Light Interception Capacity Research Articles

Contrasting light capture strategies between shade-tolerant and -intolerant tree seedlings responding to solar canopy spectral composition

Forest regeneration is a crucial ecological process for promote self-reproduction and restoration, which is essential for maintaining complex community structure and preserving biological resources. Although sunlight have been considered as the main driver of forest regeneration, how light quality shapes functional traits of seedlings is poorly understood in the forest understorey, where spectral compositions of solar radiation change dramatically. We investigated the responses of 15 typical functional traits of Pinus koraiensis and Quercus mongolica to five filter treatments that differed in the spectral transmittance: (a) 95 % of solar radiation was transmitted (280–700 nm); (b) ultraviolet (UV)-B radiation was attenuated (>315 nm); (c) all UV radiation was attenuated (>400 nm); (d) all UV radiation and blue light was attenuated (>500 nm); (e) all UV radiation, blue-green light was attenuated (>580 nm). Our results showed that functional traits responded to UV-B radiation (contrasting treatment [a] vs. [b]) with species-dependence, but consistently showed a positive response to blue light (contrasting treatment [c] vs. [d]). UV-B radiation decreased the relative growth rate (RGR) and leaf area ratio (LAR) of P. koraiensis seedlings by 48 % and 42 %, respectively; however, it increased seedling height, total leaf area (TLA), and above-ground biomass of Q. mongolica. Blue light consistently increased LAR and RGR of two species. Furthermore, Q. mongolica was more plastic in morphological traits (including plant height and TLA) and root/shoot ratio than P. koraiensis to the single spectral region (UV-B, UV-A, blue, and green light), but opposite in physiological and biochemical traits (such as chlorophyll and anthocyanidin). These suggest that two studied species have evolved different light capture strategies in the understorey: Q. mongolica seedlings tended to adjust morphology and biomass allocation to enhance light interception capacity, while P. koraiensis seedlings preferred to adjust physiological and biochemical traits to enhance light utilization efficiency. A better understanding how canopy spectral compositions affect seedling regeneration may provide a new insight for future forest management (i.e. the appropriate gap creation or tree species combination).

Multi-environment assessment of a yellow hemp (Cannabis sativa L.) cultivar’s eco-physiology and productivity under varying levels of nitrogen fertilisation

Yellow stalked cultivars of hemp (Cannabis sativa L.) were reported to have a superior fibre processability than green cultivars, but the effects of the yellow trait on productivity and ecophysiology of hemp remain unexplored. It is hypothesised that yellow stalked cultivars are characterised by a low Nitrogen Uptake Efficiency. Three field scale experiments involving a yellow cultivar ('Fibror 79') and a green one ('Futura 75') grown under varying levels of nitrogen fertilisation were conducted in Northern Italy and in Wales, to investigate the effects of the yellow trait on hemp productivity and eco-physiology. The results showed that 'Fibror 79' displays a slightly lower biomass productivity than 'Futura 75' under nitrogen-limiting conditions, owing to lower Leaf Area Index and light interception capacity during the early growth phase, and potentially due to a lower radiation use efficiency. However, the productivity was not significantly different between cultivars under non-limiting nitrogen conditions. The Nitrogen Uptake Efficiency did not differ between the two cultivars, which failed to support the hypothesis of this work. Instead, Nitrogen Use Efficiency and Nitrogen Utilisation Efficiency were significantly higher for 'Futura 75' than for 'Fibror 79' under nitrogen-limiting conditions. 'Futura 75' appeared better suited than 'Fibror 79' for dual- and multi-purpose production in Italy, while the reverse was true in Wales. 'Fibror 79' better suits a strategy of single-use fibre production owing to its higher bast fibre content and fibre yield.

