植物凋落物影响土壤有机质分解的研究进展

植物凋落物是土壤动物和土壤微生物的主要生命物质和能量来源,其类型、组成以及物理化学等性质直接决定了土壤有机质的品质。对植物凋落物的类型、品质、物理性质、层效应和激发效应以及根际碳淀积与土壤有机质分解的关系进行了总结,可为研究植物凋落物对土壤有机质的影响提供理论参考,指出要在全球变暖背景下进一步加强凋落物分解过程中土壤微生物和酶活性变化的研究。

土壤有机碳和氮分解对温度变化的响应趋势与研究方法

总结了土壤中碳和氮贮量与温度的关系、土壤碳和氮分解对温度时空差异和直接加热升温的响应,以及土壤碳和氮分解对低温冻结及冻融循环的响应趋势,讨论了其研究方法的误差和不确定性,并对今后的研究提出了一些建议.气候变暖在短期内将使土壤碳和氮分解加速并引起CO2释放量增加,而长期过程中却并不一定会引起土壤碳和氮分解加速.合理解释不同研究结果的差异,除了需要系统分析土壤碳和氮分解对温度变化响应的机制外,还需要充分认识土壤碳和氮分解对温度变化响应的长期过程和短期过程的差异,以及研究方法、植被、土壤和气候等因素的影响.

综论土壤呼吸各组分区分方法

研究土壤呼吸各个组分对土壤总呼吸的贡献是定量评价植物和土壤碳平衡及能量平衡的重要基础。目前区分土壤有机质分解呼吸和根呼吸的方法主要有成分综合法、壕沟法、根分离法、林隙法、根生物量外推法、同位素法,区分纯根呼吸和根际微生物呼吸的方法有同位素稀释法、模拟根际沉降物法1、4CO2动态法、根系分泌物洗涤法、1δ3C微生物量法及一些非同位素法的联合。土壤呼吸各组分区分研究中,区分纯根呼吸和根际微生物呼吸将是未来研究的一个重大课题,区分方法的改进、完善和创新,不同区分方法间的比较研究将是未来研究的一个重要方向。

三峡库区兰陵溪小流域3种林分类型土壤呼吸特征

森林生态系统作为陆地生态系统的主体，其土壤碳库约占全球碳库的73％（Post et a1．，1982），森林土壤呼吸各组分的微小变化都会对大气CO2浓度产生显著影响，进而影响全球气候变化（Rustad et a1．，2000；Schlesinger et a1．，2000）。土壤呼吸即土壤表面的CO：通量，主要由自养呼吸（根呼吸）和异养呼吸（动物微生物呼吸、土壤有机物及凋落物分解等）组成（Shi et a1．，2012，韩天丰等，2011）。

利用天然~(13)C示踪根箱法测定水曲柳、落叶松大树根际激发效应

根际激发效应是调控土壤有机碳和养分循环的第三大因子,仅次于温度、水分因子。以水曲柳和落叶松成年大树为研究对象,利用一种新颖的天然~(13)C同位素示踪的根箱法,测量了野外条件时的根际激发效应。结果表明:天然~(13)C同位素示踪技术与根箱相结合的方法,成功测定了森林中成年大树的根际激发效应,并评估了该方法的优缺点。利用该方法,测得的水曲柳、落叶松的根际激发效应强度,平均值分别为8.7%、9.3%,其范围分别为-11.0%~35.4%、-3.8%~27.5%,但种间的根际激发效应没有显著性差异。

长白山自然保护区生态系统碳平衡研究

运用已建立的EPPML生物地球化学循环模型 ,对 1 995年长白山自然保护区生态系统的碳平衡状况进行了模拟 .模拟结果表明 ,该保护区植被的年净初级生产力 [NPP(碳量 ) ]为 1 3 3 2× 1 0 6 t·a- 1,以阔叶红松林和云冷杉林最高 ,分别为 0 5 4 0× 1 0 6 t·a- 1和 0 4 2 8× 1 0 6 t·a- 1.这 2种林型是长白山面积最大、生产力最高的林型 ,其生产力的模拟结果对整个保护区的碳循环和碳平衡影响最大 ,前者的准确性决定了后者的可靠性 .总的来说 ,模拟值不仅在整个保护区不同植被带和气候带的相对比较中是符合常规的 ,而且在与相当分散的实测数据的绝对比较中也是比较准确的 .该保护区的植被具有明显的碳汇功能 ,主要表现为植被碳量的增长 ,每年增长约 1 0 5 8×1 0 6 t·a- 1.阔叶红松林的年碳量增长最大 (0 4 5 2× 1 0 6 t·a- 1) ,云冷杉林其次 (0 3 3 9× 1 0 6 t·a- 1) .这 2种林型对整个保护区的碳汇功能起着至关重要的决定性作用 .其它依次为 :长白落叶松林、阔叶林、草甸、灌丛、高山苔原、岳桦林和高山流砾滩草类 .1 995年该保护区土壤有机质的分解碳量比凋落物碳量高 0 1 69× 1 0 6 t·a- 1,除草灌土壤出现有机质的积累 。

Responses of Earthworms to Organic Matter at Different Stages of Decomposition

This study was conducted to examine the responses of earthworms to soil organic matter and litter at different decomposition stages and their contributions in litter decomposition processes in southern subtropical areas of China. Two plantations were selected as the study sites: Site I was dominated by the exotic endogeic earthworm species Ocnerodrilus occidentalis; Site II was dominated by epigeic species Amynthas corticis. After the fallen litter and earthworms were removed or expelled, four treatments were set up as: reserving the top soil (0–5 cm, equal to H layer) (H), removing the top soil and adding fresh litter (Le), removing the top soil and adding semi-decomposed litter (Li), and a control with no top soil nor any litter (CK). Five randomized blocks that were enclosed with nylon nets on the top were set up in each site, and then the four treatments were arranged randomly in each block. After 2–3 months, earthworms were collected using the formalin method. The results showed that Ocnerodrilus occidentalis preferred Treatment H though it was found in Treatments Le and Li as well; Amynthas corticis preferred Treatment Li though sometimes it also appeared in Treatment H; and Amynthas sp., another epigeic species, was mainly present under Treatment Le and only appeared in Treatment H occasionally. These findings confirmed that earthworm species belonging to different ecological groups had different responses to organic matter at different decomposition stages. The impacts of earthworm communities dominated by O. occidentalis mainly appeared at the later periods of litter decomposition.

