L. A. Ivanova

Shading-induced changes in the leaf mesophyll of plants of different functional types

Changes in the structural characteristics of mesophyll induced by shading were investigated in ten species of wild plants of diverse functional types. In all plant types, shading reduced leaf thickness and density by 30–50% and total surface of mesophyll, by 30–70%. The extent and mechanisms of mesophyll structural rearrangement depended on the plant functional type. In the ruderal plants, integral parameters of mesophyll, such as the surface of cells and chloroplasts and mesophyll resistance, changed threefold predominantly because of changes in the dimensions of the cells and chloroplasts. In these plants, shading reduced the volume of chloroplasts by 30%, and the chloroplast numbers per cell declined. The competitor plants showed a twofold increase in mesophyll resistance due to a decrease in the number of photosynthesizing cells per leaf area unit. Moreover, these plants maintained constant dimensions of mesophyll cells, ratios mesophyll surface/mesophyll volume and chloroplast surface/cell surface. In stress-tolerant plants, diffusion resistance of mesophyll remained the same irrespective of the growing conditions, and mesophyll rearrangement was associated with inversely proportional changes in the dimensions of the cells and cell volume per chloroplast. Noteworthy of these plants were relatively constant chloroplasts number per cell, per leaf area unit and total surface area of chloroplasts. The nature of relationship between the mesophyll diffusion resistance and structural parameters of leaf mesophyll differed in plants of diverse functional types.

Changes in Leaf Characteristics as Indicator of the Alteration of Functional Types of Steppe Plants along the Aridity Gradient

Changes in some leaf characteristics: leaf mass area (LMA), content of photosynthetic pigments and nitrogen in the leaves, leaf mass ratio (LMR) and leaf area ratio (LAR) were investigated in steppe plants of the Volga land along the gradient of aridity. When drought stress became stronger, the content of chlorophylls in the leaves, LMR and LAR decreased, whereas LMA and the proportion of carotenoids in the leaves rose. In the North to South direction, the content of pigments and nitrogen per unit whole plant weight considerably decreased (4 and 2 times, respectively). The relationship between leaf indices (chlorophyll and nitrogen contents and LMA) differed along this gradient. It was concluded that adaptation of steppe plants to drought stress generally depended on predominant development of heterotrophic tissues in the leaf and the whole plant. During aridization, the stress-tolerant species became more numerous.

Adaptive features of leaf structure in plants of different ecological groups

It is well known that the structure of leaves plays an important role in adaptation, but there are still no accurate structural criteria to indicate ecological characteristics of the species. We have studied parameters of leaves in 100 herbaceous plant species growing in the southern taiga subzone that belong to different ecological groups in relation to irradiance and moisture supply. The results show that leaf area, thickness, and anatomical type are less correlated with ecological characteristics of the species than structural parameters of photosynthetic tissues. In the series shade-loving mesophytes—light-loving hygromesophytes—mesophytes—xeromesophytes—mesoxerophytes, the concentration of cells and chloroplasts in the leaf gradually increases by a factor of up to 7–10, their size decreases two-to threefold, and the ratio of mesophyll surface area to leaf surface area increases fourto fivefold. It is concluded that characteristics of mesophyll are of adaptive significance. A system of characters is proposed for identification of ecological groups of plants growing in the boreal zone.

Changes in the specific density of leaves of Eurasian plants along the aridity gradient

The specific surficial density of a leaf (SSDL or dryweight of the leaf area unit) is a fundamental characteristic of a plant [1, 2] and is used in global models ofthe Earth’s vegetation [3]. The SSDL is related tomany aspects of plant growth and development [4] andcorrelates with such paramete rs as the level of net photosynthesis [5], content of nitrogen in leaves [6], thelifetime of leaves, and the relative growth rate [4].Generally, the SSDL is an integral parameter of a leafbecause it reflects the adaptation of the photosyntheticapparatus of plants to the complex of environmentalconditions. It is known that plants from differentbiomes differ in the density of the leaf blade [2].The SSDL of plants along global climatic gradients[6–9] are intensively investigate due to the necessity offorecasting the state of vegetation during climatechange. Earlier, it was shown that the SSDL of plantscorrelates with the average annual temperature,potential evapotranspiration, and the solar radiationlevel [6]. The plants of arid regions of Eurasia are stillinadequately known in this respect.In the present study, 495 species of steppe anddesert territories of Russia and Mongolia are investigated. It is shown that in arid regions of Eurasia, thechange in the SSDL of plants is nonlinear under conditions of linear change in the aridity index of the territory.Investigations were conducted during 1995–2007in Russia and Mongolia within 43.25° and 56.5° N(Table 1). Plants with typical flat leaves were studied,mainly belonging to dominants and edificatory plantsof the plant cover. Succulents and plants with aphylllous shoots were not studied. The SSDL (mg/dm

Changes in the chlorophyll and carotenoid contents in the leaves of steppe plants along a latitudinal gradient in South Ural

We studied the content of chlorophylls and carotenoids in the leaves of steppe plants of South Ural growing along a latitudinal gradient from southern steppe to forest-steppe. The content of chlorophylls (a + b) was 5–6 mg per 1 g of the leaf dry weight and did not depend on the latitude, whereas the content of carotenoids in the leaves increased northward from 1.0 to 1.5 mg/g dry wt. At the same time, the greatest changes occurred in the ratios between the forms of pigments: the chlorophyll a/b ratio increased from 1.8 to 2.8, and the chlorophyll/carotenoid ratio decreased from 5.6 to 3.5. The obtained results indicate that adaptation of the pigment apparatus of steppe plants growing along the latitudinal gradient occurs due to the transformation of the light-harvesting complex.

