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Abstract. Fluctuations in wetland hydrology create an interplay between aerobic and anaerobic conditions, controlling vegetation composition and microbial community structure and activity in wetland soils. In this study, we investigated the vegetation composition and microbial community structural and functional changes along a wetland hydrological gradient. Two different vegetation communities were distinguished along the hydrological gradient; Caricetum gracilis at the wet depression and Arrhenatheretum elatioris at the drier upper site. Microbial community structural changes were studied by a combined in situ 13 CO 2 pulse labeling and phospholipid fatty acid (PLFA) based stable isotope probing approach, which identifies the microbial groups actively involved in assimilation of newly photosynthesized, root-derived C in the rhizosphere soils. Gram negative bacterial communities were relatively more abundant in the surface soils of the drier upper site than in the surface soils of the wetter lower site, while the lower site and the deeper soil layers were relatively more inhabited by gram positive bacterial communities. Despite their large abundance, the metabolically active proportion of gram positive bacterial and actinomycetes communities was much smaller at both sites, compared to that of the gram negative bacterial and fungal communities. This suggests much slower assimilation of rootderived C by gram positive and actinomycetes communities than by gram negative bacteria and fungi at both sites. Ground water depth showed a significant effect on the relative abundance of several microbial communities. Relative abundance of gram negative bacteria significantly decreased with increasing ground water depth while the relative abundance of gram positive bacteria and actinomycetes at the surface layer increased with increasing ground water depth.

The objective of this study was to apply phospholipid fatty acid (PLFA)-based stable isotope probing to assess the temporal variation of active microorganisms associated with rhizosphere-C flow in a natural wetland. We applied (CO2)-C-13 pulse labeling at three different times throughout the vegetation period: spring (April), early summer (June), and early autumn (October). Soil redox potentials (Eh) at 10 cm depth ranged from moderately reduced (October) to oxidized conditions (June). Based on combined PLFA relative abundance and C-13 enrichment results, we suggest that gram-negative bacteria play a main role in rhizodeposit-C uptake in these wetland ecosystems, especially when reduced soil conditions prevail in October. Arbuscular and saprotrophic fungi also take up a significant proportion of the belowground allocated C, though mostly in the summer period. Gram-positive bacteria showed only a minor reliance on rhizodeposit-C throughout the year. It is concluded that rhizodeposit-C-assimilating microbial communities are heterogeneous and temporal variable entities with groups that are capable of adapting differently to seasonally varying environmental conditions

Biofilms are complex communities of multiple microbial species which are attached to surfaces or physical interfaces in nature. Such biofilms can also be developed in vitro using beneficial microbes, and can be used as Biofilm biofertilizers (BFBFs). Once applied, the BFBFs can supply sub network components to the bulk network of soil-plant-microbe parameters in agro-ecosystems degraded due to excessive use of chemical inputs. Thus, the degraded ecosystems can get their bulk network repaired through the sub network substitutions for improved interactions. Here, we analyzed selected soil, plant and microbial parameters with the application of farmers' chemical fertilizers (CF) alone practice [425 kg CF/ha (Urea 284, TSP 76 and MOP 66 kg/ha)] and BFBF practice [2.5 L of BFBF with 225 kg CF/ha (Urea 150, TSP 40 and MOP 35 kg/ha)] in 37 different locations in Sri Lanka using rice (Oryza sativa L.) as the test crop. Further, the data were analyzed to reveal the effect of BFBF in re-establishing networks in the agro-ecosystems. The BFBF application helped in cutting down farmers' CF use up to ca. 50%, while increasing grain yield up to ca. 25%. This was attributed to the positive effects of the BFBF towards strengthening the network interactions of the soil, plant and microbes. In this manner, BFBF practice clearly showed its potential as an ecofriendly and economically viable method to replace the farmers' current adverse practice of CF alone application. However, further studies should be conducted to collect data of a large number of variables, and they should be analyzed using more advanced methods to understand, particularly biotic and abiotic stresses for addressing them more effectively. This will eventually lead to design eco-friendly agro-ecosystems for sustainable agriculture.

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Abstract. Fluctuations in wetland hydrology create an interplay between aerobic and anaerobic conditions, controlling vegetation composition and microbial community structure and activity in wetland soils. In this study, we investigated the vegetation composition and microbial community structural and functional changes along a wetland hydrological gradient. Two different vegetation communities were distinguished along the hydrological gradient; \\textit{Caricetum gracilis} at the wet depression and \\textit{Arrhenatherum elatioris} at the drier upper site. Microbial community structural changes were studied by a combined in situ 13CO2 pulse labeling and phospholipid fatty acid (PLFA) based stable isotope probing approach, which identifies the microbial groups actively involved in assimilation of newly photosynthesized, root-derived C in the rhizosphere soils. Gram negative bacterial communities were relatively more abundant in the surface soils of the drier upper site than in the surface soils of the wetter lower site, while the lower site and the deeper soil layers were relatively more inhabited by gram positive bacterial communities. Despite their large abundance, the metabolically active proportion of gram positive bacterial and actinomycetes communities was much smaller at both sites, compared to that of the gram negative bacterial and fungal communities. This suggests much slower assimilation of root-derived C by gram positive and actinomycetes communities than by gram negative bacteria and fungi at both sites. Ground water depth showed a significant effect on the relative abundance of several microbial communities. Relative abundance of gram negative bacteria was significantly decreased with increasing ground water depth while the relative abundance of gram positive bacteria and actinomycetes at the surface layer increased with increasing ground water depth.

Bio-fertilizer is one of the Eco-Friendly Technologies (EFT) developed through a multiphased project to reduce the quantity and frequency of Chemical Fertilizer (CF) usage in paddy farming. What factors trigger farmers to adopt EFTs in the field, and more importantly, the "role of economics" in adoption of such technologies is, however, not yet fully understood. This study explores the outcome of an economic analysis carried out to determine the willingness-to-pay (WTP) of farmers, as potential end-users, for Biofertilizer. Structured questionnaire-based, face-to-face interviews were conducted aiming a set of paddy farmers (n=120) registered with a multi-stage, multi-criteria project in Anuradhapura and Kurunegala Districts to collect data. Choice Experiment (CE) method was employed to elicit farmers' Marginal Willingness-To-Pay (MWTP) for the deliverables of the product. The estimates from Conditional Logit model revealed that certain attributes, including 'high nutrient solubilizing rate' (i.e. the highest value of Rs. 908 per acre), 'promotional activities through farmer meetings' (Rs. 749 per acre), 'low environmental damage' (Rs. 471 per acre), 'powdered form of fertilizer' (Rs. 458 per acre) and 'availability through private markets' (Rs. 320 per acre) possess a significant relationship with farmer's WTP. The outcome of the study implies that the farmers, in general, exhibits positive attitudes and willing to pay relatively high prices for eco-friendly attributes associated with EFTs like Bio-fertilizer, but needs to expose a modified product according to farmer preferences to offset short-term benefits of chemical fertilizer use.