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Effects Of Freezing-Thawing On Soil Nitrogen/Phosphorus Mineralization Over The Songnen Grasslands

Posted on:2017-01-03Degree:MasterType:Thesis
Country:ChinaCandidate:N DengFull Text:PDF
GTID:2310330485460055Subject:Ecology
Abstract/Summary:PDF Full Text Request
Nitrogen(N)and phosphorus(P)play critical roles in regulating plant growth.Normally,these elements are enclosed in organic matters,needing mineralization for plants uptake.Frequent freezing-thawing cycling occurrs in the Songnen Grasslands during late autumn and early spring,where belongs to the seasonal freezing-thawing region.Therefore,freezing-thawing events play an important ecological role in soil mineralization.We selected six soils with vegetation covers in the Songnen Grasslands,i.e.the Meadow Soils with Leymus chinensis,Phragmites australis associated with Artemisia scoparia,Leymus chinensis associated with Kalimeris interifolia,the Aeolian Soils with Cleistogenes squarrosa,the Saline-alkali Soils with Chloris virgata associated with Kochia scoparia,Artemisia anethifolia,and took intact soils to explore the effects of freezing-thawing events on soil nitrogen and phosphorus mineralizations.In laboratory simulation,we installed prerequisite soil moistures,defined freezing temperatures and freezing-thawing times.Soil total N,dissolved organic N,inorganic N,total P and available P under different treatments,were measured,respectively.Results are drawn as follows:(1)Freezing temperature,freezing-thawing duration and soil water content had no significant effect on soil total N,dissolved organic N,total P and available P in the Songnen Grasslands.However,freezing temperature and soil water content had significant effects on inorganic N.Freezing-thawing event can significantly increase the concentration of soil inorganic N in the Songnen Grasslands.(2)Freezing-thawing event and soil water content had no significant effect on total N in the six vegetated soils.Freezing temperature and freezing-thawing duration only had significant effects on dissolved organic N in the Meadow Soils with Leymus chinensis,where the concentration of dissolved organic N declined obviously after freezing-thawing event.Freezing-thawing event and soil water content had significant effects on inorganic N in all the six vegetated soils.After 5 cycles of freezing-thawing,the inorganic N concentration of the six vegetation soils significantly increased,where nitrate increased much than ammonium.The results implied that freezing-thawing alternations can enhance soil organic nitrogen mineralization especially under lower freezing temperatures and higher soil water contents.(3)Freezing-thawing incidence and soil water content took no significant effects on total P in the six vegetated soils.Freezing temperature and freezing-thawing duration only took effects on available P in the Meadow Soils with Leymus chinensis,Leymus chinensis associated with Kalimeris interifolia,where the available P level declined after freezing-thawing event.In short,our results indicated that freezing-thawing incidence can promote soil organic nitrogen mineralization processes in the Songnen Grasslands.The concentration of soil inorganic N increased significantly to favor the growth of plants,and also facilitate maintaining grassland ecosystem stability.
Keywords/Search Tags:Songnen Grasslands, freezing-thawing cycles, freezing temperature, soil moisture, nitrogen mineralization, phosphorus mineralization
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