Variation In Specific Leaf Area Research Articles

Leaf area index from litter collection: impact of specific leaf area variability within a beech stand

Litter fall collection is a direct method widely used to estimate leaf area index (LAI) in broad-leaved forest stands. Indirect measurements using radiation transmittance and gap fraction theory are often compared and calibrated against litter fall, which is considered as a reference method, but few studies address the question of litter specific leaf area (SLA) measurement and variability. SLA (leaf area per unit of dry weight, m2·g‐1) is used to convert dry leaf litter biomass (g·m‐2) into leaf area per ground unit area (m2·m‐2). We paid special attention to this parameter in two young beech stands (dense and thinned) in northeastern France. The variability of both canopy (closure, LAI) and site conditions (soil properties, vegetation) was investigated as potential contributing factors to beech SLA variability. A systematic description of soil and floristic composition was performed and three types of soil were identified. Ellenberg's indicator values were averaged for each plot to assess nitrogen soil content. SLA of beech litter was measured three times during the fall in 23 plots in the stands (40 ha). Litter was collected bimonthly in square-shaped traps (0.5 m2) and dried. Before drying, 30 leaves per plot and for each date were sampled, and leaf length, width, and area were measured with the help of a LI-COR areameter. SLA was calculated as the ratio of cumulated leaf area to total dry weight of the 30 leaves. Leaves characteristics per plot were averaged for the three dates of litter collection. Plant area index (PAI), estimated using the LAI-2000 plant canopy analyser and considering only the upper three rings, ranged from 2.9 to 8.1. Specific leaf area of beech litter was also highly different from one plot to the other, ranging from 150 to 320 cm2·g‐1. Nevertheless, no relationship was found between SLA and stand canopy closure or PAI. On the contrary, a significant relationship between SLA and soil properties was observed. Both SLA and leaf area had the lowest values in the most hydromorphic soil with the highest nitrogen content. On the other hand, the highest values of SLA and leaf area were observed on the plots with the lowest nitrogen content. This spatial variability of SLA was taken into account to estimate LAI from litter collected at eight plots. For our study site, we conclude that neglecting SLA spatial variability is at the source of 8‐24% error in the calculation of LAI.

Growth temperature influences the underlying components of relative growth rate: an investigation using inherently fast‐ and slow‐growing plant species

AbstractWe examined the effect of growth temperature on the underlying components of growth in a range of inherently fast‐ and slow‐growing plant species. Plants were grown hydroponically at constant 18, 23 and 28 °C. Growth analysis was conducted on 16 contrasting plant species, with whole plant gas exchange being performed on six of the 16 species. Inter‐specific variations in specific leaf area (SLA) were important in determining variations in relative growth rate (RGR) amongst the species at 23 and 28 °C but were not related to variations in RGR at 18 °C. When grown at 18 °C, net assimilation rate (NAR) became more important than SLA for explaining variations in RGR. Variations in whole shoot photosynthesis and carbon concentration could not explain the importance of NAR in determining RGR at the lower temperatures. Rather, variations in the degree to which whole plant respiration per unit leaf area acclimated to the different growth temperatures were responsible. Plants grown at 28 °C used a greater proportion of their daily fixed carbon in respiration than did the 18 and 23 °C‐grown plants. It is concluded that the relative importance of the underlying components of growth are influenced by growth temperature, and the degree of acclimation of respiration is of central importance to the greater role played by NAR in determining variations in RGR at declining growth temperatures.

Anatomical variation in juvenile eucalypt leaves accounts for differences in specific leaf area and CO2 assimilation rates

