Different Levels Of Light Intensity Research Articles

The Thickness Changes of Anatomical Ornamental Monocotyledon Plant Leaves Affected by the Interactions between Plant Types and Light Intensity

The different levels of light intensity affect the anatomical thickness of monocotyledon ornamental plant leaves. The aim of this research was to determine the anatomical thickness of several monocotyledon ornamental plant leaves under different light intensities. The research used a factorial complete randomized design with two main factors, namely plant type and different light intensity, repeated three times. The first factor was the plant type, which consisted of six plant species of monocotyledon ornamental plants which were Chlorophytum laxum, Dracaena reflexa, Rhoeo discolor, Aglaonema commutatum, Cordyline fruticosa and Hymenocallis littoralis. The second factor was light intensity, which consisted of high light intensity (open areas) and low light intensity (shaded areas). The observation was carried out on preserved leaf anatomy made using the paraffin method with modification. The observation variables were the total thickness of the leaf, upper and lower epidermis, mesophyll (for undifferentiated mesophyll), and palisade and sponge (for differentiated mesophyll). Data were analyzed using analysis of variance followed by the LSD test if the treatment was significant. Correlation tests were carried out between total leaf thickness and each leaf anatomical part under conditions of high and low light intensity. The results showed that the interaction between plant types and light intensity influenced the total thickness of the leaves, upper and lower epidermis, and palisade. The plant types independently influenced the mesophyll and sponges, while the light intensity independently influenced only the mesophyll but not the sponge thickness. Hymenocallis littoralis was the only plant that showed thicker under low light intensity, with an increase in the thickness of the upper and lower epidermis. The palisade mainly influenced leaf thickness changes in the differentiated mesophyll.

Carbon isotope values of hazelnut shells: a new proxy for canopy density

Hazel (Corylus avellana) has been abundant in the vegetation of northern and central Europe since the early Holocene and has provided food and materials for humans ever since. Here we use stable carbon isotope (δ13C) values of hazelnut shells to infer woodland openness based on the premise of the “canopy effect”. It is well established that plants growing in dense, shaded forests have lower carbon isotope (δ13C) values than plants growing in open areas. By measuring δ13C values in hazelnuts collected from trees growing in different levels of light intensity, we show that the canopy effect is preserved in hazelnuts and that their δ13C values can be used to infer woodland openness in the past. We apply the method to hazelnuts recovered from sites dated to between the Mesolithic and Iron Age (c. 7000 BCE−1000 CE) in southern Sweden. Our results show that the nuts dated to the Mesolithic were harvested from hazels growing in a range of closed to open settings while nuts from subsequent periods were harvested from progressively more open environments. Given the abundance of hazelnuts recovered from many archaeological contexts, this method has the potential to reconstruct the microhabitats exploited by humans in the past and explore the impact of humans on their environment.

Effects of light on the seedling growth and photosynthetic physiology of the sympatric invasive lianas Dolichandra unguis-cati and Anredera cordifolia

In order to explore the adaptation of sympatric invasive lianas Dolichandra unguis-cati and Anredera cordifolia to light intensity, and to study the effects of different levels of light intensity on their seedling growth and photosynthetic physiology, field shading experiments were conducted. We also selected the sympatric native lianas Hedera nepalensis var. Sinensis as a control. The results showed that, under light shade and strong light, the growth of D. unguis-cati was the best. The growth parameters, net photosynthetic rate, and water use efficiency of D. unguis-cati were the highest, and the contents of photosynthetic pigments were the highest under different light conditions. These results indicated that sufficient light could significantly promote the biomass accumulation and gas exchange of D. unguis-cati, and that D. unguis-cati could maintain efficient light trapping and light protection abilities under different light environments. Under heavy shade, the growth rate of A. cordifolia was the best. The growth parameters of A. cordifolia were significantly greater than those of D. unguis-cati and H. nepalensis var. Sinensis, and the gas exchange parameters were significantly greater than those of H. nepalensis var. Sinensis. However, the growth of the shoot system of A. cordifolia was almost halted under strong light, and the growth indexes were weaker than those of H. nepalensis var. Sinensis. In conclusion, the seedlings of D. unguis-cati had a strong ability to withstand strong light stress, and the seedlings of A. cordifolia had a strong shade tolerance but not strong light stress.

