Effects of night warming on the uptake of inorganic nitrogen by two dominant species in subalpine coniferous forests

Aims Plant roots play a critical role in the uptake of nutrients, and nitrogen (N) absorption is considered as the first step and a pivotal process in N metabolism of plants. Our objective was to better understand the absorption of two major inorganic N forms (NH₄⁺ and NO₃^-) in subalpine coniferous forests under global warming Methods Experimental warming using infrared heater was applied to two dominant species in subalpine coniferous forests of Sichuan, China, Picea asperata and Abies fargesiivar. faxoniana. The non-invasive micromeasurement technology was used to investigate the effects of warming on the uptake rates of NH₄⁺ and NO₃^- and the potential interactions between these two ions.Important findings Results showed that the maximal net root uptake of NH₄⁺ and NO₃^-occurred at a distance of 17-18 mm and 17 mm from root tips, respectively for P. asperata. and at a distance of 11 mm and 11.5 mm from root tips respectively for A. fargesiivar. faxoniana. Experimental warming elevated the uptake rates of NH₄⁺ and NO₃^- in both species, but the interactions between NH₄⁺ and NO₃^- differed between the two species. While NO₃^- uptake was inhibited in the presence of NH₄⁺ for both P. asperataand A. fargesiivar. faxoniana, net NH₄⁺ uptake was promoted by NO₃^- supply only in P. asperata roots under experimental warming.     

夜间增温和施氮对川西亚高山针叶林土壤有效氮和微生物特性的短期影响

开展亚高山针叶林典型林地土壤有效氮和微生物特性对气候变化的响应研究, 对预测未来气候变化背景下亚高山针叶林生态系统C、N的源/汇功能具有重要意义。该文采用红外辐射加热器模拟增温结合外施氮肥的方法, 研究了川西亚高山针叶林下土壤化学特性、有效氮含量以及微生物生物量对夜间增温和施氮的短期响应。结果表明: 在模拟增温试验期间(2009年4月-2010年4月), 空气平均温度和5 cm土壤平均温度分别比对照提高了1.93和4.19 ℃, 增温幅度分别以夏季和冬季最为显著。增温对土壤pH值、有机碳、全氮和微生物生物量无显著影响。增温在试验前期降低了土壤NH₄ ⁺-N含量, 增加了NO₃ ^--N含量, 其影响程度随着增温时间的延长而下降。施氮显著增加了有效氮和微生物生物量氮, 降低了土壤pH值, 使土壤表现出明显的酸化现象。与单独的增温和施氮处理相比, 增温和施氮联合处理对林下土壤的有效氮和微生物特性有显著的交互作用, 显著增加了土壤的有机碳、有效氮及土壤微生物生物量氮含量, 并导致土壤进一步酸化。结果说明, 川西亚高山针叶林的土壤有效氮和微生物特性对土壤氮素状况的变化反应敏感, 而林下土壤有效氮和微生物特性对单独的温度升高表现出一定的适应性, 但更对增温和施氮双因素结合处理反应敏感且表现出不同的响应方式。因此, 该区域在未来全球变化下的氮沉降状况及气候变化的多因素协同效应值得长期深入的探讨。     

短期夜间增温对亚高山针叶林云杉幼苗根系分泌物速率和化学成分的影响

以连续7a红外辐射增温处理下的云杉幼苗为对象,定量分析了增温对植物根系碳(C)、氮(N)分泌速率以及主要挥发性化学成分的影响。结果表明:(1)增温显著增加了云杉幼苗根系C分泌速率,而对N分泌速率无显著影响,并伴随着根系分泌物C∶N化学计量比显著增加;(2)不同化学组分输入含量变化对增温的响应具有明显差异,其响应幅度和方向与化学组分种类有关。其中糖类、氨基酸和酚类化合物的含量在增温处理下均显著增加,而酯类、醚类相对含量显著降低;(3)进一步分析表明,同组分中不同化合物成分含量对增温的响应也有所差异。例如,增温仅导致酚类化合物中2,6-二叔丁基-4-甲基苯酚和4-叔丁基杯[4]芳烃含量显著增加(分别比对照增加了88.9%和375.7%),而对其余酚类化合物成分含量无显著影响。结果表明增温可导致植物根系分泌物各组分相对含量发生深刻地变化,这对于进一步认识不同环境变化下根系分泌物输入及其所诱导的特异性土壤微生物养分过程具有重要的理论意义。     

