Effect of Spatial-Temporal Light Competition on Cotton Yield and Yield Distribution

The photosynthetically active radiation (PAR) of crop canopy is highly related to yield formation, but how it relates to yield and yield distribution is not well understood. The focus of this study was to explore the relationship between light competition under different densities and yield distributions of cotton. The experiment was conducted in 2019 and 2020 at the Cotton Research Institute of the Chinese Academy of Agricultural Sciences in Anyang city, Henan Province, China. A randomized block design was employed, with a total of three repeats. Each repeat had six density treatments: D1: 15,000; D2: 33,000; D3: 51,000; D4: 69,000; D5: 87,000; and D6: 105,000 plants·ha−1. As predicted, the results showed that the canopy light interception, leaf area index, plant height, and biomass of high-density cotton were higher than those of low-density cotton. The aboveground biomass produced by D6 was the highest, and was 12.9, 19.5, 25.4, 46.3, and 69.2% higher in 2019 and 14.3, 19.9, 32.5, 53.7, and 109.9% higher in 2020 than D5, D4, D3, D2, and D1, respectively. Leaf area, plant height, biomass, boll number, and boll weight were significantly correlated with the light interception rate. D5 (87,000 plants·ha−1) had a higher light interception rate and the highest yield. The highest lint yields produced by D5 were 1673.5 and 1375.4 kg·ha−1 in two years, and was 3.2, 4.3, 5.6, 9.7, and 24.7% higher in 2019, and 6.8, 10.6, 13.5, 21.5, and 34.4% higher in 2020 than D6, D4, D3, D2, and D1, respectively. The boll retention of the lower fruit branch under D5 reached 0.51 and 0.57 in two years, respectively. The shedding rate of the upper fruit branch decreased with the increase in cotton density in two years. The boll retention rate and shedding rate in the lower part of cotton plants were most closely related to light interception, with R2 values of 0.91 and 0.96, respectively. Our study shows cotton yield could be improved through higher light interception by optimizing planting density and canopy structure.

Smaller species experience mild adversity under shading in an old-field plant community

Plant competition experiments commonly suggest that larger species have an advantage, especially in light acquisition. However, within crowded natural vegetation, where competition evidently impacts fitness, most resident species are relatively small. It remains unclear, therefore, whether the size-advantage observed in controlled experiments is realized in habitats under intensive competition. We tested for evidence of a size-advantage in competition for light in an old-field plant community composed of herbaceous perennial species. We investigated whether larger species contributed to reduced light penetration (i.e., greater shading), and examined the impact of shade on smaller species by testing whether their abundance and richness were lower in plots with less light penetration. Light penetration in plots ranged from 0.3-72.4%. Plots with greater mean species height had significantly lower light penetration. Plots with lower light penetration had significantly lower small species abundance and richness. However, the impact of shade on small species abundance and richness was relatively small (R values between 8% and 15%) and depended on how we defined “small species”. Significant effects were more common when analyses focused on individuals that reached reproduction; focusing on only flowering plants can clarify patterns. Our results confirm that light penetration in herbaceous vegetation can be comparable to levels seen in forests, that plots with taller species cast more shade, and that smaller species are less abundant and diverse in plots where light penetration is low. However, variation in mean plot height explained less than 10% of variation in light penetration, and light penetration explained 5-15% of variation in small species abundance and richness. Coupled with the fact that reproductive small species were present even within the most heavily shaded plots, our results suggest that any advantage in light competition by large species is limited. One explanation is that some small species in these communities are shade tolerant.

Liana optical traits increase tropical forest albedo and reduce ecosystem productivity

