Leaf Growth Patterns Research Articles

Restriction of nyctinastic movements and application of tensile forces to leaves affects diurnal patterns of expansion growth.

Leaves of Ricinus communis L. show strong nyctinastic movements as well as diurnal variations of growth activity, combined with prominent basipetal gradients of relative growth rate. A novel technique, using digital image sequence processing, is able to resolve such spatio-temporal patterns of leaf growth with high resolution. In this paper we analyse the impact of prevention of nyctinastic movements, and the potential of tensile forces to overcome the retarding effects. Tensile forces affected leaf expansion and tissue expansibility in a dose-response relation. In a comparison with freely-growing leaves, an appropriate, optimal tensile force was identified that rebuilt the natural diurnal course of leaf expansion. With this tensile force, undisturbed patterns of temporal and spatial growth distribution as well as undisturbed concentrations of major cations, amino acids or soluble sugars were observed. However, diurnal fluctuations in starch content of almost fully-grown leaves were affected by the treatment and could not be compensated by tensile forces. This effect might point to a connection between diurnal growth variations of the leaf vein, biomechanical forces that synchronize growth within the vein, and metabolism of carbohydrates as growth substrates of the vein. We therefore hypothesize that interveinal tensions, which are produced during nyctinastic leaf movements, are (i) required for undisturbed leaf growth and (ii) can be simulated by application of adequate tensile forces.

Compensation for Herbivory in Cruciferous Plants: Specific Responses to Three Defoliating Insects

Plant compensation may be specific to the defoliation of a particular insect herbivore, or a generalized response to herbivory. These alternate hypotheses were tested by measuring biomass and seed production of Brassica napus L. and Sinapis alba L. in response to 0, 25, or 75% defoliation of seedling plants. The herbivores were adults of Phyllotreta cruciferae (Goeze), larvae of Plutella xylostella L., and larvae of Mamestra configurata (Walker). Although defoliated to the same extent, both B. napus and S. alba compensated most for defoliation by M. configurata and least for defoliation by P. cruciferae. Both plant species compensated better for 25% than for 75% defoliation, and S. alba compensated better than B. napus. Laboratory and field experiments showed similar patterns of compensatory leaf growth, but recovery was more rapid in a controlled environment. Compensation was associated with changes in root biomass that were correlated with foliage biomass, indicating that root-shoot ratios were maintained. Complete recovery of foliage after defoliation did not assure complete recovery of plant fitness. For these three herbivorous insects, compensation by two plant species for defoliation was specific to the insect defoliator, and not a generalized response to herbivory. The compensatory responses of the two plant species explain, in part, the differential impact the three herbivores have on the crops.

The leaf development process and its significance for reducing self-shading of a tropical pioneer tree species.

On a monoaxial erect stem of trees with continuous leafing, the older leaves would be quickly shaded by newer (upper) leaves if the trees did not have any compensating mechanisms to avoid self-shading. We hypothesized that the dynamic adjustment of leaf deployment, by regulating the patterns of leaf growth and by changing leaf orientation as leaves age, is a compensating mechanism. To verify this hypothesis, we analyzed leaf development and crown structure of a Far Eastern tropical pioneer tree species, Macaranga gigantea (Rub. f. et Toll.) M.A., which unfolds huge leaves directly on a monoaxial stem with a short leafing interval. Petioles required more than 90days for full elongation and the petiole angle (the angle between the petiole axis and the vertical) increased over time. Thus, a series of leaves on a stem progressively increased in petiole length and petiole angle from the youngest to the oldest leaves. This is beneficial because it decreases the degree of self-shading within a crown. A simulation suggested that an average crown for the M. gigantea seedlings, which was constructed using empirically determined morphometric data cannot entirely eliminate self-shading within the crown. But an average crown had a lower degree of self-shading, with less dry mass allocation to the petiole than simulated crowns that were identical to the average crown in all but one respect: they had constant petiole lengths or petiole angles. We conclude that M. gigantea seedlings reduce self-shading by regulating elongation of the petiole and changes in the petiole angle with increasing leaf age.

