林冠氮添加和林下植被去除对杉木林土壤有机碳组分的影响

为探讨氮添加和林下植被管理对杉木人工林土壤有机碳组分的影响,以福建沙县官庄国有林场杉木人工林为对象,设置对照（CK）、林冠氮添加（CN）、林下植被去除（UR）、林冠氮添加和林下植被去除（CNUR）4个处理的野外控制实验,研究林冠氮添加和林下植被去除对土壤总有机碳、惰性有机碳、易氧化有机碳、颗粒有机碳、微生物生物量碳和水溶性有机碳的影响。结果表明：5年CN添加处理显著降低易氧化有机碳（10—20 cm）和微生物生物量碳（20—40 cm）含量,增加表层土壤颗粒有机碳占总有机碳的比例。UR处理对土壤有机碳组分的作用不显著,而CNUR处理显著降低表层土壤水溶性有机碳含量及其比例。土壤各有机碳组分均与土壤含水量、可溶性有机氮、微生物生物量氮和铵态氮呈显著正相关。研究表明,土壤活性有机碳比惰性有机碳对林冠氮添加（5年）的响应更敏感,且表现为中下层土壤响应大于表层土壤,短期氮添加能促进土壤活性有机碳的分解,而林下植被去除在短时间内可能通过改变土壤含水量和可利用氮减缓有机碳的分解与转化,从而补偿由于氮添加引起的土壤活性有机碳下降,未来需要通过长期氮添加实验进一步研究土壤有机碳动态变化的响应机制。     

Effects of elevated CO2 and nitrogen addition on soil organic carbon fractions in a subtropical forest

Aims

The aim of this study was to investigate the effects of elevated CO₂ concentration and nitrogen addition on soil organic carbon fractions in subtropical forests where the ambient N deposition was high.

Methods

Seedlings of typical subtropical forest ecosystems were transplanted in ten open-top chambers and grown under CO₂ and nitrogen treatments. The treatments included: 1) elevated CO₂ (700?μmol?mol^-1); 2) N addition of 100?kg NH₄NO₃ ha^-1?yr^-1; 3) combined elevated CO₂ and N addition; and 4) control. We measured soil total organic carbon (TOC), particulate organic carbon (POC), readily oxidizable organic carbon (ROC), and microbial biomass carbon (MBC).

Results

Results showed that elevated CO₂ alone did not significantly affect soil TOC, POC and ROC after 4?years of treatment, but increased soil MBC and soil respiration compared to the control. N addition alone had no significant effect neither on soil TOC, POC and ROC, but decreased MBC and soil respiration over time. However, the elevated CO₂ and N addition together significantly increased soil POC and ROC, and had no significant effect on soil MBC.

Conclusions

This study indicated that even in N-rich subtropical forest ecosystems, inputs of N are still needed in order to sustain soil C accumulation under elevated CO₂.     

凋落物去除和氮添加对亚热带阔叶林土壤不同组分碳、氮的影响

人类活动显著增加了氮沉降,对森林生态系统产生了不同程度的影响;凋落物在其分解过程中输入的大量有机碳、氮也会影响土壤碳氮的形成、稳定及转化.本研究选择亚热带常绿阔叶林,对样地进行8年氮添加[对照(0)、低氮(75 kg·hm^-2·a^-1)、高氮(150 kg·hm^-2·a^-1)]和控制凋落物处理(保留凋落物、去除凋落物),之后采集土壤样品,通过K₂SO₄、Na₂B₄O₇、Na₄P₂O₇、NaOH、H₂SO₄、Na₂S₂O₄、HF等化学试剂逐级浸提土壤,测定各浸提液和残渣中的碳、氮含量,研究凋落物及氮添加对土壤矿物结合态碳、氮的影响.结果表明: 整体上,胡敏素(humin,H)组分的土壤碳、氮含量均为最高,分别占土壤全量的33.5%和33.3%.Na₂B₄O₇溶液提取的土壤可溶性碳、氮含量最高,其次是NaOH和Na₄P₂O₇溶液,3种试剂提取的土壤可溶性总碳、可溶性总氮以及可溶性有机氮分别占提取总量的46.2%、47.9%和76.5%.与对照相比,氮添加增加了Na₂S₂O₄和H组分碳、氮含量;与保留凋落物比较,去除凋落物降低了Na₂B₄O₇、H₂SO₄、Na₂S₂O₄和H组分的碳含量,以及NaOH、HF和H组分的氮含量.保留凋落物和氮添加显著增加了K₂SO₄组分氮含量.可见,保留凋落物和外源氮通过影响化学稳定性不同的土壤组分的碳氮变化来改变土壤碳氮过程.     

