Transpiration Efficiency Research Articles

Mesophyll conductance in Zea mays responds transiently to CO2 availability: implications for transpiration efficiency in C4 crops.

Mesophyll conductance (gm ) describes the movement of CO2 from the intercellular air spaces below the stomata to the site of initial carboxylation in the mesophyll. In contrast with C3 -gm , little is currently known about the intraspecific variation in C4 -gm or its responsiveness to environmental stimuli. To address these questions, gm was measured on five maize (Zea mays) lines in response to CO2 , employing three different estimates of gm . Each of the methods indicated a significant response of gm to CO2 . Estimates of gm were similar between methods at ambient and higher CO2 , but diverged significantly at low partial pressures of CO2 . These differences are probably driven by incomplete chemical and isotopic equilibrium between CO2 and bicarbonate under these conditions. Carbonic anhydrase and phosphoenolpyruvate carboxylase invitro activity varied significantly despite similar values of gm and leaf anatomical traits. These results provide strong support for a CO2 response of gm in Z.mays, and indicate that gm in maize is probably driven by anatomical constraints rather than by biochemical limitations. The CO2 response of gm indicates a potential role for facilitated diffusion in C4 -gm . These results also suggest that water-use efficiency could be enhanced in C4 species by targeting gm .

Drought Response in Wheat: Key Genes and Regulatory Mechanisms Controlling Root System Architecture and Transpiration Efficiency.

Abiotic stresses such as, drought, heat, salinity, and flooding threaten global food security. Crop genetic improvement with increased resilience to abiotic stresses is a critical component of crop breeding strategies. Wheat is an important cereal crop and a staple food source globally. Enhanced drought tolerance in wheat is critical for sustainable food production and global food security. Recent advances in drought tolerance research have uncovered many key genes and transcription regulators governing morpho-physiological traits. Genes controlling root architecture and stomatal development play an important role in soil moisture extraction and its retention, and therefore have been targets of molecular breeding strategies for improving drought tolerance. In this systematic review, we have summarized evidence of beneficial contributions of root and stomatal traits to plant adaptation to drought stress. Specifically, we discuss a few key genes such as, DRO1 in rice and ERECTA in Arabidopsis and rice that were identified to be the enhancers of drought tolerance via regulation of root traits and transpiration efficiency. Additionally, we highlight several transcription factor families, such as, ERF (ethylene response factors), DREB (dehydration responsive element binding), ZFP (zinc finger proteins), WRKY, and MYB that were identified to be both positive and negative regulators of drought responses in wheat, rice, maize, and/or Arabidopsis. The overall aim of this review is to provide an overview of candidate genes that have been identified as regulators of drought response in plants. The lack of a reference genome sequence for wheat and non-transgenic approaches for manipulation of gene functions in wheat in the past had impeded high-resolution interrogation of functional elements, including genes and QTLs, and their application in cultivar improvement. The recent developments in wheat genomics and reverse genetics, including the availability of a gold-standard reference genome sequence and advent of genome editing technologies, are expected to aid in deciphering of the functional roles of genes and regulatory networks underlying adaptive phenological traits, and utilizing the outcomes of such studies in developing drought tolerant cultivars.

Tuning Transpiration by Interfacial Solar Absorber-Leaf Engineering.

Plant transpiration, a process of water movement through a plant and its evaporation from aerial parts especially leaves, consumes a large component of the total continental precipitation (≈48%) and significantly influences global water distribution and climate. To date, various chemical and/or biological explorations have been made to tune the transpiration but with uncertain environmental risks. In recent years, interfacial solar steam/vapor generation is attracting a lot of attention for achieving high energy transfer efficiency. Various optical and thermal designs at the solar absorber–water interface for potential applications in water purification, seawater desalination, and power generation appear. In this work, the concept of interfacial solar vapor generation is extended to tunable plant transpiration by showing for the first time that the transpiration efficiency can also be enhanced or suppressed through engineering the solar absorber–leaf interface. By tuning the solar absorption of membrane in direct touch with green leaf, surface temperature of green leaf will change accordingly because of photothermal effect, thus the transpiration efficiency as well as temperature and relative humidity in the surrounding environment will be tuned. This tunable transpiration by interfacial absorber‐leaf engineering can open an alternative avenue to regulate local atmospheric temperature, humidity, and eventually hydrologic cycle.

