箭叶锦鸡儿群落加速亚高山草甸-箭叶锦鸡儿-硕桦林演替系列的演替进程(英文)

利用PVC管顶盖埋管原位培育法测定了东灵山顶亚高山草甸 (紫苞风毛菊 (SaussureaiodostegiaHonce) 丝柄苔草 (CarexcapillarisL .)_箭叶锦鸡儿 (Caraganajubata (Pall.Poir.) )灌丛_硕桦林 (BetulacostataTrautv .)演替序列中土壤有机N的年度净矿化与硝化作用 ,并以之作为土壤供氮能力的指标 ,比较了锦鸡儿灌丛与硕桦林和草甸土壤的供氮能力和维持氮素的能力。结果表明 ,3个生态系统土壤无机氮库 (包括NH 4 N和NO-3 _N)及净N矿化与硝化速率都存在明显的季节变化 ;除 1996年 6月硕桦林 (P <0 .0 1)和草甸NH 4_N显著高于锦鸡儿灌丛 (P <0 .0 1) ,1996年 8月锦鸡儿灌丛NO-3 _N显著高于草甸 (P <0 .0 5 )外 ,在不同取样时期无机氮库大小在 3个生态系统之间都不存在显著差异 ;锦鸡儿灌丛每公顷的年度总矿化量 (16 .0 1kg·hm-2 )高于硕桦林 (12 .0 5kg·hm-2 )和草甸 (1.6 4kg·hm-2 ) ;净硝化量 (11.37kg·hm-2 )略高于草甸 (10 .90kg·hm-2 ) ,低于硕桦林 (14.36kg·hm-2 )。尽管锦鸡儿灌丛土壤无机氮含量 ,矿化、硝化速率并不明显高于硕桦林和草甸 ,但其总年度净矿化量最高 ,所以锦鸡儿灌丛土壤的供氮能力在 3个群落中最强。此外 ,由于锦鸡儿灌丛的总年度硝化量低于硕桦林 ,略高于草甸 ,因此 ,锦鸡儿灌     

放牧对滇西北高原纳帕海沼泽化草甸湿地土壤氮转化的影响

选择位于滇西北高原纳帕海国际重要湿地内的典型沼泽化草甸湿地为研究对象,采用原位土柱室内控制实验法研究了放牧干扰(猪翻拱扰动和牲畜践踏)对沼泽化草甸湿地土壤氮转化的影响。研究结果表明,放牧活动显著提高了沼泽化草甸湿地表层土壤的容重和pH值,降低了土壤含水率、TOC、TN和NH_4~+-N含量,而对NO_3~--N含量影响不显著。放牧干扰下沼泽化草甸湿地土壤的矿化速率和硝化速率均表现为猪翻拱扰动样地(ZG)牲畜践踏样地(JT)对照样地(CK);表现为ZGJTCK。放牧干扰促进了沼泽化草甸湿地土壤的矿化和硝化作用,猪的翻拱活动比牲畜践踏活动对土壤氮矿化和硝化作用的促进作用更显著。放牧干扰下沼泽化草甸湿地土壤的反硝化速率表现为ZGCKJT,猪的翻拱活动促进了土壤N_2O气体的排放,而牲畜践踏活动抑制了土壤N_2O气体的排放。相关性分析表明,受放牧干扰的沼泽化草甸湿地土壤的矿化和硝化速率均与土壤容重、pH呈显著正相关,与土壤含水率、NH_4~+-N、TOC、TN含量呈显著负相关;反硝化速率与TOC含量呈显著负相关。     

东灵山油松纯林和油松-辽东栎针阔混交林土壤氮素矿化/硝化作用研究

利用PVC顶盖埋管原位培育法测定了北京东灵山地区一个油松纯林和一个油松-辽东栎落叶阔叶混交林生态系统土壤无机氮库、氮素净矿化/硝化速率的季节动态以及年度净矿化/硝化量。结果发现：1）两个生态系统的土壤无机氮库和氮素净矿化/硝化速率都存在比较明显且比较一致的季节动态,但个别时期也存在较大差异;2）纯林与混交林土壤NH+4-N浓度在各月都没有显著差异,而NO-3-N浓度,除了1995年11月和1996年8月纯林显著高于混交林外,其它月份也都差异不显著;3）无论是年度净矿化总量（纯林,22.7kg.hm-2;混交林,55.5kg.hm-2）及其占总全N量的百分比（纯林,0.694%;混交林,2.128%）,还是年度净硝化总量（纯林,26.7kg.hm-2;混交林,44.6kg.hm-2）及其占总全N量（纯林,0.815%;混交林,1.707%）的百分比,油松针阔混交林生态系统均显著大于油松纯林,高达后者的两倍左右,而净硝化氮占净矿化氮的百分比则相反,油松纯林（100%）显著高于油松-辽东栎混交林（80.2%）。上述结果表明：油松-辽东栎针阔混交林生态系统土壤的氮素有效性（即土壤的供氮能力）以及维持土壤中植物可利用氮素的能力都显著高于油松纯林。物种构成及在其影响下所产生的林下微生境和人为干扰活动可能是造成这种差异的主要原因。     

