作物种内相互作用关系随生长和密度的变化规律 #

董传聪1,2，吴凡1,2，陈仁飞1,2，董龙伟1,2，刘涛3，楚启鹏1，刘雪梅1，邓建明1,2**

（1. 兰州大学生命科学学院, 兰州 730000；
2. 兰州大学草地与农业生态系统国家重点实验室，兰州 730000；
3. 青海师范大学生命与地理科学学院， 西宁 810008）

2.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.02.0School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000;School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000;School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000;School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000;School of Life and Geographical Science, XiNing 810008, China;School of Life Science, LanZhou University, LanZhou 730000;School of Life Science, LanZhou University, LanZhou 730000;School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000;兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000;兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000;兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000;青海师范大学生命与地理科学学院， 西宁 810008;兰州大学生命科学学院, 兰州 730000;兰州大学生命科学学院, 兰州 730000;兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000730000;;;;;;;73000018793182990;;;;;;;1389341486918793182990;;;;;;;13893414869甘肃省兰州市城关区天水南路222号兰州大学逸夫生物楼803室;;;;;;;甘肃省兰州市城关区天水南路222号兰州大学逸夫生物楼812室ecologydong@163.com;wuf2014@lzu.edu.cn;chenrenfei1hao@163.com;donglw123@163.com;532226527@qq.com;chuqp14@lzu.edu.cn;liuxm2014@lzu.edu.cn;dengjm@lzu.edu.cn董传聪（1991-），男，硕士，主要研究方向：理论生态学;;;;;;;邓建明（1978-），男，教授、博导，主要研究方向：理论生态学、植物生态学董传聪;吴凡;陈仁飞;董龙伟;刘涛;楚启鹏;刘雪梅;邓建明DONG Chuancong;WU Fan;CHEN Renfei;DONG Longwei;LIU Tao;CHU Qipeng;LIU Xuemei;DENG Jianming邓建明国家自然科学基金优青项目（31322010）和面上项目（31270753）；兰州大学中央高校基本科研业务费（lzujbky-2016-k03）2.02.02.02.02.02.02.02.02.02.02.02.01*|*期刊*|*Connell J H. 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Chicago, USA: University of Chicago Press, 1931.作物种内相互作用关系随生长和密度的变化规律|Variation of intraspecific interaction along with crop ontogeny and density|国家自然科学基金优青项目（31322010）和面上项目（31270753）；兰州大学中央高校基本科研业务费（lzujbky-2016-k03）|1|董传聪|DONG Chuancong|兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000|School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000|董传聪（1991-），男，硕士，主要研究方向：理论生态学|甘肃省兰州市城关区天水南路222号兰州大学逸夫生物楼803室|730000|ecologydong@163.com|18793182990|18793182990<CR>|2|吴凡|WU Fan|兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000|School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000||||wuf2014@lzu.edu.cn||<CR>|3|陈仁飞|CHEN Renfei|兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000|School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000||||chenrenfei1hao@163.com||<CR>|4|董龙伟|DONG Longwei|兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000|School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000||||donglw123@163.com||<CR>|5|刘涛|LIU Tao|青海师范大学生命与地理科学学院， 西宁 810008|School of Life and Geographical Science, XiNing 810008, China||||532226527@qq.com||<CR>|6|楚启鹏|CHU Qipeng|兰州大学生命科学学院, 兰州 730000|School of Life Science, LanZhou University, LanZhou 730000||||chuqp14@lzu.edu.cn||<CR>|7|刘雪梅|LIU Xuemei|兰州大学生命科学学院, 兰州 730000|School of Life Science, LanZhou University, LanZhou 730000||||liuxm2014@lzu.edu.cn||<CR>*|8|邓建明|DENG Jianming|兰州大学生命科学学院, 兰州 730000；兰州大学草地与农业生态系统国家重点实验室，兰州 730000|School of Life Science, LanZhou University, LanZhou 730000; State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000|邓建明（1978-），男，教授、博导，主要研究方向：理论生态学、植物生态学|甘肃省兰州市城关区天水南路222号兰州大学逸夫生物楼812室|730000|dengjm@lzu.edu.cn|13893414869|13893414869

