Soil Microbial Biomass Nitrogen and Its Relationship to Uptake of Nitrogen by Plants

The contents of the soil microbial biomass nitrogen (SMBN) in the soils sampled from the Loess Plateau of China were determined using chloroform fumigation aerobic incubation method (CFAIM), chloroform fumigation anaerobic incubation method (CFANIM) and chloroform fumigation-extraction method (CFEM).The N taken up by ryegrass on the soils was determined after a glasshouse pot experiment. The flushes of nitrogen (FN) of the soils obtained by the CFAIM and CFANIM were higher than that by the CFEM, and there were significantly positive correlations between the FN obtained by the 3 methods. The N extracted from the fumigated soils by the CFAIM, CFANIM and CFEM were significantly positively correlated with the N uptake by ryegrass. The FN obtained by the 3 methods was also closely positively correlated with the plant N uptake. The contributions of the SMBN and mineral N and mineralized N during the incubation period to plant N uptake were evaluated with the multiple regression method. The results showed that the N contained in the soil microbial biomass might play a noticeable role in the N supply of the soils to the plant.

氮硫共掺杂生物炭的制备及其对Ni^(2+)和Co^(2+)的吸附

以芦荟皮为原料、(NH_(4))_(2)SO_(4)为氮源和硫源,采用水热法制备了炭前驱体,再经高温热解制备了氮硫共掺杂生物炭(NSBC)。采用SEM、BET、XPS、Zeta电位对其进行了表征,考察了不同温度热解制备的NSBC对水溶液中Ni^(2+)、Co^(2+)的吸附性能,探究了NSBC吸附Ni^(2+)、Co^(2+)的热力学和动力学过程,分析了温度和pH对其吸附性能的影响,并推测其吸附机理。结果表明,NSBC表面为层片状堆积的多孔结构,热解温度800℃制备的NSBC_(800)具有分级多孔结构,微孔总体积0.07 cm^(3)/g,比表面积149 m^(2)/g,非微孔体积占比46%,其表面具有摩尔分数29.94%的O元素、4.79%的N元素和6.21%的S元素。NSBC_(800)对Ni^(2+)和Co^(2+)的最大平衡吸附量分别为245.70和223.71 mg/g。NSBC表面由O、N和S元素组成的化学官能团吸附Ni^(2+)和Co^(2+)反应生成盐或络合物,沉积在生物炭表面;Langmuir模型和拟二级动力学模型描述的NSBC对Ni^(2+)和Co^(2+)的吸附表明,该过程由化学吸附控制,通过络合作用、共沉淀、离子交换和静电吸引等机制实现对Ni^(2+)和Co^(2+)的吸附。

Effect of Ammonium Fixation on Estimation of Soil Mi－crobial Biomass Nitrogen

The effect of ammonium fixation on the estimation of soil microbial biomass N was studied bv thestandard fumigation-incubation (FI) and fumigation-extraction (FE) methods. NO_3-N content of fumigatedsoil changed little during incubation, while the fixed NH in soils capable of fixing NH increased withthe increase of K_2SO_4-extractable NH_4-N. One day fumigation increased both extractable NH and fixedNH. However, prolonged fumigation gave no further increase. One day fumigation caused significant loss ofNO_3-N, while prolonged fumigation caused no further loss. For soils tested, the net increases of fixed NHin fumigated soil equaled to 0-94% of NH_4-N flush measured by the FI method, and 1-74% of extractable Nmeasured by the FE method, depending on different soils. It is concluded that the ammonium fixation wasone of the processes taking place in soils during fumigation as well as incubation after fumigation and shouldnot be neglected in the estimation of microbial biomass nitrogen by either FI or FE method.

