黄土丘陵区撂荒对土壤酶活性的影响

为了解侵蚀环境下植被恢复对土壤酶活性的影响,以典型侵蚀环境黄土丘陵区纸坊沟流域生态恢复1至50年撂荒地长期定位试验点为研究对象,选取坡耕地为对照,分析了植被恢复过程中土壤脲酶、磷酸酶、蔗糖酶、淀粉酶、纤维素酶、过氧化氢酶、多酚氧化酶及理化性质的演变特征。结果表明,土壤酶活性前期变化波动较大,后期(20-30a)年变化趋于稳定;尿酶、碱性磷酸酶、蔗糖酶、过氧化氢酶和多酚氧化酶与其他因子相关性相对较强,可以作为评价土壤质量的生物学指标;尿酶、淀粉酶、碱性磷酸酶、蔗糖酶、过氧化氢酶和纤维素酶活性随恢复年限而增加,多酚氧化酶则减少;土壤酶指数可以作为评价土壤质量的方法。

退耕草地演替过程中的碳储量变化

退耕草地演替的研究对了解现有退耕草地的变化趋势有重要意义,也可以为退耕地的植被恢复提供科学依据。本研究采用以空间代替时间的方法,对处于不同演替时间阶段退耕草地的土壤碳储量以及植被的地上部分与根系生物碳储量变化进行了研究,结果表明,退耕草地演替过程中,地上部分生物碳储量呈阶梯式上升趋势,演替初期地上部分生物碳储量先降后升,并在演替的22~32年,保持相对平稳,之后在演替的40~60年,达到第2个相对平稳的阶段。根系生物碳储量也呈分阶段的阶梯式上升趋势,但第1个相对平稳的阶段出现在演替的第12~28年,在演替的第32~60年出现第2个相对平稳的阶段。退耕草地的土壤碳储量在退耕演替的初期下降,且在演替的第1~12年一直小于农地,在演替的第15年之后,土壤碳储量逐步上升。在0~150 cm的不同土层中,土壤有机碳含量以0~15 cm最高,在演替的1~12年,各土层有机碳含量均小于农地,之后在演替的第15~60年,各土层土壤有机碳含量均随演替时间的增加有所增加,且0~50 cm表层土壤有机碳含量在演替第34~60年迅速积累,增幅较大。在演替初期,草地地上部分生物碳储量、根系生物碳储量和土壤碳储量较演替第1年均表现为下降...

Assessing the consequence of land use change on agricultural productivity in China

China's cultivated land has been undergoing dramatic changes along with its rapidly growing economy and population. The impacts of land use transformation on food production at the national scale, however, have been poorly understood due to the lack of detailed spatially explicit agricultural productivity information on cropland change and crop productivity. This study evaluates the effect of the cropland transformation on agricultural productivity by combining the land use data of China for the period of 1990-2000 from TM images and a satellite-based NPP (net primary production) model driven with NOAH/AVHRR data. The cropland area of China has a net increase of 2.79 Mha in the study period, which causes a slightly increased agricultural productivity (6.96 Mt C) at the national level. Although the newly cultivated lands compensated for the loss from urban expansion, but the contribution to production is insignificant because of the low productivity. The decrease in crop production resulting from urban expansion is about twice of that from abandonment of arable lands to forests and grasslands. The productivity of arable lands occupied by urban expansion was 80% higher than that of the newly cultivated lands in the regions with unfavorable natural conditions. Significance of cropland transformation impacts is spatially diverse with the differences in land use change intensity and land productivity across China. The increase in arable land area and yet decline in land quality may reduce the production potential and sustainability of China's agro-ecosystems. (C) 2008 Elsevier B.V. All rights reserved.

网络成瘾者心率变异性频谱特征及人格相关因素的研究

The aim of this research is to explore heart rate variability frequency field characteristics and personality influential factors of internet addicts by experimentation and questionnaire. Two studies were carried out: study 1 was to explore the pathological and mental mechanism of internet addicts by heart rate variability physiological index and EPQ and internet addiction scale. Study 2 was to compare the personality and mental characteristics between internet addicts and Non-addicts. The testees were 30 internet addict schoolboys who were in-patient and 43 schoolboys who accorded with qualification from grade 2 in senior high school and sophomore. It is found that: 1、 Internet addicts have obviously lower HFNU than Non-addicts， but have obviously higher LFNU and LF/HF ratio than Non-addicts. Internet addicts have dysfunction in their sympathetic and parasympathetic system; 2、 Internet addicts and Non-addicts have no significant difference in their EPQ except their lying point, but the nervous characteristics of EPQ of internet addicts have influence on their equipoise of parasympathetic system, that is to say when the score of nervous characteristics of EPQ become higher, equipoise of parasympathetic system become worse and worse. However the EPQ personality characteristics of non-addicts have no influence on their sympathetic and parasympathetic system. 3、 The extent of internet addiction of the internet addicts is independent of their equipoise of parasympathetic system, but non-addicts use internet more time, their equipoise of parasympathetic system become lower, there is the significant difference in the neurophysiology between internet addicts and non-addicts. That is to say internet environment is safe to most adolescent, they can make use of internet environment accurately, but internet addicts, their physiological and psychological level has changed to a certain, need to be treated.； 4、 Serious internet game addicts have the metal characteristics of low social support, low purpose in life and low adventure; 5、 The objective support、support utilization of social support questionnaire and sensation seeking characteristics have prognosticative function for internet addiction degree; 6、 Serious internet game addicts have the metal characteristics of low social support, low lying particularity, they are inclined to self abandonment. Serious internet game addicts of low N characteristic have high sensation seeking characteristic, and at the same E personality foundation, they also seek new stimulus with higher intension. There is a prompt that we should pay attention to internet addicts’ personality so that obtain better curative effect for internet addiction therapy.