[Effects of Modified Distiller's Lees Biochar on Nutrients and Enzyme Activities in Purple Soil].

In order to investigate the effects of distiller's lees biochar and different modified distiller's lees biochars on soil properties, pot experiments were conducted to study the effects of different soil amendments (CK:no amendment, JZ:distiller's lees biochar, TiO2/JZ:Nano-TiO2 supported by distiller's lees biochar, and Fe/TiO2/JZ:titanium dioxide supported by iron-modified distiller's lees biochar) and the application rates of different amendments (1%, 3%, and 5%) on the characteristics of soil nutrients and enzyme activities under irrigation-drought rotation. The results showed the following:①the modified distiller's lees biochar significantly increased soil pH and CEC (P<0.05). At the 5% Fe-TiO2/JZ addition level, the soil pH reached 7.95 during the rice season, an increase of 2.3 units compared with that in the CK treatment; the CEC reached 12.06 cmol·kg-1, increasing by 21.38%; the soil pH reached 5.99 during the cabbage season and increased by 1.5 units compared with that in the CK treatment; and CEC reached 8.91 cmol·kg-1 at 3% Fe-TiO2/JZ addition and increased by 13.11%. ②At the same time, the contents of soil total nitrogen and available phosphorus were significantly increased (P<0.05). Compared with that in the CK treatment, the soil total nitrogen of 5% JZ, 5% TiO2/JZ, and 5% Fe-TiO2/JZ increased by 20.56%, 85.04%, and 59.61% in the rice season and 12.39%, 22.68%, and 23.70% in the cabbage season, respectively. In the rice season, the increase in soil available P under 5% Fe-TiO2/JZ was the highest, reaching 10.49 mg·kg-1, which was 1.64 times that under CK treatment. In the cabbage season, the soil available phosphorus (P) reached 90.15 mg·kg-1 under 5% TiO2/JZ addition, which increased by 93.38% compared with that in the CK treatment. ③Modified distiller's lees biochar increased catalase and urease activities and decreased alkali-hydrolytic nitrogen content and acid phosphatase activity. At the 3% addition level, catalase activity increased by 12.19%, 48.17%, and 37.30% in the rice season and 5.95%, 8.34%, and 17.42% in the cabbage season, respectively. In the rice season, the soil urease activity reached the maximum under 5% Fe-TiO2/JZ addition, which was increased by 40.90% compared with that in the CK treatment. In the cabbage season, the soil urease activity reached the maximum under 5% TiO2/JZ addition, which was increased by 58.53% compared with that in the CK treatment. The activity of acid phosphatase decreased by 5.39%-24.66% in the rice season and by 54.46%-61.40% in the cabbage season. Distiller's lees biochar and modified distiller's lees biochar could effectively increase soil pH and soil nutrient content, thus affecting soil enzyme activities. The application of iron modified-titanium dioxide-loaded distiller's lees biochar of 3% to 5% in acidic purple soil is more suitable.

[Effects of Chemical Fertilizer Reduction Combined with Organic Fertilizer Application on Bacterial Community Structure in Rhizosphere/Non-Rhizosphere Soil of Lemon].