Specific leaf area (SLA) is an important leaf attribute representing a compromise between the capture of light and CO2 and the limitations imposed by leaf structure, herbivore resistance and the mitigation of water loss. We examined three Eucalyptus L'Her. species to determine whether variation in CO2 assimilation rate was related to SLA and leaf anatomy. Seedlings were grown in a naturally illuminated glasshouse with adequate water and nutrients. Light-saturated rates of photosynthesis were measured on the youngest fully expanded leaves. Mesophyll characteristics were measured from sections thick of the interveinal leaf lamina. Significant interspecies variation in SLA corresponded to clear trends in anatomy and photosynthesis. Low-SLA leaves were thicker, having increased thickness of palisade mesophyll because of a greater number of palisade layers. E. occidentalis, E.camaldulensis and E. grandis had 3.7, 2.0 and 1.0 layers of palisade cells which corresponded to an SLA of 14.8, 17.6 and 21.8 m2 kg-1, respectively. High investment of dry mass in photosynthetic tissue was associated with higher leaf N (area and mass) concentration, chlorophyll concentration and photosynthetic capacity per leaf area. Leaf morphology affected use of the resources N, water and CO2. In contrast to the thin leaves of E. grandis, thick leaves of E. occidentalis had low N-use efficiency and high instantaneous water-use efficiency. Differences in leaf structure of these species appear to reflect the most limiting resource experienced in the environments to which they have adapted.

SPAD readings and associated leaf traits in durum wheat, barley and triticale cultivars

SPAD readings may represent a useful screening criterion in breeding programs aimed at increasing the rate and duration of leaf photosynthesis. A two-year trial was conducted on 17 cultivars of durum wheat, 8 of triticale and 18 of barley at two experiment stations in Sardinia, Italy, to evaluate the existence of genetic variation for SPAD readings, and to quantify the genetic associations between SPAD readings, area per leaf blade (LA), specific leaf area (SLA), leaf nitrogen concentration (LNC) and leaf nitrogen per unit of leaf surface (LN) in the period between beginning of tillering and flag leaf appearance. Plants were grown at sufficient nitrogen fertilization. The average SPAD reading of barley was 9–10 units lower than that of durum wheat and triticale. The combined ANOVA indicated that, in all the three species, the genotype by environment interaction variance associated with SPAD readings was lower than the genetic variance. In durum wheat and barley, SPAD readings exhibited a greater genetic variance in comparison with LNC, LN and SLA. In durum wheat and triticale, SPAD readings were genetically correlated with LN and SLA. Durum wheat differed from triticale because its genetic variation in SLA was not associated with LA. A screening based on both SPAD readings and LA values should identify lines with good photosynthetic machinery that is not associated with low area per leaf blade.

Consistency of species ranking based on functional leaf traits.

• Specific leaf area (leaf area to dry mass ratio), leaf dry matter content (leaf dry mass to saturated fresh mass ratio) and leaf nitrogen concentration (LNC) have been proposed as indicators of plant resource use in data bases of plant functional traits. • We tested whether species ranking based on these traits was repeatable by studying spatio-temporal variations in specific leaf area and leaf dry matter content of water-saturated leaves (SLASAT and LDMCSAT ), as well as in LNC, for 57 herbaceous and woody species (or subsets thereof) growing under the Mediterranean climate of southern France. • Interseason and intersite variations were more pronounced than interannual variations, but species ranking for a given trait remained mostly consistent in space and time. Classifications based on LDMCSAT were generally more repeatable across years and sites, whereas those based on SLASAT were more stable over seasons. LNC usually gave the least repeatable classifications. • Species rankings were not completely similar for the three traits. Discussion of reproducibility, ease of trait measurement, as well as trait-function relationships led us to propose that measurements of the leaf traits, SLASAT and/or LDMCSAT , were the most suitable in large screening programmes.

Morphological and stomatal responses of Norway spruce foliage to irradiance within a canopy depending on shoot age

