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三峡水库完工后形成的消落带使库区两岸植物遭受了长时间、高强度的反季节水淹胁迫[1-2],造成植物根部缺氧,影响根系呼吸. 植株长时间缺氧会导致根系对营养元素的运输与吸收受阻[2],继而导致与植物根系密切相关的土壤养分质量分数随之发生变化. 适生植物与实生土壤生态系统养分通量的关键途径是通过根系死亡和分解等过程释放养分[3]. 植物细根是直径小于2 mm、极具生理活性的根系,其作为连接地上和地下部分的重要营养器官,对土壤环境变化的敏感性较强[4],极大地影响着生态系统的循环过程和性质[5]. 相对于叶片来说,细根C,N,P质量分数特征更直接地受到土壤养分的影响[6-7],因为实生土壤中养分的变化首先会影响到植物根系,养分限制作用将首先体现在植物的细根上[8]. 在每年的C和实生土壤养分输入方面,适生植物细根的贡献往往等于或超过分解的叶片[9],其生态化学计量特征则有助于建立植物组织、土壤等不同生态系统成分之间的联系[10-11],所以细根在三峡库区消落带生态系统的C和养分循环中起着重要的作用.
C,N,P是组成库区消落带适生植物的主要元素,其与植物体关键结构的合成以及相应功能的发挥密切相关[12-13]. 同时,3种元素之间的比值关系也能够反映适生植物的生长状态与相应代谢条件. 目前已有大量关于植物C,N,P化学计量特征的研究,但大多集中在湿地、森林、草原等生态系统[11, 14-15],且主要是针对植物地上部分(茎和叶片)[16-17]及土壤[18-19]生态化学计量学进行研究. 较少有研究关注三峡库区消落带特定水文节律下植物—实生土壤生态系统的化学计量特征,而且由于三峡库区植物根系分布复杂、根系难获取等条件限制[20],对库区消落带植物地下部分(尤其是细根)C,N,P化学计量特征随水淹程度的变化规律及其与土壤养分关系的研究也较少. 关于细根C,N,P化学计量特征与土壤养分间的关系,陈晓萍等[21]研究武夷山不同海拔黄山松(Pinus hwangshanensis)细根化学计量特征对土壤养分的适应性,发现细根的P质量分数主要受土壤P供应量的限制; Ladanai等[22]研究瑞典苏格兰松(Pinus sylvestris)和挪威云杉(Pinus abies)森林发现植物细根与土壤之间的C,N,P质量分数及化学计量比呈显著正相关; 但Wurzburger等[23]研究热带森林发现植物细根和土壤养分间无显著的相关性. 由于细根寿命较短、周转较快,并且其死亡和分解后会释放大量的C和养分归还给土壤[24],故本实验选择三峡库区消落带的植物细根进行C,N,P生态化学计量特征及其与土壤养分间的关系研究,这对于明确三峡库区消落带植物—土壤系统结构稳定的维持机制有重要意义.
落羽杉(Taxodium distichum)是杉科,落羽杉属落叶乔木,具有根系发达、耐水淹等特点,是三峡库区消落带最适宜的先锋树种,广泛用于消落带地区的种植[25]. 基于此,本实验选择消落带落羽杉为研究对象,分析其细根C,N,P生态化学计量特征及其与土壤养分间的关系,探究消落带不同水淹处理下落羽杉细根C,N,P化学计量特征的差异以及土壤养分对落羽杉细根C,N,P化学计量特征的影响. 本研究可为揭示适生植物落羽杉对消落带特殊环境的适应机制及后续消落带植被修复工作提供理论依据.