夜间增温和施肥对川西亚高山针叶林两种树苗根际效应的影响

开展植物根际效应对全球变化响应的研究是深入认识根际微生态系统中植物根系与土壤微生物相互作用过程及机制的关键。以川西亚高山针叶林两种主要树种幼苗--云杉(Picea asperata)和岷江冷杉(Abies faxoniana)为研究材料,采用红外辐射模拟增温和外施NH₄NO₃氮肥的方法,研究了夜间增温和施肥对两种幼苗根际效应的影响。结果表明:红外辐射增温导致气温增加了1.62 ℃,土壤5 cm和10 cm层月均温度显著增加了2.89 ℃和3.10℃。增温和施肥处理对两种幼苗不同参数根际效应的影响各不相同,表现为不同程度的正根际效应、负根际效应或者无影响。增温使云杉幼苗根际与非根际土SMB-C含量均显著增加(分别为42.28%和31.02%),非根际土有机碳含量降低了7.03%;而增温对两种幼苗土壤肥力因素根际效应的影响总体并不显著,增温仅对云杉全氮有显著的负根际效应(79.43%),而岷江冷杉通过根际土全氮和SMB-N含量的增加,其根际效应大小在增温处理下显著增强。施肥处理和两因子的联合作用显著提高了两种幼苗的NO^-₃-N、NH⁺₄-N和云杉非根际土SMB-N含量,并使岷江冷杉NH⁺₄-N表现出正根际效应,而云杉SMB-N表现出明显的负根际效应(120.80%和253.06%)。这种响应差异可能与不同植物种类地下碳分配及其植物根系所吸收的养分有关,从而赋予了不同植物种类在未来全球变化背景下可能具有不同的适应力和竞争优势,并进一步对亚高山针叶林地下过程及其早期更新产生潜在影响。     

利用海拔差异模拟增温对高山森林土壤溶解性有机碳和有机氮含量的影响

在2010年5月—2011年4月和2011年5月—2012年4月2个培养周期内,采用原状土柱野外控制试验,利用海拔梯度变化研究了温度增加对川西高山森林土壤溶解性有机碳(DOC)和有机氮(DON)动态的影响.结果表明: 经模拟增温处理(降低海拔)的土壤有机层和矿质土壤层DOC和DON含量在2个连续培养周期内的各关键时期均呈现明显的动态变化.海拔3300和3000 m样地比海拔3600 m 样地土层DOC含量分别增加6.8和26.6 mg·kg^-1.海拔3600、3300和3000 m样地土层DOC含量均在第1个培养周期的生长季末最高,分别为408.0、317.9和448.2 mg·kg^-1,在第2个培养周期的生长季节中期最低, 分别为33.1、32.4和36.5 mg·kg^-1.与海拔3600 m样地相比,海拔3300和3000 m样地土层DON含量分别增加2.3和30.4 mg·kg^-1.除海拔3000 m样地以外,海拔3600和3300 m样地土层DON含量在第1个培养周期内的生长季节中期最高,分别为65.9和64.6 mg·kg^-1,在第1个培养周期内的融化期最低,分别为31.9和37.1 mg·kg^-1.模拟增温处理增加了样地内土壤有机层DOC和DON含量,降低了矿质土壤层DOC含量、土壤有机层及矿质土壤层DOC/DON值.土壤有机层DOC/DON值与DOC含量呈显著正相关,与DON含量呈显著负相关;矿质土壤层DOC/DON值与DOC含量呈显著负相关,与DON含量呈显著正相关.未来全球气候变暖可能通过影响高寒森林土壤温度和冻融循环格局,增加整个土层DOC和DON含量,进而影响高寒森林土壤碳、氮循环过程.     

