草甸草原土壤与植物系统自然丰度氮稳定同位素的年际变化及其指示作用

Interannual variations in natural abundance of nitrogen stable isotopes in soil and plant and their implications in a meadow steppe

氮是陆地生态系统生产力的首要限制性养分,利用自然丰度δ^(15)N(^(15)N/^(14)N)可以有效指示生态系统氮循环过程。本试验研究了内蒙古草甸草原土壤与植物系统自然丰度δ^(15)N、土壤净氮矿化潜势的年际变化。结果表明:2017-2020年,土壤NO_(3)^(-)-N含量(9.83~^(14).79 mg·kg^(-1))均显著高于NH_(4)^(+)-N含量(3.92~5.00 mg·kg^(-1));土壤NH_(4)^(+)的δ^(15)N值(13.3‰~18.3‰)显著高于NO_(3)^(-)的δ^(15)N值(3.76‰~6.^(14)‰),土壤NO_(3)^(-)的δ^(15)N值与土壤NO_(3)^(-)含量呈显著负相关;干旱年NH_(4)^(+)的δ^(15)N值相对较高,降水较高或较低年NO_(3)^(-)的δ^(15)N值显著降低。干旱年土壤净氮矿化速率、净氨化速率显著高于湿润年,而土壤硝化速率与年降水量无显著相关性。植物δ^(15)N值与土壤δ^(15)N值无显著相关性,但与植物N含量呈显著负相关;豆科植物与非豆科植物δ^(15)N值、N含量均呈显著正相关,在一定程度上表明豆科植物对非豆科植物的N吸收具有促进作用。研究结果可为草原土壤-植物系统氮循环过程及其对降水变化的响应提供数据支撑。

Nitrogen is the most limiting nutrient for ecosystems.The natural abundance ofδ15N(15N/14N)can effi-ciently indicate ecosystem nitrogen cycling processes.We investigated the interannual variations in natural abun-dance ofδ^(15)N in soil-plant system and soil net nitrogen mineralization in a meadow steppe of Inner Mongolia.Results across the four sampling years(2017-2020)showed that the content of soil NO_(3)^(-)-N(9.8_(3)^(-)14.79 mg·kg^(-1))was significantly higher than that of NH_(4)^(+)-N(3.92-5.00 mg·kg^(-1))and thatδ15N value of soil NH_(4)^(+)(13.3‰-18.3‰)was significantly higher than that of NO_(3)^(-)(3.76‰-6.14‰).Theδ^(15)N value of soil NO_(3)^(-)was negatively correlated with soil NO_(3)^(-)content.Theδ^(15)N value of soil NH_(4)^(+)was relatively higher in the dry years,while theδ15N value of soil NO_(3)^(-)significantly decreased in the wetter and drier years.Soil net mineralization and ammonification rates were significantly higher in the dry years than that of the wet years,while soil nitrification rates showed no correlation with annual precipitation.Theδ^(15)N values of plants were not related to that of soils,but negatively correlated with plant nitrogen content.Bothδ^(15)N values and nitrogen contents were significantly and positively correlated between the leguminous and non-leguminous plants,suggesting that legume could facilitate nitrogen uptake of non-leguminous plants.These results could provide supporting data for nitrogen cycling and their responses to changes in precipitation in grassland soil-plant systems.