Edaphic Characteristics of Rafflesia Habitats in Indonesia: Implications for Conservation and Propagation

Rafflesia , a holoparasitic and endophytic plant, depends on its host, Tetrastigma spp., for survival, thus highlighting the critical interdependence between these species. Given the endangered status of Rafflesia due to anthropogenic pressures and narrow distribution, comprehensive conservation efforts are crucial. Ecological data on edaphic conditions, particularly the presence of the host, are important for effective conservation strategies. This study assessed soil properties across Rafflesia habitats on Sumatera, Borneo, and Java islands, revealing similarities in pH, carbon, nitrogen, cation exchange capacity (CEC), while the soil texture varied. These findings contribute valuable insights for informed conservation initiatives, both in-situ and ex-situ. Copyright: © 2024, J. Tropical Biodiversity Biotechnology (CC BY-SA 4.0)

Rafflesia is a unique and endemic plant species of Indonesia.It has single biggest flower among flowering plants species in the world.Despite being large in size, Rafflesia is actually a holoparasitic and endophytic plant without vegetative organs such as stems, leaves roots or any photosyntentic systems (Molina et al. 2014;Mursidawati et al. 2020).Hence its life cycle, survival and establishment depend on its host, which is known as Tetrastigma spp.(Vitaceae).Thus, the distribution of the Rafflesia spp. in the forest are entirely dependent on the existence of its host species and its supporting plants.Because these plants are influence each other, all plant forms (lifeforms) and their habitat must be equally conserved (Adnan & Hadisusanto 2023).
In Indonesia, Rafflesia can be found on three of the largest islands: Sumatra, Borneo, and Java, as well as on some smaller surrounding islands like Nusa Kambangan (van Steenis et al. 1954) and Mursala Island (Mahyuni et al. 2016).All the Rafflesia species in Indonesia are considered endangered due to their unique biological and ecological characteristics, as well as the impact of human activities (Hidayati & Walck 2016;Lestari & Susatya 2022).Therefore, ex-situ conservation of Rafflesia is strongly recommended as a solution, especially because it can be challenging to access Rafflesia in its natural habitat for research purposes (Lestari & Susatya 2022).Wicaksono et al. (2016) also proposed the artificial or human intervention cultivation of Rafflesia spp.
To propagate or conserve Rafflesia in ex-situ area, ecological data which provide conditions required for its growth are needed, especially the edaphic conditions where the host exists (Hayati et al. 2021).In previous study, Wahab et al. (2021) mentioned that the presence of Tetrastigma sp. in the different Rafflesia habitats has its own relationship with the soil and is not influenced by one factor.Therefore, a more comprehensive study related to the edaphic habitat of various Rafflesia species must be carried out.
In Indonesia, studies related to the edaphic habitat of Rafflesia are still limited and mostly focused on aspects like soil pH.For example, Ramadhani et al. (2017) found that the area where Rafflesia arnoldi is found are usually have temperatures between 25 and 29 degrees Celsius, humidity levels of 95%, and an acidic pH of 5.5, with the soil consists of sandy clay soil with varying percentages of sand, silt, and clay.R. patma in Bojonglarang Jayanti Nature Reserve grows in more acidic soil with a pH of 5.5 and pH KCl at 4.8, with soil classified as sandy clay soil with different percentages of sand, silt, and clay, with the organic nutrient content is higher compared to the Tetrastigma plot, while the inorganic nutrient content or mineral soil elements in the Rafflesia plot are lower (Ali et al. 2015).R. patma in Leweung Sancang live in regosol soil, sandy loam, with loose and well-drained soil, acidic to neutral soil pH, very high organic C and Ca content, total N, Mg, high CEC, very low available P, and moderate K and Na (Priatna et al. 1989).R. patma in Ciletuh also grows on acidic soils with pH ranging from 5.8 to 7 (Triana et al. 2017).Laksana et al. (2018) found that the types of soil in the permanent plots of R. zollingeriana in Krecek are latosol soil, generally dark reddish in colour, and with a clay texture, with soil pH considered neutral, as it is close to 7. Rambey et al. (2023) observed that the habitat of R. meijeeri in Batang Gadis National Park Pagar Gunung indicating a neutral soil pH as it is close to 7 overalls (6.8 -6.9).But there are also studies that do not address soil acidity.In addition, Renjana et al. (2022) mentioned that soil organic carbon was the most important variable affecting the occurrence of the host plants of R. arnoldii.