Lianas are a key growth form in tropical forests. Their lack of self-supporting tissues and their vertical position on top of the canopy make them strong competitors of resources. A few pioneer studies have shown that liana optical traits differ on average from those of colocated tree. Those trait discrepancies were hypothesized to be responsible for the competitive advantage of lianas over trees. Yet, in the absence of reliable modelling tools, it is impossible to unravel their impact on the forest energy balance, light competition and on the liana success in Neotropical forests. To bridge this gap, we performed a meta-analysis of the literature to gather all published liana leaf optical spectra, as well as all canopy spectra measured over different levels of liana infestation. We then used a Bayesian data assimilation framework applied to two radiative transfer models (RTMs) covering the leaf and canopy scales to derive tropical tree and liana trait distributions, which finally informed a full dynamic vegetation model. According to the RTMs inversion, lianas grew thinner, more horizontal leaves with lower pigment concentrations. Those traits made the lianas particularly efficient at light interception and completely modified the forest energy balance and its carbon cycle. While forest albedo increased by 14% in the shortwave, light availability was dramatically reduced in the understory (-30% of the PAR radiation) and soil temperature decreased by 0.5 degree Celsius. Those liana-specific traits were also responsible for a significant reduction of tree (-19%) and ecosystem (-7%) gross primary productivity (GPP) while lianas benefited from them (their GPP increased by +27%). This study provides a novel mechanistic explanation to the increase in liana abundance, new evidence of the impact of structural parasitism on forest functioning, and paves the way for the evaluation of the large-scale impacts of woody vines on forest biogeochemical cycles.

Modeling light competition in the Amazon forest: the effects of high CO2 in functional diversity and biogeochemical cycle.

<p>The increase of CO<sub>2</sub> concentrations implies direct and indirect (by changing climate) impacts on the terrestrial ecosystem. Several Dynamic Global Vegetation Models (DGVMs) have been developed to better understand the response of vegetation to climate change. However, the representation of plant diversity through a small set of Plant Functional Types (PFTs) adopted by the majority of DGVMs undermines their ability to represent functional diversity and fundamental interactions between these different life strategies of plants, like competition, which has been shown to be paramount in determining ecosystem functioning. Studies have shown that increasing CO<sub>2</sub> concentration may determine the outcome of vegetation competition and, as a consequence, the ability to adapt to the environment, functional diversity, and community assembly mechanisms. Thus, the inclusion of competitive dynamics in these models becomes strategic to improve predictions and understanding the effects of climate change on vegetation and how it affects change in carbon fluxes and stocks in the community. In that sense, this project aims to contribute to the development of a light competition module within CAETÊ model (<strong>C</strong>Arbon and <strong>E</strong>cosystem functional <strong>T</strong>rait <strong>E</strong>valuation model) which involves the implementation of allometric relations between plant organs. As a trait-based model, CAETÊ seeks to represent plant functional diversity in a less discrete way through the usage of variant values for functional traits. For this purpose, two key functional traits that are closely related to competition for light are employed as variants: <em>wood density </em>(WD) and <em>specific leaf area </em>(SLA). The main objective is to understand how light competition related to plant functional traits alters the response of Amazon plant communities under changing environmental conditions. As preliminary results, the algorithms containing the allometric and competition equations were developed outside the main model code and represent plant dynamics trade-offs between the variant functional traits and plant physiology and survivorship: WD relates to strategies of mortality and height growth. For example, high values of WD [1g/cm<sup>-3</sup>] are related to low heights [~30m.] and, low heights incur higher mortality rates; SLA relates to light competitive effect, Leaf Economics Spectrum, and LAI (leaf area index) determination, one of the most important parameters that determine the absorption of light by different life strategies. These trade-offs allow the representation of different plant life competition strategies. We expected that the light restriction for some functional strategies may incur a decrease in functional dominance and photosynthesis rate, consequently changing net primary productivity and after all the functional structure of the community. For functional diversity, it is expected changes in functional richness and functional divergence (related to the strength that competition exerts in the community) in order to favor strategies that better deal with the new environmental conditions simulated by CAETÊ with increasing [CO<sub>2</sub>] to 600 ppmv, for example. Finally, it is expected that this approach may contribute to improving the representation of competition for light in DGVMs to more assertively obtain the effects of climate changes on vegetation and ecosystem dynamics. Final results will be obtained until the EGU Congress takes place.</p>

The effect of flooding and light competition on the planting success of degraded tropical peatland

