Internal leaf anatomy and photosynthetic resource-use efficiency: interspecific and intraspecific comparisons

Intraspecific variations of leaf hydraulic, economic, and anatomical traits in Cinnamomum camphora along an urban-rural gradient

Urbanization brings numerous benefits to residents, but it also introduces complex, variable, and heterogeneous habitat conditions to urban plants, resulting in an arid and hot urban environment that decreases tree growth and the ecological service capacity of trees. In this study, we evaluated leaf hydraulic, economic, and anatomical traits and their covariations of Cinnamomum camphora along an urban-rural gradient in Hefei, Eastern China. We found that Cinnamomum camphora in urban adopted a conservative hydraulic strategy with low leaf turgor loss point (Tlp), leaf hydraulic conductance (Kleaf), and leaf water potential resulting in 50 % loss of hydraulic conductance (P50), as well as a quick investment-return economic strategy with low unit leaf dry matter content (LMA) and high leaf nitrogen content (Leaf N). P50, Kleaf and LMA were significantly positively correlated with the urban-rural gradient (PC1urban-rural gradient), while Leaf N exhibited a negative correlation with it. The results showed a trade-off between intraspecific safety and efficiency in leaf hydraulic traits along the urban-rural gradient and an intraspecific coordinated variation in leaf hydraulic and economic traits. In addition, based on the analysis of a trait coordination network, it was revealed that leaf mesophyll and stomata were key structures for trait adjustment and coordination. Furthermore, our findings offer a significant theoretical underpinning for the effective management of landscape trees and the strategic planning of urban tree species.

Photosynthetic performance under adaxial and abaxial illumination in three Mediterranean Quercus species differing in branch architecture and individual leaf area

Light availability effects on canopy-level carbon balance constitute an especially difficult issue to address, owing to the strong spatial and temporal changes of the light environment within the canopy. One of the least explored aspects in relation to light environment is the interaction between leaf angle and leaf anatomy. The inclination of the leaf may affect the distribution of light between the adaxial and abaxial surface. The purpose of this study is determining the proportions of the leaf area receiving light from the abaxial side in branches of isolated trees in three Mediterranean oaks, as well as the photosynthetic responses to light under adaxial and abaxial illumination. The proportions of the leaf area illuminated from below were low for sun incidence angles near 0° with respect to the main axis of the branch. However, for sun incidence angles about 45°, the proportion of leaves receiving abaxial illumination was considerable. PPFD levels on the sunlit part of the abaxial surface were always lower than those in the upper leaf side, as a consequence of the lower projection efficiency for the leaves facing the sun by the lower side. Light absorptance was also lower on the abaxial side. The differences between both sides of the leaf tended to be stronger for thicker, longer-living leaves. We conclude that mean C assimilation of the canopy is significantly decreased by the presence of leaves facing the sun by the lower side and that this decrease is stronger in evergreen species with thicker leaves.

Leaf physiological and morphological constraints of water-use efficiency in C3 plants

The increasing evaporative demand due to climate change will significantly affect the balance of carbon assimilation and water losses of plants worldwide. The development of crop varieties with improved water-use efficiency (WUE) will be critical for adapting agricultural strategies under predicted future climates. This review aims to summarize the most important leaf morpho-physiological constraints of WUE in C3 plants and identify gaps in knowledge. From the carbon gain side of the WUE, the discussed parameters are mesophyll conductance, carboxylation efficiency and respiratory losses. The traits and parameters affecting the waterside of WUE balance discussed in this review are stomatal size and density, stomatal control and residual water losses (cuticular and bark conductance), nocturnal conductance and leaf hydraulic conductance. In addition, we discussed the impact of leaf anatomy and crown architecture on both the carbon gain and water loss components of WUE. There are multiple possible targets for future development in understanding sources of WUE variability in plants. We identified residual water losses and respiratory carbon losses as the greatest knowledge gaps of whole-plant WUE assessments. Moreover, the impact of trichomes, leaf hydraulic conductance and canopy structure on plants' WUE is still not well understood. The development of a multi-trait approach is urgently needed for a better understanding of WUE dynamics and optimization.

Plant trait networks reveal adaptation strategies in the drylands of China

BACKGROUND

Plants accomplish multiple functions by the interrelationships between functional traits. Clarifying the complex relationships between plant traits would enable us to better understand how plants employ different strategies to adapt to the environment. Although increasing attention is being paid to plant traits, few studies focused on the adaptation to aridity through the relationship among multiple traits. We established plant trait networks (PTNs) to explore the interdependence of sixteen plant traits across drylands.

RESULTS

Our results revealed significant differences in PTNs among different plant life-forms and different levels of aridity. Trait relationships for woody plants were weaker, but were more modularized than for herbs. Woody plants were more connected in economic traits, whereas herbs were more connected in structural traits to reduce damage caused by drought. Furthermore, the correlations between traits were tighter with higher edge density in semi-arid than in arid regions, suggesting that resource sharing and trait coordination are more advantageous under low drought conditions. Importantly, our results demonstrated that stem phosphorus concentration (SPC) was a hub trait correlated with other traits across drylands.

CONCLUSIONS

The results demonstrate that plants exhibited adaptations to the arid environment by adjusting trait modules through alternative strategies. PTNs provide a new insight into understanding the adaptation strategies of plants to drought stress based on the interdependence among plant functional traits.

Shrubs Should Be Valued: The Functional Traits of Lonicera fragrantissima var. lancifolia in a Qinling Huangguan Forest Dynamics Plot, China

Previous studies have focused on the functional traits of trees, while undergrowth shrubs have not received the same attention. We collected 97 shrubs from 6 habitats in 3 diameter classes to measure the functional traits of Lonicera fragrantissima var. lancifolia, which is one of the dominant species in the shrub layer of the Qinling Huangguan plot. We found that leaf thickness (LT) decreased with an increase in diameter classes. Other functional traits did not change significantly with the diameter classes. Most of the functional traits changed with the habitats, which may be influenced by topography and soil. On the whole, Lonicera fragrantissima var. lancifolia showed low variation, which indicates that its growth was stable and good. The relationships between functional traits within species was in accordance with the leaf economic spectrum. The positive correlation between soil total nitrogen (STN) and C:N verified the “nutrition luxury hypothesis”.

Coordination of leaf hydraulic and economic traits in Cinnamomum camphora under impervious pavement

BACKGROUND

Paved urban environments can pose great threats to the physiological functioning and ecological services of street trees. In this context, assessment of leaf phenotypic plasticity is crucial for understanding the ecological strategy of tree species under impervious pavements.

RESULTS

In this study, we measured a set of leaf economic traits, hydraulic traits of Cinnamomum camphora, and surrounding environmental factors in a street site (the soil was covered by the impervious pavement) and a park site (the soil was covered by grass) in Hefei, eastern China. Compared with the park site, trees in the street site had higher stomatal length (SL), leaf thickness (LT), maximum photochemical quantum yield of photosystem II (Y(II)), and lower stomatal density (SD), specific leaf area (SLA), the leaf water potential at 50% loss of hydraulic conductance (P₅₀), and leaf turgor loss point (TLP). Redundancy analysis showed that air relative humidity and volumetric soil water content caused these traits to be altered.

