Temperature heterogeneity over leaf surfaces: the contribution of the lamina microtopography

Temperature is spatially heterogeneous over leaf surfaces, yet the underlying mechanisms are not fully resolved. We hypothesized that the 3D leaf microtopography determines locally the amount of incoming irradiation flux at leaf surface, thereby driving the temperature gradient over the leaf surface. This hypothesis was tested by developing a model of leaf temperature heterogeneity that includes the development of the leaf boundary layer, the microtopography of the leaf surface and the physiological response of the leaf. Temperature distributions under various irradiation loads (1) over apple leaves based on their 3D microtopography, (2) over simulated flat (2D) apple leaves and (3) over 3D leaves with a transpiration rate distributed as in 2D leaves were simulated. Accuracy of the predictions was quantified by comparing model outputs and thermographic measurements of leaf surface temperature under controlled conditions. Only the model with 3D leaves predicted accurately the spatial heterogeneity of surface temperature over single leaves, whereas the mean temperature was well predicted by both 2D and 3D leaves. We suggest that in these conditions, the 3D leaf microtopography is the primary driver of leaf surface heterogeneity in temperature when the leaf is exposed to a light/heat source.     

The anatomical and compositional basis of leaf mass per area

Leaf dry mass per unit leaf area (LMA) is a central trait in ecology, but its anatomical and compositional basis has been unclear. An explicit mathematical and physical framework for quantifying the cell and tissue determinants of LMA will enable tests of their influence on species, communities and ecosystems. We present an approach to explaining LMA from the numbers, dimensions and mass densities of leaf cells and tissues, which provided unprecedented explanatory power for 11 broadleaved woody angiosperm species diverse in LMA (33–262 g m^?2; R² = 0.94; P < 0.001). Across these diverse species, and in a larger comparison of evergreen vs. deciduous angiosperms, high LMA resulted principally from larger cell sizes, greater major vein allocation, greater numbers of mesophyll cell layers and higher cell mass densities. This explicit approach enables relating leaf anatomy and composition to a wide range of processes in physiological, evolutionary, community and macroecology.     

The scaling of leaf area and mass: the cost of light interception increases with leaf size

For leaves, the light-capturing surface area per unit dry mass investment (specific leaf area, SLA) is a key trait from physiological, ecological and biophysical perspectives. To address whether SLA declines with leaf size, as hypothesized due to increasing costs of support in larger leaves, we compiled data on intraspecific variation in leaf dry mass (LM) and leaf surface area (LA) for 6334 leaves of 157 species. We used the power function LM=alpha LAbeta to test whether, within each species, large leaves deploy less surface area per unit dry mass than small leaves. Comparing scaling exponents (beta) showed that more species had a statistically significant decrease in SLA as leaf size increased (61) than the opposite (7) and the average beta was significantly greater than 1 (betamean=1.10, 95% CI 1.08-1.13). However, scaling exponents varied markedly from the few species that decreased to the many that increased SLA disproportionately fast as leaf size increased. This variation was unrelated to growth form, ecosystem of origin or climate. The average within-species tendency found here (allometric decrease of SLA with leaf size, averaging 13%) is in accord with concurrent findings on global-scale trends among species, although the substantial scatter around the central tendency suggests that the leaf size dependency does not obligately shape SLA. Nonetheless, the generally greater mass per unit leaf area of larger than smaller leaves directly translates into a greater cost to build and maintain a unit of leaf area, which, all else being equal, should constrain the maximum leaf size displayed.     

植物比叶质量研究进展

比叶质量(LMA)是叶片经济型谱中最基础的叶功能性状, 也是重要的复合型结构参数。LMA不仅与植物的许多生理反应密切相关, 而且能定量测定光合产物在单位叶面积的投入, 因而被认为是反映植物生态策略的重要指标。目前, 有关LMA的深入研究已在植物生态学、农学、林学、植物生理学领域全面展开。该文系统阐述了LMA在叶片整体、组织、细胞三个水平的结构解析和计算方法; 重点分析了LMA对光合作用的影响; 讨论了LMA的内在遗传差异以及外部的环境胁迫因子(温度、水分、光照)对LMA的影响, 以期梳理比叶质量研究的思路、策略和方法, 为今后的研究提供借鉴和参考。     

Leaf age and season influence the relationships between leaf nitrogen, leaf mass per area and photosynthesis in maple and oak trees

Abstract. Seasonal changes in photosynthesis, leaf nitrogen (N) contents and leaf mass per area (LMA) were observed over three growing seasons in open-grown sun-lit leaves of red maple ( Acer rubrum ), sugar maple ( A. sacchamm ) and northern pin oak ( Quereus ellipsoidalis ) trees in southern Wisconsin. Net photosynthesis and leaf N were highly linearly correlated on both mass and area bases within all species from late spring until leaf senescence in fall. Very early in the growing season leaves had high N concentrations, but low photosynthetic rates per unit leaf N, suggesting that leaves were not fully functionally developed at that time. Leaf N per unit area and LMA had nonparallel seasonal patterns, resulting in differing relationships between leaf N/area and LMA in the "early versus late growing season. As a result of differences in seasonal patterns between leaf N/area and LMA, net photosynthesis/area was higher for a given LMA in the spring than fall, and the overall relationships between these two parameters were poor.     

