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除人类活动之外,大气中的氮气进入生物圈主要有两个过程:闪电固氮和生物固氮(BNF)[1]。在原始的生物圈中,通常认为生物固氮作用比闪电固氮作用大一个数量级,所以,生物固氮被认为是固定氮的主要来源[2]。生物固氮除了细菌和真菌的固氮作用外[3],主要来源于豆科植物的生物固氮,并被认为是土壤氮的主要来源[4]。豆科植物固定大气氮的能力主要来自于与根瘤菌、土壤中的细菌的共生。豆科植物通过光合作用向根瘤菌提供能量和碳(C),根瘤菌主要以铵的形式向豆科植物提供氮[5]。豆科植物被认为是初级生产力、固碳、氮累积和矿化的关键驱动力[6-7],可以提高植物生产力[8-9]、氮的利用率[10]和土壤有机质的含量[11]。热带森林中,尽管土壤中矿物氮相较于温带森林很高[12],生物固氮率仍然保持高固氮水平,达到15~36 kg·a−1·hm−2。这种高生物固氮率的保持不是为了获取氮本身,而可能是为了获取磷或其它限制性养分酶的产生需要很高的氮输入[13]。
豆科植物的固氮作用还会对邻体植物的生长产生影响。在农作物的研究中,通过间作,大豆可以通过根系分泌物输出,直接向邻体植物提供氮,并通过菌根活动进一步促进磷的移动[14-15]。但是,在森林群落中豆科植物对非固氮树种生长和对整个森林的初级生产力的影响是不明确的。一方面,豆科固氮植物可以通过向非固氮树木提供可利用的氮,并提高森林的生产力。Temperton等[16]认为,固氮植物与非固氮植物之间的相互促进作用的主要驱动力是减少氮竞争的氮节约,而氮转移则起次要作用。豆科植物转移到邻体植物的氮量可能占非豆类植物全氮的8%~39% [17],这取决于群落的年龄[18]。豆科植物还会通过共生菌根直接利用大气氮气,大大增加生态系统中氮的输入,形成群落中固氮物种和非固氮树种之间的互补[19]。另一方面,豆科固氮树种可能会抑制邻体非固氮树种的生长。因为,豆科树木通常具有更快的生长速度,有明显的竞争优势,使邻体物种多样性降低,长期影响下也可能降低邻体树木存活率。同时,有些豆科植物也会通过化感作用来抑制其他物种的生长,并抑制发芽和幼苗的形成[20]。另外,豆科固氮树种自身的迅速生长还可能对其他非固氮树种产生中性影响,从而导致森林总生物量的增加[21]。
因此,豆科树木对森林和其邻体的作用具有不确定性。为了进一步明确豆科树木在热带山地雨林中的角色和对邻体的作用,本文以尖峰岭60 hm2大样地内7种共9 232株豆科树木为研究对象,分析豆科树木0~16 m邻体距离范围内、2次调查间邻体非豆科树木的物种多度和丰富度的变化及邻体存活率,揭示了豆科树木对邻体树种多度、丰富度和存活率的影响,为探索豆科树木与邻体树木的共存机制提供依据。
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2012年在海南尖峰岭热带山地雨林区的五分区原始林内,参照美国史密森热带研究所热带森林研究中心(CTFS)的调查技术规范[26],建立一个东西长1 000 m,南北宽600 m,面积为60 hm2的样地(简称尖峰岭大样地),整个样地被分为1 500个20 m × 20 m的样方。样地内海拔在866.3~1 016.7 m间变化。
尖峰岭大样地首次植被调查开始于2010年年底,2012年完成,调查结果显示,尖峰大样地中共有胸径>1 cm的活体植株439 676株。第1次复查于2018年年底完成,共记录到胸径>1 cm的植株441 551株(表1)。尖峰岭60 hm2大样地中共有7种豆科树木:薄叶猴耳环、猴耳环、亮叶猴耳环,肥荚红豆、木荚红豆、软荚红豆、长脐红豆(表2)。这7种豆科树木均是具有生物固氮能力的树种。豆科树木的固氮能力可以通过豆科植物与其邻体植物叶片中的δ15N含量相比较计算得出[27]。
表 1 尖峰岭大样地内多度前10的木本植物
Table 1. Top 10 woody plants with the highest abundance in JFL 60 hm2 plot
2012年 2018年 物种 Species 多度 Abundance 物种 Species 多度 Abundance 四蕊三角瓣花 Prismatomeris tetrandra (Roxb.) K. Schum. 21 664 四蕊三角瓣花 Prismatomeris tetrandra 20 739 厚壳桂 Cryptocarya chinensis (Hance) Hemsl. 16 811 厚壳桂 Cryptocarya chinensis 16 799 香果新木姜子 Neolitsea ellipsoidea Allen 15 379 香果新木姜子 Neolitsea ellipsoidea 15 377 九节 Psychotria asiatica Wall. 15 124 九节 Psychotria asiatica 13 947 变色山槟榔 Pinanga baviensis Becc. 14 753 海南韶子 Nephelium topengii 11 219 海南韶子 Nephelium topengii (Merr.) H. S. Lo 11 873 变色山槟榔 Pinanga baviensis 11 136 柏拉木 Blastus cochinchinensis Lour. 11 567 东方琼楠 Beilschmiedia tungfangensis 10 702 钮子果 Ardisia virens Kurz 10 817 钮子果 Ardisia virens 10 280 东方琼楠 Beilschmiedia tungfangensis S. Lee et L. Lau 10 644 白颜树 Gironniera subaequalis 9 848 白颜树 Gironniera subaequalis Planch. 10 035 柏拉木 Blastus cochinchinensis 9 182 表 2 尖峰岭大样地豆科树木基本情况
