Relative Biomass Allocation Research Articles

Capital and income breeders among herbs: how relative biomass allocation into a storage organ relates to clonal traits, phenology and environmental gradients.

Perennial herbs of seasonal climates invest carbon into belowground storage organs (e.g. rhizomes) to support growth when photosynthetic acquisition cannot cover demands. An alternative explanation interprets storage allocation as surplus carbon that is undeployable for growth when plants are limited by nutrients/water. We analysed relative investments to rhizomes to see to which of these explanations they align, and asked whether they scale with biomass of aboveground organs in individual species and whether clonal growth traits, phenology or environmental conditions explain investment among populations or species. We measured biomass of rhizomes, aboveground stems and leaves in 20 temperate herbaceous perennial species, each at two localities, establishing allometric relationships for pairs of organs. We correlated relative rhizome investment with clonal traits, environmental gradients and phenology, across species. For pairs of organs, biomass typically scales isometrically. Interspecific allocation differences are largely explained by phenology. Neither interspecific nor intraspecific differences were explained by clonal traits or environment. Storage organs of perennial herbs do not comprise deposition of carbon surplus, but receive greater allocation in capital breeders (early-flowering), than among income breeders (late-flowering) relying on acquisition during growing season. Capital and income breeders in plants deserve further examination of benefits/costs.

Population genetic differentiation and phenotypic plasticity of Ambrosia artemisiifolia under different nitrogen levels.

Rapid adaptive evolution and phenotypic plasticity are two mechanisms that often underlie invasiveness of alien plant species, but whether they can co-occur within invasive plant populations under altered environmental conditions such as nitrogen (N) enrichment has seldom been explored. Latitudinal clines in plant trait responses to variation in environmental factors may provide evidence of local adaptation. Here, we inferred the relative contributions of phenotypic plasticity and local adaptation to the performance of the invasive plant Ambrosia artemisiifolia under different soil N levels, using a common garden approach. We grew A. artemisiifolia individuals raised from seeds that were sampled from six invasive populations along a wide latitudinal cline in China (23°42' N to 45°43' N) under three N (0, 5, and 10 g N m-2 ) levels in a common garden. Results show significant interpopulation genetic differentiation in plant height, number of branches, total biomass, and transpiration rate of the invader A. artemisiifolia across the N treatments. The populations also expressed genetic differentiation in basal diameter, growth rate, leaf area, seed width, root biomass, aboveground biomass, stomatal conductance, and intercellular CO2 concentration regardless of N treatments. Moreover, plants from different populations of the invader displayed plastic responses in time to first flower, hundred-grain weight, net photosynthetic rate, and relative biomass allocation to roots and shoots and seed length under different N treatments. Additionally, individuals of A. artemisiifolia from higher latitudes grew shorter and allocated less biomass to the roots regardless of N treatment, while latitudinal cline (or lack thereof) in other traits depended on the level of N in which the plants were grown. Overall, these results suggest that rapid adaptive evolution and phenotypic plasticity in the various traits that we quantified may jointly contribute to invasiveness of A. artemisiifolia under different levels of N availability. More broadly, the results support the idea that phenotypic plasticity and rapid adaptive evolution can jointly enable invasive plants to colonize a wide range of environmental conditions.

Effects of Fertilizer on Growth and Biomass Allocation of Three Evergreen Tree Species from Seasonally Dry Tropical Forests

