| The adaptability of plants to the environment has always been one of the focuses in the research field of ecology.Plants can form different survival strategies in response to environmental changes by adjusting their physical characteristics.The rapid development of urbanization has changed the environmental conditions on which vegetation rely on,resulting in fragmentation and heterogeneity of the habitats for plants.It also has a significant impact on the growth,development,reproduction and spread of plants.At present,most studies of the adaptability of plants to the environment is still conducted at natural ecosystems,and there are relatively few studies of plants in urban ecosystems.To understand how urban plant communities respond to urbanization from the perspective of functional traits is helpful to provide scientific basis for urban biodiversity conservation.We conducted this study within Chongqing metropolis and investigated the spontaneous plants distributed in our study area.We measured the functional traits of the spontaneous plant community under varying urbanization gradient in Chongqing metropolis and summarized how spontaneous plants responded to urbanization in this mountainous city.The main results are as follows:(1)Summary of functional traits of spontaneous plants in the Chongqing metropolis1)In this study,a total of 70 spontaneous plants were measured.The coefficients of variation(CV)of the plant functional traits were all less than 1,and the CV of leaf C content was the lowest(7.45%)with a certain degree of homeostasis.The average SLA of spontaneous plants is 359.33 cm~2/g,with the average SPAD being 39.62,the average height being 0.41 m,the average leaf C content being 449.53 mg/g,the average leaf N content being 24.74 mg/g,the average leaf P content being 2.81 mg/g,the average C:N ratios being 20.62,the average N:P ratios being 11.25,and the average C:P ratios being234.06.2)The correlation analysis of all spontaneous plant functional traits showed that there were correlations between certain functional traits.Specific leaf area(SLA)was significantly and positively correlated with leaf N and C content,and leaf N and P content was positively correlated.There was also a significant and positive correlation between seed size and plant height and fruit size.3)There were large differences in the functional traits by plant life forms.Annual herbs showed high relative growth rate and rapid carbon assimilation,while the SLA of perennial herbs was significantly higher than the annual herbs;The differences in functional traits between native and non-native species were not significant,indicating that plants of different life forms and origins might have different survival strategies to adapt to the urban environment.4)Four functional types were classified for the spontaneous plants using cluster analysis,and significant differences in functional traits among spontaneous plants of different functional types were found.In this study,the ecological strategies of spontaneous plants in Chongqing metropolis can be mainly summarized as the“CR”(competitor-ruderal),“R”(ruderal),and“SR”(stress-ruderal)types.The“R”strategic plant occupies a dominant position in the city,which is compatible with the characteristics of urbanization.(2)Responses of spontaneous plant functional traits to urbanization1)This study showed that as the intensity of urban growth increased,plant SLA and leaf N content decreased,with N:P ratios,C:P ratios showing a downward trend,and C:N ratios showing an upward trend.Nutrient utilization of plants increased and plant resilience is strengthened with the increase of urban growth intensity.The other plant traits did not respond significantly to the intensity of urban growth.2)There were significant differences in leaf P content,N:P ratios,and C:P ratios by habitat types.Leaf P content of plants in scrubland gaps was significantly higher than in the forest edges and vacant soil,while N:P ratios of plants in scrubland gaps was significantly lower than in the forest edges.Other functional traits were not significantly different by habitats;the relationship between plant functional traits will be affected by the habitat and shift their strategies.This study not only provided the data of plant functional traits in mountainous cities,but also help clarified the ecological strategies of urban spontaneous plants in mountain cities along the urban growth gradient.It also provided important feedbacks for the maintaining of urban ecosystem functions in mountainous cities. |