Table 2. Basic information of legume trees in JFL 60hm2 plot
树种 Species 株数 Numbers 叶片氮含量[27]
Leaf nitrogen content/ (g·kg−1)固氮能力[27]
Nitrogen fixation activity/(Ndfa%)2012年 2018年 亮叶猴耳环 A. lucidum 339 345 (286) 36.33 ± 4.75 83 猴耳环 A. clypearia 531 579 (416) 21.38 ± 2.56 71 肥荚红豆 O. fordiana 909 874 (767) 18.46 ± 3.83 60.5 木荚红豆 O. xylocarpa 86 89 (82) 25.27 ± 1.40 45 软荚红豆 O. semicastrata 4889 4859 (4404) 15.03 ± 1.74 45 长脐红豆 O. balansae 4071 3996 (3242) 17.60 ± 0.75 39 薄叶猴耳环 A. utile 43 44 (37) 37.29 ± 2.93 32 注:括号内数字表示2次调查都存活的个体数量。
Note: Number in brackets means alive individuals in two investigations. -
多度(N):N=邻体树木个体数
丰富度(S):S=邻体树木物种数
存活率(SR):SR=N2/N1
式中:N1为初次调查时某一范围内的个体数,N2为复查时该范围内依然存活的个体数
为了评估特定豆科物种的存在是否对邻体树木的多度、丰富度和存活率有显著影响,本文采用基于个体与物种的区域关系,简称ISAR (individual species-area relationship)[28],进行点标记模式统计分析。ISAR被定义为距焦点物种i的距离r以内的树木多度、丰富度或存活率的变化:
$ I S A R_{j}(r)=\frac{1}{N_{i}} \sum\nolimits_{j \in i} S_{i j}(r) $
(1) 式中:Sij(r)是在距离r范围内的物种i的j个体周围的物种多度、丰富度或存活率,Ni是物种i的单个个体的数量,在这里指尖峰岭大样地中的7种豆科树木。
为了检验豆科树木邻体相对多度、丰富度或存活率是否显著高于或低于非豆科树木,计算邻体非豆科树木的ISAR与豆科树木做比值(RISAR):
$ R I S A R_{i}(r)=\frac{\sum_{j \in i} S_{i j}(r)}{\sum_{j \in i} H_{i j}(r)} $
(2) 式中:Hij(r)为邻体非豆科树木的邻体多度、丰富度或存活率。这里邻体非豆科树木的选取标准是:与豆科树木生长在同一相似生境范围(距离豆科树木60 m内)、且处于同一径级(径级为5 cm)的非豆科树木,且r=2, 4 , ….,16 m。理论上,距离中心豆科树木距离越近,生境越相似,本文选择距离豆科树木60 m的原因是,在尽量保证生境相似前提下,保证统计有相当数量的非豆科树木可以选出作为对比。
如果RISARi(i)>1,表示豆科树种与同一生境下、同一径级内的非豆科树木相比,对邻体多度、存活率或丰富度有促进作用。如果RISARi(i)<1,表示豆科树种与同一生境下、同一径级内的非豆科树木相比,对邻体的物种多度、存活率或丰富度有抑制作用。
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离豆科树种的距离越近,邻体影响越明显。2 m和4 m是豆科树木对邻体影响最有可能起作用的距离,所以,本文单独选出2个最小尺度进行分析。为了进一步检验邻体多度、丰富度和存活率之间的关系及可能的影响因素,利用尖峰岭大样地内7种豆科树种的叶片氮含量、固氮能力[27]、2次调查中豆科树木2 m和4 m范围内的邻体多度、丰富度和存活率进行一元线性回归相关分析。
所有数据分析和绘图均通过R 4. 0. 2 (R Development Core Team, 2020)进行。
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在邻体距离0~16 m内,2012年软荚红豆和亮叶猴耳环的邻体多度均大于非豆科树种的邻体多度,长脐红豆、肥荚红豆、薄叶猴耳环和木荚红豆的邻体多度均小于非豆科树种的。在邻体距离0~8 m内,猴耳环的邻体多度小于非豆科树种的;在邻体距离8~16 m内,猴耳环的邻体多度大于非豆科树种的(图1)。
