No abstract

The Grain to Green Program in China which began in 1999 led to the conversion of 0.64 million ha of cropland to grassland on steep sloping landscapes. However, the pattern of natural vegetation succession following cropland has not been well represented in previous regional syntheses of land use change effects on soil organic carbon (SOC). A chronosequence study focusing on the vegetation succession and soil carbon stocks was conducted in the center of the Loess Plateau. The chronosequence included fields of 0, 2, 5, 8, 9, 10, 12, 15 and 25 years of self‐restoration after cropland abandonment, as well as a natural grassland reference. Plant coverage, species richness and plant biomass increased significantly with time of cropland abandonment. Over time, the species composition more nearly resembled a natural grasslands community. Cropland abandonment replenished SOC stocks by 3.6 kg C m−2 during the 25‐year self‐restoration, but the SOC accumulation was restricted to the upper soil profiles (0–60 cm). SOC accumulation rate was 88 g C m−2 y−1 in 0–30 cm and 55 g C m−2 y−1 in 30–60 cm soil depth, respectively. These carbon stocks were still significantly lower than those found in the natural grassland soil. Our results suggest that the recovery of plant communities and SOC stocks appears to be slow in this semiarid environment without revegetation effort along with appropriate field management, although the post‐agricultural soils have a high potential for carbon sequestration. Copyright © 2016 John Wiley & Sons, Ltd.

Although afforestation of nitrogen‐fixing shrubs, especially Caragana korshinskii in semiarid areas, is expected to improve ecosystem restoration and carbon sequestration, water shortage induced by these thirsty shrubs may negate potential benefits. Yet there is poor understating of the persistence of soil carbon sequestration in nitrogen‐fixing shrub plantations. Here, we selected three C. korshinskii plantations with different ages (10, 20, and 30 years) on the Loess Plateau to evaluate the persistence of soil carbon sink. We examined dynamics of soil carbon, total nitrogen, and soil water, as well as their relationships along the plantation ages. The results showed that soil organic carbon (SOC) and soil total nitrogen (STN) were tightly coupled. SOC, STN, and soil water stocks (0–100 cm) were significantly decreased by 23.9%, 19.9%, and 29.2% from 10 to 30 years, respectively. The reduction of SOC and STN was likely caused by lowered intercanopy herbaceous productivity due to soil drying and intensified competition from shrubs. We present evidence that the positive carbon sequestration by afforestation of leguminous shrub in short term may be further weakened by water shortage, making our ability to restore degraded land in semiarid regions more challenging than previously thought. Therefore, it is essential to improve management of afforestation land such as thinning for maintaining SOC sequestration persistently in water‐limited areas.

As interconnects continue to scale, enabling faster device speed and lower power consumption by reducing the κ value (capacitance) of each insulating dielectric layer becomes more imperative. Low-κ dielectrics are exposed to many process steps in fabricating a multiple-metal-layer structure, and must then withstand the stresses of packaging and assembly. The Applied Producer ® Onyx™ chamber is a newly-developed chamber for κ repair treatment in logic devices at 28 nm and beyond. The novel Onyx process and its mechanism are discussed by FTIR analysis. K repair and RC improvement are also demonstrated.

This paper addresses refractive index (n), extinction coefficient (k), uniformity, and step coverage of APFx film, which can be optimized by varying process parameters, such as precursor flow rate, spacing, chamber pressure, and power. APFx shows good uniformity. APFx has a lower extinction coefficient at 633nm, which makes possible easier alignment. Moreover, APFx has good step coverage and a wide tuning range of conformality, which improves film integrity for photoresist rework.