夜间增温对稻田甲烷排放的影响及其高光谱估算

昼夜不对称增温是全球气候变化的主要特征之一,有关夜间增温对稻田甲烷(CH_4)排放影响的报道尚不多见。通过田间模拟试验,研究了被动式夜间增温下水稻田CH_4排放及高光谱的特征,并用高光谱数据对稻田甲烷排放进行定量模拟。田间试验设夜间增温(NW)和对照处理(CK),夜间增温即在整个水稻生育期的夜间(19:00—6:00)用铝箔反射膜覆盖水稻冠层。结果表明,夜间增温显著促进水稻拔节期和抽穗期-灌浆期CH_4排放。水稻冠层近红外光谱反射率表现为,在分蘖期和拔节期时,NWCK;而在抽穗-灌浆期和成熟期时,CKNW。水稻冠层光谱反射率、一阶导数光谱及光谱特征值均与CH_4排放通量显著相关,相关系数最大可达0.8(P0.01),其中以"蓝边面积"(SD_b)构成的二次多项式模型模拟精度和检验精度综合最佳,决定系数R~2分别为0.70和0.72。研究结果对稻田CH_4排放通量遥感监测的可行性提供了理论依据和技术支持。     

增温与氮添加对不同季节杉木幼苗细根不同形态氮吸收动力学的影响

为了揭示不同季节下杉木人工林不同形态氮吸收速率对全球变暖与氮沉降的地下响应,在福建三明森林生态系统与全球变化研究站陈大观测点开展增温和氮添加双因子试验,包括对照、增温、施氮、增温+施氮4个处理。结果表明:(1)在三个季节中,4个处理的杉木细根对不同浓度下硝态氮的吸收速率基本呈现出春季较高,夏秋季较低的态势,而对不同浓度下铵态氮的吸收速率则相反,为夏秋季较高,春季较低。(2)不同季节四个处理的离体根对不同浓度下铵态氮的吸收均遵循米氏-曼氏动力学方程,而对硝态氮的吸收并不完全遵循米氏方程,表现为双相动力学。(3)春季,与无氮添加相比,氮添加提高了NH⁺₄的最大吸收速率(V_max-NH⁺₄)。夏季,与无增温相比,增温提高了V_max-NH⁺₄。秋季,与无增温相比,增温降低了NH⁺₄的半饱和常数(K_m-NH⁺₄);...     

夜间增温对江苏不同年代水稻主栽品种生育期和产量的影响

采用开放式主动增温系统,在江苏省丹阳市开展夜间增温试验,研究夜间温度升高对江苏1970s—2000s 8个主要推广水稻品种生育期和产量的影响.结果表明:不同年代水稻品种的主要生长特性对夜间增温的响应程度存在明显差异,但响应趋势基本一致.全生育期内水稻冠层夜间温度平均升高0.9℃,水稻始穗期平均提前1.1 d,全生育期缩短1.3 d.夜间增温下,花后总绿叶面积和剑叶面积呈下降趋势,成熟期生物学产量和籽粒产量分别平均降低了3.5%和5.1%,植株N含量也降低.产量构成分析发现,夜间增温主要通过降低水稻有效穗数和穗粒数使产量下降,单位面积总颖花数下降了12.6%.品种间并未随年代发展而出现明显的变化趋势,新老品种间差异不显著.     

寒温带针叶林土壤CH4吸收对模拟大气氮沉降增加的初期响应

N沉降作为驱动因子会改变森林土壤－大气界面CH4净交换通量和方向。然而,对引起北方森林土壤CH4吸收发生转变的大气N沉降临界负荷及其响应机制知之甚少。为此,本研究以我国大兴安岭北方寒温带针叶林土壤作为研究对象,参照大兴安岭站实际大气N沉降通量,构建了低剂量、多形态和高频率的大气N沉降模拟增加控制实验,研究了2010年6-10月生长季土壤CH4吸收通量及其驱动因子对增N的初期响应。研究表明：整个生长季,大兴安岭寒温带针叶林土壤作为大气CH4净汇,CH4平均吸收通量为51.5?4.70 ugm-2h-1,主要受0-10cm土壤水分驱动。短期内,0-10cm矿质土壤NH4 -N含量对增N响应敏感;0-10cm矿质土壤NO3--N含量则受NO3--N输入影响较为明显。相反,0-10cm矿质土壤pH对增N的响应不敏感。总体上,低剂量的N输入对大兴安岭寒温带针叶林生长季土壤－大气界面CH4净交换通量影响不显著,而不排除NO3--N 输入尤其是低N处理情形所呈现出促进土壤CH4氧化的趋势。大兴安岭寒温带针叶林土壤CH4吸收对增N的响应敏感程度可能和土壤CH4活性氧化区域,土壤NH4 -N、NO3--N含量空间分布格局和相对比例有关。未来长期低水平的大气N沉降是否会改变大兴安岭北方森林土壤氧化大气CH4趋势,有待研究。     

