Appendix A. Effects of the five scenarios on labeled-N fractions in belowground plant biomass.

Effects of the five scenarios on labeled-N fractions in belowground plant biomass

Aging Induced Changes in Biochar’s Functionality and Adsorption Behavior for Phosphate and Ammonium

Biochar, a form of pyrogenic carbon, can contribute to agricultural and environmental sustainability by increasing soil reactivity. In soils, biochar could change its role over time through alterations in its surface chemistry. However, a mechanistic understanding of the aging process and its role in ionic nutrient adsorption and supply remain unclear. Here, we aged a wood biochar (550 °C) by chemical oxidation with 5–15% H₂O₂ and investigated the changes in surface chemistry and the adsorption behavior of ammonium and phosphate. Oxidation changed the functionality of biochar with the introduction of carboxylic and phenolic groups, a reduction of oxonium groups and the transformation of pyridine to pyridone. After oxidation, the adsorption of ammonium increased while phosphate adsorption decreased. Ammonium adsorption capacity was nonlinearly related to the biochar’s surface charge density (<i>r</i>² = 0.94) while electrostatic repulsion and loss of positive charge due to destruction of oxonium and pyridine, possibly caused the reduced phosphate adsorption. However, the oxidized biochar substantially adsorbed both ammonium and phosphate when biochar derived organic matter (BDOM) was included. Our results suggest that aging of biochar could reverse its capacity for the adsorption of cationic and anionic species but the inclusion of BDOM could increase ionic nutrient and contaminant retention

Full_Results_Mariotte

Full data used in the manuscript. Plant C, N and P. Soil N and P. Soil moisture. Mycorrhizal root colonisation. Plant biomass

The correlations between soil microbial biomass carbon (MBC) and soil temperature (a), and between MBC and soil water content (SWC, b).

<p>The correlations between soil microbial biomass carbon (MBC) and soil temperature (a), and between MBC and soil water content (SWC, b).</p

The ratio of soil microbial biomass carbon (MBC) to soil microbial biomass nitrogen (MBC/MBN) under different treatments (CK: control, B4.5: 4.5 t ha⁻¹ yr⁻¹ biochar addition, B9.0: 9.0 t ha⁻¹ yr⁻¹ biochar addition, SR: incorporation of wheat straw) and different soil depths (a: 0–5, b: 5–10, c: 10–20, and d: 20–30 cm) during winter wheat season.

<p>Vertical bars represent the standard errors for means of each treatment (<i>n</i> = 3).</p

Coefficients of seasonal variation of MBN under different treatments (%).

<p>Note: Different small letters indicate significant differences among treatments (CK: control, B4.5: 4.5 t ha⁻¹ yr⁻¹ biochar addition, B9.0: 9.0 t ha⁻¹ yr⁻¹ biochar addition, SR: incorporation of wheat straw) at the P<0.05 level (L.S.D.).</p

Microbial biomass carbon (MBC) under different treatments (CK: control, B4.5: 4.5 t ha⁻¹ yr⁻¹ biochar addition, B9.0: 9.0 t ha⁻¹ yr⁻¹ biochar addition, SR: incorporation of wheat straw) and different soil depths (a: 0–5, b: 5–10, c: 10–20, and d: 20–30 cm) during winter wheat season.

<p>Vertical bars represent the standard errors for means of each treatment (<i>n</i> = 3).</p

Coefficients of seasonal variation of MBC under different treatments (%).

<p>Note: Different small letters indicate significant differences among treatments (CK: control, B4.5: 4.5 t ha⁻¹ yr⁻¹ biochar addition, B9.0: 9.0 t ha⁻¹ yr⁻¹ biochar addition, SR: incorporation of wheat straw) at the P<0.05 level (L.S.D.).</p

Growing season carbon fluxes in response to global changes.

<p>Growing season sums (April–October, 2006–2010) for <b>A)</b> gross ecosystem production (P_eco), <b>B)</b> ecosystem respiration (R_eco) and heterotrophic respiration (Rh) inset white bars, and <b>C)</b> net ecosystem production (NEP) for control and global change treatments at the Prairie Heating and CO₂ Enrichment Experiment in Cheyenne, WY USA. Negative (–) values indicate C uptake and positive (+) values indicate C efflux. Treatment codes are: ct = ambient [CO₂] and temperature, cT = ambient [CO₂] and warming, Ct = elevated [CO₂] and ambient temperature, and CT = elevated [CO₂] and warming. Statistically significant main and interactive treatment effects (within a given year) along with p-values are indicated (n = 5 for all measurements).</p

Warming Reduces Carbon Losses from Grassland Exposed to Elevated Atmospheric Carbon Dioxide

<div><p>The flux of carbon dioxide (CO₂) between terrestrial ecosystems and the atmosphere may ameliorate or exacerbate climate change, depending on the relative responses of ecosystem photosynthesis and respiration to warming temperatures, rising atmospheric CO₂, and altered precipitation. The combined effect of these global change factors is especially uncertain because of their potential for interactions and indirectly mediated conditions such as soil moisture. Here, we present observations of CO₂ fluxes from a multi-factor experiment in semi-arid grassland that suggests a potentially strong climate – carbon cycle feedback under combined elevated [CO₂] and warming. Elevated [CO₂] alone, and in combination with warming, enhanced ecosystem respiration to a greater extent than photosynthesis, resulting in net C loss over four years. The effect of warming was to reduce respiration especially during years of below-average precipitation, by partially offsetting the effect of elevated [CO₂] on soil moisture and C cycling. Carbon losses were explained partly by stimulated decomposition of soil organic matter with elevated [CO₂]. The climate – carbon cycle feedback observed in this semiarid grassland was mediated by soil water content, which was reduced by warming and increased by elevated [CO₂]. Ecosystem models should incorporate direct and indirect effects of climate change on soil water content in order to accurately predict terrestrial feedbacks and long-term storage of C in soil.</p></div