氮水添加对油蒿群落2种优势植物叶片氮磷化学计量比的影响

Effects of Nitrogen and Water Addition on Leaf N∶P Stoichiometry of the Two Dominant Species in Artemisia ordosica Community

【目的】在毛乌素沙地西南缘开展了为期3年(2015—2017)的氮素和水分添加控制试验,探究氮素和水分增加对毛乌素沙地油蒿群落2种优势植物油蒿和赖草叶片N∶P的影响及作用途径,为预测未来全球环境变化下荒漠生态系统养分循环以及植物生长的养分限制状况提供理论依据和案例支持。【方法】连续3年(2015—2017)在毛乌素沙地西南缘宁夏盐池采用野外控制试验,设计3个氮添加水平(N0∶0 kg·hm-2a-1;N10:10 kg·hm-2a-1;N60:60 kg·hm-2a-1)和3个水添加水平(W0:自然降水量;W20:较自然降水量增加20%;W40:较自然降水量增加40%)的2个因子9个交互处理的随机区组试验。使用双因素方差分析检测氮素和水分增加对土壤含水量、无机氮、速效磷、土壤Ca2+含量以及油蒿和赖草叶片N∶P的影响,运用结构方程模型分析土壤速效养分(无机氮、速效磷)、土壤含水量、土壤Ca2+含量与植物叶片N∶P间的关系。【结果】氮添加显著增加了土壤无机氮含量及油蒿和赖草叶片的N∶P,但对土壤速效磷和土壤Ca2+含量无显著影响;水添加对土壤无机氮、速效磷含量和油蒿叶片N∶P均无显著影响,但降低了赖草叶片N∶P和浅层土壤Ca2+含量。【结论】氮添加缓解了油蒿和赖草的N限制,但同时也加剧了P限制。水添加通过改变浅层土壤(0~20 cm)Ca2+含量,降低了2种植物叶片N∶P,一定程度上缓解了这2种植物的P限制。

【Objective】A three-year(2015-2017)nitrogen and water addition control experiment was conducted in the southwestern margin of the Mu Us sandy land to investigate the effects and action pathways of increased nitrogen and moisture on the two dominant plant species(Artemisia ordosica and Leymus secalinus).This study was aimed to provide theoretical basis and case support for predicting nutrient cycling in desert ecosystems and nutrient limiting conditions for plant growth under future global environmental changes.【Method】For three successive years(2015-2017),a field control experiments with 2 factors and 9 interactive treatments were conducted in Ningxia Yanchi,Southwestern edge of Mu Us sandy land.Three nitrogen addition levels were N0(0 kg·hm-2a-1),N10(10 kg·hm-2a-1),and N60(60 kg·hm-2a-1).Three water addition levels were W0(natural precipitation),W20(20%increase over natural precipitation),and W40(40%increase over natural precipitation).We performed two-way ANOVAs to examine the responses of soil moisture,soil inorganic nitrogen and soil available phosphorus,soil Ca2+content,and the leaf N∶P of A.ordosica and L.secalinus to nitrogen and water addition.Then we used structural equation modeling to test their relationships.【Result】Nitrogen addition significantly increased soil inorganic nitrogen and the leaf N∶P of A.ordosica and L.secalinus,while no significant effects on soil available phosphorus and soil Ca2+content were detected.Water addition decreased the leaf N∶P of L.secalinus and soil Ca2+content,but had no significant effect on soil inorganic nitrogen,soil available phosphorus,and the leaf N∶P of A.ordosica.【Conclusion】Nitrogen addition relieved the N limitation,but exacerbated P limitation.Water addition reduced the leaf N∶P by changing soil(0-20 cm)Ca2+content,therefore P limitation has been alleviated to some extents.