Management of below-ground biomass of Typha angustifolia by harvesting shoots above the water surface on different summer days

Abstract

A dynamic model of regrowth in Typha angustifolia after cutting shoots above the water surface was formulated by characterizing the phenology and mobilization of resources from below-ground to aboveground organs after the cutting. The model parameters were determined by two cutting experiments to investigate the different strategies with flowering and nonflowering shoots after cutting in 2001 and by four cutting experiments to elucidate the regrowth characteristics after cutting on different days from June to September in 2002. A difference was evident both for flowering and non-flowering shoots and for each cutting day. From June to August, non-flowering shoots regrew immediately after cutting, but flowering shoots did not. The shoot regrowth height, number of leaves and shoot biomass were higher with the earlier cutting. The model was validated using the below-ground biomass observed in December 2002 and below-ground dynamics observed in 2003. In the low-flowering shoot zone of the stands, in which the percentage of flowering shoots was small (around 10%), the decrease in below-ground biomass became larger from June (20%) to August (60%). Cutting the high-flowering shoot zone (flowering shoots: 78%) in July 2001, just 1 week after peduncle formation, decreased the below-ground biomass by about 50%. In the low-flowering shoot zone, cutting just before senescence is better for decreasing below-ground biomass with a smaller rate of flowering shoots. The difference of below-ground biomass reduction in non-flowering shoots is mainly due to the decrease in downward translocation (DWT) of above-ground material to below-ground organs during senescence, because of the decrease in regrowth biomass. As for flowering shoots, the decrease in the photosynthate transportation from above-ground to below-ground organs and that of DWT are closely related because they cannot grow again within the season.

Estimating nitrogen budgets of Typha angustifolia by considering the regrowth shoot productivity and nitrogen content after harvesting aerial organs in different growing seasons

“…The second was a nutrient submodel that was used to simulate the seasonal dynamics of internal nutrients and the nutrient budgets of the plant. Details of the growth submodel have been described by Tanaka et al (2004Tanaka et al ( , 2005. Nutrient dynamics in each organ of Typha spp.…”

“…The seasonal changes in shoot and rhizome biomasses were calculated from the equations proposed by Tanaka et al (2005), and based on these values, the N mass (gN/m 2 ) in shoot or rhizome was estimated using Eqs. 3 or 4, respectively, as shown above.…”

“…These equations were incorporated into the regrowth model (Tanaka et al 2005) in order to simulate the daily N mass in T. angustifolia after harvesting the aerial organs, as shown in Eqs. 3 and 4 above.…”

“…In contrast, a mathematical model can closely estimate the seasonal fluxes of N by estimating a nutrient budget of Typha angustifolia L. in a manner similar to a dry matter budget (Tanaka et al 2004(Tanaka et al , 2005. A method of simulating the seasonal changes in nutrient contents by formulating mathematical relationships between the plant tissue nutrient concentrations and the time was proposed by Karunaratne and Asaeda (2002) and was further improved by Tanaka et al (2004Tanaka et al ( , 2005 for Typha spp.…”

“…A method of simulating the seasonal changes in nutrient contents by formulating mathematical relationships between the plant tissue nutrient concentrations and the time was proposed by Karunaratne and Asaeda (2002) and was further improved by Tanaka et al (2004Tanaka et al ( , 2005 for Typha spp. Further, the effects of harvesting aerial organs of T. angustifolia and their subsequent productivity on the nutrient cycle in the aquatic ecosystem is still unclear.…”