Physiological and behavioral responses of feedlot sheep with and without access to artificial shade

Artificial shading is widely used to provide thermal comfort to animals and has been extensively researched due to its relationship with their welfare and performance. This study examines the physiological and behavioral traits of sheep in a feedlot system with and without access to shade. Twenty male Santa Inês × Dorper crossbred sheep with an initial average weight of 25 kg were used in the experiment. The animals were kept in two collective stalls, one of which was equipped with a polypropylene mesh shade net with 80% light interception capacity. The experiment was conducted in the feedlot of the Fazenda Escola farm at UEG, São Luís de Montes Belos Campus, state of Goiás, Brazil. Environmental indices (ambient temperature, relative humidity, temperature-humidity index), respiratory rate (RR), rectal temperature (RT) and surface temperature (ST) were measured once weekly and behavioral assessments were performed one day after the physiological assessment, between 07h00 and 19h00. The following behaviors were evaluated: feeding, rumination, rest/sleep, social, play and anomalous activities. There were no significant differences for the analyzed variables and treatments. Animals with access to shade had the following physiological results: RR - 75.06 mov. min-1; ST - 33.03 ºC; and RT - 39.21 ºC. Those without access to shade, in turn, showed the following indices: RR - 81.52 mov. min-1; ST - 33.45 ºC; and RT - 39.43 ºC. The evaluated behaviors did not differ significantly, averaging 226.11 and 225.44 min (feeding), 153.33 and 149.44 min (rumination), 341.39 and 339.72 min (rest/sleep) and 152.50 and 154.72 min (other activities) recorded in the sheep with and without access to shade, respectively. Despite the lack of differences between the analyzed responses, the animals with access to artificial shade showed greater comfort, welfare and quality of life.

Liguleless1, a Conserved Gene Regulating Leaf Angle and a Target for Yield Improvement in Wheat.

A major challenge in modern agriculture is to increase crop yield with diminishing agricultural land to feed the fast-growing global population. The erect leaf phenotype is a highly desirable trait that allows for higher planting density and maximizes light interception capacity and thus increases

Phytochrome B enhances plant growth, biomass and grain yield in field-grown maize.

Phytochrome B (phyB) is a photosensory receptor important for the control of plant plasticity and resource partitioning. Whether phyB is required to optimize plant biomass accumulation in agricultural crops exposed to full sunlight is unknown. Here we investigated the impact of mutations in the genes that encode either phyB1 or phyB2 on plant growth and grain yield in field crops of Zea mays sown at contrasting population densities. Plants of maize inbred line France 2 wild type (WT) and the isogenic mutants lacking either phyB1 or phyB2 (phyB1 and phyB2) were cultivated in the field during two seasons. Plants were grown at two densities (9 and 30 plants m-2), irrigated and without restrictions of nutrients. Leaf and stem growth, leaf anatomy, light interception, above-ground biomass accumulation and grain yield were recorded. At high plant density, all the lines showed similar kinetics of biomass accumulation. However, compared with the WT, the phyB1 and phyB2 mutations impaired the ability to enhance plant growth in response to the additional resources available at low plant density. This effect was largely due to a reduced leaf area (fewer cells per leaf), which compromised light interception capacity. Grain yield was reduced in phyB1 plants. Maize plants grown in the field at relatively low densities require phyB1 and phyB2 to sense the light environment and optimize the use of the available resources. In the absence of either of these two light receptors, leaf expansion is compromised, imposing a limitation to the interception of photosynthetic radiation and growth. These observations suggest that genetic variability at the locus encoding phyB could offer a breeding target to improve crop growth capacity in the field.

The relationship between leaf area growth and biomass accumulation in Arabidopsis thaliana.

Leaf area growth determines the light interception capacity of a crop and is often used as a surrogate for plant growth in high-throughput phenotyping systems. The relationship between leaf area growth and growth in terms of mass will depend on how carbon is partitioned among new leaf area, leaf mass, root mass, reproduction, and respiration. A model of leaf area growth in terms of photosynthetic rate and carbon partitioning to different plant organs was developed and tested with Arabidopsis thaliana L. Heynh. ecotype Columbia (Col-0) and a mutant line, gigantea-2 (gi-2), which develops very large rosettes. Data obtained from growth analysis and gas exchange measurements was used to train a genetic programming algorithm to parameterize and test the above model. The relationship between leaf area and plant biomass was found to be non-linear and variable depending on carbon partitioning. The model output was sensitive to the rate of photosynthesis but more sensitive to the amount of carbon partitioned to growing thicker leaves. The large rosette size of gi-2 relative to that of Col-0 resulted from relatively small differences in partitioning to new leaf area vs. leaf thickness.

