Adaptation of epiphytic bryophytes in the understorey attributing to the correlations and trade-offs between functional traits
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This study explores adaptive strategies of epiphytic bryophytes in the understorey by investigating the photosynthetic characteristics, pigment concentrations and nutrient stoichiometry, as well as other functional traits of three trunk-dwelling bryophytes in a subtropical montane cloud forest in SW China. The results showed that their light-saturated net photosynthetic rate (Anmax−L), light saturation point (Isat), light compensation point (Ic) and dark respiration rate (Rd) were ca 0.55, 106.72, 4.17 and 0.25 μmol m−2 s−1, respectively. Furthermore, the samples demonstrated photosynthetic down-regulation under high irradiance. These photosynthetic characteristics can be explained by higher total chlorophyll concentrations, specific leaf area, chlorophyll per unit leaf N (Chl/N), lower ratio of chlorophyll a to chlorophyll b (Chl a/b) and photosynthetic nitrogen-use efficiency. We suggest that the bryophytes adapted to the shaded understorey microhabitats through a series of correlations and trade-offs between functional traits.Keywords:
Understory
Epiphyte
Compensation point
Shade tolerance
Respiration rate
Specific leaf area
Photosynthetic capacity
S ummary Seedlings of five tree species of different shade tolerance were raised in full daylight and in three degrees of shade. Leaf chlorophyll content, the rate of respiration in darkness at 30°C and photosynthesis rates at 30°C over a range of light intensities, were measured in each case. The initial slope of the curve, relating photosynthesis rate and light intensity, provides a measure of the capacity of the photochemical system of the leaves and was usually steeper in shade grown leaves than in sun leaves. Thus all species showed a degree of adaptation to shade conditions, but, surprisingly, leaves of the shade tolerant species had slightly less steep slopes than the intolerant species. This was offset by a considerably lower rate of leaf respiration and a lower light compensation point in the tolerant species, so that considered over a range of varying low light intensities, the net photosynthesis would probably be similar in both groups. Moreover, whilst leaves of the tolerant species tended to show reduced respiratory activity when grown in shade, this was less evident in the intolerant species. The differences in rates of respiration may he the most important determinants of success or failure in woodland shade, where the plant may spend many more hours below than above the light compensation point.
Compensation point
Shade tolerance
Darkness
Daylight
Light intensity
Respiration rate
Shading
Phytochrome
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Mechanisms of shade tolerance in tree seedlings, and thus growth in shade, may differ by leaf habit and vary with ontogeny following seed germination. To examine early responses of seedlings to shade in relation to morphological, physiological and biomass allocation traits, we compared seedlings of 10 temperate species, varying in their leaf habit (broadleaved versus needle-leaved) and observed tolerance to shade, when growing in two contrasting light treatments - open (about 20% of full sunlight) and shade (about 5% of full sunlight). We analyzed biomass allocation and its response to shade using allometric relationships. We also measured leaf gas exchange rates and leaf N in the two light treatments. Compared to the open treatment, shading significantly increased traits typically associated with high relative growth rate (RGR) - leaf area ratio (LAR), specific leaf area (SLA), and allocation of biomass into leaves, and reduced seedling mass and allocation to roots, and net assimilation rate (NAR). Interestingly, RGR was not affected by light treatment, likely because of morphological and physiological adjustments in shaded plants that offset reductions of in situ net assimilation of carbon in shade. Leaf area-based rates of light-saturated leaf gas exchange differed among species groups, but not between light treatments, as leaf N concentration increased in concert with increased SLA in shade. We found little evidence to support the hypothesis of a increased plasticity of broadleaved species compared to needle-leaved conifers in response to shade. However, an expectation of higher plasticity in shade-intolerant species than in shade-tolerant ones, and in leaf and plant morphology than in biomass allocation was supported across species of contrasting leaf habit.
Shade tolerance
Specific leaf area
Shading
Habit
Relative growth rate
Allometry
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Initial growth of germinated seeds is an important life history stage, critical for establishment and succession in forests. Important questions remain regarding the differences among species in early growth potential arising from shade tolerance. In addition, the role of leaf habit in shaping relationships underlying shade tolerance-related differences in seedling growth remains unresolved. In this study we examined variation in morphological and physiological traits among seedlings of 10 forest tree species of the European temperate zone varying in shade tolerance and leaf habit (broadleaved winter-deciduous species vs needle-leaved conifers) during a 10-week period. Seeds were germinated and grown in a controlled environment simulating an intermediate forest understory light environment to resolve species differences in initial growth and biomass allocation. In the high-resource experimental conditions during the study, seedlings increased biomass allocation to roots at the cost of leaf biomass independent of shade tolerance and leaf habit. Strong correlations between relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), specific leaf area (SLA) and leaf mass fraction (LMF) indicate that physiology and biomass allocation were equally important determinants of RGR as plant structure and leaf morphology among these species. Our findings highlight the importance of seed mass- and seed size-related root morphology (specific root length—SRL) for shade tolerance during early ontogeny. Leaf and plant morphology (SLA, LAR) were more successful in explaining variation among species due to leaf habit than shade tolerance. In both broadleaves and conifers, shade-tolerant species had lower SRL and greater allocation of biomass to stems (stem mass fraction). Light-seeded shade-intolerant species with greater SRL had greater RGR in both leaf habit groups. However, the greatest plant mass was accumulated in the group of heavy-seeded shade-tolerant broadleaves. The results of our study suggest that the combinations of plant attributes enhancing growth under high light vary with shade tolerance, but differ between leaf habit groups.
