SEASONAL DYNAMIC OF ABOVE AND BELOW-GROUND DRY MATTER ACCUMULATION IN GIANT REED (ARUNDO DONAX L.)

摘要

Our previous study, carried out in an inland location of the Emilia Romagna Region, Northern Italy,indicated a summer slump for aboveground dry matter accumulation and radiation use efficiency (RUE) of giant reed.Thus, this study was driven by the need of exploring the dynamic of belowground dry matter accumulation of thecrop. The scope of this study was to gain insight on biomass accumulation of rhizomes, and on the relationshipbetween above and below-ground accumulation of giant reed. A giant reed stand, established in 2009, was sampledevery two weeks in the period between 6 May and 14 October 2011. On each sampling date three destructive samplesof 0.75 m~2. On each sampling date the following variables were measured: i) number of culms m~(-2); ii) stem heightand diameter; iii) fresh weight of leaves, stems and rhizomes; iv) dry weights of leaves, stems and rhizomes; v) drymatter yield of each component; vi) leaf area index (LAI). The total aboveground dry matter increased from 3.7 Mgha~(-1) at the first decade of May date to 28.2 Mg ha~(-1) at the end of September. The maximum average growth rate, 294kg DM ha~(-1), was observed in the second and third week of May. In the subsequent period, lasting until mid-August,the average daily growth rate was 209 DM kg ha~(-1). In the final part of the growing season, from mid-August to mid-October, the average daily growth rate daily was merely 40 kg DM ha~(-1). The belowground DM (rhizomes) was 10.8Mg ha~(-1) at the beginning of the growing season and increased to a maximum value of 19 Mg ha~(-1) at mid-August, withan average daily growth rate of 81 kg ha~(-1). The value of RUE changed abruptly during the season, confirming thesummer slump of giant reed growth observed in other location of the Region Emilia Romagna. A value of 2.80 g DMMJ-1 intercepted PAR was calculated for the period from May to mid-August. In mid August there is a breaking pointfor RUE, and the value calculated for the remaining part of the season was 0.68 g DM per MJ~(-1) intercepted PAR. TheRUE calculated for this experiment is about a half of the value calculated in more favorable conditions. Hence, giantreed reacted to harsh environment by substantially reducing both LAI and RUE.