Understory light predictions in mixed conifer mountain forests: Role of aspect-induced variation in crown geometry and openness

Predicting light availability in forest understory is a key step in the modeling of forest dynamics. Aspect is often the main source of environmental variation in mountain forests, and so aspect-induced differences in crown geometry and transparency can be expected to affect light transmission through the canopy and modify understory light predictions. To gain a better understanding of the effects of aspect on the light interception capacity of forest trees, we determined crown allometry and crown openness (CO) in 120 adult trees of three common conifer species in the Pyrenees (mountain pine, Scots pine and silver fir), sampled in eight montane-subalpine forests that each included two contrasting aspects. CO was calculated from digital photographs and several crown outlines were automatically determined to prevent user bias. We also calculated crown irregularity as the difference between crown surface area for the tightest and loosest outlines. Predictions of understory light availability obtained from a forest dynamics model were compared with actual values obtained from 115 hemispherical photographs. Crown length and CO varied across species following previous rankings of shade tolerance. Both pines had longer and wider crowns in the north aspect, whereas fir crown geometry was not affected by aspect. CO depended largely on the method chosen for determining crown outline, ranging from 0.10 to 0.56, and the tightest outline provided the best predictions of understory light (slope=0.89, R2=0.46). CO was also significantly affected by tree size and plot aspect (p<0.001): crowns in southern-oriented plots were more open for mountain pine and silver fir, whereas Scots pine showed the opposite trend. Predictions of understory light were significantly improved when crown geometry and openness were allowed to vary according to plot aspect (slope of the regression: 0.95, R2=0.50). Our results suggest that aspect should be explicitly considered when modeling ecological processes and dynamics in mixed mountain forests given its influence on both abiotic conditions and crown responses to them.

PEACH PLANTING SYSTEMS IN SOUTHERN ITALY: ECOPHYSIOLOGICAL ASPECTS AND TECHNICAL DEVELOPMENTS

PEACH PLANTING SYSTEMS IN SOUTHERN ITALY: ECOPHYSIOLOGICAL ASPECTS AND TECHNICAL DEVELOPMENTS

Do open‐top chambers overestimate the effects of rising CO2 on plants? An analysis using spring wheat

AbstractThe microclimate in facilities for studying effects of elevated CO2 on crops differs from ambient conditions. Open‐top chambers (OTCs) increase temperature by 1–3 °C. If temperature and CO2 interact in their effect on crops, this would limit the value of OTC experiments. Furthermore, interaction of CO2 and temperature deserves study because increases in atmospheric CO2 concentration are expected to cause global warming.This paper describes two experiments in which a recently developed cooling system for OTCs was used to analyse the effects of temperature on photosynthesis, growth and yield of spring wheat (Triticum aestivum L., cv. Minaret). Two levels of CO2 were used (350 and 700 ppm), and two levels of temperature, with cooled OTCs being 1.6–2.4 °C colder than noncooled OTCs.Photosynthetic rates were increased by elevated CO2, but no effect of temperature was found. Cross‐switching CO2 concentrations as well as determination of A–Ci curves showed that plant photosynthetic capacity after anthesis acclimated to elevated CO2. The acclimation may be related to the effects of CO2 on tissue composition: elevated CO2 decreased leaf nitrogen concentrations and increased sugar content. Calculations of the seasonal mean crop light‐use efficiency (LUE) were consistent with the photosynthesis data in that CO2 increased LUE by 20% on average whereas temperature had no effect. Both elevating CO2 and cooling increased grain yield, by an average of 11% and 23%, respectively. CO2 and temperature stimulated yield via different mechanisms: CO2 increased photosynthetic rate, but decreased crop light interception capacity (LAI), whereas cooling increased grain yield by increasing LAI and extending the growing season with 10 days. The effects of CO2 and temperature were not additive: the CO2 effect was about doubled in the noncooled open‐top chambers. In most cases, effects on yield were mediated through increased grain density rather than increased individual grain weights.The higher growth response to elevated CO2 in noncooled vs. cooled OTCs shows that a cooling system may remove a bias towards overestimating crop growth response to CO2 in open‐top chambers.