摘要：植物体的密度依赖(Density dependence )一直是生态学研究的焦点之一。植物密度依赖效应的实质是植物邻体间的正负相作用，且已有研究表明正负相互作用随环境胁迫强度的增加将发生转变。然而，植物种内邻体间正负相互作用是否随个体生长和密度增加发生转变尚属未知。本研究选取大豆、小麦和玉米3种作物分别进行15个不同种植密度梯度的密度效应实验。从出苗至成熟期，分别对株高、基茎、冠幅、生物量及种群密度进行 5次跟踪测定。通过对相对相互作用强度(RII)指标的计算，探究种群内正相互作用随时间和空间的动态变化。结果表明：1）作物生长初期，中等密度种群的植株间呈现出正相互作用现象，促进植物个体的生长；2）作物生长中期和后期，植株之间由正相互作用转变为净竞争作用，且竞争强度随密度增加而增加，甚至发生自疏现象。本研究为植物邻体间正负相互作用转变机制的探索提供了一定的实验基础，同时也进一步验证了生态学中的阿利效应和胁迫梯度假说，并为合理进行农业生产实践提供了科学依据。

关键词：生态学；农作物；正相互作用；竞争；相对相互作用强度；密度梯度

中图分类号：Q948.12+2.1

Variation of intraspecific interaction along with crop ontogeny and density

DONG Chuancong1,2, WU Fan1,2, CHEN Renfei1,2, DONG Longwei1,2, LIU Tao3, CHU Qipeng1, LIU Xuemei1, DENG Jianming1,2

(1. School of Life Science, LanZhou University, LanZhou 730000;
2. State Key Laboratory of Grassland and Agro-Ecosystems, LanZhou University, LanZhou 730000;
3. School of Life and Geographical Science, XiNing 810008, China)

Abstract: Plant density dependence has been a central research area in ecology. The essence of plant density dependence is neighbor plant interaction including positive and negative factors. Previous studies indicated that positive and negative interactions change along with environmental stress gradients. However, it is still unclear whether crop intra-specific interactions change along with ontogeny and density. The experiment of 15 density gradients was conducted for three crop species (soybean, wheat and corn) respectively. Five traits (plant height, basal stem diameter, canopy, biomass and density) were investigated for five times during crop growth. Relative interaction intensity (RII) was calculated based on individual biomass to explore dynamic variation of population positive interaction along with crop ontogeny and density gradients. Analysis results showed that: 1) During crop pre-stage, population positive interaction was detected with medium density, which facilitate plant growth and development; (2) During the middle and late growth stage, interactions between neighbor individuals changed from positive to negative. Meanwhile, competition intensity increase along with increasing density. Self-thinning phenomenon may occur at strong competition intensity. This study could provide experimental foundation for further exploring the mechanism of plant positive/negative interaction variation. Furthermore, the results verified Allee effect and Stress Gradient Hypothesis, and provide scientific foundation for agricultural management.

Key words: ecology; crop; interaction; competition; Relative Interaction Intensity; density gradient

引言

植物种内相互作用关系一直是生态学研究的焦点之一[1-3]，其中正相互作用是构建植物种群的重要因素之一[4-8]。自Bertness和Callaway于1994年提出环境胁迫梯度假说（Stress Gradient Hypothesis, SGH）[9]以来，正相互作用受到广泛关注[3,4,9-14]。其研究包括正相互作用对物种进化的影响[15-16]、对生态位的改变[17-18]、对干旱地区植物斑块状分布的影响[19]、对物种多样性的改变[3]及对看护物种（nurse plant）作用机理的研究[9,20-26]等。植物间的正相互作用指植物个体通过改善生境、增加资源可利用性、削弱恶劣气候的影响、增加传粉概率、保护不被啃食、消除其它潜在竞争种等促进相邻个体生存、生长或者繁殖的现象。

随着正相互作用理论研究逐步深入，其应用也逐步展开。例如，在生态恢复[27-31]和景观生态学[26]、草地管理[32]及农业等方面的应用[33-34]。农业生产上，植物间相互作用主要由立地密度引起：低密度时呈现正相互作用，高密度时呈现负相互作用即竞争，通过竞争产生自疏现象。前人通过大量实验数据研究提出植物-3/2，-4/3自疏法则，植物最终产量恒定法则等相关生态理论。Deng等通过作物的实验数据提出了植物的最适种群密度模型[43-44]。然而，该模型在低密度条件下并未考虑个体间的相互作用，尤其是正相互作用。在考虑植物正相互作用存在情况下，个体达到最大生物量（正相互作用最强）时植物种群总体产量并非最大。那么，正相互作用如何影响种群最适密度，同时个体最大生物量出现时的种群密度也有待进一步研究。而最适种群密度及最大个体生物量对指导农业生产具有重要意义。本文对此展开研究，深入探讨正相互作用存在情况下，不同作物物种的生长规律。