Planting was done as a rehabilitation effort at degraded tropical peatland. Understanding the characteristics of the species and environmental conditions that affect plant growth will determine the success of the planting. This study aims to determine the main environmental factors that affect plants in the field so that the right species can be determined. This study used a randomized completely blocked design which was conducted in two stages, namely field testing and verification under controlled conditions in the nursery. The research treatments consisted of inundation conditions and competition with understorey. The competition factor is interpreted by the difference in light intensity at the verification stage. The species used are meranti (Shorea pallidfolia), gerunggang (Cratoxylum glaucum), terentang (Campnosperma coreacea) dan tumih (Combretocarpus rotundatus). The results showed that the inundation conditions had an effect on the survival of meranti and gerunggang species where the survival rate was 8.3%—96.3%, but it did not affect the terentang and tumih with the survival rate reaching > 80%. The growth of meranti and gerunggang tends to decrease in line with the inundation conditions, while the growth of terentang and tumih tends to increase. Meranti growth requires understorey as protection from high light intensity. The tumih and terentang show better growth without competition with understorey. The trends in the field are consistent with observations during the verification stage. The difference in the response of plants to environmental conditions determines the presence of these species in the succession stage. Keywords: rehabilitation, flooding, drainage, succession, sequen

Comparative analysis of the competition of stands of different species composition in relation to the Siberian stone pine undergrowth

Under the canopy of the parent native berry-green-moss Siberian stone pine forest and derivatives berry-green-moss pine and birch forests on the Urals, using the previously proposed complex of light, root, and integral competition indices of the stand, a comparative analysis of the parameters of the Siberian stone pine undergrowth is carried out. Under the canopy of Siberian stone pine forest two main determining factors have a negative complex effect on the growth of the Siberian stone pine undergrowth: the light competition of the stand (the level of photosynthetically active radiation interception by its canopy) and, almost equal to it, the root competition for soil nutrition. Under the pine forest canopy with the combined negative effect of factors of light and root competition of the stand on the development of Siberian stone pine undergrowth, light competition is decisive. The effect of the root competition is less than almost two times. Under the birch forest canopy the main factor determining the development of Siberian stone pine undergrowth is the light competition of the stand. The connection with the root competition of stand is not expressed.

Far-red Light Interacts with Plant Density to Change Photosynthate Allocation of Cucumber Seedlings and Their Subsequent Early Growth after Transplanting

The light competition in dense plant stands may be disadvantageous in transplant production because competition stimulates stem elongation and can reduce photosynthate allocation to leaves; this, in turn, may reduce the early growth rate after transplanting. In this study, we focused on how the proportion of far-red (FR) light affected light competition among cucumber (Cucumis sativus L.) seedlings and investigated the effects of the plant density × FR interaction on photosynthate allocation and subsequent early growth after transplanting. Seedlings at the cotyledon stage were planted into plug trays at densities ranging from 109 to 1736 plants/m2; then they were grown for 4 days under light-emitting diode (LED) light containing FR light (FR+) at approximately the same red-to-FR ratio as in sunlight (1.2) or under light containing no FR (FR−). The higher density significantly stimulated stem elongation under both FR+ and FR−, but the effect was small under FR−; this indicates that light competition in the dense stands was inhibited by reducing FR light. The higher plant density significantly increased photosynthate allocation to the stem and decreased allocation to the leaves under both FR+ and FR−; however, again, the effect was smaller under FR−. After transplanting the seedlings to pots, early growth decreased in the seedlings that allocated less photosynthate to their leaves. Our results indicate that light with reduced FR can mitigate the disadvantageous photosynthate allocation of transplants and the reduction of early growth after transplanting that are likely to occur as a result of light competition at high plant density.

Approach for Image-Based Semantic Segmentation of Canopy Cover in Pea–Oat Intercropping

Intercropping systems of cereals and legumes have the potential to produce high yields in a more sustainable way compared to sole cropping systems. Their agronomic optimization remains a challenging task given the numerous management options and the complexity of interactions between the crops. Efficient methods for analyzing the influence of different management options are needed. The canopy cover of each crop in the intercropping system is a good determinant for light competition, thus influencing crop growth and weed suppression. Therefore, this study evaluated the feasibility to estimate canopy cover within an intercropping system of pea and oat based on semantic segmentation using a convolutional neural network. The network was trained with images from three datasets during early growth stages comprising canopy covers between 4% and 52%. Only images of sole crops were used for training and then applied to images of the intercropping system. The results showed that the networks trained on a single growth stage performed best for their corresponding dataset. Combining the data from all three growth stages increased the robustness of the overall detection, but decreased the accuracy of some of the single dataset result. The accuracy of the estimated canopy cover of intercropped species was similar to sole crops and satisfying to analyze light competition. Further research is needed to address different growth stages of plants to decrease the effort for retraining the networks.