[Temporal and Spatial Variations of Soil Organic Carbon and the Influencing Factors in Shaanxi Province in Recent 30 Years].

Soil organic carbon （SOC） variation is a significant indicator for the soil quality dynamic and global carbon cycle. Therefore, it is necessary to study the regional temporal and spatial distribution of SOC pool and the influencing factors. In this study, a total of 540 soil data and environmental variables were collected from Shaanxi Province during a 30-year period from 1985 to 2015, and univariate analysis of variance and path analysis were used to explore the temporal and spatial distribution characteristics of SOC content and the influencing factors of SOC change. The results showed that the SOC contents of Shaanxi Province in both 1985 and 2015 were the highest in central Shaanxi, followed by those in southern Shaanxi, and they were significantly higher than those in northern Shaanxi. From 1985 to 2015, the increase in SOC in southern Shaanxi was the highest （21.28%）, and that in central Shaanxi was 15.33%. The content of SOC in northern Shaanxi was decreased by 10.23%, caused by significant decrements in the bottom horizons of 60-80 cm and 80-100 cm. Compared with that in 1985, the increases in SOC content in the 0-100 cm soil profile （with every 20 cm as a horizon） ranged from 3.21% to 29.39% in 2015. The increase in SOC content of skeletal soils was largest, followed by that of alluvial soils. Correlation analysis and path analysis showed that SOC content was positively correlated with altitude, average annual precipitation, normalized vegetation index, and total nitrogen content and was in significant negative correlation with curvature, bulk density, and pH. Total nitrogen content was the main controlling factor affecting SOC content. The results of the study can provide reference for future carbon management measures in the region.

Magnetized bentonite modified rice straw biochar: Qualitative and quantitative analysis of Cd(II) adsorption mechanism.

Industrialization has caused a significant global issue with cadmium (Cd) pollution. In this study, Biochar (Bc), generated through initial pyrolysis of rice straw, underwent thorough mixing with magnetized bentonite clay, followed by activation with KOH and subsequent pyrolysis. Consequently, a magnetized bentonite modified rice straw biochar (Fe3O4@B-Bc) was successfully synthesized for effective treatment and remediation of this problem. Fe3O4@B-Bc not only overcomes the challenges associated with the difficult separation of individual bentonite or biochar from water, but also exhibited a maximum adsorption capacity of Cd(II) up to 241.52 mg g-1. The characterization of Fe3O4@B-Bc revealed that its surface was rich in C, O and Fe functional groups, which enable efficient adsorption. The quantitative calculation of the contribution to the adsorption mechanism indicates that cation exchange and physical adsorption accounted for 65.87% of the total adsorption capacity. In conclusion, Fe3O4@B-Bc can be considered a low-cost and recyclable green adsorbent, with broad potential for treating cadmium-polluted water.

Phosphorus acquisition strategies of wheat are related to biochar types added in cadmium-contaminated soil: Evidence from soil zymography and root morphology.

Biochar application for the remediation of cadmium (Cd)-contaminated soils may result in a relative deficiency of phosphorus (P) due to the disruption of soil nutrient balance. However, the P acquisition strategies of plants in such situation are still unclear. In this study, analyses on soil zymography and root morphology were combined for the first time to investigate the effects of pristine and P-modified biochars from apple tree branches on the P acquisition strategies of wheat under Cd stress. The results show that the application of pristine biochar exacerbated the soil's relative P deficiency. Wheat was forced to improve foraging for P by forming longer and thinner roots (average diameter 0.284 mm) as well as releasing more phosphatase to promote P mobilization in the soil. Moreover, bioavailable Cd affected the P acquisition strategies of wheat through stimulating the release of phosphatase from roots. The P-modified biochar maintained high levels of Olsen-P (>100 mg kg-1) in the soil over time by slow release, avoiding the creation of relative P deficiency in the soil; and increased the average root diameter (0.338 mm) and growth performance index, which promoted shoot growth (length and biomass). Furthermore, the P-modified biochar reduced DTPA-extracted Cd concentration in soils by 79.8 % (pristine biochar by 26.9 %), and decreased the Cd translocation factor from root to shoot as well as Cd concentration in the shoots. Therefore, P-modified biochar has a great potential to regulate the soil element balance (carbon, nitrogen, and P), promote wheat growth, and remediate the Cd-contaminated soil.

