氮磷添加对互花米草-土壤系统碳分配的影响

Effects of Nitrogen and Phosphorus Addition on Photosynthesized Carbon Allocation in Spartina alterniflora-Soil System

采用13C脉冲标记方法分析不同氮(N)、磷(P)添加水平下互花米草(Spartina alterniflora)植株及根系土壤有机碳δC13含量变化,比较不同N、P添加水平对光合碳分配和固定的差异,探讨N、P添加对光合碳在互花米草-土壤系统分配和固定的影响。结果表明第4次脉冲标记后各处理组各组分13C丰度均明显提高,除NP1处理外其他处理13C丰度均呈现茎、叶、根、根际土壤和土体递减的规律,与对照组(CK)变化一致。各处理组13C固定总量分别呈持续增加趋势,但均低于CK组,NP添加处理13C平均固定量大于单独添加N或P处理。在植物发育过程中,光合碳在互花米草地上部分(叶、茎)分配比例逐渐减小,地下部分(根、根际土壤和土体)分配比例逐渐增大,土壤中有机碳13C发生富集;且随着植物的发育,各处理组间互花米草-土壤系统各组分13C分配比例差异越来越小,趋于一致。N添加组根际土壤和土体13C分配比例随着N添加水平的增加而增加,说明施N能促进光合碳向土壤转移。P添加组在中等P水平(P2)下,植物光合碳地下部分分配比例最高,有利于光合碳向地下转移。NP添加组在中等NP配施水平(NP2)下,地下部分13C分配比例最高,根际土壤和土体13C分配比例随NP添加水平的增加而增加。N、P添加水平及营养盐类型能改变光合碳在互花米草-土壤系统的分配,表明富营养化作用对盐沼生态系统碳循环具有显著生态效应。

The changes of 13C content in 13C pulse-labeled Spartina alterniflora plants and root soil organic carbon were analyzed under different levels of nitrogen(N)and phosphorus(P). The effects of N and P addition levels on the distribution and fixation of photosynthetic carbon in S. alterniflora-soil system were studied. The results show that the abundance of 13C in each treatment group was significantly increased after four pulse marks. Except for the treatment of NP1,the abundance of 13C showed a decreasing trend in the order of stem,leaf,root,rhizosphere soil and soil,which was consistent with the control group(CK). The total amount of 13C fixed in each treatment group show a trend of continuous increase,but it was lower than that of the control group. The average fixed 13C amount of NP treatment was higher than that of N or P treatment alone. During the development of plants,the proportion of photosynthetic carbon in the aboveground gradually decreased while the proportion of underground gradually increased,and the accumulation of organic carbon 13C in soil was enhanced. With the development of plants,the differences in the distribution of 13C in each part of S. alterniflora-soil system became similar and tend to be consistent. In the N-added group,the allocation ratio of carbon in rhizosphere soil and soil increased with the increase of N addition level,indicating that N application could promote the transfer of photosynthetic carbon to soil. In the P-added group,the highest underground allocation ratio of photosynthetic carbon was observed in the medium level of P addition treatment(P2),which was conducive to the underground transfer of photosynthetic carbon. In the NP-added group,the aboveground distribution ratio was the highest at medium NP level(NP2),and the distribution ratio of rhizosphere soil and soil increased with the increase of NP addition. The addition levels of N and P and types of nutrients can change the distribution of photosynthetic carbon in S. alterniflora-soil system,indicating that eutrophication had significant ecological effects on the carbon cycle in salt marsh ecosystem.