Competition For Light Research Articles

Quercus wutaishanica shrub affects temperate forest community composition and soil properties under different restoration stage.

Quercus wutaishanica is the dominant tree species in the natural ecosystem restoration of temperate forests in China, and it plays an active role in maintaining ecological balance. However, little is known about how ecosystem versatility develops during the restoration of forest ecosystems dominated by Q. wutaishanica. In this study, we investigated the species composition of the Q. wutaishanica community, soil nutrients, and their functional traits at various restoration stages, and comprehensively analyzed the correlations among them. At the early stage of restoration (10 years of restoration), there were Spiraea pubescens and Syringa pubescens in Q. wutaishanica community (87% of the total species), while had a larger niche width. In the middle of restoration (30 years of restoration), shannon and evenness indices were the largest, while soil total carbon, ammonium nitrogen and chlorophyll content of Q. wutaishanica leaves were the highest; among them, soil total carbon was 15.7% higher than that in 10 years of restoration, 32.4% higher than that in 40 years of restoration, ammonium nitrogen was 71.7% higher than that in 40 years of restoration, and chlorophyll content was 217.9% higher than that in 10 years of restoration, and 51.8% higher than that in 40 years of restoration. At the later stage of restoration (40 years of restoration), Lonicera ferdinandii occupied the dominant ecological niche, and soil available nitrogen, available phosphorus content and leaf thickness were the largest; while AN was 10.9% higher than that of 10 years of restoration, 16.5% higher than that of 30 years of restoration, AP was 60.6% higher than that of 10 years of restoration, 21.6% higher than that of 30 years of restoration, leaf thickness was 22.3% higher than that of 10 years of restoration, 84.9% higher than that of 30 years of restoration. However, the restriction of various soil nutrients was reduced. Our study highlighted the effectiveness of soil resource availability in plant communities during restoration, reduced competition for light among plants, and altered species richness. Furthermore, changes in the interrelationship between plant community composition and leaf functional traits of the dominant species responded positively to community restoration. These results further deepen our understanding of forest management and restoration of forest communities. In the future, it is necessary to comprehensively consider the influence of various factors on forest community restoration.

The change in the biomass allocation to stems and leaves in young plants of Dimorphandra wilsonii under eCO2 may harm this endangered species in native areas

AbstractClimate change is among the main threats to ecosystems, affecting biodiversity and ecosystem services. These changes are associated with increased atmospheric carbon dioxide concentration ([CO2]). This study aimed to investigate how [CO2] influences chlorophyll a fluorescence, vegetative growth, biomass production, and the number of root nodules (NRN) of Dimorphandra wilsonii, a critically endangered species. The study was conducted in six open‐top chambers with two CO2 levels, at elevated [CO2] (eCO2, 717 ± 77 ppm) and at ambient [CO2] (aCO2, 539 ± 42 ppm). We monitored vegetative growth weekly, and at the end of the experiment, we measured chlorophyll a fluorescence and biomass production. Dimorphandra wilsonii plants under eCO2 showed higher (p < 0.05) average leaf dry mass, average leaf area, and lower (p < 0.05) root/shoot ratio than plants under aCO2. The greater aerial biomass allocation contributes to maximizing the photosynthesis performance but could also result in the self‐shading of old basal leaves by new distal leaves on branches. This adjustment could be advantageous in the competition for light; however, it would be a disadvantage for below‐ground resource competition (such as water and nutrients), which could result in decreased drought resistance. Also, this adjustment would be unfavorable to D. wilsonii, which occurs in a seasonal climate environment competing with invasive grasses. Thus, it is possible that climate change scenarios with increases in [CO2] and drought periods could negatively influence the establishment of young plants of D. wilsonii in their natural occurrence area, which could worsen the conservation status of the species.

