Abstract
Structural development and modification of bamboo culm’s anatomical characteristics occur during the maturation period. This process affects the conductivity efficiency in individual bamboo culms (above ground). The present study clarified this process in the sympodial type of bamboo rhizome (belowground). This study aimed to observe the anatomical characteristics of Gigantochloa scortechinii rhizome, examine their relationship with different study sites and rhizome ages, and investigate their relationship with hydraulic conductance. Destructive sampling on four consecutive rhizomes was conducted using a selective random sampling method. All rhizome anatomical characteristics were significantly different between study sites except parenchyma diameter, parenchyma lumen diameter, and fiber cell wall thickness. The results also indicated that the vascular bundle diameter, parenchyma diameter, parenchyma lumen diameter, parenchyma cell wall thickness, fiber diameter, fiber cell wall thickness, and fiber length increased with age, but radial to tangential ratio decreased with age. All measured characteristics including the conductance elements had no relationship with hydraulic conductance, except parenchyma diameter and parenchyma lumen diameter. The sizes parenchyma diameter and lumen diameter did not imply a determinant factor in hydraulic conductance. Further studies on rhizome chemical attributes should be carried out to isolate the cause of decreasing hydraulic conductance.
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Anatomical Characteristics of Gigantochloa scortechinii Bamboo Rhizome in Relation with Hydraulic Conductance
Johar Mohamed,a,* Hazandy A. Hamid,a,b Ahmad A. Nuruddin,a,b and Nik M. N. A. Majid a
Structural development and modification of bamboo culm’s anatomical characteristics occur during the maturation period. This process affects the conductivity efficiency in individual bamboo culms (above ground). The present study clarified this process in the sympodial type of bamboo rhizome (belowground). This study aimed to observe the anatomical characteristics of Gigantochloa scortechinii rhizome, examine their relationship with different study sites and rhizome ages, and investigate their relationship with hydraulic conductance. Destructive sampling on four consecutive rhizomes was conducted using a selective random sampling method. All rhizome anatomical characteristics were significantly different between study sites except parenchyma diameter, parenchyma lumen diameter, and fiber cell wall thickness. The results also indicated that the vascular bundle diameter, parenchyma diameter, parenchyma lumen diameter, parenchyma cell wall thickness, fiber diameter, fiber cell wall thickness, and fiber length increased with age, but radial to tangential ratio decreased with age. All measured characteristics including the conductance elements had no relationship with hydraulic conductance, except parenchyma diameter and parenchyma lumen diameter. The sizes parenchyma diameter and lumen diameter did not imply a determinant factor in hydraulic conductance. Further studies on rhizome chemical attributes should be carried out to isolate the cause of decreasing hydraulic conductance.
Keywords: Fiber; Parenchyma; Phloem; Vascular bundles; Xylem
Contact information: a: Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, UPM, Serdang, Selangor, 43400 Malaysia; b: Faculty of Forestry, Universiti Putra Malaysia, UPM, Serdang, Selangor, 43400 Malaysia; *Corresponding author: joe5587_forr@yahoo.com
INTRODUCTION
The quality and health of a bamboo stand can be quantified based on the number of culms and age ratio in a clump, maximum growth of morphometric parameters, vigor, and physiological activity (Azmy et al. 1997; Ding et al. 1997; Banik and Islam 2005). The quality and health of stand in a clump have a close relationship with rhizome growth. Rhizomes are generally subterranean and form as the foundational organ for bamboo species by allowing rapid growth at the beginning of a new growing season. Rhizomes are important for nutrient uptake, storage, water absorption and conductance, and the vegetative reproduction system (Li et al. 1998; Liese 1998).
The vegetative reproduction strategy in sympodial bamboo species is to form a large number of rhizomes that are interconnected with each other and hence enable sustainable production. The growth performance, productivity, and life cycle of an individual rhizome in a bamboo clump are strongly related to the ontogenetically and physiologically age-related factors. For example, a new bamboo sprout in a 20-year-old bamboo clump is ontogenetically old but it is physiologically young (Londona 1992; Liese and Weiner 1996; Schweingruber 2007). The growth performance of new sprouts, however, solely depends on the stimulation of rhizome buds (encompass precipitation, relative humidity, soil moisture, and soil fertility) and the sources of energy and nutrients from its interconnected rhizomes. The new sprout has neither photosynthetic leaves nor a rooting system to ensure its rapid elongation (Zhang et al. 1996; Rodrigues et al. 2003).
Structural development and modification of the bamboo culm’s anatomical characteristics occur during the maturation period (Fujii 1985; Alvin and Murphy 1988; Abd-Latif 1996; Liese and Weiner 1996; Londono et al. 2002; Gan and Ding 2005; Wahab et al. 2006). These changes include the thickening of the cell wall, deposition of additional lamella, and lignification that decreases the functional efficiency of conductance elements. The conductance elements must function for several years without secondary meristem. This leads to a breakdown in the conducting systems and dying of individual culms, both above and below ground.
This study examined the rhizome anatomical characteristics of Gigantochloa scortechinii Kurz ex Munro, including their relationship with different study sites, rhizome ages, and their relationship with hydraulic conductance.
