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Plants that grow in high density communities activate shade avoidance responses to consolidate light capture by individuals. Although this is an evolutionary successful strategy, it may not enhance performance of the community as a whole. Resources are invested in shade responses at the expense of other organs and light penetration through the canopy is increased, allowing invading competitors to grow better. Here we investigate if suppression of shade avoidance responses would enhance group performance of a monoculture community that is invaded by a competitor. Using different Arabidopsis genotypes, we show that suppression of shade‐induced upward leaf movement in the pif7 mutant increases the pif7 communal performance against invaders as compared to a wild‐type canopy. The invaders were more severely suppressed and the community grew larger as compared to wild type. Using computational modelling, we show that leaf angle variations indeed strongly affect light penetration and growth of competitors that invade the canopy. Our data thus show that modifying specific shade avoidance aspects can improve plant community performance. These insights may help to suppress weeds in crop stands., Hyponastic response in canopies facilitates light interception, but also light penetration. Inhibition of this response to neighbours increased canopy biomass, canopy closure and suppression of competitors.

Under field conditions, plants are subject to wind-induced movement which creates fluctuations of light intensity and spectral quality reaching the leaves, defined here as windflecks. Within this study, irradiance within two contrasting wheat (Triticum aestivum) canopies during full sun conditions was measured using a spectroradiometer to determine the frequency, duration and magnitude of low- to high-light events plus the spectral composition during wind-induced movement. Similarly, a static canopy was modelled using three-dimensional reconstruction and ray tracing to determine fleck characteristics without the presence of wind. Corresponding architectural traits were measured manually and in silico including plant height, leaf area and angle plus biomechanical properties. Light intensity can differ up to 40% during a windfleck, with changes occurring on a sub-second scale compared to similar to 5 min in canopies not subject to wind. Features such as a shorter height, more erect leaf stature and having an open structure led to an increased frequency and reduced time interval of light flecks in the CMH79A canopy compared to Paragon. This finding illustrates the potential for architectural traits to be selected to improve the canopy light environment and provides the foundation to further explore the links between plant form and function in crop canopies.

Plant growth and development is impacted by the ability to capture resources including sunlight, determined in part by the arrangement of plant parts throughout the canopy. This is a very complex t...

Optimizing crops to improve light absorption and CO2 assimilation throughout the canopy is a proposed strategy to increase yield and meet the needs of a growing population by 2050. Globally, the greatest population increase is expected to occur in Sub‐Saharan Africa where large yield gaps currently persist; therefore, it is crucial to develop high‐yielding crops adapted to this region. In this study, we screened 50 cowpea (Vigna unguiculata (L.) Walp) genotypes from the multi‐parent advanced generation inter‐cross (MAGIC) population for canopy architectural traits, canopy photosynthesis, and water‐use efficiency using a canopy gas exchange chamber in order to improve our understanding of the relationships among those traits. Canopy architecture contributed to 38.6% of the variance observed in canopy photosynthesis. The results suggest that the light environment within the canopy was a limiting factor for canopy CO2 assimilation. Traits favoring greater exposure of leaf area to light such as the width of the canopy relative to the total leaf area were associated with greater canopy photosynthesis, especially in canopies with high biomass. Canopy water‐use efficiency was highly determined by canopy photosynthetic activity and therefore canopy architecture, which indicates that optimizing the canopy will also contribute to improving canopy water‐use efficiency. We discuss different breeding strategies for future programs aimed at the improvement of cowpea yield for the Sub‐Saharan African region. We show that breeding for high biomass will not optimize canopy CO2 assimilation and suggest that selection should include multiple canopy traits to improve light penetration., In this study, 50 cowpea (Vigna unguiculata (L.) Walp) genotypes from the multi‐parent advanced generation inter‐cross (MAGIC) population were screened for canopy architectural traits, canopy photosynthesis, and water‐use efficiency using a canopy gas exchange chamber in order to improve our understanding of the relationship among those traits. Traits favoring greater exposure of leaf area to light such as the width of the canopy relative to the total leaf area were associated with greater canopy photosynthesis, especially in canopies with high biomass. Canopy water‐use efficiency was highly determined by canopy photosynthetic activity and therefore canopy architecture, which indicates that optimizing the canopy will also contribute to improving canopy water‐use efficiency.

