Specific Responses of Soil Microbial Residue Carbon to Long-Term Mineral Fertilizer Applications to Reddish Paddy Soils

Mineral nutrient inputs to soil may alter microbial activity and consequently influence the accumulation of microbial residues. In this study, we investigated the effects of application rates and ratios of mineral fertilizers on the microbial residue carbon(MRC) of reddish paddy soils after long-term(15-year) fertilizer applications in southern China. Contents of three soil amino sugars as microbial residue contents were determined and MRC were calculated based on amino sugars. Results showed that three individual amino sugar contents increased as fertilizer application rates increased until maximum values were reached at a rate of 450-59-187 kg ha~(-1) year~(-1)(N-P-K). The three amino sugar contents then declined significantly under the highest mineral fertilizer application rate of 675-88-280 kg ha~(-1) year~(-1)(N-P-K). In addition, to enhance the microbial residue contents, it was more beneficial to double P(N:P:K= 1:0.26:0.41) in fertilizers applied to the P-deficient reddish paddy soils than to double either N(N:P:K = 2:0.13:0.41) or K(N:P:K= 1:0.13:0.82). The contents of the three individual amino sugars and microbial residues under different fertilizer application rates and ratios were significantly and positively correlated with soil organic carbon(SOC), total N, total P, and p H. Increases in values of the fungal C to bacterial C ratios showed that soil organic matter(SOM) stability increased because of the fertilizer applications over the past 15 years. The contents and ratios of amino sugars can be used as indicators to evaluate the impact of mineral fertilizer applications on SOM dynamics in subtropical paddy soils. The results indicated that fertilizer applications at a rate of 450-59-187 kg ha~(-1) year~(-1)(N-P-K) may improve crop yields, SOC contents, and SOC stability in subtropical paddy soils.     

Nitrogen Mineralization as Influenced by Different Organic Manures in an Inceptisol in the Foothill Himalayas

Nitrogen-use efficiency can be enhanced through an understanding of the nitrogen (N) mineralization behavior of organic sources. An incubation study was conducted to assess the impact of organic manures on N mineralization. The manures, farmyard manure (FYM), Leucaena leucocephala, and poultry manure, were applied to the soil alone or along with urea. There was a rapid increase in the amount of mineral N released with a peak appearing either at 14 days (+urea treatments) or 21 days (manure only) of aerobic incubation. Thereafter the net N mineralized decreased gradually and levelled off beyond day 56. Overall the cumulative net N mineralized after 98 days of incubation was in the order urea > Leucaena + urea > poultry manure + urea _> FYM + urea > Leucaena > poultry manure > FYM > zero N. The potentially mineralizable N (N₀) was lower in treatments where urea was not applied.     

Effects of ambient gaseous pollutants on photosynthesis,growth, yield and grain quality of selected crops grown at different sites varying in pollution levels

In recent decades, ambient gaseous pollution has increased due to anthropogenic activities worldwide. The studies to evaluate the adverse effects of ambient pollutants on commonly grown food crops are still limited, especially in Asian countries like Pakistan. The present study was conducted to measure the ambient pollutants in different sites of Faisalabad and their impact on growth and yield of wheat, mung bean and peas. Plants were grown in pots and placed at three sites named as control (Wire house of Government College University, Faisalabad), low pollution (LP) (Farm Area of Ayub Agricultural Research Institute) and high pollution (HP) (GT Chowk, Faisalabad) sites. Results showed that ambient ozone (O₃) concentration was highest at HP site followed by LP site and was below AOT40 in control site. Ambient pollutants caused foliar injury in crops and decreased plant height, leaf area, biomass and grain yield. Pollutants caused a reduction in photosynthetic pigments, stomatal conductance and net photosynthetic rate and grain protein contents in all three crops. In conclusion, the ambient O₃ level was highest at HP site, this current O₃ level and other pollutants decreased the growth and yield of important food crops.     

干湿交替灌溉与施氮耦合对水稻根际环境的影响

为了探讨不同水氮耦合对水稻根际土壤环境及根系分泌有机酸总量的影响,以新稻20号为材料,进行盆栽试验,设置浅水层、轻度(-20 k Pa)和重度干湿交替灌溉(-40 k Pa)3种灌溉方式及不施氮肥,中氮(normal nitrogen,MN,240 kg/hm~2)和高氮(high nitrogen,HN,360 kg/hm~2)3种氮肥水平9个处理。结果表明:轻度干湿交替灌溉及中氮增加了土壤酶活性,提高土壤中微生物数量,根系分泌有机酸总量显著提高(P0.05);重度干湿交替灌溉及重施氮肥则降低土壤酶活性及微生物的数量,显著(P0.05)减少根系分泌有机酸的总量;相关分析表明:根际土壤酶活性及微生物数量与不同生育期根系分泌有机酸总量呈显著(P0.05)或极显著(P0.01)的正相关关系。土壤酶活性、微生物数量及有机酸总量的供氮效应为正效应,轻度干湿交替灌溉供水效应及耦合效应均为正效应,而重度干湿交替灌溉的控水及耦合效应则为负效应。研究可为通过水氮耦合调控水稻良好的根际环境提供依据。     

