Proporsi Mikrob dan Fluks CO2 dari Respirasi Heterotrof pada Bahan Tanah Gambut di Perkebunan Kelapa Sawit.

Abstract

Pemanfaatan lahan gambut untuk budidaya tanaman kelapa sawit dapat mempengaruhi aktivitas mikrob dan laju respirasi heterotrof. Hal ini dikarenakan penggunaannya diikuti dengan pembukaan saluran drainase. Menurunnya tinggi muka air tanah akan meningkatkan aerasi tanah, sehingga dapat meningkatkan aktivitas mikrob yang dapat menjadi sumber utama pelepasan CO2 pada lahan gambut. Aktivitas mikrob tidak hanya dipengaruhi penurunan muka air tanah tetapi juga oleh kerapatan akar. Perakaran tanaman kelapa sawit dapat melepaskan eksudat yang menjadi sumber energi bagi mikrob untuk beraktivitas. Atas dasar itu, penelitian ini bertujuan untuk mempelajari dinamika dari populasi total mikrob, fungi, bakteri selulolitik, fungi lignolitik, dan fluks CO2 dari respirasi heterotrof, serta faktor yang mempengaruhi aktivitas mikrob yaitu aktivitas enzim selulase dan lakase, kandungan asam-asam organik berupa asam laktat, sitrat, asetat, malat, dan oksalat pada berbagai kedalaman tanah dan jarak dari tegakkan kelapa sawit serta semak belukar. Pengambilan sampel bahan tanah gambut dilakukan di perkebunan kelapa sawit Desa Buatan Kecamatan Koto Gasib Siak Provinsi Riau (0’ 44’ 44” N 101o 46’ 22’ B) dan pelaksanaan penelitian dilakukan di Laboratorium Bioteknologi Tanah DITSL Fakultas Pertanian IPB. Sampel bahan gambut diambil dari dua lokasi yang berbeda, yaitu 1) lahan gambut di bawah tegakkan sawit berdasarkan jarak (1,5; 3,0; dan 4,5 meter dari tegakkan sawit) dan kedalaman tanah (0-20, 20- 40 dan 40-60 cm), serta 2) di semak belukar berdasarkan kedalaman tanah. Sampel bahan gambut diambil sebanyak tiga ulangan pada setiap titik sampling, total sampel di bawah tegakkan sawit didapatkan sebanyak 27 unit dan di semak belukar sebanyak 9 unit, sehingga total sampel dari lapangan sebanyak 36 unit. 1 kg bahan gambut dari 36 unit sampel selanjutnya diberi perlakuan tanpa sterilisasi dan sterilisasi menggunakan 50 mL HgCl2 500 ppm. Setelah diberi perlakuan total sampel menjadi 72 unit percobaan. Fluks CO2 diukur dengan menginkubasi 100 g bahan gambut selama tujuh hari kemudian dititrasi asam-basa. Selanjutnya dilakukan kuantifikasi populasi mikrob pada 72 unit sampel bahan gambut dengan mengekstrasi 10 g bahan gambut pada larutan fisiologis (0,85% NaCl), kemudian enumerasi total mikrob ke media Nutrient Agar, total fungi ke media Potatoes Dextrose Agar (PDA), total bakteri selulolitik ke media CMC 1%, dan fungi lignolitik ke media PDA + 0,05% Guaiacol. Proporsi mikrob dan fluks CO2 diamati dua kali dalam setahun, sedangkan aktivitas enzim selulase dan lakase serta asam- asam organik dianalisis pada pengamatan kedua. Pengaruh perbedaan jarak dan kedalaman tanah dipelajari perbedaannya berdasarkan analisis ragam dan diuji lanjut dengan Duncan New Multiple Range Test (DNMRT) pada taraf 5%. Hasil penelitian menunjukkan bahwa proporsi bakteri selulolitik (103 CFU g-1) dan fungi lignolitik (102 CFU g-1) lebih rendah dibandingkan total mikrob (107 CFU g-1) dan total fungi (105 CFU g-1) pada bahan gambut di bawah tegakkan sawit dan semak belukar. Total mikrob dan bakteri selulolitik berbeda nyata pada berbagai kedalaman tanah di bawah tegakkan sawit, namun tidak berbeda nyata di berbagai jarak dari tegakkan dan semak belukar pada pengamatan pertama. Dalam pengamatan kedua, total mikrob, total fungi, bakteri selulolitik, dan fungi lignolitik tidak berbeda nyata pada berbagai kedalaman tanah dan jarak dari tegakkan sawit di kedua lokasi. Bahan gambut yang telah diperlakukan steril masih terdapat total mikrob yang tumbuh fluktuatif, serta fungi lignolitik tidak ditemukan pada beberapa bahan gambut steril. Fluks CO2 cenderung menurun seiring dengan bertambahnya kedalaman tanah dan jarak dari tegakkan sawit serta di semak belukar. Fluks CO2 pada bahan gambut steril pada kedua pengamatan di bawah tegakkan sawit dan semak belukar fluktuatif. Aktivitas enzim selulase dan lakase pada bahan tanah gambut di berbagai jarak dari tegakkan kelapa sawit serta semak belukar tidak berbeda, asam-asam organik pada berbagai kedalaman tanah dan jarak dari tegakkan sawit serta semak belukar juga tidak berbeda.

