Correlation between trunk and branch age in trees as a new parameter in the analysis of tree architecture

A method for characterizing tree form is developed by linear regression of the age of the trunk on the average branch age at different heights. This relationship holds for a wide variety of situations, including both theoretical models and observed tree samples. The intercept of the regression, a, the ‘index of trunk distinctness’, reflects the branching pattern inherent to the species and indicates whether the trunk is erect or not. The slope, b, is termed the ‘crown thickness coefficient’, because it indicates a branching pattern. Tree forms can be classified into nine theoretical groups; three of these are physically impossible. The method was applied to real trees and a and b are shown to be useful tree form characteristics. Possible applications of the method are briefly discussed.     

Influence of leaf size on tree architecture: first branch height and crown dimensions in tropical rain forest trees

 First branch height is an important attribute of sapling architecture, as it defines the height at which prolonged lateral growth is possible. First branch height, measured on saplings of 70 species in tropical rain forests of Australia, Costa Rica, Panama, and Sabah, Malaysia, was highly correlated with leaf blade and petiole length. The observed relationship, first branch height ∝ blade length × (petiole length)^0.5, implies that the ratio of first branch height to blade length increases somewhat with increasing leaf size, among species with a given ratio of petiole to blade length. Orthotropic species, with more or less radially symmetric arrangements of leaves on ascending axes, had a mean first branch height of 7x that observed for plagiotropic species, with planar leaf arrangements. The greater first branch height of orthotropic species was associated with their larger leaves and longer petioles. Plagiotropic species had wider crowns than orthotropic species in the sapling stage, as assessed at the Costa Rican site. Thus, leaf dimensions influence the dynamics of crown construction (or visa versa), as well as affecting leaf energy balance and gas exchange. Received: 5 September 1997 / Accepted: 3 March 1998     

A mathematical model to describe the dynamic response of a spruce tree to the wind

 A mathematical, computer-based, dynamic sway model of a Sitka spruce (Picea sitchensis) tree was developed and tested against measurements of the movement of a tree within a forest. The model tree was divided into segments each with a stiffness, mass and damping parameter. Equations were formulated to describe the response of every segment which together form a system of coupled differential equations. These were solved with the aid of matrices and from the resulting modes, the transfer function of the tree was found and used to calculate the movement of the tree in the wind. Comparison of the modelled movement of a tree in response to the measured wind speed above a forest canopy gave good agreement with the measured movement of the top of the tree but less satisfactory agreement close to the base. The comparison also pointed to the complexity of tree response to the wind and inadequacies in the model. In particular, the branches need to be treated as coupled cantilevers attached to the stem rather than simply as masses lumped together. Received: 18 February 1997 / Accepted: 16 December 1997     

Hydrogen and oxygen isotope ratios of tree ring cellulose for field-grown riparian trees

The isotopic composition of tree ring cellulose was obtained over a 2-year period from small-diameter riparian-zone trees at field sites that differed in source water isotopic composition and humidity. The sites were located in Utah (cool and low humidity), Oregon (cool and high humidity), and Arizona (warm and low humidity) with source water isotope ratio values of –125/–15‰ (δD/δ¹⁸O), –48/–6‰, and –67/–7‰, respectively. Monthly environmental measurements included temperature and humidity along with measurements of the isotope ratios in atmospheric water vapor, stream, stem, and leaf water. Small riparian trees used only stream water (both δD and δ¹⁸O of stem and stream water did not differ), but δ values of both atmospheric water vapor and leaf water varied substantially between months. Differences in ambient temperature and humidity conditions between sites contributed to substantial differences in leaf water evaporative enrichment. These leaf water differences resulted in differences in the δD and δ¹⁸O values of tree ring cellulose, indicating that humidity information was recorded in the annual rings of trees. These environmental and isotopic measurements were used to test a mechanistic model of the factors contributing to δD and δ¹⁸O values in tree ring cellulose. The model was tested in two parts: (a) a leaf water model using environmental information to predict leaf water evaporative enrichment and (b) a model describing biochemical fractionation events and isotopic exchange with medium water. The models adequately accounted for field observations of both leaf water and tree ring cellulose, indicating that the model parameterization from controlled experiments was robust even under uncontrolled and variable field conditions. Received: 7 April 1999 / Accepted: 8 December 1999     

Molecular markers linked to genes affecting plant height in wheat using a doubled-haploid population

