Crop Residue Removal for Bioenergy Reduces Soil Carbon Pools: How Can We Offset Carbon Losses?

Crop residue removal for bioenergy can deplete soil organic carbon (SOC) pools. Management strategies to counteract the adverse effects of residue removal on SOC pools have not been, however, widely discussed. This paper reviews potential practices that can be used to offset the SOC lost with residue removal. Literature indicates that practices including no-till cover crops, manure and compost application, and return of biofuel co-products increase SOC pools and may thus be used to offset some SOC loss. No-till rotations that include semi-perennial grasses or legumes also offer a promise to promote soil-profile C sequestration and improve soil resilience after residue removal. No-till cover crops can sequester between 0.10 and 1 Mg ha^?1 per year of SOC relative to no-till without cover crops, depending on cover crop species, soil type, and precipitation input. Animal manure and compost contain about 15 % of C and thus their addition to soil can enhance SOC pools and boost soil biological activity. Similarly, application of biofuel co-products such as biochar, which contain between 45 % and 85 % of C depending on the feedstock source and processing method, can enhance long-term C sequestration. These mitigation strategies may maintain SOC pools under partial residue removal in no-till soils but are unlikely to replace all the SOC lost if residue is removed at excessive rates. More field research and modeling efforts are needed to assess the magnitude at which the different mitigation strategies can overcome SOC loss with crop residue removal.     

Maximum Residue Levels: Fact or Fiction?

Maximum residue levels (MRLs) are trading standards that represent the maximum residue that could be found if a crop protection product (CPP) is applied according to critical good agricultural practice (cGAP). Foodstuffs are monitored for MRL compliance and exceedence can have economic, social and political consequences. There is a trade-off when calculating MRLs, as low MRLs prevent misuse of CPPs and high MRLs prevent an ‘unlucky’ farmer exceeding the MRL by chance. Chance exceedence has not been previously investigated despite the high probability of exceedence due to small data sets and calculation method. In this study, MRL calculation methods were investigated and policy for using these methods to control chance exceedence was defined. The shape and parameters of the residue distribution, LOQ and number of trials all affected the accuracy and precision of the estimated MRL. The two European methods were least accurate and precise at small numbers of trials and high CVs, with up to four different MRLs possible. Eight to 16 trials gave the best estimate of the MRL, but exceedence by chance could occur in up to 45% of samples. Policy was defined for using existing methods, and involved calculation of the MRL by both methods and taking the highest.     

Can Cover Crop Use Allow Increased Levels of Corn Residue Removal for Biofuel in Irrigated and Rainfed Systems?

Corn (Zea mays L.) residue removal at high rates can result in negative impacts to soil ecosystem services. The use of cover crops could be a potential strategy to ameliorate any adverse effects of residue removal while allowing greater removal levels. Hence, the objective of this study was to determine changes in water erosion potential, soil organic C (SOC) and total N concentration, and crop yields under early- and late-terminated cover crop (CC) combined with five levels of corn residue removal after 3 years on rainfed and irrigated no-till continuous corn in Nebraska. Treatments were no CC, early- and late-terminated winter rye (Secale cereale L.) CC, and 0, 25, 50, 75, and 100% corn residue removal rates. Complete residue removal reduced mean weight diameter (MWD) of water-stable aggregates (5 cm depth) by 29% compared to no removal at the rainfed site only, suggesting increased water erosion risk at rainfed sites. Late-terminated CC significantly increased MWD of water-stable aggregates by 27 to 37% at both sites compared to no CC, but early-terminated CC had no effect. The increased MWD with late-terminated CC suggests that CC when terminated late can offset residue removal-induced risks of water erosion. Residue removal and CC did not affect SOC and total soil N concentration. Particulate organic matter increased with late-terminated CC at the irrigated site compared to no CC. Complete residue removal increased irrigated grain yield by 9% in 1 year relative to no removal. Late-terminated CC had no effect on corn yield except in 1 year when yield was 8% lower relative to no CC due to low precipitation at corn establishment. Overall, late-terminated CC ameliorates residue removal-induced increases in water erosion potential and could allow greater levels of removal without reducing corn yields in most years, in the short term, under the conditions of this study.     