Numerical modeling of soil water dynamics in subsurface drained paddies with midseason drainage or alternate wetting and drying management

As a supplemental practice to land consolidation projects, subsurface drainage systems have been installed in paddy fields to allow for crop diversification and to improve the overall productivity of paddy soils. The HYDRUS (2D/3D) model was applied to investigate the combined effects of different subsurface drainage systems and water management strategies on water balance, groundwater table, transpiration efficiency, and water use efficiency in paddy fields. Field experiments were conducted during four rice growing seasons (2011, 2012, 2014, and 2015) at the subsurface-drained paddies of the Sari Agricultural Sciences and Natural Resources University in northern Iran. Midseason drainage (MSD) management was applied in 2011 and 2012, while alternate wetting and drying (AWD) management was adopted in 2014 and 2015. The model performance was evaluated using the model efficiency (EF), root mean square error (RMSE), normalized root mean square error (NRMSE), and mean bias error (MBE) measures. The model had strong predictive capabilities for simulating the mid-drain water table depth for both water managements. Under MSD and AWD, daily evapotranspiration rates varied from 4.9 to 6.2mmd−1 and 4.9 to 5.9mmd−1, respectively. Drainage losses were higher under AWD than MSD, while the reverse order occurred for percolation losses. Compared with MSD, AWD improved the transpiration and water use efficiency of rice in the presence of subsurface drainage. Being capable of describing complex effects of AWD and MSD strategies in subsurface-drained paddy fields, the HYDRUS (2D/3D) model can serve as a practical tool for optimizing water productivity in these fields.

Biomass Allocation Patterns Are Linked to Genotypic Differences in Whole-Plant Transpiration Efficiency in Sunflower.

Increased transpiration efficiency (the ratio of biomass to water transpired, TE) could lead to increased drought tolerance under some water deficit scenarios. Intrinsic (i.e., leaf-level) TE is usually considered as the primary source of variation in whole-plant TE, but empirical data usually contradict this assumption. Sunflower has a significant variability in TE, but a better knowledge of the effect of leaf and plant-level traits could be helpful to obtain more efficient genotypes for water use. The objective of this study was, therefore, to assess if genotypic variation in whole-plant TE is better related to leaf- or plant-level traits. Three experiments were conducted, aimed at verifying the existence of variability in whole-plant TE and whole-plant and leaf-level traits, and to assess their correlation. Sunflower public inbred lines and a segregating population of recombinant inbred lines were grown under controlled conditions and subjected to well-watered and water-deficit treatments. Significant genotypic variation was found for TE and related traits. These differences in whole-plant transpiration efficiency, both between genotypes and between plants within each genotype, showed no association to leaf-level traits, but were significantly and negatively correlated to biomass allocation to leaves and to the ratio of leaf area to total biomass. These associations are likely of a physiological origin, and not only a consequence of genetic linkage in the studied population. These results suggest that genotypic variation for biomass allocation could be potentially exploited as a source for increased transpiration efficiency in sunflower breeding programmes. It is also suggested that phenotyping for TE in this species should not be restricted to leaf-level measurements, but also include measurements of plant-level traits, especially those related to biomass allocation between photosynthetic and non-photosynthetic organs.

