Understory plant diversity and phenolic allelochemicals across a range of Eucalyptus grandis plantation ages

Allelopathy is an important mechanism in Eucalyptus plantations that causes detrimental impacts on understory diversity.Phenolic compounds are the main allelochemicals suppressing understory plants.However,the dynamic changes in phenolic allelochemicals and their relationship with understory diversity with increasing age of Eucalyptus plantations remain largely unclear.In this study,the understory plant diversity was assessed and phenolic compounds identified from leaf litter,roots,and rhizosphere soil samples in a Eucalyptus grandis plantation at two-year intervals for ten years using ultra-performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS).The abundance and diversity of under story plant species were lowest in 4-year-old plantations and increased significantly with age.Seven phenolic acids and 10 flavonoids were identified from leaf litter,roots,and rhizosphere soils.Most of the potential phenolic allelochemicals,such as salicylic acid,gallic acid,4-hydroxybenzoic acid,and epicatechin,were more abundant in younger plantations,especially at4 years old.The concentrations of phenolic compounds in the rhizosphere zone were significantly lower than in litter and root samples and did not change significantly with an increase in age.Notably,phenolic compounds contributed more to the variation in the understory plants than soil factors.Hydroxyphenyllactic acid,ellagic acid,quercetin,salicylic acid,and 4-hydroxybenzoic acid were the main phenolic compounds explaining the variation in plant diversity with plantation age.These findings indicate that young E.grandis plantations,especially at four years of age,merit a greater focus because of their lower understory plant diversity and higher allelopathic potential.

Soil microorganisms alleviate the allelopathic effect of Eucalyptus grandis × E. urophylla leachates on Brassica chinensis

Soil microbes may be critical players in determining the allelopathic potential of some plants. Low levels of plant community biodiversity in Eucalyptus plantations have been attributed to the allelopathic potential of these tree species. The role of soil microbes in the allelopathic effect of leaf leachates of the hybrid tree Eucalyptus grandis x E. urophylla, was tested in Petri dish assays with Brassica chinensis as a receiver plant. Soils were collected from either a local garden (soil A) or a Eucalyptus plantation (soil B) and half of each soil was sterilized to remove microbes. These soils were then treated with E. grandis x E. urophylla leachates for 0-72 h. Seed germination of B. chinensis was significantly inhibited in soils treated with leaf leachates relative to untreated soils. The inhibitory effect of the leaf leachates was more pronounced in sterilized soils. Total phenolic content was obvious lower in nonsterile leachate-treated soils than in sterile soils. Biomass of B. chinensis was negatively correlated with the total phenolic content in soils. Our findings suggest that soil microbes can alleviate the allelopathic potential of Eucalyptus and thereby its negative impact on plant growth.

Comparative microsporogenesis and flower development in Eucalyptus urophylla×E.grandis

Microsporogenesis and flower development in Eucalyptus urophylla × E. grandis were examined using chromosome tableting to provide a method to predict the meiotic stages in this species. Although microsporogenesis was normal, cytokinesis during meiosis of pollen mother cells occurred simultaneously, with strong asynchronism observed in the two different lengths of stamens in a flower bud. In a single flower, the developmental period of microsporogenesis in anthers on the longer stamens was always ahead of those on the shorter stamens. Flower development was also asynchronous at different locations on a branch. Flower buds on the upper side of the branch were larger in diameter than those on the lower side. In addition, a correlation was observed between microsporogenesis development and flower bud diameter growth. The pachy- tene stage was first observed when the diameter of the flower buds increased to 3.0 mm, and the majority of the meiotic stages were observed when bud diameters ranged from 3.5 to 5.0 mm. This study showed that the developmental stages of microsporogenesis in Eucalyptus urophylla × E. grandis could be distinguished readily, which may be applicable to future breeding studies.