Impacts of litter and understory removal on soil properties in a subtropical Acacia mangium plantation in China

In forest ecosystems, the effects of litter or understory on soil properties are far from being fully understood. We conducted a study in a pure Acacia mangium Willd. plantation in southern China, by removing litter or understory or both components and then comparing these treatments with a control (undisturbed), to evaluate their respective effects on soil physical, chemical and biological properties. In addition, a litter decomposition experiment was conducted to understand the effects of understory on litter decomposition. Our data showed that the presence of understory favored litter decomposition to a large extent. In 1 year, 75.2 and 37.2% of litter were decomposed in the control and understory removal treatment (UR), respectively. Litter had a profound significance in retaining soil water and contributing to soil fertility, including organic matter (OM), available phosphorus (P) and alkali-hydrolyzable nitrogen (N), but understory exerted less influence than litter on soil physical and chemical properties. Both litter and understory played an important role in soil biological activity as indicated by microbial biomass carbon (MBC), while there were no significant impacts on soil exchangeable potassium (K) after either or both were removed. Contrary to our hypothesis, the effects of understory or litter removal were not always negative. A significant soil pH increase with litter removal was a positive factor for acid soil in the studied site. Except for soil moisture, significant effects, caused by removal of litter or/and understory, on measured soil chemical characteristics were only observed in the top 10 cm soil layer, but not in the 10–20 cm layer. Soil available P and exchangeable K contents were significantly higher in the rainy season than in the dry season, however, for the other soil properties, not substantially affected by season.     

林下植被抚育对樟人工林生态系统碳储量的影响

以亚热带东部地区48年生樟(Cinnamomum camphora)人工林为研究对象, 探讨不同林下植被处理方式对植被和土壤碳储量的影响。研究结果表明: 1)林下植被抚育增加了植被的碳储量, 增幅为48.87%, 平均每年比未抚育林分增加了0.62 t·hm^-2; 2)林下植被抚育降低了土壤有机碳含量, 降低幅度介于4.79%-34.13%之间, 其中0-10 cm、10-20 cm土层比未抚育林分分别降低了10.16 g·kg^-1和8.58 g·kg^-1, 差异达到显著水平(p < 0.05); 3)林下植被抚育降低了森林土壤碳储量, 降低幅度介于1.98%-43.45%之间, 其中0-10 cm和10-20 cm土层分别降低了15.39 t·hm^-2和11.58 t·hm^-2, 差异达到极显著水平(p < 0.01)和显著水平(p < 0.05); 4)林下植被抚育降低了森林生态系统总碳储量, 降低幅度为4.27%, 但差异不显著。因此, 林下植被抚育虽有利于植被碳储量的积累, 但降低了土壤有机碳含量和储量。     

鼎湖山亚热带常绿针阔叶混交林凋落物及矿质氮输入对土壤有机碳分解的影响

2010年7-12月,选取鼎湖山国家级自然保护区亚热带针阔叶混交林,采用全因子控制试验,研究不同类型的凋落物(针叶和阔叶凋落物)添加及氮处理(加氮模拟氮饱和、减氮模拟根吸收)对表层(0～10 cm)和下层(20～30 cm)土壤有机质分解(呼吸)的影响.结果表明： 2010年7-11月间,两种凋落物的添加使土壤-凋落物系统的呼吸速率显著增加,但这种影响在12月消失.减氮和加氮处理均显著增加了土壤-凋落物系统的呼吸.叶凋落物短期内完全分解,对土壤碳分解和积累的影响十分有限,可能不是该系统中土壤有机质的主要来源.通过减少土壤可利用氮模拟根系对氮的吸收能够明显促进土壤有机质的分解.     