Tree planting is widely accepted as a strategy to mitigate climate change, with a strong focus on use of native tree species. Various kinds of fertilizer have been recommended to produce optimal quality planting stocks for forest restoration. This study tested the hypothesis that additional fertilizer could improve seedling growth and alter biomass allocation in seedlings of evergreen tree species. Three species were studied: Aphanamixis polystachya (a slow-growing species), Eriobotrya bengalensis (a pioneer species) and Podocarpus neriifolius (a slow-growing species). These species are used to restore seasonally dry tropical forests in northern Thailand. We applied 4 different treatments of fertilizer addition (0, 150, 300 and 600 mg per seedling) and measured relative growth rate (RGR) and biomass allocation. The 3 species responded differently to the fertilizer addition in both growth and biomass allocation. Only the pioneer species, E. bengalensis, showed a significant response to fertilizer addition at the highest dose. The 600 mg treatment increased E. bengalensis’ RGR by 60 % but decreased root mass fraction by 4 %, compared with the control. Pioneer species respond to fertilizer addition with accelerated growth rate rather than by increasing nutrient stores. On the other hand, slow-growing species have a low annual requirement; therefore, they are not highly responsive to nutrient addition. Further investigation into the effects of fertilizer on growth and biomass allocation in pioneer species is needed to enable the propagation of cost-effective and high-quality planting stocks for forest restoration. HIGHLIGHTS The effect of four different amounts of fertilizer (0, 150, 300 and 600 mg) on growth and biomass allocation was investigated in three native tree species from northern Thailand - Aphanamixis polystachya, Eriobotrya bengalensis and Podocarpus neriifolius The three species responded differently to the fertilizer in both growth and biomass allocation While the addition of 600 mg of fertilizer increased the relative growth rate of bengalensis, a pioneer species, by 60 %, fertilizer addition did not affect the growth rate of relatively slow-growing species - A. polystachya and P. neriifolius The root mass fraction of the pioneer species was reduced by 4 % in the 600 mg fertilizer treatment compared with the control treatment, while the biomass allocation of the relatively slow-growing species was not affected by the fertilizer GRAPHICAL ABSTRACT

Relative Growth Rate and Biomass Allocation among Some Important Commonly Planted Trees in an Irrigated Urban Landscape

ABSTRACT The present study was conducted to estimate relative growth rates (RGR) and above- and below-ground biomass stocks of 10 tree species commonly planted in arid irrigated urban areas in Pakistan. Saplings were grown in the Botanic Garden of Government College University, Lahore. The growth was monitored for a year and a half and then trees were destructively harvested to assess biomass stocks. The mean relative growth rate ranged from 0.03 ± 0.021 cm cm−1 day−1 to 0.28 ± 0.016 cm cm−1 day−1. The mean above-ground oven dried biomass ranged from 0.51 ± 0.071 kg to 28.34 ± 3.746 kg, while the mean below-ground biomass ranged from 0.12 ± 0.053 kg to 7.35 ± 0.605 kg. Further, we found that the RGR was significantly and positively correlated with above-ground biomass, below-ground biomass, and root-shoot ratios. Across all 80 individuals of the studied species, diameter at tree base was significantly and positively related to whole tree biomass (R2 = 0.80). In this study we have developed the species-specific equations to estimate biomass in young urban species. Such data will be helpful for plantation decision makers, who may need to select the species according to relative growth rates and biomass allocation.

Functionally divergent growth, biomass allocation and root distribution of two xerophytic species in response to varying soil rock fragment content

Rock fragments are widespread in soil profiles. Despite direct effects of rock fragment content (RFC) on vegetation and soil properties, how plants respond to variations in RFC remains poorly understood. In this work, we investigated responses of two contrasting xerophytic species to varying RFC. Root biomass allocation, vertical distribution and above-ground growth were measured in Artemisia vestita and Bauhinia brachycarpa after 2 years of growth in an experiment with four levels of RFC (0, 25, 50 and 75% ν ν−1). The responses of above-ground growth and total biomass of both species showed a unimodal curve with values increasing up to intermediate RFC (25% and 50%) and then declining. Both species increased relative biomass allocation to roots at the highest RFC level (75%). A. vestita had a shallow rooting profile and greater declines in plant growth with high RFC compared with B. brachycarpa which had a deeper rooting profile. We found that intermediate RFCs were beneficial for growth of both species and both species increased root-to-shoot ratios to compensate for high RFC. The higher overall root fraction and deeper rooting profile may make B. brachycarpa more suitable than A. vestita for areas with high RFC, enabling greater extraction of increasingly limited soil resources.