 Plant height in wheat (Triticum aestivum L. em Thell) is known to be under polygenic control. Crosses involving genes Rht-B1 and Rht-D1, located on chromosomes 4BS and 4DS, respectively, have shown that these genes have major effects. Two RFLP loci were found to be linked to these two genes (Xfba1-4B with Rht-B1 and Xfba211-4D with Rht-D1) by genotyping a population of F₁-derived doubled-haploid lines [‘Courtot’ (Rht-B1b+Rht-D1b)בChinese Spring’]. Using a well-covered molecular marker map, we detected three additional regions and one interaction influencing plant height. These regions, located on chromosome arms 4BS (near the locus Xglk556-4B), 7AL (near the locus Xglk478-7A) and 7BL (near the locus XksuD2-7B) explained between 5% and 20% of the variability for this trait in this cross. The influence of 2 loci from chromosome 4B (Xfba1-4B and Xglk556-4B) suggests that there could be a duplication of Rht-B1 on this chromosome originating from Cv ‘Courtot’. Moreover, an interaction effect between loci from chromosome arms 1AS (near the locus Xfba393-1A) and 1BL (near the locus Xcdo1188-1B) was comparable to or even higher than those of the Rht-B1b and Rht-D1b alleles. A model including the main effects of the loci from chromosomes 4B and 4D (Xfba1-4B, Xglk556-4B and Xfba211-4D) and the interaction effect between Xfba393-1A and Xcdo1188-1B is proposed, which explains about 50% of the variation in plant height. The present results are discussed in relation to those obtained using nullisomic or substitution lines. Received: 13 June 1997 / Accepted: 13 October 1997     

Genetic mapping in maize with hybrid progeny across testers and generations: plant height and flowering

DNA markers were used to identify quantitative trait loci (QTLs) for plant height, ear height, and three flowering traits in hybrid progeny of two generations (F_2:3, F_6:8) of lines from a Mo17×H99 maize population. For both generations, testcross (TC) progeny were developed by crossing the lines to three inbred testers (B91, A632, B73). The hybrid progeny from the two generations were evaluated at the same locations but in different years as per an early generation testing program. QTLs were identified within each TC population and for mean testcross (MTC) performance. Overall, more QTLs were detected in the F_6:8 than the F_2:3 generation. Totalled over all five traits, 41 (B91) to 69% (B73) of the QTLs for tester effects and 67% of the QTLs for MTC detected in the F_2:3 generation were verified in the F_6:8 generation. Although differences in relative rank of the QTL effects across generations were observed, especially for the flowering traits, parental contributions were nearly always consistent. Several (8–11) QTLs were identified with effects for all three tester populations and for all traits except the anthesis-silk interval, which had only two such regions. Over all five traits, previous evaluations in this population identified 26 QTLs with consistent effects for two (F_2:3, F_6:8) inbred-progeny evaluations, and 20 (77%) were also associated with MTC in at least one of the generations evaluated herein. In all instances of common inbred and TC QTLs, parental contributions were the same. Received: 26 November 1999 / Accepted: 18 April 2000     

Internal oxygen levels decrease during the growing season and with increasing stem height

The oxygen levels in the sapwood of Norway spruce [Picea abies Karst. (L.)] trees were measured by GC-MS (gas chromatography – mass spectrometry) as stem growth progressed during the growing season. The measurements were made on 30-year-old, 13–15 m high, trees growing on three plots which were irrigated, left undisturbed or subjected to drought. The oxygen measurements were done at 1.5, 4 and 8 m above the ground. The internal oxygen levels dropped to about 5% of the level in air in irrigated trees, 1–3% in control trees and to below 1% in trees subject to drought between mid-July and mid-August. In the trees subjected to drought there where no differences in internal oxygen concentrations between the positions on the tree during the growing season except for a faster increase back to ambient concentration occurring in late August in the 1.5 m position. In trees growing on the two other plots the internal oxygen concentration was higher near the ground than at 4 or 8 m above ground during July and August. At all other dates there were no differences between the positions. The results indicate that there is an oxygen gradient with levels decreasing acropetally, giving indirect support to the hypothesis that oxygen is supplied to the growing stem in the transpiration stream. Received: 26 January 1999 / Accepted: 1 June 1999     

Effects of genetic background and environment on QTLs and epistasis for rice (Oryza sativa L.) panicle number

