Leaf Extension Research Articles

Variability in Carbon Availability and Eelgrass (Zostera marina) Biometrics Along an Estuarine Gradient in Willapa Bay, WA, USA

Because photosynthesis requires CO2, carbon limitation in aquatic environments could restrict primary production and provide signals in tissue chemistry. We took advantage of spatial variability of aqueous [CO2] in estuaries to examine within-estuary variation in biometrics of intertidal eelgrass (Zostera marina) during peak summer production. As expected from the sensitivity of carbonate equilibria to pH, aqueous [CO2] increased along an ocean-to-river gradient in Willapa Bay, WA, USA. The scale of pH variability also changed, reflecting weather-driven upwelling near the ocean, tidal advection near rivers, and reduced diel fluctuation up-estuary. Z. marina studied at eight sites in the bay integrated across these different temporal fluctuations in water chemistry to exhibit increased tissue carbon and depleted δ13C up-estuary. However, seagrass production did not change as expected from aqueous [CO2]. Instead, small standing biomass occurred at sites with organic-rich sediments or high wave energy, investment in branching showed trends along the estuarine gradient that changed seasonally, and specific growth rates based on leaf extension did not shift with the estuarine gradient or with standing biomass. These results reinforce that estuarine seagrasses are likely to experience modified mean pH and variability due not only to ocean acidification in the strict sense (anthropogenic CO2 absorbed from the atmosphere) but also from land use, upwelling, and feedbacks from biological processes. However, responses via productivity may be less evident than in tissue chemistry.

Dynamika růstu listů Festulolium a Dactylis glomerata na konci vegetačního období

The paper is focused on the assessment of leaf extension rate (LER), leaf appearance rate (LAR) and leaf senescence rate (LSR) in the Festulolium (Festuca arundinacea Schreb. × Lolium multiflorum Lam.) and in the Dactylis glomerata L. at the end of the growing season from the end of September to the beginning of December. In summer, the swards were used for a single cut (beginning of June) or for a double cut (beginning of June and end of July). Measurements were made in three periods from 14 Sept. to 11 Oct., from 11 Oct. to 29 Oct., and from 29 Oct. to 6 Dec. In the first period, LER was higher in Dactylis glomerata L. (3.770 mm tiller−1 d−1) than in Festulolium (2.376 mm tiller−1 d−1). In the second and third period, LER was higher in Festulolium (0.859 resp. 0.271 mm tiller−1 d−1) than in Dactylis glomerata L. (0.694, resp. 0.199 mm tiller−1 d−1). LAR values measured in Festulolium in the studied pe­riods were 0.277 leaf tiller−1 d−1, 0.079 leaf tiller−1 d−1 and 0.038 leaf tiller−1 d−1 and LAR values of Dactylis glomerata L. were 0.225 leaf tiller−1 d−1, 0.054 leaf tiller−1 d−1 and 0.027 leaf tiller−1 d−1. In the course of the whole pe­riod of study, LSR showed the highest values in Dactylis glomerata L. (7.869 mm til­ler−1 d−1, 5.947 mm til­ler−1 d−1 and 4.757 mm tiller−1 d−1) while the LSR values of Festulolium were lower (2.904 mm tiller−1 d−1, 2.375 mm tiller−1 d−1 and 1.205 mm tiller−1 d−1). The influence of both the species and the period of measurement on the LER, LAR and LSR values was statistically highly significant (P < 0.01) to very highly significant (P < 0.001). The interaction between the species and the period of measurement was very highly significant (P < 0.001) in the LER characteristic. The influence of the intensity of sward use in summer on the LSR values was very highly significant (P < 0.001), too.

