Priming effects on labile and stable soil organic carbon decomposition: Pulse dynamics over two years.

Soil organic carbon (SOC) is a major component in the global carbon cycle. Yet how input of plant litter may influence the loss of SOC through a phenomenon called priming effect remains highly uncertain. Most published results about the priming effect came from short-term investigations for a few weeks or at the most for a few months in duration. The priming effect has not been studied at the annual time scale. In this study for 815 days, we investigated the priming effect of added maize leaves on SOC decomposition of two soil types and two treatments (bare fallow for 23 years, and adjacent old-field, represent stable and relatively labile SOC, respectively) of SOC stabilities within each soil type, using a natural 13C-isotope method. Results showed that the variation of the priming effect through time had three distinctive phases for all soils: (1) a strong negative priming phase during the first period (≈0-90 days); (2) a pulse of positive priming phase in the middle (≈70-160 and 140-350 days for soils from Hailun and Shenyang stations, respectively); and (3) a relatively stabilized phase of priming during the last stage of the incubation (>160 days and >350 days for soils from Hailun and Shenyang stations, respectively). Because of major differences in soil properties, the two soil types produced different cumulative priming effects at the end of the experiment, a positive priming effect of 3-7% for the Mollisol and a negative priming effect of 4-8% for the Alfisol. Although soil types and measurement times modulated most of the variability of the priming effect, relative SOC stabilities also influenced the priming effect for a particular soil type and at a particular dynamic phase. The stable SOC from the bare fallow treatment tended to produce a narrower variability during the first phase of negative priming and also during the second phase of positive priming. Averaged over the entire experiment, the stable SOC (i.e., the bare fallow) was at least as responsive to priming as the relatively labile SOC (i.e., the old-field) if not more responsive. The annual time scale of our experiment allowed us to demonstrate the three distinctive phases of the priming effect. Our results highlight the importance of studying the priming effect by investigating the temporal dynamics over longer time scales

Thermostable Microspheres Consisting of Poly(<i>N</i>‑phenylmaleimide-<i>co</i>-α-methyl styrene) Prepared by Precipitation Polymerization

General polymeric microspheres are not satisfactorily thermostable. This article reports on an unprecedented type of poly­(<i>N</i>-phenylmaleimide-<i>co</i>-α-methyl styrene) [denoted as poly­(<i>N</i>-PMI-<i>co</i>-AMS)] microspheres showing remarkable thermal stability. The microspheres were prepared by free-radical precipitation polymerization in a solvent mixture consisting of methyl ethyl ketone (favorable solvent) and heptane (unfavorable solvent). Microspheres of good morphology and narrow size distribution were obtained in high yield (>85%) under appropriate conditions. Growth of poly­(<i>N</i>-PMI-<i>co</i>-AMS) microspheres was characterized by scanning electron microscopy. The microspheres, although without cross-linking, exhibited excellent thermal stability, and their decomposition temperature was up to about 370 °C. This feature cannot be achieved in typical polymeric microspheres. Also, notably, this is the first precipitation polymerization of maleimide and AMS and their derivatives for preparing microspheres. The present novel microspheres are expected to find practical applications as novel heat-resistant additives, solid carriers for catalysts, and so on

Variation in δ¹³C values of respired CO₂-C for soils with or without maize leaves amendment taken from old-field and bare fallow treatment at Hailun (left) and Shenyang (right) station throughout the 815-day incubation.

<p>Error bars show ±1 SE.</p

Characteristics of the soils and the maize leaves used in the experiment.

<p>Different letters indicate significant (P<0.05) differences in soil properties between old-field and bare fallow soils from the same site.</p

PE (priming effects, instantaneous rate, μg C g^-1 soil d^-1) of added maize leaves on SOC decomposition of soils from Hailun (left) and Shenyang (right) station.

<p>The inserts show the priming effect starting at day-90 when most treatments started to show a positive priming effect. The running average was obtained using Adjacent-Average method (OriginPro 8.5).</p

The contribution (%) of SOC-derived CO₂ to total decomposition of old-field and bare fallow soils from Hailun (left) and Shenyang (right) station when amended with maize leaves.

<p>Error bars show ±1 SE.</p

Cumulative PE (priming effects, mg C g^-1 soil) of added maize on SOC decomposition of old-field (triangle and solid line) and bare fallow (circle and dotted line) soils from Hailun (left) and Shenyang (right) station during 815 days incubation.

<p>Error bars show ±1 SE.</p

The dynamic CO₂ trapping system for accurately measuring soil respiration and δ¹³C of respired CO₂.

<p>The dynamic CO₂ trapping system for accurately measuring soil respiration and δ¹³C of respired CO₂.</p