| Eucommia ulmoides Oliver is one of a few tree species that produce trans-1,4-polyisoprene(TPI or Eucommia rubber).Raw materials from short rotation coppice(SRC)cultures for TPI industrialization are a valuable option.However,there are few researches on density effect and biomass estimation of Eucommia SRC.Meanwhile,the effect of the application of plant growth regulators on the content and yield of E.ulmoides TPI were still not systematic and comprehensive.In this study,an Eucommia SRC established in 2015 compromising five planting densities was studies.The planting densities were 13333 trees hm-2?16667 trees hm-2?22222 trees hm-2?33333 trees hm-2?66667 trees hm-2.In order to confirm the optimal planting density of Eucommia SRC coppice,growth index and three years' biomass in different densities were compared.In order to improve the precision of biomass estimation,the biomass model of single plant dry weight was fitted based on plant height,base diameter and their combination.An orthogonal experimental design consisting of the following four regulators was used: 1% brassinolide(BR)powder,2-(3,4-dichlorophenoxy)-triethyl amine(DCPTA),2-(diethylamino ethyl hexanoate)(DTA-6),and gibberellin(GA).The differences of growth index and bimass were analyzed among regulator treatments and control during the first two annual rotations.The active components,TPI content in leaf and bark were also tested.The appropriate regulator type and its concentrations suitable for field application was thus selected.The main results are as follows:1.The average sprouting branches,basal diameter,number of leaf per tree,and leaf weight ratio were significantly negative correlated with planting densities;while LAI was significant positively correlated with densities.The average dry weight of leaves,bark and trunk(without bark)per plant were negatively correlated with densities,while the biomass per unit ground area of leaf,bark and trunk(without bark)was positively correlated with densities.Particularly,they were significant positively correlated with LAI with correlation coefficient of 0.906,0.700,and 0.674,respectively.LAI under density of 66667 stems hm-2 was 7.98.The biomass of leaf,bark and trunk was 3473.06 kg hm-2?1568.58 kg hm-2?11069.38 kg hm-2,increased by 2.5-,2.8-,and 2.7-fold over those under density of 13333 stems hm-2,respectively.In third rotation,there were the maximum leaf,bark and stalk biomass in density of 33333 strains hm-2(=99999 stem hm-2)with 5157.45 kg hm-2,2008.83 kg hm-2 and 12099.91 kg hm-2,respectively.Based on the management philosophy of annually harvesting leaf,bark,and stolk,Eucommia SRC could be planted in higher densities,such as 66667 stems hm-2 or 66667 spouting branches per hm2,so as to produce more biomass per unit ground area per year.2.Quadratic term functional model was optimal for leaf and bark biomass evaluations,while both the quadratic term functional model and power functional model were most effective for stalk biomass estamations.The fitted equation was Y=2.618+1.097*(DL)+ 0.003*(DL)2 for leaf biomass estamation,Y=0.068+0.387*(DL)+0.001*(DL)2 for bark biomass,and Y=25.545+3.042*(DL)+0.010*(DL)2 /Y=0.690*(DL)1.377 for stalk biomass,respectively.The model was verified available with residual error.Model precision accuracy analysis suggested that the error was within the required range,and thus indicated that the model was applicable.This study was the beginning of biomass model database and provided the basis for biomass measurement of Eucommia SRC.Determination coefficient,standard error of estimate and residual analysis was used to reflect comprehensively and systematically merits of the model.3.100 mg L-1 DTA-6 treatment significantly increased chlorophyll a,chlorophyll a+b and carotenoid content by 40.01%,38.69%,39.56%,while 5 mg L-1 brassinolide treatment significantly increased the content of chlorophyll b 52.49%.The content of aucubin and geniposidic acid in all treatments were significantly enhanced by 35% more than that of the control.The regulator had a weak effect on the content of chlorogenic acid.The content of active components varied greatly from one regulator to another.DTA-6 and gibberellin treatments had obvious effect on chlorogenic acid,which the content of chlorogenic acid were increased by 6.36%-23.10%.DTA-6 and brassinolide treatments significantly inhenced aucubin and geniposidic acid content by more than 40%.The content of aucubin in all treatments were increased by more than 37%,while the highest that in 500 mg L-1 DTA-6 treatment increased by 72.06%.The content of geniposide increased by 63%-90% in all treatments except in 300 mg L-1 DCPTA treatment.DTA-6 significantly promoted the synthesis of photosynthetic pigments and active active components,showing a more stable effect.Overall,DTA-6 was the most effective regulator in enhancing the active ingredients in Eucommia leaves and it should be taken into account in the future practical applications.4.Foliage spray of regulators led to more and larger leaves,more bark yield,higher tree height,and higher leaf TPI content,which reflected the enhancing effects of regulators on leaf and bark biomass as well as TPI productivities in both the first and second rotations.Brassinolide at 5mg L-1,DCPTA at 500 mg L-1 and DTA-6 at 20 mg L-1 reached the highest TPI productivity among treatments of 406 kg hm-2,391 kg hm-2 and 382 kg hm-2 in the second rotation,respectively,all of which were more than 1.4 times that of the control.Meanwhile,the harvest of Eucommia leaf and bark from the coppice plantation was less labor intensive than that from tall mature trees.Our study suggested that the annual rotation period and increase of TPI from Eucommia SRC by application of regulators could reduce the payback period.Therefore,we recommend the application of growth regulators to coppice Eucommia plantations beginning from the first rotation as an economic means to increase TPI production. 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