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Tillandsia recurvata L. may show morphophysiological plasticity in response to radiation availability, since this species is found in different environments. This work aimed to evaluate the anatomical and physiological modifications of T. recurvata isolated individuals under different shading levels and the consequences of these changes on the growth of this species. The individuals were exposed for 60 days to treatments as follows: full sun (unshaded) and shading of 35%, 75%, and 85%. Growth analyses were performed, and the leaf anatomy and water content were assessed. All plants submitted to full sun or 35% shading died, whereas those under 75% and 85% shading survived. The water content in leaves and rhizomes was higher under 85% shading, and this treatment increased the leaf area and the number of leaves in T. recurvata. Leaf dry mass, leaf elongation rate, biomass allocation to rhizomes, and net assimilation rate were higher under 85% shading. The leaves had a thicker hypodermis, lower proportions of both epidermis and vascular bundles, and a higher proportion of chlorophyll parenchyma under 85% shading. Tillandsia recurvata individuals behave as sciophytic, while the formation of clusters may change microclimate conditions; the behavior of clumped plants must be further investigated. Key words: epiphytic bromeliads, sciophytes, biomass allometry, chlorophyll parenchyma, water content, Introduction Radiation exerts a strong effect on plant growth and development. This is because some of the most important processes of plant survival depend on light, particularly photosynthesis and growth [...]

Previous studies have shown that atmospheric nitrogen (N) deposition is detrimental to sphagna, which are a group of mosses that are important for carbon cycling in northern peatlands. Little is known about species interactions, such as relative responses of tall moss Polytrichum strictum Menzies ex Brid. and sphagna. We studied the effects of N deposition on growth, abundance, and C[O.sub.2] exchange of the moss species Sphagnum capillifolium (Ehrh.) Hedw. and Polytrichum strictum in an experiment at a temperate bog. Sphagnum growth and cover decreased significantly with high-dose N treatment (6.4 g N x [m.sup.-2] x [year.sup.-1]) in years 4 and 5 of treatment, whereas the same parameters increased for Polytrichum compared with the control. Net C[O.sub.2] exchange, gross photosynthesis ([P.sub.g]), and dark respiration (R) in the intact moss cores, which were measured in year 5 of treatment, were elevated in the cores that had been treated with the high-dose of N, compared with the control, and this was associated with increased abundance of Polytrichum. The moss cores where Polytrichum was removed, however, had increased mass-based R with the high-dose N treatment. Our results showed that S. capillifolium at Mer Bleue may be close to N saturation, as 5 years of high-dose N loading (6.4 g N x [m.sup.-2] x [year.sup.-1] + background) was harmful to this species, possibly as a result of increased respiratory cost. Polytrichum strictum had a competitive advantage, at least in the short-term, through allocating excess N to growth. This change in moss layer composition deserves further attention, as a shift to more easily decomposable litter, without corresponding increases in plant production, could reduce the carbon sequestration of the bog. Keywords: peatland, photosynthesis, chlorophyll fluorescence, respiration, vegetation change, moss. Des etudes precedentes ont montre que le depot de N atmospherique peut etre dommageable a la sphaigne, un genre important au recyclage de C dans les tourbieres du nord. On sait peu de choses des interactions entre les especes, telles les reponses relatives de la mousse Polytricum strictum Menzies ex Brid. et de la sphaigne. Les auteurs ont etudie les effets du depot de N sur la croissance en hauteur, l'abondance et l'echange de C[O.sub.2] des especes de mousses Sphaghum capillifolium (Ehrh.) Hedw. et Polytricum strictum lors d'une experience en tourbiere temperee. La croissance en hauteur de Sphaghum et son couvert diminuaient significativement en presence d'une forte concentration de N (6,4 g N x [m.sup.-2] x [an.sup.-1]) a la quatrieme et cinquieme annees de traitement, alors que ceux de Polytricum augmentaient, relativement au controle. L'echange net de C[O.sub.2], la photosynthese brute ([P.sub.b]) et la respiration mitochondriale (R) des mousses intactes, mesures a la cinquieme annee de traitement, etaient accrus par le traitement riche en N relativement aux controles, a cause de l'abondance accrue de Polytricum. Les mousses dont on avait retire Polytrichum presentaient cependant une R en fonction de la masse accrue par le traitement riche en N. Les resultats obtenus par les auteurs montrent que S. capillifolium de la tourbiere de Mer Bleue peut etre presqu'a saturation de N, car 5 ans de charge elevee en N (6,4 g N x [m.sup.-2] x [an.sup.-1] + niveau de base) ont ete dommageables a cette espece, possiblement a cause d'un cout respiratoire accru. Polytrichum strictum possedait un avantage competitif, du moins a court terme, reservant l'exces de N a la croissance. Ce changement dans la composition du couvert de mousse merite une plus grande attention car un deplacement vers une litiere plus facilement decomposable, sans augmentations correspondantes de la production vegetale, peut diminuer la sequestration du C par la tourbiere. [Traduit par la Redaction] Mots-cles: tourbiere, photosynthese, fluorescence de la chlorophylle, respiration, changement de la vegetations, mousse., Introduction The deposition of atmospheric nitrogen (N) drastically increased N availability in the industrialized world during the Anthropocene (e.g., Galloway et al. 2008). Excess N from deposition threatens many natural [...]

The regeneration ecology of sugar maple (Acer saccharum Marsh.) has been impacted by acid rain leaching of base cations from the soils throughout much of its range. We tracked the survival and causes of death for a natural cohort of sugar maple seedlings across 22 sites in the Hubbard Brook Valley in New Hampshire, USA, where soil acidification has been documented. Survival over 7 years averaged 3.4%; however, significant differences in survival were observed among sites, which were classified into three main groups based on the shape of their survival curves. These site groups differed in position on the landscape, seedling nutrition and leaf size, and the prevalence of damage agents, but not in soil Ca. First-season mortality was high (71%), and the main damage agents were fungal infection (Rhizoctonia spp.) and caterpillar herbivory (Geometridae). Other principal causes of mortality in order of importance were winter injury, mechanical damage, and rodent (Myodes gapperi Vigors, 1830) tunneling, and all damage agents varied significantly in severity between years. This study highlights the importance of landscape-level variation in biotic factors for predicting sugar maple regeneration success. Predictions of sugar maple regeneration will require a better understanding of controls on initial seedling growth and the suite of biotic agents that damages seedlings. Key words: Geometridae, Hubbard Brook Experimental Forest, mortality, Rhizoctonia, winter injury. Le lessivage des cations basiques du sol par les pluies acides a eu un impact sur l'ecologie de la regeneration de l'erable a sucre (Acer saccharum Marshall) presque partout dans son aire de repartition. Nous avons suivi la survie et les causes de moralite d'une cohorte naturelle de semis d'erable a sucre dans 22 stations de la vallee de Hubbard Brook au New Hampshire, E.-U., oU l'acidite du sol a ete documentee. Sur une periode de 7 ans, le taux moyen de survie a ete de 3,4 %; cependant, des differences significatives ont ete observees entre les stations qui ont ete classees en trois groupes principaux sur la base de leur courbe de survie. Ces groupes de stations se distinguaient par leur position dans le paysage, la nutrition et la taille des feuilles des semis ainsi que par la predominance des agents deteriorateurs mais non par le Ca du sol. La mortalite a ete elevee (71 %) durant la premiere saison et les principaux agents deteriorateurs etaient les infections fongiques (Rhizoctonia spp.) et l'herbivorisme des chenilles (Geometridae). Les autres causes principales de mortalite etaient en ordre d'importance: les blessures hivernales, les blessures mecaniques et les galeries de rongeur (Myodes gapperi Vigors, 1830) et la severite des dommages causes par tous les agents deteriorateurs etait significativement differente d'une annee a l'autre. Cette etude fait ressortir l'importance de la variation a l'echelle du paysage des facteurs biotiques pour predire la reussite de la regeneration de l'erable a sucre. Les predictions concernant la regeneration de l'erable a sucre necessitent une meilleure comprehension des facteurs qui regissent la croissance initiale des semis et la serie d'agents biotiques qui causent des dommages aux semis. [Traduit par la Redaction] Mots-cles: Geometridae, foret experimentale de Hubbard Brook, mortalite, Rhizoctonia, blessures hivernales., Introduction Temperate forests are confronted with an unprecedented combination of human-accelerated environmental changes, including climate warming (Dale et al. 2001), air pollution (Tomlinson 2003), and introduced pests and pathogens (Fischer [...]

