Light-saturated Photosynthetic Rate Research Articles

Life at the conservative end of the leaf economics spectrum: intergeneric variation in the allocation of phosphorus to biochemical fractions in species of Banksia (Proteaceae) and Hakea (Proteaceae).

In severely phosphorus (P)-impoverished environments, plants have evolved to use P very efficiently. Yet, it is unclear how P allocation in leaves contributes to their photosynthetic P-use efficiency (PPUE) and position along the leaf economics spectrum (LES). We address this question in 10 species of Banksia and Hakea, two highly P-efficient Proteaceae genera. We characterised traits in leaves of Banksia and Hakea associated with the LES: leaf mass per area, light-saturated photosynthetic rates, P and nitrogen concentrations, and PPUE. We also determined leaf P partitioning to five biochemical fractions (lipid, nucleic acid, metabolite, inorganic and residual P) and their possible association with the LES. For both genera, PPUE was negatively correlated with fractional allocation of P to lipids, but positively correlated with that to metabolites. For Banksia only, PPUE was negatively correlated with residual P, highlighting a strategy contrasting to that of Hakea. Phosphorus-allocation patterns significantly explained PPUE but were not linked to the resource acquisition vs resource conservation gradient defined by the LES. We conclude that distinct P-allocation patterns enable species from different genera to achieve high PPUE and discuss the implications of different P investments. We surmise that different LES axes representing different ecological strategies coexist in extremely P-impoverished environments.

Photosynthesis of rice leaves with a parallel venation is highly tolerant to vein severing.

Vein severing in plants caused by leaf damage is common in fields where crops are cultivated. It is hypothesized that leaves with complex reticulate venation can withstand hydraulic disturbances caused by vein severing, thereby preserving leaf carbon assimilation. However, limited research focuses on vein damage of leaves with parallel venation. We studied how vein-severing affected the photosynthetic traits of rice (Oryza sativa) leaves in seconds, minutes and days, under varying water-demand conditions and differing extents of water supply disruption. Rice leaves completely lost their photosynthetic capacity within 2.5 minutes after excision. Severing the midrib resulted in reduced light-saturated photosynthetic rate (A), stomatal conductance (gsw ) and transpiration rate (E) by 2.6, 6.8 and 5.9%, respectively, already after thirty minutes. We further investigated the photosynthetic trait responses to various extents of leaf width severing, while keeping the midrib functional. Surprisingly, A, gsw and E in the downstream area of the severed leaves largely remained stable, showing minimal variation across different leaf width severing ratios. These traits declined only slightly even under increased ambient light intensity and leaf-to-air vapor pressure deficit. This sustained photosynthesis post-severing is attributed to the efficient lateral water transport. Long-term leaf damage slightly but not significantly, impacted the downstream photosynthetic traits within five days post-severing. However, a more pronounced reduction in gas exchange during leaf senescence was observed nine days after severing. These findings suggested that rice leaves can tolerate hydraulic disturbances from vein severing and maintain functionality under various conditions, which is crucial for crop yield stability. However, long-term consequences require further investigation.

Photosynthetic gas exchange, plant water relations and osmotic adjustment of three tropical perennials during drought stress and re-watering.

Planting vegetation on slopes is an effective way of improving slope stability while enhancing the aesthetic appearance of the landscape. However, plants growing on slopes are susceptible to natural drought stress (DS) conditions which commonly lead to water deficit in plant tissues that affect plant health and growth. This study investigated the photosynthetic gas exchange, plant water status and proline accumulation of three tropical perennials namely Clerodendrum paniculatum, Ipomoea pes-caprae and Melastoma malabathricum after being subjected to DS and re-watering (RW). During DS, there was a significant decrease in light-saturated photosynthetic CO2 assimilation rate (Asat), stomatal conductance (gs sat), and transpiration rate (Tr) for all three plant species. Leaf relative water content, shoot water potential, and leaf, stem and root water content also declined during DS. Proline concentration increased for all three species during DS, reaching especially high levels for C. paniculatum, suggesting that it heavily relies on the accumulation of proline to cope with DS. Most of the parameters recovered almost completely to levels similar to well-watered plants after RW, apart from M. malabathricum. Strong linear correlations were found between Asat and gs sat and between gs sat and Tr. Ultimately, C. paniculatum and I. pes-caprae had better drought tolerance than M. malabathricum.