Lessons From the Past Look to the Future

Dr. Howden is now formally retired from a long career teaching mathematics in elementary school through graduate level, editing and coauthoring mathematics textbooks, serving as District Mathematics Coordinator K-12 for the Albuquerque, New Mexico, Public Schools, writing numerous professional articles, and participating on the writing team of the Curriculum and Evaluation Standards for School Mathematics. She now enjoys long walks with her dog Quincy, “becoming increasingly aware, of mathematics all around us: patterns of leaf growth, distances between consecutive veins in leaves, kinds of ant hills, snake trails in the sand, bird call patterns.” She plans to relate many such examples to mathematical patterns in the book she is currently writing.

Partitioning of Photosynthetically Fixed <sup>14</sup>CO<sub>2</sub> Into Oil and Curcumin Accumulation in Curcuma Longa Grown Under Iron Deficiency

Changes in leaf growth, photosynthetic efficiency, and incorporation pattern of photosynthetically fixed 14CO2 in leaves 1 and 2 from plant apex, in roots, and rhizome induced in Curcuma by growing in a solution culture at Fe concentration of 0 and 5.6 g m−3 were studied. 14C was incorporated into primary metabolites (sugars, amino acids, and organic acids) and secondary metabolites (essential oil and curcumin). Fe deficiency resulted in a decrease in leaf area, its fresh and dry mass, chlorophyll (Chl) content, and CO2 exchange rate at all leaf positions. The rate of 14CO2 fixation declined with leaf position, maximum being in the youngest leaf. Fe deficiency resulted in higher accumulation of sugars, amino acids, and organic acids in leaves at both positions. This is due to poor translocation of metabolites. Roots and rhizomes of Fe-deficient plants had lower concentrations of total photosynthate, sugars, and amino acids whereas organic acid concentration was higher in rhizomes. 14CO2 incorporation in essential oil was lower in the youngest leaf, as well as incorporation in curcumin content in rhizome. Fe deficiency influenced leaf area, its fresh and dry masses, CO2 exchange rate, and oil and curcumin accumulation by affecting translocation of assimilated photosynthates.

Above- and below-ground production, biomass and reproductive ecology of Thalassia testudinum (turtle grass) in a subtropical coastal lagoon

Above- and below-ground growth, biomass, phenology and reproductive effort in the seagrass Thalassia testudinum were monitored monthly for 2 yr in the Lower Laguna Madre, Texas. Annual whole plant production (953 ± 136 g DW (dry weight) m -2 yr -1 ) was calculated from monthly measurements of leaf and rhizome production made using marking techniques. Leaf growth exhibited a seasonal pattern; monthly production ranged from 8 to 95 g DW m -2 mo -1 , equivalent to 614 ± 71 g DW m - yr -1 , Rhizome growth was seasonal, and areal below-ground production ranged between 14 and 40 g DW m -2 mo - 1 , equivalent to 339 ± 65 g DW m -2 yr -1 . On an annual basis, rhizome production accounted for 35 % of total plant production. Seasonal leaf and rhizome growth patterns were correlated with underwater irradiance, daylength and temperature. Total biomass ranged between 750 and 1500 g DW m -2 , with below-ground tissues accounting for 80 to 90 % of the total. There was no seasonal pattern in the below-ground biomass of T. testudinum; variability was a result of environmental heterogeneity. Flowering was variable between years; 13 to 30 % of the shoots flowered and about 15 % of total above-ground biomass was allocated to reproduction. Flowering phenology was positively correlated with underwater daylength. During 1996, maximum fruit abundance ranged between 20 and 70 fruits m -2 and on average each fruit contained 2 seeds. The annual flowering event represents a substantial resource (e.g. carbon and nitrogen) investment, which may influence individual plant production. Seasonal fluctuations in environmental parameters are the primary factors controlling seagrass growth rates and production. Determination of total plant productivity must take into account seasonal patterns, reproductive costs and the large fraction of production occurring in the below-ground tissues.