Relationships between sclerophylly,leaf biomechanical properties and leaf anatomy in some Australian heath and forest species

ABSTRACT

A previous study of 19 south-east Australian heath and forest species with a range of leaf textures showed that they varied considerably in leaf biomechanical properties. By using an index of sclerophylly derived from botanists' rankings (botanists' sclerophylly index, BSI) we determined that leaves considered by botanists to be sclerophyllous generally had both high strength and work to fracture (particularly in punching and tearing tests), both at the level of leaf and per unit leaf thickness. In the current study we have shown that leaves from the same species also varied considerably in leaf specific mass (46–251 g m^-2), neutral detergent fibre concentration (20–59% on a dry weight basis) and in leaf anatomy. Multiple regression indicated a very strong correlation between BSI and the first two components of a principal components analysis (PCA) of leaf anatomy (R ² = 0.91). In addition, there was strong correlation between the first component of a PCA of the mechanical properties (correlated with BSI) and the two axes derived from anatomical characteristics (R ² = 0.66). The anatomical properties contributing most to the significant component axes were thickness of palisade mesophyll and upper cuticle (axis 1) and percentage fibre (neutral detergent fibre) and lower epidermis thickness (axis 2). However, whether these relationships are causal, or reflect correlations with characteristics not measured in this study, such as vascularization and sclerification, is not clear. At a finer scale, however, there is evidence that there are various ways to be sclerophyllous, both in terms of anatomical and mechanical properties. This is illustrated by comparison of two of the sclerophyllous species, Eucalyptus baxteri and Banksia marginata.     

Altitudinal variation in leaf mass per unit area,leaf tissue density and foliar nitrogen and phosphorus content along an Amazon-Andes gradient in Peru

Background: Leaf traits are important in determining the capacity for a plant to acquire carbon, but few data are available for montane cloud forests in the Andes.

Aims: To investigate the changes in leaf traits along a large altitudinal transect (220–3600 m) from lowland to montane cloud forest in Peru.

Methods: We determined leaf mass per area (LMA, g m^?2), leaf tissue density (L _d, g cm^?3), and foliar nitrogen (N) and phosphorus (P) content, both on a mass (N _m and P _m, %) and area (N _a and P _a, g m^?2) basis for the most abundant species locally.

Results: LMA increased with altitude (62.8–169.4 g m^?2), though overall, LMA was lower than in comparable tropical elevation gradients. N _m declined significantly with altitude (2.39–1.25 %, P < 0.05), but N _m contents were higher than in comparable studies. The relatively high N _m and low LMA values are consistent with published global leaf trait datasets. No altitudinal trend for P _m was found; rather, our data highlighted the spatial variability in P _m (and P _a) within and among sites at different elevations. Foliar N:P ratios did not show a trend with altitude and did not indicate N limitation except at 3000 m altitude.

Conclusions: Though leaf traits showed altitudinal trends similar to other studies, contrary to the general hypothesis, our data suggest that the tropical montane forests presented here are not N limited.     

Research progress on leaf mass per area

Leaf mass per area (LMA) is a composite structural parameter as well as a basic leaf functional trait in the leaf economics spectrum (LES). It is not only closely related to many physiological responses of plants, but also can measure the investment of dry mass per unit of light-intercepting leaf area. LMA is considered an important indicator of plant ecological strategies and has been studied widely in plant ecology, agronomy, forestry, and plant physiology. This paper elucidates the structural analysis and computational methods of LMA at the organizational scales of whole leaf, tissues and cells, examines the influence of LMA on photosynthesis, and discusses the inherent differences in LMA and the responses of LMA to environmental stresses (temperature, water and light), aiming for clarifying research frameworks and methods in studies of LMA and providing guidance on future research.     

Co-ordinated development of the leaf midrib xylem with the lamina in Nicotiana tabacum

Background and Aims

The water-transport capacity of leaf venation is positively related to the leaf-lamina area, because the number and diameter of vein-xylem conduits are controlled to match the lamina area. This study aimed to investigate how this co-ordinated relationship between the leaf-lamina area and vein-xylem characteristics is achieved by examining the midrib xylem of tobacco leaves.

Methods

The changes in the midrib-xylem characteristics over time were quantified using leaves with four different final lamina areas. The measured data were fitted to sigmoidal functions. From the constants of the fitted curves, the final values in mature leaves, maximal developmental rates (V_Dev) and developmental duration (T_Dev) were estimated for each of the xylem characteristics. Whether it is the lamina or the midrib xylem that drives the co-ordinated development was examined by lamina removal from unfolding leaves. The effects of the application of 0·1 % IAA (indole-3-acetic acid) to leaves with the laminas removed were also analysed.