Leaf Biochemical and Physiological Responses to Elevated Atmospheric Ozone Concentration in Eight Modern Rice Cultivars

This study investigated the effects of elevated O 3 level on photosynthetic traits and antioxidant systems of various rice genotypes under fully open-air conditions. Eight modern rice cultivars ( Oryza sativa L.), including 4 hybrids and 4 inbreds, were exposed to 2 O 3 treatments: the ambient atmosphere (A-O 3 ) and the 1.5 times ambient O 3 concentration (E-O 3 ) throughout the reproductive period. The measurements of gas exchange, chlorophyll a fluorescence, photosynthetic pigments, lipid oxidation, antioxidant content, and antioxidant enzyme activity were conducted on the flag leaf during the early and late grain-filling periods. The results indicated that E-O 3 had differential effects on the photosynthesis and antioxidant indicators of rice genotypes. In the hybrid rice, the reduction in the light-saturated photosynthetic rate ( A sat ) was primarily due to the nonstomatal factors, such as the changes in antioxidants, particularly ascorbate and carotenoids. In contrast, the reduction in A sat levels in inbred rice was mainly due to the stomatal factors. Additionally, the hybrid rice was more sensitive to O 3 than the inbred rice, with the sensitivity determinants varying between types. The sensitivity of hybrid rice to O 3 was influenced by the magnitude of its antioxidant capacity, whereas the inbred rice sensitivity was determined by the stomatal conductance ( g s ) and the antioxidant enzyme activity. The rice cultivars with higher antioxidant enzyme activities could help mitigate the damage caused by O 3 pollution. This study could provide valuable insights for screening the O 3 -tolerant rice cultivars and promoting the food security sustainability.

Allometries of cell and tissue anatomy and photosynthetic rate across leaves of C3 and C4 grasses.

Allometric relationships among the dimensions of leaves and their cells hold across diverse eudicotyledons, but have remained untested in the leaves of grasses. We hypothesised that geometric (proportional) allometries of cell sizes across tissues and of leaf dimensions would arise due to the coordination of cell development and that of cell functions such as water, nutrient and energy transport, and that cell sizes across tissues would be associated with light-saturated photosynthetic rate. We tested predictions across 27 globally distributed C3 and C4 grass species grown in a common garden. We found positive relationships among average cell sizes within and across tissues, and of cell sizes with leaf dimensions. Grass leaf anatomical allometries were similar to those of eudicots, with exceptions consistent with the fewer cell layers and narrower form of grass leaves, and the specialised roles of epidermis and bundle sheath in storage and leaf movement. Across species, mean cell sizes in each tissue were associated with light-saturated photosynthetic rate per leaf mass, supporting the functional coordination of cell sizes. These findings highlight the generality of evolutionary allometries within the grass lineage and their interlinkage with coordinated development and function.

Respiration in light of evergreen and deciduous woody species and its links to the leaf economic spectrum.

Leaf respiration in the light (Rlight) is crucial for understanding the net CO2 exchange of individual plants and entire ecosystems. However, Rlight is poorly quantified and rarely discussed in the context of the leaf economic spectrum (LES), especially among woody species differing in plant functional types (PFTs) (e.g., evergreen vs. deciduous species). To address this gap in our knowledge, Rlight, respiration in the dark (Rdark), light-saturated photosynthetic rates (Asat), leaf dry mass per unit area (LMA), leaf nitrogen (N) and phosphorus (P) concentrations, and maximum carboxylation (Vcmax) and electron transport rates (Jmax) of 54 representative subtropical woody evergreen and deciduous species were measured. With the exception of LMA, the parameters quantified in this study were significantly higher in deciduous species than in evergreen species. The degree of light inhibition did not significantly differ between evergreen (52%) and deciduous (50%) species. Rlight was significantly correlated with LES traits such as Asat, Rdark, LMA, N and P. The Rlight vs. Rdark and N relationships shared common slopes between evergreen and deciduous species, but significantly differed in their y-intercepts, in which the rates of Rlight were slower or faster for any given Rdark or N in deciduous species, respectively. A model for Rlight based on three traits (i.e., Rdark, LMA and P) had an explanatory power of 84.9%. These results show that there is a link between Rlight and the LES, and highlight that PFTs is an important factor in affecting Rlight and the relationships of Rlight with Rdark and N. Thus, this study provides information that can improve the next generation of terrestrial biosphere models (TBMs).