Exsertion, elongation, and senescence of leaves of Eriophorum vaginatum and Carex bigelowii in Northern Alaska

The seasonal patterns of leaf exsertion, elongation, and senescence were described and compared for two of the most abundant graminoid species of Alaskan moist tussock tundra, Eriophorum vaginatum and Carex bigelowii. In addition the responses of both species to NPK fertilizer and to variation in site fertility (water track vs. non‐track areas) were also assayed and compared. The research was done over two full growing seasons at two sites near Toolik Lake, Alaska, where other aspects of the ecology of both species have been the subject of intensive and ongoing research.Both species showed the typical graminoid pattern of sequential leaf growth, in which the exsertion and elongation of new leaves is coincident with the senescence of old leaves. However, the rates of these processes were much slower and steadier in Eriophorum than in Carex, with much greater overlap in the life histories of individual leaf cohorts. The total and green leaf lengths of whole tillers in Eriophorum were also less variable over the entire year than in Carex. The conclusion is that leaf growth in Carex should depend more on external storage of carbon and nutrients than Eriophorum, with a much greater seasonal variation in demands on storage and retranslocation to and from leaves.The effects of fertilizer and the water track on leaf growth dynamics and turnover rates were largely nonsignificant, despite major effects on total tiller size and productivity. This is in contrast to previous research on evergreen leaf dynamics, but similar to results of previous research on overall production and biomass regulation in Eriophorum. It is concluded that the graminoid response to increased nutrient availability in the Arctic is to dilute the greater amounts of nutrient uptake by greater growth, so that nearly the same metabolic homeostasis is achieved as under low nutrient availability, but at a higher biomass.

Generation of Form and Associated Mass Deposition during Leaf Development in Grasses: a Kinematic Approach for Non-steady Growth

Abstract Growing leaves of tall fescue (Festuca arundinaceaSchreb.) were studied from emergence to a short time before the leaf ceases growth. Leaf form (width, average thickness, number of vascular bundles and height of associated ridges) and growth patterns were determined. The tissue elements produced at the point of leaf insertion are wider and thicker with time, as the intercalary meristem develops. These elements undergo further width and thickness changes as they traverse the elongation zone, and leaf width and average thickness can continue to increase after passing the elongation zone. In order to relate the generation of leaf form and dry matter (DM) deposition, three methods were used to describe DM fluxes: (1) we followed the path lines of material elements and determined that they accumulate DM as they are displaced away from leaf base, even when expansive growth and maturation are complete; (2) we calculated DM deposition on a unit length basis, which represents the total sink strength of the zone studied, and we deduced that the sink strength of the elongation zone increases with time, in concert with the changes in width and thickness of the elements that are successively produced at leaf base; (3) we calculated DM deposition on a unit volume basis, which represents the net metabolic activity of the zone considered, and we found that growth activity and associated DM deposition were high 3 d after the leaf emerged, then decreased gradually, whereas maturation and associated DM deposition were low at emergence, but increased as the leaf gradually became autotrophic. Our data indicate that different descriptors and measurements are needed during the totality of leaf growth.

Seasonal cycle of shoot development in selected Actinidia species

Seasonal cycles of shoot development for 10 Actinidia species are described. A female and a male vine were studied for six species. Shoots were sampled at monthly intervals during the growing season and timing of budbreak, shoot lengths, numbers of nodes, areas of leaves, numbers and node positions of flowers or fruit, and fruit size were measured. Budbreak, shoot growth, and leaf growth patterns were not clearly related to taxonomic affinities although vines of A. deliciosa behaved very similarly to vines of the closely related species, A. chinensis and A. eriantha. Male and female vines differed in flowering behaviour with male vines having higher percentages of flowering shoots, more flowering nodes on a shoot, and often, more flowers in an inflorescence. The growth habits of the A. chinensis and A. eriantha vines appear to be suited to pruning and training in the same manner as A. deliciosa ’Hayward’. The selected A arguta vines have very unfavourable growth characteristics for commercial production, including the long vigorous shoots and sparse flowering habit.