Soybean Cultivars and Insect Defoliation: Yield Loss and Economic Injury Levels

AbstractUnderstanding the response of soybean [Glycine max (L.) Merr.] cultivars to insect defoliation is important for identifying differences in insect tolerance and compensation among soybean genotypes, for assessing yield loss differences among cultivars, and for determining if a single economic injury level (EIL) can be used for all cultivars. Therefore, this study was conducted to evaluate the relative tolerance of selected soybean cultivars to insect defoliation. Field experiments were conducted in 1994 and 1995 on three indeterminate soybean cultivars: Dunbar, Corsica, and Clark. Sequential defoliation (46‐66%) was imposed manually at the R2 stage (reproductive development of soybean at full flowering), guided by an insect consumption model. Leaf area index, percent light interception, growth, and yield data were determined. Because of ample rainfall during the soybean growing period in 1994, defoliation did not affect soybean yield; all cultivars compensated for all levels of defoliation via delayed leaf senescence and compensatory regrowth, which enhanced the light interception capacity of defoliated soybean canopies. In 1995, however, defoliation caused a significant yield reduction (15‐70%) in all cultivars; this yield reduction was greater for Dunbar than the other two cultivars. In both years, yields were directly related to the light interception capacity of soybean canopies after defoliation. There were significant EIL differences among soybean cultivars. Large differences in EILs among cultivars suggest a need to revise existing EILs for defoliating pest species.

Soybean Leaf Morphology and Defoliation Tolerance

AbstractPlant tolerance to pest injury is an ideal component of integrated pest management (IPM) programs, because it places no selection pressure on pest populations, but tolerance is little understood and its use in pest management is limited. In field experiments in 1994, 1995, and 1996, we characterized tolerance to defoliation in ‘Clark’ soybean [Glycine max (L.) Merr.] isolines differing in leaf morphology: 3‐ and 5‐leaflet, narrow and wide leaflet. Sequential defoliation was imposed manually at the R2 stage (full flowering), based on an insect consumption model. In 1994 and 1996, with ample rainfall, all isolines expressed yield compensation or overcompensation for defoliation as high as 75%, due to compensatory regrowth and delayed leaf senescence; in 1995, however, when rainfall was marginal, defoliation caused significant yield reduction. Equal amounts of leaf tissue removed resulted in different leaf area indices (LAIs). Wide‐leaflet isolines had higher LAI than narrow‐leaflet isolines, but the narrow‐leaflet isolines, particularly Clark‐3N, had greater light interception capacity for a given LAI level and had a higher light extinction coefficient in 1995. This shows that light was available to leaves in the lower canopy in the narrow‐leaflet isoline. Both low and high defoliation treatments caused significant yield reductions in all isolines, except that low defoliation did not significantly affect the yield of Clark‐3N in 1995. The narrow‐leaflet isolines apparently tolerated defoliation better than the wide‐leaflet isolines because the narrow‐leaflet isolines had greater light interception and maintained equal or better yields, despite similar defoliation. In addition to LAI, both canopy light interception and light extinction coefficient are important criteria for selecting cultivars tolerant to defoliation.

LEAF DISPLAY, CANOPY STRUCTURE, AND LIGHT INTERCEPTION OF TWO UNDERSTORY PALM SPECIES

The implications of leaf size, leaf display, and crown size for whole‐plant light interception were investigated in Geonoma cuneata and Asterogyne martiana, two understory palm species native to Central American rain forests. Adults of A. martiana had longer leaves, more leaves per plant, and greater total leaf area than G. cuneata adults. Geometric measurements within whole crowns were used to calculate light interception efficiency, a leaf‐based measure of the proportion of total incident light that is intercepted by a crown. Light interception efficiency was higher in adult G. cuneata than in adult A. martiana; seedlings of the two species did not differ significantly in light interception efficiency. Decreased efficiency of adult A. martiana crowns was largely due to an increased proportion of pendent leaves. Compared to G. cuneata, adults of A. martiana had greater light interception capacity (the product of light interception efficiency and total leaf area), but they also had higher biomass costs of light interception. Lower biomass costs of light interception in adult G. cuneata enable this species to exploit successfully the most deeply shaded microsites in the rain forest understory.