植被恢复的土壤固碳效应：动态与驱动机制

植被恢复是影响土壤有机碳库动态变化的关键过程之一,阐明植被恢复过程中土壤有机碳的固持动态及其驱动机制,是全球变化下碳循环研究的热点和前沿问题。本文综述了近年来国内外关于植被恢复过程中土壤有机碳固定动态及其驱动机制方面的研究,剖析植被恢复中土壤有机碳固持动态及其影响因素,探讨植物碳输入对土壤有机碳动态变化的影响机制,揭示植被恢复中土壤有机碳固定的物理、化学和微生物驱动机制,并对目前研究中存在的问题进行总结,进而提出关于植被恢复的土壤固碳效应研究,亟需在土壤有机碳组分的动态、微生物结构和功能,以及植物—土壤—微生物对土壤有机碳固持的协同作用机制等方面进一步加强。本综述可为植被恢复与土壤固碳稳定机制研究指明未来的方向,进而为促进我国植被恢复的土壤碳循环研究,科学评价生态系统土壤固碳潜力和有效实施生态系统碳汇管理提供科学参考。     

黑土长缓坡地形与横垄对土壤有机碳空间分异的交互作用

横坡垄作对坡耕地土壤有机碳（soil organic carbon,SOC）流失有一定的阻控作用,但黑土区特有长而缓的地形与横垄对坡耕地SOC空间分异会产生交互作用,而这种交互作用引发的SOC流失风险没引起足够的重视。该研究以典型黑土区黑龙江省黑河市北安分局红星农场为研究区域,2022年在横坡垄作与顺坡水线方向上共布设25个采样点,采用地理探测器模型、单因素方差分析（one-way ANOVA）和Pearson相关性分析,探讨土壤有机碳的空间分异及其交互作用。结果表明,横坡垄作方向上垄沟土壤有机碳含量从坡顶到水线呈现逐渐增大的变化趋势;在垄台从坡顶到水线呈现先增大后减小的变化趋势。顺坡水线方向,土壤有机碳含量在垄沟呈现从上坡到下坡增大的变化趋势;在垄台呈现先增大后减小的变化趋势。由于断垄产生水线,顺坡土壤有机碳含量上坡与下坡仍有显著差异（P＜0.05）。Pearson相关性分析表明, 有机碳与可蚀性K因子呈显著负相关（垄沟和垄台相关系数分别为–0.228和–0.238,P＜0.05）,与碳循环相关的β-葡萄糖苷酶和微生物生物量碳在垄沟呈极显著正相关（相关系数为0.398和0.676,P<0.01）。地理探测器分析表明,顺坡水线对土壤有机碳空间分异的影响最大,其对垄沟和垄台SOC的解释力分别达到61%和52%以上;顺坡水线与其他因子的交互作用共同增强了对土壤有机碳的解释力,尤其是顺坡水线与高程的交互作用最为明显。黑土区坡耕地土壤有机碳空间分异主要受顺坡水线与高程的交互作用,横坡垄作虽然能够拦截径流,但由于长缓坡地形影响产生的断垄会加剧土壤侵蚀诱发的有机碳流失。因此,黑土坡耕地治理需要同时考虑横垄与地形的共同影响,从而实现防蚀的优化效果。     

Carbon isotopic ratios of wetland and terrace soil sequences in the Maya Lowlands of Belize and Guatemala

