【Objective】 This study explored the effects of acid rain-based changes in soil nutrient content and Chinese fir (Cunninghamia lanceolata) fine root growth, to provide a theoretical basis for improving soil acidification of C. lanceolata plantations in acid rain-stressed areas.【Method】 A one-year simulated acid rain field experiment was conducted at the Tongshan Forest Farm in Nanjing, Jiangsu Province. Three acid rain acidity levels (pH=4.5, 3.5, and 2.5) were applied with each of three acid rain types: sulfuric acid rain, with 5∶1 concentration ratio of sulfur (S, SO42-) to nitrogen (N, NO3-); mixed acid rain, with 1∶1 S/N ratio; nitric acid rain, with 1∶5 S/N ratio; and a control (CK, pH=6.6, local river water). There were thus 10 total experimental treatments. Outcome measures of acid rain stress included soil chemical properties, fine root physiological characteristics, and fine root element contents. Correlations and structural equation model analyses were used to explore the direct and indirect effects of acid rain type on C. lanceolata fine root growth.【Result】 With decreasing acid rain pH and S/N ratios, the fine root biomass and root activity of C. lanceolata decreased. The catalase activity of all strong acid rain treatments (pH=2.5) was lower than that of other acid rain treatments. Compared with nitric acid rain types, the catalase activity incrementally decreased and was lower than CK; Mg and Al content, as well as the c(Ca)/c(Al) and c(Mg)/c(Al) in fine roots also differed. Compared with CK, all acid rain treatments increased fine root Ca and Al contents, while K content decreased with acid rain stress. However, there were not significant differences in soil total C, total N, C/N ratio, total S, available P, or available K among S/N ratios or pH levels. Correlation analysis showed that soil pH was extremely significant positively correlated with c(Mg)/c(Al), root biomass, and root activity (P<0.01), and that root biomass was significantly positively correlated with peroxidase, catalase, but extremely significant negative correlated with Al content (P<0.05). 【Conclusion】 After one year of experimental acid rain stress, acidity significantly impacted both soil and C. lanceolata fine roots. Acid rain type affected fine roots more strongly than it affected soil. As the S/N ratio decreased, the inhibitory effect of acid rain on C. lanceolata fine root growth was more pronounced.
【Objective】 This study explored the effects of Serratia marcescens N1.14, X-45 bacterial fertilizer inoculated with different carrier substrates on the growth, photosynthetic characteristics, soil pH and available nutrients of Amorpha fruticosa. Based on this, bacterial fertilizer carriers that can effectively replace rare resource peat were determined in order to provide a theoretical basis for the development of microbial fertilizers.【Method】 Taking A. fruticosa seedlings as the object, the peat bacterial fertilizer (T0, CK), straw bacterial fertilizer (T1), wheat bran bacterial fertilizer (T2), straw and wheat bran as carrier bacterial fertilizer (volume ratio = 1∶1, T3), straw wheat bran and cotton seed hull as carrier bacterial fertilizer (volume ratio = 1∶1∶1, T4), and straw wheat bran and soybean cake as carrier bacterial fertilizer (volume ratio = 1∶1∶1, T5) were applied. Through comparative analysis, the effects of the application of different carrier bacterial fertilizer on the growth characteristics, photosynthetic characteristics and soil nutrients of A. fruticosa were explored, and treatment groups that can replace peat bacterial fertilizer were selected.【Result】 Compared with CK, there were three key findings. First, the growth statuses of T2, T3, T4, and T5 were significantly improved, especially T3. Second, the photosynthetic characteristic parameters of Amorpha fruticosa leaves under T1, T3, T4, and T5 improved to varying degrees. Among the gas exchange parameters, T5 had the most significant improvement effect, and T3 had the most obvious improvement effect on chlorophyll content. At the same time, the improvement effect of compound carrier bacterial fertilizer was better than that of single bacterial fertilizer. Third, the soil nutrient content of A. fruticosa under T3, T4, and T5 treatments increased.【Conclusion】 The straw, wheat bran and soybean cake as carrier bacterial fertilizers can promote the growth and development of A. fruticosa, improve photosynthetic characteristics, optimize the soil nutrient environment, improve soil fertility, and effectively replace peat carrier bacterial fertilizer.