Exogenous Silicon Mediates Alleviation of Cadmium Stress by Promoting Photosynthetic Activity and Activities of Antioxidative Enzymes in Rice

We examined the role of silicon (Si) in alleviating cadmium (Cd) toxicity effects on photosynthesis and antioxidant homeostasis in rice. Rice (Oryza sativa L.) was planted in an aged field soil in a pot experiment, with or without exogenous Si. Brown rice Cd concentration decreased with Si addition, and the lowest value occurred at 4 g kg−1 Si. Si application significantly improved photosynthesis by increasing the photosynthesis rate, intercellular CO2 concentration, and transpiration efficiency. Although minimal fluorescence (F 0) changed only slightly, a significant increase was observed in variable fluorescence (F v), maximal fluorescence (F m), F v/F m, and F v/F 0 with 4 g kg−1 Si. Furthermore, exogenous Si markedly lowered oxidative stress by increasing superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase activities and reducing Cd-induced malondialdehyde and ROS accumulation. However, excessive sodium silicate could cause salt stress, which could trigger excessive reactive oxygen species production, causing oxidative damage. Our results confirmed that exogenous Si application mitigates the negative effects of Cd stress in rice by promoting photosynthetic and antioxidative enzyme activities. The photosynthetic and chlorophyll fluorescence parameters can be used to determine the sufficiency of Si treatment for recovery from Cd-stress in rice and production of rice with low Cd-accumulation.

Increasing drought and diminishing benefits of elevated carbon dioxide for soybean yields across the US Midwest.

Elevated atmospheric CO2 concentrations ([CO2 ]) are expected to increase C3 crop yield through the CO2 fertilization effect (CFE) by stimulating photosynthesis and by reducing stomatal conductance and transpiration. The latter effect is widely believed to lead to greater benefits in dry rather than wet conditions, although some recent experimental evidence challenges this view. Here we used a process-based crop model, the Agricultural Production Systems sIMulator (APSIM), to quantify the contemporary and future CFE on soybean in one of its primary production area of the US Midwest. APSIM accurately reproduced experimental data from the Soybean Free-Air CO2 Enrichment site showing that the CFE declined with increasing drought stress. This resulted from greater radiation use efficiency (RUE) and above-ground biomass production at elevated [CO2 ] that outpaced gains in transpiration efficiency (TE). Using an ensemble of eight climate model projections, we found that drought frequency in the US Midwest is projected to increase from once every 5years currently to once every other year by 2050. In addition to directly driving yield loss, greater drought also significantly limited the benefit from rising [CO2 ]. This study provides a link between localized experiments and regional-scale modeling to highlight that increased drought frequency and severity pose a formidable challenge to maintaining soybean yield progress that is not offset by rising [CO2 ] as previously anticipated. Evaluating the relative sensitivity of RUE and TE to elevated [CO2 ] will be an important target for future modeling and experimental studies of climate change impacts and adaptation in C3 crops.

Elevated Atmospheric CO2 Increases Root Exudation of Carbon in Wetlands: Results from the First Free-Air CO2 Enrichment Facility (FACE) in a Marshland

Experiments employing free-air CO2 enrichment (FACE) facilities have indicated that elevated atmospheric carbon dioxide (eCO2) stimulates growth in diverse terrestrial ecosystems. Studies of the effects of eCO2 on wetland plants have indicated a similar response, but these studies were mostly performed in growth chambers. We conducted a 2-year FACE experiment [CO2 ≈ 582 µmol mol−1] in a marsh in Spain to test whether the common reed (Phragmites australis) responds to carbon enrichment, as previously reported in other macrophytes. More specifically, we tested the effect of eCO2 on P. australis growth, photosynthesis, transpiration, and biomass, its effect on modifying plant and soil ratios of carbon, nitrogen, and phosphorus, and whether the strong environmental variability of this wetland modulates these responses. Our findings show that effects of eCO2 in this wetland environment are more complex than previously believed, probably due to hydrological effects. The effects of eCO2 on reed plants were cumulative and manifested at the end of the growing season as increased 38–44% instantaneous transpiration efficiency (ratio of net photosynthesis to transpiration), which was dependent on plant age. However, this increase did not result in a significant increase in biomass, because of excessive root exudation of carbon. These observations contrast with previous observations of wetland plants to increased atmospheric CO2 in growth chambers and shed new light on the role of wetland plants as a carbon sink in the face of global climate change. The combined effects of water stress, eCO2, and soil carbon processes must be considered when assessing the function of wetlands as a carbon sink under global change scenarios.