Nonlinear drought plasticity reveals intraspecific diversity in a dominant grass species

Abstract Intraspecific diversity of dominant species in native plant communities can modulate ecosystem function under both optimal and stressful conditions. Yet, few genotype by environment interaction studies quantify differences in the shape of plasticity functions or phenotypic breakpoints across genotypes in natural populations. Using three genotypes with a history of drought selection, we performed a greenhouse study on the dominant tallgrass prairie species Andropogon gerardii. We investigated phenotypic plasticity and recovery differences among genotypes across a water availability gradient, measuring growth‐related, instantaneous and cumulative phenotypes. To further understand genotype by environment effects, we quantified plasticity functions and breakpoints among genotypes. Like other studies, we found strong evidence for phenotypic and plasticity differences among genotypes. However, we also found nonlinear plasticity functions and breakpoints were common across phenotypes, especially relative growth rates, biomass allocation and root architecture. Drought selected genotypes were also more likely to flower during recovery, but all genotypes were resilient to drought across treatments. We demonstrate that plasticity functions may help explain intraspecific diversity, patterns of selection and nonlinear community responses to more variable rainfall within an experimental population. In particular, plasticity functions can help disentangle drought/variability tolerance versus acquisitive strategies. A better understanding of intraspecific diversity in this grass species will provide more mechanistic insight into its ability to buffer ecosystem changes and provide resiliency in the tallgrass prairie under future droughts. A free Plain Language Summary can be found within the Supporting Information of this article.

Sugar maple (Acer saccharum Marsh.) shoot architecture reveals coordinated ontogenetic changes between shoot specialization and branching pattern

Trees display contrasting specialized annual shoots during their life-span and along with ontogeny-driven modifications in their branching pattern, they can fulfill different combinations of light exploitation and space exploration functions Tree ontogeny is related to major changes in tree structure and function at different scales, from individual organs to the whole tree. Yet, little is known about the direct effects of tree ontogeny on shoot specialization and branching patterns. Such specific architectural changes occurring with tree growth and aging are of critical importance for understanding the response of trees to their environment. The uppermost branching system of 0.1- to 23-m-tall sugar maple trees was sampled at the end of the growing season. Measurements were made at both the branching system (n = 40) and annual shoot scales (n = 803). An algorithm for automated shoot typology was developed to characterize branching pattern variations. Sugar maple shoots were divided into four types with contrasting sizes and levels of foliage (i.e., relative biomass allocation into leaves, LMF). These morphological differences were interpreted as functional specializations for light exploitation (high LMF) or space exploration and support (low LMF). Only annual trunk shoots exhibited trait value changes during ontogeny such as a minimum allocation to foliage in the current-year shoots for the 5-m-tall trees, which is related to lower light interception capabilities but higher space exploration abilities. However, this relative loss of light interception function is compensated by ontogenetic changes at the branching system scale, which are associated with higher rates of ramification to produce lateral shoots. This study reveals how branching system and annual shoot traits change simultaneously during tree ontogeny to fulfill different functions, particularly light exploitation and space exploration.

The role of beach and sand dune vegetation in mediating wave run up erosion

The role of beach and sand dune vegetation in mediating wave run up erosion

Rapid alignment of functional trait variation with locality across the invaded range of Sahara mustard (Brassica tournefortii).

Mechanisms by which invasive species succeed across multiple novel environmental contexts are poorly understood. Functional traits show promise for identifying such mechanisms, yet we lack knowledge of which functional traits are critical for success and how they vary across invaded ranges and with environmental features. We evaluated the widespread recent invasion of Sahara mustard (Brassica tournefortii) in the southwestern United States to understand the extent of functional trait variation across the invaded range and how such variation is related to spatial and climatic gradients. We used a common garden approach, growing two generations of plants in controlled conditions sourced from 10 locations across the invaded range. We measured variation within and among populations in phenological, morphological, and physiological traits, as well as performance. We found nine key traits that varied among populations. These traits were related to phenology and early growth strategies, such as the timing of germination and flowering, as well as relative allocation of biomass to reproduction and individual seed mass. Trait variation was related most strongly to variation in winter precipitation patterns across localities, though variations in temperature and latitude also had significant contributions. Our results identify key functional traits of this invasive species that showed significant variation among introduced populations across a broad geographic and climatic range. Further, trait variation among populations was strongly related to key climatic variables, which suggests that population divergence in these traits may explain the successful colonization of Sahara mustard across its invaded US range.

