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The current challenges in Lebanon are multifaceted, and among them is an impending food security crisis. Much of this can be attributed to a lack of sustainable planning within the agricultural sector. Decision-makers in agriculture and other connected sectors are disconnected and further hindered by the absence of national platforms and methods for assessing the trade-offs of potential interventions. This study aims to: (1) identify and quantify the critical interconnections between water, energy, nutrition, and food systems in Lebanon; (2) develop a framework to quantify the trade-offs associated with adopting interventions within current water, energy, and agriculture portfolios and practices; (3) evaluate producers' perceptions toward their willingness to implement proposed changes in crop production, renewable energy, and water reuse. The research shows that investing in local production of broad beans, lentils, chickpeas, and peas can lead to cost savings, increased nutritional value in locally produced foods, and reduced reliance on foreign markets. However, this also leads to increased water, energy, land and carbon usage which needs to be taken into account. Given the volatility of future currency exchange rates, it is increasingly important to identify a strategic food basket that can be produced locally to reduce dependence on imports. The findings of this study can aid in shaping policy and planning in Lebanon, and may also be adapted and applied in other countries in the MENA region.

Agriculture is a large source of greenhouse gas (GHG) emissions but changing management practices to those more beneficial to the environment could help mitigate climate change as long as they are economically and environmentally viable. This study examines the environmental (public) and economic (private) effects of adopting ten different beneficial management practices on a representative corn farm in Ontario, Canada. The study integrates changes in GHG emissions in carbon equivalents (CO2e) and changes in profit from changes in costs and revenues in two dimensions to reveal the scope and scale of different kinds of practices. 4R nitrogen management practices are smaller in scale compared to cropping practices and, therefore, have smaller potential costs and benefits. Land use changes, from practices including biomass, afforestation, crop rotation and cover cropping, have larger impacts on soil sequestration and carbon-equivalent GHG reduction, but with significantly greater costs. Seven practices were found to, at least partially, be economically and environmentally beneficial. The adoption of no-till and N-rate reduction is firmly positive, whereas the production of biomass has the largest potential economic and environmental gains. Crop rotation and diversification and cover cropping can be mutually beneficial, as can changing N-application practices. The use of inhibitors may be economically beneficial if yield gains outweigh purchase costs.

Soil temperature affects the rate of C-cycle processes by influencing the activities of microbial communities but little is known about whether the effects on these communities are consistent in different soils. We studied bacterial and fungal communities in six different soils, originating from two different Canadian climatic regions and incubated for three years at a common field site under ambient or warming (ca. +4.6 °C for 653 d of warming) conditions. Similar to early responses (reported after 295 d of warming), soil respiration is consistently higher (up to 2.8-fold) for 653 d of warming. However, soil origin-related differences in the community structure of bacteria were smaller at the end of the experiment, suggesting that environmental factors and management practices are important in shaping the structure of communities, but that this is a cumulative effect over time. In contrast, warming-induced shifts were greater and consistent across soils after longer period of soil warming. These shifts coincided with significant increases in the relative proportions of some potentially copiotrophic bacteria (e.g., Thermoleophilia, Alphaproteobacteria, and Bacilli). Fungal responses to warming, determined at the end of incubation, were largely soil-specific. The relative proportions of some fungi (e.g., Nectriaceae) increased with warming while several other taxa (e.g., Mortierellaceae and Lasiosphaeriaceae) showed significant reductions with warming. Unlike community structure, differences in the DNA content, microbial biomass carbon (MBC), and abundance of bacteria or fungi between the control and warmed soils were minor. This might be related to depletion of readily available substrates because measurements were made a year after the annual addition of litter. Our observation that community shifts became more pronounced over time suggests that these differences may have been realized through physiological temperature optima and through resulting shifts in resource availability.

The soil microbial community regulates decomposition of plant litter, but little is known about how the composition of the community responds to litter quality. To evaluate this, we applied 13C-labelled oat [Avena sativa] leaf or stem litter to soil at a rate of 5 mg C g−1 soil and incubated it at 20 °C for 170 days. We measured total C mineralized and litter-derived C remaining in soil over the incubation. Quantitative real-time PCR and Illumina MiSeq sequencing of marker genes were used to characterize shifts in abundance and composition of bacteria and fungi. We found no difference in litter-derived C remaining in the amended soils during the incubation; but more C (~23%) was mineralized from soil amended with leaf litter than those amended with stems, suggesting that leaf litter enhanced decomposition of the native soil organic matter. Leaf and stem litter supported the growth of bacteria and fungi throughout the incubation, but fungal growth and the fungal to bacterial ratio were more pronounced with the addition of stem litter. These changes in relative abundance as well as more pronounced shifts in fungal community structure in stem vs. leaf litter amended soils highlights the importance of fungi in degrading relatively resistant fractions of the lignin-enriched stem litter. Unlike the control soil (no litter added), the modularity (i.e., communities with some degree of independence) of co-occurrence in microbial networks increased, and this coincided litter-induced enrichment of specific taxa and with reduced alpha diversity. Leaf addition enriched a few bacterial (e.g., Bacilli) and many fungal (e.g., Nectriaceae, Didymellaceae, and Stachybotryaceae) taxa, whereas stem addition caused enrichment of fungi (e.g., Trichocomaceae and Chaetomiaceae) that are known to degrade resistant plant material. The findings of this study show that litter composition has a stronger influence on the composition of fungal than bacterial communities. Our results also suggest that some key fungal taxa have greater advantage in degrading relatively resistant plant material thereby supporting the growth of other bacterial and fungal taxa through release of simple, more degradable, compounds.

