The addition of labile carbon alters litter fungal communities and decreases litter decomposition rates

Many field and laboratory studies have demonstrated that the addition of easily available carbon can increase rates of decomposition of plant litter or humified soil organic matter, though opposite trends are also common. In boreal forests, a large part of labile carbon enters soil via tree roots and ectomycorrhizal (EM) network. The influence of increased C availability and the presence of EM roots on litter decomposition was studied in a long-term field experiment in a 50-year-old Picea abies plantation. Litterbags containing litter of three species (Populus tremula, Quercus robur, or P. abies) were buried to the depth of ca. 2.5 cm. The experiment was set up in a full-factorial design with carbon availability and presence of roots as factors. Carbon was added as an aqueous sucrose solution (50 g C m⁻²) every second week during snow-free period. Spruce roots around and underneath experimental plots were cut once a month. Subsets of litterbags were analysed after 12, 21 and 24 months. The serial dilution technique was used to assess the fungal community composition. The addition of labile carbon led to a strong decrease in litter decomposition rates, associated with consistent shifts in the composition of saprotrophic microfungal communities, and to an increase in the overall density of culturable fungal species (r-strategists), but not of specialized cellulolytic microfungi (K-strategists), isolated on Hutchinson agar. Sucrose addition did not affect the number of species isolated but the dominance structure was shifted toward the domination of the 2–4 most abundant species. The presence of EM roots significantly reduced moisture content in decomposing litter but had only weak and inconsistent effect on the decomposition rates and on the community composition of saprotrophic microfungi; these effects did not depend on the level of carbon availability.     

Leaf litter decomposition in the pure and mixed plantations of <Emphasis Type="Italic">Cunninghamia lanceolata</Emphasis> and <Emphasis Type="Italic">Michelia macclurei</Emphasis> in subtropical China

Leaf litter decomposition of Cunninghamia lanceolata, Michelia macclurei, and their mixture in the corresponding stands in subtropical China was studied using the litterbag method. The objective was to assess the influence of native evergreen broadleaved species on leaf litter decomposition. The hypotheses were: (1) M. macclurei leaf litter with lower C/N ratio and higher initial N concentration decomposed faster than C. lanceolata litter, (2) decomposition rates in litter mixtures could be predicted from single-species decay rates, and (3) litters decomposed more rapidly at the site that contained the same species as in the litterbag. The mass loss of leaf litter was positively correlated with initial N concentration and negatively correlated with C/N ratio. The decomposition rate of M. macclurei leaf litter was significantly higher than that of C. lanceolata needle litter in the pure C. lanceolata stand. Contrary to what would be predicted, the litter mixture decomposed more slowly than expected based on the results from component species decomposing alone. There was no significant difference in litter decomposition rate between different habitats.     

Thermal Decomposition Characteristics and Kinetics of Tea Stalk北大核心CSCD

In order to provide comprehensive utilization of tea stalk waste by thermochemical conversion, the thermal decomposition process of tea stalk and its kinetics were studied with simultaneous measurements of thermogravimetry (TG)/differential thermal analysis (DTA). The TG-DTG-DTA curves of tea stalk were acquired in a nitrogen atmosphere. The results indicated that the mass loss process of the samples could be divided into five stages. Among the five stages, most of the decomposition occurred in the third and fourth stages. The two main stages were indicated as exothermic processes, with the average weight loss rates of 55.12% and 28.48% at different heating rates of 10, 15, 20, 25 K/min, respectively. At higher heating rate, the fourth stage of the decomposition reaction was shifted to higher temperature range. The thermal decomposition kinetic parameters were calculated by Kissinger, FWO peak maximum evolution and FWO isoconversional methods. The results showed that the Kissinger and FWO peak maximum evolution methods were more suitable for the thermal decomposition kinetic parameters. The apparent activation energies were calculated to be 666.53 and 642.80 kJ/mol by the two methods, respectively. And natural logarithm of the pre-exponential factor (lnA) calculated by Kissinger method was given as 145.83. © 2018, Editorial Board of «Chemistry and Industry of Forest Products». All right reserved.     

