Girish Kumar Rasineni

Elevated atmospheric CO2 mitigated photoinhibition in a tropical tree species, Gmelina arborea

Effects of elevated CO₂ on photosynthetic CO₂ assimilation, PSII photochemistry and photoinhibition were investigated in the leaves of a fast growing tropical tree species, Gmelina arborea (Verbenaceae) during summer days of peak growth season under natural light. Elevated CO₂ had a significant effect on CO₂ assimilation rates and maximal efficiency of PSII photochemistry. Chlorophyll a fluorescence induction kinetics were measured to determine the influence of elevated CO₂ on PSII efficiency. During midday, elevated CO₂-grown Gmelina showed significantly higher net photosynthesis (p<0.001) and greater F(V)/F(M) (p<0.001) than those grown under ambient CO₂. The impact of elevated CO₂ on photosynthetic rates and Chl a fluorescence were more pronounced during midday depression where the impact of high irradiance decreased in plants grown under elevated CO₂ compared to ambient CO₂-grown plants. Our results clearly demonstrate that decreased susceptibility to photoinhibition in elevated CO₂ grown plants was associated with increased accumulation of active PSII reaction centers and efficient photochemical quenching. We conclude that elevated CO₂ treatment resulted in easy diminution of midday photosynthetic depression.

DROUGHT TOLERANCE IN MULBERRY (MORUS SPP.): A PHYSIOLOGICAL APPROACH WITH INSIGHTS INTO GROWTH DYNAMICS AND LEAF YIELD PRODUCTION

The present study documents critical analysis of drought-induced physiological responses in mulberry (Morus spp.) with insights into growth dynamics and leaf productivity. The study was performed for two years in a two-phase experimental design combining both field (experiment no. 1) and glasshouse (experiment no. 2) observations. In field assays, we surveyed 15 mulberry genotypes under two irrigation regimes: well-watered (20 to 24 irrigations in each growing season) and water-limited (irrigated once in a fortnight in each growing season). The genotypes were assessed for variation in key leaf gas exchange characteristics: net photosynthetic rates (P(n)), stomatal conductance of CO2 (g(s)), transpiration rates (E) and instantaneous water use efficiency (WUE(i)). Leaf yield/plant was considered to determine the tolerance index (TI). Drought stress severely down-regulated leaf-level physiological variables in the susceptible genotypes resulting in poor leaf yield. However, genotypes S-13 and V-1 performed better in terms of leaf gas exchange and proved their superiority over other genotypes in drought tolerance. Conversely, genotypes DD and Bogurai were highly susceptible to drought. Under glasshouse conditions, the combined leaf gas exchange/chlorophyll a fluorescence measurements further dissected out stomatal and non-stomatal restrictions to P(n). As internal/ambient CO2 ratio (C(i)/C(a)) decreased concurrently with g(s) in non-irrigated stands, it appeared that greater stomatal limitation to P(n) was associated with decreased photo-assimilation and leaf yield production. Further, higher leaf temperature (T(L)) (>35 °C) and down-regulation of maximum quantum yield of photosystem II (F(v)/F(m)) were apparent in the susceptible compared to the tolerant genotypes, which indicated chronic photoinhibition due to photo-inactivation of photosystem II centres in the susceptible genotypes. Drought-induced trade-offs in biomass allocation were also highlighted. Overall, our results suggest that greater rooting vigour and leaf hydration status, minimal stomatal inhibition and stabilized photochemistry might play major roles in maintaining higher P(n) and associated gas exchange functions in drought-tolerant mulberry genotypes under water stress conditions. The higher leaf yield production in tolerant than susceptible genotypes can be attributed to minimal plasticity in foliar gas exchange traits and better quantitative growth characteristics under low water regimes.

Responses of Gmelina arborea, a tropical deciduous tree species, to elevated atmospheric CO2: growth, biomass productivity and carbon sequestration efficacy.

The photosynthetic response of trees to rising CO(2) concentrations largely depends on source-sink relations, in addition to differences in responsiveness by species, genotype, and functional group. Previous studies on elevated CO(2) responses in trees have either doubled the gas concentration (>700 μmol mol(-1)) or used single large addition of CO(2) (500-600 μmol mol(-1)). In this study, Gmelina arborea, a fast growing tropical deciduous tree species, was selected to determine the photosynthetic efficiency, growth response and overall source-sink relations under near elevated atmospheric CO(2) concentration (460 μmol mol(-1)). Net photosynthetic rate of Gmelina was ~30% higher in plants grown in elevated CO(2) compared with ambient CO(2)-grown plants. The elevated CO(2) concentration also had significant effect on photochemical and biochemical capacities evidenced by changes in F(V)/F(M), ABS/CSm, ET(0)/CSm and RuBPcase activity. The study also revealed that elevated CO(2) conditions significantly increased absolute growth rate, above ground biomass and carbon sequestration potential in Gmelina which sequestered ~2100 g tree(-1) carbon after 120 days of treatment when compared to ambient CO(2)-grown plants. Our data indicate that young Gmelina could accumulate significant biomass and escape acclimatory down-regulation of photosynthesis due to high source-sink capacity even with an increase of 100 μmo lmol(-1) CO(2).

