刺槐林下凋落物浸提液对刺槐种子萌发和胚生长的化感作用

  目的  探究不同世代和不同林龄刺槐Robinia pseudoacacia林下凋落物浸提液对自身种子萌发和胚生长的化感作用，旨在阐明刺槐林实生更新困难的原因。  方法  以刺槐人工林凋落物浸提液为化感物质来源，以刺槐种子为研究对象，采用培养皿滤纸法，分析不同经营世代及不同林龄的刺槐林下凋落物浸提液对刺槐种子发芽率、发芽势、发芽速度指数、活力指数以及胚生长的影响。  结果  刺槐林下凋落物浸提液抑制刺槐自身种子萌发和胚生长，且凋落物浸提液对胚根生长的抑制作用强于胚芽，不同林分以及不同质量浓度浸提液之间差异显著。在二代林和三代林中，随着林龄的增加，刺槐凋落物浸提液对种子萌发和胚生长的抑制作用呈减弱的趋势；在一代林中，中龄林凋落物浸提液对种子萌发具有促进作用，对胚生长的抑制作用较弱，化感综合效应指数分别为0.006和?0.032。随着经营世代的增加，幼龄林和中龄林下，刺槐凋落物浸提液对种子萌发和胚生长的抑制作用增强；成熟林下，随着经营世代的增加，其凋落物浸提液对种子萌发的抑制作用呈增加趋势，化感综合效应指数从0.044增加至0.097，对胚生长的抑制作用呈下降趋势，化感综合效应指数从0.124下降至0.050。部分林分下的凋落物浸提液具有质量浓度效应，对种子萌发和胚生长的抑制作用随着质量浓度的降低而减弱。  结论  不同林分刺槐林下凋落物浸提液对自身种子萌发和胚生长呈抑制作用；在二代和三代林下，凋落物浸提液随着林分年龄的增加，对刺槐种子萌发和胚生长的抑制作用呈减弱趋势；在幼龄林和中龄林下，凋落物浸提液随着经营世代的增加，对刺槐种子萌发和胚生长的抑制作用呈上升趋势。综上所述，连栽阻碍了刺槐实生苗的天然更新，但随着林龄的增加，对实生苗更新的阻碍作用会减弱。图3表1参38

Allelopathy of the litter extracts from Robinia pseudoacacia forest on its seed germination and embryo growth

  Objective  This study, with an exploration of the allelopathic effects of understory litter extracts from different stand types of Robinia pseudoacacia on seed germination and embryo growth, is aimed to clarify causes of the difficulty in seedling regeneration under R. pseudoacacia forest.   Method  With the litter extracts of R. pseudoacacia plantation used as the source of allelochemicals and the seeds of R. pseudoacacia being the subjects of study, the Petri dish filter paper method was emoloyed to analyze the effects of the understory litter extracts of different management generations and different stand ages on the germination rate, germination potential, germination speed index, vigor index and embryo growth of R. pseudoacacia.   Result  (1) The litter extracts under the R. pseudoacacia forest inhibited the germination and embryo growth of R. seudoacacia and the inhibitory effect of the litter extract on the growth of the radicle was stronger than that of the embryo. (2) There were significant differences between different forest types and different concentrations in the second-generation forest and the third-generation forest, the inhibitory effect of R. pseudoacacia litter extract on seed germination and embryo growth decreased with the increase of forest age. (3) In the first-generation forest, the litter extracts of middle-aged forests could promote seed germination, but had a weak inhibitory effect on embryo growth with the allelopathic effect composite index being 0.006 and ?0.032 respectively. (4) In middle-age forests, the inhibitory effect of R. pseudoacacia litter extract on seed germination and embryo growth increased with the increase of forest generations. (5) In mature forests, with the increase of forest generations, the inhibitory effect of the litter extract on seed germination showed an increasing trend with the allelopathy composite index increased from 0.044 to 0.097, whereas the inhibitory effect on embryo growth showed a decreasing trend, with the allelopathy composite index falling from 0.124 to 0.050. (6) The litter extract in some forest types had a concentration effect, and its inhibitory effect on seed germination and embryo growth weakened as the concentration decreased.  Conclusion  The litter extracts of different stand types of R. pseudoacacia undergrowth have an inhibitory effect on their own seed germination and embryo growth. In the second and third generation stands, the litter extract showed a weakening effect on the seed germination and embryo growth of R. pseudoacacia with the increase of stand age. In young-aged and middle-aged forests, the inhibitory effect of litter extract on seed germination and embryo growth of R. pseudoacacia increased with the increase of forest generation. In other words, continuous planting hinders the natural regeneration of seedlings of R. pseudoacacia, but as the forest age increases, the hindering effect on the regeneration of seedlings will be weakened. Ch, 3 fig. 1 tab. 38 ref.]