A new compartmentalised rhizotron system for root phenotyping

Although roots are the key organs for plant fitness, studies on root phenotyping and dynamics of water uptake are difficult and costly. Here we present a new compartimentalised rhizotron system that attempts to integrate some positive features of conventional methods for assessing root patterns at field and laboratory scale. The system has a petrolatum/paraffin hydrophobic film, which allows the com-partmentalisation of soil layers along the cylinder profile, thus roots and soil moisture content are split into completely independent segments. In this preliminary study, we tested the system by creating a top-bottom split root arrangement that mimic the fluctuating levels of a water table to determine the dynamic interrelationship of canopy water conservation and root water acquisition from both shallow and deep roots of giant reed. Thanks to its versatility, the system enabled us to perform a root phenotyping study within distinct and independent soil portions

The effects of integrated food and bioenergy cropping systems on crop yields, soil health, and biomass quality: The EU and Brazilian experience

Integrated food and bioenergy production is a promising way to ensure regional/national food and energy security, efficient use of soil resources, and enhanced biodiversity, while contributing to the abatement of CO2 emissions. The objective of this study was to assess alternative crop rotation schemes as the basis for integrating and enhancing the sustainable biomass production within the food-energy agricultural context. Sunn hemp (Crotalaria spp.) in rotation with wheat (Triticum spp.) in the EU and with sugarcane (Saccharum spp.) in Brazil were evaluated. Sunn hemp did not negatively affect crop's productivity and soil fertility; wheat grain yields were maintained around the mean regional production levels (6, 7, 3 and Mg ha(-1) in Greece, Italy, and Spain, respectively), and the cumulative biomass in the extended rotation (wheat straw+sunn hemp) was between 1.5 and 2.0 times higher than in the conventional rotation. In Brazil, sugarcane stalks yield in clay soils increased by around 15 Mg ha(-1) year(-1) under sunn hemp rotation in comparison with bare fallow. Moreover, sunn hemp in the EU rotations did not have negative effects on soil available macronutrients, organic matter, pH, and cation exchange capacity, neither on C and N stocks in Brazil. The qualitative characteristics (mineral, ash, and hemicelluloses contents) of the cumulated biomass were somehow higher (in average +26%, +35%, and +3.4%, respectively) than in the conventional system. In summary, in temperate and tropical climates the integration of dedicated biomass legume crops within conventional systems could lead to enhanced biomass availability, crop diversification, and efficient use (in space and time) of the land resources

Transcriptional and Physiological Analyses to Assess the Effects of a Novel Biostimulant in Tomato

: This work aimed to study the effects in tomato (Solanum lycopersicum L.) of foliar applications of a novel calcium-based biostimulant (SOB01) using an omics approach involving transcriptomics and physiological profiling. A calcium-chloride fertilizer (SOB02) was used as a product reference standard. Plants were grown under well-watered (WW) and water stress (WS) conditions in a growth chamber. We firstly compared the transcriptome profile of treated and untreated tomato plants using the software RStudio. Totally, 968 and 1,657 differentially expressed genes (DEGs) (adj-p-value < 0.1 and |log2(fold change)| ≥ 1) were identified after SOB01 and SOB02 leaf treatments, respectively. Expression patterns of 9 DEGs involved in nutrient metabolism and osmotic stress tolerance were validated by real-time quantitative reverse transcription PCR (RT-qPCR) analysis. Principal component analysis (PCA) on RT-qPCR results highlighted that the gene expression profiles after SOB01 treatment in different water regimes were clustering together, suggesting that the expression pattern of the analyzed genes in well water and water stress plants was similar in the presence of SOB01 treatment. Physiological analyses demonstrated that the biostimulant application increased the photosynthetic rate and the chlorophyll content under water deficiency compared to the standard fertilizer and led to a higher yield in terms of fruit dry matter and a reduction in the number of cracked fruits. In conclusion, transcriptome and physiological profiling provided comprehensive information on the biostimulant effects highlighting that SOB01 applications improved the ability of the tomato plants to mitigate the negative effects of water stress

Deep Root Water Uptake Ability and Water Use Efficiency of Pearl Millet in Comparison to Other Millet Species

