Intra-specific competition and the radial development of wood density, microfibril angle and modulus of elasticity in plantation-grown Eucalyptus nitens

In eucalypt plantations managed for solid-wood products, radial trends in wood density, microfibril angle (MFA) and stiffness (modulus of elasticity, MoE) are properties of potential commercial importance that can be affected by competition from neighbouring trees. In this study, wood properties at breast height (1.3?m) were studied on radial strips prepared from 12-mm pith-to-bark wood cores taken from 20 trees in a 22-year-old Eucalyptus nitens (Deane and Maiden) Maiden thinning trial in north-eastern Tasmania, Australia. Thinning treatments were applied at age 6?years. Trees were sampled from each of the 200, 400?stems ha^?1 and unthinned control treatments. Intra-specific competition for each sampled tree was estimated using the basal area growth of surrounding trees. SilviScan? technology was used to produce radial profiles of wood density, MFA and MoE. Results indicate a reduction in intra-specific competition through thinning of E. nitens plantations at an early age leads to a transient increase in MFA but has no significant effect on wood density or the intra-annual cycle of wood density. The correlation between the level of intra-specific competition and initial change in MFA following thinning, and a significant relationship between tree shape and mean MFA at breast height suggests the change in MFA is a post-thinning response to increased exposure and wind sway.     

Inheritance of growth and solid wood quality traits in a large Norway spruce population tested at two locations in southern Sweden

Unfavorable genetic correlations between growth and wood quality traits are one of the biggest challenges in advanced conifer breeding programs. To examine and deal with such correlation, increment cores were sampled at breast height from 5,618 trees in 524 open-pollinated families in two 21-year-old Norway spruce progeny trials in southern Sweden, and age trends of genetic variation, genetic correlation, and efficiency of selection were investigated. Wood quality traits were measured on 12-mm increment cores using SilviScan. Heritability was moderate (~0.4–0.5) for wood density and modulus of elasticity (MOE) but low (~0.2) for microfibril angle (MFA). Different age trends were observed for wood density, MFA, and MOE, and the lower heritability of MFA relative to wood density and MOE in Norway spruce contrasted with general trends of the three wood quality traits in pine. Genetic correlations among growth, wood density, MFA, and MOE increased to a considerably high value from pith to bark with unfavorable genetic correlations (?0.6 between growth and wood density, ?0.74 between growth and MOE). Age–age genetic correlations reached 0.9 after ring 4 for diameter at breast height (DBH), wood density, MFA, and MOE traits. Early selections at ring 10 for diameter and at ring 6 or 7 for wood quality traits had similar effectiveness as selection conducted at reference ring 15. Selection based on diameter alone produced 19.0 % genetic gain in diameter but resulted in 4.8 % decrease in wood density, 9.4 % decrease in MOE, and 8.0 % increase in MFA. Index selection with a restriction of no change in wood density, MOE, and MFA, respectively, produced relatively lower genetic gains in diameter (16.4, 12.2, and 14.1 %, respectively), indicating such index selection could be implemented to maintain current wood density. Index selection using economic weights is, however, recommended for maximum economic efficiency.     

Effect of growth rate on mean microfibril angle and cross-sectional shape of tracheids of Norway spruce

The variation of the mean microfibril angle (MFA) and the shape of the cross-section of lumen with the distance from the pith in fast grown Norway spruce were studied by X-ray scattering and optical microscopy. The samples were from stems of a clone of Norway spruce [ Picea abies (L.) Karst.] grown in a fertile site at Nurmijärvi, southern Finland Both the mean MFA and the circularity index of the lumen of the fast-grown trees decreased more gradually as the distance from the pith increased than those in reference trees grown in a medium fertility site. However, in mature wood the mean MFA reached the same level in fast-grown trees as in reference trees (5°–10°) but the cross-sections of the cells remained more circular in fast-grown trees than in reference trees. The dependence of the mean MFA on the distance from the pith was similar for earlywood and latewood, but the values of the mean MFA of latewood were systematically smaller than those of earlywood. Two different X-ray diffraction geometries were compared from the points of view of biology and data analysis.     

Wood properties and ring width responses to long-term atmospheric CO2 enrichment in field-grown loblolly pine (Pinus taeda L.)

