Relationship Between Evolution Of Understory Plant Functional Groups And Soil Nutrient In Eucalyptus Plantations

Eucalyptus plantation is the main source of commercial timber in China.It is of great significance to maintain the sustainable management of Eucalyptus plantations.In this study,by using space-for-time substitution approach,we chose a chronosequence representing the low generation rotations(1-2 generation,EP12),middle generation rotations(3-4 generation,EP34)and high generation rotations(5-6 generation,EP56)of Eucalyptus plantations to comparatively analyze the effects of high generation successive rotations on understory plants,soil nutrients and enzyme activities.The dynamic changes of plant community structure under Eucalyptus plantations and the relationship between species composition and soil nutrients were analyzed by multidimensional scale analysis and redundancy analysis.The correlation analysis method was used to analyze the correlation among plant diversity,soil nutrients and enzyme activity.The main results are as follows:(1)The diversity indices of the understory plant community significantly decreased,and the structure of understory plant community significantly changed over successive rotations.(2)The plant species component and functional groups of the understory changed significantly over successive rotations.The dominant species in EP12 were the native woody plants such as Alchornea trewioides,Litsea pungens and Mallotus apelta,and the important value of the native woody plant functional group accounted for 67.46%.In EP34 stands,the nativOttochloa nodosa and Microstegium vagans were the dominant e herbaceous plants such as species with important values taking up 78.69%.Invasive plants,such as Bidens pilosa,Eupatorium odoratum and Borreria latifolia,dominated in EP56,with important values accounting for 86.25%.These results showed that the understory plant functional groups of have evolved from native woody plant functional groups,to native herbaceous plant functional groups,and then to invasive plant functional groups over successive rotations.(3)The results showed that 9 soil nutrient indexes,such as soil organic matter,total nitrogen,total potassium,total phosphorus,ammonium nitrogen,nitrate nitrogen,available phosphorus,available potassium and water content,and 6 soil enzyme activities,such as soil phenoloxidase,peroxidase,acid phosphatase,urease,?-1,4-glucosidase and N-acetyl-?-glucosaminidase,were significantly decreased over successive rotations,but the change of soil pH was not significant.Soil available potassium content and peroxidase activity were positively correlated with Axis 1 axis.Soil organic matter content,total potassium content,water content,ammonium nitrogen content,nitrate nitrogen content,C/N ratio,N/P ratio,soil urease,?-1,4-glucosidase and N-acetyl-?-glucosaminidase were negatively correlated with Axis 1 axis.With the increase of successive rotations,the changes of these nutrients and enzyme activities are related to the evolution of understory plant functional groups of with the increase of successive rotations.(4)The correlation analysis showed that the diversity of understory plants in Eucalyptus plantations was positively correlated with soil nutrient indices and soil enzyme activities(except soil acid phosphatase)(p<0.01).Soil acid phosphatase was positively correlated with Shannon-Wiener index and Pielou evenness index(p<0.05).With the increase of successive planting generations of Eucalyptus plantation,the evolution of understory plant functional groups of,the diversity of understory plants,soil nutrient and enzyme activities showed a significant downward trend.(5)Redundancy analysis(RDA)of the understory plant community structure and soil nutrient indices showed that there were significant differences in the tested soil nutrient,and the tested soil enzyme activities were the key factors in regulating plant functional groups in Eucalyptus plantations,and the accumulative effects explained 39.6%of total variations in understory plant functional groups.There were significant differences in understory plant community structure of Eucalyptus plantations under different successive generations.