The Relationship Between Near-Surface Morphological Traits At The Initial Stage Of Typical Plants Growth And Their Ability For Sediment Retention In Dry-Hot Valley

Under the background of fragile ecological environment and frequent mountain disasters,declining vegetation coverage caused by serious soil erosion in dry-hot river valley of the Jinsha River has resulted in a vicious cycle of environmental degradation and aggravated soil erosion.The near-surface part of plant specie has a major effect on reducing erosion dynamics and soil losses by intercepting sediment transported during the formation of near-surface runoff.Identifying the relationship between near-surface morphological traits of specie individual and its ability for sediment retention is of great interest to restore ecology and control soil and water losses in dry-hot river valley of the Jinsha River.By lab simulation and out-site flume experiment,we studied the ability for sediment retention of six typical species（Leucaena leucocephala（LL）,Melia azedarach（MA）,Dodonaea viscose（DV）,Coriaria sinica（CS）,Heteropogon contortus（HC）,and Eulaliopsis binate（EB））at two growing periods.We analyzed the particle size distribution characteristics of sediment and the relationship between near-surface morphological traits of species individuals and their ability for sediment retention.Based on the experimental data,we identified the key factors affecting the ability for sediment retention by near-surface morphological traits of species,and built up the model for evaluating the ability of sediment retention.The study results are reflected in the following aspects:（1）Three-month seedlings and one-year old seedlings of the six species had different ability for sediment retention in this flume experiment.In the three-month seedlings,the ability for sediment retention of CS was the highest,followed by MA and LL,and the lowest in HC and EB.However,in one-year old seedlings,the ability for sediment retention of CS was also the highest,but the ability for sediment retention of HC and EB were better than MA and LL.In different growing periods,the ability for sediment retention of the six species had different changes,the one-year old seedlings of CS,HC and EB trapped respectively 3.09,11.15,and 6.77 time more sediment than their three-month seedlings.Besides,the sediment trapped by one-year old seedlings of LL,MA and DV was also more than their three-month seedlings,but the differences were not significant.（2）The sediment trapped by the three-month seedlings and one-year old seedlings of the six species had different particle size distribution in this flume experiment.In the three-month seedlings,the particle size of sediment trapped by LL,MA,DV and EB mainly concentrated in 0～1mm,5～10mm by CS,and the particle size of sediment trapped by HC mainly concentrated in 5～10mm and 0～1mm.In one-year old seedlings,the particle size distributions of sediment trapped by LL and CS were same as their primary seedlings,5～10mm by HC,and the particle size of sediment trapped by MA,DV and EB mainly concentrated in 5～10mm and 0～lmm.The fine particle（0～1mm）of sediment trapped by three-month seedlings and one-year old seedlings of the six species all concentrated in sand（0.05～1mm）and silt（0.002～0.05mm）,but the clay（0～0.002mm）was rarely trapped by the six species during the flume experiment.By comparing two growing periods of the six species,the content of particles at each size of coarse and fine particle all increased or decreased,but their change degrees were different.（3）The three-month seedlings and one-year old seedlings of the six species all showed different near-surface morphological traits.With the growth of plants,the near-surface morphological traits had different degree changes,and resulted in changes of main near-surface morphological traits for trapping sediment.（4）Principal component and correlation analysis showed that the sediment mass was significantly positively correlated with near-surface leaf area,crown length,crown width,stem dry matter density in the interception volume and above-ground biomass（p<0.01）,but significantly negatively correlated with the angle between stem and ground（p<0.01）.So they were the main near-surface morphological traits factors affected the ability for sediment retention.Besides,the sediment mass was also correlated（positively and negatively）with stem epidermal crack number,stem dry matter content,leaf dry matter content in the interception volume and dry mass per unit volume of the interception volume（p<0.05）.So they could also reflect the ability of sediment retention.（5）Taking the angle between stem and ground（X₁）,stem epidermal crack number in the interception volume（X₂）,stem dry matter content in the interception volume（X₃）,stem dry matter density in the interception volume（X₄）,near-surface leaf area in the interception volume（X₅）,leaf dry matter content in the interception volume（X₆）,crown length in the interception volume（X₇）,crown width in the interception volume（X₈）,dry mass per unit volume of the interception volume（X₉）,above-ground biomass(X₁₀)as independent variables and the sediment mass（Y）as dependent variable,the model of the ability for sediment retention was built by liner regression analysis as Y=-0.116X₁-0.162X2-0.011X₃-0.107X₄+0.837X₅-0.140X₆+0.013X₇+0.184X₈+0.089X₉+0.118X₁₀+10^-7,and the model fitted well.So this model could provide a reference for the building of assessment indicator system for sediment trapping and the future research of the relationship between near-surface morphological traits of species individuals and their ability for sediment retention in dry-hot valley.（6）The scores of species individuals ability for sediment retention at two growing periods followed the rule as CS1（2.623）>HCl（0.923）>EB1（0.371）>CSS（0.077）>DV1（-0.383）>MA1（-0.393）>DVS（-0.434）>HCS（-0.448）>LL1（-0.482）>LLS（-0.576）>MAS（-0.639）>EBS（-0.640）,and these results were consistent with observed values.This study found that throughout the growing periods,CS was the most affective in sediment retention compared to DV,HC,EB,LL and MA.The HC and EB had strong ability for sediment retention after reaching the age of one year while LL,MA and DV had low sediment retention capacity throughout their growing periods.Therefore it is advisable to take CS into primary consideration for vegetation restoration and soil erosion control.