Spatial Variation in the Storages and Age-Related Dynamics of Forest Carbon Sequestration in Different Climate Zones—Evidence from Black Locust Plantations on the Loess Plateau of China

<div><p>Knowledge about the long-term influences of climate change on the amount of potential carbon (C) sequestration in forest ecosystems, including age-related dynamics, remains unclear. This study used two similar age-sequences of black locust forests (<i>Robinia pseudoacacia L</i>.) in the semi-arid and semi-humid zones of China’s Loess Plateau to assess the variation in C stocks and age-related dynamics. Our results demonstrated that black locust forests of the semi-humid zone stored significantly more C than did forests in the semi-arid zone, across the chronosequence (<i>p</i> < 0.001). The C carrying capacity of the plantations was measured at 166.4 Mg C ha⁻¹ (1 Mg = 10⁶ g) in the semi-humid zone, while the semi-arid zone had a capacity of only 79.4 Mg C ha⁻¹. Soil organic C (SOC) increased continuously with stand age in the semi-arid zone (R² = 0.84, <i>p</i> = 0.010). However, in the semi-humid zone, SOC declined sharply by 47.8% after the initial stage (5 to 10 y). The C stock in trees increased continuously with stand age in the semi-humid zone (R² = 0.83, <i>p</i> = 0.011), yet in the semi-arid zone, it decreased dramatically from 43.0 Mg C ha⁻¹ to 28.4 Mg C ha⁻¹ during the old forest stage (38 to 56 y). The shift from being a net C sink to a net C source occurred at the initial stage in the semi-humid zone versus at the old forest stage in the semi-arid zone after reforestation. Surprisingly, with the exception of the initial and later stages (55 y), the patterns of C allocation among trees, soils, understory and litter were not statistically different between the two climate zones. Our results suggest that climate factors can alter the potential amount and age-related dynamics of forest C sequestration.</p></div

Spatial variety of component C stocks between drier region and wetter region across the chronosequence.

<p>ANOVA test was conducted under <i>P</i> < 0.05, the bars represent standard deviation and the letters represent the significance of difference, no shrub was found at 5-y-old stand in drier zone and at 10-y-old stand in wetter zone, respectively.</p

Dynamics of C allocation of plantations in the drier zone and the wetter zone.

<p>The proportion was the ratio of the component’ C stock to the total ecosystem C stock, denoted by the values with standard errors between parentheses; <i>P</i> values represent the results of ANOVA on proportions between two sites at the similar forest ages, all the <i>P</i> values were conducted under 0.05 level.</p><p>§9/10, represents 9-y-old in the drier zone and 10-y-old in the wetter zone</p><p>♀DZ: drier zone</p><p>♂ WZ: wetter zone</p><p>⊕SBC: secondary biomass carbon, was constituted of shrubs, herbages, and leaf litters of plantation</p><p>Dynamics of C allocation of plantations in the drier zone and the wetter zone.</p

Details of the samplings in two sites.

<p>♀SW: southward</p><p>♂SSW: semi-southward</p><p>Details of the samplings in two sites.</p

Plasma-Assisted Synthesis of Self-Supporting Porous CoNPs@C Nanosheet as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

The utilization of a highly active and robust bifunctional catalyst for simultaneously producing H₂ and O₂ is still a major challenging issue, which is vital for improving the efficiency of overall water splitting. Herein, we employ a novel plasma-assisted strategy to rapidly and conveniently synthesize the three-dimensional (3D) porous composite nanosheets assembled on monodispersed Co nanoparticles encapsulated in a carbon framework (CoNPs@C) on a carbon cloth. Such a novel 3D hierarchical porous nanosheet improves the exposure and accessibility of active sites as well as ensures high electroconductibility. Moreover, the coating of a few graphene layers on the surface of catalysts favors improvement of the catalytic activity. Benefited from these multiple merits, the CoNPs@C composite nanosheets enable a low overpotential of 153 mV at −10 mA cm^–2 for hydrogen evolution reaction. Furthermore, they are also capable of catalyzing the oxygen evolution reaction with high efficiency to achieve current density of 10 mA cm^–2 at the overpotential of 270 mV. Remarkably, when assembled as an alkaline water electrolyzer, the bifunctional CoNPs@C composite nanosheets can afford a water-splitting current density of 10 mA cm^–2 at a cell voltage of 1.65 V