Effect of Ammonium Fixation on Determination of N Mineralized from Soil Microbial Biomass

Two soils with relatively high (Soil 1) and low (Soil 2) ammonium fixation capacities were used in thisstudy to extalne the effect of ammonium fixation on the determination of N mineralised from soil ndcrobialbiomass. organism suspellsioll was quantitatively introduced to Soil 1 at various rates. Both fumigation-incubation (FI) and fumigation-ext raction (FE ) met hods were used to t reat t he soil. The amount of ffeedNH4+-N increased with increasing rate of organism-N addition. A close correlation was found between theamoun of fixed aznmonium and the rate of organism-N addition. The net increso of fixed NH4+-N wereequivalent to 38% and 12% of the added organism-N for FI and FE treatments, respectively in this specificsoil. To provide isotopic evidence, 15N-labelled organism-N was added to Soils 1 and 2 at 121.4 mg N kg-1.In FI treatment, 22 and 3 mg N kg-1 of labelled N were found in the fraction of fixed NH4+-N in Soils 1 and2 respectively; while in FE treatment, 9 mg N kg-1 of labelled N was found in the fraction of fixed NH4+-Nin Soil 1 only. There was no labelled N in the fraction of fixed NH4+-N in Soil 2. In all of the unfumigated(check) soils, there was little or no labelled N in the fixed fractions, probably because the organism-N addedwas easily mineralized and nitrified. A mean of 0.64 for KN value, the fraction of N ndneralized in the killedmicrobial biomass, was obtained with inclusion of the net increase of fixed NH4+-N. The corresponding valuecalculated with exclusion of the net increase of fixed NH4+-N was 0.46. It was concluded that ammniumfixation was a problem in determination of KN, particularly for soils with a high ammonium fixation capacity.Results also showed that microbial biomass N measurement by FE method was less affected by ammoniumprocess than that by FI method.

Effects of Lanthanum on Microbial Biomass Carbon and Nitrogen in Red Soil

The result of soil. culture experiment shows that lanthanum has inhibitory effect on the microbial biomass C and N in red soil, and the inhibition is strengthened with increasing concentration of La. The result of rice pot culture experiment shows that low concentration of La has slight stimulative effect on the microbial biomass C and N in red soil, but its high concentration has inhibitory effect and the inhibition is strengthened with increasing concentration of La. Soil microbial biomass is an important indicator for evaluating rare earths-polluted soil. It is assumed that the critical La concentration is 100 mg.kg(-1) at which red soil tends to be polluted.

Influence of chlorsulfuron herbicide on size of microbial biomass in the soil

A laboratory incubation experiment was conducted to study the effect of chlorsulfuron herbicide on the size of the microbial in loamy sand soil. The herbicide was applied, at four levels that were control, field rate 0\^01 (FR), 0\^1 (10FR) and 1 (100FR) μg/g. Determinations of microbial biomass C content and microbial biomass N content were carried out 1, 3, 5, 7, 10, 15, 25 and 45 days after herbicide application. In comparison to untreated soil, the microbial biomass carbon and biomass nitrogen decreased significantly in soil treated with herbicide in levels 10FR and 100FR within the first 10 days incubation. A more considerable increase in the microbial biomass C∶N ratio was observed in the herbicide treated soil than the non treated control. This effect was transitory and only at the higher rates of chlorsulfuron was significant.

Assessment of bacterial biomass in the highly contaminated urban Nanming River,Guiyang,SW China

High anthropogenic N loads and abundant bacteria are characteristic of highly contaminated urban rivers.To better understand the dispersal and accumulation of bacteria, we determined contents and isotopic compositions of suspended particulate organic matter(SPOM) and bacteria in a highly contaminated urban river(the Nanming)and effluents in winter and summer of 2013. Relative to SPOM, bacterial biomass in the river was depleted in ^(13)C and ^(15)N and its C/N ratio was lower(δ^(13)C:-33.2% ± 3.1%; δ^(15)N:-1.5% ± 1.2%; C/N:4.8 ± 0.6), while effluents showed higher ^(13)C and ^(15)N contents and C/N ratios(δ^(13)C:-25% ± 2.1%; δ ^(15)N:-8.5% ± 1.1%; C/N: 8.1 ± 1.2). Source recognition of SPOM was based on carbon isotopes because they are conservative and distinct between end-members(effluent detritus and bacterial biomass). Using a mixing model,bacterial biomass in the river was calculated to account for <20% and <56% of bulk suspended particulate organic nitrogen in winter and summer, respectively. An N budget showed that bacterial N was a small proportion of total nitrogen(<7.4%) in the riverwater.

