Morphological Characteristics and Nutrient Content of Fine Roots of 2-Year-Old and 3-Year-Old Eucalyptus grandis Plantation

[ Objective] This study aimed to explore the morphological characteristics and nutrient content of f＇me roots of 2-year-old and 3-year-old Euca/yptus grand/s plantation and investigate the correlation. [ Method] Fine roots of 2-year-old and 3-year-old Eucalyptus grandis plantation were collected as experimental materials, to determine the root diameter （D）, root length （L）, specific root length （SRL） and contents of major nutrient elements N, P, K, Ca, Mg and C of fine roots （level 1 -5）, study the morphological characteristics and major nutrient element content and investigate the correlation. [ Result] The results showed that morphological differences of fine roots （ level 1 - 5 ） of Eucalyptus grandis plantation were great with the increase of root order, to be specific, D and L increased and SRL decreased with the increasing root order; SRL, L and D of 3-year-old Eucalyptus grauclis plantation were greater than those of 2-year-old Euca/yptus grand/s plantation. Contents of N, Ca, Mg and C of fine roots of 2-year-old and 3-year-old Eucalyptus grandis plantation showed consistent orders with the increase of root order： N and Mg contents were reduced, while Ca and C contents were enhanced; P and K contents varied with different forest ages; both 2-year-old and 3-year- old Eucalyptus grandis showed an order of C 〉 K 〉 Ca （Mg） 〉 N. Major nutrient element content and morphological characteristics of Eucalyptus grand/s fine roots （level 1 -5 ） were extremely significantly correlated （P 〈0.01 ）, SRL, L and D could be adopted as reference indices to evaluate nutrient status of Eucalyptus grand/s. Required nutrients and fine root morphology of Eucalyptus grandis plantation changed with the increase of forest age, and the nutrient cycling and energy flow patterns also changed; major nutrient dements in fine roots of 2-year-old and 3-year-old Eucalyptus grandis plantation transferred in a different order from the growth order, therefore N fertilizer could be applied to improve the growth of fine roots. [ Condusion] This study laid the foundation for understanding the fine root morphology and nutrient variation pattern of Eucalyptus grandis plantation and enriching the response and adaptation mechanism theory of roots to environment, pos- sessing important reference significance for the sustainable development of Eucalyptus grand/s plantation.

Effects of Silicon on Physiology and Biochemistry of Dendrobium moniliforme Plantlets under Cold Stress

[ Objective] The study aimed to investigate the effects of silicon on physiology and biochemistry of Dendrobium moniliforme plantlets under low tempera- ture stress. [ Method ] By using Dendrobium monilforme as the experimental material, different concentrations of Na2SiO3 （0, O. 2, 0.4, 0.6, 0.8, 1.0, 5.0 and 10.0 mmol/L） was added to the basic medium[ 1/2MS ＋ 6-BA （0.1mg/L） ＋ NAA （ 1 mg/L） ＋ agar （7.2 g/L） ＋ sucrose （30 g/L） ] for tissue culture; af- ter hardening and transplanting, Dendrobium moniliforme plantlets were treated under low temperature stress at 4 ~C for 0, 24 and 48 h, in order to investigate the physiological response of Dendrobium ranniliforme leaves to different concentrations of Na2SiO3. [ Result] Under low temperature stress at 4℃, Dendrob/um mon//i- fortns leaves have certain osmotic regulation ability, and the three osmotic regulation substances show different variation trends at different stages. Appropriate con- centration of NshSiO3 can increase the contents of free proline, soluble sugar and soluble protein to varying degrees, reduce MDA content and further improve the cold resistance of Dendrobium moniliforme plantlets. The order of the effects of Na2SiO~ on various physiological indicators is ： free proline 〉 MDA 〉 soluble sugar （or soluble protein）. According to the correlation analysis among various physiological indicators, free proline, soluble sugar, soluble protein and MDA contents can all be used as reference indicators to identify the cold resistance of Dendrobium moniliforme. [ Conclusion] The addition of Na2SiO3 （0.4 retool/L） can moder- ately decrease the thermal energy for normal growth of Dendrobium moniliforme, which is conducive to reducing the cost of cultivation. Key words Na2SiO3 ;Dendrobium monlifforme;Low temperature stress;Physiological and biochemical characteristics