Características morfogênicas e estruturais da Brachiaria brizantha cv. Marandu submetida a diferentes doses de nitrogênio e alturas de resíduos

The objective of this study was to evaluate the rate of leaf appearance, leaf elongation rate, number of green leaves, length of blade and stem of Brachiaria brizantha cv. Marandu under different nitrogen levels and two residue heights. A randomized block design was used in a 4 x 2 factorial scheme, four doses of nitrogen (100, 200, 300 and 400 kg N ha-1 year-1) and two residue heights (5 and 15 cm). There was significant interaction between residue height and nitrogen levels for leaf appearance rate (P> 0.05) of signal grass, which was influenced negatively and linearly (P 0.05) between the levels of nitrogen x residue height on the number of green leaves. The dosage that provided the highest stalk in the residue height of 5 cm was of 271.5 kg N ha -1. An increase of 0.0745 cm tiller -1 day-1 for 1 kg of N ha -1 applied to height of 15 cm of residue was observed. Nitrogen fertilization contributes positively to growth and development of rates of appearance and leaf extension. The management of pasture of Brachiaria brizantha cv. Marandu with 5 cm of residue and fertilization with 100 kg N ha -1 provided better answer morphogenic traits.

Variation in chilling tolerance for photosynthesis and leaf extension growth among genotypes related to the C4 grass Miscanthus ×giganteus

The goal of this study was to identify cold-tolerant genotypes within two species of Miscanthus related to the exceptionally chilling-tolerant C4 biomass crop accession: M. ×giganteus 'Illinois' (Mxg) as well as in other Mxg genotypes. The ratio of leaf elongation at 10 °C/5 °C to that at 25 °C/25 °C was used to identify initially the 13 most promising Miscanthus genotypes out of 51 studied. Net leaf CO2 uptake (A sat) and the maximum operating efficiency of photosystem II (ФPSII) were measured in warm conditions (25 °C/20 °C), and then during and following a chilling treatment of 10 °C/5 °C for 11 d. Accessions of M. sacchariflorus (Msa) showed the smallest decline in leaf elongation on transfer to chilling conditions and did not differ significantly from Mxg, indicating greater chilling tolerance than diploid M. sinensis (Msi). Msa also showed the smallest reductions in A sat and ФPSII, and greater chilling-tolerant photosynthesis than Msi, and three other forms of Mxg, including new triploid accessions and a hexaploid Mxg 'Illinois'. Tetraploid Msa 'PF30153' collected in Gifu Prefecture in Honshu, Japan did not differ significantly from Mxg 'Illinois' in leaf elongation and photosynthesis at low temperature, but was significantly superior to all other forms of Mxg tested. The results suggested that the exceptional chilling tolerance of Mxg 'Illinois' cannot be explained simply by the hybrid vigour of this intraspecific allotriploid. Selection of chilling-tolerant accessions from both of Mxg's parental species, Msi and Msa, would be advisable for breeding new highly chilling-tolerant Mxg genotypes.

On a class of graphs between threshold and total domishold graphs

A total dominating set in a graph is a subset of vertices such that every vertex in the graph has a neighbor in it. A graph is said to be total domishold if it admits a total domishold structure, that is, a hyperplane with non-negative coefficients that separates the characteristic vectors of its total dominating sets from the characteristic vectors of other vertex subsets. Hereditary total domishold graphs, that is, graphs every induced subgraph of which is total domishold, were recently characterized in terms of forbidden induced subgraphs; this characterization leads to an O(|V(G)|6) recognition algorithm of hereditary total domishold graphs.In this paper, we study a subclass G of the hereditary total domishold graphs obtained by replacing two of the forbidden induced subgraphs of order 6 with two of their proper induced subgraphs of order 5. We show that every connected graph in G is a leaf extension of a threshold graph, that is, it can be obtained from some threshold graph G by attaching some pendant vertices to each vertex of G. Using this property, we develop a structural characterization of graphs in G, which implies a linear time recognition algorithm for graphs in this class. We also give a linear time algorithm for computing a total domishold structure of a graph in G. In contrast to the algorithm for the general case of (hereditary) total domishold graphs, which relies on solving a linear program, our algorithm is purely combinatorial and works directly with the graph.