巨桉(Eucalyptus grandis)人工林土壤动物群落对采伐干扰的初期响应

为了解采伐干扰对巨桉（Eucalyptus grandis）人工林土壤动物的影响,于2005～2007年采用手捡法和干湿漏斗法对四川省洪雅县巨桉人工林采伐干扰前和采伐干扰后土壤动物群落进行调查,采伐干扰前四季共获土壤动物4775头,分属4门11纲27目,采伐干扰后获土壤动物4640头,分属4门10纲23目。采伐干扰后秋季（10月）、冬季（1月）和春季（4月）土壤动物个体数较采伐干扰前分别上升224头、368头和443头,而夏季（7月）下降了1170头。采伐干扰前巨桉人工林土壤动物个体数与类群数季节变化趋势基本一致,而采伐干扰后土壤动物类群数变化受土壤动物个体数变化的影响较小。与采伐干扰前相比,采伐干扰后枯落物层各季节土壤动物密度均低于采伐前,0～5 cm土层土壤动物密度与干扰前呈相反的变化趋势,其波动较5～10 cm和10～15 cm土层大。采伐干扰后土壤动物类群数四季共减少4个,采伐干扰前后土壤动物优势类群类群数波动小,采伐后常见类群类群数上升（除冬季外）,稀有类群对采伐干扰较敏感,其类群数下降幅度较大。采伐干扰前后同功能种团均以杂食性和腐食性土壤动物为主,两者百分比之和均在89%以上。密度-类群指数（DG）和多样性指数（H′）的变化趋势相似,采伐干扰前后的变化趋势相反,表明采伐干扰对巨桉人工林土壤动物季节变化有较大影响。

A Study of the Distribution and Accumulation of Major Nutrient Elements in Different Densities of Eucalyptus grandis

This study was conducted to investigate the distribution and accumulation of major elements of 5-year-old Eucalyptus grandis forests with the densities of 556 trees/hm2 and 1 667 trees/hm2. The results showed that： （1） The distribution of ma- jor nutrient element contents in various organs of the E. grandis with the 2 densi- ties was nearly the same, and the ranked order was leaf〉tree trunk〉branch or branchlet〉fruit〉bark. （2） From the distribution of nutrient elements and organic mat- ter in the trunk, P, K, Mg and Ca contents presented basically a trend of increasing with the trunk height increasing. And the organic matter content increased with the trunk height increasing in the low density stand, while the result was opposite in the high density stand. Furthermore, N content increased with the trunk height increas- ing in the low density stand, but the content in the high density stand exhibited a trend of decreasing at first, increasing then and increasing at the last. （3） From the distribution of biomass, the ranked order was tree trunk〉bark or branch〉branchlet〉 leaf〉fruit. And （4） The accumulated amounts of major nutrient elements in various organs under the 2 stand densities was nearly same. Ca content was the highest in the 2 kinds of plantations, followed by N, K, Mg and P contents. Ca content was 601.78 kg/hm2 in the low density stand and 1 204. 43 kg/hm2 in the high density stand.

Distribution and Accumulation of Nutrient Elements in Organic Tissue of Eucalyptus grandis Saplings

The biomass, macroelements （N, P, K, Ca, Mg） and microelements （Fe, Zn） contents were detected in organs of 1a-3a Eucalyptus grandis saplings, as well as their accumulated amount. Results showed that contents of nutrient elements varied greatly in different organs. Total contents of macroelements N, P, K, Ca and Mg in1a-3a E. grandis were distributed in the order of stem phloem, leaves 〉 branch- es, roots 〉 stem xylem. Accumulated amount of macroelements in 1a-3a E. grandis were in the order of leaves 〉 branches 〉 stem phloem 〉 roots or stem xylem 〉 stem xylem or roots. Accumulated amount law of nutrient elements was not affected by the plant age. Microelements Fe and Zn were mainly concentrated in the leaves and roots. The accumulation of macroelements was in the order of Ca 〉 N 〉 K 〉 Mg 〉 P; and the microelements was in the order of Fe 〉 Zn. Accumulated amounts of microelements in 1a-3a E. grandis were 12.45 136.19 and 420.23 g per plants, respectively. Among the annual net accumulated amount of nutrient ele- ments per plant in 1a-3a E. grandis, Ca element was the maximum, N and K ele- ments took the second and third places. Mg element was relatively small and P el- ement was the minimum.

Eucalyptus grandis plantations:effects of management on soil carbon,nutrient contents and yields

The expansion of fast-growing tree plantations is a worldwide process,with consequences on soil fertility and soil carbon storage.Disparate results were found on the effects of afforestation with Eucalyptus on soil carbon and other nutrient contents.These discrepancies are usually caused by differences in climate,land use history,soil texture as well as by management related factors such as plantation age,number of rotations,method of establishment(plantation or coppice),harvest residue management and soil preparation.We studied the effect of plantation age,number of rotations,and method of establishment on soils and plant nutrient concentrations in Eucalyptus grandis plantations in NE Argentina on different textured soils.We also determined if yields changed with nutrient variations in soils,and compared soils under plantations to soils under grasslands they replaced.Thirty-one E.grandis stands of different ages,number of rotations and method of establishment were evaluated as well as eight grassland sites.Levels of carbon,nitrogen,phosphorus,potassium,calcium and magnesium were determined for soils and plants.Soil carbon and nitrogen decreased over the number of rotations and were more pronounced in soils with 50-60%sand than soils with>75%sand.Coppice stands showed higher soil carbon and nitrogen levels than plantations,suggesting a negative effect of site preparation before planting on soil nutrient conservation,especially in fine-textured soils.Foliar nutrient concentrations did not follow the trends observed for soil nutrients nor did they reflect nutrient limitations.There was no evidence of decreased yields over successive rotations.Soil carbon and nitrogen contents decrease when grasslands are replaced by E.grandis plantations,and therefore a yield limitation may occur in a medium to long-term frame,especially in stands re-established for short-rotation management.Harvest residue management and site preparation must be specifically designed for improving soil nutrient management.

