鸡公山典型落叶阔叶林土壤呼吸对食叶虫灾爆发的响应

土壤呼吸是陆地生态系统碳循环的关键环节之一。随着极端气候事件的频发,森林虫害的发生频率和强度也趋于增加,森林虫害爆发已经是影响森林生态系统碳循环过程的一种重要的自然干扰。气候过渡带典型森林生态系统虫灾的爆发是否会影响土壤的碳排放过程目前仍不清楚。本研究利用鸡公山地区麻栎-枫香混交林大规模爆发食叶性害虫的机会,比较虫灾爆发当年(2014)与正常年份(2015)的土壤碳排放通量,以阐明森林虫灾爆发对土壤碳排放通量的影响。结果表明:虫灾爆发当年7、8、9、10月份土壤平均温度比正常年份相应各月份分别高0.26、0.51、0.83、0.07℃,土壤呼吸分别显著提高了129.9%、77.1%、61.6%和58.9%。虫灾爆发年份生长季的平均土壤呼吸为3.55μmol m~(-2)s~(-1),比正常年份(2.77μmol m~(-2)s~(-1))高36.2%;生长季期间的平均土壤异养呼吸比正常年份增加了29.7%。该研究表明森林食叶虫害的爆发至少在短期内可导致森林土壤碳排放量呈显著的增加趋势,近而对森林生态系统土壤碳库积累产生重要影响。因此,充分认识病虫害对森林生态系统的干扰和影响,将有助于陆地生态系统碳循环的准确估算和模拟。     

Heterotrophic production of Chlorella sp. TISTR 8990—biomass growth and composition under various production conditions

The green microalga Chlorella sp. TISTR 8990 was grown heterotrophically in the dark using various concentrations of a basal glucose medium with a carbon‐to‐nitrogen mass ratio of 29:1. The final biomass concentration and the rate of growth were highest in the fivefold concentrated basal glucose medium (25 g L^?1 glucose, 2.5 g L^?1 KNO₃) in batch operations. Improving oxygen transfer in the culture by increasing the agitation rate and decreasing the culture volume in 500‐mL shake flasks improved growth and glucose utilization. A maximum biomass concentration of nearly 12 g L^?1 was obtained within 4 days at 300 rpm, 30°C, with a glucose utilization of nearly 76% in batch culture. The total fatty acid (TFA) content of the biomass and the TFA productivity were 102 mg g^?1 and 305 mg L^?1 day^?1, respectively. A repeated fed‐batch culture with four cycles of feeding with the fivefold concentrated medium in a 3‐L bioreactor was evaluated for biomass production. The total culture period was 11 days. A maximum biomass concentration of nearly 26 g L^?1 was obtained with a TFA productivity of 223 mg L^?1 day^?1. The final biomass contained (w/w) 13.5% lipids, 20.8% protein and 17.2% starch. Of the fatty acids produced, 52% (w/w) were saturated, 41% were monounsaturated and 7% were polyunsaturated (PUFA). A low content of PUFA in TFA feedstock is required for producing high quality biodiesel. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1589–1600, 2017     

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.     

Microbial communities in terrestrial surface soils are not widely limited by carbon

Microbial communities in soils are generally considered to be limited by carbon (C), which could be a crucial control for basic soil functions and responses of microbial heterotrophic metabolism to climate change. However, global soil microbial C limitation (MCL) has rarely been estimated and is poorly understood. Here, we predicted MCL, defined as limited availability of substrate C relative to nitrogen and/or phosphorus to meet microbial metabolic requirements, based on the thresholds of extracellular enzyme activity across 847 sites (2476 observations) representing global natural ecosystems. Results showed that only about 22% of global sites in terrestrial surface soils show relative C limitation in microbial community. This finding challenges the conventional hypothesis of ubiquitous C limitation for soil microbial metabolism. The limited geographic extent of C limitation in our study was mainly attributed to plant litter, rather than soil organic matter that has been processed by microbes, serving as the dominant C source for microbial acquisition. We also identified a significant latitudinal pattern of predicted MCL with larger C limitation at mid- to high latitudes, whereas this limitation was generally absent in the tropics. Moreover, MCL significantly constrained the rates of soil heterotrophic respiration, suggesting a potentially larger relative increase in respiration at mid- to high latitudes than low latitudes, if climate change increases primary productivity that alleviates MCL at higher latitudes. Our study provides the first global estimates of MCL, advancing our understanding of terrestrial C cycling and microbial metabolic feedback under global climate change.     

