不同干湿交替频率对土壤速效养分、水溶性有机碳的影响

为了探究不同干湿交替频率对速效养分、DOC的影响机理,选择北京褐土(表层0—10cm土壤)为研究对象,采用室内模拟控制实验法,控制其他变量,设计一系列不同频率的干湿交替实验,在58d内设置了10d土壤培育期和48d试验期,其中48d试验期设置0、1、2、3、4次干湿交替,试验结束(第58天)进行速效养分、水溶性有机碳(DOC,Dissolved organic carbon)等主要土壤速效养分指标测定。采用单因素方差分析与LSD多重比较法进行数据分析,研究结果显示:恒湿组的速效钾、硝态氮含量比干湿交替组高;低频率的干湿交替使得土壤速效钾含量减少,高频率可能在后期出现释钾现象,速效钾含量随着干湿交替频率增加可能会有所增加,趋近恒湿组速效钾水平,4次干湿交替频率是出现速效钾回升的临界次数;硝态氮含量随着频率增加也有增加趋势,低频率的1次干湿交替(DW1,1 drying-rewetting cycle)硝态氮含量最低,高频率的4次干湿交替(DW4,4 dryingrewetting cycles)最高,干湿交替频率增加更频繁的打破平衡,促进矿化,干湿交替组也趋近恒湿组的硝态氮水平。经过干湿交替,土壤中速效钾、铵态氮、DOC的含量下降,硝态氮含量增加,速效磷、pH的变化不明显。在固定时间内(48d),随着干湿交替的频率增加(从1次到2、3、4次),周期变短(从48d到24、16、12d),干燥与湿润的持续时间变短(从24d到12、8、6d),干湿交替组的速效钾、硝态氮含量分别趋于恒湿组的速效钾、硝态氮水平。     

Biosynthesis and biotechnological application of non-canonical amino acids: Complex and unclear

Compared with the better-studied canonical amino acids, the distribution, metabolism and functions of natural non-canonical amino acids remain relatively obscure. Natural non-canonical amino acids have been mainly discovered in plants as secondary metabolites that perform diversified physiological functions. Due to their specific characteristics, a broader range of natural and artificial non-canonical amino acids have recently been applied in the development of functional materials and pharmaceutical products. With the rapid development of advanced methods in biotechnology, non-canonical amino acids can be incorporated into peptides, proteins and enzymes to improve the function and performance relative to their natural counterparts. Therefore, biotechnological application of non-canonical amino acids in artificial bio-macromolecules follows the central goal of synthetic biology to: create novel life forms and functions. However, many of the non-canonical amino acids are synthesized via chemo- or semi-synthetic methods, and few non-canonical amino acids can be synthesized using natural in vivo pathways. Therefore, further research is needed to clarify the metabolic pathways and key enzymes of the non-canonical amino acids. This will lead to the discovery of more candidate non-canonical amino acids, especially for those that are derived from microorganisms and are naturally bio-compatible with chassis strains for in vivo biosynthesis. In this review, we summarize representative natural and artificial non-canonical amino acids, their known information regarding associated metabolic pathways, their characteristics and their practical applications. Moreover, this review summarizes current barriers in developing in vivo pathways for the synthesis of non-canonical amino acids, as well as other considerations, future trends and potential applications of non-canonical amino acids in advanced biotechnology.     

Natural and engineered polyhydroxyalkanoate (PHA) synthase: key enzyme in biopolyester production

Applied Microbiology and Biotechnology - With the finite supply of petroleum and increasing concern with environmental issues associated with their harvest and processing, the development of more...