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With rapid economic growth and urbanization, self-sufficiency in crop production has become central to China's agriculture policy. Accurate crop production statistics are essential for research, monitoring, and planning. Although researchers agree that China's statistical authority has considerably modernized over time, China's economic statistics have still been viewed as unreliable and often overstated to meet growth targets at different administrative levels. Recent increases in crop production reported by national statistics have also come under increasing scrutiny. This paper investigates crop production data quality from a planetary boundary perspective--comparing net primary production (NPP) harvested obtained from national statistics with satellite-driven NPP estimates that are supported by detailed observation of land cover, combined with observations on physical factors that limit plant growth. This approach provides a powerful means to check the plausibility of China's grain production statistics at different administrative levels that can generate insights about their discrepancies and can contribute to improved crop production measurements. We find some evidence of potential misreporting problems from the lower administration level where the risk of manipulation of statistics is higher. We also find problems from provincial-level major grain producers. These values can also affect the national totals. Although the numbers are affected by large uncertainties, we find that improving the spatial resolution of key agricultural parameters can greatly improve the reliability of the indicator that in turn can help improve data quality. More reliable production data will be vital for relevant research and provide better insights into food security problems, the carbon cycle, and sustainable development. [ABSTRACT FROM AUTHOR]

Biological carbon pumping (BCP) is a key process in which dissolved inorganic carbon in terrestrial aquatic ecosystems is utilized by aquatic autotrophs for photosynthesis and transformed into autochthonous organic matter (AOC). However, the mechanisms underlying BCP and the amount of generated AOC deposited effectively, are still poorly understood. Therefore, we conducted a systematic study combining modern hydrochemical monitoring and a sediment trap experiment in Fuxian Lake (Yunnan, SW China), the second-deepest plateau, oligotrophic freshwater lake in China. Temperature, pH, EC (electrical conductivity), DO (dissolved O2), [HCO3−], [Ca2+], SIc, partial CO2 (pCO2) pressure, and carbon isotopic compositions of HCO3− (δ13CDIC) in water from Fuxian Lake all displayed distinct seasonal and vertical variations. This was especially apparent in an inverse correlation between pCO2 and DO, indicating that variations of hydrochemistry in the lake water were mainly controlled by the metabolism of the aquatic phototrophs. Furthermore, the lowest C/N ratios and highest δ13Corg were recorded in the trap sediments. Analyses of the C/N ratio demonstrated that the proportions of AOC ranged from 30% to 100% of all OC, indicating that AOC was an important contributor to sedimentary organic matter (OC). It was calculated that the AOC flux in Fuxian Lake was 20.43 t C km−2 in 2017. Therefore, AOC produced by carbonate weathering and aquatic photosynthesis could potentially be a significant carbon sink and may have an important contribution to solving the lack of carbon sinks in the global carbon cycle. [ABSTRACT FROM AUTHOR]

The carbon budgets in terrestrial ecosystems in China are strongly coupled with climate changes. Over the past decade, China has experienced dramatic climate changes characterized by enhanced summer monsoon and decelerated warming. However, the changes in the trends of terrestrial net ecosystem production (NEP) in China under climate changes are not well documented. Here, we used three ecosystem models to simulate the spatiotemporal variations in China's NEP during 1982–2010 and quantify the contribution of the strengthened summer monsoon and warming hiatus to the NEP variations in four distinct climatic regions of the country. Our results revealed a decadal-scale shift in NEP from a downtrend of –5.95 Tg C/yr2 (reduced sink) during 1982–2000 to an uptrend of 14.22 Tg C/yr2 (enhanced sink) during 2000–10. This shift was essentially induced by the strengthened summer monsoon, which stimulated carbon uptake, and the warming hiatus, which lessened the decrease in the NEP trend. Compared to the contribution of 56.3% by the climate effect, atmospheric CO2 concentration and nitrogen deposition had relatively small contributions (8.6 and 11.3%, respectively) to the shift. In conclusion, within the context of the global-warming hiatus, the strengthening of the summer monsoon is a critical climate factor that enhances carbon uptake in China due to the asymmetric response of photosynthesis and respiration. Our study not only revealed the shift in ecosystem carbon sequestration in China in recent decades, but also provides some insight for understanding ecosystem carbon dynamics in other monsoonal areas. [ABSTRACT FROM AUTHOR]

δ13C and D14C measurements on dissolved inorganic carbon (DIC), particulate organic carbon (POC) and aquatic plants from a karst spring and two spring-fed ponds in Laqiao, Maolan Township, Libo County, southeastern Guizhou of China in January, July and October of 2013 have been carried out to understand the roles of aquatic photosynthesis through DIC uptake in surface karst waters. The mean D14C and δ13C values of DIC for the spring, midstream pond (MP) and downstream pond (DP) are −26 ± 36‰ and −13 ± 2‰, 6 ± 56‰ and −12 ± 3‰, and 0 ± 64‰ and −9 ± 2‰, respectively. The carbon source for the DIC is mainly from biogenic CO 2 rather than the dissolution of limestone rock as the D14C and δ13C of limestone are about −1000‰ and 2‰, respectively. The enrichment trend of D14C DIC and δ13C DIC from the spring to the DP indicates CO 2 exchange between atmospheric CO 2 and DIC, because D14C and δ13C values of atmospheric CO 2 are ca. 50‰ and −8‰, respectively. The average D14C POC values in the spring, MP and DP were −325‰, −123‰ and −158‰, respectively, which are all lower than these of the DIC in each reservoir. The lower D14C values of the POC may be caused by older soil carbon from surface runoff and dust fall. More aquatic algae were formed through photosynthesis in the stream ponds, especially in summer, shown by strongly increased D14C POC and evidence of growth in EDS/SEM analyses. Furthermore, the D14C values of the submerged aquatic plants range from −153‰ to −26‰, reflecting that the aquatic plants used DIC for photosynthesis. The D14C value of an emergent plant which uses atmospheric CO 2 during photosynthesis is 52.5 ± 0.3‰, equivalent to the atmospheric D14C. Seasonal variations of D14C DIC and δ13C DIC are influenced by soil CO 2 input, primary productivity in the ponds, and CO 2 exchange; hydrochemical condition show lower D14C values but higher δ13C values in cold/dry season, and vice versa in summer rainy season. A simple mass balance calculation indicates ~90% of carbon for the spring DIC is from biogenic CO 2 , with higher contribution in summer due to higher productivity. Although this simple calculation may overestimate the biogenic CO 2 , it indicates that organic decomposition is a major carbon source for DIC in the karst hydrological system. The results of the present study have implications for 14C dating on aquatic plant remains, regional and perhaps global carbon budgets, and the different behaviors of 13C and 14C in karst systems. • The DIC carbon source of the karst spring is mainly from biogenic CO2. • 13C and 14C tracing C source and transformation including photosynthesis CO 2 uptake • Aquatic plants uptake DIC CO 2 may cause an older 14C age. • Biological pump effect in terrestrial water can be an important natural carbon sink. [ABSTRACT FROM AUTHOR]