| In order to describe the effects of artificial vegetation restoration on soil organic matter and nitrogen,the carbon content of soil organic matter,the free organic matter,the physically protected organic matter and the mineral-associated organic matter,nitrogen content of total nitrogen,ammonium nitrogen,nitrate nitrogen,soluble organic nitrogen,microbial biomass nitrogen,light group and particulate organic nitrogen in six kinds plantation: manchurian ash(Fraxinus mandshurica),poplar(Populus nigra var.italica × P.cathayan),phelloendron(Phelloendron amurense),larch(Larix gmelini),scots pine(Pinus sylvestris var.mongolica),spruce(Picea koraiensis)(represents the type of artificially restored vegetation)and 21 a,35 a,46 a and 55 a larch plantations(representing different restoration stages of vegetation),the adjacent cultivated land(representing the stage before vegetation restoration)and Populus davidiana natural secondary forest(representing the stage before reclamation as there is no reclamation interference)was measured,calculated and analyzed.To explore the effects of vegetation restoration types and different restoration stages on soil organic matter and its fractions and different forms of nitrogen,the main research results are as follows:(1)Compared with cultivated land,each plantation increased the carbon content of the bulk soil organic matter,the increase range is 7.78-62.16%.Except that there is no significant difference between the total organic matter carbon content of the phellodendron plantations and the secondary forest.The carbon content of free organic matter in the soil of each plantation has returned to the level before reclamation;the carbon content of organic matter in the physical protection state of the six plantations was significantly higher than that of the cultivated soil,the increase range is 97.01～347.13%.In conclusion,the effect of artificial vegetation restoration soil organic matter and its fractions of black soil were mainly achieved by increasing the content of free organic matter and physically protected organic matter.There was no significant difference in total organic matter,free and physical protected organic matter between phellodendron plantations and secondary forest,indicating that phellodendron plantations had the best effect on the improvement and restoration of degraded black soil.(2)The content of soil total nitrogen each plantation was significantly higher than that of before cultivated land,the increase range is 13.18～70.91%,there was no significant difference in total nitrogen content between phellodendron plantations and natural secondary forest.The soluble organic nitrogen content of phellodendron,larch,pinus sylvestris and spruce plantations was significantly higher than that of cultivated land,and there was no significant difference between spruce plantations and natural secondary forest.Except for larch plantations microbial biomass nitrogen content which was not significantly different from cultivated land,other plantations were significantly higher than cultivated land soil,the poplar plantations and phellodendron plantations was not significantly different from that of secondary forest.The content of organic nitrogen in the light group of each plantation was significantly higher than that of cultivated land,and there was no significant difference in the secondary forest.In six plantations the content of particulate organic nitrogen was significantly higher than that in cultivated land,and the particulate organic nitrogen phellodendron plantations was not significantly different from that in secondary forest.The yellow pineapple forest significantly increased the soil total nitrogen and active organic nitrogen content,while there was no significant difference with the secondary forest,indicating that the phellodendron plantations had the most significant improvement on soil nitrogen.(3)The soil organic matter carbon content in the larch plantations with 46 a,55 a was significantly higher than that in the cultivated land,but was significantly lower than that in the natural secondary forest.The soil free organic matter carbon content in the larch plantations with 35 a,46 a and 55 a was significantly higher than that in the cultivated land,the increase range is 48.81～103.57%.At the same time,there was no significant difference in the soil free organic matter carbon content between the larch plantations with 35 a,46 a,55 a and the natural secondary forest.The 46 a and 55 a larch plantation have significantly higher organic matter carbon content in the protected state than cultivated soil,accounting for 252.41% and309.66% of cultivated land,respectively.Only the carbon content of physical protected organic matter in surface soil of 55 a larch plantation is not significantly different from that of secondary forest.Soil free organic matter can be used as a sensitive index for evaluating the change of soil organic matter of black soil due to the shorter recovery time.(4)Although the total nitrogen content of the 55 a larch plantation increased significantly by nearly 22% compared with cultivated land,but significantly lower than that in secondary forest.The content of soluble organic nitrogen in the larch plantations with 35 a,46 a and 55 a was significantly higher than that in cultivated soil and significantly lower than that in secondary forest.The microbial biomass nitrogen was significantly higher than that of cultivated land after 55 a of restoration,but it is only 90.17% of the secondary forest;light and particulate organic nitrogen in the larch plantations with 35 a,46 a and 55 a was significantly higher than those in cultivated soil.There is no significant difference between the content of organic nitrogen in light group of 55 a larch plantation and secondary forest.The particulate organic nitrogen was only 46.67% of the secondary forest after 55 a of vegetation restoration.It can be concluded that larch plantation can restore soil total nitrogen and active organic nitrogen,but there is still a certain gap between larch plantations and natural secondary forest. |
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