Nutrient relations of the halophytic shrub, Sarcobatus vermiculatus, along a soil salinity gradient

Recent water level declines of a saline and alkaline lake (Mono Lake, California, USA) have exposed large areas of former lake bottom substrates that have been sparsely colonized by the halophytic shrub, Sarcobatus vermiculatus. To increase understanding of the interaction of salt and nutrient relations in halophytes we investigated spatial and seasonal patterns of leaf elemental composition and growth for Sarcobatus along an extreme salinity gradient using four sites varying in age since exposure. Soil and groundwater Na and EC increased from non-saline at the site farthest from the Lake to highly saline at the site closest to the Lake. Leaf and stem length growth declined along this same transect. In June, when shoot growth rates were maximal, leaf Na paralleled substrate availability and reached a high of 130 g kg−1 leaf dry weight near the Lake. Through the remainder of the growing season, plants on the lower salinity site continued to accumulate increasing amounts of leaf Na, whereas plants at the highest salinity site reached a plateau earlier in the season. The similarity of high leaf Na at all sites by the end of the season indicates a dominance of Na nutrition over the entire gradient, and a possible upper bound of Na accumulation and tolerance for this species. In June, Sarcobatus leaf N, P were higher at sites further from the Lake and did not correspond to soil N (total) and P that were highest near the Lake. Leaf K, Ca, and Mg in June also did not match substrate availability, and were low enough to indicate marginal sufficiency for growth. However, the increasing substrate Na did not interfere with K, Ca and Mg uptake based on selectivity coefficients (e.g. (leaf K/leaf Na)/ (soil K/soil Na)) that did not decline with increasing substrate salinity. Uptake and transport to leaves, of K and Ca relative to Na, remained proportional to what was in the soil across the entire gradient of soil salinity. Uptake and transport of Mg relative to Na increased dramatically in inverse proportion to declining soil availability near the Lake, indicating that Mg may be a critical limiting factor for tolerance of high salinity sites. The key determinants of Sarcobatus growth and ecological dominance along this extreme salinity gradient (non-saline to highly saline) are the propensity to accumulate large amounts of leaf Na over the entire gradient, and the ability to maintain adequate uptake of N, P, K, Ca, and Mg under highly variable substrate combinations of nutrients and Na.

Seasonal Pattern of Leaf Growth and Senescence of Nardus stricta and Responses of Tussocks to Differing Severity, Timing and Frequency of Defoliation

1. A field study of the seasonal growth of Nardus stricta showed that leaf turnover was slow, averaging 2.5 leaves per tiller over the growing season. Periods of lamina extension growth and senescence were generally separated in time; fastest growth, at 4-5 mm per tiller per day, occurred in June July and the senescence rate was low until early autumn when it rose to 6 mm per tiller per day. Sheathing tiller bases, already well developed in May, increased in weight by 27% between May and October; total water-soluble carbohydrate (TWSC) concentration increased by 150% (from 75 to over 165 g per kg dry weight) while N, P and K concentrations declined over this period. 2. A pot study showed that the age class of inter-connected tillers on rhizome tips greatly influenced growth; mean rates of lamina extension and production of daughter tillers were higher in younger tillers while the likelihood of flowering was greater for older (3-4 leaf) tillers. The pattern of growth provided evidence for acropetal movement of assimilate. 3. Field cutting experiments showed that Nardus was relatively insensitive to defoliation in the short term. Removal of 50% or 100% of the length of the leaf lamina in June only, July only or in both June and July resulted in a temporary reduction in lamina extension rate per tiller but did not significantly affect the weight of leaf produced in the first season. There was a non-significant trend for the size of tiller base to be reduced as the severity of cutting was increased. Concentrations of TWSC and N,P, and K in tiller bases showed no variation attributable to cutting. 4. In a long-term cutting experiment lasting 4 years, Nardus was cut so as to leave 1, 4 or 8 cm of lamina in June only, July only, or in June and July. Two seasons elapsed before lamina extension was reduced on cut plants. The weights of clippings were greatly reduced over successive years when tillers were cut to leave only 1 cm oflamina but were little affected when 8 cm of lamina remained, with the 4-cm treatment intermediate; the reduction was greatest with plants cut in both June and July and least with plants cut in June only with those cut only in July being intermediate. 5. Tussock biomass, assessed after 4 years of cutting and a season of uninterrupted growth, was decreased as the height of cut was reduced and by repeated cutting; timing (June compared with July) was unimportant. Both tiller numbers and mean weight per tiller were reduced. Flowering vigour was increased by cutting. Timing was important, with plants cut in July only or in both June and July having more flowers than those cut in June only. The amounts of TWSC and N, P and K reserves were reduced by cutting with reduction in tiller base size being more important than effects on concentration. 6. In a comparative field study, the rate of lamina extension in Nardus averaged less than half that of Agrostis capillaris or A. canina growing in the same sward. This underlines the importance of selective grazing as an influence on species balance in acid grasslands.

