Aboveground litter input is not important for soil microbes during the non-growing season

Macro- and microplastic accumulation in soil after 32 years of plastic film mulching

黑土地保护中不容忽视的一个问题：地膜残留及其污染

【目的】“黑土地保护”作为一项国家战略，已经写进我国“十四五”规划和“2035 年远景目标纲要”，中国科学院与东北三省政府签署了“黑土粮仓”科技会战框架协议，全力开展“黑土地保护”科技会战。当前“黑土地保护”科技攻关主要关注提升土壤有机质、降低土壤侵蚀、减少面源污染、推广保护性耕作等热点问题，而黑土地上地膜残留与污染已经日渐严重，需要引起社会各界的高度关注和重视【结果】从东北地区地膜应用及污染概况、地膜残留与污染的影响因素、地膜残留对黑土地农业的危害进行了综述，并提出黑土地地膜污染研究亟待开展的研究方向，包括：（1）摸清东北黑土地地膜残留的分布和数量；（2）明确残膜对作物/蔬菜等农产品安全的负面作用；（3）评价长期地膜覆盖对 土壤健康的影响程度。【结论】当前“黑土地保护”科技会战中，不能忽视东北地膜碎片（粒径大于 5 mm）及微塑料（小于 5 mm）的残留与污染问题。 【Objective】 “Black Soil Protection”, as a national strategy, was listed into China's the 14th Five-Year Plan and the Long-Range Objectives through 2035. Chinese Academy of Sciences signed the framework agreement of "Black Soil Granary" with the governments of Liaoning, Jilin and Heilongjiang provinces in Northeast China, to fight for black soil protection. At present, “Black Soil Protection” mainly focuses on soil organic matter, soil erosion, non-point source pollution, and conservation tillage. However, plastic film accumulation and pollution is becoming increasingly serious in black soils, which needs to be highly concerned. 【 Results】 This paper summarized the current situation of plastic film application and pollution in Northeast China, influencing factors of plastic film pollution, effects of plastic film residues on agriculture in black soils. The future research directions for plastic film accumulation and pollution are pointed: 1) to estimate the amount and distribution of plastic film residue accumulation in Northeast China; 2) to explicit the negative effect of plastic film residue on crop and vegetable safety; 3) to evaluate the effect of long-term effects of plastic film mulch on soil heath. 【 Conclusion】 Current national "Black Soil Protection" should not overlook plastic film accumulation and pollution.

Increased soil organic matter after 28 years of nitrogen fertilization only with plastic film mulching is controlled by maize root biomass

Belowground plant inputs exert higher metabolic activities and carbon use efficiency of soil nematodes than aboveground inputs

Soil nematodes are key components of soil food web and, through their metabolic activities, play a crucial role in soil carbon (C) cycling. Aboveground and belowground plant C inputs can directly, or indirectly via soil microbes, modify nematode abundance and community composition. Aboveground and belowground C inputs differ in chemical composition, amounts, and frequency, so we hypothesized that the two input pathways affect nematode communities differently. To assess the relative contributions of aboveground versus belowground inputs to nematode community composition and activity, we subjected grassland soils to four plant input pathways over two consecutive years: no input, only aboveground input (+A), only belowground input (+B), and both aboveground and belowground inputs (+A + B). Nematode metabolic footprints, as estimates of C used in growth/reproduction and C lost by respiration, and C use efficiency (C used/(C used + C lost)) were calculated. We predicted that soils with belowground inputs, which are more directly linked to the soil biota, and which contain a more labile blend of molecules, would support richer and more complex nematode communities, and also favor a bacterial-driven decomposition channel. Accordingly, we showed that + B soils supported higher nematode numbers than + A soils, and that the bacterial decomposition channel was dominant in + B soils, while the fungal decomposition channel dominated in + A soils. Compared with + A soils, +B input system increased nematode structure footprints (the metabolic footprints of nematodes in upper functional guilds) rather than enrichment footprints (the metabolic footprints of enrichment opportunistic nematodes). Moreover, we observed that, compared to + A soils, +B soils had higher growth and respiration rates of bacterivores, omnivores-predators, and total nematodes. Finally, we found higher C use efficiency values for omnivores-predators and total nematodes in + B than in + A soils. We thus conclude that belowground plant-derived resources, by changing the ratio between fungivores and bacterivores, induce a faster carbon turnover rate, and higher metabolic activity of soil nematodes within soil food web, ultimately spurring richer and more efficient soil food web than aboveground inputs.

