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Conventional maps of soil parent material (SPM) types obtained by field survey and manual mapping or predictions from other map data have limited accuracy. Digital soil mapping of SPM types necessitates accurate acquisition of SPM distribution information, which is still a challenge in hilly areas. This study developed a high-accuracy method for SPM identification in hilly areas at the county scale. Based on geographic information system technology, seven feature variables were extracted from the geological map, geomorphic map, digital elevation model, and remote sensing image data of Shanggao County, Jiangxi Province, China. Different feature combination schemes were designed to develop SPM identification models based on random forest (RF), support vector machine (SVM), and maximum likelihood classification (MLC) algorithms. The best SPM identification results were obtained from the RF algorithm using the combination of geological type, geomorphic type, elevation, and slope. Confusion matrices were constructed based on a field survey of 586 validation samples, and the results were evaluated in terms of overall accuracy, precision, recall, F1 score, and Kappa coefficient. The overall accuracy and Kappa coefficient of the results from the optimal RF model were 83.11% and 0.79, respectively, which were 26.11% and 0.31 higher than those of the conventional map, respectively. Its precision and recall for various SPM types were greater than 75%. A comprehensive comparison of the accuracy, uncertainty, and plotting performance of the SPM recognition results reveals that the RF algorithm outperforms the SVM algorithm and the MLC algorithm. Geological type was the largest contributor to SPM identification, followed by geomorphic type, elevation, and slope. The importance of different feature variables varied for distinct SPM types. The accuracy of SPM identification was not improved by selecting more feature variables, such as land use type, normalised difference vegetation index, and topographic wetness index. This study demonstrates the feasibility of high-accuracy county-level SPM mapping in hilly areas based on the RF algorithm using geological type, geomorphic type, elevation, and slope as feature variables. As hilly areas have typical topographic features and SPM types, the proposed method of SPM mapping can be useful for application in other similar areas. There are a few limitations in this study with regard to data quality and resolution, feature variable selection, classification algorithm generalisation, and study area representativeness, which may affect the outcomes and need to be solved.

Carbon (C) storage and accumulation in forests is of growing importance as climate change focuses our attention on rising greenhouse gas emissions. In 2012, we measured total ecosystem C pools (including live vegetation, dead wood, and soils) in two unmanaged, mixed-species stands in central Maine, USA. The stands are adjacent to one another and serve as references against which silvicultural treatments can be compared. The soil parent material of the stands was different (marine sediments versus glacial till), which provided an ideal opportunity to compare C stocks between these stands. We used tree ring analysis and repeated forest inventories to estimate tree and dead wood recruitment patterns and past disturbance severity. Site quality influenced C trajectories through its influence on tree species composition, which in turn strongly determined stand susceptibility to insect outbreaks. In 2012, total ecosystem C stocks were 196.3 ± 9.6 Mg ha–1 (mean ± SD) in the stand on soils derived from marine sediments and 247.0 ± 17.7 Mg ha–1 in the stand on soils derived from glacial till. Differences in average total ecosystem C stocks were primarily driven by the live tree C pool. Despite the occurrence of several partial disturbance events from 1954 to 2012, live tree C stocks increased over time in both stands. Average C accumulation in recruited dead wood was also positive, indicating that aboveground biomass served as a C sink. Our results can be used to inform decisions related to C objectives in unmanaged stands of similar species composition and soils.

Phospholipid fatty acid analysis was used to investigate spatial variations in microbial communities of rhizosphere and bulk soil in rubber plantations in Hainan Island. Rhizosphere and bulk soil were collected from immature and mature rubber trees in areas with four different soil parent material types. For each site, total microbial biomass and biomass of bacteria, fungi, actinomycetes and ratio of fungi to bacteria in rhizosphere were significantly higher than those in bulk soil. The rhizosphere/bulk soil ratio for fungi in soil derived from basalt ranged from 10.44 to 12.33, which were significantly higher than those in soil derived from granitic gneiss, shallow marine deposits and granite (2.22-6.00). Total microbial biomass and bacterial biomass were positively correlated with soil organic carbon and total N in both rhizosphere and bulk soil. Total microbial biomass and biomass of bacteria, fungi and actinomycetes were correlated with soil total P in the rhizosphere. Rhizosphere total microbial biomass decreased in soil derived from basalt and increased in soil derived from shallow marine deposits with increasing age of rubber trees. The main factor affecting the composition of microbial communities in bulk and rhizosphere soil was soil parent material.

