Whole-plant Leaf Area Research Articles

Heritability of Morphophysiological Traits in Popcorn for Drought Tolerance and Their Use as Breeding Indicators of Superior Genotypes

This study aimed to identify the genetic control of morphological, water status, and root traits in four inbred lines and their pre-selected hybrid combinations of popcorn, and to identify the best parents and hybrids. The plants were grown under greenhouse conditions, and with two water conditions—water-stressed (WS) and well-watered (WW). We evaluated shoot biomass (SB), whole plant leaf area (WPLA), chlorophyll content, carbon isotope discrimination, net CO2 assimilation rate, the stomatal conductance, transpiration, cumulative plant transpiration, and root weight density in three sections. The reductions in SB and WPLA are attributed to stomatal causes, given the maintenance of water condition values in water-stressed plants. In fact, the stomata were closed for long periods during plant growth under the water-stressed condition, as indicated by the more negative carbon isotope discrimination values. The root weight density, regardless of soil depth and water conditions, was higher in hybrids. There was a preponderance of non-additive effects in the control of morphological and root traits, especially in the WS condition, and heterosis was shown to be the fundamental strategy for obtaining superior hybrids. For water status traits, it is essential to choose the female parent in the crossing block, given the maternal effect expressed by net CO2 assimilation rate, stomatal conductance, and transpiration.

Abscisic acid signalling mediates biomass trade-off and allocation in poplar.

Abscisic acid (ABA) is a well known stress hormone regulating drought adaptation of plants. Here, we hypothesised that genetic engineering of genes involved in ABA stress signalling and photoperiodic regulation affected drought resistance by trade-off with biomass production in perennial poplar trees. We grew Populus tremula×tremuloides wild-type (T89) and various transgenic lines (two transformation events of 35S::abi1-1, 35S::RCAR, RCAR:RNAi, 35S::ABI3, 35S::AREB3, 35S::FDL1, FDL1:RNAi, 35S::FDL2 and FDL2:RNAi) outdoors and exposed them to drought in the second growth period. After the winter, the surviving lines showed a huge variation in stomatal conductance, leaf size, whole-plant leaf area, tree height, stem diameter, and biomass. Whole-plant leaf area was a strong predictor for woody biomass production. The 35S::AREB3 lines were compromised in biomass production under well irrigated conditions compared with wild-type poplars but were resilient to drought. ABA signalling regulated FDL1 and FDL2 expression under stress. Poplar lines overexpressing FDL1 or FDL2 were drought-sensitive; they shed leaves and lost root biomass, whereas the FDL RNAi lines showed higher biomass allocation to roots under drought. These results assign a new function in drought acclimation to FDL genes aside from photoperiodic regulation. Our results imply a critical role for ABA-mediated processes in balancing biomass production and climate adaptation.

Convergent xylem widening among organs across diverse woody seedlings.

Xylem conduit diameter (Dmax ) of woody angiosperm adults scales with plant size and widens from the stem apex downwards. We hypothesized that, notwithstanding relative growth rate (RGR), growth form or leaf habit, woody seedling conduit Dmax scales linearly with plant size across species; this scaling should be applicable to all vegetative organs, with consistent conduit widening from leaf via stem to main root and coupling with whole-leaf area and whole-stem xylem area. To test these hypotheses, organ-specific xylem anatomy traits and size-related traits in laboratory-grown seedlings were analyzed across 55 woody European species from cool-temperate and Mediterranean climates. As hypothesized, conduit Dmax of each organ showed similar scaling with plant size and consistent basipetal widening from the leaf midvein via the stem to the main root across species, independently of growth form, RGR and leaf habit. We also found a strong correlation between Dmax and average leaf area, and between stem xylem area and whole-plant leaf area. We conclude that seedlings of ecologically wide-ranging woody species converge in their allometric scaling of conduit diameters within and across plant organs. These relationships will contribute to modeling of water transport in woody vegetation that accounts for the whole life history from the trees' regeneration phase to adulthood.