Fire has an important role for regeneration of many boreal forest tree species, and this includes both wildfire and prescribed burning following clear-cutting. Depending on the severity, fire can have a variety of effects on above- and belowground properties that impact tree seedling establishment. Very little is known about the impacts of ground fire severity on post-fire seedling performance, or how the effects of fire severity interact with those of canopy structure. We conducted a full-factorial experiment that manipulated surface-burn severity (no burn; light, medium, or heavy burn; or scarification) and canopy (closed forest or open clear-cut) to reveal their interactive effects on ecophysiological traits of establishing broadleaf and conifer seedlings in a Swedish boreal forest. Medium and heavy surface burns increased seedling growth, photosynthesis, respiration, and foliar N and P concentrations, and these effects were most apparent in open clear-cuts. Growth rates of all species responded similarly to surface-burn treatments, although photosynthesis, foliar P, and specific leaf area were more responsive to burning treatments for broadleaf species than for conifers. Our study demonstrates that the positive impacts of fire on tree seedling physiology are dependent on a minimum severity threshold and are more effective when combined with clear-cutting. Key words: boreal forest, fire severity, fire management, foliar nutrients, photosynthesis, respiration, scarification, tree seedling regeneration. Le feu joue un role important pour la regeneration de plusieurs especes d'arbre de la foret boreale et cela inclut les feux de foret et le brulage dirige apres une coupe a blanc. Selon la severite, le feu peut avoir une variete d'effets sur les proprietes aeriennes et souterraines qui ont un impact sur l'etablissement des semis. On connait mal les impacts de la severite des feux de surface sur la performance des semis apres feu ou la fa^on dont les effets de la severite du feu interagissent avec ceux de la structure du couvert forestier. Nous avons realise une experience selon un plan factoriel complet dans laquelle nous avons fait varier la severite d'un brulage de surface (aucun brulage; brulage leger, moyen ou severe; ou scarifiage) et le couvert forestier (ferme ou ouvert a la suite d'une coupe a blanc) dans le but de reveler leurs effets interactifs sur les caracteristiques ecophysiologiques des semis de coniferes et de feuillus qui s'etablissent dans une foret boreale suedoise. Les brulages de surface moyen et severe ont augmente la croissance, la photosynthese, la respiration et la concentration foliaire de N et P des semis mais ces effets etaient davantage apparents dans les coupes a blanc. Le taux de croissance de toutes les especes a reagi de fa^on similaire aux traitements de brulage de surface bien que la photosynthese, le P foliaire et la surface foliaire specifique aient reagi davantage aux traitements de brulage chez les feuillus que chez les coniferes. Notre etude demontre que les impacts positifs du feu sur la physiologie des semis d'arbre dependent d'un seuil de severite minimum et sont plus efficaces lorsque le feu est combine a la coupe a blanc. [Traduit par la Redaction] Mots-cles: foret boreale, severite du feu, gestion du feu, nutriments foliaires, photosynthese, respiration, scarifiage, regeneration de semis d'arbre., Introduction It is well recognized that fire is a major driver of regeneration patterns in boreal forest systems (Zackrisson 1977; Engelmark 1984; Payette 1992; Lampainen et al. 2004; Nilsson and [...]

Early flowering plants are thought to have been woody species restricted to warm habitats (1-3). This lineage has since radiated into almost every climate, with manifold growth forms (4). As angiosperms spread and climate changed, they evolved mechanisms to cope with episodic freezing. To explore the evolution of traits underpinning the ability to persist in freezing conditions, we assembled a large species-level database of growth habit (woody or herbaceous; 49,064 species), as well as leaf phenology (evergreen or deciduous), diameter of hydraulic conduits (that is, xylem vessels and tracheids) and climate occupancies (exposure to freezing). To model the evolution of species' traits and climate occupancies, we combined these data with an unparalleled dated molecular phylogeny (32,223 species) for land plants. Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits (5) and/or shutting down hydraulic function by dropping leaves during freezing. Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue. Growth habit has long been considered labile (6), but we find that growth habit was less labile than climate occupancy. Additionally, freezing environments were largely filled by lineages that had already become herbs or, when remaining woody, already had small conduits (that is, the trait evolved before the climate occupancy). By contrast, most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing (that is, the climate occupancy evolved before the trait). For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions; our results suggest that many of these solutions were probably acquired before their foray into the cold., Flowering plants (angiosperms) today grow in a vast range of environmental conditions, with this breadth probably related to their diverse morphology and physiology (7). However, early angiosperms are generally thought [...]

Coccolithophores are marine algae that use carbon for calcification and photosynthesis. The long-term adaptation of these and other marine algae to decreasing carbon dioxide levels during the Cenozoic era (1) [...]

About 8,000 years ago in the Fertile Crescent, a spontaneous hybridization of the wild diploid grass Aegilops tauschii (2n = 14; DD) with the cultivated tetraploid wheat Triticum turgidum (2n [...]

