Relationship between soil CO2 concentrations and forest-floor CO2 effluxes

To better understand the biotic and abiotic factors that control soil CO₂ efflux, we compared seasonal and diurnal variations in simultaneously measured forest-floor CO₂ effluxes and soil CO₂ concentration profiles in a 54-year-old Douglas fir forest on the east coast of Vancouver Island. We used small solid-state infrared CO₂ sensors for long-term continuous real-time measurement of CO₂ concentrations at different depths, and measured half-hourly soil CO₂ effluxes with an automated non-steady-state chamber. We describe a simple steady-state method to measure CO₂ diffusivity in undisturbed soil cores. The method accounts for the CO₂ production in the soil and uses an analytical solution to the diffusion equation. The diffusivity was related to air-filled porosity by a power law function, which was independent of soil depth. CO₂ concentration at all depths increased with increase in soil temperature, likely due to a rise in CO₂ production, and with increase in soil water content due to decreased diffusivity or increased CO₂ production or both. It also increased with soil depth reaching almost 10 mmol mol⁻¹ at the 50-cm depth. Annually, soil CO₂ efflux was best described by an exponential function of soil temperature at the 5-cm depth, with the reference efflux at 10 °C (F₁₀) of 2.6 μmol m⁻² s⁻¹ and the Q₁₀ of 3.7. No evidence of displacement of CO₂-rich soil air with rain was observed.Effluxes calculated from soil CO₂ concentration gradients near the surface closely agreed with the measured effluxes. Calculations indicated that more than 75% of the soil CO₂ efflux originated in the top 20 cm soil. Calculated CO₂ production varied with soil temperature, soil water content and season, and when scaled to 10 °C also showed some diurnal variation. Soil CO₂ efflux and concentrations as well as soil temperature at the 5-cm depth varied in phase. Changes in CO₂ storage in the 0–50 cm soil layer were an order of magnitude smaller than measured effluxes. Soil CO₂ efflux was proportional to CO₂ concentration at the 50-cm depth with the slope determined by soil water content, which was consistent with a simple steady-state analytical model of diffusive transport of CO₂ in the soil. The latter proved successful in calculating effluxes during 2004.     

Growth and mineral content of roots and shoots of maize seedlings in response to increasing water deficits induced by peg solutions

Abstract

The effects of polyethylene glycol (PEG) solutions of increasing osmotic potentials (ψπ=?0.44 and ‐0.88 MPa) on the growth of the seedlings and on the concentrations of Mn, Cu, Pb, Zn, Ni, Co, Mo, Cr, Cl, Fe, Ca, Mg, K, Na, P, and N were determined in the shoots and roots of maize (Zea mays L. cv. Summer II) grown in Hoagland's solution in a growth chamber. Water stress was imposed for three days with PEG 4000 on six‐day‐old seedlings. Despite a reduction in the leaf water potential (ψw), which decreased with increasing PEG concentrations, and despite an increase in the water saturation deficit (W.S.D.), the pressure potentials (ψp) were maintained in both treatments at levels quite similar to that in the control seedlings.

At ψπ=?0.44 MPa of the growth medium, both the length and dry weight of the shoots and roots significantly decreased, whereas at ψπ=?0.88 MPa only the root length continued to decrease with the consequence of an increase in the total mass production of the seedlings. At ψπ=?0.88 MPa, PEG was absorbed by the seedlings in significant amounts, although the roots were undamaged.

The effects of the imposed water stress on nutrient absorption and accumulation differed in the two treatments, depending on the plant tissue and nutrient; nevertheless, the element contents generally showed their lowest values at ψπ=?0.44 MPa, as consequence of the reduction in dry matter. The water stress experienced by the maize seedlings grown at ψπ=?0.88 MPa did not induce further decreases in either the macro‐ or micronutrients.     

Rheological Hardness Index for Assessing Hardness of Hexaploids and Durums

Kernel hardness of cereal grains is a fundamental phenotype, and various protocols for its characterization have been proposed. Although, from different perspectives, each has proved useful, these methods do not directly address the rheological (fracturing) response of a grain when subjected to compression. Such information is hidden in the individual crush response profiles (iCRPs) obtained by measuring the response of individual grains to crushing on an SKCS 4100 device. Here, the appropriateness and utility of rheological phenotypes, based on single‐kernel measurements, are demonstrated by proposing and validating a new wheat grain hardness phenotype, the rheological hardness index (RHI). It is defined in terms of the rheological phenotype phases (RPPs) of the averaged CRPs (aCRPs) obtained by averaging a large number of iCRPs. The utility of RHI is illustrated by showing how it provides improved insight about the differences in brittleness and compactness of grains from different wheat varieties. This investigation highlights the opportunity that the RPP of the aCRPs represent for obtaining specific quantitative phenotypes for the study of hardness in cereal grains. In particular, successful plant breeding relies on segregating a breeding population into appropriate end‐use categories, for which RHI has a potential role to play.     

