Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate

Summary Which factors cause fast-growing plant species to achieve a higher relative growth rate than slow-growing ones? To answer this question 24 wild species were grown from seed in a growth chamber under conditions of optimal nutrient supply and a growth analysis was carried out. Mean relative growth rate, corrected for possible ontogenetic drift, ranged from 113 to 356 mg g^–1 day^–1. Net assimilation rate, the increase in plant dry weight per unit leaf area and unit time, varied two-fold between species but no correlation with relative growth rate was found. The correlation between leaf area ratio, the ratio between total leaf area and total plant weight, and relative growth rate was very high. This positive correlation was mainly due to the specific leaf area, the ratio between leaf area and leaf weight, and to a lesser extent caused by the leaf weight ratio, the fraction of plant biomass allocated to the leaves. Differences in relative growth rate under conditions of optimum nutrient supply were correlated with the soil fertility in the natural habitat of these species. It is postulated that natural selection in a nutrient-rich environment has favoured species with a high specific leaf area and a high leaf weight ratio, and consequently a high leaf area ratio, whereas selection in nutrient-poor habitats has led to species with an inherently low specific leaf area and a higher fraction of root mass, and thus a low leaf area ratio.     

Does seed mass drive the differences in relative growth rate between growth forms?

The idea that herbaceous plants have higher relative growth rates (RGRs) compared with woody plants is fundamental to many of the most influential theories in plant ecology. This difference in growth rate is thought to reflect systematic variation in physiology, allocation and leaf construction. Previous studies documenting this effect have, however, ignored differences in seed mass. As woody species often have larger seeds and RGR is negatively correlated with seed mass, it is entirely possible the lower RGRs observed in woody species is a consequence of having larger seeds rather than different growth strategies. Using a synthesis of the published literature, we explored the relationship between RGR and growth form, accounting for the effects of seed mass and study-specific effects (e.g. duration of study and pot volume), using a mixed-effects model. The model showed that herbaceous species do indeed have higher RGRs than woody species, and that the difference was independent of seed mass, thus at all seed masses, herbaceous species on average grow faster than woody ones.     

Differential chemical allocation and plant adaptation: A Py-MS Study of 24 species differing in relative growth rate

The chemical composition of leaves of 24 wild species differing in potential relative growth rate (RGR) was analysed by pyrolysis-mass spectrometry. The variation in RGR significantly correlated with differences in chemical composition: slow-growing species were richer in glucan-based polysaccharides and in C16:0 fatty acid, whereas fast growing ones contained more protein (other than those incorporated in cell walls) and chlorophyll, sterols and diglycerides. Other, apparently significant correlations, e.g. for pentose-based hemicellulose and for guaiacyl lignin appeared solely based on a group separation between mono- and dicotyledonous species.Considering the eleven monocotyledonous and thirteen dicotyledonous species separately, correlations were found in addition to the previously mentioned general ones. Within the group of the monocotyledons the low-RGR species were significantly enriched in pentose-based hemicellulose, ferulic acid and (hydroxy)proline-rich cell wall protein and nearly significant in guaiacyl and syringyl lignin, fast-growing species contained more potassium. Within the group of the dicotyledons slow-growing species were enriched in triterpenes and aliphatic wax esters.In general, the monocotyledons contained more cell wall material such as pentose-based hemicellulose, ferulic acid, glucans (including cellulose) and guaiacyl-lignin, and also more aliphatic wax esters, than the dicotyledons. The dicotyledons, on the other hand, contained somewhat more protein than the grasses.Per unit weight of cell wall, the amount of (hydroxy)proline- rich protein in low-RGR species was comparatively low. A higher investment of cell wall proteins to explain the low rate of photosynthesis per unit of leaf nitrogen of slow-growing species as suggested by Lambers and Poorter (1992), therefore, seems unlikely.Abbreviations HPRP (hydroxy)proline-rich protein(s) - LAR leaf area ratio - LWR leaf weight ratio - MVA multivariate analysis - NAR net assimilation rate - PC principal component - PNUE photosynthetic nitrogen use efficiency - PyGCMS pyrolysis-gas chromatography-mass spectrometry - PyMS pyrolysis mass spectrometry - RGR relative growth rate - SLA specific leaf area - SLM specific leaf mass     

Chemical composition of 24 wild species differing in relative growth rate

The chemical composition of 24 plant species which showed a three-fold range in potential growth rate was investigated. The carbon content of whole plants was lower for fast-growing species than for slow-growing ones. Fast-growing species accumulated more organic N-compounds, organic acids and minerals, whereas slow-growing species accumulated more (hemi)cellulose, insoluble sugars and lignin. No correlations with relative growth rate were found for soluble phenolics, soluble sugars and lipids. The costs to construct 1 g of plant biomass were rather similar for fast- and slow-growing species, both when expressed as C needed for C-skeletons, as glucose to provide ATP and NAD(P)H, and as total glucose costs. Therefore, we conclude that, despite the differences in chemical composition between fast- and slow-growing species, variation in the costs of synthesis of whole plant biomass cannot explain interspecific variation in relative growth rate of herbaceous species.     

