紫色土区不同秸秆还田量对土壤线虫群落的影响

为了研究不同秸秆还田量对紫色土区土壤线虫群落的影响, 作者于2011年5月和9月对川中丘陵区的100% (RMW1)、50%(RMW2)、30%(RMW3)和空白对照(CK)4种秸秆还田量的农田土壤线虫进行了调查。结果发现, 随着秸秆还田量的下降, 土壤线虫的群落结构有一定变化。总体上, 群落密度、食真菌类群和捕食-杂食类群的密度呈波动增加; 食细菌类群的密度持续增加; 植物寄生类群密度、Shannon-Wiener多样性指数(H')、植物寄生成熟指数(PPI)和瓦斯乐斯卡指数(WI)呈先增加后下降的变化趋势, 且多样性指数在秸秆还田量为30-50%之间最高; 类群数、自由生活成熟指数(MI)、线虫通路比值(CR)则先下降后增加; 所有变化均不显著(P > 0.05)。土壤速效钾含量随秸秆还田量的增加显著提高(P < 0.05), 且与线虫群落多样性指数呈显著负相关(P < 0.05)。研究结果表明, 在紫色土区秸秆还田主要是通过改变土壤钾含量对土壤线虫群落产生影响, 且秸秆还田量在30-50%之间时有利于维持线虫群落多样性。     

南方双季稻田稻草还田的碳汇效应

利用长期稻草还田定位试验和短期不同稻草还田模式试验,研究稻草还田对南方双季稻田土壤固碳、甲烷排放和综合碳汇的影响.结果表明： 稻草还田能增加土壤有机碳,长期还田的耕层土壤碳汇年增长率为0.07 t C·hm^-2·a^-1,土壤有机碳的表观转化率随着稻草还田量的增加而减少.稻草还田导致稻田甲烷排放量显著增加,其中,NPK添加稻草（NPK+RS）处理早、晚稻期间甲烷排放通量比仅施NPK分别增加了75.0%和251.5%（P<0.01）.稻田甲烷排放随着稻草还田量的增加而增加,在水稻产量和耕作方式相近的条件下,稻草（茬）的甲烷表观转化率接近.综合土壤固碳和甲烷排放的稻田净碳汇,NPK+RS处理负碳汇效应显著,基本与其水稻生物固碳接近,比稻草不还田处理（NPK）增加158.3%;不同还田模式中,稻草覆盖免耕处理能显著减少甲烷排放,其净碳汇（负值）比高桩翻耕处理减少50.9%,有利于水稻高产稳产.     

蚯蚓和秸秆对铜污染土壤微生物类群和活性的影响

试验设置4个Cu浓度水平：0、100、200和400 mg·kg^-1 Cu²⁺,每个Cu浓度水平设置4个处理：对照(CK)、表施秸秆(M)、接种蚯蚓(E)、同时加入蚯蚓和秸秆(ME),研究了在Cu污染土壤中加入蚯蚓和秸秆对土壤微生物数量及活性的影响.结果表明：Cu污染、秸秆和蚯蚓均明显影响土壤微生物类群; Cu污染对细菌、放线菌具有抑制作用,而对真菌没有影响;秸秆显著提高了真菌数量;蚯蚓使土壤细菌、放线菌数量显著增加,而对真菌数量影响不大.Cu污染浓度＞200 mg·kg^-1处理对微生物量碳具有抑制作用;加入秸秆或蚯蚓,可显著提高土壤微生物量碳,而且同时加蚯蚓和秸秆处理土壤微生物量碳增加最显著.加入蚯蚓和秸秆后,土壤呼吸值显著增高.Cu<200 mg·kg^-1时,蚯蚓处理土壤呼吸值最大,平均比对照高3.06～5.58倍;Cu≥200mg·kg^-1时,蚯蚓、秸秆同时加入处理土壤呼吸值最高.4个处理土壤代谢商大小顺序为：ME>E>M>CK.蚯蚓和秸秆处理对土壤NH₄⁺-N没有影响,而对土壤NO₃^--N影响各异.接种蚯蚓,可显著提高土壤NO₃^--N含量;加入秸秆,可显著降低土壤NO₃^--N含量;同时加入蚯蚓和秸秆处理NO₃^--N含量最低.相关分析表明,土壤有效态Cu(DTPA-Cu)与土壤放线菌、细菌呈显著负相关,而与土壤呼吸、土壤NO₃^--N、NH₄⁺-N含量呈显著正相关.引入秸秆和蚯蚓,可在一定程度上减缓Cu污染对微生物数量和活性的影响.     

