Variable use of plant- and soil-derived carbon by microorganisms in agricultural soils

In this study we used compound specific ¹³C and ¹⁴C isotopic signatures to determine the degree to which recent plant material and older soil organic matter (SOM) served as carbon substrates for microorganisms in soils. We determined the degree to which plant-derived carbon was used as a substrate by comparison of the ¹³C content of microbial phospholipid fatty acids (PLFA) from soils of two sites that had undergone a vegetation change from C3 to C4 plants in the past 20-30 years. The importance of much older SOM as a substrate was determined by comparison of the radiocarbon content of PLFA from soils of two sites that had different ¹⁴C concentrations of SOM.The ¹³C shift in PLFA from the two sites that had experienced different vegetation history indicated that 40-90% of the PLFA carbon had been fixed since the vegetation change took place. Thus PLFA were more enriched in ¹³C from the new C4 vegetation than it was observed for bulk SOM indicating recent plant material as preferentially used substrate for soil microorganisms. The largest ¹³C shift of PLFA was observed in the soil that had high ¹⁴C concentrations of bulk SOM. These results reinforce that organic carbon in this soil for the most part cycles rapidly. The degree to which SOM is incorporated into microbial PLFA was determined by the difference in ¹⁴C concentration of PLFA derived from two soils one with high ¹⁴C concentrations of bulk SOM and one with low. These results showed that 0-40% of SOM carbon is used as substrate for soil microorganisms. Furthermore a different substrate usage was identified for different microorganisms. Gram-negative bacteria were found to prefer recent plant material as microbial carbon source while Gram-positive bacteria use substantial amounts of SOM carbon. This was indicated by ¹³C as well as ¹⁴C signatures of their PLFA. Our results find evidence to support ‘priming’ in that PLFA indicative of Gram-negative bacteria associated with roots contain both plant- and SOM-derived C. Most interestingly, we find PLFA indicative of archeobacteria (methanothrophs) that may indicate the use of other carbon sources than plant material and SOM to a substantial amount suggesting that inert or slow carbon pools are not essential to explain carbon dynamics in soil.     

The effect of land cover/vegetation on soil water dynamic in the hilly area of the loess plateau,China

Severe soil and water loss has lead to widespread land degradation in China's loess plateau. During the past decades, a great deal of effort was made on vegetation restoration to reduce soil and water loss in the loess plateau. However, due to water shortage the efficiency of vegetation restoration was not as satisfactory as expected. As part of a vegetation restoration project, we conducted research aiming to understand the relationship between vegetation pattern and soil water dynamics. The goal was to find vegetation types appropriate for the loess plateau with scarce water resources. In 1986, fifteen plots of land were planted with five vegetation types: pine woodland, shrubland, sloping cropland, alfalfa and semi-natural grassland. Soil water content, runoff, soil erosion were measured for each plot. Environmental variables, such as rainfall, evaporation and temperature, were recorded simultaneously by an automated meteorological station. The relationship between land cover pattern and soil water dynamic was evaluated by using statistical models. We found that: (1) soil water loss occurred during the growing season, and it reached the maximum in the second half of July; (2) soil water was not fully replenished from rainfall during the rainy season; (3) pine woodland induced the largest water loss to surface runoff, followed by sloping cropland, alfalfa, semi-natural grassland and shrubland; the poor capability of pine woodland for water conservation may be attributed to soil compaction and poor ground coverage under the tree; (4) in most cases, soil water of the five vegetation types was low except for shrubland and semi-natural grassland where it was moderate-high during a few periods. These conditions inhibit sustainable vegetation growth in the semi-arid loess hilly area of the loess plateau, China.     

Flow-microcalorimetry measurements of aerobic and anaerobic soil microbial activity

Heat output can be used as an indicator of microbial activity and is usually measured in a microcalorimeter with closed ampoules. In long-term experiments particularly, interpretation of the data is hindered by the changing environment in the closed ampoules because of O₂ consumption and CO₂ enrichment. We used a combination of a flow-microcalorimeter and a gas chromatograph to measure the heat flux and CO₂ and N₂O production rates under controlled conditions. Simultaneous detection of the heat output and CO₂ emission allowed calculation of the calorimetric: CO₂ (Cal/CO₂) ratio. A mean ratio of-435 kJ mol^-1 CO₂ was detected in six different soils amended with glucose and incubated under aerobic conditions. This ratio indicated that CO₂ was the end-product of catabolism. In wet 10–12 mm soil aggregates of a gleyic vertisol amended with glucose, values of-285 kJ mol^-1 CO₂ under an aerobic and-141 kJ mol^-1 CO₂ under a N₂ atmosphere was determined. These findings indicated that fermentative metabolism occurred. The Cal/CO₂ ratio was not affected when enough NO _inf3 ^sup- was available and denitrification processes (N₂O production) were possible.     

Mineralization of Organic Nitrogen in Soils with Contrasting Fertility Was Regulated Differently by Addition of Biochar and Animal Manures

ABSTRACT

How to restore the soil fertility and productivity in a damaged and then reclaimed area with extremely low fertility is a big concern worldwide. To explore the method of soil restoration in the coal mining subsidence area, the effects of biochar application coupled with organic fertilizer (animal manures) on the process of organic nitrogen (N) mineralization were studied in a 149 days leaching experiment. Biochar were applied (wt/wt) at the rates of 0%, 1%, and 3%. Two organic fertilizers with different C/N ratio (chicken and sheep manures) were applied at the rate of 200 mg N·kg^?1 soil. A vegetable soil with high-fertility was used as the comparison. The results showed that when treated with chicken manure, the reclaimed soil had 11.13% lower mineralization potential and 20.00% lower inorganic nitrogen production from mineralization than the vegetable soil. Compared with the non-biochar treatment, biochar at both application rates decreased N leaching in chicken manure-treated reclaimed soil, i.e., by 21.49% (1% biochar) and 28.31% (3% biochar), respectively, whereas only high rate of biochar application decreased N leaching in chicken manure-treated vegetable soil by 8.10%. However, N leaching in sheep manure-treated reclaimed soil was unaffected by the biochar application. Thus, the effect of the biochar on the organic nitrogen mineralization was affected by both soil and organic fertilizer type.     

