The effects of annual fertilization and complete competition control on fascicle morphology of different aged loblolly pine stands

The goal of this study was to determine how increased nutrient availability affects foliage morphology of loblolly pine (Pinus taeda L.) without introducing the confounding influence of light availability. Morphology of fascicles from the terminal leader (radius, length, specific needle area, density, and needles per fascicle) and terminal leader traits (length, foliated length, total leaf area, and total fascicles) were measured for different aged (ranged from 5-year-old to 12-year-old) loblolly pine stands growing on the Piedmont and lower Coastal Plain of Georgia, USA. A factorial combination of annual fertilization and complete interspecific competition control was applied as stand level treatments. Competition control and stand age generally did not affect fascicle morphology. In contrast, annual fertilization significantly increased fascicle length (5%), needles per fascicle (4%), and total leaf area of the terminal (18%), while decreasing specific needle area (4%). Fertilization also increased terminal leader growth (5%) and total number of fascicles (6%). Therefore, loblolly pine foliage morphology does have plasticity to respond to increased nutrient availability. However, the magnitude of these morphological changes is small compared to changes in total canopy leaf area.     

Effect of shade stress on growth,morphology, and carbon dynamics of loblolly pine branches

Summary Shade treatments were applied to the terminal portions of branches in loblolly pine trees to test whether portions of branches were autonomous with respect to carbohydrates. The shade treatments reduced light by 50% and 72% compared with full sun conditions resulting in significant reductions in net photosynthesis. Branch growth (branch diameter and length, branch and needle biomass) decreased significantly within the shaded portion of the branch. Branch and needle morphology were also affected by shading. Lateral branches subtending terminal shoots were labelled with ¹⁴C 2 times during the growing season. No movement of ¹⁴C into the terminal portions of the branch was evident during the first growth flush. However, during the second flush of growth small but statistically significant amounts of ¹⁴C were imported into the terminal portion of the shaded branches from subtending laterals. It was concluded that loblolly pine shoots were usually autonomous with respect to carbohydrate supply, but that carbohydrate movement into the terminal shoot from subtending foliage could occur under conditions of very high stress.     

火烧对马尾松林土壤酶活性和有机碳组分的影响

土壤酶参与土壤有机质矿化过程,林火能通过改变土壤中微生物的群落结构等来改变土壤酶的活性,进而影响土壤有机碳的动态过程。土壤有机碳库是陆地碳库的重要组成部分,火烧会使土壤有机碳组分发生变化,研究火烧后土壤有机碳组分的变化对于土壤有机碳库的管理具有重要意义。以我国中亚热带典型马尾松人工林火烧迹地为研究对象,通过对比研究,探讨了火烧对土壤酶活性和土壤有机碳组分的影响以及两者之间的关系。结果表明:(1)与对照相比,火烧后一年0—10 cm土层土壤p H值明显升高(P0.05),土壤总碳含量显著降低(P0.05),土壤全氮含量平均降低17.5%(P0.05)。0—10 cm土层和10—20 cm土层土壤含水量均显著低于对照(P0.05)。(2)相比对照,土壤β-葡萄糖苷酶活性在0—10 cm土层显著降低(P0.05),土壤酚氧化物酶活性和过氧化物酶活性显著升高(P0.05)。(3)火烧后一年0—10 cm土层土壤微生物量碳、土壤颗粒性有机碳、土壤易氧化碳含量比对照分别降低26.4%、30.9%和2.69%,但无显著差异,土壤溶解性有机碳含量则显著降低(P0.05);两个土层土壤不稳定有机碳含量和粘粒有机碳含量变化不显著。     

Inheritance of foliar stable carbon isotope discrimination and third-year height in Pinus taeda clones on contrasting sites in Florida and Georgia

