Changes in carbon storage and fluxes in a chronosequence of ponderosa pine

Forest development following stand‐replacing disturbance influences a variety of ecosystem processes including carbon exchange with the atmosphere. On a series of ponderosa pine (Pinius ponderosa var. Laws.) stands ranging from 9 to> 300 years in central Oregon, USA, we used biological measurements to estimate carbon storage in vegetation and soil pools, net primary productivity (NPP) and net ecosystem productivity (NEP) to examine variation with stand age. Measurements were made on plots representing four age classes with three replications: initiation (I, 9–23 years), young (Y, 56–89 years), mature (M, 95–106 years), and old (O, 190–316 years) stands typical of the forest type in the region. Net ecosystem productivity was lowest in the I stands (?124 g C m^?2 yr^?1), moderate in Y stands (118 g C m^?2 yr^?1), highest in M stands (170 g C m^?2 yr^?1), and low in the O stands (35 g C m^?2 yr^?1). Net primary productivity followed similar trends, but did not decline as much in the O stands. The ratio of fine root to foliage carbon was highest in the I stands, which is likely necessary for establishment in the semiarid environment, where forests are subject to drought during the growing season (300–800 mm precipitation per year). Carbon storage in live mass was the highest in the O stands (mean 17.6 kg C m^?2). Total ecosystem carbon storage and the fraction of ecosystem carbon in aboveground wood mass increased rapidly until 150–200 years, and did not decline in older stands. Forest inventory data on 950 ponderosa pine plots in Oregon show that the greatest proportion of plots exist in stands ～ 100 years old, indicating that a majority of stands are approaching maximum carbon storage and net carbon uptake. Our data suggests that NEP averages ～ 70 g C m^?2 year^?1 for ponderosa pine forests in Oregon. About 85% of the total carbon storage in biomass on the survey plots exists in stands greater than 100 years, which has implications for managing forests for carbon sequestration. To investigate variation in carbon storage and fluxes with disturbance, simulation with process models requires a dynamic parameterization for biomass allocation that depends on stand age, and should include a representation of competition between multiple plant functional types for space, water, and nutrients.     

川西亚高山森林土壤呼吸和微生物生物量碳氮对施氮的响应

随着全球大气氮沉降的明显增加,将有可能显著影响我国西部地区受氮限制的亚高山森林生态系统。土壤微生物是生态系统的重要组成部分,是土壤物质循环和能量流动的重要参与者。由于生态系统类型、土壤养分、氮沉降背景值等的差异,土壤呼吸和土壤生物量碳氮对施氮的响应存在许多不确定性。而施氮会不会促进亚高山森林生态系统中土壤呼吸和微生物对土壤碳氮的固定?基于此假设,选择了川西60年生的四川红杉(Larix mastersiana)亚高山针叶林为研究对象,通过4个水平的土壤施氮控制试验(CK:0 g m~(-2) a~(-1)、N1:2 g m~(-2)a~(-1)、N2:5 g m~(-2) a~(-1)、N3:10 g m~(-2)a~(-1)),监测了土壤呼吸及土壤微生物生物量碳氮在一个生长季的动态情况。结果表明:施氮对土壤呼吸各指标和土壤微生物碳氮都有极显著的影响,施氮能促进土壤全呼吸、自养呼吸、异养呼吸通量和土壤微生物生物量碳氮的增长,施氮使土壤呼吸通量提高了11%—15%,土壤微生物量碳提高了5%—9%,土壤微生物量氮提高了23%—34%。在中氮水平下(5 g m~(-2) a~(-1))对土壤呼吸的促进最显著。相关分析发现,土壤呼吸与微生物生物量碳氮和微生物代谢商极呈显著正相关,微生物量碳氮与土壤温度呈极显著的正相关,与土壤湿度呈极显著负相关。通过一般线性回归拟合土壤呼吸速率与土壤10 cm温湿度的关系,发现土壤呼吸速率与土壤温度呈极显著的正相关,与土壤湿度极显著负相关(P0.001),中氮水平下土壤温度敏感性系数Q_(10)值(7.10)明显高于对照(4.26)。     

Anthropogenic nitrogen deposition in boreal forests has a minor impact on the global carbon cycle