Effect of heat treatment on internal atmosphere and leaf extension of minimally processed leek stalks

SummaryLeeks trimmed at 20 cm from their base were immersed in a 55 °C hot water bath. During the heat treatment (HT), the internal gases released from each stalk were collected, and their volume as well as CO2 and O2 concentrations were determined. After HT, cooling and storage at 10 °C for 8 days, the weight, maximum leaf extension and internal atmosphere (volume and gas composition) were measured. It was found that HT inhibited leaf extension during storage at 10 °C for 8 days and induced significant modification of the stalk internal atmosphere, both immediately after HT and after storage. Therefore, in heat‐treated leek stalks, the growth zone of the innermost leaves was subjected to an environment of elevated CO2 concentration, which was accompanied by the inhibition of leaf extension growth.

Complete submergence escape with shoot elongation ability by underwater photosynthesis in African rice, Oryza glaberrima Steud.

Flooding imposes severe selection pressure on plants, principally because excess water in their surroundings deprives the plants certain basic resources such as oxygen, carbon dioxide, and light for photosynthesis. In recent years, reports of damage caused by flooding to rice plants have increased concomitantly with the expansion of rainfed lowland rice cultivation throughout the world. Strong submergence-induced elongation, a common escape mechanism, helps submerged individuals regain and retain contact with the aerobic environment. This study analyzed physiological mechanisms of escape from complete submergence by evaluating photosynthesis, photochemical reaction, and plant behavior during and after submergence in Oryza glaberrima Steud. Partially submerged plants were unaffected by excess water because their photosynthetic rate was maintained during and after submergence. Escape mechanisms, when under complete submergence, restrain shoot elongation per shoot dry weight per day during submergence (shoot elongation index). Our results demonstrate that the leaf area and shoot biomass of the submerged plants during submergence affects their post-submergence photosynthetic rate and the PSII maximum efficiency to some degree. Under deeply prolonged submergence, O. glaberrima genotypes were characterized by faster shoot elongation, anaerobic tillering, larger leaf area extension, higher photosynthetic rate, and maintenance of PSII maximum efficiency compared with Oryza sativa genotypes without an escape mechanism. O. glaberrima employs a submergence escape strategy that effectively uses stored carbohydrates for shoot elongation and leaf extension in a severely photosynthesis-limited environment under complete submergence.

Effects of elevated CO2 and cyclic drought on potato under varying radiation regimes

Climate change predictions include increased frequency of episodic drought in many potato (Solanum tuberosum L.) producing regions in the world. Quantitative data on potato response to periodic drought under elevated atmospheric carbon dioxide (CO2) conditions is lacking, but is needed to improve crop modeling tools suitable for investigating adaptation strategies. Two experiments E1 and E2 were conducted in sunlit soil-plant-atmosphere research (SPAR) chambers to evaluate effects of short-term drought cycles at ambient and twice-ambient CO2. Experiments were conducted in the same growing season, but at different planting dates in order to further examine effects of variation in solar radiation during the drought periods (daily average photosynthetically active radiation of 43.9molm−2d−1 in E1 and 24.7molm−2d−1 in E2). Drought cycles were applied at post-tuber initiation (R) or at both vegetative and post tuber-initiation (VR) stages. While total dry matter in E1 was nearly twice that of E2 as a result of the radiation differences, relative responses to drought and CO2 were consistent. Total dry matter production was reduced proportionately based on the number of drought cycles, with twice-droughted VR plants producing less biomass than non-droughted controls. Harvest index and the ratio of tuber to total dry matter growth rate increased with drought frequency, suggesting that tuber sink strength was higher for VR plants than R. Harvest index, the ratio of tuber to total plant growth rate, and tuber dry matter for VR and R treated plants were also higher at elevated versus ambient CO2. Water use efficiency for water deficient versus water sufficient plants was correlated with harvest index and also increased at the higher CO2 concentration. As there was also little influence of drought or CO2 on leaf extension characteristics, differences in dry matter production and allometric responses were assumed to predominantly be a function of assimilation rate and carbon partitioning. These results confirm potato drought sensitivity in terms of yield response is influenced by developmental stage and CO2 regardless of light environment, and provide necessary data for calibration and testing modeling tools for climate change studies.