施硅对夜间增温下南方水稻生长、产量和品质的影响

气温增幅夜间大于白天是全球气候变暖的显著特征之一。夜间增温引起南方单季稻减产,而施硅可提高水稻产量。本研究通过田间模拟试验,分析了施硅对夜间增温下水稻主要生育期植株分蘖数、生物量等生长指标以及产量和品质的影响。增温设2水平：常温对照(CK)和夜间增温(NW),采用被动式夜间增温方法,即夜间(19:00—6:00)用铝箔膜覆盖植株冠层以模拟夜间增温;硅肥(钢渣)用量设2水平：不施硅(Si₀)和施硅(Si₁,200 kg SiO₂·hm^-2)。结果表明：与常温对照比,夜间增温使水稻生长期冠层和5 cm土层夜间平均温度分别升高0.51～0.58℃和0.28～0.41℃。夜间增温使分蘖数和叶绿素含量分别较CK降低2.5%～15.9%和0.2%～7.7%;而施硅使分蘖数和叶绿素含量较不施硅分别提高1.7%～16.2%和1.6%～16.6%。与CK相比,夜间增温下施硅显著提高了灌浆-成熟期地上部干重、全株干重和产量,增幅分别为64.1%、55.3%和7.1%;显著增加了精米率、整精米率和淀粉含量,增幅分别为2....     

Enhanced root exudation stimulates soil nitrogen transformations in a subalpine coniferous forest under experimental warming

Despite the perceived importance of exudation to forest ecosystem function, few studies have attempted to examine the effects of elevated temperature and nutrition availability on the rates of root exudation and associated microbial processes. In this study, we performed an experiment in which in situ exudates were collected from Picea asperata seedlings that were transplanted in disturbed soils exposed to two levels of temperature (ambient temperature and infrared heater warming) and two nitrogen levels (unfertilized and 25 g N m^?2 a^?1). Here, we show that the trees exposed to an elevated temperature increased their exudation rates I (μg C g^?1 root biomass h^?1), II (μg C cm^?1 root length h^?1) and III (μg C cm^?2 root area h^?1) in the unfertilized plots. The altered morphological and physiological traits of the roots exposed to experimental warming could be responsible for this variation in root exudation. Moreover, these increases in root‐derived C were positively correlated with the microbial release of extracellular enzymes involved in the breakdown of organic N (R² = 0.790; P = 0.038), which was coupled with stimulated microbial activity and accelerated N transformations in the unfertilized soils. In contrast, the trees exposed to both experimental warming and N fertilization did not show increased exudation rates or soil enzyme activity, indicating that the stimulatory effects of experimental warming on root exudation depend on soil fertility. Collectively, our results provide preliminary evidence that an increase in the release of root exudates into the soil may be an important physiological adjustment by which the sustained growth responses of plants to experimental warming may be maintained via enhanced soil microbial activity and soil N transformation. Accordingly, the underlying mechanisms by which plant root‐microbe interactions influence soil organic matter decomposition and N cycling should be incorporated into climate‐carbon cycle models to determine reliable estimates of long‐term C storage in forests.     

模拟增温对川西亚高山西类针叶林土壤酶活性的影响

采用开顶式生长室(open top chamber,OTC)模拟增温,同步监测了亚高山人工针叶林和天然针叶林表层土壤温、湿度的变化,以及模拟增温初期土壤转化酶、脲酶、过氧化氢酶和多酚氧化酶活性的变化.结果表明:在整个生长季节中,OTC使人工林和天然林5 am土壤日平均温度分别增加0.61 oC和0.56 ℃,10 am体积含水量分别下降4.10%和2.55%;模拟增温增加了土壤转化酶、脲酶、过氧化氢酶和多酚氧化酶活性.增温与林型的交互作用对土壤脲酶和过氧化氢酶活性有显著影响,而对转化酶和多酚氧化酶影响不显著.增温对过氧化氢酶活性的影响与季节变化相关.在各处理下,天然林土壤酶活性显著高于人工林.土壤酶活性季节动态与土壤温度有着较大相关性,而与土壤水分季节变化关系不明显.模拟增温易于增加土壤酶活性,但增温效应和林型、酶种类和季节变化有一定关系;亚高山针叶林土壤酶活性主要受控于土壤温度,而与土壤水分关系不大.     

