土地利用变化对土壤有机碳的影响研究进展

土壤有机碳是陆地碳库的重要组成部分,也是当前全球碳循环和全球变化研究的热点。土地利用/覆被变化及土地管理变化通过影响土壤有机碳的储量和分布,进而影响温室气体排放和陆地生态系统的碳通量。研究土地利用变化影响下的土壤有机碳储量及其动态变化规律,有助于加深理解全球气候变化与土地利用变化之间的关系。在阅读国内外有关文献的基础上,分别从土地利用及其管理方式变化的角度,概括了土地利用变化对土壤有机碳的影响过程与机理;针对当前研究的两大类方法,即实验方法和模型方法,分类详细介绍了它们各自的特点以及存在的一些问题。在此基础上,提出今后土地利用变化对土壤有机碳影响研究的发展趋势。

AN INSIGHT ON DRIVERS OF LAND USE CHANGE AT REGIONAL SCALE

The studies of driving forces of regional land use change (LUC) are to reveal the real motivation behind the LUC and its interacting mechanism, so as to simulate and predict the process of LUC. Presently, studies rooting from different natural and socio-economic backgrounds and from different scales have deepened the people’s understanding and cognition to driving forces of regional LUC. Biophysical driving forces are relatively stable, and have the cumulating effects. Human driving forces are relatively active, and are main driving forces of short-term regional LUC. Existing regional LUC models can answer the three main problems: which contribution (why), which location (where) and what rate (when). But, regional land use system is defined as the self-organized system, usually affected by the cri- tical value area and sudden change, and controlled by different stages. To reduce the impact of critical threshold and break on land use system, the studies of LUC driving forces will aim at following priority areas: data linkage between remote sensing and no-remote sensing data; underlying driving force identification; driving factor quantification; driving factor scale dependence; and driving process integration simulation.

Soil pH Management across Spatially Variable Soils

Knowledge and management of soil pH, particularly soil acidity across spatially variable soils is important, although this is greatly ignored by farmers. The objective of the study was to evaluate in-field spatial variability of soil pH, and compare the efficiency of managing soil pH through site-specific method vs. uniform lime application. The study was conducted on three sites with study sites I and II （23°50＇ S; 29°40＇ E）, and study sites IIl （23°59＇ S; 28°52＇ E） adjacent to each other in the semi-arid regions of the Limpopo Province, South Africa. Soil samples were taken in four replicates from geo-referenced locations on a regular grid of 30 m. Soils were analyzed for pH, and SMP buffer pH. Soil maps were produced with Geographic Information System （GIS） software, and soil pH datasets were interpolated using a geostatistical tool of inverse distance weighing （IDW）. Soil pH in the fields varied from 3.93 to 7.00. An excess amount of lime as high as 30 t/ha under uniform lime application were recorded. These recommendations were in excess on field areas that needed little or no lime applications. Again, there was an under applications of lime as much as 35 t/ha for uniform liming applications. This under- and over-recommendations of lime based on average soil pH values suggests that uniform soil acidity correction and soil pH management strategy is not an appropriate strategy to be adopted in these fields with spatially variable soils. The field can be divided into lime application zones of （1） high rates of lime, （2） low rates of lime and （3） areas that requires no lime at all so that lime rates are applied per zone. A key to site-specific soil acidity correction with lime is to reach ideal soil pH for the crop in all parts of the field.

Paleoclimatic record from Chumbur-Kosa section in Sea of Azov region since Marine Isotope Stage 11

Abstract： Loess-paleosol sequences preserve records of climatic change during the Quaternary, which is important for paleoclimate study. In this study, a loess-palaeosol sequence from the Chumbur- Kosa （CK） site in the Sea of Azov region was investigated to reconstruct climatic variability during the Marine Isotope Stage （MIS）11- MIS 1, using proxies of grain size （GS）, magnetic susceptibility （xlf and Xfd（%））, carbonate content （CaCO3%） and soil color The results enabled formulation of a detailed description of the climatic characteristics related to each individual layer. The sequence indicates that the paleoclimate shifted progressively towards increasingly cooler, somewhat drier conditions. The CK section may thus be ideal for reconstructing climatie eondifions during the Middle and Late Pleistocene in the Sea of Azov region. However, the ）Of value of paleosol $2 in the CK profile indicates different characteristics from the other paleosol layers, dilution of carbonate resulting from carbonate leaching in L2 may be the main reason for the decrease in magnetic susceptibility. Furthermore, through simple analysis part of the environmental evolution process in the Sea of Azov region and Serbia during Middle and Late Pleistocene cycles. The climate cycle expressed by Xfd（%） and Xlf variations show similar patterns, with rapidly alternating cold and warm intervals. Nevertheless, although the two areas had different climatic regimes, geographical settings, and loess source areas, both exhibited similar climate change trends since the MIS 11.

Stakeholder Perspectives on Use,Trade,and Conservation of Medicinal Plants in the Rasuwa District of Central Nepal

People's livelihood in several Himalayan regions largely depends on collection,use,and trade of medicinal plants.Traditional use is generally not a problem,but commercial gathering of selected species to meet increasing national and international demand can result in over-exploitation.Sustainable management of medicinal plants requires a clear understanding of the respective roles,responsibilities and viewpoints of the various stakeholders involved.Through personal interviews and group discussions,this study aimed at investigating the views of two stakeholder groups on use,trade and conservation of medicinal plants in the Rasuwa district of Nepal.Local people and district and national organizations agreed that medicinal plants are collected for a combination of commercial and personal uses.Perceptions on market availability differed significantly:100 % of the respondents from district and national organizations saw markets as easily available,against only 36 % for local people.This could explain why medicinal plants were perceived by local people to contribute less to income generation than to livelihood improvement.Different viewpoints were also expressed concerning the status of medicinal plants in the district:81 % of the respondents from district and national organizationsconsidered that medicinal plants were threatened,compared to only 28 % for local people.Despite this disparity,both stakeholder groups agreed upon potential threats to medicinal plants:over-harvesting;habitat loss due to land-use change and deforestation;and over-grazing by livestock.Several challenges were identified regarding sustainable management of medicinal plants,such as ambiguous policies;lack of resources,information and infrastructures;habitat degradation;and over-exploitation.Despite these challenges,respondents agreed that the medicinal plants sector offers huge opportunities in the Rasuwa district,given resource availability,community awareness and motivation,and the priority given to the sector by governments and other agencies.Proper collaboration,communication and coordination among stakeholders are needed to grab these opportunities.