Quantifications And Influencing Mechanisms Of Rainfall Interception Characteristics For Urban Landscape Plants

Landscape plants are important parts of urban green space ecosystem,and can intercept natural rainfall and reduce surface runoff,thus altering regional water cycle and environment,which had great significances for alleviating urban waterlogging and managing rainfall resources.Rainfall interception capacity is the key variable to select suitable landscape plant and evaluate the ecohydrological effects of urban green space.In this study,30 common and3 typical landscape plants were selected in Hefei city,for clarifying the interspecific and seasonal variabilities of leaf and canopy rainfall interception characteristics,and determining the relationships between leaf rainfall interception with leaf wettability and leaf functional traits,and the relationships between canopy rainfall interception with meteorological conditions and canopy structures.The main results are as follows:（1）leaf rainfall interception characteristics had obvious interspecific and seasonal variations.Leaf area and leaf wettability were the best predictors of leaf interception capacity and leaf interception capacity per unit leaf area（PSC）,respectively.Leaf rainfall interception characteristics of 30 landscape plants were measured by water immersion and water spraying methods.PSC ranged from 10.6 to 212.3 g m^-2 and 53.2 to265.0 g m^-2,respectively.The results obtained by the immersion method were significantly（p<0.05）lower than the spray method.The ranking and cluster analysis of PSC showed that Buxus sinica（BS）,Loropetalum chinense（LCr）,Spiraea salicifolia（SS）and Oxalis corniculate（OC）had the highest PSC,with the values of 149.3,113.6,128.3 and 122.6 g m^-2,respectively,by immersion method.The lowest PSC was recorded in Phyllostachys sulphurea（PSv）,Photinia serratifolia（PSk）,Cynodon dactylon（CD）and Hypericum monogynum（HM）,with the values of 47.8,52.9,49.4 and 38.5 g m^-2,respectively.From spring to winter,PSC gradually increased and reached the significantly highest in winter.The PSC obtained by immersion method in spring,summer,autumn and winter were 73.2,76.8,83.3 and 105.7 g m^-2,respectively.There were no significant differences in PSC among trees,shrubs,herbs,and among evergreen broadleaved,deciduous broadleaved,evergreen coniferous,and deciduous coniferous plants.However,deciduous species showed greater variations in PSC during the growth period than broadleaved species,with a more pronounced rise in winter.Leaf wettability was the best variable for determining PSC,whereas the functional traits such as leaf length,leaf area and leaf perimeter had no correlations with PSC.（2）The interspecific and seasonal variabilities of leaf wettability were related to PSC,and leaf surface micromorphology affected both leaf wettability and PSC.There were significant differences in leaf wettability among 30 common landscape plants,with the leaf adaxial and abaxial contact angles(CA_ad,CA_ab)ranged from 62.5°to 133.5°and 66.1°to 133.6°,respectively.CA_adwas typically lower than CA_ab.HM,Albizia julibrissin（AJ）,CD,LCr and Liriodendron chinense（LCs）had the highest CA,and Ophiopogon bodinieri（OB）,Ulmus pumila（UP）,Pinus parviflora（PP）,Gardenia jasminoides（GJ）and Pittosporum tobira（PT）were the lowest.From spring to winter,the variations in CA were opposite to PSC.CA showed a decreasing trend and reached the lowest in winter,with greater decline in CA_adthan CA_ab.No significant correlations were found between CA and all measured leaf functional traits,and it was difficult to accurately judge leaf wettability by a single surface microscopic parameter.Species with a dense waxy layer,more epidermal cell projections,the presence of trichomes and shorter stomata on the leaf surface tended to have higher hydrophobicity.（3）Rainfall redistribution characteristics of typical landscape plants were mainly determined by rainfall amount and intensity.The rainfall redistribution characteristics of three typical landscape plants Sophora japonica（SJ）,Platanus orientalis（PO）and Cinnamomum camphora（CC）during 12 rainfall events were monitored in the field.The average interceptions were 3.8 mm,3.6 mm and 3.3mm,accounting for 17.1%,16.0%and 14.7%of the total rainfall,respectively.Rainfall amount was the main factor affecting rainfall redistribution,followed by rainfall intensity.Interception,throughfall and stemflow increased linearly with rainfall,and the interception rate,throughfall and stemflow rates were exponential function of rainfall.Interception,throughfall,and stemflow increased with larger rainfall intensity.Rainfall redistribution characteristics were not significantly affected by rainfall duration and other meteorological factors.Throughfall and interception were not significantly correlated with canopy structure,and only stemflow was significant negatively correlated with leaf biomass and canopy area.There were differences in the rainfall interception capacity for different landscape plants.Clarifying the rainfall interception magnitude and its influencing factors（meteorological factors,canopy structure and surface micromorphology,etc.）contributes to reveal the regulation mechanism of green space system on urban ecohydrological processes.