山西太岳山油松林无机氮添加对土壤微生物养分限制类型的影响

Effect of inorganic nitrogen addition on soil microbial nutrient requirement strategy in the Pinus tabuliformis forest in Taiyue Mountain,Shanxi Province

土壤微生物胞外酶活性及其化学计量比对土壤养分的有效性和微生物生长的限制因子具有良好的指示作用.然而,在解除氮抑制作用的情况下,微生物的生长策略会呈现何种转变,目前还不明确.在山西太岳山油松林内,按N_(0)(CK)、N_(5)(5 g m^(-2)a^(-1))、N_(10)(10 g m^(-2)a^(-1))、N_(20)(20 g m^(-2)a^(-1))、N_(40)(40 g m^(-2)a^(-1))5种施氮量向土壤施撒硝酸铵,探讨无机氮添加对土壤酶活性及其化学计量特征的影响.钻取不同氮添加梯度的表层土壤样品,分析土壤的养分含量、微生物生物量和5种胞外酶的活性,并计算不同氮添加梯度下土壤酶的化学计量比、矢量长度和角度等生态学指标.结果表明:氮添加使土壤可溶性有机氮(DON)含量从10.64 mg/kg显著提高到55.94 mg/kg,增加了5.3倍;而氮添加使可溶性有机碳氮比值(DOC:DON)显著降低了6.5倍;氮添加使β-1,4-葡萄糖苷酶(BG)活性和酸性磷酸酶(AP)活性分别提高了53.78%和32.12%,均在N_(40)达到最大值;氮添加使酚氧化酶(PHO)和亮氨酸氨基肽酶(LAP)活性分别降低了55.30%和80.42%;氮添加提高了酶C:N(EEA_(C:N))、矢量长度和矢量角度,降低了酶N:P(EEAN:P).其中,土壤pH值、可溶性有机碳氮比和微生物生物量的变化构成了氮添加改变土壤酶活性和触发微生物生长的磷限制性的关键解释因子.综上所述,研究区域山西太岳山油松林土壤微生物的碳氮磷代谢对无机氮添加响应显著,微生物代谢呈现出一定的磷限制,高氮(N_(40))添加背景下微生物碳限制和磷限制加剧.

Soil microbial extracellular enzyme activity and its stoichiometric ratio are good indicators of the availability of soil nutrients and the limiting factors of microbial growth.However,it is unclear what changes in microbial growth strategy occur when nitrogen is no longer a limiting factor.This study was carried out in the Pinus tabuliformis forest of Taiyue Mountain in Shanxi,China.Five nitrogen addition treatments of N_(0)(CK),N_(5)(5 g m^(-2)a^(-1)),N_(10)(10 g m^(-2)a^(-1)),N_(20)(20 g m^(-2)a^(-1)),N_(40)(40 g m^(-2)a^(-1))were applied to the soil in the form of NH4NO3,and the effect of inorganic nitrogen addition on soil enzyme activity and stoichiometric characteristics was observed.Surface soil samples with different nitrogen addition gradients were collected by drilling to analyze soil nutrient content,microbial biomass,and activities of five extracellular enzymes.The ecological indicators of soil enzyme stoichiometric ratios,vector length,and angle under different nitrogen addition gradients were also calculated.The results showed that the addition of nitrogen increased the content of soil dissolved organic nitrogen(DON)by 5.3 times,from 10.64 mg/kg to 55.94 mg/kg,while reducing the ratio of dissolved organic carbon to nitrogen(DOC:DON)by 6.5 times.Moreover,with nitrogen addition,β-1,4-glucosidase(BG)and acid phosphatase(AP)activities were increased by 53.78%and 32.12%,respectively,reaching their maximum values at N_(40).Phenol oxidase(PHO)and leucine aminopeptidase(LAP)activities were reduced by 55.30%and 80.42%,respectively.Nitrogen addition also increased enzyme C:N(EEA_(C:N)),vector length,vector angle,and reduced the enzyme N:P(EEAN:P).Changes in soil pH,DOC:DON,and microbial biomass constitute the key explanatory factors for the effects of nitrogen addition on soil enzyme activity and phosphorus limitation that trigger the growth of microorganisms.The carbon,nitrogen,and phosphorus metabolism of soil microorganisms responded significantly to inorganic nitrogen addition,and microbial metabolism showed a certain degree of phosphorus restriction.The microbial carbon and phosphorus restrictions intensified with the addition of high amounts of nitrogen(N_(40)).