It is proposed that increases in anthropogenic reactive nitrogen (N_r) deposition may cause temperate and boreal forests to sequester a globally significant quantity of carbon (C); however, long‐term data from boreal forests describing how C sequestration responds to realistic levels of chronic N_r deposition are scarce. Using a long‐term (14‐year) stand‐scale (0.1 ha) N addition experiment (three levels: 0, 12.5, and 50 kg N ha⁻¹ yr⁻¹) in the boreal zone of northern Sweden, we evaluated how chronic N additions altered N uptake and biomass of understory communities, and whether changes in understory communities explained N uptake and C sequestration by trees. We hypothesized that understory communities (i.e. mosses and shrubs) serve as important sinks for low‐level N additions, with the strength of these sinks weakening as chronic N addition rates increase, due to shifts in species composition. We further hypothesized that trees would exhibit nonlinear increases in N acquisition, and subsequent C sequestration as N addition rates increased, due to a weakening understory N sink. Our data showed that understory biomass was reduced by 50% in response to the high N addition treatment, mainly due to reduced moss biomass. A ¹⁵N labeling experiment showed that feather mosses acquired the largest fraction of applied label, with this fraction decreasing as the chronic N addition level increased. Contrary to our hypothesis, the proportion of label taken up by trees was equal (ca. 8%) across all three N addition treatments. The relationship between N addition and C sequestration in all vegetation pools combined was linear, and had a slope of 16 kg C kg⁻¹ N. While canopy retention of N_r deposition may cause C sequestration rates to be slightly different than this estimate, our data suggest that a minor quantity of annual anthropogenic CO₂ emissions are sequestered into boreal forests as a result of N_r deposition.     

植物与微生物碳利用效率及影响因子研究进展

陆地生态系统碳循环是生物地球化学循环的关键过程之一。碳利用效率（carbon use efficiency,CUE）是描述生物用于形成生物量的碳占其所吸收总碳比例的一个定量指标,反映了生物的碳同化能力和固碳潜力,是研究生态系统碳循环中碳通量和碳分配模式的重要参数,能有效预测生物与周围环境之间的碳流通和碳反馈。目前,关于CUE的研究还不充分,尤其是对CUE及其影响因子的系统性综合论述还较少。为此,本文综述了国内外有关碳利用效率（植物碳利用效率（CUE_a）和微生物碳利用效率（CUE_h））的研究方法和研究进展,分析了CUE_a和CUE_h的异同、内在联系及作用机理。基于分析对今后的研究提出几点展望：（1）优化测量手段和计算方法,适当地调整参数,将模型方法与实测数据结合,使CUE的定量描述结果更准确;（2）结合不同尺度的研究结果,探究个体、种群、群落、生态系统等不同空间尺度和时间尺度上CUE的联系及变化规律,为碳循环和碳流通的时空变化规律提供新证据;（3）研究CUE对全球变化（如高温、干旱、CO₂浓度增加等）的响应,探讨CUE对未来气候情景的响应和适应机制;（4）开展有关物种丰富度或生物多样性的梯度变化对CUE的影响研究,阐释物种多样性减少或物种灭绝等现象对碳循环过程的影响,将生态系统物种多样性与生态系统功能相联系;（5）加强对CUE_h的研究,定量探究其与CUE_a的异同,并将二者结合起来,更全面地解释地上-地下生态系统碳的分配特征。同时适当开展动物CUE的研究,目前该类研究还缺乏系统性。     

Combination of herbivore removal and nitrogen deposition increases upland carbon storage

Ecosystem carbon (C) accrual and storage can be enhanced by removing large herbivores as well as by the fertilizing effect of atmospheric nitrogen (N) deposition. These drivers are unlikely to operate independently, yet their combined effect on aboveground and belowground C storage remains largely unexplored. We sampled inside and outside 19 upland grazing exclosures, established for up to 80 years, across an N deposition gradient (5–24 kg N ha^?1 yr^?1) and found that herbivore removal increased aboveground plant C stocks, particularly in moss, shrubs and litter. Soil C storage increased with atmospheric N deposition, and this was moderated by the presence or absence of herbivores. In exclosures receiving above 11 kg N ha^?1 year^?1, herbivore removal resulted in increased soil C stocks. This effect was typically greater for exclosures dominated by dwarf shrubs (Calluna vulgaris) than by grasses (Molinia caerulea). The same pattern was observed for ecosystem C storage. We used our data to predict C storage for a scenario of removing all large herbivores from UK heathlands. Predictions were made considering herbivore removal only (ignoring N deposition) and the combined effects of herbivore removal and current N deposition rates. Predictions including N deposition resulted in a smaller increase in UK heathland C storage than predictions using herbivore removal only. This finding was driven by the fact that the majority of UK heathlands receive low N deposition rates at which herbivore removal has little effect on C storage. Our findings demonstrate the crucial link between herbivory by large mammals and atmospheric N deposition, and this interaction needs to be considered in models of biogeochemical cycling.     

