Leaf functional traits and resource use strategies facilitate the spread of invasive plant Parthenium hysterophorus across an elevational gradient in western Himalayas

Abstract

Parthenium hysterophorus L. (Asteraceae) is a highly prevalent invasive species in subtropical regions across the world. It has recently been seen to shift from low (subtropical) to high (sub-temperate) elevations. Nevertheless, there is a dearth of research investigating the adaptive responses and the significance of leaf functional traits in promoting the expansion to high elevations. The current study investigated the variations and trade-offs among 14 leaf traits (structural, photosynthetic, and nutrient content) of P. hysterophorus across different elevations in the western Himalayas, India. Plots measuring 20 × 40 m were established at different elevations (700 m, 1100 m, 1400 m, and 1800 m) to collect leaf trait data for P. hysterophorus. Along the elevational gradient, significant variations were noticed in leaf morphological parameters, leaf nutrient content, and leaf photosynthetic parameters. Significant increases were observed in the specific leaf area, leaf thickness, and chlorophyll a, total chlorophyll and carotenoid content, as well as leaf nitrogen and phosphorus content with elevation. On the other hand, there were reductions in the amount of chlorophyll b, photosynthetic efficiency, leaf dry matter content, leaf mass per area, and leaf water content. The trait-trait relationships between leaf water content and dry weight and between leaf area and dry weight were stronger at higher elevations. The results show that leaf trait variability and trait-trait correlations are very important for sustaining plant fitness and growth rates in low-temperature, high-irradiance, resource-limited environments at relatively high elevations. To summarise, the findings suggest that P. hysterophorus can expand its range to higher elevations by broadening its functional niche through changes in leaf traits and resource utilisation strategies.

Keywords: Leaf functional traits; Nutrient content; Specific leaf area; Trait‒trait relationship.

Fig. 1

Map of the study area representing study sites at different elevations (700 m, 1100 m, 1500 m, and 1800 m) in the western Himalayas, India, and sketch diagram showing plot establishment and plant selection method for leaf trait measurement in the study sites

Fig. 2

Pattern of leaf functional traits of Parthenium hysterophorus across an elevation gradient: a Leaf area; b Specific leaf area; c Leaf dry weight; d Leaf mass per area; e Leaf dry-matter content; and f Leaf thickness. The 95% confidence interval is represented by the shaded area, and the model patterns are represented by the line

Fig. 3

Pattern of Parthenium hysterophorus leaf photosynthetic characteristics: a photosynthetic efficiency, b chlorophyll a, c chlorophyll b, d total chlorophyll content, and e total carotenoid content across an elevational gradient. The 95% confidence interval is represented by the shaded area, and the model patterns are represented by the line

Fig. 4

Pattern of (a) leaf nitrogen content, b leaf phosphorus content, and c leaf water content of Parthenium hysterophorus across an elevational gradient. The 95% confidence interval is represented by the shaded area, and the model patterns are represented by the line

Fig. 5

Standardized major axis (SMA) regressions depicting the relationships between leaf functional traits across an elevational gradient. a leaf area (Log_LA) ~ leaf dry weight (Log_LDW), b leaf water content (Log_LWC) ~ leaf dry weight (Log_LDW), c leaf area (Log_LA) ~ leaf thickness (Log_LT), and d leaf dry weight (Log_LDW) ~ leaf thickness (Log_LT)

Fig. 6

Pattern of R² values of the scaling exponents of a LA ~ LDW and b LWC ~ LDW with elevation. LA = leaf area; LDW = leaf dry weight; and LWC = leaf water content