材料与方法

试验地概况

兰州大学榆中校区植物种质资源圃试验地（35°56′N，104°09′E），海拔1750m，年均温7.1℃，年均降雨量300mm，年均蒸发量1450mm，无霜期130d，年均日照时数2666h，土壤类型为黑垆土，土壤容重1.25 g cm-2[35]、有机质7.66 g kg-1、pH 8.26。

试验设计

本试验于2015年和2016年生长季（3月到9月）开展，选用3种当地常见的粮食和经济作物：玉米、春小麦、大豆。3种作物均为单独种植，样方面积为2.25m2，玉米和大豆播种密度（株/m2）均分别为：900、625、400、225、169、100、81、64、49、36、25、16、9、4、1；小麦种植密度（株/m2）分别为：10000、4900、3600、1600、900、625、324、225、100、49、25、16、9、4、1。为避免植物边际效应，每个样方周围种植等密度宽为0.5m的缓冲样带。同时为便于实验测量和避免样方之间的影响，每个样方之间预留0.5m宽的间距。在作物的生长过程中，对所有样方中的作物进行定期浇水、施肥、除草和打药。

测量指标与方法

本试验从植物幼苗期开始对各样方植株进行抽样跟踪测量，直至植株成熟期，各物种分别跟踪测量5次。具体测量方法为：取样时统计每个样方内的植株个体数。然后随机从每个样方中（非缓冲带）采样10株，对每个个体的株高、基茎、冠幅以及叶、茎、果、鞘、柄的生物量进行测定。干重的测定方法为：先把鲜样置于120 ℃烘箱进行杀青2 h，然后在80 ℃恒温条件下烘干72 h至恒重，最后称量各部分的生物量干重。

本论文选取相对相互作用强度指数（RII: Relative Interaction Intensity）作为衡量相互作用强度的指标,其定义如下：

RII = (Wt - Wc) /(Wt + Wc)

其中，Wc为去除邻体后孤立个体的生物量，Wt为保留邻体的目标植物的生物量。RII的取值范围从-1到1，正值表示正相互作用，负值表示竞争[36]。

数据处理

所有数据的分析处理均使用软件 SPSS21.0完成，所有图则用 Origin 8.0进行制作。

结果与分析

大豆种内正负相互作用随生长、密度的变化

基于空间尺度分析，大豆五次的RII指数随立地密度的变化均体现了相似规律（图1），即：随种群密度的增加，RII指数从快速下降到趋于平衡。表明种群密度由低到高时，相邻个体间的负相互作用（竞争作用）随密度的增加快速增强，即正相互作用（促进作用）越来越弱，RII指数快速降低；密度到达一定值之后，相邻个体间的负相互作用（竞争作用）随密度的增加不再快速增强，而是趋于平衡，即RII指数缓慢下降，趋于平衡。幼苗期（图1，first time），RII指数几乎全部为正值，说明个体间几乎全为正相互作用（促进作用）；成熟期（图1，fifth time），RII指数几乎全部为负值，证明个体间几乎全为负相互作用（竞争作用）。

图1 第一次至第五次测量的大豆RII指数随密度变化趋势

Fig. 1 Variation of relative interaction intensity(RII) with soybean density for five measurement times respectively

而密度小于35株时大豆五次的RII指数随立地密度变化呈现如下规律：从幼苗期至成熟期，随种群密度增加，RII指数由明显上升趋势（图2,first time）转变为明显下降趋势（图2,fourth and fifth time）。表明幼苗期，低密度植株间的正相互作用与密度正相关，种群适合度随密度增加而增加，而成熟期，植株间的负相互作用与密度正相关。

图2 第一次至第五次测量的大豆RII指数随密度（< 35/m2）变化趋势

Fig. 2 Variation of relative interaction intensity(RII) with soybean density for five measurement times respectively（< 35/m2）

从时间动态角度分析，低中高三个密度梯度（密度分别为9，100，900）的RII指数随大豆生长均呈现下降趋势（图3）。说明相同密度时，随大豆生长，相邻个体间负相互作用（竞争作用）越来越强。种群密度为900时，五次的RII指数全部小于0，且不断下降，表明高密度种群中，植株间净相互作用从幼苗期到成熟期都体现为竞争关系；种群密度为9和100时，初期的RII指数大于0，体现为正相互作用（促进作用），末期的RII指数小于0，体现为负相互作用（竞争作用）。此外，种群密度为100时的RII指数比种群密度为9时的RII指数下降更快，表明大豆种群密度为100时更有利于种子的萌发和前期生长。

图3 三种种植密度下大豆的RII随时间的变化趋势

Fig. 3 Variation of relative interaction intensity(RII) with time for soybean under three different density gradients.