A double-haploid (DH) population and a recombinant inbred (RI) line population, derived from a cross between a tropical japonica variety, Azucena, as male parent and two indica varieties, IR64 and IR1552, as female parents respectively, were used in both field and pot experiments for detecting QTLs and epistasis for rice panicle number in different genetic backgrounds and different environments. Panicle number (PN) was measured at maturity. A molecular map with 192 RFLP markers for the DH population and a molecular map with 104 AFLP markers and 103 RFLP markers for the RI population were constructed, in which 70 RFLP markers were the same. Six QTLs were identified in the DH population, including two detected from field experiments and four from pot experiments. The two QTLs, mapped on chromosomes 1 and 12, were identical in both field and pot experiments. In the RI population, nine QTLs were detected, five QTLs from field conditions and four from the pot experiments. Three of these QTLs were identical in both experimental conditions. Only one QTL, linked to CDO344 on chromosome 12, was detected across the populations and experiments. Different epistasitic interaction loci on PN were found under different populations and in different experimental conditions. One locus, flanked by RG323 and RZ801 on chromosome 1, had an additive effect in the DH population, but epistatic effects in the RI population. These results indicate that the effect of genetic background on QTLs is greater than that of environments, and epistasis is more sensitive to genetic background and environments than main-effect QTLs. QTL and epistatic loci could be interchangeable depending on the genetic backgrounds and probably on the environments where they are identified. Received: 26 May 2000 / Accepted: 19 October 2000     

Flow cytometric analysis of the chromosomes and stability of a wheat cell-culture line

A rapidly growing, long-term suspension culture derived from Triticum aestivum L. (wheat) was synchronized using hydroxyurea and colchicine, and a chromosome suspension with chromosomes was made. After staining with the DNA-specific fluorochromes Hoechst 33258 and Chromomycin univariate and bivariate flow-cytometry histograms showed 15 clearly resolved peaks corresponding to individual chromosome types or groups of chromosomes with similar DNA contents. The flow karyotype was closely similar to a histogram of DNA content measurements of Feulgen-stained chromosomes made by microdensitometry. We were able to show the stability of the flow karyotype of the cell line over a year, while a parallel subculture had a slightly different, stable, karyotype following different growth conditions. The data indicate that flow cytometric analysis of plant karyotypes enables accurate, statistically precise chromosome classification and karyotyping of cereals. There was little overlap between individual flow-histogram peaks, so the method is useful for flow sorting and the construction of chromosome specific-recombinant DNA libraries. Using bivariate analysis, the AT:GC ratio of all the chromosomes was remarkably similar, in striking contrast to mammalian flow karyotypes. We speculate about a fundamental difference in organization and homogenization of DNA sequences between chromosomes within mammalian and plant genomes. Received: 24 April 1996 / Accepted: 24 May 1996     

QTL mapping of genes controlling ear emergence time and plant height on chromosome 5A of wheat

 Chromosome 5A of wheat carries major gene loci for agronomic traits including the vernalization requirement (Vrn-A1) and ear morphology (Q). To determine whether the genetic variation for ear emergence time and plant height is attributable to either of these major genes as pleiotropic effects or independent QTL, we combined a RFLP map constructed from 120 recombinant substitution lines derived from a cross between ‘Chinese Spring’ (Cappelle-Desprez 5A) and CS(Triticum spelta 5A) with data collected from field trials over 3 years. For ear emergence time the main effects on flowering time were by Vrn-A1 and QEet.ocs-5A.1, the latter a QTL in the 28.6-cM Xcdo584/Q interval linked to Q by less than 10 cM. The CS(T. spelta 5A) allele at QEet.ocs-5A.1 contributed to an earlier ear emergence time by 2.7–6.0 days, which was approximately equal to the effects of Vrn-A1. For plant height, three QTLs were identified on the long arm and linked in repulsion. The CS(T. spelta 5A) allele at Vrn-A1 or closely linked to Xfba068 contributed to a height reduction of 3.5–6.1 cm, whereas both the Q allele and Qt.ocs-5A.1 allele within the Xcdo1088/Xbcd9 interval from CS(Cappelle-Desprez 5A) produced a shorter plant. When plant height was partitioned into culm length and ear length, the Vrn-A1 allele and CS(Cappelle-Desprez 5A) allele at QCl.ocs-5A.1 within the Xcd1088/Xbcd9 interval were found to contribute to a shorter culm. CS(T. spelta 5A) allele at q was a major determinant of a long ear, together with minor effects at QEl.ocs-5A.1 within the Xcdo1088/Xbcd9 interval. Received: 1 April 1998 / Accepted: 13 July 1998     

