Bacterial communities associated with natural and commercially grown rooibos (Aspalathus linearis)

Aspalathus linearis is a commercially important plant species endemic to the Cape Floristic Region of South Africa and is used to produce a herbal tea known as rooibos tea. Symbiotic interactions between A. linearis and soil bacteria play an important role in the survival of Aspalathus plants in the highly nutrient-poor, acidic fynbos soil. The aim of this study was to characterize and compare rhizosphere and bulk soil bacterial communities associated with natural and commercially grown A. linearis, as well as the effect of seasonal changes on these communities. Bacterial communities were characterized using high throughput amplicon sequencing, and their correlations with soil chemical properties were investigated. The N-fixing bacterial community was characterized using terminal restriction fragment length polymorphism and real time quantitative polymerase chain reaction. Actinobacteria, Proteobacteria, and Acidobacteria were the most dominant bacterial phyla detected in this study. Highly similar bacterial communities were associated with natural and commercially grown plants. Significant differences in the bacterial community were observed between rhizosphere and bulk soils collected in the dry season, while no significant differences were detected in the wet season. This study provides insights into bacterial community structure and potential factors shaping bacterial community structure with commercially important A. linearis.     

Air-drying changes the distribution of Hedley phosphorus pools in forest soils

Hedley labile phosphorus(P)pools in soil tend to be several times larger than annual forest requirements,even in highly weathered soils characterized by P limitation.The discrepancy between plant and soil P status could be partly attributable to the frequently adopted air-drying pretreatment that tends to increase soil P solubility.In this study,the effects of air-drying on the distribution of Hedley P fractions were examined using soils collected under 4 forest types at Gongga Mountain,southwestern China.The results showed that the microbial biomass P(Pmic)in the organic horizon decreased markedly after air-drying.The concentrations of Hedley labile P in the air-dried samples were 31%–73%more than those in the field-moist samples.Consequently,the air-drying-induced increments of Hedley labile P pools in the surface soil horizons were 0.8–3.8 times the annual plant P requirements.The organic horizon was more susceptible to the air-drying-induced increases in Hedley labile P than the mineral horizon,probably because of the stronger release of Pmicand disruption of soil organic matter.The quality of P,indexed by the ratio of Hedley labile P to slowly cycling P,shifted in favor of the Hedley labile fractions after air-drying,further revealing that air-drying changed the distribution of Hedley P pools in forest soils.These indicated that the effects of air-drying could not be ignored when interpreting the discrepancy between the P status of plants and the Hedley labile P pools in forest soils.To more efficiently evaluate the P status in forest soils via the Hedley fractionation procedure,the use of field-moist soils is recommended.     

Response of soil respiration to nitrogen addition in two subtropical forest types

Anthropogenic activities have increased nitrogen (N) deposition in terrestrial ecosystems, which directly and indirectly affects soil biogeochemical processes, including soil respiration. However, the effects of the increases in N availability on soil respiration are not fully understood. In this study, soil respiration was measured using an infrared gas analyzer system with soil chambers under four N treatments (0, 5, 15, and 30 g N m^-2 year^-1 as control, low N (LN), moderate N (MN), and high N (HN), respectively) in camphor tree and slash pine forests in subtropical China. Results showed that soil respiration rates decreased by 37% in the camphor tree forest and 27% in the slash pine forest on average on an annual base, respectively, in the N-fertilized treatments when compared with the control. No significant differences were found in the soil respiration rate among the LN, MN, and HN treatments in both forest types as these fertilized plots reached an adequate N content zone. In addition, soil microbial biomass carbon (C) content and fine root biomass declined in N-treated plots compared to the control. Our results indicated that elevated N deposition might alter the tree growth pattern, C partitioning, and microbial activity, which further affect soil C sequestration by reducing soil respiration in subtropical forests of China.     

Effect of organic amendment amount on soil nematode community structure and metabolic footprints in soybean phase of a soybean-maize rotation on Mollisols

It has been well documented that organic amendment affects soil nematode community structure. However, little is known about the effect of organic amendment amount on soil nematodes. To assess the effect of the amount of organic amendments on soil nematode community structure and metabolic activity, the community composition, abundance, and metabolic footprints of soil nematodes were determined in a long-term field experiment with various amounts of organic amendment in Northeast China. Fertilization treatments included an unfertilized control (CK), chemical fertilizer without manure amendment (OM₀), manure applied at 7.5 Mg ha^-1 plus chemical fertilizer (OM₁), and manure applied at 22.5 Mg ha^-1 plus chemical fertilizer (OM₂). A total of 46 nematode genera were found. Treatments with the largest amount of organic amendment had the smallest number of plant parasite genera (5), but a largest number of dominant genera (7). Soil nematodes, bacterivores, and fungivores were the most abundant in OM₂, followed by OM₁, and the lowest in OM₀ and CK. Organic amendment increased the enrichment index (EI), and the large amount of organic amendment increased the metabolic footprints of bacterivore (Baf) and fungivore (Fuf) and enrichment footprint (Ef). The relationships between Baf (or Fuf) and the increases in soil organic carbon (ΔSOC) and total nitrogen (ΔTN) were stronger than those of bacterivore (or fungivore) abundance with ΔSOC and ΔTN, except for the relationship between bacterivore abundance and ΔSOC. The EI and Ef were positively correlated with ΔSOC and ΔTN. These findings suggest that the amount of organic amendment affects soil nematode activity and function at entry levels in soil food web, and that metabolic footprints of soil nematodes may be better indicators than their abundances in assessing their relationships with soil nutrients.     