Latitudinal variation in plant size and relative growth rate in Arabidopsis thaliana

Latitude is an important determinant of local environmental conditions that affect plant growth. Forty ecotypes of Arabidopsis thaliana were selected from a wide range of latitudes (from 16°N to 63°N) to investigate genetic variation in plant size and relative growth rate (RGR) along a latitudinal gradient. Plants were grown in a greenhouse for 31 days, during which period three consecutive harvests were performed. Plants from high latitudes tended to have smaller plant size in terms of seed size, cotyledon width, rosette size, number of rosette leaves, size (leaf area) of the largest leaves, total leaf area, and total dry weight per plant than those from low latitudes. The mean (±SE) RGR across ecotypes was 0.229 (±0.0013) day⁻¹. There was, however, significant ecotypic variation, with RGR being negatively correlated with latitude. The two main components of RGR, leaf area ratio (LAR) and unit leaf rate (ULR), were also correlated with latitude: LAR increased with increasing latitude while ULR decreased with increasing latitude. It was also found that RGR tended to be negatively correlated with LAR, specific leaf area (SLA) and specific root length (SRL) but to be positively correlated with mean area per leaf (MAL) and ULR. The variation in RGR among ecotypes was relatively small compared with that in the other traits. RGR may be a conservative trait, whose variation is constrained by the trade-off between its physiological (i.e. ULR) and morphological (i.e. LAR) components. Received: 2 November 1997 / Accepted: 28 February 1998     

Effects of nitrogen supply on the anatomy and chemical composition of leaves of four grass species belonging to the genus Poa, as determined by image-processing analysis and pyrolysis–mass spectrometry

Previous experiments have shown that the anatomy and chemical composition of leaves of inherently fast- and slow-growing grass species, grown at non-limiting nitrogen supply, differ systematically. The present experiment was carried out to investigate whether these differences persist when the plants are grown at an intermediate or a very low nitrogen supply. To this end, the inherently fast-growing Poa annua L. and Poa trivialis L., and the inherently slow-growing Poa compressa L. and Poa pratensis (L.) Schreb. were grown hydroponically at three levels of nitrate supply: at optimum (RGR_max) and at relative addition rates of 100 and 50 mmol N (mol N)^?1 d^?1 (RAR₁₀₀ and RAR₅₀), respectively. As expected, at the lowest N supply, the potentially fast-growing species grew at the same rate as the inherently slow-growing ones. Similarly, the differences in leaf area ratio (LAR, leaf area:total dry mass), specific leaf area (SLA, leaf arear:leaf dry mass) and leaf mass ratio (LMR, leaf dry mass:total dry mass) disappeared. Under optimal conditions, the fast-growing species differed from the slow-growing ones in that they had a higher N concentration. There were no significant differences in C concentration. With decreasing N supply, the total N concentration decreased and the differences between the species disappeared. The total C concentration increased for the fast-growing species and decreased for the slow-growing ones, i.e. the small, but insignificant, difference in C concentration between the species at RGR_max increased with decreasing N supply. The chemical composition of the leaves at low N supply, analysed in more detail by pyrolysis–mass spectrometry, showed an increase in the relative amounts of guaiacyl lignin, cellulose and hemicellulose, whereas those of syringyl lignin and protein decreased. The anatomy and morphology of the leaves of the four grass species differing in RGR_max were analysed by image-processing analysis. The proportion of the total volume occupied by mesophyll plus intercellular spaces and epidermis did not correlate with the amount of leaf mass per unit leaf area (specific leaf mass, SLM) at different N supply. The higher SLM at low N supply was caused partly by a high proportion of non-veinal sclerenchymatic cells per cross-section and partly by the smaller volume of epidermal cells. We conclude that the decrease in relative growth rate (and increase in SLM) at decreasing N supply is partly due to chemical and anatomical changes. The differences between the fast- and slow-growing grass species at an optimum nutrient supply diminished when plants were growing at a limiting nitrogen supply.     