Key Results

For both the leaf lamina and the midrib-xylem characteristics, the differences in final values among leaves with different lamina areas were more strongly associated with those in V_Dev. Notably, the V_Dev values of the midrib-xylem characteristics were related to those of the leaf-lamina area. By lamina removal, the conduit diameter was reduced but the number of conduits did not significantly change. By IAA application, the decrease in the conduit diameter was halted, and the number of conduits in the midrib xylem increased.

Conclusions

According to the results, the V_Dev values of the lamina area and the midrib-xylem characteristics changed in a co-ordinated manner, so that the water-transport capacity of the midrib xylem was positively related to the leaf-lamina area. The results also suggest that IAA derived from the leaf lamina plays a crucial role in the development of the leaf venation.     

Global meta-analysis shows that relationships of leaf mass per area with species shade tolerance depend on leaf habit and ontogeny

It was predicted that relationships of leaf mass per area (LMA) with juvenile shade tolerance will depend on leaf habit, and on whether species are compared at a common age as young seedlings, or at a common size as saplings. A meta-analysis of 47 comparative studies (372 species) was used to test predictions, and the effect of light environment on this relationship. The LMA of evergreens was positively correlated with shade tolerance, irrespective of ontogeny or light environment. The LMA of young seedlings (相似文献   

Wheat leaf photosynthesis loss due to leaf rust, with respect to lesion development and leaf nitrogen status

In wheat (Triticum aestivum cv. Soissons) plants grown under three different fertilisation treatments, we quantified the effect of leaf rust (Puccinia triticina) on flag leaf photosynthesis during the whole sporulation period. Bastiaans' model: Y = (1 - x)beta was used to characterize the relationship between relative leaf photosynthesis (Y) and disease severity (x). The evolution of the different types of symptoms induced by the pathogen (sporulating, chlorotic and necrosed tissues) was evaluated using image analysis. The beta-values varied from 2 to 11, 1.4-2, and 0.8-1 during the sporulation period, when considering the proportion of sporulating, sporulating + necrotic, and total diseased area, respectively. Leaf nitrogen (N) content did not change the effect of the disease on host photosynthesis. We concluded that leaf rust has no global effect on the photosynthesis of the symptomless parts of the leaves and that the large range in the quantification of leaf rust effect on the host, which is found in the literature, can be accounted for by considering the different symptom types. We discuss how our results could improve disease assessments and damage prediction in a wheat crop.     

Leaf structure and specific leaf mass: the alpine desert plants of the Eastern Pamirs, Tadjikistan

This study examines interrelationships between eight leaf attributes (specific leaf mass, area, dry mass, lamina thickness, mesophyll cell number per cm², mesophyll cell volume, chloroplast volume, and number of chloroplasts per mesophyll cell) in field-grown plants of 94 species from the Eastern Pamir Mountains, at elevations between 3800 and 4750 m. Unlike most other mountain areas, the Eastern Pamirs, Karakorum system, Tadjikistan provide localities where low temperatures and radiation combine with moisture stress at high altitudes. For all the attributes measured, significant differences were found between plants with different mesophyll types. Leaves with dorsiventral palisade structure (dorsal palisade, ventral spongy mesophyll cells) had thicker leaves with larger but fewer mesophyll cells, containing more and larger chloroplasts. These differences in mesophyll type are reflected in differences in the total surface of mesophyll cells per unit leaf area ( A _mes/ A ) or volume ( A _mes/ V ). Plants with isopalisade leaf structure (palisade cells under both dorsal and ventral surfaces) are more commonly xerophytes and their increased values of A _mes/ A and A _mes/ V decrease CO₂ mesophyll resistance, which is an important adaptation to drought. Path analysis shows the critical importance of mesophyll cell volume in leading to the covariance between the different leaf attributes and hence to specific leaf mass (SLM), even though mesophyll cell volume is not itself strongly correlated with SLM. This is because mesophyll cell volume increases SLM through its effects on leaf thickness and chloroplast number per cell, but decreases SLM through its negative effect on mesophyll cell density.     

Effects of leaf shape plasticity on leaf surface temperature

干旱区植物叶片形态可塑性是植物适应高温干旱环境的重要生存策略, 但目前仍缺乏直观的数据予以证明。该研究应用热成像技术和图像分析技术, 同步测定真实叶片与模拟叶片的叶温、形态及风速、辐射和温度等环境参数。研究结果显示: 在干旱、高温环境下, 除了蒸腾, 叶片形态变化也是调控叶温的重要因子。干旱区植物叶片变小, 有利于加速叶片与环境的物质及热量交换, 从而达到降低叶温的目的。样地数据显示, 在高温、低风速环境下, 叶片宽度每减少1 cm, 叶片表面温度降低约2.1 ℃, 而模拟叶片叶宽度每减少1 cm, 叶片表面温度降低0.60-0.86 ℃。该研究对深入理解植物生存策略与环境适能力具有重要意义。