菌剂挂膜3D-RBC联合BCO工艺处理养猪沼液废水

针对养猪沼液废水寡营养、高氨氮的水质特征，该研究采用耐高氨氮、适应贫营养生长的异养硝化-好氧反硝化（Heterotrophic Nitrification-Aerobic Denitrification，以下简称HN-AD）菌挂膜启动三维结构生物转盘+生物接触氧化反应器（3D-RBC+BCO）组合工艺对沼液进行处理。该文研究了3D-RBC+BCO组合工艺在真实沼液条件下的启动过程及污染物去除效果，重点考察了溶解氧（Dissolved Oxygen，DO）浓度和C/N比2个关键因素对组合工艺污染物去除效果的影响。同时，借助高通量测序技术对DO和C/N比优化过程中微生物群落结构的变化规律进行解析。结果表明：在真实沼液条件下，采用HN-AD菌剂挂膜启动方法，仅用12和18 d就分别完成3D-RBC和BCO反应器的挂膜启动，同时组合工艺对COD、NH4+-N和TN的去除率分别稳定在94.8%、95.7%和80.1%，出水优于城镇污水厂排放一级B标准。在对3D-RBC反应器DO和C/N比的优化过程中，增设底曝后COD、NH4+-N和TN等指标的去除率分别降低了25.4%、15.4%和15.5%。高通量测序结果显示，增加底曝后3D-RBC盘片生物膜中微生物菌属的数量小幅下降，但HN-AD优势菌属的种类与丰度显著降低，导致脱氮效率下降；贫营养型Acinetobacter、Pseudomonas菌属是3D-RBC可以对真实沼液高效脱氮的关键，提高C/N比会显著降低其丰度，进而影响脱氮效果。     

小麦-玉米轮作体系不同旋耕和深耕管理对潮土微生物量碳氮与酶活性的影响

【目的】通过研究黄淮平原潮土区两年不同轮耕模式下土壤微生物量碳氮、酶活性的差异和变化特征,为该地区选择适宜的耕作制度提供理论依据。【方法】2016-2018年采用裂区设计进行田间小麦–玉米轮作系统下的轮耕试验。主处理为小麦季旋耕(RT)和深耕(DT),3个副处理为玉米季免耕(NT)、行间深松(SBR)、行内深松(SIR),共6个处理。2017、2018年玉米收获后,每10 cm一个层次,测定了0-50 cm土层土壤有机质、全氮、速效养分、微生物量碳(SMBC)、微生物量氮(SMBN)和脲酶、蔗糖酶、中性磷酸酶活性。【结果】各处理土壤有机质、全氮、速效养分、SMBC、SMBN及酶活性均随土层深度的增加而降低,40-50cm土层不受耕作方式的影响。小麦季深耕和玉米季深松对表层土壤有机质和全氮影响不明显,但显著提高了深层土壤有机质和全氮含量。小麦季旋耕显著增加了玉米季0-10 cm土层中速效养分含量,而小麦季深耕条件下的DT-SBR和DT-SIR处理则显著增加了20-40 cm土层中的速效养分含量。在0-20 cm土层,小麦季旋耕条件下的RT-NT、RT-SBR和RT-SIR处理的SMBC明显高于小麦季深耕条件下的DT-NT、DT-SBR和DT-SIR处理,但在20-40 cm土层,SMBC和SMBN均表现为小麦季深耕处理显著高于旋耕处理,且以DT-SIR处理SMBC (67.99 mg/kg)和SMBN (45.96 mg/kg)最高。小麦季深耕处理提高了深层(30-40 cm)土壤微生物量氮/全氮值,但降低了表层(0-20 cm)土壤中的微生物熵。玉米季深松处理(RT-SBR、RT-SIR、DT-SBR和DT-SIR)较免耕处理(RT-NT和DT-NT)均提高了土壤酶活性,其中,在0-20 cm土层,RT-SBR和RT-SIR处理土壤脲酶活、蔗糖酶和中性磷酸酶活性较高;而DT-SBR和DT-SIR处理则提高了深层(20-40 cm)土壤中这三种酶的活性。【结论】在本试验期内,小麦季旋耕–玉米季深松处理(RT-SBR和RT-SIR)能明显提高0-10 cm土壤速效养分含量、0-20 cm土壤微生物量碳含量,而小麦季深耕–玉米季深松处理(DT-SBR和DT-SIR)则提升了20-40 cm土层土壤有机质、全氮、速效养分、微生物量碳和氮含量;小麦季深耕处理提高了深层(30-40 cm)微生物量氮/全氮比,但降低了表层(0-20 cm)土壤微生物熵。     