Effect of Reduction Associated with Organic Matter Decomposition on Magnetic Properties of Red Soils

Five soils derived from different parent materials were sampled from red soilregion of southern China and studied by magnetic methodology to understand to what extent ironreduction would affect soil magnetic properties and how iron reduction would affect the magneticminerals in soils. Reduction associated with organic matter decomposition strongly affected soilmagnetic parameters at low pH. The losses of original soil magnetic signals in terms of magneticsusceptibility (X), 'Soft' isothermal remanent magnetization ('Soft' IRM), anhysteretic remanentmagnetization (ARM) and saturation isothermal remanent magnetization (SIRM) at pH 4～6 during thetwo-month saturation treatment, were 66%～94%, 54%～90%, 64%～95% and 33%～83%, respectively. Thesechanges were interpreted as a consequence of substantial dissolution of maghaemite and haematite inthe soils. At pH 10, however, there was no significant magnetic change observed. Moreover, stablesingle domain soil maghaemite grains were also sensitive to reduction, which suggested that bothpedogenic and detrital maghaemite were not stable in acid and reducing environments. Goethite,instead, was the most stable iron form under reducing conditions.

关于酸雨问题

酸雨是包括雨、雪、霜、露、雾、雹等各种形式酸性降水的总称,它对农业生产的影响是随着工业的大规模发展而出现的新问题。酸雨的形成90％以上归因于人为的向大气排放污染物,特别是在燃烧大量煤与石油的能源、冶金、造纸等工厂集中区的下风向地方,问题比较严重。目前世界上以北欧和北美的大湖附近区域为两个酸雨严重污染的中心,日本。

Correlation Between CO_2 Efflux and Net Nitrogen Mineralization and Its Response to External C or N Supply in an Alpine Meadow Soil

In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.

Effects of Temperature and Moisture on Soil Organic Matter Decomposition Along Elevation Gradients on the Changbai Mountains, Northeast China

Decomposition of soil organic matter(SOM) is of importance for CO_2 exchange between soil and atmosphere and soil temperature and moisture are considered as two important factors controlling SOM decomposition. In this study, soil samples were collected at 5 elevations ranging from 753 to 2 357 m on the Changbai Mountains in Northeast China, and incubated under different temperatures(5, 10, 15, 20, 25, and 30?C) and soil moisture levels(30%, 60%, and 90% of saturated soil moisture) to investigate the effects of both on SOM decomposition and its temperature sensitivity at different elevations. The results showed that incubation temperature(F = 1 425.10, P < 0.001), soil moisture(F = 1 327.65, P < 0.001), and elevation(F = 1 937.54, P < 0.001) all had significant influences on the decomposition rate of SOM. The significant effect of the interaction of incubation temperature and soil moisture on the SOM decomposition rate was observed at all the 5 sampling elevations(P < 0.001). A two-factor model that used temperature and moisture as variables fitted the SOM decomposition rate well(P < 0.001) and could explain 80%–93% of the variation of SOM decomposition rate at the 5 elevations. Temperature sensitivity of SOM decomposition, expressed as the change of SOM decomposition rate in response to a 10?C increase in temperature(Q_(10)), was significantly different among the different elevations(P < 0.01), but no apparent trend with elevation was discernible. In addition, soil moisture and incubation temperature both had great impacts on the Q_(10) value(P < 0.01), which increased significantly with increasing soil moisture or incubation temperature. Furthermore, the SOM decomposition rate was significantly related to soil total Gram-positive bacteria(R^2= 0.33, P < 0.01) and total Gram-negative bacteria(R^2= 0.58, P < 0.001). These findings highlight the importance of soil moisture to SOM decomposition and its Q_(10) value,which needs to be emphasized under warming climate scenarios.

Temperature Affects New Carbon Input Utilization by Soil Microbes: Evidence based on a Rapid δ^(13)C Measurement Technology

Strong and rapid responses of soil microbial respiration to pulses,such as those from available soil organic matter(SOM)or water input from precipitation(especially in arid areas),are common.However,how soil microbes utilize new SOM inputs and the effects that temperature may have on their activities are unclear owing to the limitation in the application of traditional isotopic techniques at minute scales.In the present study,we developed a system of measuring 12CO2 and δ^13C minutely and synchronously under controlled incubation temperatures,i.e.,for 48 h at 7,10,15,20,and 25℃,to explore the carbon utilization strategies of soil microbes.We measured the respiration rates of soil microbes in response to different carbon sources,i.e.,added glucose(Rg)and initial SOM(Rs),as well as the total respiration rate(Rt).All responses were rapid and characterized by unimodal curves.Furthermore,the characteristic values of these curves,such as the maximum of rate(R-max),the time required to achieve R-max,and the ratio of the duration of R-max to that of 1/2 R-max,were all dependent on incubation temperature.Interestingly,temperature greatly influenced the strategy that microorganisms employed to utilize different carbon sources.The effects of temperature on the intensity of the microbial respiratory response and the ratio of Rg/Rs are important for evaluating the effect of land-use changes or variations in seasonal temperature on SOM turnover and should be considered in ecological models in future studies.