亚热带丘陵区集约化养猪场氨气近源沉降的土壤和植物氮素响应

The nitrogen in soil and plant tissues responding to ammonia deposition in the neighboring of an intensive pig farm in subtropical hilly area of China

选取中国亚热带丘陵区一集约化育肥猪场为研究对象,采用环形扩散管大气采样系统(DELTA),开展为期1 a养殖场500 m近源区大气氨浓度监测,采用双向交换模型,估算氨沉降量。采集养猪场近源区土壤、植株样品,探究大型集约化养殖场近源区土壤、植物氮素对氨沉降梯度的响应特征。结果表明:养猪场近源区土壤无机氮含量为2.3—32.4 mg·kg^(-1)(以铵态氮为主),随氨沉降量增加而增加。草本(白茅)盖度随氨沉降量增加而增加,500 m范围内增幅平均可达45.7%;灌木(黄荆)盖度随氨沉降量增加而减小,降幅平均为27.5%。植株叶片氮含量与氨沉降间关系不明显,灌木、苔藓叶片δ^(15)N值为-13‰—-2‰,且随氨沉降增加而减小。δ^(15)N可用于识别植物叶片氮素来源,与植株叶片总氮含量相比,植株叶片δ^(15)N对氨沉降具有更好的生物指示作用。

Background,aim,and scope China is widely recognized as the largest producer and consumer of pig.However,pig farming has led to significant ammonia(NH_(3))emissions,which have resulted in high NH_(3) deposition in the surrounding areas.This high level of NH_(3) deposition can cause adverse effects on natural and semi-natural ecosystems around the farms.In this paper,we aim to investigate the impact of NH_(3) deposition on soil and plant nitrogen around an intensive fattening pig farm located in the subtropical hilly area of China.Materials and methods Monthly monitoring of NH_(3) concentrations within 500 m of the pig farm was conducted between Jul.2018 and Jun.2019 using DELTA(Denuder for Long-Term Atmospheric sampling)systems.NH_(3) deposition was calculated using a bidirectional NH_(3) exchange model.Soil and plant samples were collected along the farm to explore the response characteristics of soil and plant nitrogen to NH_(3) deposition gradient in the neighborhood of the farm.Results The soil inorganic nitrogen content,mainly ammonium,significantly increased with increasing NH_(3) deposition in the neighborhood of the pig farm(2.3-32.4 mg·kg^(−1)).With increasing NH_(3) deposition,the percentage cover of grass species Imperata cylindrica(L.)Beauv increased significantly(by 45.7%on average),while that of the bush species Vitex negundo L.decreased significantly(by 27.5%on average).Bush and moss leafδ^(15)N values(−13‰-−2‰)were negatively correlated with NH_(3) deposition,while no clear relationship was found between plant leaf nitrogen content and NH_(3) deposition.Compared to leaf nitrogen content,leafδ^(15)N values were found to be a better bioindicator for NH_(3) deposition.Discussion Our results indicated that NH_(3) deposition caused by intensive pig farms can induce the increase of soil inorganic nitrogen content in the neighborhood of the farm.The high soil inorganic nitrogen,especially ammonium nitrogen,will cause soil acidification and increase of soil greenhouse gases emissions(e.g.,N2O).The changed plant cover and leaf nitrogen content at different distance from the farm means that the NH_(3) deposition might have changed plant biodiversity.Thus,it is necessary to take measures to reduce NH_(3) emissions from intensive animal farms.Conclusions This study demonstrates that there was a high level of NH_(3) deposition in the neighborhood of an intensive pig farm,and that this has significant impacts on soil inorganic nitrogen content and plant cover.Recommendations and perspectives The study recommends that the regions around intensive animal farms with the natural nitrogen deposition gradient be ideal places for studying the effects of nitrogen deposition.