Effects of Elevated CO_2 Concentration on the Biomasses and Nitrogen Concentrations in the Organs of Sainfoin(Onobrychis viciaefolia Scop.)

In forage grasses, the nitrogen concentration is directly related to the nutritional value. The studies examined the hypothesis that global elevation of CO2 concentration probably affects the biomass, nitrogen （N） concentration, and allocation and distribution patterns in the organs of forage grasses. While sainfoin （Onobrychis viciaefolia Scop.） seedlings grew on a low nutrient soil in closed chambers for 90 days, they were exposed to two CO2 concentrations （ambient or ambient＋350 μmol mol^-1 CO2） without adding nutrients to them. After 90 days exposure to CO2, the biomasses of leaves, stems, and roots, and N concentrations and contents of different parts were measured. Compared with the ambient CO2 concentration, the elevated CO2 concentration increased the total dry matter by 25.07%, mainly due to the root and leaf having positive response to the elevated CO2 concentration. However, the elevated CO2 concentration did not change the proportions of the dry matters in different parts and the total plants compared with the ambient CO2 concentration. The elevated CO2 concentration lowered the N concentrations of the plant parts. Because the dry matter was higher, the elevated CO2 concentration had no effect on the N content in the plants compared to the ambient CO2 concentration. The elevated CO2 concentration promoted N allocations of the different parts significantly and increased N allocation of the underground part. The results have confirmed the previous suggestions that the elevated CO2 concentration stimulates plant biomass production and decreases the N concentrations of the plant parts.

The Fluxes of Organic C and N, and Microbial Biomass and Maize Yield in an Organically Manured Ultisol of the Guinea Savanna Agroecological Zone of Nigeria

Field experiments were conducted to evaluate the effects of integrated use of agricultural wastes and a compound mineral fertilizer on the fluxes of soil nutrients. Agricultural wastes applied were: livestock manure (cow dung and poultry litter), shoots of Chromolaena odorata and Parkia biglosa (locust bean), Neem (Azadiracta inidca) seed powder/cake and melon shell. These materials were applied at zero (control), 100% (i.e. organic wastes applied at the recommended rates of 10 t/ha) and 70% of their recommended rates plus 30% of the recommended rate of the mineral fertilizer (NPK: 400 Kg/ha). Average values of soil organic carbon (SOC) were 1.94, 1.68, 1.36 and 1.38 for organic wastes alone, organic waste plus mineral fertilizer (NPK) and unamended control. Mineral N ( N plus N) pools were relatively high at 30 and 60 days after planting, and were significantly higher for organically amended soils (550) and wastes applied at reduced rates combined with 120 kg/ha mineral NPK (470) than the unamended control (277). Across sampling dates, SOC values were the highest in poultry manure and neem seed cake. The values of N plus exchangeable N which constitutes plant available nitrogen (PAN) were significantly higher for organically amended soils and wastes applied at reduced rates combined with 120 kg/ha mineral NPK than the unamended control. The % C microbial to C organic ratio was higher in organically amended soils. The temporal profile of SOC, NH4-N and NO3-N showed declines with time, the relationship was linear for SOC (Y = 0.18x + 1.07;R2 = 0.34), by a power function for N (Y = 48.084x-1.79;R2 = 0.91) and a polynomial function for NH4-N (Y = -28.75x + 130.65x - 57.25;R2 = 0.61). The time dynamics of microbial population (cfu) followed trends obtained for SOC.