The utilization of peatland for oil palm cultivation affect to microbial activity and respiration rate. This is because it followed by the open of drainage channels. The decrease in groundwater level will increase soil aeration, microbial activity, and CO2 release. Microbial activity not only affected by the decrease in groundwater level but also by root density. The roots of oil palm trees can release exudate, it can be source of energy to increase microbial activities. This research aims to study the dynamics of population total microbes, fungi, cellulolytic bacteria, ligninolytic fungi, and heterotroph CO2 flux, cellulase and laccase enzymes activity, also organic acids such as lactic, citric, acetic, malic, and oxalic acids from peat soil at different soil layers, distance from oil palm trees, and at shrubs. This research was conducted at oil palm plantation in the Buatan Village, Koto Gasib, Siak District, Riau Province (0' 44' 44" N 101o 46' 22' B) and the research was carried out at the Soil Biotechnology Laboratory, Department of Soil Science and Land Resource, Faculty of Agriculture, IPB. Peat samples were taken from two different locations, 1) peatland under oil palm trees based on distance (1,5; 3,0; and 4,5 m from oil palm trees) and soil depth (0-20, 20-40 and 40-60 cm), then 2) at shrubs based on soil depth. Peat samples were taken in three replications at each sampling point. Total samples under oil palm trees was 27 units, and in the shrub were 9 units, total samples from the field were 36 units. 1 kg of peat soil from 36 samples was treated unsterile and sterilization using 50 ml HgCl2 500 ppm. After being treated, the total sample became 72 units. CO2 flux was measured by incubating 100 g of peat soil for seven days by the acid-base titration. The microbial population from 72 peat samples was enumerated by extracted 10 g of peat material in physiological solution (0,85% NaCl). Total microbes were enumerated to Nutrient Agar (NA), total fungi to Potatoes Dextrose Agar (PDA), total cellulolytic bacteria to 1% Carboxymethyl cellulose (CMC), and ligninolytic fungi to PDA + 0,05% Guaiacol. The microbial population and heterotroph CO2 flux were observed twice a year, while the activity of cellulase and laccase enzymes, also organic acids were analyzed in the second observation. The effect of differences in distance and soil depth analyzed based on variance analysis and further tested with Duncan's New Multiple Range Test (DNMRT) at 5% level. The results showed that the proportion of cellulolytic bacteria (103 CFU g- 1) and ligninolytic fungi (102 CFU g-1) were lower than the total microbes (107 CFU g-1) and total fungi (105 CFU g-1) on peat soil under oil palm trees and shrubs. Total microbes and cellulolytic bacteria were significantly different at various soil depths in under oil palm trees, but not different at various distances and in shrubs at the first observation. In the second observation, total microbes, fungi, cellulolytic bacteria, and lignolytic fungi were not significantly different at both vegetations. Total microbes, fungi, cellulolytic bacteria, and ligninolytic fungi still found at peat sterile, but in others some peat sterile ligninolytic fungi and cellulolytic bacteria were not found. CO2 flux tends to decrease followed by soil depth and distance, also at shrubs. The CO2 flux in sterile peat soil in the first and second observations in both vegetations was fluctuative. The activity of cellulase and laccase enzymes activity at various distances from oil palm trees and shrubs were not different, organic acids on peat soil at various soil depth and distances from oil palm trees and shrubs also were not different.