在邻体距离0~16 m内,2018年只有软荚红豆多度大于非豆科树种的,亮叶猴耳环、荚红豆、薄叶猴耳环和木荚红豆的邻体多度均小于非豆科物种的。在邻体距离0~6 m内,猴耳环的邻体多度小于非豆科树种的;在邻体8~16 m内,猴耳环的邻体多度大于非豆科树种的(图1)。
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在邻体距离0~16 m内,2012年软荚红豆、亮叶猴耳环和猴耳环的邻体相对丰富度均大于非豆科树种的,长脐红豆、肥荚红豆、薄叶猴耳环和木荚红豆的邻体相对丰富度小于非豆科树种的。2018年结果与2012年相似(图2)。
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在邻体距离0~16 m内,软荚红豆和猴耳环的邻体相对存活率均大于非豆科树种的,亮叶猴耳环、木荚红豆、长脐红豆和薄叶猴耳环的邻体相对存活率均小于非豆科树种的。在邻体距离0~4 m内,肥荚红豆的邻体相对存活率大于非豆科树种的;在邻体距离6~16 m内,肥荚红豆的邻体相对存活率小于非豆科树种的(图3)。
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2 m和4 m是豆科树木对邻体最可能的影响距离。在邻体距离2 m和4 m时,2012年和2018年2次调查,豆科树木邻体相对多度和丰富度无显著变化,7种不同豆科树木邻体其他种树的多度和丰富度的影响结果保持不变(图4)。
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从表3可看出:在尖峰岭60 hm2大样地中,豆科树木的邻体多度和丰富度有着显著的线性相关关系(p<0.05),但是邻体多度、丰富度与自身的叶片氮含量和固氮能力无显著的关系。存活率方面,只有邻体距离为4 m范围的存活率与叶片氮含量有显著的线性相关关系(p=0.042 5)。
表 3 7种豆科树木的邻体多度、丰富度、存活率与叶片氮含量、植株固氮能力的相关关系
Table 3. Relationship among neighbor abundance, richness, survival rates, leaf nitrogen content and nitrogen fixation abilities of seven leguminous trees
X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X1 X2 0.875** X3 0.974*** 0.912*** X4 0.692* 0.926*** 0.784** X5 0.954*** 0.752* 0.916*** 0.564 X6 0.972*** 0.915*** 0.974*** 0.762** 0.945*** X7 0.972*** 0.767*** 0.941*** 0.574* 0.989*** 0.944*** X8 0.848** 0.964*** 0.903** 0.928*** 0.766*** 0.909*** 0.763* X9 0.246 0.246 0.295 0.283 0.374 0.361 0.299 0.368 X10 0.334 0.132 0.356 0.073 0.528 0.359 0.485 0.188 0.280* X11 0.154 0.037 0.110 0.002 0.285 0.226 0.261 0.004 0.373 0.595* X12 0.089 0.032 0.132 0.040 0.120 0.081 0.149 0.006 0.046 0.246 0.023 注:***代表p<0.001,**代表p<0.01,*代表p<0.05。X1: 2012年豆科树木邻体距离2 m范围内的相对多度;X2: 2012年豆科树木邻体距离4 m范围内的相对多度;X3: 2012年豆科树木邻体距离2 m范围内的相对丰富度;X4: 2012年豆科树木邻体距离4 m范围内的相对丰富度;X5: 2018年豆科树木邻体距离2 m范围内的相对多度;X6: 2018年豆科树木邻体距离4 m范围内的相对多度;X7: 2018年豆科树木邻体距离2 m范围内的相对丰富度;X8: 2018年豆科树木邻体距离4 m范围内的相对丰富度;X9: 豆科树木2 m范围内相对存活率;X10: 豆科树木 4 m范围内相对存活率;X11: 叶片氮含量 X12: 固氮能力。