深圳福田红树林植被碳储量和净初级生产力

红树林是滨海湿地“蓝碳”的主要类型之一.准确和定位评估不同植物群落的固碳能力,对于红树林保育管理和恢复造林具有指导作用.本研究对深圳福田红树林4种代表性群落(白骨壤群落、秋茄群落、海桑群落、无瓣海桑群落)的各个植被碳库组分(乔木植物生物量碳库、林下灌丛碳库、呼吸根碳库、枯立木碳库、枯倒木碳库和枯枝落叶层碳库等)进行调查,计算各群落的植被碳储量,并通过生长增量-凋落物产量法计算得到各群落的净初级生产力.结果表明: 白骨壤群落、秋茄群落、海桑群落和无瓣海桑群落的植被碳储量分别为28.7、127.6、100.1、73.6 t C·hm^-2,各群落的净初级生产力分别为8.75、7.67、9.60、11.87 t C·hm^-2·a^-1.位于深圳市中心的福田红树林,每年固定大气CO₂高达4000 t.本研究结果将为红树林“蓝碳”碳汇功能的评估提供理论指导,并为我国红树林碳汇林建设提供依据.     

氮沉降对森林凋落物分解的影响

氮沉降增加作为全球变化的重要现象之一,已经并将继续对森林凋落物分解产生影响.综述了国内外氮沉降对森林凋落物分解影响及其机理的研究现状.氮沉降对凋落物分解的影响可分为直接影响和间接影响.氮沉降通过影响森林地被物组成和凋落物化学成分,间接影响凋落物分解.氮沉降对凋落物分解的直接影响表现为促进、无影响和抑制3种效果.分析了产生以上影响效果的作用机理,介绍了氮沉降对森林凋落物分解影响的研究方法,探讨了目前研究存在的问题,讨论了未来该方面研究的重点和方向.     

Different types of nitrogen deposition show variable effects on the soil carbon cycle process of temperate forests

Nitrogen (N) deposition significantly affects the soil carbon (C) cycle process of forests. However, the influence of different types of N on it still remained unclear. In this work, ammonium nitrate was selected as an inorganic N (IN) source, while urea and glycine were chosen as organic N (ON) sources. Different ratios of IN to ON (1 : 4, 2 : 3, 3 : 2, 4 : 1, and 5 : 0) were mixed with equal total amounts and then used to fertilize temperate forest soils for 2 years. Results showed that IN deposition inhibited soil C cycle processes, such as soil respiration, soil organic C decomposition, and enzymatic activities, and induced the accumulation of recalcitrant organic C. By contrast, ON deposition promoted these processes. Addition of ON also resulted in accelerated transformation of recalcitrant compounds into labile compounds and increased CO₂ efflux. Meanwhile, greater ON deposition may convert C sequestration in forest soils into C source. These results indicated the importance of the IN to ON ratio in controlling the soil C cycle, which can consequently change the ecological effect of N deposition.     