具有超低镍负载的Ni-C_(3)N_(4)高效催化5-羟甲基糠醛氢解制2,5-二甲基呋喃

生物质平台化合物的选择性氢解对生产可持续化学品和燃料具有重要意义.2,5-二甲基呋喃(DMF)是一种重要的生物基化学品,其不仅可作为汽油添加剂,还可与乙烯发生Diels-Alder环加成脱水反应直接合成生物基对二甲苯.DMF主要通过5-羟甲基糠醛(HMF)氢解制备.当以氢气为氢源时,常用的催化剂体系包括贵金属(如Ru,Pt,Pd)及多种非贵金属(如Ni,Cu,Co)复合催化剂体系.虽然上述催化剂表现出良好的催化性能,但是贵金属的高成本以及非贵金属复合催化剂的回收难等问题阻碍了其工业应用.因此,利用单一非贵金属催化剂实现高效HMF氢化制DMF具有重要意义.本文采用简单的配位-浸渍-热解法制备了超低Ni负载的非贵金属Ni-C_(3)N_(4)/HC催化剂,Ni负载量低至0.86 wt%.在190℃及1.5 MPa氢气条件下,经过4 h反应,HMF完全转化,DMF产率达到94.2%,DMF生产能力可达12.8 mmolDMF mmolNi-1 h^(-1),在已报道的Ni,Co和Cu基催化剂中处于较高水平.此外,Ni-C_(3)N_(4)/HC催化剂表现出良好的稳定性,在固定床反应器中连续反应120 h未见明显失活.透射电镜结果表明,Ni物种高度分散在活性炭载体上,其平均粒径约为2.6 nm.Ni纳米颗粒被约1.3 nm厚的C_(3)N_(4)壳层紧密包裹,有效稳定了Ni纳米颗粒并抑制了其在反应过程中团聚.X射线能谱分析显示,Ni和N元素呈现均匀分布,表明可能形成了Ni_(3)N物种.X射线光电子能谱和电子能量损失谱结果进一步证实了Ni_(3)N物种的存在.密度泛函理论计算结果表明,Ni_(3)N是氢解反应的本征活性组分,它表现出良好的C-O键活化性能.推测反应主要遵循HMF先转化为MF(5-甲基糠醛),再转化为MFA(5-甲基-2-呋喃甲醇),最终生成DMF的路线进行.鉴于Ni-C_(3)N_(4)/HC催化剂中的Ni_(3)N物种表现出了较好的C-O键活化性能,进一步考察了该催化剂对木质素衍生单体和木质素模型化合物的催化性能.实验结果表明,Ni-C_(3)N_(4)/HC催化剂在C-O键活化断裂加氢反应中表现出广泛的适用性.另外,H_(2)处理的活性炭载体也发挥了重要作用:(1)降低了活性炭的含氧量,提高载体热稳定性,并减弱了载体的酸性,从而有效避免了底物的HMF聚合;(2)有助于Ni物种的均匀分散,减少了NiO物种的生成,增加了Ni_(3)N活性物种的含量,从而提升了催化剂的性能.综上,本文制备了超低Ni负载的非贵金属Ni-C_(3)N_(4)/HC催化剂,其表现出高效的HMF氢解制DMF性能及良好的稳定性.同时,该催化剂对木质素衍生单体和木质素模型化合物也有广泛的适用性.本研究为开发用于生物质加氢和氢解反应的单一非贵金属催化剂提供了新思路.

Effects of spring fire and slope on the aboveground biomass, and organic C and N dynamics in a semi-arid grassland of northern China

