| Soil humification is an important sign of the formation of soil fertility.The humification of forest and grassland litter is very important to the maintenance of soil fertility.With the frequent occurrence of global climate anomalies,the alternating changes of temperature and humidity will inevitably affect the process of forest and grassland soil humus.Therefore,this paper takes the typical plantation grassland in loess area as the research object(including broad-leaved arbor forest: Populus simonii,Robinia pseudoacacia,Quercus liaotungensis,and Ulmus pumila;coniferous arbor forest: Pinus tabuliformis,Larix principis-rupprechtii,Picea asperata and Platycladus orientalis;shrub forests: Hippophae rhamnoides,Caragana microphylla,Amorpha fruticosa,and Ziziphus jujuba and grassland: Medicago sativa,Melilotus officinalis,Coronilla varia and Vicia villosa).By collecting the litter and wasteland soil of the current year,the crushed sample of litter and the screened sample of soil are fully mixed according to the dry weight ratio of 3:100(the dry weight of the mixed sample is 2kg)and then put into the plastic culture bowl.After maintaining the soil humidity at 20%WHC,50%WHC and 80%WHC,the temperature is 10℃,20℃and 30℃ respectively.Under the above conditions,the continuous humification test of indoor incubator with 9 treatments was carried out.The experiment was terminated after 100 days.The effects of temperature and humidity change on soil humification were studied by measuring the content of organic carbon,optical properties of humus,nutrient availability and various enzyme activities of soil.The main conclusions are as follows:(1)In broad-leaved arbor forest,when the litter of four broad-leaved trees was humified at 30℃,the content of available nitrogen was the highest.At 20%WHC,the increase of temperature will lead to the increase of humus degree(Hu Fu ratio and PQ value)of the litter of Ulmus pumila,Robinia pseudoacacia and Populus simonii.At 50%WHC,the increase of temperature will lead to the decrease of sucrase activity in Ulmus pumila,Quercus liaotungensis and Populus simonii forests.At 80%WHC,the increase of temperature will reduce the humus degree of the litter of Robinia pseudoacacia and Populus simonii.At 10℃,the humification degree of litter of Robinia pseudoacacia and Quercus liaotungensis increased with the increase of humidity.At 20℃,the increase of humidity will lead to the decrease of humus degree of Robinia pseudoacacia litter.At 30℃,the increase of humidity will lead to the decrease of humin content in four broad-leaved tree forests,and the decrease of humic acid content in Robinia pseudoacacia,Quercus liaotungensis and Populus simonii forests.The comprehensive results showed that the climatic conditions most conducive to the improvement of soil properties of the four broad-leaved tree woodlands were Ulmus pumila and Robinia pseudoacacia(30℃+20%WHC),Quercus liaotungensis(20℃+20%WHC)and Populus simonii(20℃+50%WHC).(2)In coniferous arbor forest,at 20%WHC,the increase of temperature will lead to the increase of humification degree of litter of Platycladus orientalis and Pinus tabuliformis,the increase of Humin content in four coniferous arbor forests,the increase of fulvic acid content and the decrease of available potassium content in Larix principis-rupprechtii,Pinus tabuliformis and Picea asperata forests.At 50%WHC,the increase of temperature will lead to the increase of humification degree of Pinus tabuliformis litter,the decrease of humification degree of Picea asperata litter.At 80%WHC,the increase of temperature will reduce the humus degree of litter of Platycladus orientalis and Pinus tabuliformis.At 10℃,the increase of humidity will lead to the increase of humification degree of Pinus tabuliformis litter.At20℃,the increase of humidity will reduce the humus degree of litter of Platycladus orientalis and Picea asperata.At 30℃,the increase of humidity will lead to the decrease of humus degree of litter of Platycladus orientalis,the decrease of humin content in four coniferous tree forests.The comprehensive results show that the climatic conditions most conducive to the improvement of soil properties of the four coniferous trees are Platycladus orientalis and Picea asperata(30℃+20%WHC),Larix principis-rupprechtii(20℃+20%WHC)and Pinus tabuliformis(10℃+80%WHC).