Effect of Magnesium on Gas Exchange and Photosynthetic Efficiency of Coffee Plants Grown under Different Light Levels

The aim of the present study was to investigate the effects of magnesium on the gas exchange and photosynthetic efficiency of Coffee seedlings grown in nutrient solution under different light levels. The experiment was conducted under controlled conditions in growth chambers and nutrient solution at the Department of Plant Pathology of the Federal University of Lavras. The treatments consisted of five different Mg concentrations (0, 48, 96, 192 and 384 mg·L−1) and four light levels (80, 160, 240 and 320 µmol photon m−2·s−1). Both the Mg concentration and light levels affected gas exchange in the coffee plants. Photosynthesis increased linearly with the increasing light, indicating that the light levels tested were low for this crop. The highest CO2 assimilation rate, lowest transpiration, and highest water use efficiency were observed with 250 mg·Mg·L−1, indicating that this concentration was the optimal Mg supply for the tested light levels.

Do the nutrition and physiology of eucalyptus seedlings respond to silicon (Si) supply?

In Brazil, Eucalyptus plantations are found, generally in soils with naturally low chemical fertility. Silicon (Si) can improve photosynthesis, decrease plant transpiration and increase water use efficiency (WUE). This study aimed to evaluate the effect of Si supply at five rates (0, 0.25, 0.50, 0.75 and 1.00 mmol L-1) for growing Eucalyptus clone IPB8 seedlings (E. urophylla E. grandis) in Clark's nutrient solution in a greenhouse. Plant growth, nutritional status, gas exchange, leaf water potential (?w), leaf area (LA), inclination angle of leaves and stomatal density (SD) were measured. There was no significant response in Eucalyptus seedling growth due to Si application, which was related to the absence of benefits provided by Si in plant nutritional status and physiology. The efficiency of assimilation (EA), efficiency of translocation (ET) and efficiency of utilization (EU) did not show significant results either. The low ET indicates that Si was highly accumulated in the root (75.4 % in relation to total Si absorbed by plants), which may also have contributed to the lack of the benefits expected. Despite that, Si application promoted higher rates of photosynthesis when compared to plants with 0 mmol Si L-1, increasing the total dry matter production by up to 28 % at an Si rate 0.50 mmol L-1, which also provided a trend of higher growth, EU, LA and SLA, showing it to be the best rate for this Eucalyptus species.

Stomatal conductance, mesophyll conductance, and transpiration efficiency in relation to leaf anatomy in rice and wheat genotypes under drought.

Increasing leaf transpiration efficiency (TE) may provide leads for growing rice like dryland cereals such as wheat (Triticum aestivum). To explore avenues for improving TE in rice, variations in stomatal conductance (gs) and mesophyll conductance (gm) and their anatomical determinants were evaluated in two cultivars from each of lowland, aerobic, and upland groups of Oryza sativa, one cultivar of O. glaberrima, and two cultivars of T. aestivum, under three water regimes. The TE of upland rice, O. glaberrima, and wheat was more responsive to the gm/gs ratio than that of lowland and aerobic rice. Overall, the explanatory power of the particular anatomical trait varied among species. Low stomatal density mostly explained the low gs in drought-tolerant rice, whereas rice genotypes with smaller stomata generally responded more strongly to drought. Compared with rice, wheat had a higher gm, which was associated with thicker mesophyll tissue, mesophyll and chloroplasts more exposed to intercellular spaces, and thinner cell walls. Upland rice, O. glaberrima, and wheat cultivars minimized the decrease in gm under drought by maintaining high ratios of chloroplasts to exposed mesophyll cell walls. Rice TE could be improved by increasing the gm/gs ratio via modifying anatomical traits.