The aim of this study was to examine the effects of different fertilization methods on the physicochemical properties and bacterial community structure of lemon rhizosphere/non-rhizosphere soil in order to provide theoretical basis for scientific and rational fertilization of orchards. A pot experiment was carried out, and six fertilization treatments were set up:control (CK), conventional fertilization (FM), organic fertilizer (P), fresh organic fertilizer (NP), 70% chemical fertilizer+30% organic fertilizer (70FP), and 50% chemical fertilizer+50% organic fertilizer (50FP). Chemical analysis, real-time fluorescence quantitative PCR, and terminal restriction fragment length polymorphism (T-RFLP) were used to study the effects of different fertilization treatments on the physicochemical properties of rhizosphere and non-rhizosphere soils, the abundance of the bacterial 16S rRNA gene, and bacterial community structure. Redundancy analysis (RDA) was used to explore the environmental factors affecting the bacterial community structure of lemon rhizosphere/non-rhizosphere soil. The results showed the following:① the pH and contents of organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, and nitrate nitrogen in rhizosphere/non-rhizosphere soil were significantly increased by reducing the amount of chemical fertilizer and applying organic fertilizer (50FP and 70FP) (P<0.05). Compared with conventional fertilization (FM) and single application of organic fertilizer (P and NP), the soil available P content, available K content, and nitrate nitrogen content increased by 24.76%-97.98%, 6.87%-45.11%, and 18.42%-55.82%, respectively. ② Fertilizer reduction combined with organic fertilizer significantly increased the abundance of soil bacteria and soil respiration intensity (P<0.05), and the abundance of soil rhizosphere bacteria and soil respiration intensity under the 50FP treatment increased by 15.83%-232.98% and 8.0%-162.5% compared with that under conventional fertilization and organic fertilizer alone, respectively. The bacterial abundance of rhizosphere soil was positively correlated with the pH and contents of organic matter, total nitrogen, and total phosphorus. ③ The PCoA and RDA analysis results showed that the single organic fertilizer and organic fertilizer and chemical fertilizer de-weighting of rhizosphere bacterial community structure and not adding fertilizer had a bigger difference between processing, and the main environmental factors influencing the rhizosphere/non rhizosphere bacterial community structure were organic matter, total nitrogen, total phosphorus, total potassium, alkali solution nitrogen, nitrate nitrogen, and available potassium. Fertilizer reduction combined with organic fertilizer could significantly increase soil nutrient content, increase soil bacterial abundance, and change the bacterial community structure of rhizosphere soil, and the 50FP treatment yielded better results. Therefore, 50% Chemical fertilizer+50% organic fertilizer (50FP) was a better fertilization method to improve the physical and chemical properties of orchard soil, increase the abundance of soil bacteria, and improve the soil respiration intensity.

Concurrent effects of flooding regimes and floodwater quality on sediment properties in a Yangtze River-connected floodplain wetland: Insights from field investigations during 2011-2020.

Changes in flood regimes, floodwater quality, and macrophyte types may affect sediment characteristics post-flooding. However, few studies have attempted to unravel their complex influences in floodplain wetlands. From 2011 to 2020, the physical and chemical properties of surface layer sediment pre- and post-flooding was investigated through field surveys in the Dongting Lake wetland. Results indicated that the pre-flooding soil total phosphorus (TP) and total nitrogen (TN) exhibited an increasing trend during 2011-2020. Soil TP increased post-flooding relative to that pre-flooding. The changes in TN, sediment organic matter (SOM), sediment moisture content (SMC), and sediment bulk density (SBD) fluctuated over the years. The best-fitting multi-regression model demonstrated that the changes in sediment variables post-flooding showed a parabolic trajectory along the inundation duration (ID), except for SMC. Changes in soil properties post-flooding were negatively correlated with ID for sediment with a low IDs (<148 days). Meanwhile, changes in soil properties post flooding were positively correlated with ID for sediment with a high IDs (>193 days). Changes in SBD and SOM post-flooding were positively influenced by the TP content in the floodwater. These findings indicate that changes in the flooding regime, and water quality generated by anthropogenic disturbances such as the Three Gorges Dam significantly affect sediment properties, and subsequently influence the ecological functions of the Dongting Lake wetland.

[Effects of selenium valence states and application concentrations on plant growth, ascorbate-glutathione cycle in Citrus junos cv. Ziyang Xiangcheng]. / 硒的价态与浓度对香橙幼苗生长和AsA-GSH循环的影响.

Potted Citrus. junos cv. Ziyang Xiangcheng seedlings were used to study the effects of selenium (Se) valence states (Se6+ and Se4+) on plant growth and antioxidants and antixodases in ascorbate(AsA)-glutathione (GSH) cycle. The results showed that Se6+ and Se4+ (from 1.0 mg·L-1 to 8.0 mg·L-1) stimulated the seedling growth by increasing plant height, leaf areas, and fresh or dry mass. Applying Se6+significantly increased plant Se levels mainly in leaf, and applying Se4+ slightly increased Se content mainly in root. Certain valence states and concentrations of Se increased leaf chlorophyll and hydrogen peroxide (H2O2) content. Se6+≤2.0 mg·L-1 treatments enhanced the activates of glutathione reductase (GR) and glutathione peroxidase (GPX), and the contents of GSH and oxidized glutathione (GSSG), while Se6+≥4.0 mg·L-1 treatments reduced the antioxidant contents and antixodase activities of GSH cycle. Moreover, Se4+≤ 2.0 mg·L-1 treatments increased the activities of dehydroascorbate reductase (DHAR) and ascorbate peroxidase (APX), and resulted in higher AsA/[AsA+dehydroascorbic acid (DHA)] ratio. When Se4+≥4.0 mg·L -1, the antioxidant contents and antixodase activities of GSH cycle were increased. Together, this study showed that different valence states and application concentrations of Se showed different influences on AsA-GSH cycle in citrus, and 2.0 mg·L-1 Se6+ and 4.0 mg·L-1 Se4+ were the best concentrations for plant growth.

