Changes in forest soil organic matter pools after a decade of elevated CO2 and O3

The impact of rising atmospheric carbon dioxide (CO₂) may be mitigated, in part, by enhanced rates of net primary production and greater C storage in plant biomass and soil organic matter (SOM). However, C sequestration in forest soils may be offset by other environmental changes such as increasing tropospheric ozone (O₃) or vary based on species-specific growth responses to elevated CO₂. To understand how projected increases in atmospheric CO₂ and O₃ alter SOM formation, we used physical fractionation to characterize soil C and N at the Rhinelander Free Air CO₂-O₃ Enrichment (FACE) experiment. Tracer amounts of ¹⁵NH₄⁺ were applied to the forest floor of Populus tremuloides, P. tremuloides-Betula papyrifera and P. tremuloides-Acer saccharum communities exposed to factorial CO₂ and O₃ treatments. The ¹⁵N tracer and strongly depleted ¹³C-CO₂ were traced into SOM fractions over four years. Over time, C and N increased in coarse particulate organic matter (cPOM) and decreased in mineral-associated organic matter (MAOM) under elevated CO₂ relative to ambient CO₂. As main effects, neither CO₂ nor O₃ significantly altered ¹⁵N recovery in SOM. Elevated CO₂ significantly increased new C in all SOM fractions, and significantly decreased old C in fine POM (fPOM) and MAOM over the duration of our study. Overall, our observations indicate that elevated CO₂ has altered SOM cycling at this site to favor C and N accumulation in less stable pools, with more rapid turnover. Elevated O₃ had the opposite effect, significantly reducing cPOM N by 15% and significantly increasing the C:N ratio by 7%. Our results demonstrate that CO₂ can enhance SOM turnover, potentially limiting long-term C sequestration in terrestrial ecosystems; plant community composition is an important determinant of the magnitude of this response.     

Addition of Leucaena-KX2 mulch in a shaded coffee agroforestry system increases both stable and labile soil C fractions

Agroforestry systems have the potential to increase sequestration of atmospheric carbon dioxide (CO₂) as soil organic carbon (SOC) because of the increased rates of organic matter addition and retention. However, few studies have characterized the relative stability of sequestered SOC in soil. We characterized SOC storage in aggregate size and chemical stability classes to estimate the relative stability of SOC pools after the addition of Leucaena-KX2 pruning residues (mulch) from 2006 to 2008 in a shaded coffee agroforestry system in Hawaii. Soil samples were separated by microaggregate isolation, density flotation and dispersion, and acid hydrolysis, resulting in five distinct fractions that differed in relative stability: coarse particulate organic matter (POM), fine POM, microaggregate-protected POM, silt + clay hydrolyzable soil organic matter (SOM), and silt + clay non-hydrolyzable SOM. With mulch addition, the fine POM fraction increased. There was also a shift in the proportion of SOC to more stable silt + clay fractions. In the absence of mulch there was no significant change in SOC fractions. Given that the turnover time of SOC in silt + clay fractions is on the order of decades to centuries, the potential benefits of active shade management and mulching compensate for the loss of C sequestration in tree biomass from pollarding.     

不同发育期及授粉方式对设施甜瓜中稳定同位素比值变化的影响研究

为探究不同发育期及授粉方式对设施甜瓜稳定同位素比值变化的影响,本研究基于元素分析——稳定同位素比率质谱(EA-IRMS),测定在不同发育期和授粉方式中设施甜瓜的4种稳定同位素比值(δ¹³C、δ¹⁵N、δ¹⁸O和δ²H),采用单因素方差分析法解析激素授粉和中华蜜蜂授粉对甜瓜稳定同位素比值的差异性。结果表明,在相同的种植和环境条件下,自然分馏效应导致设施甜瓜在不同发育时期的同位素差异。在甜瓜发育期间,不同授粉方式设施甜瓜的δ¹³C、δ¹⁵N和δ¹⁸O值较稳定,无显著差异(P>0.05),而在发育30 d时激素授粉与蜜蜂授粉甜瓜的δ²H值分别为-43.63‰和-53.50‰,存在显著差异(P<0.05)。本研究初步揭示了稳定同位素在甜瓜发育过程中以及不同授粉方式下的分馏情况,其中δ²H值可作为甜瓜授粉方式的一项标识性指标,对丰富设施甜瓜溯源体系具有重要意义。     

模拟池塘底泥无机磷形态与上覆水体可溶性活性磷含量的关系及其控制

取两个池塘底泥和上覆水进行室内模拟水体小环境试验,设对照组及5个处理组,进行4个月培养,采用连续分组法测定底泥中无机磷形态及其含量,分析底泥潜在无机磷变化及其与上覆水体可溶性活性磷(DRP)含量的关系.结果表明,池塘底泥中无机磷各形态含量依次为钙10结合磷(Ca10-P)＞闭蓄态磷(O-P)＞铝结合磷(Al-P)＞铁结合磷(Fe-P)＞钙8结合磷(Ca8-P)＞钙2结合磷(Ca2-P);4个月后两池塘底泥中的Ca2-P和Fe-P增加,Ca10-P、O-P、Al-P减少;上覆水体中DRP含量与O-P、Ca2-P、Ca8-P和Ca10-P之间呈显著正相关;底泥中无机磷各形态对上覆水体中DRP含量的直接影响大小依次为O-P＞Ca8-P＞Ca2-P＞Ca10-P＞Fe-P＞Al-P;5个处理组上覆水体中DRP含量都低于对照组;沸石与芽孢杆菌组合处理的上覆水体中DRP含量最低,表明采用沸石与芽孢杆菌组合进行底泥处理是控制上覆水中DRP含量的有效方法.     

