Positive feedback of elevated CO₂ on soil respiration in late autumn and winter

Soil respiration of terrestrial ecosystems, a major component in the global carbon cycle is affected by elevated atmospheric CO2 concentrations. However, seasonal differences of feedback effects of elevated CO2 have rarely been studied. At the Gießen Free-Air CO2 Enrichment (GiFACE) site, the effects of +20% above ambient CO2 concentration have been investigated since 1998 in a temperate grassland ecosystem. We defined five distinct annual seasons, with respect to management practices and phenological cycles. For a period of 3 years (2008–2010), weekly measurements of soil respiration were carried out with a survey chamber on vegetation-free subplots. The results revealed a pronounced and repeated increase of soil respiration under elevated CO2 during late autumn and winter dormancy. Increased CO2 losses during the autumn season (September–October) were 15.7% higher and during the winter season (November–March) were 17.4% higher compared to respiration from ambient CO2 plots. However, during spring time and summer, which are characterized by strong above- and below-ground plant growth, no significant change in soil respiration was observed at the GiFACE site under elevated CO2. This suggests (1) that soil respiration measurements, carried out only during the growing season under elevated CO2 may underestimate the true soil-respiratory CO2 loss (i.e. overestimate the C sequestered), and (2) that additional C assimilated by plants during the growing season and transferred below-ground will quickly be lost via enhanced heterotrophic respiration outside the main growing season

Responses of a Grassland Ecosystem to 17 Years of Free-air CO2 Enrichment

AbstractGrasslands comprise 70% of all agricultural land worldwide, and provide fodder for life-stock and besides being habitats for flora and wildlife, they contain large carbon and nitrogen stocks. Elevated CO2 concentrations usually increase plant growth in the short-term, particularly in well- fertilized and irrigated crops. Furthermore, plant tissue nutrient concentrations decrease and the subsequent increase in the CN ratio is assumed to be a symptom of a “progressive nitrogen limitation” (PNL), which is still under debate since long-term FACE experiments are scarce.The Giessen FACE experiment started in a N-limited, species-rich grassland ecosystem near Giessen, Germany in 1998. The CO2 concentration was enriched (eCO2) +20% above ambient (aCO2) year-round during daylight hours. Biomass was harvested twice: in spring and late summer, sorted into the functional groups grasses, forbs and legumes, and the plant material was analyzed (Inductively Coupled Plasma Mass Spectrometer ICP–MS and MS) for N and other nutrients.Biomass of grasses was increased by elevated CO2 during the whole 17 years (1998-2014) indicating that dominant grasses react quickly to elevated CO2, while biomass of forbs was first smaller under elevated CO2 until 2007, and then became larger at eCO2 from 2008 to 2014.Elemental concentrations (Ca, Mg, S, N) were decreased by elevated CO2 in grasses, forbs and legumes. However, K and Zn concentrations in forbs and Mn in legumes increased under elevated CO2. During the first 11 years (1998-2008), the removed net N pool with the harvested biomass, was identical under elevated and ambient CO2 conditions, revealing increased N use efficiency under elevated CO2. Weather conditions (extreme summers) should also be taken into account to better understand the mechanisms of long-term biomass response.Our preliminary conclusions are (1) the increasing yield response over time does not support PNL in N-limited grassland, (2) co-existing functional plant groups have different response patterns

Serum antibodies against CD28-- a new potential marker of dismal prognosis in melanoma patients.

BACKGROUND: Autoantibodies against CD28 have been found in patients with autoimmune and atopic diseases. These antibodies may act as superagonists and activate T cells but may also be antagonistic or induce immunosuppressive effects by activating regulatory T cells. Autoimmunity in melanoma patients has been discussed controversially. OBJECTIVE: We investigated 230 melanoma patients for the occurrence of CD28 antibodies and the effect of the latter on overall and progress-free survival. METHODS: We constructed an ELISA assay to measure CD28 serum antibodies. 230 patients with melanoma and a control-group of 625 patients consistent of 212 patients with virus hepatitis b or c, 149 patients with allergies, 78 patients with psoriasis, 46 patients with plasmocytoma and 140 healthy blood donors were investigated for the occurrence of CD28 antibodies. RESULTS: CD28 abs occur at a higher percentage in patients with melanoma and in patients with viral hepatitis than in other groups investigated (p<0.001). Occurrence of CD28 abs is significantly higher in patients receiving interferons independent from the underlying disease (p<0.001). In vitro CD28 serum antibodies have an inhibitory effect on the CD28 receptor as they lead to reduced stimulation of Jurkat cells. Presence of CD28 was correlated with a higher risk of dying from melanoma (p = 0.043), but not with a significantly shortened overall survival or progression-free survival. CONCLUSION: Interferon therapy appears to induce the production of CD28 abs. In light of reports that these CD28 abs induce immunosuppressive Tregs and - as our data show - that they are inhibitors of CD28 receptor mediated stimulation, the continuation of therapies with interferons in melanoma patients developing CD28 antibodies should be critically reconsidered, since our data indicate a worse outcome of patients with CD28 abs

Seroconversion with progress of disease.

<p>CD28 abs measured in one female patient during a period of more than 10 years in association with the course of the disease.</p

CD28 abs and death risk, overall survival and progress-free survival. CD28 abs and death risk

<p>(<b>A</b>). Distribution of patients with or without CD28 abs according to whether patients died from melanoma or not (p = 0.043, chi-square test), n = 230; <b>CD28 abs and overall survival</b> (<b>B</b>). Kaplan-Meier curve showing correlation between overall survival and occurrence of CD28 abs in melanoma patients (p = 0.559, Log-rank test), n = 230; <b>CD28 abs and progress-free survival</b> (<b>C</b>). Kaplan-Meier curve showing correlation between progress-free survival and occurrence of CD28 abs in melanoma patients (p = 0.952, Log-rank test), n = 230.</p

Analysis of recombinant CD28 expression in HEK cells.

<p>(A) Coimmunoprecipitation. Recombinant HEK cells were lysed with lysis buffer, and 200–500 µl of cell lysate was incubated with rabbit αFLAG antibody at 4°C for 2 hours, then 20 µl of protein A agarose slurry (GE Healthcare) was added for another 2 hours. The beads were washed three times with at least 10 volumes of lysis buffer before resolving by SDS-PAGE. Detection was done either with mouse αFLAG or mouse αCD28. As control HEK293-SLP2-FLAG was used. 1: HEK293 lysate, 2: HEK293-CD28-FLAG lysate, HEK293-SLP2-FLAG lysate. (B) Westernblot. Cells were lysed and analysed by immunoblot using αFLAG or αCD28 antibodies. 1: HEK293 lysate, 2: HEK293-CD28-FLAG lysate (C) Elisa. Recombinant CD28 is recognized by a commercial αCD28 mAb. HEK293-CD28-FLAG lysate is coated on NUNC maxisorp via FLAG-tag. Detection was done with 1: αCD30 or 2: αCD28.</p