Efficient removal of Cd(II) by phosphate-modified biochars derived from apple tree branches: Processes, mechanisms, and application.

Phosphate (P)-modified biochar is a good material for cadmium (Cd) immobilization, and the pore-forming effect of potassium ions (K+) can favor the P loading on biochar. However, few studies have been done specifically on Cd(II) removal by composites of potassium phosphates with biochar, and the removal potential and mechanisms are not clear. Herein, apple tree branches, a major agricultural waste suitable for the development of porous materials, were pyrolyzed individually or together with KH2PO4, K2HPO4·3H2O, or K3PO4·3H2O to obtain biochars to remove Cd(II), denoted as pristine BC, BC-1, BC-2, and BC-3, respectively. The results showed that the orthophosphates containing more K+ enlarged the specific surface area, total pore volume and phosphorus loading of biochar. Co-pyrolysis of apple tree branches and P promoted the thermochemical transformation of P species. Only weak signal of orthophosphate was observed in the pristine BC, while the presence of orthophosphate, pyrophosphate and metaphosphate were detected in BC-1, and BC-2 and BC-3 showed the presence of orthophosphate and pyrophosphate. The maximum Cd(II) adsorption capacities of pristine BC, BC-1, BC-2 and BC-3 were 10.4, 88.5, 95.8, and 116 mg·g-1, respectively. Orthophosphate modification enhanced the Cd(II) adsorption capacity due to the formation of Cd-P-precipitates, namely Cd5(PO4)3Cl, Cd5(PO4)3OH, Cd3(PO4)2, Cd2P2O7, and Cd(PO3)2. Furthermore, higher cation exchange efficiencies between Cd(II) and K+ in P-modified biochars also contributed to their high Cd(II) adsorption capacity. Cd(II) removal by BC-3 from artificially polluted water bodies showed more than 99.98% removal rates. Application of BC-3 also reduced the diethylene triamine pentaacetic acid-extracted Cd(II) in soil by 69.1%. The co-pyrolysis of apple tree branches and potassium phosphates shows great prospect in Cd(II) wastewater/soil treatment and provide a promising solution for agricultural waste utilization and carbon sequestration.

Synthesis of an environmentally friendly binding material using pyrolysis by-products and modified starch binder for slow-release fertilizers.

Biochar-based slow-release fertilizers (BSRFs) are vital for the development of eco-friendly and sustainable agriculture. Considerable attention has been given to enhancing the efficiency of fertilizers (EEFs) by appropriate modification or binding to reduce nutrient waste and improve the slow-release effect on the growth of plants. In this study, sustained binding materials were presented for BSRF synthesis, including pyroligneous acids (PA), bio-oil (BO), and modified starch binder (MSB). The results show that the release ratio of phosphorus from PA + BO+MSB was 4.7%, 15.2%, and 21.2% slower than that of PA, BO, and MSB alone, respectively. The BSRFs were characterized by SEM, XRD, FT-IR, XPS, and EDS, and the release kinetic outcome revealed that PA + BO+MSB contributed to the formation of a satisfactory structure in the BSRFs. The MSB viscosity significantly influences the slow-release performance and accumulation of N, P, and K nutrients. Moreover, economic assessments showed that PA + BO+MSB exhibited the lowest cost.

The interplay of labile organic carbon, enzyme activities and microbial communities of two forest soils across seasons.

Soil labile organic carbon (LOC) responds rapidly to environmental changes and plays an important role in carbon cycle. In this study, the seasonal fluctuations in LOC, the activities of carbon-cycle related enzymes, and the bacterial and fungal communities were analyzed for soils collected from two forests, namely Betula albosinensis (Ba) and Picea asperata Mast. (Pa), in the Qinling Mountains of China. Results revealed that the seasonal average contents of microbial biomass carbon (MBC), easily oxidized organic carbon (EOC), and dissolved organic carbon (DOC) of Pa forest soil were 13.5%, 30.0% and 15.7% less than those in Ba soil. The seasonal average enzyme activities of ß-1,4-glucosidase (ßG), and ß-1,4-xylosidase (ßX) of Ba forest soils were 30.0% and 32.3% higher than those of Pa soil while the enzyme activity of cellobiohydrolase (CBH) was 19.7% lower. Furthermore, the relative abundance of Acidobacteria was significantly higher in summer than in winter, whereas the relative abundance of Bacteroidetes was higher in winter. Regarding the fungal communities, the relative abundance of Basidiomycota was lowest in winter, whereas Ascomycota predominated in the same season. In addition, the soil LOC was significantly positively correlated with the CBH, ßG and ßX activities. Changes in LOC were significantly correlated with Acidobacteria, Bacteroidetes and Basidiomycota. We conclude that the seasonal fluctuations in forest soil LOC fractions relied on carbon cycle-associated enzymatic activities and microorganisms, which in turn were affected by climatic conditions.