Size of the leaf as a marker of birch productivity at a distance from the climatic optimum

Morphometric parameters of mature leaves (area, venation density, and shape coefficient) and trunks (size and biomass) of two edificatory birch species, Betula pendula Roth and B. pubescens Ehrh., were characterized. These species inhabit a 1600-km transect of the Urals, from forest-tundra to forest-steppe. In both species, the highest trunk biomass was observed in the subzone of south taiga. Trunk parameters and leaf sizes of B. pendula varied in a narrower range than in B. pubescens. As distinct from leaf shape, leaf size was correlated with the average multiyear climate characteristics but not with the weather during a given growth season. In B. pubescens, which range extends wide from its climatic optimum, leaf area was positively correlated with trunk biomass. In B. pendula, growing mainly within the area of its climatic optimum, such correlation was not observed. We concluded that such parameter as mature leaf size could be used for prediction of tree productivity growing outside of the zone of their climatic optimum.

Restructuring of the leaf mesophyll in a series of plant life forms

386 The diversity of plant life forms has resulted from the plant adaptation to the environment in the course of their evolutionary development [1]. Aridization of the climate caused the transition from woody to her baceous plants, which are different not only in their morphology, but also in some physiological features related to the transport system type, growth rate, life span, shoot lignification degree, etc. [2]. Recent stud ies showed that the alteration of life forms is also con nected with changes in the genome size, which is larger in the case of herbaceous plants [3, 4]. The tran sition from woody to herbaceous plants was accompa nied by an increase in the relative mass of photosyn thetic organs and structural changes of leaves. For example, it is known that the leaves of woody plants are usually more heavy and dense than those of herba ceous plants [4–6]. A clear difference between trees and herbs concerning the epidermis characteristics [3, 4] and the structure of the transport system in leaves [2] evidences a significant reorganization of the photosynthetic apparatus in the series of plant life forms. However, the structure of the mesophyll, repre senting the main leaf tissue, still remains unstudied because of some methodical problems connected with its internal location and a complex shape of its cells.

Changes of leaf morphology in Betula pendula roth and B. pubescens Ehrh. along a zonal-climatic transect in the Urals and Western Siberia

Leaf size, shape, and parameters of venation in Betula pendula and B. pubescens have been studied along a 1600-km latitudinal zonal transect in the Urals and Western Siberia. The results show that leaf size and venation density depend on the geographic location of population, with these parameters in the two species changing in opposite directions along the transect. In its northern part (forest tundra-southern taiga), B. pubescens shows a positive correlation of leaf area with long-term-average air temperature, while this correlation in B. pendula is negative. In the southern part, correlations of leaf size with long-term average precipitation in the two species are also opposite in sign. Parameters of leaf shape in both species depend mainly on weather conditions in the current year rather than on long-term average climatic parameters. The conclusion is drawn that B. pendula and B. pubescens have different mechanisms of structural adaptation of leaves to climate and weather conditions that are based on changes in leaf size and shape.

Leaf acclimation to experimental climate warming in meadow plants of different functional types

The use of open-top chambers (OTCs) installed in natural plant cover is one of the approaches to study plant responses to climate change. Three OTCs made from polyethylene film were installed on a herbgrass meadow in the subzone of the southern taiga before the beginning of the growing season. A significant increase in the average daily temperature values (by 0.5°C) and the relative humidity (by 10%) compared to control conditions was observed inside the chambers. Plant height, leaf parameters, and the pigments content were studied for six species of meadow plants during the growing season in two variants—inside the chamber and outside the chamber (control); more than 20 quantitative parameters of the mesophyll were studied for four of the species. It was found that the differences in microclimatic conditions had no effect on plant height and leaf area. A slight decrease in the thickness and density of the leaves and an increased water content were noted inside the OTCs. In contrast to weak changes in external leaf parameters, the internal leaf structure and the content of photosynthetic pigments varied considerably. Warming caused the reduction of the content of chlorophyll and carotenoids per unit leaf area in the majority of studied species, except for Veronica chamaedrys L., but the ratio of pigment forms did not change. Changes in the pigments content in the leaf were associated with some structural rearrangements in the mesophyll, whose mechanism depended on the functional properties of the species. Increased size of palisade cells and the number of chloroplasts per cell was noted in the ruderal species (R/CSR-strategist) Taraxacum officinale Wigg. s. l.; the reduction of chlorophyll content per leaf area occurred due to the decrease in chlorophyll content per a single chloroplast. Decreased number of cells and chloroplasts per leaf unit area without any changes in their size was marked for the species with S/CSR strategy Alchemilla vulgaris L. s. 1. and V. chamaedrys L. in a chamber, but the content of chlorophyll per a chloroplast increased. An increase in the number of cells and a simultaneous decrease in their size was observed in CR-strategist Cirsium setosum (Willd.) Bess. inside the OTC; the chlorophyll content per chloroplast did not change. It was concluded that the acclimation of plants to short-term climate warming was associated with the restructuring of leaf mesophyll, whose mechanism depended on the functional properties of the species.

Mesostructure of the ginseng photosynthetic apparatus in relation to ecological strategy of the species

Mesostructure of the photosynthetic apparatus was investigated in the wild plants of ginseng (Panax ginseng C.A. Mey, Araliaceae) taken from various habitats. The revealed features of the structure of phototrophic tissues (large cells, small number of photosynthesizing cells and chloroplasts per leaf area unit, low values of membrane indices of the cells and chloroplasts) point to stress-tolerant type of ecological strategy ginseng pursues in Nature.