中亚热带几种典型森林生态系统碳、氮储存功能研究

采用定位研究方法,从生态系统服务功能角度,对比研究了中亚热带区域7种典型森林生态系统碳、氮储存功能。结果表明,次生常绿阔叶林碳、氮储存功能最强,杉阔混交林碳、氮储存功能比同林龄的杉木纯林强,而第1代杉木纯林碳、氮储存功能强于连栽杉木纯林。生态系统碳、氮储存功能空间分布基本一致,土壤层是主要部分,其次为乔木层,然后是根系,林下植被层和凋落层所占比例最小。相关分析表明,土壤碳、氮储存功能与林下植被生物量、森林凋落物现存量之间都具有良好的线性关系,但与地下部分生物量相关性不明显。

大豆原油充氮储存品质变化规律的研究

通过对充氮储存和常规储存条件下大豆原油品质指标的检测分析,研究充氮储存条件下大豆原油品质的变化。结果表明:与常规储存的大豆原油相比,在北京地区充氮储存22个月的条件下,大豆原油的气味、滋味、色泽、透明度、羰基值无显著改变,加热试验后色泽变浅,溶剂残留量总体下降;充氮储存的大豆原油酸值、过氧化值较常规储存的上升缓慢。充氮储存对延缓油脂劣变有明显效果,可以延缓油脂氧化速度,对保证油脂储存品质有良好作用。

挪威森林生态系统中的氮在不同大气输入量下的储存和迁移转化

人们对挪威南部和西南部一些森林生态系统中氮的储存和氮的迁移转化情况进行了估计。考察的林分在氮的大气输入量和立地性质上都存在差异,氮的大气输入量为10～25kg/hm^2·a。来自大气的氮,多数被固定在森林生态系统的土壤和现存生物量中。Dal流域氮的大气沉降率最低,年输入量约为12kg/hm^2·a,只略高于树木的吸收量。该流域内森林林分的NO_3-N淋失量约为0.5kg/hm^2·a。相比之下,挪威西南部受干扰更多的Svela和Hφgmo流域,氮的大气沉降率达到20kg/hm^2·a,高于树木的吸收量,沉降的氮多数被固定在生态系统的其他部分内(也许是在土壤中)。在后两个流域中NO_3^-N的淋失量似乎略高于Dal流域。森林生态系统的破坏(如皆伐)对NO_3的流量有显著影响。氮的动态过程受到自然因素、森林管理和大气氮沉降等因素的影响,且很难区分各要素的单独作用。这就难以评价诸如大气氮沉降等单一要素对NO_3流量的影响。

不同储存条件对浓香花生油风味及综合品质的影响

将浓香花生油置于室外自然环境中的钢制储油罐,分别采用常规储存、添加叔丁基对二苯酚(tertiary butylhydroquinone,TBHQ)储存、充氮储存18个月,每月定期取油样,采用顶空固相微萃取-气相色谱-质谱联用仪及气相色谱-嗅闻仪对花生油中挥发性风味成分进行定量检测和风味嗅闻评价,并检测其酸价、过氧化值和VE、甾醇含量,研究不同储存条件对花生油风味及综合品质的影响。结果表明:浓香花生油中共分离鉴定出9类64种挥发性风味成分,其中吡嗪类和醛类占挥发性风味成分总量的一半以上,这两类挥发性风味成分构成了浓香花生油特有的坚果香味、烧烤味、甜香味等基础风味。花生油经常规储存、添加TBHQ储存、充氮储存18个月后,吡嗪类物质相对含量从36.42%分别降低至16.33%、21.92%、27.02%,醛类物质相对含量从23.82%分别增加至24.61%、2.26%、17.52%,花生油的坚果味、烘烤味、甜香味及总体风味等明显减弱,酸败味增强;与常规储存相比,添加TBHQ和充氮储存均能有效延缓花生油特征风味物质、VE、甾醇的损失,将保质期分别延长至18个月以上和10个月;但添加TBHQ储存的花生油中检测出了TBHQ分解产物——叔丁基对苯醌。因此,充氮储存花生油不仅可以避免抗氧化剂添加对油脂的污染,也可以达到保质保鲜的目的。

