根系作为植物与土壤物质交换和养分循环的桥梁,长期以来一直是生态学研究的热点。于2017年7月植物生长季,对长白山模拟11年氮(N)沉降控制试验样地的白桦(Betula platyphylla)山杨(Populus davidiana)天然次生林进行了根系采样,并利用根序法研究了根系形态特征和解剖结构对不同梯度N添加处理的响应,旨在探求两物种根系之间潜在生态联系。本试验共设置了三个N添加梯度,分别为对照(CK,0 g N m^-2a^-1)、低N处理(TL,2.5 g N m^-2a^-1)和高N处理(TH,5.0 g N m^-2a^-1)。研究结果如下:1)TL显著抑制白桦和山杨前三级细根皮层厚度的生长。白桦通过增加皮层细胞直径(一级根增加了72.77%,二级根增加了53.22%,三级根增加了39.96%)但减少皮层层数来降低皮层厚度,而山杨主要通过皮层细胞直径的减少(一级根下降了40.80%,二级根下降了28.17%)来降低其皮层厚度。2)TH显著抑制山杨前三级细根生长。主要通过增加皮层厚度(一级根增加了68.78%,二级根增加了50.81%,三级根增加了88.53%)以及降低导管横截面积来抑制吸收养分,从而达到影响生长的目的。3)白桦TH相比于TL细根直径呈抑制生长状态。其主要通过抑制中柱直径(一级根下降了17.61%,二级根下降了16.89%,三级根下降了20.62%)的生长来实现。以上结果表明,在同一立地条件下,白桦和山杨的细根对不同浓度N沉降的响应方式不同。
Background:The nitrogen isotope natural abundance(δ^(15)N)provides integrated information on ecosystem N dynamics,and carbon isotope natural abundance(δ^(13)C)has been used to infer how water-using processes of plants change in terrestrial ecosystems.However,howδ^(13)C andδ^(15)N abundances in plant life and soils respond to N addition and water availability change is still unclear.Thus,δ^(13)C andδ^(15)N abundances in plant life and soils were used to investigate the effects of long-time(10 years)N addition(+50 kg N·ha^(−1)·yr^(−1)and precipitation reduction(−30%of throughfall)in forest C and N cycling traits in a temperate forest in northern China.Results:We analyzed theδ^(13)C andδ^(15)N values of dominant plant foliage,litterfall,fungal sporophores,roots,and soils in the study.The results showed thatδ^(15)N values of foliage,litterfall,and surface soil layer’s(0–10 cm)total N were significantly increased by N addition,whileδ^(15)N values of fine roots and coarse roots were considerably decreased.Nitrogen addition also significantly increased theδ^(13)C value of fine roots and total N concentration of the surface soil layer compared with the control.The C concentration,δ^(13)C,andδ^(15)N values of foliage andδ^(15)N values of fine roots were significantly increased by precipitation reduction,while N concentration of foliage and litterfall significantly decreased.The combined effects of N addition and precipitation reduction significantly increased theδ^(13)C andδ^(15)N values of foliage as well as theδ^(15)N values of fine roots andδ^(13)C values of litterfall.Furthermore,foliarδ^(15)N values were significantly correlated with foliageδ^(13)C values,surface soilδ^(15)N values,surface soil C concentration,and N concentrations.Nitrogen concentrations andδ^(13)C values of foliage were significantly correlated withδ^(15)N values and N concentrations of fine roots.Conclusions:This indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15
Guoyong YanShijie HanMingxin ZhouWenjing SunBinbin HuangHonglin WangYajuan XingQinggui Wang
本研究试验样地位于黑龙江省伊春市五营区丰林国家级自然保护区,于2010年5月开始氮沉降控制试验,共设置4个N添加梯度,分别为低N (LN 5 g N m?2 a?1)、中N (MN 10 g N m?2 a?1)、高N (15g N m?2 a?1)和对照(CK 0 g N m?2 a?1),应用两种不同孔径网袋(150目,300目)排除不同类型土壤动物的方法,对比研究N沉降及土壤动物活动对针叶、阔叶、混叶凋落物的分解作用,旨在探讨小兴安岭针阔混交林凋落物在N沉降下的分解动态及其与土壤动物活动的关系。结果表明:1) 不同类型凋落叶分解速率表现为阔叶凋落物 >针叶凋落物 >混叶凋落物,差异显著(P <0.05);在有土壤动物活动作用下的150目孔袋内的凋落叶分解速度快于基本排除土壤动物作用条件下的300目孔袋的分解样品,对针叶凋落物作用达到显著水平(P <0.05);土壤动物活动与C的损失率呈显著负相关关系(P <0.05),与N、P损失率呈正相关,差异显著(P <0.05)。2) 不同N处理均抑制了针叶凋落物的分解,LN处理抑制明显(P <0.05);MN、HN处理促进了阔叶凋落物的分解,LN处理呈现抑制,作用不显著;有土壤动物参与下的混叶HN处理显著抑制分解(P <0.05)、LN和MN处理显著促进分解(P <0.05);基本排除土壤动物作用下混叶表现为LN处理抑制分解、HN处理显著促进分解(P <0.05)。在施N处理下,养分释放率与分解速率一致。本试验研究表明:土壤动物活动加速了凋落叶质量的损失,加速了N、P元素的释放;N沉降处理对不同类型凋落叶影响不同,对混叶凋落物的影响与土壤动物的活动存在交互作用。
