The Study Of Ecology Of Root System Of Eucalyptus Dunnii

Eucalyptus dunnii is a species with the characteristics of fast growing and low -temperature-tolerance. Increasingly reducing the region of cultivating eucalyptus,the north limitation of cultivation is constantly moving northern.Comparing with other species of eucalyptus which can not tolerance low temperature, E.dunnii had been planted in large scale for ten years.Because there is little knowledge about the root system(RS)ecological characteristics,it is urgently to study the RS ecology.After investigation of the biomass of major organs of E.dunnii,the root biomass(RB)and root length(RL)of three age and four level soil,the correlation and relationship of the biomass between above- and under-ground,the characteristics of root biomass and length of different diameter,difference in summer and winter,special root length and its spatial distribution were studied.The difference of RB and RL distributed up- and down-slope in a tree region was illustrated.The results can help further study in the field of root system of E.dunnii.The relationship and regression between the major organs and RS were studied with the parameter of DBH.When the model functions of linear,power,logarithmic,exponential and polynomial function simulated their relationships,all they were very significantly.That showed that the biomass of stump and RS are close to DBH which can be as the parameter to estimate the RB.At the same time,the relationship of the RB and RL distributed every layer in the soil and DBH the biomass of,trunk,branches,leaf were analysised with canonical correlation,finding that there are four coefficient for former,and later are three. There are obviously linear correlation between organs and RS.The correlation of above- and under-ground biomass of E.dunnii was studied.According the age of stand from 1 to 3 years the RB occupied the percentage of all tree was 17.04%,14.38%,11.25%in summer, respectively,22.58%,24.09%,20.12%in winter.The percentage of RB reduced with aging,and RB in summer less than in winter,showing that the RB will sharply increase in winter,sometimes in double its number,and more younger,more increasing,most of them accumulating in stump.The regression of RS with truck,branches,leaf and stump is significantly with power function simulating it.The RB and RL of E.dunnii had been investigated with the methods of soil coring and excavation.According the results of soil coring,the biomass of E.dunnii from 2-3 years was estimated 1.672t/hm²,1.852 t/hm²,1.693 t/hm²,1.970t/hm² in summer,comparing with the excavation,1.466t/hm², 1.524t/hm²,1.304t/hm²,2.058t/hm² in winter;respectively,the RL were 4.311m/m²,4.499m/m²,4.420m/m² 5.235m/m² with soil coring,and 2.038m/m²,4.450m/m²,2.411m/m^2,,5.772m/m² with excavation. Although the RL in summer differed in winter,there were no significant after using analysis of variance.It is suitable to estimate RB and RL of E.dunnii with soil coring.The level distribution of RS of E.dunnii was studied.The experiment show that there was obvious change of distribution of fine root(FR)of 0-1 mm and 1-2 mm in diameter in different distance from 1/3 of canopy,to 2/3 and to all canopy.The FR of one year had not extend the canopy,mainly developed in the vertical direction,accumulated in the fertilization in the level direction.It showed obviously the feature of moving to fertilizer,reducing the RB with the depth adding.The FR of two-year decreased linearly with the distance from truck,as same the other soil layers.The FR of three-year varied the formers,the most biomass distributed in the scope of 1/3 of canopy,then decreased in 2/3 of canopy,but increased in the edge of canopy.,speculating that it is intraspecific competiton leading the results.The longest of FR in summer distributed in the top-soil,the 46%-79%of FR of 0-2mm in diameter distributed in it,80%-93%in top- and sub-topsoil,the Length of FR(FRL)increased with old.But the FRB did not decreased before winter,only 23.74%-36.74%in top-soil.Even if the total FRB of topsoil and sub-topsoil only occupied 58.13%-68.72%,far less than in summer.48.09%-68.73%of FRL distributed in the soil from 10 to 30 cm depth,The RS of bigger than 2 mm in diameter did not obey the law.At the same time,the percentage of RB of one-year-old is the largest in the topsoil,of three-year-old is the least, however,the difference disappeared if the RB of topsoil summed up the RB of sub-topsoil,the percentage extent more than 80%.The FR in 10-30 cm soil layers died less than in the topsoil in winter so that the most of FR distributed in two layers.The reason is that there is less precipitation in winter drying the topsoil.The more depth was in vertical direction,the more biomass of coarse root with old.The RB distributed up-slope differed from down-slope in summer.The RL nearer to the truck is more significant,however the RB farther to the truck is significantly more than nearer.There are no significant of the special root length(SRL)in summer and all in winter.The law of RB in different season was studied.The RB in summer differed greatly from in winter,the biomass of stump doubled entering into winter,but the fine root biomass(FRB)multiplied reduction.The law of changing RB were showed that the percentage of RB occupied all of tree had been changing. Although the RB increased,but the percentage decreased,most of increase RB was onto the stump,the total RB was no change.The peak of RB increase is in August to December.The law of SRL was studied.The SRL of 0-1 mm,1-2 mm,and 2-5 mm in diameter in summer, respectively were in the scope of 900-2 500 cm/g,90-300 cm/g,20-100 cm/g.The SRL of one-old-year was usually in the lower limit,closely contacted to the growing period of seedlings of E.dunnii,because it had no fully grown.The SRL distributed in the every soil layers differed in summer from in winter,the former always were far bigger than the latter.Whether in summer or in winter and age,the root of 2-5 mm in diameter slowly increased from topsoil to down till the depth of 30 cm,but reduced gently in the fourth soil layer.For>5 mm in diameter,the SRL only occupied a small part of total SRL.