A kinetic model for lutein production by the green microalga Chlorella protothecoides in heterotrophic culture

Production of lutein by the green microalga Chlorella protothecoides grown heterotrophically in a fermentor using glucose as the carbon source and urea as the nitrogen source was investigated. An unstructured kinetic model was proposed to describe the microalgal culture system including cell growth, lutein formation, as well as glucose and nitrogen consumption. The inhibition potentials of biomass, product and substrates on growth and lutein formation were examined and incorporated into the kinetic model. Values of the kinetic model parameters were estimated. The resulting model predictions were in good agreement with the experimental results. The model can be helpful in scale-up, optimization and control of the C. protothecoides culture process, and can also be used as a guideline for similar microalgal cultivation systems. Received 28 January 1999/ Accepted in revised form 27 August 1999     

Change of Microbial Populations in a Suspended-sludge Reactor Performing Completely Autotrophic N-removal

Summary In recent years, several novel processes for N-removal almost without consumption of organic carbon under oxygen-limited conditions have been discovered, which may be a promising option for low-cost N-removal from ammonia-rich wastewater. In this study, a laboratory scale suspended-sludge reactor was continuously operated under low dissolved oxygen concentration. High N-removal efficiency and subsequently degradation of the reactor were observed. Molecular analysis based on a partial-16S rRNA gene library showed that, at the stage of high efficiency, the biomass was composed of Planctomycete-like bacteria (up to 40%) and heterotrophic organisms (approximately 60%) as well as a few ammonia-oxidizing bacteria and at the stage of degradation, the autotrophic ammonia-oxidizing bacteria were dominant (up to 70%) and Planctomycete-like bacteria were no longer found in the sludge. Three specific Planctomycete-16S rRNA-targeted probes were used for fluorescence in situ hybridization (FISH). The results showed that at the high-efficiency stage, Planctomycete-like bacteria, present at approximately 20% of the total bacteria, lay frequently in the middle of flocs, while the heterotrophic bacteria occurred within the outer layers. This work revealed that the change of the microbial populations is the key reason for reactor deterioration, and the heterotrophic bacteria probably play an important role in sustaining the biomass structure of the sludge.     

Pseudomonas oryzihabitans EN-F4菌株的脱氮特征及羟胺对其脱氮过程的促进作用

【目的】异养硝化-好氧反硝化（heterotrophic nitrification-aerobic denitrification，HN-AD）微生物在生物脱氮中具有重要作用，而能同时去除废水中多种无机氮尤其是羟胺的HN-AD微生物报道较少。本研究从菜地中分离筛选出一株能同时去除羟胺和亚硝酸盐的HN-AD菌株EN-F4，探究其脱氮特征以及羟胺对其脱氮过程的影响，为提高废水处理效率奠定基础。【方法】通过形态学和16S rRNA基因测序对该菌株进行鉴定，并利用批量试验研究该菌株的脱氮特征，结合氮平衡、酶活性和特异性酶抑制剂探索菌株的HN-AD机理，最后通过添加羟胺研究其对不同氮源转化的影响。【结果】菌株EN-F4经鉴定为栖稻假单胞菌（Pseudomonas oryzihabitans），该菌株在25℃条件下对铵盐、羟胺、亚硝酸盐和硝酸盐的去除效率分别为99.27%、99.13%、87.01%和85.20%，对应的最大去除速率分别为8.27、1.85、5.10和5.31 mg/（L·h）。更突出的是，外加羟胺后不会抑制该菌的反硝化能力，反而促进了亚硝酸盐和总氮的去除，其最大去除速率分别提升至7.80 mg/（L·h）和7.51 mg/（L·h）。结合酶活性的成功检测、氮平衡和HN-AD特异性酶抑制剂分析证实了菌株具有优异的HN-AD能力。【结论】菌株Pseudomonas oryzihabitans EN-F4可以在25℃条件下高效地进行HN-AD去除废水中的多种无机氮，且羟胺能显著促进亚硝酸盐和总氮的去除。     