Implications of Heat Treatment and Systemic Delivery of Foliar-Applied Oxytetracycline on Citrus Physiological Management and Therapy Delivery.

Huanglongbing is an economically devastating disease of citrus in Florida and around the world. This study was undertaken to assess two grower-used therapies, heat treatment, and foliar anti-bacterial application. Specifically, there was an industry claim that heat treatment improved subsequent systemic uptake of foliar-applied anti-bacterial compounds. We hypothesized that new vegetative growth induced by heat treatment could lead to increased foliar delivery because of a greater number of new leaves in which cuticles would be more permeable. The study included two factors (1) heat treatment (with or without) and (2) pruning, in which all new leaves, all mature leaves, or no leaves were removed. A commercial formulation of oxytetracycline (OTC) was applied to plants with a non-ionic penetrant surfactant, but one branch on each tree was covered to assess direct versus systemic delivery. The study was repeated twice, destructively assessing whole-plant leaf area and dry weights, as well as OTC content in directly applied and covered leaves. Heat treatment and defoliation treatments reduced growth, but did not affect systemic delivery of OTC. OTC was detected in nearly all covered leaf samples in both repetitions, though at lower concentrations than in directly applied leaves. We conclude that neither heat treatment nor leaf age strongly affect systemic OTC delivery. Implications of this study for leaf age effects on foliar delivery and for phloem delivery of foreign compounds through foliar application are discussed.

A common thermal niche among geographically diverse populations of the widely distributed tree species Eucalyptus tereticornis: No evidence for adaptation to climate-of-origin.

Impacts of climate warming depend on the degree to which plants are constrained by adaptation to their climate-of-origin or exhibit broad climatic suitability. We grew cool-origin, central and warm-origin provenances of Eucalyptus tereticornis in an array of common temperature environments from 18 to 35.5°C to determine if this widely distributed tree species consists of geographically contrasting provenances with differentiated and narrow thermal niches, or if provenances share a common thermal niche. The temperature responses of photosynthesis, respiration, and growth were equivalent across the three provenances, reflecting a common thermal niche despite a 2,200km geographic distance and 13°C difference in mean annual temperature at seed origin. The temperature dependence of growth was primarily mediated by changes in leaf area per unit plant mass, photosynthesis, and whole-plant respiration. Thermal acclimation of leaf, stem, and root respiration moderated the increase in respiration with temperature, but acclimation was constrained at high temperatures. We conclude that this species consists of provenances that are not differentiated in their thermal responses, thus rejecting our hypothesis of adaptation to climate-of-origin and suggesting a shared thermal niche. In addition, growth declines with warming above the temperature optima were driven by reductions in whole-plant leaf area and increased respiratory carbon losses. The impacts of climate warming will nonetheless vary across the geographic range of this and other such species, depending primarily on each provenance's climate position on the temperature response curves for photosynthesis, respiration, and growth.

Tuber yield prognosis model and agronomic nitrogen use efficiency of potato cultivars

Adjusting nitrogen (N) fertilization rates to crop requirements optimizes N efficiency and reduces environmental pollution. In accordance with such precision agriculture, methods facilitating rapid and simple real-time crop yield prognostication are desirable. The aims of this study are to establish a prognostic model for tuber yield; early characterization of a properly N-nourished plant and to determine the N use efficiency by the Asterix and Atlantic potato cultivars. In two separate experiments, on for each cultivar, five pre-planting N fertilization rates (0, 50, 100, 200, and 300 kg ha -1 ) were evaluated. A randomized complete block design with four replicates per experiment was utilized. Variable chosen for early evaluation, 21 days after emergence, were categorized into four named groups. Group one, linked to chlorophyll (SPAD index and total fourth leaf chlorophyll concentration). Group two, concerning with physiological indexes (leaf, fourth leaf, stem, and shoot dry matter; fourth- and whole-plant leaf area; fourth leaf and plant specific leaf area; and leaf area ratio). The third group linked to fourth leaf N indexes (N concentration per unit dry matter and per unit leaf area, and total N content). The fourth group referring to N use efficiency (fourth leaf N use efficiency and agronomic N use efficiency). For both cultivars, there are a significant positive correlation between tuber yield and physiologic and N indexes, while there is a significant negative correlation between tuber yield and N use efficiency. Regression models utilising the SPAD index as an independent variable are effective in predicting the marketable tuber yield of potato plants, and have the added advantage of real-time determination of the SPAD index in relationship a another methods.