Pulse Oximetry Based on Quadrature Multiplexing of the Amplitude Modulated Photoplethysmographic Signals

In this research, a pulse oximeter based on quadrature multiplexing of AM-PPG signals is proposed. The oximeter is operated by a microcontroller and employs a simple amplitude modulation technique to mitigate noise interference during SpO2 measurement. The two AM-PPG signals (RED and IR) are quadrature multiplexed using carrier signals with equal frequencies but a 90-degree phase difference. The study focused on noise interference caused by light intensity and hand movement. The experiment was conducted under three different levels of light intensity: 200 Lux, 950 Lux, and 2200 Lux. For each light intensity level, the SpO2 level was measured under three scenarios: hand still, shadow movement over the hand, and hand shaking. A comparison between the proposed technique and the conventional method reveals that the proposed technique offers a superior performance. The relative error of the measured SpO2 level using the proposed technique was less than 3.1% overall. Based on the study, the proposed technique is less affected by noise interference caused by light intensity and hand movement compared to the conventional method. In addition, the proposed technique has an advantage over contemporary methods in terms of computational complexity. Consequently, the proposed technique can be applied to wearable devices that include SpO2 measurement functionality.

Cabin aircraft comfort evaluation over high fidelity simulated flight.

The primary purpose of this paper is to investigate the possibility of using a Full Flight Simulator (FFS) as an experimental setup for passengers' comfort analysis. Results based on subjective measurements are thus presented to assess comfort levels experienced during a simulated flight. A preliminary investigation has been conducted on a sample of 125 candidates to gain insight into the elements influencing the comfort level perceived based on the participants' actual flight experience; this suggested that the seat configuration is of great importance. Then, the experiment carried out by means of the FFS have been conducted on a reduced sample of 20 candidates for economic and organizational reasons. The behaviour of the 65% of the candidates has been analysed in a seating configuration comparable to the seat of a business-class aircraft. While the experience of the remaining 35% has been studied in an economy-type seat arrangement. Although the main variable under consideration was the seat, several environmental parameters were also considered during the experimental tests to evaluate their effects on perceived comfort level. During each simulated flight, passengers have been subjected to different levels of light intensity, noise, temperature and vibration associated with the different flight phases. Subjective data were collected using a questionnaire concerning every parameter and submitted to the passengers for each flight phase. The aim of varying the environmental parameters inside the cabin was to look for a relation between the subjective comfort level and each comfort parameter. In addition to perceived comfort based on the questionnaire, statistical analysis with parametric and non parametric tests revealed significant effects of environmental variables.

Morpho-Physiological Strategies of Shorea leprosula Miq. and Shorea acuminata Dyer in Response to Light Intensity and Nutrient Amendments

Successfully restoring degraded forest areas depends on seedlings adapting their growth to suit harsh environments. Hence, the requirements for seedlings’ growth need to be addressed before replanting degraded sites. The present study determines the effect of abiotic factors viz. light irradiance (8%, 30%, and 100%), nutrient addition (no fertiliser (NF), NPK, and vermicompost) on the growth performance and photosynthetic capacity of two dipterocarp species seedlings, Shorea leprosula Miq. and Shorea acuminata Dyer. The morphological characteristics assessed for growth performance comprised plant height, stem diameter, leaf count, leaf area, relative chlorophyll concentration, biomass, and root-to-shoot ratio. Li-Cor 6400 and 6800 were used to measure the leaf gas exchange traits, including photosynthetic rate (A), transpiration rate (E), intercellular CO2 concentration (Ci), stomatal conductance (gsw), and water-use efficiency (WUE). Our results demonstrated that different levels of light intensity and nutrient amendment significantly impacted plant-growth performance. Plants grown in 30% irradiance showed better growth performance in terms of relative height growth rate (RHGR), mean number of leaves, and leaf areas 41%, 24%, and 32% higher than the control. The A value was also higher in 30% irradiance, but no significant differences were observed between each level of light irradiance. The addition of vermicompost gave better growth for RHGR, relative diameter growth rate (RDGR), mean number of leaves, biomass, and relative chlorophyll concentrations 47%, 40%, 131%, 19%, and 27% higher than the control, respectively. However, the results obtained for photosynthetic parameters were contrary to growth performance. The photosynthesis rate (A) was higher (14.8%) in NPK compared to the control, and the other photosynthetic parameters did not differ significantly despite different nutrient amendments. In terms of species, S. leprosula has better growth performance and photosynthetic characteristics than S. acuminata in different light irradiance and nutrient amendments, thereby rendering S. leprosula the preferred rehabilitation species. Generally, nutrient addition of either NPK or vermicompost and 30% light irradiance gave better morphological and physiological growth for both species. The outcome of this study could provide a better understanding on the forest rehabilitation strategy to reduce the seedling-mortality rate, particularly for climax tree species.

