施氮与凋落物去除影响下中亚热带阔叶林土壤氮素矿化潜势和硝化潜势研究

氮沉降影响土壤氮循环,而凋落物是土壤有机氮的主要来源,因此,为了探讨氮沉降和凋落物是否去除作用下,亚热带森林土壤潜在的氮素矿化与硝化作用,选择已进行8年模拟氮沉降试验的亚热带罗浮栲(Castanopsis fabri)常绿阔叶林土壤为研究对象,野外样地氮添加设置3个水平:对照(CK,0 kg·hm^?2·a^?1)、低氮(LN,75 kg·hm^?2·a^?1)、高氮(HN,150 kg·hm^?2·a^?1),两种凋落物管理方式(保留凋落物,L和去除凋落物,R),土壤采样后,通过室内间歇淋洗好气培养法,研究土壤氮素矿化潜势差异,以及不同底物条件下(铵态氮水平:N 0,100、150、200 mg·kg^?1)土壤硝化潜势的差异。结果表明:土壤氮素快速矿化主要在培养前7 d,矿化累积量(Nt)为102.81—153.71 mg·kg^?1,矿化潜势(N0)范围为193.84—289.80 mg·kg^?1,N0依次为:保留凋落物低氮(LN-L)>保留凋落物对照(CK-L)>去除凋落物低氮(LN-R)>去除凋落物对照(CK-R)>去除凋落物高氮(HN-R)>保留凋落物高氮(HN-L);两种凋落物处理方式下,LN水平土壤的Nt与N0均高于CK、HN。保留凋落物情况下,有较高的土壤硝化潜势;在无添加硝化底物(铵态氮水平为N 0 mg·kg^?1)的条件下,野外氮添加水平高的土壤硝化潜势也高;而在添加不同硝化底物(铵态氮)的条件下,土壤硝化潜势并未随硝化底物水平的增加而增加,且硝化底物水平为N 100 mg·kg^?1时硝化潜势最大。研究表明,虽然保留凋落物可以增加土壤氮矿化潜势,而氮沉降则影响氮矿化潜势。当研究土壤硝化潜势时,应当根据土壤类型等因素选择合适的硝化底物(铵态氮)添加量。

Study on the Potential of Nitrogen Mineralization and Nitrification in Mid-subtropical Broad-leaved Forest Soil Already Treated with Nitrogen Addition and Litter Removal

Nitrogen (N) deposition impacts soil N cycling by changing nitrogen availability,mineralization rate,and nitrate leaching in a forest ecosystem.Litter input is the main source of soil organic N.However,how N deposition and litter removal or not affect the N cycling remains unclear.Therefore,it is important to study the effects of nitrogen deposition and litter on nitrogen mineralization and nitrification potential in subtropical forest soil.Soil samples were collected from subtropical evergreen broad-leaved forest soil subjected with N depositioncontrol (CK,0),low nitrogen (LN,75),high nitrogen (HN,150 kg·hm^-2·a^-1)]and litter removal or notlitter retained (L),litter removal (R)]for 8 years.Then,the difference of N mineralization potential among these soils was studied by intermittent leaching incubation method.The change of nitrification potential under different addition of ammonium N levels (N,0,100,150,200 mg·kg^-1) was also investigated.The results showed that the rapid mineralization of soil N mainly occurred before 7 days of incubation.The cumulative amount of N mineralization (Nt) in different soils ranged from 102.81 to153.71 mg·kg^-1,and mineralization potential (N0) ranged from 193.84 to 289.80 mg·kg^-1.N0 value was in the order:(LN-L)>(CK-L)>(LN-R)>(CK-R)>(HN-R)>(HN-L).Under the conditions with or without litter,Nt and N0 in LN treatment were higher than those in CK and HN,suggesting the organic N in LN soil would be easier to be mineralized,and the N deposition altered the N mineralization potential in the field soil.Under the conditions without the addition of (NH₄)₂SO₄,the nitrification potential was higher in soils subjected with higher N deposition levels.However,the nitrification potential was not increased with the enhancement of the added (NH₄)₂SO₄,and the nitrification potential was the maximum when the (NH₄)₂SO₄ addition was N 100 mg·kg^-1 soil.These results suggest that N deposition might alter the N mineralization potential in the subtropical forest soil,even though litter input could increase it.N deposition increases soil nitrate concentration,which might result in a decline of (NH₄)₂SO₄ required for the optimal nitrification potential.Thus,the concentration of (NH₄)₂SO₄ applied in studying soil nitrification potential should be considered according to the soil types and other factors.