Responses to shade and subsequent recovery of soya bean in maize-soya bean relay strip intercropping

In relay intercropping systems, late-planted crops often grow under the shade of the canopy of early-planted tall crops and then transfer to full sunlight after the harvest of the early-planted crops. In order to know the effects of recovery growth of the late-planted soya bean in maize–soya bean relay intercropping, a field experiment was carried out to observe architectural, morphological, physiological and anatomical traits of soya bean plants related to shade and subsequent removal in intercropping before and after maize harvest, respectively. During shade period, soya bean biomass was severely reduced, and stem elongation was stimulated. Typical features of shade grown leaves were found, such as lower LMA (leaf mass per unit area), thinner thickness, higher chlorophyll content, lower chlorophyll a:b ratio. Whole-plant leaf area analysis found that soya bean increased leaf area ratio by adjusting leaf morphology rather than by dry mass allocation. After maize harvest, leaf area and leaf mass increased rapidly, contributing to compensation growth in intercropped soya bean. Meanwhile, physiological and anatomical traits of leaf went back to similar levels as grown in sole cropping. However, stem morphological traits were irreversible after removal of shade. Finally, no difference on seed weight per plant of soya bean was observed between relay intercropping and sole cropping. Based on these findings, we speculated the recovery growth might be the direct determining factor on pod formation in soya bean, and improvement on the capacity of recovery growth could increase yield of relay intercropped soya bean.

Dynamic scaling in the growth of a non-branching plant, Cardiocrinum cordatum.

We investigated whole-plant leaf area in relation to ontogenetic variation in leaf-size for a forest perennial herb, Cardiocrinum cordatum. The 200-fold ontogenetic variability in C. cordatum leaf area followed a power-law dependence on total leaf number, a measure of developmental stage. When we normalized for plant size, the function describing the size of single leaves along the stem was similar among different-sized plants, implying that the different-sized canopies observed at different times in the growth trajectory were fundamentally similar to each other. We conclude that the growth trajectory of a population of C. cordatum plant leaves obeyed a dynamic scaling law, the first reported for a growth trajectory at the whole-plant level.

Genetic variability for leaf growth rate and duration under water deficit in sunflower: analysis of responses at cell, organ, and plant level

Plants under water deficit reduce leaf growth, thereby reducing transpiration rate at the expense of reduced photosynthesis. The objective of this work was to analyse the response of leaf growth to water deficit in several sunflower genotypes in order to identify and quantitatively describe sources of genetic variability for this trait that could be used to develop crop varieties adapted to specific scenarios. The genetic variability of the response of leaf growth to water deficit was assessed among 18 sunflower (Helianthus annuus L.) inbred lines representing a broad range of genetic diversity. Plants were subjected to long-term, constant-level, water-deficit treatments, and the response to water deficit quantified by means of growth models at cell-, leaf-, and plant-scale. Significant variation among lines was found for the response of leaf expansion rate and of leaf growth duration, with an equal contribution of these responses to the variability in the reduction of leaf area. Increased leaf growth duration under water deficit is usually suggested to be caused by changes in the activity of cell-wall enzymes, but the present results suggest that the duration of epidermal cell division plays a key role in this response. Intrinsic genotypic responses of rate and duration at a cellular scale were linked to genotypic differences in whole-plant leaf area profile to water deficit. The results suggest that rate and duration responses are the result of different physiological mechanisms, and therefore capable of being combined to increase the variability in leaf area response to water deficit.