Effects of light intensity on growth performance, blood components, carcass characteristics, and welfare of broilers.

This study investigated the effects of light intensity on growth performance, blood components, eye condition, and carcass characteristics of broiler chickens. Three hundred and fifty-two 1-day-old male chicks were assigned to one of four treatments (four repetitions per treatment, 22 birds per repetition) and reared in a floor pen for 5 weeks. From the second week, chicks were reared under four different levels of light intensity (5, 20, 35, and 50 lx) and the lighting duration was maintained at 18-hours light : 6-hours dark (18L : 6D). The feed intake and body weight were measured weekly. At 35 days of age, 12 birds per treatment were randomly selected for blood sampling, eye measurement, and carcass analysis. There were no significant differences in body weight gain, feed intake, and feed conversion ratio among treatments. Triglyceride levels in the serum were significantly higher in the 5 lx treatment, and creatinine was significantly lower in the 5 lx treatment (p < 0.05). The heterophil : lymphocyte ratios decreased significantly as light intensity increased (p < 0.05); however, other blood cell compositions were not affected by light intensity. Interleukin-6 content was significantly higher in the 5 lx treatment than in other treatments (p < 0.05), but the content of tumor necrosis factor-α was not significantly different among treatments. Serum corticosterone concentration was significantly higher at 5 lx than at 20, 35, and 50 lx (p < 0.05). The corneal diameter was the highest in 5 lx treatment (p < 0.05), and tended to increase as the light intensity decreased. Other eye parameters were not significantly different among treatments, but displayed a tendency to increase as the light intensity decreased. Carcass yield and part yields were not affected by light intensity. Meat quality parameters (pH, color, cooking loss, and water-holding capacity) did not show significant difference among the treatments. The results indicate that a light intensity of 5 lx may increase physiological stress or have a negative effect on broiler welfare, even if the performance and carcass characteristics are not affected. Therefore, a light intensity of 20 lx or above is recommended considering both the growth performance and welfare of broilers.

Selection for Upland Rice Varieties Under Different Levels of Light Intensity

Upland rice varieties were selected under varying levels of light intensity. This study identified shade-tolerant upland rice varieties with a high yield. From November 2016 to March 2017, the experiment was conducted at King Mongkut's Institute of Technology in Ladkrabang, Prince of Chumphon, Thailand. For this, ten varieties of upland rice i.e. Dawk Pa-yawm, Nangdam, Dokkam, Nangchuan, Lebnokrai, Samduen, Maepeung, Damgatondom, Lebmuenang, Pukaotong were grown at different levels of 0%, 50%, 60%, and 70% shading levels. The experiment was conducted in a randomized complete block design with four replications. The results of qualitative characteristics indicated that shadowing conditions didn’t have any significant effect on plant height, 50% flowering age, harvesting age, and panicle length. On the other hand, shaded conditions have a substantial effect on the number of plants per tiller, the number of panicles per tiller, the number of perfect grains per panicle, and the amount of empty grain per panicle since there was a quantitative character. Among the tested varieties, Lebmuenang, Pukaotong, Damgatondom, and Nangchuan varieties are suited for growing under 50% shade conditions while Samduen was only suited for cultivation in 70 % shaded conditions, whereas Pukaotong was good for growing in 50% and 60% shade situations. The results of this experiment did not encourage farmers to use the other varieties as cultivars under shaded conditions due to low yields. However, the outcomes of this study can be used as a reference for breeding programs in low-light conditions.