去除根系和凋落物对滨海沙地3种防护林土壤碳氮库的短期影响

以福建长乐滨海沙地上3种人工林(尾巨桉、纹荚相思、木麻黄)土壤为研究对象,设置去除凋落物、去除根系和对照3种处理,观测1年后分析改变地上、地下有机质输入对沙地土壤碳氮储量、可溶性有机碳(DOC)氮(DON)和微生物量碳(MBC)氮(MBN)的影响。结果表明:不同树种人工林间土壤碳氮储量无显著差异;不同树种人工林间土壤活性碳氮组分差异显著,木麻黄土壤DOC含量显著高于纹荚相思,纹荚相思土壤DON显著高于木麻黄和尾巨桉,尾巨桉土壤MBN显著高于木麻黄和纹荚相思。改变地上地下有机质输入对滨海沙地土壤碳氮库有显著影响且这种影响随树种而异。去除凋落物后纹荚相思、木麻黄土壤碳储量分别下降38.0%、25.1%,氮储量分别下降12.9%、12.5%;去除凋落物后尾巨桉、纹荚相思、木麻黄土壤DOC分别下降37.5%、30.6%、52.9%,MBC分别下降31.0%、56.9%、29.7%,MBN分别下降50.7%、34.9%、42.2%;去除根系后尾巨桉、纹荚相思土壤MBC分别下降57.7%、15.4%。回归分析显示,滨海沙地土壤DOC、MBC与土壤碳储量呈显著正相关,土壤DOC和MBC分别能够解释土壤碳储量变化的47.7%和57.7%。研究表明:树种通过调控地上、地下输入影响可溶性有机碳氮和微生物量碳氮,进而影响土壤碳氮库。     

长白山天然次生林土壤微生物量对氮沉降的响应

土壤微生物作为土壤养分的生物驱动因素,氮沉降会改变其活性和生物量,从而打破土壤养分循环动态平衡。氮沉降对热带、亚热带森林以及温带原始林生态系统土壤微生物量影响的研究较多,但对温带天然次生林影响的研究鲜有报道。于2016年5月(春)、7月(夏)和9月(秋)分别对长白山模拟10年氮沉降的控制试验样地——白桦山杨次生林进行了野外调查。控制试验分为3个氮添加处理,对照(CK 0 kg N hm~(-2)a~(-1))、低氮(LN 25 kg N hm~(-2)a~(-1))和高氮(HN 50 kg N hm~(-2)a~(-1)),按照土壤层(0—10 cm和10—20 cm)分别测试了不同处理的土壤微生物量碳(MBC)和氮(MBN)、土壤全碳(TC)、全氮(TN)和全磷(TP)、p H、土壤可溶性有机碳(DOC)和氮(DON)等指标。结果表明:1)土壤p H在氮沉降的作用下显著降低;上层土壤TC、TN在氮沉降下变化较小,下层土壤TC、TN的含量显著增加;氮沉降下春、夏两季土壤TP含量上升,LN处理在秋季对TP有抑制作用;氮沉降对DOC、DON的影响不显著。2)上层土壤MBC春季到秋季呈现递减的趋势,下层土壤呈现先升后降的趋势,HN对MBC有抑制作用,LN对下层土壤MBC有促进作用;土壤MBN由春季到秋季呈现递减的趋势,且上、下层土壤MBN差异显著;氮处理对春、秋两季MBN有促进作用,夏季有抑制作用;氮沉降使春、秋两季MBC/MBN降低,夏季土壤MBC/MBN升高。3)氮处理、季节变化和土层深度对MBC、MBN存在显著影响,其交互影响也显著。总之,长期氮沉降在生长季对土壤微生物量的影响具有季节性差异,且受到土层深度的影响。未来研究在重视年际变化的同时,也要注重时空动态对氮沉降作用表现出的差异性。     

Carbon and nitrogen cycling in North American boreal forests

A model of boreal forest dynamics was adapted to examine the factors controlling carbon and nitrogen cycling in the boreal forests of interior Alaska. Empirical relationships were used to simulate decomposition and nitrogen availability as a function of either substrate quality, the soil thermal regime, or their interactive effects. Test comparisons included black spruce forests growing on permafrost soils and black spruce, birch, and white spruce forests growing on permafrost-free soils. For each forest, simulated above-ground tree biomass, basal area, density, litterfall, moss biomass, and forest floor mass, turnover, thickness, and nitrogen concentration were compared to observed data. No one decay equation simulated forests entirely consistent with observed data, but over the range of upland forest types in interior Alaska, the equation that combined the effects of litter quality and the soil thermal regime simulated forests that were most consistent with observed data. For black spruce growing on permafrost soils, long-term simulated forest dynamics in the absence of fire resulted in unproductive forests with a thick forest floor and low nitrogen mineralization. Fires were an important means to interrupt this sequence and to restart forest succession.     

