Tree age-dependent changes in photosynthetic and respiratory CO2 exchange in leaves of micropropagated diploid, triploid and hybrid aspen (original) (raw)
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Tree Physiology, 2011
Phenotypic variation in plant traits is strongly influenced by genetic and environmental factors. Over the life span of trees, developmental factors may also strongly influence leaf phenotypes. The objective of this study was to fill gaps in our understanding of developmental influences on patterns of phenotypic trait variation among different-aged ramets within quaking aspen (Populus tremuloides Michx.) clones. We hypothesized that phenotypic variation in leaf functional traits is strongly influenced by developmental cues as trees age. We surveyed eight aspen clones, each with eight distinct age classes ranging from 1 to 160 years in age, and selected three ramets per age class for sample collection. Leaf traits measured included photosynthesis, stomatal conductance, water use efficiency, specific leaf area, and concentrations of N, phosphorus, sucrose, starch, condensed tannins and phenolic glycosides. Using regression analysis, we examined the relationships between ramet age and expression of leaf functional traits. The data showed significant correlations between ramet age and 10 of the 12 phenotypic traits measured. Eight of the phenotypic traits demonstrated a non-linear relationship in which large changes in phenotype occurred in the early stages of ramet development and stabilized thereafter. Water relations, nutrient concentration, leaf gas exchange and phenolic glycosides tended to decrease from early to late development, whereas sucrose, condensed tannin concentrations and water use efficiency increased with ramet age. We hypothesize that ontogenetically derived phenotypic variation leads to fitness differentials among different-aged ramets, which may have important implications for clone fitness. Age-related increases in phenotypic diversity may partially underlie aspen's ability to tolerate the large environmental gradients that span its broad geographical range.
Tree Physiology, 2008
A quantitative analysis was applied to the stomatal and biochemical limitations to light-saturated net photosynthesis under optimal field conditions in mature trees and seedlings of the co-occurring evergreen oak, Quercus ilex L., and the deciduous oak, Q. faginea Lam. Stomatal limitation to photosynthesis, maximal Rubisco activity and electron transport rate were determined from assimilation versus intercellular leaf carbon dioxide concentration response curves of leaves that were subsequently analyzed for nitrogen (N) concentration, mass per unit area, thickness and percent internal air space. In both species, seedlings had a lower leaf mass per unit area, thickness and leaf N concentration than mature trees. The root system of seedlings during their third year after planting was dominated by a taproot. A lower leaf N concentration of seedlings was associated with lower maximal Rubisco activity and electron transport rate and with assimilation rates similar to or lower than those of mature trees, despite the higher stomatal conductances and potential photosynthetic nitrogenuse efficiencies of seedlings. Consequently, stomatal limitation to photosynthesis increased with tree age in both species. In both seedlings and mature trees, a lower assimilation rate in Q. ilex than in Q. faginea was associated with lower stomatal conductance, N allocation to photosynthetic functions, maximal Rubisco activity and electron transport rate, and potential photosynthetic nitrogen-use efficiency but greater leaf thickness and leaf mass per unit area. Tree-age-related changes differed quantitatively between species, and the characteristics of the two species were more similar in seedlings than in mature trees. Despite higher stomatal conductances, seedlings are more N limited than adult trees, which contributes to lower biochemical efficiency.
Tree Physiology, 1998
Biochemical models of photosynthesis suggest that rising temperatures will increase rates of net carbon dioxide assimilation and enhance plant responses to increasing atmospheric concentrations of CO 2. We tested this hypothesis by evaluating acclimation and ontogenetic drift in net photosynthesis in seedlings of five boreal tree species grown at 370 and 580 µmol mol −1 CO 2 in combination with day/night temperatures of 18/12, 21/15, 24/18, 27/21, and 30/24 °C. Leafarea-based rates of net photosynthesis increased between 13 and 36% among species in plants grown and measured in elevated CO 2 compared to ambient CO 2. These CO 2-induced increases in net photosynthesis were greater for slower-growing Picea mariana (Mill.) B.S.P., Pinus banksiana Lamb., and Larix laricina (Du Roi) K. Koch than for faster-growing Populus tremuloides Michx. and Betula papyrifera Marsh., paralleling longer-term growth differences between CO 2 treatments. Measures at common CO 2 concentrations revealed that net photosynthesis was down-regulated in plants grown at elevated CO 2. In situ leaf gas exchange rates varied minimally across temperature treatments and, contrary to predictions, increasing growth temperatures did not enhance the response of net photosynthesis to elevated CO 2 in four of the five species. Overall, the species exhibited declines in specific leaf area and leaf nitrogen concentration, and increases in total nonstructural carbohydrates in response to CO 2 enrichment. Consequently, the elevated CO 2 treatment enhanced rates of net photosynthesis much more when expressed on a leaf area basis (25%) than when expressed on a leaf mass basis (10%). In all species, rates of leaf net CO 2 exchange exhibited modest declines with increasing plant size through ontogeny. Among the conifers, enhancements of photosynthetic rates in elevated CO 2 were sustained through time across a wide range of plant sizes. In contrast, for Populus tremuloides and B. papyrifera, massbased photosynthetic rates did not differ between CO 2 treatments. Overall, net photosynthetic rates were highly correlated with relative growth rate as it varied among species and treatment combinations through time. We conclude that interspecific variation may be a more important determinant of photosynthetic response to CO 2 than temperature.
