Aktivitas fosfatase dan produksi asam organik di rhizosfer dan hifosfer bibit kelapa sawit bermikoriza *) Phosphatase activity and organic acid production in rhizosphere and hyphosphere of mycorrhizal oil palm seedling

Abstract

Summary
Studies on the mechanism of the higher P
uptake of oil palm seedling colonized with
arbuscular mycorrhizal fungi through
solubilizing of fixed P by organic acid or
hydrolysis of organic P by phosphatase activity
have not been reported yet. This experiment was
aimed to examine the phosphatase activity and
production of organic acids in rhizosphere and
hyphosphere, mycorrhizal and non-mycorrhizal
oil palm seedling. Oil palm seedling were grown
for 26 weeks in sterilized Cikopomayak acid soil
in 20.5 cm diameter pots with three compart-
ments, a central one for root growth
(rhizosphere) and two adjacent on both side next
to the root compartment for hyphal growth
(hyphosphere). Compartmentation was accom-
plished by a 0.25 mm stainless steel filter. All
compartment received a uniform concentration of
phosphorus (300 P mg kg -1 soil) either in organic
(Na-phytate) or inorganic NH 4 HPO 4 form.
Acaulospora tuberculata inoculum was establish-
ed in pot culture using Pueraria phaseoloides as a
host, while Gigaspora margarita was propagated
using maize as a host. AM fungal inoculum
applied as mixed propagules in optimum dosage.
The experiment was conducted to asses nine
treatments combination between AM inoculation
(without, A. tuberculata, and G. margarita) and
sources of P (without P, inorganic P NH 4 HPO 4 ,
and organic P Na phytate). Factorial in complete
randomized design with two factors and three
replications was used in this research. In the
hyphal compartment acid phosphatase activity
was much higher than alkaline phosphatase
activity, while in the rhizosphere alkaline
phosphatase activity was higher compared to
acid phosphatase activity. Acid phosphatase
activity in rhizosphere of oil palm seedlings
inoculated with A. tuberculata was significantly
higher compared to uninoculated seedlings.
However, both acid phosphatase activity and
alkaline phosphatase activity were slightly
enhanced by mycorrhizal inoculation. In contrast,
organic acid production between inoculated
seedling and uninoculated seedling was not
significantly different. It seems that AM fungal
symbiosis with oil palm enhance mineralization
of organic P in spite of solubilization of
inorganic P.

Ringkasan
Mekanisme peningkatan pertumbuhan
kelapa sawit bermikoriza khususnya yang
disebabkan aktivitas pelarutan P anorganik yang
terfiksasi melalui pelarutan oleh asam organik
atau hidrolisis P organik oleh aktivitas fosfatase

elum dilaporkan. Percobaan ini bertujuan
menetapkan aktivitas fosfatase dan produksi asam
organik di rhizosfer dan hifosfer, bibit kelapa
sawit bermikoriza dan tidak bermikoriza. Kelapa
sawit ditumbuhkan selama 26 minggu pada tanah
masam Cikopomnayak steril pada pot ber-
diameter 20,5 cm yang terbagi atas tiga daerah,
ruang tengah untuk pertumbuhan akar (rhizosfer)
dan dua daerah di sebelahnya untuk pertumbuhan
hifa (hifosfer). Penyekatan pot menggunakan
filter stainless steel berukuran lubang 0,25 mm.
Semua daerah dipupuk P pada konsentrasi
300 P mg kg -1 tanah baik dalam bentuk organik
(Na-phytate) maupun anorganik (NH 4 HPO 4 )
Inokulum CMA merupakan hasil perbanyakan
dengan sistem kultur pot menggunakan inang
Pueraria phaseoloides untuk Acaulospora
tuberculata sedangkan untuk Gigaspora
margarita menggunakan inang jagung. Inokulum
CMA berupa propagul campuran pada dosis
optimum. Percobaan dilakukan untuk menguji
sembilan perlakuan yang merupakan kombinasi
antara inokulasi CMA (tanpa, A. tuberculata,
dan G. margarita) dan sumber P (tanpa P,
anorganik P NH 4 HPO 4 , dan organik P Na
phytate). Rancangan percobaan ialah rancangan
acak lengkap faktorial dengan tiga ulangan untuk
masing-masing perlakuan. Di hifosfer aktivitas
fosfatase asam lebih tinggi daripada fosfatase
alkalin, sedangkan di rhizosfer aktivitas fosfatase
alkalin lebih tinggi dibandingkan dengan aktivitas
fosfatase asam. Aktivitas fosfatase asam di
rhizosfer bibit kelapa sawit yang diinokulasi A.
tuberculata nyata lebih tinggi dibandingkan
dengan bibit yang tidak diinokulasi. Aktivitas
fosfatase asam dan fosfatase alkalin sedikit lebih
tinggi dengan inokulasi CMA. Sebaliknya,
produksi asam organik antara bibit yang
diinokulasi dan bibit yang tidak diinokulasi tidak
berbeda nyata. Tampak bahwa simbiosis CMA
dengan kelapa sawit lebih meningkatkan
mineralisasi P organik dan kurang meningkatkan
pelarutan P anorganik.