| American Black Walnut (ABW) belongs to Juglandaceae, Juglans, Sect. Rhysocauyon and is a general designation of woody plant, the Sect. Rhysocauyon is composed of 16 species, of which 8 species originated from America. The materials we used are J.nigra, J.hindsii, J.major and J.paradox etc.The Effects of soil drought stress on water architecture parameters and growth dynamics of American Black Walnut with different genotypes were studied in this studies, the osmotical adjustment, photosynthesis efficiency , antioxidation, ultra-weak biophoton emission(UBE) and compensation growth effect were analyzed, as well as the drought-resistance in the black walnut were valued comprehensively and explored. The main results are as follows:1. Drought stress have an important impacts on the features of water and architecture, growth dynamics in different genotypes. Moderate water stress caused decrease of "Daily growth rate(DRG)" in seedlings of American Black Walnut, however, when the seedlings were rewatering, they showed the compensation or overcompensation effect, but water stress and rewatering had not changed the inherent rhythms of growth of ABW, The studies on the different genotypes of ABW showed that, J.nigra belonged to "Fast growth patterns in earlier of year", whereas the J.hindsii and J.major belonged to "Fast growth patterns in later of year". Such a difference was determined by their genetics, although water stress have some influence on them.2. In this study , the overcompensation resulted from different stress was divided into two types for the first time. The overcompensation caused by damage of living beings was designated to "Compensation Type I" and overcompensation caused by non-biological factors was designated to "Compensation Type II". The latter was also divided into "All compensation" and "Distribution compensation". J.major showed the "Distribution compensation" because their accumulation of the dry biomass was lower than the conrtrols. The prelinmilary study on the mechanisms of overcompensationshowed that: although water stress inhibited the extension of leaf areas in the seedlings of J.nigra temporarily, the leaf area did not decease in J.hindsii and J.major and dry biomass increased considerable^. The result indicated that the parameters such as SI, LDW/SA, and LA/SA increased by a large extent. Suitable water architecture are the basics for J.major to remain fast growth.3. There were considerable osmotic adjustment(OA) and elastic adjustment in different genotypes of ABW. The lowest water potential in J.nigra, J.hindsii and J.major reached -2.15Mpa,-1.52Mpa and -1.93Mpa, respectively. The most OA is 0.74Mpa.In general, J.hindsii and J.major depended mainly on a better water architecture and a relative higher water potential to fight against water stress, thus they belonged to drough- tolerant plants with high water potential.4. The osmoticas in dirrerent ABW under water stress included: proline, soluble sugar, amino acid, K+, ,Ca2+, Mg2" etc, the increase in the content of proline was the most significant, but soluble sugar, amino acid and Ca2+ have the greatest contribution to osmotic adjustment.5. Under water stress, the type of hormones and their ratio were different in different genotypes. After water stress, the content of ABA in J.nigra was 2-3 folds of that in J.hindsii and J.major the content of IAA in J.major was far higher than that in other genotypes. This was mechanism of hormones regulation of overcompensation.6.The elimination of Active oxygen species(AOS) by the co-work of the enzymes such as SOD,CAT ,APX etc. in antioxidation systems of ABW. In this study, it was the first time to discover that there was a large difference in the activities of POD. The activities in three genotypes remained very low all the time, however, the activities of POD in J.regia was 5-9 folds of the ABW. We speculated that it was the low activities of POD that caused J.hindsii and J.major to remain the fast growth rate under water stress, this was probabl...
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