Effects of continuous nitrogen addition on microbial properties and soil organic matter in a Larix gmelinii plantation in China

Continuous increases in anthropogenic nitrogen（N） deposition are likely to change soil microbial properties, and ultimately to affect soil carbon（C） storage.Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch（Larix gmelinii） plantation. In a 9-year experiment in the plantation, N was applied at100 kg N ha-1 a-1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However,soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However,microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, d13 C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition（1） altered microbial biomass and activity without affecting soil C in light fractions and（2） resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.

Variation patterns of fine root biomass, production and turnover in Chinese forests

China's forests cover 208.3 million ha and span a wide range of climates and a large variety of forest types, including tropical, temperate, and boreal forests. However, the variation patterns of fine root (< 2 mm in diameter) biomass, production, and turnover from the south to the north are unclear. This study summarizes fine root biomass (FRB), production (FRP) and turnover rate (FRT) in China's forests as reported by 140 case studies published from 1983 to 2014. The results showed that the mean values of FRB, FRP and FRT in China's forests were 278 g m(-2), 366 g m(-2) a(-1), and 1.19 a(-1), respectively. Compared with other studies at the regional or global scales, FRB in China's forests was lower, FRP was similar to estimates at the global scale, but FRT was much higher. FRB, FRP, and FRT in China's forests increased with increasing mean annual precipitation (MAP), indicating that fine root variables were likely related to MAP, rather than mean annual temperature or latitude. This is possibly due to the small variation in temperature but greater variation in precipitation during the growing season. These findings suggest that spatiotemporal variation in precipitation has a more profound impact on fine root dynamics in China's forests, and this will impact carbon and nutrient cycles driven by root turnover in the future.

Nutrient retranslocation from the fine roots of Fraxinus mandshurica and Larix olgensis in northeastern China

Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash （Fraxinus mandshurica） and a Larch （Larix olgensis） plantation in northeastern China. Nutrient retranslocation in the fine roots was investigated using three methods, specifically, nutrient concentration, the ratio of Ca to other elements （Ca/other elements ratio） and nutrient content. The method based on nutrient content proved most suitable when investigating nutrient retranslocation from fine roots of the two species. The nutrient-content-based method showed that there were retranslocations of N, P, K and Mg from the fine roots of Manchurian Ash, with retranslocation efficiencies of 13, 25, 65, and 38 %, respectively, whereas there were no Ca retranslocations. There were retranslocations of N, P, K, Ca and Mg from the fine roots of Larch, with retranslocation efficiencies of 31, 40, 52, 23 and 25 %, respectively.

AI及大数据技术在逆合成路线设计中的应用

随着化学信息学以及人工智能技术的发展,计算机辅助合成路线设计已开始崭露头角.早期逆合成的预测主要依赖人工定义的专家规则,近年来依赖数据驱动的人工智能模型取得诸多进展,不少工具已经应用在现今化学合成的实际工作中.本文就目前AI算法在逆合成路线设计中的应用展开系统的综述,主要论述逆合成所涉及的三个重要组成部分,包括用于存储与表征化学信息的技术、单步逆合成反应的预测模型与算法和合成路线的多步策略.最后还介绍了如今比较成熟的逆合成设计平台以及模型评价方法,从而能更系统地了解到逆合成系统的构成以及目前所面临的一些挑战.

Estimation of fine root production, mortality and turnover with Minirhizotron in Larix gmelinii and Fraxinus mandshurica plantations

Fine root turnover is a major pathway for carbon and nutrient cycling in forest ecosystems.However,to estimate fine root turnover,it is important to first understand the fine root dynamic processes associated with soil resource availability and climate factors.The objectives of this study were:(1)to examine patterns of fine root production and mortality in different seasons and soil depths in the Larix gmelinii and Fraxinus mandshurica plantations,(2)to analyze the correlation of fine root production and mortality with environmental factors such as air temperature,precipitation,soil temperature and available nitrogen,and(3)to estimate fine root turnover.We installed 36 Minirhizotron tubes in six monospecific plots of each species in September 2003 in the Mao’ershan Experimental Forest Station.Minirhizotron sampling was conducted every two weeks from April 2004 to April 2005.We calculated the average fine root length,annual fine root length production and mortality using image data of Minirhizotrons,and estimated fine root turnover using three approaches.Results show that the average growth rate and mortality rate in L.melinii were markedly smaller than in F.mandshurica,and were highest in the surface soil and lowest at the bottom among all the four soil layers.The annual fine root production and mortality in F.mandshurica were significantly higher than in L.gmelinii.The fine root production in spring and summer accounted for 41.7% and 39.7% of the total annual production in F.mandshurica and 24.0% and 51.2% in L.gmelinii.The majority of fine root mortality occurred in spring and summer for F.mandshurica and in summer and autumn for L.gmelinii.The turnover rate was 3.1 a^(-1) for L.gmelinii and 2.7 a^(-1) for F.mandshurica.Multiple regression analysis indicates that climate and soil resource factors together could explain 80% of the variations of the fine root seasonal growth and 95%of the seasonal mortality.In conclusion,fine root production and mortality in L.gmelinii and F.mandshurica have different patterns in different seasons and at different soil depths.Air temperature,precipitation,soil temperature and soil available nitrogen integratively control the dynamics of fine root production,mortality and turnover in both species.

Comparison of soil chemical and microbial properties in monoculture larch and mixed plantations in a temperate forest ecosystem in Northeast China

Background:The introduction of broadleaved tree species in monoculture larch plantations to establish mixed plantations is a feasible way to improve soil properties.However,our understanding of how mixed plantations of larch and broadleaved tree species affect soil properties,particularly microbial community structures and functions,remains limited.We compared three paired monoculture larch(Larix gmelinii)and mixed[L.gmelinii–Fraxinus mandshurica(a dominant broadleaved species)]plantations to investigate the effect of a larch–broadleaved tree species combination on the carbon(C)and nitrogen(N)content,abundance and composition of microbial communities,and enzyme activities associated with litter and soil.Results:The bacterial abundance in the litter,soil N availability,pH and electronic conductivity were significantly higher in the mixed-species plantation in comparison with those of the monoculture plantation.However,in the litter of mixed-species plantation,the relative levels of Agaricomycetes fungi were lower than those of the monoculture plantation,indicating that soil fungal communities were affected more than bacterial communities.In contrast,soil in the mixed-species plantation showed increased exoglucanase and N-acetyl-β-glucosaminidase activities.However,the C and N levels,δ^(13)C andδ^(15)N values,and fungal abundance in litter and soil were not significantly different between the monoculture and mixed-species plantations.Conclusions:Our findings suggest that fungal community compositions and enzyme activities are sensitive to the introduction of broadleaved tree species into larch plantations.Thus,these parameters can be used as important indicators to evaluate the effects of tree species selection on soil restoration.