Morphological and stomatal responses of Norway spruce ( Picea abies) foliage to light availability were studied in respect to shoot age. Needle minor diameter ( D 1, anatomical width), major diameter ( D 2, anatomical thickness), dry weight ( M), and tissue density index ( I D) increased, and needle flatness ( Fl) and specific leaf area (SLA) decreased with foliage age, while shade foliage demonstrated higher morphological plasticity as compared to sun foliage. Needle minor diameter, dry weight, and the ratio of total to projected leaf area increased, and needle flatness and specific leaf area decreased with daily average photosynthetic photon flux density ( Q D). The current-year foliage exhibited the highest variation with irradiance, while the morphological plasticity decreased with needle ageing. The morphological characteristics of needles were independent of irradiance if Q D was above 300 μmol m −2 s −1. D 1 was the only linear needle characteristic which significantly changed with light availability within a canopy, and thus determined needle flatness, SLA, as well as the ratio of total to projected leaf area (TLA/PLA). Needle flatness was a characteristic responding most sensitively to the photosynthetic photon flux density, R 2 was 0.68, 0.44, and 0.49 for the current-year, 1-year-old, and 2-year-old foliage, respectively. TLA/PLA ranged from 2.2 to 4.0 depending on D 1. Variation in SLA in response to light availability can be attributed to changes both in needle shape and tissue density. Stomatal responses to photosynthetic photon flux density ( Q P) depended on foliage type (sun or shade) and age. Sun needles demonstrated higher daily maximum leaf conductances to water vapour compared to shade needles. The shade needles responded more sensitively to changes in Q P at dawn and sunset than the sun needles, while older needles of both foliage types exhibited faster stomatal responses. The light-saturation of leaf conductance ( g L) was achieved by 20 μmol m −2 s −1 for shade foliage, and approximately by 50 μmol m −2 s −1 for sun foliage. As a rule, g L changed in response to irradiance faster in the evening, i.e. at decreasing irradiance. Stomata were not usually completely closed in the dark before sunrise and after sunset, the phenomenon being more pronounced in older shoots and sun needles. Nightly water losses from spruce foliage are attributable primarily to older shoots, and are related to age-dependent changes in stomatal responsiveness.

Understanding seedling growth relationships through specific leaf area and leaf nitrogen concentration: generalisations across growth forms and growth irradiance.

Seedling relative growth rate (RGR) achieved under favourable growth conditions can be thought of as a useful bioassay of the potential ability of species to take advantage of favourable growth opportunities; that is, of a species' growth strategy. The consistency of relationships between RGR and its component attributes leaf nitrogen productivity (LNP), leaf N per area (LNCa), specific leaf area (SLA) and leaf mass ratio (LMR) was assessed across 12 datasets comprising three growth forms (grasses, herbaceous dicots and woody plants; 250 species in total). These relationships were characterised in terms of scaling slopes (regressions on log-log axes, the slopes giving the proportional relationship between the variables). Mathematically, the expected scaling slope between RGR and each component is 1.0, giving an appropriate null hypothesis to test against (whereas the widely used null hypothesis of zero correlation is in fact inappropriate for this situation). Deviations below 1:1 scaling slopes indicate negative covariance between the components. Consequently, the correlation structure between the components of RGR should also be investigated. Biologically, RGR should scale 1:1 with SLA at a given LNCa and somewhat more weakly with LNCa at a given SLA. SLA and LNCa should themselves scale with a slope of between 0 and -1, with the actual slope indicating the extent to which between-species variation in SLA dilutes leaf N on an area basis versus the ability of species to maintain LNCa at a given growth irradiance. On average, across the 12 datasets RGR scaled close-to-proportionally with SLA, and 1:1 with SLA at a given LNCa. RGR scaled with LNCa with null or negative slopes, since SLA and LNCa scaled negatively (with slopes generally shallower than -1); however, RGR scaled positively (but less than proportionally) with LNCa at a given SLA. For these key relationships there were no qualitatively different conclusions with respect to the growth form under consideration or the growth irradiance at which the seedlings were grown. RGR also scaled close-to-proportionally with LNP, while LNP and LNCa were negatively associated. These relationships involving LNP are difficult to interpret since it can be shown that they are, at least potentially, the result of the interactions between RGR, SLA and LNCa, as well as reflecting intrinsic differences in the efficiency of nitrogen use in the growth process.

