Research Article |
Corresponding author: Joshua C. Buru ( joshuacomradeburu@gmail.com ) Academic editor: Mark van Kleunen
© 2016 Joshua C. Buru, Kunjithapatham Dhileepan, Olusegun O. Osunkoya, Jennifer Firn.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Buru JC, Dhileepan K, Osunkoya OO, Firn J (2016) Comparison of growth traits between abundant and uncommon forms of a non-native vine, Dolichandra unguis-cati (Bignoniaceae) in Australia. In: Daehler CC, van Kleunen M, Pyšek P, Richardson DM (Eds) Proceedings of 13th International EMAPi conference, Waikoloa, Hawaii. NeoBiota 30: 91–109. https://doi.org/10.3897/neobiota.30.8495
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Cat’s claw creeper vine, Dolichandra unguis-cati (L.) Lohmann (syn. Macfadyena unguis-cati (L.) Gentry) (Bignoniaceae), is a major environmental weed in Australia. Two distinct forms of this weed (‘long’ and ‘short’ pod), with differences in leaf morphology and fruit size, occur in Australia. The long pod form has only been reported in less than fifteen localities in the whole of south-east Queensland, while the short pod form is widely distributed in Queensland and New South Wales. This study sought to compare growth traits such as specific leaf area, relative growth rate, stem length, shoot/root ratio, tuber biomass and branching architecture between these forms. These traits were monitored under glasshouse conditions over a period of 18 months. Short pod exhibited higher values of relative growth rates, stem length, number of tubers and specific leaf area than long pod, but only after 10 months of plant growth. Prior to this, long and short pod did not differ significantly. Higher values for these traits have been described as characteristics of successful colonizers. Results from this study could partly explain why the short pod form is more widely distributed in Australia while long pod is confined to a few localities.
Cat’s claw creeper, invasive species, competitiveness, relative growth rate, successful colonizers, traits, biomass, tubers
Invasive plant species continue to threaten biodiversity and ecosystem function globally (
It has proven difficult to consistently find a correlation of the same set of traits with invasiveness, likely because of the varying effects of environmental factors on different plant species (
Invasive species were shown to have higher values of traits like SLA (
Most studies aimed at understanding differences in traits associated with invasion success have used native species as control plants (
Our understanding of invasiveness traits could be better enhanced by comparing related non-native species of varying levels of colonization success (
Dolichandra unguis-cati prefers forested and riparian habitats, although it also grows vigorously on dry road side sunny environments. It also appears to thrive in most soil types, tolerating a wide range of soil pH (
In a field experiment using plants generated from tuberlings,
Herbarium records and field surveys suggest that LP is widely distributed in the native range, occurring from Mexico, Nicaragua, Costa Rica, Columbia to Brazil, whereas SP appear to be restricted to Paraguay (
The cause for the observed differences in abundance levels between LP and SP is not yet established, but introduction pressure may be one explanation. Reconstructing the invasion history of this exotic species (or the two forms) is not possible because there are no records of their introduction, except that the species was first reported in a Melbourne Nursery catalogue in 1865 (
Another explanation could be differences in growth strategies between LP and SP. Rapid growth and efficient resource allocation enhance success in colonization, especially during the early stages of plant life history (
In 2013 seeds of LP and SP were collected from various sites around the greater Brisbane area in southeast Queensland, Australia. Sites were chosen based on accessibility and availability of mature seeds at the time of experimentation. Once collected, seeds were stored for two weeks at room temperature in paper envelopes that were placed in containers with silica gel to ensure they were dry before germination commenced. Seeds were sterilised by soaking in 1% sodium hypochlorite (NaOCl) for 5 minutes followed by rinsing in water for 3 minutes (
After two weeks of germination, seedlings were transferred into plastic pots (dimensions: Width = 200 mm, Height = 190 mm, Length = 200 mm) filled with locally available commercial multi-purpose potting mix (Osmocote) containing a professional wetting agent and trace elements. This seedling growth experiment was set up at the Ecosciences Precinct glasshouse facilities (GPS coordinates: 27°29'41.5248"S; 153°1'49.2132"E) in Brisbane, Australia. The average temperature during the warmer months (October – April) ranged from 18 °C to 35 °C while during the cooler months (May – September) it was between 10 °C and 23 °C. Relative humidity ranged between 50 – 60% during this study. Plants were watered once a day but no additional fertilizer/nutrients were added. For this experiment, plants were left to grow without any support. Seedlings were left to grow in a light environment (range: 60–250 µmol.m-2.s-1) over 18 months (October 2013–March 2015), with sub-samples of plants taken at 5 and 10 months. Seven seedlings (replicates) were used per form (LP and SP) at each observation time. These replicates were randomly selected from an initial pool of over 100 plants raised from seeds. The remaining plants were used for other eco-physiological studies.
