P. Yu. Voronin

Structural and Functional Changes in the Leaves of Plants from Steppe Communities as Affected by Aridization of the Eurasian Climate

Morphological and physiological characteristics of leaves from plant species collected in steppe communities in the various climatic zones in Eurasia were compared. The changes in leaf structure correlated with the major climatic factors. The mean thickness of leaves increased with increasing mean temperature of July and decreasing mean precipitation, which corresponded to aridity increase. The increased leaf thickness correlated with an increase in the specific leaf weight. The content of chlorophylls (a + b) in leaves greatly varied with plant habitats, whereas the chlorophyll a/b ratio remained unchanged. The chlorophyll content in leaf tissues had a general tendency to decrease with increasing leaf thickness. The leaf chlorophyll content positively correlated (R2 = 0.77) with the proportion of chlorenchyma in leaf tissues. It is concluded that steppe plants adapt to climate aridization at the structural level by increasing the proportion of protective heterotrophic components of the leaf without changing the functional activity of photosynthetic tissues.

Respiratory CO2 Fluxes in Photosynthesizing Leaves of C3 Species Varying in Rates of Starch Synthesis1

The rates of CO2 fixation and respiratory CO2 fluxes in six C3 species, namely Solanum tuberosum, Nicotiana tabacum, Arabidopsis thaliana, Hordeum vulgare, Triticum aestivum, and Secale cereale, were determined under steady-state photosynthesis. The plants may be divided into two groups: (a) cereals with a low rate of starch synthesis (7–5% of true photosynthesis); (b) plants with a high rate of starch synthesis (45–35% of true photosynthesis). In the light, primary and stored photosynthates are consumed as substrates for both respiratory and photorespiratory pathways. In leaves of cereals, the total rate of respiratory and photorespiratory decarboxylations of stored photosynthates was higher in the light than in the dark, while, in starch-synthesizing species, stored photosynthates were consumed at a higher rate in the dark. Under normal environmental conditions, respiratory decarboxylation of stored photosynthates was suppressed by light in all species studied. The total rate of respiration as the sum of decarboxylation of stored and primary photosynthates was not affected by light in cereals, but suppressed in starch-accumulating plants. This suppression was not compensated for by the additional supply of respiratory substrates from primary photosynthates in the light.

Methane emission from living tree wood

The time courses of CO2, CH4, and H2 accumulation and O2 absorption at the exposure of trunk wood samples taken from living trees of birch (Betula pendula Roth.), bird cherry tree (Padus avium Mill.), and pine (Pinus sylvestris L.) in the closed volume were studied. The activity of these processes at different temperatures (from 5 to 55°C) was also examined. The main components of gas exchange in all three tree species were O2 absorption and CO2 evolution. The fluxes of these gases were equal. In experiments with dehydration-hydration of wood samples, the intrawood origin of “woody” methane was established. Emission of CH4 and H2 from the wood depended on temperature. The temperature dependence of CH4 emission was similar to the temperature dependence of wood respiration. The high correlation between CO2, CH4, and H2 release and O2 absorption was noted. The relationships between these gas-exchange parameters were not species-specific. Temperature maxima of CH4 emission and the respiratory activity coincided. This implies that the highest methane emission should be expected in the period of the growth season most favorable for tree physiology. For the wood from all tree species, the ratio between released CH4 and CO2 volumes was close to 1: 160. This means that the annual methane emission from living tree is about 2 Mt C, attaining 4% of total methane emission from the territory of North Eurasia. However, taking into account a temperature dependence of methane exchange between the vegetation cover and atmosphere, we can expect that, at global climate warming, methane emission volume might be substantial.

Development of storage roots in radish (Raphanus sativus) plants as affected by light quality

Summary The development of storage roots was studied in radish plants grown under blue or red light. Unlike blue light-grown plants, no tuber development was found in red light-grown plants. Instead of the storage root formation, a larger development of petioles was observed in red light-grown plants. Reduced leaf matter was found in red light-grown plants compared with blue light-grown ones. At the growth chamber photon flux density (170 µmol m −2 s −1 ), similar rates of photosynthetic CO 2 fixation were found under red and blue light. Higher leaf starch accumulation was observed in red light-grown radish plants, whereas the level of soluble carbohydrates was lower than in blue light-grown plants. The absolute contents of several Calvin cycle metabolites were higher in blue light-grown plants, but the diurnal changes in their levels were similar in leaves of both variants examined. The portion of photosynthetically fixed carbon accumulated in roots was quantified as 0.50 and 0.31 for blue light-grown and red light-grown plants, respectively. The levels of two phytohormones, indole-3-acetate and zeatin plus zeatin riboside were found to be several-fold higher in roots of blue light-grown plants compared with red light-grown ones. Thus, the above hormones obviously create a higher sink demand from roots to leaves in blue light-grown plants, which facilitate the development of under-ground storage tissues. Petioles, not roots, were assumed to act as a main sink organ in red light-grown radish plants. A less strong sink demand probably also accounts for reduced assimilatory leaf matter in red light-grown plants.