To better understand the availability of plant resources on the forest floor in the Amazon and also to show the effect of their heterogeneity on tree seedlings, I described the spatial and temporal variation of light and soil water along a 100 m transect in a terra firme forest for 6 months and recorded responses of three tree species planted on that transect after 1 year's growth. I found that (i) the spatial heterogeneity across the transect was greater than the temporal heterogeneity at any given microsite on the transect for both light and water and there was a positive correlation between them, (ii) Couepia obovata Ducke, the largest seeded and the only subcanopy tree, survived the best and showed both the largest relative height growth rate (RHGR) and the largest specific leaf area (SLA), while among the two early successional trees, Tapirira guianensis J.B. Aublet had the largest leaf area ratio (LAR) and the largest leaf mass ratio (LMR) and Duguethia spixiana Mart. had the largest root to shoot ratio (RTOS), (iii) for T. guianensis, SLA increased with increasing light and soil water potential predicted both increasing LMR and decreasing RTOS with increasing soil water, and (iv) soil water potential could also predict increasing LAR with increasing water for D. spixiana and, for C. obovata, soil water potential predicted more survivorship, LMR, and RHGR but less RTOS, all with increasing soil water. I conclude that some subcanopy trees may survive and grow more than open-canopy trees when presented with water stress in the forest understory and that within the ranges of light and soil water sampled here, plants responded more to spatial variation in water compared with light. Resume: Afin de mieux comprendre la disponibilite des ressources pour les plantes dans la couverture morte de la foret amazonienne et de montrer l'effet de leur heterogeneite sur les semis d'arbre, j'ai decrit la variation spatiale et temporelle de la lumiere et de l'eau du sol le long d'un transect de 100 m dans la foret de terra firme sur une periode de 6 mois. J'ai aussi note les reactions de trois especes d'arbre plantees dans ce transect apres 1 annee de croissance. J'ai trouve que (i) l'heterogeneite spatiale etait plus grande que l'heterogeneite temporelle dans n'importe quel microsite le long du transect dans le cas de la lumiere et de l'eau sol et qu'il y avait une correlation positive entre les deux, (ii) Couepia obovata Ducke, le plus gros arbre ensemence et le seul arbre de sous-bois, a le mieux survecu et avait a la fois le plus fort taux relatif de croissance en hauteur (TRCH) et la plus grande surface foliaire specifique (SFS), tandis que parmi les deux essences pionnieres, Tapirira guianensis J.B. Aublet avait les plus grands rapports de surface foliaire (RSF) et de masse foliaire (RMF) et Duguetia spixiana Mart. avait le plus grand rapport racine a tige (RRT), (iii) dans le cas du T. guianensis, la SFS augmentait avec l'augmentation de la lumiere; le potentiel hydrique du sol predisait a la fois l'augmentation du RMF et la diminution du RRT avec l'augmentation de l'eau du sol et (iv) le potentiel hydrique du sol pouvait egalement predire l'augmentation du RSF avec l'augmentation de l'eau du sol dans le cas de D. spixiana et, dans le cas de C. obovata, le potentiel hydrique du sol predisait une augmentation de la survie, du RMF et du TCRH, mais une diminution du RRT, dans tous les cas a la suite d'une augmentation de l'eau du sol. Je conclus que certains arbres de sous-bois peuvent survivre et croitre plus que les arbres dans un couvert clairseme lorsqu'ils sont soumis a un stress hydrique en sous-etage, et que dans les gammes de valeurs de disponibilite de la lumiere et de l'eau du sol echantillonnees dans le cadre de cette etude les plantes reagissent davantage a la variation spatiale de la disponibilite de l'eau qu'a celle de la lumiere, contrairement a l'opinion traditionnelle selon laquelle la lumiere est la ressource la plus limitative dans les forets tropicales. [Traduit par la Redaction], Introduction The Amazon River basin contains the world's largest tropical rainforest (Walter 1973; Myster 2009). Researchers have historically regarded this forest as a shifting mosaic (Watt 1947) composed of patches [...]

The browning and death of needles of evergreen conifers in alpine regions occur mainly in early spring at the point where the shoot protrudes from the snowpack. They are thought to be caused by excessive transpiration due to mechanical damage to the cuticle or to a thinner cuticle. However, there are a few studies that do not necessarily agree with this idea. We assessed needle browning and death in Pinus pumila (Pallas) Regel. in the alpine region of Japan in relation to mechanical damage to the cuticle, cuticular resistance, and cuticle thickness. Mechanical damage was not observed on needle cuticles of Pinus pumila browning in a natural environment. The color of needles with artificially abraded cuticles changed from green to brown in the abraded part. However, the brown color at the abraded part differed from the brown of a browning needle in its natural environment. There was no correlation between cuticular resistance and cuticle thickness. Needle browning and death in P. pumila were not related to mechanical damage of the cuticle or to cuticle thickness but might be due to changes in the quality and structure of the cuticle and other stresses. Resume: Le brunissement et la mort des aiguilles des coniferes dans les regions alpines surviennent surtout au debut du printemps sur les pousses qui emergent du couvert nival. On croyait que le brunissement et la mort des aiguilles etaient causes par la transpiration excessive due a des blessures mecaniques a la cuticule et a une cuticule amincie. Cependant, il existe quelques etudes dont les resultats ne correspondent pas necessairement a cette hypothese. Nous avons etudie le brunissement et la mort des aiguilles de Pinus pumila (Pallas) Regel. dans la region alpine du Japon en lien avec les blessures mecaniques a la cuticule ainsi que la resistance et l'epaisseur de la cuticule. Il s'ensuit qu'aucune blessure mecanique a la cuticule des aiguilles n'a ete observee en milieu naturel. La portion des aiguilles dont la cuticule avait ete artificiellement endommagee avec un abrasif a bruni. Cependant, le ton de brun de la portion traitee avec un abrasif etait different de celui des aiguilles qui brunissent en milieu naturel. Il n'y avait pas de correlation entre la resistance de la cuticule et son epaisseur. Le brunissement et la mort des aiguilles de P. pumila n'etaient pas relies aux blessures mecaniques a la cuticule ni a l'epaisseur de la cuticule, mais pourraient etre dus a des changements dans la qualite et la structure de la cuticule et a d'autres facteurs de stress. [Traduit par la Redaction], Introduction High mountainous habitat is one of the most severe habitats for plants (Korner 2003). In Europe and North America, the timberline of the uppermost subalpine zone transits the alpine [...]