CONCLUSIONS

Our results showed that C. camphora adapted to the street pavement environment through the coordination of leaf economic and leaf hydraulic traits, and adopted the slow investment return type in the leaf economic spectrum and high drought resistance to meet its actual physiological needs. This finding provides a new perspective for understanding the physiological strategies of street trees to adapt to urban pavement environments.

Contrasting effects of plant inter- and intraspecific variation on community trait responses to nitrogen addition and drought in typical and meadow steppes

BACKGROUND

Inter- and intraspecific variation in plant traits play an important role in grassland community assembly under global change scenarios. However, explorations of how these variations contribute to the responses of community traits to nitrogen (N) addition and drought in different grassland types are lacking. We measured the plant height, leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf N content (LNC) and the ratio of leaf carbon (C) to leaf N (C:N) in a typical and a meadow steppe after three years of N addition, drought and their interaction. We determined the community-weighted means (CWMs) of the six traits to quantify the relative contribution of inter- and intraspecific variation to the responses of community traits to N addition and drought in the two steppes.

RESULTS

The communities in the two steppes responded to N addition and the interaction by increasing the CWM of LNC and decreasing C:N. The community in the meadow steppe responded to drought through increased CWM of LNC and reduced C:N. Significant differences were observed in SLA, LDMC, LNC and C:N between the two steppes under different treatments. The SLA and LNC of the community in the meadow steppe were greater than those of the typical steppe, and the LDMC and C:N exhibited the opposite results. Moreover, variation in community traits in the typical steppe in response to N addition and drought was caused by intraspecific variation. In contrast, the shifts in community traits in the meadow steppe in response to N addition and drought were influenced by both inter- and intraspecific variation.

CONCLUSIONS

The results demonstrate that intraspecific variation contributed more to community functional shifts in the typical steppe than in the meadow steppe. Intraspecific variation should be considered to understand better and predict the response of typical steppe communities to global changes. The minor effects of interspecific variation on meadow steppe communities in response to environmental changes also should not be neglected.

The three-dimensional construction of leaves is coordinated with water use efficiency in conifers

Conifers prevail in the canopies of many terrestrial biomes, holding a great ecological and economic importance globally. Current increases in temperature and aridity are imposing high transpirational demands and resulting in conifer mortality. Therefore, identifying leaf structural determinants of water use efficiency is essential for predicting physiological impacts due to environmental variation. Using synchrotron-generated microtomography imaging, we extracted leaf volumetric anatomy and stomatal traits in 34 species across conifers with a special focus on Pinus, the richest conifer genus. We show that intrinsic water use efficiency (WUE_i ) is positively driven by leaf vein volume. Needle-like leaves of Pinus, as opposed to flat leaves or flattened needles of other genera, showed lower mesophyll porosity, decreasing the relative mesophyll volume. This led to increased ratios of stomatal pore number per mesophyll or intercellular airspace volume, which emerged as powerful explanatory variables, predicting both stomatal conductance and WUE_i . Our results clarify how the three-dimensional organisation of tissues within the leaf has a direct impact on plant water use and carbon uptake. By identifying a suite of structural traits that influence important physiological functions, our findings can help to understand how conifers may respond to the pressures exerted by climate change.

Effects of Water Availability on the Relationships Between Hydraulic and Economic Traits in the Quercus wutaishanica Forests

Water availability is a key environmental factor affecting plant species distribution, and the relationships between hydraulic and economic traits are important for understanding the species' distribution patterns. However, in the same community type but within different soil water availabilities, the relationships in congeneric species remain ambiguous. In northwest China, Quercus wutaishanica forests in the Qinling Mountains (QM, humid region) and Loess Plateau (LP, drought region) have different species composition owing to contrasting soil water availability, but with common species occurring in two regions. We analyzed eight hydraulic traits [stomatal density (SD), vein density (VD), wood specific gravity (WSG_branch), lower leaf area: sapwood area (Al: As), stomatal length (SL), turgor loss point (Ψ_Tlp), maximum vessel diameter (Vd_max) and height (Height)] and five economic traits [leaf dry matter content (LDMC), leaf tissue density (TD), leaf dry mass per area (LMA), Leaf thickness (LT) and maximum net photosynthetic rate (P_max)] of congeneric species (including common species and endemic species) in Q. wutaishanica forests of QM and LP. We explored whether the congeneric species have different economic and hydraulic traits across regions. And whether the relationship between hydraulic and economic traits was determined by soil water availability, and whether it was related to species distribution and congeneric endemic species composition of the same community. We found that LP species tended to have higher SD, VD, WSG_branch, Al: As, SL, Ψ_Tlp and Vd_max than QM species. There was a significant trade-off between hydraulic efficiency and safety across congeneric species. Also, the relationships between hydraulic and economic traits were closer in LP than in QM. These results suggested that relationships between hydraulic and economic traits, hydraulic efficiency and safety played the role in constraining species distribution across regions. Interestingly, some relationships between traits changed (from significant correlation to non-correlation) in common species across two regions (from LP to QM), but not in endemic species. The change of these seven pairs of relationships might be a reason for common species' wide occurrence in the two Q. wutaishanica forests with different soil water availability. In drought or humid conditions, congeneric species developed different types of adaptation mechanisms. The study helps to understand the environmental adaptive strategies of plant species, and the results improve our understanding of the role of both hydraulic and economic traits during community assembly.

Leaf economic strategies of a sclerophyllous plant (Eurya japonica): commonalities and particularities of trait correlation structures in low-moisture and low-phosphorus habitats

Sclerophylly proves an advantageous strategy in a variety of stressful environments. However, it is less clear how multiple phenotypic traits in sclerophyllous plants are integrated to accomplish proper functions under specific stressors. This study measured 10 leaf traits in a sclerophyllous species, Eurya japonica Thunb., in the Zhoushan Archipelago, eastern China, to examine how the structures of trait correlation (i.e. phenotypic integration) vary between two habitats with contrasting moisture and phosphorus (P) availability. Overall, the trait correlation matrices were similar between the two habitats under study (Mantel r > 0.5), reflecting a consistent trade-off between leaf outspreading (i.e. leaf area/mass ratio) and water-use efficiency (measured by δ13C). Stomatal conductance was correlated with leaf area, thickness and area/mass ratio only in the dry, P-rich habitat, whereas it was robustly correlated with leaf P per unit area in the wet, P-poor habitat. Moreover, leaf water-use efficiency was robustly correlated with leaf P and N per unit area in the dry habitat, but not so in the low-P one. These differences in trait correlation structures illustrate that the pathways of strategic compromise under contrasting stressors were locally specialised. This study highlights the importance of phenotypic integration as an emergent 'trait' in sustaining viable strategies.