Pearl millet is better adapted to hot and semi-arid conditions than most other major cereals. The objective of this study was to compare the deep water uptake ability and water use efficiency (WUE) of pearl millet among millet species. First, the WUE of six millet species was evaluated in pots under waterlogging, well-watered (control), and drought conditions. Secondly, the water uptake from deep soil layers by pearl millet and barnyard millet, which showed the highest drought and waterlogging tolerance, respectively, was compared in long tubes which consisted of three parts (two loose soil layers separated by a hardpan and a Vaseline layer). Soil moisture was adjusted to well-watered and drought conditions in the upper (topsoil) layer, while the lower (deep) layer was always kept wet. WUE was significantly reduced in all millet species by waterlogging but not by drought. The ratio of WUE to the control condition indicated that pearl millet had the highest and lowest resistances to drought and waterlogging conditions, respectively, while barnyard millet was the most stable under both conditions. The deuterium concentration in xylem sap water, relative water uptake from deep soil layers, and water uptake efficiency of deep roots were significantly increased in barnyard millet but not in pearl millet by drought in topsoil layers. In conclusion, the drought resistance of pearl millet is explained by higher WUE but not by increased water uptake efficiency in deep soil layers as compared to barnyard millet, another drought-resistant millet species

Sixteen-Year Biomass Yield and Soil Carbon Storage of Giant Reed (Arundo donax L.) Grown Under Variable Nitrogen Fertilization Rates

High and stable biomass yields for long periods (15\u201320\ua0years) are indispensable for the successful establishment of a well-developed bioenergy sector. However, the effects of management practices, particularly nitrogen fertilization, on productivity and soil organic carbon (SOC) are difficult to understand, especially when considering that continuous harvesting cycles may have cumulative effects on the crop and its resources use capacity. The objective of this study was to evaluate the effects of different N fertilization levels on biomass production and SOC accumulation of giant reed over 16\ua0years. Every year, starting from the second one, two N fertilization rates were applied: 80 (N80) and 160 (N160) kg N\ua0ha 121. The control treatment (N0) was unfertilized. Nitrogen content and use capacity, and SOC gains were determined. Mean 16-year biomass yields were 16.2, 17.1, and 19.5\ua0Mg\ua0ha 121 in the N0, N80, and N160 treatments, respectively. Variable yielding phases were observed in the N160 treatment with declining yields towards the last sampling season, whereas the N0 was characterized by increasing yields up to the fourth growing season; thereafter, declining yields were observed. Nitrogen concentration and removed N in the aboveground harvested biomass increased from N0 to N160 and as the stand become older. Mean total SOC stock gains were 1.0 and 0.6\ua0Mg C\ua0ha 121\ua0year 121 in the N160 and N0 treatments, respectively. The largest SOC stocks were found in the topsoil, with the largest amount (12\ua0Mg C\ua0ha 121 in 16\ua0years) in the N160 treatment. In conclusion, long-term high N fertilization rates result in marginal increments in biomass productivity (about 3\ua0Mg\ua0ha 121\ua0year 121), but in substantial increments in SOC, especially in surface soil layers. A farmer might prefer to grow giant reed without the burdens of fertilization despite the seemingly benefits on SOC and lower yields of unfertilized plots

Photosynthetic response of sweet sorghum to drought and re-watering at different growth stages

Sweet sorghum (Sorghum bicolor ) is a C4 drought resistant species with a huge potential for bioenergy. Accentuated reductions in water availability for crop production and altered rainfall distribution patterns, however, will have direct impact on its physiological attributes, metabolic functions and plant growth. The objective of this study was to evaluate the effects of drought and re-watering on the photosynthetic efficiency of sweet sorghum. Durable or short transient drought stress periods were imposed at early and late growth stages and compared with well-watered plants. In spite of very similar drought levels at early and late growth stages (soil= 121.6 and 121.7 MPa), the decrements in maximum quantum yield (\u3d5Po) and performance index (PI) were about twice at late than at early growth stages. All the PI components, that is, density of active reaction centers (RCs), excitation energy trapping and conversion of excitation energy into electron flow followed a similar decreasing pattern. Upon re-watering and regardless the duration and growth stage of the drought period, all the photosynthetic functions, and particularly those of photosystem II (PSII), fully recovered. Such effective self-regulating functional activity by PSII photochemistry likely contributes to both high drought resistance and photosynthetic recovery capacity of sweet sorghum. At vegetative growth stages, the down regulation of the photochemistry seems to be the main photoprotective/regulative mechanisms, while at late growth stages, the accumulation of compatible solutes likely has amore preponderant role. The observed sugar concentration increments likely contributed to prevent permanent photo-oxidative destruction of the PSII RCs of mature droughted sweet sorghum plants