Soil organic carbon stocks and belowground biomass in patches in heterogeneous grassland

AbstractBackgroundSelective grazing creates stable patches of contrasting sward height, thereby providing different growth conditions for the grass sward above and below ground and potentially affecting soil organic carbon (SOC) stocks. We hypothesized that the presence of patches leads to greater spatial variability in belowground biomass (BGB) and SOC stocks than occurs between pastures managed under different stocking intensities.MethodsA long‐term grazing experiment consisting of three stocking intensities was used for this study. We studied BGB, SOC, and soil total nitrogen (Ntot) stocks in the 0–15 cm soil depth. Shannon diversity of plant species, soil bulk density, soil phosphorus, potassium, and magnesium contents were considered.ResultsThere were no significant effects of patch or stocking intensity on BGB, SOC, and Ntot stocks. Short patches had a greater Shannon diversity than tall patches (p < 0.05) and plant‐available nutrients in soil correlated positively with sward height (p < 0.05).ConclusionsWe conclude from the current results and previous studies that higher plant species diversity with lower soil nutrient contents in short‐patch areas and higher nutrient contents together with light competition in tall‐patch areas might balance each other out with respect to BGB and SOC stocks.

Are agroforestry systems more productive than monocultures in Mediterranean countries? A meta-analysis

Agroforestry is gaining interest due to its potential in enhancing climate resilience and sustainability of farming systems. In this meta-analysis, the crop yield in agroforestry system compared to the control (sole crop) from thirty-six experimental field trials in Mediterranean countries was assessed. The response variable Wlog(RR) (i.e., the weighted natural logarithm of the response ratio) was analyzed by the 95% confidence intervals of mean and by fitting eight linear mixed models. Fixed effects, namely the tree cover (low, medium, high), the tree species (ash tree, chestnut, cork oak, holm oak, olive, poplar, walnut), and the crop species (alfalfa, barley, durum wheat, faba bean, forage, oat, pasture, pea, winter wheat) were significant (P = 0.030, P = 0.017, and P = 0.014, respectively), while the system type (alley cropping, silvo-arable, silvo-pastoral) was not. Among management practices (variety, pruning, fertilization, irrigation, crop age classes, imposed warming and drought, harvest time), only the fertilization significantly improved the response variable (P = 0.006), while the interaction of pruning × crop species was marginally significant (P = 0.065). Relatively large study heterogeneity was observed (Q = 72.6, I2 = 72%), which is quite common for agronomic meta-analysis. On the contrary, publication bias based on funnel plots and the Trim and Fill method suggested symmetrical distribution of studies. The sensitivity analysis for significant models identified room for improvements. Overall, we observed a negative effect of trees on crop yield that could be ascribed to the competition for light. Nonetheless, facilitation could be expected under extreme climate events, provided that agricultural practices will maximize synergies among tree cover, tree species, crop species, and management. Future works are encouraged to focus on the overall benefit agroforestry can provide at the field and landscape level, along with long-term monitoring to assess the whole lifespan of these systems and other companion planting options and designs in the Mediterranean region.

The Herbicidal Activity of Nano- and MicroEncapsulated Plant Extracts on the Development of the Indicator Plants Sorghum bicolor and Phaseolus vulgaris and Their Potential for Weed Control

Weeds decrease yield in crops through competition for water, nutrients, and light. Due to the circumstances mentioned above and the challenge of the emergence of herbicide-resistant weeds, developing sustainable alternatives becomes imperative. Plant extracts formulated into nano- and micro-encapsulates (NPs) emerge as a viable option for weed management. The objectives of this study were to identify phytochemical compounds within the ethanolic extracts of Carya illinoinensis, Ruta graveolens, and Solanum rostratum; determine their pre-emergence herbicidal activity on the indicator plants Sorghum bicolor and Phaseolus vulgaris; produce and characterize NPs with plant extracts; and assess their phytotoxicity under greenhouse conditions. The extracts were provided by Greencorp Biorganiks de México. Phytochemicals were identified through colorimetric assays and HPLC-MS, while pre-emergence tests were conducted in vitro, assessing concentrations of 12.5, 25, and 50% for each extract. NPs were synthesized using the ionotropic pre-gelation method, with size, zeta potential, and encapsulation efficiency (EE) being characterized. Finally, post-emergence tests were carried out in a greenhouse with seedlings. Compounds belonging to the hydroxycinnamic acid, flavonol, methoxyflavonol, hydroxybenzoic acid, methoxyflavone, tyrosol, stilbene, and lignan families were identified in all extracts. The pre-emergence herbicidal activity was observed for all extracts, with germination percentages ranging from 0 to 41% in both indicator plants. NPs exhibited sizes between 290 and 345 nm, zeta potentials ranging from −30 to −35 mV, and EE up to 94%. Finally, enhanced herbicidal activity was observed with plant extract NPs, with the species S. bicolor being more susceptible. NPs containing plant extracts are a viable option for bioherbicide production; however, continued research is necessary to refine formulations and enhance efficacy.