Eucalypts forming a canopy functional type in dry sclerophyll forests respond differentially to environment

Eucalyptus dives Schauer,E. mannifera Mudie, and E. rossiiR.Baker & H.G. Smith are sympatric trees that form a canopy functionaltype in dry sclerophyll forests of south-eastern Australia. Although theirranges broadly overlap, distributions of the three species differ subtlywithin an abstract environmental space defined by mean annual temperature andprecipitation. We used a combination of common environment and field studiesto assess the extent to which these eucalypts might respond differentially toenvironmental conditions and to determine whether distributional differencesare related to physiological or morphological attributes of leaves. In threeglasshouse experiments, gas exchange characteristics ofE. dives and E. rossii seedlingswere remarkably similar. However, data indicated thatE. rossii makes more efficient use of nutrients and,under some conditions, has higher water-use efficiency than the other species.In five natural stands, there were significant differences among sites andamong species for leaf nitrogen and phosphorus content, carbon isotopediscrimination, and specific leaf area. Significant site × leaf-variableinteractions showed that the species responded differentially to unique siteconditions. At four of the five sites, 13Cdiscrimination was significantly higher in E. manniferathan in the other two species, and it was significantly higher inE. mannifera than in E. rossii atall five sites. Lower water-use efficiency may restrictE. mannifera to sites on the higher end of theprecipitation gradient, whereas higher water-use efficiency may giveE. rossii an advantage on arid sites. Variation inspecific leaf area across sites was greater inE. mannifera and E. rossii than inE. dives; in contrast, E. diveswas more variable in 13C discrimination. Greaterphysiological plasticity could explain why E. divesoccupies a broader range of habitats than the other two species. Contrary toexpectations, no leaf variable was strongly correlated with the amount ofrainfall received at the sites, but 13C discriminationwas negatively related to mean annual radiation received, which may be abetter index of water availability. Despite similarities in gas exchangephysiology, members of this putative functional type clearly responddifferentially to varying environmental conditions, implying that accurateprediction of responses to environmental change would require knowledge ofattributes of each species. However, differential responses might contributeto functional stability on a site subjected to environmental variability.

Competitive ability of two Brassica varieties in relation to biomass allocation and morphological plasticity under varying nutrient availability

Green cabbage (Brassica campestris, leafy variety) and turnip (Brassica campestris var. rapifera, rooty variety) were grown in both monocultures and mixtures at three nutrient levels to investigate their responses to nutrient availability with respect to biomass allocation, morphological plasticity and competitive ability. Their allocation parameters and leaf morphological traits were affected by both nutrient availability and developmental stage. Both of the varieties had a smaller biomass allocation to leaf blades, but a greater allocation to petioles at high nutrient levels. Root:shoot ratio (RSR) of green cabbage decreased with increasing nutrient availability, whereas that of turnip increased. Turnip had a smaller leaf blade weight ratio (LBWR) than cabbage, being compensated for by larger leaf area ratio (LAR) and specific leaf area (SLA). Leaf area ratio and SLA of both the varieties increased with increasing nutrient availability as did their mean dry weights. The mean dry weight of turnip was slightly greater than that of green cabbage in their respective monocultures, while that of green cabbage was greater than that of turnip in their 1:1 mixture. Therefore, green cabbage, having inherently greater biomass allocation to leaves, was generally more competitive than turnip with more biomass allocation to roots, especially at higher nutrient levels. However, within a variety, morphological plasticity (variation in LAR and SLA) was more important than the plasticity in biomass allocation (e.g. variation in RSR and LBWR) in determining competitive ability. The implication of our results is that competition models based on biomass allocation pattern alone may fail to predict competitive outcomes and that such models should also take morphological plasticity into full account.

Specific leaf area and leaf dry matter content as alternative predictors of plant strategies

A key element of most recently proposed plant strategy schemes is an axis of resource capture, usage and availability. In the search for a simple, robust plant trait (or traits) that will allow plants to be located on this axis, specific leaf area is one of the leading contenders. Using a large new unpublished database, we examine the variability of specific leaf area and other leaf traits, the relationships between them, and their ability to predict position on the resource use axis. Specific leaf area is found to suffer from a number of drawbacks; it is both very variable between replicates and much influenced by leaf thickness. Leaf dry‐matter content (sometimes referred to as tissue density) is much less variable, largely independent of leaf thickness and a better predictor of location on an axis of resource capture, usage and availability. However, it is not clear how useful dry matter content will be outside northwest Europe, and in particular in dry climates with many succulents.

