The effects of using N-fertilizers in soil on karst carbon sink in karst system

In previous research,it has been shown that the carbon flux of atmospheric CO2 caused by terres-trial carbonate weathering has a similar magnitude with that of the global forests.However,the dissolution of carbonate rocks by nitric acid due to the overuse of N-fertilizers in agricultural areas will greatly weaken the karst carbon sinks,which proportion may up to 7%-38%.The moderate use of N-fertilizers will not only increase the crop yield,but also decrease the ratio of C/N in soil,enhance the microbial activities in soil,and promote the decomposition of organic matters,thereby increasing the CO2 concentration in soil and the dissolution rate of carbonate rocks under subsoil.Therefore,it should be analyzed from two aspects to the effects of using N-fertilizers in soil on karst carbon sink in karst system.Meanwhile,the soil formed by carbonate weathering in karst areas has higher pH and base saturation,which will has a stronger buffer ac-tion to H+.This may be one of the reasons why the DIC in rivers and the Ca2+,Mg2+,etc.are not conser-vative in natural condition.In this view,the quantity of carbonate rocks dissolved by nitric acid may be over-estimated using end element method.In addition,how much nutric acid caused by the nitrification in the soil environment of karst area can be used to dissolve the carbonate rocks and then has an effect on karst carbon sinks still needs to be studied futher.Accordingly,it is necessary to obj ectively evaluate the effect of N-fer-tilizer using in soil on karst carbon sink in karst system by considering the characteristics of soil and biogeo-chemical prosess of rivers and conprehensively studing the N-fertilizer using level,soil nitrification and the dissolution of carbonate rocks under subsoil and karst carbon sink process under the influence of them.And we can find the techical method of improving karst carbon sink effect through the reasearch on moderate u-sing of N-fertilizer how to promote the karst carbon cycle process.