Climatic determinants impacting the distribution of greenness in China: regional differentiation and spatial variability.

This study investigated climatic determinants for regional greenness in China and spatially variable correlations between climatic determinants and vegetation in specific regions using the geographical detector and geographically weighted regression (GWR) methodologies. The analyses were based on normalized difference vegetation index (NDVI) and interpolations of climatic determinants from 652 Chinese meteorological stations. The study period (1982-2013) was divided into two stages (T1-T2) before and after the inflection year identified by the accumulative anomaly of NDVI. Three typical regions (R1-R3) were then selected according to the same NDVI variation trend as China in the two periods. Precipitation was the dominant climatic factor of NDVI in China, and the effect of temperature on greenness increased with warming from T1 to T2. In a relatively arid region (R1), the effect of precipitation in T2 was further strengthened compared to T1. Meanwhile, the effect of minimum temperature in T2 also increased compared with T1 in a relatively humid region (R2), becoming the major climatic determinant. In addition to the regional differentiation, spatial variability was investigated by comparing normalized coefficients of GWR for climatic determinants; this showed significant spatial heterogeneity within each region. Temperature impact areas also existed within precipitation-dominated regions (R1 and R3), where areas of precipitation impact expanded from T1 to T2. Furthermore, regression coefficients between NDVI dynamics and climate variability revealed relationships between regional differentiation and spatial variability. For example, the increasing precipitation rate could mediate the adverse impacts on greenness caused by the higher warming rate in relatively arid regions (R1).

Carbon cycle responses to climate change across China's terrestrial ecosystem: Sensitivity and driving process.

Investigations into the carbon cycle and how it responds to climate change at the national scale are important for a comprehensive understanding of terrestrial carbon cycle and global change issues. Contributions of carbon fluxes to the terrestrial sink and the effects on climate change are still not fully understood. In this study, we aimed to explore the relationship between ecosystem production (GPP/SIF/NDVI) and net ecosystem carbon exchange (NEE) and to investigate the sensitivity of carbon fluxes to climate change at different spatio-temporal scales. Furthermore, we sought to delve into the carbon cycle processes driven by climate stress in China since the beginning of the 21st century. To achieve these objectives, we employed correlation and sensitivity analysis techniques, utilizing a wide range of data sources including ground-based observations, remote sensing observations, atmospheric inversions, machine learning, and model simulations. Our findings indicate that NEE in most arid regions of China is primarily driven by ecosystem production. Climate variations have a greater influence on ecosystem production than respiration. Warming has negatively impacted ecosystem production in Northeast China, as well as in subtropical and tropical regions. Conversely, increased precipitation has strengthened the terrestrial carbon sink, particularly in the northern cool and dry areas. We also found that ecosystem respiration exhibits heightened sensitivity to warming in southern China. Moreover, our analysis revealed that the control of terrestrial carbon cycle by ecosystem production gradually weakens from cold/arid areas to warm/humid areas. We identified distinct temperature thresholds (ranging from 10.5 to 13.7 °C) and precipitation thresholds (approximately 1400 mm yr-1) for the transition from production-dominated to respiration-dominated processes. Our study provides valuable insights into the complex relationship between climate change and carbon cycle in China.

Sequestration and Distribution Characteristics of Cd(II) by Microcystis aeruginosa and Its Role in Colony Formation.

To investigate the sequestration and distribution characteristics of Cd(II) by Microcystis aeruginosa and its role in Microcystis colony formation, M. aeruginosa was exposed to six different Cd(II) concentrations for 10 days. Cd(II) exposure caused hormesis in the growth of M. aeruginosa. Low concentrations of Cd(II) significantly induced formation of small Microcystis colonies (P < 0.05) and increased the intracellular polysaccharide (IPS) and bound extracellular polysaccharide (bEPS) contents of M. aeruginosa significantly (P < 0.05). There was a linear relationship between the amount of Cd(II) sequestrated by algal cells and the amount added to cultures in the rapid adsorption process that occurred during the first 5 min of exposure. After 10 d, M. aeruginosa sequestrated nearly 80% of 0.2 mg L-1 added Cd(II), while >93% of Cd(II) was sequestrated in the groups with lower added concentrations of Cd(II). More than 80% of the sequestrated Cd(II) was bioadsorbed by bEPS. The Pearson correlation coefficients of exterior and interior factors related to colony formation of M. aeruginosa revealed that Cd(II) could stimulate the production of IPS and bEPS via increasing Cd(II) bioaccumulation and bioadsorption. Increased levels of cross-linking between Cd(II) and bEPS stimulated algal cell aggregation, which eventually promoted the formation of Microcystis colonies.