El Niño-Southern Oscillation affects the water relations of tree species in the Yucatan Peninsula, Mexico

We evaluated the effect of ENSO 2015/16 on the water relations of eight tree species in seasonally dry tropical forests of the Yucatan Peninsula, Mexico. The functional traits: wood density, relative water content in wood, xylem water potential and specific leaf area were recorded during the rainy season and compared in three consecutive years: 2015 (pre-ENSO conditions), 2016 (ENSO conditions) and 2017 (post-ENSO conditions). We analyzed tree size on the capacity to respond to water deficit, considering young and mature trees, and if this response is distinctive in species with different leaf patterns in seasonally dry tropical forests distributed along a precipitation gradient (700–1200 mm year⁻¹). These traits showed a strong decrease in all species in response to water stress in 2016, mainly in the driest site. Deciduous species had lower wood density, higher predawn water potential and higher specific leaf area than evergreen species. In all cases, mature trees were more tolerant to drought. In the driest site, there was a significant reduction in water status, regardless of their leaf phenology, indicating that seasonally dry tropical forests are highly vulnerable to ENSO. Vulnerability of deciduous species is intensified in the driest areas and in the youngest trees.

Specific leaf metabolic changes that underlie adjustment of osmotic potential in response to drought by four Quercus species

Osmotic adjustment is almost ubiquitous as a mechanism of response to drought in many forest species. Recognized as an important mechanism of increasing turgor under water stress, the metabolic basis for osmotic adjustment has been described in only a few species. We set an experiment with four species of the genus Quercus ranked according to drought tolerance and leaf habit from evergreen to broad-leaved deciduous. A cycle of watering deprivation was imposed on seedlings, resulting in well-watered (WW) and water-stressed (WS) treatments, and their water relations were assessed from pressure-volume curves. Leaf predawn water potential (Ψpd) significantly decreased in WS seedlings, which was followed by a drop in leaf osmotic potential at full turgor (Ψπ100). The lowest values of Ψπ100 followed the ranking of decreasing drought tolerance: Quercus ilex L. < Quercus faginea Lam. < Quercus pyrenaica Willd. < Quercus petraea Matt. Liebl. The leaf osmotic potential at the turgor loss point (ΨTLP) followed the same pattern as Ψπ100 across species and treatments. The pool of carbohydrates, some organic acids and cyclitols were the main osmolytes explaining osmotic potential across species, likewise to the osmotic adjustment assessed from the decrease in leaf Ψπ100 between WW and WS seedlings. Amino acids were very responsive to WS, particularly γ-aminobutyric acid in Q. pyrenaica, but made a relatively minor contribution to osmotic potential compared with other groups of compounds. In contrast, the cyclitol proto-quercitol made a prominent contribution to the changes in osmotic potential regardless of watering treatment or species. However, different metabolites, such as quinic acid, played a more important role in osmotic adjustment in Q. ilex, distinguishing it from the other species studied. In conclusion, while osmotic adjustment was present in all four Quercus species, the molecular processes underpinning this response differed according to their phylogenetic history and specific ecology.

Summit evergreen shrubs living at a semi-arid treeline: photoprotection systems activation in an open vs an understory site

High-mountain-ecosystems in the Mediterranean-type climate are exceptional because of their outstanding biodiversity but also because of their characteristic drought stress in summer. Still, plant functioning in these habitats has been largely understudied. Here, morphological, photochemical, and biochemical traits were seasonally assessed in six shrubs characterized by contrasting morphological traits, in the Teide mountain in the Canary Islands. Two adjacent populations, the first located in an open site and the second in the understorey of Pinus canariensis treeline forest, were evaluated. We aimed at disentangling (1) the role of morphological and biochemical photoprotective strategies and of their seasonal plasticity to cope with changing environmental conditions in this semiarid ecosystem, (2) how the interspecific differences in biochemical photoprotection are related to leaf morphology and phenology and (3) how living in the understory of the treeline may affect those responses. Our results indicate that both morphological and biochemical traits (particularly leaf habit, morphology and carotenoids from the β-branch) play an intricate role in photoprotection, and that a high interspecific variability exists. According to the down-regulation of photochemical activity and the upregulation of photoprotective molecules, species could be grouped into three types: (1) those more responsive to summer stress (e.g. Descurainia bourgeauana); (2) those more responsive to winter stress (e.g. Pterocephalus lasiospermus, Scrophularia glabrata and Adenocarpus viscosus); and (3) those showing rather constant behavior across seasons (e.g. Spartocytisus supranubius and Erysimum scoparium). In all the species, plants in the open site showed a marked seasonal physiological response in most of the studied parameters. Pinus canariensis canopy buffers environmental abiotic constrains. On a global change scenario, and provided further functional studies are needed, our results pinpoints heterogeneity in the sensitivity of these species against for instance late-frost or summer-heat/drought events, which could easily shift current species distribution in the coming years.

High differentiation in functional traits but similar phenotypic plasticity in populations of a soil specialist along a climatic gradient

BACKGROUND AND AIMS

Plants experiencing contrasting environmental conditions may accommodate such heterogeneity by expressing phenotypic plasticity, evolving local adaptation or a combination of both. We investigated patterns of genetic differentiation and plasticity in response to drought in populations of the gypsum specialist Lepidium subulatum.

METHODS

We created an outdoor common garden with rain exclusion structures using 60 maternal progenies from four distinct populations that substantially differ in climatic conditions. We characterized fitness, life history and functional plasticity in response to two contrasting treatments that realistically reflect soil moisture variation in gypsum habitats. We also assessed neutral genetic variation and population structure using microsatellite markers.

KEY RESULTS

In response to water stress, plants from all populations flowered earlier, increased allocation to root tissues and advanced leaf senescence, consistent with a drought escape strategy. Remarkably, these probably adaptive responses were common to all populations, as shown by the lack of population × environment interaction for almost all functional traits. This generally common pattern of response was consistent with substantial neutral genetic variation and large differences in population trait means. However, such population-level trait variation was not related to climatic conditions at the sites of origin.

CONCLUSIONS

Our results show that, rather than ecotypes specialized to local climatic conditions, these populations are composed of highly plastic, general-purpose genotypes in relation to climatic heterogeneity. The strikingly similar patterns of plasticity among populations, despite substantial site of origin differences in climate, suggest past selection on a common norm of reaction due to similarly high levels of variation within sites. It is thus likely that plasticity will have a prevalent role in the response of this soil specialist to further environmental change.

Plasticity to drought and ecotypic differentiation in populations of a crop wild relative

Populations of widely distributed species often exhibit geographic variation in functional traits in response to environmental heterogeneity. Such trait variation may be the result of different adaptive mechanisms, including genetically based differentiation, phenotypic plasticity or a combination of both. Disentangling the genetic and environmental components of trait variation may be particularly interesting in crop wild relatives, since they may provide unique reservoirs of genetic diversity for crop improvement. In this study, we assessed ecotypic differentiation and patterns of plasticity to drought in populations of Lupinus angustifolius, a Mediterranean crop wild relative, from two climatically distinct regions in the Iberian Peninsula. Using an outdoor common garden, we compared phenotypic responses of inbred maternal families to two ecologically meaningful water availability treatments (drought and high-moisture). We measured 18 different functional traits related to growth, morphology, phenology and reproduction. Plants in the drought treatment grew less, had lower leaf chlorophyll content and photochemical efficiency, but also reproduced faster, produced larger seeds and altered leaflet morphology through increased leaflet thickness, higher leaflet dry matter content and lower specific leaf area. We also found significant differences between regions that likely reflect adaptation to climatically distinct environments, with populations from the south showing a faster onset of reproduction, higher leaf thickness and higher seed size, consistent with the drier conditions experienced in southern sites. Plasticity to drought was in most cases in the same direction as quantitative genetic differentiation (i.e. cogradient variation), providing evidence of the adaptive value of the plastic change. Our results show that both genetic differentiation and plasticity can generate adaptive phenotypic variation in L. angustifolius, and help to identify potentially valuable genetic resources to incorporate into breeding programmes.