However, these studies only provide partial information, and more comprehensive research is needed to fully understand the specific edaphic conditions preferred by different Rafflesia species.Therefore, this study aims to assess the physical and chemical properties of soil at three distinct locations where three different Rafflesia species are found on different islands in Indonesia: Java, Sumatera, and Borneo.By gaining deeper insights into the physical and chemical properties of the soil in the natural habitat of these Rafflesia species, we can identify the factors that contribute to their growth and survival.The information of edaphic characteristics also plays a crucial role in determining the suitable locations for these species to thrive and reproduce, as well as their susceptibility to environmental changes and disturbances.This knowledge can be used to develop effective conservation strategies, such as habitat restoration or management, to support the survival of these unique species in their natural environments.
The study was conducted in three different islands of Indonesia where four populations of Rafflesia spp.were identified (Table 1).These study locations comprise Tempursari-Lumajang in East Java, Palak Siring Kemumu in Bengkulu, Sumatera island and Kayan Mentarang National Park in North Kalimantan, which is located in the island of Borneo (Figure 1).
The first sample was collected from Argosari, a protected forest of Perhutani, that adjacent to human settlement in Tempursari, Lumajang, East Java, located at 450 m above sea level (asl) (Table 1).The new record for R. zollingeriana in East Java was detected from this area (Lestari & Susatya 2022).
Kayan Mentarang National Park is lies between Malinau and Nunukan Regency, North Kalimantan, Indonesia.This national park is reported as habitat for R pricei (Jayasilan et al. 2004;Lestari et al. 2020).The soil sample was collected from R. pricei habitat in hillside of montane forest at 60 0 slopes, at 1277 m a.s.l. in Pa' Pulid forest near to Pa' Api, Nunukan, Kalimantan Utara.Soil sampling was carried out based purposive random sampling method in three different sites.Soil samples were collected from 0-20cm depth.After taken from the plots, the soil sample then air dried and analysed in Indonesian Coffee and Cocoa Research Institute (ICCRI) laboratory.The parameters soil were soil chemical and physical property.The chemical properties consist of soil pH, organic carbon (%), total nitrogen content (%), Phosphorus (ppm), K, Ca, Na, Mg (me 100g -1 ), Electron Exchange Capacity (CEC) (me 100g -1 ) and Base Saturation (%).Additionally, the observation of soil physical property focused on the soil texture.
Soil pH determine in water (1:2.5)using pH meter, organic carbon used wet oxidation method by Walkey and Black.Phosphorus extraction by Bray and Olsen method and K, Ca, Mg, Na, CEC and Base saturation through leaching with NH 4 SO 4 .Soil parameters ranking based on Indonesian Soil Research Institute (Balittanah 2009).The determination of soil texture was using the soil texture triangle (Figure 3).The percentage of each particles obtained then applied to the soil texture triangles and cross point between the percentage of particles to determine the texture class.
Based on our results, there were variations in soil texture and chemical properties among the three habitats of Rafflesia.The pH level in all three locations was found to be slightly acidic, ranging from 5.8 to 6.The Palak Siring Kemumu site had higher levels of total carbon and nitrogen content, with measurements of 7.67% and 0.69%, respectively, in comparison to the Tempursari-Lumajang and Kayan Mentarang Nation-al Park areas.Nevertheless, according to Balai Penelitian Tanah (Indonesian Soil Research Institute) (Balittanah 2009), the soil carbon percentage in the three Rafflesia habitats was classified as high to very high, while the nitrogen content was classified as medium to high.The ratio of carbon to nitrogen (C/N) in the soil can be influenced by various factors such as the type of vegetation, organic matter, and microbes.The optimum C/N ratio for plant growth is between 10-20.Our results showed that the C/N ratio in the three Rafflesia habitats was within this range, indicating that the soil has a higher level of decomposition and a faster release of nutrients (Kitayama et al. 1998;Eiland et al. 2001;Li et al. 2020) In terms of phosphorus content, the Kayan Mentarang National Park site had the highest value at 96 ppm, which is considered very high, while the other two locations had lower levels with Palak Siring Kemumu at 13 ppm and Tempursari-Lumajang at 20 ppm (Table 2).In contrast, the Palak Siring Kemumu site had the highest base saturation at 99.3 %, followed by Tempursari-Lumajang at 86.99%, both of which were  categorized as very high.The Kayan Mentarang National Park site had the lowest base saturation at 24.28%.Additionally, the cation exchange capacity (CEC) in all three habitats of Rafflesia spp. was high, with the highest value found in the Tempursari-Lumajang location at 29.29 me 100g -1 , followed by Palak Siring Kemumu at 28.54 me 100g -1 and Kayan Mentarang National Park at 21.83 me 100g -1 .Moreover, the sulphur content varied among the three locations, with the highest content observed in the Tempursari-Lumajang location at 216, followed by Kayan Mentarang National Park at 211 and the lowest content in the Palak Siring Kemumu location at 58.The sodium content found at the low level.The highest sodium content was observed in the soil of the Palak Siring Kemumu location at 0.22 me 100g -1 , followed by Tempursari-Lumajang at 0.19 me 100g -1 and Kayan Mentarang National Park at 0.14 me 100g -1 .Sodium serves as an essential cation for plants, but excessive concentrations can be detrimental to plant growth, leading to root damage, compromised water and nutrient absorption, as well as disruptions in metabolic and cellular functions (Chang & Dregne 1955;Subbarao et al. 2003).