长江流域水患的思考和对策

长江流域水患由来已久,长江流域的水患是多种因素造成的,除了全球的气候因素外,也有长江流域的环境因素影响。其中一个重要因素是人口压力过大,具有水源涵养功能的森林生态系统自清代后遭到严重破坏,并呈加剧的趋势,失去了涵养水源的功能,表土大量流失,使河床不断抬高是造成1998年特大洪灾的根本原因。应发挥森林作为陆地生态系统主体的作用,调整林业的工作重点。将森林改善环境,防止水土流失,保障可持续发展放在首位。围绕人类与自然协调发展的主题,结合长江流域经济发展与自然资源保护所面临的问题,做出长江流域人口、资源、环境可持续发展的科学规划。建立长江流域资源、环境可持续发展的信息系统和决策支持系统,提高林业的管理水平。政府应以法律和税收的形式保证每年要逐步增加对林业的财政投入,真正发挥森林在保护环境,国土保安和社会经济可持续发展的主导作用。     

南方红豆杉内生真菌产油及降解纤维素的研究

从油脂植物南方红豆杉Taxusmairei茎中分离到26株内生真菌,用形态学方法鉴定表明,交链孢霉属Alternaria、无孢菌群MyceliaSterilia和硬内囊霉属Sclerocystis为优势类群;用苏丹黑染液对这26株内生真菌菌丝染色后,在光学显微镜下观察,发现其中14株内生真菌菌丝中有明显的油滴存在,选出其中油滴较大较多的7株在PDA液体培养基中培养6d后提取油脂,结果它们的油脂含量为细胞干重的13.2%~29.5%;这26株内生真菌在以微晶纤维为唯一碳源的液体培养基中培养8d后,测定发酵液的滤纸酶活,发现酶活为6.5~17.8μg葡萄糖/mL·min。研究结果表明南方红豆杉内生真菌中存在大量产油菌株,且它们有以纤维素为碳源生长的潜力。本研究为筛选能以秸秆中纤维素为碳源积累油脂的菌株打下基础。     

Effects of various straw incorporation strategies on soil phosphorus fractions and transformations

Returning straw to the field is an effective method for optimizing the soil phosphorus (P) availability, in which bacteria play an important role. However, the effects of various straw incorporation strategies on P transformation between different soil P pools remain unclear. In this study, variations in soil P fractions, phosphatase activities and the abundance of phosphatase genes (phoD, phoX and phoC) as well as a P-solubilizing gene (pqqC) at DNA (total) and cDNA (transcribed) levels were analysed in three straw incorporation treatments, including chopped straw (StrawD), straw compost (Compost) and straw-derived biochar (Biochar), and control (no straw, CK). Compared with the CK, the moderately labile inorganic P (NaOH I-P_i) content significantly decreased and the non-available P (Residual P) content significantly increased in the StrawD treatment. At the same time, phosphodiesterase (PD) activity and the transcribed phoC and phoX genes as well as total pqqC gene abundance significantly increased in the StrawD treatment, suggesting that the input of chopped straw stimulated P transformations from both organic and inorganic P pools. In addition, the stable P_i (NaOH II-P_i) content and total pqqC gene abundance in the Biochar treatment were significantly higher than that in the CK, indicating that the input of biochar increased the NaOH II-P_i that could release available P by Pi-solubilizing bacteria. In comparison to the CK, the Compost input significantly decreased one labile Pi (resin-P_i) only. However, its P fractions were significantly different from that of CK, Biochar and StrawD treatments, suggesting that the effects of compost input on P should not be ignored. In conclusion, chopped straw input increased soil P transformation but not available P, biochar input may promote inorganic P transformation, and compost input has a latent effect on P transformation. The study provided a comprehensive understanding of straw incorporation strategies for regulating soil P availability.     