Leaf structure and seed histochemistry analyses provided structural insights into the improved yield and quality of tree peony seed under light shading conditions

In biology, structure is the basis of function. For plants, changes in their physiological and ecological functions are usually caused by structural changes. To understand how shading conditions change the plant structures, thereby providing structural insights into the improved yield and quality, oilseed tree peony were shaded with different densities of polyethylene nets from 28 days after pollination (DAP) until harvesting. The thickness of the leaf (LT), vein (VT), upper epidermis (UET), lower epidermis (LET), palisade tissue (PT), sponge tissue (ST), as well as the accumulation and distribution of starch, protein, and fat, were observed at 14-day intervals. The results showed that shading had a significant effect on the anatomical structure of the leaves. In the rapid growth period (before 70 DAP), the LT, ET, and VT under shading were significantly lower than under non-shading. During this period, the accumulation of starch and protein under shading was lower than that under non-shading. At the maturation period (99-112 DAP), the LT and PT under shading were higher than under non-shading, indicating that light shading delayed leaf senescence and increased photosynthetic capacity. Shading delayed the degradation of the integument cells and prolonged seed development and nutrient accumulation.

Drought Stress Effects and Olive Tree Acclimation under a Changing Climate

Increasing consciousness regarding the nutritional value of olive oil has enhanced the demand for this product and, consequently, the expansion of olive tree cultivation. Although it is considered a highly resilient and tolerant crop to several abiotic stresses, olive growing areas are usually affected by adverse environmental factors, namely, water scarcity, heat and high irradiance, and are especially vulnerable to climate change. In this context, it is imperative to improve agronomic strategies to offset the loss of productivity and possible changes in fruit and oil quality. To develop more efficient and precise measures, it is important to look for new insights concerning response mechanisms to drought stress. In this review, we provided an overview of the global status of olive tree ecology and relevance, as well the influence of environmental abiotic stresses in olive cultivation. Finally, we explored and analysed the deleterious effects caused by drought (e.g., water status and photosynthetic performance impairment, oxidative stress and imbalance in plant nutrition), the most critical stressor to agricultural crops in the Mediterranean region, and the main olive tree responses to withstand this stressor.

Convergence of ecophysiological traits drives floristic composition of early lineage vascular plants in a tropical forest floor

BACKGROUND AND AIMS

Tropical understorey plant communities are highly diverse and characterized by variable resource availability, especially light. Plants in these competitive environments must carefully partition resources to ensure ecological and evolutionary success. One mechanism of effective resource partitioning is the optimization of functional traits to enhance competition in highly heterogeneous habitats. Here, we surveyed the ecophysiology of two early lineage vascular plant groups from a tropical forest understorey: Selaginella (a diverse lineage of lycophytes) and ferns.

METHODS

In a lowland rain forest in Costa Rica, we measured a suite of functional traits from seven species of Selaginella and six fern species. We evaluated species microclimate and habitat; several photosynthetic parameters; carbon, nitrogen and phosphorus content; chlorophyll concentration; leaf mass per area (LMA); and stomatal size and density. We then compare these two plant lineages and search for relationships between key functional parameters that already exist on a global scale for angiosperms.

KEY RESULTS

Convergence of trait function filtered Selaginella species into different habitats, with species in heavily shaded environments having higher chlorophyll concentrations and lower light compensation points compared with open habitats. Alternatively, lower foliar nitrogen and higher stomatal densities were detected in species occupying these open habitats. Selaginella species had denser and smaller stomata, lower LMA and lower foliar nutrient content than ferns, revealing how these plant groups optimize ecophysiological function differently in tropical forest floors.

CONCLUSIONS

Our findings add key pieces of missing evidence to global explorations of trait patterns that define vascular plant form and function, which largely focus on seed plants. Broadly predictable functional trait relationships were detected across both Selaginella and ferns, similar to those of seed plants. However, evolutionary canalization of microphyll leaf development appears to have driven contrasting, yet successful, ecophysiological strategies for two coexisting lineages of extant homosporous vascular plants.

Metallic nanoparticles influence the structure and function of the photosynthetic apparatus in plants

The applications of nanoparticles continue to expand into areas as diverse as medicine, bioremediation, cosmetics, pharmacology and various industries, including agri-food production. The widespread use of nanoparticles has generated concerns given the impact these nanoparticles - mostly metal-based such as CuO, Ag, Au, CeO₂, TiO₂, ZnO, Co, and Pt - could be having on plants. Some of the most studied variables are plant growth, development, production of biomass, and ultimately oxidative stress and photosynthesis. A systematic appraisal of information about the impact of nanoparticles on these processes is needed to enhance our understanding of the effects of metallic nanoparticles and oxides on the structure and function on the plant photosynthetic apparatus. Most nanoparticles studied, especially CuO and Ag, had a detrimental impact on the structure and function of the photosynthetic apparatus. Nanoparticles led to a decrease in concentration of photosynthetic pigments, especially chlorophyll, and disruption of grana and other malformations in chloroplasts. Regarding the functions of the photosynthetic apparatus, nanoparticles were associated with a decrease in the photosynthetic efficiency of photosystem II and decreased net photosynthesis. However, CeO₂ and TiO₂ nanoparticles may have a positive effect on photosynthetic efficiency, mainly due to an increase in electron flow between the photosystems II and I in the Hill reaction, as well as an increase in Rubisco activity in the Calvin and Benson cycle. Nevertheless, the underlying mechanisms are poorly understood. The future mechanistic work needs to be aimed at characterizing the enhancing effect of nanoparticles on the active generation of ATP and NADPH, carbon fixation and its incorporation into primary molecules such as photo-assimilates.

