Atmosphere (CO2)→ Plant (plant biopolymer-HA)→ Soil(C-sequestered-HA)
In the last three years my research was focused to better understand the origin of HA-like material in plant (maize plant) and its role in the soil-C cycle. HA-likes were isolated directly form both plant and pre-isolated cell-wall, at different maturity stage and investigated by 13C-CPMAS NMR, surface area, porosity, wet analysis and complete mass balance. Moreover, maize plants were incubated in soil for long time (8 months) and HA-like material recovered and investigated. Results presented at this Conference suggest that the alkali-soluble part of the cell wall results in small domains formed by cross-linked polymers, mainly represented by lignin and cutin, and partially conserving the original cell wall-like structure, represented the HA-like fraction of plant. This HA is conserved in soil for long time representing a part of CO2 sequestered in soil. Plant maturation, i.e. lignification and cutinization processes, plays a main role in the definition of the structure of HA-like material, because these two processes well correlated with HA characteristics. Therefore, biochemical pathways forming cutin and above all lignin are implicated in the plant HA-like formation and its recalcitrant properties. To better investigate this aspect, mutant and wild type maize plants (W23: wild type and Brown MIBRID ľ Stock Center Resources of Maize GDB- USA) for lignin, are, now, under investigation in order to better understand the contribution of lignin to HA-like formation and C-sequestration in soil. Soil incubation of maize plant, shows low HA degradability that it seems caused by both chemical and physical properties of HA. High lignin content gives refractory properties to HA (Scobbie et al. 1993). On the other hand the low surface area (0.58 m2 g-1) that characterizes HA limits enzyme activity. Moreover, not all HA-surface area is available to enzymes because pores of diameters under 5 nm, representing 19 % of the total surface area of HA, are not accessible to enzymes (Chesson 2002). These results suggest the biochemical pathways to form HA play an important role in the C-sequestration and that more in deep studies need to better investigated i) the effect of atmospheric CO2 increasing on plant-HA balance; ii) to develop new strategies to increase HA-plant contents, and iii) to investigate the impact of the use of genetic modified plant on soil-C cycle.
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