Loblolly pine (Pinus taeda L.) were grown in the field, under non-limiting nutrient conditions, in open-top chambers for 4 years at ambient CO₂ partial pressures (pCO₂) and with a CO₂-enriched atmosphere (+ 30 Pa pCO₂ compared to ambient concentration). A third replicate of trees were grown without chambers at ambient pCO₂. Wood anatomy, wood density and tree ring width were analysed using stem wood samples. No significant differences were observed in the cell wall to cell lumen ratio within the latewood of the third growth ring formed in 1994. No significant differences were observed in the density of resin canals or in the ratio of resin canal cross-sectional area to xylem area within the same growth ring. Ring widths were significantly wider in the CO₂-enrichment treatment for 3 of 4 years compared to the ambient chamber control treatment. Latewood in the 1995 growth ring was significantly wider than that in the ambient control and represented a larger percentage of the total growth-ring width. Carbon dioxide enrichment also significantly increased the total wood specific gravity (determined by displacement). However, when determined as total sample wood density by X-ray densitometry, the density of enriched samples was not significantly higher than that of the ambient chamber controls. Only the 1993 growth ring of enriched trees had a significantly higher maximum latewood density than that of trees grown on non-chambered plots or ambient chambered controls. No significant differences were observed in the minimum earlywood density of individual growth rings between chambered treatments. These results show that the most significant effect of CO₂ enrichment on wood production in loblolly pine is its influence on radial growth, measured as annual tree ring widths. This influence is most pronounced in the first year of growth and decreases with age.     

Cellulose microfibril angle variation in Picea crassifolia tree rings improves climate signals on the Tibetan plateau

Microfibril angle (MFA) is an important factor in determining the mechanical properties of individual cells and wood as a whole. While some studies have described the variation of MFA within trees, little work has been done on the extent to which MFA is influenced by climate, despite it being known to respond to climatic events. Year-to-year variation in MFA and ring width was measured at high resolution by SilviScan-3^? on 30 dated Picea crassifolia trees growing in the northeastern Tibetan plateau. The climate signals registered in MFA and ring width were analyzed using dendroclimatological methods. The response function of MFA accounted for 67% of total variance, of which 60% was explained by climate elements. The response function of ring width explained 57% total variance, 37% of which was explained by climate variables. MFA significantly responded to July–August temperatures, and to precipitation in March, May and September. Over the period 1987–2009 temperatures generally increase and appeared to have a greater influence on MFA. A decrease in the strength of the relationship between MFA and ring width over the period 1987–2009 was also observed. MFA offers the potential to build robust climate proxies. The strong climate sensitivity of MFA to increasing temperature or the observed changes in the MFA–ring width relationship may contribute to resolving the “divergence problem” in temperature reconstructions. As far as we are aware, this study is the first to show a strong climate response in MFA and suggests that it might be a useful climate proxy.     

Bayesian analysis of Douglas-fir hydraulic architecture at multiple scales

We used a Bayesian hierarchical model to analyze the variation in xylem anatomy, hydraulic properties, and the relationship between anatomy and properties within Douglas-fir trees. The hierarchical scales in our study included fertilization treatments (fertilized and unfertilized), trees within the treatments, and positions within the trees. We measured tracheid diameter, tracheid length, percent latewood, number of pits per cell, density, and specific conductivity (K _s) on seven positions in each of 16 fertilized and 16 unfertilized trees: the trunk at cambial age 52 (breast height), 25, and 5; a branch at cambial age 20 and 7; and a root at cambial age 42 and 22. Vulnerability to embolism was also measured on the oldest trunk, branch, and root positions. For any measurement, there was little variation between treatments, however, there was great variation among positions. Tracheid diameter, tracheid length, number of pits per cell, K _s, and vulnerability to embolism decreased vertically from the roots to the branches. Correlations were evident between some positions for tracheid diameter, percent earlywood, pits per cell, and vulnerability to embolism, mostly in the fertilized treatment. We found evidence for large-scale relationships (among all observations from all trees) between density and tracheid diameter, K _s and diameter, vulnerability and diameter, K _s and pits per cell, and vulnerability and pits per cell. At a smaller scale of within position, however, usually only the branches and roots maintained the relationship.     