LEAF AREA DEVELOPMENT IN SOYBEAN AS AFFECTED BY PHOSPHORUS NUTRITION AND WATER DEFICIT

Leaf area development is an important factor in crop production because it affects the amount of radiation intercepted and, therefore, plant growth. Even though phosphorus (P) deficit and water stress have been studied as isolated factors limiting leaf area development in soybean (Glycine max (L.) Merr.), little has been done on their possible interactions. A pot experiment was conducted to determine the effects of P supply and water deficit on leaf-area development in soybean, and whether P nutrition affects soybean response to water stress. Plants were grown in pots for 49 days. The soil used was a Sadler silt loam (fine-silty, mixed, mesic Glossic Fragiudalf), which contained 5.3 mg P kg−1 (Mehlich III). Additional P was added at 0, 20, and 80 mg P kg−1 soil. Water treatments consisted of keeping the soil-water content at 85% (well watered), 60% (mild water stress) and 35% (severe water stress) of the 10 kPa soil-water content. Phosphorus nutrition did not affect the response of soybean to water stress in most of the measured variables. Relative reductions due to water stress were similar at every P level for individual leaf area, whole-plant leaf area, aboveground biomass, stomatal conductance, and transpiration. Only plant development was slowed to a greater extent by water stress in P-deficient plants. Water stress had no effect on P nutrition, since it did not affect P concentration in plant tissue.

Early Growth and Development of Pawpaw [Asimina triloba (L.) Dunal] Seedlings in the Greenhouse as Influenced by Shade and Root-zone Modification

This experiment was designed to determine the optimal light level for growing pawpaw seedlings in the greenhouse. In addition, we wanted to determine if modifying the root-zone would positively impact pawpaw seedling growth and development. Experimental treatments were imposed from seed sowing until the plants were destructively harvested. The experimental design was a split-plot, where blocking was done by position in the greenhouse. The main plot of the experiment was shade. This was accomplished by growing seedlings under a wooden frame covered with shadecloth to reduce incident light intensity received by the plant by 30%, 55%, 80%, or 95%. The control treatment was 0% shade or ambient greenhouse light level. The split-plot was root-zone modification. Half of all growing containers were untreated (control) while the other half were painted with SpinOut™, a commercially available product used to reduce root spiraling in nursery containers. There were 40 replicate seedlings per experimental treatment combination per block. Seedling shoot length and unfolded leaf number was recorded twice a week from seedling emergence until destructive harvest. Whole-plant leaf area was also determined. Leaves, stems, and tap and lateral roots were separated and dried to determine biomass partitioned to the respective organs. Up to 55% shade did not significantly reduce whole-plant biomass, while plants at 80% and 95% shade were stunted. Shade in the greenhouse is not required as was previously thought. Specific leaf mass and lateral root mass decreased as shade increased. Neither tap or lateral root dry weights were significantly affected by root-zone modification. New recommendations for container production of pawpaws in the greenhouse will be discussed.

Influence of soil water on the physiological and morphological components of plant water balance in Populus trichocarpa, Populus deltoides and their F(1) hybrids.