Artificial Vision Adaption Mimicked by an Optoelectrical In2O3 Transistor Array.

Simulation of biological visual perception has gained considerable attention. In this paper, an optoelectrical In2O3 transistor array with a negative photoconductivity behavior is designed using a side-gate structure and a screen-printed ion-gel as the gate insulator. This paper is the first to observe a negative photoconductivity in electrolyte-gated oxide devices. Furthermore, an artificial visual perception system capable of self-adapting to environmental lightness is mimicked using the proposed device array. The transistor device array shows a self-adaptive behavior of light under different levels of light intensity, successfully demonstrating the visual adaption with an adjustable threshold range to the external environment. This study provides a new way to create an environmentally adaptive artificial visual perception system and has far-reaching significance for the future of neuromorphic electronics.

Visual Perception in External Lighting Conditions

LED street lighting is a topical trend in modern outdoor lighting. High light output of LEDs creates all conditions for modernization of electric lighting networks in Ukraine. Human vision is a complex process associated with retinal light perception. Vision is divided into: day vision, night vision, and twilight vision. The function of the eye is highly dependent on the distribution of brightness in the field of vision. The spectral sensitivity of photoreceptors varies for different wavelengths of the visible spectrum and different levels of light intensity. The rationing of the lighting installation is based on detailed studies of the observer’s visual performance depending on different lighting conditions. One of the main luminous parameters that can easily be measured objectively is illumination. Brightness as a function of illumination, the observer’s position and the spectral coefficient of the working surface reflection is more informative, but has some difficulty in measuring. There is a clear need to develop a system that would make it possible to uniquely assess the visual efficiency of a given spectral composition under certain observation conditions. It was decided to introduce the term equivalent brightness as the parameter of such a system. The difficulty of using the function Vek(λ,Lek) to calculate the equivalent brightness is the function’s dependence Vek(λ,Lek) on Lek. The aim of the study is to approximate the function of the relative spectral luminous efficiency in mesopathic regions by a set of standard CIE functions that do not depend on the value of equivalent luminosity. The calculation method Vek(λ,Lek) is proposed using only two normalized functions of the relative spectral radiation efficiency for day V(λ) and night V'(λ) vision. The use of such approximation function makes it possible to determine the equivalent brightness, which adequately reflects the level of visual perception under the conditions of ambient illumination, based on the photometric brightness of the light source. To calculate Vek(λ,Lek) we use the ICE recommended functions of relative spectral light efficiency for the twilight vision, which are based on the spectral composition of the blackbody radiation with a color temperature of 2042 K. The use of the developed methodology provides results that more accurately characterize the efficiency of light sources in outdoor lighting installations compared to the results of calculations obtained when using standard methods.

Fire effects on vegetation and environmental variables in grasslands of the eastern hills (Sierras del Este), Uruguay

Disturbances are biomass removal events and have global relevance as they are capable of causing changes in the structure and functioning of ecosystems over time. Fire is employed in grasslands as a management tool to release space and improve the quality of forage for livestock. This thesis evaluated the effects of fire, and in some cases the interaction with grazing, at different levels of organization and at different spatial-temporal scales, on the plant structure of a grassland community dominated by Saccharum angustifolium in the Sierras del Este region from Uruguay. Through a field study, the succession process was described in patches with different time since fire through a spatial chrono-sequence. Through a laboratory study, the effects of heat shock and smoke, at different levels of light intensity, on the germination of six native species were evaluated. By means of a field experiment, along three growing stations, the effects of fire-grazing interaction on the structure of vegetation at different levels of organization were analyzed. Field burning carried out in a patchy and asynchronous manner seemed to be necessary to maintain heterogeneity at a landscape scale and the diversity of the community in the Sierras del Este grasslands.

