PHOTOSYNTHETICA

Photosynthetica 2015, 53(3):419-429 | DOI: 10.1007/s11099-015-0137-y

Response of invasive Chromolaena odorata and two coexisting weeds to contrasting irradiance and nitrogen

G. M. Quan^1,2, D. J. Mao¹, J. E. Zhang^1,*, J. F. Xie¹, H. Q. Xu³, M. An⁴

¹ Institute of Tropical and Subtropical Ecology, South China Agricultural University, Guangzhou, China

² Department of Urban Construction Engineering, Guangzhou City Polytechnic, Guangzhou, China

³ Agricultural College, Hunan Agricultural University, Changsha, China

⁴ Environmental and Analytical Laboratories, Faculty of Science; E H Graham Centre for Agricultural Innovation (Industry & Investment NSW and Charles Sturt University), Charles Sturt University, Wagga Wagga, Australia

Chromolaena odorata is a widespread exotic weed in southern China and other regions of the world. To better understand its invasive strategies, we compared leaf pigment contents and gas-exchange traits of the invader with its two coexisting species (native Urena lobata and invasive Bidens pilosa) under combined conditions of irradiance (full, medium, and low) and nitrogen (full, medium, and low) supplies. The chlorophyll (Chl) a+b content of U. lobata was the highest and the Chl a/b ratio of C. odorata was the lowest among the three weed species. In most treatments, leaf pigment, light-saturated photosynthetic rate (P _max), and light saturation point (LSP) of all the species increased, while their Chl a/b ratios decreased with the increasing nitrogen. The P _max and LSP of U. lobata were greater than those of the coexisting weeds under full irradiance (FI), but significantly declined with the decreasing irradiance. The invasive weeds, especially C. odorata, showed lower P _max and LSP under FI, but they showed slight decrease under low irradiance. Compared to U. lobata, C. odorata exhibited the lower light compensation point (LCP) in most treatments, higher LSP under low and medium irradiance, and lower dark respiration rate under FI. In addition, all the three species showed similar responses to different irradiance and nitrogen conditions, mean phenotypic plasticity index (MPPI) of most photosynthetic variables of the two invasive species was lower than that of U. lobata. These results suggested that C. odorata behaved as a facultative shadetolerant weed, being able to grow in moderately sheltered environments; the lower MPPI might be one of the important competitive strategies during its invasion. However, its invasion should be limited to some very shady habitats. In the field, control should be mainly directed against populations growing in the open or nutrient-rich habitats, where its expansion speed could be much faster. Deep shade by intact canopies or luxuriant forests might be an effective barrier against its invasion.

Keywords: gas exchange; invasive species; irradiance; nitrogen supply; pigment

Received: January 23, 2014; Accepted: August 18, 2014; Published: September 1, 2015Show citation