Quantitative trait locus (QTL) analysis of wood quality traits in <Emphasis Type="Italic">Eucalyptus nitens</Emphasis>

To identify the chromosomal regions affecting wood quality traits, we conducted a genome-wide quantitative trait locus (QTL) analysis of wood quality traits in Eucalyptus nitens. This information is important to exploit the full potential of the impending Eucalyptus genome sequence. A three generational mapping population consisting of 296 progeny trees was used to identify QTL associated with several wood quality traits in E. nitens. Thirty-six QTL positions for cellulose content, pulp yield, lignin content, density, and microfibril angle (MFA) were identified across different linkage groups. On linkage groups (LG)2 and 8, cellulose QTL cluster with pulp yield and extractives QTL while on LG4 and 10 cellulose and pulp yield QTLs cluster together. Similarly, on LG4, 5, and 6 QTL for lignin traits were clustered together. At two positions, QTL for MFA, a physical trait related to wood stiffness, were clustered with QTL for lignin traits. Several cell wall candidate genes were co-located to QTL positions affecting different traits. Comparative QTL analysis with Eucalyptus globulus revealed two common QTL regions for cellulose and pulp yield. The QTL positions identified in this study provide a resource for identifying wood quality genes using the impending Eucalyptus genome sequence. Candidate genes identified in this study through co-location to QTL regions may be useful in association studies.     

Optimization of sampling procedures for DNA‐based diagnosis of wood decay fungi in standing trees

Aims: To develop fast and reliable sampling procedures for DNA‐based diagnosis of wood decay fungi in standing trees. Methods and Results: A total of 250 trees were tested for the presence of a suite of wood decay fungi by collecting wood frass obtained by drilling each tree once with a 4‐mm‐diameter, 43‐cm‐long bit. We identified at least one of 11 target wood decay fungi in 56 trees through multiplex PCR assays. The presence of target wood decay taxa was further investigated in these 56 trees, by analysing independently wood from each of six drillings. Results were then compared with those obtained using sampling schemes differing in terms of number and position of drillings. Samples of 1–4 drillings were either analysed separately, and the results were combined, or pooled together before analysis was performed. In comparison with taxa identified by the analysis of six drillings, diagnostic efficiency ranged from 56·6% for the scheme based on a single drill to 96·8% for the scheme based on four drillings analysed separately. Both schemes significantly differ (P < 0·05) from those based on two and three drillings, whose efficiency was 72·6% and 83·9%, respectively. Diagnostic efficiency of pooled samples was comparable to that of samples analysed separately. Conclusions: Highest diagnostic efficiency was obtained by analysing wood from four drillings. It is advisable to pool samples deriving from different drillings to reduce laboratory costs. Significance and Impact of the Study: Fast and reliable sampling procedures make DNA‐based diagnosis more suitable for tree inspection procedures.     

Soil warming and CO2 enrichment induce biomass shifts in alpine tree line vegetation

Responses of alpine tree line ecosystems to increasing atmospheric CO₂ concentrations and global warming are poorly understood. We used an experiment at the Swiss tree line to investigate changes in vegetation biomass after 9 years of free air CO₂ enrichment (+200 ppm; 2001–2009) and 6 years of soil warming (+4 °C; 2007–2012). The study contained two key tree line species, Larix decidua and Pinus uncinata, both approximately 40 years old, growing in heath vegetation dominated by dwarf shrubs. In 2012, we harvested and measured biomass of all trees (including root systems), above‐ground understorey vegetation and fine roots. Overall, soil warming had clearer effects on plant biomass than CO₂ enrichment, and there were no interactive effects between treatments. Total plant biomass increased in warmed plots containing Pinus but not in those with Larix. This response was driven by changes in tree mass (+50%), which contributed an average of 84% (5.7 kg m^?2) of total plant mass. Pinus coarse root mass was especially enhanced by warming (+100%), yielding an increased root mass fraction. Elevated CO₂ led to an increased relative growth rate of Larix stem basal area but no change in the final biomass of either tree species. Total understorey above‐ground mass was not altered by soil warming or elevated CO₂. However, Vaccinium myrtillus mass increased with both treatments, graminoid mass declined with warming, and forb and nonvascular plant (moss and lichen) mass decreased with both treatments. Fine roots showed a substantial reduction under soil warming (?40% for all roots <2 mm in diameter at 0–20 cm soil depth) but no change with CO₂ enrichment. Our findings suggest that enhanced overall productivity and shifts in biomass allocation will occur at the tree line, particularly with global warming. However, individual species and functional groups will respond differently to these environmental changes, with consequences for ecosystem structure and functioning.     