Seasonal Patterns of Leaf Growth and Loss, Flowering and Fruiting on a Subtropical Central Pacific Island

We studied the phenology of leaf production and loss, flowering, and fruiting on Henderson Island, a raised limestone island situated at 24?S in the Central South Pacific. The one-year study encompassed 19 of the 22 wide-spread indigenous tree and shrub species found in the plateau forest. Of 11 species showing significant annual variation in leaf production, all grew most new leaves immediately after the solar zenith between January and March, when temperatures were highest. Thirteen species showed significant annual variation in leaf loss, with peaks in October/ November or January/February. In most species, January-June saw net leaf gain, while the converse was true from July-December. Only one species, Premna serratifolia, was deciduous, shedding leaves and then remaining leafless for approximately two months until new shoots grew leaves. Flowering and fruiting were more evenly distributed through the year than leaf production. This could be related to the scarcity of pollinating insects and/or of fruit dispersers on this exceptionally remote island.

Phenology, Leaf and Twig Growth Pattern and Leaf Nitrogen Dynamics of Some Multipurpose Tree Species of Himalaya:

This study was camied out to determine the suitability of commonly occurring multipurpose tree species (MPTS) found in the Central Himalayan region for agroforestry practices. To meet this objective, periodicity of major phenophases, leaf and twig growth pattern and leaf nitrogen dynamics of five MPTS of Kumaun Himalaya were studied. These species grow in and around the cropfields and were utilized by the inhabitants for centuries. In general, our analyses indicate that the phenophases occur in such a fashion that competition with agricultural crops for soil, water, nutrients and sunlight is minimal. Their wide distribution range over varied habitats, short stature and profuse branching suitable for lopping, high foliage biomass production, capacity to provide firewood of high calorific value, fodder of high protein during lean months, etc. and addition of a large amount of nitrogen to soil through litterfall are reasons why villagers have selected them after a long period of trial and error. These same c...

Some Evidence for an Adaptive Linkage Between Leaf Phenology and Shoot Architecture in Sapling Trees

1. We test an expectation regarding the phenology of leafing in sapling trees: that the inclination of the terminal shoot from the vertical in species with a flushing type leaf emergence will be greater than that of species with successive leafing. 2. A large inclination of the terminal shoot will minimize self-shading among leaves that emerge simultaneously; this may be an advantage in maximizing carbon gain. A small inclination leads to more self-shading but allows a sapling to attain a greater height within a shorter period; this may be an advantage in situations where shading by adjacent plants is a greater potential problem than self-shading. 3. We observed that the shoot inclination in Tilia japonica and Quercus crispula, which have a flushing type leaf emergence, was more than 30 ° in open, sunlit habitat. In contrast, the shoot inclinations of Betula platyphilla var japonica and Alnus hirsuta, which have successive type leaf emergence, were less than 10°. These observations suggest a functional linkage between leaf-emergence pattern and shoot inclination that can be considered adaptive if selection is maximizing carbon gain by the whole shoot over the growing season.

Short term drying of half the root system reduces growth but not water status or photosynthesis in leaves of passionfruit ( Passiflora sp.)

The impact of soil water deficits and non-hydraulic root signals on the expansion, functioning and water status of leaves and the opening of flowers of passionfruit was studied in a series of pot experiments. Hydraulic and non-hydraulic signals were separated by withholding water from half the root system. The leaves of well-watered plants expanded in a sigmoid pattern to about 65 cm 2 over 15 to 18 days. Drying the whole root system stopped leaf expansion after 6 days, but did not change the pattern of leaf growth. Growth resumed after rewatering but the final leaf size was halved. As leaf growth slowed, the net photosynthesis, P n , of mature leaves fell from 11 ± 1 μmol CO 2 m −2 s −1 to less than zero as the leaves wilted. Leaf water potential, Ψ 1, of mature leaves at midday ranged from −0.9 MPa in well-watered plants to −3.1 to −3.7 MPa in wilted plants. After rewatering, Ψ 1 returned to −0.9 MPa within 1 day, but P n took 3 days to return to control levels. A midday Ψ 1 of −1.5 MPa was associated with a 50% reduction in relative leaf expansion and net photosynthesis. Drying half of the root system reduced leaf expansion by 26%, compared with well-watered plants, and water use by 21 to 27%, without influencing Ψ 1 or P n . Plants with half the root system dry for 13 days flowered earlier than well-watered plants but had the same number of open flowers 1 month after treatments ended. Non-hydraulic root signals affect leaf expansion and flowering in passionfruit.

