Leaf Photosynthetic Responses Research Articles

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.

Contributions of species shade tolerance and individual light environment to photosynthetic induction in tropical tree seedlings.

It has long been debated whether tree leaves from shady environments exhibit higher photosynthetic induction efficiency (IE) than those from sunny environments and how the shade tolerance of tree species and the light environment of leaves contribute to the dynamics of photosynthesis. To address these questions, we investigated leaf photosynthetic responses to simulated changes of light intensity in seedlings of six tree species with differential shade tolerance. The seedlings were growing under different light environments in a lowland tropical forest. We proposed an index of relative shade tolerance (RST) to assess species-specific capacity to tolerate shade, and we quantified the light environment of individual leaves by the index of daily light integral (DLI), the averaged daily total light intensity. We obtained the following results. Photosynthetic IE, which is the ratio of the achieved carbon gain to the expected carbon gain, was significantly higher for species with a higher RST than for that with a lower RST. The impacts of light environment on the IE of individual leaves within the same species varied largely among different species. In the three species with relatively low RST, the IE of individual leaves decreased at higher DLIs when DLI<10molm-2 d-1. Seedlings with high initial stomatal conductance before induction (gs50) possessed a higher IE than those with low gs50 from the same species. A trade-off existed between IE and steady-state photosynthetic rates. These results suggest a complex interaction between the shade tolerance of species and the light environments of individual leaves for photosynthetic induction and provide new insights into the adaptation strategy for understory seedlings under sunfleck environments.

Effect of nitrogen supply on stay-green sorghum in differing post-flowering water regimes.

The expression of stay-green (SG) characteristic in sorghum under water stress was related to N supply. SG genotype performed better than a non-stay-green (NSG) genotype at medium and high N levels. The differences in physiological parameters between SG and NSG genotypes were not significant at low N level and severe water stress. Grain sorghum [Sorghum bicolor (L.) Moench] with stay-green (SG) trait has the potential to produce more biomass and use soil water and nitrogen (N) more efficiently under post-flowering water stress. Previous studies were mostly conducted without N deficiency and more information is needed for interactions among soil N availability, SG genotype, and post-flowering water stress. In this study, the differences in leaf growth and senescence, shoot and root biomass, evapotranspiration (ET), water use efficiency (WUE), leaf photosynthetic responses, and nitrogen use efficiency (NUE) between a SG genotype (BTx642) and a non-stay-green (NSG) genotype (Tx7000) were examined. The two genotypes were grown at three N levels (Low, LN; Medium, MN; High, HN) and under three post-flowering water regimes (No water deficit, ND; Moderate water deficit, MD; Severe water deficit, SD). The genotypic difference was generally significant while it frequently interacted with N levels and water regimes. At medium and high N levels, SG genotype consistently had greater green leaf area, slower senescence rate, more shoot biomass and root biomass, and greater WUE and NUE than the NSG genotype under post-flowering drought. However, differences in several variables (e.g., leaf senescence, ET, WUE and NUE) between genotypes were not significant under SD at LN. At HN and MN, photosynthetic function of SG genotype was better maintained under drought. At LN, SG genotype maintained greater green leaf area but had lower photosynthetic activity than the NSG genotype. Nonetheless, adequate N supply is important for SG genotype under drought and greater root biomass may contribute to greater NUE in SG genotype.

Characteristics of Leaf Stomata and Their Relationship with Photosynthesis in Saccharum officinarum Under Drought and Silicon Application.

