Carbon sequestration potential in perennial bioenergy crops: the importance of organic matter inputs and its physical protection

To date, only few studies have compared the soil organic carbon (SOC) sequestration potential between perennial woody and herbaceous crops. The main objective of this study was to assess the effect of perennial woody (poplar, black locust, willow) and herbaceous (giant reed, miscanthus, switchgrass) crops on SOC stock and its stabilization level after 6 years from plantation on an arable field. Seven SOC fractions related to different soil stabilization mechanisms were isolated by a combination of physical and chemical fractionation methods: unprotected (cPOM and fPOM), physically protected (iPOM), physically and chemically protected (HC‐μs + c), chemically protected (HC‐ds + c), and biochemically protected (NHC‐ds + c and NHC‐μs + c). The continuous C input to the soil and the minimal soil disturbance increased SOC stocks in the top 10 cm of soil, but not in deeper soil layers (10–30; 30–60; and 60–100 cm). In the top soil layer, greater SOC accumulation rates were observed under woody species (105 g m^?2 yr^‐1) than under herbaceous ones (71 g m^?2 yr^‐1) presumably due to a higher C input from leaf‐litter. The conversion from an arable maize monoculture to perennial bioenergy crops increased the organic C associated to the most labile organic matter (POM) fractions, which accounted for 38% of the total SOC stock across bioenergy crops, while no significant increments were observed in more recalcitrant (silt‐ and clay‐sized) fractions, highlighting that the POM fractions were the most prone to land‐use change. The iPOM fraction increased under all perennial bioenergy species compared to the arable field. In addition, the iPOM was higher under woody crops than under herbaceous ones because of the additional C inputs from leaf‐litter that occurred in the former. Conversion from arable cropping systems to perennial bioenergy crops can effectively increase the SOC stock and enlarge the SOC fraction that is physically protected within soil microaggregates.     

Sowing density and harvest time affect fibre content in hemp (Cannabis sativa) through their effects on stem weight

Sowing density and harvest time are considered important crop management factors influencing fibre quantity and quality in hemp (Cannabis sativa). We investigated whether the effects of these factors are essentially different or that both factors affect stem weight and thereby total and long‐fibre content. The effects of all combinations of three sowing densities and three harvest times were studied for six different stem parts. Almost 500 samples consisting of stem parts from 50 plants and with a length of 50 cm were tested. Fibres were extracted by a controlled warm‐water retting procedure, followed by breaking and scutching. The initial sample weight was fractionated into retting losses, wood, tow and long fibre. In both Italy and the Netherlands, crops were successfully established with different stem densities (99–283 m^?2), plant heights (146–211 cm) and stem diameters (4.5–8.4 mm) at harvest. Stem dry matter yields (6.8–11.7 Mg ha^?1) increased with a delay in harvest time but were not affected by sowing density. Retting loss percentages were lower in lower stem parts and decreased with later harvest because maturation was associated with increasing amounts of fibre and wood. Within a certain stem part, however, the absolute retting losses were constant with harvest time. Multiple linear regression analyses showed that the amount of fibre in a hemp stem is almost completely determined by the weight and the position of that stem part. When the plant grows, the increase in dry matter is split up into fibres and wood in a fixed way. This total fibre/wood ratio was highest in the middle part of the stem and lower towards both bottom and top. Sowing density and harvest time effects were indirect through stem weight. The long‐fibre weight per stem increased with the total fibre weight and hence with stem weight. Stem weight increased with harvest time; as harvest time did not affect plant density, the highest long‐fibre yields were obtained at the last harvest time. The long fibre/total fibre ratio was lowest in the bottom 5 cm of the stems but similar for all other parts. Sowing density and harvest time effects again were indirect. Fibre percentages in retted hemp decreased with increasing stem weights towards a level that is presumably a variety characteristic. The dry matter increase between harvests, however, is much more important with respect to total and long‐fibre yield.     

Flaws in the interpretation phase of bioenergy LCA fuel the debate and mislead policymakers

The International Journal of Life Cycle Assessment - We hypothesize that the current heated scientific debate on bioenergy sustainability is fuelled by flaws in the interpretation phase of...     

Growth, fructan yield, and quality of chicory (Cichorium intybus L.) as related to photosynthetic capacity, harvest time, and water regime

Fructans are polymers that are widely used in several industrial applications. In the last few years they have received increasing interest because of their positive effects on health. At present, fructans are mostly supplied by chicory, which is only grown and processed in The Netherlands, France, and Belgium. It would therefore be an attractive concept to expand its cultivation to the southern European countries, although water shortage and high temperatures may hinder its growth and yield. So far, few experiments have been carried out on the effects of water, so the present research was focused on the course of growth and fructan quality in rainfed (W(0)) and well-watered (W(1)) conditions. The positive effects of water restoration mostly concerned the above-ground dry weight (ADW), whereas the root dry weight (RDW) was less influenced. No significant differences on RDW were found in 1999, whereas it was 14% higher (P <0.01) in W(1) in 2000. The effect of water was very clear on assimilate allocation: the overall priority at the whole plant scale seemed to be root structures, then storage reserves, and finally ADW. Therefore, the fructan content was higher in W(0), and insignificant differences between W(0) and W(1) were found on fructan yield at the final harvests. The only significant effect of the water regime on fructans was to speed up their storage. The leaf photosynthetic capacity (A) was poorly affected by water availability, whereas it appeared consistently modulated by leaf temperature and leaf nitrogen content. Stomatal conductance appeared to be mostly affected by the soil water content and it was mostly related to A up to about 300 mmol m(-2) s(-1). The fructan chain length (DP) was not affected by water regime. Besides, DP classes showed a normal statistical distribution; skewness and kurtosis significantly changed only when the harvest was very late. Equally, a very late harvest time significantly lowered DP.     