Morphology and Anatomy of the Fused Vein Trait in Cucurbita pepo L.

The morphology, growth rate and anatomy of the fused vein trait were characterized in Cucurbita pepo using the inbreds NH2405 (fused vein), NH7210 (moderately fused vein), and NH614 (normal). Morphological analysis showed that the trait is characterized by a partial fusion of the five primary leaf veins. Fusion begins at the distal point of the petiole and extends along the central vein. Branching of the veins is delayed and there is a reduction of the interveinal leaf blade. Consequently, the upper leaf surface appears puckered or wrinkled. Depending on genetic background, the onset of fused vein leaf production starts at the fourth to tenth leaf stage and continues throughout vegetative growth. The extent of fusion increases with leaf number but stabilizes by the twentieth leaf stage maximum extent of vein fusion also varies with genetic background (5-20 cm). Though fused vein and normal inbreds differed in the rate and pattern of leaf growth, examination of F2 and BC populations revealed no significant effect of the fused vein trait on leaf number, leaf size, and rate of leaf initiation. Anatomical examination revealed different vascular patterns in the transition zone between petiole and leaf blade for normal and fused vein leaves. In normal leaves, the vascular bundles of the petiole enlarge and coalesce to form a vascular crescent. The crescent reorganizes and diverges as large vascular columns and pairs of smaller flanking vascular bundles into each vein. In contrast, two cycles of enlargement, coalescence, and dispersal occur in fused vein leaves.

Leaf phenology as an optimal strategy for carbon gain in plants

Since leaves are essentially energy-gaining organs, the arrangement of leaves in time (leaf phenology) and in space (canopy architecture) in both seasonal and nonseasonal environments can be viewed as a central element in plant strategies for carbon gain. Interrelationships among leaf longevity, leaf habit, and leaf-emergence pattern together with shoot architecture affect plant productivity. Leaf longevity is shown to maximize carbon gain through three parameters: leaf photosynthetic rate, the decrease in photosynthetic rate with leaf age, and the initial construction costs of the leaf. This theoretical approach has been extended to seasonal environments and effectively simulated the geographical pattern of leaf habits. To avoid self-shading, plants adopt two alternative modes of leaf emergence. One is successive leaf emergence, in which plants expand one leaf at a time on a shoot; this unshaded leaf utilizes full sunlight and is only replaced by a second leaf when its photosynthetic ability declines. Plants with successive leaf emergence attain high production and have straight shoots with multilayered canopy architecture. The alternative is simultaneous leaf emergence on shoots inclined to minimize self-shading through a monolayered canopy architecture. By the inclination of the shoot, each leaf on the shoot can receive sufficient light. Plants with simultaneous leaf emergence utilize the entire growing period effectively. Taken together and in the context of shoot and canopy architecture these interrelationships among leaf longevity, habit, and emergence pattern provide the basis for a synthetic theory of leaf phenology. Key words: leaf phenology, leaf longevity, leaf emergence, evergreen, deciduous habit.

Leaf Emergence Pattern of Late-maturing Cultivars in Soybeans.