间伐和林下植被剔除对毛竹林土壤氮矿化速率及其温度敏感性的影响

选择中亚热带毛竹人工林为研究对象,利用野外原位和室内培养相结合的方法,探讨不同间伐强度(25%间伐、50%间伐)和林下植被剔除对土壤氮矿化速率及其温度敏感性的影响。结果表明,25%间伐显著增加土壤氨化速率(P0.01),但降低硝化速率(P0.01);50%间伐显著增加土壤硝化速率(P0.01),而林下植被剔除显著降低土壤硝化速率(P0.01)。相关分析的结果表明,土壤氨化速率与有机碳(SOC)、全氮(TN)及全磷(TP)含量呈显著负相关关系;硝化速率与SOC、含水量(SWC)呈显著正相关关系,与铵态氮(NH~+_4-N)含量呈显著负相关关系。随着温度的升高,不同处理下的氨化速率均显著增加(P0.01),而硝化速率显著降低(P0.01)。25%间伐显著降低土壤净氮矿化和氨化过程的Q_(10)值,对硝化过程的Q_(10)值影响不显著;50%间伐对氨化和硝化过程的Q_(10)值影响均不显著;林下植被剔除对氨化过程的Q_(10)值影响不显著,但显著增加硝化过程的Q_(10)值。不同处理下的土壤氮矿化过程的Q_(10)值介于1.17—1.36之间。25%间伐和林下植被保留有利于毛竹林土壤氮素的供给。     

氮添加对亚热带常绿阔叶林土壤溶液化学特性的影响

土壤溶液被称作"土壤的血液",是土壤中各种生物化学反应的中介物质,在外界环境发生变化时,土壤溶液化学成分能在其他土壤指标尚无变化之前对环境变化做出迅速响应。为了探索持续增加的大气氮（N）沉降对森林生态系统的影响,以华西雨屏区亚热带常绿阔叶林为对象,设置对照（CK,0 g m^-2 a^-1）,低N（LN,5 g m^-2 a^-1）,高N（HN,15 g m^-2 a^-1）三种N处理,通过人工施加硝酸铵（2017年9月起改施硝酸钠及氯化铵）的方法模拟N沉降增加情景,N处理42个月后,使用负压土壤溶液采样器定位收集A层（37-45 cm）及B层（52-60 cm）土壤溶液,并进行分析（每月1次,为期1 a）。结果表明：对照处理中A、B两层土壤溶液NO₃^-浓度达（3.94±0.77）mg/L、（4.27±1.13）mg/L,N添加显著提高两层土壤溶液NO₃^-浓度和B层NH₄⁺浓度;N添加显著降低土壤溶液pH,且显著增加Al³⁺浓度,Ca²⁺和Mg²⁺含量有增加趋势,但影响不显著;N处理使A层土壤溶液可溶性有机碳（DOC）浓度显著降低,对两层土壤溶液芳香化指数（AI）无显著影响;两层土壤溶液电导率（EC）及氧化还原电位（Eh）显著增加;此外,两层土壤溶液中许多化学成分均呈现极显著相关,特别是NO₃^-与EC相关系数达到了0.855。本研究中,对照处理极高的NO₃^-含量以及B层土壤溶液硝酸盐浓度高于A层,表明该亚热带常绿阔叶林N的有效性超过植物和微生物的总营养需求而发生淋溶,该生态系统已达到氮饱和状态,此外N添加会显著促进土壤酸化和铝离子活化,表层土壤溶液DOC的降低一定程度反映了凋落物分解受N添加的抑制作用,显著升高的氧化还原电位可能导致土壤中某些金属元素的迁移率降低。     

Asynchronous responses of soil microbial community and understory plant community to simulated nitrogen deposition in a subtropical forest

Atmospheric nitrogen (N) deposition greatly affects ecosystem processes and properties. However, few studies have simultaneously examined the responses of both the above- and belowground communities to N deposition. Here, we investigated the effects of 8 years of simulated N deposition on soil microbial communities and plant diversity in a subtropical forest. The quantities of experimental N added (g of N m⁻² year⁻¹) and treatment codes were 0 (N0, control), 6 (N1), 12 (N2), and 24 (N3). Phospholipid fatty acids (PLFAs) analysis was used to characterize the soil microbial community while plant diversity and coverage were determined in the permanent field plots. Microbial abundance was reduced by the N3 treatment, and plant species richness and coverage were reduced by both N2 and N3 treatments. Declines in plant species richness were associated with decreased abundance of arbuscular mycorrhizal fungi, increased bacterial stress index, and reduced soil pH. The plasticity of soil microbial community would be more related to the different responses among treatments when compared with plant community. These results indicate that long-term N deposition has greater effects on the understory plant community than on the soil microbial community and different conservation strategies should be considered.     