Joint species distribution modeling with competition for space

AbstractJoint species distribution models (JSDM) are among the most important statistical tools in community ecology. However, existing JSDMs cannot model mutual exclusion between species. We tackle this deficiency in the context of modeling plant percentage cover data, where mutual exclusion arises from limited growing space and competition for light. We propose a hierarchical JSDM where latent Gaussian variable models describe species' niche preferences and Dirichlet‐Multinomial distribution models the observation process and competition between species. We also propose a decision theoretic model comparison and validation approach to assess the goodness of JSDMs in four different types of predictive tasks. We apply our models and methods to a case study on modeling vegetation cover in a boreal peatland. Our results show that ignoring the interspecific interactions and competition reduces models' predictive performance and leads to biased estimates for total percentage cover. Models' relative predictive performance also depends on the predictive task highlighting that model comparison and assessment should resemble the true predictive task. Our results also demonstrate that the proposed JSDM can be used to simultaneously infer interspecific correlations in niche preference as well as mutual competition for space and through that provide novel insight into ecological research.

Competitive asymmetry in a forest composed of a shade-tolerant species depends on gap formation

Competitive asymmetry is one of the most important determinants of size structure in plant communities. Light competition was believed to be size-asymmetric, as taller individuals preempt light. In fact, many studies indicated that light competition is size-asymmetric in monospecific stands of herbaceous plants. However, competition is size-symmetric in multispecific stands because shorter, shade-adapted species compensate for the low light availability through higher leaf area per aboveground mass (leaf area ratio; LAR) or higher light use efficiency for growth (LUE). Then, a question arises on whether light competition is asymmetric or symmetric if the stand is occupied by a shade-tolerant species. Moreover, it is also interesting how gap dynamics affect competitive asymmetry, given the fact that gap formation can improve light availability in lower layers of the canopy. We investigated the plant size, growth rate, and three-dimensional distribution of foliage and light availability in a natural forest dominated by a shade-tolerant tree, Fagus crenata. We found that competitive asymmetry varied dynamically across the forest. In closed canopies, the relative growth rate (RGR) was higher in taller trees, indicating size-asymmetric growth. Shorter trees partly compensated for their light interception by having higher LAR but did not achieve comparative RGR to taller trees. Conversely, in gaps, the RGR of shorter trees was equivalent to those of taller trees because of the improved light availability for smaller trees, indicating size-symmetric growth. These results suggest that changes in competitive asymmetry driven by gap dynamics can influence the spatiotemporal diversity of size structures in forests.

Plant-Plant Interdependence and Mutualism Interactions in Heterogeneous Ecosystems still hide a lot of secrets

Plant-Plant Interdependence and Mutualism Interactions in Heterogeneous Ecosystems still hide a lot of secrets

Multidimensional beta-diversity across local and regional scales in a Chinese subtropical forest: The role of forest structure.

Beta-diversity, or the spatio-temporal variation in community composition, can be partitioned into turnover and nestedness components in a multidimensional framework. Forest structure, including comprehensive characteristics of vertical and horizontal complexity, strongly affects species composition and its spatial variation. However, the effects of forest structure on beta-diversity patterns in multidimensional and multiple-scale contexts are poorly understood. Here, we assessed beta-diversity at local (a 20-ha forest dynamics plot) and regional (a plot network composed of 19 1-ha plots) scales in a Chinese subtropical evergreen broad-leaved forest. We then evaluated the relative importance of forest structure, topography, and spatial structure on beta-diversity and its turnover and nestedness components in taxonomic, functional, and phylogenetic dimensions at local and regional scales. We derived forest structural parameters from both unmanned aerial vehicle light detection and ranging (UAV LiDAR) data and plot inventory data. Turnover component dominated total beta-diversity for all dimensions at the two scales. With the exception of some components (taxonomic and functional turnover at the local scale; functional nestedness at the regional scale), environmental factors (i.e., topography and forest structure) contributed more than pure spatial variation. Explanations of forest structure for beta-diversity and its component patterns at the local scale were higher than those at the regional scale. The joint effects of spatial structure and forest structure influenced component patterns in all dimensions (except for functional turnover) to some extent at the local scale, while pure forest structure influenced taxonomic and phylogenetic nestedness patterns to some extent at the regional scale. Our results highlight the importance and scale dependence of forest structure in shaping multidimensional beta-diversity and its component patterns. Clearly, further studies need to link forest structure directly to ecological processes (e.g., asymmetric light competition and disturbance dynamics) and explore its roles in biodiversity maintenance.