GrassView - the form and function of grass: a multimedia program

GrassView - the form and function of grass is an interactive computer programme which uses video footage, narration, sound, computer based 3D animation, graphical displays of information, charts and quizzes to present a description of the morphology of a grass tiller and the implications for sward behaviour. The programme is designed for flexibility of use. In interactive mode it could be used for self-directive study, whereas in linear mode it could be video-projected as a presentation to a class of students or to an assembled group. It has been optimised to run under Windows 95 or NT 4.0 and is distributed as a CD. Keywords: computer program, grass form and function, grass morphology, interactive program, leaf extension,

Quantitative Trait Locus (QTL) meta-analysis and comparative genomics for candidate gene prediction in perennial ryegrass (Lolium perenne L.)

BackgroundIn crop species, QTL analysis is commonly used for identification of factors contributing to variation of agronomically important traits. As an important pasture species, a large number of QTLs have been reported for perennial ryegrass based on analysis of biparental mapping populations. Further characterisation of those QTLs is, however, essential for utilisation in varietal improvement programs.ResultsA bibliographic survey of perennial ryegrass trait-dissection studies identified a total of 560 QTLs from previously published papers, of which 189, 270 and 101 were classified as morphology-, physiology- and resistance/tolerance-related loci, respectively. The collected dataset permitted a subsequent meta-QTL study and implementation of a cross-species candidate gene identification approach. A meta-QTL analysis based on use of the BioMercator software was performed to identify two consensus regions for pathogen resistance traits. Genes that are candidates for causal polymorphism underpinning perennial ryegrass QTLs were identified through in silico comparative mapping using rice databases, and 7 genes were assigned to the p150/112 reference map. Markers linked to the LpDGL1, LpPh1 and LpPIPK1 genes were located close to plant size, leaf extension time and heading date-related QTLs, respectively, suggesting that these genes may be functionally associated with important agronomic traits in perennial ryegrass.ConclusionsFunctional markers are valuable for QTL meta-analysis and comparative genomics. Enrichment of such genetic markers may permit further detailed characterisation of QTLs. The outcomes of QTL meta-analysis and comparative genomics studies may be useful for accelerated development of novel perennial ryegrass cultivars with desirable traits.

Is the control of green area index of barley crops by application of alkaline materials possible in field conditions?

The risk of excessive leaf canopy growth in winter barley (Hordeum vulgare L.) grown in the UK is usually reduced by avoiding very early sowing at high seed rates, and in spring by delaying and reducing nitrogen fertilizer application. A preliminary study was conducted of a possible additional agronomic method for retarding winter barley leaf growth in spring. The study was based on previous plant physiological experiments showing that drought-induced reduction in leaf growth of barley is mediated by increasing alkalinity of the xylem sap. Leaf extension was measured in plants detached from the roots and fed artificial xylem sap adjusted to a wide range of pH. A field experiment tested the effects on barley canopy growth of solid calcium carbonate and alkaline pH buffer solution application to the foliage. Rate of leaf extension in the detached plant experiments decreased linearly with increasing artificial xylem sap pH, confirming the previous results in a different cultivar. Rate of canopy growth in the field experiment was halved by application of 1000kg/ha of calcium carbonate up to four days after application. In contrast at six and eight days after application, following rain, compensatory growth occurred and the rate of increase in canopy size was larger with increasing calcium carbonate application rate. A pH buffer spray gave similar results but was less effective at reducing canopy growth. An improvement in persistence of the reduction in canopy growth by alkaline materials is needed before the potential for retarding leaf growth as an additional agronomic practice can be assessed.