Unravelling the Functional Diversity of the Soil Microbial Community of Chinese Fir Plantations of Different Densities

The structure and function of forest ecosystems are directly or indirectly affected by their stand density. However, what effect the density of Chinese fir plantations has on the functional diversity of the soil microbial community remains unclear. The microbial metabolic functional diversity of soils sampled at the topsoil (0–20 cm) of 35-year-old Chinese fir plantations of five initial densities (D1: 1667 stems∙hm−2, D2: 3333 stems∙hm−2, D3: 5000 stems∙hm−2, D4: 6667 stems∙hm−2, and D5: 10,000 stems∙hm−2) was studied by using Biolog ECO technology. The results showed that the soil pH, oxidizable organic carbon (SOOC), available N (AN), available P (AP), and available K (AK) contents all showed a gradual increase from D1 to D4 and a decrease from D4 to D5, while the number of culturable bacteria and total microorganisms, the average well color development (AWCD) values for the single carbon substrate and six types of carbon sources used by the microbial community, as well as the Shannon-Wiener diversity index (H’), Pielou evenness index (J), and McIntosh Diversity Index (U), were the opposite, suggesting that low-densities favored C and N mineralization and the nutrient cycle. The density of Chinese fir plantations had a significant effect on the use of carbohydrates, amino acids, carboxylic acids, and phenolic acids by the soil microbial community, but it had no significant effect on the use of polymers (p < 0.05). Principal component analysis (PCA) revealed that carbohydrates, polymers, and phenolic acids were sensitive carbon sources that caused differences in the metabolic functions of soil microbial communities in Chinese fir plantations. Redundancy analysis (RDA) showed that physicochemical factors have a significant influence on the metabolic function of soil microbial communities (RDA1 and RDA2 explained >85% variance). The changes in density affected the soil physicochemical properties, the composition, and the metabolic functional diversity of microbial communities in Chinese fir plantations, which is certainly useful for the stand density regulation of Chinese fir plantations.

Ecophysiological responses of Betula pendula, Pinus uncinata and Rhododendron ferrugineum in the Catalan Pyrenees to low summer rainfall

Climate change is producing modifications in the intensity and frequency of rainfall in some regions of the planet. According to predictions, annual rainfall distribution in Western Europe will result in an increase in episodes of drought, thereby negatively affecting nutrient availability. Since high mountain systems will be particularly vulnerable, the physiological and nutritional responses to changes in summer rainfall were monitored over the course of two consecutive summers on three species, which are representative of subalpine forests: birch (Betula pendula Roth.), rhododendron (Rhododendron ferrugineum L.) and mountain pine (Pinus uncinata Mill.). Birch was especially susceptible to scarce precipitation showing alterations in leaf morphology and a decline in net photosynthesis (A) due to stomatal closure, which led to photoinhibition and to early leaf senescence as shown by the photosynthetic nitrogen-use efficiency (PNUE), carbon/nitrogen (C/N) ratio, foliar N and ¹³C isotope discrimination (Δ¹³C) results. The Δ¹³C of the soluble fraction is a good estimator of intrinsic water-use efficiency in this species. Rhododendron and mountain pine had sclerophyllous leaves, as indicated by leaf mass per area, Δ¹³C, PNUE and C/N results. Rhododendron was particularly affected by short periods of scarce rainfall, which negatively affected gas exchange and photochemistry, and reduced the remobilization of leaf N and P. Mountain pine was the most tolerant species since alterations of gas exchange, photochemistry and Δ¹³C were not observed. Its highest investment of N in RuBisCo and highest potassium, iron and magnesium leaf concentration contributed to the highest A rates observed.

Limited acclimation in leaf anatomy to experimental drought in tropical rainforest trees

Dry periods are predicted to become more frequent and severe in the future in some parts of the tropics, including Amazonia, potentially causing reduced productivity, higher tree mortality and increased emissions of stored carbon. Using a long-term (12 year) through-fall exclusion (TFE) experiment in the tropics, we test the hypothesis that trees produce leaves adapted to cope with higher levels of water stress, by examining the following leaf characteristics: area, thickness, leaf mass per area, vein density, stomatal density, the thickness of palisade mesophyll, spongy mesophyll and both of the epidermal layers, internal cavity volume and the average cell sizes of the palisade and spongy mesophyll. We also test whether differences in leaf anatomy are consistent with observed differential drought-induced mortality responses among taxa, and look for relationships between leaf anatomy, and leaf water relations and gas exchange parameters. Our data show that trees do not produce leaves that are more xeromorphic in response to 12 years of soil moisture deficit. However, the drought treatment did result in increases in the thickness of the adaxial epidermis (TFE: 20.5 ± 1.5 µm, control: 16.7 ± 1.0 µm) and the internal cavity volume (TFE: 2.43 ± 0.50 mm³ cm^-2, control: 1.77 ± 0.30 mm³ cm^-2). No consistent differences were detected between drought-resistant and drought-sensitive taxa, although interactions occurred between drought-sensitivity status and drought treatment for the palisade mesophyll thickness (P = 0.034) and the cavity volume of the leaves (P = 0.025). The limited response to water deficit probably reflects a tight co-ordination between leaf morphology, water relations and photosynthetic properties. This suggests that there is little plasticity in these aspects of plant anatomy in these taxa, and that phenotypic plasticity in leaf traits may not facilitate the acclimation of Amazonian trees to the predicted future reductions in dry season water availability.

Losses of leaf area owing to herbivory and early senescence in three tree species along a winter temperature gradient

In temperate climates, evergreen leaves have to survive throughout low temperature winter periods. Freezing and chilling injuries can lead to accelerated senescence of part of the leaf surface, which contributes to a reduction of the lifespan of the photosynthetic machinery and of leaf lifetime carbon gain. Low temperatures are also associated with changes in foliar chemistry and morphology that affect consumption by herbivores. Therefore, the severity of foliar area losses caused by accelerated senescence and herbivory can change along winter temperature gradients. The aim of this study is to analyse such responses in the leaves of three evergreen species (Quercus ilex, Q. suber and Pinus pinaster) along a climatic gradient. The leaves of all three species presented increased leaf mass per area (LMA) and higher concentrations of structural carbohydrates in cooler areas. Only the two oak species showed visible symptoms of damage caused by herbivory, this being less intense at the coldest sites. The leaves of all three species presented chlorotic and necrotic spots that increased in size with leaf age. The foliar surface affected by chlorosis and necrosis was larger at the sites with the coldest winters. Therefore, the effects of the winter cold on the lifespan of the photosynthetic machinery were contradictory: losses of leaf area due to accelerated senescence increased, but there was a decrease in losses caused by herbivory. The final consequences for carbon assimilation strongly depend on the exact timing of the appearance of the damage resulting from low temperature and grazing by herbivores.

Leaf morphological and physiological adaptations of a deciduous oak (Quercus faginea Lam.) to the Mediterranean climate: a comparison with a closely related temperate species (Quercus robur L.)

'White oaks'--one of the main groups of the genus Quercus L.--are represented in western Eurasia by the 'roburoid oaks', a deciduous and closely related genetic group that should have an Arcto-Tertiary origin under temperate-nemoral climates. Nowadays, roburoid oak species such as Quercus robur L. are still present in these temperate climates in Europe, but others are also present in southern Europe under Mediterranean-type climates, such as Quercus faginea Lam. We hypothesize the existence of a coordinated functional response at the whole-shoot scale in Q. faginea under Mediterranean conditions to adapt to more xeric habitats. The results reveal a clear morphological and physiological segregation between Q. robur and Q. faginea, which constitute two very contrasting functional types in response to climate dryness. The most outstanding divergence between the two species is the reduction in transpiring area in Q. faginea, which is the main trait imposed by the water deficit in Mediterranean-type climates. The reduction in leaf area ratio in Q. faginea should have a negative effect on carbon gain that is partially counteracted by a higher inherent photosynthetic ability of Q. faginea when compared with Q. robur, as a consequence of higher mesophyll conductance, higher maximum velocity of carboxylation and much higher stomatal conductance (gs). The extremely high gs of Q. faginea counteracts the expected reduction in gs imposed by the stomatal sensitivity to vapor pressure deficit, allowing this species to diminish water losses maintaining high net CO2 assimilation values along the vegetative period under nonlimiting soil water potential values. In conclusion, the present study demonstrates that Q. faginea can be regarded as an example of adaptation of a deciduous oak to Mediterranean-type climates.