(3)In shrub forest,at 20%WHC,the increase of temperature will lead to the increase of available nitrogen content and sucrase activity in Ziziphus jujuba and Amorpha fruticosa forest land.At 50%WHC,the increase of temperature will lead to the decrease of urease activity in four shrub forests,the decrease of humification degree of Caragana microphylla litter and the increase of humification degree of Ziziphus jujuba litter.At 80%WHC,the increase of temperature will lead to the decrease of urease activity in four shrub forests.At 10℃,the humification degree of Caragana microphylla litter increased and that of Hippophae rhamnoides litter decreased with the increase of humidity.At 20℃,the increase of humidity will lead to the decrease of humus degree of Caragana microphylla litter,the decrease of phosphatase activity and urease activity in Caragana microphylla and Hippophae rhamnoides forest land.At 30℃,the increase of humidity will lead to the decrease of phosphatase activity in four shrub forests,the decrease of humin and available phosphorus content and urease activity in Ziziphus jujuba and Amorpha fruticosa forests.The comprehensive results showed that the climatic conditions most conducive to the improvement of soil properties of shrub forest land were Caragana microphylla(10℃+50%WHC),Hippophae rhamnoides,Ziziphus jujuba and Amorpha fruticosa(30℃+20%WHC).(4)In grassland,at 20%WHC,the increase of temperature will reduce the humus degree of Medicago sativa litter and increase the content of humin in four kinds of pasture.At50%WHC,the increase of temperature will lead to the increase of available nitrogen content and the decrease of urease activity.At 80%WHC,the increase of temperature will increase the degree of humus in the litter of Vicia villosa and Coronilla varia,and reduce the activities of phosphatase and urease in the four pastures.At 10℃,the humification degree of Melilotus officinalis litter increased and that of Medicago sativa litter decreased with the increase of humidity.At 20℃,the increase of humidity will lead to the decrease of phosphatase activity in four kinds of pasture,and the decrease of protease activity,urease and sucrase activity of Melilotus officinalis and Coronilla varia.At 30℃,the increase of humidity will lead to the increase of humus degree of Coronilla varia litter,the decrease of phosphatase in four grasslands.The comprehensive results showed that the climatic conditions most conducive to the improvement of soil properties of the four grazing grasslands were 30℃+20%WHC respectively.(5)The change of climate temperature and humidity has a great impact on the humus of litter.The degree of impact is not only related to climate temperature and humidity,but also depends on the types of litter.Relevant tests showed that the increase of available phosphorus content was beneficial to promote the humus degree of Populus simonii litter.The increase of available phosphorus and sucrase activity was beneficial to promote the humus of Platycladus orientalis litter.The increase of protease activity is beneficial to promote the humus formation of Larix principis-rupprechtii.The increase of available potassium content is beneficial to promote the humus of Picea asperata litter.The increase of available nitrogen content was beneficial to promote the humus of Hippophae rhamnoides litter.The decrease of hue coefficient is conducive to promote the humus of Ziziphus jujuba litter.On the whole,it is more suitable for the improvement of soil properties to humify the litter of Robinia pseudoacacia,Quercus liaotungensis,Platycladus orientalis,Larix principis-rupprechtii,Pinus tabuliformis,Hippophae rhamnoides,Ziziphus jujuba,Amorpha fruticosa and four forages under the conditions of high temperature and low humidity.Humification of Ulmus pumila and Populus simonii at 50%WHC is more suitable for the improvement of soil properties.The humification of Picea asperata under high temperature is more suitable for the improvement of soil quality.The humification of Caragana microphylla under low temperature is more suitable for the improvement of soil properties.The main conclusions of this study can provide guidance for forest and grassland soil fertility maintenance and vegetation management. |
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