三江平原典型小叶章湿地土壤氨挥发特征及影响因素

采用通气法对三江平原典型草甸小叶章湿地和沼泽化草甸小叶章湿地土壤的氨挥发进行了原位测定,并对其主要影响因素进行了分析。结果表明,二者的氨挥发速率在生长季内的变化趋势基本一致,7月中旬前出现两次挥发高峰和一次低值,之后整体呈严格单调下降趋势,后者的氨挥发速率较高,平均为前者的1.35±0.53倍;二者累计氨挥发量的变化趋势也基本一致,7月中旬前增加迅速,且值比较接近;之后增加缓慢,但其值发生明显分异,表现为后者大于前者;生长季内,典型草甸小叶章湿地土壤的氨挥发总量为6.35 kg N.hm-2,而沼泽化草甸小叶章湿地则为6.87 kg N.hm-2,二者之比为1∶1.08;氮素物质基础不是影响二者氨挥发过程的重要限制因素,大气温度及其所引起的其它温度波动是影响氨挥发速率变化的重要因素;降水及土壤水分波动与散失是引起氨挥发速率局部波动的重要原因;土壤pH和质地是导致氨挥发速率普遍较低的根本原因;而各种因素综合作用的结果则是引起二者氨挥发速率和氨挥发量变化及差异的主要原因。     

三江平原不同群落小叶章氮素的累积与分配

2004年5—10月,对三江平原典型小叶章草甸和小叶章-苔草沼泽化草甸群落优势植物小叶章的氮素累积与分配特征进行了研究.结果表明：典型草甸和沼泽化草甸小叶章地上器官及枯落物的全氮含量在生长季均呈递减变化,符合指数衰减模型(T_N=Aexp(-t/B₁)+B₂,R²≥0.94),二者根的全氮含量波动较大,且在生长高峰期前的15～30 d存在一个明显的养分蓄积时期.不同器官和枯落物的氮累积量和累积速率(V_N)季节变化明显,且典型草甸小叶章地上部分的氮累积量和V_N明显高于沼泽化草甸,而地下部分则相反.两个群落小叶章不同部位的氮分配比差异明显,其中根分配比高达(59.38±12.86)%和(84.58±3.38)%,地上部分的氮分配比以叶最高,为(24.28±12.09)%和(8.18±3.32)%,其他部分较低.二者地上与地下部分的氮分配比呈相反规律变化,反映了其在氮供给方面的密切联系.典型草甸和沼泽化草甸小叶章氮的年吸收量和最大现存量分别为23.02、36.30 g·m^-2和28.18、51.43 g·m^-2,前者的氮吸收系数(0.017)和利用系数(0.634)明显高于后者(0.015和0.548),说明典型草甸在氮的吸收与利用方面强于沼泽化草甸.     

三江平原不同群落小叶章氮素的累积与分配

2004年5—10月,对三江平原典型小叶章草甸和小叶章-苔草沼泽化草甸群落优势植物小叶章的氮素累积与分配特征进行了研究.结果表明：典型草甸和沼泽化草甸小叶章地上器官及枯落物的全氮含量在生长季均呈递减变化,符合指数衰减模型(T_N=Aexp(-t/B₁)+B₂,R²≥0.94),二者根的全氮含量波动较大,且在生长高峰期前的15～30 d存在一个明显的养分蓄积时期.不同器官和枯落物的氮累积量和累积速率(V_N)季节变化明显,且典型草甸小叶章地上部分的氮累积量和V_N明显高于沼泽化草甸,而地下部分则相反.两个群落小叶章不同部位的氮分配比差异明显,其中根分配比高达(59.38±12.86)%和(84.58±3.38)%,地上部分的氮分配比以叶最高,为(24.28±12.09)%和(8.18±3.32)%,其他部分较低.二者地上与地下部分的氮分配比呈相反规律变化,反映了其在氮供给方面的密切联系.典型草甸和沼泽化草甸小叶章氮的年吸收量和最大现存量分别为23.02、36.30 g·m^-2和28.18、51.43 g·m^-2,前者的氮吸收系数(0.017)和利用系数(0.634)明显高于后者(0.015和0.548),说明典型草甸在氮的吸收与利用方面强于沼泽化草甸.     