Mycogenic decomposition of wood and carbon emission in forest ecosystems

Problems related to biological decomposition of wood and volumes of mycogenic emission of carbon dioxide and carbon in forests of Western Siberia are considered. Annual C-CO2 emission in the region reaches 31 million tons of carbon, which is equivalent to 116 million tons of carbon dioxide. With respect to the volume of emission, natural zones may be arranged in the following descending series: southern taiga (38%), middle taiga (29%), subtaiga (16%), forest-steppe (10%), northern taiga (6%), and forest-tundra (1%).

Membrane receptors of cytokinin and their regulatory role in Arabidopsis thaliana plant response to photooxidative stress under conditions of water deficit

Mild photooxidative stress combined with water deficit affected the expression of genes of cytokinin (CK) signal transduction. According to qRT-PCR data, these stress factors suppressed the expression of CK receptor genes AHK2 and AHK3 and the ARR5 response regulator gene, and slightly activated the expression of AHK4 gene. The absence of AHK2 and AHK3 receptors in Arabidopsis thaliana (L.) Heynh. mutants affected markedly the content of low-molecular-weight antioxidants (anthocyanins, carotenoids, proline) and resulted in the CK-dependent changes in the expression of genes, markers of oxidative stress, including RAB18, CHS, P5CS1, and PRODH1, under both normal and stressful conditions. At the same time, knockout of a single receptor gene or their combination did not induce CK-specific changes in the stress-activated expression of AOX1a, the marker gene of oxidative stress. CK receptor mutants lacked a statistically significant genotype influence on the photosystem II and photosystem I fluorescence yield under normal and stressful conditions. However, the system of CK perception was shown to be involved in the transcription regulation of the genes of the photosynthetic apparatus, ELIP2 and PSBS. Thus, CKs play an important role in plant responses to the photooxidative stress. The inactivation of the CK signaling system components proves to be one of the main strategies of Arabidopsis plant adaptation to the high light under conditions of water deficit.

Experimental installation for measurements of chlorophyll fluorescence, CO 2 exchange, and transpiration of a detached leaf

An original experimental installation is described to illustrate the unit-based principle in the open-mode design construction of a modern system for the combined fluorometric and CO2/H2O gas exchange measurements in the studies of the light and dark reactions of photosynthesis and the transpiration of a detached leaf.

A new source of methane in boreal forests

Methane was found among the gases evolved during natural wood decay caused by bracket fungi in boreal forests. Methane was detected both in decaying wood and fungal fruiting bodies. A scheme of symbiotic association of wood-degrading fungi and anaerobic microorganisms providing the methanogenesis in the wood was proposed. The scale of mycogenic methane emission has to be consistent with the huge volume of decaying wood in boreal forest ecosystems.

Methanogenic activity of woody debris

The paper is devoted to the phenomenon of methanogenic activity of woody debris, i.e., methane production in the course of wood decomposition by fungi, which are not directly involved in methane synthesis but form an initial link in the trophic chain leading to methanogenic archaea. Expert evaluation of probable amounts of methane emission is made. The results show that woody debris is an important global source of this greenhouse gas.

Methane emission during wood fungal decomposition

159 It was traditionally believed that methane is generated only under anaerobic conditions, and, therefore, recent discovery [1] that green plants emit methane was a real scientific sensation [2–3]. Hence, the concepts of this problem should be reevaluated, and novel natural sources of methane should be found. One of such sources can be processes of biological decomposition of wood, because development of wood-decomposing organisms inside such a substrate occurs under the conditions of physiological hypoxia and anoxia [4]. Under natural conditions, decomposition of dead wood is mainly performed by basidial fungi, which are the only known group of microorganisms capable of biological conversion of all wood compounds. These fungi, as shown in [5], are accompanied by bacteria, which may include methane-generating species. In this work, we showed that wood decomposition by a group of basidial fungi, namely, polypore, is accompanied by generation and emission of methane. Three types of polypore studied were the following: Fomes fomentarius (L. : Fr.) Fr. (hoof fungus), Fomitopsis pinicola (Sw. : Fr.) P. Karst (red banded polypore), and Piptoporus betulinus (Bull. : Fr.) P. Karst (birch polypore). They are widespread ecological dominants, which are responsible for wood decomposition in Western Siberia and the Urals [6]. They are lignindecomposing (hoof fungus) and cellulose-decomposing (birch and red banded polypore) fungi. We used fragments of trunks of white birch ( Betula pendula Roth.) and Scotch pine ( Pinus sylvestris L.) with a length of 20 cm and a diameter of 5–9 cm with basidioma of the fungi studied. The trunks were sampled in April 2, 2006 in the preforrest–steppe pine– birch forests of Sverdlovskaya oblast (region). The samples were placed in hermetic polyethylene 5 l chambers with tubes for taking gas samples. CO 2 , O 2 , and CH 4 were assessed in the volume percents with the GENERAL BIOLOGY