Efficient Bayesian automatic calibration of a functional-structural wheat model using an adaptive design and a metamodelling approach.

Functional-structural plant models are increasingly being used by plant scientists to address a wide variety of questions. However, the calibration of these complex models is often challenging, mainly because of their high computational cost, and, as a result, error propagation is usually ignored. Here we applied an automatic method to the calibration of WALTer: a functional-structural wheat model that simulates the plasticity of tillering in response to competition for light. We used a Bayesian calibration method to jointly estimate the values of five parameters and quantify their uncertainty by fitting the model outputs to tillering dynamics data. We made recourse to Gaussian process metamodels in order to alleviate the computational cost of WALTer. These metamodels are built from an adaptive design that consists of successive runs of WALTer chosen by an efficient global optimization algorithm specifically adapted to this particular calibration task. The method presented here performed well on both synthetic and experimental data. It is an efficient approach for the calibration of WALTer and should be of interest for the calibration of other functional-structural plant models.

Effects of tree canopy on herbaceous understorey throughout the developmental cycle of a temperate mountain primary forest

Temporal dynamics of temperate montane primary forests were described based on data from Central-European nature reserves in the 20th century as a long-term cycle involving tree regeneration, growth, maturation, and disintegration. However, the lack of chronosequences focusing on the herbaceous understory has limited our understanding of plant community dynamics within this developmental cycle. To address questions regarding whether the herbaceous understory follows the cyclic trajectory of the tree layer and if the properties of the tree layer drive the dynamics of the herbaceous understory, we investigated a 19-year chronosequence in ten plots (with five sampling periods) within an unmanaged primary beech-fir forest in the Western Carpathians. The vegetation data from the resampled plots, including herb species frequencies and dendrometric variables, covered a significant portion of the developmental cycle of a single plant community type. The results confirmed the cyclical nature of herbaceous understory development in terms of species composition and diversity trajectories, demonstrating transitions between developmental stages. Diversity was highest during the disintegration stage, with a rapid decline towards the growth stage, followed by a slow recovery as it progressed towards the optimum stage. Temporal responses of individual species, along with ordination analyses, allowed for the separation of taxa associated with the disintegration, growth, and optimum stages, as well as the most stable ones throughout the entire cycle. The proportion of therophytes slightly increased after gap-opening events during disintegration, geophytes were most represented during the growth stage, and hemicryptophytes culminated during the optimum stage. The composition of herb species was significantly affected by the above-ground tree biomass (AGTB), which explained 21.4% of the temporal variability. The sum of the diameter at breast height (Sum of DBH) described an additional 7.2%. The relationship between the frequency of the herbaceous understory and AGTB followed a “U” shape, while the relationship with Sum of DBH was negative and linear. The relationship between the herbaceous understory and the tree overstory is likely driven by competition for light, water, and nutrient resources. These findings provide new insights into the temporal relationships between the herbaceous understory and tree layer development, and they may inspire future studies and management strategies aimed at conserving or enhancing biodiversity in temperate forests.