Experimental litterfall manipulation drives large and rapid changes in soil carbon cycling in a wet tropical forest

Global changes such as variations in plant net primary production are likely to drive shifts in leaf litterfall inputs to forest soils, but the effects of such changes on soil carbon (C) cycling and storage remain largely unknown, especially in C‐rich tropical forest ecosystems. We initiated a leaf litterfall manipulation experiment in a tropical rain forest in Costa Rica to test the sensitivity of surface soil C pools and fluxes to different litter inputs. After only 2 years of treatment, doubling litterfall inputs increased surface soil C concentrations by 31%, removing litter from the forest floor drove a 26% reduction over the same time period, and these changes in soil C concentrations were associated with variations in dissolved organic matter fluxes, fine root biomass, microbial biomass, soil moisture, and nutrient fluxes. However, the litter manipulations had only small effects on soil organic C (SOC) chemistry, suggesting that changes in C cycling, nutrient cycling, and microbial processes in response to litter manipulation reflect shifts in the quantity rather than quality of SOC. The manipulation also affected soil CO ₂ fluxes; the relative decline in CO ₂ production was greater in the litter removal plots (?22%) than the increase in the litter addition plots (+15%). Our analysis showed that variations in CO ₂ fluxes were strongly correlated with microbial biomass pools, soil C and nitrogen (N) pools, soil inorganic P fluxes, dissolved organic C fluxes, and fine root biomass. Together, our data suggest that shifts in leaf litter inputs in response to localized human disturbances and global environmental change could have rapid and important consequences for belowground C storage and fluxes in tropical rain forests, and highlight differences between tropical and temperate ecosystems, where belowground C cycling responses to changes in litterfall are generally slower and more subtle.     

黄土高原不同乔木林土壤微生物量碳氮和溶解性碳氮的特征

选取黄土丘陵区子午岭4种不同乔木林下的0—5 cm和5—20 cm的土壤为研究对象,通过氯仿熏蒸浸提方法测定了微生物量碳氮、溶解性碳氮以及土壤的理化性质。研究结果表明,不同乔木林下0—5 cm土层土壤微生物量氮(MBN)土壤微生物量碳(MBC)均表现为:辽东栎侧柏油松刺槐,5—20 cm土层为:侧柏辽东栎油松刺槐,说明不同乔木林对土壤表层和下层的微生物量有明显的影响。上层土壤溶解性碳(DOC)、溶解性氮(DON)大于下层土壤。土壤微生物量碳氮比(MBC/MBN)在4—8之间,MBC/MBN、MBN、MBC均表现为随着土层的深度逐渐降低的趋势。MBC与MBN具有显著的正相关性,MBN、MBC与有机碳(SOC)、土壤全氮(TN)、MBC/MBN、溶解性碳与微生物量碳之和(DOC+MBC)、溶解性氮与微生物量氮之和(DON+MBN)呈现出极显著的正相关性(P0.01)。DOC+MBC、DON+MBN比DOC、DON、MBC、MBN更能反映土壤微生物量与活性碳氮库。总体来说,人工刺槐林对土壤碳氮库的增加有一定的作用,但是相对于辽东栎和侧柏等天然次生林有一定的差距。     

Anthropogenic nitrogen deposition enhances carbon sequestration in boreal soils

It is proposed that carbon (C) sequestration in response to reactive nitrogen (N_r) deposition in boreal forests accounts for a large portion of the terrestrial sink for anthropogenic CO₂ emissions. While studies have helped clarify the magnitude by which N_r deposition enhances C sequestration by forest vegetation, there remains a paucity of long‐term experimental studies evaluating how soil C pools respond. We conducted a long‐term experiment, maintained since 1996, consisting of three N addition levels (0, 12.5, and 50 kg N ha^?1 yr^?1) in the boreal zone of northern Sweden to understand how atmospheric N_r deposition affects soil C accumulation, soil microbial communities, and soil respiration. We hypothesized that soil C sequestration will increase, and soil microbial biomass and soil respiration will decrease, with disproportionately large changes expected compared to low levels of N addition. Our data showed that the low N addition treatment caused a non‐significant increase in the organic horizon C pool of ~15% and a significant increase of ~30% in response to the high N treatment relative to the control. The relationship between C sequestration and N addition in the organic horizon was linear, with a slope of 10 kg C kg^?1 N. We also found a concomitant decrease in total microbial and fungal biomasses and a ~11% reduction in soil respiration in response to the high N treatment. Our data complement previous data from the same study system describing aboveground C sequestration, indicating a total ecosystem sequestration rate of 26 kg C kg^?1 N. These estimates are far lower than suggested by some previous modeling studies, and thus will help improve and validate current modeling efforts aimed at separating the effect of multiple global change factors on the C balance of the boreal region.     

