Population of Phosphate Solubilizing Bacteria and Arbuscular Mycorrhizae in the Rhizosphere of Maize and Peanut in Different Cropping Patterns on Dry Land

Dry land has several limiting factors, namely low organic C, low soil fertility, and limited water caused by very low rainfall. Strategies to increase the productivity of dry land can be done by combining the use of organic matter, cover crops, and intercropping crop systems. The existence of functional microbiota including phosphate solubilizing bacteria (PSB) and arbuscular mycorrhiza (AM) could be used as an indicator to evaluate the status of soil health in agricultural dry land areas. The purpose of this study was to analyze and compare the population density and diversity of PSB and AM in the rhizosphere of maize and peanut in mon-oculture and intercropping dry lands. A descriptive exploration method was conducted by sampling the rhizosphere soil of maize and peanut in the monoculture and intercropping dry lands to analyze the population density and diversity of PSB and AM spores. Each plot was analyzed in 3 replications. The results showed that the rhizosphere soil of maize in the monoculture dry land had the highest population density and diversity of PSB followed by maize in the intercropping dry land. The rhizosphere soil of maize in the intercropping dry land showed the highest AM spore density and diversity followed by maize in the monoculture dry land. So, this finding indicated that maize plants provide more conducive services in dry land.


Introduction
Dry land has different soil characteristics from wet climates, especially from its biophysical properties (Mulyani et al., 2023).According to Subagyo et al., (2014) areas with dry climates have several limiting factors, namely organic C and low soil fertility, as well as limited water caused by very low rainfall (Rochayati & Dariah, 2012).The management of dry land that can be carried out as a strategy to increase the productivity of dry land is to combine the use of organic matter, cover crops, and intercropping systems (FAO, 2018).
Several types of plants on dry land can also affect population density and microbial diversity, in research (Burrows & Pfleger, 2002) states that a variety of plant species diversity can increase plant root area or increase photosynthetic production so that it can increase the indigenous microbial population in soil (Goomaral et al., 2013).
This study aimed to analyze and compare the population densities and diversity of Phosphate Solubilizing Bacteria (PSB) and Arbuscular Mycorrhizae (AM) in the rhizosphere of maize and peanut monocultures and intercropping on dry land.Several studies have studied the effects of plant species on microbial populations and diversity, such as the study of Dhawi et al., (2016) which examined the effect of sorghum plants on microbial populations and Arbuscular Mycorrhiza (AM) in marginal lands, and Astuti et al., (2013) regarding the effect of tomato plants on the population of Phosphate Solvent Bacteria (PSB) and Nitrogen Fixing Bacteria (BPN) on dry land.However, research on population density and diversity of PSB and AM in the rhizosphere of maize and peanut plants in monoculture and intercropping systems is still very limited.This research is expected to produce information about the population density and diversity of Phosphate Solubilizing Bacteria (PSB) and Arbuscular Mycorrhiza (AM) in the rhizosphere of monoculture and intercropping maize and peanut plants.

Preparation of soil sample Soil sampling
The rhizosphere soil-type alfisols were taken from Sukosari Village, Kec.Jumantono, Karanganyar, and include a monoculture cropping pattern of maize and peanuts (7.63010 o S, 110.94830 o T), and maize cropping pattern of intercropping with peanuts.(7.63010 o S, 110.94830 o T).Approximately 500 g of rhizosphere soil from each plant type was taken from each location with three replicates (Cahyani et al., 2019) for use in mycorrhizal spore analysis and the isolation of phosphate-solubilizing bacteria.Rhizosphere soil was taken randomly representing each type of plant at a depth of 0-20 cm.The rhizosphere soil samples were then analyzed for chemical properties of the soil, including pH and availability of C, N, P.

