The Characteristics of Soil C, N, and P Stoichiometric Ratios as Affected by Geological Background in a Karst Graben Area, Southwest China

Abstract

Understanding ecological stoichiometric characteristics of soil nutrient elements is crucial to guide ecological restoration and agricultural cultivation in karst rocky desertification region, but the information about the effect of the geological background on ecological stoichiometric ratios remains unknown. Soils from different landforms, including a basin, slope, and plateau, were sampled to investigate the spatial variance of the ecological stoichiometric characteristics of soil carbon (C), nitrogen (N), and phosphorus (P) under different rocky desertification grades (LRD: light rocky desertification; MRD: moderate rocky desertification; and SRD: severe rocky desertification) in a karst graben basin of Southwest China. Soil C:N ratio was not significantly influenced by rocky desertification grade, which was at a relatively stable level in the same landform, but soil C:P and N:P ratios increased with increasing rocky desertification grade. This change was consistent with increased soil organic carbon (SOC) and total nitrogen (TN) concentrations in the same geomorphic location along with the intensification of rocky desertification, but soil P concentration remained at a relatively stable level, indicating that P may be the limiting macronutrient for plant growth during vegetation restoration in a karst graben area. The soil C:N ratio of slope land was larger than that of the basin and plateau, while the soil C:P ratio and N:P ratio of the slope and plateau were significantly larger than that of the basin. The correlations between pH and C, N, and P stoichiometry decreased significantly when Ca was used as a control variable. In sharp contrast, the correlations between Ca and C, N, and P stoichiometry were highly significant no matter whether pH was used as a control variable, suggesting the important role of Ca in soil C, N, and P stoichiometry in karst graben basins.

Effects of Plum Plantation Ages on Soil Organic Carbon Mineralization in the Karst Rocky Desertification Ecosystem of Southwest China

“…Soil pH was determined at a 1:2.5 (w/v) soil/water ratio by a digital millivolt pH Meter-2 (DMP-2 mV/pH) detector (Quark Ltd., Nanjing, China); SOC was determined using the K 2 Cr 2 O 7 -H 2 SO 4 volumetric dilution heating method; total nitrogen was determined using the Kjeldahl procedure [15]; total potassium (TK) concentration was determined with the HF-HClO 4 flame photometric method; and total phosphorus (TP) was measured using HClO 4 -H 2 SO 4 digestion followed by an Mo-Sb colorimetric assay [1]; soil calcium (Ca) was extracted by HNO 3 -HF-HClO 4 and analyzed by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Three replicates were performed for each soil sample.…”

“…Due to the fragile geological and ecological conditions, rocky desertification widely occurs in the southwest karst region of China [1], which is characterized by serious soil erosion, devoid of vegetation and soil [2]. To effectively prevent rocky desertification, a series of ecological restorations have been carried out to increase the forest cover and to mitigate soil erosion by the Chinese government [3].…”

“…In particular, it is not clear whether plum plantation age is the key factor controlling SOC stability and how other factors influence SOC decomposition dynamics. In addition, calcareous soil developed on carbonate rock is characterized by high pH and Ca materials in a karst region [1], which may lead to the obvious differences in SOC mineralization compared to other soil types. The lack of knowledge regarding SOC mineralization under plum plantation during karst rocky desertification restoration limits the ability to predict how this ecosystem will respond to climate change.…”

Disturbance Effects on Soil Carbon and Greenhouse Gas Emissions in Forest Ecosystems

“…Rock desertification is a process of land degradation that may reduce soil productivity and some natural environmental factors can induce this process [10], but the effect of desertification on forest soil stoichiometry remains poorly understood. Yang et al reported that soil C:N (nitrogen) ratio was not significantly affected by the degree of desertification, but soil C:P (C: phosphorus) and N:P ratios increased with increasing degree of desertification [11]. Yang et al also pointed out that P might be the limiting factor for plant growth during restoration and calcium could play an important role in soil C, N and P stoichiometry in the ecosystem they studied [11].…”

“…Yang et al reported that soil C:N (nitrogen) ratio was not significantly affected by the degree of desertification, but soil C:P (C: phosphorus) and N:P ratios increased with increasing degree of desertification [11]. Yang et al also pointed out that P might be the limiting factor for plant growth during restoration and calcium could play an important role in soil C, N and P stoichiometry in the ecosystem they studied [11].…”