Silicon (Si) plays an important role in the sustainable agriculture industry. The increasing demand for crop production with a significant reduction of synthetic chemical fertilizers and pesticide use is a big challenge nowadays. The use of Si has been proven to be an environmentally sound way of enhancing crop productivity by facilitating plant growth and development through either a direct or indirect mechanism, especially in tropical and subtropical regions. In particular, it has been investigated for its role in water stress management. The aim of the current experiment was to examine the protective role of Si in the photosynthetic capacity of different leaf segments and the ultrastructure of sugarcane (Saccharum officinarm) plants under water stress. Sugarcane cv. GT 42 plants were supplied with 0, 100, 300, and 500 mg L–1 Si and exposed for 60 days under each stress condition such as 100–95, 55–50, and 35–30% of field capacity. For the photosynthetic responses, each leaf was observed and separated into three equal parts (base, middle, and tip). We used intact leaves and were able to assess leaf photosynthetic responses. Under moderate and severe stress conditions, applied Si increased the photosynthesis (base, ∼16–143%; middle, 20–66%; and tip leaf part, 41–71%), transpiration rate (base, 15–97%; middle, 26–68%; and tip leaf part, 6–61%), and stomatal conductance (base, 26–137%; middle, 12–70%; and tip leaf part, 7–75%) in sugarcane plants. Ultrastructural examination of sugarcane leaves using scanning electron microscopy showed the remarkable effects on stomata ultrastructure. Silicon increased plant growth development, photosynthetic efficiency, and biomass/yield, and promoted better adaptation of stomata to drought. This study suggests that the application of Si may be used to increase the stress tolerance of sugarcane plants.

Characterization and Detection of Leaf Photosynthetic Response to Citrus Huanglongbing from Cool to Hot Seasons in Two Orchards

HighlightsAn abnormal accumulation of sucrose and glucose was found in HLB-infected leaves, and it presented a similar pattern in different orchards from cool to hot seasons.A decreasing value of the actual quantum yield of PSII (FPSII) in HLB-infected leaves was mainly related to an increase of non-regulated energy quenching (FNO) due to the irreversible damage of PSII.Chlorophyll fluorescence imaging combined with a random forest was able to identify HLB at the asymptomatic stage.Abstract Citrus Huanglongbing (HLB) poses a serious threat to citrus production. This research aimed to explore chlorophyll fluorescence imaging for characterizing the photosynthetic response to HLB-infected citrus leaves in different orchards and seasons. Chlorophyll fluorescence images of citrus leaves were acquired with an in-house chlorophyll fluorescence imaging system. It was found that sucrose and glucose accumulated earlier than starch in HLB-infected leaves, and a similar carbohydrate metabolic pattern was observed in HLB-infected leaves grown in different orchards from cool to hot seasons. The pathogen damaged the thylakoid structure of chloroplasts with a higher value of Fo. It decreased photosynthetic activity of the host by reducing the number of active photosynthetic centers and the maximum quantum yield of PSII (Fv/Fm) with lower values of Fv/Fo and Fv/Fm. Additionally, the pathogen modified the allocation of excitation energy in citrus leaves by reducing the actual quantum yield of PSII (FPSII) due to an increase of non-regulated energy quenching (FNO), which indicated irreversible PSII damage before symptom development. Moreover, photosynthetic signatures combined with the random forest method were able to identify HLB in the asymptomatic stage with an overall accuracy of 91.8%. These results demonstrated the potential of chlorophyll fluorescence imaging for evaluating the photosynthetic response to HLB as well as disease diagnosis. Keywords: Carbohydrate metabolism, Chlorophyll fluorescence imaging, Citrus Huanglongbing, Photosynthetic efficiency, Random forest model.

Vertical distributions of chlorophyll and nitrogen and their associations with photosynthesis under drought and rewatering regimes in a maize field

In this study, we characterize the vertical leaf distribution of chlorophyll (Chl) and nitrogen (N) content and their associations with leaf photosynthetic responses in Zea mays L. under field watering regimes. We simulated five precipitation patterns, including a drought-rewatering sequence using an electric-powered, rainproof shelter. The results indicate the vertical leaf Chl and N distribution versus the cumulative leaf-area index (LAIc) fit well into a significant quadratic function. The simulated precipitation patterns significantly influenced the parabolic curve trajectory patterns and their parameters. Chlorophyll and N contents had the same trend, with a close and positive relationship. Drought stress followed by rewatering increased the slopes of the linear equations but narrowed the parabolic opening of the quadratic functions. This finding implies that the relationship between Chl and N content can be used to estimate responses to drought and rewatering. The findings also suggested that the relationship patterns between Chl and N levels could be an assessment tool for N-fertilizer managements under different drought conditions to maintain high yields in maize production. Principal component analysis indicated the correlations between functional traits in maize leaves and the responses to drought and rehydration. These findings help to improve drought management and cultivar selection, which will be important in coping with the severe intensity and high frequency of episodic drought events expected from climate change.