Activation of Plant Nod-like Receptors: How Indirect Can It Be?

Pioneering plant research has shown that many Nod-like receptors (NLRs) detect pathogens indirectly via recognizing modifications of other host proteins. In this issue, two groups show that the RPM1 NLR is activated by phosphorylation of the host protein RIN4, probably resulting from activation of a host kinase by pathogen effectors.     

What Does It Mean to Be Musical?

Music can be seen as a model system for understanding gene × environment interactions and how these can influence neurocognitive development. The concept of musicality, however, is underspecified and not well understood. Here, I propose a framework for defining musicality to provide a foundation for studying the contributions of biological and environmental factors.     

Can CO2 Fertilization Enhance Phytoremediation of Organic Soil Contamination?

Low efficiency is a key problem confronting the development and application of phytoremediation technology. Based on political pressure to reduce CO₂ emissions in China and the fact that CO₂ is necessary for plant photosynthesis, the effects of captured CO₂ fertilization on phytoremediation of soil di-(2-ethylhexyl) phthalate (DEHP) pollution by C₃ plant (mung bean, Vigna radiata L.) and C₄ plant (maize, Zea mays L.) were investigated. Results showed that DEHP pollution negatively affected the growth and rhizosphere environments of both plants. After CO₂ fertilization, both plants had more biomass (aboveground, belowground, and total dry weight), higher alkaline phosphatase activity, and more microbes with DEHP tolerance in their rhizospheres. Superoxide dismutase activity in leaves of both plants decreased significantly. Microbial community composition in both rhizospheres changed. CO₂ fertilization also increased plant uptake of DEHP, particularly in the roots, and decreased residual DEHP concentrations in the rhizospheres. These effects were more evident in the C₃ than in the C₄ plant. This study indicated that CO₂ fertilization can enhance the phytoremediation process of polluted soil through promoting plant growth, improving the rhizosphere environment, and increasing plant uptake of DEHP, particular in a C₃ plant. CO₂ fertilization could be considered as a measure to enhance phytoremediation.     

How Fast Can Carbon Be Sequestered When Restoring Degraded Subtropical Thicket?

Is the maximum rate of carbon sequestration reported for the CAM‐C₃ plant Portulacaria afra (spekboom), viz. 15.4 t CO₂ ha^?1 yr^?1, unusual in comparison with other plants with similar physioliogies, or could such rates be expected routinely in restoration with P. afra? Private sector investors in thicket restoration need an answer to this question in order to assess the feasibility of using carbon finance as the main income stream from their investments. A literature review showed that 15.4 t CO₂ ha^?1 yr^?1 is not an unusual rate of carbon sequestration for CAM plants in arid and semi‐arid environments, which suggests that investors in thicket restoration should not consider this an outlier value. The results also suggest that carbon finance could be used to fund restoration using other CAM plants in degraded xeric thickets in countries such as Argentina, Chile, Mexico, and Madagascar.     

Montane Meadows: A Soil Carbon Sink or Source?

Ecosystems - As the largest biogeochemically active terrestrial reserve of carbon (C), soils have the potential to either mitigate or amplify rates of climate change. Ecosystems with large C stocks...     

Fluctuation Analysis: Can Estimates Be Trusted?

The estimation of mutation rates and relative fitnesses in fluctuation analysis is based on the unrealistic hypothesis that the single-cell times to division are exponentially distributed. Using the classical Luria-Delbrück distribution outside its modelling hypotheses induces an important bias on the estimation of the relative fitness. The model is extended here to any division time distribution. Mutant counts follow a generalization of the Luria-Delbrück distribution, which depends on the mean number of mutations, the relative fitness of normal cells compared to mutants, and the division time distribution of mutant cells. Empirical probability generating function techniques yield precise estimates both of the mean number of mutations and the relative fitness of normal cells compared to mutants. In the case where no information is available on the division time distribution, it is shown that the estimation procedure using constant division times yields more reliable results. Numerical results both on observed and simulated data are reported.     

Can Joint Carbon and Biodiversity Management in Tropical Agroforestry Landscapes Be Optimized?