Photosynthetic and biochemical responses of four subtropical tree seedlings to reduced dry season and increased wet season precipitation and variable N deposition.

Interspecific variations in phenotypic plasticity of trees that are affected by climate change may alter the ecosystem function of forests. Seedlings of four common tree species (Castanopsis fissa, Michelia macclurei, Dalbergia odorifera and Ormosia pinnata) in subtropical plantations of southern China were grown in the field under rainout shelters and subjected to changing precipitation (48L of water every 4days in the dry season, 83L of water every 1day in the wet season; 4gm-2year-1 of nitrogen (N)), low N deposition (48L of water every 2days in the dry season, 71L of water every 1day in the wet season; 8gm-2year-1N), high N deposition (48L of water every 2days in the dry season, 71L of water every 1day in the wet season; 10gm-2year-1N) and their interactive effects. We found that the changes in seasonal precipitation reduced the light-saturated photosynthetic rate (Asat) for C. fissa due to declining area-based foliar N concentrations (Na). However, we also found that the interactive effects of changing precipitation and N deposition enhanced Asat for C. fissa by increasing foliar Na concentrations, suggesting that N deposition could alleviate N limitations associated with changing precipitation. Altered precipitation and high N deposition reduced Asat for D. odorifera by decreasing the maximum electron transport rate for RuBP regeneration (Jmax) and maximum rate of carboxylation of Rubisco (Vcmax). Ormosia pinnata under high N deposition exhibited increasing Asat due to higher stomatal conductance and Vcmax. The growth of D. odorifera might be inhibited by changes in seasonal precipitation and N deposition, while O. pinnata may benefit from increasing N deposition in future climates. Our study provides an important insight into the selection of tree species with high capacity to tolerate changing precipitation and N deposition in subtropical plantations.

Long-term field translocation differentially affects arbuscular mycorrhizal and ectomycorrhizal trees in a sub-tropical forest

Arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) trees are commonly represented in tropical forests, but their response to warming is generally not known. We conducted a long-term (9-year) field experiment in subtropical China by translocating AM tree species (Machilus breviflora and Schima superba) and EcM tree species (Syzygium rehderianum and Castanopsis hystrix) from a cooler high-elevation site (300 m) to a 1 °C warmer low-elevation site (30 m). Here, we report leaf chemical and physiological data from the last three years (Years 7–9) of the translocation experiment. Translocation to warmer site induced higher air (Tair) and soil (Tsoil) temperatures, but lower soil volumetric water content (SVWC). Translocation treatment significantly increased the light-saturated photosynthetic rate (Asat) for AM trees due to higher stomatal conductance (gs) and Rubisco carboxylation capacity (Vcmax), generating increased growth in AM trees. Translocation treatment reduced the maximum efficiency of photosynthetic quantum yield (Fv/Fm) and growth in EcM trees. Translocation treatment increased leaf turgor loss point (TLP) in AM trees, but reduced TLP in EcM trees. Translocation treatment increased foliar nitrogen (N) concentrations and phosphorus (P) concentrations for AM trees. In EcM trees, stable foliar N and P concentrations were related to higher N and P resorption efficiencies. Translocation treatment was more beneficial for the growth of AM trees than EcM trees, while EcM trees were more tolerant of soil water deficit. Differential responses to these co-occurring climate drivers may alter the composition of tree functional groups and ecosystem function in tropical forests in response to future warmer and drier climate conditions.

Comparative physiology of canopy tree leaves in evergreen and deciduous forests in lowland Thailand

The typical seasonally dry forests in Southeast Asia are the mixed deciduous forest (MDF), dry dipterocarp (deciduous) forest (DDF), and dry evergreen forest (DEF). We obtained 21 physiological traits in the top/sunlit leaves of 107, 65 and 51 tree species in MDF, DEF and DDF, respectively. Approximately 70%, 95% and 95% of canopy tree species which consist of MDF, DEF and DDF are sampled, respectively. Light-saturated photosynthetic rates (Asat) exhibit a positive correlation with foliar nitrogen (N) and phosphorus (P) on leaf mass and area bases across tree species. Decreased leaf mass-based P reduces the positive slope of the mass-based N and Asat relationship across species and habitats. The differences in nutrient and water use and leaf habits are well matched to the variation in soil properties among the forest types, highlighting the reliability of this comprehensive database for revealing the mechanism of niche segregation based on edaphic factors.