[Effects of Biochar Application on Soil Microbial Nutrient Limitations and Carbon Use Efficiency in Lou Soil].

Soil microbial metabolism is vital for nutrient cycling and stability of an ecosystem. To elucidate the long-term effects of biochar application on nutrient limitations and carbon use efficiency (CUE) of soil microbial metabolisms, biochars pyrolyzed at 450℃ from trunks and branches of fruit trees under an oxygen-limited condition were mixed with the top Lou soils (0-20 cm) with application amounts of 0, 20, 40, 60, and 80 t·hm-2 in 2012. Corn-wheat rotation was carried out afterwards for seven years. The nutrient limitations of soil microbial metabolisms were analyzed quantitatively through ecoenzymatic stoichiometry in 2019. The results indicated that:① With an increase in the biochar application amount, soil moisture, organic carbon, total nitrogen, C:N, C:P, and N:P significantly increased, whereas there were no clear patterns for the active components of carbon, nitrogen, and phosphorus, microbial biomass carbon, nitrogen, phosphorus and total phosphorus. In contrast, the activities of five extracellular enzymes (ß-1,4-glucosidase, cellobiohydrolase, leucine aminopeptidase, ß-1,4-N-acetylglucosaminidase, and phosphatase) were significantly reduced. ② The soil microorganisms suffered from the phosphorus limitation under all treatments in this study. In the treatments of biochar application, the carbon and phosphorus limitations of microbial metabolisms increased significantly with increasing application amount, whereas the microbial CUE decreased significantly. When the application amount was 20 t·hm-2, the carbon limitation (0.625±0.022) and phosphorus limitation (62.153°±0.892°) were lowest, and the microorganism CUE (0.511±0.007) was highest. ③ Partial least-squares path modeling (PLS-PM) showed that soil carbon, nitrogen, phosphorus, and their stoichiometry had a very direct positive effect on phosphorus limitation (P<0.01), and there was a positive correlation between carbon limitation and phosphorus limitation (R2=0.242, P<0.001); in contrast, the carbon and phosphorus limitations had a very significant negative effect on CUE (P<0.001). It was revealed that the excessive application of biochar had caused a soil element stoichiometry imbalance, which deteriorated the phosphorus limitation of the soil microbial metabolism and further led to carbon limitation and reduction of CUE. When the biochar application amount was 20 t·hm-2, C and P limitations were lowest, and microbial CUE was highest. Therefore, 20 t·hm-2 was optimal for regulating soil microbial metabolism, maintaining ecological functions, and reducing carbon dioxide emission produced by microbial metabolism.

Surface properties and suspension stability of low-temperature pyrolyzed biochar nanoparticles: Effects of solution chemistry and feedstock sources.

Intensive application of biochar requires better understanding of their environmental behaviors such as stability, fate, and mobility. The release of bulk biochar into biochar nanoparticles (NPs) may bring risks because of their potential flowing into downstream water bodies with nutrients/containments attached. Low-temperature pyrolyzed biochars, namely fruit tree branch biochar of 350/450/550 °C (FB350, FB450 and FB550), corn straw biochar of 350 °C (CB350) and peanut straw biochar of 350 °C (PB350), were produced, and their NPs were extracted. The yield, elemental composition, mineral composition, surface functional groups and zeta potential of biochar NPs were characterized. Subsequently their suspension stability was evaluated in NaCl and CaCl2 solutions by dynamic light scattering technique. The Hamaker constants and particle interaction energy of the biochar NPs were calculated by adopting Derjaguin-Landau-Verwey-Overbeek theory. For biochar NPs of same feedstock, the stability of FB350/450/550-NPs could be predicted well by their zeta potential values. The types of their surface functional groups were the same while their adsorption intensity differed. The scenarios for biochar NPs of different feedstock sources were different, that is, inconsistent variation was observed between their zeta potential and suspension stability, which were rooted in the variable type and quantity of surface functional groups. In conclusion, feedstock was the most significant factor that influenced the suspension stability of biochar NPs, followed by the pyrolysis temperature and solution chemistry, which were highly dependent on surface potential. The findings provide references for the environmental risk evaluation of biochar NPs and reasonable application of biochar in field.