The salinization and water deficit of soil are widespread environmental problems in limiting plant survival, growth, and productivity. However, some plants could adopt some strategies to resist salinity and drought stresses. Among these strategies, the mechanism of osmotic adjustment could help plants and algae to avoid ion toxicity and maintain water uptake in both stresses by accumulating large quantities of osmolytes. Two types of osmolytes, organic solutes and inorganic ions, play a key role in osmotic adjustment. Different osmolytes and their osmotic adjustment actions are different according to their distribution in different plants. Organic solutes, known as compatible solutes, include amino acids, glycerol, sugars, and other low molecular weight metabolites, serve a function in cells to lower or balance the osmotic potential of intracellular and extracellular ions in resistance to osmotic stresses. Inorganic ions for osmotic adjustment are mainly [Na.sup.+],[K.sup.+],[Ca.sup.2+], and [Cl.sup.-]. Inorganic ions make great contribution in osmotic adjustment by ion transport processes with related ion antiporters and ion channels. The aim of this review is to integrate recent data on the mechanisms of osmotic adjustment by osmolytes in plants and algae, and to illustrate the variety of related molecular mechanisms, to introduce new concepts and techniques into this research field. Genetic manipulation including the application of transgenic techniques in plants provides promising strategies to elevate the tolerance capability of plants under osmotic stress conditions. Key words: compatible solutes, drought stress, ion transport process, osmotic adjustment, salinity stress, transgenic plants. La salinisation et le deficit en eau du sol constituent des problemes environnementaux tresrepandus et limitent la survie des plantes et leur productivite. Cependant, certaines plantes peuvent adopter des strategies pour resister a la salinite et au stress hydrique. Parmi ces strategies, le mecanisme d'ajustement osmotique peut aider les plantes et les algues a eviter la toxicite ionique et a maintenir l'absorption de l'eau, dans ces deux situations stressantes, en accumulant de grandes quantites d'osmolytes. Deux types d'osmolytes, soit les solutes organiques ou les ions inorganiques, jouent un role cle dans l'ajustement osmotique. Diffeerents osmolytes et leurs actions d'ajustement osmotique different selon leur distribution dans differentes plantes. Les solutes organiques, reconnus comme solutes compatibles, incluent les acides amines, le glycerol, les sucres et autres metabolites de faibles poids moleeculaires, jouant un role dans les cellules pour reduire ou balancer le potentiel osmotique des ions intra- et extracellulaires dans la resistance aux stress osmotiques. Les ions inorganiques intervenant dans l'ajustement osmotique sont surtout les [Na.sup.+],[K.sup.+],Ca+2 et [Cl.sup.-]. Les ions inorganiques contribuent fortement a l'ajustement osmotique via le processus de transport des ions, en relation avec les antitransporteurs et les canaux ioniques. Le but de cette revue consiste a inteegrer les donnees recentes sur les mecanismes d'ajustement osmotique chez les plantes et les algues, et d'illustrer la diversite des mecanismes moleeculaires relies, afin s'introduire de nouveaux concepts et nouvelles techniques dans ce champ de recherche. Chez les plantes, les manipulations genetiques incluant l'application de techniques transgeniques constituent des strategies prometteuses pour augmenter la capacite; de tolerance des plantes aux conditions de stress osmotiques. Mots-cles: solutes compatibles, stress hydriqeue, mecanisme de transport des ions, ajustement osmotique, stress salin, plantes transgeniques. [Traduit par la Redaction], Introduction In nature, many plants are adversely affected by several environmental factors that have a negative effect on survival and development. Among these environmental factors (including drought, salinity, nutrient imbalances, [...]

* Premise of the study: The goal of this study was to illuminate the evolutionary history and ecological importance of plant mixotrophy--the uptake and utilization of exogenous organic compounds. * Methods: We quantitatively assessed the effect of sugar amendments on laboratory growth of Sphagnum compactum as a representative emergent peat moss and two species of ecologically associated zygnematalean algae, Cylindrocystis brebissonii and Mougeotia sp. * Key results: Together with observations published elsewhere, our results suggest that under carbon or light limitation, the uptake of exogenous sugars by cells of charophycean algae and peat mosses may help these organisms maintain positive carbon balance. Utilization of 1% glucose by aquatic-grown algae helped to relieve dissolved inorganic carbon limitation, enhancing photoautotrophic growth by factors of 9.0 and 1.7, respectively. After an 8-wk growth period, amendments of 1% and 2% glucose enhanced air-grown moss biomass by 28 and 39 times, respectively, that of controls lacking sugar amendments. After 9 wk, 1% fructose enhanced biomass by 21 times, and 2% sucrose enhanced biomass by 31 times. * Conclusion: Our results indicate that plant mixotrophy is an early-evolved trait. The results also indicate that quantitative differences in sugar utilization by bryophytes and charophycean algae correlate with relative investments in protective cell-wall polyphenolics measured in previous studies, suggesting that sugar utilization may subsidize the cost of producing phenolic wall compounds in bryophytes. Key words: charophycean algae; Cylindrocystis; fructose; glucose; mixotrophy; Mougeotia; peat moss; Sphagnaceae; Sphagnum; sucrose. doi: 10.3732/ajb.0900341

Moisture stress and high temperatures during the summer are major factors limiting white clover (Trifolium repens L.) productivity in Uruguay. Our objective was to determine the influence of irrigation and defoliation on the growth of white clover. Two white clover cultivars were sown with tall fescue [Schedonorus arundinaceus (Schreb.) Dumort = Lolium arundinaceum (Schreb.) Darbysh.] and subjected to three defoliation regimes with and without low volume irrigations during the summer. Dry matter (DM) yield, botanical composition, number of stolons, and volunteer seedlings were recorded for 3 yr. Irrigation was the main factor affecting clover growth. Clover yields under irrigation were 5.0, 7.4, and 6.9 Mg DM [ha.sup.-1] in the first, second, and third year compared with 3.0, 5.1, and 1.6 Mg DM [ha.sup.-1] for the same years in the nonirrigated swards, Defoliation frequency did not affect pasture yields in the nonirrigated swards but the more frequent defoliation produced higher yields under irrigation after the second year. Deferring defoliation during summer did not improve clover yield or persistence. Stolons increased during autumn and winter and decreased in spring and summer. White clover declined after the second summer in the nonirrigated swards while irrigation maintained good clover stand and yield. Profuse seedlings emergences were observed but only 1% survived, suggesting that they were not a reliable mechanism for persistence. Successful reseeding occurred only at the end of the experiment after a severe drought followed by a long wet season. doi: 10.2135/cropsci2009.10.0614

Soybean [Glycine max (L.) Merr.] cultivars with increased [beta]-conglycinin (BC) and reduced glycinin (Gly) may have both food production and human health benefits. The stability of BC and Gly concentrations over different environmental conditions will be an important factor in the production of these cultivars. The objective of this study was to evaluate the effect of locations and planting dates on the protein composition of soybean genotypes with varied combinations of Gy and gy alleles for reduced Gly and increased BC concentration. Six soybean lines with different gy allele combinations and one common cultivar with only wild-type Gy alleles were grown at four locations with three planting dates at each location in 2008. There were no significant differences among planting dates for the mean concentration of BC, Gly, or their subunits. The means of locations were significantly different for all of the protein components, except for the A124 subunit of Gly. The genotype with four gy alleles produced 0 g [kg.sup.-1] of Gly across locations and planting dates, but only three of the mutant gy alleles were required to maximize BC concentration. Grain produced at different locations likely would differ in BC and Gly concentration, but planting dates at a location would not be expected to significantly affect the protein components. doi: 10.2135/cropsci2009.09.0478