Tillage effects on soil organic matter in density fractions of a Cerrado Oxisol

Reclamation of Brazilian cerrados (savannas) has been intensified in the last decades, with implications for soil quality and soil organic matter (SOM) dynamics. Studying the impact of different tillage systems is essential to define better strategies for land use in Cerrado, which may favor C sequestration and improve soil quality. We used density fractionation and ¹³C natural abundance to assess changes in SOM in an Oxisol previously under a cerrado sensu-stricto following 30 years of cultivation. The objectives of the study were to: (i) evaluate the long-term impact of tillage systems on SOM stocks in a Dark Red Latosol (Oxisol) from the Cerrado Biome, and (ii) better understand the dynamics of SOM in different density fractions of this soil. Cultivation led to compaction, which significantly increased soil bulk density. This resulted in the systematic overestimation of C and N stocks in cultivated areas when compared to the natural cerrado. Conversion of the cerrado into cropland using plow tillage (PT) or no-tillage (NT) system did not alter the total C (100 Mg ha⁻¹) and N (7 Mg ha⁻¹) stocks in the first 45 cm depth at the end of 30 years of cultivation. However, about 22% of the total C was replaced by C from maize. The relative replacement of C decreased following the order: free light fraction (F-LF)>heavy fraction (HF)>occluded light fraction (O-LF). The low substitution in the O-LF was attributed to a possible presence of charcoal. Converting cerrado into cropland significantly decreased F-LF quantity. The proportions of C replacement in this fraction were higher in PT than NT, suggesting a faster turnover in PT. Nevertheless, because most C (95%) was held in the HF, C dynamics in the whole soil were controlled by the behavior of this fraction. The maintenance of C levels even at the end of 30 years of cultivation and the lack of differentiation between NT and PT were attributed to the high clay contents and Fe+Al oxi-hydroxides concentrations of the studied soil as well as to a sufficient C supply by the maize crop.     

泥鳅生长及抗氧化 解毒酶系统对水体中转Cry1Ab/Ac基因水稻残遗物的响应

在泥鳅养殖水体中添加稻秆粉模拟水稻残遗物生境,研究了泥鳅生长和肝胰脏抗氧化酶(SOD、CAT)与解毒酶(GST)活性对转Cry1Ab/Ac基因水稻‘华恢1号’(HH1)的响应。设计以HH1稻秆粉10 mg·L?1、50 mg·L?1、100 mg·L?1和200 mg·L?1 4个梯度浓度处理泥鳅为试验组,以非转Bt基因水稻‘明恢63’(MH63)稻秆粉处理组为阴性对照,不加稻秆粉的基础饲养组为空白对照。结果显示:在4种稻秆粉浓度下,HH1组与MH63对照组泥鳅的特定生长率、肥满度、内脏系数及SOD、CAT和GST酶活性均无显著差异(P0.05);与空白对照比较,稻秆粉浓度升高对泥鳅生长的抑制逐渐增强,当浓度达到200 mg·L?1时,HH1组和MH63对照组泥鳅的特定生长率、内脏系数与CAT活性降低。研究结果表明,水体中低含量的转融合基因Cry1Ab/Ac水稻HH1稻秆粉对泥鳅的生长与生理酶活性没有明显影响,高浓度HH1和MH63稻秆粉均使泥鳅的生长和生理酶活性显著降低,这可能与养殖水体中浓度较高的悬浮稻秆粉妨碍了泥鳅的呼吸和滤食,及稻秆粉的分解降低了水体p H和溶氧量有关。     

烟台地区近13年土地利用/土地覆盖变化分析

利用1992年和2005年的TM影像及2005年的土地利用现状图,运用GIS与RS技术,分析了烟台地区13年来土地利用的具体变化状况。研究结果表明,1992-2005年期间烟台地区耕地面积明显减少,城乡工矿建设用地、交通用地呈明显增加趋势,林地、河流变化较小,略有增加。同时对该地区的土地利用格局进行了分析,并对驱动这种格局的因素进行了简单分析。烟台地区在快速城市化过程中,耕地减少没有明显减缓迹象,迫切需要加强保护耕地措施。     

基于MODIS和NOAA/AVHRR的荒漠化遥感监测方法

土地荒漠化是中国西部最严重的生态环境问题，荒漠化遥感监测技术是掌握荒漠化发展趋势的重要手段。基于空间分辨率为1 km的NOAA/AVHRR和MODIS遥感数据，首先依据湿润指数法确定了荒漠化范围和气候分区。然后选取出了可以反映不同荒漠化特征，并且能够通过中低分辨率的NOAA/AVHRR和MODIS遥感影像反演出来的5个荒漠化遥感监测指标，通过精度评价分析，确定了最佳指标组合。由于MODIS和NOAA/AVHRR数据的影像特征存在较大差异，针对每一气候分区， 建立了分别适用于MODIS和NOAA/AVHRR数据的两套遥感指标分类体系。通过不同分类方法的比较，确定了最佳分类方法－决策树分类法。通过对中国1995年和2001年的荒漠化动态变化状况进行了分析，结果表明，本文提出的荒漠化遥感监测方法，不仅能够成功地进行大尺度的荒漠化遥感监测，而且能够取得较好的监测效果。