Lysosomal enzymes in experimental allergic encephalomyelitis: Time course and evidence of the source

The lysosomal enzymes acid proteinase and -glucuronidase, were assayed in spinal cords of rats during the course of experimental allergic encephalomyelitis (EAE). Histological and histochemical examination was carried out versus controls, in selected areas of the same cords biochemically assayed, to look at the distribution of the lysosomal enzyme acid phosphatase. The biochemical assay showed a significant increase of the enzyme activities during the disease and the increase was significantly correlated with the intensity of the disease. The distribution in the nervous tissue of the increase in acid phosphatase activity observed in animals with EAE, suggests that endogenous nervous cells may contribute to the lysosomal enzyme increase in EAE.     

A possible mechanism for cholesteryl ester formation during demyelination

Lecithin: cholesterol acyltransferase (LCAT) activity has been examined in the rat by using a brain homogenate preparation as the phospholipid substrate and blood plasma as the enzyme source. LCAT activity was detected on using 60 l of serum onwards. Successive experiments have also shown that LCAT activity is present in the edematous rat brain tissue homogenate when incubated with inactivated rat plasma as substrate. The results are discussed in relation to cholesteryl ester accumulation in brain during demyelinating diseases.     

Computational fluid dynamics simulation to evaluate aortic coarctation gradient with contrast-enhanced CT

Coarctation of aorta (CoA) is a narrowing of the aorta leading to a pressure gradient (ΔP) across the coarctation, increased afterload and reduced peripheral perfusion pressures. Indication to invasive treatment is based on values of maximal (systolic) trans-coarctation ΔP. A computational fluid dynamic (CFD) approach is herein presented for the non-invasive haemodynamic assessment of ΔP across CoA. Patient-specific CFD simulations were created from contrast-enhanced computed tomography (CT) and appropriate flow boundary conditions. Computed ΔP was validated with invasive intravascular trans-CoA pressure measurements. Haemodynamic indices, including pressure loss coefficient (PLc), time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI), were also quantified. CFD-estimated ΔP values were comparable to the invasive ones. Moreover, the aorta proximal to CoA was exposed to altered TAWSS and OSI suggesting hypertension. PLc was found as a further geometric marker of CoA severity. Finally, CFD-estimated ΔP confirmed a significant reduction after percutaneous balloon dilatation and stenting of the CoA in one patient (e.g. from ΔP～52 mmHg to ΔP～3 mmHg). The validation of the ΔP computations with catheterisation measurements suggests that CFD simulation, based on CT-derived anatomical data, is a useful tool to readily quantify CoA severity.     

The effect of transient and continuous drought on yield, photosynthesis and carbon isotope discrimination in sugar beet (Beta vulgaris L.)

Stable carbon isotope discrimination (delta13C), photosynthetic performance (A), dry matter accumulation (DW), and sucrose yield (Y(s)) of sugar beet were evaluated in a glasshouse experiment under transient (TS) and permanent (PS) water stress. A was significantly reduced under drought, to an extent depending on stress duration. The reduced A was strictly associated with a low DW and Y(s), the later being 42% lower in PS than control plants (C). Restoring water steeply increased A and the associated leaf traits (RWC, leaf water potential etc.), but the increase of Y(s) was negligible. Therefore, the negative effects of severe water stress in the early growth period, though reversible on gas-exchange and most leaf traits, can drastically reduce Y(s) of sugar beet. Furthermore, A seems not to be effective in predicting sucrose accumulation, although it was very effective in detecting the occurrence of plant water stress. The A/C(i) model was used to assess the photosynthetic adjustments to continuous or transient drought by calculating the photosynthetic parameters Vcmax and Jmax and then compared with delta13C. Mesophyll conductance (g(m)) was estimated by comparing delta13C measured on soluble sugars and gas-exchange data. This approach confirmed the expectation that g(m) was limiting A and that there was a significant drop in [CO2] from the substomatal cavities and the chloroplast stroma both in favourable and drought conditions. Therefore, the carbon concentration at the carboxylation site was overestimated by 25-35% by conventional gas-exchange measurements, and Vcmax was consistently underestimated when g(m) was not taken into account, especially under severe drought. Root delta13C was found to be strictly related to sucrose content (brix%), Y(s) and root dry weight, and this was especially clear when delta13C was measured on bulk dry matter. By contrast, leaf delta13C measured in soluble sugars (delta(s)) and bulk dry matter (delta(dm)) were found to correlate weakly to brix% and yield, and this was not surprising as the integration time-scale of leaf delta(s) and delta(dm) were found to be shorter than that of root delta13C in bulk dry matter. The effect of water stress on diffusive and biochemical limitations with different integration times ranged from 1 d (leaf delta(s)) to more than 1 month (root delta(dm)).