[Application of stable isotope techniques in soil food web research]. / ç¨³å®šåŒä½ç´ æŠ€æœ¯åœ¨åœŸå£¤é£Ÿç‰©ç½‘ç ”ç©¶ä¸­çš„åº”ç”¨.

Stable isotope technique is important for understanding the structure and function of soil food web, which is considered as a belowground black box. We reviewed typical application cases of stable isotope techniques in the research of soil food webs, including to determine food sources and feeding preferences of soil fauna by using isotopes, and to analyze the trophic structure of soil food webs through isotope fractionation effects during the process of feeding and nutrient sequestration by soil fauna. Additionally, stable isotope techniques could reveal the role of soil biota at different trophic levels within soil food web in ecosystem matter and energy flow, which favored to carry out accurate and efficient research on the contribution of soil food webs to soil carbon and nitrogen cycling process and the corresponding influence mechanism. We further put forward the limitations of current stable isotope techniques and the future development directions.

Biological characterization and regulation of soil health.

How to determine the soil health status effectively is the basic issue to realize the agriculture green development. In the existing soil health assessment system, the importance of soil organi-sms in the maintenance of soil health is rarely considered. From the perspective of soil biological health, we discussed the connotation of soil health, and summarized the biological indicators of soil health, including soil microorganisms, soil enzyme activity, soil micro-food web and earthworm. Based on the above-mentioned indicators, the regulation approaches were elaborated from the aspects of crop and soil management practices. In addition, the future research on soil biological health was prospected. The main aim of this study is to enhance the understanding of scientists and decision makers on the maintenance of soil biological health, and to give full consideration of the important role of soil organisms in ecosystem services.

[Effects of conservation tillage on the composition of soil exchangeable base].

Taking the soil in Zhangwu County of Liaoning Province as test object, a comparative study was made to understand the composition of soil exchangeable base under traditional tillage and 6-year conservation tillage (no-tillage plus straw mulch). Comparing with traditional tillage, conservation tillage increased the total amount of exchangeable base (SEB) and the contents of exchangeable K, Ca, and Mg in top (0-15 cm) soil, suggesting its positive effect in increasing soil nutrient holding capacity and buffering ability. This effect had a close relationship with the changes of soil organic matter and clay contents, according to correlation analysis. In addition, the K/SEB and Ca/Mg ratios were higher, while the (Ca+Mg)/SEB, Ca/K, and Mg/K ratios were lower under conservation tillage than under traditional tillage, illustrating that the effects of conservation tillage on soil exchangeable base were mainly presented in the relative enrichment of soil exchangeable Ca and K, especially K. Conservation tillage increased the stratification ratio (0-5 cm/5-15 cm and 0-5 cm/15-30 cm) of soil exchangeable K, Ca, and Mg, and SEB, suggesting the increase of the vertical variability of SEB in plough layer.

[Distribution characteristics of soil phosphorus in maize belt farmlands of Northeast China].

The study on the vertical distribution and latitudinal differentiation of soil total and organic phosphorus (P) down to 100 cm depth in maize belt farmlands of Northeast China showed that in Hailun and Harbin of Heilongjiang Province, Gongzhuling of Jilin Province, and Dashiqiao of Liaoning Province, soil total P decreased with soil depth, being significant higher in 0-40 cm than in 40-100 cm (P < 0.01). In Dehui of Jilin Province and in Changtu and Shenyang of Liaoning Province, soil total P was relatively lower in 40-60 cm, but no significant difference was observed among different layers. Soil organic P was significantly higher in 0-20 cm than below 20 cm (P < 0.05). Soil total and organic P increased with increasing latitude (P < 0.05). The differences in climate conditions and soil types were considered as the main reasons induced the latitudinal differentiation of soil P. Soil total and organic P were significantly correlated with soil organic carbon (P < 0.01), indicating that soil organic matter was one of the most important factors affecting the soil P content and its distribution in maize belt farmlands of Northeast China.

[Profile distribution of exchangeable calcium and magnesium in an aquic brown soil as affected by land use type].

A comparative study was made on the profile distribution of exchangeable Ca and Mg and Ca/Mg ratio at the depth of 0-150 cm in an aquic brown soil under four land use patterns, i. e., paddy field, maize field, fallow field, and woodland. The results showed that less difference was observed in the soil exchangeable Ca content and storage among different land use patterns. For soil exchangeable Mg, it was significantly higher in woodland than in paddy field, and its storage was in the sequence of woodland > maize field > fallow field > paddy field (P <0.05). The exchangeable Ca/Mg ratio tended to decrease with soil depth, and was significantly lower in paddy field than in other three land use patterns in the soil layers below 40 cm (P <0.05). The preferential retention of Mg in soil ecosystem, soil management practices, and plant characteristics, e. g., biomass cycling rate, biomass above- and below-ground allocation, root distribution, and maximum rooting depth) might play important roles in shaping soil exchangeable Ca and Mg profiles and in reconstructing soil exchangeable Ca and Mg pools.

Effect of free-air CO2 enrichment on nematode communities in a Chinese farmland ecosystem.

At a rice-wheat rotational free-air CO2 enrichment( FACE) platform, the effect of elevated atmospheric CO2 on soil nematode communities in a farmland ecosystem was studied. Wheat plots were exposed to elevated atmospheric CO2 (ambient 370 microl/L + 200 microl/L). 32 families and 40 genera of nematode were observed in soil suspensions during the study period. Under FACE treatment, the numbers of total nematodes, bacterivores and fungivores exhibited an increasing trend. Because of the seasonal variation of soil temperature and moisture, the effect of elevated atmospheric CO2 on soil nematodes was only observed under favorable conditions. The response of nematode communities to elevated atmospheric CO2 may indicate the change of soil food web.