Coordination of leaf photosynthetic traits and chloroplast relocation of the C4 plant Setaria palmifolia

Setaria palmifolia (Poaceae), an NADP-malic enzyme type C4 grass, is distributed from the understory to the margins of forests. To reveal how this C4 plant acclimates to habitats with contrasting light regimes, we documented the behavior of chloroplast relocation and determined patterns of chloroplast relocation and photosynthetic characteristics in response to the light of S. palmifolia grown under different light regimes. Through the observation of leaf sections and measurement of leaf transmittance (T), we confirmed that mesophyll (M) cells of S. palmifolia performed avoidance and accumulation responses, resulting in an increase and decrease in T, respectively. Measurements of gas exchange revealed that the leaf photosynthetic characteristics of S. palmifolia were modulated by growth light. Shade-grown plants significantly increased dry-weight-based chlorophyll (Chl) contents and specific leaf area (SLA), indicating increased light capture. These plants, however, displayed a reduced light-saturated photosynthetic rate (Pmax) and light saturation point (LSP) compared to unshaded plants. The patterns of chloroplast relocation were closely aligned with the photosynthetic response. Shade-grown plants displayed significantly faster kinetics, a greater extent of chloroplast relocation, and lower incident light for the induction of the avoidance response than unshaded plants. The coordination patterns of chloroplast relocation and photosynthetic response suggest that chloroplast relocation in S. palmifolia complements its leaf photosynthetic responses to light availability. The ability to adjust its photosynthetic behavior and perform chloroplast relocation may enable this C4 species to thrive in habitats with various light conditions.

Are small trees more responsive to nutrient addition than large trees in an evergreen broadleaved forest?

Nitrogen (N) and phosphorus (P) availability exert a profound influence on forest productivity and function. However, forecasting tree responses is still challenging because trait plasticity among different size classes and tree species remains largely unclear.We conducted a field experiment in an evergreen broadleaved forest fertilized with four treatments: +N (100 kg N ha−1 yr−1), +P (50 kg P ha−1 yr−1), N+P (100 kg N ha−1 yr−1 + 50 kg P ha−1 yr−1), and a control. We selected four species across size classes (small trees, DBH < 15 cm; large trees, DBH ≥ 15 cm) to quantify the relative growth rate (RGR) and functional traits related to the leaf economic spectrum (LES).+P increased the RGR in small trees rather than in large trees, and its effect on RGR varied with tree species in small trees. In contrast, +N and N+P did not affect the RGR in small or large trees. Small trees exhibited greater trait plasticity in light-saturated photosynthetic rate (Pmax) and photosynthetic N and P use efficiencies (PNUE and PPUE) than large trees under P addition. In contrast, nutrient addition did not change LES traits in large trees. Most notably, treatment-induced changes in RGR were significantly correlated with changes in Pmax and PNUE in small trees and with leaf mass per area (LMA) in large trees in this subtropical forest, suggesting that trait plasticity drives tree growth responses.Our results highlight that small subtropical trees have a greater capacity to respond to nutrient alterations and have the potential to change species abundance under future N and P deposition.

Advantages of growth and competitive ability of the invasive plant Solanum rostratum over two co-occurring natives and the effects of nitrogen levels and forms.

Atmospheric nitrogen (N) deposition has often been considered as a driver of exotic plant invasions. However, most related studies focused on the effects of soil N levels, and few on those of N forms, and few related studies were conducted in the fields. In this study, we grew Solanum rostratum, a notorious invader in arid/semi-arid and barren habitats, and two coexisting native plants Leymus chinensis and Agropyron cristatum in mono- and mixed cultures in the fields in Baicheng, northeast China, and investigated the effects of N levels and forms on the invasiveness of S. rostratum. Compared with the two native plants, S. rostratum had higher aboveground and total biomass in both mono- and mixed monocultures under all N treatments, and higher competitive ability under almost all N treatments. N addition enhanced the growth and competitive advantage of the invader under most conditions, and facilitated invasion success of S. rostratum. The growth and competitive ability of the invader were higher under low nitrate relative to low ammonium treatment. The advantages of the invader were associated with its higher total leaf area and lower root to shoot ratio compared with the two native plants. The invader also had a higher light-saturated photosynthetic rate than the two native plants in mixed culture (not significant under high nitrate condition), but not in monoculture. Our results indicated that N (especially nitrate) deposition may also promote invasion of exotic plants in arid/semi-arid and barren habitats, and the effects of N forms and interspecific competition need to be taken into consideration when studying the effects of N deposition on invasion of exotic plants.

