Perubahan Fisiologi dan Biokimia Tanaman Mahoni (Swietenia macrophylla King) Meliaceae Akibat Artificial Light at Night (ALAN)

Abstract

Tanaman membutuhkan cahaya untuk berbagai proses biologis, namun keberadaan cahaya buatan pada malam hari (Artificial Light at Night/ALAN) telah meningkat secara global dan berdampak pada tanaman. ALAN dapat mengubah panjang hari, mengganggu jam sirkadian tanaman, serta memengaruhi pertumbuhan, fotosintesis, dan ketahanan terhadap cekaman lingkungan. Dampak ALAN juga meluas hingga ke ekosistem, memengaruhi penyerbukan, pembungaan, dan biodiversitas. Studi mengenai ALAN telah dilakukan di daerah subtropis, menunjukkan efek negatif pada fotosintesis, pertumbuhan, dan metabolisme berbagai spesies tanaman. Namun, penelitian serupa di daerah tropis, khususnya di Kebun Raya Bogor (KRB) Badan Riset dan Inovasi Nasional (BRIN), belum banyak dilakukan. Mahoni (Swietenia macrophylla King) merupakan salah satu spesies yang tumbuh di KRB yang berpeluang terdampak ALAN. Jenis ini memiliki nilai ekologis serta ekonomi tinggi, dan berstatus Endangered (EN) sehingga menghadapi ancaman kepunahan. Oleh karena itu, penelitian ini bertujuan menganalisis pengaruh ALAN terhadap perubahan fisiologi dan biokimia pada mahoni. Hasil penelitian diharapkan dapat mengisi kesenjangan pengetahuan mengenai pengaruh ALAN terhadap tumbuhan tropis, serta menjadi dasar pertimbangan dalam penerapan ALAN di kawasan konservasi tropis. Penelitian dilaksanakan dari bulan Juni 2023 hingga Agustus 2024. Pemberian perlakuan dilakukan selama 12 bulan di Pembibitan 2 KRB BRIN. Preparasi dan analisis sampel tanaman dilakukan di Laboratorium KRB BRIN, Laboratorium Departemen Biologi IPB serta Laboratorium Riset Unggulan IPB. Rancangan penelitian dilakukan menggunakan rancangan petak terbagi dalam rancangan acak kelompok faktorial dengan 3 ulangan. Perlakuan terdiri atas tiga faktor: warna cahaya sebagai petak utama, durasi penyinaran sebagai anak petak, dan intensitas cahaya sebagai anak-anak petak. Setiap faktor perlakuan terdiri atas beberapa taraf. Bahan utama yang digunakan adalah bibit mahoni yang berumur 1 tahun dengan kriteria tinggi dan jumlah daun yang relatif seragam. Parameter yang diamati terdiri atas pertumbuhan, anatomi, fisiologi, dan metabolit. Data pertumbuhan yang diukur meliputi pertambahan tinggi tajuk, diameter batang, jumlah cabang, jumlah daun, luas daun, serta bobot basah dan bobot kering mahoni. Pengamatan data anatomi meliputi ketebalan daun dan kerapatan stomata. Pengukuran fisiologi meliputi laju fotosintesis, konduktasi stomata dan laju transpirasi menggunakan instrumen LI-COR 6400, serta pengukuran kandungan klorofil yang dilakukan menggunakan spektrofotometer. Profil metabolit mahoni dianalisis menggunakan LC-MS/MS. Data morfologi, anatomi, dan fisiologi dianalisis menggunakan ANOVA pada taraf kepercayaan 95% dan bila terdapat perbedaan yang nyata dilanjutkan dengan DMRT pada taraf a=5%. Data metabolomik dianalisis menggunakan program Mzmine 3.9 dan MetaboAnalyst 6.0 untuk menghasilkan heatmap. Identifikasi kelompok metabolit menggunakan website PubChem. Hasil penelitian menunjukkan bahwa ALAN menyebabkan perubahan pada fisiologi dan biokimia mahoni. Perubahan ritme sirkadian akibat ALAN menyebabkan pertumbuhan mahoni yang terpapar ALAN lebih lambat dibandingkan tanaman kontrol. Gangguan ini memengaruhi ekspresi gen sirkadian, mengurangi efisiensi penangkapan dan pemanfaatan energi, serta menurunkan laju fotosintesis dan pertumbuhan tanaman. Paparan ALAN juga memengaruhi morfologi daun, menyebabkan luas daun berkurang tetapi ketebalan meningkat. Fenomena ini terjadi karena alokasi karbon lebih banyak diarahkan untuk mekanisme pertahanan dibandingkan untuk pertumbuhan. ALAN juga meningkatkan biosintesis klorofil sebagai respons adaptasi terhadap cahaya rendah, meskipun tidak berkorelasi positif dengan laju fotosintesis. Intensitas ALAN yang rendah pada penelitian ini tidak cukup untuk mendukung fotosintesis, sehingga menyebabkan penurunan laju fotosintesis pada mahoni. Penurunan laju fotosintesis juga dipengaruhi oleh faktor stomata berupa penurunan konduktasi stomata yang menyebabkan penurunan laju transpirasi pada mahoni. Perubahan alokasi karbon juga menyebabkan perubahan pada profil metabolit mahoni. ALAN menurunkan konsentrasi flavonoid, seperti sianidin, homoorientin, dan phellopterin yang berperan dalam perlindungan tanaman terhadap stres oksidatif. Namun, ALAN meningkatkan produksi senyawa pertahanan, seperti asam salisilat (pada cahaya merah), astilbin (pada cahaya hijau), dan asam jasmonat (pada cahaya biru) yang membantu tanaman beradaptasi terhadap stres ALAN. Secara keseluruhan, paparan ALAN mengubah morfofisiologi dan metabolit mahoni, berupa penurunan laju pertumbuhan, konduktansi stomata, laju transpirasi, dan laju fotosintesis, serta penurunan dan peningkatan konsentrasi senyawa metabolit tertentu.