The soil texture classes of the habitat of four species Rafflesia also varied.The Tempursari-Lumajang location exhibited a sandy clay loam texture class, whereas the Palak Siring Kemumu location, situated in Sumatera, had a clay loam texture class.On the other hand, the Kayang Mentarang National Park location, located on the island of Borneo, had a silty clay loam texture class.These differences in soil texture can have implication for the existing of Rafflesia species and its host.
The soil texture affects the ability of soil to hold the available water and nutrients for plants thus directly affecting the plants growth.In Lumajang area, R. zollingeriana found in the sandy clay loam soil texture with higher percentage of sand in the soil.The previous studies reported that the R. zollingeriana found in Meru Betiri National Park, East Java found in soil with a high percentage of clay, sandy clay and sandy loam (Zuhud 1988;Laksana et al. 2018).Furthermore, previous study in the same national park, Maulidiyan et al. (2019) reported that R. zollingeriana occurred in an inclined rocky terrain, leading to the development of root buttresses in its host plant, Tetrastigma spp.
The two species of Rafflesia; R. gadutensis and R. kemumu found in clay loam, while the R. pricei found in silty clay loam soil texture.The silty clay loam soils tend to have moderate to high water-holding capacity and can retain water for relatively long periods of time compare to the sandy clay loam soil.The water uptake of Rafflesia is entirely dependent on its host plant, and therefore, the soil texture affects the water intake required for both the host plant and Rafflesia.The sandy clay loam, clay loam, and silty clay loam soil textures are considered have the ability to meet the water requirements of Tetrastigma and Rafflesia.Sandy clay loam soils are typically well-draining and can hold water for moderate periods, while clay loam soils, with their higher proportion of clay particles, have a higher water-holding capacity and are generally considered to be some of the most productive and versatile soils.Silty clay loam soils show a balance between water-holding capacity and drainage (Saxton et al. 1986;Andrenelli et al. 2016).Furthermore, Rafflesia required the soil texture that can support good drainage, which prevents waterlogging, root damage and Rafflesia decaying.The soil should able to hold onto sufficient moisture to meet the needs of the host and Rafflesia, but also allow excess water to drain away relatively quickly.
Calcium (Ca), magnesium (Mg), and potassium (K) are essential soil nutrients for the growth of plants including the host of Rafflesia: Tetrastigma spp., although they are required in smaller quantities compared to other nutrients.The result showed that Potassium concentrations varied slightly among the study sites, ranging from 0.9 me 100g -1 to 1.79 me 100g -1 (figure 4).Calcium concentrations were highest at Palak Siring Kemumu, with a value of 22.92 me 100g -1 , followed by Tempursari, Lumajang, with a value of 17.98 me 100g -1 , and Kayan Mentarang National Park, with a value of only 1.73 me 100g -1 .The magnesium content also varied across the study sites, with the highest concentration found at Tempursari, Lumajang (6.16 me 100g -1 ), and the lowest concentration found at Kayan Mentarang National Park.The Kayan Mentarang National Park, where R. pricei was discovered, exhibited the lowest base saturation.Low base saturation refers to a condition where the relative proportion of exchangeable base cations compared to the total soil cation exchange capacity (CEC), is relatively low (Juo et al. 1976;Chapman 2016).This indicates a reduced proportion of positively charged ions such as calcium, magnesium, potassium, and sodium in relation to the overall ion-holding capability of the soil.Moreover, the calcium content within the soil of Karang Mentarang was comparatively lower than that found in the other two locations.As a consequence of these distinctive soil attributes, the nutritional requirements of distinct Tetrastigma and Rafflesia species may exhibit variations contingent upon their respective geographic placements.