At observation time, vernier callipers were used to measure basal stem diameter (BSD) at the root-stem junction. Leaf area was determined by taking leaf pictures against a graduated background using a Panasonic DMC-ZS7, Lumix camera and then using the open access software Image J 1.47v (www.imagej.nih.gov/ij) to calculate the leaf area in cm2. Two mature leaves (including petiole) per replicate were used for this purpose. Fresh and dry masses of these leaves were also determined.
For each replicate plant, stem length, number of primary branches and ramifications (secondary branches), number of tubers and tuber fresh weight were also recorded. Apical dominance index (ADI) was calculated by dividing the number of ramifications by the total length of the branch in metres according to
Differences in RGR and other traits such as SLA, LDMC, total dry mass, belowground/aboveground biomass ratio, number of tubers, tuber mass ratio (TMR), shoot mass ratio (SMR) and root mass ratio (RMR) were compared using two-way MANOVA model, with form and age of plant as independent variables. Interactions of form and age of plants were also included in the model. When significant differences were found, a Tukey LSD post-hoc test was performed to check differences between specific means. Differences or similarities in plant traits between LP and SP were further analysed using a Principal Component Analysis (PCA). The clusters were projected on the graphical representation of the first two PCA axes. All statistical tests were conducted using R version 3.1.0 (
The overall total dry mass differed significantly between the two forms after 18 months of plant growth (F1, 36 = 73.802, p < 0.001). There was a significant interaction between form and age of the plant on the total dry mass (F2, 36 = 6.371, p < 0.004). During the earlier stages of growth up to 10 months, there was no significant difference between the two forms in terms of total dry mass accumulation, although generally SP weighed more (Table
Total biomass production and allocation patterns (± SE; N = 7) to tubers and leaves for long pod and short pod over time. a Total dry mass b Specific leaf area (SLA) c Tuber/root ratio d Tuber dry mass and e leaf area ratio. The legend in panel a applies to the rest of the panels.
Mean (± SE) growth traits calculated at 5, 10 and 18 months after planting for LP and SP. Different letters indicate significant differences among age groups and between the two forms of Dolichandra unguis-cati. Summary ANOVA refers to F- and P-values of a MANOVA model of growth traits using fixed effects of form and age of plants, and an interaction of form: age of plants; d.f = 5, 36. Within each row, representing means across the age of plants, means with the same subscripts are not significantly different at α ≤ 0.05 using a Tukey LSD multiple comparison procedure. “***”= P≤0.0001; “**” = P≤0.001; “*” = P≤0.05; n.s = not significant.
Traits | Age of plants in months | Summary ANOVA | ||||||
---|---|---|---|---|---|---|---|---|
5 | 10 | 18 | ||||||
LP | SP | LP | SP | LP | SP | F-ratio | Signif. | |
Aboveground dry mass (g) | 0.099a ± 0.023 | 0.200a ± 0.021 | 0.201a ± 0.047 | 0.430a ± 0.081 | 4.460b ± 0.922 | 7.580c ± 0.677 | 6.968 | * |
Root dry mass (g) | 0.097a ± 0.023 | 0.057ab ± 0.009 | 0.073ab ± 0.019 | 0.137ab ± 0.027 | 1.043b ± 0.328 | 1.903c ± 0.295 | 5.524 | * |
Root mass ratio (RMR) | 0.512a ± 0.062 | 0.151b ± 0.018 | 0.245c ± 0.035 | 0.221c ± 0.043 | 0.151b ± 0.016 | 0.154b ± 0.015 | 17.990 | *** |