The stability of soil organic matter (SOM) as it relates to resistance to microbial degradation has important implications for nutrient cycling, emission of greenhouse gases, and C sequestration. Hence, there is interest in developing new ways to quantify and characterise the labile and stable forms of SOM. Our objective in this study was to evaluate SOM under widely contrasting management regimes to determine whether the variation in chemical composition and resistance to pyrolysis observed for various constituent C fractions could be related to their resistance to decomposition. Samples from the same soil under permanent pasture, an arable cropping rotation, and chemical fallow were physically fractionated (sand: 2000-50 μm; silt: 50-5 μm, and clay: K -edges. Relative to the pasture soil, SOM in the arable and fallow soils declined by 30% and 40%, respectively. The mineralization bioassay showed that SOM in whole soil and soil fractions under fallow was less susceptible to biodegradation than that in other management practices. The SOM in the sand fraction was significantly more biodegradable than that in the silt or clay fractions. Analysis by XANES showed a proportional increase in carboxylates and a reduction in amides (protein) and aromatics in the fallow whole soil compared to the pasture and arable soils. Moreover, protein depletion was greatest in the sand fraction of the fallow soil. Sand fractions in fallow and arable soils were, however, relatively enriched in plant-derived phenols, aromatics, and carboxylates compared to the sand fraction of pasture soils. Analytical pyrolysis showed distinct differences in the thermal stability of SOM among the whole soil and their size fractions; it also showed that the loss of SOM generally involved preferential degradation of H-rich compounds. The temperature at which half of the C was pyrolyzed was strongly correlated with mineralizable C, providing good evidence for a link between the biological and thermal stability of SOM.

Decomposition of soil organic matter (SOM) and plant litter has been shown to be affected by high solar radiation; this could partly explain why biogeochemical models underestimate decomposition in arid and semi-arid ecosystems. We set out to test the effect of using traditional PVC chambers for measuring soil gas fluxes versus quartz chambers that allowed passage of light during field measurements in a dry-land field in Davis, CA. Results showed that fluxes from quartz-top chambers were on average 29% higher than from opaque chambers. We also studied the effect of solar light exposure on decomposition of native grass litter and SOM in a field experiment where plots were shaded or left exposed for 157 days during summer; litter did not seem to be affected by exposure to light. However, we concluded that SOM decomposition was affected by light exposure since shaded soil had similar respiration to sunlight-exposed soil indicating that microbial respiration occurred under the shade while photo-degradation likely occurred under the sun. Additionally, 15N-labeled grass was placed in litter bags in the field with either clear filters to allow light or aluminum covers to block light; 3-month exposure caused a change in lignin degradability as indicated by the change in the Ad/Al ratio. Incubation of that litter showed 9.3% more CO2 produced from litter in clear and aluminum bags than unexposed litter. This showed that photo-facilitation occurred although to a small degree and was a result of light exposure and/or heat degradation. We attributed the similar respiration from clear- and aluminum-exposed litter to heat degradation of the aluminum-exposed litter. In conclusion, our results show that in hot dry ecosystems conventional PVC chambers underestimate measured CO2 flux rates; sunlight exposure changes litter chemistry and appears to affect the degradation of soil organic matter, but the magnitude of degradation depends on an interaction of factors such as soil temperature and moisture.

Climate change may profoundly influence soil organic carbon (SOC) dynamics through effects on soil temperature and water, but the mechanisms and magnitude of those effects remain uncertain. We measured the response of residue-C and native SOC in six soils with diverse texture subjected to artificial heating after transplanting to a common field site. The soils, three from each of two climatic zones in Canada, were amended with 13C labelled oat (Avena sativa) residue to distinguish turnover of recently-applied C and native SOC. The soils were either kept at ambient temperature or heated to 5 °C above ambient and CO2 emission was monitored over two growing seasons. Temperature was the primary factor regulating soil respiration across all six soils; water content did not have any additional explanatory effect, probably because the study site conditions were generally wet and thus decomposition was not limited by water. Soil aggregation and loss of residue-C (68% after 295 days) were not affected by warming. Compared to residue-C, native-SOC was more sensitive to loss by warming. The effect of physical aggregate protection against loss of SOC under warming was not evident. Bacterial community structure (16S rRNA gene sequencing) showed that there was a strong and persistent legacy effect on microbial communities. These differences among soils were far greater than those between heating and ambient treatments despite transplanting to a common location. Our results show that decomposition of residue-C and SOC were strongly governed by soil temperature rather than water content, even among transplanted soils with different textures and bacterial communities.