不同林龄杉木林下套种阔叶树对土壤磷组分的影响

套种是杉木人工林经营的重要措施,磷是南方森林生态系统中主要限制性养分元素之一,但套种模式对土壤磷素的影响尚不明确。以亚热带杉木人工林表层(0-10 cm)土壤为对象,研究套种林(杉阔套种幼林、杉阔套种成熟林)和杉木幼林土壤理化性质和土壤各形态磷含量差异,分析套种对杉木人工林土壤磷含量的影响。结果表明:(1)不同套种林显著改变土壤总磷、土壤总无机磷、土壤总有机磷、土壤微生物生物量磷(MBP)和土壤酸性磷酸酶活性(APA),大小顺序均为杉阔套种成熟林>杉阔套种幼林>杉木幼林。(2)土壤各磷组分中活性磷含量较低,其中NaHCO3-Po在活性组分中占主导;土壤NaOH-Po是中等活性磷的主要组分,杉阔套种成熟林尤为显著;闭蓄态磷(Residual-P)在总磷含量中最高。(3)与杉木幼林相比,杉阔套种成熟林显著增加了树脂提取态磷(Resin-Pi)、碳酸氢钠提取态有机和无机磷(NaHCO3-Pi、NaHCO3-Po)、氢氧化钠提取态有机和无机磷(NaOH-Pi、NaOH-Po)、氢氧化钠残留提取态有机磷(NaOHu.s-Po)、盐酸提取态磷(HCl-Pi)和闭蓄态磷(Residual-P)含量;土壤总无机磷、NaHCO3-Po、HCl-Pi、NaHCO3-Pi、NaOHu.s-Pi和Residual-P对杉阔套种幼林的响应不敏感。(4)除含水率外不同林龄下杉阔套种林土壤磷形态与土壤理化性质(土壤总碳氮、土壤可溶性有机氮、土壤微生物生物量磷、酸性磷酸酶)呈正相关性(P<0.05)。冗余分析表明,土壤磷组分的变化主要受MBP调控,且MBP与有机磷组分(NaOHu.s-Po、NaOH-Po)和HCI-Pi呈显著正相关。总之,套种林的土壤磷素有效性高于杉木幼林,土壤养分状况更佳。     

保水剂和微生物菌肥配施对旱作燕麦土壤微生物生物量碳、氮含量及酶活性的影响

为探讨保水剂和微生物菌肥配施后旱作燕麦土壤微生物生物量碳、氮含量及酶活性的影响,在内蒙古黄土高原旱作农田设置不施用保水剂和微生物菌肥(CK)、保水剂和微生物菌肥配施(A)、单施微生物菌肥(B)和单施保水剂(C)4个处理,分析燕麦全生育期内0—10,10—20,20—40 cm土壤微生物生物量碳、氮含量及酶活性时空动态变化和产量变化。结果表明:(1)全生育期,土壤微生物量碳含量呈"双峰"曲线变化,峰值均出现在孕穗期和灌浆期;氮含量呈先降低后升高再降低趋势,苗期含量最高;过氧化氢酶、蔗糖酶、脲酶活性均呈"单峰"曲线变化,过氧化氢酶、土壤蔗糖酶峰值在孕穗期,土壤脲酶则在抽穗期。(2)除CK外,土壤微生物量碳、氮含量及过氧化氢酶、蔗糖酶和脲酶活性表现为0—10 cm10—20 cm20—40 cm,其中配施(A)对0—10,10—20 cm影响均显著(p0.05),单施(B、C)仅对10—20 cm土层影响显著(p0.05)。(3)10—20 cm土层,配施(A)与其他3个处理间差异均显著(p0.05),提高微生物量碳含量4.82%～40.28%、微生物生物量氮含量8.44%～68.66%、过氧化氢酶活性13.32%～60.16%、蔗糖酶活性10.45%～39.14%、脲酶活性12.40%～55.62%。(4)配施(A)能同时显著(p0.05)提高燕麦籽粒产量和生物产量,提高幅度分别为8.40%～20.12%和10.80%～25.09%。因此,保水剂和微生物菌肥配施在黄土高原旱作区具有较好改善土壤微生物活性效果,提高旱作燕麦产量。