氮负荷增强对闽江口短叶茳芏湿地植物-土壤系统氮累积与分配的影响

Effects of enhanced nitrogen load on nitrogen accumulation and allocation in plant-soil system of Cyperus malaccensis marsh in the Minjiang estuary

选择闽江河口短叶茳芏(Cyperus malaccensis)湿地为研究对象,基于野外氮负荷增强模拟实验,探讨了不同氮负荷水平下(NNT对照处理,0 g N m^(-2)a^(-1);LNT低氮处理,12.5 g N m^(-2)a^(-1);MNT中氮处理,25.0 g N m^(-2)a^(-1);HNT高氮处理,75.0 g N m^(-2)a^(-1))湿地植物-土壤系统的氮累积与分配特征。结果表明,不同氮负荷处理下湿地土壤(TN)、NH+4-N和NO-3-N含量均发生了明显改变。相较于NNT,LNT和MNT的TN、NH+4-N和NO-3-N含量均明显增加,增幅分别为9.44%、3.57%、11.99%(LNT)和6.71%、9.37%、46.50%(MNT)。与之不同,HNT的TN含量相比NNT增幅不大,而其NH+4-N、NO-3-N含量均显著降低,降幅分别为9.26%和40.77%。不同氮负荷处理下土壤氮含量的垂直分布特征亦发生了明显变化。除HNT外,LNT和MNT的TN、NH+4-N和NO-3-N含量均以表层土壤最高。不同氮负荷处理下的TN和NH+4-N含量分布主要受SOM的影响,而NO-3-N含量分布主要受植物吸收和垂直淋失的影响。氮负荷增强条件下植物不同器官的TN含量整体表现为叶>茎>根。不同氮负荷处理下植物-土壤系统的氮储量整体以LNT和MNT较高,而HNT最低。研究发现,短叶茳芏在中低氮负荷条件下可能将更多的氮优先分配给根系,进而以拓展地下空间和提高地下生物量的方式来适应环境;而在高氮负荷条件下,其可能通过增强“自疏效应”,并通过拓展地上空间的方式来适应环境。

The typical Cyperus malaccensis marsh in the Minjiang estuary was selected as the study object.The effects of enhanced nitrogen(N)load on accumulation and allocation of N in plant-soil system were determined by field N load experiment which included four N load levels(NNT,no N treatment,0 g N m^(-2)a^(-1);LNT,low N treatment,12.5 g N m^(-2)a^(-1);MNT,medium N treatment,25 g N m^(-2)a^(-1);and HNT,high N treatment,75 g N m^(-2)a^(-1)).Results showed that the contents of total nitrogen(TN),NH+4-N and NO-3-N in soils of different N load levels were greatly altered.Compared with the NNT,the contents of TN,NH+4-N and NO-3-N in the LNT and MNT significantly increased and the increase magnitudes were 9.44%,3.57%,11.99%(LNT)and 6.71%,9.37%,46.50%(MNT),respectively.The TN contents in the HNT increased slightly,while the NH+4-N and NO-3-N contents declined greatly and the decrease magnitudes were 9.26%and 40.77%,respectively.The vertical distributions of N contents in soils of different N load levels were also greatly changed.Except for the HNT,the highest contents of TN,NH+4-N and NO-3-N in the LNT and MNT were observed in topsoil.The distributions of TN and NH+4-N contents in the profiles were mainly affected by soil organic matter(SOM),while that of NO-3-N contents was primarily influenced by plant absorption and its vertical leaching.The TN contents in organs of plants generally showed leaf>stem>root.Stocks of N in plant-soil systems of different N load levels were much higher in the LNT and MNT,while the lowest value was observed in the HNT.The study found that the C.malaccensis in the LNT and MNT might preferentially allocate more N nutrient to the roots and adapt the N enriched environment by expanding belowground space and elevating belowground biomass,while those in the HNT might adapt the high N load environment through enhancing“self-thinning effect”and expanding aboveground space.