Relative growth rate, biomass partitioning and nutrient allocation in seedlings of two threatened trees grown under different light conditions

Relative growth rate, biomass partitioning and nutrient allocation in seedlings of two threatened trees grown under different light conditions

Light energy partitioning, photosynthetic efficiency and biomass allocation in invasive Prunus serotina and native Quercus petraea in relation to light environment, competition and allelopathy

This study addressed whether competition under different light environments was reflected by changes in leaf absorbed light energy partitioning, photosynthetic efficiency, relative growth rate and biomass allocation in invasive and native competitors. Additionally, a potential allelopathic effect of mulching with invasive Prunus serotina leaves on native Quercus petraea growth and photosynthesis was tested. The effect of light environment on leaf absorbed light energy partitioning and photosynthetic characteristics was more pronounced than the effects of interspecific competition and allelopathy. The quantum yield of PSII of invasive P. serotina increased in the presence of a competitor, indicating a higher plasticity in energy partitioning for the invasive over the native Q. petraea, giving it a competitive advantage. The most striking difference between the two study species was the higher crown-level net CO2 assimilation rates (Acrown) of P. serotina compared with Q. petraea. At the juvenile life stage, higher relative growth rate and higher biomass allocation to foliage allowed P. serotina to absorb and use light energy for photosynthesis more efficiently than Q. petraea. Species-specific strategies of growth, biomass allocation, light energy partitioning and photosynthetic efficiency varied with the light environment and gave an advantage to the invader over its native competitor in competition for light. However, higher biomass allocation to roots in Q. petraea allows for greater belowground competition for water and nutrients as compared to P. serotina. This niche differentiation may compensate for the lower aboveground competitiveness of the native species and explain its ability to co-occur with the invasive competitor in natural forest settings.

Biomass allocation in five semi-arid afforestation species is driven mainly by ontogeny rather than resource availability

The changes in the relative biomass allocation to roots in juvenile stands of fast-growing ( Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L.) and slow-growing ( Anacardium occidentale L. and Parkia biglobosa Jacq.) afforestation species are driven mainly by ontogeny rather than resource availability. However, silvicultural management aiming at increasing availability of water and particularly nutrients enhances biomass production in all species. Understanding the patterns of biomass allocation among tree species in response to ontogeny and to variation in resource availability is key to the successful restoration of degraded land using forest plantations. This study assessed the effects of resource availability and ontogeny on biomass accumulation and partitioning in five semi-arid afforestation species. The aboveground and belowground biomass production of fast-growing Leucaena leucocephala Lam., Moringa oleifera Lam., and Jatropha curcas L. and slow-growing Anacardium occidentale L. and Parkia biglobosa Jacq. was monitored following the application of manure (1 kg plant−1) and/or supplemental irrigation (0.5 L per sapling daily) during the first two rainy seasons and the intervening dry season on degraded cropland in Northern Benin. Biomass accumulation in the fast-growing species was positively impacted by fertilization and irrigation during both rainy seasons. The slow-growing species responded positively to the silvicultural treatments during the dry and second rainy season. The application of fertilizer alone increased the biomass of P. biglobosa by up to 335% during the dry season. Fifteen months after planting, manure-treated L. leucocephala accumulated the most biomass (2.9 kg tree−1). The root fraction decreased with increasing tree size in all species. The comparison of root versus shoot allocation in trees of equal size indicated that the treatment-induced shifts in biomass partitioning were controlled by ontogeny, which explained 86–95% of the variation in root-shoot biomass relationships. While ontogeny was the main driver of biomass partitioning, increased resource availability induced a larger production of biomass, overall leading to greater aboveground production in all species.