[Remediation Effects of Different Composite Materials on Cadmium-Contaminated Farmland Soil].

A pot experiment was conducted to study the application effects of three composite materials, namely SC (lime:organic compound fertilizer=2:3), LS (ferrous sulfate:lime=1:1) and LB (ferrous sulfate:biochar in combinations of 1:1, 1:2, 1:3, 1:4 and 1:5), on soil Cd bioavailability, Cd cumulative distribution in different wheat organs, and wheat yield. The results indicated that:① Addition of composite materials all significantly decreased the soil available Cd content by 50.2%-81.8% (SC), 29.4%-48.1% (LS), and 18.7%-42.2% (LB). Composite materials significantly increased soil pH by 1.37-2.28 (SC), 0.41-0.86 (LS), and 0.14-0.17 (LB) units. ② The Cd cumulative distribution in different wheat organs were in the order of root > leaf > stem > glume > grain. The translocation abilities of Cd in different organs were in the order of root > glume > stem and leaf. ③ Compared with the control, 0.67% SC addition and 0.67% LS addition significantly increased the wheat yields by 56.4% and 51.2%; LB addition significantly increased wheat yield by 39.6% to 51.2%. ④ The correlation analysis showed that soil pH was significantly negatively correlated with soil available Cd and Cd contents in different wheat organs. There were significant positive correlations between soil available Cd and Cd contents in different wheat organs, and the correlation coefficients were 0.711 (grain), 0.817 (glume), 0.593 (stem), 0.630 (leaf) and 0.622 (root). Meanwhile, there is also a significant positive correlation between Cd content in different wheat organs. ⑤ Comprehensively, the addition of 0.93% SC increased soil pH by a maximum of 2.28 units, and the soil available cadmium content was decreased by a maximum of 81.8%. Therefore, adding 0.93% SC was the most suitable treatment for repairing and controlling the Cd pollution in farmland soil.

[Impact of Biochar on Soil Bulk Density and Aggregates of Lou Soil].

The effect of biochar on the bulk density and aggregate stability of Lou soil was evaluated and compared after biochar was applied for 2 years and 5 years through a field-positioning experiment. Five biochar amounts were applied in this study, as follows:0 t·hm-2 (B0), 20 t·hm-2 (B20), 40 t·hm-2 (B40), 60 t·hm-2 (B60), and 80 t·hm-2 (B80). The biochar was produced by pyrolysis of stems and branches from fruit trees at the temperature of 450℃ with limited oxygen apply. At the beginning of the study, biochar was mixed thoroughly with the surface soil (0-20 cm). After 5 years, the soil bulk density and aggregate stability of 0-30 cm soil layers (0-10, 10-20, and 20-30 cm) were measured and compared with the results obtained after 2 years with the purpose of observing the long-term and persist effects of biochar application. The results showed that:① compared with the results after 2 years of application, the effect of biochar on the aggregates at depths of 0-10 cm and 10-20 cm after 5 years were less distinct, and the effect on soil aggregates at depths of 20-30 cm was significantly enhanced; ② compared with the 2 year application, the aggregate stability and the content of the>0.25 mm aggregate size fraction were significantly increased at 0-10 cm depths after 5 years of biochar application at a rate of 40 t·hm-2, while bulk density was significantly decreased; at 10-20 cm and 20-30 cm soil depths, the stability of aggregates and the content of the>0.25 mm aggregate size fraction was significantly increased, while the bulk density was significantly decreased after 5 years of biochar application at a rate of 60-80 t·hm-2;③ when the biochar application rate was 60 t·hm-2, the increase in soil organic carbon was the highest after 5 years. After biochar was applied for 5 years, its effect was more significant lower in the soil profile; the soil bulk density was significantly reduced, and aggregate stability and the content of>0.25 mm aggregates were significantly increased at depths of 20-30 cm. Based on a comprehensive evaluation of the improvement effects and economic benefits, the most suitable biochar application rate was found to be 40-60 t·hm-2. It was further concluded that the effect of biochar on soil aggregates was gradual and sustainable.