Threshold responses of soil organic carbon concentration and composition to multi-level nitrogen addition in a temperate needle-broadleaved forest

Responses of soil organic carbon (SOC) cycling and C budget in forest ecosystems to elevated nitrogen (N) deposition are divergent. Little is known about the N critical loads for the shift between gain and loss of SOC storage in the old-growth temperate forest of Northeast China. The objective of this study was to investigate the nonlinear responses of SOC concentration and composition to multiple rates of N addition, as well as the microbial mechanisms responsible for SOC alteration under N enrichment. Nine rates of urea addition (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha^?1 year^?1) with 4 replicates for each treatment were conducted. Soil samples in the 0–10 cm mineral layer were taken after 3 years of N fertilization. Soil aggregate size distribution and SOC physical fractionation were performed to examine SOC dynamics. Phospholipid fatty acid (PLFA) technique was used to measure the abundance and structure of microbial community. Three years of N addition led to significant increases in the concentrations of soil particulate organic C and aggregate-associated organic C fractions only. The responses of total N and each labile SOC fraction to the rates of N addition followed Gaussian equations, with the N critical loads being estimated to be between 80 and 100 kg N ha^?1 year^?1. The change in SOC concentration (ΔSOC) was positively correlated with the changes in aggregate associated OC (r² > 0.80) and POC concentrations (r² > 0.50). Significant correlations among the concentrations of labile SOC fractions, the percentages of soil aggregates, and the abundances of microbial PLFAs were observed, which implies a close linkage between microbial community structure and SOC accumulation and stability. Our results suggest that increase in soil moisture and shift of microbial community structure could control the critical N load for the switch between C accumulation and loss. The current N deposition rate (~ 11 kg N ha^?1 year^?1) to the northeast China’s forests is favorable for soil C accumulation over the short term.     

氮添加对亚热带毛竹林土壤微生物群落结构的影响

氮沉降会影响森林生态系统地上(如植物生产力和组成)和地下特性(如土壤养分循环),进而影响土壤微生物群落结构和功能。本研究以亚热带戴云山毛竹林为对象,设置N0(0 kg N·hm^-2·a^-1)、N20(20 kg N·hm^-2·a^-1)、N80(80 kg N·hm^-2·a^-1) 3个施氮水平,进行3年的氮沉降模拟实验。通过测定土壤基本理化性质、腐殖化指数和微生物磷脂脂肪酸等指标,研究氮添加对毛竹林土壤养分、腐殖化指数和微生物群落结构的影响。结果显示,N20显著增加土壤腐殖化指数,降低土壤中碱性阳离子总量(K⁺,Na⁺,Ca²⁺,Mg²⁺)、革兰氏阳性菌(G⁺)、革兰氏阴性菌(G^-)、总磷脂脂肪酸含量和G⁺/G^-。与N20相比,N80处理土壤NO₃^-     

Organic carbon and nitrogen losses influenced by vegetation removal in a semiarid mediterranean soil

A reduction in plant cover can lead to an increase in the erosionprocesses that diminish soil quality. Any rise in temperature resulting frompredicted climate changes may aggravate this effect, particularly in semiaridMediterranean areas. Bearing this in mind, the capacity of a soil to preserveorganic matter becomes very important if the soil is to maintain its physicaland chemical properties. Soil organic carbon and nitrogen changes wereevaluatedin a non-disturbed (with natural vegetation) and a disturbed (all vegetationmanually clipped to ground level) pine system. Nine years after vegetationremoval significant differences (p < 0.01) were found in the soil organiccarbon content between plots (top 20 cm), but not in totalnitrogen. In the disturbed plot 0.0232 Mg ha^–1y^–1 of soil organic carbon were lost through erosionand4.30 Mg ha^–1 y^–1 throughmineralization. In the first 48 months after vegetation removal the soilorganiccarbon content fell from 40.3 to 28.0 g kg^–1. Inthe last 60 months of the experiment the amount of organic carbon in the soilfell from 28.0 to 27.7 g kg^–1. This result wasmainly attributable to the intense oxidization, which took place during thefirst 60 months, of organic matter linked to the coarse soil mineral fraction.Up to the 72^nd month the losses by erosion were a total of 532.7g, which rose to 1284.4 g by the end of theexperiment(108 months). The effect of vegetation removal in a Mediterranean semiarid arealeads to a rapid decline in the amount of organic carbon stored in the soil.Such perturbation is irreversible if left to nature.     

