Effect Of Vegetation Restoration On Nutrients Distribution And Stoichiometric Characteristics Within Soil Aggregate Of Mid-subtropical Eroded Red Soil Region

Changting County,located in Southwest Fujian Province of Southeast China is a the typical subtropical red soil erosion region,but a series of vegetation restoration measures have been taken to improving ecological structure and function including surface soil and water conservation in the past three decades.So vegetation coverage has been increased and soil physical-chemical properties were improved remarkably though management of erosional control.In order to overall understand the soil physical-chemical properties,Six typical eroded red soil sample plots from different restoration time(0,5,10,15,30 and 80 years)were selected that located in Hetian Town,Changting County,Fujian Province of subtropical China in this paper,where investigated nutrients distribution characteristics of soil aggregate nutrients and stoichiometric characteristics.The research not only revealed the effect of vegetation restoration on the accumulation and transformation of soil aggregate nutrient,but also provides a scientific support for soil quality evaluation and evaluation of ecological benefits.Soil nutrient content from different soil aggregate sizes(>5 mm,2?5 mm,0.5?1 mm,1?2 mm,0.25?5 mm and<0.25 mm)and different depth of soil layer(0?20 cm and 20?40 cm)were measured,and the correlation of nutrient content between soil and aggregate were analyzed as well.The results are as follow:1.Soil physical-chemical properties and nutrient stoichiometric characteristics of soil with the vegetation restoration processThe content of soil water change from 7.07%to 9.71%(the average value was 8.02%),which showed quite low level.The values of soil bulk density change from 1.25 g/cm3 to 1.53 g/cm3(1.48 g/cm3),which showed high values in eroded red soil area.Value of pH ranging from 4.28 to 4.84,showed middle-strong acidity except for the content of soil.They were also characterized decreased trend with the soil layer deepening.The sand content and silt content accounted for most of proportion,while clay content was quite low proportion.Variation coefficients of soil water content,the bulk density and pH value were lower than 16%at light variation level,and variation coefficients of soil particle fraction ranged from 17.28%to 20.52%at moderate variation level.The ranges of soil organic C,total nitrogen,total phosphorus total potassium,available phosphorus and available potassium contents were 2.24?18.07 g/kg,0.55?1.67 g/kg,0.049?0.141 mg/kg,2.9?6.69 g/kg,0.5?2.35 g/kg,respectively.Their mean contents were 6.98 g/kg,0.82 g/kg,0.087 g/kg,3.73 g/kg,1.26 mg/kg,and 28.98 mg/kg,respectively.The content of soil organic carbon,total nitrogen,total phosphorus and available phosphorus increased with the vegetation restoration time,while the content of total potassium was no significant difference in different vegetation restoration period except for 30a.However,the content of available potassium showed up-down-up trend.Variation coefficient of the soil nutrient ranged from 39.99%to 70.12%at highly variable level.Soil C:N?C:P and N:P ranged 4.02?10.81?35.7?134?4.6.62?12.45,respectively.With the soil layer depth deepening,the ratios of C:N and C:P got lower,and soil N:P ratios has no significant difference with the increase of soil depth.The order of nutrient stoichiometric characteristics was C:P>C:N>N:P,variation coefficients of them were more than 36%at height variation level,and the variation coefficient of C:P was the largest.2.Composition of soil aggregates and distribution of soil aggregates nutrients under vegetation restoration timeThe contents of organic carbon,total nitrogen,total phosphorus,total potassium,available phosphorus and available potassium within soil aggregate ranged 2.06?27.71 g/kg,0.54?2.12 g/kg,0.034?0.171 g/kg,2.20?6.89 g/kg,0.31?3.30 mg/kg and 7.35?85.71g/kg,respectively,with the process of vegetation restoration;the contents of organic carbon,total nitrogen,total phosphorus and available phosphorus generally increased with aggregate-size fraction decreasing(P<0.05),but the contents of total potassium and available potassium had no significant difference(P>0.05);during different aggregate size fractions,the contents organic carbon,total nitrogen,total phosphorus and available phosphorus within soil aggregate generally increased with the years of restoration prolong(P<0.05),the content of total potassium increased first and decreased finally,the content of available potassium showed a fluctuant increasing tendency;at the early years of vegetation restoration(0 and 5 years),the nutrient contents of two layers within soil aggregate kept relatively consistent,and soil aggregate nutrient contents at 0?20 cm were significantly higher than the depth of 20?40 cm;the diminishing order of contributing rate of aggregate fractions to soil nutrient was(>5 mm)>(2?5 mm)>(0.5?1 mm)>(1?2 mm)>(0.25?5 mm)>(<0.25 mm),the contribution rate of the faction in(>2 mm)were 34.18%?49.93%;soil nutrient contents were highly related to the soil aggregate size with>0.25 mm(P<0.01).In summary,soil erosion were controlled by measure of vegetation restoration,soil aggregate nutrient contented increased obviously associated with soil structure improving and nutrient sequestration promoting markedly.3.The effect of vegetation restoration on stoichiometic characteristics of soil aggregates over time.The soil aggregates C:N ratios,C:P ratios,N:P ratios were ranged 3.06?13.05,21.4?185.58,5.62?18.2,respectively,and their mean value were respectively 7.52,81.70 and 10.97 with vegetation restoration time.Soil C:N ratios in different soil aggregate size fractions were increased with the restoration year,while soil C:P ratios and N:P ratios in different soil aggregate size fractions showed up-down-up trend.The ratios of soil aggregates C:N and C:P generally increased with aggregate-size 'fraction decreasing(P<0.05),but the ratios of soil aggregates N:P had no significant difference among the different aggregate size fraction(P>0.05).And soil aggregate C:N ratios and C:P ratios at 0?20 cm were significantly higher than the depth of 20?40 cm,however,the N:P ratios had no significant difference in two layers.The ratios of soil C:N had a significant correlation with 0.5?1mm size soil aggregates(P<0.01),and 2?5mm size soil aggregates had a significant effect on soil C:P ratios and N:P ratios(P<0.01).Vegetation restoration is significant to balance and improve the structure and cycling of soil aggregate.