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 above-ground organs after the cutting. The model parameters were determined by two cutting experiments to investigate the different strategies with flowering and non-flowering 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.

Appendix

Governing equations of rhizome, roots, new rhizome, shoot and panicle are as follows:

$$ \frac{{{\text{d}}B_{{rhi}} }} {{{\text{d}}t}} = - R_{{rhi}} - D_{{rhi}} - Rhif \cdot f_{{rhi}} + y \cdot {\sum\limits_{i = 1}^{i = i{\text{max}}} {\varepsilon _{{sht}} \cdot b_{{sht}} (i)} } \cdot f_{{sht}} {\text{ }} + y \cdot {\sum\limits_{i = 1}^{i = i{\text{max}}} {\varepsilon _{{ph}} \cdot Ph_{{sht}} } }(i) \cdot f_{{ph}} $$

(16)

$$ \frac{{{\text{d}}B_{{{\text{rt}}}} }} {{{\text{d}}t}} = G_{{{\text{rt}}}} \cdot f_{{{\text{rt}}}} - R_{{{\text{rt}}}} - D_{{{\text{rt}}}} + x \cdot Rhif \cdot f_{{rhi}} $$

(17)

$$ \frac{{{\text{d}}B_{n} }} {{{\text{d}}t}} = - R_{n} - D_{n} + (1 - y) \cdot {\sum\limits_{i = 1}^{i = i{\text{max}}} {\varepsilon _{{sht}} \cdot b_{{sht}} (i) \cdot f_{{sht}} } }{\text{ }} + (1 - y) \cdot {\sum\limits_{i = 1}^{i = i{\text{max}}} {\varepsilon _{{ph}} \cdot Ph_{{sht}} (i) \cdot } }f_{{ph}} $$

(18)

$$ \begin{aligned} \frac{{{\text{d}}b_{{sht}} (i)}} {{{\text{d}}t}} & = Ph_{{sht}} (i) - R_{{sht}} (i) - D_{{sht}} (i) - G_{{rt}} \cdot f_{{rt}} \cdot (b_{{sht}} (i)/B_{{sht}} ) \\ & \quad + (1 - x) \cdot Rhif \cdot f_{{rhi}} \cdot (b_{{sht}} (i)/B_{{sht}} ) - \varepsilon _{{sht}} \cdot b_{{sht}} (i) \cdot f_{{sht}} - \varepsilon _{{ph}} \cdot Ph_{{sht}} (i) \cdot f_{{ph}} \\ & \quad - b_{{sht}} (i) \cdot \varepsilon _{p} \cdot ff - Ph_{{sht}} (i) \cdot k \cdot ff \\ \end{aligned} $$

(19)

$$ \frac{{{\text{d}}B_{p} }} {{{\text{d}}t}} = - R_{p} - D_{p} + {\sum\limits_{i = 1}^{i = i{\text{max}}} {Ph_{{sht}} (i) \cdot k \cdot ff} } + {\sum\limits_{i = 1}^{i = i{\text{max}}} {\varepsilon _{p} \cdot b_{{sht}} (i) \cdot ff} } $$

(20)

The notations are listed in Table 3. The above-ground plant stand was stratified into 1-cm horizontal layers in which the dry matter budget and elongation were calculated separately. For mobilization of stored material from rhizome to shoots, respiration, mortality and shoot elongation, see Asaeda and Karunaratne (2000). Figure 9 shows the relation of each term in the five governing equations.

Table 3 Notations used in the governing equations

Fig. 9

Schema of the relation between the differential equations