黄土丘陵区几种退耕还林地土壤固存碳氮效应

探讨了黄土丘陵区退耕10a和30a的柠条、刺槐、油松及侧柏林地0～60cm不同土层有机碳、氮数量和分布的变化特征。结果表明:相比坡耕地,退耕还林10a后,仅侧柏与油松林地各土层有机碳、氮含量和密度显著提升。退耕还林30a与10a相比,各土层有机碳含量增幅表现为侧柏>油松>刺槐>柠条,总体0～60cm土层碳固存速率分别达到1.06、0.71、0.43、0.36mgC·hm-2·a-1;氮固存速率以刺槐最高,达到0.051mgN·hm-·2a-1,其他还林地固存氮速率接近,为0.014～0.026mgN·hm-·2a-1。30a还林有机碳的增加主要来自0～20cm土层,平均贡献达51.9%,而全氮增加除刺槐林地外,主要来自40～60cm土层,平均贡献达42.5%。各还林地C/N仅在0～20cm表层均有显著提高,但有机碳与氮均表现出显著的回归相关性。综上,长期退耕还林地能够固存碳氮,且以侧柏林地提升有机碳库较佳,而刺槐林地提升氮库较好。

Soil Carbon and Nitrogen Sequestration Under Several Different Forest Lands Converted by Farmland in Loess Hilly Area

This research was conducted to determine the change of soil organic carbon and nitrogen in 0～60 cm soil layers under four types forested lands:Caragana,robinia,Chinese pine and orientalis,which has been converted by farmland for 10 years and 30 years in loess hilly area.The results showed that,compared with sloped farmland,either content or density of soil organic carbon and nitrogen in different soil layers were significantly increased in Chinese pine and orientalis forest land after 10 years forestation.Compared with 10 years forestation,the soil organic carbon and nitrogen was further increased after 30 years forestation,with the order of organic carbon:orientalis>Chinese pine>robinia>caragana,and that organic carbon sequestration rate(0～60 cm soil layers)reached 1.06,0.71,0.43,0.36 mgC·hm-2·a-1,respectively.In contrast,the rate of nitrogen sequestration was the highest by 0.051 mgN·hm-2·a-1 under planting robinia,and was not significantly different among other forest lands by 0.014～0.026 mgN·hm-2·a-1.After the 30 years forestation,the soil organic carbon increased mainly from 0～20 cm soil layer with average contribution ratio of 51.9% under all forest land,and the soil nitrogen increased mainly from 40～ 60 cm deep soil layer with average contribution ratio of 42.5% in all forest land except for robinia.The ratio of C/N also increased in 0～20 cm soil layer under different forest lands.There was significant regression correlation between soil organic carbon and nitrogen.In summary,conversion of cropland to forest could sequestrate carbon and nitrogen in soil,from which,buckthorn and robinia were a better to improve soil organic carbon pool and soil nitrogen pool,respectively.