Environmental impacts of agricultural plastic film mulch: Fate, consequences, and solutions

Crop residue decomposition and nutrient release are independently affected by nitrogen fertilization, plastic film mulching, and residue type

我国棉花主产区变化与地膜残留污染研究

目的】地膜覆盖是我国农业应用最为广泛的农艺技术之一，极大地促进了我国棉花产业的发展，推动了我国棉花主产区的变化。本文总结了我国棉花生产格局的变化特点，分析了地膜覆盖技术对我国棉花产业的影响，探讨了主要棉区农田土壤地膜残留污染特点和趋势。【方法】本研究采用了两种方法，一是实地调研，对我国主要棉区地膜应用和残留污染特点进行大范围采样，获取第一手数据，二是文献和统计数据收集，对过去几十年中与棉花地膜覆盖技术应用、数据进行整理归纳。【结果】研究结果显示，我国棉花的主产区也从过去的黄河和长江流域迁移到现在的西北内陆地区，其种植面积占全国的70%。新疆等西北内陆地区自1986年开始规模化应用地膜覆盖技术后，棉花单产（皮棉）快速上升，现在已经超过2000 kg/hm2，大幅度超过长江和黄河流域的棉花单产。同时，新疆棉区地膜覆盖应用所带来的残留污染已成为该区域农业可持续发展面临的一个重大问题，新疆连续10年和20年覆膜的棉田土壤中残膜量分别为259.7±36.78 kg/hm2和307.9±35.84 kg/hm2。【结论】因此，地膜覆盖是我国棉花生产格局变化的主要驱动力之一，对保持我国棉花生产的稳定至关重要，但同时棉田地膜残留污染非常严重，必须尽快研究棉田地膜残留污染的应对策略，实现地膜残留污染的有效防控。 [Objectives] Plastic film mulching (PFM) is one of the most widely applied agricultural technology in China, which changes cotton planting distribution and greatly improves the development of cotton industry in China. [Methods] In this study, two methods are adopted: one is large-scale field investigation in the main cotton planting region for plastic residue accumulation and pollution; The other is collection of relative literature and statistics data, and review and analysis the effect of PFM on cotton production in the past decades. [Results] Cotton yield increased sharply to today’s 2000 kg/hm2 in Xinjiang province after wide application of PFM technology, which is much larger than that in the Yangtze or Yellow River basin. Therefore, China’s main cotton planting area has migrated from previous Yangtze and Yellow River basin to today’s Northwest inland region. However, plastic film residue accumulation has become a serious problem and influence sustainable development of cotton industry. Plastic film residue accumulation were 259.7±36.78 kg/hm2和307.9±35.84 kg/hm2 in the soil after 10 and 20 years of PFM application in Xinjiang province, respectively. [Conclusions] Therefore, PFM technique will continue to play a key role to maintain the stability of cotton production, and plastic film pollution will be more and more serious in the future. We must take some powerful actions to control plastic residual pollution derived from PFM in China.

Does long-term use of biodegradable plastic mulch affect soil carbon stock?

Divergent above‐ and below‐ground biodiversity pathways mediate disturbance impacts on temperate forest multifunctionality

Agronomic performance of polyethylene and biodegradable plastic film mulches in a maize cropping system in a humid continental climate

Microbial assimilation dynamics differs but total mineralization from added root and shoot residues is similar in agricultural Alfisols

Opposite effects of nitrogen fertilization and plastic film mulching on crop N and P stoichiometry in a temperate agroecosystem

Aims Crop nitrogen (N) and phosphorus (P) stoichiometry can influence food nutritive quality and many ecosystem processes. However, how and why N and P stoichiometry respond to long-term agricultural management practices (e.g., N fertilization and film mulching) are not clearly understood. Methods We collected maize tissues (leaf, stem, root, and seed) and soil samples from a temperate cropland under 30- years continuous N fertilization and plastic film mulching treatments, measured their C, N, and P concentrations (the proportion (%) relative to the sample mass), and used structural equation models to uncover the responding mechanisms for crop N and P contents (the total amount (g/m 2) in crop biomass). Important findings Long-term nitrogen fertilization increased N concentrations in all crop tissues but sharply decreased P concentrations in vegetative tissues (leaf, stem, and root), thereby reducing their C/N ratio and increasing C/P and N/P ratios. The drop in P concentration in vegetative tissues was due to the dilution effect by biomass increment and the priority of P supply for seed production. In contrast, film mulching decreased N concentration but increased P concentrations in most crop tissues, thereby increasing C/N ratio and reducing C/P and N/P ratios. Film mulching increased crop P content by increasing soil temperature and moisture; whereas, mulching showed little effect on crop N content, because a positive effects of soil temperature may have canceled out a negative effect by soil moisture. This indicated a decoupling of P and N uptake by crops under film mulching. In conclusion, N fertilization and plastic film mulching showed opposite effects of on crop N and P stoichiometry.

Phytolith-Occluded Carbon Storages in Forest Litter Layers in Southern China: Implications for Evaluation of Long-Term Forest Carbon Budget

Phytolith-occluded carbon (PhytOC) can be preserved in soils or sediments for thousands of years and might be a promising potential mechanism for long-term terrestrial carbon (C) sequestration. As the principal pathway for the return of organic matters to soils, the forest litter layers make a considerable contribution to terrestrial C sequestration. Although previous studies have estimated the phytolith production fluxes in the above-ground vegetations of various terrestrial ecosystems, the storages of phytoliths and PhytOC in litter layers have not been thoroughly investigated, especially in forest ecosystems. Using analytical data of silica, phytoliths, return fluxes and storages of forest litter, this study estimated the phytolith and PhytOC storages in litter layers in different forest types in southern China. The results indicated that the total phytolith storage in forest litter layers in southern China was 24.34 ± 8.72 Tg. Among the different forest types, the phytolith storage in bamboo forest litter layers (15.40 ± 3.40 Tg) was much higher than that in other forests. At the same time, the total PhytOC storage reached up to 2.68 ± 0.96 Tg CO2 in forest litter layers in southern China, of which approximately 60% was contributed by bamboo forest litter layers. Based on the current litter turnover time of different forest types in southern China, a total of 1.01 ± 0.32 Tg of PhytOC per year would be released into soil profiles as a stable C pool during litter decomposition, which would make an important contribution to the global terrestrial long-term biogeochemical C sink. Therefore, the important role of PhytOC storage in forest litter layers should be taken into account in evaluating long-term forest C budgets.