【Objective】 This study aimed to scientifically manage abandoned mine slopes, explore the application and promotion of the soil bacteria permanent greening method in restoration, optimize the fermentation conditions, and analyze the application effect of the isolated and screened high-efficiency solubilizing bacteria.【Method】 A variety of solubilizing microorganisms were isolated from the weathered rock wall soil in Nanjing Mufu Mountain, and a prominent solubilizing strain, NL-11, identified as Bacillus thuringiensis by 16S rRNA, was selected to optimize fermentation conditions, and its application effect was observed with the potting test. The three main factors affecting the growth of the strain (liquid volume, temperature, and time), were screened using the univariate and Plackett Burman tests; on this basis, the steepest climbing path was used to approximate the maximum response area; then, the Box-Behnken experimental design was used and the response surface analysis method was used for regression analysis. Finally, model reliability was verified by comparing the predicted values with the measured values. The optimized results were used to prepare the bacterial solution, and then adjusted to low (10 cfu/mL), medium (1 × 105 cfu/mL), and high (1 × 109 cfu/mL) concentrations and mixed into the substrate (T1, T2, and T3 treatments, respectively) for the pot experiments, and the treatment without the bacterial solution was set as a blank control (CK) to study the effects of the different bacterial solution concentrations on mineral weathering and plant and root growth.【Result】 The model was accurate and reliable, and the optimal fermentation culture conditions for NL-11 were as follows: a liquid volume of 19.51 mL, an inoculum level of 2%, an initial pH of 7.0, a temperature of 30.30 ℃, and a time of 22.07 h. The number of viable bacteria in the fermentation broth under these optimized conditions reached 1.47 × 1010 cfu/mL, which was 2.03 times higher than that before optimization. The results of the pot tests showed that strain NL-11 could promote mineral weathering, and the effect of the high concentration of the bacterial solution was the most significant. Furthermore, strain NL-11 could promote the dissolution of mineral nutrients, and the effect of the high concentration of the bacterial solution was the most significant. Strain NL-11 could also promote plant and root growth, and the effect of the medium concentration was the most significant. 【Conclusion】 The optimization test significantly improved the production of fermentation of the live bacteria of strain NL-11 and provided technical support for the application of the strain in the management of slopes. The suitable concentration of the bacterial solution in spraying practice is 1 × 105 cfu/mL by the comprehensive evaluation of the application effect and consideration of the production cost and other factors.
【Objective】 The aim of the present study was to investigate the changes of soil physical and chemical properties of Pinus massoniana plantations of different ages in Karst areas in southwest China, as well as comprehensively analyze the effects of topographic factors, stand characteristics and plant diversity on soil properties to provide reference for environmental management in degraded Karst areas.【Method】 In the present study, 11 P. massoniana plantations at three different ages, namely, middle-aged plantation, near-mature plantation, and over-aged plantation, were selected in Fenggang County, Zunyi City, Guizhou Province. The area of the plots was 25.82 m × 25.82 m. The species name, height and diameter at breast height (DBH) of the tree layer were investigated, and the altitude, position, slope and species composition of each plot were recorded. Five 2 m × 2 m shrub quadrats were set up in the southwest, northwest, northeast, southeast and middle areas of each plot to investigate the species name and number of plants in the shrub layer. A 1 m × 1 m herb quadrat was set up in each shrub quadrat to investigate the species name and coverage of herbs. The changes of soil physical and chemical properties were quantified, and the influencing factors were analyzed.【Result】 There were no significant differences in soil bulk density, porosity, water content, organic carbon content and total phosphorus content among the different age groups of the P. massoniana plantations (P>0.05). The total nitrogen content increased initially and then decreased with the increase in plantation age in the 0-20 cm soil layer, and the alkali-hydrolyzable nitrogen content decreased gradually with the increase of plantation age in the 20-40 cm soil layer. Moreover, the available phosphorus content decreased initially and then increased with the increase in plantation age in the 0-20 cm and 20-40 cm soil layers (P<0.05). No significant differences were found in the soil bulk density, porosity, and water content between the 0-20 cm and 20-40 cm soil layers within the same age group (P>0.05). The soil organic carbon content of the three age groups, the total nitrogen content and alkali-hydrolyzable nitrogen content of the near-mature and over-aged plantations, and the total phosphorus and available phosphorus content of the over-aged plantation were significantly different between the 0-20 cm and 20-40 cm soil layers (P<0.05). These contents decreased with the deepening of soil layer. Correlation analysis showed that topographic factors, stand characteristics, and plant diversity were the factors affecting soil physical properties and nutrient changes in the P. massoniana plantations. Stepwise regression analysis showed that stand density and plant diversity were the main factors affecting soil physical properties, while topographic factors, stand characteristics, and plant diversity were the factors affecting soil nutrients. Redundancy analysis (RDA) showed that stand characteristics, plant diversity, and topographic factors explained 36.60%, 27.00% and 10.30% of the variation in the soil physicochemical properties, respectively.【Conclusion】 The plantation age has a significant impact on the soil nitrogen and phosphorus contents of P. massoniana plantations, suggesting that nitrogen fertilizer and phosphorus fertilizer should be added appropriately with the growth and development to maintain the productivity and sustainable development of P. massoniana plantations. Changes in the plantation age has no significant effect on soil physical properties, while the stand density and tree height are the main factors affecting the soil physical and chemical properties in P. massoniana plantations.
