城市森林土壤有机碳密度及影响因子变化研究

Study on changes of soil organic carbon density and influencing factors in urban forest

以上海市阔叶混交林、杉林、软阔林和硬阔林土壤为研究对象,分析2013年不同森林土壤有机碳密度(SOCD),并以其为本底值探讨不同森林植被经历4年自然生长后SOCD的变化特征,讨论了土壤容重、电导率(EC)、pH、全氮、全磷、C/N对其的影响,为上海市森林资源合理配置提供建议。结果表明:(1)2013年,上海城市森林的SOCD由大到小的排列顺序为:杉林>硬阔林>软阔林>阔叶混交林。相比2013年,2017年上海市阔叶混交林、杉林、软阔林和硬阔林的SOCD均降低,年均降低速率为0.59 t/(hm^(2)·a)、6.81 t/(hm^(2)·a)、3.89 t/(hm^(2)·a)和6.95 t/(hm^(2)·a)。上海市森林土壤有机碳密度年降低速率较大,且0—10 cm和0—30 cm的SOCD在0—100 cm的贡献率较低。(2)不同时期不同林型的SOCD影响因子不同。2013年,阔叶混交林、软阔林、硬阔林的SOCD受土壤容重、EC、pH、全氮、全磷、C/N影响不显著(P>0.05),杉林SOCD受全氮影响较显著(P<0.05)。2017年,阔叶混交林SOCD主要受凋落物影响,杉林的主要影响因子为容重和全氮,硬阔林的SOCD主要受C/N影响。软阔林受土壤容重、EC、pH、全氮、全磷、C/N影响不显著(P>0.05)。(3)结合土壤有机碳密度本底值以及年均降低速率,上海市在森林配置管理时可优先种植阔叶混交林和软阔林,并应通过添加氮肥、疏松森林土壤等措施改良土壤性状。研究为上海市林分管理在资源合理配置方面提供数据支撑,也为城市森林土壤固碳能力评价研究提供重要参考。

Soil samples were collected from broad-leaved mixed forests,fir forest,softwood forest and hardwood forest in Shanghai in 2013 and 2017 to investigate the changes of soil organic carbon density(SOCD).Furthermore,the variation of SOCD after 4 years of natural growth in different forest vegetations was analyzed,and the effects of soil bulk density,EC,pH,total nitrogen,total phosphorus and C/N on the SOCD were studied,which could provide recommendations for the rational allocation of forest resources in Shanghai.The results showed that:(1)In 2013 year,the order of SOCD was:fir forest>hard broad forest>soft broad forest>broad-leaved mixed forest.The SOCD of the four urban forests all decreased from 2013 to 2017 in Shanghai,and the average annual decrease rate was 0.59 t/(hm^(2)·a),6.81 t/(hm^(2)·a),3.89 t/(hm^(2)·a)and 6.95 t/(hm^(2)·a),respectively.The annual decrease rate of soil organic carbon density in Shanghai was relatively high,while the contribution rate of 0-10 cm and 0-30 cm SOCD possessed relatively lower contribution rate in 0-100 cm.The influencing factors of SOCD in different forest types were discrepancy in different periods.In 2013 year,the SOCD of broad-leaved mixed forest,soft broad-leaved forest and hard broad-leaved forest wss not significantly affected by soil bulk density,EC,pH,total nitrogen,total phosphorus or C/N(P>0.05),while that of China fir forest was significantly influenced by total nitrogen(P<0.05).In 2017 year,the SOCD of broad-leaved mixed forest was mainly affected by litter.The main factors influencing SOCD of China fir forest were bulk density and total nitrogen,and the SOCD of hard broad-leaved forest was mainly affected by C/N.Soft broad-leaved forest was not significantly affected by soil bulk density,EC,pH,total nitrogen,total phosphorus or C/N(P>0.05).(3)Considering both the initial SOCD and the annual average decrease rate,the broad-leaved mixed forest and the soft broad-leaved forest were suggested as precedence plant preferentially in the forest land allocation management in Shanghai.These artificial forests can be maintained by applying nitrogen fertilizer and loosing soil texture.This study provides data support for the rational allocation of forest resources in Shanghai,and has implications for the evaluation of urban forest soil carbon sink function.