age (0–120 years) are described well by an increasing power function in the Hailuogou chronosequence (error bars = standard errors, Adj. R2: adjusted R2) (Image by ZHOU Jun).
Figure 2. Changes in RLP with age (100–12 000 years) are described well by a decreasing power function (only literature data were fitted to the curve; Adj. R2: adjusted R2) (Image by ZHOU Jun).
Dr. ZHOU Jun
Institute of Mountain Hazards and Environment, Chinese Academy of Sciences
Chengdu, Sichuan, 610041, China