Genotype × environment × management interactions of canola across China: A simulation study

Understanding the interactions of genotype (G)×environment (E)×management (M) and their impact on crop yield enables prediction of the performance of genotypes across environment. It can help select the most suitable cultivars in target regions and identify contributions of novel traits in crop breeding. In this study, we used the process-based APSIM-Canola model to investigate the G×E×M interactions for the purpose of increasing canola yield in contrasting climatic regions of China. A dataset with observations for nine cultivars and 30 site-years was used to test the performance of APSIM-Canola model. Two representative genotypes (as base cultivars) were used to simulate canola potential yield and evaluate potential contributions of putative traits to increase canola yield at three representative sites. Our results show that APSIM-Canola was able to simulate seed yield of both spring and winter canola cultivars across contrasting climatic regions with acceptable accuracy. In the Upper and Middle Yangtze River Basin where rainfall is sufficient or irrigation is available, the yield potential of current winter canola cultivar was simulated to be 6.4 and 4.8tha−1, respectively. In the Northern Region with limited rainfall, the yield potential was only 1.1tha−1 due to severe water stress. Traits that extended the grain filling duration by 20% could increase potential yield by 10% for winter canola, but 5% for spring canola. A 20% increase in radiation use efficiency (RUE) would increase yield by 10–20% in Yangtze River Basin, but had no impact on yield in the Northern Region. Traits that increased transpiration efficiency (TE) had the opposite impact, with 20% increase in TE leading to 30% increase in yield in the Northern Region, but with no significant yield increase in wet areas. A 20% increase in harvest index (HI) increased potential yield by nearly 20% across contrasting environments. A much larger yield gap for winter canola in the Yangtze River Basin was also found, indicating a much greater potential to increase canola seed yield there than in the Northern Region. This study highlights that very different traits need to be targeted for canola breeding across the contrasting climatic regions of China.

Heritability and genetic variation of plant biomass, transpiration, and water use efficiency for an apple core-collection

To study the heritability and genetic variation of plant biomass, transpiration and water use efficiency (WUE) in apple (Malus × domestica Borkh.), 193 genotypes from an INRA apple core-collection were evaluated in 2014. Four grafted replicates per genotype grown as one-year-old scions were studied in a high-throughput phenotyping platform (PhenoArch). Individual pot weight was recorded twice a day and irrigation was scheduled to maintain constant soil water content (SWC) and avoid any water stress during 46 days. Plant 3D pictures were automatically taken every two days. Analysis of pictures and pot weights differences allowed the estimation of whole-plant biomass and transpiration during the experiment. WUE was calculated as the ratio of accumulated biomass to transpiration. For each trait, we tested nine mixed models to account for the genetic effect and spatial variability inside PhenoArch. The Best Linear Unbiased Predictors (BLUPs) of genetic values were estimated after model selection. For each trait, broad-sense heritability (H2) was calculated from variance estimates. Plant biomass, transpiration and WUE had H2 values of 0.76, 0.54, and 0.73, respectively. The H2 value of WUE is high enough to consider that this trait is under genetic control in apple. The genetic variation of WUE indicated that apple genetic resources such as the INRA core-collection could be extremely useful to improve apple plant material for the use of water.

