Title : How harvest date affect physiological status of Miscanthus x giganteus and Miscanthus seed-based hybrids cultivated on heavy metal contaminated arable land?
Renewable energy and bioeconomy targets are set to increase market demand for lignocellulosic biomass in Europe. Different environments and end uses, i.e. combustion vs. conversion to liquid fuel, will require the introduction of much more diverse energy crop varieties. As there are different conversion technologies the harvest date will vary depending on the selected process. The harvesting of the lignocellulosic biomass for the anaerobic digestion required green plants. This required earlier harvest date and may cause disturbance in the senescence process which might affect the plantation efficiency in the following years. The aim of this study was to assess Miscanthus x giganteus (Mxg) and two Miscanthus seed-based hybrids (GNT41, GNT34) physiological status in the following year after autumn harvest (October) when compare to the regular harvest time (March). A field trial was established in 2015 on arable land contaminated in the past with Pb, Cd and Zn from nearby metal smelting industry in Southern Poland. The trial design was a complete randomized block including three replicates. At the end of the second growing season half of each plot was harvested green in October (2016), while the other half in March (2017). During the following growing season (2017) gas exchange, chlorophyll content, Nitrogen Balance Index as well as prompt chlorophyll a fluorescence measurements were performed twice at the beginning of July and September. Data obtained from chlorophyll fluorescence were used to calculate JIP-test parameters. A the end of the growing season (October) samples for analysis of N, P, K, Pb, Cd, Zn concentration in above-ground biomass were collected. Additionally, measurements of shoot height, shoot die of height and stem number were performed. GNT41 was the most affected variety by the previous year green harvest, what appeared as lower shoot height, delayed senescence as well as the reduction of the photosynthesis intensity (Asat), intrinsic water use efficiency and fluorescence parameters in July. The nitrogen content was the main factor conditioning differences between green and brown harvest, thus impact photosynthetic apparatus. Green harvest in all of the investigated plants was associated with the lower nitrogen concentration and were more pronounced later in the growing season, what was particularly reflected in chlorophyll content and differences among JIP-test parameters. Lower values of the Asat for brown harvested Mxg and GNT41 during September measurements might be associated with the shift of the growing season in time, what could be observed in the delayed senescence in case of those two varieties.
Take Away Notes:
• Presented work had strong practical implication as it refer to the energy crops cultivated in the field conditions.
• This work may indicate features of plants which denote unsuitability for the autumn harvest.