Plants require light for various biological processes, but the presence of artificial light at night (ALAN) has increased globally and is impacting plants. ALAN alters day length, disrupts plant circadian rhythms, affects growth, photosynthesis, and resilience to environmental stress. The impacts also extend to ecosystems, affecting pollination, flowering, and biodiversity. Studies on ALAN have been conducted in subtropical regions, showing negative effects on photosynthesis, growth, and metabolism of various plant species. However, similar studies in the tropic area, particularly in the Bogor Botanical Gardens (Kebun Raya Bogor/KRB), have not been conducted. Mahogany (Swietenia macrophylla King) is one of the species that grows in the KRB. It has high ecological and economic value, classified as Endangered (EN) and facing the threat of extinction. Therefore, this study aims to analyze the effects of ALAN on physiological and biochemical changes in mahogany. The results of the research are expected to serve as a basis for consideration in the application of ALAN in tropical conservation areas. The findings will contribute to the broader understanding of ALAN's ecological consequences and serve as a scientific basis for managing artificial lighting in urban and conservation areas, particularly in Bogor Botanical Garden and other tropical conservation centers. The findings will enhance the overall understanding of the ecological impacts of ALAN and provide a scientific foundation for regulating artificial lighting in tropical conservation areas. The research was conducted from June 2023 to August 2024. The treatment was conducted over 12 months at Nursery 2, KRB, under the supervision of the National Research and Innovation Agency (BRIN). The preparation and analysis of plant samples were conducted at the KRB BRIN Laboratory, the Department of Biology Laboratory IPB, and the IPB Advanced Research Laboratory. The experimental design followed a split-plot arrangement within a randomized complete block design with three replications. The treatments consisted of three factors: light color as the main plot, light duration as the sub-plot, and light intensity as the sub-sub-plot. Each treatment factor included multiple levels. The plant material used was 1-year-old mahogany seedlings. Observed parameters included growth, anatomical structure, physiological responses, and metabolite profiles. Growth parameters measured included the increase in shoot height, stem diameter, number of branches, number of leaves, leaf area, and fresh and dry weight of mahogany plants. The anatomical structure observations included measurements of leaf thickness and stomatal density. Physiological responses comprised the photosynthetic rate, stomatal conductance, and transpiration rate, measured using a LI-COR 6400 instrument, as well as chlorophyll content, assessed using a spectrophotometer. The metabolite profile of mahogany was analyzed using LC-MS/MS. Morphological, anatomical, and physiological data were analyzed using ANOVA at the 95% confidence level, and if significant differences were found, they were followed by DMRT at the a = 5% level. Metabolomic data were analyzed using Mzmine 3.9 and MetaboAnalyst 6.0 software to generate heatmaps, while metabolite group identification was conducted using the PubChem database. The results showed that ALAN induced alterations in the physiological and biochemical characteristics of mahogany. Disruption of the circadian rhythm due to ALAN exposure led to slower growth in mahogany compared to control plants. This disturbance affected the expression of circadian genes, reduced the efficiency of energy capture and utilization, and ultimately decreased the rate of photosynthesis and plant growth. ALAN exposure also influenced leaf structure, resulting in reduced leaf area but increased leaf thickness. This phenomenon likely occurs due to carbon allocation being redirected toward defense mechanisms rather than growth. ALAN also stimulated chlorophyll synthesis as an adaptive response to low light conditions; however, this increase was not always positively correlated with photosynthetic rate. The low intensity of ALAN in this study was not sufficient to support effective photosynthesis, resulting in a reduced photosynthetic rate in mahogany. The decline was further influenced by stomatal factors, decreased stomatal conductance which causes a decrease in the rate of transpiration. Changes in carbon allocation also resulted in alterations to the metabolite profile of mahogany. ALAN exposure led to a decrease in flavonoid concentrations such as cyanidin, homoorientin, and phellopterin, which are essential for plant protection against oxidative stress. However, ALAN increased the production of defense compounds—such as salicylic acid (under red light), astilbin (under green light), and jasmonic acid (under blue light)—which help plants adapt to ALAN-induced stress. Overall, ALAN exposure caused significant alterations in the physiology and biochemical characteristics of mahogany, including reduced growth rate, stomatal conductance, transpiration rate, and photosynthetic rate, along with both decreased and increased concentrations of specific metabolite compounds.