The aboveground primary production is a major source of carbon(C) and nitrogen(N) pool and plays an important role in regulating the response of ecosystem and nutrient cycling to natural and anthropogenic disturbances. To explore the mechanisms underlying the effect of spring fire and topography on the aboveground biomass(AGB) and the soil C and N pool, we conducted a field experiment between April 2014 and August 2016 in a semi-arid grassland of northern China to examine the effects of slope and spring fire, and their potential interactions on the AGB and organic C and total N contents in different plant functional groups(C_3 grasses, C_4 grasses, forbs, Artemisia frigida plants, total grasses and total plants).The dynamics of AGB and the contents of organic C and N in the plants were examined in the burned and unburned plots on different slope positions(upper and lower). There were differences in the total AGB of all plants between the two slope positions. The AGB of grasses was higher on the lower slope than on the upper slope in July. On the lower slope, spring fire marginally or significantly increased the AGB of C_3 grasses, forbs, total grasses and total plants in June and August, but decreased the AGB of C_4 grasses and A.frigida plants from June to August. On the upper slope, however, spring fire significantly increased the AGB of forbs in June, the AGB of C_3 grasses and total grasses in July, and the AGB of forbs and C_4 grasses in August. Spring fire exhibited no significant effect on the total AGB of all plants on the lower and upper slopes in 2014 and 2015. In 2016, the total AGB in the burned plots showed a decreasing trend after fire burning compared with the unburned plots. The different plant functional groups had different responses to slope positions in terms of organic C and N contents in the plants. The lower and upper slopes differed with respect to the organic C and N contents of C_3 grasses, C_4 grasses, total grasses, forbs, A. frigida plants and total plants in different growing months. Slope position and spring fire significantly interacted to affect the AGB and organic C and N contents of C_4 grasses and A. frigida plants. We observed the AGB and organic C and N contents in the plants in a temporal synchronized pattern. Spring fire affected the functional AGB on different slope positions, likely by altering the organic C and N contents and, therefore,it is an important process for C and N cycling in the semi-arid natural grasslands. The findings of this study would facilitate the simulation of ecosystem C and N cycling in the semi-arid grasslands in northern China.

Plant Biomass, Primary Production and Mineral Cycling of a Mixed Oak Forest in Linnebjer, Sweden

Plant biomass, primary production and mineral cycling were studied in a mixed deciduous forest (Quercus robur L., Tilia cordata L. and Corylus avellana L.) in southern Sweden. Plant biomass amount above and below ground was 201 and 37 t&middotha-1, respectively. Primary production above and below ground was an estimated 13.3 and 2.3 t&middotha-1, respectively. Carbon was the dominant element in the forest ecosystem, comprising 133 t&middotha-1. Other major elements were: N > Ca > K > Si > Mg > S > Mn > P > Fe and Na (range 1123 to 18 kg&middotha-1), followed by some trace elements. Yearly litterfall restored 6.0 t&middotha-1 organic matter or 2.3 t&middotha-1 carbon. Approximately 45% decomposed and returned to the soil during the year. Monitoring of other elements revealed that the ecosystem received inputs through dry and wet deposition, in particular 34.4 kg&middotha-1 S and 9.4 kg&middotha-1 of N yearly as throughfall. Determination of yearly biomass increase showed that the oak forest ecosystem was still in an aggradation or accumulation phase.

Mn对Ru/SiO_(2)催化2,5-己二酮与伯胺合成N-取代-2,5-二甲基吡咯烷的促进作用

采用共浸渍法制备了Mn掺杂的Ru/SiO_(2)催化剂,将其用于2,5-己二酮与伯胺经Paal-Knorr/加氢级联反应合成N-取代-2,5-二甲基吡咯烷,利用XRD,TEM,NH3-TPD,XPS等方法探究了Mn对催化剂结构和性质的影响,并考察了催化剂的稳定性与适用性。实验结果表明,Mn掺杂可提高催化剂中Ru纳米粒子的分散度和催化剂的酸性位,进而提高催化剂的性能。当Ru/Mn摩尔比为1∶2时,催化剂的催化活性最高,在H2O溶剂中130℃、氢气压力3 MPa下反应90 min,2,5-己二酮转化率和N-丁基-2,5-二甲基吡咯烷的收率均达到100%。催化剂重复使用9次后仍保持高活性,且催化剂具有良好的普适性,为N-取代吡咯烷类化合物的绿色合成提供了一种新思路。