Chemical differences between wildtype and gibberellin mutants of tomato determined by pyrolysis-mass spectrometry

Leaf, stem and root material of wild-type and gibberellin (GA)-deficient mutants of tomato (Lycopersicum esculentum L.) were analysed by pyrolysis-mass spectrometry for possible differentiation in chemical allocation pattern among cell wall and cytoplasm. GA-deficiency is accompanied by changes in the relative growth rate (RGR). RGR-correlated changes were found in leaves in the comparative amounts of cellulose- and protein-derived fragments. The low-RGR genotypes contained more protein and nucleic acid, the high-RGR ones more cellulose. In root material, a higher contribution of cellulose, hemicellulose and G- and S-lignin was found for the lower-RGR plants and comparatively high protein in the high-RGR genotypes. For stems, less clear results were obtained, possibly because of variation in the ratio of syringyl- and guaiacyl-lignin. Part of the results might be explained by a GA-dependent change in cell size.     

Free energies of protein-protein association determined by electrospray ionization mass spectrometry correlate accurately with values obtained by solution methods

The advantages of electrospray ionization mass spectrometry (ESIMS) to measure relative solution-phase affinities of tightly bound protein-protein complexes are demonstrated with selected variants of the Bacillus amyloliquefaciens protein barstar (b*) and the RNAase barnase (bn), which form protein-protein complexes with a range of picomolar to nanomolar dissociation constants. A novel chemical annealing procedure rapidly establishes equilibrium in solutions containing competing b* variants with limiting bn. The relative ion abundances of the complexes and those of the competing unbound monomers are shown to reflect the relative solution-phase concentrations of those respective species. No measurable dissociation of the complexes occurs either during ESI or mass detection, nor is there any evidence for nonspecific binding at protein concentrations < 25 microM. Differences in DeltaDeltaG of dissociation between variants were determined with precisions < 0.1 kcal/mol. The DeltaDeltaG values obtained deviate on average by 0.26 kcal/mol from those measured with a solution-phase enzyme assay. It is demonstrated that information about the protein conformation and covalent modifications can be obtained from differences in mass and charge state distributions. This method serves as a rapid and precise means to interrogate protein-protein-binding surfaces for complexes that have affinities in the picomolar to nanomolar range.     

Resolution of batch variations in pyrolysis mass spectrometry of bacteria by the use of artificial neural network analysis

A simple, but stringent, three group model of bacterial interstrain identity (two cultures of the same strain ofEscherichia coli) and difference (a culture of a serologically distinct strain) was used in multiple serial weekly subcultures for five weeks to demonstrate the effect of both growth-related (phenotypic) and machine-related variation on pyrolysis mass spectra. An aliquot of serum from a single sample was included in each pyrolysis batch to distinguish machine drift from culture drift. Conventional principal component (PC) canonical variate (CV) analysis was successful within each pyrolysis batch but the variations between batches precluded the use of data from more than one batch in successful PCCV analysis. In contrast, artificial neural networks (ANNs) trained with data from one batch could be successfully used to identify groups in data from non-contemporaneous pyrolysis batches. Although the ANN method will require validation in more complex settings than this simple model, it is a promising approach to the problem of batch constraint in pyrolysis mass spectrometry.     

The chemical composition and anatomical structure of leaves of grass species differing in relative growth rate

To arrive at a better understanding of variation in specific leaf mass (SLM, leaf weight per unit leaf area), we investigated the chemical composition and anatomical structure of the leaves of 14 grass species varying in potential relative growth rate. Expressed on a dry weight basis, the fast-growing grass species with low SLM contained relatively more minerals and organic N-compounds, whereas slow-growing species with high SLM contained more (hemi)cellulose and lignin. However, when expressed per unit leaf area, organic N-compounds, (hemi)cellulose, total structural carbohydrates and organic acids increased with increasing SLM. For the 14 grasses, no trend with SLM was found for the leaf volume per unit leaf area. Leaf density was positively correlated with SLM. Variation in density was not caused by variation in the proportion of intercellular spaces. The proportion of the total volume occupied by mesophyll and veins did not differ either. A high SLM was caused, at least partly, by a high proportion of non-veinal sclerenchymatic cells per cross-section. The epidermal cell area was negatively correlated with SLM. We conclude that the differences in SLM and in the relative growth rate (RGR) between fast- and slow-growing grass species are based partly on variation in anatomical differentiation and partly on chemical differences within cell types.     

