Interactions between Soil Water and Fertilizer Application on Fine Root Biomass Yield and Morphology of Catalpa bungei Seedlings

Through a pot experiment using rotatable central composite design (RCCD) with three factors, five levels, twenty runs, fine root biomass yield (BY), total length (TL), surface area (SA) and total volume (TV) of clone 004-1 ofCatalpa bungeiseedlings under different treatments was determined, and then the mathematical models were established to study the main factor effects, monofactor effect and coupling effects of soil water(W), nitrogen application (N) and phosphorus application (P) on fine root biomass yield and morphological characteristics ofC.bungeiseedlings. Results showed thatNhad a significantly positive effect on BY, TL, SA and TV,Phad a significantly positive effect on BY, TL and SA,Whad a significantly negative effect on TL and SA, and the size sequence of main factor effects was:N>P>W. Monofactor effect analysis results showed that the values of BY, TL, SA and TV first increased and then decreased withNincreasing, and BY, TL, SA increased linearly withPincreasing. ForW, TL, SA decreased linearly and TV first increased and then decreased withWincreasing. Interaction ofW×Nhad a significantly positive effect on BY, TL, SA and TV ofC. bungeiseedlings, and the values of four parameters increased gradually withWandNincreasing. However, interactions ofW×P,N×Pboth affected four parameters non-significantly. In conclusion, root biomass and morphological characteristics ofC. bungeiseedlings showed distinct responses to soil water and fertilizer factors, andW, NandPalso influenced fine root growth ofC. bungeiseedlings differently. We recommended that fine root growth ofC. bungeiseedlings could be promoted by the rational method combined irrigation and fertilizer application.