Vertical patterns of photosynthesis and related leaf traits in two contrasting agricultural crops.

To include within-canopy leaf acclimation responses to light and other resource gradients in photosynthesis modelling, it is imperative to understand the variation of leaf structural, biochemical and physiological traits from canopy top to bottom. In the present study, leaf photosynthetic traits for top and bottom canopy leaves, canopy structure and light profiles, were measured over one growing season for two contrasting crop types, winter barley (Hordeum vulgare L.) and rape seed (Brassica napus L.). With the exception of quantum yield, other traits such as maximum photosynthetic capacity (Amax), dark respiration, leaf nitrogen and chlorophyll contents, and leaf mass per area, showed consistently higher (P<0.05) values for top leaves throughout the growing season and for both crop types. Even though Amax was higher for top leaves, the bottom half of the canopy intercepted more light and thus contributed the most to total canopy photosynthesis up until senescence set in. Incorporating this knowledge into a simple top/bottom-leaf upscaling scheme, separating top and bottom leaves, resulted in a better match between estimated and measured total canopy photosynthesis, compared with a one-leaf upscaling scheme. Moreover, aggregating to daily and weekly temporal resolutions progressively increased the linearity of the leaf photosynthetic responses to light for top leaves.

Leaf photosynthetic responses of passion fruit genotypes to varying sunlight exposure within the canopies

Passion fruit plants (Passiflora spp.) have very dense canopies so that leaves located at the top of them can shade the ones more internally located. This shade can change physiological and morphological leaf traits. Here we used gas exchange and chlorophyll a fluorescence parameters as tools to evaluate the responses of full sun-light exposed (FSE) leaves, leaves at intermediate position (IP) and shaded leaves (S) of three Passiflora genotypes [P. edulis f. flavicarpa (Maguary selection—FB 100) (M); P. giberti (G) and P. cincinnata (C)]. FSE leaves presented greater net photosynthetic rates (A net ), what accounted for increasing both intrinsic water use efficiency and water use efficiency. Otherwise, leaves grown and adapted to shade environments tended to always show low A net values, although such values were increased at 12:00, when light availability was improved. Leaves at IP and S leaves presented higher ratio of internal to ambient CO2 concentration (C i /C a ) likely due to reduced carboxylation efficiency. FSE leaves presented photoprotection mechanisms against high light intensities, while leaves under lower light intensities (IP and S) showed variable responses of chlorophyll a fluorescence, depending on the genotype.

Photosynthetic phenological variation may promote coexistence among co-dominant tree species in a Madrean sky island mixed conifer forest.

