Photosynthetic performance of switchgrass and its relation to field productivity: A three-year experimental appraisal in semiarid Loess Plateau

To reveal photosynthetic characteristics and biomass yield is important for evaluating introduced species adaptation to local environments. A field experiment was conducted over three consecutive years (2011-2013) to evaluate photosynthetic characteristics, soil water content, aboveground biomass accumulation, and water use efficiency (WUE) in switchgrass (Panicum virgatum L.) populations exposed to three row spacing (20, 40 and 60 cm) treatments in two growth months (June and August) on the semiarid Loess Plateau of China. Results indicated that net photosynthetic rate (Pn), transpiration rate (Tr), instantaneous water use efficiency (WUEi) and plant height of switchgrass showed an increased trend, but aboveground biomass production and WUE showed an decreased trend with enlarged row spacings over the three years. The maximum daily mean Pn values (17.9, 18.4 and 19.7 µmol CO2 m−2 s−1) were observed in 2011, and the highest aboveground biomass production (67 771.8, 6 976.8 and 6 609.2 kg ha−1) were recorded in 2012 for 20, 40 and 60 cm, respectively. A close correlation between tiller numbers and aboveground biomass production (r=0.907) was observed. Pn was positively and significantly correlated with biomass per tiller, but it showed a negative correlation with aboveground biomass production. Our results confirm that wide row spacing is beneficial for single plant development, while narrow row spacing favors biomass production and water use of switchgrass in the region. It also implies that single leaf growth and performance could explain the switchgrass community density differences, while fails to account for the aboveground biomass production.