Tandem size exclusion chromatography-Polyacrylamide gel electrophoresis of humic acids

Humic acids (HAs) from four soils were fractionated by size exclusion chromatography (SEC) on Sephadex G-75. Three fractions were obtained in all humic acids, collected and assayed by Polyacrylamide gel electrophoresis (PAGE). The unfractionated HA from each soil was used as reference. Each chromatographic fraction formed one electrophoretic zone corresponding closely to one band of the reference sample with some admixture of the fractions preceding or following. The results indicate that fractionation of HAs by tandem SEC-PAGE can be successfully used for obtaining fractions of reduced polydispersity and different electrophoretic mobilities. Pyrolysis/methylation-gas chromatography-mass spectrometry of the full size preparations of HA and fractions with exactly defined molecular size and electrophoretic mobility showed a different distribution in humic components, mainly lipids, lignin derivatives and N-containing compounds.     

长期施肥对稻麦轮作紫色土有机碳组分及酶活性的影响

为了探明西南地区长期不同施肥处理对稻麦轮作紫色土有机碳组分和碳循环相关水解酶活性的影响,依托重庆北碚29年稻麦轮作紫色土长期定位试验,选取不施肥(CK)、单施氮磷钾肥(NPK)、有机无机配施(NPKM)、秸秆还田配施含氯化肥[(NPK)clS]和秸秆还田配施无机肥(NPKS)5个处理,测定土壤各组分有机碳含量及与土壤碳...     

The impact of sugarcane filter cake on the availability of P in the rhizosphere and associated microbial community structure

This study aimed to evaluate the interaction between filter cake (FC), and phosphorus fertilizers with differing solubility on the growth and P nutrition of sugarcane. Effects of soil amendment with FC on different soil P fractions and influence on microbial community structure in the rhizosphere were also assessed. Two glasshouse experiments were conducted with completely randomized block designs. The first experiment evaluated rates of FC using a factorial design (5 × 2): 0, 2.5, 5, 10 and 15 g FC kg^?1 soil applied as either broadcast in bulk soil or in the planting furrow. The second experiment used a factorial design (2 × 3): without and with FC (5 g kg^?1 soil, dry basis), both without P (NP) and with P supplied as either triple superphosphate (TSP) or as rock phosphate (RP), both at the rate of 78.4 mg kg^?1 based on total P. Microbial community structure was determined using TRFLP and dynamics of soil P by Hedley fractionation. Filter cake applied at increasing rates in the absence of P was effective in increasing shoot growth and P uptake by plant, particularly when applied to bulk soil as compared to furrow application. Also, FC improved P uptake and increased the availability of labile inorganic P in the rhizosphere and modified the structure of fungal and bacterial communities, whereas only bacterial and archaea communities were influenced by P fertilizer use. Filter cake was more effective when combined with RP, with increased growth and P utilization and thus can be considered as a feasible and practical option for farmer use in substitution to TSP, a more expensive source.     

温带针阔叶林土壤有机碳动态和微生物群落结构对有机氮添加的响应特征

森林生态系统土壤有机碳(soil organic carbon,SOC)转化和碳储量动态对大气氮沉降增加的响应是具有特异性的,取决于土壤初始氮状态、施氮类型、剂量与持续时间。过去相关研究主要集中在无机氮沉降效应方面,对有机氮沉降如何影响温带针阔混交林SOC及其组分含量尚不清楚,鲜有研究关注氮素富集条件下SOC变化的微生物学机制。以长白山温带针阔混交林为研究对象,设置4个尿素添加水平(0、40、80、120 kg·hm~(–2)·a~(–1),以N计,下同)的原位控制试验。施肥三年后,采集0～10 cm矿质层土壤样品,测定土壤不同形态氮含量、土壤团聚体比例和不同粒径SOC含量;利用磷脂脂肪酸(PLFA)技术测定土壤微生物不同种群相对丰度与群落结构,探讨SOC含量变化与微生物群落变化之间的相关关系。结果表明,施氮三年显著增加了土壤NO_3~--N、DON和TN含量,土壤酸化明显。施氮虽然未显著增加表层土壤总SOC含量,但是显著增加活性SOC组分(颗粒态有机碳和团聚体结合态有机碳)含量,增幅介于27.5%～96.3%,导致SOC组分发生累积的大气氮沉降临界负荷为80kg·hm~(–2)·a~(–1)以N计下同。SOC含量的变化(ΔSOC)与团聚体结合态有机碳、颗粒态有机碳含量的变化正相关。除好氧细菌丰度外,施氮总体上未改变微生物种群丰度,但是显著改变了微生物的群落结构,革兰氏阳性细菌/革兰氏阴性细菌(G+/G–)丰度比例增加而好氧/厌氧细菌(A/AN)丰度比例下降。有机氮富集倾向于促进温带针阔混交林土壤团聚体的形成,局域产生厌氧微环境,好氧/厌氧细菌(A/AN)丰度比例下降。活性SOC组分含量、土壤团聚体百分比和微生物PLFA丰度之间显著相关,暗示微生物群落结构与SOC积累和稳定之间关系密切。上述研究结果表明,氮素富集会改变温带针阔混交林土壤微生物群落结构,进而导致土壤碳积累。     

黑荆树皮单宁不同级分的生物活性研究

通过对黑荆(Acacia mearnsii)树皮单宁进行纯化和分级处理,研究了分子量及其分布范围不同的单宁各级分与明胶反应、抑酶、抑菌等生物活性差异,探讨了反应体系的pH值及反应物的质量比等因素对单宁生物活性的影响.研究表明,分子量大的单宁级分与明胶的结合能力强、对某些水解酶的抑制作用大;而分子量适中的单宁级分,对某些细菌的抑制作用最明显.