Recent work suggests that savanna woody plant species utilise two different strategies based on their defences against herbivory; a low nutrient/high chemical defence strategy and a nutrition paired with mostly architectural defences strategy. The concept that chemical and structural defences can augment each other and do not necessarily trade-off has emanated from this work. In this study, we examine woody plant defence strategies, how these respond to herbivore removal and how they affect plant growth in an East African savanna. At three paired long-term exclosure sites with high browser and mixed-feeder densities at Mpala Ranch, Kenya, we investigated: (a) whether defences employed by the dominant fine- and broad-leaved woody savanna species form defence strategies and if these align with previously proposed strategies, (b) how nine key plant defence traits respond to herbivore removal and (c) how effective the different defence strategies are at protecting against intense herbivory (by measuring plant growth with and without herbivores present). We identified three defence strategies. We found a group (a) with high N, short spines and high N-free secondary metabolites, a group (b) with high N, long spines and low N-free secondary metabolites and a group (c) with moderate N, no spines and low N-free secondary metabolites (most likely defended by unmeasured chemical defences). Structural defences (spine length, branching) were generally found to be induced by herbivory, leaf available N increased or did not respond, and N-free secondary metabolites decreased or did not respond to herbivory. Species with long spines combined with increased “caginess” (dense canopy architecture arising from complex arrangement of numerous woody and spiny axis categories) of branches, maintained the highest growth under intense browsing, compared to species with short spines and high N-free secondary metabolites and species with no spines and low N-free secondary metabolites. Synthesis. At our study site, structural traits (i.e. spines, increased caginess) were the most inducible and effective defences against intense mammalian herbivory. We propose that high levels of variability in the way that nutrient and defence traits combine may contribute to the coexistence of closely related species comprising savanna woody communities.

Little is known about how water deficit affects cotton (Gossypium hirsutum L.) canopy architecture and the vertical distribution of photosynthesis within the canopy. The objective of this 2-yr field experiment was to determine the effects of reduced water supply on (i) surface area distribution within a cotton canopy, (ii) the transmission of photosynthetically active radiation (PAR) within the canopy, and (iii) the contribution of leaves and non-leaf organs at different positions within the canopy to whole-canopy photosynthesis. The results showed that compared with conventional irrigation, water deficit reduced leaf surface area in the upper canopy layer by 20 to 46% and increased PAR transmission into the mid-canopy layer by 38 to 73%. Slight water deficit reduced leaf photosynthetic rates in the upper canopy layer by 24%, but increased leaf photosynthetic rates in the mid-canopy layer by 23% and the lower canopy layer by 79%. Compared with conventional irrigation, slight water deficit had no significant effect on yield, whereas moderate water deficit significantly reduced both variables. Leaves, especially those in the upper canopy layer, were the main drivers of whole-canopy photosynthesis. On a percentage basis, non-leaf organs accounted for

Crop reflectance using ground-based sensors has the potential to provide information on crop N status in real-time. However, the unique physiological and structural characteristics of cotton (Gossypium hirsutum, L.) complicate normalized difference vegetation index (NDVI)-based inferences on cotton N status. Therefore, the objectives of this study were to (i) determine the sensitivity of selected sensors and resulting NDVI measurements to different levels of fertilizer N; (ii) determine relationships between sensors and biophysical measurements; and (iii) compare absolute NDVI readings reported by each sensor. Field trials were conducted during crop years conducted from 2008 through 2010 at Mississippi State, MS. Fertilizer N rates of 0, 45, 90, and 135 kg N ha -1 were applied and replicated four times to establish N-induced growth differences. Sensors used included the Yara N Sensor (Yara International ASA, Oslo, Norway), GreenSeeker (GS) Model 505 Optical Sensor Unit (NTech Industries, Inc., Ukiah, CA) and Crop Circle (CC) Model ACS-210 (Holland Scientific, Inc., Lincoln, NE). Sensor readings failed to consistently predict cotton leaf N status before early flowering; however, plant height relationships with NDVIs were strong. Comparison of sensor response curves to fertilizer N resulted in no significant differences in slope values, although consistent, significant differences in y intercepts were noted beginning at early flowering and continuing through peak flowering. Greater accuracy in the detection of cotton leaf N status may require the utilization of an index which is less responsive to changes in plant height or canopy architecture. Furthermore, the magnitude of canopy reflectance-based NDVI values differed across sensors.