Belowground dry mass (g) | 0.101a ± 0.029 | 0.174a ± 0.034 | 0.089b ± 0.018 | 0.253c ± 0.030 | 2.211c ± 0.723 | 4.719d ± 1.019 | 5.440 | * |
Tuber dry mass (g) | 0.004a ± 0.003 | 0.117b ± 0.028 | 0.016c ± 0.007 | 0.118b ± 0.024 | 1.169d ± 0.412 | 2.816d ± 0.745 | 4.923 | * |
Tuber mass ratio (TMR) | 0.020a ± 0.015 | 0.303b ± 0.053 | 0.071a ± 0.029 | 0.170c ± 0.020 | 0.148c ± 0.026 | 0.210d ± 0.038 | 9.163 | ** |
Total dry mass (g) | 0.200a ± 0.039 | 0.374a ± 0.034 | 0.290a ± 0.061 | 0.683b ± 0.116 | 6.671c ± 1.591 | 12.299d ± 1.391 | 7.455 | ** |
Shoot/root ratio (SRR) | 1.100a ± 0.270 | 4.556b ± 1.439 | 3.367c ± 0.726 | 3.540c ± 0.738 | 5.023d ± 0.615 | 4.543d ± 0.762 | 4.990 | * |
Tuber/root ratio (TRR) | 0.040a ± 0.026 | 0.637bd ± 0.073 | 0.225b ± 0.085 | 0.451bd ± 0.044 | 0.481bc ± 0.060 | 0.558cd ± 0.039 | 17.189 | *** |
Number of tubers | 0.286a ± 0.184 | 1.571a ± 0.297 | 0.858a ± 0.261 | 1.286a ± 0.184 | 2.000a ± 0.309 | 5.143b ± 1.299 | 3.063 | n.s |
Tuber fresh mass (g) | 0.009ab ± 0.006 | 0.399ab ± 0.091 | 0.075ab ± 0.030 | 0.541ab ± 0.107 | 4.597b ± 1.221 | 11.866c ± 2.709 | 7.630 | ** |
Basal stem diameter (mm) | 1.129a ± 0.083 | 1.283a ± 0.063 | 1.236a ± 0.062 | 1.371a ± 0.084 | 3.660b ± 0.234 | 3.236b ± 0.285 | 2.080 | n.s |
Stem length (cm) | 7.143a ± 0.969 | 16.428bc ± 3.176 | 7.329a ± 0.997 | 31.958ac ± 3.755 | 99.786c ± 35.862 | 326.500d ± 38.305 | 20.430 | *** |
Number of branches | 0.000a ± 0.000 | 0.143a ± 0.143 | 0.143a ± 0.143 | 0.429a ± 0.202 | 2.143b ± 0.340 | 3.857c ± 0.404 | 7.837 | ** |
Apical dominance index | N/A | N/A | N/A | N/A | 1.1471a ± 0.436 | 6.461b ± 3.883 | 3.191 | n.s |
Leaf area (cm2) | 6.074ac ± 1.254 | 4.100ac ± 0.954 | 7.234ac ± 0.697 | 4.571ac ± 1.356 | 39.747b ± 3.194 | 5.288c ± 0.922 | 60.977 | *** |
Leaf fresh mass (g) | 0.086ac ± 0.018 | 0.062ac ± 0.013 | 0.116ac ± 0.014 | 0.067ac ± 0.021 | 0.562b ± 0.054 | 0.076c ± 0.015 | 55.677 | *** |
Leaf dry mass (g) | 0.027a ± 0.006 | 0.019a ± 0.003 | 0.052ac ± 0.008 | 0.020ac ± 0.007 | 0.192b ± 0.029 | 0.022c ± 0.005 | 39.144 | *** |
Specific leaf area | 248.93a ± 26.260 | 231.901a ± 27.795 | 173.174ab ± 20.3 | 251.3a ± 24.819 | 224.211a ± 23.352 | 320.035ab ± 45.317 | 3.180 | n.s |
Leaf matter per area | 0.004a ± 0.0003 | 0.005a ± 0.001 | 0.008ab ± 0.002 | 0.005a ± 0.0002 | 0.005a ± 0.001 | 0.004a ± 0.001 | 0.434 | n.s |
Leaf water content (g) | 0.059ac ± 0.012 | 0.043ac ± 0.011 | 0.064ac ± 0.014 | 0.047ac ± 0.014 | 0.370b ± 0.030 | 0.054c ± 0.011 | 52.280 | *** |
Leaf dry matter content (mg g-1) | 32.871a ± 4.009 | 31.619a ± 2.083 | 51.44a ± 14.085 | 31.153a ± 1.317 | 33.377a ± 2.136 | 27.057a ± 2.368 | 0.037 | n.s |
Shoot mass ratio | 0.468a ± 0.061 | 0.546ab ± 0.056 | 0.684ab ± 0.031 | 0.609ab ± 0.050 | 0.701b ± 0.027 | 0.636b ± 0.046 | 1.778 | n.s |
Above- and below-ground biomass allocation (also shown by shoot/root ratio) did not vary significantly between forms (F1, 39 = 2.568, p > 0.08), and no significant interactions of form and age of plant were detected on this trait. A Tukey test of multiple comparisons of means showed that the proportion of dry biomass allocated to shoots, roots and tubers differed significantly between LP and SP after 18 months of plant growth (P < 0.0005, 0.021 and 0.002, respectively). SP allocated more biomass to tubers, shoots (leaves + stems) and roots than LP, especially after 18 months of growth (Fig.