Unexpected drought resistance strategies in seedlings of four Brachychiton species.

Functional traits associated with drought resistance can be useful for predicting tree responses to a drying climate. Yet drought resistance is likely achieved through a complex combination of constitutive traits (traits expressed even in benign environments) and plastic traits (traits expressed only in response to drought). Because few studies measure multiple traits for multiple species under both well-watered and drought conditions, we often struggle to identify suites of constitutive and plastic traits indicative of drought resistance strategies. Using a greenhouse experiment, we examined nine drought resistance traits (six morphological/allocation traits plus assimilation, stomatal conductance and water-use efficiency) in well-watered and water-stressed seedlings of four Brachychiton (Malvaceae Juss.) species with ranges spanning a strong aridity gradient in east-central Australia. In benign conditions, constitutive biomass allocation was consistent with expectations, with xeric species investing more heavily in roots and stem tissue and less in leaf tissue than mesic species (P = 0.004). Under drought conditions, xeric species decreased relative biomass allocation below-ground while mesic species increased relative below-ground allocation (treatment × species interaction P = 0.0015). Relative water content of the stems was slightly higher in xeric species (P = 0.055), and remained stable during drought while decreasing in mesic species (treatment × species P = 0.001). Specific leaf area (SLA) and leaf dry matter content (LDMC) did not fit with expectations under either benign or water-limited conditions. Moreover, stomatal conductance and carbon assimilation were unexpectedly highest and intrinsic water-use efficiency (WUEi) lowest in the xeric species in benign conditions. Only under drought did the xeric species manifest higher WUEi than the mesic species (treatment × species P < 0.0001). We found that even closely related species exhibited diverse combinations of drought resistance traits. Notably, traits commonly used as proxies for drought tolerance (e.g., SLA, LDMC, well-watered WUEi) performed more poorly than constitutive allocation traits. This study highlights the need to consider multiple traits and phenotypic plasticity when assessing species' drought resistance for forest management in the face of climate change.

Importance of whole-plant biomass allocation and reproductive timing to habitat differentiation across the North American sunflowers.

Trait-based plant ecology attempts to use small numbers of functional traits to predict plant ecological strategies. However, a major gap exists between our understanding of organ-level ecophysiological traits and our understanding of whole-plant fitness and environmental adaptation. In this gap lie whole-plant organizational traits, including those that describe how plant biomass is allocated among organs and the timing of plant reproduction. This study explores the role of whole-plant organizational traits in adaptation to diverse environments in the context of life history, growth form and leaf economic strategy in a well-studied herbaceous system. A phylogenetic comparative approach was used in conjunction with common garden phenotyping to assess the evolution of biomass allocation and reproductive timing across 83 populations of 27 species of the diverse genus Helianthus (the sunflowers). Broad diversity exists among species in both relative biomass allocation and reproductive timing. Early reproduction is strongly associated with resource-acquisitive leaf economic strategy, while biomass allocation is less integrated with either reproductive timing or leaf economics. Both biomass allocation and reproductive timing are strongly related to source site environmental characteristics, including length of the growing season, temperature, precipitation and soil fertility. Herbaceous taxa can adapt to diverse environments in many ways, including modulation of phenology, plant architecture and organ-level ecophysiology. Although leaf economic strategy captures one key aspect of plant physiology, on their own leaf traits are not particularly predictive of ecological strategies in Helianthus outside of the context of growth form, life history and whole-plant organization. These results highlight the importance of including data on whole-plant organization alongside organ-level ecophysiological traits when attempting to bridge the gap between functional traits and plant fitness and environmental adaptation.