Preparation of Phosphate Solubilizing Bacteria Isolation of Phosphate Solubilizing Bacteria
Before isolating phosphate solubilizing bacteria, first make a selective medium.The selective media used to isolate PSB bacteria is Pikovskaya (Jha et al., 2009).Then the media was sterilized by autoclaving at 121 o C for 15 minutes.Furthermore, rhizosphere soil samples were taken from each type of plant, followed by a dilution of 10 -1 to 10 -5 .Then it was inoculated with the spread plate method (Sanders, 2012).A total of 0.1 ml of sample from each dilution was poured aseptically into the middle of the cup using a micropipette.

Preparation of Mikoriza Arbuscular Mycorrhizal Isolation
Mycorrhizal isolation using the wet pour filter method (Cahyani et al., 2019).100 g of soil samples were taken put in 500 ml of distilled water, and stirred until homogeneous.The soil solution was filtered sequentially using three different filter sizes, namely 120 microns, 90 microns, and 45 microns.The filtrate suspension was transferred to a centrifugation tube, and a 60% sugar solution was added and centrifuged at 5000 rpm for 5 minutes.The supernatant was filtered using filter paper,and then the filter paper was transferred into a petri dish.Mycorrhizal spores retained on filter paper were transferred to a petri dish and observed for spore density using a binocular microscope with 400x magnification.The spore density was calculated from 100 g of the rhizosphere of each plant type.

Mycorrhizal Infectivity
Mycorrhizal infectivity was analyzed using a method (Phillips & Hayman, 1970).Observation of this method was carried out by washing with running water first to remove the soil that was still attached, then cutting the roots of the plant into as many as 25 pieces with a length of about 1-1.5 cm.The cut roots are poured with 70% alcohol to sterilize the roots, then put in 10% KOH liquid heated to 80 o C, then rinsed with distilled water first, then soaked in HCl solution for 5-8 minutes, then soaked in trypan blue for 24 hours, then observed under a microscope.Root infection is calculated using the calculation formula:

Results and Discussion
Population density and PSB diversity in monoculture and intercropping maize and peanut plants Based on table 1. shows the highest PSB population density in the MM2 isolate code of 103x105, where JM2 is an isolate obtained from monoculture maize plants, followed by a population of 17,46x10 MI1, where MI1 was obtained from intercropped maize plants.The high population of this monoculture maize plant can be caused because the monoculture maize has a pH of 6.4, which pH is the highest pH among the others.This is supported by the research of Aisah et al., (2022) which explains that pH values can affect the growth of phosphate-dissolving bacteria because some types of phosphate-dissolving bacteria can survive in the pH range of 4−8.The diversity of PSB obtained based on Table 2. shows that there are 5 types of diversity in monoculture maize, while in intercropping maize only 3 types of diversity are obtained.The high diversity in monoculture maize can be triggered because the organic C value of monoculture maize is higher compared to other types of plants.According to research by Firdausi et al., (2016), the presence of PSB is related to the amount of organic C content which directly affects the number and living activity of PSB.High organic C content makes it easier for active microorganisms to carry out the decomposition process (Marista et al., 2013).Table 3 shows that the highest population results were obtained by isolate PM1, which was 9.8x105, PM1 isolates were obtained from monoculture pea plants, followed by PM2 populations of 0.94x105, where PM2 was also obtained from monoculture pea plants.The lowest population results were obtained in PI1 isolates of 0.0014x105, where PI1 was obtained from intercropping peanut plants.The high population of monoculture peanuts is consistent with the available P value of monoculture peanuts, which is 6.38, which is higher than the available P value of intercropped peanuts.Therefore, according to Iswara and Nuraini (2022), high population of PSB will help produce organic acids which can help help increase the available P is also higher.Monoculture peanuts have higher diversity than intercropped peanuts.This is shown in table 4. where monoculture peanuts have 5 types of diversity and intercropped peanuts have 3 types of diversity.This could be due to the chemical properties of monoculture peanuts, especially the available P value.The P value available for monoculture peanuts was 6.38, while the P value available for intercropped peanuts was 4.58.The high available P value can affect the presence of soil microbes.This is also supported by the research of Oktaviani et al. (2020) who said that the presence of phosphate-dissolving bacteria in the soil rhizosphere can also affect the amount of P that can be absorbed by plants because of the bacteria's ability to dissolve phosphates.
So, it can be concluded that maize plants in both monoculture and intercropping have the potential to be developed on dry land.The high number of spores in intercropped plants can be caused by having more than one host plant.This is supported by (Chen et al., 2017) reported that mycorrhiza consisting of several hosts can produce higher spores than spores obtained from only one type of plant.Another reason for the greater abundance of spores in the intercropping system is also explained by the results of research (Xiao et al., 2019), where the reason for the greater abundance of spores in the intercropping system is that compared to monoculture, the intercropping planting system has more advantages in terms of quantity and quality of litter, better soil nutrients and stand structure.