Genetic variability for grain yield and water use efficiency in blackgram genotypes

Transpiration efficiency (TE, g biomass kg-1 water transpired) is the preferred measure for examining po- tential genetic variation in crop water use efficiency (WUE). TE was assessed gravimetrically from sowing to grain harvest in fifteen blackgram accessions, two checks and two local varieties under well-watered conditions during kharif season. TEbiomass varied from 2.87 - 5.27 g kg-1 and TEseed varied from 1.10 - 2.03 g kg-1 among genotypes. High coefficient of variability was observed for seed yield and TEseed.Total biomass, TEbiomass, HI and water transpired recorded medium coefficient of variability. High heritability in broad sense was observed for seed yield, TEseed and total biomass. High genetic advance as percent of mean was observed for seed yield, TEseed, total biomass and TEbiomass. High heritability coupled with high genetic advance as per cent of mean was observed for seed yield, total biomass and TEseed.TEseed is significantly positively correlated with TEbiomass (0.883**), seed yield/ plant (0.805**), HI (0.757**) and biomass (0.572*). TEbiomass, seed yield per plant, total biomass and HI were the important components of TEseed as revealed by correlation studies.D2 analysis partitioned the nineteen genotypes in to five clusters. The maximum inter cluster distance was observed between cluster II and V (24.94) and III and IV (22.6). Genotypes IC436665, IC343952 and Local II (Cluster III) had high mean values for TEbiomass and TEseed along with total biomass and seed yield. These genotypes should be useful in future breeding programs for higher water use efficiency.

Effect of fertigation with potassium and nitrogen on gas exchange and biomass accumulation in eggplant1

ABSTRACT Adequate crop fertilization is one of the challenges for agriculture. Measuring gas exchange and biomass accumulation may be used to adjust crop management. The effect of fertigation with potassium (0 kg ha-1, 54 kg ha-1, 108 kg ha-1 and 216 kg ha-1) and nitrogen (0 kg ha-1, 67 kg ha-1, 134 kg ha-1 and 268 kg ha-1) on gas exchange and biomass accumulation in eggplant was assessed under greenhouse conditions. The net photosynthesis, stomatal conductance, transpiration, internal CO2 concentration, instantaneous carboxylation efficiency, water-use efficiency and total dry weight were evaluated. With the exception of K for water-use efficiency and N for internal CO2 concentration, all the other gas exchange parameters were significantly affected by the K and N doses. There was an interaction between N and K doses for net photosynthesis, stomatal conductance, transpiration and instantaneous carboxylation efficiency. The highest values for net photosynthesis, stomatal conductance, transpiration rate, carboxylation instantaneous efficiency and total dry weight were found in the range of 125-185 kg ha-1 of K and 215-268 kg ha-1 of N.

Accessing the agronomic and photosynthesis-related traits of high-yielding winter wheat mutants induced by ultra-high pressure

To generate new wheat breeding lines, ultra-high pressure (UHP) (using castor oil as the medium) was used to induce mutant lines from the wheat variety ‘Yanzhan 4110′. Three high-yielding mutant lines (Gaoya 2, Gaoya 3 and Gaoya 9) were selected from 1580 mutants induced by UHP and were evaluated for agronomic and photosynthesis-related traits in this study. Our results showed that these mutant lines retained higher grain yield than Yanzhan 4110 and exhibited higher biomass and harvest index, significantly higher plant height, spikelet numbers per spike and higher kernel numbers per spike but similar or lower thousand-kernel weight (α=0.05). The reading of relative leaf chlorophyll content (SPAD) and photosynthetic traits of the high-yielding mutant lines varied to different degrees. The mutant lines had higher SPAD and higher stomatal conductance (Gs) than Yanzhan 4110 at two grain-filling stages. The net photosynthetic rate (Pn), apparent mesophyll conductance, Gs and transpiration rate (Tr) of Gaoya 2 were significantly higher than those of Yanzhan 4110 at the mid grain-filling stage (GF-2) (α=0.05). The decreases in SPAD, Pn, Gs, transpiration efficiency (TE) and Tr in the high-yielding mutant lines were smaller than those in Yanzhan 4110 during the early grain-filling stage (GF-1) and GF-2. Fluorescence parameters, including F0, Fm, Fv, Fv/F0, and Fv/Fm, were higher in the three high-yielding mutant lines, while qN was significantly lower at GF-1 and GF-2 compared with those in Yanzhan 4110 (α=0.05). Higher qP and ΦPSII values were also observed in the three high-yielding mutant lines. These results indicate that wheat mutations induced by UHP exhibited high yield, improved photosynthetic efficiency, decreased thermal dissipation and altered photoinhibition.