Life history trait divergence among populations of a non‐palatable species reveals strong non‐trophic indirect effects of an abundant herbivore

When large herbivores exert selection on their prey plant species, co‐occurring, non‐prey species may experience selection through non‐trophic indirect effects. Such selection is likely common where herbivores are overabundant. Yet, empirical studies of non‐trophic indirect effects as drivers of non‐prey trait evolution are lacking. Here we test for adaptive shifts in life history traits in an unpalatable species, Arisaema triphyllum, a common forest perennial that is unique because it exhibits size‐dependent sex switching. We collected A. triphyllum from six sites that experience a gradient in abiotic stress caused by deer browse pressure on prey plant species that generate indirect effects. We grew A. triphyllum from these sites in a common garden for five years to evaluate life history predictions linking strong indirect effects and abiotic stress to changes in life history traits: flowering onset size threshold, female flowering size threshold, relative growth rate (RGR), biomass allocation, and asexual reproduction. Despite observed differences among phenotypes in the field, expression of flowering onset size threshold, biomass allocation, and asexual reproduction did not differ among the six populations in the garden, indicating common plastic responses. In contrast, A. triphyllum collected from sites experiencing the two highest deer impacts exhibited smaller female flowering size thresholds and the highest RGR. Responses in these traits support the predictions of adaptive divergence in response to indirect effects. Our results reinforce the idea that non‐trophic indirect effects of large herbivores can elicit evolutionary responses in some traits of non‐prey species. In general, life history traits of unpalatable species may be cryptically adapting to stressful indirect effects where large herbivores are overabundant.

Root architecture might account for contrasting establishment success of Pseudotsuga menziesii var. menziesii and Pinus sylvestris in Central Europe under dry conditions

Pinus sylvestris seedlings quickly expand their roots to deeper soil layers while Pseudotsuga menziesii concentrates its root system in the topsoil, thereby running the risk of desiccation during long dry spells, as indicated by lower survival after simulated summer drought. Pseudotsuga menziesii (Douglas-fir) is regarded as a promising species to maintain the productivity of Central European lowland forests given the projected increase of long dry spells. Will the species be able to regenerate from seed and spread outside plantations in a drier temperate Europe? We measured the relative growth rate, biomass allocation, root architecture, and phenotypic plasticity of Pseudotsuga menziesii seedlings sown in a common garden and grown under current precipitation and prolonged drought, respectively. The species’ competitive ability with respect to Pinus sylvestris L., the most drought-tolerant native conifer in Central Europe, was assessed during three growing seasons. Pinus sylvestris seedlings had higher relative growth rates than did Pseudotsuga menziesii seedlings, first in terms of aboveground biomass and later in terms of shoot height. This resulted in heavier and taller seedlings after three growing seasons under both moist and dry conditions. Shorter vertical roots corresponded with lower survival of Pseudotsuga menziesii seedlings under dry conditions. Fast root proliferation allows Pinus sylvestris seedlings to reach deeper water pools that are less rapidly depleted during transient drought. By contrast, the shallow root system might put Pseudotsuga menziesii seedlings at the risk of desiccation during prolonged dry spells.

Acclimation of Betula alleghaniensis Britton to moderate soil water deficit: small morphological changes make for important consequences in crown display.

In the context of the predicted increasing frequency of summer droughts in the northeastern deciduous forest of North America due to climate change, we investigated the acclimation capacity of yellow birch, an economically important native tree species, to soil water deficit. We carried out an integrated examination of allocation of biomass, leaf physiology, branching pattern and in situ 3D crown display. Potted seedlings were subjected to moderate soil water deficit for four consecutive months during their second growing season. Individuals under soil water deficit showed a 40% decrease in biomass accumulation but no change in the relative allocation of biomass to the different plant compartments. Net CO2 assimilation rates at leaf level decreased under water deficit (~15%) but could not alone explain the total reduction in growth, excluding the carbon starvation hypothesis. The observed reduction in net CO2 assimilation rates was related to a decrease in stomatal conductance and chlorophyll content. STARzen (in situ silhouette to total leaf area ratio; a proxy for light interception efficiency) decreased under soil water deficit due to shifts in biomass allocation within the branch compartment from long upper axes to short bottom axes. Despite the fact that the understanding of the processes involved in growth reduction and branching pattern alteration will need more attention in future research, we conclude that under water deficit yellow birch at young stages will: (i) experience a substantial loss of growth and biomass; and (ii) acclimate through architectural plasticity rather than through changes in the relative allocation of root biomass to enhance its water management.