Season and shading affect emetine and cephalin production in Carapichea ipecacuanha plants

Ipecacuanha [Carapichea ipecacuanha) (Brot) L. Andersson] has a high commercial value due to the presence of emetine and cephalin in its roots, which can be enhanced by different levels of light intensity. This study aimed to study the physiological response of ipecacuanha plants under different shading levels (50, 70, and 90%) in all seasons. Plants were cultivated in a greenhouse with sombrite® (shading) for 395 days, in beds containing sandy soil, after which we evaluated chlorophyll (Chl) a fluorescence, photosynthetic pigments and emetine and cephalin. Chl a fluorescence was higher in plants under 50% shading in all seasons while plants under 90% shading showed increases in Chl a fluorescence in the summer. The changes in Chl a fluorescence under 50% shading reveal difficulties in adaptation to high light levels, since high light intensity causes disorders in the dynamic dissipation of photosynthetic energy, and a decrease in photosynthetic pigments. The highest content of cephalin was recorded in winter under 70% shading, whereas for emetine it was recorded in spring, under 90% shading. Autumn (70% shading) was the only season in which the amount of both emetine and cephalin was similar. Therefore, both the season and the shading level affect ipecacuanha metabolism.

Design and implementation of an indoor solar emulator based low-cost autonomous data logger for PV system monitoring

With the growing interest in renewable energy resources, a various number of studies and development for photovoltaic (PV) systems have investigated to satisfy global needs in energy. The larger interest in PV resources has increased request for suitable apparatus with which to test PV systems. This paper deals with the design of an indoor PV source emulator using an actual PV panel to facilitate PV system testing under real environment conditions. A low-cost Arduino Mega256 microcontroller-based data acquisition system (DAQ) approach has been developed to collect the data in term of voltage, power and current based on different levels of light intensity and temperature as well as under partial shading conditions. Hence, the proposed system is not just a solar emulator but it’s a complete solar emulator-DAQ system that can emulate the sunlight and monitor the PV parameters and then collect and store the data for further research investigation. The proposed monitoring system provides real time update of the solar panel characteristics at any time in the year without relying on the weather changes. This data acquisition system will be of superior interest for undergraduate and graduate students as it is both open-source and flexible. The details design of the proposed PV solar emulator and data logger and its implementation are described.

Increased CO2 and light intensity regulate growth and leaf gas exchange in tomato.

Carbon dioxide concentration (CO2 ) and light intensity are known to play important roles in plant growth and carbon assimilation. Nevertheless, the underlying physiological mechanisms have not yet been fully explored. Tomato seedlings (Solanum lycopersicum Mill. cv. Jingpeng No. 1) were exposed to two levels of CO2 and three levels of light intensity and the effects on growth, leaf gas exchange and water use efficiency were investigated. Elevated CO2 and increased light intensity promoted growth, dry matter accumulation and pigment concentration and together the seedling health index. Elevated CO2 had no significant effect on leaf nitrogen content but did significantly upregulate Calvin cycle enzyme activity. Increased CO2 and light intensity promoted photosynthesis, both on a leaf-area basis and on a chlorophyll basis. Increased CO2 also increased light-saturated maximum photosynthetic rate, apparent quantum efficiency and carboxylation efficiency and, together with increased light intensity, it raised photosynthetic capacity. However, increased CO2 reduced transpiration and water consumption across different levels of light intensity, thus significantly increasing both leaf-level and plant-level water use efficiency. Among the range of treatments imposed, the combination of increased CO2 (800 µmol CO2 mol-1 ) and high light intensity (400 µmol m-2 s-1 ) resulted in optimal growth and carbon assimilation. We conclude that the combination of increased CO2 and increased light intensity worked synergistically to promote growth, photosynthetic capacity and water use efficiency by upregulation of pigment concentration, Calvin cycle enzyme activity, light energy use and CO2 fixation. Increased CO2 also lowered transpiration and hence water usage.

Environmental variations mediate duckweed (Lemna minor L.) sensitivity to copper exposure through phenotypic plasticity.

