长江下游滨江湿地虉草-芦苇集合种群竞争共存的维持机制

Metapopulation theory often can explain the coexistence of certain species which can not be explained by classical competitive exclusion theory from the general population level. Competition-colonization trade-off may serve as a basis for some metapopulations to maintain competitive coexistence. In this project, Phragmites australis and Phalaris arundinacea are used as experimental materials. Both species have strong competitive capabilities and are widely distributed in the waterfront wetlands along the mid-lower reaches of the Yangtze River. This study investigates the extent and manner of ecological response of the allelopathic dose effect to the soil moisture environment through temporal and spatial dynamic analyses of the allelopathic effect of P. australis on the coexisting P. arundinacea under different soil moisture situations, and static analyses of the allelopathic effect of P. australis on the potted P. arundinacea by using P. australis tissue aqueous extracts and litters under different s soil moisture situations. The extent and manner of interspecific competition alleviation and complementary resource utilization between the two species are also studied through distribution analyses of the temporal (growth period) and spatial (plant vertical distribution) niche of P. australis and P. arundinacea. Moreover, the effect of litters of P. australis and P. arundinacea on the acceleration of substance cycle, alleviation of nutrient competition, and maintenance of high productivity of metapopulation is studied through the analyses of litters-soil nutrient cycling, related soil enzyme activity, and population biomass accumulation. Multi-channel of competition-colonization trade-off is explored based on the above researches. The maintenance competitive mechanism of the coexistence of the metapopulation of P. arundinacea and P. australis is then revealed. The results of this project not only have significant implications on comprehensive understanding interspecific relationship, exploration of channels of competition-colonization trade-off,and construction of constructed wetlands vegetation, but also to further verify the specificity of the scale range of ecological principles applicable.

集合种群理论常可解释一般种群水平下经典竞争排斥理论难以解释的某些物种共存现象，该理论认为竞争-拓殖能力妥协是多物种集合种群竞争共存的基础。本项目以长江滨江湿地极富竞争力的芦苇和虉草为研究对象，通过不同土壤水分下芦苇对共存虉草化感效应时空动态分析，及芦苇组织浸提液和枯落物腐解物对单生虉草化感效应静态分析，研究芦苇化感剂量效应对土壤水分环境生态响应的方式和强度；通过对物种时（生育期）空（植株垂直分布）生态位分布分析，研究两物种对种间竞争削弱和资源互补利用的方式和程度；通过对枯落物-土壤养分循环及相关土壤酶活性以及种群生物量积累分析，研究枯落物对加速物质循环、缓解养分竞争和维持种群高生产力的效应。在此基础上，探索物种间竞争-拓殖能力妥协的途径，揭示虉草-芦苇集合种群竞争共存的维持机制。该研究对种间竞争-拓殖妥协途径探索、人工湿地植被构建以及生态学一般原理适用尺度范围特定性的验证，均具有重要意义。

本项目从化感效应、生态位分布和枯落物养分循环三个方面探究了极富竞争力的虉草和芦苇两物种在湿地中竞争共存的维持机制。. 芦苇对虉草具明显的化感抑制效应，且这一抑制效应随土壤水分含量降低明显增强。当土壤相对含水量约降至70%时，虉草便难以维持正常生长；芦苇体内酚酸类化感物质主要为没食子酸、香豆酸、香草酸、丁香酸、对香豆酸、阿魏酸、水杨酸和苯甲酸，每种物质水环境响应特性明显，且以香豆酸、没食子酸和阿魏酸响应最强。. 两物种时间生态位分离度为70.4%，重叠度为29.6%；植株垂直空间生态位的分离度随重叠期的延长由72.5%降至0后升为57.1%，两物种根系垂直空间生态位的分离度为50.0%。两物种时空生态位分离特征明显，从而有效缓解二者对某些资源的竞争。. 虉草对群落下部弱光虽具明显的补偿利用特性，但芦苇种群的密度决定了群落内虉草光能补偿利用率的高低。其中，芦苇密度分别约为25、35、和45株/m2（芦苇种群处于半成熟、中后期和近成熟阶段）时，群落内虉草的光能补偿利用率分别为74.72%、66.43%和36.18%。虉草主要利用0-10cm表土层养分，而芦苇主要利用20-30cm土层的养分，二者可互补利用不同土层的养分资源。. 虉草枯落物分解过程中释放于表土层约40.90%的总氮和71.75%的速效磷被芦苇优先利用，约47.72%的总氮和21.91%速效磷被自身优先利用，而约11.38%的总氮和6.34%速效磷被处于生长期重叠的两物种共同利用；芦苇落物分解过程中释放于表土层约55.93%的总氮和72.32%的速效磷被虉草优先利用，约37.29%的总氮和29.84%的速效磷被自身优先利用，而约6.78%的总氮被处于生长期重叠的两物种共同利用，两物种养分互补利用特征明显。. 综上结果可知，化感作用的水环境响应特性是虉草芦苇维持竞争共存格局的主导机制，而源自生态位分离的光照资源和养分资源互补以及源自于枯落物养分循环的养分互补则是两物种维持竞争共存格局的辅助机制。因此，在虉草-芦苇人工湿地中，可通过控制湿地土壤水分（相对含水量70%以上）和群落内芦苇的密度（35株/m2以下），确保虉草和芦苇维持较为稳定的竞争共存格局。

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