Optimal Weeding Interval for Grevillea robusta Nursery Seedlings

Weeding for young tree seedlings is critical for their growth. Weeds offer stiff competition for water, nutrients, light and space with the companion crops. Most tree nurseries do not have a formal weeding interval, hence the need for the current research. A nursery experiment was set up to investigate the best weeding interval for Grevillea robusta seedlings for a period of 8 months in Njoro, Kenya. The experiment was laid down in a RCBD with 4 treatments replicated 3 times. The treatments were as follows: Continuous weeding, 1-month weeding interval, 2-months weeding interval and non-weeding. Data was analyzed using ANOVA while LSD was applied to separate the significantly different treatments at P<.05. Results showed that survival for non-weeding (83.33%) was significantly lower (P =.04) compared with 1-month and 2-months weeding interval (100.00 and 96.67%) respectively. Continuous weeding and 1-month weeding interval showed significantly higher height (23.00 and 25.27cm) respectively compared with 2-months weeding interval and non-weeding (17.67 and 13.83cm) respectively. On the other hand, 1-month weeding interval showed the highest root length (22.67cm) which was significantly different (P=.05) compared with non-weeding (15.67cm). Root biomass was significantly higher (P=.02) for 1-month weeding interval (4.67g) compared with non-weeding (2.50g). Grevillea robusta seedlings should be weeded at an interval of one month during the nursery period in order to attain favorable growth. Non-weeding compromises the seedling growth due to severe competition from weeds. Even though continuous weeding favors seedling growth, it is not economical due to high labor demand. Further research should be conducted using different soil mixtures and other species.

Towards increased shading capacity: A combined phenotypic and genetic analysis of rice shoot architecture

Societal Impact StatementRice farming is transitioning from transplanting rice seedlings towards the less labour‐intensive and less water‐demanding method of directly seeding rice. This, however, is accompanied by increased weed proliferation. To tackle this issue, this study seeks to identify how the crop itself can better suppress weeds, with a focus on light competition via shading. Using a rice diversity panel, traits were identified that contribute to enhanced shading capacity, and these traits were encapsulated into a single shading capacity metric. This was followed by the identification of the genetic loci underpinning variation in the core traits. The identified haplotypes can be used in breeding programmes to improve weed suppression by rice, thus contributing to sustainable agriculture.Summary In modern rice farming, one of the major constraints is weed proliferation and the entailed ecological impact of herbicide application. This requires increased weed competitiveness in current rice varieties, achieved via enhanced shade casting to limit the growth of shade‐sensitive weeds. To identify traits that increase rice shading capacity, we exhaustively phenotyped a rice diversity panel of 344 varieties at an early vegetative stage. A genome‐wide association study (GWAS) revealed genetic loci underlying variation in canopy architecture traits linked with shading capacity. The screen shows considerable natural variation in shoot architecture for 13 examined traits, of which shading potential is mostly determined by projected shoot area, number of leaves, culm height and canopy solidity. The shading rank, a metric based on these core traits, identifies varieties with the highest shading potential. Five genetic loci were found to be associated with canopy architecture, shading potential and early vigour. Identification of traits contributing to shading capacity and underlying allelic variation will serve future genomic‐assisted breeding programmes. Implementing the presented genetic resources for increased shading and weed competitiveness in rice breeding will make its farming less dependent on herbicides and contribute towards more environmentally sustainable agriculture.

Interacting Effects of Nitrogen Addition and Mowing on Plant Diversity and Biomass of a Typical Grassland in Inner Mongolia

It is unclear how N addition and mowing interactively affect grassland community structure and function. We studied the short-term effects of N addition and mowing on the species diversity and biomass of a typical grassland in Inner Mongolia using a split-plot design, with the whole plot representing the mowing treatment and the subplot representing the N addition rate. Three stubble heights were set at 10 cm (M2), 6 cm (M3) and 3 cm (M4), and a no-mowing treatment (M1) was also included. N addition consisted of five rates, i.e., 0 (N1), 2 (N2), 5 (N3), 10 (N4) and 20 (N5) g N m2.yr−1. Mowing significantly increased species diversity. Mowing with a stubble height of 10 cm (M2) significantly increased both species biomass and community biomass. Heavy mowing (3 cm stubble height, M4) weakened the difference in C. squarrosa biomass caused by N addition. Species richness decreased, while community biomass and Leymus chinensis biomass increased significantly with increasing N addition rate. Mowing alleviated the negative effects of N addition on species richness, and this effect was influenced by stubble height. Community biomass and L. chinensis biomass tended to be stable when N addition was greater than 10 g N m2.yr−1. The N saturation threshold of C. squarrosa biomass was much lower than that of community biomass and L. chinensis biomass. Species richness was negatively correlated with the Gini coefficient and litter production, which indicated that light competition and litter accumulation were important factors affecting the decrease in species richness in our study.