Quantifying foliar stable carbon isotope discrimination (Δ) is a powerful approach for understanding genetic variation in gas exchange traits in large populations. The genetic architecture of Δ and third-year height is described for more than 1,000 clones of Pinus taeda tested on two contrasting sites. for Δ was 0.14 (±0.03), 0.20 (±0.07), and 0.09 (±0.04) at Florida, Georgia, and across sites, respectively. for stable carbon isotope discrimination ranged from 0.25 (±0.03) at the Florida site to 0.33 (±0.03) at the Georgia site, while the across-site estimate of was 0.19 (±0.02). For third-year height, ranged from 0.13 (±0.05) at the Georgia site to 0.20 (±0.06) at the Florida site with an across-site estimate of 0.09 (±0.05). Broad-sense heritability estimates for third-year height were 0.23 (±0.03), 0.28 (±0.03), and 0.13 (±0.02) at the Florida site, Georgia site, and across sites, respectively. Type B total genetic correlation for Δ was 0.70 ± 0.06, indicating that clonal rankings were relatively stable across sites, while for third-year height, rankings of clones were more unstable across the two trials . Third-year height and Δ were negatively correlated at the parental , full-sib family , and clonal levels, suggesting that genetic variation for Δ in P. taeda may be a result of differences in photosynthetic capacity. We conclude that Δ may be a useful selection trait to improve water-use efficiency and for guiding deployment decisions in P. taeda.     

马尾松(Pinus massoniana)人工林林窗对土壤不同形态活性有机碳的影响

研究了四川盆地低山丘陵区马尾松人工林不同大小林窗对表层土壤活性有机碳(水溶性有机碳、微生物量碳、易氧化碳)含量、分配比例及碳库管理指数的影响。结果表明:(1)林窗下土壤微生物量碳含量与分配比例较林下土壤有所升高,而水溶性有机碳与易氧化碳含量及水溶性有机碳分配比例有所降低。(2)林窗大小显著影响林窗中心土壤活性有机碳含量与分配比例。随林窗面积增大,水溶性有机碳、微生物量碳与易氧化碳含量呈现较为一致的升高趋势;水溶性有机碳和微生物量碳分配比例也升高,易氧化碳分配比例先下降后升高,稳定态碳先升高后降低;总体表现为较大林窗(900—1225m2)微生物活性强,活性有机碳含量高,且有机碳库稳定性较好。(3)土壤碳库管理指数随林窗面积增大无显著变化,但与各形态活性有机碳含量及总有机碳含量显著相关,说明土壤碳库管理指数能够相对全面地反映林窗大小对土壤碳库的影响。     

Effects of nitrogen supply and elevated carbon dioxide on construction cost in leaves of Pinus taeda (L.) seedlings

Seedlings of loblolly pine (Pinus taeda L.) were grown under varying conditions of soil nitrogen and atmospheric carbon dioxide availability to investigate the interactive effects of these resources on the energetic requirements for leaf growth. Increasing the ambient CO₂ partial pressure from 35 to 65 Pa increased seedling growth only when soil nitrogen was high. Biomass increased by 55% and photosynthesis increased by 13% after 100 days of CO₂ enrichment. Leaves from seedlings grown in high soil nitrogen were 7.0% more expensive on a g glucose g^–1 dry mass basis to produce than those grown in low nitrogen, while elevated CO₂ decreased leaf cost by 3.5%. Nitrogen and CO₂ availability had an interactive effect on leaf construction cost expressed on an area basis, reflecting source-sink interactions. When both resources were abundant, leaf construction cost on an area basis was relatively high (81.8±3.0 g glucose m^–2) compared to leaves from high nitrogen, low CO₂ seedlings (56.3±3.0 g glucose m^–2) and low nitrogen, low CO₂ seedlings (67.1±2.7 g glucose m^–2). Leaf construction cost appears to respond to alterations in the utilization of photoassimilates mediated by resource availability.     