Old tall durum wheat cultivars are suited for dual-purpose utilization

Abstract The lateness, tallness and high vigour of old tall durum wheat cultivars could be advantageous for dual-purpose use and their high propensity for lodging should be reduced by grazing. A 3-year field trial was performed in Sardinia, Italy, in a typical Mediterranean environment. Crops of the durum wheat cultivar Senatore Cappelli were sown in October, and grazing was simulated by clipping half of the plots at the terminal spikelet stage of development. The forage biomass derived from clipping varied greatly between seasons (from 0.8 to 3.3 t ha−1 dry matter) in response to the notable inter-seasonal variability in weather conditions. Cultivar Senatore Cappelli showed good recovery following clipping, with the ability to attain almost complete radiation interception well before anthesis. The high number of leaves that emerged after clipping might have contributed to this good recovery. Nevertheless, clipping reduced the dry matter produced by anthesis (16 t ha−1 in clipped compared to 21 t ha−1 in unclipped crops) as well as the final dry matter (DMMAT) (19 t ha−1 in clipped compared to 23 t ha−1 in unclipped crops), although these differences disappeared when the clipped biomass was included. The lower lodging observed at anthesis in the clipped (21%) compared with unclipped crops (63%) likely reduced the difference between treatments. The lower DMMAT of clipped treatments was reflected in a lower grain yield (GY) (3.4 t ha−1 vs 4.2 t ha−1 in the unclipped treatment). Clipping did not affect the amount of nitrogen present in the biomass, nitrogen uptake efficiency or radiation use efficiency. GY reduction after clipping was mediated by the reduction in spikes m−2 and kernels m−2 (KNO). Spike fertility was not affected by clipping, because the same amount of radiation was available for each spike (about 1 MJ). The period with reduced ground cover after clipping was reflected in an increased evaporation and reduced transpiration, which did not alter the total water used and increased the transpiration efficiency in terms of DMMAT. Old tall durum wheat cultivars manifested good suitability for dual-purpose use in environments with low attainable yields because their low grain yield potential contributed to reducing the negative effects of clipping on GY. Their high straw yield and kernel protein percentage represented an advantage with respect to semi-dwarf cultivars.

PIF4 Promotes Expression of LNG1 and LNG2 to Induce Thermomorphogenic Growth in Arabidopsis.

Arabidopsis plants adapt to high ambient temperature by a suite of morphological changes including elongation of hypocotyls and petioles and leaf hyponastic growth. These morphological changes are collectively called thermomorphogenesis and are believed to increase leaf cooling capacity by enhancing transpiration efficiency, thereby increasing tolerance to heat stress. The bHLH transcription factor PHYTOCHROME INTERACTING FACTOR4 (PIF4) has been identified as a major regulator of thermomorphogenic growth. Here, we show that PIF4 promotes the expression of two homologous genes LONGIFOLIA1 (LNG1) and LONGIFOLIA2 (LNG2) that have been reported to regulate leaf morphology. ChIP-Seq analyses and ChIP assays showed that PIF4 directly binds to the promoters of both LNG1 and LNG2. The expression of LNG1 and LNG2 is induced by high temperature in wild type plants. However, the high temperature activation of LNG1 and LNG2 is compromised in the pif4 mutant, indicating that PIF4 directly regulates LNG1 and LNG2 expression in response to high ambient temperatures. We further show that the activities of LNGs support thermomorphogenic growth. The expression of auxin biosynthetic and responsive genes is decreased in the lng quadruple mutant, implying that LNGs promote thermomorphogenic growth by activating the auxin pathway. Together, our results demonstrate that LNG1 and LNG2 are directly regulated by PIF4 and are new components for the regulation of thermomorphogenesis.