Quantification of different silicon fractions in broadleaf and conifer forests of northern China and consequent implications for biogeochemical Si cycling

Net N2O production from soil particle size fractions and its response to changing temperature

Previous studies demonstrated that finer soil particles have smaller rates of CO2 emission but the larger Q10 values (the proportionate increase in the rate for a warming of 10 oC) than coarser particles. However, it has not been tested whether there is a regular pattern for rates and Q10 for N2O emission (net production) across soil particle size fractions, considering the known positive correlation between soil CO2 and N2O emissions. A short-term incubation study with different soil particle fractions was conducted for soils from a grassland, a forest, an upland (including organic manure (OM) and chemical nitrogen, phosphorus, and potassium fertilizers (NPK) treatments), and a paddy (including manure plus chemical fertilizer (MNPK) and NPK treatments) under a series of increasing and decreasing temperatures between 5°C and 30°C with 5°C intervals. For all the soils, net N2O production per unit mass of soil N was smaller from the silt (2–50 μm) fraction than from the sand (>50 μm) and clay (

Mineralization of plant residues and native soil carbon as affected by soil fertility and residue type

Crop residue return is an effective and low-cost agricultural approach for soil organic carbon (SOC) sequestration. Yet, it is largely unknown to what extent the soil fertility and residue type affect the mineralization of maize (Zea mays L.) residue carbon (C) and the decomposition of native SOC. Therefore, a better understanding of the mineralization of C derived from residues and it’s priming on native SOC is crucial to accurate assessment of the benefits of crop residue returning in agricultural systems. Materials and methods A 360-day laboratory incubation experiment was carried out with a Cambisol of low and high fertility amended with three types of 13C-labeled maize residues (root, stem, leaf). The abundance of 13C (δ13C) in the soil samples were measured during different incubation stages. Results and discussion The results showed that the total mineralization of residue C was significantly higher in the low fertility soil than in the high fertility soil, but there were no significant differences among residue types. For the high fertility soil, all the residue types induced a negative priming on native SOC mineralization during the early incubation stage, but a significant total positive priming by the end of incubation; whereas, for the low fertility soil, there was no significant effect of residue return on SOC mineralization. The accumulated priming by the end of incubation did not vary across residue types. Moreover, the sum of mineralization of residue C and native SOC in the high fertility soil was 1.4 times as large as that in the low fertility soil. Conclusions We conclude that mineralization of crop residue C and native SOC are affected by soil fertility rather than residue type.

Dynamics of maize straw residue 13C incorporation into aggregates of a Mollisol as affected by long-term fertilization

A meta-analysis and critical evaluation of influencing factors on soil carbon priming following biochar amendment

Previous studies have found biochar-induced effects on native soil organic carbon (NSOC) decomposition, with a range of positive, negative and no priming reported. However, many uncertainties still exist for which parameters driving the amplitude and the direction of the biochar priming. Materials and methods: We conducted a quantitative analysis of 1170 groups of data from 27 incubation studies using boosted regression trees (BRT). BRT is a machine learning method combining regression trees and a boosting algorithm, which can effectively partition independent influences of various factors on the target variable in the complex ecological processes. Results and discussion: The BRT model explained a total of 72.4% of the variation in soil carbon (C) priming following biochar amendment, in which incubation conditions (36.5%) and biochar properties (33.7%) explained a larger proportion than soil properties (29.8%). The predictors that substantially accounted for the explained variation included incubation time (27.1%) and soil moisture (5.0%), biochar C/N ratio (6.2%), nitrogen content (5.5%), pyrolysis time during biochar production (5.1%), biochar pH (4.5%), soil C content (5.2%), sand (4.7%) and clay content (4.1%). In contrast, other incubation conditions (temperature, biochar dose, whether nutrient addition), biochar properties (biochar C, feedstock type, ash content, pyrolysis temperature, whether biochar being activated), and soil properties (nitrogen content, silt content, C/N ratio, pH, land use type) had small contribution (each

The Impact of Afforestation on Soil Organic Carbon Sequestration on the Qinghai Plateau, China

Decomposition of Organic Carbon in Fine Soil Particles Is Likely More Sensitive to Warming than in Coarse Particles: An Incubation Study with Temperate Grassland and Forest Soils in Northern China

A synthesis of change in deep soil organic carbon stores with afforestation of agricultural soils

Changes in soil organic carbon and total nitrogen stocks after conversion of meadow to cropland in Northeast China