Ecological Stoichiometric Characteristics of Carbon, Nitrogen, and Phosphorus in the Fine Root of Taxodium distichum and Their Correlation with Soil Nutrients in the Riparian Zone of the Three Gorges Reservoir Region
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摘要: 为了进一步明确落羽杉在消落带的生态适应策略,对三峡库区消落带适生木本植物落羽杉细根C,N,P生态化学计量特征及其与土壤养分间的关系进行了研究. 实验样地为重庆市忠县石宝镇汝溪河流域的三峡库区消落带植被修复示范基地,以消落带浅淹(SS,即对照)、中度水淹(MS)、深度水淹(DS)3个处理组的落羽杉(Taxodium distichum)幼林为研究对象,分别测定其植株生长指标、细根(d≤2 mm)元素质量分数(C,N,P)以及对应0~20 cm土壤样品元素质量分数(C,N,P,AN,AP). 结果表明:随着水淹时间的延长和水淹强度的增加,落羽杉的株高、冠幅、基径和胸径差异均有统计学意义(p<0.05),结果从大到小依次为:SS组、MS组、DS组;不同的水淹处理对落羽杉细根C,N,P生态化学计量特征的影响不同,MS和DS组的C,N,P质量分数及其比值均与SS组差异有统计学意义(p<0.05);相关性分析表明,细根C质量分数、C: N、C: P和N: P比值与落羽杉的生长指标呈显著或极显著正相关关系,细根N,P质量分数与落羽杉的生长指标呈现显著或极显著负相关关系;除土壤P质量分数与细根P质量分数显著正相关外,土壤养分质量分数与落羽杉细根C,N元素质量分数的相关性无统计学意义或呈负相关关系. 实验表明:三峡库区消落带适生植物落羽杉对P元素的需求主要依赖于实生土壤中的P元素,C,N,P元素质量分数和实生土壤养分处于不完全同步的模式.Abstract: In order to clarify on the ecological adaptation strategies of suitable riparian restoration woody plants, stoichiometric characteristics of C, N and P in the fine roots as well as the relationships between C, N, P and soil nutrients of Taxodium distichum were studied in the riparian zone of the Three Gorges Reservoir (TGR). The research was carried out in a demonstration base for vegetation restoration in the Three Gorges Reservoir area in Ruxi River Basin, Shibao Town, Zhong County, Chongqing. In this study, young forests of T. distichum were divided into three groups according to the elevation as shallow waterlogging (SS, control), moderate waterlogging (MS), and deep waterlogging (DS). Plant growth indices, element content (C, N, P) in fine roots (d≤2 mm) and element content (C, N, P, AN, AP) of soil samples between 0-20 cm depths were determined. The results showed that the height, crown width, basal diameter and DBH of T. distichum were significantly different with the increase in the duration and intensity of flooding (p < 0.05). Different waterlogging treatments i.e., SS group, MS group and DS group had different effects on the C, N and P ecological stoichiometry of fine roots of T. distichum. The C, N and P contents and ratios of MS and DS groups were significantly different from those of the SS group (p < 0.05). Correlation analysis showed that C content, C: N, C: P and N: P ratios in the fine roots were significantly positively correlated with the growth indexes of T. distichum. The N: P contents in fine roots were significantly negatively correlated with the growth indexes of T. distichum. There was no significant negative correlation between soil nutrient content and C and N content in the fine roots of T. distichum, except that P content in soil was significantly positively correlated with the P content in fine roots. The results showed that the demand for P in the water-level-fluctuation zone of the Three Gorges Reservoir area was mainly dependent on P in the growing soil. The contents of C, N and P elements were not completely synchronized with the nutrients in the soils.
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Key words:
- Three Gorges Reservoir /
- riparian zone /
- Taxodium distichum /
- fine root /
- soil nutrient /
- ecological stoichiometry .
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表 1 不同水淹处理下落羽杉的生长特征参数
处理 株高/m 冠幅/m2 基径/mm 胸径/mm DS 5.19±0.01a 5.21±0.22a 83.95±1.74a 54.94±0.22a MS 5.35±0.02b 6.55±0.20b 92.01±1.97b 63.12±0.58b SS 6.70±0.08c 8.16±0.27c 102.43±1.05c 71.26±2.01c 注:数据为平均值±标准误(n=5); 不同小写字母表示不同水淹处理之间的差异有统计学意义(p<0.05). 下同. 表 2 水淹处理对落羽杉细根生态化学计量特征的影响
碳质量分数 氮质量分数 磷质量分数 碳氮比C: N 碳磷比C: P 氮磷比N: P F检验 6.239 5.176 32.822 8.898 53.708 36.211 p 0.014* 0.024* 0.000** 0.004** 0.000** 0.000** 注:** p<0.01; * p<0.05. 下同. 表 3 细根C,N,P质量分数及其比值与植物生长相关性分析
参数 株高 冠幅 基径 胸径 C 0.721** 0.554* 0.597* 0.528* N -0.650** -0.608* -0.562* -0.584* P -0.907** -0.811** -0.774** -0.796** C: N 0.746** 0.690** 0.639* 0.644** C: P 0.935** 0.832** 0.784** 0.819** N: P 0.926** 0.805** 0.764** 0.782** 表 4 细根C,N,P化学计量特征与土壤养分间的相关性分析
参数 土壤C 土壤N 土壤P 土壤碱解氮 土壤速效磷 C 0.454 0.502 -0.464 0.626* -0.203 N -0.050 -0.369 0.479 -0.571* -0.082 P -0.235 -0.592* 0.770** -0.769** -0.233 C: N 0.148 0.456 -0.543* 0.668** 0.054 C: P 0.279 0.615* -0.797** 0.800** 0.177 N: P 0.314 0.632* -0.833** 0.792** 0.281 -
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