Asymptotic height as a predictor of growth and allometric characteristics in malaysian rain forest trees

The growth and physiological characteristics of canopy trees are expected to differ systematically from those of understory trees on the basis of size-dependent aspects of biomechanics, resource availability, and life history. Although such differences have previously been noted, there has been relatively little effort to quantify these in terms of interspecific allometric relationships. Asymptotic maximal height (H_max) is advocated as a measure of the size of dicotyledonous woody plants for this purpose. Height diameter (H–D) relationships in 38 species within six genera of Malaysian rain forest trees are well described by an asymptotic model, and thus provide a basis for estimating H_max using static observational data. Three important aspects of tree growth strategies are shown to be predictable on the basis of these values: average tree growth rates are positively related to H_max, while wood density and the initial allometric slope of (species-specific) H–D relationships are negatively related to H_max. These patterns may be explained by an association of low light levels with slow growth and high density wood in understory species; the latter property may in turn allow for relatively high allometric slopes of H–D relationships in saplings of small-statured species. Analyses that control for phylogenetic differences provide evidence that such interspecific allometric patterns are the product of convergent evolution. These results are consistent with the idea that much ecological variation within species-rich taxa of southeast Asian rain forest trees is related to differentiation along a vertical axis of tree size.     

Wood properties of two silver birch clones exposed to elevated CO2 and O3

Effects of elevated carbon dioxide (CO₂) and ozone (O₃) on wood properties of two initially 7‐year‐old silver birch (Betula pendula Roth) clones were studied after a fumigation during three growing seasons. Forty trees, representing two fast‐growing clones (4 and 80), were exposed in open‐top chambers to the following treatments: outside control, chamber control, 2 × ambient [CO₂], 2 × ambient [O₃] and 2 × ambient [CO₂]+2 × ambient [O₃]. After the 3‐year exposure, the trees were felled and wood properties were analyzed. The treatments affected both stem wood structure and chemistry. Elevated [CO₂] increased annual ring width, and concentrations of extractives and starch, and decreased concentrations of cellulose and gravimetric lignin. Elevated O₃ decreased vessel percentage and increased cell wall percentage in clone 80. In vessel percentage, elevated CO₂ ameliorated the O₃‐induced decrease. In clone 4, elevated O₃ decreased nitrogen concentration of wood. The two clones had different wood properties. In clone 4, the concentrations of extractives, starch, soluble sugars and nitrogen were greater than in clone 80, while in clone 80 the concentrations of cellulose and acid‐soluble lignin were higher. Clone 4 also had slightly longer fibres, greater vessel lumen diameter and vessel percentage than clone 80, while in clone 80 cell wall percentage was greater. Our results show that wood properties of young silver birch trees were altered under elevated CO₂ in both clones, whereas the effects of O₃ depended on clone.     

Unravelling the impact of lignin on cell wall mechanics: a comprehensive study on young poplar trees downregulated for CINNAMYL ALCOHOL DEHYDROGENASE (CAD)

Lignin engineering is a promising tool to reduce the energy input and the need of chemical pre‐treatments for the efficient conversion of plant biomass into fermentable sugars for downstream applications. At the same time, lignin engineering can offer new insight into the structure–function relationships of plant cell walls by combined mechanical, structural and chemical analyses. Here, this comprehensive approach was applied to poplar trees (Populus tremula × Populus alba) downregulated for CINNAMYL ALCOHOL DEHYDROGENASE (CAD) in order to gain insight into the impact of lignin reduction on mechanical properties. The downregulation of CAD resulted in a significant decrease in both elastic modulus and yield stress. As wood density and cellulose microfibril angle (MFA) did not show any significant differences between the wild type and the transgenic lines, these structural features could be excluded as influencing factors. Fourier transform infrared spectroscopy (FTIR) and Raman imaging were performed to elucidate changes in the chemical composition directly on the mechanically tested tissue sections. Lignin content was identified as a mechanically relevant factor, as a correlation with a coefficient of determination (r²) of 0.65 between lignin absorbance (as an indicator of lignin content) and tensile stiffness was found. A comparison of the present results with those of previous investigations shows that the mechanical impact of lignin alteration under tensile stress depends on certain structural conditions, such as a high cellulose MFA, which emphasizes the complex relationship between the chemistry and mechanical properties in plant cell walls.     