Across much of western North America, forests are predicted to experience a transition from snow- to rain-dominated precipitation regimes due to anthropogenic climate warming. Madrean sky island mixed conifer forests receive a large portion of their precipitation from summertime convective storms and may serve as a lens into the future for snow-dominated forests after prolonged warming. To better understand the linkage between physiological traits, climate variation, and the structure and function of mixed conifer forests, we measured leaf photosynthetic (A) responses to controlled variation in internal CO2 concentration (Ci) to quantify interspecific phenological variation in A/Ci-derived ecophysiological traits among ponderosa pine (Pinus ponderosa Lawson and C. Lawson), southwestern white pine (Pinus strobiformis Engelm.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Species had similar, positive responses in net photosynthesis under ambient conditions (Anet) to the onset of summertime monsoonal precipitation, but during the cooler portions of the year P. ponderosa was able to maintain greater Anet than P. menziesii and P. strobiformis. Moreover, P. ponderosa had greater Anet in response to ephemerally favorable springtime conditions than either P. menziesii or P. strobiformis. Monsoonal precipitation was associated with a sharp rise in the maximum rates of electron transport (Jmax) and carboxylation (VCmax) in P. menziesii in comparison with P. ponderosa and P. strobiformis. In contrast, species shared similar low values of Jmax and VCmax in response to cool winter temperatures. Patterns of relative stomatal limitation followed predictions based on species' elevational distributions, reinforcing the role of stomatal behavior in maintaining hydraulic conductivity and shaping bioclimatic limits. Phenological variation in ecophysiologial traits among co-occurring tree species in a Madrean mixed conifer forest may promote temporal resource partitioning and thereby contribute to species' coexistence. Moreover, these results provide a physiological basis for predicting the ecological implications of North American mixed conifer forests currently transitioning from snow- to rain-dominated precipitation regimes.

Comparative response of Brassica carinata and B. napus vegetative growth, development and photosynthesis to nitrogen nutrition

Nitrogen availability is a major limiting factor controlling growth, CO2 assimilation and productivity of oilseed brassicas, however, little is known about the physiological and morphological responses of B. carinata to N. A greenhouse study was conducted at North Florida Research and Education Center, Quincy, Florida during 2014/2015 to determine the effects of N rate on carinata (B. carinata A. Braun) cv. AAC A110 and (B. napus L.) cv. Canterra 1918 growth, development and photosynthesis. Four N treatments (0, 33, 66 and 100% of N in full strength Hoagland solution) were imposed 30days after planting. Plant height, leaf area, node number, branches and total biomass and its components (leaf, stem and root dry weights) in both species decreased linearly with N reduction. Intra-specific total dry matter and photosynthetic capacity did not vary 55days after treatment (DAT). However, partitioning biomass to various plant components differed between the species and was modified by N availability. At all N rates, carinata apportioned >53% of total biomass to the stem component while in canola stems comprised 17–34% of total biomass. Roots contributed more to total dry weight in canola (33–46%) than in carinata (23–29%) except at the highest N level. In both species, root dry matter increased with decreasing N availability. At 55 DAT, total chlorophyll, Chla and Chlb concentrations, specific leaf area and photosynthetic capacity for both species decreased with N deficiency. Parameters of leaf photosynthetic responses to photosynthetically active radiation and internal CO2 concentration curves were also altered by N availability. During the vegetative stage, N deficiency restricted plant growth, biomass production and also modified resource allocation which may have implications for N use efficiency and recovery during reproductive development.

Variation in leaf photosynthetic response of rice genotypes to post-anthesis water deficit

Variation in the response of six diverse rice genotypes to imposed water stress was investigated in terms of leaf photosynthetic traits and leaf water potential measurements (Ψleaf) during and following a period of water stress. The Ψleaf reduced from 0 days up to 6th day of irrigation deprivation and the reduction in Ψleaf was more pronounced in Swarna and minimum in PA-6201. A gradual recovery in Ψleaf was observed in all the tested varieties after re-irrigation. Similarly, water stress significantly reduced rate of photosynthesis (P N), stomatal conductance (g s), transpiration (E) and internal CO2 concentration (C i). Significant differences were noticed amongst the varieties in their response to water stress. The P N partially recovered in all tested varieties after re-irrigation. Vandana recorded greater recovery (65 %), where as the recovery was only 32 % in Sugandha Samba. Water stress (6 days of irrigation deprivation) significantly decreased the mean Chl a, Chlb, total chlorophyll and total carotenoid content. However, a marginal increase in total chlorophyll was observed under water stress in Vandana and N-22. Water stress had no significant effect on maximum photochemical efficiency (F v/F m) for all the tested varieties. However, in Sugandha Samba and Swarna a significant reduction was noticed. Water stress reduced the efficiency of excitation capture (Φe), in vivo quantum yield of PSII photochemistry (ΦPSI), coefficient of photochemical quenching (qP) and increased the coefficient of non-photochemical quenching (qN). The data on photosynthetic traits and chlorophyll fluorescence parameters indicate that Vandana, N-22, DRR-Dhan-38 and PA-6201 which maintained relatively higher, Ψleaf, P N and g s under water stress and could also maintain high values of photochemical efficiency (Fv/Fm, Φe, ΦPSI and ETR) than Sugandha Samba and Swarna and the genotypic differences in the response of PSII activity could be exploited as traits for the selection of drought tolerant rice genotypes.