免耕与留茬对土壤微生物量C、N及酶活性的影响

2005～2008年在内蒙古呼和浩特市清水河县进行定位试验,设免耕留低茬(NL)、免耕留高茬覆盖(NHS)和传统耕翻(T)3种耕作处理方式。结果表明:(1)免耕留高茬覆盖及免耕留低茬长期实施,能显著提高表层土壤有机质、全氮、全钾、碱解氮、速效磷和速效钾含量,且免耕留高茬覆盖处理比传统耕翻分别提高了11%、41%、22%、15%、29%、27%、13%;在测定各个时期内,土壤各营养指标含量整体趋势为NHS>NL>T。(2)免耕留高茬覆盖及免耕留低茬耕作方式有利于提高土壤微生物量C、N含量,在各测定时期均以免耕留高茬覆盖处理的土壤微生物量C、N含量最高,传统耕翻最低。与传统耕翻相比,免耕留高茬覆盖处理土壤微生物量C、N含量分别平均提高了69%、43%;测定各个时期,不同处理土壤生物量C、N含量均以7月份含量最高、5月份次之、10月份最低。(3)免耕留高茬覆盖及免耕留低茬处理土壤碱性磷酸酶、蔗糖酶、过氧化氢酶活性和脲酶活性高于传统耕翻,整个测定期内免耕留高茬覆盖处理4种酶平均活性,分别较传统耕翻增加了57%、82%、93%和25%;春季土壤酶活性开始增强,在7月份蔗糖酶、过氧化氢酶和脲酶活性达到最大值,而碱性磷酸酶的峰值出现在6月份。土壤微生物量C、N及土壤酶活性是评价土壤质量的重要因子。

人工油松林(Pinus tabulaeformis)恢复过程中土壤微生物生物量C、N的变化特征

采用时空替代法,选取15a（PF15）、25a（PF25）、30a（PF30）的人工油松林作为样地,并选取灌丛作为参考植被,研究了植被恢复过程中土壤微生物生物量C、N以及土壤养分的变化特征,同时探讨了它们之间的相互关系。研究结果表明随着恢复的进行,土壤质量得到了改善,主要表现为有机碳、全氮、粘粒含量、土壤含水量的上升和pH值、容重的下降。土壤微生物生物量C、N分别在155.00~885.64mg/kg和33.73~237.40mg/kg的范围内变化。土壤微生物生物量C、N在植被恢复的初期显著低于灌丛,而后随着恢复的进行逐步增长。土壤微生物生物量C、N与植被恢复时间的相关性没有达到统计学上的显著水平,但是土壤微生物生物量C与土壤有机碳、全氮、全磷呈显著正相关,这表明植被恢复过程中土壤微生物生物量与土壤养分状况关系密切,植被恢复通过改善土壤养分状况间接地影响土壤微生物生物量的变化。Cmic/TOC在1.38%~4.75%的范围内变化。Cmic/TOC随着植被恢复不断下降,Cmic/TOC与植被恢复时间和土壤有机碳呈显著负相关,这表明植被恢复过程中,惰性有机质积累导致供应土壤微生物的活性有机质减少,Cmic/TOC同时受土壤有机质的数量和质量影响。

稻鸭与稻鱼生态系统土壤微生物量N和土壤酶活性动态

在一个水稻生长季节,采用田间采样与室内分析的方法,利用氯仿熏蒸培养法、苯酚钠比色法、TTC比色法、高锰酸钾滴定法和茚三酮比色法测定和研究了稻鸭与稻鱼生态系统稻田土壤微生物量N(MBN)和土壤脲酶、脱氢酶、过氧化氢酶和蛋白酶活性的动态变化,及其与土壤养分和水稻吸N量的相关性。结果表明,(1)随着水稻的生长,土壤微生物量N表现为先上升随后下降,于成熟期有所回升趋势;土壤微生物量N与土壤速效N、全N和全P不相关;由于水稻与微生物对养分的竞争,土壤微生物量N与水稻吸N量不相关;稻田养鸭,养鱼显著地提高了土壤微生物量N。(2)土壤脲酶、脱氢酶和蛋白酶活性都表现出先上升后下降趋势,而过氧化氢酶活性变化不大;稻鸭与稻鱼共作显著地提高了土壤脲酶、脱氢酶和蛋白酶活性,而对过氧化氢酶活性影响不大;线性相关分析表明,在一个稻季内,土壤脲酶和脱氢酶活性与土壤速效N负相关,土壤脲酶、脱氢酶、过氧化氢酶和蛋白酶活性与土壤全N和全P不相关;土壤脲酶、脱氢酶和蛋白酶活性与水稻吸N量呈显著相关。(3)稻田土壤微生物量N与土壤酶不相关。