滇西北高原纳帕海湿地土壤氮矿化特征

采用树脂芯原位培育法,研究了纳帕海沼泽、沼泽化草甸和草甸土壤氮的矿化特征。结果表明,铵态氮（NH₄⁺-N）为沼泽、沼泽化草甸土壤中无机氮的主要存在形式,分别占无机氮含量的96.76%和75.24%,而硝态氮（NO₃^--N）为草甸土壤中无机氮的主要存在形式,占无机氮含量的58.77%。植物生长期内,纳帕海湿地土壤的净氮矿化速率表现为沼泽化草甸 > 草甸 > 沼泽,表明干湿交替的土壤环境更利于土壤氮矿化作用的进行,土壤中氮素有效性和维持植物可利用氮素的能力更强。整个生长季,沼泽和草甸土壤氮矿化为硝化作用,而沼泽化草甸土壤氮矿化为氨化作用。土壤硝态氮含量、有机质含量、碳氮比和含水量均对纳帕海沼泽、沼泽化草甸和草甸土壤的氮矿化产生显著影响。     

晋西北不同年限小叶锦鸡儿灌丛土壤氮矿化和硝化作用

利用PVC管顶盖埋管法研究了晋西北黄土高原区小叶锦鸡儿人工灌丛不同定植年限(5,10,20,30,40a)土壤氮矿化与硝化速率的动态和净矿化与硝化总量。结果表明,⑴小叶锦鸡儿灌丛土壤无机氮主要以NO_-~3-N形式存在,不同生长年限相同月份的土壤硝态氮(NO-3-N)含量分别是铵态氮(NH+4-N)含量的1.5—15.4倍;⑵土壤氮素硝化速率和矿化速率随生长年限延长而加快,30年生时达到高峰,数值达40.2,44.1 mg m~(-2)d~(-1)。从季节性变化看,7—8月份是硝化速率和矿化速率快速增长期,30年生小叶锦鸡儿灌丛土壤硝化速率和矿化速率分别达到86.9,93.1 mg m~(-2)d~(-1),显著高于其它生长年限(P0.05);(3)土壤氮素硝化与矿化总量同样随小叶锦鸡儿生长年限延长而增加,30年生时达到最高,与5年生相比,分别增加了3.7和3.1倍。(4)5—10月份小叶锦鸡儿生长期内,各年限土壤全氮量的2.3%被矿化成无机氮,其中87%最终被转化成NO-3-N形式存在于土体中。     

氮磷添加对亚热带常绿阔叶林土壤氮素矿化的影响

设计了2种处理(即氮添加,100 kg N·hm-2·a-1;氮磷添加,100 kgN·hm-2·a-1+50kgP·hm-2·a-1),研究了氮磷添加对亚热带北部常绿阔叶林土壤无机氮和氮素矿化的影响.结果表明,不同处理0 ～ 10 cm和10 ～ 20 cm土层无机氮(铵态氮+硝态氮)含量年平均值分别为:对照7.27和6.80 mg·kg-1、氮添加13.94和8.92 mg·kg-1、氮磷添加11.20和7.13 mg·kg-1,其中铵态氮分别占90.66％和91.15％、65.78％和72.85％、84.64％和85.08％.不同处理0～10 cm和10 ～20 cm土层的净氨化、净硝化和净氮矿化速率具有相似的季节性变化规律,即夏季氮素净转化速率最高,冬季氮素净转化速率最低,春季和秋季氮素净转化速率有一定差异,但不显著.研究表明,养分添加使土壤年平均净氮矿化速率下降,氮添加使土壤硝化速率下降,氨化速率上升;而氮磷添加使硝化速率上升,氨化速率下降.养分添加对森林生态系统的氮动态影响效应尚需长期定位观测.     