Effect of peanut and foxtail millet intercropping on crop photosynthetic response and fluorescence parameters

Peanut and foxtail millet intercropping can produce a better production increase and synergy, but there is not any research report on the photosynthetic response characteristics of the intercropping system. In this test, a research was conducted on the variation characteristics of leaf photosynthetic response and chlorophyll fluorescence parameters under the intercropping conditions of peanut and foxtail millet. The increase in Fo (dark level fluorescence) of intercropping foxtail millet leaves can reduce the reversible inactivation of hard light on foxtail millet leaves; increase in Fm (maximum fluorescence) and Fv/Fm (maximum quantum yield of photosystem II) of intercropping peanut can improve conversion efficiency of the PS II (photosystem II) original light energy of peanut. Meanwhile, dark respiration rate and light compensation point of crops in the intercropping system decreased and the apparent quantum efficiency and light saturation point increased, which can show that the peanut and foxtail millet intercropping can improve the light energy utilization efficiency of them.

Effects of elevated CO_2 concentration and pot size to leaf photosynthetic responses of willow (Salix pet-susu Kimura)

Effects of elevated CO_2 concentration and pot size to leaf photosynthetic responses of willow (Salix pet-susu Kimura)

Growth, leaf photosynthesis and canopy light use efficiency under differing irradiance and soil N supplies in the forage grass Brachiaria decumbens Stapf

AbstractIrradiance and soil nitrogen effects on growth, net photosynthesis and radiation use efficiency (RUE) of Brachiaria decumbens were investigated in fertilized and non‐fertilized stands. Three levels of photosynthetic photon flux (PPF: S0 = 100%, S1 = 50% and S2 = 30%) and two N supplies, with (N+) and without (N−), were used. Forage biomass and nutrient accumulation, specific leaf area (SLA), leaf area index (LAI), fractional intercepted photosynthetic photon flux (fPPF), leaf photosynthetic response to light and efficiency of radiation use at leaf (A/Q) and canopy (RUE) levels were measured. Shade effects were mostly independent of soil N. Final yield was decreased by 34% (S1) and 57% (S2). Shade increased SLA (25–46%), so maximum LAI (2·4–3·3) was similar among light regimes. In N− stands, reductions in leaf biomass (14%), SLA (17%) and LAI (27%) were recorded, although forage yield was similar between soil N conditions. Under shade, peaks of A were comparable to those at full light, so A/Q was higher around midday. Derived parameters of the A‐PPF curves were similar between S0 and S2. A maximum fPPF = 0·8 (S0N+, S1N+) was recorded at LAI = 3–4. Under limited sunlight, relatively high RUE (1·6–2·8 g MJ−1) were observed over both soil N conditions. We concluded that B. decumbens had a high plasticity to shade, thus explaining its success under silvopastoral systems.