Plastic responses of 4 tree species of successional subalpine coniferous forest serals to different light regimes

The morphological and physiological plasticity to 6 light conditions was investigated for seedlings of 4 tree species dominating at different successional serals in subalpine coniferous forests in eastern Qinghai-Tibet Plateau, China. Abies faxoniana is a late successional species, while Betula albo-sinensis is a pioneer tree species, with Picea asperata and Acer davidii among other mid-late successional species. To compare the responses of photosynthetic characters to different growth light conditions, the seedlings were potted and placed in artificially shaded chambers with gradients of 100%, 55%, 40%, 25%, 15% and 7% of the full sunlight, respectively. During two and a half years' cultivation, various morphological and photosynthetic parameters were measured and analyzed. The results were: 1) all seedlings of the four species under the low growth light conditions showed decrease in root collar diameter, relative growth rate, leaf thickness, root mass ratio, leaf area-based photosynthetic capacity, dark respiration rate, light saturation point and light compensation point, while showed increase in specific leaf area, above-ground to under-ground mass ratio, specific stem length, leaf mass ratio and stem mass ratio; 2) under most light conditions, A. faxoniana of the two conifers revealed lower values in both leaf area-based photosynthetic capacity and respiration rates than P. asperata; the same fact held true for the two broad-leaved trees with lower values observed in B. albo-sinensis; 3) under higher light conditions, relative growth rates of P. asperata and B. albo-sinensis got higher values than those of A. faxoniana and A. davidii, while contrary results were obtained under lower light regimes; 4) the means of phenotypic plastic indices of the eleven morphological and physiological parameters of P. asperata and B. albo-sinensis were higher than those of A. faxoniana and A. davidii, respectively. The findings indicate that A. faxoniana has better adaptation to low light regimes, but as a shade-tolerant species, it is not so adapted to low light regimes as the trees of earlier successional serals, especially P. asperata and B. albo-sinensis. Of the four tree species, physiological plastic indices were higher than morphological plastic indices, suggesting that morphological plasticity plays an important role in their adaptation to different growth light conditions. The results also support the hypothesis that ecophysiological traits of tree species determine their successional status and associate habitats of their seedlings.     

亚高山针叶林土壤有机层有效氮动态及其对外源C、N增加的响应

为了解川西亚高山针叶林土壤有机层有效N的动态及其对外源C、N增加的响应,2005年4～10月采用人为施加C、N的控制实验方法,研究了川西亚高山紫果云杉(Picea purpurea Masters)林和岷江冷杉(Abies faxoniana Rehder & E. H. Wilson)林下土壤有机层(OL)的半分解层(FL)和完全分解层(HL)及矿质土壤层(MS)有效氮(NH+4-N + NO-3-N)动态及其对外源C、N的响应.云杉和冷杉林FL和HL的有效氮含量均显著高于MS.云杉林FL、HL和MS的NH+4-N分别为总有效氮含量的77.4%、72.4%和76.6%,而冷杉林分别为65.2%、57.6%和67.2%.有效氮和NH+4-N含量均以10月份最高,而NO-3-N含量以8月份最高.外源C输入使云杉林土壤FL、HL和MS有效氮含量提高了14.6%、21.2%和28.0%,使冷杉林提高了16.7%、25.3%和5 2%.外源N输入使云杉林土壤FL、HL和MS有效氮含量提高了53.9%、11.6%和13.2%,冷杉林提高了14.2%、23.8%和50.5%.OL对外源C、N输入的响应比MS更敏感,且云杉林大于冷杉林.处理时间越长,外源C、N输入对OL和MS有效氮含量的影响越大.     