We examined rock-soil-plant relationships of three endemic Cactaceae species [Cephalocereus apicicephalium E.Y. Dawson, C nizandensis (Bravo & T. MacDoug.) Buxb., and C. totolapensis (Bravo & T. MacDoug.) Buxb.] from the tropical deciduous forest of the Tehuantepec River basin, Mexico. The goal was to explain the relationships between the species, rock, soil, and calcium oxalate. The x-ray diffraction patterns from the rock and soil analyses showed that the species do not share either a rock or a soil type. Cephalocereus apicicephalium grew exclusively on outcrops of limestone with quartz on the summit to backslope of the hill and C. nizandensis grew in metalimestone outcrops on the summit and shoulder of the hill, while C. totolapensis preferred acid soils from andesite, growing also on siltstones or on mica schist on the shoulder to toeslope of the hill. Although only insignificant quantities of soluble Ca were found in the soil, weddellite is abundant in the plant tissue. This suggests that the plants take up the Ca they need and that weddellite is a genetically fixed characteristic related to deflection of excess radiation or an herbivore deterrent. Energy dispersive x-ray analysis showed that calcium oxalate crystals contained other elements (Si, Mg, Na, K, Cl, and Fe) and that these impurities modified the crystal shape, as for bipyramids in C. totolapensis. Biominerals did not change the mineral composition of the soil. The three species are distributed as edaphic or rocky islands, giving rise to their allopatric and patchy distribution across the landscape. Finally, the endemicity of the three Cephalocereus species is promoted by the parent material and the particular soil conditions in the area in which each one grows. doi: 10.2136/sssaj2009.0310

Cool-season annual clovers are used in the southeastern United States as a N source but there is limited information on the N concentration and distribution in the clover plant during the growing season. The objective of the study was to document N concentration and accumulation in shoots and roots of 'Yuchi' arrowleaf (Trifolium vesiculosurn Savi), 'Tibbee' crimson (T. incarnatum L.), 'Mt. Barker' subterranean (T. subterraneum L.), and 'Overton R-18' rose (T. hirtum All.) clovers for three growing seasons when uncut, and after cutting once, or cutting twice. When uncut, shoot N concentration decreased throughout the growing season with plant maturity from about 35 to 40 g [kg.sup.-1] in autumn to 10 to 15 g [kg.sup.-1] at maturity in late spring. Shoot N concentration after cutting once or twice was greater than in the uncut treatment on the same sampling date. Root N concentrations were about one-half that of the shoot N concentration and declined slowly during the growing season regardless of cutting treatment. When uncut, average maximum shoot N accumulations were 382 kg [ha.sup.-1] for arrowleaf, 227 kg [ha.sup.-1] for crimson, 203 kg [ha.sup.-1] for subterranean, and 226 kg [ha.sup.-1] for rose clovers. Cutting once or twice reduced maximum shoot N accumulations of all clovers except subterranean clover. Root N accumulations increased during the growing season when uncut, were not affected after cutting once but decreased after a second cutting. The optimum species as a N source would be crimson clover through April and arrowleaf clover in May and June. doi: 10.2135/cropsci2009.09.0491

Virginia wildrye (Elymus virginicus L.), a perennial cool-season grass native to the northeastern United States, grows in moist low ground and could be useful in revegetating riparian areas. In this field study, we compared six populations of Virginia wildrye originally collected from Maryland and New York with a commercial ecotype and a cultivar ('Omaha') on wet soils at three locations. All entries were transplanted into single-row field plots of 15 plants per plot at Wye, MD, Klingerstown, PA, and Big Flats, NY, in April 2004. Rows were oriented perpendicular to the slope so that each population was evaluated at the top, middle, and bottom slope positions. Survivorship, tillers per plant, and plant dry weight were assessed in 2007. Survivorship after 3 yr ranged from 57 to 76% for the six populations and averaged 85% for the ecotype and 77% for the cultivar. Tillers per plant ranged from 26 to 52 for the populations compared with 32 for the cultivar and 29 for the ecotype. Landscape position affected wildrye plants only at the Maryland site where frequently saturated soils at the bottom slope position reduced survivorship by 50%, tiller number by 60%, and plant dry weight by 82% compared with plants at the top of the slope. Most of the wild populations of Virginia wildrye were similar to the commercial cultivar and ecotype in survival, number of tillers per plant, and biomass indicating that locally adapted native populations can be used directly in conservation plantings. doi: 10.2135/cropsci2009.09.0542

Kentucky bluegrass (Poa pratensis L.) is frequently established on sports fields that receive wear during one or more seasons. Differences exist among Kentucky bluegrass cultivars for seasonal performance characteristics such as spring green-up and summer stress tolerance. The objective of this study was to determine whether the wear tolerance and recovery of Kentucky bluegrass cultivars were dependent on season. Twenty-two Kentucky bluegrass cultivars, representing nine genetically diverse Kentucky bluegrass types, were established in September 2002 in North Brunswick, NJ on a loam. The effects of simulated wear were evaluated during spring, summer, and fall in 2004 and 2005. Generally, Kentucky bluegrass was more tolerant of wear during spring than summer or fall and recovery was more rapid after spring wear. The performance of many cultivars depended on season of wear; however, 'Julia' consistently exhibited the greatest wear tolerance as well as recovery. Compact-Midnight Type cultivars ('Midnight', 'Midnight II', and 'Liberator') had good wear tolerance during fall wear, however were slow to recover after fall wear. 'Cabernet', 'Lakeshore', 'Moon Shadow', 'Limousine', and 'Jefferson' exhibited more rapid recovery from fall wear during the next spring. 'Langara', 'Bedazzled', and 'Touchdown' had poor wear tolerance and recovery during all seasons. The season(s) of play should be considered when selecting Kentucky bluegrass cultivars for sports fields. doi: 10.2135/cropsci2009.09.0479

Few studies have examined grain quality of food-grade sorghum hybrids. The objective of this study was to determine the effects of environment and hybrid on grain quality of commercially available food-grade sorghums. A randomized complete block experiment with three replications was planted in 12 environments, which included the 2004 and 2005 growing seasons and irrigated and dryland water regimes in eastern, central, and west central Nebraska and a dryland low-N environment in eastern Nebraska. Environment accounted for 5 to 140 times greater variation in measured parameters than hybrid, and the hybrid x environment interaction accounted for less than 2% of the total variation. Grain yield and kernel mass varied, with low yields of 1.4 Mg [ha.sup.-1] and kernels weighing 9.5 g 1000 [kernels.sup.-1] in the low-N 2004 environment, high grain yields of 10.5 Mg [ha.sup.-1] under irrigated conditions in central Nebraska in 2005, and kernels weighing 27.8 g 1000 [kernels.sup.-1] in the eastern Nebraska dryland 2005 environment. Harder grain was produced in 2005 than in 2004, with the west central and central 2005 environments having the lowest tangential abrasive dehulling device (TADD) removals of 14%. Non-food-grade hybrids produced higher grain yields and kernel mass than food-grade hybrids. Grain hardness was greater for non-food-grade and medium maturity hybrids when environmental means were lower (i.e., softer) but showed little or no difference in hardness when environmental means were high. Nebraska production environments have the capability to produce high quality food-grade sorghums for specific food uses to benefit both the producer and the food processor. doi: 10.2135/cropsci2009.08.0463