Cultivar differences in the rate of nitrate uptake by intact wheat plants as related to growth rate

Six Argentinian wheat ( Triticum aestivum L.) cultivars grown in nutrient solutions in controlled environment were compared for their nitrate uptake rates on a root dry weight basis. Up to 3-fold differences were observed among the cultivars at 16, 20 and 24 days from germination, either when measured by depletion from the nutrient solution in short-term experiments, or by total N accumulation in the tissue during 8 days.
No differences in total N concentration in root or shoots were found among cultivars. Although the different cultivars showed significant differences in shoot/root ratio and nitrate reductase activity (EC 1.6.6.1) in the roots, none of these parameters was correlated with the nitrate uptake rate. However, nitrate uptake was found to be positively correlated (r = 0.99) with the shoot relative growth rate of the cultivars. The three cultivars with the highest nitrate uptake rates and relative growth rates showed a positive correlation between root nitrate concentration and uptake. However, this correlation was not found in the cultivars with the lowest growth and uptake rates.
Our results indicate that the difference in nitrate uptake rate among these cultivars may only be a consequence of their differences in growth rate, and it is suggested that at least two mechanisms regulate nitrate uptake, one working when plant demand is low and another when plant demand is high.     

Differences in construction costs and chemical composition between deciduous and evergreen woody species are small as compared to differences among families

We tested to what extent differences in construction costs (CC) and chemical composition of woody species are attributed to leaf habit. Eight evergreen and eight deciduous species belonging to six families were selected to form eight phylogenetic independent contrasts (PICs). The plants were grown from seed in a glasshouse. Differences in leaf, stem and root CC between evergreen and deciduous species were minor, the proportion of variance explained by leaf habit generally being less than 6%. Surprisingly, differences in leaf chemical composition between deciduous and evergreen species were small as well. Variation in CC and chemical composition among families was substantial, the factor 'family' explaining 50-85% of variance. We therefore conclude that in this case, phylogeny is a more important factor than functional group. Leaves of the fast-growing species in this experiment showed high levels of minerals, organic acids, proteins and lipids, whereas leaves of the slow-growing species had higher concentrations of soluble phenolics, lignin as well as higher carbon/nitrogen (C/N) ratio. These relationships suggest a trade-off between growth and defence. In contrast, CC of leaves, stems, roots or whole plants showed no or only a weak correlation with relative growth rate (RGR). The C/N ratio of the leaves is an easily measured parameter that correlated strongly in a negative way with the RGR of the plants and reflected better the balance between investment in structure and physiological functioning than CC.     

The accumulation pattern of ferruginol in the heartwood-forming Cryptomeria japonica xylem as determined by time-of-flight secondary ion mass spectrometry and quantity analysis

Background and Aims

Heartwood formation is a unique phenomenon of tree species. Although the accumulation of heartwood substances is a well-known feature of the process, the accumulation mechanism remains unclear. The aim of this study was to determine the accumulation process of ferruginol, a predominant heartwood substance of Cryptomeria japonica, in heartwood-forming xylem.

Methods

The radial accumulation pattern of ferruginol was examined from sapwood and through the intermediate wood to the heartwood by direct mapping using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The data were compared with quantitative results obtained from a novel method of gas chromatography analysis using laser microdissection sampling and with water distribution obtained from cryo-scanning electron microscopy.

Key Results

Ferruginol initially accumulated in the middle of the intermediate wood, in the earlywood near the annual ring boundary. It accumulated throughout the entire earlywood in the inner intermediate wood, and in both the earlywood and the latewood in the heartwood. The process of ferruginol accumulation continued for more than eight annual rings. Ferruginol concentration peaked at the border between the intermediate wood and heartwood, while the concentration was less in the latewood compared wiht the earlywood in each annual ring. Ferruginol tended to accumulate around the ray parenchyma cells. In addition, at the border between the intermediate wood and heartwood, the accumulation was higher in areas without water than in areas with water.

Conclusions

TOF-SIMS clearly revealed ferruginol distribution at the cellular level. Ferruginol accumulation begins in the middle of intermediate wood, initially in the earlywood near the annual ring boundary, then throughout the entire earlywood, and finally across to the whole annual ring in the heartwood. The heterogeneous timing of ferruginol accumulation could be related to the distribution of ray parenchyma cells and/or water in the heartwood-forming xylem.