Plant physiological changes along an encroachment gradient: an assessment of US Mid-Atlantic serpentine barrens

Serpentine barrens of the Mid-Atlantic United States are globally rare, grass-dominated ecosystems thought to exclude C₃ species and characterized by unique soil composition. However, like many grassland ecosystems globally, these sites are presently facing encroachment by surrounding forest. In this ecosystem, the tendril climbing vine, Smilax rotundifolia, forms dense thickets around barrens that typically precede forest encroachment. While numerous factors speculatively initiate and promote encroachment in these systems, few studies have examined photosynthetic responses of serpentine grasses to changes in resource availability initiated by encroachers or physiological ability of encroaching S. rotundifolia to colonize high-light barren environments. We sought to understand both environmental and physiological dynamics of encroachment along an irradiance gradient in these systems. At three serpentine barren sites in southeastern Pennsylvania, physiological responses of the native grasses Sorghastrum nutans and Schizachyrium scoparium to increased shading by S. rotundifolia were examined. Additionally, the physiological performance of S. rotundifolia in the forest understory was compared to that in sunlit barrens environments. Light-saturated photosynthesis (Aₛₐₜ), stomatal conductance (gₛ), instantaneous transpiration efficiency (ITE), maximum efficiency of photosystem II (Fᵥ/Fₘ), midday leaf water potential (ψₗₑₐf) and specific leaf area (SLA) were measured for all species over the course of the 2014 growing season. Two-way analyses of variance were used to assess changes in these parameters across growing environments, as well as seasonally for each species. Multiple regression analyses were also performed to investigate the influence of vapor pressure deficit (D) and leaf temperature (Tₗₑₐf) on Aₛₐₜ and ITE. Light-saturated photosynthesis was significantly greater in S. rotundifolia growing in sun than in the shade (P < 0.001) and early in the season (P = 0.012). Sun S. rotundifolia had up to 27% greater Aₛₐₜ than shaded plants. Even with reduced ψₗₑₐf in the barrens, S. rotundifolia maintained high gₛ though Aₛₐₜ was limited by high D later in the growing season. These data are in agreement with recent research suggesting that plants are not subject to water limitation in Mid-Atlantic barrens. Unexpectedly, shaded grasses at the encroachment interface did not exhibit any significant reduction in Aₛₐₜ. Declines in grass photosynthesis do not likely occur until S. rotundifolia rhizomes transition into monotypic thickets, completely excluding grasses. Encroachment by S. rotundifolia appears to be primarily facilitated by its ability to capitalize on light resources early on in the summer growing season, when environmental conditions are less stressful.

Responses of transpiration and transpiration efficiency of almond trees to moderate water deficits

The majority of world almond acreage is grown under rainfed conditions but most of the production is obtained under irrigation. Increased water scarcity is reducing water availability for irrigation thus the need to characterize the responses of almond to water deficits. Several works have defined well the stomatal closure in almond leaves under water deficits, but the behavior at the canopy level is not well understood. A field experiment was conducted in an almond (cv. Guara) orchard in Córdoba (Spain) under four different levels of irrigation supply to investigate the responses of almond tree transpiration (T) and transpiration efficiency (TE) to water stress. Stem water potential (Ψx), whole tree transpiration (T) and leaf gas-exchange were periodically measured throughout the 2013 growing season. Tree T decreased linearly as midday Ψx decreased below a threshold value of about −1.1MPa, and declined to about 50% of the Control value when midday Ψx reached −1.6MPa. The quick decline in T in response to the lowering of ψx suggests a high sensitivity of almond T to water deficits. The instantaneous transpiration efficiency (TE) of almond leaves was unaffected by water and varied essentially with vapor pressure deficits. On a daily scale, the leaf TE of stressed trees followed the same pattern as in the non-stressed trees. Then, contrary to the behavior observed in olive and citrus, there were no instantaneous or daily TE increments in almond trees in response to water deficits.