Wood properties of Populus and Betula in long‐term exposure to elevated CO2 and O3

We studied the interactive effects of elevated concentrations of CO₂ and O₃ on radial growth and wood properties of four trembling aspen (Populus tremuloides Michx.) clones and paper birch (Betula papyrifera Marsh.) saplings. The material for the study was collected from the Aspen FACE (free‐air CO₂ enrichment) experiment in Rhinelander (WI, USA). Trees had been exposed to four treatments [control, elevated CO₂ (560 ppm), elevated O₃ (1.5 times ambient) and combined CO₂ + O₃] during growing seasons 1998–2008. Most treatment responses were observed in the early phase of experiment. Our results show that the CO₂‐ and O₃‐exposed aspen trees displayed a differential balance between efficiency and safety of water transport. Under elevated CO₂, radial growth was enhanced and the trees had fewer but hydraulically more efficient larger diameter vessels. In contrast, elevated O₃ decreased radial growth and the diameters of vessels and fibres. Clone‐specific decrease in wood density and cell wall thickness was observed under elevated CO₂. In birch, the treatments had no major impacts on wood anatomy or wood density. Our study indicates that short‐term impact studies conducted with young seedlings may not give a realistic view of long‐term ecosystem responses.     

Effect of elevated [CO2] on stem wood properties of mature Norway spruce grown at different soil nutrient availability

The objective of the present study was to investigate the interactive effects of elevated [CO₂] and soil nutrient availability on secondary xylem structure and chemical composition of 41‐year‐old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated‐fertilized trees were, for 3 years, continuously exposed to elevated [CO₂] in whole‐tree chambers. Elevated [CO₂] decreased concentrations of soluble sugars, acid‐soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO₂] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO₂]. In the latter, the CO₂ effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO₂] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end‐use purposes.     

Effect of carbon dioxide, fertilization and irrigation on loblolly pine branch morphology

 Foliage and wood parameters of branches of 12-year-old loblolly pine (Pinus taeda L.) trees were characterized after 21 months of exposure to fertilizer, irrigation and elevated CO₂ treatments. Branches of loblolly pine trees were enclosed in plastic chambers and exposed to ambient, ambient +175 and ambient +350 umol mol^–1 CO₂ concentrations. Measurements of foliage and wood at the fascicle, flush and branch levels were made at the end of the 21 month study period. The +350 CO₂ treatment did not significantly increase fascicle radius or length but did increase the number of fascicles on the first flush. Fertilization significantly increased fascicle radius and length, while irrigation significantly increased number of fascicles and flush length of first flush. The +350 CO₂ treatment also significantly increased flush length of the first flush. Significant interaction of fertilization and irrigation with CO₂ was observed for fascicle length. Significant interactions of fertilization and irrigation were also observed for flush length, number of fascicles and fascicle length. Observed increases in fascicle radius, fascicle length, number of fascicles and flush length may have been responsible for the significantly higher flush leaf area observed for the all three treatments. Also, a combination of fertilization and irrigation increased leaf area by 82% compared to that in the control when averaged across CO₂ treatments. At the branch level +350 CO₂ treatment significantly increased shoot length but not the number of flushes on the branch. In general with the exception of bark density and total number of needle scales, neither fertilization nor irrigation had any significant effect on other branch level parameters. Results from this study indicate that with ‘global change’ an increase in CO₂ alone may increase leaf area via an increase in flush length and number of fascicles. Combining increases in CO₂ with fertilization and irrigation could greatly enhance leaf area which when coupled to observed increases in net photosynthesis as a result of elevated CO₂ could greatly increase productivity of loblolly pine trees. Received: 22 August 1996 / Accepted: 5 March 1997     

Plant functional traits explain interspecific differences in immediate cyclone damage to trees of an endangered rainforest community in north Queensland