Studies on root development, soil physical properties, and yield are important for identifying suitable soil management practices for sustainable crop production. Field experiments with winter wheat (Triticum aestivum L.) were conducted in silt loam soil from 2005 through 2007 in arid northwestern China to determine the effects of five tillage systems on soil strength, soil moisture, crop root development, grain yield, and yield components. The five treatments were conventional tillage without wheat stubble (T), conventional tillage with wheat stubble incorporated (TSI), no-tillage without wheat stubble mulching (NT), no-tillage with wheat stubble standing (NTSS), and no-tillage with wheat stubble mulching (NTS). Compared with the T treatment, the NTSS and NTS treatments improved soil water content in the 0- to 130-cm soil depth by 10 to 17% and 15 to 25%, respectively (P < 0.05). The NTSS treatment also increased mean root length density (RLD) by 8 to 40% and crop yield by 13 to 24%, and NTS by 17 to 48% and 17 to 31%, compared with the T treatment. Yield components analysis indicated that thousand-grain weight and spike density considerations helpee explain the grain yield increases under conservation tillage systems (NT, NTSS, NTS), while spike length, number of grains per spike, and grain weight per spike failed to contribute to the model. Our results suggest that Chinese farmers should consider adopting conservation tillage practices in arid northwestern China because of benefits to soil strength, water storage, RLD, and wheat yield. doi: 10.2135/cropsci2008.10.0590

Preharvest sprouting (PHS) results in unacceptable flour quality for a portion of the mid-Atlantic soft red winter wheat (SRWW) (Triticum aestivum L.) crop annually. This research evaluates inherent dormancy in current mid-Atlantic wheat cultivars using grain falling number after delayed harvest and the weighted germination index (WGI) to predict PHS. Individual spikes from 15 wheat cultivars grown in Virginia in 2007 and 2008 were harvested at physiological maturity and seeds germinated under controlled conditions. A WGI was calculated that gave greater weight to cultivars with seeds that germinated more quickly. The WGI effectively identified very high and low dormancy SRWW cultivars; however, the influence of environment during grain fill was important, especially for cultivars with moderate dormancy. To evaluate PHS tolerance by line under natural conditions, plots were left standing up to 6 wk after normal harvest date. Final harvest falling numbers were used to separate cultivars into PHS resistance groups. Strong relationships were found among PHS resistance groups, and WGI was determined at both 10 and 30[degrees]C. This indicates that PHS resistance groups were good predictors of dormancy and relative response of cultivars to delayed harvest. The morphological characteristics of head angle, glume tenacity, and awn length had no significant effect on PHS. Artificial wetting resulted in a major loss of quality after just one event, emphasizing the need for timely wheat harvest. doi: 10.2135/cropsci2009.09.0497

Prediction of phenology is based on thermal time (TT) computation, which requires the correct definition of base ([T.sub.B]) and optimum ([T.sub.O]) temperatures. Most information on these traits came from controlled environments using a wide range of mean air temperatures ([T.sub.x]), including [T.sub.x] > [T.sub.o] and [T.sub.x]< [T.sub.B]. These conditions are rarely found in field environments. We assessed the effect on development of day-time temperatures above To during late-vegetative growth of maize (Zea mays L), and established a model based on TT computation on a per hour (T[T.sub.h], in [degrees]C h) rather than per day basis (T[T.sub.d]) for [T.sub.O] estimation. Field experiments included two temperature regimes ([T.sub.C]: control; [T.sub.H]: heated) between [V.sub.11] and tasseling of [T.sub.C]. We registered temperature at ear level, and dates of anthesis and silking. We computed developmental rates (DR), T[T.sub.h] above 8[degrees]C during treatment period (T[T.sub.h1]) and between [V.sub.11] and silking (T[T.sub.h2]), a stress index based on the quotient of differences in T[T.sub.h] ([DELTA]T[T.sub.h]) between [T.sub.H] and [T.sub.C] (SI = [DELTA]T[T.sub.h2][DELTA]T[T.sub.h1]), and [T.sub.O]. Heat stress caused a delay in flowering events, and a decline in DRs. Estimated [T.sub.B] was higher (12.7[degrees]C) than normally used in computations. Estimated [T.sub.O] was within the expected range (36[degrees]C > [T.sub.O] > 30[degrees]C), independently of [T.sub.B]. Stressful temperatures promoted a delayed in silking, identified as an increase of at least 2.14[degrees]C h in T[T.sub.h] for each degree above [T.sub.O]. Estimated [T.sub.O] differed between growing seasons (P = 0.04), suggesting possible variation due to climatic effects. doi: 10.2135/cropsci2009.07.0400

Soybean cyst nematode (Heterodera glycines Ichinohe) is the most damaging pathogen of soybean [Glycine max (L.) Merr.] in the United States. Observations in fields suggest that high H. glycines population densities are associated with high soil pH, but H. glycines and soil pH have not been linked to soybean yield. The objective of our study was to assess the relationship between soil pH and H. glycines population densities and subsequent effect on yield. Experiments were conducted in Wisconsin from 1997 to 2000 and in Iowa from 1996 to 1998. Results were consistent among the experiments and showed a positive correlation between soil pH and H. glycines population densities and a negative correlation between yield and both soil pH and H. glycines population densities in both states. In the Wisconsin experiment, yield of both H. glycines-resistant and H, glycines-susceptible cultivars decreased as pH increased, but the decrease was less with H. glycines-resistant cultivars. Overall, results indicate that H. glycines population densities and the impact of nematode population densities on soybean yield are related to soil pH; however, the mechanism of these interactions is unknown. doi: 10.2135/cropsci2009.08.0432

Field measurements of leaf gas exchange in maize (Zea mays L.) often indicate stomatal conductances higher than required to provide substomatal carbon dioxide concentrations saturating to photosynthesis. Thus maize leaves often operate at lower transpiration efficiency (TE) than potentially achievable for species with [C.sub.4] metabolism. I tested whether several maize lines described as drought resistant or drought tolerant operated with higher leaf TE than less drought-adapted lines. Field measurements of leaf TE were conducted over two seasons for five reputedly drought-resistant lines of maize and three locally grown lines not regarded as drought resistant. Midday photosynthesis, transpiration, stomatal conductance, and substomatal carbon dioxide concentration measurements were made under the ambient field conditions of air temperature and humidity in Beltsville, MD. Soil moisture was not limiting. Consistent and significant differences among the lines occurred for stomatal conductance, substomatal carbon dioxide concentration, and TE, but no significant differences among the lines occurred in photosynthesis. One drought-tolerant line had higher TE than all others tested, and one of the local lines had the lowest TE, but the drought-tolerant lines as a group did not have significantly higher TE. It is concluded that significant genotypic variation in leaf TE exists in maize, and that TE could be improved without reducing photosynthesis. doi: 10.2135/cropsci2009.11.0650