秋ダイズの主茎の出葉経過における出葉転換点の有無を明らかにするため, 九州地方の主要な秋ダイズ品種であるフクユタカを中心に5品種を供試して, 1984年から1991年まで8年間にわたり, 九州大学農学部箱崎地区において, 栽培年次, 品種, 播種期および温度が主茎の出葉に及ぼす影響について実験を行い, 以下の結果を得た. 出葉経過には年次変動や品種間差異がほとんど認められず, 出芽から最頂葉の出葉まで全出葉期間を通じて出葉速度はほぼ一定であることが確認された. 播種期, 温度条件については早播(6月18日播種), 低温(20℃)条件下での出葉速度がやや小さかったが, いずれの処理区とも全出葉期間を通じて出葉速度はほぼ一定であった. 本実験に供試された秋ダイズ品種は感光性の大きい有限伸育性の品種であることから, 播種期が早いほど, あるいは生育温度が高いほど出葉数(主茎葉数)は多くなったが, 栽培年次, 品種, 播種期, 栽培温度に関わらず, 出芽から最頂葉の出葉まで出葉速度に変化はなく, 出葉転換点は認められなかった. よって, 九州地方で適期に栽培された秋ダイズの出葉速度は全出葉期間にわたりほぼ一定しており, 出葉経過を1本の直線回帰で示すことが可能であると思われる. この結果, 秋ダイズの生長における同伸性を考える場合, 生長モデルを単純化できるものと推察された.

Leaf growth pattern in evergreen and deciduous species of the Central Himalaya, India

Leaf growth patterns were investigated in 11 evergreen (with leaf life-spans of just more than 1 year) and 15 deciduous species, occurring along an elevational gradient of 600–2200 m elevation in the Central Himalaya. Records were made of the leaf initiation period, leaf population dynamics, leaf expansion, leaf mass changes, leaf longevity and related parameters. Species of both groups produced leaves at similar rates during March to April, the driest period of the year. Species of both groups had approximately fully developed foliage during the warm, wet period (mid-June to mid-September) of the monsoon. However, significant differences were found at group level in other characters: shoot length (19.5 cm per shoot for deciduous and 11.7 cm for evergreen species); leaf population per 10 cm shoot length (4.7 vs 15.0); leaf area (107.9 vs 41.4 cm2/ leaf); specific leaf mass (106.9 vs 191.3 g/m2); and leaf mass loss after the monsoon period, being rapid and higher (31.6%) in deciduous species and slow and limited in the evergreens (26.2%). However, species of the two groups showed considerable overlaps in the values of above characters. The evergreen species of the Central Himalaya resembled the deciduous species of the region more than the multi-year leaves of clearly evergreen species. The evergreens bear leaves throughout the year, but like deciduous species bear the cost of annual replacement of old leaves by new leaves. They seem to outcompete deciduous species by producing annually a greater mass of leaves of low-carbon cost (per unit leaf mass), which is capable of conducting photosynthesis all year round. A situation of less marked contrast between favourable and nonfavourable periods, with respect to temperature, seems to favour the leaf characters of the evergreens.

Influence of soil water on the physiological and morphological components of plant water balance in Populus trichocarpa, Populus deltoides and their F(1) hybrids.

Patterns of leaf growth, transpiration and whole-plant water balance in Populus trichocarpa, P. deltoides and their F(1) hybrids were studied during a soil drying cycle. Plant responses were analyzed during three distinct stages of dehydration. In stage I, the transpiration rate of drought-stressed plants remained constant and equal to that of well-watered plants even though soil water content declined by more than 40%. Stage II began as soil and plant water deficits induced stomatal closure. When soil water was expressed as a fraction of transpirable soil water, the transition from stage I to stage II occurred at soil water fractions of 0.35, 0.45 and 0.60 for P. trichocarpa, P. deltoides and their F(1) hybrids, respectively. Reductions in leaf growth coincided with the shift from stage I to stage II. As soil water declined further, decreases in relative transpiration and whole-plant leaf area were significantly greater in parental species than in F(1) hybrids. Inherent feedbacks controlling stomatal water loss and the maintenance and growth of leaf tissue appeared to differ between F(1) and parental genotypes in a pattern characteristic of an overdominant mode of inheritance.Stage III began once the ability of stomata to compensate for water loss had been exhausted. Substantial differences were found in plant survival during stage III, with F(1) hybrids surviving longer than parental species. Survival was more strongly correlated with the hydraulic conductivity of xylem tissues than with the dehydration tolerance of leaf tissues. Collectively, these responses suggest that F(1) hybrids were more drought resistant than either parental species and highlight the importance of whole-plant studies of functional relationships between plant growth, water balance and hydraulic conductivity.