Abstract Cyclones cause profound immediate impacts on tropical rainforest trees, including defoliation, limb loss, snapping of stems and uprooting. Some studies have shown that plant functional traits such as tree size, buttress roots and wood density are correlated with these forms of cyclone damage. On 20 March 2006, Severe Tropical Cyclone Larry crossed the north Queensland coast and proceeded inland across the Atherton Tablelands, impacting the critically endangered Mabi Type 5b rainforest. We investigated the effects of Cyclone Larry on common tree species by categorizing damage to trees as uprooted, snapped, limbs damaged (light, moderate, severe) or upright and estimating levels of defoliation. Damage was then related to functional traits including tree size, presence of buttress roots, wood density, and leaf size and strength. Levels of damage differed between species. Tree size (diameter at breast height) and the presence of buttress roots were not related to damage levels. Wood density was significantly negatively correlated to proportion of trees with snapped stems and significantly positively correlated with the proportion of trees upright with no or light limb damage. Levels of defoliation were significantly related to leaf strength (specific leaf area – SLA) and to leaf width, but not other components of leaf size (area or length) or petiole length. Species with high wood density and low SLA (e.g. Argyrodendron spp.) were found to have high cyclone resistance, the ability to resist damage, while species with low wood density and high SLA (e.g. Dendrocnide photinophylla) exhibited low resistance. However, traits related to low resistance are also those linked to rapid growth and high cyclone resilience, the ability to recover from damage, so it is unlikely that the Mabi forest will experience long‐term changes in floristic composition following Cyclone Larry.     

Effect of initial fertilisation on biomass and nutrient contentof Norway spruce and Douglas-fir plantations at the same site

Norway spruce (NS) and Douglas-fir (DF) are among the main species used for production forestry in France. In low-elevation mountains and under-acidic conditions, they often occupy the same ecological situations. It is therefore of paramount interest to have a good understanding of how the two species behave under similar conditions and how they react to site improvement by fertilisation. The study stands are part of an experimental stand located in the estate forest of Breuil-Chenue in the Morvan (east central part of France). Its aim is to compare the impact of change in species on ecosystem functions. Destructive sampling of 10 trees per stand, distributed over the whole spectrum of inventoried classes of circumference at breast height (c _1.30), was carried out within four stands, e.g., fertilised and control (non-fertilised) NS; fertilised and control (non-fertilised) DF. Allometric relationships between c _1.30 and biomass or nutrient content per tree compartment were calculated. These equations were applied to the stand inventory for quantifying stand biomass and nutrient content on a hectare basis. The standard deviations of results were estimated using Monte-Carlo simulations. Specific emphasis was given to explain the origin of differences observed between species and treatments, i.e., changes in carbon allocation leading to specific allometric relationships, changes in stand structure (tree size distributions) and changes in stand density due to mortality.DF was more productive than NS (+28% for total tree biomass, +50% for ligneous biomass and +53% for stem wood). Both NS and DF were affected by fertilisation but in the case of NS, effects on the crown_c _1.30 relationship and on average tree growth were predominant while in the case of DF, the stem_c _1.30 relationship and stand density were affected by changes in soil fertility. The general fertilisation effect was an increment of 40% of ligneous dry matter for DF and only 22% for NS. In both cases, the amount of wood biomass produced per unit of leaf biomass (on a tree basis and, to a lesser extent, on a per hectare basis) was greater in fertilised plots. However, in the case of NS, the same amount of wood biomass was produced from a smaller quantity of leaves while in the case of DF, the same amount of leaves produced more wood biomass.The amount of nutrients in total ligneous biomass was higher for N, P and K, but lower for Ca and Mg, in DF than in NS. A high variability was observed between nutrient content of the different compartments, e.g., DF < NS for needles (except Mg), DF < NS for K, Ca and Mg for stem wood and DF > NS for N and P of stem wood. Fertilisation did not considerably change the hierarchy. On the basis of this study, all the indexes concerning stand production, wood density, nutrient use efficiency and response to fertilisation gave a net advantage to DF. This information is highly relevant for both ecological and practical purposes.     

Effects of simulated insect damage and weed interference on cotton growth and reproduction

Early-season insect pests of cotton (Gossypium hirsutum L.) crops, including Lepidoptera larvae and mirids, feed on vegetative buds. The loss of vegetative buds transiently delays the plant's development and growth and has the potential to reduce its competitive ability. Yield reductions due to weed interference and insect damage, therefore, could be greater than expected from the additive effects of weeds and damage acting separately. Three varieties, two levels of weed infestation, and two levels of simulated damage were combined in a factorial experiment designed to assess the responses of cotton plants to the combined effects of damage and weeds. Weed treatments were: with (+W) and without weeds (-W), and damage treatments included: undamaged control (-D) and damaged plants (+D) which had their active vegetative buds removed at 30 and 49 days after sowing. Variety and interactions between variety and other factors were normally nonsignificant for all the response variables measured in this experiment. Cotton height, width, production of flowerbuds and production of fruit were all affected by both damage and weeds. While the effects of damage on these growth variables were transient, the effects of weeds normally increased with time throughout the season. Non-additive effects of weeds and damage were minor for plant height and width, and large for flowerbud and fruit production. At maturity, weed dry matter ranged from about 20 g m^-2 (-W treatments) to 300 gm^-2 (+W), cotton dry matter from 144 gm (+W+D) to 945 gm^-2 (-W-D), and seed cotton production from 54gm^-2 (+W+D) to 417 gnT^-2 (-W+D). Damage did not affect vegetative dry matter and marginally increased seed production in -W plots. Non-additive effects of weeds and damage were negligible for vegetative dry matter but highly significant for seed production (P < 0.0001). These contrasting responses of vegetative and reproductive growth are in agreement with neighbouring models of plant competitive interactions that emphasise the effects of neighbour interference on the fecundity of target plants that are not mediated by changes in target-plant size.     

