Soil Fertility Of Coniferous And Broad-leaved Plantations In The Eastern Mountain Area Of Northeast China

Plantation can reduce soil fertility,understanding the characteristics of fertility between plantations and natural forests and the degree of decline of plantation can provide theoretical basis for the improvement of plantation soil fertility.Secondly,studying the growth status of broad-leaved seedlings in the coniferous plantation soil is of great significance for transforming pure coniferous plantations into mixed conifer-broadleaf forests.In this study,the artificial coniferous and broad-leaved forests in Linjiang,Lushui River and Mengjiagang areas in the east of Northeast China were taken as the research objects,and the secondgrowth forests were taken as the reference.Through the comparison of soil chemical indexes and enzyme activities in 0-20 cm and 20-40 cm of different forest stands to explore the differences of soil fertility between coniferous and broad-leaved plantations and secondgrowth forests.In addition,the growth status of 1-year-old Juglans mandshurica and Fraxinus mandshurica seedlings in Larch and Korean pine pure forest soil under full light and 60%full light were studied to analyze the effects of soil fertility on seedling growth in coniferous forest under different light environment were.The results show that:(1)Compared with secondgrowth forest,soil nutrient and enzyme activity of artificial forest decreased,mainly in soil organic matter,total nitrogen,alkali hydrolyzable nitrogen,available potassium and phosphatase activity,and decreased significantly in surface layer(0-20 cm).The contents of soil organic matter(SOC),total nitrogen(TN),alkali hydrolyzable nitrogen(AN),available potassium(AK)and phosphatase activity(APA)in soil surface of plantation were significantly lower than those of secondgrowth forests.Compared with secondary forest,coniferous forests decreased by 29%-65%,7%-49%,32%-51%,24%-88%,18%-53%,broadleaf forests decreased by 25%-53%,4%-45%,21%-40%,16%-52%,19%-34%.The total phosphorus content and soil pH were not significantly different between plantations and secondgrowth forests in soil surface.The total potassium content in soil surface of broad-leaved forest,is significantly higher than that of secondgrowth forest,is not significant between coniferous forests and secondgrowth forests.The content of available phosphorus does not have a consistent pattern between secondgrowth forests and plantation forests in soil surface.Invertase activity(1A)and urease activity(UA)in secondgrowth forests were significantly higher than coniferous plantations in soil surface,which were inconsistent with the characteristic of broad-leaved forests.(2)There was a significant correlation between enzyme activity and soil chemical indexes.IA has a very significant positive correlation with TN.AN,and AK,and has a significant positive correlation with SOC.UA is extremely significantly positively correlated with TN,AN,and AK.APA is significantly negatively correlated with TP,and extremely significantly positively correlated with AN,AP,and AK.(3)The comprehensive fertility analyzed by soil nutrients and enzyme activities of plantation and secondary forest was secondgrowth forests>broad-leaved forests>coniferous forests.The comprehensive soil fertility scores of different forest stands in Linjiang are secondgrowth forest(1.319)>Poplar forest(0.631)>Larix forest(-0.022);the comprehensive soil fertility score of different forest stands in Lushui River is secondgrowth forest(0.258)>Poplar forest(-0.199)>Larix forest(-0.868);the comprehensive soil fertility score of different forests in Mengjiagang Forest Farm is secondgrowth forest(0.330)>Fraxinus mandshurica forest(0.258)>Larix forest(-0.053)>Pinus koraiensis forest(-0.199)>Pinus sylves'tris var.mongolica(-0.868).(4)Compared with secondgrowth forests,coniferous forest soil may limit the growth of seedlings.The soil nutrients in Korean pine forest significantly restricted the growth of walnut and ash seedlings,and the restriction was aggravated under 60%full light;the soil nutrients in larch has less impact on seedlings.Under full light,walnut biomass in Korean pine forest soil was significantly lower than that in secondgrowth forest soil by 39.5%(P<0.05),ash biomass was not significantly different in the two soils.Under 60%full light conditions,the biomass of walnut in the Korean pine forest soil was significantly lower than that in the secondgrowth forest soil by 52.5%(P<0.05),and the biomass of ash in the Korean pine forest was significantly lower than that in the secondgrowth forest by 41.9%.Under the two kinds of light,the accumulation of nitrogen and potassium in the seedlings of walnut and ash in the Korean pine forest soil was significantly lower than that in the secondgrowth forest soil.Under full light,the shoot to root ratio of walnut and ash seedlings in Korean pine forest soil was the lowest;the opposite was true under 60%full light conditions.The differences in biomass and nitrogen,phosphorus,and potassium accumulation between larch forest and secondgrowth forest were not significant.In summary,the soil fertility of plantation was significantly lower than that of secondgrowth forest,the reduction of SOC,TN,AN,AK content and APA mainly,and the reduction of soil fertility of coniferous forests is more significant.The main ways to solve the problems about coniferous plantation degradation is to convert pure coniferous plantations into mixed conifer-broadleaf forests or promote the regeneration of broadleaved tree species in coniferous plantations.For the main coniferous forests in Northeast China(larch and Korean pine).the soil fertility of Korean pine forest decreased more obviously.During the transformation of Korean pine forests,the nitrogen and potassium may restrict the growth of newer seedlings,and low light(60%full light)will exacerbate this restriction.