Nitrogen addition changed the relationships of fine root respiration and biomass with key physiological traits in ozone-stressed poplars

Increasing ozone (O3) and nitrogen (N) addition may have contradictory effects on plant photosynthesis and growth. However, it remains unclear whether these effects on aboveground parts further change the root resource management strategy and the relationships of fine root respiration and biomass with other physiological traits. In this study, an open-top chamber experiment was conducted to investigate the effects of O3 alone and in combination with nitrogen (N) addition on root production and fine root respiration of poplar clone 107 (Populus × euramericana cv. ‘74/76’). Saplings were grown with (100 kg ha−1 year−1) or without (+0 kg ha−1 year−1) N addition under two O3 regimes (non-filtered ambient air or non-filtered ambient air + 60 ppb of O3). After about two to three months of treatment, elevated O3 significantly decreased fine root biomass and starch content but increased fine root respiration, which occurred in tandem with inhibited leaf light-saturated photosynthetic rate (Asat). Nitrogen addition did not change fine root respiration or biomass, neither did it alter the effect of elevated O3 on the fine root traits. However, N addition weakened the relationships of fine root respiration and biomass with Asat, fine root starch and N concentrations. No significant relationships of fine root biomass and respiration with soil mineralized N were observed under elevated O3 or N addition. These results imply that changed relationships of plant fine root traits under global changes should be considered into earth system process models to project more accurately future carbon cycle.

Identification of photosynthetic parameters for superior yield of two super hybrid rice varieties: A cross-scale study from leaf to canopy.

Enhancing photosynthetic capacity is widely accepted as critical to advancing crop yield. Therefore, identifying photosynthetic parameters positively related to biomass accumulation in elite cultivars is the major focus of current rice research. In this work, we assessed leaf photosynthetic performance, canopy photosynthesis, and yield attributes of super hybrid rice cultivars Y-liangyou 3218 (YLY3218) and Y-liangyou 5867 (YLY5867) at tillering stage and flowering stage, using inbred super rice cultivars Zhendao11(ZD11) and Nanjing 9108 (NJ9108) as control. A diurnal canopy photosynthesis model was applied to estimate the influence of key environmental factors, canopy attributes, and canopy nitrogen status on daily aboveground biomass increment (AMDAY). Results showed that primarily the light-saturated photosynthetic rate at tillering stage contributed to the advancing yield and biomass of super hybrid rice in comparison to inbred super rice, and the light-saturated photosynthetic rate between them was similar at flowering stage. At tillering stage, the higher CO2 diffusion capacity, together with higher biochemical capacity (i.e., maximum carboxylation rate of Rubisco, maximum electron transport rate (J max), and triose phosphate utilization rate) favored leaf photosynthesis of super hybrid rice. Similarly, AMDAY in super hybrid rice was higher than inbred super rice at tillering stage, and comparable at flowering stage partially due to increased canopy nitrogen concentration (SLNave) of inbred super rice. At tillering stage, model simulation revealed that replacement of J max and g m in inbred super rice by super hybrid rice always had a positive effect on AMDAY, and the averaged AMDAY increment was 5.7% and 3.4%, respectively. Simultaneously, the 20% enhancement of total canopy nitrogen concentration through the improvement of SLNave (TNC-SLNave) resulted in the highest AMDAY across cultivars, with an average increase of 11.2%. In conclusion, the advancing yield performance of YLY3218 and YLY5867 was due to the higher J max and g m at tillering stage, and TCN-SLNave is a promising target for future super rice breeding programs.

Predicting ecosystem productivity based on plant community traits.