Mediterranean and Continental Tall Fescue: I. Effects of Endophyte Status on Leaf Extension, Proline, Mono‐ and Disaccharides, Fructan, and Freezing Survivability

ABSTRACTTall fescue [Festuca arundinacea Schreb. syn. Lolium arundinaceum (Schreb.) Darbysh.] is widely used for hay and pasture in the Eastern regions of the United States, with new types of Mediterranean tall fescue possessing superior growth under cool growing conditions. However, they do not survive Midwestern winters. To date, little research has examined the role of endophyte infection on the ability of tall fescue to grow under cold conditions or survive freezing conditions. This study's objectives determined the endophyte's role in tall fescue growth and production of metabolites for nonfreezing conditions. Additionally, the role of endophyte infection on the ability of plants to survive freezing temperatures was determined. This experiment used five genotypes of tall fescue. Half of the plants from each genotype were endophyte infected (E+), with the remaining genotypes being endophyte free (E–). We report for the first time the effects of endophyte status on proline, simple sugars, and fructan accumulation when plants were grown under cold, nonfreezing temperatures and the survivability at various freezing temperatures. Endophyte removal only affected fructan concentrations at 4.5°C; however, plant genotype affected leaf extension rate, proline, sugars, and fructan concentration. The freezing test found no effect of the endophyte on tiller survival, while plant genotype was significant. These data indicate that endophyte removal has little influence on the measured traits, and plant genotype is more critical for survival under cold conditions.

Mediterranean and Continental Tall Fescue: II. Effects of Cold, Nonfreezing Temperatures on Leaf Extension, Proline, Fructan, and Abscisic Acid

ABSTRACTContinental tall fescue [Festuca arundinacea Schreb. syn. Lolium arundinaceum (Schreb.) Darbysh.] is the predominant forage used by cattle producers throughout much of the Midwest. However, Mediterranean tall fescue is gaining popularity in warmer, drier climates. One major difference of Mediterranean tall fescue is that it enters a semidormant period during hot dry summers but resurges during the fall and winter months. During the autumn resurgence it has exceptional growth but does not survive prolonged freezing conditions typically found in the Midwest. To determine how both Continental and Mediterranean tall fescues respond to low temperatures that are typically encountered during the fall, the leaf extension rate (LER) was measured along with proline, simple sugars, fructan, and abscisic acid (ABA). Three Mediterranean and four Continental accessions were tested, including Kentucky‐31 and Flecha as “typical” Continental and Mediterranean accessions, respectively. The greatest difference observed between these types of tall fescue occurred at 4.5°C. The Mediterranean genotypes had greater LER and fructan concentrations while the Continental genotypes possessed greater proline, ABA, and simple sugar concentrations. Kentucky‐31 was typically found in the middle between the Mediterranean and the remaining Continental accessions. These data indicate that Mediterranean germplasm possesses superior cold growth, but the high proline levels produced by the Continental types may be critical for survival under cold conditions.

Effects of water stress on growth, biomass partitioning, and water-use efficiency in summer maize (Zea mays L.) throughout the growth cycle

The aim of this study was to explore the effects of water stress on the growth, biomass partitioning, and water-use efficiency (WUE) of summer maize (Zea mays L.) throughout the growth cycle. Maize field trials were conducted under a completely randomized design with three field water capacity (FC) regimes. Water was delivered to plants as follows: 75% FC was considered low water stress and the control, 55% FC medium stress, and 35% FC high stress. The controlled irrigation was initiated from the third leaf stage until maturity. The results of 2 years of field trials indicated that maize development and grain yield responses to water stress depended on the severity of stress, including intensity and duration, but also on maize developmental stage. Medium water stress (55%) affected leaf area at the seventeenth (V17) leaf stage, tasseling and silking emergence, leaf extension, and final leaf number to a minor degree. However, 55% FC significantly decreased plant height, leaf area (except for V17), stem diameter, biomass accumulation, net photosynthesis and transpiration rates at different developmental stages. In particular, tasseling and silking, and yield parameters, including ear kernel number and 100-kernel dry weight decreased with increasing medium water stress duration. Severe water stress (35% FC) exhibited increased detrimental effects on all vegetative and yield parameters at different development stages, and resulted in a maturation period delay. Severe stress caused notable reductions in WUE at vegetative and reproductive stages, whereas moderate stress resulted in WUE increases at early and middle stages, and significant decreased WUE at late stages. Overall, these results collectively showed that the negative effects of 2 years of high stress conditions (35% FC) on maize plants were evident in vegetative and yield parameters. We recommend that water deficits or reduced irrigation, and 55% water field capacity, be considered for irrigation scheduling before the maize tasseling stage in neutral loam, meadow soil for sub-humid regions under water limited conditions.