Refuge use by fish as a function of body weight changes

Refuge use provides a good model for the study of trade-offs between the benefits of predator avoidance and the costs of lost feeding opportunities. We manipulated the latter costs by subjecting similar-sized three-spine sticklebacks to 2 days of food deprivation followed by a 2-day re-feeding period and recorded associated changes in body weight and refuge use. Food deprivation resulted in a decrease and re-feeding in an increase in the duration of refuge use by fish. Emergence times of fish from the refuge were extremely variable (with a ratio of 1:127 between the shortest and the longest ones) but individual ranks were highly consistent between different days of testing, suggesting that emergence times were individually characteristic. Percentage weight change of fish in response to the experimental treatments also showed a high level of inter-individual variation ranging from 0–17%. A significant positive correlation was found between the percentage weight lost and the percentage decrease in emergence time from a refuge after food deprivation and similarly between the percentage weight gained and the percentage increase in refuge use after re-feeding. The relationship between energy turnover and behavioural strategies is discussed. Received: 13 December 1998 / Received in revised form: 2 May 1999 / Accepted: 7 June 1999     

Diverse scaling relationships of tree height and diameter in five tree species

Background: Allometric scaling relationships are important in ecology and forestry. The metabolic scaling theory (MST) predicts a universal invariant scaling relationship for tree growth, relating height and diameter to each other.

Aims: Data on five tree species (Pinus taeda L., Pinus virginiana Mill., Liquidambar styraciflua L., Liriodendron tulipifera L., and Pinus palustris Mill.) were used to test the predictions from MST on the scaling of height–diameter and also diameter growth.

Methods: Data on tree height and diameter for five tree species from both natural forests and plantations were collected to study two types of scaling relationships: tree height–diameter and stem diameter growth. A reduced major axis of regression analysis model type II was used to determine scaling exponents from each species under different environmental conditions.

Results: No universal invariant scaling exponent was found in height–diameter and diameter growth for the five species. The scaling varied across natural forests, plantations and scales (e.g., time and number of measured trees). However, in some situations the scaling exponents failed to show significant difference with the predicted values (e.g., 2/3 or 1).

Conclusions: Diverse scaling exponents were observed for the five tree species with the scaling relationships varying with environmental settings.     

Highly polymorphic microsatellites of rice consist of AT repeats, and a classification of closely related cultivars with these microsatellite loci

Microsatellites consisting of AT repeats are highly polymorphic in rice genomes and can be used to distinguish between even closely related japonica cultivars in Japan. Polymorphisms of 20 microsatellite loci were determined using 59 japonica cultivars, including both domestic and modern Japanese cultivars. Although the polymorphisms of these 20 microsatellite loci indicated that the Japanese cultivars were genetically quite similar, microsatellites consisting of AT repeats showed high gene diversity even among such closely related cultivars. Combinations of these hypervariable microsatellites can be employed to classify individual cultivars, since the microsatellites were stable within each cultivar. An identification system based on these highly polymorphic microsatellites could be used to maintain the purity of rice seeds by eliminating contamination. A parentage diagnosis using 17 polymorphic microsatellite loci clearly demonstrated that plants which carried desired chromosome regions had been selected in breeding programs. Thus, these hypervariable microsatellites consisting of AT repeats should promote the selection of plants which carry desired chromosomes from genetically similar parents. Backcrossing could also help to eliminate unnecessary chromosome regions with microsatellite polymorphisms at an early stage in breeding programs. Received: 8 July 1996 / Accepted: 12 July 1996     

Assessing bias in diameter at breast height estimated from tree rings and its effects on basal area increment and biomass

