Potential of tea plants in carbon sequestration in North-East India.

The potential of carbon (C) sequestration through photosynthesis depends on the nature of different plant species. Tea (Camellia sinensis L.) is an evergreen perennial plant and cultivated over a wide region in the world, and its potential to sequestrate atmospheric carbon dioxide (CO2) in plant biomass is already evaluated. However, proportions of assimilated CO2 which tea plant can sequestrate in their biomass and in soil are not evaluated before. In this experiment, ten (10) 6-month old tea plants of four different cultivars (TV1, TV20, S3A/3, and TV23) were transplanted in the field and CO2 assimilation flux of tea plants was periodically measured under in situ condition using close-chamber method at 15 days interval throughout the year. The cumulative CO2 assimilation flux of young tea plants varied within 31.82-249.22 g CO2 plant-1 year-1; however, it was estimated that tea bushes also emitted 5.2-70.8 g CO2 plant-1 year-1 due to aerobic respiration. After 1 year, tea plants were uprooted and the changes in their biomass were compared as the measure of their C-sequestration within the study duration. The weight gain in the whole plant biomass was proportional to the CO2 assimilation potential of tea cultivars. Overall, tea plants sequestrated 50.8% of the assimilated atmospheric CO2 in their biomass. The study revealed that tea bushes release organic C through the root exudates, the amount of which was equivalent to 5.9-8.6% of the assimilated CO2. Those secreted root exudates have potential to increase organic C up to 44-48 kg ha-1 year-1 in tea-growing soil.

Enhanced microbial respiration due to carbon sequestration in pruning litter incorporated soil reduced the net carbon dioxide flux from atmosphere to tea ecosystem.

BACKGROUND: Tea (Camellia sinensis L.) bushes are periodically (at 3-4 year intervals) pruned (cut from top) to maintain vegetative growth stage and constant height. Plant residues (prunings litter) generated after pruning are generally left in the field as a potential source of organic matter in soil. Organic carbon (C) sequestration due to pruning litter incorporation is expected to increase microbial activity in soil. Being an evergreen plant, tea bushes assimilate atmospheric carbon dioxide (CO2 ) throughout the year; however, the relation between decomposition of pruning litters and net CO2 flux for tea plantation have not been studied before. The objective of this experiment was to evaluate the relation between organic C accumulation and microbial respiration in pruning litters incorporated soil and its subsequent effect on the net CO2 flux from the atmosphere to tea plantation. RESULTS: Tea bushes assimilated 1878.2-2371.2 kg CO2 ha-1 from the atmosphere within December to November; however, pruned bushes assimilated 1451.7-1840.8 kg CO2 ha-1 within the same period. Decomposition of pruning litters added organic matter in soil, which was mostly accumulated in larger soil aggregates having 2.0-0.25 mm size. Such organic matter accumulation significantly increased microbial respiration in those aggregates, which in turn increased the overall rate of CO2 emission from soil to the atmosphere. CONCLUSION: Decomposition of pruning litters leads to emission of 426.5-530.4 kg CO2 ha-1 from soil. Hence, pruned areas recorded relatively lower (16.0-27.4%) net CO2 flux from the atmosphere to tea ecosystem as compared to unpruned tea bushes. © 2019 Society of Chemical Industry.

Assimilating atmospheric carbon dioxide in tea gardens of northeast India.

Carbon dioxide (CO2) is the most important greenhouse gas in the atmosphere and phyto-assimilation is the most effective technique to mitigate global warming effect of CO2 gas in the atmosphere. Tea is an evergreen perennial plant and cultivated worldwide under subtropical humid climatic condition for harvesting its tender shoots. Tea bushes of different cultivars and ages are grown in combination to minimize possible adverse effect of biotic and abiotic stresses; hence distribution of tea plantation in a tea garden is complex in nature. Large shade trees are also an integral part of tea garden. Those plantations in tea garden have huge potential to capture atmospheric CO2; however, ability of tea bushes to mitigate global warming while producing tea shoots is not quantified before. The objective of this study was to quantify the potential of tea plantation to mitigate greenhouse effect (global warming mitigation potential, GWMP) due to assimilation of atmospheric CO2 gas. High yielding TV23 cultivar assimilated significantly higher amount of CO2 as compared to quality tea producing cultivars (S3A/3) and mature 25-30 years old tea bushes absorb more CO2 from the atmosphere as compared to younger tea bushes. Considering the mixed population of cultivars in tea gardens, overall, tea bushes sequestrated 5134.4 ± 831.6 kg CO2 ha-1 yr-1 in their biomass and had GWMP 3.47 ± 0.64 kg CO2 KMTH-1 yr-1. Shade trees sequestrated 4037.4 ± 589.9 kg CO2 ha yr-1 from the atmosphere. Hence, the GWMP of whole plantation ((both tea bushes and shade trees) was 6.19 ± 1.7 kg CO2 KMTH-1 yr-1. In this study, tea bushes sequestrated 52.7-61.3% of the total CO2 sequestrated by the plantations in tea garden. This study enabled to understand that tea bushes play significant role in mitigating global warming by assimilating and sequestrating atmospheric CO2 and the estimated value of global warming mitigation potential may be used for direct estimation of C sequestration by plantations in tea garden using its productivity value.

Electronic grade and flexible semiconductor film employing oriented attachment of colloidal ligand-free PbS and PbSe nanocrystals at room temperature.

Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies: (i) use of ligand-free nanocrystals and (ii) oriented attachment of nanocrystals. Colloidal ligand-free PbS and PbSe nanocrystals were synthesized at 70 °C with high yield (∼70%). However, these nanocrystals start to agglomerate with time in formamide, and upon the removal of the solvation energy, nanocrystals undergo oriented attachment, forming larger elongated crystals. PbS and PbSe nanocrystal films made on both glass and flexible substrates at room temperature exhibit Ohmic behavior with optimum DC conductivities of 0.03 S m(-1) and 0.08 S m(-1), respectively. Mild annealing of the films at 150 °C increases the conductivity values to 1.1 S m(-1) and 137 S m(-1) for PbS and PbSe nanocrystal films, respectively. AC impedance was measured to distinguish the contributions from grain and grain boundaries to the charge transport mechanism. Charge transport properties remain similar after the repeated bending of the film on a flexible polymer substrate. Reasonably high thermoelectric Seebeck coefficients of 600 µV K(-1) and 335 µV K(-1) for PbS and PbSe nanocrystal pellets, respectively, were obtained at room temperature.