Correlations among indices of forest soil nutrient availability in fertilized and unfertilized loblolly pine plantations

Summary Various laboratory indices of N and P availability in forest soils correlated poorly among themselves and with on-site ion exchange resin (IER) estimates in both unfertilized and N+P fertilized loblolly pine plantations. IER nutrient availability estimates had greatest within-site variability than laboratory indices. Net nitrification was minimal in laboratory incubation of the mineral soil despite high rates of ammonification. In contrast, IER NO₃–N values were usually of the same magnitude as IER NH₄–N values. In both fertilized and unfertilized stands, at least one N availability index was negatively correlated with at least one P index. Soil N and P availabilities were generally higher on fertilized plots than on unfertilized plots 3.5 years after fertilization, and IER estimates showed the greatest number of plots with increased levels. The greater ability of the IER method to distinguish between fertilized and unfertilized plots indicated the method was affected by on-site factors that the laboratory methods do not assess.     

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。     

近自然化改造对马尾松人工林土壤团聚体有机磷组分含量变化的影响

有机磷(Po)是土壤磷库的重要组成部分。为探究马尾松人工林近自然化改造对土壤团聚体Po分布特征的影响,该研究以南亚热带的马尾松纯林(PP)和近自然化改造后的马尾松-阔叶树种混交林(CP)为对象,采集0～10 cm土样后利用干筛法将其筛分为>2 mm、0.25～2 mm和<0.25 mm三部分粒径团聚体,并测定原土及各粒径团聚体中各Po组分、微生物生物量磷(MBP)含量和酸性磷酸酶(ACP)活性。结果表明:(1)CP的土壤Po组分与PP相比发生了变化,高稳定性有机磷(HRO-P)和中度活性有机磷(MLO-P)在原土以及各团聚体径级中均显著高于PP(P<0.05),而活性有机磷(LO-P)和中度稳定性有机磷(MRO-P)在CP和PP中并无显著差异,PP和CP各组分Po在原土和各团聚体径级中无明显变化规律。(2)各形态Po在PP中占比大小为HRO-P>MRO-P>MLO-P>LO-P,而在CP中为HRO-P>MLO-P>MRO-P>LO-P。(3)CP中的MBP含量和ACP活性在原土及各团聚体径级中均显著高于PP,并且随着团聚体径级的减小,ACP活性上升。(4)冗余分析发现,土壤有效磷(AP)、土壤团聚体平均重量直径(MWD)、MBP和全氮(TN)为土壤Po组分的主要驱动因子。综上认为,近自然化改造有利于马尾松人工林土壤中磷的积累与转化,该研究结果为马尾松人工林土壤质量和生产力的提升提供了理论依据。     

Effects of clear-cutting and burning on characteristics of nitrogen mineralization and microbes in the forest soil of a Pinus massoniana plantation in Southern China

The aim of this study was to clarify the effects of clear-cutting and burning (CCB) on soil fertility in a Pinus massoniana (Masson pine) plantation after CCB in Fujian Province, China. We investigated changes in nitrogen (N) mineralization potential (N₀), N mineralization rate constant (k) and the apparent activation energy (Ea) of the soil, with a mathematical analysis using a kinetics model based on the results of in vitro incubation. Changes in the amount of microbial biomass nitrogen (MBN), as well as the number of heterotrophic and nitrite-oxidizing bacteria, were also investigated. The N₀, MBN and the number of fungi and actinomycetes in forest soil was reduced for at least 18 months after CCB. The number of heterotrophic and nitrite-oxidizing bacteria increased, and k, Ea and N mineralization became greater after 6 months of CCB, compared with the control plots. Because there were few young trees planted, which would have taken up mineralized N in the post-CCB site, it is probable that a high proportion of the mineralized N that accumulated in the soil may have been lost during the summer rainy season. Therefore, it is suggested that CCB led to a deficiency in available N during short rotations, which resulted in soil degradation.     