稻鸭、稻鱼共作生态系统土壤可溶性有机N的动态和损失

通过田间试验研究了稻鸭、稻鱼共作生态系统土壤可溶性有机N(SON)的动态和损失,及其与土壤微生物量N和水稻吸N量的相关性。结果表明,(1)土壤SON是稻田土壤主要的可溶性N,其中处理CK,RD和RF土壤SON库分别为121.16,109.30和113.71 kg/hm2,高于土壤无机N库。(2)土壤SON与土壤可溶性无机N显著正相关(p<0.01);在水稻生育期间,土壤SON含量随水稻的生长而逐渐降低;同时由于鸭和鱼的存在,处理RD和RF土壤SON含量显著低于处理CK;土壤SON与水稻累积吸N量呈显著负相关(p<0.01),表明水稻生长强烈影响着土壤SON。(3)在水稻生长前期,渗漏水各形态N含量最大;溶解性有机N(DON)是稻田渗漏水N素的主要形态;同时,统计分析显示,相对于处理CK,RF土壤SON的下渗淋失量显著降低,RD土壤SON的下渗淋失量则略为降低。(4)水稻生育期间,土壤微生物量N不断地变化着,此外,由于鸭和鱼的存在,相对与处理CK,处理RD和RF土壤显著的提高了土壤MBN。同时,由于水稻吸收和N的淋失,土壤微生物量N与土壤SON不相关。总之,在水稻生长期间,土壤可溶性有机N受水稻吸N、微生物吸N与分解和N淋失的共同作用。

杭州湾滨海湿地芦苇生物量及N、P储量动态变化

以慈溪杭州湾滨海湿地GEF项目区内芦苇(Phragmites australis)为研究对象,采用定位监测和实验室分析相结合的方法,系统分析了其地上生物量、氮、磷含量和储量在生长季节的动态变化,旨在为GEF项目的实施提供科学依据.结果发现,随着时间的推移,各器官生物量逐渐增加,叶片和地上生物量在9月份达到最大,此后又稍有降低,茎则在10月份达到最大;生长初期(4～5月份)叶片生物量氮、磷含量较高,6～7月份随着生物量剧增而迅速下降,8～9月份由于叶片生长放缓,含量又逐渐增加,此后随着叶片衰老又逐渐下降,而茎氮、磷含量在整个生长季节均呈现逐渐下降的过程;各器官氮、磷储量与生物量间存在较好的相关性,其变化趋势与生物量基本相同;叶片氮、磷储量在8月份达到最大值[分别为(10.28±3.88),(0.53±0.21)g/m2];茎和地上储量最大值则出现在9月份[分别为(7.33±2.22),(0.57±0.04),(16.48±1.07),(1.01±0.10)g/m2].

有机、无机肥料施用后土壤生物量C、N、P的变化及N素转化

研究结果表明，有机、无机肥施用后，土壤微生物量C、N、P开始增加很快，随着时间的推移，土壤微生物量C又有所降低，但生物量N和P则基本保持稳定。硫铵施入土壤后，微生物对肥料(15)N的生物固持10天后达到最高峰，以后被固持在体内的(15)N有一部分被逐渐释放出来，但一个月后仍有17％左右的(15)N被固持在微生物体内。硫铵与有机肥配合施用时，微生物对硫铵(15)N固持比例有所增加。有机肥中的15N被微生物固持的比例也较大，在肥料施入20天左右达到最大值，一个月后仍有19—25％存在于微生物体内。硫铵施用一个月后(15)N损失高达18％，有机肥中的N也有少量被损失。

农牧交错带退耕还草对土壤微生物量CN的影响

在农牧交错带以小麦为对照,研究了退耕还草对土壤微生物量C、N的影响。结果表明,0～20cm土层微生物量C、N的大小顺序为:混播草地>相应的单播草地>小麦地。不同单播处理对土壤0～20cm微生物量C、N影响明显。无芒雀麦+冰草(1∶1)在增加土壤微生物量C、N方面效果较佳。一个生长季结束后,单播牧草比小麦能更好地提高土壤的微生物量C、N。