嘉陵江上游低山暴雨区不同植被类型土壤磷素的比较

以广元市水土流失定位观测站内的3个不同植被恢复模式为研究对象,通过野外调查与室内实验分析,测定了湿地松纯林,刺槐纯林及湿地松刺槐混交林的土壤有机质与P素含量。结果表明：（1）混交林的土壤结构明显好于湿地松与刺槐纯林;（2）混交林中有机质含量高于刺槐与湿地松纯林,3个林地的土壤有机质多集中在土壤上层,并随着土壤深度的增加而减少。（3）土壤全磷与有效磷含量大小顺序基本为：刺槐林〉混交林〉湿地松     

沟渠对湿地生物地球化学循环影响初析——以三江平原湿地为例

湿地有其独特的生物地球化学循环,其间许多化学迁移和转化过程不为其它生态系统所共享。沟渠的修建改变了湿地的水文状况,因此影响了湿地的生物地球化学循环。以三江平原湿地为例,从沟渠对湿地化学元素迁移转化、湿地化学元素输入输出和湿地化学质量平衡影响方面分析了沟渠对湿地生物地球化学循环的影响。结果显示,沟渠的修建导致湿地大量化学元素丧失,湿地化学质量失衡,最终引起湿地退化。     

堆肥过程中水溶性有机物常规荧光与固体表面荧光光谱比较

为研究固体表面荧光表征堆肥有机质结构及物质转化特征的可行性,采集堆肥原样,提取水溶性有机物,分别对两者的含碳量及前者的固体表面荧光和后者的常规荧光光谱进行分析。结果显示：堆肥过程中,水溶性有机物占总堆肥有机物的比例不断下降,第40天降至5.1 g/kg。堆肥进行时,水溶性有机物的发射、激发光谱及同步荧光光谱中的类腐殖质荧光的强度均不断增强,而堆肥原样的激发、发射和同步3种扫描形式的固体表面荧光却不断降低。3种荧光光谱中,堆肥原样和水溶性有机物的同步荧光光谱在常规荧光光谱和固体表面荧光中都出现了类蛋白和类腐     

Effective retention of litter-derived dissolved organic carbon in organic layers

This study aimed to gain insight into the generation and fate of dissolved organic carbon (DOC) in organic layers. In a Free Air CO₂ Enrichment Experiment at the alpine treeline, we estimated the contribution of ¹³C-depleted recent plant C to DOC of mor-type organic layers. In an additional laboratory soil column study with 40 leaching cycles, we traced the fate of ¹³C-labelled litter-DOC (22 and 45 mg l⁻¹) in intact Oa horizons at 2 and 15 °C. Results of the field study showed that DOC in the Oa horizon at 5 cm depth contained only 20 ± 3% of less than six-year-old C, indicating minor contributions of throughfall, root exudates, and fresh litter to leached DOC. In the soil column experiment, there was a sustained DOC leaching from native soil organic matter. Less than 10% of totally added litter-DOC was leached despite a rapid breakthrough of a bromide tracer (50 ± 7% within two days). Biodegradation contributed only partly to the DOC removal with 18-30% of added litter-DOC being mineralized in the Oa horizons at 2 and 15 °C, respectively. This was substantially less than the potential 70%-biodegradability of the litter-DOC itself, which indicates a stabilization of litter-DOC in the Oa horizon. In summary, our results give evidence on an apparent ‘exchange’ of DOC in thick organic layers with litter-DOC being retained and ‘replaced’ by ‘older’ DOC leached from the large pool of indigenous soil organic matter.     

潮棕壤不同利用方式营养元素随剖面深度的变化特征

对中国科学院沈阳生态实验站潮棕壤水稻田、玉米地、撂荒地和人工林地营养元素随剖面深度变化的研究表明,4种土地利用方式的有机C、全N、全S及DTPA浸提态Fe、Mn、Cu、Zn等具有随剖面深度增加而下降的趋势,交换性Ca、Na及交换性盐基总量在土层间的分异不明显。有机C、全N、碱解N、NO3^-N、全S及DTPA浸提态微量元素在0～10cm和0～20cm的含量与0～100cm含量的比值分别为0．1和0．2以上．表明这些养分指标具有明显的表聚性特征;NH4^-N、全P、速效S无明显的表聚性;交换性Mg、Na及交换性盐基总量在0～20cm与0～100cm含量的比值小于0．2．反映了供试潮棕壤较强的淋溶作用。不同土地利用方式营养元素在土壤剖面中的分布差异及表聚性特征,主要受到植物循环的影响,另外还受到淋溶及人为干扰的影响。     