Iron compounds significantly affect the behaviour of trace elements in soils. Sequential chemical extractions are widely used to estimate not only the solid phase speciation of chemical elements but to study their mobilisation conditions. In this paper, we present results about the effect of iron fractionation on that of trace metals (Co, Cr, Cu, Ni, Pb and Zn) in representative soils for Hungary. Our aim was to study the effect of pedogenic processes and soil parent material on trace metal association with soil iron phases. Two major soil groups, such as Luvisols and non-Luvisols could be established based on trace metal content, distribution and fractionation in the studied soils. Such differences were found to be primarily due to the differences in the pedogenic processes in the studied soils, whereas soil parent material has not affected these characteristics significantly. We found that Fe phases affect trace metal fractionation and mobilisation as their host in form of both inherited and pedogenic phases. However, pedogenic processes, primarily iron and organic matter accumulation in our case, generally overwrite the effect of inherited iron phases on trace metal accumulation, distribution and fractionation. Among the studied metals, fractionation of Co and Cr were found to be much more affected by that of Fe, followed by Cu, Zn and Ni, whereas Pb could be associated with iron phases only subordinately.

Inspired by previous studies that have indicated consistent or even well-constrained (relatively low variability) relations among carbon (C), nitrogen (N) and phosphorus (P) in soils, we have endeavored to explore general soil C:N:P ratios in China on a national scale, as well as the changing patterns of these ratios with soil depth, developmental stages and climate; we also attempted to determine if well-constrained C: N:P stoichiometrical ratios exist in China's soil. Based on an inventory data set of 2,384 soil profiles, our analysis indicated that the mean C:N, C:P and N:P ratios for the entire soil depth (as deep as 250 cm for some soil profiles) in China were 11.9, 61 and 5.2, respectively, showing a C: N: P ratio of ~ 60: 5:1. C:N ratios showed relatively small variation among different climatic zones, soil orders, soil depth and weathering stages, while C:P and N:P ratios showed a high spatial heterogeneity and large variations in different climatic zones, soil orders, soil depth and weathering stages. No well-constrained C:N:P ratios were found for the entire soil depth in China. However, for the 0-10 cm organic-rich soil, which has the most active organism-environment interaction, we found a well-constrained C:N ratio (14.4, molar ratio) and relatively consistent C:P (136) and N: P (9.3) ratios, with a general C:N:P ratio of 134:9:1. Finally, we suggested that soil C:N, C:P and N:P ratios in organic-rich topsoil could be a good indicator of soil nutrient status during soil development.

Nutrient limitation to primary productivity and other biological processes is widespread in terrestrial ecosystems, and nitrogen (N) and phosphorus (P) are the most common limiting elements, both individually and in combination. Mechanisms that drive P limitation, and their interactions with the N cycle, have received less attention than mechanisms causing N limitation. We identify and discuss six mechanisms that could drive P limitation in terrestrial ecosystems. The best known of these is depletion-driven limitation, in which accumulated P losses during long-term soil and ecosystem development contribute to what Walker and Syers termed a \"terminal steady state\" of profound P depletion and limitation. The other mechanisms are soil barriers that prevent access to P; transactional limitation, in which weathering of P-containing minerals does not keep pace with the supply of other resources; low-P parent materials; P sinks; and anthropogenic changes that increase the supply of other resources (often N) relative to P. We distinguish proximate nutrient limitation (which occurs where additions of a nutrient stimulate biological processes, especially productivity) from ultimate nutrient limitation (where additions of a nutrient can transform ecosystems). Of the mechanisms that drive P limitation, we suggest that depletion, soil barriers, and low-P parent material often cause ultimate limitation because they control the ecosystem mass balance of P. Similarly, demand-independent losses and constraints to N fixation can control the ecosystem-level mass balance of N and cause it to be an ultimate limiting nutrient.

Background Soil phosphorus (P) availability can be an important regulator of ecosystem processes. Changes in P availability over time have long been studied, but the P concentration of soil parent materials—which determines ecosystem P concentration at the onset of soil formation—have never been systematically explored. Here we ask two questions: 1) how does P concentration vary among soil parent materials? and 2) under what range of conditions do those differences influence soil P concentration? Methods We used the Earthchem webportal to compile the P concentration of 263,539 rocks. We then gathered data from 62 sites (MAT ranging from 200-5,000 mm yr⁻¹ and soil age from 0.3-4, 100 ky) and assessed the correlation between rock and soil P concentration. Results We found a 30 fold difference in median P concentration among rock types, ranging from 120 ppm (several ultramafic rocks) to >3,000 ppm (several alkali basalts). Median P was significantly lower in common silica-rich rocks (e.g. granite - 436 ppm) and higher in common iron-rich rocks (e.g. andesite - 1,000 ppm). In sedimentary rocks, which make up 70 % of the ice-free land surface, median P was highest in mudstone (1,135 ppm) and decreased with increasing grainsize (siltstone-698 ppm, sandstone-500 ppm). Where soil P and parent material P were measured in the same site, parent material P explained 42 % of the variance in total soil P (n=62), and explanatory power was higher for sites with similar climate. Conclusion The variation in P concentration among common rock types is on a comparable scale to the changes in total P, and several P pools, over long-term soil development. Quantifying these differences may be an important step towards characterizing regional and global variation in soil and ecosystem P status.