Flowering control in Watsonia: Effects of corm size, temperature, photoperiod and irradiance

The role of corm size, light and temperature in flowering of Watsonia species was evaluated to facilitate their commercial production. In addition to exhibiting desirable ornamental attributes, the species selected represented the major climatic regions in South Africa. A day/night temperature regime of 12/7 °C released vegetative dormancy in all species and thereafter elicited vernalization in Watsonia pillansii – highlighting an obligate cold requirement for this species. Flowering of Watsonia borbonica and Watsonia tabularis was not enhanced by additional chilling, but rather by long (16 h) or day-neutral (12 h) photoperiods. Microscopic examination of the shoot apical meristem revealed that extension of the 2nd leaf was a critical stage developmentally, and signified the anatomical transition to flowering. Late-development temperatures to a maximum of 25 °C ensured healthy vegetative growth and supported the maturation of the inflorescence and the opening of floret buds. Irradiance did not affect flower induction, but a minimum light intensity of 150 μmol m −2 s −1 proved essential in sustaining the energetic demands of the competitive growth and reproductive processes. Excessively high irradiance (950 μmol m −2 s −1) impacted negatively on attractiveness through increased bud blasting. Flowering success was not correlated to corm mass, but rather to the environment under which the corm was stored, or the conditions under which the plant was grown. Understanding the phenology of these species in situ and the link between flowering and season provide a useful tool for predicting the artificial requirements necessary to elicit optimal flowering under industry conditions.

Involvement of root ABA and hydraulic conductivity in the control of water relations in wheat plants exposed to increased evaporative demand

We studied the possible involvement of ABA in the control of water relations under conditions of increased evaporative demand. Warming the air by 3°C increased stomatal conductance and raised transpiration rates of hydroponically grown Triticum durum plants while bringing about a temporary loss of relative water content (RWC) and immediate cessation of leaf extension. However, both RWC and extension growth recovered within 30min although transpiration remained high. The restoration of leaf hydration and growth were enabled by increased root hydraulic conductivity after increasing the air temperature. The use of mercuric chloride (an inhibitor of water channels) to interfere with the rise on root hydraulic conductivity hindered the restoration of extension growth. Air warming increased ABA content in roots and decreased it in shoots. We propose this redistribution of ABA in favour of the roots which increased the root hydraulic conductivity sufficiently to permit rapid recovery of shoot hydration and leaf elongation rates without the involvement of stomatal closure. This proposal is based on known ability of ABA to increase hydraulic conductivity confirmed in these experiments by measuring the effect of exogenous ABA on osmotically driven flow of xylem sap from the roots. Accumulation of root ABA was mainly the outcome of increased export from the shoots. When phloem transport in air-warmed plants was inhibited by cooling the shoot base this prevented ABA enrichment of the roots and favoured an accumulation of ABA in the shoot. As a consequence, stomata closed.

STUDY OF THE EFFECT OF NITROGEN FERTILIZATION SUPPLIED BY FOLIAR SPRAYS OR BY FERTIGATION IN APPLE TREES - PRELIMINARY RESULTS

Nitrogen overfertilization of 'Golden Reinders' apple trees, applied as extra doses to the soil or as a foliar aqueous solution led to different effects on plants. While soil applications had no effects on growth and cropping parameters, as compared with the control trees, foliar sprays promoted shoot growth and leaf extension, and resulted in a decrease in yield and crop-load, presumably due to a greater preharvest fruit drop. Phytotoxic damage was observed on leaves, but net photosynthesis remained unaffected, and mineral element concentration did not change due to the overfertilization, except for N, which increased only in the foliar spray treatment, and only late in the growing season.