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.     

大气CO2浓度上升和氮添加对南亚热带模拟森林生态系统土壤碳稳定性的影响

大气CO₂浓度升高和氮(N)添加对土壤碳库的影响是当前国际生态学界关注的一个热点。为阐述土壤不同形态有机碳的抗干扰能力, 运用大型开顶箱, 研究了4种处理((1)高CO₂浓度(700 µmol·mol^-1)和高氮添加(100 kg N·hm^-2·a^-1) (CN); (2)高CO₂浓度和背景氮添加(CC); (3)高氮添加和背景CO₂浓度(NN); (4)背景CO₂和背景氮添加(CK))对南亚热带模拟森林生态系统土壤有机碳库稳定性的影响。近5年的试验研究表明: (1) CN处理能明显地促进各土层中土壤总有机碳含量的增加, 其中, 下层土壤(5-60 cm土层)中的响应达到统计学水平。(2)活性有机碳库各组分对处理的响应有所差异: 不同土层中微生物生物量碳(MBC)的含量对各处理的响应趋势基本一致, 各土层中的MBC含量均为CN > CC > NN > CK, 其中0-5 cm、5-10 cm、10-20 cm 3个土层的处理间差异都达到了显著水平; 10-20 cm与20-40 cm两个土层中的易氧化有机碳处理间有显著差异; 而对于各土层中水溶性有机碳, 处理间差异均不明显。(3)各团聚体组分中的有机碳含量的响应也有所差异: 20-40 cm与40-60 cm土层中250-2000 μm组分的有机碳含量存在处理间差异; 40-60 cm土层中53-250 μm组分的有机碳对各处理响应敏感, CC处理和NN处理都有利于该组分碳的深层积累, 尤其CN处理下的效果最为明显; 在各处理10-20 cm、20-40 cm及40-60 cm土壤中, < 53 μm组分中的碳含量间差异显著。大气CO₂浓度上升和N添加促进了森林生态系统中土壤有机碳的增加, 尤其有利于深层土壤中微团聚体与粉粒、黏粒团聚体等较稳定组分中有机碳的积累, 增加了土壤有机碳库的稳定性。     

Plasticity of fine-root functional traits in the litter layer in response to nitrogen addition in a subtropical forest plantation

Plant and Soil - Lead (Pb) is one of the most dangerous soil pollutants with high toxicity to plants and animals. However, the molecular mechanisms behind Pb tolerance are poorly understood. Here...     

氮沉降下不同碳添加模式对亚热带毛竹林土壤激发效应的影响

激发效应(PE)在调控陆地土壤碳(C)循环中发挥着重要作用,但在氮(N)沉降日益严重的亚热带森林生态系统中,不同C添加模式对PE的影响尚不清楚。本研究通过添加¹³C标记的葡萄糖,进行90 d的室内培养试验,探究不同施N水平下(0、20、80 kg N·hm^-2·a^-1)C添加模式(单次C添加、重复C添加)对土壤PE的影响。结果表明: 不同模式葡萄糖添加均显著增加了土壤有机C(SOC)矿化,产生了正PE,且单次的葡萄糖添加比重复添加引起的PE更大;随着施N水平的增加,PE显著减弱,表明N沉降抑制了毛竹林土壤激发。相关分析显示,累积PE与β-N-乙酰氨基葡萄糖苷酶(NAG)、过氧化物酶(PEO)活性呈显著负相关,与微生物生物量磷(MBP)、酸碱度(pH)呈显著正相关。综上,施N和C添加共同作用于土壤时,可以通过刺激亚热带森林中原生土壤有机质矿化而对土壤C储量产生强烈影响。本研究证明,单次C添加模式可能高估了外源易分解有机C对PE的影响,而忽略了N沉降对PE的影响,进而高估了森林SOC的矿化损失。