影响不同林型天然红松混交林林隙更新的土壤特征因子

采用野外调查、样品采集和统计分析等相结合的方法,对小兴安岭天然红松混交林3种不同林型(椴树红松混交林(TP)、枫桦红松混交林(BP)、云冷杉红松混交林(PAP))的林隙及其邻近郁闭林分的土壤特征因子和树木更新的相关性进行了研究,旨在阐明林隙土壤特征因子对树木更新的影响,从而为小兴安岭天然红松混交林植被更新、退化生态系统的恢复和可持续经营提供基础数据和实践参考。结果表明:郁闭林分土壤有机质、全氮质量分数显著高于3种不同林型的林隙。有效磷和速效钾含量在BP内与其他林型之间差异显著。3种林型林隙内p H值均略高于其郁闭林分,但与其差异均不显著。3种林型林隙内更新总密度、幼树更新密度与郁闭林分差异显著(P0.05),PAP林隙中更新总密度和幼树更新密度最高。BP林隙面积与更新密度相关不显著,乔木幼苗、幼树更新密度与有机质(r=-0.400,r=-0.475)、全氮均呈显著负相关(r=-0.519,r=-0.603)。TP林隙内全氮与乔木幼苗更新密度呈正相关(r=0.092),而与乔木幼树更新密度呈显著负相关(r=-0.585)。PAP林隙内全氮与乔木幼苗、幼树更新密度均呈负相关。郁闭林分幼苗更新密度分别与有机质、全氮、速效钾、p H值、脲酶和蛋白酶呈负相关。主成分分析表明,全氮是影响林隙和郁闭林分树木更新的关键因素。     

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.     

氮沉降对温带森林土壤甲烷氧化菌的影响

大量研究显示氮沉降影响森林甲烷吸收量,但其中的微生物驱动机制仍缺乏研究。基于长白山典型温带森林长期氮沉降模拟实验平台样地,采用定量PCR和克隆测序技术,研究了长期施加不同形态氮((NH_4)_2SO_4、NH_4Cl和KNO_3)处理下森林土壤甲烷氧化菌的数量和群落组成随季节变化的特征。结果表明,夏季,森林土壤甲烷氧化菌pmo A基因丰度在不同施氮处理之间无显著性差异(每克干土1.54×10~6-3.20×10~6拷贝数);秋季,pmo A基因丰度在施加NH_4Cl和(NH_4)_2SO_4处理小区(每克干土1.93×10~5-7.6×10~5拷贝数)与对照(每克干土(4.03×10~6±1.2×10~6)拷贝数)相比有所降低,尤其在(NH_4)_2SO_4处理小区(每克干土(4.61×10~5±2.61×10~5)拷贝数)显著降低;无论夏季还是秋季,施加不同形态氮处理土壤甲烷氧化菌均以Type I型为主(相对丰度在70.6%-85.4%之间),并以Methylobacter-group(Type I)为优势类群,占Type I型的55.1%-91.7%;Methylobacter-group(Type I)的相对丰度在夏季不同形态氮处理土壤样品中无显著差异,但秋季样品中在施加(NH_4)_2SO_4(52.7%±6.5%)和NH_4Cl(56.1%±8.9%)的处理显著低于对照土壤(77.0%±2.9%),Methylococcus-group(Type I)的相对丰度则在(NH_4)_2SO_4和NH_4Cl处理土壤呈增加的趋势。这些结果表明铵态氮肥添加对温带森林土壤甲烷氧化菌的生长具有抑制作用并导致其群落结构发生改变,受夏季温度和水分的影响,这种抑制作用在秋季表现更明显,而NO_3~--N添加对土壤甲烷氧化菌的群落组成和丰度无显著影响。这些结果解释了以往观测到的施铵态氮肥显著降低秋季温带林地土壤甲烷净吸收量,而在夏季无显著影响的观测结果,解释了长期氮沉降影响森林土壤甲烷吸收的微生物机制。     