Exposure pathways matter: Aquatic phototrophic communities respond differently to agricultural run‐off exposed via sediment or water

Abstract Small shallow ponds are widespread but understudied water bodies in agricultural landscapes. Agricultural run‐off (ARO) transports pesticides and nutrients into adjacent aquatic ecosystems where they occur dissolved in the water column or are bound to sediments. Consequently, aquatic communities are affected by ARO via different exposure pathways. We hypothesize that sediment‐bound ARO mainly affects submerged rooted macrophytes, while phytoplankton and periphyton are more prone to ARO in water. These primary producers compete for resources resulting in a regime shift between alternative stable states of macrophyte or phytoplankton dominance. We hypothesize that warming increases nutrient release from sediments and thereby facilitates the occurrence of phytoplankton dominance. Using a full‐factorial microcosm design, we exposed aquatic primary producers to either sediment or water application of a mixture of common pesticides (terbuthylazine, pirimicarb, tebuconazole and copper) and nitrate at two concentrations and two temperatures (22°C and 26°C) for 4 weeks. Initial and final concentrations of pesticides and nitrate, final biomass of macrophytes, periphyton and phytoplankton, pesticide accumulation in macrophytes and changes in carbon, nitrogen and phosphorus content and selected exoenzyme activities in the sediment were measured. We found lower final macrophyte biomass for both ARO treatments compared to controls, indicating a prevalence of negative effects by herbicides and competition for light with other phototrophs. In contrast, phytoplankton and periphyton biomass increased, but only when exposed to ARO via the water column, indicating a prevalence of positive effects by nutrient supply. Microbial carbon and nutrient cycling in sediments was not affected by ARO. Higher temperature mitigated ARO‐related effects on macrophytes under sediment exposure. Synthesis and application. ARO poses a strong risk of submerged macrophyte loss and establishment of turbid conditions with phytoplankton dominance in aquatic ecosystems. In conclusion, exposure pathways as well as indirect and interacting effects of multiple stressors need to be considered when designing appropriate mitigation measures. Under climate change, we suggest to prioritize local measures as buffer strips a reduced use of pesticides and fertilizers, and sediment removal as appropriate measures to protect these vulnerable but widespread aquatic systems, which are highly relevant for biodiversity in agricultural landscapes.

Supplemental far-red light influences flowering traits and interactions with a pollinator in tomato crops

Plants sense a reduction in the red to far-red light ratio as a cue of light competition and respond by accelerated growth and reproduction. These responses can be exploited in horticulture by applying far-red light-emitting diodes (LEDs). Responses to far-red light also have marked effects on plant defences and influence plant-herbivore and plant-carnivore interactions. It is, however, not known how changes in flowering traits induced by far-red light affect plant-pollinator interactions. We studied the effects of supplemental far-red light on tomato truss development, floral volatiles, pollen sugar and amino acid content, and the foraging behaviour of the buff-tailed bumblebee (Bombus terrestris).Far-red light significantly increased plant height, accelerated flowering and increased the number of flowers per truss. Floral volatile emission was increased in the early stages of tomato development, and sugar content was higher in pollen of plants exposed to far-red light. Pollen amino acid content was not affected. Bumblebees spent more time foraging on far-red-exposed plants and visited more flowers on these plants.We conclude that plant exposure to far-red light leads to changes in flower traits that increase the attraction of bumblebees, which has promising implications for the use of supplemental far-red LEDs in greenhouse tomato crops.

Beyond trait distances: Functional distinctiveness captures the outcome of plant competition