Testing the generality of above‐ground biomass allometry across plant functional types at the continent scale

Accurate ground‐based estimation of the carbon stored in terrestrial ecosystems is critical to quantifying the global carbon budget. Allometric models provide cost‐effective methods for biomass prediction. But do such models vary with ecoregion or plant functional type? We compiled 15 054 measurements of individual tree or shrub biomass from across Australia to examine the generality of allometric models for above‐ground biomass prediction. This provided a robust case study because Australia includes ecoregions ranging from arid shrublands to tropical rainforests, and has a rich history of biomass research, particularly in planted forests. Regardless of ecoregion, for five broad categories of plant functional type (shrubs; multistemmed trees; trees of the genus Eucalyptus and closely related genera; other trees of high wood density; and other trees of low wood density), relationships between biomass and stem diameter were generic. Simple power‐law models explained 84–95% of the variation in biomass, with little improvement in model performance when other plant variables (height, bole wood density), or site characteristics (climate, age, management) were included. Predictions of stand‐based biomass from allometric models of varying levels of generalization (species‐specific, plant functional type) were validated using whole‐plot harvest data from 17 contrasting stands (range: 9–356 Mg ha^?1). Losses in efficiency of prediction were <1% if generalized models were used in place of species‐specific models. Furthermore, application of generalized multispecies models did not introduce significant bias in biomass prediction in 92% of the 53 species tested. Further, overall efficiency of stand‐level biomass prediction was 99%, with a mean absolute prediction error of only 13%. Hence, for cost‐effective prediction of biomass across a wide range of stands, we recommend use of generic allometric models based on plant functional types. Development of new species‐specific models is only warranted when gains in accuracy of stand‐based predictions are relatively high (e.g. high‐value monocultures).     

黄河故道不同灌水方式刺槐人工林幼树水分利用效率和生长特性

干旱一直是限制黄河故道沙区树木生长的重要因素之一,而刺槐(Robinia pseudoacacia)以其较强的耐旱性、较高的成活率在造林时备受重视。适宜的灌水方式不但可以提高当地水资源的高效利用,而且可以促进刺槐迅速生长,改善当地环境生态。因此,在2011至2012年间,对黄河故道沙地进行刺槐人工林的建设与培育,开展滴灌(DI)、沟灌(FI)和软管喷灌(HSI)3种灌水方式对刺槐人工林幼树水分利用效率(WUE)和生长特性影响的研究。结果表明,在不同的水文年份,滴灌刺槐的净光合速率(Pn)、蒸腾速率(Tr)高于软管喷灌,软管喷灌高于沟灌。水分利用效率受年份影响较大,但均表现为前期下降,8月份前后降到最低值,随后缓慢回升。不同灌水方式叶绿素含量(CC)差异显著,滴灌条件下刺槐叶绿素含量最高,其次为软管喷灌,沟灌最低。不同树龄,不同灌水方式刺槐株高、地径和胸径差异显著。一年生林,滴灌刺槐的株高、地径和胸径分别比软管喷灌高出23.4、0.27 cm和0.14 cm;二年生林,滴灌刺槐的株高、地径和胸径分别比软管喷灌高53.7 cm、0.61 cm和0.54 cm。滴灌刺槐的株高、地径和胸径的年度生长量分别为软管喷灌的112.1%、107.1%和111.8%,同时分别为沟灌的121.8%、191.8%和343.6%。不同灌水方式刺槐幼树水分利用效率受年际间气象因素影响较大,滴灌可以显著地改善刺槐幼树的光合生理特性,促进其快速生长。