Specific leaf area
Shade tolerance
Habit
Understory
Relative growth rate
Leaf size
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Summary Shade tolerance can be defined as the light level at which plants can survive and possibly grow. This light level is referred to as the whole‐plant light compensation point ( LCP ). The LCP depends on multiple leaf and architectural traits. We are still uncertain how often interspecific trait differences allow species to specialize for separate light niches, as observed between shade‐tolerant species and light‐demanding species. Alternatively, trait plasticity may allow many species to grow in similar light conditions. We measured leaf and architectural traits of up to 1.5‐year‐old seedlings of 15 sympatric P sychotria shrub species grown at three light levels. We used a 3 D plant model to estimate the impacts of leaf traits, architectural traits and plant size on the whole‐plant light compensation point ( LCP plant ). Plant growth rates were estimated from destructive harvests and allometric relationships. At lower light levels, plants of all species achieved a lower leaf light compensation point ( LCP leaf ). The light interception efficiency ( LIE ), an index of self‐shading, decreased with increasing plant size and was therefore lower in high‐light treatments where plants grew more rapidly. When corrected for size, LIE was lower in the low‐light treatment, possibly as a result of lower investments in woody support. Species did not show trade‐offs in growth under low‐ and high‐light conditions, because species with the greatest plasticity in LCP plant and underlying traits ( LCP leaf and LIE ) achieved the highest growth rates at lower light levels. Synthesis . The interspecific differences in LCP plant did not result in a growth or survival trade‐off between low‐ and high‐light conditions. Instead, these differences were more than offset by the greater plasticity in LCP plant in some species, which was driven by greater plasticity in both leaves and architecture. The most plastic species achieved the fastest growth at different light levels. The results show that plasticity largely neutralizes the separation of light niches amongst species in this forest understorey genus and imply that differential preferences of species for either gaps or forest understorey occur in later life phases or are driven by other stress factors than low light alone.
Compensation point
Shade tolerance
Specific leaf area
Interception
Understory
Allometry
Shade avoidance
Niche differentiation
Leaf size
Trait
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To study the shade tolerance of Miscanthus,different shading treatments were imposed on the 5 Miscanthus ornamental grasses.The morphological and photosynthetic indexes including plant height,leaf length,leaf width,total chlorophyll content,chlorophyll a,chlorophyll b,chlorophyll a/b,maximum net photosynthetic rate(Pmax),light saturation point(LSP),light compensation point(LCP) and apparent quantum yield(AQY) were measured.The shade tolerance of these tested grasses were ranked.The results showed that shading treatments had effected on their morphological and physiological indexes to different extends.By using membership function to evaluate the shade tolerant ability,the order of the shade tolerance from strong to weak was M.sinensis 'Morning Light',M.sinensis,M.floridulus,M.sinensis 'Variegatus' and M.sinensis 'Gracilimus'.
Shading
Shade tolerance
Compensation point
Miscanthus sinensis
Ornamental plant
Light intensity
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1 Species differences in growth and shade tolerance might contribute to coexistence of tree species. To explore how such differences depend on underlying plant traits, 14 tree species were investigated in temperate forests on sand and loess soils in the Netherlands. Plant traits were measured for 0.5–1 m tall saplings: 10 saplings growing at low light conditions and 10 at high light conditions. Growth was determined from annual lengths of leader shoots, and shade tolerance from an independently tested scale. 2 Shade tolerance and extension growth of the leader shoot were negatively correlated. Plant traits that related positively with shade tolerance were negatively related to extension growth, and vice versa. Photosynthetic capacity, leaf dark respiration and total leaf mass related weakly to shade tolerance and extension growth. Specific leaf area (SLA, leaf area/leaf mass) and wood density were the traits most strongly correlated to shade tolerance and extension growth. 3 Shade-tolerant species had denser wood and slower extension growth. They also had larger crowns, suggesting that dense stems provide strength for supporting larger crowns. 4 More shade-tolerant species had a higher SLA, which is opposite to tree communities with larger leaf life span variation. In winter deciduous tree communities, more shade-tolerant species benefit from investing leaf area at low costs (high SLA) rather than from investing in durable leaves (low SLA). 5 Species on sand had higher growth rates and higher light requirements than species on loess. In line with the resource-ratio hypothesis, the dominance of the more shade-tolerant species on nutrient rich loess soils may be attributed to the denser vegetation supported and the resultant lower light availability for saplings compared with saplings on infertile and drought-prone sand soils. 6 Synthesis: These results provide plant trait-based predictions for the regeneration success and composition of species of temperate forests with management based on natural regeneration. These forests are expected to become dominated by shade-tolerant species with high wood density and high SLA on the more productive soils, and by light demanding species with low wood density and low SLA on poorer soils.