Seeding date, photoperiod and nitrogen effects on specific leaf area of field-grown wheat

Specific leaf area (SLA), the ratio of leaf area to leaf weight, is an important plant characteristic that affects the rate of dry matter production of crop canopies. It is affected by the conditions of growth of both isolated plants and crop communities, but the extent to which various environmental factors impact on SLA under field conditions is not clearly understood. This study was conducted to study the variability in SLA of leaves on the main culm, and in the leaf canopy as an entity, under different conditions of photoperiod, nitrogen and temperature for a number of wheat genotypes grown under field conditions. Five plantings at approximately bimonthly intervals on 12 May, 5 July and 22 September 1993; and on 9 June and 10 August 1994 were made under both natural photoperiod and an extended photoperiod of 20 h. A split plot design with two levels of nitrogen (0 kg N ha−1 and 150 kg N ha−1) as main plots and four genotypes of wheat comprising two spring types (Norseman and Roblin) and two winter types (Ruby and Harus) as subplots was used.SLA of individual leaves varied among leaf positions, but the pattern of variation was dependent on sowing date and genotype. For May and June sowing dates, SLA increased with leaf number up to leaf 5 and then declined with subsequent leaf numbers for the spring genotypes, but increased to leaf 5 and changed little thereafter for the winter types. For July or August sowing and for both spring and winter genotypes, the change in SLA with leaf position was less clear. The results further showed that some of this variability in SLA with leaf position could be accounted for by the mean air temperatures over which the leaves developed. As temperatures increased from 8 °C to 26 °C, SLA increased to a maximum value achieved at 18–20 °C and then declined. However, there was a large scatter of SLA values around 18–20 °C, due partly to some lower SLA values for the July and August sowing dates. This suggests the impact of other factors such as radiation and the degree of mutual shading within the canopy on SLA. Mean canopy SLA reflected the individual leaf values during the period of leaf production, and varied with sowing date and genotype, although the pattern of genotypic variability was inconsistent over sowing dates; it decreased rapidly after spike emergence presumably reflecting leaf aging. Neither nitrogen nor photoperiod had significant effects on SLA on both individual leaf and canopy bases.The results suggest that temperature is one factor affecting SLA under field conditions, but that further work to identify other factors impacting on SLA in the field will be necessary. For application of simulation models to situations in which temperatures are likely to vary, an accounting for the impact of temperature on the SLA of individual leaves would be desirable. Key words: Specific leaf area (SLA), sowing date, temperature, simulation, wheat

Foliar nutrients in relation to growth, allocation and leaf traits in seedlings of a wide range of woody plant species and types.

This study aimed to identify functional correlates of seedling leaf nutrient content among woody species and to characterise functional species groups with respect to leaf nutrient attributes. Seedlings of 81 woody species from the temperate zone of western Europe were grown in a standard laboratory environment with standard, near-optimal nutrient availability. Weight-based leaf N content (Nwght) was positively correlated with mean relative growth rate (RGR), but the correlation with mean RGR was tighter when leaf N was expressed on a whole-plant weight basis: leaf nitrogen weight ratio (LNWR). Area-based leaf N content (Narea) was not associated with mean RGR, but was closely correlated with the quotient of saturated leaf weight and leaf area. Weight-based leaf K content (Kwght) was a close correlate of the saturated/dry weight ratio of the foliage. Within the lower range, Kwght corresponded with growth-related nutrient attributes, but higher values appeared to indicate succulence or remobilisable stored water. Functional groups of species and genera could be distinguished with respect to seedling leaf nutrient attributes. Deciduous woody climbers and scramblers had consistently higher leaf Nwght, LNWR and (apparently) leaf Kwght than other deciduous species or genera, and shrubs had higher values than trees. These differences seemed due partly to variation in specific leaf area. Evergreens had consistently higher leaf Narea than deciduous plants, but there were no significant differences in weight-based leaf nutrient attributes between these two groups, possibly because of `luxury nutrient consumption' by the slow-growing evergreens. Another functional group was that of the nitrogen-fixing species, which had consistently high innate leaf Nwght compared to non-N-fixers. The ecological significance of the leaf nutrient attributes in this study is discussed by comparing the seedling data with those from field-collected material, and by brief reference to the natural habitats of the species.