Managing ecosystems for carbon storage may also benefit biodiversity conservation, but such a potential ‘win-win’ scenario has not yet been assessed for tropical agroforestry landscapes. We measured above- and below-ground carbon stocks as well as the species richness of four groups of plants and eight of animals on 14 representative plots in Sulawesi, Indonesia, ranging from natural rainforest to cacao agroforests that have replaced former natural forest. The conversion of natural forests with carbon stocks of 227–362 Mg C ha⁻¹ to agroforests with 82–211 Mg C ha⁻¹ showed no relationships to overall biodiversity but led to a significant loss of forest-related species richness. We conclude that the conservation of the forest-related biodiversity, and to a lesser degree of carbon stocks, mainly depends on the preservation of natural forest habitats. In the three most carbon-rich agroforestry systems, carbon stocks were about 60% of those of natural forest, suggesting that 1.6 ha of optimally managed agroforest can contribute to the conservation of carbon stocks as much as 1 ha of natural forest. However, agroforestry systems had comparatively low biodiversity, and we found no evidence for a tight link between carbon storage and biodiversity. Yet, potential win-win agroforestry management solutions include combining high shade-tree quality which favours biodiversity with cacao-yield adapted shade levels.     

Does Grazing Matter for Soil Organic Carbon Sequestration in the Western North American Great Plains?

Ecosystems - Considerable uncertainty remains regarding grazing-induced influences on soil organic carbon (SOC) sequestration in semiarid grassland ecosystems due to three important complications...     

Can Organic Amendments Be Useful in Transforming a Mediterranean Shrubland into a Dehesa?

Transforming a shrubland into a dehesa system may be useful for recovering certain productive and regulatory functions of ecosystems such as grazing potential, soil erosion control, and also for reducing the risk of wildfire. However, the productivity of the herbaceous cover and tree development in the transformed system may be limited by soil fertility, especially after wildfire events. Previous studies have shown that adequate doses of sewage sludge may improve soil fertility and facilitate plant recovery, but few studies have focused on plant biodiversity assessment. Here, we compare the effects of sewage sludge that has undergone different post‐treatments (dewatering, composting, or thermal drying) as a soil amendment used to transform a fire‐affected shrubland into a dehesa, on tree growth and pasture composition (vegetation cover, species richness, and diversity). In the short term, sewage sludge causes changes in both pasture cover and tree growth. Although no major differences in vegetation species richness and composition have been detected, fertilization using sewage sludge was shown to modify the functional diversity of the vegetation community. Rapid replacement of shrubs by herbaceous cover and ruderal plants (e.g. Bromus hordeaceus and Leontodon taraxacoides) and of the three grass species sown (Festuca arundinacea, Lolium perenne, and Dactylis glomerata) was observed, whereas N‐fixing species (leguminous) tended to be more abundant in nonfertilized soils and soils amended with composted sludge. These results indicate that sewage sludge modifies the functionality of vegetation when applied to soils, and that the response varies according to the treatment that the sludge has undergone.     

Plant Communities, Soil Microorganisms, and Soil Carbon Cycling: Does Altering the World Belowground Matter to Ecosystem Functioning?

Soil microorganisms mediate many critical ecosystem processes. Little is known, however, about the factors that determine soil microbial community composition, and whether microbial community composition influences process rates. Here, we investigated whether aboveground plant diversity affects soil microbial community composition, and whether differences in microbial communities in turn affect ecosystem process rates. Using an experimental system at La Selva Biological Station, Costa Rica, we found that plant diversity (plots contained 1, 3, 5, or > 25 plant species) had a significant effect on microbial community composition (as determined by phospholipid fatty acid analysis). The different microbial communities had significantly different respiration responses to 24 labile carbon compounds. We then tested whether these differences in microbial composition and catabolic capabilities were indicative of the ability of distinct microbial communities to decompose different types of litter in a fully factorial laboratory litter transplant experiment. Both microbial biomass and microbial community composition appeared to play a role in litter decomposition rates. Our work suggests, however, that the more important mechanism through which changes in plant diversity affect soil microbial communities and their carbon cycling activities may be through alterations in their abundance rather than their community composition.     

DXA: Can It Be Used as a Criterion Reference for Body Fat Measurements in Children?