玉米种内正负相互作用随生长、密度的变化

基于空间尺度分析，玉米五次的RII指数随立地密度的变化均体现了相似的规律（图4），即：随种群密度的增加，RII指数从快速下降到趋于平衡。表明密度由低到高过程中，相邻个体间的负相互作用（竞争作用）随密度增加快速增强，即正相互作用（促进作用）越来越弱，RII指数快速降低；密度到达一定值之后，相邻个体间的负相互作用（竞争作用）随密度的增加不再快速增强，而是趋于平衡，即RII指数缓慢下降，趋于平衡。幼苗期（图4，first time）的RII指数几乎全部大于0，表明个体之间的净效应几乎全为正相互作用（促进作用）；成熟期（图4，fifth time）的RII指数几乎全部小于0（少部分低密度的RII指数大于0，表明成熟期低密度玉米依然存在正相互作用），表明个体之间的净效应几乎全为负相互作用（竞争作用）。

图4 第一次至第五次测量的玉米RII指数随密度变化趋势

Fig. 4 Variation of relative interaction intensity(RII) with corn density for five measurement times respectively

而密度小于25株时玉米五次的RII指数随种群密度变化呈现如下规律：从幼苗期至成熟期，随密度的增加，RII指数由明显上升趋势（图5, first）转变为明显下降趋势（图5, fourth and fifth）。表明幼苗期，低密度植株间的正相互作用与密度正相关，而成熟期，植株间的负相互作用与密度正相关。

图5 第一次至第五次测量的玉米RII指数随密度（< 25/m2）变化趋势

Fig. 5 Variation of relative interaction intensity(RII) with corn density for five measurement times respectively（< 25/m2）

从时间动态角度考虑，低中高三种种群密度（分别为9，100，900）的RII指数随玉米生长均呈现下降趋势（图6）。该趋势表明相同种群密度时，随玉米生长，相邻个体间负相互作用（竞争作用）越来越强。种群密度为100和900时，五次的RII指数全部小于0，且不断降低，表明高密度种群中，从幼苗期到成熟期，植株间的净效应均为竞争；种群密度为9时，幼苗期的RII指数大于0，中期的RII指数增大，而成熟期的RII指数小于0，体现为由幼苗期微弱的正相互作用（促进作用）转变为中期强烈的正相互作用，再转变为成熟期的负相互作用（竞争作用）。种群密度为100和900的RII指数在120天（第四次测量）到159天（第五次测量）之间有微弱增加。

图6 三种种植密度下玉米的RII随时间的变化趋势

Fig. 6 Variation of relative interaction intensity(RII) with time for corn under three different density gradients

小麦种内正负相互作用随生长、密度的变化

基于空间尺度分析，小麦五次的RII指数随立地密度的变化均体现了相似的规律（图7），即：随种群密度的增加，RII指数从快速下降到趋于平衡。表明密度由低到高过程中，相邻个体间的负相互作用（竞争作用）随密度的增加快速增强，即正相互作用（促进作用）越来越弱，RII指数快速降低；密度达到一定值之后，相邻个体间的负相互作用（竞争作用）随密度的增加不再快速增强，而是趋于平衡，即RII指数缓慢下降，趋于平衡。幼苗期（图7，first time）的RII指数几乎全部大于0，表明个体间的净效应几乎全为正相互作用（促进作用）；成熟期（图7，fifth time）的RII指数几乎全部小于0，表明个体间的净效应几乎全为负相互作用（即竞争作用）。

图7 第一次至第五次测量的小麦RII指数随密度变化趋势

Fig. 7 Variation of relative interaction intensity(RII) with wheat density for five measurement times respectively

而密度小于400株时小麦的RII指数随种群密度变化呈现如下规律：从幼苗期至成熟期，随密度的增加，RII指数由明显上升趋势（图8, first）转变为明显下降趋势（图8, third, fourth and fifth）。表明幼苗期，低密度植株间的正相互作用与密度正相关，而小麦进入生殖生长后，植株间的负相互作用与密度正相关。

图8 第一次至第五次测量的小麦RII指数随密度（< 400/m2）变化趋势

Fig. 8 Variation of relative interaction intensity(RII) with wheat density for five measurement times respectively（< 400/m2）