Ontogenetic patterns of leaf CO2 exchange, morphology and chemistry in Betula pendula trees
Trees, 2000
In order to explore ontogenetic variation in leaf-level physiological traits of Betula pendula trees, we measured changes in mass-(A mass ) and area-based (A area ) net photosynthesis under light-saturated conditions, mass-(RS mass ) and area-based (RS area ) leaf respiration, relative growth rate, leaf mass per area (LMA), total nonstructural carbohydrates (TNC), and macro-and micronutrient concentrations. Expanding leaves maintained high rates of A area , but due to high growth respiration rates, net CO 2 fixation occurred only at irradiances >200 µmol photons m -2 s -1 . We found that full structural leaf development is not a necessary prerequisite for maintaining positive CO 2 balance in young birch leaves. Maximum rates of A area were realized in late June and early July, whereas the highest values of A mass occurred in May and steadily declined thereafter. The maintenance respiration rate averaged ≈8 nmol CO 2 g -1 s -1 , whereas growth respiration varied between 0 and 65 nmol CO 2 g -1 s -1 . After reaching its lowest point in mid-June, leaf respiration increased gradually until the end of the growing season. Mass and area-based dark respiration were significantly positively correlated with LMA at stages of leaf maturity, and senescence. Concentrations of P and K decreased during leaf development and stabilized or increased during maturity, and concentrations of immobile elements such as Ca, Mn and B increased throughout the growing season. Identification of interrelations between leaf development, CO 2 exchange, TNC and leaf nutrients allowed us to define factors related to ontogenetic variation in leaf-level physiological traits and can be helpful in establishing periods appropriate for sampling birch leaves for diagnostic purposes such as assessment of plant and site productivity or effects of biotic or abiotic factors.
Tree Physiology, 2002
Foliar light-saturated net assimilation rates (A) generally decrease with increasing tree height (H) and tree age (Y), but it is unclear whether the decline in A is attributable to size-and age-related modifications in foliage morphology (needle dry mass per unit projected area; M A ), nitrogen concentration, stomatal conductance to water vapor (G), or biochemical foliage potentials for photosynthesis (maximum carboxylase activity of Rubisco; V cmax ). I studied the influences of H and Y on foliage structure and function in a data set consisting of 114 published studies reporting observations on more than 200 specimens of various height and age of Picea abies (L.) Karst. and Pinus sylvestris L. In this data set, foliar nitrogen concentrations were independent of H and Y, but net assimilation rates per unit needle dry mass (A M ) decreased strongly with increasing H and Y. Although M A scaled positively with H and Y, net assimilation rates per unit area (A A = M A × A M ) were strongly and negatively related to H, indicating that the structural adjustment of needles did not compensate for the decline in mass-based needle photosynthetic rates. A relevant determinant of tree height-and age-dependent modifications of A was the decrease in G. This led to lower needle intercellular CO 2 concentrations and thereby to lower efficiency with which the biochemical photosynthetic apparatus functioned. However, V cmax per unit needle dry mass and area strongly decreased with increasing H, indicating that foliar photosynthetic potentials were lower in larger trees at a common intercellular CO 2 concentration. Given the constancy of foliar nitrogen concentrations, but the large decline in apparent V cmax with tree size and age, I hypothesize that the decline in V cmax results from increasing diffusive resistances between the needle intercellular air space and carboxylation sites in chloroplasts. Increased diffusive limitations may be the inevitable consequence of morphological adaptation (changes in M A and needle density) to greater water stress in needles of larger trees. Foliage structural and physiological variables were nonlinearly related to H and Y, possibly because of hyperbolic decreases in shoot hydraulic conductances with increasing tree height and age. Although H and Y were correlated, foliar characteristics were generally more strongly related to H than to Y, suggesting that increases in height rather than age are responsible for declines in foliar net assimilation capacities.
Plants
Micropropagation of fast-growing tree genotypes such as the hybrid aspen (Populus tremuloides Michx. × Populus tremula L.) is increasing. The efficiency of micropropagation depends on the luminaires, hence luminescent electric diodes (LED), which emit light of a narrow spectrum, are gaining popularity. Mostly, different LEDs are combined to increase the photosynthetic efficiency. However, light also acts as an environmental signal, which triggers specific responses in plants, which are genotype specific, and regarding hybrid aspen, are likely affected by heterosis. In this study, morphological and physiological responses of clones of hybrid aspen with contrasting field performance to the spectral composition of illumination were studied in vitro. Among the 15 variables measured, area of leaves and concentration and ratio of chlorophyll a and b explained most of the variance (58.6%), thereby linking a specific combination of traits to productivity. These traits and their responses to...
Abbreviations: A n , net photosynthetic rate on a leaf area basis at CO 2 condition of 360 mmol mol -1 ; A on , net photosynthetic rate on a leaf area basis assuming no internal CO 2 transfer resistance; A pg , gross photosynthetic rate on a leaf area basis assuming no stomatal and internal resistances; A pn , net photosynthetic rate on a leaf area basis assuming no stomatal and internal resistances; C c , CO 2 concentration in the chloroplast stroma; C i , CO 2 concentration in the substomatal cavities; FLE, the time of full leaf area expansion; g i , internal CO 2 transfer conductance; g s , stomatal conductance to water vapour, LMA, leaf dry mass per unit area; L i , limitation of photosynthesis by internal CO 2 conductance; L s , limitation of photosynthesis by stomatal conductance; L r , limitation of photosynthesis by respiration; r day , day respiration rate on a leaf area basis; S c , surface area of chloroplasts facing the intercellular air spaces on a leaf area basis; S mes , surface area of mesophyll cells directly exposed to the intercellular air spaces on a leaf area basis.