珠江河网密刺苦草种群衰退的表观性状特征指示

Morphological Traits Indicating Decline of the Vallisneria denseserrulata Population in the Pearl River Network

探讨珠江河网密刺苦草现存种群衰退特征及其主要影响因素,可为珠江河网水草床种群复建,珠江河网水生态功能和渔业资源持续利用和发展提供基础依据。于2017-2019年对珠江河网水草床及其中外海(S3)、小塘(S5)和榄核(S8)的密刺苦草开展调查,利用冗余分析(RDA)和主成分分析(PCA)等。多元统计方法分析密刺苦草的株高、株重、叶片指标等参数与环境因子关系,并结合2019年该区域密刺苦草种群急剧衰退情况探讨其衰退前的表观性状特征指示意义。结果显示,珠江河网密刺苦草衰退前一年度种群表观性状时空分布特征差异明显,S3和S8站位密刺苦草株高、株重等在2月、8月至12月期间呈现先增加后下降的趋势,而S5站位密刺苦草上述指标持续增加;12月,不同站位密刺苦草种群出现生长特征分化,S5站位密刺苦草进入花果期,而S3和S8站位密刺苦草则开始衰退。RDA结果显示,密刺苦草株高主要受水深、沉积物中粒径组分及沉积物总磷含量等影响,株重主要受沉积物总磷含量影响,不同站位群丛受到不同环境因子的影响制约。PCA结果显示,密刺苦草的9种表观性状可表征其克隆生长力、有性繁殖力和多年生长力,并决定其种群维持策略:一种以S5站位为代表,种群越冬期保持持续生长力,并进行有性繁殖资源分配,能适应环境变化,种群在次年得以维持和延续;另一种以S3和S8为代表,种群在越冬期生长力减弱,无有性繁殖资源分配,未能有效应对不利环境条件,最终导致两站位种群在次年急剧退化甚至消失。

Submerged macrophyte beds(SMBs)play important roles in aquatic ecosystem,but the succession characteristics of SMBs in urban river systems are still poorly understood.In this study,Vallisneria denseserrulata in the Pearl River network was selected for research,and we investigated the morphologic traits of V.denseserrulata at different sites in different months and explored the decline characteristics and main influencing factors.We also discussed strategies for maintaining V.denseserrulata beds in different river sections based on differentiation of morphologic traits.In February,August and December of 2017,the spatial distribution investigation of submerged macrophyte beds in the lower Pearl River network was carried out at 13 sites(S1-S13)by field investigation and fishery survey.In the same months of 2018 and 2019,monitoring of the morphologic traits of the V.denseserrulata population was conducted at S3,S5 and S8.The relationship of V.denseserrulata morphologic traits and environmental factors were then analyzed using multivariate statistical methods including redundancy analysis(RDA)and principal component analysis(PCA).Results show that the morphologic traits of V.denseserrulata presented obvious differences in temporal-spatial distribution in 2018.The plant height and weight of V.denseserrulata in beds at S3 and S8 increased from February to August,then decreased from August to December,while the plant height and weight of V.denseserrulata at S5 continued to increase.In December,growth characteristics of V.denseserrulata differed among sites,with the population at S5 entering the flowering and fruiting stage,while the populations at S3 and S8 were in recession.The RDA results show that plant height was primarily affected by water depth,medium particle size components and total phosphorus content in sediments,while the plant weight was primarily affected by total phosphorus content in sediments.The PCA results show that the 9 morphological traits comprehensively characterized the clonal growth ability,sexual reproduction ability and multi-year growth ability,and determined population maintenance strategies.The V.denseserrulata population at S5 was characterized by sustained growth during the winter and allocation of resources for sexual reproduction,adapting to environmental changes,and this enabled the population to persist in the following year.Another case,represented by the V.denseserrulata populations at S3 and S8,shows that the growth capacity of the populations declined during the winter,with no allocation of sexual reproduction resources.Having failed to meet adverse environmental conditions,the populations faced rapid population decline and even disappearance the following year.