Ecological Stoichiometry Characteristics Of Carbon,Nitrogen,Phosphorus And Kalium In Eucalyptus Urophylla×E.grandis Plantation At Different Stand Ages

In order to understand the influence of different ages on the growth of E.urophylla×E.grandis plantation and reveal the correlation between the characteristics of plant growth and restrictive elements,to research the quantitative relationship between the E.urophylla×E.grandis plantation in the process of growth and the chemical elements.In this paper,1,2,3,5 and 7-year-old five ages of Eucalyptus urophylla×E.grandis plantation were studied the biomass allocation and Ecological stoichiometry characteristics in Leizhou Peninsula,using the quadrat harvesting method,layered cutting method and analytical wood method to detemine the biomass and ecological stoichiometry.The results are as follows:1.The biomass distribution characteristics of Eucalyptus urophylla×E.grandis plantations of five agesThe total biomass increased with the increasing of plantation age,the total biomass changed between the 14.08 and 300.86 t·hm^-2,Wooden arbor layer at all levels in Eucalyptus urofhylla×E.grandis are the largest proportion in the total biomass accounting for38.71%⁹1.52%,and with the increasing of forest age the shrub layer?herbaceous layer and the proportion of litter layer substantially decreased with an increasing of the stand age and accounting for 4.84%²0.1%?1.56%²4.9% and 2.84%²5.85% respectively;The trunk in the wooden arbor accounting the largest proportion for 24.95%⁶6.84%,1³ a is on the rising,among 3⁵ a being a downward trend and gradually increase in 5⁷ a;Leaves,branch,root and fur accounting for 2.37%²3.67%,8.9%²0.73%,17.35%³0.5%,4.55%⁸.08%respectivrly,5⁷ years old last grandis stand biomass than other plantation species stands,it is a rapid growth,superior carbon sequestration potential of afforestation species.2.Ecological stoichiometry on different organs of five ages1,2,3,5 and 7-year-old organic C,N,P,K content in an average of 476.6 ± 8.19 g·kg^-1,6.24± 1.68 g·kg^-1,0.98 ± 0.12 g·kg^-1,3.46 ± 0.60 g·kg^-1,the organic C along with the growth of theforest age first fall after rise,total N with the growth stand ages showed a diminishing trend,total P with the growth of forest age firstly increased and then decreased,total K with the growth of forest age was lower before the change trend of rese;In various organs,the highest content was C,Organic C content of leaves reached 518.28 ± 6.33,the lowest content was P,among them the lowest total P content in root was 0.58 ± 0.06;In the N,the minimum content of stem was 2.4±0.36,the highest content of leaves was 18.59 ± 0.68;In the K,the minimum content of stem was 1.33 ± 0.16,the highest content of leaves was 7.27 ± 0.23;In five plantation forest,C:N,C:P,C:K,N:P,N:K ratio of average were 152.50±14.34,635.2±50.81,229.88±21.50,6.08±0.48,1.76±0.10;In each organ element ratio,C:P ratio was the highest,Among them,the root of C:P ratio was the maximum for 1055 ± 183.30,P:K ratio was the minimum,the lowest P:K ratio was leaves for 0.21 ± 0.01.3.soil-litter ecological stoichiometry Characteristics at five agesFive forest ages,organic C content in 0 to 60 cm soil layer was 14.99 19.66 g·kg^-1,expressed as 2 a>5 a>3 a>7 a>1 a;Total N content ranged from 1.07 to 1.31 g·kg^-1,expressed as 2 a>3 a>1 a>7 a>5 a;Total P content ranged from 0.69 to 0.82 g·kg^-1,the highest and the lowest content respectly for 1 a and 5 a,there was no difference;Total K content ranged from0.33 to 0.82 g·kg^-1,the highest levels in 2 a and the lowest content in 5 a,effective N content was 123.57 to 127.60 mg·kg^-1,effective P content ranged from 0.41 to 6.17 mg·kg^-1,rapidly available K content was 33.09 to103.18 mg·kg^-1.Soil nutrients increased with the increasing of forest age variability was large,C:N ratios variation ranged from 9.1 to 22.03 and had no difference in ages;C:P ratios variation ranged from 16.14 to 38.06,there was a significant difference in the 3 a,5 a and 7 a in 40-60 cm soil layer,C:K ratios variation ranged from 6.73 to41.94,there was a significant difference in the 3 a of 40-60 cm soil layer;N:P ratios ranged from 1.02 to 2.06,there was a significant difference in 5 a of 40-60 cm soil layer;Litter organic C,N and P in the highest content in 1 a and respectively were 497.37±41.80,9.18±0.36 and0.69 ±0.11,with the increasing of forest stand age continues to be reduced to 7 years and increase unceasingly,K increased with the increasing of forest age firstly then decreased,there was no difference in forest age addition N;C:N,C:P increased with the increasing of forest agefirstly and then decreased;C:K,N:K and P:K with the growth of forest age firstly decreased then increased;N:P with the growth of forest age firstly decreased then increaseand then decreased again.There was no correlation between litter and available nutrients of soil,but it had a significant negative correlation with soil organ C and a significant negative correlation with total N.In summary,the biomass of Eucalyptus reaches its maximum when 5 a and 7 a,with the increasing of forest age the biomass has also been increased,the N:P ratio of leaves of Eucalyptus grandis indicates in the process of growth is limited by factors of N,P less restrictive,in the soil organic C and K are the main elements of the impact,in the growth of Eucalyptus grandis should pay attention to reasonable regulation element assignment to improve land productivity.