Leaf Mass per Area (LMA) and Its Relationship with Leaf Structure and Anatomy in 34 Mediterranean Woody Species along a Water Availability Gradient

Leaf mass per area (LMA) is a morphological trait widely used as a good indicator of plant functioning (i.e. photosynthetic and respiratory rates, chemical composition, resistance to herbivory, etc.). The LMA can be broken down into the leaf density (LD) and leaf volume to area ratio (LVA or thickness), which in turn are determined by anatomical tissues and chemical composition. The aim of this study is to understand the anatomical and chemical characteristics related to LMA variation in species growing in the field along a water availability gradient. We determined LMA and its components (LD, LVA and anatomical tissues) for 34 Mediterranean (20 evergreen and 14 deciduous) woody species. Variation in LMA was due to variation in both LD and LVA. For both deciduous and evergreen species LVA variation was strongly and positively related with mesophyll volume per area (VA or thickness), but for evergreen species positive relationships of LVA with the VA of epidermis, vascular plus sclerenchyma tissues and air spaces were found as well. The leaf carbon concentration was positively related with mesophyll VA in deciduous species, and with VA of vascular plus sclerenchymatic tissues in evergreens. Species occurring at the sites with lower water availability were generally characterised by a high LMA and LD.

Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits

We explored potential of morphological and anatomical leaf traits for predicting ecophysiological key functions in subtropical trees. We asked whether the ecophysiological parameters stomatal conductance and xylem cavitation vulnerability could be predicted from microscopy leaf traits. We investigated 21 deciduous and 19 evergreen subtropical tree species, using individuals of the same age and from the same environment in the Biodiversity-Ecosystem Functioning experiment at Jiangxi (BEF-China). Information-theoretic linear model selection was used to identify the best combination of morphological and anatomical predictors for ecophysiological functions. Leaf anatomy and morphology strongly depended on leaf habit. Evergreen species tended to have thicker leaves, thicker spongy and palisade mesophyll, more palisade mesophyll layers and a thicker subepidermis. Over 50% of all evergreen species had leaves with multi-layered palisade parenchyma, while only one deciduous species (Koelreuteria bipinnata) had this. Interactions with leaf habit were also included in best multi-predictor models for stomatal conductance (gs ) and xylem cavitation vulnerability. In addition, maximum gs was positively related to log ratio of palisade to spongy mesophyll thickness. Vapour pressure deficit (vpd) for maximum gs increased with the log ratio of palisade to spongy mesophyll thickness in species having leaves with papillae. In contrast, maximum specific hydraulic conductivity and xylem pressure at which 50% loss of maximum specific xylem hydraulic conductivity occurred (Ψ50 ) were best predicted by leaf habit and density of spongy parenchyma. Evergreen species had lower Ψ50 values and lower maximum xylem hydraulic conductivities. As hydraulic leaf and wood characteristics were reflected in structural leaf traits, there is high potential for identifying further linkages between morphological and anatomical leaf traits and ecophysiological responses.

Is there a species spectrum within the world-wide leaf economics spectrum? Major variations in leaf functional traits in the Mediterranean sclerophyll Quercus ilex

The leaf economics spectrum is a general concept describing coordinated variation in foliage structural, chemical and physiological traits across resource gradients. Yet, within this concept,the role of within-species variation, including ecotypic and plastic variation components, has been largely neglected. This study hypothesized that there is a within-species economics spectrum within the general spectrum in the evergreen sclerophyll Quercus ilex which dominates low resource ecosystems over an exceptionally wide range. An extensive database of foliage traits covering the full species range was constructed, and improved filtering algorithms were developed. Standardized data filtering was deemed absolutely essential as additional variation sources can result in trait variation of 10–300%,blurring the broad relationships. Strong trait variation, c. two-fold for most traits to up to almost an order of magnitude, was uncovered.Although the Q. ilex spectrum is part of the general spectrum, within-species trait and climatic relationships in this species partly differed from the overall spectrum. Contrary to world-wide trends, Q. ilex does not necessarily have a low nitrogen content per mass and can increase photosynthetic capacity with increasing foliage robustness. This study argues that the within-species economics spectrum needs to be considered in regional- to biome-level analyses.

How do leaf anatomies and photosynthesis of three Rhododendron species relate to their natural environments?

BACKGROUND

Rhododendron is one of the most well-known alpine flowers. In order to identify performances relating to Rhododendron's natural habitats we investigated the leaf anatomical structures and photosynthetic characteristics of R. yunnanense, R. irroratum and R. delavayi, which showed different responses after being transplanted into a common environment.

RESULTS

When compared with R. irroratum and R. delavayi, R. yunnanense had lower leaf dry mass per unit area (LMA) and larger stomata, but smaller stomatal density (SD) and total stomata apparatus area percent (At), lower stomatal conductance (Gs), transpiration rate (Tr), light compensation point (LCP), light saturation point (LSP), light-saturated photosynthetic rate (Amax) and leaf nitrogen content per unit area (Na). LMA was positively correlated with Amax and maximum rates of carboxylation (Vcmax). However, leaf N content was not significantly correlated with Amax. Thus, the variation in leaf photosynthesis among species was regulated largely by changes in LMA, rather than the concent of nitrogen in leaf tissue.

CONCLUSIONS

R. yunnanense plants are vulnerable to moisture and light stress, while R. irroratum and R. delavayi are better suited to dry and high radiation environments. The present results contribute to our understanding physiological trait divergence in Rhododendron, as well benefit introduction and domestication efforts for the three species of Rhododendron studied in this work.

Exploring variation in leaf mass per area (LMA) from leaf to cell: an anatomical analysis of 26 woody species

PREMISE OF THE STUDY

Plant species differ widely in the leaf biomass invested per unit area (LMA). LMA can be explained by variation in leaf thickness and/or density, both of which are influenced by anatomical tissue composition. The aim of this study is to quantify the anatomical characteristics that underlie variation in LMA in a range of woody species. •

METHODS

Twenty-six woody species, forming 13 species pairs with a deciduous and evergreen species from the same genus or family, were grown in a glasshouse. The youngest full-grown leaves were analyzed for LMA and morpho-anatomical characteristics at leaf, tissue, and cell level. •

KEY RESULTS

Considered over all species studied, leaf thickness and density were equally important to explain the variation in LMA, but the class difference between deciduous and evergreen species was mainly determined by thickness, whereas variation within each group was largely due to density. Evergreens had thicker leaves, predominantly caused by a larger volume of mesophyll and air spaces, whereas the higher leaf density within each group was due to a lower proportion of epidermis and air spaces, and overall smaller cells. •

CONCLUSIONS

The anatomical basis for variation in LMA in woody species depends on the contrast made. Higher LMA in evergreens is mainly due to a greater leaf thickness, caused by a larger volume of mesophyll and air spaces. Within deciduous species and evergreens, higher LMA is caused by a higher density, due to higher volumetric fractions of mesophyll and lower fractions of air spaces and epidermis.