从时间动态角度分析，低中高三种种群密度（分别为9，1600，10000）的RII指数随小麦生长均呈现下降趋势（图9）。表明相同密度时，随小麦生长，相邻个体间负相互作用（竞争作用）越来越强。种群密度为10000时，五次的RII指数全部小于0，且不断降低，表明高密度种群中，从幼苗期到成熟期，植株间的净效应为竞争；种群密度为9和1600时，幼苗期的RII指数大于0，体现为正相互作用（促进作用），成熟期的RII指数小于0，体现为负相互作用（竞争作用）。种群密度为1600时的RII指数比密度为9时的RII指数下降更快，即种群密度为9时五次的RII指数下降缓慢。第78天（第三次取样）之后，无论密度为多少，其RII指数变化不大，说明小麦进入生殖生长后，植株间的相互作用强度基本稳定。

图9 三种种植密度下小麦的RII随时间的变化趋势

Fig. 9 Variation of relative interaction intensity(RII) with time for wheat under three different density gradients

讨论

相互作用关系随密度梯度的变化

本研究结果表明，作物幼苗期的RII指数随种群密度的增加先升高后降低（图2、5、8），正相互作用强度随密度胁迫增加呈先增后减趋势，种群适合度随密度增加也呈相同趋势。关于此现象的解释如下：随种群密度增加，一些环境因子例如疾风、蒸腾等对植物的负作用影响逐渐减弱，因此更有利于植株的生长发育；然而随密度进一步增加，植株对空间资源的竞争作用将超过植株间的促进作用，最终表现为净的负效应。本文的这一分析结果与先前很多研究结论一致。例如，储诚进等在2008年[42]指出：在恶劣的高寒草甸环境中，随种群密度的增大，垂穗披碱草的平均个体生物量呈现先增加后减小的模式，最大值出现在中等密度水平[41]。其内在机制为随种群密度的增大，正相互作用先增强后减弱，在中等密度时出现最大值。本文进一步分析发现；大豆、玉米和小麦的最适密度分别为35、25、400左右，即在此相应密度下大豆、玉米和小麦的单株生物量达到最大值。三种作物单株最大生物量出现时的种群密度是否与单位面积产量最高时的最适密度重合仍需通过理论建模和试验验证。

近年来大量研究[37-40]均聚焦于随种群密度的增加，植株邻体间的竞争越来越激烈。Deng等[43-44]通过作物单位面积生物量产量与密度梯度之间的关系，从种群角度探讨了作物的最佳种植密度。而本文从植株邻体间相互作用强度动态变化的角度，系统分析了邻体间正负相互作用随动态生长和邻体竞争强度（密度）的增加而发生转变的规律。此外，该研究结果也进一步完善了环境胁迫梯度假说（SGH）[45-49]，同时也验证了种群的阿利效应[50-51]。

相互作用关系随时间动态的变化

本研究通过实验证明相同密度条件下，三种作物种内竞争作用在中后期随植株的生长或密度的增加均表现为增强趋势（图1、3、4、6、7、9）。且在高密度种群中，植株间净相互作用从幼苗期到成熟期都体现为竞争关系；而在低密度种群的幼苗期，邻体间相互作用均表现为正相互作用，在成熟期则均表现为负相互作用。但幼苗期中等种群密度的RII指数比低密度的更大，表明适当提高种植密度更有利于种子的萌发和幼苗的生长。然而，分析结果也显示玉米的种群密度为100和900时RII指数在测量后期随时间呈微弱增加趋势（图6）这可能是因为此时间段内浇水不足，导致中高密度种植的玉米遮荫防止水分蒸发的正相互作用增强。

结论

本研究通过三种作物的密度梯度实验得出如下结论：1）植株间的正相互作用仅存在于作物个体的幼苗期，且在中等密度出现正相互作用的最大值，即植物个体生物量最大；2）作物生长中期和成熟期，随种群密度增加，植株间的竞争作用越来越激烈；3）随着植株的生长，植株间对空间资源的竞争越来越激烈。

基于上述研究结果，在农业生产实践中，对于以多次刈割或动物啃食植物幼苗生物量为目标的（比如牧草），可运用正相互作用理论适当增加初始种植密度以促进个体的生长，进而增加植物生长季期间的总生物量产量；而对于以收获成熟生物量或繁殖器官（即种子）产量为目标的，则应以单位面积最终产量最大化的最适种植密度理论[43-44]为指导，进行最优种植。

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基金项目：国家自然科学基金优青项目（31322010）和面上项目（31270753）；兰州大学中央高校基本科研业务费（lzujbky-2016-k03）

作者简介：董传聪（1991-），男，硕士，主要研究方向：理论生态学

通信联系人：邓建明（1978-），男，教授、博导，主要研究方向：理论生态学、植物生态学. E-mail: dengjm@lzu.edu.cn