Above-ground forest productivity can be reliably estimated from tree-ring width measurements. In doing so, annual growth is linked to the tree’s basal area increment (BAI), which is the change in cross-sectional area associated with each annual ring. When BAI is estimated from ring-width series, a value for the diameter of the tree is required. This diameter is ideally measured in the field, but can also be estimated as the sum of the annual ring widths. Tree biomass can also be estimated directly from the diameter estimates derived from tree-rings. Summing the ring widths, however, typically underestimates the tree’s true diameter. To evaluate this potential bias in diameter, we compared field-measured diameter and diameter estimated from the sum of the ring widths using tree-ring chronologies for seven common species in the eastern United States. We then evaluated the impacts of using the biased diameter estimates on derived BAI and biomass values. To simulate field-sampling error (i.e., failure to reach the pith when obtaining a core sample), we re-calculated BAI and biomass after removing a portion of the innermost rings from each tree. Comparisons of these various methods quantify the substantial and consistent underestimations in forest productivity estimates. To reduce the bias in diameter when using ring widths, we developed a regression model to adjust the diameter using core samples. This model is predicated on having some field-measured diameter values available at a site to calibrate and validate the model, but it can then be used to produce estimates at similar sites with similar species where no field-measured diameter values are available. Values of BAI and biomass derived from model-estimated diameter were more accurate at representing absolute growth than values produced by using the sum of the ring widths. Assessing the interannual variations in tree-growth is dependent on having metrics that accurately reflect the area and mass of wood produced. Our results suggest that published estimates of BAI and biomass using the sum of the ring widths to estimate diameter have substantially underestimated these productivity metrics. Our new procedure allows for more reliable estimates of productivity metrics that use diameter-at-breast height derived from tree rings.     

Forest structure of a subtropical mangrove along a river inferred from potential tree height and biomass

The hypothesis was tested that potential tree height and biomass in mangroves decrease downstream with the tidal gradient along the Okukubi River in Okinawa Island, Japan. The mangrove stands consisted of Bruguiera gymnorrhiza (L.) Lamk. and Kandelia obovata (S., L.) Yong (Rhizophoraceae). Four sites were selected considering the distance from the mouth of the river. Soil salinity increased downstream, while soil total nitrogen content decreased. The soil redox potential did not vary along the river. Maximum gross photosynthesis and tree height for each species decreased downstream. The potential tree height (H_max) inferred from the stem diameter (D_0.1)–tree height (H) relationship ( a, h, coefficient) in each species decreased downstream. The tree density (ρ)–mean tree size () relationships ( K, α, coefficient) determined for four sites revealed that the mean tree size at any given tree density decreased downstream, which indicates the decrease of potential biomass. Furthermore, an index for biomass () was homogeneous within a site regardless of tree density, i.e. the value of α at each site did not differ significantly from 1.0 (p > 0.05). The decreases in potential tree height and biomass may be partially ascribed to the stressful environments at the downstream sites characterized by high salinity (>2.6%) and nitrogen-poor soils (<0.25 ppt) in our study area.     

Polymorphism, distribution, and segregation of AFLP markers in a doubled haploid rice population

We exploited the newly developed amplified fragment length polymorphism (AFLP) technique to study the polymorphism, distribution and inheritance of AFLP markers with a doubled haploid rice population derived from ‘IR64’/‘Azucena’. Using only 20 pairs of primer combinations, we detected 945 AFLP bands of which 208 were polymorphic. All 208 AFLP markers were mapped and distributed over all 12 chromosomes. When these were compared with RFLP markers already mapped in the population, we found the AFLP markers to be highly polymorphic in rice and to follow Mendelian segregation. As linkage map of rice can be generated rapidly with AFLP markers they will be very useful for marker-assisted backcrossing. Received: 11 April 1996 / Accepted: 14 June 1996     

Elevated CO2 enhances resprouting of a tropical savanna tree

The savannas (cerrado) of south-central Brazil are currently subjected to frequent anthropogenic burning, causing widespread reduction in tree density. Increasing concentrations of atmospheric CO₂ could reduce the impact of such frequent burning by increasing the availability of nonstructural carbohydrate, which is necessary for resprouting. We tested the hypotheses that elevated CO₂ stimulates resprouting and accelerates replenishment of carbohydrate reserves. Using a factorial experiment, seedlings of a common Brazilian savanna tree, Keilmeyera coriacea, were grown at 350 ppm and 700 ppm CO₂ and at two nutrient levels. To simulate burning, the plants were either clipped at 15 weeks or were left unclipped. Among unclipped plants, CO₂ and nutrients both stimulated growth, with no significant interaction between nutrient and CO₂ effects. Among clipped plants, both CO₂ and nutrients stimulated resprouting. However, there was a strong interaction between CO₂ and nutrient effects, with CO₂ having a significant effect only in the presence of high nutrient availability. Under elevated CO₂, carbohydrate reserves remained at higher levels following clipping. Root total nonstructural carbohydrate remained above 36% in all treatments, so carbohydrate reserves did not limit regrowth. These results indicate that under elevated CO₂ this species may be better able to endure the high frequency of anthropogenic burning in the Brazilian savannas. Received: 19 May 1999 / Accepted: 8 November 1999