Light Interception Distribution Research Articles

High tree diversity enhances light interception in tropical forests

Abstract Understanding the processes that underlie the effects of tree diversity on primary production is of foremost importance to enhance climate change mitigation by tropical forests. Here, we investigated the effects of tree diversity on light interception over space and time in two tropical tree experiments, located in Panama—Sardinilla site (monocultures to 18‐species mixtures), and in Brazil—Anhembi site (20‐ to 114‐species mixtures). We assessed intercepted photosynthetically active radiation (iPAR) over horizontal grids and vertical transects (up to 5 m high in Sardinilla and up to 4 m high in Anhembi), in plots containing different richness levels and combinations of species. Light interception increased from monocultures to 5‐species mixtures in Sardinilla and from 20‐ to 114‐species mixtures in Anhembi (during the dry season). At the Sardinilla site, five‐species mixtures showed iPAR comparable to the best performing monocultures, despite substantial differences observed among monocultures. Diversity‐iPAR relationships changed seasonally and were more pronounced during the dry season. Tree richness promoted a less variable temporal and spatial (i.e. both horizontal and vertical) distribution of light interception. Synthesis. High tree diversity (i.e. over a hundred species in mixture) maximizes the amount of light intercepted by the canopy in restored tropical forests through more even capture in space and time. Diversity‐light interception relationships should be critically considered for designing cost‐efficient large‐scale tropical forest restoration programs.

Genotypic variation in spatiotemporal distribution of canopy light interception in relation to yield formation in cotton

BackgroundWithin-canopy interception of photosynthetically active radiation (PAR) impacts yield and other agronomic traits in cotton (Gossypium hirsutum L.). Field experiments were conducted to investigate the influence of 6 cotton varieties (they belong to 3 different plant types) on yield, yield distribution, light interception (LI), LI distribution and the relationship between yield formation and LI in Anyang, Henan, in 2014 and 2015.ResultThe results showed that cotton cultivars with long branches (loose-type) intercepted more LI than did cultivars with short branches (compact-type), due to increased LI in the middle and upper canopy. Although loose-type varieties had greater LI, they did not yield significantly higher than compact-type varieties, due to decreased harvest index. Therefore, improving the harvest index by adjusting the source-to-sink relationship may further increase cotton yield for loose-type cotton. In addition, there was a positive relationship between reproductive organ biomass accumulation and canopy-accumulated LI, indicating that enhancing LI is important for yield improvement for each cultivar. Furthermore, yield distribution within the canopy was significantly linearly related to vertical LI distribution.ConclusionTherefore, optimizing canopy structure of different plant type and subsequently optimizing LI distribution within the cotton canopy can effectively enhance the yield.

Spatial distribution of light interception by different plant population densities and its relationship with yield

Light interception (LI) by the canopy is an important environmental factor that determines dry matter production and crop development. Using a geostatistical sampling-based method, we studied the spatial distribution of LI at different points, in different layers and profiles and in the entire cotton canopy. The results showed that the LI decreased with increasing height. During early development, the horizontal changes in LI were large for a given vertical point. However, the horizontal changes in LI were smaller during later development. Profile maps of the LI for the six plant densities showed that different LIs occurred during the early growth stage. In addition, the linear regressions between the total accumulated LIs of the different layers and the cottonseed yield revealed that the LI in the bottom layer and in the middle of two cotton rows significantly contributed to the cottonseed yield. Thus, a higher economic yield could be obtained by improving the micro-environment in these two layers.

A three-dimensional statistical reconstruction model of grapevine (Vitis vinifera) simulating canopy structure variability within and between cultivar/training system pairs.

In grapevine, canopy-structure-related variations in light interception and distribution affect productivity, yield and the quality of the harvested product. A simple statistical model for reconstructing three-dimensional (3D) canopy structures for various cultivar-training system (C x T) pairs has been implemented with special attention paid to balance the time required for model parameterization and accuracy of the representations from organ to stand scales. Such an approach particularly aims at overcoming the weak integration of interplant variability using the usual direct 3D measurement methods. This model is original in combining a turbid-medium-like envelope enclosing the volume occupied by vine shoots with the use of discrete geometric polygons representing leaves randomly located within this volume to represent plant structure. Reconstruction rules were adapted to capture the main determinants of grapevine shoot architecture and their variability. Using a simplified set of parameters, it was possible to describe (1) the 3D path of the main shoot, (2) the volume occupied by the foliage around this path and (3) the orientation of individual leaf surfaces. Model parameterization (estimation of the probability distribution for each parameter) was carried out for eight contrasting C x T pairs. The parameter values obtained in each situation were consistent with our knowledge of grapevine architecture. Quantitative assessments for the generated virtual scenes were carried out at the canopy and plant scales. Light interception efficiency and local variations of light transmittance within and between experimental plots were correctly simulated for all canopies studied. The approach predicted these key ecophysiological variables significantly more accurately than the classical complete digitization method with a limited number of plants. In addition, this model accurately reproduced the characteristics of a wide range of individual digitized plants. Simulated leaf area density and the distribution of light interception among leaves were consistent with measurements. However, at the level of individual organs, the model tended to underestimate light interception.

Light Interception, Nitrogen and Leaf Mass Distribution in a Multilayer Plant Community

The distribution of light interception, foliar nitrogen and leaf mass between three community layers (tree, herbaceous and moss layers) were investigated along productivity gradient in a west-Estonian wooded meadow. A two-resource model is applicable to describe the vertical structure of a multilayer community. Upper layers have better access to light compared to lower layers of the canopy, whereas lower layers have higher nitrogen-use efficiency and/or better ability to acquire nitrogen. The amount of foliar nitrogen per unit of intercepted light is highest in the herbaceous layer if compared to the tree and moss layers but mosses have the highest nitrogen-use-efficiency (assessed from the dry mass :nitrogen ratio). The growth of the herbaceous layer in communities along the productivity gradient is co-limited by light and nitrogen but growth of the moss layer is limited only by light availability.