Notes:*** means p<0.001, ** means p<0.01, * means p<0.05. X1: Relative abundance in 2 m radius in 2012 of leguminous trees. X2: Relative abundance in 4 m radius in 2012 of leguminous trees. X3: Relative richness in 2 m radius in 2012 of leguminous trees. X4: Relative richness in 4 m radius in 2018 of leguminous trees. X5: Relative abundance in 2 m radius in 2018 of leguminous trees. X6: Relative abundance in 4 m radius in 2018 of leguminous trees. X7: Relative richness in 2 m radius in 2018 of leguminous trees. X8: Relative richness in 4 m radius in 2018 of leguminous trees. X9: Relative survival rate in 2m radius of leguminous trees. X10: Relative survival rate in 4m radius of leguminous trees. X11: Leaf nitrogen content (g/kg). X12: Nitrogen fixation ability(Ndfa%)。
尖峰岭热带山地雨林豆科树木对邻体树种的影响
The Effects of Leguminous Tree on the Neighboring Trees in Tropical Mountain Rainforest in Jianfengling
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摘要:
目的 分析海南典型热带山地雨林分布区域尖峰岭60 hm2大样地内豆科树种对邻体树木的影响,并探讨其可能的影响机制。 方法 利用尖峰岭60 hm2大样地的2012年和2018年2次调查数据,对样地内7种豆科树木的邻体非豆科树木的多度、丰富度和存活率进行比较分析。 结果 2次调查期间,7种豆科树木的邻体多度和丰富度无显著变化。与非豆科树木相比,软荚红豆(Ormosia semicastrata Hance)、猴耳环(Archidendron clypearia (Jack) I.C.Nielsen)和亮叶猴耳环(A. lucidum (Benth.) Nielsen)具有较高的邻体多度和丰富度,而肥荚红豆(O. fordiana Oliv.)、木荚红豆(O. xylocarpa Chun ex L. Chen)、长脐红豆(O. blansae Drake)和薄叶猴耳环(A. utile Chun et How)具有较低的邻体多度和丰富度。软荚红豆、肥荚红豆和猴耳环具有较高的邻体树木的存活率,而长脐红豆、薄叶猴耳环、亮叶猴耳环和木荚红豆具有较低的邻体树木的存活率;7种豆科树木对邻体多度、丰富度的影响与其叶片氮含量和固氮能力无显著相关关系,但邻体距离为4 m的豆科树木邻体存活率与叶片氮含量有显著相关关系。 结论 总体上,不同豆科树木对邻体的影响不尽相同,软荚红豆更倾向于对邻体产生有利作用,薄叶猴耳环和木荚红豆对邻体产生抑制作用,而其它4种豆科树木对邻体的多度、丰富度和存活率的影响不一致。 Abstract:Objective To explore how legumes influence other species in the tropical mountain rainforest, and mechanism related to these influences. Method Their neighboring abundance, richness, and survival rates of these seven leguminous trees were calculated and compared with the neighboring non-leguminous trees. Result There was no significant differences on the neighboring abundance, richness, and survival rates from 2012 to 2018. Relative neighboring abundance and richness of Ormosia semicastrata, Archidendron clypearia and A. lucidum were higher than those of non-leguminous trees both in 2012 and 2018. Relative neighboring abundance and richness of other four leguminous were lower than those of non-leguminous trees. In terms of neighboring survival rates, O. semicastrata, O. fordiana, and A. clypearia were higher than those of non-leguminous trees, which suggests that O. semicastrata is inclined to have facilitation effects on the