Shade tolerance
Specific leaf area
Photosynthetic capacity
Shading
Drought Tolerance
Dominance (genetics)
Temperate forest
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Abstract Light requirements and functional strategies of plants to cope with light heterogeneity in the field have a strong influence on community structure and dynamics. Shade intolerant plants often show a shade avoidance strategy involving a phytochrome‐mediated stem elongation in response to changes in red : far red ratio, while shade‐tolerant plants typically harvest light very efficiently. We measured plant size, stem diameter, internode and leaf lengths in randomly chosen saplings of 11 woody species differing in their shade tolerance in both a secondary forest and an old‐growth temperate evergreen rainforest in southern Chile. We also recorded the irradiance spectrum and the diffuse and direct light availabilities at each sampling point. Significant differences were found for the mean light environment of the saplings of each species, which also differed in basal stem diameter, internode length and leaf length, but not in plant height. Both plant slenderness (plant height/stem diameter) and mean internode length increased with increasing light availability, but no relationship was found between any of these two traits and red : far red ratio. The change in plant slenderness with light availability was of lesser magnitude with increasing shade tolerance of the species, while internode change with light availability increased with increasing shade tolerance of the species. Shade tolerators afford higher costs (thicker stems and plants), which render more biomechanically robust plants, and respond more to the light environment in a trait strongly influencing light interception (internode length) than shade intolerant species. By contrast, less shade‐tolerant plants afforded higher risks with a plastic response to escape from the understorey by making thinner plants that were biomechanically weaker and poorer light interceptors. Thus, species differing in their shade tolerances do differ in their plastic responses to light. Our results contribute to explain plant coexistence in heterogeneous light environments by improving our mechanistic understanding of species responses to light.
Shade tolerance
Shade avoidance
Specific leaf area
Interception
Phytochrome
Leaflet (botany)
Understory
Far-red
Shading
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To explain the coexistence of plant species in a mixed deciduous broad-leaved forest in Abruzzo, Italy, a number of leaf traits were analyzed, and the shade tolerance was investigated. Bud break started at the end of April and the rapid leaf growth during the first stages was attested by the highest relative growth rates. The leaf area index (LAI) increased from 0.7 at the beginning of the leaf growth to 2.6 at full lamina expansion. Most of the species of the dominated layer were shade-tolerant and most of the species of the dominant and co-dominant layers were shade-intolerant. There was a fairly well defined specific leaf area (SLA) range between the shade-tolerant (271.1 cm g) and shade-intolerant species (159.2 cm g). The SLA, the chlorophyll content (Chl) and the leaf water content showed the same trend from the top to the bottom of the forest canopy. The chlorophyll a/b ratio ranged from 2.78 (dominant + co-dominant layers) to 2.95 (dominated layer). Laburnum anagyroides Medicus, one of the most shade-tolerant species (305.1 cm g SLA), showed the highest total chlorophyll content (2.69 mg g) and Quercus cerris L., one of the most shade-intolerant (148.2 cm g SLA), the lowest (0.70 mg g).
Shade tolerance
Specific leaf area
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Abstract Tropical canopies are complex, with multiple canopy layers and pronounced gap dynamics contributing to their high species diversity and productivity. An important reason for this complexity is the large variation in shade tolerance among different tree species. At present, we lack a clear understanding of which plant traits control this variation, e.g., regarding the relative contributions of whole-plant versus leaf traits or structural versus physiological traits. We investigated a broad range of traits in six tropical montane rainforest tree species with different degrees of shade tolerance, grown under three different radiation regimes (under the open sky or beneath sparse or dense canopies). The two distinct shade-tolerant species had higher fractional biomass in leaves and branches while shade-intolerant species invested more into stems, and these differences were greater under low radiation. Leaf respiration and photosynthetic light compensation point did not vary with species shade tolerance, regardless of radiation regime. Leaf temperatures in open plots were markedly higher in shade-tolerant species due to their low transpiration rates and large leaf sizes. Our results suggest that interspecific variation in shade tolerance of tropical montane trees is controlled by species differences in whole-plant biomass allocation strategy rather than by difference in physiological leaf traits determining leaf carbon balance at low radiation.
Shade tolerance
Specific leaf area
Leaf size
Drought Tolerance
Shade avoidance
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Shade tolerance
Specific leaf area
Carpinus betulus
Photosynthetic capacity
Quercus petraea
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