水杉人工林细根和粗根碳氮磷计量特征对N添加的响应

Response of C,N,P Stoichiometry of Fine and Coarse Roots of Metasequoia glyptostroboides Plantation to Nitrogen Addition

[目的]研究水杉细根和粗根碳(C)、氮(N)、磷(P)计量特征对N添加的响应,揭示细根和粗根N、P养分分配格局的变化,为科学认识水杉对N沉降的适应策略提供参考。[方法]在江苏省东台市林场水杉人工林进行长期N添加试验,设置对照(CK,0 kg·hm^(−2)·a^(−1))、低N(LN,56 kg·hm^(−2)·a^(−1))、中N(MN,168 kg·hm^(−2)·a^(−1))、高N(HN,280 kg·hm^(−2)·a^(−1))4个N添加处理,测定水杉细根(直径<2 mm)和粗根(2 mm≤直径≤5 mm)C、N、P含量及土壤理化性质指标。[结果](1)N添加对水杉人工林土壤有机碳和水解氮含量存在明显促进作用,且随着N添加量增加,这种促进作用有所减弱。N添加对土壤全磷含量、有效磷含量和pH均无显著影响。(2)随着N添加量的增加,水杉细根和粗根N含量、C:P、N:P显著增加,P含量和C:N显著下降。此外,细根和粗根N含量、C:N和N:P在HN处理下对N添加的响应存在明显差异,表现为细根N含量、C:N和N:P在HN处理下对N添加响应减弱。(3)水杉粗根N含量和C:N可塑性响应在HN处理下显著高于细根,粗根N:P可塑性响应在MN和HN处理下显著高于细根。[结论]水杉细根和粗根C、N、P计量特征对N添加的响应较为一致,分析发现粗根N含量、C:N、N:P的可塑性响应在HN处理下显著高于细根。研究结果为认识N沉降持续增加背景下林木地下部分养分分配策略提供新的思路,也为沿海防护林养分管理措施的制定提供科学依据。

[Objective]The responses of fine roots and coarse roots stoichiometric characteristics to nitrogen(N)addition were determined to reveal the difference between fine roots and coarse roots for Metasequoia glyptostroboides,which would provide theoretical guidance for understanding plant strategies under soil nutrient changing.[Method]We conducted a long-term N addition experiment in M.glyptostroboides plantations in Forest Farm of Dongtai City,Jiangsu Province,with four levels of N addition including control(CK,0 kg·hm^(−2)·a^(−1)),low N(LN,56 kg·hm^(−2)·a^(−1)),medium N(MN,168 kg·hm^(−2)·a^(−1)),and high N(HN,280 kg·hm^(−2)·a^(−1)).The carbon(C),N,phosphorus(P)concentrations of fine roots(diameter<2 mm)and coarse roots(2 mm≤diameter≤5 mm)and the soil physical and chemical properties were measured.[Result](1)N addition significantly promoted soil organic carbon and Alkali-hydrolyzable N content,and the promotion effect weakened with the increase of N addition.(2)P concentration,C:N in both fine roots and coarse roots decreased,while N concentration,C:P,N:P increased with the increase of N addition.In addition,the response of N concentration,C:N and N:P in fine roots and coarse roots to N addition were significantly different under HN treatment,which showed the response of N concentration,C:N and N:P in fine roots to N addition weakened.(3)The plastic response of N concentration and C:N in coarse root were significantly higher than those in fine root under high N treatments.Also,the plastic response of N:P in coarse root was significantly higher than that in fine root under medium N and high N treatments.[Conclusion]The response of C,N,P stoichiometry in both fine roots and coarse roots to N deposition was consistent,while,plasticity response of C,N,P stoichiometry in coarse root was stronger than that in fine root under HN treatment.Overall,our findings would provide insights into the understanding of plant belowground nutrient allocation strategies under N addition,and also support for management of coastal shelterbelt.