neighboring species, while O. xylocarpa and A. utile have negative effects on the neighboring species. Neighboring abundance, richness, and survival rates of seven leguminous trees showed no significant linear correlations with leaf nitrogen contents and nitrogen fixation activities, although it showed significant correlations between the neighboring survival rates and leaf nitrogen contents at the 4 m radius distance from the focal legume trees. Conclusion In general, different legumes have various effects on the neighboring species. O. semicastrata is more likely to have facilitative effects on the neighboring trees. A. utile and O. xylocarpa exhibit negative effects on the neighboring trees. The effects of other four leguminous trees on the neighboring trees vary on three neighboring abundance, richness, and survival rate indices. -
Key words:
- tropical mountain rainforest
- / leguminous trees
- / community dynamics
- / neighboring trees
- / abundance
- / richness
- / survival rates
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表 1 尖峰岭大样地内多度前10的木本植物
Table 1. Top 10 woody plants with the highest abundance in JFL 60 hm2 plot
2012年 2018年 物种 Species 多度 Abundance 物种 Species 多度 Abundance 四蕊三角瓣花 Prismatomeris tetrandra (Roxb.) K. Schum. 21 664 四蕊三角瓣花 Prismatomeris tetrandra 20 739 厚壳桂 Cryptocarya chinensis (Hance) Hemsl. 16 811 厚壳桂 Cryptocarya chinensis 16 799 香果新木姜子 Neolitsea ellipsoidea Allen 15 379 香果新木姜子 Neolitsea ellipsoidea 15 377 九节 Psychotria asiatica Wall. 15 124 九节 Psychotria asiatica 13 947 变色山槟榔 Pinanga baviensis Becc. 14 753 海南韶子 Nephelium topengii 11 219 海南韶子 Nephelium topengii (Merr.) H. S. Lo 11 873 变色山槟榔 Pinanga baviensis 11 136 柏拉木 Blastus cochinchinensis Lour. 11 567 东方琼楠 Beilschmiedia tungfangensis 10 702 钮子果 Ardisia virens Kurz 10 817 钮子果 Ardisia virens 10 280 东方琼楠 Beilschmiedia tungfangensis S. Lee et L. Lau 10 644 白颜树 Gironniera subaequalis 9 848 白颜树 Gironniera subaequalis Planch. 10 035 柏拉木 Blastus cochinchinensis 9 182 表 2 尖峰岭大样地豆科树木基本情况
Table 2. Basic information of legume trees in JFL 60hm2 plot
树种 Species 株数 Numbers 叶片氮含量[27]
Leaf nitrogen content/ (g·kg−1)固氮能力[27]
