Daily changes of leaf water content

transpiration rate

leaf water potential

and root water potential of Robinia Pseu doacacia from different stand densities and soil water within 60 cm of soil surface in the proving ground were studied on typical clear days during the peak season. Results are listed as following : (1) Daily average leaf water content of different stand densities was lower in August than J uly and was in the sequence ofρ2200>ρ2000>ρ1400>ρ1600>ρ1800 in the two months. (2) Diurnal variation of t ranspiration rate was similar in both months

meaning that the curves changed f rom“double peak”style to“single peak”with increased stand density and all the peak values appeared between 13 :00 and 14 :00. Daily average transpiration rate wasρ1800>ρ1600>ρ1400>ρ2000>ρ2200 in July and August . (3) Daily average leaf water potential of different stand densities was in the following order in both months :ρ1800<ρ1600<ρ1400<ρ2000<ρ2200 and was apparently lower in August than in July

with more obvious daily variation in August than in July. (4) Root water potential was higher than leaf water potential

with daily variation obviously less than leaf water potential

and daily average root water potential of five stands with different densities was in the order ofρ1800>ρ1600>ρ1400>ρ2000>ρ2200 and was lower in August than in July

with more obvious daily variation in August than in July.(5) Difference between leaf and root water potential ( S —L ) was negatively related with transpiration rate ( Tr) and such a relationship can befitted by logarihmic curve. (6) Leaf water potential of R. Pseudoacacia increases with leaf water content

the relationship between them can be described by logarithmic curve. (7) With the increased soil depth

soil water variation was lower in July than in August and the average soil water in 0 —60 cm layer declined with increased stand density. From the respective of effective water utilization and the best growth vigor

1800 st rains/ hm2 is the reasonable stand density.