Abstract Functional trait distances between coexisting organisms reflect not only complementarity in the way they use resources, but also differences in their competitive abilities. Accordingly, absolute and relative trait distances have been widely used to capture the effects of niche dissimilarity and competitive hierarchies, respectively, on the performance of plants in competition. However, multiple dimensions of the plant phenotype are involved in these plant–plant interactions (PPI), challenging the use of relative trait distances to predict their outcomes. Furthermore, estimating the effects of competitive hierarchy on the performance of a group of coexisting plants remains particularly difficult since relative trait distances relate to the effects of a focal plant on another. We argue that trait distinctiveness, an emerging facet of functional diversity that characterizes the eccentric position of a species (or genotype) in a phenotypic space, can reveal the unique role played by a given individual plant in a group of competing plants. We used the model crop species Oryza sativa spp. japonica to evaluate the ability of trait distances and trait distinctiveness to predict the outcome of intraspecific PPI on the performance of single genotype and genotype mixtures. We performed a screening experiment to characterize the phenotypic space of 49 rice genotypes based on 11 above‐ground and root traits. We selected nine genotypes with contrasting positions in the phenotypic space and grew them in pots following a complete pairwise interaction design. Relative distances and distinctiveness based on traits associated with light competition were by far the best predictors of the performance of single genotypes—taller genotypes that acquired resource faster being the best competitors—while absolute trait distances had no effect. These results indicate that competitive hierarchy for light dominates PPI in this experiment. Consistently, trait distinctiveness in plant height and age at flowering had the strongest, positive effects on mixture performance, confirming that functional distinctiveness captures the effects of trait hierarchies and asymmetric PPI at this scale. Our findings shed new light on the role of trait diversity in regulating PPI and ecosystem processes and call for a greater consideration of functional distinctiveness in studies of coexistence mechanisms. Read the free Plain Language Summary for this article on the Journal blog.

Which demographic processes control competitive equilibria? Bayesian calibration of a size‐structured forest population model

AbstractIn forest communities, light competition is a key process for community assembly. Species' differences in seedling and sapling tolerance to shade cast by overstory trees is thought to determine species composition at late‐successional stages. Most forests are distant from these late‐successional equilibria, impeding a formal evaluation of their potential species composition. To extrapolate competitive equilibria from short‐term data, we therefore introduce the JAB model, a parsimonious dynamic model with interacting size‐structured populations, which focuses on sapling demography including the tolerance to overstory competition. We apply the JAB model to a two‐“species” system from temperate European forests, that is, the shade‐tolerant species Fagus sylvatica L. and the group of all other competing species. Using Bayesian calibration with prior information from external Slovakian national forest inventory (NFI) data, we fit the JAB model to short time series from the German NFI. We use the posterior estimates of demographic rates to extrapolate that F. sylvatica will be the predominant species in 94% of the competitive equilibria, despite only predominating in 24% of the initial states. We further simulate counterfactual equilibria with parameters switched between species to assess the role of different demographic processes for competitive equilibria. These simulations confirm the hypothesis that the higher shade tolerance of F. sylvatica saplings is key for its long‐term predominance. Our results highlight the importance of demographic differences in early life stages for tree species assembly in forest communities.

Optimal coordination between photosynthetic acclimation strategy and canopy architecture in two contrasting cucumber cultivars

AbstractCrop varieties differing in architectural characteristics (AC) vary in their intra-canopy light distribution. To optimize canopy photosynthesis, we hypothesize that varieties with contrasting AC possess different photosynthetic acclimation strategy (PAS) with respect to photosynthetic nitrogen (Np) partitioning. We firstly used in silico experiments to test this hypothesis and suggested a trade-off in Np partitioning between carboxylation and light harvesting to achieve optimal coordination between PAS, AC and growing light environment. Then, two cucumber (Cucumis sativus L.) cultivars, Aramon and SC-50, which were bred under greenhouse vertical single-stem and field creeping multi-branch canopy, were selected for studying their differences in AC and PAS using greenhouse and growth chamber experiments, respectively. In the greenhouse, more horizontal leaves of SC-50 resulted in steeper intra-canopy light gradient and a higher degree of self-shading, especially in the upper canopy layer. In growth chamber experiments, Aramon invested more leaf nitrogen into photosynthesis than SC-50, and the proportion (pNp) increased as light was reduced. In contrast, pNp of SC-50 did not respond to light but SC-50 partitioned its limited Np between carboxylation and light harvesting functions more effectively, showing a strategy particularly advantageous for canopies with a high degree of self-shading. This is further confirmed by additional in silico experiments showing that Np partitioning of SC-50 coped better with the impact of strong light competition caused by low light and by leaf clumping under high planting density. These findings provide a comprehensive perspective of genotypic variation in PAS, canopy architectures and their optimal coordination.

Catching up with the trees: empirical advancements to improve herbaceous representation in models.

This article is a Commentary on Curasi et al. (2023), 239: 562–575.