LP appears to have allocated a significantly higher percentage of its biomass belowground at 5 months; while, SP invested significantly more biomass to tubers than LP at the same time (Table
Except for BSD, other growth related traits such as number and size of tubers, length of stems, and number of branches differed significantly between 10th and 18th month old LP and SP (Fig.
The pattern of resource allocation of LP and SP plants of varying ages in months, (mean ± SE, N=7). a Maximun stem length (cm) b Number of branches c Number of tubers dBasal stem diameter –(BSD) (mm).
Estimates of growth rate such as change in total biomass (F1, 39 = 47.03, p < 0.001), stem length (F1, 39 = 47.05, p < 0.0001) tuber dry weight (F1, 39 = 19.43, p < 0.005) and number of branches (F1, 39 = 61.49, p < 0.0001) differed significantly between the two forms over time (Fig.
Comparison of absolute change of variables between long pod (LP) and short pod (SP) plants in the glasshouse (mean ± SE, N = 7) calculated between 10 and 18 months: a change in total dry weight per month b change in basal stem diameter (BSD) per month c change in stem length per month d change in tuber dry weight per month and e increase in the number of branches per month.
Overall, the observed differences between LP and SP can be summarized by the PCA graphical representation (Fig.
Graphical representation of the first and second PCA axes of different plant traits analysed for form (LP vs SP) and age of the plants (5, 10 and 18 months).
Principal component loadings of the data set, eigenvalues and their contributions to the correlations, showing only the first four components.
Traits | PC1 | PC2 | PC3 | PC4 |
---|---|---|---|---|
Total dry mass (g) | 1.037 | 0.211 | 0.184 | -0.086 |
Shoot dry mass (g) | 1.021 | 0.089 | 0.134 | -0.061 |
Root dry mass (g) | 0.994 | 0.272 | 0.292 | -0.099 |
Tuber dry mass (g) | 0.942 | 0.424 | 0.206 | -0.124 |
Shoot mass ratio | 0.294 | -0.749 | -0.492 | -0.243 |
Root mass ratio | -0.632 | 0.417 | 0.704 | 0.222 |
Tuber mass ratio | 0.465 | 0.334 | -0.328 | -0.002 |
Shoot/root ratio | 0.409 | -0.471 | -0.671 | -0.095 |
Tuber/root ratio | 0.647 | 0.042 | -0.548 | 0.001 |
Number of tubers | 0.838 | 0.460 | -0.037 | -0.229 |
Basal stem diameter (mm) | 0.927 | -0.266 | 0.232 | 0.129 |
Stem height (cm) | 0.844 | 0.217 | -0.083 | -0.114 |
Number of branches | 0.974 | 0.116 | 0.035 | -0.040 |
Apical dominance index | 0.588 | 0.528 | 0.109 | -0.245 |
Leaf area (cm2) | 0.517 | -0.757 | 0.457 | 0.313 |
Leaf area ratio (cm2g-1) | -0.637 | -0.128 | 0.268 | -0.173 |
Specific leaf area (cm2g-1) | 0.285 | 0.354 | -0.402 | 0.569 |
LDMC (mg g-1) | -0.275 | -0.232 | 0.422 | -0.878 |
Importance of components | ||||
Eigen values | 11.811 | 4.729 | 3.523 | 2.220 |
Proportion explained | 0.422 | 0.169 | 0.126 | 0.079 |
Cumulative proportion | 0.422 | 0.591 | 0.717 | 0.796 |
The SP form, which is more widely distributed within eastern Australia, showed faster growing strategies. Higher values of RGR, stem length, number of tubers, and SLA are often indicators of successful colonizers (
Recent evidence, however, suggests the same carbon assimilation strategies are used by invasive and non-invasive plants (
Our results also seem to contradict findings by
Although SP had slightly higher values of SLA, it had lower values of LAR when compared to LP. Because LAR is a measure of the leafiness of a plant (
Transformer plants such as vines like D. unguis-cati, thrive in growing vertically and spreading horizontally to monopolise light environments (
This study shows that SP develops subterranean tubers early in its development while LP seems to delay tuber development. Tubers are used as a sink or storage organs for moisture and photo-assimilates and they may also regenerate producing new plants (
Previous studies have shown SP to exhibit more rapid and higher germination rates than LP at various temperatures (
We acknowledge both the Government of Botswana and the Department of Agriculture and Fisheries (Queensland, Australia) for part-sponsorship of this study through student scholarships to J.C Buru. We thank members of the Plant Structure and Systematics Research Group and Dr. Tanya Scharaschkin for providing valuable feedback on earlier versions of the manuscript. We also thank three reviewers who gave very useful comments that helped improve the manuscript greatly.