With the rapid accumulation of plant trait data, major opportunities have arisen for the integration of these data into predicting ecosystem primary productivity across a range of spatial extents. Traditionally, traits have been used to explain physiological productivity at cell, organ, or plant scales, but scaling up to the ecosystem scale has remained challenging. Here, we show the need to combine measures of community-level traits and environmental factors to predict ecosystem productivity at landscape or biogeographic scales. We show how theory can extend the production ecology equation to enormous potential for integrating traits into ecological models that estimate productivity-related ecosystem functions across ecological scales and to anticipate the response of terrestrial ecosystems to global change.

Asian tropical forests assimilating carbon under dry conditions: water stress or light benefits?

AbstractTropical forests are characterized by vast biomass, complex structures and mega-biodiversity. However, the adaptation processes of these forests to seasonal water availability are less understood, especially those located in the monsoonal and mountainous regions of tropical Southeast Asia. This study used four representative tropical forests spanning from 2° N to 22° N in continental Southeast Asia to address dry-condition photosynthesis at the seasonal scale. We first provided novel and reliable estimations of ecosystem photosynthesis (gross primary production; GPP) seasonality at all four sites. As expected, both evergreen and deciduous seasonal forests exhibited higher GPPs during the rainy season than during the dry season. A bimodal pattern corresponding to solar radiation occurred in the GPP of the perhumid forest. The surface conductance (Gs) was consistently lower both in the dry season and during dry spells (DSPs) than during the wet season and non-dry spells. However, this did not prevent GPP from increasing alongside increasing irradiance in the perhumid forest, suggesting that other ecosystem physiological properties, for example, the light-saturated photosynthetic rate, must have increased, thus surpassing the effect of Gs reduction. Thus, perhumid forests could be defined as light-demanding ecosystems with regard to their seasonal dynamics. Seasonal forests are water-stressed ecosystems in the dry season, as shown by the reductions in GPP, Gs and related ecosystem physiological properties. At all four forest sites, we observed a lack of consistent adaptive strategy to fit the water seasonality due to the diversity in leaf phenology, soil nutrient availability, root depth and other potential factors.

Photosynthetic mechanism of maize yield under fluctuating light environments in the field.

The photosynthetic mechanism of crop yields in fluctuating light environments in the field remains controversial. To further elucidate this mechanism, we conducted field and simulation experiments using maize (Zea mays) plants. Increased planting density enhanced the light fluctuation frequency and reduced the duration of daily high light, as well as the light-saturated photosynthetic rate, biomass, and yield per plant. Further analysis confirmed a highly significant positive correlation between biomass and yield per plant and the duration of photosynthesis related to daily high light. The simulation experiment indicated that the light-saturated photosynthetic rate of maize leaves decreased gradually and considerably when shortening the daily duration of high light. Under an identical duration of high light exposure, increasing the fluctuation frequency decreased the light-saturated photosynthetic rate slightly. Proteomic data also demonstrated that photosynthesis was mainly affected by the duration of high light and not by the light fluctuation frequency. Consequently, the current study proposes that an appropriate duration of daily high light under fluctuating light environments is the key factor for greatly improving photosynthesis. This is a promising mechanism by which the photosynthetic productivity and yield of maize can be enhanced under complex light environments in the field.

Physiological traits and response strategies of four subtropical tree species exposed to drought

World-wide, forests are experiencing drought-induced mortality. However, physiological adaptation to drought is highly variable, which may lead to differential mortality patterns and alter community structure. In this study, saplings of four common tree species ( Ormosia pinnata , Dalbergia odorifera , Castanopsis fissa and Michelia macclurei ) grown in subtropical plantations in southern China were subjected to average rainfall and three drought treatments, consisting of low (25% rainfall reduction), moderate (50% rainfall reduction) and high (75% rainfall reduction) drought. To investigate their drought response strategies and select tree species with higher drought tolerance, we examined plant traits, including tree growth, stomatal regulation, water relations, carbon dynamics and morphology, that might contribute to drought tolerance. We found that O. pinnata adapted to drought by decreasing turgor loss point (TLP) and increasing leaf dry matter content and leaf mass per area (LMA). D. odorifera exhibited low leaf minimum conductance and high LMA as the key drought traits to reduce water loss. C. fissa was slowest to initiate stomatal closure but completed stomatal closure more rapidly than the other species. Drought reduced light-saturated photosynthetic rates (A sat ) for O. pinnata , D. odorifera and C. fissa primarily due to declining stomatal conductance (g s ), with lesser limitations due to the biochemical capacity of Rubisco carboxylation (V cmax ) and electron transport (J max ). M. macclurei was the first species to close stomata. Drought did not affect A sat for M. macclurei due to stable photosynthetic biochemical processes; however, V cmax regulation of A sat increased with drought intensity. There was trait variation in the capacity of study trees to tolerate drought, with M. macclurei exhibiting the highest capacity to tolerate drought due to key stomatal (earlier stomatal closure) and hydraulic (lower TLP) traits reducing plant water loss with progressive drought stress. • Selecting species with morphological and physiological traits that confer high drought tolerance and resistance will be critical for designing and managing plantations. • M. macclurei might be the best adapted plantation tree for growth in future drier climates. • M. macclurei exhibited high drought avoidance and resistance, and maintained photosynthesis.