Leaf hydraulic conductance for a tank bromeliad: axial and radial pathways for moving and conserving water

Epiphytic plants in the Bromeliaceae known as tank bromeliads essentially lack stems and absorptive roots and instead take up water from reservoirs formed by their overlapping leaf bases. For such plants, leaf hydraulic conductance is plant hydraulic conductance. Their simple strap-shaped leaves and parallel venation make them suitable for modeling leaf hydraulic conductance based on vasculature and other anatomical and morphological traits. Plants of the tank bromeliad Guzmania lingulata were investigated in a lowland tropical forest in Costa Rica and a shaded glasshouse in Los Angeles, CA, USA. Stomatal conductance to water vapor and leaf anatomical variables related to hydraulic conductance were measured for both groups. Tracheid diameters and numbers of vascular bundles (veins) were used with the Hagen-Poiseuille equation to calculate axial hydraulic conductance. Measurements of leaf hydraulic conductance using the evaporative flux method were also made for glasshouse plants. Values for axial conductance and leaf hydraulic conductance were used in a model based on leaky cable theory to estimate the conductance of the radial pathway from the vein to the leaf surface and to assess the relative contributions of both axial and radial pathways. In keeping with low stomatal conductance, low stomatal density, low vein density, and narrow tracheid diameters, leaf hydraulic conductance for G. lingulata was quite low in comparison with most other angiosperms. Using the predicted axial conductance in the leaky cable model, the radial resistance across the leaf mesophyll was predicted to predominate; lower, more realistic values of axial conductance resulted in predicted radial resistances that were closer to axial resistance in their impact on total leaf resistance. Tracer dyes suggested that water uptake through the tank region of the leaf was not limiting. Both dye movement and the leaky cable model indicated that the leaf blade of G. lingulata was structurally and hydraulically well-suited to conserve water.

Patterns of leaf morphology and leaf N content in relation to winter temperatures in three evergreen tree species

The competitive equilibrium between deciduous and perennial species in a new scenario of climate change may depend closely on the productivity of leaves along the different seasons of the year and on the morphological and chemical adaptations required for leaf survival during the different seasons. The aim of the present work was to analyze such adaptations in the leaves of three evergreen species (Quercus ilex, Q. suber and Pinus pinaster) and their responses to between-site differences in the intensity of winter harshness. We explore the hypothesis that the harshness of winter would contribute to enhancing the leaf traits that allow them to persist under conditions of stress. The results revealed that as winter harshness increases a decrease in leaf size occurs in all three species, together with an increase in the content of nitrogen per unit leaf area and a greater leaf mass per unit area, which seems to be achieved only through increased thickness, with no associated changes in density. P. pinaster was the species with the most intense response to the harshening of winter conditions, undergoing a more marked thickening of its needles than the two Quercus species. Our findings thus suggest that lower winter temperatures involve an increase in the cost of leaf production of evergreen species, which must be taken into account in the estimation of the final cost and benefit balance of evergreens. Such cost increases would be more pronounced for those species that, like P. pinaster, show a stronger response to the winter cold.

Photosynthesis, water use efficiency and stable carbon isotope composition are associated with anatomical properties of leaf and xylem in six poplar species

Although fast-growing Populus species consume a large amount of water for biomass production, there are considerable variations in water use efficiency (WUE) across different poplar species. To compare differences in growth, WUE and anatomical properties of leaf and xylem and to examine the relationship between photosynthesis/WUE and anatomical properties of leaf and xylem, cuttings of six poplar species were grown in a botanical garden. The growth performance, photosynthesis, intrinsic WUE (WUE(i) ), stable carbon isotope composition (δ(13) C) and anatomical properties of leaf and xylem were analysed in these poplar plants. Significant differences were found in growth, photosynthesis, WUE(i) and anatomical properties among the examined species. Populus cathayana was the clone with the fastest growth and the lowest WUE(i) /δ(13) C, whereas P. × euramericana had a considerable growth increment and the highest WUE(i) /δ(13) C. Among the analysed poplar species, the highest total stomatal density in P. cathayana was correlated with its highest stomatal conductance (g(s) ) and lowest WUE(i) /δ(13) C. Moreover, significant correlations were observed between WUE(i) and abaxial stomatal density and stem vessel lumen area. These data suggest that photosynthesis, WUE(i) and δ(13) C are associated with leaf and xylem anatomy and there are tradeoffs between growth and WUE(i) . It is anticipated that some poplar species, e.g. P. × euramericana, are better candidates for water-limited regions and others, e.g. P. cathayana, may be better for water-abundant areas.

Near infrared spectroscopy for the analysis of macro and micro nutrients in sugarcane leaves

About ten years ago, NIR technology was implemented at the Colombian Sugarcane Research Center Cenicaña for the analysis of sugarcane quality, followed by the development of methodologies for the quantification of some elements in soils and sugarcane leaves. Methodologies were based on the presence of high content materials, such nitrogen, potassium, calcium, and magnesium; however, determination of micronutrients which are found in soils and leaves in the range of parts per million has been challenging. Development of a NIR methodology for quantification of macro (N, P, K, Ca, Mg) and micronutrients (Cu, Zn, Mn, Fe) in a single experiment is here reported. Calibration curves were constructed using approximately 500 samples that were previously analyzed by methods of reference such atomic absorption. Statistical analysis of the data showed that there are not significant differences between the methods of reference and NIR, suggesting that NIR is a very fast, economical and convenient methodology for the daily analysis of sugarcane leaves.

Ecophysiological significance of leaf traits in Cypripedium and Paphiopedilum

There is a close phylogenetic relationship between Paphiopedilum and Cypripedium, but these two genera diverge considerably in terms of their leaf traits. To understand the evolution and the ecophysiological significance of leaf traits, we investigated the leaf traits of three Paphiopedilum species and three Cypripedium species in southwestern China. Cypripedium tibeticum and C. flavum showed a significantly higher light-saturated photosynthetic rate (P(max) ), stomatal conductance (g(s) ), photosynthetic nitrogen utilization efficiency (PNUE) and specific leaf area (SLA), but lower ratio of leaf carbon to nitrogen content (C/N) and leaf construction cost (CC) than Paphiopedilum. These leaf traits of Cypripedium suggest its high resource use efficiency and high growth rate reflecting adaptation to a short growing period and abundant soil nutrients and water in alpine habitats. Conversely, the low P(max) , g(s) , PNUE, SLA and the ratio of chlorophyll a to chlorophyll b (Chl a/b), but high leaf nitrogen investment in light-harvesting component (P(L) ), CC and C/N in Paphiopedilum indicate its adaptation to a low light, nutrient-poor and limited soil water habitats in karst areas. As a sympatric species of Paphiopedilum, although C. lentiginosum retained the phylogenetic leaf traits of Cypripedium, such as high mass-based light-saturated photosynthetic rate (P(max-M) ), g(s) and PNUE, it had some similar leaf traits to those of Paphiopedilum, such as low mesophyll conductance (g(m) ) and Chl a/b, and high P(L) , which reflected an adaptation to the same habitat. Our results show that the evolution of the leaf traits of Paphiopedilum and Cypripedium are shaped by both phylogeny and environment.