Comparisons of nutrient recovery and specific leaf area variation between Carex lasiocarpa var. occultans and Carex thunbergii var. appendiculata with reference to nutrient conditions and shading by Phragmites australis

AbstractThe distribution of two sedge species was studied in two mires which differ in abiotic environments and in distribution of Phragmites australis. Carex lasiocarpa var. occultans dominated in nutrient‐poor valley mire, and Carex thunbergii var. appendiculata dominated in nutrient‐rich flood plain subject to water fluctuations. Phragmites australis grew well in nutrient‐rich conditions. The distribution of C. lasiocarpa showed a strong negative correlation with P. australis coverage, whereas C. thunbergii coverage was not affected by P. australis. The leaf area per dry leaf mass (specific leaf area: SLA) of C. thunbergii increased with shading by P. australis, but that of C. lasiocarpa was stable. The SLA flexibility of C. thunbergii to light interception might enable this species to invade P. australis patches in nutrient‐rich environments. The residual nutrient ratio of nitrogen and phosphorus (the ratio of the residual nutrient content at the end of the growing season to peak nutrient content) in the vegetative ramet of C. thunbergii was 1.7 times higher than that of C. lasiocarpa. This low residual ratio may indicate effective nutrient recovery to storage organs. The effective nutrient recovery in C. lasiocarpa might enable this species to grow even in nutrient‐poor environments. However, it may be difficult for C. lasiocarpa to expand its habitat to nutrient‐rich areas where P. australis dominates as it is not shade tolerant.

Variation in Early Vigor between Wheat and Barley

In dryland Mediterranean‐like climates, barley (Hordeum vulgare L.) generally has higher grain and biomass yields than other temperate cereals. The advantage of barley compared with wheat (Triticum aestivum L.) is associated with barley's faster leaf area growth during vegetative development. Experiments were conducted in a glasshouse (average 25/15°C) and outdoors (average 17/5°C) to determine the traits associated with barley's greater early growth. Five cultivars each of barley and wheat were grown in large pots. Five harvests were made from the time there were about 2 leaves on the main stem to the time plants had about 4.5 leaves on the main stem. The weight of the caryopsis of all seeds sown was 35 mg. Barley produced ≈40% more aboveground biomass and two times greater leaf area than wheat by the two‐leaf stage. Barley had a 17% faster average leaf appearance rate and a 35% faster average tiller appearance rate than wheat but there was no evidence that either contributed to the differences in vigor between the two species. The relative growth rates for biomass and leaf area were also similar in the two species, although it was achieved in different ways. The average net assimilation rate (NAR) was 25% greater in wheat than in barley in both experiments, whereas the average leaf area ratio (LAR) was 23% higher in barley. Variation in specific leaf area (SLA) was largely responsible for the variation in NAR and LAR in both the glasshouse and outside. Factors between germination and the appearance of the second main stem leaf must be responsible for the greater early vigor in barley compared with that of wheat.

Needle area relationships of Scots pine in the Netherlands

To analyse the foliage area characteristics of Scots pines of different sizes, 12 trees were selected out of 4 stands of different ages. From the selected trees, total needle area and needle area distribution were estimated from branch samples. Stem discs were collected to determine sapwood area at breast height. Variation in specific leaf area (SLA), the relationship between sapwood area and needle area and the vertical distribution of the needle area in the tree crown were estimated. SLA decreased with needle age and increased with depth in the tree crown. Vertical distribution of the needle area within a tree crown was described by a generalized logistic model. The relationship between needle area and sapwood area was described by a linearized model. The ratio between needle and sapwood area ranged from 902 to 1295 cm 2 cm −2.