Canopy storage capacity is influenced by several variables, including canopy surface area, canopy architecture, and wind. Different species with the same canopy area, but with differences in leaf hydrophobicity and water droplet retention, may produce different values of canopy storage capacity. The objective of this study was to investigate if leaf hydrophobicity and water droplet retention are additional influences on canopy storage capacity. Specifically, this study tested the hypothesis that species with the highest leaf hydrophobicity and the lowest water droplet retention had the lowest canopy storage capacity on a per leaf area basis. Seven tree species from Colorado, United States were selected for experimentation. Five branches from each species were lopped, positioned under a rainfall simulator, and connected to a balance to record the mass gain of the branches by rainfall interception during 17 min of rainfall simulation. Each branch was destructively sampled following rainfall simulation to calculate the leaf and woody surface areas. The rank order of leaf surface storages at canopy storage capacity for each species corresponded to the rank order of leaf hydrophobicity and water droplet retention for each species. Species with the highest leaf surface storage had the lowest leaf hydrophobicity and the lowest water droplet retention. The significance of leaf hydrophobicity and water droplet retention as variables that influence canopy storage capacity is a largely unexplored topic in ecohydrology. Copyright © 2012 John Wiley & Sons, Ltd.

Summary Fractal analysis can provide a unique mathematicaltool to quantify the geometry of irregular andcomplex plant canopies. This study demonstrated thata single numerical fractal dimension (FD) valuederived from an image taken from above the plantcanopy could differentiate between and rank thecanopies of a range of plant species. We alsoinvestigated the influence of canopy architecture andsurface characteristics on spray retention. Multipleregressions were used to derive mathematical relation-ships and develop a spray retention model. It wasdiscovered that the FD value can successfully be usedto replace the statistically generated plant morpho-logical factor (M p4 ) used in a previous retentionmodel, with the major advantage being that theretention model now only involves variables that canbe readily measured. There is an excellent relationship(R 2 = 0.99) between actual spray retention per plant(lL) and that predicted by the model incorporatingthe FD. The spray retentiveness of the plant speciesstudied was ranked using a numerical index based onplant canopy architecture and surface characteristics.Keywords: fractals, fractal dimension, plant canopycharacterisation, spray retention, spray retentiveness,retention model, arable crops and weeds.P

Over the past two decades, an ecophysiological model has been developed for annual horticultural crops and weeds, which has the powerful ability to predict the growth of plants in monoculture and mixed species stands from parameter values derived from plants grown in isolation, even if the species display contrasting canopy architecture. The model can also simulate the effects of different spatial arrangements on plant growth. The purpose of the model is to describe, in simple yet mechanistically-based terms, the effects of contrasting environments and competitive interactions on the growth of individual plants. In the simplest form of the model, growth is described by an empirical growth equation, using time calculated from an integration of the growth-promoting effects of environmental factors. More complex versions of the model include a self-shading component, which provides an algorithm for inter-plant competition based on crown zone areas. This model is termed the 'Conductance model' and this article outlines its development, applications to date, goodness of fit to experimental data, and discusses its strengths and weaknesses and scope for further testing and application. This article, which is dedicated to the late David Aikman, also sets out how the model can be applied to simulating weed-crop competition from simple data sets.

Summary 1Many studies discuss the adaptive value of plant architecture, but few have actually measured architectural effects on plant growth and survival. In this study, sapling growth and survival are related to crown traits for two tree species, Trophis mexicana (Liebm.) Bur. and Pseudolmedia oxyphyllaria Donn. Sm., in the Los Tuxtlas lowland rainforest of Mexico. The traits investigated were crown width, crown depth, number of leaves, number of leaves per unit crown area (horizontal self-shading), and number of leaves per unit silhouette area (vertical self-shading). 2Self-shading indices decreased with crown size, but were unaffected by the number of leaves per tree. Larger crowns thus had more diffuse foliage, with less self-shading. 3The number of leaves had positive effects on growth and survival, while self-shading indices had no effect. This indicates that shaded leaves do not necessarily have negative carbon balances. 4Negative effects of crown width on horizontal crown growth, and positive effects on vertical crown growth, suggest that saplings tend to grow towards a shape intermediate between the narrow and wide crown extremes. 5Survival was positively correlated with crown width in Pseudolmedia, and with the number of leaves in Trophis. Apparently, dependence of survival on crown traits differed among species. 6Crown traits affected plant growth and survival, but the hypothesis emerging from light-limited carbon acquisition was confounded by other factors, such as tree size and the inherent branching patterns. 7Crown traits are good and rather simple predictors of future sapling growth and survival, and may help foresters to select potential crop trees.

