THE DYNAMICS AND ROLES OF MESOARTHROPODS AND RHIZOSPHERE BACTERIA COMMUNITY IN NUTRIENT MINERALIZATION AT COFFEE AGROFORESTRY

• Main Author: Rachmawati M Sc, Dian
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/69966
• Institution: Institut Teknologi Bandung

The Forest that is converted into agroforestry has the potential to experience changes in the soil physical and the biota communit. In addition, the plants composition and land management such as the shade trees and the length of land age can also affect the soil biota community structure and composition, especially mesoarthropods and rhizosphere bacteria. Environmental physical factors helped interactions within the soil mesoarthropod community and rhizosphere bacteria. As a consequence, ecological processes occur, including nutrient cycling. Through the decomposition process, the soil mesoarthropod community plays a role in cutting the litter into smaller parts. In contrast to the rhizosphere bacterial community, which roled in changing the organic matter into inorganic nutrients available for plants. The study of soil mesofauna community and rhizosphere bacteria dynamics and their role in nutrient release aimed to examine the decomposition, nutrient release and soil mesoarthropods and rhizosphere bacteria community structure that had roles in nutrient release at coffee agroforestry. In addition, this study aims to examine the potential of the rhizosphere bacterial community as an important PGPR in nutrient release. Based on land use and differences in vegetation cover, 5 sampling locations were selected consisting of four coffee agroforestry in Kamojang, West Java, Indonesia at an altitude of 1500 meters above sea level, and one mixed forest at 1600 meters above sea level. The five locations selected were: 1) Coffee-mix forest 1 (CM1); 2) Coffeemix forest 2 (CM2); 3) Coffee -pine forest (CP); 4) Coffee plantations (OCP), and 5) Mixed forests (MF). The decomposition process was determined using litter bag method, and mineralization was determined using the soil incubation method. Soil and litter bags were sampled twice a month. The decomposition rate was calculated by measuring the weight loss of the litter, and the nutrient release was measured by soil nutrients analysis chemically. Isolation of rhizosphere bacteria by the spread plate method using NA general media which was previously carried out with serial dilution. The bacterial colonies were then counted and observed for morphology and isolated. The PGPR potential of the rhizosphere bacterial community consisted of N fixation and ammonification using NFB media. Phosphate dissolution test by measuring the transparent zone diameter around the bacterial colonies using Pikovskaya media. The IAA production test was carried out using the colorimetric method by growing an inoculum of bacterial isolates in King's B + Tryptophan media using Salkowski's reagent. IAA production was quantified by measuring the color absorbance by spectrophotometer at a wavelength of 535 nm. A total of 12,099 individual soil mesoarthropods consisting of 45 species were collected during the observation period. The highest species richness was found in coffee plantations-pine forests (CP) and mixed forests (MF) (36 species), while the lowest was found in coffee plantations (OCP) (26 species). The highest total soil mesoarthropod individuals were found in coffee-mixed forest plantation 2 (CM2), (4731 individuals), and the lowest was found in mixed forest (MF) (1123 individuals). The highest decomposition rate was found in November (799,88% ± 29.81%), while the lowest decomposition rate was found in June (119.44% ± 4.34%). Each type of nutrient released were different at each time and location. The highest soil nutrient release was found at CM2 and MF. The highest increase in soil nutrients was NH4+ in OCP, while the lowest nutrient decrease was P in CP. In addition, there was a temporal change in the character of Collembola species, where epigeic species played a role at the beginning of the decomposition period, then they were replaced by hemiedaphic and endogeic Collembola in the later stages of decomposition in all agroforestry. In contrast to other agroforestry, in the coffee-pine forest (CP), the hemiedaphic and endogeic Collembola were found since the early stages of decomposition. The rhizosphere bacterial community consisted of 16 isolates with different morphological characteristics of macro isolates. Using the MALDITOF-MS method, the genus Bacillus was the most collected rhizosphere bacteria (5 isolates). Other isolates consisted of the genera Pseudomonas, Streptomyces, Micrococcus, Brevundimonas, Lysinibacillus, Paenibacillus and Kocuria. The highest abundance of rhizosphere bacteria was found in MF (1,27.107 cfu.g-1 or log = 7,1 cfu.g-1), while the lowest abundance was found in CP (6,53.106 cfu.g-1 or log = 6,8 cfu.g-1). 7 bacterial isolates had the ability of N fixation (Bacillus cereus group 1, Pseudomonas chlororaphis, Bacillus cereus group 2, Lysinibacillus fusiformis, Paenibacillus lautus, Isolate 15, and Isolate 16). Bacillus cereus group 1 had ammonification abilities (1,798 mg.L-1) and the highest P solubility (1,19). Bacillus altitudinis can produce the highest IAA (6,15 mg.L-1). Bacillus cereus group 1 had the highest ammonification ability (1,798 mg.L-1 ± 0,86 mg.L-1). 12 isolates of rhizosphere bacteria that can produce IAA. The three isolates with the highest IAA values were Streptomyces griseus (6,11 mg.L-1 ± 0,27 mg.L-1), Bacillus altitudinis (6,15 mg.L-1 ± 0,3 mg.L-1), and Bacillus simplex (5,7 mg.L-1 ± 0,27 mg.L-1). Bacillus simplex (1,21cm ± 0,05 cm), Bacillus cereus group 1 (1,19 cm ± 0,14 cm), and Pseudomonas chlororaphis (1,11cm ± 0,16 cm) are some of the rhizosphere bacteria that can form the transparent zones on Pikovskaya media. Soil moisture was found as factor that affects the presence and activity of rhizosphere bacteria at the beginning of the nutrient release. After going through August (midobservation), soil temperature, soil pH and soil moisture content were related to the presence of rhizosphere bacterial communities. The nutrient release at each observation time can indicate the presence and activity of rhizosphere bacteria. The type of nutrients released at any time can represent the stages of the formation of the rhizosphere bacterial community.