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土壤有机碳分解并释放二氧化碳的过程是土壤重要的生物化学过程,对维持土壤碳库的动态平衡和温室气体的形成起着重要作用[1],并直接关系到养分循环及土壤质量。土壤微生物呼吸是由微生物活动利用有机碳引起的,作为原始驱动力,微生物量碳(MBC)含量的动态和周转与微生物呼吸有着密切关系[2]。微生物呼吸主要以可溶性有机碳(DOC)为碳源,有机碳的解聚和溶解是微生物呼吸的先决条件,有机碳在转化为二氧化碳(CO2)前通常必须先进入溶液中形成DOC[3]。可以说,在土壤微生物呼吸过程中DOC同样起着关键作用[4-5]。温度是影响土壤MBC和DOC含量重要的外部环境因子。大量研究表明:在自然条件下的季节性升温后森林土壤MBC含量显著升高[6-7],而DOC则明显降低[8-9],但也有部分研究得出相反的结果[10-11]。RINNAN等[12]通过对样地实施增温处理时发现在增温到第9年,土壤MBC相比对照地降低,而到第12年却又显示没有明显差异。由于野外土壤生态系统是一个复杂环境体系,且不同研究区域、林分类型[13-14]、处理时间及取样尺度都有可能导致两者对温度的响应方向和程度不同[15]。因此,要进一步理清森林土壤MBC和DOC含量与温度变化的关系机制,还需要结合室内培养实验,排除和控制一些不必要的影响因素。目前,一些学者在这方面进行过一定的探索研究[16-18],但各研究的侧重点有所不同,涵盖的内容还不尽全面。调查结果显示:浙江凤阳山国家级自然保护区原生地带性常绿阔叶林遭受过大规模“判青山”毁林破坏,现存的人工林是由植被破坏后种植的杉木Cunninghamia lanceolata和柳杉Cryptomeria fortunei等针叶树种形成,同时还存在大面积通过自然飞籽传播形成的黄山松Pinus taiwanensis针阔混交林和自然恢复形成的次生常绿阔叶林。上述林分类型在浙江、福建、江西等中国东部中亚热带地区广泛分布,具有一定的区域典型性和代表性。本研究通过室内不同温度培养实验,重点研究微生物呼吸过程中该4种林分土壤MBC和DOC质量分数的动态,明确温度及林分因子对两者的影响程度,并分析因果机理。在当前全球变暖的大背景下,为揭示森林土壤碳循环对气候变化的响应特征及环境驱动机制提供科学参考。
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研究区位于浙江省龙泉市凤阳山国家级自然保护区(27°46′~27°58′N, 119°06′~119°15′E),属于武夷山脉东伸的洞宫山系。保护区属亚热带湿润季风气候,雨水充沛,四季分明。年平均气温为12.3 ℃,年均降水量2 325.0 mm[19],雨季集中在4-6月。土壤为黄壤,质地为中壤土,土层厚度为60~80 cm。
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在研究区分别选取典型的常绿阔叶林(主要树种有木荷Schima superba, 甜槠Castanopsis eyrei,光皮桦Betula luminfera,短尾柯Lithocarpus brevicaudatus),杉木林,针阔混交林(主要树种有黄山松Pinus taiwanensis,中华石楠Photinia beauverdiana,亮叶水青冈Fagus lucida,华东山柳Clethra barbinervis,木荷)与柳杉林为研究对象。4种不同森林的林龄、气候、立地条件及恢复前植被等基本一致,且在生长过程中未受到人为干扰,即4种不同森林是在相同条件下进行演替的。在每种森林内设置3个20 m × 20 m的重复固定样地,共计12个固定样地,对样地进行植物本底调查(表 1)。
表 1 各林分类型的基本情况
Table 1. Basic information of various stand types
森林类型 海拔/m 坡向 坡度/(°) 林龄/a 郁闭度 平均胸径/cm 平均树高/m 常绿阔叶林 1 390 北 30 46 0.85 12.0 12.0 杉木林 1 400 北 28 42 0.80 20.0 14.0 针阔混交林 1 570 北 26 45 0.75 16.0 9.0 柳杉林 1 550 北 28 42 0.90 32.0 15.0 -
于2014年8月,在各个样地内按S型设置4个采集点,取0~20 cm表层土,混合后作为该样地的土壤样品。土样用冷藏箱迅速带回实验室后,剔除石砾、植物残根等。新鲜土样过2 mm筛后直接用于室内培养及活性有机碳的测定;另一部分风干后用于土壤有机碳的测定。
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将相当于干质量120 g的新鲜土样分别装入高14.3 cm内径10.7 cm的圆柱状塑料瓶中,调整土壤水分含量至80%。瓶口采用组培所用的封口膜进行封口,以减少水分散失,同时在每个瓶的封口膜上扎15个左右细孔,保证空气的自由流通[20]。先将装有土样的塑料瓶在20 ℃中预备培养3 d,然后分别放入10 ℃,20 ℃,30 ℃的3个培养箱中进行暗培养,培养期间通过称量法定期补充水分以保持土壤含水量不变。在培养后的第7天、第14天、第28天、第56天取样,测定土壤微生物量碳、可溶性有机碳质量分数。另外,在培养前还需先测定土样的微生物量碳和可溶性有机碳的初始质量分数。
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土壤有机碳(SOC)采用硫酸重铬酸钾-外加热法;微生物量碳(MBC)采用氯仿熏蒸浸提法[21],用0.5 mol·L-1硫酸钾浸提熏蒸和未熏蒸土样,m(水):m(土)比为4:1,后在有机碳自动分析仪(TOC-2500,日本)上直接测定浸提液中有机碳质量分数。微生物量碳质量分数=CE/0.45,其中,0.45为转换系数,CE为熏蒸和未熏蒸土样浸提液中的有机碳质量分数的差值;可溶性有机碳(DOC)质量分数=未熏蒸土样浸提液中的有机碳质量分数[22]。
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采用SPSS 13. 0对数据进行描述统计,然后进行单因素方差分析,并用最小显著差法(LSD)进行多重比较。
Varieties of active soil organic carbon of four forest types with varying incubation temperatures in Fengyang Mountain
