氮沉降及菌根真菌对长白落叶松苗木根系构型及根际酶活性的影响

为探究氮沉降和接种菌根真菌对长白落叶松苗木根系构型和根际土壤酶活性的影响,以1年生长白落叶松(Larix olgensis)的盆栽菌根苗(简称+M,混合接种8种外生菌根真菌)和非菌根苗(简称-M,未接种处理)为研究对象,设置4个氮沉降处理(不施氮(0N,0 kg·N·hm^-1·yr^-1)、低氮(LN,15 kg·N·hm^-1·yr^-1)、中氮(MN,30 kg·N·hm^-1·a^-1)和高氮(HN,60 kg·N·hm^-1·a^-1)),测定直径0~0.5 mm根系的总根长、总表面积、总体积和根尖数等根系形态指标,对比分析氮沉降和接种菌根真菌处理对苗木根际土壤酶(β-1,4葡萄糖苷酶(BG)、亮氨酸氨基肽酶(LAP)、β-1,4-N-乙酰-氨基葡糖氨糖苷酶(NAG)、酸性磷酸酶(ACP)和碱性磷酸酶(ALP))活性的影响。结果表明:①长白落叶松苗木直径0~0.5 mm根系的总根长、总表面积、总体积和根尖数均随氮浓度的递增呈下降的趋势;在0N、LN和MN处理下,-M处理的根系形态指标均高于+M处理。②随氮浓度增加,+M和-M处理苗木根际土壤中BG、LAP、ACP和ALP活性均呈先增加后下降的趋势,而NAG活性呈下降的趋势。③+M和-M处理下,长白落叶松直径0~0.5 mm根系的形态指标与根际土壤BG活性均呈显著负相关关系(P<0.05);除根尖数外,其它根系形态指标与NAG活性相关性均为正相关(P<0.05)。综上所述,苗木菌根化处理削弱了氮沉降对落叶松苗木根系构型的影响;而低氮处理下,+M处理对苗木根际土壤酶的活化程度高于-M处理。

Effects of Nitrogen Deposition and Ectomycorrhizal Fungi on Root Architecture and Rhizosphere Soil Enzyme Activities of Larix olgensis Seedlings

In order to explore the responses of root morphology and rhizosphere soil enzyme activities of oneyear-old Larix olgensis seedlings to different simulated nitrogen deposition and ectomycorrhizal fungi,the morphology of roots with diameter of 0-0.5 mm(including the total root length,surface area,volume and tips)and soil enzyme activities(including β-1,4-glucosidase(BG),L-leucine aminopeptidase(LAP),β-1,4-Nacetylglucosaminidase(NAG),acid phosphatase(ACP) and alkaline phosphatase(ALP)) were measured respectively.The different inoculated seedlings of L.olgensis were selected,including the not noculated(-M)and inoculated with 8 ectomycorrhizal fungi(+M) respectively.Four nitrogen deposition treatments were set,including no nitrogen(ON,0 kg·N·hm^-1·yr^-1),low nitrogen(LN,15 kg·N·hm^-1·yr^-1),middle nitrogen(MN,30 kg·N·hm^-1·yr^-1) and high nitrogen(HN,60 kg·N·hm^-1·yr^-1).The results indicated that:①The nitrogen deposition concentration had a negative effect on the total root length,surface area,volume,tips with a diameter 0-0.5 mm of L.olgensis seedlings under+M and-M treatments.The root morphology indexes of-M was higher than that of+M treatment under ON,LN,and MN treatments,respectively.②With the increasing of nitrogen deposition,the activities of BG,LAP,ACP,ALP in the rhizosphere soils showed a tendency of first rising and then decreasing under the two inoculation treatments,but the activities of NAG showed a decreasing tendency.③The morphology of roots with diameter of 0-0.5 mm was significantly negatively correlated with the activities of BG in the rhizosphere soils(P<0.05),under the+M and-M treatments.There was significantly positive correlation between the activities of NAG and root morphology(P<0.05),except the number of the tips.The effect of nitrogen deposition on root morphology of L.olgensis seedlings was weakened by ectomycorrhizal fungi inoculation treatment.However,the activation of soil enzyme activity by+M was higher than that of-M treatment under low nitrogen deposition.