Environmentally mediated sensitivity of Lemna minor to copper (Cu) was evaluated for the first time in three experiments: the effects of two levels of nutrient concentration, light irradiance or Cu pre-exposure were tested. Various Cu concentrations (ranging from 0.05 to 0.25mg/L) were used to assess the sensitivity of L. minor to this metal, using one common strain previously acclimatized to two different levels of light intensity, nutrient enrichment and Cu pre-exposure. Our results showed a phenotypic plastic response of the relative growth rates based on frond number and fresh mass production, and maximum quantum yield of photosystem II (Fv/Fm). Growth was affected by the three environmental conditions both prior and during Cu exposure, whereas Fv/Fm was mostly affected during Cu exposure. Copper significantly influenced all the parameters measured in the three experiments. Environmental conditions significantly modified L. minor sensitivity to Cu in all experiments, with up to twofold difference depending on the treatment. Growth rate was the parameter that was most impacted. Our study revealed for the first time the existence of phenotypic plasticity in L. minor sensitivity to chemical contamination, and implies that environmental context needs to be taken into account for a relevant risk assessment.

Extraction of p-n junction properties and series resistance in GaAs nanowire-based solar cells using light concentration

Series resistance in solar cells limit their maximum conversion efficiency and thus should be minimized. Generally, such losses originate from deficiencies at the contact or absorber level. Quantifying them is the first step for tackling its reduction. In this work, we provide a new way to assess the series resistance in nanowire-based solar cells, which significantly underperforms predicted theoretical efficiency. We illuminate the devices at different levels of light intensity (from 1 to 1000 suns), which gives us insight in the carrier transport and series losses mechanism. We demonstrate the method on a device obtained by self-assembled GaAs nanowire p-n junction arrays on silicon. This analysis method provides a platform to distinguish the intrinsic response of the nanowire p-n junction from the series resistance effects. More generally, we provide a means of optimizing the efficiency in next generation solar cells, where contacts still have to be developed.

Lower light intensity reduces larval aggression in matrinxã, Brycon amazonicus

Brycon amazonicus shows a high frequency of aggressive behavior, which can be a limiting factor in intensive farming systems. Environmental changes can modulate the social interactions of fish and reduce aggression during the different stages of production. Groups of three larvae at 12 h after hatching (HAH) were subjected to different levels of light intensity: low (17 ± 3 lx), intermediate (204 ± 12.17 lx) and high (1,613.33 ± 499.03 lx), with eight replicates for each level. The lower light intensity reduced the frequency of aggressive interactions and locomotor activity exhibited by the animals. Based on these results, light intensity modulates aggression in B. amazonicus larvae. Manipulation of this factor could improve the social conditions of this species during farming and contribute to the development of new production technologies.

Effects of light intensity on photosynthetic capacity and light energy allocation in Panax notoginseng.

To explore the effects of light intensity on photosynthetic characteristics and light adaptation of the shade-demanding species Panax notoginseng, the responses of photosynthesis to photosynthetic photon flux density, CO2 and sunflecks in the two-year-old Panax notoginseng were investigated under different levels of light intensity (29.8%, 9.6%, 5.0%, 1.4% and 0.2% of full sunlight). Meanwhile, chlorophyll a fluorescence parameter and light energy partitioning were also recorded and calculated in the responsive process. P. notoginseng grown under 29.8% full sunlight (FL) had a lower apparent quantum yield (AQY), potential photochemical quantum yield (Fv/Fm) and potential photochemical activity (Fv/Fo), however, it had a higher maximum net photosynthetic rate (Pn max), maximum electron transport rate (Jmax), F/Fm', electron transport rate (ETR), photochemical quenching (qP) and the proportion of light energy allocated to photochemistry dissipation (ΦPS2), but the non-photochemical quenching (NPQ) was not the highest. There were no significant differences in Pn max, light compensation point (LCP), light saturation point (LSP), dark respiration rate (Rd) among 9.6%FL and 5.0% FL treatments, but these treatments had relatively higher values of NPQ, AQY, carboxylation efficiency (CE), maximum carboxylation rate (Vc max), Fv/Fm and Fv/Fo. In addition, the Pn max, CE, Vc max, Jmax, ETR,F/Fm', qP, NPQ and ΦPSII decreased with the decrease in light intensity from 5.0%FL to 0.2%FL, and the proportion of light energy allocated to fluorescent dissipation (Φf,d) were increased. Under 500 μmol·m-2·s-1 light-flecks inducting, the ΦPSⅡof P. notoginseng increased slowly with the extension of time except for the treatment of less than 5.0%FL, and under the circumstance of 1.4%FL and 0.2%FL, ΦPSⅡreached significantly a perfect result, moreover, Φf,dincreased rapidly. These results suggested that the enhancement in photosynthetic electron transport to use the light energy and the moderate photoinhibition of PS2 might avoid the irreversible oxidative damage of photosynthetic organization in P. notoginseng under high levels of light intensity. Moderate shading was beneficial to maintain its higher non-photochemical quenching ability. However, its photosynthetic capacity depressed and the proportion of light energy allocated to non-photochemical pathway increased obviously in excessive shading, and it easily caused a light oxidative damage.