FUNCTIONAL PHYCOBILISOMES FROM TOLYPOTHRIX TENUIS (CYANOPHYTA) GROWN HETEROTROPHICALLY IN THE DARK1

Phycobiliproteins produced in dark-grown cells of Tolypothrix tenuis Kützing formed Phycobilisomes functionally capable of energy transfer. The phycobilisomes could be recovered in high yield (80% of extracted phycobiliproteins). Phycobilisomes from cells grown without light and in red light had the same size, morphology, and spectral characteristics. They had a phycocyanin to allophycocyanin malar ratio of 3:1. Phycocyanin and allophycocyanin in phycobilisomes were energetically coupled as indicated by their fluorescence emission (maximum of ca. 690 nm at –196° C) and excitation spectra. Phycobilisomes were attached to the outer surface of thylakoids and were hemidiscoidal in shape. In thin sections they had a diameter of 42 ± 3nm, a height of 24 ± 4 nm and a thickness of 10 ± 2 nm. Isolated and negatively stained Phycobilisomes were larger with a diameter of 51 ± 2 nm and height of 33 ± 2 nm, Isolated phycobilisomes in face view had a central core of three units and six peripheral rods. Each rod appeared to be composed of three hexamers (three double discs), consistent with the observed dimensions and substructure. After Phycoerythria synthesis was induced by a 15 min green light exposure, phycobilisomes of dark-grown cells exhibited energy transfer from phycoerythrin to a long wavelength allophycocyanin, indicating that phycoerythrin synthesized in darkness was incorporated into functional phycobilisomes.     

Physics underlying the formation of protocells

The emergence of the first cellular organization on the primitive earth could be associated with pronounced heterotrophic activity embodied in heat engines actualized in local material aggregates. Heterotrophic activity intrinsically rests upon the capacity of local detection upholding the conservation of energy on the global scale.     

Seasonal cycling of putrescine and amino acids in relation to biological production in a stratified coastal salt pond

Seasonal cycles of concentrations and microbial uptake of dissolved free amino acids and the polyamine, putrescine, were followed during summer stratification of a coastal salt pond. Stratification began in May and was clearly seen in profiles of temperature, salinity, pH and alkalinity. Primary production exhibited a mid-August maximum and the O₂-H₂S interface shoaled at that time. POC and phytopigments roughly followed the pattern of primary production. Cycling of putresince, like the amino acids, was strongly influenced by primary production and microbial decomposition. Putrescine concentration profiles appeared to follow the pattern of primary production more closely, while amino acids appeared to follow the pattern of microbial production. The absence of production of putrescine during the decomposition of dissolved ornithine and the correlation of putrescine concentration with primary production suggest a direct source from algae in the water column.Microbial uptake of amino acids and putrescine together accounted for 60–90% of the bacterial C production measured in oxic waters and almost 300% of that measured in the anoxic bottom layer. Since other organic carbon and nitrogen compounds are also being taken up, these data suggest that tracer uptake methods as we used them may overestimate the true microbial uptake rates, or release of other organic compounds by microbes occurs at the same time. Further work on carbon and nitrogen budgets is needed to resolve the apparent imbalance between organic C and N incorporation and bacterial production.