Characteristics Of Productivity And Carbon And Nitrogen Dynamics Of Chinese Fir Plantation

Chinese fir（Cunninghamia lanceolata） is a unique tree species in southern China and is widely used for fast-growing timber plantation. In this study, a total of 18 trees were harvested in order to obtain the optimal biomass allometric equations for Chinese fir in Dabie Mountain region of Anhui. In combination with the stand survey,the carbon storages in biomass, forest floor and mineral soil for the different aged stands were estimated. In addition, an experiment of N addition was conducted in a11-year-old stand to reveal the effects of N addition on stand growth, soil C and N dynamics, and soil respiration. The main results obtained are as follows.The optimal biomass allometric equations for branch, trunk, roots and whole tree were power function models in the form of W=a D^b, while was polynomial models in the form of W=a+b D²+c D⁴ for foliage regardless of ages. The result for model fitting was ranked by the order: trunk > whole plant > root > branch. The optimal models of biomass estimation for organs of Chinese fir plantation can used D or D² as variable regardless of stand age.The estimated biomasses of Chinese fir plantations from 10 to 50 years old ranged from 117.24·hm^-2 to 392.47 t·hm^-2. The carbon storages in biomass was from59.39 t·hm^-2to 201.25 t·hm^-2.The allocation of carbon storage in tree layer was changed with satnd age. The proportion of carbon storage in trunk contributed 58.68% ～ 60.15% of the total with a slight change with stand age. while there were relative great changes with the increase of stand age in the other biomass components. The order of carbon storage in the different components was ranked as trunk > branch > root > leaf for stands from 10 to22 years old. For the overmatured stands with ages from 45 to 50 years old, the order was trunk >root >branch >leaf. The carbon storages in forest floor were differed with stand age, matured stands( 12.47 t·hm^-2) > prematured stands(11.93 t·hm^-2) >overmatured stands(9.76 t·hm^-2) > mid-aged and young satnds(7.21 t·hm^-2).The carbon storage in 0～50 cm soils in the different aged satnds was ordered as overmatured stands(108.04 t·hm^-2) > matured stands(98.22 t·hm^-2) > prematured stands(67.02 t·hm^-2) > mid-aged and young stands(62.28 t·hm^-2). The total carbon storage in the Chinese fir plantation ecosystems increased with stand age, and the most rapid increase was appeared in the period from prematured to matured stage.The increments of mean DBH and total basal area were, respectively, 2.09m2·hm^-2 and 0.39 cm in the first year after N addition, which were slightly higher than in the control(basal area 1.75 m2·hm^-2and DBH 0.34 cm). This result indicate that the response of Chinese fir plantation growth to N additionwas slow in the first year.The SOC concentration decreased with soil depth. In the surface soil(0^-10 cm),SOC concentration was 9.59 g·kg^-1in the stands with N addition, which was significant greater in the controls(7.55 g·kg^-1). In the deep soil layer（10-30 cm）, SOC content was slightly higher in stands with N addition than in the controls. The soil organic carbon density ranged from 0.78 kg·m^-2to 1.79 kg·m^-2in 0^-10 cm soil layer,from 0.26 kg·m^-2 to 1.40 kg·m^-2 in 10-30 cm and from 0.22 kg·m^-2 to 0.70 kg·m^-2 in30-50 cm soils.The concentrations of soil DOC and DON were higher in the stands with N addition than in the controls, but the difference was not significant. Soil DOC and DON had a clearly seasonal trends in both N addition and the control stands, with the highest DOC content in spring. N addition had no significant impact on the seasonal variation of soil DOC and DON.The average contents of MBC and MBN were higher in the stands with N addition than in the controls for the whole soil profile. MBC content in 0 ～ 30 cm soil layer had significant seasonal variation, with the highest in summer and lowest in autumn. There were no significant differnce in MBC contents in autumn and winter between the N addition and the control stands. The result from regression analysis showed that soil MBC content was significantly positively correlated with NH₄⁺-N,NO₃^--N, total P and N; MBN content was significantly positively correlated with NH₄⁺-N, NO₃^--N, total P and N, and significantly negatively correlated with water content. DOC content was significantly positively correlated with NH₄⁺-N, total P and N, while was significantly negatively correlated with water content and total Mg.DON content was significantly positively correlated with NH₄⁺-N, NO₃^--N, total P and N; while was significantly negatively correlated with total Mg.During the experimental period, NH₄⁺-N content was always higher in the N addition stands, and the differences between N addition the the control satnds became larger as time went. The response of soil NH₄⁺-N to N addition was more sensitive in surface soil（0 ～10 cm） than in the deep soil（10 ～20 cm）.The content of NO₃^--N in soil fluctuated in the different seasons. Within 0 ～ 30 cm soil layer, the content of NO₃^--N was significantly higher in N addition stands than in the controls. In the control stands, the content of NO₃^--N was lower.The N mineralization rate varied significantly in annual cycle. The mineralization rate maintained a high level in May to July of 2014. In October to December 2013, two processing mineralization rate difference is the most significant.The nitrification rate greater than ammonification rate both in the two treatments stands.The soil respiration rate ranged from 0.19 to 3.09 μmol·m^-2·s^-1, with highest average rate in summer and lowest in winter. The diurnal variations were similar in both N addition and control stands. Soil respiration rate was higher in N addition stands than in the control stands in spring, autumn and winter.The macronutrients（N, P, K, Ca, Mg） contents of Chinese fir was quite different between organs, with an order of foliage > branch > root > stem. The contents of all elements were higher in foliage(total 36.36 g·kg^-1), while low in stem(total9.37g·kg^-1). The trend of nutrient contents in foliage was N > Ca > K > Mg > P. The trend of nutrient contents in branch was Ca > K > N > Mg > P, and in trunk, Ca >N > K > Mg > P, in root N > K > Mg > Ca > P.The contents of N, P and K elements in undergrowth plants were all higher than those in Chinese fir. The range of total element contents undergrowth plants was26.80 ～ 57.94 g·kg^-1, in which N concentration was 12.32 ～ 21.94 g·kg^-1 and P 0.74 ～1.87 g·kg^-1, K 9.58 ～ 23.31 g·kg^-1, Ca 0.64 ～ 4.41 g·kg^-1, Mg 3.52 ～ 8.33 g·kg^-1.