模拟氮沉降对太岳山油松林土壤酶活性的影响

为研究土壤酶活性对氮沉降增加的响应,以山西太岳山油松人工林和天然林为研究对象,于2009年8月开始实施模拟氮沉实验,试验设置对照(CK,0 kg N hm-2a-1);低氮(LN,50 kg N hm-2a-1);中氮(MN,100 kg N hm-2a-1);高氮(HN,150 kg N hm-2a-1)4种氮处理,自2012年起每年5、7、9月在各处理样方采集表层0—20 cm土壤,测定土壤酶活性(过氧化物酶、多酚氧化酶、纤维素酶、蔗糖酶、脲酶、中性磷酸酶)。研究结果表明:施氮处理下的脲酶与中性磷酸酶活性均有所提高,而低氮处理下天然林中的多酚氧化酶与人工林中的蔗糖酶显著低于对照,中氮、高氮处理下过氧化物酶、多酚氧化酶、天然林中的纤维素酶以及人工林中的蔗糖酶显著降低。总的来说,人工模拟氮沉降促进了土壤中脲酶和中性磷酸酶的活性,抑制了过氧化物酶和多酚氧化酶的活性,并降低了天然林土壤中的纤维素酶活性和人工林中的蔗糖酶活性,但对天然林中蔗糖酶和人工林中的纤维素酶无影响。主导木质素降解的多酚氧化酶活性与纤维素酶、蔗糖酶活性显著相关,纤维素酶与蔗糖酶活性的下降可能是由木质素降解受到抑制,土壤微生物可利用碳源减少所引起。另外,受到天然林土壤含氮量较高的影响,与人工林相比,天然林的多酚氧化酶活性对模拟氮沉降更敏感。由于被抑制的酶均与土壤有机质降解密切相关,氮沉降增加将减缓山西油松林土壤有机质的降解,有利于有机质在土壤中的积累。     

Comparative effects of four mycorrhizal fungi on loblolly pine seedlings growing in a greenhouse in a Piedmont soil

Summary A greenhouse study was conducted to evaluate the effect of ectomycorrhizae on loblolly pine (Pinus taeda L.) growing in a Piedmont soil. Pine seedlings were inoculated with one of four species of fungi (Scleroderma aurantium, Pisolithus tinctorius, Thelophora terrestris, andRhizopogon roseolus). The seedlings were grown in pots containing a Cecil sandy clay loam amended to create a gradient of extractable P ranging from 5.9 to 52.5 g/g. After ten months, all colonized seedlings were significantly larger than control seedlings. However, of the four fungi,Scleroderma aurantium mediated a far superior shoot growth response to increasing levels of soil P; the seedlings were significantly larger than those colonized by any other fungus and also had the largest root systems and greatest degree of mycorrhizal colonization.     

不同火烈度对四川泸山林场云南松林土壤有机碳组分的影响

林火通过改变土壤理化性质显著影响土壤固碳能力及土壤有机碳各组分含量。阐明不同火烈度对云南松林土壤有机碳的影响,对于云南松林火后生态系统恢复及土壤碳库管理具有重要意义。以火烧2年后四川泸山林场云南松林0-5、5-10、10-15、15-20cm层土壤为研究对象,根据不同火烈度（未过火、低烈度、中烈度、高烈度）设置3块20m×30m样地,共12块样地,野外采集土壤样品,室内测定土壤全氮、容重等理化性质和土壤有机碳（Soil organic carbon,SOC）、土壤活性有机碳（易氧化有机碳,Readily oxidizable carbon,ROC;颗粒有机碳,Particulate organic carbon,POC;微生物生物量碳,Microbial biomass carbon,MBC;水溶性有机碳,Water-soluble organic carbon,WSOC）,采用方差分析研究不同火烈度下土壤有机碳各组分含量的差异性和变化趋势,并采用相关性分析和冗余分析从土壤理化性质角度探究林火对土壤有机碳的影响机制。研究结果表明：（1）不同火烈度显著影响土壤理化性质,其中土壤全氮、有效磷、阳离子交换量、毛管孔隙度、总孔隙度随火烈度增大而增加,而土壤pH、速效钾、碱解氮、容重随火烈度增大而减少。（2） SOC随火烈度增大而减少,其中5-10cm土层降幅最大为44.79%;4种土壤活性有机碳随火烈度增大而减小,其中0-5cm土层下降幅度最明显,各组分降幅大小依次为ROC （36.31%-61.31%） > POC （30.05%-53.61%） > MBC （20.60%-48.19%） > WSOC （13.47%-29.29%）,不同组分对林火的不同响应显著影响了土壤ROC、POC、WSOC的占比。（3）土壤有机碳及其活性组分与阳离子交换量、毛管孔隙度、总孔隙度、有效磷、碱解氮呈显著正相关（P<0.05）,与容重呈极显著负相关（P<0.01）。火烧后土壤有机碳的变化主要与阳离子交换量、容重、全氮、含水率有关,且阳离子交换量影响最大（解释率为61.7%）。     

