岩溶系统中土壤氮肥施用对岩溶碳汇的影响

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

有资料显示陆地碳酸盐岩风化消耗大气CO2的碳通量与世界森林碳汇通量量级相当。但农业地区过量施用氮肥形成的硝酸对碳酸盐岩的溶解会减弱岩溶碳汇效应,其量可达到7%~38%,而适量施用氮肥在增加农作物产量的同时,能降低土壤C/N比,增加土壤微生物活性,促进有机物料分解,从而提高土壤CO2浓度,提高土下碳酸盐岩的溶解速率。因此,要从两方面分析岩溶系统中土壤氮肥施用对岩溶碳汇效应的影响。同时,岩溶区碳酸盐岩风化形成的土壤具有较高的pH值及盐基饱和度,对H＋有较强的缓冲作用,可能是导致自然条件下,河流中溶解无机碳（DIC）与水体中钙、镁等离子并不守恒的原因之一,因此,运用端元法可能过高估算了硝酸对碳酸盐岩的溶解量。岩溶区土壤环境中硝化作用产生的硝酸到底多少能对碳酸盐岩产生溶蚀,并影响到岩溶碳汇效应还有待研究。应结合土壤本身的特性及河流生物地球化学过程,综合研究不同施氮水平、土壤硝化产酸及其影响下的土下碳酸盐岩溶解及碳汇效应过程,客观评价岩溶区土壤氮肥施用对岩溶碳汇的影响,并寻求适宜氮肥施用量及促进岩溶碳循环,提高岩溶碳汇效应的技术方法。

In previous research,it has been shown that the carbon flux of atmospheric CO2 caused by terrestrial 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 action to H＋.This may be one of the reasons why the DIC in rivers and the Ca2＋,Mg2＋,etc.are not conservative in natural condition.In this view,the quantity of carbonate rocks dissolved by nitric acid may be overestimated 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 objectively evaluate the effect of N-fertilizer using in soil on karst carbon sink in karst system by considering the characteristics of soil and biogeochemical 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 using of N-fertilizer how to promote the karst carbon cycle process.