Photosynthetic limitations caused by different rates of water-deficit induction in Glycine max and Vigna unguiculata

Plants are constantly subjected to variations in their surrounding environment, which affect their functioning in different ways. The influence of environmental factors on the physiology of plants depends on several factors including the intensity, duration and frequency of the variation of the external stimulus. Water deficit is one of the main limiting factors for agricultural production worldwide and affects many physiological processes in plants. The aim of this study was to analyse the effects of different rates of induced water deficit on the leaf photosynthetic responses of soybean (Glycine max L.) and cowpea (Vigna unguiculata L.). The plants were subjected to two types of water deficit induction: a rapid induction (RD) by which detached leaves were dehydrated by the exposure to air under controlled conditions and a slow induction (SD) by suspending irrigation under greenhouse conditions. The leaf gas exchange, chlorophyll (Chl) a fluorescence, and relative water content (RWC) were analysed throughout the water-deficit induction. V. unguiculata and G. max demonstrated similar dehydration as the soil water percentage declined under SD, with V. unguiculata showing a greater stomatal sensitivity to reductions in the RWC. V. unguiculata plants were more sensitive to water deficit, as determined by all of the physiological parameters when subjected to RD, and the net photosynthetic rate (P N) was sharply reduced in the early stages of dehydration. After the plants exposed to the SD treatment were rehydrated, V. unguiculata recovered 65% of the P N in relation to the values measured under the control conditions (initial watering state), whereas G. max recovered only 10% of the P N. Thus, the better stomatal control of V. unguiculata could enable the maintenance of the RWC and a more efficient recovery of the P N than G. max.

Characteristics of rice leaf photosynthetic light response curve with different water and nitrogen regulation

Characteristics of rice leaf photosynthetic light response curve with different water and nitrogen regulation

Ecophysiological Responses of Giant Reed (Arundo donax) to Herbivory

AbstractThe effect of invasive species might be lessened if herbivores reduced transpiration and growth rates; however, simply removing photosynthetic material might not ensure that the transpiration rate of active leaf tissue decreases. We assessed whether biological control has an injurious effect on the target plant species, giant reed (Arundo donax), by quantifying leaf photosynthetic and transpiration responses to two herbivores: an armored scale, Rhizaspidiotus donacis, and a stem-galling wasp, Tetramesa romana. Herbivory by a sap-feeding scale and a stem-galling wasp both separately and together, reduces the rates of leaf level physiological processes in A. donax. The effect of the wasp increases with density and reduces photosynthesis by reducing the carboxylation rate of ribulose-1,5-bisphosphate carboxylase oxygenase, which controls CO2 fixation in photosynthesis. The scale insect reduces photosynthesis by decreasing the maximum rate of electron transport, which determines how much light energy can be captured in photosynthesis. The effect of the armored scale takes approximately 5 mo after infestation, which coincides with generation time. When both insects are present at the same time, the effect of their herbivory appears additive after time for the scale to reproduce. We conclude that a combination of two herbivores can have a stronger physiological effect than one type of herbivore, likely because of their different effects on leaf function.

Leaf photosynthetic responses and related nitrogen changes associated with crown reclosure after thinning in a young Chamaecyparis obtusa stand

In order to quantify the effects of thinning on biochemical photosynthesis parameters and changes in leaf nitrogen contents associated with the process of crown reclosure, the maximum rate of carboxylation (Vcmax), the leaf nitrogen concentration per unit area (Na), and the photosynthetic photon flux density (PPFD) were measured at four crown heights in both thinned (1500 trees ha−1) and unthinned control (3000 trees ha−1) stands of ten-year-old Chamaecyparis obtusa (36°3′N, 140°7′E) trees during four consecutive growing seasons after thinning. Thinning increased Vcmax in the lower and middle crowns in the first year after thinning, and leaves in the lower crown of the thinned stand maintained high Vcmax for four years, whereas they abscised in the second year in the control stand. Significant increases in Vcmax were detected even in the upper crowns of trees in the thinned stand in the second year. Thinning did not affect Na at any of the crown positions in the first year, but significantly increased Na in the middle crowns from the second year after thinning. Thus, the redistribution of nitrogen between leaves, driven by increases in light and nutrient availability due to the 50% thinning, appears to have enhanced photosynthetic rates in the thinned stand. Thinning also significantly affected the slope of the linear relationship between Na and Vcmax initially after thinning, but its effect on this relationship was negligible after the second year. These quantitative results may be used to simplify the estimation of the likely effects of management practices on carbon fixation in forest canopies.