模拟火干扰对森林土壤微生物活性及氮矿化的影响

火干扰产生热能从而诱导土壤有机质的化学氧化,改变碳和氮转换,对土壤的结构与功能产生严重影响,影响程度取决于火强度、火干扰持续时间和热渗透。在湖南省株洲市高枧林场选取马尾松次生林火烧迹地,按两种土壤、3个温度和3种土壤水势进行试验设计与方差分析,探讨火干扰对土壤微生物及氮矿化的影响。结果表明:无机氮的浓度与火强度和初始土壤有机质含量呈正相关关系;火干扰后短期内土壤碳和氮浓度较高,微生物生物量碳和潜在可矿化氮较低,温度和土壤水势对基础呼吸速率没有显著影响;当土壤温度达160℃时,未受火干扰土壤中潜在可矿化氮浓度迅速不稳定增加,温度达350℃时破坏90%的非微生物组织;土壤加热后水势对氮矿化过程有显著影响,水势越高,潜在可矿化氮损失越大,火干扰土壤的含水量与硝态氮之间呈正相关关系;培养14d期间,土壤火灾历史、热处理和土壤水势对微生物活性、碳和氮矿化有显著影响,-1.5 MPa水势下加热到380℃后两种土壤的微生物生物量碳含量最高,土壤水势和可溶性糖呈负相关关系;水势和火干扰之间的交互作用显著影响微生物活性和氮转换,低水势土壤中的微生物生物量碳、可溶性糖和潜在可矿化氮浓度较高。     

施氮对湿地松(Pinus elliottii)林土壤呼吸和相关因子的影响

人类活动引起陆地生态系统氮输入水平持续升高,对全球碳循环产生影响。为探究氮素对土壤呼吸的影响,2010年6月至2012年1月,采用氮添加试验对亚热带湿地松林的土壤呼吸进行了研究。试验共设置4种氮添加水平:对照CK,0 g m~(-2)a~(-1);低氮LN,5g m~(-2)a~(-1);中氮MN,15 g m~(-2)a~(-1);高氮HN,30 g m~(-2)a~(-1);每月上、下旬采用Li-cor 8100测定土壤呼吸速率。结果表明:(1)氮添加对土壤呼吸有着显著的抑制作用,LN、MN和HN处理的土壤呼吸年累积量较CK处理分别降低了26.6%、23.7%和29.5%,而施氮处理间的土壤呼吸无显著差异;(2)林分生长期间(6-9月),施氮第1年的土壤呼吸所受抑制作用显著高于第2年同期的水平,显示施氮对土壤呼吸的影响随时间的推移而降低;(3)湿地松林土壤呼吸存在明显的季节动态,最大值出现在8月(356.32 mgCO_2 m~(-2)h~(-1)),最小值出现在1月(99.12 mg CO_2 m~(-2)h~(-1)),施氮处理并不改变土壤呼吸的季节性变化规律;(4)CK处理林分中,土壤呼吸与土壤温度间存在极显著的指数关系,而与土壤湿度无显著相关。施氮处理没有改变土壤呼吸与土壤温度之间的相互关系,但抑制了土壤呼吸的温度敏感性(Q_(10));(5)施氮处理显著减少了林分凋落物量、土壤微生物碳、氮量,并轻微抑制了细根生物量,这些改变导致了土壤呼吸的下降。上述结果表明施氮会显著抑制亚热带湿地松林的土壤呼吸速率,而这种抑制作用将随着时间的推移而降低。     