Sorghum [Sorghum bicolor (L.) Moench] is generally not cold tolerant. Enhanced germination and emergence at low temperatures would facilitate early planting and adaptation to cooler regions due to latitude or elevation. This study examined the relationship between respiration, germination, elongation, and early seedling growth, with a view toward evaluating respiration as a selection trait for improved cold tolerance in sorghum. Germination, elongation, seedling fresh wt., and [O.sub.2] uptake of 12 cultivars from different genetic backgrounds were measured at temperatures from 5 to 30[degrees]C. For most cultivars, the rates of germination and elongation were positively and linearly correlated with [O.sub.2] uptake. Other cultivars showed a plateau of germination rates at around 25[degrees]C even though respiration continued to increase at higher temperatures. Cultivars from high elevations in Ethiopia and Rwanda had the greatest respiration, germination, and elongation rates, and those from Egypt had the smallest. Factor analysis showed that germination and elongation rates were not strongly associated with shoot and root fresh wt., but respiration was associated with all variables. Respiration rates measured at 10 and 15[degrees]C had the highest association with germination and elongation rates, while respiration at 25[degrees]C was associated with seedling growth characteristics. Our study suggests that respiration can serve as a useful selection criterion for early cold tolerance in sorghum. doi: 10.2135/cropsci2009.08.0448

Cassava (Manihot esculenta Crantz) roots spoil 2 to 3 d after harvest because of postharvest physiological deterioration (PPD), which has remained an unsolved problem. Roots from different sources of germplasm were evaluated 5, 10, 20, and 40 d after harvest and some were found to be tolerant to PPD. Three genotypes showed zero levels of PPD even 40 d after harvest. Tolerance to PPD in roots with high carotenoid levels may be explained by their anti-oxidant properties. Irradiation of seeds in mutagenized populations may have silenced one of the genes involved in the expression of PPD. The tolerance to PPD found in other sources cannot be properly explained. The identification of several sources of resistance (and at least two different modes of action) suggests that now there are alternatives available for solving this problem, benefiting millions of resource-limited farmers worldwide. doi: 10.2135/cropsci2009.11.0666

The lentil improvement program of ICARDA benefits from the information generated by the Legume International Nursery Network operating globally. Over the period 1996 to 2002, 12 different types of trials comprising lentil genotypes with weights doi: 10.2135/cropsci2009.06.0342

Plants flower in particular seasons even in natural, fluctuating environments. The molecular basis of temperature-dependent flowering-time regulation has been extensively studied, but little is known about how gene expression is controlled in natural environments. Without a memory of past temperatures, it would be difficult for plants to detect seasons in natural, noisy environments because temperature changes occurring within a few weeks are often inconsistent with seasonal trends. Our 2-y census of the expression of a temperature-dependent flowering-time gene, AhgFLC, in a natural population of perennial Arabidopsis halleri revealed that the regulatory system of this flowering-time gene extracts seasonal cues as if it memorizes temperatures over the past 6 wk. Time-series analysis revealed that as much as 83% of the variation in the AhgFLC expression is explained solely by the temperature for the previous 6 wk, but not by the temperatures over shorter or longer periods. The accuracy of our model in predicting the gene expression pattern under contrasting temperature regimes in the transplant experiments indicates that such modeling incorporating the molecular bases of floweringtime regulation will contribute to predicting plant responses to future climate changes. Arabidopsis halleri | FLOWERING LOCUS C | gene regulation | natural temperature fluctuation | plant phenology modeling doi/ 10.1073/pnas.0914293107

Determining the location of buds and bud-forming meristems and hence the level of protection from heat is essential to understanding plant response to fire. Most eucalypts resprout readily from the stem (epicormic resprouting) and the base after felling or high intensity fire. In contrast, Eucalyptus regnans is one of the few eastern Australian fire-sensitive, obligate seeder eucalypts. Some authors have suggested that the relatively weak epicormic resprouting is due to a lack of bud-forming structures. Epicormic strands from the bark and outer xylem of three very large trees and two saplings were examined anatomically. Epicormic bud-forming structures were found in all samples examined. The bud-forming capacity consisted of narrow, radially elongated strips of cells of meristematic appearance. These strips were continuous from the outermost secondary xylem through to the outer bark. Bark was relatively thick at the base of the large trees, but remarkably thin above this basal skirt. Eucalyptus regnans was found to possess the apparently fire-adapted epicormic strands previously described in other eucalypts, thus showing its fire-adapted lineage. However, this fire-sensitive species apparently directs much of its resources to rapid height-growth rates in younger trees, rather than to vegetative fire survival. Key words: accessory meristems; epicormic: eucalypts; Eucalyptus regnans; fire; leaf axil; meristematic: mountain ash; Myrtaceae; resprouting. doi: 10.3732/ajb.0900158

Temporal environmental variation has profound influences on population dynamics and community structure. Examination of functional traits that influence resource uptake and allocation can illuminate how co-occurring species translate environmental variation into different demographic outcomes, yet few studies have considered interspecific differences in trait plasticity. We experimentally manipulated soil moisture to test the hypothesis that differences in morphological plasticity contribute to species differences in demographic response to unpredictable precipitation in Sonoran Desert winter annual plants. We compared plasticity of leaf traits and biomass allocation between Pectocarya recurvata (Boraginaceae) and Stylocline micropoides (Asteraceae), co-occurring species that differ in long-term demographic patterns. The species with highly variable population dynamics, Stylocline, had striking increases in leaf area and root biomass in response to an experimental increase in soil moisture. In contrast, the species with buffered long-term population dynamics, Pectocarya, did not differ in leaf morphology or biomass allocation between soil moisture treatments. Regardless of water treatment, Pectocarya had earlier reproductive phenology and greater fecundity than Stylocline, suggesting that differences in the timing of the phenological transitions from vegetative to reproductive growth may affect species' responses to precipitation pulses. Combining long-term observations with experimental manipulations provides a window into the functional underpinnings and demographic consequences of trait plasticity. Key words: Asteraceae; biomass allocation; Boraginaceae; functional trait; Pectocarya recurvata; pulse response; species coexistence; specific leaf area; Stylocline micropoides. doi: 10.3732/ajb.0900242

Circadian clocks synchronize internal processes with environmental cycles to ensure optimal timing of biological events on daily and seasonal time scales. External light and temperature cues set the core molecular oscillator to local conditions. In Arabidopsis, EARLY FLOWERING 3 (ELF3) is thought to act as an evening-specific repressor of light signals to the clock, thus serving a zeitnehmer function. Circadian rhythms were examined in completely darkgrown, or etiolated, null elf3-1 seedlings, with the clock entrained by thermocycles, to evaluate whether the elf3 mutant phenotype was light-dependent. Circadian rhythms were absent from etiolated elf3-1 seedlings after exposure to temperature cycles, and this mutant failed to exhibit classic indicators of entrainment by temperature cues, consistent with global clock dysfunction or strong perturbation of temperature signaling in this background. Warm temperature pulses failed to elicit acute induction of temperature-responsive genes in elf3-1. In fact, warm temperature-responsive genes remained in a constitutively 'ON' state because of clock dysfunction and, therefore, were insensitive to temperature signals in the normal time of day-specific manner. These results show ELF3 is broadly required for circadian clock function regardless of light conditions, where ELF3 activity is needed by the core oscillator to allow progression from day to night during either light or temperature entrainment. Furthermore, robust circadian rhythms appear to be a prerequisite for etiolated seedlings to respond correctly to temperature signals. temperature signaling | temperature entrainment | luciferase | circadian rhythms | transcription www.pnas.orglcgi/doi/10.1073/pnas.0911006107