三江平原草甸湿地土壤呼吸和枯落物分解的CO2释放

利用静态箱-碱液吸收法研究了三江平原草甸湿地土壤呼吸和枯落物分解的CO2释放速率,讨论了影响CO2释放的环境因素,估算了枯落物分解的CO2释放对于总释放的贡献.结果表明,生长季,小叶章沼泽化草甸和小叶章湿草甸各部分CO2释放均具有明显的时间变化特征,温度和水分是重要制约因素.两类草甸湿地的平均土壤呼吸速率分别为4.33g·m-2·d-1和6.15g·m-2·d-1,枯落物分解的CO2平均释放速率分别为1.76g·m-2·d-1和3.10g·m-2·d-1,枯落物分解的CO2释放占总释放量的31%和35%,说明在碳素由地上植物碳库转移到地下土壤碳库的过程中,湿地枯落物是一个不可忽略的碳损失源.     

In situ soil net nitrogen mineralization in coastal salt marshes (Suaeda salsa) with different flooding periods in a Chinese estuary

Flooding periods can be one of the most important factors influencing nitrogen (N) biogeochemical processes in wetlands ecosystem. We conducted a field study using in situ incubation method to investigate the seasonal dynamics of soil net N mineralization in three coastal salt marshes (Suaeda salsa) with different flooding periods (i.e., short-term (STF), seasonal (SF), and tidal (TF) flooding wetland) in the Yellow River Delta. Selected soil inorganic N pools (ammonium, nitrate and inorganic N) and N transformation (mineralization, nitrification and ammonification) rates in the top 0–10 cm soils were repeatedly quantified from April to October. Clear seasonal patterns in inorganic N pools and transformation rates were observed in accord with the seasonal variations of temperature and moisture. Generally, higher levels of soil inorganic nitrogen, ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^－-N) occurred in the early-growing season (April), and NH₄⁺-N contents got a small accumulative peak in midsummer (September). The lower rates (negative) of net mineralization (R_min), nitrification (R_nit) and ammonification (R_amm) were observed in the early-growing season (April–June) and fall (September–October), whereas higher values (positive) in midsummer (August–September). Flooding had a significant influence on inorganic N pools (except for NH₄⁺-N) and transformation rates (p < 0.05). R_min values in SF wetland were significantly higher in the August-September period than those in other incubation periods. R_nit values in TF wetland exhibited a small variation and the highest value occured in the June–August period. The results of principal component analysis showed that soil samples were clearly divided into two groups before and after flow-sediment regulation. After flooding events, the R_min and R_amm values generally increased in the three wetlands, whereas a significant decrease in R_nit values was observed in SF wetland (p < 0.05), thus the differences in NO₃^－-N among these wetlands were eliminated. These results suggested that seasonal variations in temperature and moisture are important factors influencing inorganic N pools and transformation rates.     

Net nitrogen mineralization and net nitrification rates in soils following deforestation for pasture across the southwestern Brazilian Amazon Basin landscape

Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO₃ ^?-N and total inorganic N concentrations than pasture soils, but substantial NO₃ ^?-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing.     

Effects of precipitation intensity and temporal pattern on soil nitrogen mineralization in a typical steppe of Nei Mongol grassland

Aims Our objective is to: 1) explore the dynamics of soil nitrogen (N) mineralization in a grassland ecosystem in response to the changes in precipitation intensity and temporal distribution, and 2) identify the controlling factors.Methods The two study sites located in a typical steppe of the Nei Mongol grassland were fenced in 2013 and 1999, respectively. Our field experiment includes manipulations of three levels of precipitation intensity (increased 50%, decreased 50%, control) in three temporal patterns (increased or decreased precipitation for three years; increased or decreased precipitation for two years and no manipulation for one year; increased or decreased precipitation for one year and no manipulation for one year).Important findings 1) The soil net N mineralization and net nitrification rates decreased with changes in the temporal distributions of precipitation from one year to three years, with the maximum values of soil net N mineralization and nitrification rates observed in the treatments of increased or decreased precipitation for one year and no manipulation for one year (+PY1 or -PY1). This indicates that the high precipitation intensity and longer precipitation may have negative effects on soil net N mineralization and nitrification rates, while the moderate soilmoisture and temperature may stimulate soil mineralization. 2) The soil net N mineralization and nitrification rates, soil cumulative N mineralization, and nitrification in the fenced site in 1999 were higher than those in the site fenced in 2013, implying that a long-term enclosure may have promoted nutrient storage and soil quality restoration. 3) The long-term treatments of increased or decreased precipitation had significant effects on soil water content and temperature, whereas the short-term, discontinuous precipitation produced minor effects on soil moisture and temperature. Moreover, the controlling factors for soil N mineralization were different between the two fields. Soil moisture had a major effect on soil inorganic N content and net N mineralization rate in the site fenced in 2013, while soil temperature played a dominant role in the site fenced in 1999, with the net N mineralization rate depressed by higher soil moisture. Our findings suggest that the precipitation intensity and temporal distribution had important impacts on soil N mineralization in the Inner Mongolia grassland; these effects was site-dependent and particularly related to soil texture, community composition, and disturbance, and other factors.     