Proteomic approach to study leaf proteins in a fast-growing tree species, Gmelina arborea Linn. Roxb

Foliar proteome studies have become highly significant for a comprehensive understanding of complex processes associated with plant growth and development. In the present study, we present a proteomic approach to analyze leaf proteins in an important timber-yielding and fast-growing forest tree species, Gmelina arborea Linn. Roxb. (Verbanaceae). Foliar protein analysis involved protein extraction, two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time of flight (MALDI–TOF–TOF). From the 2-DE protein profile of Gmelina leaves, we identified and isolated 150 well-separated protein spots; among these, 64 protein spots were identified by mass spectrometric (MS/MS) analysis. These proteins were classified according to their involvement in basic biological functions, such as photosynthesis, amino acid metabolism, cytoskeleton, cell wall metabolism, stress-related proteins, redox maintenance, electron transport chain, phytohormone metabolism and protein translation and folding. Analytical variance was determined for the protein spots of samples from different plants. The present study is believed to provide a foundation for the use of leaf proteomics in addressing fundamental physiological and biochemical processes associated with growth and productivity of tree species such as Gmelina arborea.

Shape-Changes of the Fast Chlorophyll a Fluorescence Transient (OJIP) and Antioxidative Enzymes in High Salt Tolerant Mangrove Trees of Bruguiera Gymnorrhiza

True Mangrove trees of the costal habitats are now threaten of extinction because of climate change linked to global warming, sea level raise and fluctuating salinity. The key adaptation ability of the true tree mangroves having no salt secreting gland to survive in water logged high salt and anoxic condition seems to be shedding of lower leaves. The detailed mechanism of survival from high salt stress in this sea-shore mangroves is not known. We have examined the high salt stress effect in Bruguiera gymnorhiza a true tree mangrove in this study. Hydroponic culture of three months old nursery raised seedlings on B. gymnorizha were treated in 500 mmol NaCl (high salt) for 7 and 45 days. Both fast chlorophyll transients as well as the specific activity of key antioxidative enzymes were monitored to characterize the recovery potential of this mangrove from salt stress.

Influence of Elevated CO2 Concentration on Photosynthesis and Biomass Yields in a Tree Species, Gmelina Arborea Roxb

The present study dissects out the CO2 fertilization effects on photosynthetic gas exchange characteristics, key responses of photosynthetic and carbohydrate metabolizing enzymes and overall plant growth performance in a fast growing tree species, Gmelina arborea Roxb (Verbenaceae). The main objective of this investigation was to unravel and evaluate the role of elevated CO2 on tree photosynthesis and productivity. Gmelina plants were grown under ambient (360 μmol mol−1) and CO2-enriched conditions (460 μmol mol−1) in open top chambers for two marked growth seasons, subsequently for three years. The leaf gas exchange characteristics and associated biochemical measurements were carried out at regular intervals. Gmelina plants were harvested and growth parameters were measured at the end of two growth seasons for three consecutive years. Gmelina plants significantly responded to CO2 enrichment. Gmelina plants grown under elevated CO2 showed 52% more plant biomass compared with those grown under ambient CO2. We conclude that fast growing tree species like Gmelina, exhibiting high CO2-mediated photosynthetic up-regulation, can be used as potential tree species for efficient carbon sequestration under predicted future climate change scenario.

The Effects of Elevated CO2 Concentration on Photosynthesis and Photosystem II Photochemistry in a Fast Growing Tree Species, Gmelina Arborea Roxb

Sequestering atmospheric carbon and storing it in the terrestrial biosphere is one of the options to mitigate green house gas emissions. Young fast growing tree species are believed to be major potential sinks which could absorb large quantities of CO2 from the atmosphere. The ability of plant to capture light energy, associated with the rate of CO2 fixation per se, is crucial to understand the growth dynamics under varying environmental regimes. The role of enriched CO2 atmosphere in the kinetics of photosynthesis and Chl a fluorescence could be an index to understand the photosystem II photochemistry associated with carbon sequestration potential. In this study, the effects of elevated CO2 (460 μmol mol−1) on diurnal courses of net CO2 assimilation and chlorophyll a fluorescence were investigated under natural high light during summer days in a fast growing tree species, Gmelina arborea (Verbenaceae). High CO2 atmosphere led to easy recovery from the midday photosynthetic depression in the leaves. Elevated CO2 also enhanced the utilization of captured light energy, alleviated photoinhibition and enhanced the growth of Gmelina arborea. Data on fluorescence induction curves and JIP-test parameters also demonstrated a positive impact of elevated CO2 on PSII photochemical performance suggesting Gmelina to be a better performer for carbon sequestration even during high irradiance regimes.