Nutrient remobilization is a key process in nutrient conservation in plants and in nutrient cycling in ecosystems. To predict the productivity of terrestrial ecosystems, we thus need to improve our understanding of the factors that control remobilization. We studied the remobilization rates of several major nutrients (N, P, S, K, Ca, and Mg) in 102 forest ecosystems representing large environmental gradients at the country scale (France). Total amounts or availability of nutrients in soils were correlated with nutrient remobilization: the larger the soil nutrient pool, the lower the remobilization rate (e.g., P remobilization decreased with increasing total or extractable inorganic P in soils). Soil type and soil parent material influenced nutrient remobilization indirectly through their effect on soil nutrients. Nutrient remobilization was also affected by the quality of soil organic matter (C:N and C:P ratios) and K‐Ca‐Mg antagonisms. In addition to soil properties, plant‐related parameters (nutrient concentrations in foliage and leaf life span) and climate variables (e.g., precipitation and actual evapotranspiration) were also correlated with nutrient remobilization. Using multivariate analysis, we found that soil nutrient richness and the life span of the leaf were generally the two most important factors controlling nutrient remobilization. As a whole, the nutrient remobilization rate is regulated by soil nutrients through negative feedback. This general ecological pattern is modulated by ecophysiological constraints of plants, mainly leaf life span or the capability of plants to move Ca through the phloem sap.

Few studies have investigated the potential amount of Cd needing remediation in karst soils, despite the importance of such strategies for managing and restoring Cd-polluted soils. This study focuses on a typical karst region in Guangxi, China, where 12,547 surface soil samples and 48 soil profiles (collected every 20 cm from 0 to 200 cm depth) were analyzed. We conducted a comprehensive analysis of Cd in these soils and developed a formula for determining the necessary remediation. The findings indicated that the baseline concentration of Cd in surface soils was 0.383 mg/kg, demonstrating a wide-ranging variability, with content spanning from 0.031 to 16.192 mg/kg. Notably, the depth-wise distribution of Cd in the soils showed an extensive range from the detection limit up to 8222 mg/kg. The regional distribution of Cd generally showed higher concentrations in the southwest and lower concentrations in the northeast, as revealed by principal component analysis linking Cd sources to soil parent material characteristics, agricultural activities, and industrial activities. One-way analysis of variance indicated significant influences of soil type, soil use, and topography on surface soil Cd concentrations, whereas soil type, topography, and parent rock material significantly affected deep soil Cd concentrations. Analysis of the Cd distribution patterns revealed a logarithmic distribution trend with increasing depth. Consequently, a logarithmic model was fitted to derive a formula for the potential remediation requirements of Cd. The formula for estimating potential Cd repair was deduced and summarized, enabling the calculation of potential Cd repair under different land use modes, parent material types and soil types. The formula is scientifically sound, representative, and innovative. These methods offer scientific guidance for the control, remediation, and production practices in relation to Cd-contaminated soils in the karst region and can be applied in karst regions globally.

Background and aims Plant and soil microbes can reduce their phosphorus (P)-requirements by replacing phospholipids with non-P containing lipids (e.g., galactolipids, sulfolipids, and betaine lipids). There have been few studies of this process in the field (i.e., in natural ecosystems); thus, it is unclear whether a similar replacement of phospholipids with non-P lipids occurs across natural gradients of soil P-availability. Methods We compared the membrane lipid profiles of plant leaves, roots, and soil microbial communities between two adjacent native Australian sclerophyll forest ecosystems—one situated on a severely P-deficient sandstone-derived soil and the other on a comparatively P-rich shale-derived soil. The herbaceous species, Lomandra longifolia, which occurred across both soils was sampled, along with two Myrtaceae tree species associated with each soil type. Results The phospholipid content of plant leaves and soil microbes was two- to three-fold greater in the shale site than the sandstone site, but non-P lipid content did not differ between sites. Conclusion Our results indicate that plants and soil microbes can have a lower investment of P into phospholipids in response to P-deficiency without a concomitant increase in non-P lipid content. Modulations in phospholipid concentration occurred across all plant- and soil microbial-associated phospholipid classes.