黄土高原不同土壤微生物量碳、氮与氮素矿化势的差异

以采自于黄土高原差异较大的25个农田石灰性耕层土壤为供试土样,对黄土高原主要类型土壤中微生物量碳(Bc)、微生物量氮(BN)和氮素矿化势(NO)的差异性进行了比较研究.结果表明,Bc、BN和NO在不同类型土壤间存在显著差异,由关中平原至陕北风沙区,BC、Bn和NO总体呈现下降趋势,其中以土垫旱耕人为土最高,简育干润均腐土最低,黄土正常新成土和干润砂质新成土居中:土垫旱耕人为土、简育干润均腐土、黄土正常新成土和干润砂质新成土等各土类平均BC分别为305.2μg·g-1,108.4μg·g-1,161.7μg·g-1和125.4μg·g-1,BN分别为43.8μg·g-1,20.3μg·g-1,26.0μg·g-1和30.6μg·g-1,NO分别为223μ·g-1,75μg·g-1,163μg·g-1和193μg·g-1.土壤氮素矿化速率(k)则以简育干润均腐土最大,干润砂质新成土最低,土垫旱耕人为土和黄土正常新成土居中:土垫旱耕人为土、简育干润均腐土、黄土正常新成土和干润砂质新成土的k分别为0.039w-1,0.044w-1,0.031w-1和0.019w-1.不同类型土壤BC、BN与NO的差异,主要与土壤形成过程、输入土壤的植物同化产物和土壤有机质的差异等有关,从较大尺度进一步证明了在黄土高原,土壤有机质是影响BC、BN的主要因子.研究结果对分析黄土高原土壤生产力形成过程具有一定参考价值.     

有机肥氮投入比例对双季稻田根际土壤微生物生物量碳、氮和微生物熵的影响

为探明不同有机肥氮素占总氮投入的百分比对双季稻区早、晚稻各生育时期稻田根际土壤微生物的影响,本研究以大田定位试验为平台,应用氯仿熏蒸-K₂SO₄提取法和化学分析法系统分析了施用化肥N(M₁)、30%有机肥N(M₂)、50%有机肥N(M₃)、100%有机肥N(M₄)和无N对照(M₀)5个不同施肥处理双季稻田根际土壤微生物生物量碳(MBC)、微生物生物量氮(MBN)和微生物熵的差异.结果表明: 在早稻和晚稻各主要生育时期,施肥措施均能提高稻田根际土壤MBC、MBN和微生物熵,各施肥处理根际土壤MBC、MBN和微生物熵均随水稻生育期推进呈先增加后降低的变化趋势,均于齐穗期达到最大值,成熟期为最低值;其中,各处理双季稻田根际土壤MBC、MBN、MBC/MBN值和微生物熵一般均表现为M₄＞M₃＞M₂＞M₁＞M₀,M₂、M₃和M₄处理间均无显著差异,但均显著高于M₀处理.可见,单独施用化肥措施对提高根际土壤微生物生物量碳、氮和微生物熵效果有限,施用有机肥或有机无机肥配施提高根际土壤微生物生物量碳、氮和微生物熵的效果较好.     

Nonlinear root-derived carbon sequestration across a gradient of nitrogen and phosphorous deposition in experimental mesocosms

Enhanced sequestration of plant‐carbon (C) inputs to soil may mitigate rising atmospheric carbon dioxide (CO₂) concentrations and related climate change but how this sequestration will respond to anthropogenic nitrogen (N) and phosphorous (P) deposition is uncertain. We couple isotope, soil C fractionation and mesocosm techniques to assess the sequestration of plant‐C inputs, and their partitioning into C pools with different sink potentials, under an experimental gradient of N and P deposition (0, 10, 30, 60 and 100 kg N ha^?1 yr^?1; and 0, 2, 6, 12 and 20 kg P ha^?1 yr^?1). We hypothesized that N deposition would increase sequestration, with the majority of the C being sequestered in faster cycling soil pools because N deposition has been shown to accelerate the turnover of these pools while decelerating the turnover of slower cycling pools. In contrast to this hypothesis, sequestration into all soil C pools peaked at intermediate levels of N deposition. Given that P amendment has been shown to cause a net loss of soil C, we postulated that P deposition would decrease sequestration. This expectation was not supported by our data, with sequestration generally being greater under P deposition. When soils were amended simultaneously with N and P, neither the shape of the sequestration relationship across the deposition gradient, nor the observed sequestration at the majority of the deposition rates, was statistically predictable from the effects of N and P in isolation. The profound nonlinearities we observed, both for total sequestration responses and the partitioning of C into soil pools with different sink potentials, suggests that the rates of N and P deposition to ecosystems will be the critical determinant of whether they enhance or decrease the long‐term sequestration of fresh plant‐C inputs to soils.     