Seasonal variations in nitrogen mineralization under three land use types in a grassland landscape

Soil nitrogen (N) mineralization is an important component of the N cycling process in ecosystems. In this study, we assessed the seasonal patterns of net soil N mineralization and nitrification using an intact soil core incubation method in the upper 0–10 cm soil layer in three representative land use types. These included a fenced steppe, an abandoned field and a crop field in a grassland landscape of Inner Mongolia, China. The study was conducted from September 2004 to August 2005. Our results demonstrate marked seasonal variations in inorganic N pools, net nitrogen mineralization and net nitrification. Net N mineralization was higher in the crop field than in the fenced steppe and the abandoned field. Daily rates of N mineralization and nitrification during the growing season were approximately twice their corresponding mean annual rates. Accumulative mineralization and nitrification of N during the growing season accounted for about 90 and 85% of that measured for the entire year. Rates of mineralization and nitrification were positively correlated with soil bulk density, but negatively correlated with soil pH. Net N mineralization and nitrification were strongly regulated by land use, precipitation, soil water and temperature.     

亚热带不同林分土壤矿质氮库及氮矿化速率的季节动态

以亚热带地区天然林、格氏栲人工林和杉木人工林为对象,采取PVC管原位培养连续取样法,对不同林分土壤净氨化速率、净硝化速率及净氮矿化速率进行为期一年(2014年9月—2015年8月)的研究,分析林分类型和季节动态对土壤矿质氮库和净氮矿化速率的影响.结果表明: 硝态氮是该地区土壤矿质氮库的主要存在形式,天然林和杉木人工林土壤硝态氮含量分别占总土壤矿质氮库的55.1%～87.5%和56.1%～79.1%,林分间土壤铵态氮含量差异不显著,硝态氮含量差异显著,其中格氏栲人工林土壤硝态氮含量显著低于天然林和杉木人工林.土壤硝态氮库和矿质氮库在不同月份间差异显著,在植物非生长季节(10月至次年2月)较大,在植物生长季节(3—9月)较小.各林分全年土壤净硝化速率均较低,净氨化速率是净氮矿化速率的主要存在形式,林分类型对土壤净氨化速率有显著影响,其中杉木人工林显著低于天然林和格氏栲人工林.月份对土壤净氨化速率有显著影响,各林分土壤净氨化速率变化规律不一致,但均在11月和2月达到一年中的最低值.重复测量方差分析显示,林分类型和季节动态对土壤矿质氮库及氮矿化速率均有显著影响.温度和水分是影响土壤矿质库及氮矿化速率的重要因素,凋落物对土壤氮矿化速率的影响主要是通过质量控制而非数量控制.     

降水变化对科尔沁沙地樟子松人工林土壤氮矿化和淋溶的影响

为研究降水量减少对沙地森林土壤氮循环过程的影响,以科尔沁沙地15年生樟子松人工林为研究对象,野外模拟不同降水量（自然降水、减少30%和50%）对沙地樟子松人工林土壤无机氮（SIN）含量、氮矿化速率和淋溶动态的影响。研究结果发现,沙地樟子松人工林SIN主要以硝态氮形态存在,模拟降水减少降低土壤硝态氮含量（P<0.05）和硝态氮/SIN值（P<0.001）,而增加土壤铵态氮含量（P<0.05）。与自然降水相比,降水减少降低土壤净硝化速率和净矿化速率（P=0.002）,但不同降雨处理的土壤净氨化速率差异不显著（P=0.86）。科尔沁沙地樟子松人工林土壤以硝态氮淋溶为主,不同降雨处理土壤硝态氮淋溶量差异不显著（P=0.09）,但模拟降水减少降低土壤铵态氮淋溶（P=0.04）。此外,沙地樟子松人工林SIN含量、净氮矿化速率和淋溶量具有明显月动态特征,与降雨月动态规律基本一致。降水处理和采样时间对SIN含量和净氮矿化速率具有显著交互作用,但土壤氮淋溶量的交互作用不显著。可见,降水变化能够显著影响科尔沁沙地樟子松人工林土壤氮有效性、氮矿化速率和淋溶等过程,未来干旱加剧可能降低科尔沁沙地樟子松人工林土壤氮的可利用性。