Stability of soil organic carbon changes in successive rotations of Chinese fir （Cunninghamia lanceolata （Lamb.） Hook） plantations

The importance of soil organic carbon (SOC) under forests in the global carbon cycle depends on the stability of the soil carbon and its availability to soil microbial biomass. We investigated the e ects of successive rotations of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations on the stability of SOC and its availability to microbes by adopting the two-step hydrolysis with H2SO4 and density fractionation. The results showed that successive rotations of Chinese fir decreased the quantity of total SOC, recalcitrant fraction, and carbohydrates in Labile Pool I (LP I), and microbial properties evidently, especially at 0–10 cm horizon. However, cellulose included in Labile Pool II (LP II) and the cellulose/total carbohydrates ratio increased in successive rotations of Chinese fir. The noncellulose of carbohydrates included in LP I maybe highly available to soil microbial biomass. Hence the availability of SOC to microbial biomass declined over the successive rotations. Although there was no significant change in recalcitrance of SOC over the successive rotations of Chinese fir, the percentage of heavy fraction to total SOC increased, suggesting that the degree of physical protection for SOC increased and SOC became more stable over the successive rotations. The degradation of SOC quality in successive rotation soils may be attributed to worse environmental conditions resulted from disturbance that related to “slash and burn” site preparation. Being highly correlated with soil microbial properties, the cellulose/total carbohydrates ratio as an e ective indicator of changes in availability of SOC to microbial biomass brought by management practices in forest soils.     

pH值对SBR生物反应器出水溶解态有机质含量与构成的影响

为探讨污水二级生化出水中有机物(EfOM)的构成特点和变化规律,采用配置生活污水,对不同pH值运行条件下, SBR生物反应器出水中的溶解态有机质(DOM)含量和构成进行了比较研究.结果表明,运行期间pH值的调节对SBR反应器出水DOM含量与构成的影响均较大.初始pH为6.5的SBR反应器, pH值降低为6.0后,出水DOC由原来的4.0mg·L-1不断升高,进一步提高pH值,能够起到一定的缓解作用;初始pH为8.0的SBR反应器,出水DOC从4.0mg·L-1快速降低并保持在2mg·L-1左右, pH值降低为6.5后, DOC变化不大.单宁酸和蛋白质、碳水化合物、DNA等微生物代谢产物(SMPs)是出水DOM的主要组成部分, pH值对SMPs生成的影响是一个长期的过程,运行过程中降低pH值,造成出水SMPs含量不断升高. pH值对整个循环过程中溶解态有机物降解情况的影响,在厌氧阶段发挥了主要作用,较高pH值有利于厌氧阶段有机物的降解,而好氧阶段的有机物降解受pH值影响不大.     

“一切皆有可能”

生物让人联想到色彩缤纷、活蹦乱跳、生生不息;塑料则令人感觉毫无生气、化学合成、白色污染。若将生物与塑料"合二为一"为生物塑料,也许有人会说不可能。但事实是这已经成为"事实"。生物塑料一般以淀粉类天然物质为基础,在微生物作用下生成塑料,它具有可再生性,但唯一的缺点是要使用粮食。不过,最近生物塑料又有了新进展,美国两位生物科学家为了改变以往生物塑料原料来自粮食碳水化合物的现实,他们利用庭院废弃物,并从     

光照度对蓝藻垂直迁移特性影响研究

通过水柱和摇瓶试验研究了蓝藻细胞胞内碳水化合物含量及蓝藻细胞在水体中的垂直分布对光照度变化的响应。结果表明,水柱试验中,在无光照和光照度为5000lx的条件下,铜绿微囊藻出现明显的表面浮聚现象,经过24h后,表层的藻细胞数分别占总藻细胞数的47%和26%;水柱试验中,在不同光照条件下,铜绿微囊藻胞内碳水化合物含量都呈现出表层低、底层高的现象;摇瓶试验中,水华鱼腥藻和铜绿微囊藻胞内碳水化合物含量对光照度的变化有很好的响应,光照度适量时,胞内碳水化合物含量上升,光照度不足或者过高时,胞内碳水化合物含量下降;光照度的变化能够在短时间内引起蓝藻细胞胞内碳水化合物含量变化,改变蓝藻细胞密度,从而影响到蓝藻细胞在水体中的垂直分布。