四川盆地亚热带常绿阔叶林表层土壤氮截留与淋溶流失特征

以四川盆地典型桢楠（Phoebe zhennan）和马尾松（Pinus massoniana）人工林为研究对象,于2013年12月至2014年12月,采用原位培养法监测了雨季（3个时期）和旱季（2个时期）5个关键时期土壤N截留和淋溶输出特征。结果表明：马尾松人工林土壤的N截留和淋溶输出总量分别为17.82,26.95kg/（hm2·a）,桢楠人工林土壤的N截留和淋溶输出总量分别为8.90,17.98kg/（hm2·a）,2种人工林土壤均表现出明显的N截留作用,且硝态氮和水溶性有机氮的输入与输出量显著高于铵态氮和亚硝态氮（P〈0.01）。此外,2种人工林土壤N输入和输出均表现出显著的季节性差异,59.64%～77.14%的N输入过程都发生于旱季末期和雨季早期,且这2个时期的土壤N淋溶输出量分别占全年的44.86%～52.70%。2种人工林土壤在旱季主要表现为N截留效应,而雨季主要表现为N流失。相关性分析结果表明,除桢楠人工林的铵态氮和马尾松人工林的硝态氮外,2种人工林土壤N库的其余N组分淋溶输出量与降水量呈极显著正相关（P〈0.01）,土壤对可溶性无机氮的截留量则与降水量呈负相关。总体而言,桢楠和马尾松人工林土壤N输入、输出和截留作用主要发生于旱季末期,且以硝态氮和水溶性有机氮为主。

生态环境条件与自然灾害及土壤养分的关系

土壤处于岩石圈、水圈,大气圈、生物圈相互紧密交接地带.由于各种物质与能量及各种自然地理要素不断向土壤输入,引起土壤存在的性态变化,形成颜色各异,肥瘦不一,土体构型多样的各种土壤。西藏由于海拔高,气候的独特,土壤类型及其土壤的养分状况有着与其相应的自然因素和人为因素。一.自然条件下西藏的土壤的种类及其养分含量西藏因平均海拔4000多米且相对高差悬殊,高原面广阔、生物气候条件复杂,在土壤的形成发育上极为特殊,成为我国以至世界上颇为罕见的一个自然地域。

土壤有机碳动态对增温的响应及机制研究进展

陆地生态系统碳循环对气候变暖的响应受到土壤有机碳动态的调控。以往的研究开发了多样化的增温方法(如室内培养实验、野外增温实验和温度梯度采样等)来探究土壤有机碳动态对气候变暖的响应及其机制。然而,由于不同增温方法都存在一定的局限性,目前有关增温对土壤有机碳动态影响的研究无法形成一致结论。从过程上看,土壤有机碳动态主要包括碳输入与碳分解两个过程,并受到碳稳定性的调控,这三者的变化共同决定了土壤有机碳动态对增温的响应。先前的研究表明,碳输入和碳分解对增温存在积极响应,这与植物和土壤微生物活性的增强有关。但也有研究指出,由增温导致的土壤理化性质改变(如土壤水分含量降低)以及生物过程变化(如土壤微生物热适应),可能会影响碳输入和碳分解对增温的响应。需要注意的是,表层(0-30 cm)与深层(>30 cm)土壤有机碳动态对增温的响应机制可能存在差异,这是因为深层土壤有机碳的输入和分解过程受环境因子的限制,且稳定性与表层土壤存在较大差异。未来的研究应致力于开发新的增温方法,增加对深层土壤有机碳动态和气候敏感的生态系统的研究,引入新技术研究土壤有机质的来源、结构、保护机制等,关注植物-土壤动物-土壤微生物体系对增温的响应及其对土壤有机碳动态的调控作用,以改善碳循环模型中的不确定性,更准确地预测全球碳循环对气候变暖的反馈。

Improvement of Physical and Biological Quality of Soil in a Sugarcane Plantation through the Management of Organic Matter Input

Changes in soil quality of sugarcane plantation as a result of changes in land management can not be measured directly, but must be demonstrated by measuring the change in the properties of the ecosystem as an indicator. This research aimed to study the effect of the addition of various quality and quantity of organic matter on soil biology （earthworms） and physical quality （aggregate stability, macroporosity and infiltration rate）. There were i 5 treatment combinations tested. The first factor is the type of organic matter： （1） cattle manure （CM）, （2） filter cake （FC）, （3） sugarcane trash （ST）, （4） a mixture ofCM ＋ FC and （5） a mixture of CM ＋ ST. The second factor is the application dose of organic matter, which consists of three levels-5, l0 and 15 Mg/ha. The treatments were arranged in a factorial randomized block design with three replicates and one control treatment （without organic matter input）. The result of this research showed that the highest population density of earthworms was found in the treatment of ST （78 individuals/m2） and a mixture of CM ＋ ST （84 individuals/m2）. The type of organic matter with C/N ratio ranged from 15.5 to 34.7 and cellulose content in 33.3%-40.1% gave better growth of earthworm. The effect of increase in earthworm growth on soil physical improvement is more apparent in the treatment of mixture of low quality and high quality organic matter. The increase of earthworm density and biomass enhanced soil macroporosity （from r = 0.683 to r = 0.606） and infiltration rate （from r = 0.669 to r = 0.756）. The results of this study suggest a mixture of CM ＋ ST or ST alone as organic matters, which is recommended to improve soil physical and biological quality of sugarcane land, with the dose application ranged from 10 Mg/ha to 15 Mg/ha.