Amination of biorefinery technical lignin by Mannich reaction for preparing highly efficient nitrogen fertilizer.

To develop a novel lignin-based highly efficient nitrogen fertilizer, the amination of the biorefinery technical lignin was conducted by Mannich reaction synergy with phenolation pretreatment. Subsequently, the structural transformations of lignin samples and the reaction mechanism were investigated in detail. The soil column leaching experiment was also performed to research the nitrogen release behavior of aminated lignin in soil. The results indicated that the amounts of active sites in lignin were significantly increased to 8.26 mmol/g from the original 2.91 mmol/g by phenolation. In addition, the Mannich reaction was highly selective for occurring at ortho- and para-positions of phenolic hydroxyl groups in the phenolated lignin, in which the latter was favored. Moreover, the nitrogen content in the aminated lignin was highly depended on the types of amination reagent instead of the proportion of reactants in this study. Under an optimal condition, aminated lignin with a high nitrogen content (10.13%) and low C/N ratio (6.08) could be obtained. Besides, it was especially noteworthy that the prepared APL in this study has a favorable nitrogen release behavior in soil. Thus, it is believed that these aminated lignin derivatives could be used for the preparation of various lignin-based highly efficient nitrogen fertilizer.

[Patterns of Bacterial Community Through Soil Depth Profiles and Its Influencing Factors Under Betula albosinensis Burkill in the Xinjiashan Forest Region of Qinling Mountains].

In this study, vertical changes in bacterial α-diversity and community composition were investigated at four soil depths(0-10, 10-20, 20-40 and 40-60 cm) in Betula albosinensis Burkill forest of Qinling Mountains by sequencing of the 16S rDNA regions using Illumina MiSeq high-throughput technology. The results showed that the decreases of OTUs, Chao1 and Shannon were numerical but not significant, and the highest values of 1688, 2314 and 8.66 were obtained in 0-10 cm, respectively. At the phylum level, Acidobacteria and Proteobacteria were the most dominant bacteria in four soil layers. At the genus level, Gp4, Gp6 and Gp16 were the most dominant bacteria. The relative abundance of Acidobacteria in 40-60 cm soil depth(62.88%) was higher than those in other soil depths. Proteobacteria in 0-10 cm(23.62%) was more abundant than that in 40-60 cm. The relative abundance of Acidobacteria was significantly correlated with the total N, soil organic carbon, C/N, and soil dissolved organic carbon. Soil water content, soil organic matter and soil dissolved organic carbon were the key factors affecting soil Proteobacteria. RDA sequencing results showed that soil dissolved organic carbon was the key factor contributing to the bacteria community abundance. The results demonstrated that there are plenty of bacterial distribution in all four soil layers, which provides a fundamental basis for vertical soil bacterial community diversity, and possesses very important research value in biogeochemical cycling.

[Effect of Biochar on CH4 and N2O Emissions from Lou Soil].

In order to investigate the effect of biochar on CH4 and N2O emissions from Lou soil, field plot experiments of winter wheat were conducted with five levels of biochar addition (0, 20, 40, 60, and 80 t·hm-2). The fluxes of CH4 and N2O, wheat production, soil organic carbon, soil water content, and temperature of each soil layer were measured. The results showed that the fluxes of CH4 and N2O changed significantly in different growth periods of winter wheat. Compared with the control, the cumulative CH4 uptake under the biochar amendment increased by 12.88%-71.61%. When the biochar addition was ≥ 40 t·hm-2, the cumulative CH4 uptake was significantly higher and the highest uptake was at the level of 40 t·hm-2. Biochar amendment had no significant effect on cumulative N2O emissions and the global warming potential (GDP). The greenhouse gas intensity (GHGI) decreased by 13.24%-22.14%. The wheat yield increased by 1.72%-32.19% after biochar addition. When the applied biochar level was ≥ 40 t·hm-2, the wheat yield increments were significantly higher. The biochar addition of 40 t·hm-2 was the optimal level for increasing the wheat yield. The soil organic carbon and water content under biochar amendment increased by 1.42-2.69 times and 7.08%-11.96%, respectively. The results suggested that Lou soil was the sink of atmospheric CH4 and the emission source of N2O during the winter wheat growth period, and the biochar level of 40 t·hm-2 was the optimal addition amount.

