The reduced growth due to elevated CO2 concentration hinders the sexual reproduction of mature Northern pipevine (Aristolochia contorta Bunge )

Abstract

The phenology has gained considerably more attention in recent times of climate change. The transition from vegetative to reproductive phases is a critical process in the life history of plants, closely tied to phenology. In an era of climate change, understanding how environmental factors affect this transition is of paramount importance. This study consisted of field surveys and a greenhouse experiment on the reproductive biology of Northern pipevine (Aristolochia contorta Bunge). During field surveys, we investigated the environmental factors and growth characteristics of mature A. contorta, with a focus on both its vegetative and reproductive phases. In its successful flowering during the reproductive phase, A. contorta grew under the conditions of 40% relative light intensity and 24% soil moisture content, and had a vertical rhizome. In the greenhouse experiments, we examined the impact of increased CO₂ concentration on the growth and development of 10-year-old A. contorta, considering the effect of rhizome direction. Planted with a vertical rhizome direction, A. contorta exhibited sufficient growth for flowering under ambient CO₂ concentrations. In contrast, when planted with a horizontal rhizome direction, it was noted to significantly impede successful growth and flowering under elevated CO₂ concentrations. This hindered the process of flowering, highlighting the pivotal role of substantial vegetative growth in achieving successful flowering. Furthermore, we observed a higher number of underground buds and shoots under the conditions of elevated CO₂ concentration and a horizontal rhizome direction instead of flowering. Elevated CO₂ concentrations also exhibited diverse effects on mature A. contorta's flower traits, resulting in smaller flower size, shorter longevity, and reduced stigma receptivity, and pollen viability. The study shed light on elevated CO₂ concentrations can hinder growth, potentially obstructing sexual reproduction and diminishing genetic diversity.

Keywords: CO2 concentration; climate change; growth inhibition; phenology; reproduction; rhizome direction.

Figure 1

Comparison of environmental variables between vegetative and reproductive phases. (A) relative light intensity, (B) soil water content, (C) soil organic matter content, (D) pH, (E) EC, (F) PO₄–P, (G) NH₄–N, (H) NO₃–N, (I) Ca²⁺, (J) K⁺, (K) Na⁺, (L) Mg²⁺. Bars indicate standard errors. *p < 0.05; ***p < 0.001.

Figure 2

Growth traits of A. contorta in vegetative and reproductive phases. (A) stem thickness, (B) length of the first internode, (C) number of branches, (D) number of leaves, (E) single leaf area, (F) total leaf area, (G) rhizome thickness, (H) rhizome length, (I) direction of rhizome, (J) chlorophyll content, (K) dry weight of stem, leaves, rhizome and root. Bars indicate standard errors. **p < 0.01; ***p < 0.001.

Figure 3

C/N ratio of each part in the vegetative phase and reproductive phase. Bars indicate standard errors. *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 4

Canonical correlation analysis (CCA) plots to determine the relationships among the environmental factors and growth traits. The percentage (%) of each axis represents the explained variance. Dotted curves indicate groups of individuals in the vegetative and reproductive phases, which are represented by pink triangles. The arrows are strongly correlated with the axis.

Figure 5

Sum of nutrient uptake by A. contorta and nutrient losses under two CO₂ concentrations (400 ppm, 540 ppm), and two rhizome directions (horizontal rhizome planting, H; and vertical rhizome planting, V). (A) PO₄–P, (B) NH₄–N, (C) NO₃–N, (D) Ca²⁺, (E) K⁺, (F) Na⁺, (G) Mg²⁺, (H) pH, (I) EC, (J) soil C/N ratio. Letters on the graph indicate significant differences at the 5% level, based on Duncan’s test. Bars indicate standard errors.

Figure 6

The growth traits of A. contorta under two CO₂ concentrations (400 ppm, 540 ppm), and two rhizome directions (horizontal rhizome planting, H; and vertical rhizome planting, V). (A) stem length, (B) length of the first internode, (C) stem thickness, (D) number of branches, (E) total branch length, (F) number of leaves, (G) single leaf area, (H) total leaf area, (I) chlorophyll content. Letters on the graph indicate significant differences at the 5% level, based on Duncan’s test. Bars indicate standard errors.

Figure 7

Dry weight of each part of A. contorta and allocation of dry weight under two CO₂ concentrations (400 ppm, 540 ppm), and two rhizome directions (horizontal rhizome planting, H; and vertical rhizome planting, V). (A) stem weight, (B) leaves weight, (C) rhizome and root weight, (D) allocation of dry weight. Letters on the graph indicate significant differences at the 5% level, based on Duncan’s test. Bars indicate standard errors.

Figure 8

Number of flowers of A. contorta under two CO₂ concentrations and two rhizome directions.

Figure 9

Reproductive (sexual and asexual) traits of A. contorta under two CO₂ concentrations and two rhizome directions. (A) flower longevity, (B) perianth size, (C) diameter of utricle, (D) pollen diameter, (E) number of underground buds, (F) number of shoots. Letters on the graph indicate significant differences at the 5% level, based on Duncan’s test. Bars indicate standard errors.

Figure 10

C/N ratio of each part of A. contorta under two CO₂ concentrations and two rhizome directions. (A) stem C/N ratio, (B) leaf C/N ratio, (C) rhizome C/N ratio, (D) flower C/N ratio, (E) ovary C/N ratio.

Figure 11

Canonical correlation analysis (CCA) plots to determine the relationships between growth and reproductive traits. The percentage (%) of each axis represents the explained variance. The dotted curves indicate the groups of individuals in the treatment groups, which are represented by the blue triangles. The arrows are strongly correlated with the axis.

Figure 12

Comprehensive understanding of various factors that influence the asexual and sexual reproductions in mature A. contorta.