Labile, recalcitrant, and inert organic matter in Mediterranean forest soils

The biochemical quality of soil organic matter (SOM) was studied in various profiles under Quercus rotundifolia Lam. stands on calcareous parent material. Special attention was paid to the question of how biochemical quality is affected by position within the soil profile (upper versus lower horizons). The following global SOM characteristics were investigated: (a) overall recalcitrance, using hydrolysis with either hydrochloric or sulphuric acid; (b) hydrolyzable carbohydrates and polyphenolics; (c) extractability by hot water and quality of the extract; and (d) abundance of inert forms of SOM: charcoal and soot-graphite. The recalcitrance of soil organic carbon (OC) decreases with depth, following the order: H horizons>A horizons>B horizons. In contrast, the recalcitrance of nitrogen is roughly maintained with depth. The ratio carbohydrate C to total OC increases from H to B horizons, due to the increasing importance of cellulosic polysaccharides in B horizons, whereas other carbohydrates are maintained throughout the soil profile at a relatively constant level, 12-15% of the total OC in the horizon. Whereas the quality of the hydrolyzable carbon (measured by the carbohydrate to polyphenolic C ratio) decreases with depth from H to B horizons, the quality of the hot-water extractable organic matter is much higher in B horizons than in A or H horizons. The relative importance of both charcoal and soot-graphitic C and N tends to increase with depth. The ratio black/total is usually higher for N than for C, a result that suggests that inert SOM may represent a relevant compartment in the nitrogen cycle. Overall, our data suggest that in Mediterranean forest soils the organic matter in B horizons could be less stable than often thought.     

Influence of cropping on the content,composition and dynamics of organic residue in the soil of the plough layer

Organic residue (OR) forms the undecomposed part of soil organic matter (SOM). The majority of it originates from plant remains, but to a certain extent it may also be derived from manure and from the remains of heterotrophic soil organisms. The OR content and dynamics are influenced by management practices (crop rotation, tillage, manuring). The main objective of this work was to study the effect of cropping on the content, fractional composition (coarse and fine fragments) and annual turnover of nonhumified SOM or OR in arable Podzoluvisol in the conditions of south Estonia and to evaluate the role of OR in the humus status of soil. Using the soil-coring method, the OR content and composition and underground phytomass (UGP) as a source of OR in the plough layer were studied. The soil cores (252) were taken during 1991–1992 from three long-term field trials cropped with wheat, barley, rye, potatoes and short-term clover-grass mixtures. The sample plots selected from field trials were tilled conventionally and fertilized according to normal Estonian soil management practice (with a mean rate of N₈₀P₂₃K₄₀ kg ha^-1 year^-1). The average OR content in arable soil ranged from 1.0 to 1.6 g ash-free dry matter (DM_af) kg^-1 soil. The greatest amount of UGP (2.85 g DM_af kg^-1), as a source of OR in soil, was estimated for the 2-year clovergrass mixture. Soil organic carbon accumulated in the composition of OR forms 5.7% of the total organic carbon pool of the plough layer. In regular cropping systems the OR content and pool seem to fluctuate within limits determined by the pedoecological conditions of the soil.     

Earthworm activities and the soil system

Summary Earthworms find in soil the energy, nutrient resources, water and buffered climatic conditions that they need. According to the food resource they exploit and the general environmental conditions, earthworms can be grouped into different functional categories which differ essentially in morphology, size, pigmentation, distribution in the soil profile, ability to dig galleries and produce surface casts, demographic profiles and relationships with the soil microflora. Soil characteristics are both the determinant and the consequence of earthworm activities, since these animals greatly influence the functioning of the soil system. When present, they build and maintain the soil structure and take an active part in energy and nutrient cycling through the selective activation of both mineralization and humification processes. By their physical activities and resultant chemical effects, earthworms promote short and rapid cycles of nutrients and assimilable carbohydrates. Thus earthworms represent a key component in the biological strategies of nutrient cycling in soils and the structure of their communities gives a clear indication of the type of soil system that they inhabit.     

基于多分辨率遥感数据与随机森林算法的土壤有机质预测研究

遥感数据已经在数字土壤制图中得到广泛应用,并且可以一定程度上提高土壤属性预测的精度。本文以榆阳区的黄土丘陵和风沙滩地两种地貌区为例,利用不同分辨率的专题制图仪(thematic mapper,TM)、先进宽视场传感器(advanced wide field sensor,AWIFS)和中等分辨率成像仪(Moderate resolution imaging spectroradiometer,MODIS)的遥感影像数据(分辨率分别为30 m、56 m和250 m)和基于高级热量散射和反射辐射仪全球数字高程模型(advanced spaceborne thermal emission and reflection radiometer global digital elevation model,ASTER GDEM)的地形衍生数据,结合其他影响土壤有机质分布的辅助因子,用随机森林算法(random forest,RF)对表层土壤有机质进行模拟预测,并通过实测数据的百分比抽样对预测结果进行了验证。结果表明,在榆阳区的黄土丘陵区,基于TM数据的土壤有机质预测结果较好;在风沙滩地区,基于AWIFS数据的土壤有机质预测结果较好。基于RF的土壤有机质预测在榆阳区的黄土丘陵区结果较好,三个分辨率下的平均绝对误差在1.27~1.57 g kg-1之间,在风沙滩地区预测精度较低,平均绝对误差在1.46~2.08 g kg-1之间。高程、地理位置和植被是影响黄土丘陵区土壤有机质预测的主要因素,在风沙滩地区,植被、高程和离水源地的距离是影响有机质预测的主要因素。可见,在地貌相对简单的地区进行土壤有机质含量的预测时可以使用较低分辨率的数据代替较高分辨率的数据,同时,RF算法在复杂地貌区的土壤有机质预测更有效。