Decomposition characteristics of organic materials and their effects on labile and recalcitrant organic carbon fractions in a semi-arid soil under plastic mulch and drip irrigation

Labile organic carbon(LC) and recalcitrant organic carbon(RC) are two major fractions of soil organic carbon(SOC) and play a critical role in organic carbon turnover and sequestration. The aims of this study were to evaluate the variations of LC and RC in a semi-arid soil(Inner Mongolia, China) under plastic mulch and drip irrigation after the application of organic materials(OMs), and to explore the effects of OMs from various sources on LC and RC by probing the decomposition characteristics of OMs using in-situ nylon mesh bags burying method. The field experiment included seven treatments, i.e., chicken manure(CM), sheep manure(SM), mushroom residue(MR), maize straw(MS), fodder grass(FG), tree leaves(TL) and no OMs as a control(CK). Soil LC and RC were separated by Huygens D's method(particle size-density), and the average soil mass recovery rate and carbon recovery rate were above 95%, which indicated this method was suitable for carbon pools size analysis. The LC and RC contents significantly(P0.01) increased after the application of OMs. Moreover, LC and RC contents were 3.2%–8.6% and 5.0%–9.4% higher in 2016 than in 2015. The applications of CM and SM significantly increased(P0.01) LC content and LC/SOC ratio, whereas they were the lowest after the application of TL. However, SOC and RC contents were significantly higher(P0.01) after the applications of TL and MS. The correlation analysis indicated the decomposition rate of OMs was positively related with LC content and LC/SOC ratio. In addition, lignin, polyphenol, WOM(total water-soluble organic matter), WHA(water-soluble humic acid), HSL(humic-like substance) and HAL(humic acid-like) contents in initial OMs played important roles in SOC and RC. In-situ nylon mesh bags burying experiment indicated the decomposition rates of CM, SM and MS were significantly higher than those of MR, FG, and TL. Furthermore, MS could result in more lignin derivatives, WHA, and HAL polymers in shorter time during the decomposition process. In conclusion, the application of MS in the semi-arid soil under a long-term plastic mulch and drip irrigation condition could not only improve soil fertility, but also enhance soil carbon sequestration.     

植被退化对尕海湿地枯落物分解的影响

[目的]分析植被退化对青藏高原东部尕海湿地枯落物分解的影响,为湿地生源要素生物地球化学循环过程研究提供基础依据。[方法]采用分解袋法,研究尕海泥炭沼泽和沼泽化草甸不同植被退化梯度湿地枯落物分解特征及其影响因素。[结果]各植被退化阶段湿地枯落物分解过程存在显著差异,植被退化总体抑制了枯落物分解,但不同湿地类型枯落物分解对植被退化响应有所不同;在生长季内(5—9月),沼泽泥炭植被未退化枯落物分解速率显著高于退化(p0.05);沼泽化草甸平均分解速率排序为:未退化(0.028 9g/d)中度退化(0.028 7g/d)轻度退化(0.028 0g/d);各植被退化阶段湿地的枯落物分解过程具有明显的年际变化特征,总体表现为2014年分解较快,2015,2016年相对较慢;温度和降雨对各退化阶段枯落物分解速率具有促进作用,但作用不显著。[结论]尕海湿地植被退化过程中枯落物分解动态受到枯落物自身性质、气候条件、土壤营养状况等自然环境条件的共同影响,相比而言,受枯落物性质的影响更大。     

Temperature sensitivity of anaerobic labile soil organic carbon decomposition in brackish marsh

The global warming has a potential for acceleration of labile soil organic carbon decomposition. Arrhenius equation is one of the useful equation for predicting temperature sensitivity of carbon decomposition, with the activation energy of rate constant being a key factor. The purpose of this study is the evaluation of temperature sensitivity of labile soil organic carbon decomposition under anaerobic condition in wetland soil using the activation energy of rate constant among different vegetation types. The soil samples were incubated at three different temperatures (10, 20, and 30°C) under anaerobic condition and carbon decomposition rates (sum of CO₂ and CH₄ production) were measured by gas chromatography. The first-order kinetic model with Arrhenius equation was used for approximate of anaerobic carbon decomposition. For determination of activation energy of rate constant, non-linear least-squares method was conducted between observed carbon decomposition rate and predicted carbon decomposition rate which calculated by Arrhenius equation. The activation energy of rate constant of anaerobic labile soil organic carbon decomposition was different among vegetation types. We successfully determined the activation energy of rate constant of CO2 or CH4 production from Phragites, Juncus, and Miscanthus+Cirsium-dominated vegetation soil with Arrhenius equation. Hence, this study suggests that Arrhenius equation was useful for evaluation of temperature sensitivity of labile soil organic carbon decomposition not only aerobic condition, but also anaerobic condition among several vegetation types in the wetland ecosystem. Moreover, gaseous carbon production from soil under Juncus yocoscensis dominated soil appeared higher activation energy and temperature sensitivity than that from soil under other vegetation types.     

