Hybrid Napier grass (Pennisetum purpureum Schumach × P. americanum (L.) Leeke cv. Pakchong1) and Giant reed (Arundo donax L.) as candidate species in temperate European paludiculture: Growth and gas exchange responses to suboptimal temperatures

Abstract

Hybrid Napier grass (Pennisetum purpureum × P. americanum cv. Pakchong1) and Giant reed (Arundo donax) are candidate bio-energy crops in temperate European paludiculture, due to their high growth and biomass production rates, ease of harvesting and resistance to temporary flooding. We conducted a growth chamber experiment with the two species in two different temperature regimes (15 °C and 20 °C of daytime growth temperature, respectively), to investigate whether the two species were capable of acclimating to typical growth season temperatures of temperate Europe, which are sub-optimal for the two species. After a 7-week period of growing in the climatized chambers, measurements of photosynthetic responses to light and CO2 were conducted. Surprisingly, the C4 species hybrid Napier grass was the most productive species in both temperature regimes and had the highest photosynthetic rates, but it was also more sensitive and responded with stronger differences to the temperatures than the C3 species Giant reed. Giant reed exhibited a more stable physiology (for example with quantum yield, dark respiration rate, maximum electron transport rate and maximum carboxylation rate of Rubisco), but had lower photosynthesis and produced less biomass than hybrid Napier grass. In contrast, hybrid Napier grass had a stable allocation to biomass fractions under both temperature regimes, while Giant reed responded to 15 °C with lower leaf allocation and higher root allocation. Both species showed individual limitations to suboptimal temperatures, but grew comparably well, especially at 20 °C. We showed that both hybrid Napier grass and Giant reed are potential paludiculture candidate species even in cooler climates, and prolonged outdoor trials are needed to verify our results under field conditions.