Objective: Dual‐energy X‐ray absorptiometry (DXA) is often cited as a criterion method for body composition measurements. We have previously shown that a new DXA software version (Hologic Discovery V12.1) will affect whole‐body bone mineral results for subjects weighing <40 kg. We wished to reanalyze pediatric whole‐body scans in order to assess the impact of the new software on pediatric soft‐tissue body composition estimates. Methods and Procedures: We reanalyzed 1,384 pediatric scans (for ages 1.7–17.2 years) using Hologic software V12.1, previously analyzed using V11.2. Regression analysis and ANCOVA were used to compare body fat (total body fat (TBF), percentage fat (%BF)), and non‐bone lean body mass (LBM) for the two versions, adjusting for gender, age and weight. Results: Software V12.1 yielded values that were higher for TBF, lower for LBM, and unchanged for DXA‐derived weight in subjects weighing <40 kg. Body composition values for younger, smaller subjects were most affected, and girls were more affected than boys. Using the new software, 14% of the girls and 10% of the boys were reclassified from the “normal” %BF range to “at risk of obesity,” while 7 and 5%, respectively, were reclassified as obese. Discussion: Hologic's newest DXA software has a significant effect on soft‐tissue results for children weighing <40 kg. The effect is greater for girls than boys. Comparison of TBF estimates with previous studies that use older DXA instruments and software should be done with caution. DXA has not yet achieved sufficient reliability to be considered a “gold standard” for body composition assessment in pediatric studies.     

Can Global Weed Assemblages Be Used to Predict Future Weeds?

Predicting which plant taxa are more likely to become weeds in a region presents significant challenges to both researchers and government agencies. Often it is done in a qualitative or semi-quantitative way. In this study, we explored the potential of using the quantitative self-organising map (SOM) approach to analyse global weed assemblages and estimate likelihoods of plant taxa becoming weeds before and after they have been moved to a new region. The SOM approach examines plant taxa associations by analysing where a taxon is recorded as a weed and what other taxa are recorded as weeds in those regions. The dataset analysed was extracted from a pre-existing, extensive worldwide database of plant taxa recorded as weeds or other related status and, following reformatting, included 187 regions and 6690 plant taxa. To assess the value of the SOM approach we selected Australia as a case study. We found that the key and most important limitation in using such analytical approach lies with the dataset used. The classification of a taxon as a weed in the literature is not often based on actual data that document the economic, environmental and/or social impact of the taxon, but mostly based on human perceptions that the taxon is troublesome or simply not wanted in a particular situation. The adoption of consistent and objective criteria that incorporate a standardized approach for impact assessment of plant taxa will be necessary to develop a new global database suitable to make predictions regarding weediness using methods like SOM. It may however, be more realistic to opt for a classification system that focuses on the invasive characteristics of plant taxa without any inference to impacts, which to be defined would require some level of research to avoid bias from human perceptions and value systems.     

Can Establishment Success Be Determined through Demographic Parameters? A Case Study on Five Introduced Bird Species

The dominant criterion to determine when an introduced species is established relies on the maintenance of a self-sustaining population in the area of introduction, i.e. on the viability of the population from a demographic perspective. There is however a paucity of demographic studies on introduced species, and establishment success is thus generally determined by expert opinion without undertaking population viability analyses (PVAs). By means of an intensive five year capture-recapture monitoring program (involving >12,000 marked individuals) we studied the demography of five introduced passerine bird species in southern Spain which are established and have undergone a fast expansion over the last decades. We obtained useful estimates of demographic parameters (survival and reproduction) for one colonial species (Ploceus melanocephalus), confirming the long-term viability of its local population through PVAs. However, extremely low recapture rates prevented the estimation of survival parameters and population growth rates for widely distributed species with low local densities (Estrilda troglodytes and Amandava amandava) but also for highly abundant yet non-colonial species (Estrilda astrild and Euplectes afer). Therefore, determining the establishment success of introduced passerine species by demographic criteria alone may often be troublesome even when devoting much effort to field-work. Alternative quantitative methodologies such as the analysis of spatio-temporal species distributions complemented with expert opinion deserve thus their role in the assessment of establishment success of introduced species when estimates of demographic parameters are difficult to obtain, as is generally the case for non-colonial, highly mobile passerines.