Patterns of leaf growth, transpiration and whole-plant water balance in Populus trichocarpa, P. deltoides and their F(1) hybrids were studied during a soil drying cycle. Plant responses were analyzed during three distinct stages of dehydration. In stage I, the transpiration rate of drought-stressed plants remained constant and equal to that of well-watered plants even though soil water content declined by more than 40%. Stage II began as soil and plant water deficits induced stomatal closure. When soil water was expressed as a fraction of transpirable soil water, the transition from stage I to stage II occurred at soil water fractions of 0.35, 0.45 and 0.60 for P. trichocarpa, P. deltoides and their F(1) hybrids, respectively. Reductions in leaf growth coincided with the shift from stage I to stage II. As soil water declined further, decreases in relative transpiration and whole-plant leaf area were significantly greater in parental species than in F(1) hybrids. Inherent feedbacks controlling stomatal water loss and the maintenance and growth of leaf tissue appeared to differ between F(1) and parental genotypes in a pattern characteristic of an overdominant mode of inheritance.Stage III began once the ability of stomata to compensate for water loss had been exhausted. Substantial differences were found in plant survival during stage III, with F(1) hybrids surviving longer than parental species. Survival was more strongly correlated with the hydraulic conductivity of xylem tissues than with the dehydration tolerance of leaf tissues. Collectively, these responses suggest that F(1) hybrids were more drought resistant than either parental species and highlight the importance of whole-plant studies of functional relationships between plant growth, water balance and hydraulic conductivity.

CO_2 and Temperature Effects on Leaf Area Production in Two Annual Plant Species

We studied leaf area production in two annual plant species, Abutilon theophrasti and Amaranthus retroflexus, under three day/night temperature regimes (18°/14°, 28°/22°, and 38°/31°C) and two concentrations of carbon dioxide (400 and 700 @mL/L). The production of whole—plant leaf area during the first 30 d of growth was analyzed in terms of the leaf initiation rate, leaf expansion, individual leaf area, and, in Amaranthus, production of branch leaves. Temperature and CO2 influenced leaf area production through effects on the rate of development, determined by the production of nodes on the main stem (the plastochron index), and through shifts in the relationship between whole—plant leaf area and the number of main stem nodes. In Abutilon, leaf initiation rate was highest at 38°, but area of individual leaves was greatest 28°. Total leaf area was greatly reduced at 18° due to slow leaf initiation rates. Elevated CO2 concentration increased leaf initiation rate at 28°, resulting in an increase in whole—plant leaf area. In Amaranthus, leaf initiation rate increased with temperature, and was increased by elevated CO2 at 28°. Individual leaf area was greatest at 28°, and was increased by elevated CO2 at 28° but decreased at 38°. Branch leaf area displayed a similar response to CO2, but was greater at 38°. Overall, wholeplant leaf area was slightly increased at 38° relative to 28°, and elevated CO2 levels resulted in increased leaf area at 28° but decreased leaf area at 38°. The effects on leaf area closely parallel rates of biomass accumulation in the same experiment, suggesting that responses of developmental processes to elevated CO2 and interacting factors may play an important role in mediating effects on plant growth.

An examination of selection criteria for salt tolerance in wheat, barley and triticale genotypes

This study of 20 genotypes of barley, wheat, durum wheat and triticale had three aims: (1) To determine whether simple measurements on plants grown in salinity tanks in a glasshouse would reflect the documented reputations for salinity tolerance of the genotypes; (2) to test whether rapid development, commonly associated with barleys, is linked with salinity tolerance; (3) to assess several types of measurements as screening tools for salinity tolerance. Measurements of whole-plant leaf area expansion rates were well correlated with biomass production and ranked the genotypes largely in accord with their documented reputations. There was no evidence, either from experimental manipulation of rate of development, or from regression analysis amongst genotypes, that rapid development was linked with salinity tolerance. The origins of tolerance were twofold, deriving from (1) a physiological tolerance - this was defined as a small relative reduction in growth due to salinity, and (2) an absolute tolerance - this was shown as an intrinsic high growth rate of the genotype, i.e. apparent both in and out of salinity. A good indicator of high absolute tolerance, and of potential for screening purposes, was large area of seedling leaves. Regression analysis indicated that absolute tolerance contributed more to productivity in saline conditions than physiological tolerance. Indeed, in one study the latter failed to correlate significantly with productivity. Cl- concentration also was a poor general indicator of productivity in salinity, as was extension rate of single leaves during 10 days after NaCl was applied. It is proposed that screening for intrinsic high growth rate and physiological tolerance should go hand in hand, with more emphasis on the former. This is the reverse of the usual situation.