Genecology ofAgrostis capillarisL. (Poaceae) — an invader into New Zealand: 2. Responses to light, soil fertility, and water availability

Abstract Fifteen populations of the naturalised grass, Agrostis capillaris, sampled from southern New Zealand, were examined for responses to a range of levels of light, fertility, and water availability. Populations from open, dry areas had genetically low, but plastic, allocation to shoots. Populations from shady areas were more upright than average, and had greater leaf areas, whereas a lawn population was prostrate, but had high allocation to shoots. There was evidence of genecological variation in response to the marked site differences in soil-water availability. Population-based variation in specific leaf area was correlated with rainfall and soil nitrogen and phosphate levels. Differences between populations in other characters did not correlate with environmental trends. Responses indicate some adaptation of populations to their local environments in New Zealand, but also high within-population variation and some instances of nonadaptation. Plasticity is high — as much as 80% of the total variati...

Relationship between specific leaf area of a Cryptomeria japonica foliage shoot segment and its diameter

AbstractDependency of specific leaf area (SLA) on shoot diameter (x) was studied for Cryptomeria japonica foliage shoot segments about 5 cm in length taken from 18 branches at different height levels on 3 trees in August 1987. The leaf area of a shoot segment (S) was defined as half the sum of the needle area (s) estimated by the allometric relationship between s and needle length. The dry weight of woody tissue (Ww) and needles (Wn) of a segment and its S were divided by the segment length (L) to give linear densities as Ww/L, Wn/L and S/L, respectively. The densities were related to x by power‐form equations. S/L values tended to be constant around 1.2 [cm2 cm−1] within the discussed range of x, while Ww/L and Wn/L values clearly increased with x. The approximately reciprocal relationship between average needle area (s) and linear density of the number of needles supported the fact that S/L values were roughly constant regardless of x. SLA and SNA were defined as S/(Ww+Wn) and S/Wn, respectively. The SLA‐x relationship expected from the average value of S/L and the Ww/L‐x and the Wn/L‐x relationships was well fitted to the observed decrease in SLA with increasing x. SNA also decreased as x increased. Variations in SLA and SNA among the shoot segments with similar x were not systematically related to their height levels. An empirical equation with a maximum value of x (Xmax) was also proposed in order to formulate the SLA‐x relationship.

Sources of Variation in Specific Leaf Area in Wheat Grown at High Temperature

In the belief that specific leaf area (SLA, cm2 g1 dry weight) may be correlated with plant growth rate under certain conditions, and thus may be used in selecting genotypes for high growth rates, studies were commenced to examine the main sources of variation in SLA. In most studies, wheat plants were grown in controlled environments with high mean temperature and vapour pressure deficit and with varying radiation regimes. All environmental variables followed cosine patterns which in amplitude mimicked field conditions. Specific leaf area varied depending on: (1) location along a leaf: it decreased from tip to base by some 35%; (2) leaf age: SLA declined between leaf appearance and 10-12 days later then, after a plateau of varying length, it rose again; (3) leaf insertion: SLA of the flag leaf was the most stable with leaf age; (4) plant density: in canopies the final rise in SLA with leaf age occurred earlier than in spaced plants; (5) radiation: SLA declined at approximately 4 cm2 g-1 for each mol quanta m-2 day-1 increase in radiation; (6) genotype: SLA differed among genotypes and the ranking was unchanged by changes in radiation. In two genotypes studied in detail, higher SLA equated with faster leaf area production and larger leaves, but not with chlorophyll content per unit area, stornatal frequency or net CO2 exchange rate per unit area (CER), though it was noted that both SLA and CER changed inversely with leaf aging after the leaf was fully expanded. The importance of SLA in active (positive and negative) and passive roles in plant growth is discussed.

Specific leaf area, photosynthesis, and respiration in two sympatric nymphaeaceae populations

Sympatric populations of Nuphar variegatum Engelm and Nymphaea tuberosa Paine, sharing the same light regime, developed different patterns of leaf thickness vs. surface area during a growth season. The leaves of Nymphaea surfaced slightly later than those of Nuphar and, within the restricted spaces available, were smaller but thicker, i.e. they had a lower specific leaf area (area per unit weight). Nymphaea leaves exhibited higher rates of photosynthesis per unit are throughout the growing season, and lower rates of respiration for most of the season, than did the thinner leaves of Nuphar. Induction of variations in specific leaf area (SLA) and related metabolic responses by a light intensity gradient, the normally observed causal relationship in plants, was not a factor here. Competition for water surface area is suggested as an alternative mechanism.