Evaluation of soil nutrients under Eucalyptus grandis plantation and adjacent sub-montane rain forest

A study was conducted to evaluate the status of soil nutrients under E. grandis plantation in comparison with that in its adjacent submontane rain forest. Twenty sequare plots, with an area of 20 m×20 m for each, were established in both of E.grandis plantation and its adjacent sub-montane rain forest, independently. Soil samples were collected from each square plot, at five points （at the four comers and at the center） of each plot. The collected soil samples were mixed to make a composite and representative sample for each plot, independently. The analyses were done in a soil laboratory following appropriate methods. The analysis result indicated that there were no significance differences between E. grandis plantation and its adjacent sub-montane rain forest in the level of major soil nutrients （total N, available P, exchangeable K, Ca and Mg）, pH and total carbon of soils （p 〈 0.05）. There were significance differences between two sites of forest soils in percentage of clay particles, and exchangeable Na content. E. grandis plantation was found improving soil nutrients and total carbon as compared with that of its adjacent submontane rain forest.

Fire alters the availability of soil nutrients and accelerates growth of Eucalyptus grandis in Zambia

Fire has been used to prepare land during tree plantation establishment for many years but uncertainty about how ecosystems respond to prescribed burning makes it difficult to predict the effects of fire on soil nutrients.The aim of this study was to determine the effect of burning accumulated forest residues(slash)on soil chemical properties and how trees respond.We analyzed 40 burned and unburned sites and compared growth of Eucalyptus grandis W.Hill ex Maiden between sites.Soil pH increased by 39%after fire,suggesting reduced soil acidity and increased liming.Total nitrogen increased by 100%;other nutrients(Ca^2+,Mg^2+and K^+)also increased.Increase in nutrients had a significant effect on the growth of E.grandis;larger and taller trees were associated more with burned than unburned sites.This study provides evidence that burning accumulated slash during land preparation prior to plantation establishment alters soil nutrient status and enhances the growth of E.grandis.

Variation of basic density,calorific value and volumetric shrinkage within tree height and tree age of Ugandan grown Eucalyptus grandis wood

Insufficient knowledge on Ugandan grown Eucalyptus grandis W.Hill ex Maiden wood properties,high demand,and processing challenges led to a study into its physical properties.We obtained the variation of basic density(BD),calorific value(CV)and volumetric shrinkage(VS)within tree height and tree-age of E.grandis,and its appropriate use based on these properties.Trees with good boles were harvested from Kabarole District in western Uganda to produce specimens as prescribed by British Standards and ASTM standard wood testing procedures.Secondary data reviews and statistical analysis using ANOVA,Tukey’s test and multivariate analysis were done to obtain property estimates and their variation within trees and amongst tree ages.The mean BD of E.grandis is 413.6,380.5,471.0,and 501.1 kg m^(−3)at 3,6,9,and 12 years,respectively,showing significant increase with tree age(p=0.003).The pattern of BD with tree height showed a reduction with tree height although with higher values in the middle portion of the tree.The CV increases(p=0.014)with tree age and reduces with tree height with values of 14,560.32,15,447.3,16,079.11,and 16,932.6 kJ kg^(−1)at 3,6,9,and 12 years,respectively.The percentage VS was 11.02,9.84,12.31,and 14.45 for 3-,6-,9-,and 12-year-old trees,respectively,and it did not vary significantly(p=0.088)with tree height.Basing on these property values,E.grandis wood could be used for scaffolding,light constructions and fuel wood production.Its seasoning needs to be longer with well monitored drying schedules to reduce seasoning defects caused by the high VS.Further studies on strength properties,seasoning schedules,panel products properties and tree-age chemical variations would improve the knowledge about its wood quality and would enhance its efficient utilization.

