The Effects Of The Plant Canopies And Fine Roots On Soil Physical And Chemical Properties In Slope Scale On The Loess Plateau

Vegetation restoration is the one of the main measures to prevent and control soil erosion,and improve soil quality on slopes of the Loess Plateau.In the process of vegetation restoration,plants effect soil physical,and chemical properties.Among vegetation effects,the individual plant canopies affect soil physical,chemical,and biological process by changing the micro-environment between or under canopies,and the plant fine roots are the main ways by which plant absorb water,and nutrients from soils.There have been few studies on the effects of plant canopies and fine roots on soil physical,and chemical properties on the slope scale.In this study,we conducted a field survey,and an experiment in Shenmu Erosion and Environment Research Station of the Institute of Soil and Water Conservation in Liudaogou small watershed in 2014.We selected a full slope where Prunus armeniaca,and Korshinsk peashrub both grew on the lower,middle,and upper position,and then investigated the vertical distributions of soil physical,and chemical parameters between and under the plant canopies.The vertical distributions of plant fine roots,and the relationships between plant fine root parameters,and soil parameters were studied.The results are shown as below.1.For Prunus armeniaca,soil mass water content,and soil saturated hydraulic conductivity were higher than in Korshinsk peashrub land in 0⁴0 and 0¹00 soil layers respectively,but the opposite for soil bulk density in 0²0 cm soil layers.The difference between different slope positions were not significant?P>0.05?for the soil bulk density but significant?P<0.05?for soil saturated hydraulic conductivity soil moisture in 0¹00 cm and10¹00 cm soil layers.Soil bulk density was greater under the plant canopies compared with outer the plant canopies in 0²0 cm soil layers,but was lower under canopies in 20¹00cm soil layers for both the two plants.However,the soil saturated hydraulic conductivity showed an absolutely opposite trend.For soil moisture,the values were greater under canopies in 0⁴0 cm layers but were lower in 40¹00 cm layers for Prunus armeniaca,where the values were alway lower under canopies for Korshinsk peashrub.There existed larger differences between and under vegetation canopies for the three soil physical parameters in Prunus armeniaca than in Korshinsk peashrub land.2.All the soil nutrient parameters were greater in Prunus armeniaca land than in Korshinsk peashrub land except the concentration of soil nitrate nitrogen.Plants played a significant role in changing soil ammonium nitrogen concentration in 0¹0 cm soil layers,and soil nitrate nitrogen concentration,and extractable phosphorus concentration in 0²0 cm soil layers?P<0.05?while did not alter other nutrient parameters significantly?P>0.05?.Slope positions had significant effects on the concentration of soil organic carbon,total nitrogen,total phosphorus as well as soil C/N,and C/P below the 20 cm soil depth?P<0.05?.Soil positions significantly affected the concentration of soil ammonium nitrogen in 60¹00 cm soil layers?P<0.05?.The order of soil nutrients on different slope positions for Prunus armeniaca,and Korshinsk peashrub land were not the same for different parameters.The patterns of soil nutrients under,and between the plant canopies were different with varied plant types,and slope positions.The concentrations of soil organic carbon,total nitrogen,and total phosphorus were larger under the plant canopies in 0²0 cm soil layers.3.The stocks of soil organic carbon,total nitrogen,and total phosphorus were greater in Prunus armeniaca land(namely 26.92,2.74,8.49 Mg ha^-1)than in Korshinsk peashrub land(namely 24.12?2.70?8.17 Mg ha^-1).In the area of Prunus armeniaca,the storages of soil organic carbon,and total nitrogen differed little in 0²0 cm soil layers,while the greatest values were in the lower position for 20¹00 cm soil layers.In Korshinsk peashrub land,the stocks of soil organic carobon,and total nitrogen were lowest in the lower position for all soil layers.The patterns of soil total phosphorus stock were in the opposite of soil organic carbon stock,and total nitrogen stock for the two plants.In Korshinsk peashrub land,the storages of organic carbon,and total nitrogen were larger under the plant canopies in 0⁴0 cm,and 0¹00 cm soil layers respectively.In Prunus armeniaca land,the stocks of total phosphorus were greater under the plant canopies in 0¹00 cm soil layers.The effects of individual plant canopiez did not have sigificant effects on the stocks of soil organic carbon,total nitrogen,and total phosphorus?P>0.05?.In our experiment,whether to consider the influence of the plant canopies,and the degree of vegetation coverage did not affect significantly among different calculation methods?P>0.05?.4.In Prunus armeniaca,and Korshinsk peashrub land,the plant fine root biomass,fine root density,and fine root surface area decreased with increasing soil depth,and differed litter in 40⁸0 cm soil layers,however,the plant fine root specific root length,and fine root diameter increased first and then decreased with increasing soil depth.The fine root biomass,fine root density,and fine root surface area were greater in Korshinsk peashrub land compared with in Prunus armeniaca land,while the specific fine root length,and fine root diameter differed little under the two vegetation types.In Korshinsk peashrub land,there were not signifcant differences of fine root biomass,fine root density,fine root surface area,specific fine root length,and fine root diameter showed similar pattern among different slope positions.In Prunus armeniaca land,the fine root biomass,fine root density,and fine root surface area were lowest in the middle slope position while the specific fine root length was highest in the middle position.There did not exist significant difference of fine root diameter among slope positions?P>0.05?.There existed extremely sigficant positive correlations between fine root biomass,and fine root length density,and fine root surface area?P<0.001?,while extremely negative correlation between fine root biomass,and specific root length?P<0.001?,and no significant relationship between fine root biomass,and fine root diameter?P>0.05?.5.There existed extremely significant positive correlations between specific soil parameters?soil saturated hadraulic conductivity,soil mass water concent,and the concentration of soil organic carbon,total nitrogen,nitrate nitrogen,and extractable phosphorus?,and some vegetation fine root indexes?fine root biomass,fine root density,fine root surface area??P<0.001?,while extremely negative correlation between soil bulk density,and the three fine root indexes?P<0.001?.In addition,correlation indexes between the consentration of soil orgainc carbon,and total nitrogen with the three fine root parameters were closer than soil physical paremeters with thoes fine root indexes.There did not exist sigfinicant correlated relationships between the concentraion of soil total phosphorus,and ammonium nitrogen with all fine root paremeters in this study?P>0.05?.As to fine root specific length,only soil organic carbon concentration negatively correlated with it?P<0.05?.All the tested soil parameters did significantly correlate with plant fine root diameter?P>0.05?.The results showed that,there existed significant difference for soil bulk density,and soil saturated hydraulic conductivity between,and under the plant canopies,while not for soil water content,and soil nutrients with the vegetation restoration in slope scale on the Loess Plateau.Althogh there did exist the higher values under the plant canopies for specific soil paremters in some soil layers,we could not confidently confirm that the phenomenon of"fertility islands"happened in our study area.The reason of this could be ascribed to the effect of vegetation types,and terrain conditions.All the soil physical,and chemical properties tested in our study affected the ability of plant fine roots developing soil resources,and the concentrations of soil organic,and total nitrogen affected the efficiency of plant fine roots development.With the study in the effects of terrian conditions,and plant factors,we could have a better understanding of the effect of slope land vegetation restoration on soil proerties.