Comparison of gas exchange characteristics between invasive Parthenium hysterophorus and Bidens pilosa and co-occurring native Cirsium setosum (Asteraceae)

The severe damage caused by some invasive species on natural ecosystems is prompting increasing global concern. Many studies have focused on exotic invasive species. Generally,exotic invasive plants have higher resource capture abilities and utilization capacities,and lower leaf construction costs( CC) compared with native plants. However,the physiological mechanisms that determine their invasiveness are poorly understood. Both Parthenium hysterophorus and Bidens pilosa are annual herbs originating from tropical and Central America. These have been introduced into China unintentionally through agriculture, or intentionally for ornamental purposes, and have become an extremely serious agricultural and rangeland weed,threatening native fauna,and are a physical nuisance. We hypothesized that exotic invaders may have higher resource capture abilities and utilization efficiencies compared with native species. To test this hypothesis,ecophysiological traits including net photosynthetic rate( P_n),water use efficiency( WUE),photosynthetic nitrogen use efficiency( PNUE),photosynthetic energy use efficiency( PEUE),specific leaf area( SLA),leaf P content per unit mass( P_(mass)),leaf N content per unit mass( N_(mass)),chlorophyll content,and mass-based and area-based leaf construction cost( CC_(mass) and CC_(area)) were measured. We compared the above traits between P. hysterophorus,B. pilosa,and the co-occurring native( Cirsium setosum) populations in Shandong, China. The results showed that the Pn,chlorophyll content,leaf SLA,leaf P_(mass),PEUE,and PNUE of P. hysterophorus and B. pilosa were significantly higher than those of C. setosum( P 0. 05). Stomatal conductance( G_s),transpiration rate( T_r),leaf N_(mass),and leaf CC_(mass) of P. hysterophorus were significantly higher than those of C. setosum,only( P 0. 05). B. pilosa was significantly higher than C. setosum in WUE,only( P 0. 05). Correlation analysis demonstrated that leaf WUE,P_(mass),and SLA were significantly positively correlated with Pn( P 0. 01). Leaf CC_(mass) did not increase significantly with increasing P_n. Leaf SLA,CC_(mass),and chlorophyll content were significantly positively correlated with N_(mass) P 0. 01). Compared with native plants,higher gas exchange characteristics and leaf biochemical indicators may contribute to the successful invasion of P.hysterophorus and B. pilosa. The results indicated that these two invasive species had a higher resource capture ability and resource utilizati