Preliminary evaluation of liquefaction behavior of Eucalyptus grandis bark in glycerol

Eucalyptus grandis W.Hill ex Maiden bark was liquefied in glycerol with two types of catalysts.The chemical components of the residues with respect to temperature were examined to investigate the liquefaction behavior of bark.The results reveal that sulfuric acid was more efficient in converting bark into fragments in glycerol at low temperatures B 433.15 K,equivalent to 160C than phosphoric acid.The liquefaction order of chemical components was lignin,hemicelluloses,and cellulose.The decrease of liquefaction yields at high temperatures(≤453.15 K)catalyzed by sulfuric acid was possibly a result of the recondensation of lignin and/or hemicelluloses.

The effect of methylbenzene/ethanol ratios on chemical composition of extractives from Eucalyptus grandis

Chemical components of methylbenzene/ethanol extractives of Eucalyptus grandis were identified by GC/MS and different methylbenzene/ethanol solutions （9/1, 4/1, 2/1, 1/1, 1/2） were used to describe their distinctions. The distributions of micro particles in each extractive were studied simultaneously. The results show that there were significant differences between the various extrac- tives, although the extractives were essentially the same, i.e., alcohols, alkanes, esters and acids. With the increase of ethanol compo- sition in the solutions, the total amount of extractives increased; in solvent with higher amounts of ethanol, some acidic structures or acids, such as glutaric acid, could be seen. An investigation of micro particles indicated that the distribution of particle size of each sample did not change greatly between the solutions. A slight decrease in size was seen with the reduction in the amount of methylbenzene.

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.

Corrective Interventions to End-Splitting and Surface Cracking in Kenya Grown Eucalyptus grandis Poles

This study determined the effect of three pole pre-drying handling techniques, on end-splitting and surface checking in Eucalyptus grandis poles from highland and low land areas in Kenya. A total of 144 Eucalyptus grandis trees were sampled from two sites;Kericho, representing the wet highlands and Londiani representing the drier lowlands regions of Kenya. Pole samples from both sites were subjected to the three pre-drying handling techniques for the first 30 days after felling and allowed to dry to the required moisture level under observations. The number of end splits and surface checks on each sample pole were counted and the length of the worst ones was measured in millimeters after every 15 days until all the poles reached 25% MC. The sap wood and heart wood ratios were determined from selected samples. Results showed that on the overall, poles from high land areas had the highest sapwood proportions and similarly had the highest number and the longest end splitting and surface checks. On the other hand, pre-drying techniques that allowed felled trees to dry slowly with their foliage intact for the first 30 days of felling produced the best quality poles, with fewer and shallower end splits and surface checks. The study recommended that felling and leaving poles to dry slowly with foliage intact be considered in reducing losses incurred as a result of wood stresses during drying of poles.

Density effect and self-thinning in Eucalyptus urophylla stands

Density effects on the growth and self-thinning of Eucalyptus urophylla stands were examined for 7 years.The reciprocal equation of the competition-density(C–D)effect was used to describe the C–D effect in even-aged pure stands of E. urophylla during course of self-thinning and showed a good fit to the data. The time trajectories of mean stem volume-density nearly paralleled the y-axis during early growth stages of stands, and then began to curve left. Finally, the mean stem volume-density trajectories of the low-, middle-and high-density stands tended to follow the self-thinning lines with slopes of-2.01,-1.90 and-1.99, respectively. With increasing physical time t, the biological time s increased rapidly during early growth stages and became slow gradually during later growth stages. Realized density-initial density curves tended to become more or less flat with increasing initial density, indicating the existence of an asymptotic value for density at a given time. The coefficient e, the reciprocal of which represents the asymptotic density at a given time,increased with increasing biological time s, indicating that the asymptotic density decreased with increasing stand age.Final yield Y(t) increased gradually with increasing stand age.

Impact of Natural Selection on Lignin and Cellulose Candidate Genes in a Natural Population of <i>Eucalyptus urophylla</i>

Wood plays a major role in land ecosystems and in human activity. Better understanding the genetic basis and evolutionary implication of wood variability are thus key issues with both ecological and economical implications. The present paper addresses the question of the extending and the nature of natural selection on wood related genes in Eucalyptus urophylla, a tropical tree species with key economical importance. We conducted a genetic study on an E. urophylla population from Timor Island using a set of 17 SSR characterized on a main sample of 43 individuals and six candidate genes sequenced on a subset of 18 individuals. The candidate genes include three cellulose synthase genes (EuCesA1, EuCesA2 and EuCesA3), and three genes involved in lignin synthesis (EuCAD2, EuC4H1 and EuC4H2). Based on SSR data, the investigated population appeared to have no structure and have undergone past population expansion. Accounting for this demographic history, we were able to draw neutral expectation for polymorphism distribution on candidate genes and to determine their potential selective status. We hence identified two gene portions exhibiting unexpected polymorphism pattern, consistent with natural selection imprint.

