Throughfall And Its Controlling Factors Of Typical Xerophytic Shrubs In The Loess Plateau Of China

Hydrological processes in arid regions control the distribution,structure and composition of vegetation.At the same time,vegetation has feedback effects on hydrological processes at various scales.Throughfall is an important component of the rainfall redistribution.It changes the spatial distribution pattern of rainfall under the canopy and affects the speed and direction of water and nutrient cycling in the soil.It is of great significance to the water use and growth of plants.In this study,the main sand-fixing shrubs in the northern Loess Plateau were taken as the research object.Through field observation experiments in 2016-2017,the formation process of throughfall of two dominant drought-bearing shrubs and the number of influencing factors?meteorological factors and morphological structures?were studied.The relationship was analyzed and the distribution pattern of the sub-canopy rain,The distribution patterns,spatial variability and the influencing mechanism of the leaf during throughfall were analyzed.The main conclusions are as follows:?1?During the experimental period,the effective rainfall events of C.korshinskii and S.psammophila were observed in 49 and 45 fields,respectively,the critical rainfall was 1.29 and 0.23 mm,respectively,and the total rainfall was 855.15 mm and 855.95mm,respectively.The total throughfall was 734.46 mm and 641.24 mm,and the throughfall percentage of C.korshinskii was in the range of 40.98-94.40%with an average value of 76.06%.The throughfall percentage of S.psammophila ranged from40.03 to 83.41%with an average of 69.37%.?2?There was a significant linear positive correlation between turoughfall and precipitation,rainfall intensity,and rainfall duration,throughfall percentage was a logarithmic function of then;And the correlation coefficient between throughfall and precipitation was highest.Throughfall percentage has the highest correlation with I₃₀.Throughfall percntage was negatively correlated with LAI,canopy thickness,branch length,and positively correlated with branch angle;the correlation between canopy thickness,branch angle and throughfall percentage was significant?P<0.05?,and canopy thickness is the most important form factor that affects the throughfall.?3?The mean values of the spatial coefficient of variation of the penetrating rain of C.korshinskii and S.psammophila were 20.95%and 20.17%,respectively.The coefficient of variation of throughfall decreases with the eigenvalue of rainfall.The main rainfall factors that affect the spatial variation of rain penetration are rainfall and I₃₀.The correlation between coefficient of variation and I₃₀ is the highest?P<0.01?.The frequency of aggregation effect of C.korshinskii and S.psammophila were 8.16%and2.41%,respectively.The effect of aggregation effect was significant under heavy rainfall and high rainfall intensity.Affected by the prevailing wind direction,the penetrating rain on the downwind side is higher than the leeward side;the penetrating rain increases with the complexity of the canopy structure and the farther the penetrating rain is from the base.?4?Leafless shurbs of C.korshinskii had a higher penetration rate of 10.95%than the normal,and the coefficient of variation decreased by 9.51%.The leafless of S.psammophila had a 10.67%increase in throughfall percentage and the coefficient of variation decreased by 4.84%.During the process of throughfall,the leaves increase the loss of rainfall during humid canopy at the beginning of rainfall and the time delay of reaching the wet conditions.At the point where the aggregation effect can occur,the leaves strengthen the canopy“water gathering”effect,improves the spatial variaton of throughfall.In the initial stage of rainfall or small rainfall condition,the impact of the leaves to throughfall process is greater.With the continuous or enhanced rainfall,the effect of the leaves on the penetration rate and the coefficient of variation is reduced.