As plants are major contributors to soil organic matter (OM), the chemical composition of plant tissues entering the soil should be related to the soil OM composition. We examined the OM composition of maize leaves, stems, and roots, to determine if differences in plant tissue composition altered the soil OM composition during a 36-week degradation experiment. Lignin phenols were measured by gas chromatography/mass spectrometry (GC/MS), and soil OM and humic substances were characterized using solid-state 13 C and solution-state 1 H nuclear magnetic resonance (NMR) spectroscopy respectively. Lignin phenol composition, oxidation, and depletion relative to cutin-derived OH-acids changed less in leaf- compared to stem- and root-amended soils over time, and may be due to greater vanillyl concentrations in leaves. Soil amended with stems had higher concentrations of carbohydrates in soil OM. Humic substances from leaf-amended soils had higher concentrations of aliphatic components, likely due to higher concentrations of aliphatic compounds in leaf tissues, which suggests that compounds derived from leaves are potential contributors to the stable pool of soil OM. After 36-weeks of incubation, the contribution of microbial-derived OM was greatest in humic extracts from root-amended soils, and increased contribution from these compounds was detected earlier in these soils than stem- and leaf-amended soils. This indicates that root amendment may enhance contributions from microbial-derived OM. Our study suggests that changes in soil OM composition over time was related to the chemical composition of the plant tissue, and demonstrates the important link between plant chemistry and soil OM turnover.

Bt (Bacillus thuringiensis) corn (Zea mays L.) accounted for 74.5% of the corn acreage in eastern Canada in 2009. Reports that Bt corn has greater yield and lignin concentrations than unmodified corn have raised questions about its effect on the soil ecosystem. Our objectives were to evaluate the biomass of field-grown Bt and non-Bt corn, the chemical composition of different corn components that remain as residues in the field after harvest, and the effect of the Bt modification on residue decomposition. Nine Bt corn hybrids and their near isolines were field-grown in 2008 and 2009. Grain and stover yields were measured and leaves, stems, and roots were collected and analyzed for lignin, C, and N concentrations. Stem sections from a Bt/non-Bt corn pair were buried in the field and sampled periodically during 1 yr. No difference in yield or lignin concentrations due to the Bt gene was noted; however, N concentration in Bt stems was significantly greater than in non-Bt stems in 1 yr of the 2-yr study. Leaves had less lignin and a lower C/N ratio than stems and roots in both years. In buried field litterbags, the decline in C/N ratio and mass loss suggests that Bt stems were decomposing more rapidly than non-Bt stems. We conclude that the Bt gene does not affect the agronomic performance or the chemical composition of corn in fields without herbivory, and that Bt corn residue may be more susceptible to decomposition than non-Bt corn residue.

Bt ( Bacillus thuringiensis ) corn is reported to produce lignin-rich residues, compared to non-Bt (NBt) corn, suggesting it is more resistant to decomposition. As the Bt gene is expressed selectively in stem and leaf tissue, it could affect lignin distribution in corn, which naturally has greater lignin content in roots than in stems and leaves. Our objective was to evaluate the effects of corn plant components, the Bt gene and elevated-lignin inputs on decomposition. Roots, stems and leaves from Bt corn and NBt corn isolines enriched with 13 C and 15 N were finely ground and mixed separately with soil, then incubated at 20 °C for 36 weeks. The effect of elevated lignin on decomposition was tested by adding a commercial lignin source (indulin lignin) to half of the samples. In addition to weekly CO 2 analysis and regular measurement of N mineralization, the degree of lignin degradation was evaluated at 1 and 36 weeks from the acid to aldehyde ratio (Ad/Al) of vanillyl and syringyl lignin-derived phenols. The CO 2 production and N mineralization was lower in root-amended soils than stem- and leaf-amended soils. The Bt genetic modification increased CO 2 production from stem-amended soils ( P 13 C and 15 N results also showed more residue-C and -N retained in soils mixed with NBt stem residues. After 36 weeks leaf- and stem-amended soils with indulin lignin had a lower Ad/Al ratio and were less degraded than soils without exogenous lignin. In conclusion, plant lignin and nitrogen contents were good predictors of CO 2 production and N mineralization potential. Corn roots decomposed more slowly than aboveground components emphasizing the importance of recalcitrant root residues in sustaining the organic matter content of soil.