| Catalpa bungei is common high-quality timber and ornamental tree species, which has been traditionaly planted in warm temperate and sub-tropical regions of China, and it is warmly welcomed by public due to its excellent material quality and aesthetics. As always, the government pays great attention to its promotion and development. For the moment, the related cultivation techniques(irrigation, fertilization, etc.) coordinated with C. bungei are rarely reported, also, as one of previous fast growing tree species, C. bungei will be easily focused by public for its water and fertilizer consumption problem when planted widely in China, especially in arid regions. In addition, C. bungei will grow under different light conditions when planted in different densities and regions, and it is worthwhile to explore to determine whether these differences in light conditions will affect the responses of C. bungei to soil water and fertilizer factors. Thus, to timely study the mechanism of interactions of light with water and fertilzier has a theoretical significance and important practical value, and the main research results can provide theoretical support for water and fertilizer management, site selection, and density control in the process of C. bungei’s afforestation. In this paper, C. bungei clones 004-1 and 008-1 seedlings were respectively selected as the research object, in pot experiments using two experiment designs: rotatable central composite design with 3 factors(soli water content(W), nitrogen application(N), and phosphorus(P)) and 5 levels and completely randomized design(3×2×2) with three factors(light intensity(L), W, and N), the key growth, morphological and physiological indexes of these seedlings under different treatments wer examined, then the coupling effects of soil water and fertilizer and intercations of light intensity with soil water and fertilizer on the growth, morphological and physiological characteristics were respectively analyzed using mathematical model and mathematical statistics methods. The main results were showed as follows:(1) In terms of coupling effects of soil water and fertilizer on Catalpa bungei seedlings, W, N and W×N all showed significant positive effects on the growth, biomass yield, leaf SPAD values(SPAD-502 meter readings of leaf chlorophyll) and net photosynthetic rate, and the size sequence of the effects was N>W. The optimized combination was determined by establishing a multi-objective decision model based on the four parameters(stem height, ground diameter, biomass yield, and leaf area per plant), when the actual W, N, and P values reached 74.605% of the field capacity(FC), 4.710 g·plant-1, and 2.009 g·plant-1, respectively. Also, results showed that W and N both significantly positively affected the area and expansion rate of single new-developed leaves; N, P and W×N all significantly positively affected the growth and morphological characteristics valued of fine roots; W and W×N both significantly negatively affected leaf long-term water use effeciency(δ13C values), whereas N significantly positively affected leaf δ13C values. In terms of non-structural carbohydrates(NSC), NSC content at individual-level and NSC concentration at organ-level were observed to perform different responses to soil water and fertilizer factors, and NSC concetrations of different organs also performed different responses to soil water and fertilizer factors. As for NSC content, W, N, P, and W×N all significantly positively affected NSC content in seedlings, and the maximum NSC content was obtained when the actual W, N, and P values reached 69.25%FC, 4.84 g·plant-1, and 2.03 g·plant-1, respectively. In general, W and N are both important limited factors for the growth, morphological and physiological characteristics of C. Bungei seedlings, and the two effects were interactive. However, P, P×W, and N×P performed limited impacts on the growth, morphological and physiological characteristics of C. Bungei seedlings.(2) In terms of interactions of light with water and fertilizer on Catalpa bungei seedlings, L was also an important limited factor for the growth, morphological and physiological characteristics of C. Bungei seedlings, the two effects of L and W were interactive. In addition, results showed that L×N and L×W×N performed different impacts on all parameters. Overall, C. bungei seedlings under treatment with higher L+W+N had greater growth performance, whereas the growth of those seedlings under treatment with lower L+W+N was inhibited. Also, L was observed to significantlyaffected the responses of C. Bungei seedlings to W and N. In general, the seedlings under low L were more weakly affected by W and N in the growth, morphological and physiological characteristics compared with those seedlings under high L.(3) In terms of environmental adaptation strategies, results indicated that C. bungei seedlings adapted to weaker light condition mainly through promoting leaf chlorophyll content, increasing specific leaf area, and maintaining organs metabolism of NSC at the sacrifice of growth. On the other hand, C. bungei seedlings were observed to adapt to drought stress mainly through decreasing specific leaf area, controlling leaf stomata, and extending the length and surface area of fine roots.(4) Overall, C. bungei was observed to enjoy light, water, and fertilizer, and it would keep rapid growth only when subjected to good conditons with enough light and soil water and fertilizer. However, C. bungei’s growth was observed to be inhibited when excessive application of water and fertilizer was executed. In additon, results demonstrated that C. bungei was one of fast-growing tree species which had stronger adaptability to environment, and it could adapt to adverse environmental conditions(low light, drought, etc.) through its morphological and physiological adjustment mechanism. On ther other hand, results manifested that irrigation and fertilization performed different impacts on the growth of C. bungei under different light conditions. Specifically, under high light intensity, C. bungei’s growth would be enhanced by the proper manipulation of irrigation and fertilization, whereas irrigation and fertilization had relative poorer impacts on yield-increasing of C. bungei under low light condition, and it should be raised concern that it maybe lead to wasting water and fertilizer resources. |
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