Extension, anatomy and metabolic activity of leaves in minimally processed leek stalks

When leeks are processed as trimmed stalks, the major problem that arises is inner leaf extension. With the aim to study leaf extension in trimmed stalks, leek pseudostems were initially trimmed at 20 cm from their base and sorted into three experiments. In the first experiment, the stalks were further cut at 2, 4, 6, 8, 10, 12, 14, 16 or 18 cm from the base resulting in two complementary parts: the lower part of 0–2, 0–4, 0–6, 0–8, 0–10, 0–12, 0–14, 0–16 or 0–18 cm and the respective upper part of 2–20, 4–20, 6–20, 8–20, 10–20, 12–20, 14–20, 16–20 or 18–20 cm; in the second experiment, the leaves were detached from the stalk base and marked at 2 cm intervals (leaf-parts), and in the third experiment, detached leaves were grouped into inner (1st–4th), intermediate (5th–7th), and outer (8th–10th) leaves and all experimental material was then stored at 8 °C for 10 d. Maximum leaf extension and leaf-part extension were measured at the end of storage in the first and second experiments, respectively, while metabolic activity measured as CO 2 and C 2H 4 production was monitored during storage in the third experiment. Additionally, leaf material was sampled from the base and mid leaf area of an inner and an outer leaf for anatomical evaluation. The results showed that after 10 d storage at 8 °C of leek pseudostems with 10 leaves trimmed at 20 cm from the base, the inner four leaves were metabolically very active and had the highest leaf extension, which was restricted to the basal 0–8 cm leaf-part. This inner leaf-part constitutes the growth zone in trimmed leek stalks, where cell division and subsequent cell elongation occur, while the outer leaf tissues have already fully expanded.

A size‐mediated effect can compensate for transient chilling stress affecting maize (Zea mays) leaf extension

*In this study, we examined the impact of transient chilling in maize (Zea mays). We investigated the respective roles of the direct effects of stressing temperatures and indirect whorl size-mediated effects on the growth of leaves chilled at various stages of development. *Cell production, individual leaf extension and final leaf size of plants grown in a glasshouse under three temperature regimes (a control and two short chilling transfers) were studied using two genotypes contrasting in terms of their architecture. *The kinetics of all the leaves emerging after the stress were affected, but not all final leaf lengths were affected. No size-mediated propagation of an initial growth reduction was observed, but a size-mediated effect was associated with a longer duration of leaf elongation which compensated for reduced leaf elongation rates when leaves were stressed during their early growth. Both cell division and cell expansion contributed to explaining cold-induced responses at the leaf level. *These results demonstrate that leaf elongation kinetics and final leaf length are under the control of processes at the n - 1 (cell proliferation and expansion) and n + 1 (whorl size signal) scales. Both levels may respond to chilling stress with different time lags, making it possible to buffer short-term responses.

A field experiment to determine the effect of dry-season precipitation on annual ring formation and leaf phenology in a seasonally dry tropical forest

Abstract:Trees growing in a seasonally tropical dry forest, with its characteristic 5–7-mo rainless interval, possess a variety of physiological adaptations to drought, the most common being leaf abscission. At the Estacion Biologia de Chamela in western Mexico, we experimentally examined the relationship between one-time experimental irrigation ranging as 0 (control) to 200 mm, and (1) the degree of bud burst (and, for a single species, flowering), and (2) the formation of a false ring. Additionally, we used long-term records at a nearby meteorological station to determine the probability of a rain event exceeding a particular intensity (mm). For our seven species (particularly the two most common species: Cordia alliodora and Piptadenia constricta), we found that the degree of budburst and leaf extension was a function of irrigation intensity. In no case, however, did we find false rings, or indeed any indication of cambial activity initiated by the irrigation event. Further, there was no effect of intensity on subsequent relative growth rate in the following wet season. While sufficient rainfall (200 mm) to cause full leaf deployment is rare, nonetheless we estimate that a canopy tree in the study area would experience an event of this magnitude at least a few times per century. In any case, it will have no effect on the reliability of annual rings in this biome, nor any effect on diameter growth in (at least) the following year.