| In this paper, a port experiment was conducted at the early growth, fast growth stage and late growth stage, respectively under five soil moisture regimes (40%, 52.2%, 70%, 87.8, and 100% of field water-holding capacity). We tested the early morning water potential, leaf relative soil water content, special leaf area, leaf dry matter content and leaf area and the dry matter accumulation and partitioning of young trees. In order to investigate effects of drought stress on the leaf moisture status,and dry matter accumulation and partitioning of young Robinia pseudoacacia at its different growth stages. The main results as follows:1. Drought stress had an overall impact on the trees and trees had a synergistic response to water deficit. Affected by drought stress, the leaves water status tended to deteriorate, and young trees growth was in decline. The total leaf area, the dry matte accumulation of different organs of young trees was reduced under drought stress, and the dry matter partitioning corresponding changes. However, drought stress had no significant effect on special leaf area and leaf dry matter content.2. The effects of soil moisture on the young trees followed by 40% of field water-holding capacity >52.2%>70%>87.8%>CK (100% 40% of field water-holding capacity). The early morning leaf water potential and relative leaf water content of R. pseudoacacia declined significantly under sever drought stress, and with less effect under medium and mild drought stress. Young trees leaves were very sensitive to drought stress. Total leaf area stop growing under mild drought stress, and decreased remarkably under sever and medium drought stress with some leaves shriveled and fell. The dry matter accumulation of leaf, stem, branch, total shoot, and total dry matter accumulation of R. pseudoacacia seedlings, the dry matter partitioning ratio of leaf, total shoot had a remarkable decrease, the course root dry matter partitioning and total root/ total shoot ratio raised under sever drought stress. But mild drought stress had less effect on the dry matter accumulation and partitioning of R. pseudoacacia seedlings.3. The effects of drought stress became worse on young trees growth with the extending drought stress time, but no significant impact on young trees leaf moisture status. Short-term (15 d) drought stress had no remarkable effect on young tress growth, however, long-term (45～60 d) drought stress had significantly declined the leaf, stem, total shoot dry matter accumulation, and leaf, total shoot dry matter partitioning ratio of R. pseudoacacia seedlings.4. Drought stress had different effects on different parts of R. pseudoacacia seedlings, for the dry matter accumulation, the effects leaf> stem>course root> fine root; total shoot>total root; and for the dry matter partitioning ratio, the effect leaf>fine root>course root>stem. As affected by the inherited growth characteristics of R. pseudoacacia itself and the variation of weather conditions of among seasons, drought stress had different extents of effects on the dry matter partitioning of R. pseudoacacia seedlings at its different growth stages, with the most significant effect occurred of early growth stage and the least at late growth stage.5. Rewatering simulated the aboveground growth of R. pseudoacacia seedlings, which had an obvious compensatory growth. However, the underground growth rate slowed by rewatering. The dry matter partitioning ratio had corresponding changes after rewatering. Rewatering after sever drought stress, the leaf, stem, total shoot had no obvious compensatory growth phenomenon, but the compensatory phenomenon happened under mild drought stress. The leaf and total shoot dry matter partitioning ratio increased after rewatering, and the course root and total root dry matter partitioning decreased but still higher or approaching CK treatment after rewatering. However, rewatering had no remarkable effects on the stem and fine root dry matter partitioning ratio. |
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