Effects of Grassland Degradation and Re-vegetation on Carbon and Nitrogen Storage in the Soils of the Headwater Area Nature Reserve on the Qinghai-Tibetan Plateau,China

Both overgrazing and climate change contribute to grassland degradation in the alpine regions of China and negatively affect soil carbon and nitrogen pools. We quantified changes in soil organic carbon （SOC） and total nitrogen （TN） in black soil beach （BSB）. We measured SOC and TN in severely degraded and non-degraded grasslands to calculate differences in carbon and nitrogen storage, and field survey results were extrapolated to the entire headwaters area of the Qinghai-Tibetan Plateau （36.3xlos krn~） to determine SOC and TN losses from these grasslands. We also evaluated changes in SOC and TN in severely degraded grasslands that were artificially re-vegetated five, seven and nine years ago. Totally 92.43 Tg C and 7.08 Tg N were lost from the BSB in the headwater area, which was approximately 50% of the original C and N soil pools. Re-vegetation of the degraded grasslands in the headwater area would result in a gain of 32.71 Tg C in the soil after five years, a loss of 5.5a Tg C after seven years and an increase of 44.15 Tg C after nine years. The TN increased by 53.09% and 59.98% after five and nine years, respectively, while it decreased by 4.92% after seven years of re-vegetation. The results indicate that C and N stocks followed a ＂V＂ shaped pattern with re- vegetation time. Understanding plant-soil interactions during succession of artificially planting grassland ecosystems is essential for developing scientifically sound management strategies for the effectively re-vegetated BSB.

线性回归和动力学方程在大豆原油储存品质预测上的应用

通过对北京市常规储存和充氮储存条件下大豆原油过氧化值和酸值的跟踪检测,使用线性回归和动力学方程对不同储存条件下大豆原油储存3年时的品质做出了预测。结果表明,常规储存的大豆原油储存3年时的过氧化值约是入库时的2.3倍,酸值约是入库时的1.1倍;充氮储存的大豆原油储存3年时的过氧化值约是入库时的1.3倍,酸值约是入库时的1.1倍。由此确定了北京市油脂储存入库品质的要求为过氧化值不大于2.0 mmol/kg,酸值不大于2.0 mgKOH/g,为油脂出库品质指标的估算提供了新的思路,为北京市地方储备油储存轮换提供了数据支持。

Carbon and Nitrogen Storage in Inner Mongolian Grasslands: Relationships with Climate and Soil Texture

Understanding the spatial variability of soil carbon （C） storage and its relationship with climate and soil texture is critical for developing regional C models and for predicting the potential impact of climate change on soil C storage. On the basis of soil data from a transect across the Inner Mongolian grasslands, we determined the quantitative relationships of C and nitrogen （N） in bulk soil and particle-size fractions （sand, silt, and clay） with climate and soil texture to evaluate the major factors controlling soil C and N storage and to predict the effect of climate changes on soil C and N storage. The contents of C and N in the bulk soil and the different fractions in the 0 20 and 20 40 cm soil layers were positively correlated with the mean annum precipitation （MAP） and negatively correlated with the mean annual temperature （MAT）. The responses of C storage in the soil and particle-size fractions to MAP and MAT were more sensitive in the 0-20 cm than in the 2（~40 cm soil layer. Although MAP and MAT were both important factors influencing soil C storage, the models that include only MAP could well explain the variation in soil C storage in the Inner Mongolian grasslands. Because of the high correlation between MAP and MAT in the region, the models including MAT did not significantly enhance the model precision. Moreover, the contribution of the fine fraction （silt and clay） to the variation in soil C storage was rather small because of the very low fine fraction content in the Inner Mongolian grasslands.