[Influence of Biochar on Greenhouse Gases Emissions and Physico-chemical Properties of Loess Soil].

Biochar is known to be a good soil amendment to improve soil physical and biochemical characteristics, to increase crop yield, and to mitigate greenhouse gas emissions from soils. In this study, five addition levels of apple tree branches-derived biochar (0, 20, 40, 60, 80 t·hm-2) were used in field plot test. The effects of biochar on soil temperature, soil aggregates, NO3--N, NH4+-N, microbial biomass carbon and greenhouse gas fluxes were investigated during the whole pepper growth season. The results showed that biochar amendment increased the temperature moderation capability of soil and increased the content of soil macro-aggregates, especially the content of aggregates with sizes >5 mm, 5-2 mm and 1-0.5 mm. As compared with the control, the contents of NO3--N, NH4+-N and microbial biomass carbon increased by 4.9%-33.9%, 9.1%-41.1% and 11.8%-38.5% with the increase of biochar content respectively. Biochar amendment increased CO2 emissions and CH4 uptake by 6.73%-23.35% and 3.62%-14.17%, respectively. N2O emissions and global warming potential (GWP) decreased at biochar levels of 20 and 40 t·hm-2 and increased when the biochar levels were 60 and 80 t·hm-2 as compared with the control. The results suggested that as a soil conditioner, biochar improved soil quality, soil fertility and function of agriculture soil on carbon sequestion and decreased emission cut. In addition, the choice of biochar level is very important.

[Effects of biochar on water thermal properties and aggregate stability of Lou soil].

A field trail was carried out to study the impact of biochar on soil bulk density, soil moisture content, soil temperature and soil aggregate stability in Lou soil. Five treatments of different biochar amounts were set in this study as follows: 0 (B0), 20 (B20), 40 (B40), 60 (B60), 80 (B80) t . hm-2. The results showed that, after applying biochar two years, compared with the control(B0), the soil bulk density in 0-30 cm soil layer significantly decreased by 7.7%-10.9%, and the soil moisture content significantly increased by 10.0% - 13.4%. Applying biochar at 40-60 t . hm-2 could buffer the change of soil temperature, and increase the soil thermal capacity. The water stable aggregates (WR0.25) with diameters greater than 0.25 mm significantly increased by 30.3%, the mean mass diameter (MWD) under dry sieving and wet sieving significantly increased by 15.2% and 31.6%, respectively, and the proportion of aggregate destruction (PAD) and unstable aggregate index (ELT) significantly decreased by 19.1% and 17.5%, respectively. The results indicated that applying biochar could significantly improve the water thermal properties of Lou soil and increase soil aggregate stability, and the best applying amount was 40-60 t . hm-2

[Vertical distribution of soil active carbon and soil organic carbon storage under different forest types in the Qinling Mountains].

Adopting field investigation and indoor analysis methods, the distribution patterns of soil active carbon and soil carbon storage in the soil profiles of Quercus aliena var. acuteserrata (Matoutan Forest, I), Pinus tabuliformis (II), Pinus armandii (III), pine-oak mixed forest (IV), Picea asperata (V), and Quercus aliena var. acuteserrata (Xinjiashan Forest, VI) of Qinling Mountains were studied in August 2013. The results showed that soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidizable carbon (EOC) decreased with the increase of soil depth along the different forest soil profiles. The SOC and DOC contents of different depths along the soil profiles of P. asperata and pine-oak mixed forest were higher than in the other studied forest soils, and the order of the mean SOC and DOC along the different soil profiles was V > IV > I > II > III > VI. The contents of soil MBC of the different forest soil profiles were 71.25-710.05 mg x kg(-1), with a content sequence of I > V > N > III > II > VI. The content of EOC along the whole soil profile of pine-oak mixed forest had a largest decline, and the order of the mean EOC was IV > V> I > II > III > VI. The sequence of soil organic carbon storage of the 0-60 cm soil layer was V > I >IV > III > VI > II. The MBC, DOC and EOC contents of the different forest soils were significanty correlated to each other. There was significant positive correlation among soil active carbon and TOC, TN. Meanwhile, there was no significant correlation between soil active carbon and other soil basic physicochemical properties.

