High-resolution mapping of the global silicate weathering carbon sink and its long-term changes.

Climatic and non-climatic factors affect the chemical weathering of silicate rocks, which in turn affects the CO2 concentration in the atmosphere on a long-term scale. However, the coupling effects of these factors prevent us from clearly understanding of the global weathering carbon sink of silicate rocks. Here, using the improved first-order model with correlated factors and non-parametric methods, we produced spatiotemporal data sets (0.25° × 0.25°) of the global silicate weathering carbon-sink flux (SCSFα ) under different scenarios (SSPs) in present (1950-2014) and future (2015-2100) periods based on the Global River Chemistry Database and CMIP6 data sets. Then, we analyzed and identified the key regions in space where climatic and non-climatic factors affect the SCSFα . We found that the total SCSFα was 155.80 ± 90 Tg C yr-1 in present period, which was expected to increase by 18.90 ± 11 Tg C yr-1 (12.13%) by the end of this century. Although the SCSFα in more than half of the world was showing an upward trend, about 43% of the regions were still showing a clear downward trend, especially under the SSP2-4.5 scenario. Among the main factors related to this, the relative contribution rate of runoff to the global SCSFα was close to 1/3 (32.11%), and the main control regions of runoff and precipitation factors in space accounted for about 49% of the area. There was a significant negative partial correlation between leaf area index and silicate weathering carbon sink flux due to the difference between the vegetation types. We have emphasized quantitative analysis the sensitivity of SCSFα to critical factors on a spatial grid scale, which is valuable for understanding the role of silicate chemical weathering in the global carbon cycle.

Limitations of soil moisture and formation rate on vegetation growth in karst areas.

Vegetation changes in karst areas are controlled by the soil formation rate (SFR) and soil moisture (SM). However, little is known about their thresholds and global control patterns. To this end, based on high-precision climate and vegetation data for 2000-2014, using Pearson correlation analysis, the Hurst index, and change-point analysis, the thresholds of the SFR and SM in vegetation growth in karst areas were identified. Furthermore, a spatial map (0.125° × 0.125°) of the global karst ecosystem with a static/dynamic limitation zone was established. We found that the net primary productivity (NPP) in 70% of the global climate zones exhibited a dual restriction relationship with the SM and SFR. The limitations of the SFR and SM in vegetation growth were most obvious in subpolar and semi-arid climates. In addition, their ecological thresholds were 25.2 t km-2 yr-1 and 0.28 m3 m-3, respectively. The static limitation of the SFR on the NPP in karst areas accounted for 28.37%, and the influence of the SM enhanced this limit (21.79%). The limitation of the SFR on vegetation was mainly concentrated in Boreal forests (17%), and the limitation of the SM was mainly concentrated in tropical savannas (12%). The NPP and the Normalized Difference Vegetation Index (NDVI) were the most sensitive to changes in the SM and SFR. Moreover, the analysis based on 14 ecologically limitation karst areas further revealed that the reduction in these factors may cause the tropical rain forest to experience degradation. It can be seen that the SM enhanced the limiting effect of the SFR on vegetation in karst areas. In short, this interpretation of karst vegetation limitations provides a deeper understanding of and approach to ecosystem evolution and vegetation restoration in these regions.

The responses of weathering carbon sink to eco-hydrological processes in global rocks.

Eco-hydrological processes affect the chemical weathering carbon sink (CS) of rocks. However, due to data quality limitations, the magnitude of the CS of rocks and their responses to eco-hydrological processes are not accurately understood. Therefore, based on Global Erosion Model for CO2 fluxes (GEM-CO2 model), hydrological site data, and multi-source remote sensing data, we produced a 0.05° × 0.05° resolution dataset of CS for 11 types of rocks from 2001 to 2018. The results show that the total amount of CS of global rocks is 0.32 ± 0.02 Pg C, with an average flux of 2.7 t C km-2 yr-1, accounting for 53% and 3% of the "missing" carbon sink and fossil fuel emissions, respectively. This is 23% higher than previous research results, which may be due to the increased resolution. Although about 60% of the CS of global rocks are in a stable state, there are obvious differences among rocks. For example, the CS of carbonate rocks exhibited a significant increase (0.30 Tg C/yr), while the CS of siliceous clastic sedimentary rocks exhibited a significant decrease (-0.06 Tg C/yr). Although temperature is an important factor affecting the CS, the proportion of soil moisture in arid and temperate climate zones is higher (accounting for 24%), which is 3.6 times that of temperature. Simulations based on representative concentration pathways scenarios indicate that the global CS of rocks may increase by about 28% from 2050 to 2100. In short, we produced a set of high-resolution datasets for the CS of global rocks, which makes up for the lack of datasets in previous studies and improves our understanding of the magnitude and spatial pattern of the CS and its responses to eco-hydrological processes.

Processes controlling programmed cell death of root velamen radicum in an epiphytic orchid.

BACKGROUND AND AIMS: Development of the velamen radicum on the outer surface of the root epidermis is an important characteristic for water uptake and retention in some plant families, particularly epiphytic orchids, for survival under water-limited environments. Velamen radicum cells derive from the primary root meristem; however, following this development, velamen radicum cells die by incompletely understood processes of programmed cell death (PCD). METHODS: We combined the use of transmission electron microscopy, X-ray micro-tomography and transcriptome methods to characterize the major anatomical and molecular changes that occur during the development and death of velamen radicum cells of Cymbidium tracyanum, a typical epiphytic orchid, to determine how PCD occurs. KEY RESULTS: Typical changes of PCD in anatomy and gene expression were observed in the development of velamen radicum cells. During the initiation of PCD, we found that both cell and vacuole size increased, and several genes involved in brassinosteroid and ethylene pathways were upregulated. In the stage of secondary cell wall formation, significant anatomical changes included DNA degradation, cytoplasm thinning, organelle decrease, vacuole rupture and cell wall thickening. Changes were found in the expression of genes related to the biosynthesis of cellulose and lignin, which are instrumental in the formation of secondary cell walls, and are regulated by cytoskeleton-related factors and phenylalanine ammonia-lyase. In the final stage of PCD, cell autolysis was terminated from the outside to the inside of the velamen radicum. The regulation of genes related to autophagy, vacuolar processing enzyme, cysteine proteases and metacaspase was involved in the final execution of cell death and autolysis. CONCLUSIONS: Our results showed that the development of the root velamen radicum in an epiphytic orchid was controlled by the process of PCD, which included initiation of PCD, followed by formation of the secondary cell wall, and execution of autolysis following cell death.