Impact of addition of different rates of rice-residue biochar on C and N dynamics in texturally diverse soils

Impacts of crop residue biochar on soil C and N dynamics have been found to be subtly inconsistent in diverse soils. In the present study, three soils differing in texture (loamy sand, sandy clay loam and clay) were amended with different rates (0%, 0.5%, 1%, 2% and 4%) of rice-residue biochar and incubated at 25°C for 60 days. Soil respiration was measured throughout the incubation period whereas, microbial biomass C (MBC), dissolved organic C (DOC), NH₄⁺-N and NO₃^–N were analysed after 2, 7, 14, 28 and 60 days of incubation. Carbon mineralization differed significantly between the soils with loamy sand evolving the greatest CO₂ followed by sandy clay loam and clay. Likewise, irrespective of the sampling period, MBC, DOC, NH₄⁺-N and NO₃^–N increased significantly with increasing rate of biochar addition, with consistently higher values in loamy sand than the other two soils. Furthermore, regardless of the biochar rates, NO₃^–-N concentration increased significantly with increasing period of incubation, but in contrast, NH₄⁺-N temporarily increased and thereafter, decreased until day 60 in all soils. It is concluded that C and N mineralization in the biochar amended soils varied with the texture and native organic C status of the soils.     

玉米秸秆还田量对土壤性质、秸秆腐解及玉米纹枯病的影响

研究秸秆还田对土壤pH值、EC值、土壤腐解的影响及秸秆还田土壤腐解液对玉米纹枯病菌的影响。研究表明,随着玉米秸秆还田量的增加,土壤pH值降低,EC值升高。随着玉米秸秆3个处理(9 000、4 500、2 250 kg/hm2)还田量下降,秸秆纤维素腐解率升高,分别为54.4%、67.4%、83.9%。秸秆倍量还田(18 000 kg/hm2)土壤腐解液浓度(0.041 g/mL)对玉米纹枯病菌有抑制作用,全量(9 000 kg/hm2)、1/2量(4 500 kg/hm2)、1/4量(2 250 kg/hm2)秸秆还田的土壤腐解液对病菌有促进作用。秸秆还田玉米纹枯病病害流行田间调查表明,病情指数为秸秆还田量9 000 kg/hm24 500 kg/hm22 250 kg/hm2不还田处理。     

国际玉米价格波动对国内玉米价格的冲击——基于STR2模型的实证分析

以2000年1月~2017年8月国内外玉米现货价格月度数据为实证基础,选择STR2对国内外玉米现货价格联动的非线性特征进行实证分析。测度得到价格波动传导机制转化的临界阈值为c1=-0.105 84,c2=0.092 41,γ=1.918 14,根据平滑转化机制及其阈值,将连续平滑转化的国内外玉米价格波动传导效应分解为3种不同影响机制。结果表明,当国内玉米价格发生大幅波动时,国际玉米价格波动对国内玉米价格的冲击存在显著的非线性特征,且由线性冲击向非线性冲击的转化过程具有连续平滑的特点。随着国内玉米价格波动幅度的不断扩大,国际玉米价格波动对国内玉米价格的冲击越发严重,滞后期也更长,国内玉米价格受自身波动的影响不断弱化。在此基础上,提出平抑我国玉米价格波动的政策启示。     

湖北省耕地面积变化与各产业发展的关系

[目的]研究湖北省耕地资源变化与第一、二、三产业发展之间内在联系与相互影响机制,为合理利用与保护耕地资源,推动区域社会经济可持续发展提供重要参考。[方法]利用湖北省1991—2014年24a来的耕地面积、第一产业产值、第二产业产值、第三产业产值之间的时间序列统计资料,采用协整检验方法验证各变量间是否存在长期稳定的均衡关系,并通过脉冲响应函数和方差分解技术进一步分析湖北省耕地面积与各产业产值间相互关系。[结果]湖北省耕地面积与各产业产值之间存在长期均衡关系,可以运用脉冲响应函数做进一步分析;第一、第三产业发展一定程度上有利于耕地的保护,但影响力有限,第二产业发展需要消耗大量耕地,但随着时间推移会逐渐调整其结构以降低其对耕地的依赖程度;方差分解结果中,第二产业对其自身及第一、第三产业发展具有促进作用,而耕地资源对各产业发展的贡献率则普遍较低,所消耗的耕地资源未被充分高效利用。[结论]湖北省应协调好耕地保护与经济发展的关系,提高土地利用效率、经济效率并优化产业结构,使两者间形成良性循环,以推动社会经济可持续发展。