Problem statement: In order to meet the ever increasing demand of medicinal plants, for the indigenous systems of medicine as well as for the pharmaceutical industry, some medicinal plants need to be cultivated commercially and moldavian balm (Dracocephalum moldavica) is one of them. Approach: To determine the effects of zeolite and water stress on aforementioned plant's phisiomorphological characteristics, an experiment was conducted with applying four zeolite levels and three water discharge levels during plant growth. Some growth and development parameters were measured. Results: Summarized that, zeolite did not have any significant effect on plant height and number of inteniodes but had, on the other traits. There were not a significant effect of water discharge on plant height, number of flowers and number of inteniodes but its effect on the flowering time and essential oil content was significant. Moreover, there was not an interaction between zeolite and water stress on number of flowers and number of inteniodes but this interaction was significant on the other parameters. Conclusions/Recommendations: Finally, 2 g zeolite with 50% water losses was recommended to obtain higher essential oil. Additional researches are needed to confirm the results for data from other fields and crops. Key words: Dracocephalum moldavica, moldavian balm, zeolite, water discharge, essential oils, INTRODUCTION Moldavian balm (Dracocephalum moldavica L.) is a hardy annual plant (2 ft) with aromatic, balm-scented, green foliage and belongs to family Lamiaceae. The oil content and its composition showed [...]

The study of plant responses to touch, particularly the responses of leaves, stems, and roots, has a long history. By contrast, floral responses are relatively unexplored. Stigma closure is common in the Bignoniaceae, but the factors influencing it are not well understood. We investigated factors influencing stigma closure and reopening and its effects on pollen receipt in seven Oroxylum indicum trees near Hat Yai, Thailand. The effects of pressure, conspecific and heterospecific pollen, and pollen load (the amount of pollen deposited) on stigma behavior were examined in 270 flowers (of the total 430 flowers evaluated in the entire study). Pressure alone resulted in faster closure than did conspecific pollination and faster reopening than did heterospecific pollination. Stigmas never reopened after conspecific pollination. Pollen load had no effect on stigma behavior. Stigmas discriminated between conspecific and foreign pollen; they reopened only after pollination with the latter. A manipulative experiment revealed that stigma closure did not affect the number of conspecific pollen grains received. We also counted pollen tubes in styles that were either hand-supplemented with outcross conspecific pollen or open-pollinated. Pollen tube numbers were highest after light pollination (~900 grains), indicating that interference among pollen grains may occur after pollination with very heavy loads (>6000 grains). Possible fitness consequences of these responses are discussed. Key words: bat pollination: Bignoniaceae floral movement: Oroxylum indicum; stigma closure. doi: 10.3732/ajb.0900100

The adaptation of introduced perennial grasses in southern Australia expanded with the discovery of the Mediterranean grass phalaris (Phalaris aquatica L.) as a valuable pasture species, and the introduction of Mediterranean ecotypes of orchardgrass (Dactylis glomerata L.), and tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] displaying summer dormancy. In contrast, native grasses of agricultural importance appear to have little or no endogenous summer dormancy. A brief history of cultivar development from Mediterranean germplasm is presented. Recent developments include cultivars based on summer-dormant subsp, hispanica orchardgrass and the release of Mediterranean-type cultivars of tall fescue. Phalaris depends on a deep root system and summer dormancy for its summer survival. Cultivars based on more summer-dormant Moroccan ecotypes have been developed for drier environments. Work to improve phalaris for hotter, summer-dominant rainfall areas is being extended to enhance the range of perennials for the cropping zone. In addition to ecotype evaluation, breeders should employ recurrent selection in cultivars and populations such as those developed recently for low-to medium-rainfall areas in orchardgrass and tall fescue. doi: 10.2135/cropsci2009.06.0321

The significantly lower annual rainfall experienced in Australia over the past decade together with projections of long-term climate change has placed increased emphasis on the use of pasture plants with superior tolerance to environmental stress, particularly drought, to ensure persistence for the grazing industries. Summer dormancy is one of the more important traits that grasses have to adapt to environments where there is little, variable, or no summer rainfall. In this article, the role that the summer dormancy trait has played in enhancing the survival of temperate perennial grasses in Australia is reviewed with special reference to orchardgrass (cocksfoot; Dactylis glomerata L.) and tall fescue [Lolium arundinaceurn (Schreb.) Darbysh.]. The performance of cultivars and populations with this trait is assessed in comparison to germplasm without the trait. Other major factors such as the contribution of rooting depth to stress tolerance and their possible relationship with summer dormancy are documented and evaluated. Current knowledge of the physiological basis by which summer dormancy improves survival of summer drought is also summarized. doi: 10.2135/cropsci2009.06.0320

Plant evolution in climatic areas with marked seasonal changes has led to species adaptation to periods of high and low temperatures and drought and to significant changes in their morphological structure and annual developmental cycles. One characteristic of these adaptations is the state of dormancy, in which the plants do not exhibit any visible external growth. This paper reviews dormancy and florogenesis as main components of the survival strategies of perennial herbaceous plants. Summer dormancy protects plants from negative effects of water deficit and high temperatures on vegetative and reproductive organs, and forces plant species to schedule their active development in more favorable seasons. Mechanisms of summer survival vary among species and provide different modes of adaptation to harsh environments. The interrelationship between florogenesis and dormancy is most probably controlled in meristems, where the survival strategy of the plant, including vegetative growth, flowering, drought tolerance, and formation of storage organs, is determined. Mechanisms by which summer dormancy confers summer drought survival warrant further investigation for improving agronomic and environmental traits of perennial plants. doi: 10.2135/cropsci2009.06.0318

Summer dormancy can lead to increased drought tolerance and persistence in coolseason grasses. Here we describe efforts to develop summer-dormant cultivars in the United States. Summer-dormant grasses are generally well adapted to the Southern Plains but have poor persistence as well as low productivity east and north of this region because of limited winter hardiness and other factors. This limited geographic adaptation is thought to be due to germplasm background rather than the summer dormancy trait. Depending on the target environment, improved cultivars could be developed by selecting within existing summer-dormant material or by crossing the trait into adaptive germplasm. Difficulties in phenotyping summer dormancy, and in some instances fertility barriers across germplasm sources, will need to be overcome to utilize the latter approach. doi: 10.2135/cropsci2009.06.0329