Summary • Although canopy architecture is a prime determinant of forest functioning and productivity, it has received little attention when examining forest responses to rising atmospheric CO2 concentrations. In this study different characteristics of crown architecture of two Populus species and one hybrid were investigated within a high-density poplar plantation. A free-air CO2 enrichment (FACE) facility was used to mimic future elevated CO2 concentrations. • Canopy depth and branching patterns were studied, and detailed branch characteristics such as branch dimension, inclination, and internodal length were assessed for the three poplar species in the FACE and control treatments. • Effects of elevated CO2 were restricted to a significantly increased canopy depth and longer internodal lengths after two years of CO2 enrichment. Additionally, branch dimensions and sylleptic branch numbers were increased by FACE, but responses were variable among growing seasons and species. However, FACE did not affect branch angles of origin and termination. • Crown architecture was modified mainly through a growth stimulation in response to FACE. Nevertheless, important differences among species were observed which may influence future CO2 responses when competition will become more important.

Identifying corn (Zea mays L.) genotypes with faster rates of seedling emergence and leaf appearance is important in developing a corn crop with earlier canopy closure and better seasonal light interception. A greenhouse experiment was conducted twice to investigate whether corn genotypes known to vary in canopy architecture and yield potential differed in rates of seedling emergence and leaf appearance. The experiment was arranged in a randomized complete block design utilizing seven genotypes: five of the newly developed Leafy reduced-stature (LRS) types (LRS1, LRS2, LRS3, LRS4 and LRS5), one conventional type [Pioneer 3979 (P3979)], and one late-maturing big-leaf (LMBL) type. Five seeds were planted in each pot and seedling emergence was recorded every day until all seeds emerged. Leaf appearance was recorded from seedling emergence until the plants reached anthesis. There was variability among the genotypes for both seedling emergence and leaf appearance rate. Mean seedling emergence values of greater than 90 % were achieved by four of the five LRS genotypes, and the LRS types generally emerged more rapidly than the others. Leaf appearance rate showed linear increases over time; however, LRS genotypes (in particular LRS3, LRS4 and LRS5) had more rapid leaf appearance rates than the others. The LMBL hybrid ranked last for both seedling emergence (