Variations in the edaphic characteristics were observed among populations of the same Rafflesia species.These differences can be due to multiple factors, including variations in elevation, geographical region, and the geological composition of soil formation.For instance, R. zollingeriana that found in Meru Betiri National Park, was encountered in soil of the Latosol type, characterized rich iron and aluminium oxide (Laksana et al. 2018).Previous study mentioned that this species tends to thrive in soils exhibiting a moderate to high Cation Exchange Capacity (CEC), high base saturation, and a high to very high concentration of potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg).The carbon content of these soil ranges from moderate to high, while total nitrogen (N) content varies from low to moderate, accompanied by notably low phosphorus (P) levels (Zuhud 1988).The disparities in location and elevation contribute to variations in soil chemical character within the habitat of R. zollingeriana and its host plant.In Meru Betiri National Park, R. zollingeriana was found at elevations ranging from 0 to 300 meters above sea level (Zuhud 1988;Lestari et al. 2014), while in the Lumajang region of East Java, it was encountered at elevations of 450 meters above sea level (Lestari & Susatya 2022).
Edaphic variation also found in R. gadutensis habitat.Despite its presence in Palak Siring Kemumu, R. gadutensis also distributed within West Sumatera (Meijer 1984;Meijer 1997;Nais 2001;Rahma et al. 2017).Based on the observation of Akhriadi et al. (2010), the population of R. gadutensis could be found elevations ranging from 350 to 750 meters above sea level, specifically within old secondary rainforest in West Sumatera.Additionally, the presence of R. gadutensis populations have been recorded on the diminutive island of Mursala, proximate to Sibolga along the western coastline of North Sumatra (Mahyuni et al. 2016).Meanwhile, R. kemumu is a new species of Rafflesia found in the lowland forests of Bengkulu (Susatya et al. 2017) and there has been no study regarding the presence of R. kemumu in areas other than Bengkulu.
This study has confirmed that each species of Rafflesia requires a distinct set of soil characteristics in its edaphic habitat.Despite variations between the habitats studied, we observed that the soil pH was slightly acidic, while carbon and nitrogen levels ranged from moderate to high.These findings emphasize the essential significance of nutrient-rich soil and a resilient cation exchange capacity (CEC) in facilitating the growth of both the host plant and Rafflesia.As such, these pivotal factors must be considered in the both in situ and ex-situ conservation initiatives aimed at safeguarding and nurturing Rafflesia populations.By acknowledging and integrating these soil-related insights, we can enhance the efficacy and success of conservation efforts for these remarkable species.
In terms of in-situ conservation, environmental changes, such as soil compaction and erosion, can adversely affect the growth and survival of Tetrastigma, directly impacting Rafflesia as well.Given the high sensitivity of Rafflesia to environmental changes, especially when its host plant is compromised, it is necessary to maintain the original edaphic conditions of both the host and Rafflesia undisturbed.
Due to the fact that the selection of an appropriate host for Rafflesia is determined by intricate physiological compatibility rather than a single factor alone (Renjana et al. 2022), in terms if ex situ conservation, it becomes crucial to replicate all abiotic and biotic factors present in natural habitat of Rafflesia as closely as possible to improve host compatibility with Rafflesia, to enhance the success of Rafflesia propagation.
The soil characteristics from the three locations reflect fertile soil with an adequate supply of macronutrients for the growth of the host plant.Our ongoing study has indicated that the combination of soil, compost, and fermented bamboo leaves present the potential medium for the cultivation of Tetrastigma, providing fertile soil and a favorable texture.However, further investigation is required to determine the optimal proportions for this media composition.
In addition to soil composition, the water and nutrient requirements of the soil are critical factors influencing the growth of both Tetrastigma and Rafflesia.This correlation arises because the development of the Rafflesia bud intricately tied to the host plant vine, acquiring water and nutrients (Nais 2001;Iman et al. 2021).Consequently, more comprehensive studies are imperative to identify the specific essential nutrients essential for the growth and development of the Rafflesia.This detailed observation will contribute to valuable insights towards creating an optimal environment that supports the thriving coexistence of Tetrastigma and Rafflesia.

Figure 1 .
Figure 1.Map of Three Rafflesia Habitats in Three Island of Indonesia.

Figure 4 .
Figure 4.The Exchangeable Pottasium, Calsium and Magnesium content in the soil.

Table 1 .
The study sites of four species of Rafflesia.

Table 2 .
Soil Texture and Soil Chemical properties of three habitats of Rafflesia spp.