添加葡萄糖对中亚热带阔叶林土壤氮转化的影响

Effects of Adding Glucose on Soluble and Microbial Nitrogen in Subtropical Broad-leaved Forest Soil

针对中亚热带阔叶林(罗浮栲林)土壤,设置7个碳添加梯度(C量分别是0,300,600,900,1 000,1 100,1 300 mg/kg),在25℃、土壤饱和持水量(WHC)的60%条件下室内培养21 d,研究活性碳对阔叶森林土壤氮的影响。结果表明:随着碳添加量增加,NO_3~–-N迅速降低且在C 900 mg/kg水平达到最低,此时NO_3~–-N降低28.35 mg/kg。可溶性有机氮(SON)在第7天随葡萄糖碳添加量而降低,但是到第21天在900～1 300 mg/kg C水平,SON高于第7天,且用氯仿熏蒸提取后来自微生物的SON开始增加;总的SON增加15.09～17.10 mg/kg。可见,通过NO_3~–-N的微生物同化转化为有机氮,使该地区在降雨较多的情况下降低NO_3~–-N的淋溶或反硝化气态损失风险,增加SON的淋溶风险。但是在生态系统氮需求发生改变时SON能迅速响应使该地区森林土壤氮有效矿化,并满足植物生长需求,提高生态系统中氮的可利用性。凋落物残体氮浓度增加,且残余土壤氮增加5.64 mg/kg。红外光谱显示,碳添加量为900 mg/kg降低罗浮栲土壤经K_2SO_4溶液提取后残体在各波数处的吸收峰比例,且在吸收峰最高的426～600 cm^(–1)、900～1 200 cm^(–1)范围内,碳添加的影响最小,表明碳添加使土壤矿物对氮的保持增加,且有机氮变得更加稳定。

Soil available carbon source and concentration regulate soil nitrogen transformation and soil nitrogen is affected significantly by carbon level in coniferous forest soil.Soil soluble carbon is higher in broad-leaved forest than that in coniferous forest,but the effect of carbon level on broad-leaved forest soil nitrogen is unclear.The broad-leaved forest(Castanopsis fargesii)soil from Wanmulin Nature Reserve in Fujian was selected and different carbon addition rates(0,300,600,900,1 000,1 100 and1 300 mg/kg soil added as glucose)were designed to study the effect of carbon on nitrogen after being incubated for 21 days at 25℃and 60%of soil water holding capacity.The results showed that with the increase of carbon addition,nitrate nitrogen decreased rapidly and reached the minimum at 900 mg/kg soil.At this time,nitrate nitrogen decreased by 28.35 mg/kg.Soluble organic nitrogen(SON)decreased at 7th day with the amount of carbon addition,but at 21th day in the 900–1 300 mg/kg soil,SON was higher than that at 7th day,and SON from microbial after soil treated with the chloroform fumigation began to increase with carbon addition,increased by 15.09–17.10 mg/kg.Therefore,nitrate nitrogen was assimilated by the microbe into organic nitrogen,which reduced nitrate leaching or gaseous loss by denitrification risk in subtropical area in the case of more rainfall,whereas increased the risk of SON leaching.However,when nitrogen demand of ecosystem changed,SON could respond rapidly,so that the forest soil in this area could be effectively mineralized to meet the needs of plant growth,and improve the availability of nitrogen in the ecosystem.The nitrogen concentration in the litter of soil increased with more carbon addition,and nitrogen in the residual soil increased by 5.64 mg/kg.The IR spectrum showed that the carbon addition of 900 mg/kg decreased absorption peaks in the proportion of each wave number in residue after soil extracted by K2SO4 solution,and the effect of carbon addition was minimum in the highest absorption peak,426–600 cm–1 and 900–1 200 cm–1.These results indicated that carbon addition increased nitrogen in mineral matrix and organic nitrogen in soil becomes more stable.