Acclimation of nitrogen uptake capacity of rice to elevated atmospheric CO2 concentration.

Nitrogen (N) is a major factor affecting yield gain of crops under elevated atmospheric carbon dioxide concentrations [CO(2)]. It is well established that elevated [CO(2)] increases root mass, but there are inconsistent reports on the effects on N uptake capacity per root mass. In the present study, it was hypothesized that the responses of N uptake capacity would change with the duration of exposure to elevated [CO(2)]. The hypothesis was tested by measuring N uptake capacity in rice plants exposed to long-term and short-term [CO(2)] treatments at different growth stages in plants grown under non-limiting N conditions in hydroponic culture. Seasonal changes in photosynthesis rate and transpiration rate were also measured. In the long-term [CO(2)] study, leaf photosynthetic responses to intercellular CO(2) concentration (Ci) were not affected by elevated [CO(2)] before the heading stage, but the initial slope in this response was decreased by elevated [CO(2)] at the grain-filling stage. Nitrate and ammonium uptake capacities per root dry weight were not affected by elevated [CO(2)] at panicle initiation, but thereafter they were reduced by elevated [CO(2)] by 31-41 % at the full heading and mid-ripening growth stages. In the short-term study (24 h exposures), elevated [CO(2)] enhanced nitrate and ammonium uptake capacities at the early vegetative growth stage, but elevated [CO(2)] decreased the uptake capacities at the mid-reproductive stage. This study showed that N uptake capacity was downregulated under long-term exposure to elevated [CO(2)] and its response to elevated [CO(2)] varied greatly with growth stage.

Injured and uninjured leaf photosynthetic responses after mechanical injury on Nerium oleander leaves, and Danaus plexippus herbivory on Asclepias curassavica leaves

Insect herbivory has variable effects on plant physiology; so greater understanding is needed about how injury alters photosynthesis on individual injured and uninjured leaves. Gas exchange and light-adapted leaf chlorophyll fluorescence measurements were collected from uninjured and mechanical partial leaf defoliation in two experiments with Nerium oleander (Apocynaceae) leaves, and one experiment with Danaus plexippus herbivory on Asclepias curassavica (Asclepiadaceae) leaves. Gas exchange impairment (lower photosynthetic rate (Pn), stomatal conductance (gs)) indicates water stress in a leaf, suggests stomatal limitations causing injury Pn impairment. The same pattern of gas exchange impairment also occurred on uninjured leaves opposite from injured leaves in both N. oleander experiments. This is an interesting result because photosynthetic impairment is rarely reported on injured leaves near injured leaves. No photosynthetic changes occurred in uninjured A. curassavica leaves opposite from D. plexippus-fed leaves. Partially defoliated leaves that had Pn and gs reductions lacked any significant changes in intercellular leaf [CO2], Ci. These results neither support, nor are sufficient to reject, stomatal limitations to photosynthesis. Manually imposed midrib vein severance in N. oleander experiment #1 significantly increased leaf Ci, indicating mesophyll limitations to photosynthesis. Maximal light-adapted leaf photochemical efficiency (\( {F^{\prime }_{{\text{V}}} } \mathord{\left/ {\vphantom {{F^{\prime }_{{\text{V}}} } {F^{\prime }_{{\text{M}}} }}} \right. \kern-\nulldelimiterspace} {F^{\prime }_{{\text{M}}} } \)) and also non-photochemical quenching (qN) were reduced by mechanical or insect herbivory to both study species, suggesting leaf trouble handling excess light energy not used for photochemistry. Midrib injury on N. oleander leaves and D. plexippus herbivory on A. curassavica leaves also reduced effective quantum yield (ΦPSII) and photochemical quenching (qP); so reduced plastoquinone pools could lead to additional PSII reaction center closure.