Temperature sensitivity and substrate quality in soil organic matter decomposition: results of an incubation study with three substrates

Kinetic theory suggests that the temperature sensitivity of decomposition of soil organic matter should increase with increasing recalcitrance. This ‘temperature–quality hypothesis’ was tested in a laboratory experiment. Microcosms with wheat straw, spruce needle litter and mor humus were initially placed at 5, 15 and 25 °C until the same cumulative amount of CO₂ had been respired. Thereafter, microcosms from each single temperature were moved to a final set of incubation temperatures of 5, 15 and 25 °C. Straw decomposed faster than needle litter at 25 and 15 °C, but slower than needle litter at 5 °C, and showed a higher temperature sensitivity (expressed as Q₁₀) than needle litter at low temperatures. When moved to the same temperature, needle litter initially incubated at 5 and 15 °C had significantly higher respiration rates in the final incubation than litters initially placed at 25 °C. Mor humus placed at equal temperatures during the initial and final incubations had higher cumulative respiration during the final incubation than humus experiencing a shift in temperature, both up‐ and downwards. These results indicate that other factors than substrate quality are needed to fully explain the temperature dependence. In agreement with the hypothesis, Q₁₀ was always higher for the temperature step between 5 and 15 °C than between 15 and 25 °C. Also in agreement with the temperature–quality hypothesis, Q₁₀ significantly increased with increasing degree of decomposition in five out of the six constant temperature treatments with needle litter and mor humus. Q₁₀s for substrates moved between temperatures tended to be higher than for substrates remaining at the initial temperature and an upward shift in temperature increased Q₁₀ more than a downward shift. This study largely supports the temperature–quality hypothesis. However, other factors like acclimation and synthesis of recalcitrant compounds can modify the temperature response.     

Effects of ground cover (straw and compost) on the abundance of natural enemies and soil macro invertebrates in vineyards

1 Herbicides are commonly applied under grapevines in Australia to remove weeds and thereby to avoid water loss through transpiration. 2 Interest in sustainability promotes a reduction in chemical inputs, including herbicides, leading to trials with surface mulches to suppress weeds. 3 Surface mulches may also influence the abundance of a range of invertebrates. Potentially, an increase in natural enemies will contribute to pest control and encourage a reduction in pesticide application. 4 We used three trapping methods and direct soil sampling to assess invertebrates at ground level, in the canopy and in the soil to determine the influence of mulch on natural enemies, potential pests and soil macroinvertebrates, including earthworms. 5 Collections sorted to family demonstrated that the addition of straw or compost mulches increased natural enemies collected with pitfall traps and soil organisms. However, there was no clear indication of the overall superiority of either mulch. 6 Abundance of ground beetles, parasitoid Hymenoptera and spiders collected with pitfall traps were increased by the addition of mulches. In the canopy, predatory and parasitic Diptera and predatory Hemiptera increased after mulching. 7 Earthworms collected by hand sorting soil increased with straw mulching. 8 No influence on pests was detected. Although Lepidoptera and Sigmurethra, collected in pitfall traps, increased with straw mulching, neither included pest species. 9 The results are discussed with reference to the potential economic impact of mulches.     

Lactobacillus pentosus CECT 4023 T co-utilizes glucose and xylose to produce lactic acid from wheat straw hydrolysate: Anaerobiosis as a key factor

Lactic acid is a versatile chemical that can be produced via fermentation of lignocellulosic materials. The heterolactic strain Lactobacillus pentosus CECT 4023 T, that can consume glucose and xylose, was studied to produce lactic acid from steam exploded wheat straw prehydrolysate. The effect of temperature and pH on bacterial growth was analyzed. Besides, the effect of oxygen on lactic acid production was tested and fermentation yields were compared in different scenarios. This strain showed very high tolerance to the inhibitors contained in the wheat straw prehydrolysate. The highest lactic acid yields based on present sugar, around 0.80 g g⁻¹, were obtained from glucose in presence of 25%, 50%, and 75% v v⁻¹ of prehydrolysate in strict anaerobiosis. Lactic fermentation of wheat straw hydrolysate obtained after enzymatic hydrolysis of the prehydrolysate yielded 0.39 g of lactic acid per gram of released sugars, which demonstrated the high potential of L. pentosus to produce lactic acid from hemicellulosic hydrolysates. Results presented herein not only corroborated the ability of L. pentosus to grow using mixtures of sugars, but also demonstrated the suitability of this strain to be applied as an efficient lactic acid producer in a lignocellulosic biorefinery approach. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2739, 2019