Allometric equations for estimating aboveground biomass of Coffea arabica L. grown in the Rift Valley escarpment of Ethiopia

Coffee, Coffea arabica L., which is native to Ethiopia, is the world’s most widely traded tropical agricultural commodity. While much is known about the productivity and management of coffee for coffee beans little attention has been given to the plants overall biomass production and carbon sequestration. The objective of this study was to develop and evaluate allometric equations for estimating the aboveground biomass of C. arabica plants growing in indigenous agroforestry system in the Rift Valley escarpment of south-eastern Ethiopia. Coffee plays an important role in providing income and in sustaining these productive systems. Biomass harvesting of 31 plants with 54 stems was carried out in a 40 km² area varying in elevation from 1,500 to 1,900 m. The stem accounted for most (56 %) of plant biomass, followed by branches (39 %) and twigs plus foliage (5 %). Plant mean biomass was 22.9 ± 15.8 kg. Power equations using stem diameter measured at either 40 cm (d ₄₀) or at breast height (d, 1.3 m) with and without stem height (h) were evaluated. The square power equation, $ Y \; = \; b_{ 1} d_{ 40}^{ 2} $ , was found to be the best (highest ranked using goodness-of-fit statistics) for predicting total and component biomass. The reliability of the prediction decreased in the order: stem > branches > twigs plus foliage. A cross-validation procedure showed that equation parameterization was stable and coefficients reliable. Our parameterized square power equation for total aboveground biomass was also found to be better than the equations parameterized by Hairiah et al. (Carbon stocks of tropical land use systems as part of the global C balance: effects of forest conversion and options for clean development activities, International Centre for Research in Agroforestry, Bogor, 2001) and Segura et al. (Agroforest Syst 68:143–150, 2006) for C. arabica grown in agroforestry systems, confirming the importance of parameterization of allometric equations with site specific data when possible.     

Natural (auto)antibodies in calves are affected by age and diet

Background: Natural autoantibodies (N(a)ab) were found in every species tested so far, and are likely important in maintaining homeostasis.

Objectives: (1) To determine N(a)ab in Bos taurus calves, (2) evaluate effects of diet and age on N(a)ab binding repertoires in calves, and (3) delineate bovine liver cell lysate (BLL) antigens related with variation in rumen score and body weight.

Animals and methods: Effects of age and diet on staining of BLL fragments by IgM and IgG antibodies in serum samples collected at 20 or at 26 weeks of age from bull calves either fed a restricted or ad libitum diet were analyzed using quantitative Western blotting. Correlations between fragments stained and grouping of calves were done by Principal Component Analysis (PCA). Redundancy analysis (RDA) was done to relate rumen score and body weight variation at slaughter at 27 weeks of age with stained BLL fragments.

Results: In sera from all calves IgM and IgG antibodies binding BLL antigens were found. Corresponding fragments were stained, but quantitative differences in staining intensities were related to diet and age for both IgM and IgG. PCA revealed that age had a greater influence than diet on BLL fragment staining. RDA suggested that staining by IgM or IgG of specific BLL fragments was related with variation in rumen score and body weight.

Conclusions and clinical importance: Analyses of N(a)ab in serum could be a potential tool to estimate the health status of cattle, and be used to evaluate effects of husbandry practices.     

Effects of long-term exposure to enriched CO<Subscript>2</Subscript> on the nutrient-supplying capacity of a grassland soil

Altered soil nutrient cycling under future climate scenarios may affect pasture production and fertilizer management. We conducted a controlled-environment study to test the hypothesis that long-term exposure of pasture to enriched carbon dioxide (CO₂) would lower soil nutrient availability. Perennial ryegrass was grown for 9 weeks under ambient and enriched (ambient + 120 ppm) CO₂ concentrations in soil collected from an 11.5-year free air CO₂ enrichment experiment in a grazed pasture in New Zealand. Nitrogen (N) and phosphorus (P) fertilizers were applied in a full factorial design at rates of 0, 12.5, 25 or 50 kg N ha⁻¹ and 0, 17.5 or 35 kg P ha⁻¹. Compared to ambient CO₂, under enriched CO₂ without P fertilizer, total plant biomass did not respond to N fertilizer, and tissue N/P ratio was increased indicating that P was co-limiting. This limitation was alleviated with the lowest rate of P fertilizer (17.5 kg P ha⁻¹). Plant biomass in both CO₂ treatments increased with increasing N fertilizer when sufficient P was available. Greater inputs of P fertilizer may be required to prevent yield suppression under enriched CO₂ and to stimulate any response to N.     

How long can a herbicide remain in the spray tank without losing efficacy?

Five field trials were conducted over a three-year period (2006–2008) at two locations in southwestern Ontario to determine the length of time herbicides can remain in the spray tank prior to application in the field without impacting efficacy. Four pre-emergence and five post-emergence herbicides were mixed at their labelled rates and then applied in maize. Herbicides were either applied immediately after mixing in water, or after being held in solution for 1, 3 or 7 days. The most common weed species in the trials were Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, and Chenopodium album. Holding the herbicides in spray solution for up to 7 days did not affect the efficacy of the post-emergence herbicides in this study. Similarly, control of A. retroflexus and C. album with the pre-emergence herbicides was not affected holding the herbicides in spray solution for up to 7 days. However, control of A. theophrasti was decreased when isoxaflutole plus atrazine, dimethenamid plus dicamba/atrazine, or rimsulfuron plus S-metolachlor plus dicamba was in spray solution for more than 1 day. Nonetheless, there were no decreases in yield for any of the treatments evaluated. These data provide valuable information which growers can use to make informed decisions on whether to apply herbicides in non-ideal weather or to postpone application. The results of this study suggest that for the herbicides and weed species tested it is better to postpone application rather than make applications under non-ideal conditions.