Growth of Eucalyptus marginata (Jarrah) seedlings in a greenhouse in response to shade and soil temperature

Micromorphology and monolignols of leaf epidermis in Phragmites australis (Poaceae) of air-aquatic and terrestrial ecotypes

The microstructure of leaf epidermis, the localization, and content of syringyl (S) and guajacyl (G) monolignol in epidermal cells of Phragmites australis grown in water and moderate drought soil on the bank of the Venetian strait of the Dnipro River in Kiev (Ukraine) were studied with the electron microscopic method and laser confocal microscopy. The trichomes, guard cells of stomata, epidermal cells of vaulted zones over veins of adaxial and abaxial surface contained syringyl and guajacyl, the content of which depended on plant ecotype. We established that moisture soil influenced the leaf epidermis ultrastructure, on the change of monolignols content and S/G ratio in epidermis leaf of reed. The investigations show that trichomes and the cells of the vaulted zone in the leaf epidermis were the main accumulator of monolignols. The obtained results suggest that change of the microstructure of leaves, content of the monolignols, and S/G ratio in leaves contribute to the preservation of optimal water status of plants and can be considered as the signs of plant phenotypic plasticity and adaptive marker depending on the conditions of water supply.

A meta-analysis of plant responses to light intensity for 70 traits ranging from molecules to whole plant performance

By means of meta-analyses we determined how 70 traits related to plant anatomy, morphology, chemistry, physiology, growth and reproduction are affected by daily light integral (DLI; mol photons m^-2  d^-1 ). A large database including 500 experiments with 760 plant species enabled us to determine generalized dose-response curves. Many traits increase with DLI in a saturating fashion. Some showed a more than 10-fold increase over the DLI range of 1-50 mol m^-2  d^-1 , such as the number of seeds produced per plant and the actual rate of photosynthesis. Strong decreases with DLI (up to three-fold) were observed for leaf area ratio and leaf payback time. Plasticity differences among species groups were generally small compared with the overall responses to DLI. However, for a number of traits, including photosynthetic capacity and realized growth, we found woody and shade-tolerant species to have lower plasticity. We further conclude that the direction and degree of trait changes adheres with responses to plant density and to vertical light gradients within plant canopies. This synthesis provides a strong quantitative basis for understanding plant acclimation to light, from molecular to whole plant responses, but also identifies the variables that currently form weak spots in our knowledge, such as respiration and reproductive characteristics.

Temperature gradients assist carbohydrate allocation within trees

Trees experience two distinct environments: thermally-variable air and thermally-buffered soil. This generates intra-tree temperature gradients, which can affect carbon metabolism and water transport. In this study, we investigated whether carbohydrate allocation within trees is assisted by temperature gradients. We studied pistachio (Pistacia integerrima) to determine: (1) temperature-induced variation in xylem sugar concentration in excised branches; (2) changes in carbon allocation in young trees under simulated spring and fall conditions; and (3) seasonal variability of starch levels in mature orchard trees under field conditions. We found that warm branches had less sugar in perfused sap than cold branches due to increasing parenchyma storage. Simulated spring conditions promoted allocation of carbohydrates from cold roots to warm canopy and explained why starch levels surged in canopies of orchard trees during early spring. This driving force of sugar transport is interrupted in fall when canopies are colder than roots and carbohydrate redistribution is compartmentalized. On the basis of these findings, we propose a new mechanistic model of temperature-assisted carbohydrate allocation that links environmental cues and tree phenology. This data-enabled model provides insights into thermal "fine-tuning" of carbohydrate metabolism and a warning that the physiological performance of trees might be impaired by climatic changes.

Responses to chilling of two Eucalyptus globulus clones with contrasting drought resistance

The effect of chilling on growth and plant hydraulic properties in a drought-resistant clone (CN5) and a drought-sensitive clone (ST51) of Eucalyptus globulus Labill. was evaluated. Chilling (10/5°C, day/night) led to a general decrease in growth of both clones and significant reductions in root hydraulic conductivity, rate of photosynthesis and stomatal conductance in comparison to plants grown at control temperature (24/16°C). The drought-resistant CN5 clone maintained higher root growth and lower leaf-to-root-area ratio than the drought-sensitive ST51 clone, in both temperature treatments. Conversely, ST51 exhibited greater carbon allocation to the foliage and higher hydraulic conductance than clone CN5 at both temperatures. Plants of both clones, when acclimated to chilling, maintained a higher hydraulic conductivity than control plants exposed to chilling temperatures without acclimation. Under chilling, the main differences between clones were a higher water status and anthocyanin concentration in CN5 plants, and a stronger inhibition of root growth in ST51 plants. Except for roots, the hypothesis of a lower depression of growth rate in the drought-resistant clone under chilling was not verified. However, higher root growth under low temperatures, as observed in CN5, can be an advantageous trait in Mediterranean-type environments, protecting trees against summer water-stress.