雪被斑块对川西亚高山两个森林群落冬季土壤氮转化的影响

为了解气候变暖情景下雪况变化对高寒森林冬季土壤氮转化的影响,测定了川西亚高山冷杉(Abies faxoniana)+红桦(Betula albo-sinensis)混交林(MF)和冷杉次生林(SF)三类雪被斑块(浅雪被、中厚度雪被和厚雪被)内冬季土壤氮矿化特征。结果表明:经过一个冬季(2011-2012),两个森林群落土壤净氮氨化量都为负值,净氮硝化量都为正值,且净氮硝化量显著高于净氮氨化量;冬季土壤氮氨化、硝化、矿化和固持量都是中度雪被厚度最高,但各雪被斑块之间都未达到显著水平。各雪被斑块下,冷杉次生林土壤氮矿化参数都显著高于针阔混交林,但雪被斑块和林型交互作用对冬季土壤氮矿化无显著影响。这表明,该区冬季土壤氮矿化以硝化过程为主,硝化和氨化过程可能受不同微生物群落调控;短时期内,未来气候变化所导致的雪被减少对该区森林冬季土壤氮转化影响可能不明显。     

三种不同类型亚高山森林凋落物输入对土壤腐殖化的影响

森林凋落物既是土壤腐殖质的主要来源,也可以通过新鲜凋落物中易降解组分的输入激发土壤原有腐殖质的降解,导致其相互关系并不明确。以王朗国家级自然保护区内的典型亚高山针叶林、针阔混交林以及阔叶林为研究对象,开展土壤原位培养试验,设置允许凋落物正常输入和去除凋落物两种处理,分析2017年-2019年期间不同凋落物处理下森林土壤可提取腐殖物质的光密度特征,研究土壤腐殖化程度与凋落物的关系。结果表明,在2年的试验过程中,3种森林土壤的腐殖化程度整体表现为针叶林>混交林>阔叶林,均展现出在冬季降低,生长季增加的动态规律;凋落物对3个森林的土壤腐殖化程度均无显著影响,但凋落物输入明显改变了土壤腐殖化程度的季节性变化趋势,且在冬季的阔叶林和混交林中表现更为突出。冬季凋落物的输入使得阔叶林和混交林土壤的腐殖化程度明显降低,而生长季凋落物输入对3种森林土壤腐殖化程度无显著影响。这些结果表明气候变暖情景下冬季温度的上升可能导致土壤的腐殖化程度增加,但凋落物的存在可以减缓增加的趋势。这些结果对于具有明显季节性冻融且对气候变化敏感的亚高山森林土壤肥力管理及可持续经营具有一定的科学意义。     

Differential uptakes of different forms of soil nitrogen among major tree species in subalpine coniferous forests of western Sichuan,China

Aims Although acquisition of soil organic nitrogen (N)(mainly amino acids) by plants is a widespread ecological phenomenon in many terrestrial ecosystems, the rate of organic N uptake and their contributions to plant nutrient supply are poorly understood. Our objective was to determine the relative contributions of inorganic N (NO₃^–-N and NH₄⁺-N) and organic N (amino acids) to plant N uptake in a high-frigid forest ecosystem.Methods The differences in the uptake rate of three different forms of N (NO₃^–-N, NH₄⁺-N and glycine) were quantified by exposing seedlings of two dominant tree species (Picea asperata and Betula albo-sinensis) in subalpine coniferous forests of western Sichuan, China, to trace quantities of K¹⁵NO₃,¹⁵NH₄Cl and (U-¹³C₂/¹⁵N) glycine.Important findings Both ¹³C and ¹⁵N were significantly enriched in fine roots 2 h after tracer application, indicating the occurrence of glycine uptake in P. asperata and B. albo-sinensis seedlings. The seedlings of two tree species had a significant preference for NO₃^–-N compared with glycine and NH₄⁺-N, and the uptake rate of NO₃^–-N was 5 to 10 times greater than that of glycine and NH₄⁺-N. The roots of seedlings in the two species took up glycine more rapidly than NH₄⁺-N, implying that soil organic N (i.e., amino acids) could be an important N source for the two species in subalpine coniferous forests. The results of this study are of great theoretical significance for understanding N utilization strategies and nutrient regulation processes in plants of the high-frigid forest ecosystems.