Acacia mangium and Eucalyptus urophylla in Northern Vietnam： The Relationship between Silvicultural Activity and Quality of Stand

This paper sets out to determine the link between socio-economic attributes of smallholders, silvicultural activity and the stand quality of Acacia mangium and Eucalyptus urophylla plantations in two unrelated communes in Phu Tho province, Vietnam. The necessary data was collected by interviewing the smallholders and conducting inventory of the stands. The data was analyzed with descriptive statistics, Mann-Whitney tests and Spearman correlations. More silvicultural practices were conducted by A. mangium planters with larger areas. Most of the smallholders practiced the suggested silvicultural activities. Productivity was affected by pruning in medium quality sites. This research recommends that smallholders were supported with incentives for the plantation establishment, education for smallholders in silvicultural techniques, organization and development activities for the wider market.

Heterosis Estimation for Growth Traits and Wood Properties of Eucalyptus urophylla under Two Sites in Southern China

Heterosis is a quicker,cheaper and easier method for increasing plantation production,and heterosis studies can provide the basis for exploitation of valuable hybrid combinations in breeding programs.Growth traits,wood properties,and bark percentage were assessed for 6×6 full diallel progenies of E.urophylla in southern China measured at age 4 years.Analysis of variance showed that there were significant differences on all studied traits except dynamic modulus of elasticity among combinations.The mean diameter at breast height,wood basic density,and dynamic modulus of elasticity were 9.40 to 12.20 cm,0.45 to 0.47 g cm-3,and 5.04 to 5.72 GPa,respectively.The coefficients of variation ranged from 18.18%to 50.43%for growth traits,9.07%to 55.24%for wood properties and 22.26%to 23.93%for bark percentage.The heterosis estimation on diameter at breast height,wood basic density,and dynamic modulus of elasticity were-24.07%to 18.74%,-14.23%to 9.17%and-25.53%to 16.28%.U22×U56 generally had higher heterosis of growth traits and wood properties through three sites.Same combinations had different original and reciprocal heterosis estimation at two sites even on same traits.The combinations of same parents always had similar original and reciprocal heterosis estimation.

An assessment of response of soil-based indicators to nitrogen fertilizer across four tropical eucalyptus plantations

Low nitrogen (N) availability often results in reduced productivity of Eucalyptus plantations. We studied the response of four eucalyptus plantations (two plantations of E. tereticornis on the coastal lowlands, and two plantations of E. grandis in the upland region of the Western Ghats, Kerala, India) to N addition and related this response to seasonal N mineralization as well as other indices of N availability, in order to examine the utility of soil based indicators of N mineralization for predicting the response of eucalyptus growth to added N fertilizer. Several biochemical indicators were examined for their capacity to predict response to N fertilizer, including total soil N, soil C:N ratio, and N released during anaerobic and aerobic incubation. Results show that nitrogen fertilizer addition increased productivity across the 4 sites from 7% to 70%, N released during an aerobic incubation had the highest correlation with fertilizer response across the 4 sites (R2=0.92, p<0.01), and that Modelled seasonal soil N mineralisation was a poorer predictor of fertilizer response than N released during an aerobic incubation. Whilst some of these indicators are promising, they need wider validation and testing before they could be routinely applied.

An assessment of response of soil-based indicators to nitrogen fertilizer across four tropical eucalyptus plantations

Low nitrogen （N） availability often results in reduced productivity of Eucalyptus plantations. We studied the response of four eucalyptus plantations （two plantations of E. tereticornis on the coastal lowlands, and two plantations of E. grandis in the upland region of the Western Ghats, Kerala, India） to N addition and related this response to seasonal N mineralization as well as other indices of N availability, in order to examine the utility of soil based indicators of N mineralization for predicting the response of eucalyptus growth to added N ferti- lizer. Several biochemical indicators were examined for their capacity to predict response to N fertilizer, including total soil N, soil C：N ratio, and N released during anaerobic and aerobic incubation. Results show that nitrogen fertilizer addition increased productivity across the 4 sites from 7% to 70%, N released during an aerobic incubation had the highest correlation with fertilizer response across the 4 sites （R^2=0.92/ p〈0.01）, and that Modelled seasonal soil N mineralisation was a poorer predictor of fertilizer response than N released during an aerobic incubation. Whilst some of these indicators are promising, they need wider validation and testing before they could be routinely applied.