Evolution Of Soil Nitrogen Nutrition Habitat In Burned Area Of Larix Gmelinii Forests

Nitrogen（N）is an essential element that affects the structure and function of forest ecosystems and is also a fire-sensitive element.We selected the virgin forest of Larix gmelinii in the cold-temperate zone disturbed by frequent wildfires and post-fire plots as the research objects.The contents of soil NH₄⁺-N,NO₃^--N,mineral N,dissolved amino N and free amino acid N in the Fire recovery sequence were measured using the continuous fixed-point monitoring method.We also analyzed the changes in soil mineral N form（the NH₄⁺-N/NO₃^--N ratio）and soil available N form（the free amino acid N/mineral N ratio）.The purpose of this study is to clarify the evolution regular of soil N in the Fire recovery sequence and to provide a reference for the restoration and transformation of burned cold-temperate coniferous forests.The main contributions of this paper are summarized as follows.（1）The contents of NH₄⁺-N,NO₃^--N,and mineral N initiated a temporary pulse after a severe fire and then decreased rapidly.They were similar to those of unburned forests 9 years,2 months,and 9 years after wildfire,respectively.Compared with topsoil,the effect of wildfire in subsoil NH₄⁺-N,NO₃^--N,and mineral N was less affected by wildfire.（2）The contents of soil dissolved amino N and free amino acid N were increased immediately after a severe fire and then decreased rapidly.Notable,the content of dissolved amino N was similar to that of unburned forest 1 year after the wildfire,and the change in free amino acid N content was closely related to seasons.（3）The severe fire did not lead to substantial changes in mineral N form and the dominant mineral N form was NH₄⁺-N in the fire recovery sequence.After a fire,the ratio of NH₄⁺-N/NO₃^--N significantly increased and then immediately decreased,which was recovered 9years after burning.（4）Soil available N form in Larix gmelinii forest was changed after a severe fire and showed obvious seasonal variation.The dominant available N form changed from equivalent free amino acid N and mineral N to predominance of free amino acid N in the growing season,and then the predominance of free amino acid N was decreased.Furthermore,although free amino acid N was always the dominant N form,its predominance was decreased to varying degrees in the non-growing season.（5）Soil habitat factors are closely related to nitrogen nutrient levels in the fire recovery sequence.Soil temperature was positively correlated with NH₄⁺-N,mineral N,soluble amino N,and free amino acid N and it was negatively correlated with NO₃^--N.Soil moisture was negatively correlated with NH₄⁺-N,mineral N,and soluble amino N.Soil p H was positively correlated with NO₃^--N.Soil redox potential was negatively correlated with NO₃^--N.