[Chemical properties and enzyme activities of rhizosphere and non-rhizosphere soils under six Chinese herbal medicines on Mt. Taibai of Qinling Mountains, Northwest China].

This paper studied the chemical properties and enzyme activities of rhizosphere and non-rhizosphere soils in different habitats of six Chinese herbal medicines, including Pyrola decorata, Cephalotaxus fortunei, Polygonatum odoratum, Potentilla glabra, Polygonum viviparum, and Potentilla fruticosa, on the Mt. Taibai of Qinling Mountains. In the rhizosphere soils of the herbs, the contents of soil organic matter, total nitrogen, available nitrogen, and available phosphorus and the soil cation exchange capacity (CEC) were higher, presenting an obvious rhizosphere aggregation, and the soil enzyme activities also showed an overall stronger characteristics, compared with those in non-rhizosphere soils. The soil organic matter, total nitrogen, and total phosphorus contents in the rhizosphere soils had significant positive correlations with soil neutral phosphatase activity, and the soil CEC had significant positive correlations with the activities of soil neutral phosphatase and acid phosphatase. In the non-rhizosphere soils, the soil organic matter and total nitrogen contents had significant positive correlations with the activities of soil urease, catalase and neutral phosphatase, and the soil CEC showed a significant positive correlation with the activities of soil urease, catalase, neutral phosphatase and acid phosphatase. The comprehensive fertility level of the rhizosphere soils was higher than that of the non-rhizosphere soils, and the rhizosphere and non-rhizosphere soils of P. fruticosa, P. viviparum, and P. glabra had higher comprehensive fertility level than those of P. decorata, P. odoratum and C. fortunei. In the evaluation of the fertility levels of rhizosphere and non-rhizosphere soils under the six Chinese herbal medicines, soil organic matter content and CEC played important roles, and soil neutral phosphatase could be the preferred soil enzyme indicator.

[Profile distribution of organic carbon and nitrogen in major soil types in the middle of Qilian Mountains].

This paper studied the distribution patterns of organic carbon (OC), total nitrogen (TN), NH4+ -N, and NO3- -N in the profiles of brown calcic soil, grey cinnamon soil, chestnut soil, and alpine meadow soil in the middle of Qilian Mountains. In all test soils, the contents of OC, TN, NH4+ -N, and NO3- -N decreased with increasing soil depth, and the accumulation and decomposition of OC and various N forms differed with soil types. The average content of OC in different soil profiles changed from 14.01 to 41.17 g x kg(-1), and was in the order of grey cinnamon soil > alpine meadow soil > chestnut soil > brown calcic soil; the average content of TN changed from 1.28 to 2.73 g x kg(-1), with a sequence of alpine meadow soil > grey cinnamon soil > chestnut soil > brown calcic soil. The C/N ratio was from 11.33 to 19.22, with the order of grey cinnamon soil > chestnut soil > alpine meadow soil > brown calcic soil. NH4+ -N content changed from 5.80 to 8.40 mg x kg(-1), and was in the order of brown calcic soil > alpine meadow soil > chestnut soil > grey cinnamon soil; NO3- -N content changed from 6.57 to 15.11 mg x kg(-1), being in the order of chestnut soil > alpine meadow soil > brown calcic soil > grey cinnamon soil. The ratio of NO3- -N to NH4+ -N was 1.00-2.69, with the sequence of grey cinnamon soil > chestnut soil > alpine meadow soil > brown calcic soil. The OC and N contents in the same soil types differed significantly with the conditions of climate, vegetation, and topography (e. g. , slope aspect and slope position). Correlation analysis showed that there were highly significant nositive correlations between OC, TN, and NH4+ -N, but these three items had no significant positive correlations with NO3- -N. Furthermore, there were highly significant positive correlations between available K, NH4+ -N, and NO3- -N and between available P and OC, significant positive correlations between available P, TN, and NH4+ -N, but no significant correlations between pH, total K, and total P and OC and N.