冻融循环期高寒草原典型物种紫花针茅氮吸收策略

Nitrogen absorption strategy of Stipa purpurea, a typical species in alpine grassland during freeze-thaw cycle

氮(N)是高山和极地生态系统重要的限制性生长因子。目前对冻土区植物N利用机制的研究主要集中于完全融化期,而冻融循环期植物N吸收策略仍存在不确定性。以高寒紫花针茅为研究对象,分别在冻结期(晚秋)和融化期(早春)采用同位素示踪技术,分析植物对(^(15)NH_(4))_(2)SO_(4)和Na^(15)NO_(3)的吸收量与偏好动态变化。研究结果显示冻结期紫花针茅冠层生长已停滞,融化期冠层尚未返青,但根系和立枯均可以吸收同化^(15)N,具备吸收养分的需求。融化期紫花针茅^(15)N在标记21天后^(15)N-NH^(+)_(4)和^(15)N-NO^(-)_(3)的总回收率分别为4.44%和6.91%,而冻结期紫花针茅在^(15)N标记21天后^(15)N-NH^(+)_(4)和^(15)N-NO^(-)_(3)的总回收率分别为8.65%和3.55%。融化前期紫花针茅总^(15)N回收率整体表现为^(15)N-NH^(+)_(4)高于^(15)N-NO^(-)_(3),而融化后期^(15)N-NH^(+)_(4)和^(15)N-NO^(-)_(3)回收率差异不显著或^(15)N-NO^(-)_(3)略高。冻结期全程紫花针茅^(15)N-NH^(+)_(4)回收率均高于^(15)N-NO^(-)_(3)回收率。研究补充了高寒冻土区植物在非生长季的养分吸收数据,为全面理解冻土区植物N营养策略及其对未来气候变化的响应提供科学依据。

Nitrogen is an important limiting growth factor in alpine and polar ecosystems.At present,the research on the mechanism of plant N utilization in permafrost area mainly focuses on the complete thawing period,while the strategy of plant N absorption in the freeze-thaw cycle is still uncertain.In this study,the absorption and preference of plants for(^(15)NH_(4))_(2)SO_(4)and Na^(15)NO_(3)were analyzed by isotope tracer technology in freezing period(late autumn)and thawing period(early spring).The results showed that the growth of Stipa purpurea canopy had stagnated in the freezing period,and its canopy had not turned green in the thawing period,but the root system and standing dry could absorb and assimilate^(15)N,which had the need to absorb nutrients.The total recoveries of^(15)N-NH^(+)_(4)and^(15)N-NO^(-)_(3)in thawing stage were 4.44%and 6.91%respectively after 21 days of^(15)N labeling,while the total recoveries of^(15)N-NH^(+)_(4)and^(15)N-NO^(-)_(3)in freezing stage were 8.65%and 3.55%,respectively.In the early stage of thawing,the overall recovery of^(15)N-NH^(+)_(4)was higher than^(15)N-NO^(-)_(3),but in the later thawing stage of thawing,the recovery of^(15)N-NH^(+)_(4)and^(15)N-NO^(-)_(3)was not significant or^(15)N-NO^(-)_(3)was slightly higher.The recovery rate of^(15)N-NH^(+)_(4)was higher than that of^(15)N-NO^(-)_(3)in the whole freezing period.This study supplements the nutrient absorption data of plants in the non-growing season in the alpine permafrost region,and provides a scientific basis for a comprehensive understanding of plant N nutrition strategy in the permafrost region and its response to future climate change.