Trade-off between allocation to reproductive ramets and rhizome buds in Carex brevicuspis populations along a small-scale elevational gradient.

The trade-off between allocation to sexual and clonal reproduction in clonal plants is influenced by a variety of environmental factors; however, it has rarely been examined under field conditions. In this study, we investigated the trade-off between two modes of reproduction in Carex brevicuspis C. B. Clarke across a small-scale elevational gradient (21-27 m a.s.l.) at the Dongting Lake wetlands, China. The proportion of biomass allocated to and the density of reproductive ramets were higher at low than at intermediate and high elevations. In contrast, the proportion of biomass allocated to and the density of rhizome buds were lower at low than at intermediate and high elevations. Redundancy analysis showed that sexual reproduction was positively correlated with soil moisture content, soil organic matter, total phosphorus, and pH, and negatively correlated with elevation and ramet density. Our findings suggested that allocation to sexual reproduction is favored in disturbed habitats with fertile soils, whereas allocation to vegetative propagation is favored in stable and competitive habitats. Trade-off between allocation to sexual reproduction and vegetative propagation along an elevational gradient might be a reproductive strategy of C. brevicuspis to adapt to the water level fluctuations in wetland habitats.

[Characteristics of Carex brevicuspis and its impact factors in Dingzidi, East Dongting Lake].

In recent 20 years, the area of lake grass has been drastically reduced and degraded. In order to search for reasonable recovery ways of the lake grass, the vegetational characteristics (plant height, coverage, density, biomass and biodiversity index) and soil physico-chemical characteristics (soil organic carbon, SOC; total nitrogen, TN; total phosphorus, TP; soil bulk density and moisture) were investigated in the Carex brevicuspis community from 63 sampling plots in 7 sampling belts along an elevation gradient in Dingzidi, East Dongting Lake. All biological characteristics showed an inverted "U" distribution pattern along with increasing elevation, except for diversity index, which showed a tendency of increasing at first and then decreasing. Plant growth was inhibited near water body (low elevation region) and levee (high elevation region). In contrast, the intermediate elevation region had a favorable condition for plant growth. For soil physical properties, soil water moisture decreased but soil bulk density increased along with increasing elevation. However, SOC and TN contents were higher in the intermediate elevation region and lower in both low and high elevation regions. TP content was fluctuant along with increasing elevation. The principal component analysis (PCA) showed that the key factors influencing biomass of C. brevicuspis were soil C and N contents, soil moisture and bulk density. These results indicated that increasing soil fertility and maintaining proper soil moisture might be efficient to recover the vegetation of C. brevicuspis.

[Effects of applying pig manure on lettuce yield and nitrate content and soil nutrients].

A pot experiment with two representative soils (purple soil and yellow soil) in Southwest China was conducted to study the effects of applying pig manure on the lettuce (Lactuca sativa L. var. capitata L. ) yield and nitrate content and the soil nutrients. Applying pig manure increased the lettuce yield significantly, and the increment was higher for yellow soil than for purple soil. The nitrate and total nitrogen, phosphorus, and potassium contents in lettuce plants were closely related to soil type and pig manure application rate. According to the evaluation standards of the nitrate pollution level of vegetables formulated by the Chinese Academy of Agricultural Sciences, the nitrate content in lettuce plants growing on purple soil was lower than the grade I (< or = 432 mg x kg(-1), slight pollution) in treatments CK (no pig manure application) and M1 ( applying 200 kg N x hm(-2) of pig manure), but generally higher than the grade II (< or = 758 mg x kg(-1), moderate pollution) while not exceeded the grade III (< or = 1440 mg x kg(-1), heavy pollution) in other treatments. The nitrate content in lettuce plants growing on yellow soil was lower than the grade I, except that in the treatments of chemical fertilizations and of M8 (applying 1600 kg N x hm(-2) of pig manure) where the plant nitrate content was exceeded the grade II. The critical value of Olsen-P characterizing the apparent leaching risk level of phosphorous in yellow soil and purple soil was 96.3 and 107.7 mg x kg(-1), respectively. The environmental safety capacity of pig manure was higher for yellow soil than for purple soil. Applying pig manure increased the organic carbon and total nitrogen contents of the two soils significantly.