沙化程度和林龄对湿地松叶片及林下土壤C、N、P化学计量特征影响

为阐明沙化程度和林龄对湿地松(Pinus elliottii)叶片及林下土壤碳(C)、氮(N)、磷(P)化学计量特征影响,探讨C、N、P化学计量比对沙山植被恢复的指示意义,在鄱阳湖多宝沙山沿沙化梯度测定了不同林龄湿地松叶片及林下土壤C、N、P含量。结果表明:1)在叶片C、N、P及其化学计量比中叶N与C∶N对沙化程度和林龄变化反应最为敏感。对于轻度与中度沙化区的5年生与10年生湿地松林,林龄、林龄与沙化程度的交互作用均对叶N及C∶N产生显著影响;对于中度与重度沙化区的2年生和10年生湿地松林,林龄和沙化程度均显著影响叶N与C∶N。2)叶片与土壤二者C、N、P及化学计量比对沙化程度与林龄变化的响应不完全一致。林龄、林龄与沙化程度的交互作用对轻度与中度沙化区5年生和10年生湿地松林土壤全N有显著影响;对于中度与重度沙化区2年生和10年生湿地松林,仅沙化程度对土壤全磷以及林龄对土壤有机碳影响显著。3)10年生湿地松叶片N∶P平均值为20.63,10年生以下湿地松叶片N∶P平均值为15.61,随着林龄的增加,湿地松生长由N、P共同限制逐渐转向更受P的限制。     

林窗尺度对侧柏人工林土壤微生物生物量碳氮的短期影响

为了明晰林窗尺度对侧柏人工林土壤微生物生物量碳氮的短期影响,以徐州市50年生侧柏人工林为研究对象,探讨了开设林窗2a后3种林窗尺度(半径分别为4m,S林窗;8m,M林窗;12m,L林窗)和位置(林窗内、林缘和林窗外部)对土壤微生物生物量碳氮(MBC,Microbial Biomass Carbon;MBN,Microbial Biomass Nitrogen)的影响。结果表明:(1)与对照样地相比,L林窗显著提高了春季(207.1mg/kg)和夏季(169.5mg/kg)林窗外部的土壤MBN含量;M林窗显著提高了春季林窗内部(2959.3mg/kg)和林缘(3008.8mg/kg)位置土壤MBC含量和林缘位置(207.7mg/kg)土壤MBN含量,且显著提高了夏季林窗内部(144.4mg/kg)土壤MBN含量;S林窗显著降低了春季林窗外部和林缘位置土壤MBC(分别为2159.2mg/kg和1955.1mg/kg)和MBN(分别为153.1mg/kg和131.3mg/kg)含量。(2)土壤MBC含量与土壤全碳和土壤可溶性有机碳(DOC)含量呈极显著(P0.01)正相关,与土壤温度呈极显著负相关(在3—27℃之间);土壤MBN含量与土壤含水量和DOC含量呈极显著正相关,与土壤全碳呈显著正相关;土壤MBC和MBN含量与凋落物量没有显著相关关系。本研究中,相对于S和L林窗,M林窗对土壤微生物生物量的提高作用较为明显,可促进侧柏人工林土壤碳氮循环过程,在徐州侧柏人工林中开设M林窗有利于提高土壤肥力和林木生长。