Nitrogen fixation activity/(Ndfa%)2012年 2018年 亮叶猴耳环 A. lucidum 339 345 (286) 36.33 ± 4.75 83 猴耳环 A. clypearia 531 579 (416) 21.38 ± 2.56 71 肥荚红豆 O. fordiana 909 874 (767) 18.46 ± 3.83 60.5 木荚红豆 O. xylocarpa 86 89 (82) 25.27 ± 1.40 45 软荚红豆 O. semicastrata 4889 4859 (4404) 15.03 ± 1.74 45 长脐红豆 O. balansae 4071 3996 (3242) 17.60 ± 0.75 39 薄叶猴耳环 A. utile 43 44 (37) 37.29 ± 2.93 32 注:括号内数字表示2次调查都存活的个体数量。
Note: Number in brackets means alive individuals in two investigations.表 3 7种豆科树木的邻体多度、丰富度、存活率与叶片氮含量、植株固氮能力的相关关系
Table 3. Relationship among neighbor abundance, richness, survival rates, leaf nitrogen content and nitrogen fixation abilities of seven leguminous trees
X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X1 X2 0.875** X3 0.974*** 0.912*** X4 0.692* 0.926*** 0.784** X5 0.954*** 0.752* 0.916*** 0.564 X6 0.972*** 0.915*** 0.974*** 0.762** 0.945*** X7 0.972*** 0.767*** 0.941*** 0.574* 0.989*** 0.944*** X8 0.848** 0.964*** 0.903** 0.928*** 0.766*** 0.909*** 0.763* X9 0.246 0.246 0.295 0.283 0.374 0.361 0.299 0.368 X10 0.334 0.132 0.356 0.073 0.528 0.359 0.485 0.188 0.280* X11 0.154 0.037 0.110 0.002 0.285 0.226 0.261 0.004 0.373 0.595* X12 0.089 0.032 0.132 0.040 0.120 0.081 0.149 0.006 0.046 0.246 0.023 注:***代表p<0.001,**代表p<0.01,*代表p<0.05。X1: 2012年豆科树木邻体距离2 m范围内的相对多度;X2: 2012年豆科树木邻体距离4 m范围内的相对多度;X3: 2012年豆科树木邻体距离2 m范围内的相对丰富度;X4: 2012年豆科树木邻体距离4 m范围内的相对丰富度;X5: 2018年豆科树木邻体距离2 m范围内的相对多度;X6: 2018年豆科树木邻体距离4 m范围内的相对多度;X7: 2018年豆科树木邻体距离2 m范围内的相对丰富度;X8: 2018年豆科树木邻体距离4 m范围内的相对丰富度;X9: 豆科树木2 m范围内相对存活率;X10: 豆科树木 4 m范围内相对存活率;X11: 叶片氮含量 X12: 固氮能力。
Notes:*** means p<0.001, ** means p<0.01, * means p<0.05. X1: Relative abundance in 2 m radius in 2012 of leguminous trees. X2: Relative abundance in 4 m radius in 2012 of leguminous trees. X3: Relative richness in 2 m radius in 2012 of leguminous trees. X4: Relative richness in 4 m radius in 2018 of leguminous trees. X5: Relative abundance in 2 m radius in 2018 of leguminous trees. X6: Relative abundance in 4 m radius in 2018 of leguminous trees. X7: Relative richness in 2 m radius in 2018 of leguminous trees. X8: Relative richness in 4 m radius in 2018 of leguminous trees. X9: Relative survival rate in 2m radius of leguminous trees. X10: Relative survival rate in 4m radius of leguminous trees. X11: Leaf nitrogen content (g/kg). X12: Nitrogen fixation ability(Ndfa%)。 -
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