This article provides new data and synthesizes earlier findings on the carbon isotope ratios of the humin part of soil organic matter from a range of sites in the central Maya Lowlands. Changes down the soil profile in carbon isotope ratios can provide an important line of evidence for vegetation change and erosion over time, especially in well dated aggrading profiles. Research thus far has provided substantial evidence for significant inputs from C₄ vegetation in buried layers from the Ancient Maya periods in depositional soils but equivocal evidence from sloping soils. We present new findings from soil profiles through ancient Maya wetland fields, upland karst wetlands, ancient Maya aguadas (reservoirs), and ancient Maya terraces. Most of the profiles exhibited δ¹³C enrichment greater than the 2.5–3‰ typical from bacterial fractionation. Seven of nine ancient Maya wetland profiles showed δ¹³C enrichment ranging from 4.25 to 8.56‰ in ancient Maya-dated sediments that also contained phytolith and pollen evidence of grass (C₄ species) dominance. Upland karst sinks and ancient reservoirs produced more modest results for δ¹³C enrichment. These seasonal wetland profiles exhibited δ¹³C enrichment ranging from 1 to 7.3‰ from the surface to ancient Maya-period sediments. Agricultural terraces produced mixed results, with two terraces having substantial δ¹³C enrichment of 5.34 and 5.66‰ and two producing only equivocal results of 1.88 and 3.03‰ from modern topsoils to Maya Classic-period buried soils. Altogether, these findings indicate that C₄ plants made up c. 25% of the vegetation at our sites in the Maya Classic period and only a few percent today. These findings advance the small corpus of studies from ancient terraces, karst sinks, and ancient wetland fields by demonstrating substantial δ¹³C and thus C₄ plant enrichment in soil profile sections dated to ancient Maya times. These studies are also providing a new line of evidence about local and regional soil and ecological change in this region of widespread environmental change in the Late Holocene.     

沼肥对大豆产量、品质、养分和土壤化学性质的影响

为探讨沼肥在大豆上的合理施用技术,采用田间试验,研究沼肥对大豆产量、品质、养分吸收利用及土壤化学性质的影响。结果表明：与习惯施肥处理相比,100%沼渣、30%沼渣＋化肥、20%沼渣＋化肥处理的大豆产量分别增加1.02%,10.48%,0.16%;大豆粗脂肪含量分别增加2.31%,2.70%,5.07%;磷肥利用率分别增加5.04%,23.39%,8.60%;土壤有机质含量分别升高13.39%,3.68%,0.50%;20-80 cm土层内土壤硝态氮、铵态氮含量降低幅度分别在13.70%～61.56%,15.98%～70.10%之间。说明试验条件下,无论沼渣单施还是沼渣与化肥配施均可提高大豆粗脂肪含量、磷肥利用率、土壤有机质含量,降低氮素的流失。     

Short‐term degradation of semiarid grasslands—results from a controlled‐grazing experiment in Northern China

The assessment of grassland degradation due to overgrazing is a global challenge in semiarid environments. In particular, investigations of beginning steppe degradation after a change or intensification of the land use are needed in order to detect and adjust detrimental land‐use management rapidly and thus prevent severe damages in these sensitive ecosystems. A controlled‐grazing experiment was established in Inner Mongolia (China) in 2005 that included ungrazed (UG) and heavily grazed plots with grazing intensities of 4.5 (HG4.5) and 7.5 (HG7.5) sheep per hectare. Several soil and vegetation parameters were investigated at all sites before the start of the experiment. Topsoil samples were analyzed for soil organic C (SOC), total N (N_tot), total S (S_tot), and bulk density (BD). As vegetation parameters, aboveground net primary productivity (ANPP), tiller density (TD), and leaf‐area index (LAI) were determined. After 3 y of the grazing experiment, BD increased and SOC, N_tot, S_tot, ANPP, and LAI significantly decreased with increasing grazing intensity. These sensitive parameters can be regarded as early‐warning indicators for degradation of semiarid grasslands. Vegetation parameters were, however, more sensitive not only to grazing but also to temporal variation of precipitation between 2006 and 2008. Contrary, soil parameters were primarily affected by grazing and resistant against climatic variations. The assessment of starting conditions in the study area and the application of defined grazing intensities is essential for the investigation of short‐term degradation in semiarid environments.     

半透膜微萃取方法的建立及其在测定土壤间隙水中憎水性有机污染物的应用

提出了一种新型的基于半透膜被动采样技术的微萃取方法（semi-permeable membrane based micro-extraction, SPM-ME）,并以菲为模型污染物,测试了SPM-ME用于测定土壤间隙水中自由溶解态憎水性有机污染物的可行性。结果表明,菲在该SPE-ME装置与水相间的平衡可在6 h内达到,并且随着装置中三油酸甘油酯含量的增加,单元SPE-ME对于菲的富集系数也相应增加。该装置对土壤间隙水中菲的富集在10 d内能达到平衡,整个过程主要受菲从土壤向间隙水的传质控制。该装置测得间隙水中菲的浓度与实际测得间隙水浓度十分吻合,而由传统的相平衡分配法计算所得间隙水浓度则高出实测值4-5倍。同时,该装置对体系中污染物的耗竭小于体系中污染物总量的1%。因此,SPE-ME是一种准确、有效、非耗竭式的微萃取技术。