不同碳输入方式对沿海防护林土壤氮库的影响

为探究凋落物和根系在滨海沙地人工林土壤氮循环中所扮演的角色,设置去除凋落物、切断根系、对照3种处理,分析3种典型沿海防护林(尾巨桉、纹荚相思、木麻黄)土壤氮素对不同碳输入的响应。结果表明：滨海沙地土壤矿质氮含量(2.91－4.49 mg?kg－1)远低于内陆森林土壤；3种人工林土壤矿质氮含量表现为纹荚相思>木麻黄>尾巨桉,其中纹荚相思与尾巨桉土壤矿质氮含量差异显著( P<0.05)；不同树种土壤硝态氮( NO－3－N)含量存在显著差异,表现为纹荚相思>木麻黄>尾巨桉。树种对切断根系或去除凋落物的响应不一致,切断根系后纹荚相思和木麻黄土壤NO－3－N含量显著高于对照,对铵态氮( NH＋4－N )含量影响不显著；切断根系和去除凋落物处理后土壤硝化作用均增强,对尾巨桉的影响达显著水平( P<0.05)；切断根系和去除凋落物均显著降低尾巨桉和纹荚相思土壤微生物量氮( MBN)含量,对土壤可溶性有机氮( DON)的影响与之相反。土壤NO－3－N与土壤MBN之间存在极显著的负相关关系( r＝－0.671, P<0.01),与土壤DON呈极显著正相关( r＝0.900, P<0.01),土壤DOC与NO－3－N、 NH＋4－N之间分别存在显著的负相关( r＝－0.413, P<0.05)和极显著的正相关关系( r＝0.461, P<0.01)。

Effects of different carbon input methods on soil nitrogen pool of coastal shelter forest

Litter removal, root cut and control were employed to examine the effects of organic matter input on soil nitrogen in three different plantations (Eucalyptus urophylla×E. grandis, Acacia aulacocarpa and Casuarina equisetifolia) in a sandy coastal plain area. The results showed that the content of mineral nitrogen in coastal sandy land was between 2.91 and 4.49 mg?kg-1 and much lower than that in inland forest soil. The order of soil mineral nitrogen content was Acacia aulacocarpa> Casuarina equisetifolia>Eucalyptus urophylla×E. grandis. There were significant differences in the content of nitrate nitrogen in the soil of different tree species and showed that Acacia aulacocarpa>Casuarina equisetifolia>Eucalyptus urophylla×E. grandis. The response of tree species to root or litter removal was varied significantly. After root cut, the content of nitrate nitrogen in soil was significantly higher than that of control, while the effect of the content of ammonium nitrogen was insignificant. At the same time, the soil nitrification in three plantations was enhanced after root cut or litter removal and it had a significant impact on Eucalyptus urophylla × E. grandis ( P<0.05) . Additionally, the content of MBN in Eucalyptus urophylla×E. grandis and Acacia aulacocarpa had a significant decrease after litter removed or root cut and the contents of DON had a significant increase. Correlation analysis suggested that there was a significant negative relationship between the soil nitrate nitrogen and MBN (r=-0.671, P<0.01), while there was a significant positive relationship between the soil nitrate nitrogen and DON( r=0.900, P<0.01) . DOC concentrations were negatively correlated with nitrate nitrogen ( r=-0.413, P<0.05) and positively correlated with ammonium nitrogen( r=0.461, P<0.01) , respectively.