冻融作用对大兴安岭典型森林土壤活性有机碳和氮矿化的影响

The effects of freezing-thawing process on soil active organic carbon and nitrogen mineralization in Daxing′anling Mountain forests

于2017年10月采集大兴安岭地区樟子松林和白桦林两种典型林型下0～10、10～20、20～30 cm土壤,采用室内模拟冻融实验研究了冻融循环下土壤活性有机碳变化趋势和氮素矿化特征.结果表明:①随着冻融次数增加,土壤溶解性有机碳(DOC)和土壤微生物量碳(MBC)均表现为先增加后降低的趋势,冻融作用在显著增加了土壤DOC含量的同时降低了土壤MBC含量(p<0.05),冻融温差对活性碳影响不明显(p>0.05);冻融过程中樟子松林0～10 cm土壤DOC含量高于白桦林,10～20、20～30 cm土壤DOC含量低于白桦林,而樟子松林各层土壤MBC含量始终高于白桦林.②随着冻融次数增加,土壤铵态氮表现为先减少后增加的趋势,而硝态氮表现为先增加后减少的趋势,冻融作用显著增加了土壤铵态氮和硝态氮含量(p<0.05),较大的冻融温差会促进氮矿化(p<0.05);冻融过程中白桦林土壤铵态氮和硝态氮含量始终高于樟子松林.③两种林型下土壤DOC、MBC、铵态氮和硝态氮含量均随着土层深度的增加而降低(p<0.05).以上结果表明,冻融作用导致森林土壤DOC含量流失而影响了土壤碳库的积累,但有利于无机氮的累积,为植物生长提供了氮素肥力,且不同植被类型土壤碳、氮含量对冻融作用的响应存在一定的差异.

Soil samples were collected from depths of 0~10,10~20 and 20~30 cm in two typical forest types of Pinus sylvestris var.mongolica and Betula platyphylla in Daxing′anling region in October 2017. Indoor experiment on freeze-thaw simulation was conducted to investigate the trends of change in soil active organic carbon and characteristics of nitrogen mineralization under freeze-thaw cycles. Results showed that:①soil dissolved organic carbon(DOC) and soil microbial biomass carbon(MBC) both showed increasing trends firstly and then were followed by declined tendencies with the increase of freeze-thaw cycles. Freeze-thaw significantly increased soil DOC, but with decreased soil MBC content(p<0.05). The difference in temperature of freeze-thaw had no obvious effect on activated carbon(p>0.05). Besides, we found the DOC content of Pinus sylvestris forest was higher than birch forest in 0~10 cm soil and lower in 10~20 cm and 20~30 cm soils, respectively. However, the MBC content in each soil layer of Pinus sylvestris forest was consistently higher than that of birch forest.②Freeze-thaw significantly increased soil ammonium nitrogen and nitrate nitrogen content(p<0.05), which presented different trends of change. Soil ammonium nitrogen experienced a trend of decreasing before the notable increase. However, nitrate nitrogen noted an opposite change of trend compared with soil ammonium nitrogen. The large difference of temperature in freeze-thaw accelerated nitrogen mineralization(p<0.05). Meantime, the ammonium nitrogen and nitrate nitrogen in birch forest soil were persistently larger than that in Pinus sylvestris forest during freezing and thawing.③The contents of DOC, MBC, ammonium nitrogen and nitrate nitrogen decreased with the increase of soil depth in both the forest types(p<0.05). The above results show that the loss of DOC content in forest soil caused by freeze-thaw affects the accumulation of soil carbon pool and inorganic nitrogen, which provides nitrogen fertility for plant growth. Moreover, the response to freeze-thaw action of soil carbon and nitrogen from different vegetation types vary to some extent.