Hydrogen Stable Isotope Analysis of Water Acquisition Ability of Deep Roots and Hydraulic Lift in Sixteen Food Crop Species

Deep root penetration, which allows access to deep soil water and hydraulic lift, may help plants to overcome drought stress. The aim of this study was to evaluate the ability of sixteen food crop species to take up water from deep soil layers and the extent of hydraulic lift by the use of deuterated water. Plants were grown in pots consisting of two loose soil layers separated by a hardpan and a Vaseline layer. The lower (deep) layers were always kept wet (32%; ψ = –5 kPa), while soil moisture in the upper (topsoil) ones was adjusted to 25% (ψ = –7 kPa) and 12% (ψ = –120 kPa) in the well-watered and drought treatments, respectively. The deuterium labeling of the deep soil water provided evidence that wheat, Job’s tears, finger millet, soybean, barnyard millet, rice, and rye (in decreasing order of D2O increments) extracted more water from the deep layers under drought than well-watered in topsoil. These species showed significantly greater hydraulic lift under drought, except for soybean. Most of these species also showed increased root length density in deep soil layers and sustained high photosynthetic rates under drought. In contrast, pigeon pea, cowpea, common millet, pearl millet, foxtail millet, maize, barley, and oat did not show a significant increment in either deep-water uptake or hydraulic lift under drought. In summary, increased extraction of deep soil water under drought was closely related with the magnitude of hydraulic lift

Chapter 6: Environmental Impacts of Switchgrass Management for Bioenergy Production

In this chapter, we review major environmental impacts of growing switchgrass as a bioenergy crop, including effects on carbon sequestration, greenhouse gas emissions, soil erosion, nutrient leaching, and runoff. Information from life cycle analyses, including the effects of indirect land use change (iLUC), is examined to quantify the full impact of migration to bioenergy cropping systems on both managed and natural ecosystems. Information on the environmental impacts of switchgrass cultivation is scarce and there exists a critical need for additional research. What limited information there is suggests that switchgrass provides multiple environmental benefits compared to annual crop cultivation. However, benefits generally appear to be similar to other perennial crops

Water Competition of Intercropped Pearl Millet with Cowpeaunder Drought and Soil Compaction Stresses

Intercropping pearl millet with cowpea is a common practice in semiarid areas. Under limited water environments, competition for soil water between intercropped plants may be strong. Furthermore, the increasing soil compaction problems, due to the use of heavy machinery, may intensify competition for limited resources, particularly in the topsoil. Two field trials were conducted to evaluate the water competition ability of intercropped pearl millet when subjected to drought and soil compaction during the 2004 Japanese summer. For this purpose plant water sources were determined by the hydrogen stable isotope (deuterium) technique. Plant water relations and biomass production were also evaluated. According to the deuterium concentration values in xylem sap, pearl millet water sources were changed by the competition with cowpea. Pearl millet was forced to rely more on recently supplied (irrigation/rainfall) water. In contrast, the water sources of cowpea were unchanged by plant competition. When plants were subjected to drought, the transpiration rate of pearl millet was reduced by 40 % of its monocropped potential by competition, but that of cowpea was not. Moreover, intercropped pearl millet, under drought and soil compaction, showed lower leaf water potential and biomass than their respective monocropped counterparts. Cowpea had a higher competitive ratio under wet, dry, and compaction treatments, while pearl millet was more competitive under loose conditions. In conclusion, under drought and soil compaction, water competition restricted the water use of intercropped pearl millet, forcing pearl millet to shift to the recently supplied water. In contrast, cowpea did not show any significant changes under these stress conditions