Soil microbial carbon utilization, enzyme activities and nutrient availability responses to Bidens pilosa and a non-invasive congener under different irradiances

Two Bidens species (Bidens pilosa and B. bipinnata) that originate from America have been introduced widely in pan-tropics, with the former regarded as a noxious invasive weed whereas the latter naturalized as a plant resource. Whether the two species exhibit different effects on the belowground system remains rarely studied. This study was conducted to investigate soil microbial carbon (C) utilization, enzyme activities and available nitrogen, phosphorus and potassium contents under the two species in a subtropical garden soil of southern China under different levels of light intensity. Results showed that the microbial C utilization and enzyme activities were not significantly different under the two species, implying that the strong invasiveness of B. pilosa could not be due to the plant-soil microbe interactions, at least plant-induced alterations of microbial community function to utilize C substrates. Alternatively, available soil nitrogen and potassium contents were significantly higher under B. pilosa than under B. bipinnata in full sun, indicating that the strong invasiveness of B. pilosa could result from rapid nutrient mobilizations by B. pilosa. However, the differences turned non-significant as light intensity decreased, suggesting that light availability could substantially alter the plant effects on soil nutrient mobilizations.

Characteristics of photosynthesis and light energy partitioning in Amorphophallus xiei grown along a light-intensity gradient.

The objective of the present study was to examine the adaptation strategy of Amorphophallus xiei, a shade-demanding species, grown under different levels of light intensity. The responses of leaf to photosynthetic active radiation, CO2 and simulated sunflecks were analyzed in A. xiei grown under 100% (high light), 32.6% (moderate light) and 5.98% (low light) of full sun. Meanwhile, chlorophyll a fluorescence parameter and light energy partitioning were also recorded and calculated in the above-mentioned responsive process. The results showed that in most cases, the maximum photosynthetic rate (Pmax), dark respiration rate, apparent quantum yield and carboxylation efficiency in A. xiei significantly decreased with increasing the light level, however, the light compensation point, CO2 compensation point significantly increased. The photosynthetic induction was quicker in individuals grown under moderate light (P<0.05), and the initial stomatal conductance (gs-i) during dark adaptation increased significantly with increasing the light level. There was a ne-gative correlation between gs-i and the time required to reach 30%, 50% and 90% of Pmax during the process of photosynthetic induction. Moreover, the values of actual photochemical efficiency of PS2 (ΔF/Fm') in the light, phototochemical quenching of chlorophyll fluorescence (qP) and photosynthetic electron transport rate (ETR) were higher and non-photochemical quenching (NPQ) recorded in photosynthetic induction was also higher in individuals grown under high light, nevertheless, the maximum photochemical efficiency of PS2 in the light (Fv'/Fm') was higher in individuals grown under low light. The proportion of light energy allocated to non-photochemical quenching (ФNPQ) was lower in individuals grown under high light, and, correspondingly, it was higher in ones grown under low light. The results obtained here suggested that, when exposed to high light stress, moderate- and low-light-grown A. xiei would activate the mechanism of energy dissipation to protect itself from injury. Correspondingly, high-light-grown individuals would employ the strategy of increasing heat dissipation and forming quenching complex to cope with high light stress, which, however, might be one of reasons for the sensitivity of A. xiei to high light environment.