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A drinking water distribution system (DWDS) is the final and essential step to supply safe and high-quality drinking water to customers. Biological processes, such as biofilm formation and detachment, microbial growth in bulk water, and the formation of loose deposits, may occur. These processes will lead to deterioration of the water quality during distribution. In extreme conditions, pathogens and opportunistic pathogens may proliferate and pose a health risk to consumers. It is, therefore, necessary to understand the bacteriology of DWDSs to develop effective strategies that can ensure the water quality at consumers' taps. The bacteriology of DWDSs, both the quantitative growth and the qualitative bacterial community, has attracted considerable research attention. However, the researchers have focused mainly on the pipe wall biofilm. In this review, DWDS bacteriology has been reviewed multidimensionally, including both the bacterial quantification and identification. For the first time, the available literature was reviewed with an emphasis on the subdivision of DWDS into four phases: bulk water, suspended solids, loose deposits, and pipe wall biofilm. Special concentration has been given to potential contribution of particulate matter: suspended particles and loose deposits. Two highlighted questions were reviewed and discussed: (1) where does most of the growth occur? And (2) what is the contribution of particle-associated bacteria to DWDS bacteriology and ecology? At the end of this review, recommendations were given based on the conclusion of this review to better understand the integral DWDS bacteriology.

Biochar application to croplands has been proposed as a potential strategy to decrease losses of soil-reactive nitrogen (N) to the air and water. However, the extent and spatial variability of biochar function at the global level are still unclear. Using Random Forest regression modelling of machine learning based on data compiled from the literature, we mapped the impacts of different biochar types (derived from wood, straw, or manure), and their interactions with biochar application rates, soil properties, and environmental factors, on soil N losses (NH 3 volatilization, N 2 O emissions, and N leaching) and crop productivity. The results show that a suitable distribution of biochar across global croplands (i.e., one application of <40 t ha −1 wood biochar for poorly buffered soils, such as those characterized by soil pH<5, organic carbon<1%, or clay>30%; and one application of <80 t ha −1 wood biochar, <40 t ha −1 straw biochar, or <10 t ha −1 manure biochar for other soils) could achieve an increase in global crop yields by 222~766 Tg yr −1 (4%~16% increase), a mitigation of cropland N 2 O emissions by 0.19~0.88 Tg N yr −1 (6%~30% decrease), a decline of cropland N leaching by 3.9~9.2 Tg N yr −1 (12%~29% decrease), but with a fluctuation of cropland NH 3 volatilization by −1.9~4.7 Tg N yr −1 (−12%~31% change). The decreased sum of the three major reactive N losses amount to 1.7~9.4 Tg N yr −1 , which corresponds to 3%~14% of the global cropland total N loss. Biochar generally has a larger potential for decreasing soil N losses but with less benefits to crop production in temperate regions than in tropical regions. K E Y W O R D S biochar, machine learning, N leaching, N 2 O, NH 3 , spatial variability S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Liu Q, Liu B, Zhang Y, et al. Biochar application as a tool to decrease soil nitrogen losses (NH 3 volatilization, N 2 O emissions, and N leaching) from croplands: Options and mitigation strength in a global perspective. Glob

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Over time, the relative effects of elevated [CO 2 ] on the aboveground photosynthesis, growth and development of rice (Oryza sativa L.) are likely to be changed with increasing duration of CO 2 exposure, but the resultant effects on rice belowground responses remain to be evaluated. To investigate the impacts of elevated [CO 2 ] on seasonal changes in root growth, morphology and physiology of rice, a free-air CO 2 enrichment (FACE) experiment was performed at Wuxi, Jiangsu, China, in 2002-2003. A japonica cultivar with large panicle was exposed to two [CO 2 ] (ambient [CO 2 ], 370 lmol mol À1 ; elevated [CO 2 ], 570 lmol mol À1 ) at three levels of nitrogen (N): low (LN, 15 g N m À2 ), medium (MN, 25 g N m À2 ) and high N (HN, 35 g N m À2 ). Elevated [CO 2 ] increased cumulative root volume, root dry weight, adventitious root length and adventitious root number at all developmental stages by 25-71%, which was mainly associated with increased root growth rate during early growth period (EGP) and lower rate of root senescence during late growth period (LGP), while a slight inhibition of root growth rate occurred during middle growth period (MGP). For individual adventitious roots, elevated [CO 2 ] increased average length, volume, diameter and dry weight early in the season, but the effects gradually disappeared in subsequent stages. Total surface area and active adsorption area per unit root dry weight reached their maxima 10 days earlier in FACE vs. ambient plants, but both of them together with root oxidation ability per unit root dry weight declined with elevated [CO 2 ] during MGP and LGP, the decline being larger during MGP than LGP. The CO 2 -induced decreases in specific root activities during MGP and LGP were associated with a larger amount of root accumulation during EGP and lower N concentration and higher C/N ratio in roots during MGP and LGP in FACE vs. ambient plants. The results suggest that most of the CO 2 -induced increases in shoot growth of rice are similarly associated with increased root growth.

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