Effects of nutrient availability on the amphicarpic traits of Persicaria thunbergii

Effects of nutrient availability on the amphicarpic traits of Persicaria thunbergii

Effects of artificial defoliation and simulated insect damage on the growth of Betula pendula saplings

Abstract: One-year-old silver birch (Betula pendula Roth) saplings were subjected to artificial insect damage and defoliations of varying intensities, and subsequent growth indexes, biomass allocation patterns and photosynthesis were monitored during a 60-day period. Seven treatments were conducted in which the leaves of saplings were perforated with three or six holes per each leaf, and damaged by clipping one-third of each leaf, or they received 25, 50 and 75% defoliations during a single growing season (from April to August of 2014). Simulated insect damage and artificial defoliation decreased growth. The 75% defoliation significantly reduced the total dry mass of birch saplings at harvest by 30%, while such reduction did not influence the total productivity. The dry mass of leaves was reduced by 45% when saplings were defoliated by 75% compared to not defoliated saplings. Moreover, the total production of leaves significantly increased in the 75% defoliated saplings compared with control saplings. Artificial defoliation increased the relative biomass allocation to foliage, and this was more evident in defoliated than in mechanically insect-damaged saplings. Despite losing 25, 50 or 75% of leaf mass due to clipping, defoliated birch saplings recovered similar dry masses and root/shoot ratios by harvest as the non-defoliated saplings. Perforation and clipping parts of the leaves, as well as the artificial defoliations, caused the regrowth of biomass that did not significantly change compared to healthy silver birch saplings, and this phenomenon could be assessed as equal-compensatory growth.

Biomass Accumulation and Allocation, Photosynthesis, and Carbohydrate Status of New Guinea Impatiens, Geranium, and Petunia Cuttings Are Affected by Photosynthetic Daily Light Integral during Root Development

During the propagation of herbaceous stem-tip cuttings, the photosynthetic daily light integral (DLI) inside greenhouses can be low (≈1–4 mol·m−2·d−1) during the winter and early spring when propagation typically occurs. The mechanisms by which cuttings adapt biomass allocation patterns, gas exchange, and starch accumulation in response to the photosynthetic DLI are not clearly understood. Our objectives were to quantify the impact of DLI on growth, photosynthesis, and carbohydrate concentration during the root development phase of cutting propagation. Petunia (Petunia ×hybrida ‘Suncatcher Midnight Blue’), geranium (Pelargonium ×hortorum ‘Fantasia Dark Red’), and new guinea impatiens (Impatiens hawkeri ‘Celebration Pink’) cuttings were propagated in a glass-glazed greenhouse with 23 °C air and substrate temperature set points. After callusing (≈5 mol·m−2·d−1 for 7 days), cuttings of each species were placed under either no shade or one of the two different fixed-woven shade cloths providing ≈38% or 86% shade with 16 hours of supplemental light for 14 days, resulting in DLIs of 13.0‒14.2, 5.5‒6.0, and 2.0‒2.4 mol·m−2·d−1, respectively. Leaf, stem, and root biomass accumulation increased linearly with DLI by up to 122% (geranium), 118% (petunia), and 211% (new guinea impatiens), as DLI increased by ≈11‒12 mol·m−2·d−1, while relative biomass allocation into roots increased under increasing DLI. Compared with cuttings rooted under low DLIs (2.0‒2.4 mol·m−2·d−1), cuttings of all three species generally had greater maximum gross photosynthesis under high DLIs (13.0‒14.2 mol·m−2·d−1) starting 5 or 8 days after transfer. Starch concentration increased with DLI by up to 946% (impatiens) during propagation. Taken together, the increased growth of cuttings appears to be a result of increased carbohydrate availability from elevated photosynthesis and/or photosynthetic capacity.