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摘要: 以浙江凤阳山国家级自然保护区典型常绿阔叶林、杉木Cunninghamia lanceolata林、针阔混交林、柳杉Cryptomeria fortunei林为研究对象,采用室内培养试验,研究10,20,30℃条件下4种森林土壤微生物量碳(MBC)和可溶性有机碳(DOC)的动态。结果表明:4种森林类型中,土壤总有机碳(SOC)和DOC质量分数以柳杉林为最高,MBC则以常绿阔叶林为最高,3种形态有机碳质量分数均以杉木林为最低。随着培养时间的延长,10℃下,不同森林土壤的MBC质量分数总体上呈前期下降快、后期下降慢,DOC质量分数呈先上升后下降;20℃下,不同森林土壤MBC和DOC质量分数均呈相对缓慢下降;30℃下,不同森林土壤MBC质量分数先上升后下降,DOC质量分数前期下降快、后期下降慢的趋势。同一森林土壤在不同温度条件下,土壤MBC质量分数大小顺序为30℃ > 20℃ > 10℃,土壤DOC质量分数则表现为10℃ > 20℃ > 30℃。培养56 d后,常绿阔叶林、针阔混交林土壤的MBC和DOC质量分数的下降幅度高于杉木林、柳杉林。柳杉林和常绿阔叶林SOC和DOC质量分数显著高于杉木林(P < 0.05),在较高温度条件下培养的土壤DOC质量分数较低,而MBC质量分数则较高。Abstract: As an important part of the active soil organic carbon (SOC) pool, microbial biomass carbon (MBC) is the impetus and key to nutrient and energy cycling in the soil ecosystem. To provide important scientific references for forest soil carbon sequestration and greenhouse gas emission in this region, the warming effect on forest soil MBC and dissolved organic carbon (DOC) were determined using an incubation experiment. The content dynamics of MBC and DOC of an evergreen broadleaf forest, a Cunninghamia lanceolata forest, a mixed coniferous and broadleaf forest, and a Cryptomeria fortunei forest in the National Nature Reserve of Fengyang Mountain were studied using an incubation experiment at 10℃, 20℃, and 30℃. Results showed that SOC and DOC in the Cryptomeria fortunei forest were significantly higher (P < 0.05) than other forests; MBC in the mixed broadleaf forest was significantly higher (P < 0.05)than the other forests; and SOC, MBC, and DOC in the Cunninghamia lanceolata forest were significantly lower (P < 0.05). At 10℃, MBC for various stand types declined fast at an early stage and then declined slower. However, DOC rose in the early stage and then declined later. At 20℃, MBC and DOC with various stand types slowly declined. At 30℃, MBC with various stand types rose early but declined later, and DOC quickly declined early and slowly declined later. For the same detection time, MBC for the same stand type was characterized by 30℃ > 20℃ > 10℃; whereas, DOC was 10℃ > 20℃ > 30℃. For the same temperature, MBC and DOC in the evergreen broadleaf forest as well as the mixed coniferous and broadleaf forest declined larger on the whole than in the C. lanceolata forest and the C. fortunei forest after the 56 days of incubation experiment.
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Key words:
- forest ecology /
- stand type /
- temperature /
- total organic carbon /
- soil microbial biomass carbon /
- soluble organic carbon /
- dynamic
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表 1 各林分类型的基本情况
Table 1. Basic information of various stand types
森林类型 海拔/m 坡向 坡度/(°) 林龄/a 郁闭度 平均胸径/cm 平均树高/m 常绿阔叶林 1 390 北 30 46 0.85 12.0 12.0 杉木林 1 400 北 28 42 0.80 20.0 14.0 针阔混交林 1 570 北 26 45 0.75 16.0 9.0 柳杉林 1 550 北 28 42 0.90 32.0 15.0 -
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2018.02.007