陕北不同恢复年限中国沙棘人工林土壤可溶性氮组分时空变化研究

Spatial Distribution Characteristics of Soil Soluble Nitrogen Component in Hippophae rhamnoides Plantation with Different Stand Ages in Loess Hilly Region

[目的]探究陕北黄土丘陵区退耕还林后不同林龄中国沙棘林可溶性氮组分累积的季节变化和垂直分布规律,为深入研究该区域不同恢复年限中国沙棘林的退耕效果评价和土壤氮库管理提供理论依据。[方法]以志丹县金丁镇不同恢复年限(5、15、20 a)中国沙棘人工林为研究对象,以荒草地为对照,采集0~10、10~20、20~30 cm土壤样品,分析土壤可溶性氮组分含量和比例的季节动态变化及土壤垂直分布的动态变化。[结果]随着恢复年限的延长,中国沙棘人工林均增加了土壤可溶性氮组分含量,对于土壤硝态氮和可溶性有机氮(SON)而言,20 a与5 a中国沙棘人工林间差异显著,荒草地与5 a中国沙棘林间无显著差异;土壤铵态氮在不同恢复年限间差异不显著。不同恢复年限中国沙棘林土壤硝态氮和SON变化趋势一致,均为20a中国沙棘林>15 a中国沙棘林>荒草地>5 a中国沙棘林,且均呈表聚现象。土壤铵态氮含量大小关系为15a中国沙棘林>20 a中国沙棘林>5 a中国沙棘林>荒草地,表层的铵态氮平均含量最低。土壤可溶性氮组分在不同土层间均差异不显著。土壤硝态氮表现为夏季最高,冬季或秋季最低;铵态氮表现为夏季或秋季最高,冬季最低;SON则为春冬季高于夏秋季。SON、硝态氮和铵态氮占可溶性总氮比例分别为80.3%、10.2%和9.5%。不同年限中国沙棘林SON占可溶性总氮比例为春冬季高于夏秋季,硝态氮和铵态氮大部分为夏秋季高于春冬季。[结论]在陕北黄土丘陵区,营造中国沙棘人工林可以有效提高土壤可溶性氮组分,随着林龄增加,土壤氮素累积效果越明显。

[Objective]To investigate the spatial distribution characteristics of soil soluble nitrogen component in Hippophae rhamnoides L.subsp.sinensis Rousi plantation with different stand ages in loess hilly region.[Methods]Based on the Hippophae rhamnoides plantation with three different stand ages of 5-yearold,15-year-old and 20-year-old were selected in Jinding Town of Zhidan County,soil samples were collected in 0-10 cm,10-20 cm and 20-30 cm soil layers,and seasonal dynamic variation of the proportion of soil soluble nitrogen component were analyzed.The grassland was treated as control.[Results]With the extension of the recovery years,the content of soil soluble nitrogen components in the Hippophae rhamnoides plantations increased.For soil nitrate nitrogen and soluble organic nitrogen(SON),there were significant differences between Hippophae rhamnoides plantations in 20 years and 5 years,while there was no significant difference between grassland and Hippophae rhamnoides forests in 5 years.There was no significant difference in soil ammonium nitrogen among different restoration years.The soil nitrate nitrogen and SON showed the same trend,with 20-year-old>15-year-old>grassland>5-year-old.For the ammonium nitrogen,soluble organic nitrogen in forests with 15-year-old was the largest,followed by 20-year-old,5-year-old,and grassland,and the average content of ammonium nitrogen in the surface layer was the lowest.There was no significant difference in soil soluble nitrogen components among different soil layers.Soil nitrate nitrogen was the highest in summer and the lowest in winter or autumn.Ammonium nitrogen was the highest in summer or autumn,and the lowest in winter.SON was higher in spring and winter than in summer and autumn.The proportion of SON,nitrate nitrogen and ammonium nitrogen in total soluble nitrogen was 80.3%,10.2%and 9.5%respectively.The proportion of SON in total soluble nitrogen of Hippophae rhamnoides forests with different years was higher in spring and winter than in summer and autumn,and most of nitrate nitrogen and ammonium nitrogen were higher in summer and autumn than in spring and winter.[Conclusion]In the loess hilly area of northern Shaanxi,Hippophae rhamnoides plantations can effectively improve soil soluble nitrogen components.With the increase of forest age,the soil nitrogen accumulation increases.