Do photosynthetic limitations of evergreen Quercus ilex leaves change with long-term increased drought severity?

Seasonal drought can severely impact leaf photosynthetic capacity. This is particularly important for Mediterranean forests, where precipitation is expected to decrease as a consequence of climate change. Impacts of increased drought on the photosynthetic capacity of the evergreen Quercus ilex were studied for two years in a mature forest submitted to long-term throughfall exclusion. Gas exchange and chlorophyll fluorescence were measured on two successive leaf cohorts in a control and a dry plot. Exclusion significantly reduced leaf water potential in the dry treatment. In both treatments, light-saturated net assimilation rate (A(max)), stomatal conductance (g(s)), maximum carboxylation rate (V(cmax)), maximum rate of electron transport (J(max)), mesophyll conductance to CO2 (g(m)) and nitrogen investment in photosynthesis decreased markedly with soil water limitation during summer. The relationships between leaf photosynthetic parameters and leaf water potential remained identical in the two treatments. Leaf and canopy acclimation to progressive, long-term drought occurred through changes in leaf area index, leaf mass per area and leaf chemical composition, but not through modifications of physiological parameters.

Photosynthetic responses to chromosome doubling in relation to leaf anatomy in Lonicera japonica subjected to water stress

Gas exchange, chlorophyll fluorescence, and contents of some metabolites in two Japanese honeysuckle (Lonicera japonica Thunb.) cultivars, Damaohua (2n = 2x) and Jiufengyihao (2n = 4x), were compared with explore the function of chromosome doubling under water stress conditions. Water stress significantly decreased net photosynthesis rate, stomatal conductance, and transpiration rate of both cultivars. It also decreased electron transport rate, effective quantum yield of Photosystem II, photochemical quenching, and starch content, but increased non-photochemical quenching and contents of total soluble sugars, proline, and malondialdehyde. However, the tetraploid cultivar showed higher resistance to water stress than the diploid, as indicated by the fact that gas exchange, chlorophyll fluorescence, and metabolites were less affected for the tetraploid than the diploid. Moreover, the tetraploid recovered more quickly than the diploid after re-watering. Morphological and anatomical analysis further revealed that the tetraploid possessed less whole plant leaf area, higher leaf mass per unit area, thicker epidermis (both upper and lower) and palisade tissue, as well as denser pubescence. All of those specialised structures caused by chromosome doubling might lead to greater capacity in coping with drought stress. Our findings suggest that the effect of chromosome doubling on drought resistance in L. japonica could attribute to the improvement of structure and photosynthesis-related traits.

Specific leaf area and dry matter content estimate thickness in laminar leaves

BACKGROUND AND AIMS

Leaf thickness plays an important role in leaf and plant functioning, and relates to a species' strategy of resource acquisition and use. As such, it has been widely used for screening purposes in crop science and community ecology. However, since its measurement is not straightforward, a number of estimates have been proposed. Here, the validity of the (SLA x LDMC)(-1) product is tested to estimate leaf thickness, where SLA is the specific leaf area (leaf area/dry mass) and LDMC is the leaf dry matter content (leaf dry mass/fresh mass). SLA and LDMC are two leaf traits that are both more easily measurable and often reported in the literature.

METHODS

The relationship between leaf thickness (LT) and (SLA x LDMC)(-1) was tested in two analyses of covariance using 11 datasets (three original and eight published) for a total number of 1039 data points, corresponding to a wide range of growth forms growing in contrasted environments in four continents.

KEY RESULTS AND CONCLUSIONS

The overall slope and intercept of the relationship were not significantly different from one and zero, respectively, and the residual standard error was 0.11. Only two of the eight datasets displayed a significant difference in the intercepts, and the only significant difference among the most represented growth forms was for trees. LT can therefore be estimated by (SLA x LDMC)(-1), allowing leaf thickness to be derived from easily and widely measured leaf traits.

Leaf morphology, photochemistry and water status changes in resprouting Quercus ilex during drought

Functional and morphological (structural) characteristics of Quercus ilex L. leaves under drought stress were studied in the forest and in a nursery. We compared undisturbed individuals (controls) with resprouts emerging after clear-cut or excision. When soil water availability was high, gas-exchange was similar in resprouts and controls, despite higher midday leaf water potential, midday leaf hydration and relative water content (RWC). In moderate drought, stomatal closure was found to limit photosynthesis in controls, and in severe drought non-stomatal limitations of photosynthesis were also greater than in resprouts. Leaf structure and chemical composition changed under drought stress. Leaves tended to be smaller in controls with increasing drought, and resprouts had larger leaves and lower leaf mass area (LMA). The relationship between nitrogen (N) content and LMA implied lower N investment in photosynthetic components in controls, which could be responsible for their increased non-stomatal limitation of photosynthesis. Changes were more apparent in leaf density (D) and thickness (T), components of LMA. Decreases in D were related to reductions in cell wall components: hemicellulose, cellulose and lignin. In resprouts, reduced D and leaf T accounted for the higher mesophyll conductance (g_mes) to CO₂ measured.

Current issues and uncertainties in the measurement and modelling of air-vegetation exchange and within-plant processing of POPs

Air-vegetation exchange of POPs is an important process controlling the entry of POPs into terrestrial food chains, and may also have a significant effect on the global movement of these compounds. Many factors affect the air-vegetation transfer including: the physicochemical properties of the compounds of interest; environmental factors such as temperature, wind speed, humidity and light conditions; and plant characteristics such as functional type, leaf surface area, cuticular structure, and leaf longevity. The purpose of this review is to quantify the effects these differences might have on air/plant exchange of POPs, and to point out the major gaps in the knowledge of this subject that require further research. Uptake mechanisms are complicated, with the role of each factor in controlling partitioning, fate and behaviour process still not fully understood. Consequently, current models of air-vegetation exchange do not incorporate variability in these factors, with the exception of temperature. These models instead rely on using average values for a number of environmental factors (e.g. plant lipid content, surface area), ignoring the large variations in these values. The available models suggest that boundary layer conductance is of key importance in the uptake of POPs, although large uncertainties in the cuticular pathway prevents confirmation of this with any degree of certainty, and experimental data seems to show plant-side resistance to be important. Models are usually based on the assumption that POP uptake occurs through the lipophilic cuticle which covers aerial surfaces of plants. However, some authors have recently attached greater importance to the stomatal route of entry into the leaf for gas phase compounds. There is a need for greater mechanistic understanding of air-plant exchange and the 'scaling' of factors affecting it. The review also suggests a number of key variables that researchers should measure in their experiments to allow comparisons to be made between studies in order to improve our understanding of what causes any differences in measured data between sites.