China's crop productivity and soil carbon storage as influenced by multifactor global change

Much concern has been raised about how multifactor global change has affected food security and carbon sequestration capacity in China. By using a process‐based ecosystem model, the Dynamic Land Ecosystem Model (DLEM), in conjunction with the newly developed driving information on multiple environmental factors (climate, atmospheric CO₂, tropospheric ozone, nitrogen deposition, and land cover/land use change), we quantified spatial and temporal patterns of net primary production (NPP) and soil organic carbon storage (SOC) across China's croplands during 1980–2005 and investigated the underlying mechanisms. Simulated results showed that both crop NPP and SOC increased from 1980 to 2005, and the highest annual NPP occurred in the Southeast (SE) region (0.32 Pg C yr^?1, 35.4% of the total NPP) whereas the largest annual SOC (2.29 Pg C yr^?1, 35.4% of the total SOC) was found in the Northeast (NE) region. Land management practices, particularly nitrogen fertilizer application, appear to be the most important factor in stimulating increase in NPP and SOC. However, tropospheric ozone pollution and climate change led to NPP reduction and SOC loss. Our results suggest that China's crop productivity and soil carbon storage could be enhanced through minimizing tropospheric ozone pollution and improving nitrogen fertilizer use efficiency.     

长期施肥对红壤微生物生物量碳氮和微生物碳源利用的影响

采集湖南省祁阳县红壤长期定位施肥19年的土壤样品,分析长期不同施肥红壤的微生物生物量碳、氮和微生物碳源利用率,以揭示长期施肥对红壤微生物学性状的影响.结果表明：施肥19年后,有机肥单施或与化肥配合施用均显著提高土壤微生物生物量碳、氮和微生物碳源利用率.单施有机肥的土壤微生物生物量碳、氮含量分别为231和81 mg·kg^-1,化肥有机肥配施分别为148和73 mg·kg^-1,均显著高于化肥配施秸秆、不施肥和单施化肥;施用有机肥和化肥配施秸秆的土壤微生物生物量氮占全氮的比例平均为6.0%,显著高于单施化肥和不施肥.Biolog-ECO分析中,平均吸光值(AWCD)的大小为：化肥有机肥配施、单施有机肥>对照>单施化肥、化肥配施秸秆.单施有机肥或与化肥有机肥配施增加了红壤微生物对碳水化合物、羧酸、氨基酸、聚合物、酚类和胺类的碳源利用率;化肥配施有机肥的红壤微生物对聚合物类碳源利用率最高,化肥配施秸秆的红壤微生物对碳水化合物类碳源的利用率最高.表明施用有机肥能显著提高红壤的微生物生物量碳、氮和微生物碳源利用率,提高红壤肥力,保持作物高产.     

石灰性土壤微生物量碳、氮与土壤颗粒组成和氮矿化势的关系

以黄土高原土壤类型和土壤肥力差异较大的25个农田石灰性耕层土壤为供试土样,研究了土壤微生物量碳（BC）、微生物量氮（BN）与土壤氮素矿化势（NO）、全氮（TN）、有机碳（OC）及土壤颗粒组成的关系．结果表明：BC、BN与TN、OC呈极显著正相关（P〈0．01）,表明BC、BN与土壤肥力关系密切,可作为评价土壤质量的生物学指标．BC、BN与NO均呈高度正相关,相关系数分别为0．665和0．741（P〈0．01）．BC、BN、TN、OC、NO与土壤物理性粘粒（〈0．01mm）呈显著或极显著正相关,而与物理性砂粒（〉0．01mm）呈显著或极显著负相关,与物理性粘粒和砂粒比值呈显著或极显著正相关,表明土壤有机质主要通过与土壤物理性粘粒复合而形成有机无机复合体．