Effect of light intensities on the photosynthesis, growth and physiological performances of two maple species.

Photoinhibition decreases photosynthetic capacity and can therefore affect the plant survival, growth, and distribution, but little is known about how it affects on kindred tree species. We conducted field experiments to measure the photosynthetic, growth and physiological performances of two maple species (Acer mono and A. pseudosieboldianum) seedlings at four light intensities (100%, 75%, 55%, and 20% of full light) and evaluated the adaptability of seedlings. We found that: (1) A. mono seedlings have larger light saturated photosynthetic rates (A max), the light saturation point (LSP), and lower light compensation point (LCP) than A. pseudosieboldianum seedlings, thus indicating that the former has a stronger light utilization ability. (2) A. mono seedlings under 75% light intensity and had higher seedling height (SH), basal stem diameter (BSD), leaf number (LN), leaf area per plant (LAPP) and total dry weight (TDW), while A. pseudosieboldianum seedling at 55% light intensity displayed greater growth advantages, which agreed with their response of light saturated photosynthetic rate. Morphological plasticity adjustments such as decreased root shoot ratio (RSR) and increased specific leaf area (SLA) showed how seedlings adapt to weak light environments. (3) 100% and 20% light intensities increased the malondialdehyde (MDA) content of two maple seedlings, indicating that very strong or very weak light could lead to the imbalance of reactive oxygen species (ROS) metabolism. The regulation of antioxidant enzyme activities such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), as well as the content of osmoregulation substances such as free proline and soluble protein, are the main mechanisms of plant adaptation to light stress. Although both A. mono and A. pseudosieboldianum are highly shade tolerant, subtle differences in the photosynthetic, morphological and physiological traits underpinning their shade tolerance suggest A. pseudosieboldianum has the advantage to deal with the light threat. Future studies should focus on the expression level of photosynthesis-related genes and cell, to better understand the adaptation mechanism of plants to light variation which facilitates forest development, either natural or via silvicultural practices. This information expands our understanding of the light-regulating mechanism of trees, which contributes to develop management practices to support natural forest regeneration.

Application of fertilization in changing light adaptability and improving growth of Aralia elata (Miq.) Seem. seedlings under various light conditions in temperate forests

Non-timber forest plants have always played a significant role in livelihood security by providing valuable non-timber forest products, especially in less-developed countries. Artificial cultivation is a key approach to sustainably develop non-timber forest plants, for which, in-forest planting is vital. Light conditions in forests severely affect in-forest planting, and the growth of many plants may be restricted due to inappropriate light conditions. Thus, to fully and effectively utilize forest spaces with various light environments, fertilization, as an important practice to supply nutrients for promoting plant growth, was selected to mitigate light constraints in forests. Aralia elata (a valuable non-timber forest plant species) was chosen as the subject to explore the effects of fertilization on photosynthetic and morphological adaptation to light and the growth of in-forest planted seedlings by simulating different light environments. The results showed that the effects of fertilization on light adaptability (i.e., photosynthesis and leaf traits) of A. elata seedlings were limited; that is, only the variations in light-saturated photosynthetic net rate (PNmax), specific leaf area (SLA), and chlorophyll (Chl) content of A. elata seedlings between different shade intensities were noticeably affected by fertilization. Fertilization was positive for growth, and a half fertilization treatment (50 g per plot) was optimum for improving the growth of A. elata seedlings under light conditions of 0–75% shade intensities. These results can provide some practical references for the application of fertilization in in-forest planting and management of transplanted non-timber forest plant seedlings under various light conditions in the forests.