EXPERIMENTAL
Sampling
Sampling was conducted at three different locations in Peninsular Malaysia (Table 1). Sampling was conducted using selective random sampling from healthy clumps of Gigantochloa scortechinii Kurz ex Munro. Infertile and congested clumps were ignored. Three clumps were selected for three replicates. Four consecutive rhizomes from each clump were selected, i.e., new sprout (estimated to < one month), young (estimated to one year), premature (estimated to two years), and mature (estimated to three years) (Mohamed et al. 2019). The age estimation was based on the characters of culms (Banik 1993) and the number of rhizomes in a consecutive rhizome from the new sprout (Liese 1998). Only a complete set (four consecutive rhizomes) of a sectorial rhizome with complete plant parts (above and below ground) were chosen.
Determination of Anatomical Characteristics
Fresh samples were cut and sized (10 mm × 10 mm × 10 mm); (length × width × height) prior to examine using a LEO 1455 variable pressure scanning electron microscope (VPSEM; Oberkochen, Germany). The cross section (XS) cubes were prepared using a microtome. The cubes were oven-dried at 60 °C until a constant weight was reached to avoid the presence of steam when examined using the VPSEM. The sample was evaporatively coated using a sputter coater to obtain conductivity without affecting or reduce charging during observation. This method can provide an original figure from un-modified samples; it is cheaper and less time consuming than a conventional scanning electron microscope (PEO 1996).
The anatomical characteristics such as conducting elements, ground tissue, and supporting elements were observed. This study was conducted at the Microscopy Unit, Institute of Bioscience, Universiti Putra Malaysia, Serdang.
Table 1. Information of Three Different Study Sites
Determination of Fiber Length
Fresh sample blocks (10 mm length × 10 mm width × 20 mm height) were prepared before being chipped into matchsticks of 2 mm × 2 mm × 20 mm (length x width x height). The splints were boiled for 6 h. The splints were heated at 85 °C in a solution of 1.5 g of sodium chlorite dissolved in 25 mL distilled water and eight drops of acetic acid for several hours until the splints turned white in color. The white splints were washed carefully with distilled water to remove the solution.
After maceration, splints were stained with safranin-O to contrast the fibers. Distilled water in the splints was dehydrated through an alcohol series of 50%, 70%, 95%, and absolute ethanol for 2 min in each solution. The splints were washed with xylene and mounted on a 25 mm × 75 mm slide. Two drops of Canada balsam were introduced, and samples were dried in an oven at 60 °C for three days. Fibre length was examined under an Olympus SZX-ILLK200 stereomicroscope (Tokyo, Japan). This study was conducted at Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, Serdang.
Determination of Hydraulic Conductance
Culms at selected rhizomes were felled at the culm base and connected to a high-pressure flow meter (HPFM) with a water-tight seal before hydraulic conductance was measured. Water was placed under pressure by compressed air that was controlled with a pressure regulator into the culm base opposite to the normal water flow during plant transpiration. This routine was conducted with rapidly changing the delivery pressure, P (MPa), simultaneously measuring water flow, F (kg s-1), and hence hydraulic conductance was estimated from the slope of the F versus P plot (Tyree et al. 1994; 1995). The untested culms and belowground parts were avoided, not subjecting them to any cuts or major injuries, so as to reduce the degree of disturbance of the interconnected rhizome system.
The hydraulic conductance trend inside the belowground system where four rhizomes connected consecutively (as a rhizome system) can be used as a measure of their resistance inside. In the present study, the HPFM was used instead of another method (such as evaporative flux and thermal dissipation probe method) because the HPFM permits the determination of hydraulic conductance in a short time, allows determination while the water flows in state of reverse direction, and could reduce the error factors (such as osmotic changes and transpiration of the aboveground part) (Tyree et al. 1995; Tsuda and Tyree 1997; 2000; Do and Rocheteau 2002).
Statistical Analysis
The normality and homogeneity test of variances were performed before analysis using Univariate analysis of variance. Two factors (study site and rhizome age) were involved in the analysis with a total samples, n = 84. An equal sample, n=28 for each study site and n = 21 for each rhizome age, were measured and analyzed. The relationship between anatomical characteristics with each study site, rhizome age, and hydraulic conductance was analyzed using bivariate (Pearson) correlation. The statistical analysis was conducted using IBM SPSS statistics software version 21.0 (Armonk, NY, USA).
RESULTS AND DISCUSSION
Vascular Bundles Distribution
The vascular bundles size and distribution were anecdotally observed to change continuously from inside towards the periphery of the rhizome wall (Fig. 1a, 1b, and 2a). Twisted small vascular bundles between larger vascular bundles were observed (Fig. 2d, 2e, and 2f). Regardless of the study site and rhizome age, the vascular bundle distribution ranged from 62 to 68 bundles cm-2. Table 2 shows that the vascular bundle distribution was significantly different (p < 0.05) between study sites, which could be related to the intrinsic conditions such as altitude, precipitation, and the disturbance level.
Fig. 1. Transverse section of rhizome wall with lateral buds (a), and lateral bud (b)
Furthermore, the vascular bundle distribution per centimeter square at Ayer Hitam FR was significantly different from those at Amanjaya and Kenaboi FR (Table 3). These results could be related to the smaller size and thinner wall (data not shown) of rhizomes at Ayer Hitam FR compare to rhizome at Amanjaya and Kenaboi FR. These results implied that the rhizome at Ayer Hitam FR formed in an immature planted clump. The morphology of bamboo such as height and diameter of new individual culms (rhizome in this study) increases over consecutive years after planted (Liese and Wiener 1996). Vascular bundle distribution, however, was not significantly different with rhizome age (Table 2). The results in Table 4 indicate that no significant correlation was found between vascular bundle distributions with rhizome age, which implied that the number of vascular bundles does not increase or decrease when rhizome age increases.