Weed interference with the growth and yield of corn plants is affected by both mechanical and chemical means of weed control. Recently, corn hybrids accumulating more leaf area, maturing earlier, yielding better in narrower row spacings and tolerating higher plant populations better than conventional hybrids have been developed. Because of more rapid leaf area accumulation during the earliest stages of canopy development and overall canopy architecture, they may be more susceptible to damage due to mechanical weed control. The objective of this study was to assess the response of corn hybrids with a wide range of canopy architectures to chemical and mechanical (rotary hoeing) weed control, with an emphasis on quantifying morphology and grain yield responses. Field experiments were conducted in 1997 and 1998 at Ste. Anne de Bellevue, Quebec. Three hybrids were tested: leafy reduced-stature (LRS1 and LRS2), and the conventional hybrid Pioneer 3979 (P3979). Rotary hoeing alone had very little effect, while herbicide application reduced the interference of weeds with growth and grain yield of all hybrids. Hybrid P3979 had more total leaf area than LRS1 and LRS2, but the percentage of leaf area above the ear was much higher for LRS hybrids (70 %) than for P3979 (51 %). Generally, LRS hybrids were much shorter with more leaf area above the ear than P3979, contributing to the large differences in canopy architecture between the LRS hybrids and P3979. However, morphology and grain yield response of hybrids to rotary hoeing and herbicide weed control was not different, indicating that the new hybrids were not more susceptible to damage caused by mechanical weed control than a corn hybrid with a conventional canopy architecture. Reaktionen von Maishybriden mit unterschiedlich strukturiertem Blatterdach gegenuber chemischer und mechanischer (Hackfrase) Unkrautkontrolle: Morphologie und Ertrag Unkrautwirkung hinsichtlich des Wachstums und Ertrages von Maispflanzen wird sowohl durch mechanische als auch chemische Mittel der Unkrautbekampfung beeinflusst. Kurzlich entwickelte Maishybriden mit groserer Blattflache und Fruhreife brachten in enger Reihenstellung und Toleranz gegenuber hohen Bestandesdichten bessere Ertragleistungen als konventionelle Hybriden. Aufgrund des schnelleren Blattflachenwachstums wahrend der ersten Entwicklung des Blattdaches und der Gesamtstruktur des Blattdaches konnte vermutet werden, dass sie empfindlicher gegenuber Schaden als Folge mechanischer Unkrautkontrolle sein wurden. Ziel dieser Untersuchung war es, die Reaktion von Maishybriden eines weiten Bereiches der Blattdachstruktur gegenuber chemischen und mechanischen (Hackfrase) Unkrautkontrolle wurde gepruft, wobei die Quantifizierung der Morphologie und der Kornertragsreaktionen besondere Beachtung fanden. Die Feldexperimente wurden in den Jahren 1997 und 1998 an der Ste. Anne-de-Bellevue, Quebec durchgefuhrt. Drei Hybriden wurden untersucht: Blatt-reduzierter Typ (LRS1 und LRS2) und konventionelle Hybriden pioneer 3979 (P3979) wurden gepruft. Hackfrasen allein hatte einen geringen Einfluss, wahrend Herbizidanwendung die Auswirkungen der Unkrauter hinsichtlich Wachstum und Kornertrag bei allen Hybriden reduzierte. Die Hybride P3979 hatte eine insgesamt grosere Blattflache als LRS1 und LRS2; der Prozentanteil der Blattflache oberhalb des Kolbens war bei LRS-Hybriden (70 %) erheblich hoher als bei P3979 (51 %). Grundsatzlich kann festgestellt werden, dass LRS-Hybriden wesentlich kurzer mit groserer Blattflache oberhalb des Kolbens als P3979 waren; dies trug zu den grosen Unterschieden in der Blattdachstruktur zwischen LRS-Hybriden und P3979 bei. Allerdings war die Reaktion der Morphologie und des Kornertrages der Hybriden gegenuber Hackfrase-und Herbizidanwendung in der Unkrautkontrolle nicht unterschiedlich; dies lasst vermuten, dass die neuen Hybriden nicht starker-anfallig gegenuber Schaden als Folge mechanischer Unkrautbekampfung sind als Maishybriden mit konventioneller Blattdachstruktur sind.

Water stress was imposed by watering withholding or application of PEG during the period following ligule emergence of flag leaves or fifth leaves. Treatment reduced markedly the downward rotation of these youngest fully expanded leaves, and the angle finally reached. Leaf angle changes appear to be sensitive indicators of water shortage in wheat

(...) An experiment was conducted to determine the crop responses to temperature in naturally lighted, temperature- and CO 2 -controlled plant growth chambers. The experiment was conducted at five temperatures and measurements were made of several plant parameters. A preliminary experiment showed that mepiquat chloride (MC) caused a dramatic reduction in plant height and number of main-stem nodes. (...)

Summary Competitive crop cultivars offer a potentially cheap option to include in integrated weed management strategies (IWM). Although cultivars with high competitive potential have been identified amongst cereal crops, competitiveness has not traditionally been considered a priority for breeding or farmer cultivar choice. The challenge of managing herbicide‐resistant weed populations has, however, renewed interest in cultural weed control options, including competitive cultivars. We evaluated the current understanding of the traits that explain variability in competitive ability between cultivars, the relationship between suppression of weed neighbours and tolerance of their presence and the existence of trade‐offs between competitive ability and yield in weed‐free scenarios. A large number of relationships between competitive ability and plant traits have been reported in the literature, including plant height, speed of development, canopy architecture and partitioning of resources. There is uncertainty over the relationship between suppressive ability and tolerance, although tolerance is a less stable trait over seasons and locations. To realise the potential of competitive crop cultivars as a tool in IWM, a quick and simple‐to‐use protocol for assessing the competitive potential of new cultivars is required; it is likely that this will not be based on a single trait, but will need to capture the combined effect of multiple traits. A way needs to be found to make this information accessible to farmers, so that competitive cultivars can be better integrated into their weed control programmes.