Soil pH impact on microbial tetraether lipids and terrestrial input index (BIT) in China

The distributions of microbial tetraether lipids i.e. glycerol dialkyl glycerol tetraethers (GDGTs) were investigated in a variety of Chinese soils featured by a wide range of pH values in different climate zones. The bacterial branched GDGTs and archaeal isoprenoid GDGTs were found to be widely distributed in Chinese soils and their relative abundance was controlled primarily by soil pH. The bacterial bGDGTs usually dominate over archaeal iGDGTs in abundance when the soil pH is below 8.0. However archaeal iGDGTs become dominant and the abundance of halophilic archaea characterized by GDGT V without cyclopentyl ring increases dramatically in the alkaline soil with pH greater than 8.0. The relative abundance of archaeal iGDGTs to bacterial bGDGTs was defined here as RAI index. The RAI index decreases with elevated soil pH and a linear correlation is found between them indicating that the relative abundance of archaeal iGDGTs to bacterial bGDGTs increases with increased pH. The RAI index thus could be a novel proxy of the pH values of paleosol. The terrestrial input index BIT (Branched and Isoprenoid Tetraethers Index) decreases with increased soil pH suggesting that soil pH should be taken into consideration when the terrestrial contribution to marine sediments is estimated by BIT index. Moreover the TEX86 index cannot be used to reconstruct sea surface temperature in the sediments featured by a large terrestrial input.

Impacts of changed litter inputs on soil CO_2 efflux in three forest types in central south China

Climate change is expected to cause the alteration of litter production in forests, which may result in substantial changes in soil CO2 effiux （FCO2） process as litter represents a major pathway of carbon from vegetation to the soils. In this study, we conducted an aboveground litter manipulation experiment to examine the influence of litter addition and exclusion on soil FCO2 in Camphor tree, Masson pine, and mixed Camphor tree and Masson pine forests in central south China. Litter input manipulation included three treatments： nonqitter input （litter exclusion）, double litter input （litter addition）, and natural litter input （control）. On average, litter exclusion significantly reduced soil FCO2 rate by approximately 39%, 24% and 22% in Camphor tree forests, the Mixed forests, and Masson pine forests, respectively. On a yearly basis, double litter addition significantly increased soil CO2 by 12% in the Mixed forests （P=0.02） but not in both Camphor tree and Masson pine forests （P〉0.05）, when compared with their corre- sponding control treatments. However, litter addition increased soil FCO2 rates in the months of June-August in Camphor tree and Masson pine forests, coinciding with high soil temperature of summer conditions. Litter exclusion reduced soil FCO2 more than litter addition increased it in the study sites. Responses of soil respiration to litter input treatments varied with forest types. Litter input treatments did not alter the seasonal patterns of soil temperature and soil water content. Our results indicated that changes in aboveground litter as a result of global climate change and/or forest management have a great potential to alter soil respiration and soil carbon balance in forest ecosystems.

Estimation of Soil Carbon Input in France: An Inverse Modelling Approach

Development of a quantitative understanding of soil organic carbon （SOC） dynamics is vital for management of soil to sequester carbon （C） and maintain fertility, thereby contributing to food security and climate change mitigation. There are well-established process-based models that can be used to simulate SOC stock evolution; however, there are few plant residue C input values and those that exist represent a limited range of environments. This limitation in a fundamental model component （i.e., C input） constrains the reliability of current SOC stock simulations. This study aimed to estimate crop-specific and environment-specific plant-derived soil C input values for agricultural sites in France based on data from 700 sites selected from a recently established French soil monitoring network （the RMQS database）. Measured SOC stock values from this large scale soil database were used to constrain an inverse RothC modelling approach to derive estimated C input values consistent with the stocks. This approach allowed us to estimate significant crop-specific C input values （P 〈 0.05） for 14 out of 17 crop types in the range from 1.84 =h 0.69 t C ha-1 year-1 （silage corn） to 5.15 =k 0.12 t C ha-1 year-1 （grassland/pasture）. Furthermore, the incorporation of climate variables improved the predictions. C input of 4 crop types could be predicted as a function of temperature and 8 as a function of precipitation. This study offered an approach to meet the urgent need for crop-specific and environment-specific C input values in order to improve the reliability of SOC stock prediction.

Compost Input Effect on Dryland Wheat and Forage Yields and Soil Quality

Organic agricultural systems rely on organic amendments to achieve crop fertility requirements, and weed control must be achieved without synthetic herbicides. Our objective was to determine the crop yield and soil quality as affected by a transition from grass to dryland organic agriculture in the Central Great Plains of North America. This study evaluated three beef feedlot compost(BFC)treatments in 2010–2015 following biennial application rates: 0(control), 22.9, and 108.7 t ha^(-1) on two dryland organic cropping systems: a wheat(Triticum aestivum)-fallow(WF) rotation harvested for grain and a triticale(Triticosecale)/pea(Pisum sativum)-fallow(T/P-F) rotation harvested for forage. The triticale + pea biomass responded positively to the 108.7-t ha^(-1) BFC treatment,but not the 22.9-t ha^(-1) BFC treatment. The wheat biomass was not affected by BFC addition, but biomass N content increased.Beef feedlot compost input did not increase wheat grain yields, but had a positive effect on wheat grain Zn content. Soil total C and N contents increased with the rate of 108.7 t ha^(-1) BFC after three applications, but not with 22.9 t ha^(-1) BFC. Soil enzyme activities associated with N and C cycling responded positively to the 108.7-t ha^(-1) BFC treatment. Saturated salts were high in the soil receiving 108.7 t ha^(-1) of BFC, but did not affect crop yields. These results showed that BFC was effective in enhancing forage yields, wheat grain quality, and soil C and N, as well as specific microbial enzymes important for nutrient cycling. However, the large rates of BFC necessary to elicit these positive responses did not increase grain yields, and resulted in an excessive buildup of soil P.