AM spore density in maize and peanut plants in monoculture and intercropping patterns.
Continuous monoculture systems in the long term will affect nutrient status and lower soil fertility and can change the structure of the microbial community in the soil (Wu et al., 2014) so that soil microbial activity and diversity decrease.In the monoculture system, each spore is brown with a round shape.Meanwhile, in the intercropping system, each spore was brown, clear brown, dark brown, and black, with the shape of each spore being round.In the intercropping system, more spore diversity was found compared to the monoculture system, and more mycorrhizal diversity was found, which is expected to help meet the nutrient needs of plants.As in research (Johnson et al., 2010) intercropping management can help develop new root systems and build mycorrhizal mycelial networks, which absorb more soil nutrients during the growing season.

Results of AM infectivity on peanut plants in monoculture and intercropping cropping patterns.
The high infectivity of mycorrhizae in this intercropping system indicates that the higher the mycorrhizal infection, the higher the mycorrhizal colonization.Without infection, there is also no mycorrhizal colonization (Rubin et al., 2015).The result of high mycorrhizal infectivity can make infected root systems more abundant (Sales et al., 2018).Thus, the percentage of infectivity is higher, indicating that the available inoculum can quickly colonize the host (Pires et al., 2021).

Soil nutrient elements for maize and peanuts in monoculture and intercropping systems
The pH of maize plants in the intercropping system was higher than the pH in the monoculture system.This can be caused by the interaction of mycorrhizae with humic acids which can increase soil pH.This is also supported by (Arraudah et al., 2020) report the same trend in acid soils where mycorrhizal interactions with humic acids can increase the pH of Alfisols, where the maximum increase in the pH value from pH 4.4 to 6.1 is obtained by mycorrhizal interactions.In this case, it is also supported by the higher level of infectivity and mycorrhizal spores of intercropping compared to the monoculture system (Table 7).
The highest organic C was obtained in monoculture maize, which is in line with the acquisition of phosphate solubilizing bacteria which was also found to be highest in monoculture maize (Table 1).This can happen because the high organic C content is a source of energy and nutrition for microbial growth (Solihin et al., 2017).
The high total N nutrient content in intercropping maize obtained was directly proportional to the acquisition of infectivity and the number of intercropping mycorrhizal spores.This can occur due to mycorrhizal activity through organic exudates released from host roots (Wang et al., 2021), which can lead to better accumulation and distribution of nutrients in plants compared to monoculture systems (Moraes et al., 2019).
The highest available P nutrient was found in monoculture maize.This is in line with the organic C content of monoculture maize which was also found to be the highest of other types of plants.This can happen because organic C can be said to be able to increase the availability of P through its weathering products which are easily absorbed by plants (Firdausi et al., 2016).

Conclusion
The conclusion obtained in this research is that the rhizosphere of monoculture corn and Intercropping on dry land has a higher population density and BPF diversity compared with monoculture and intercropping pea rhizosphere.Meanwhile, the rhizosphere soil Corn intercropping and monoculture on dry land show density and diversity MA spores were higher compared to the rhizosphere of intercropped and monocultured beans.

Table 1 .
Population density and colony diversity of Phosphate Solubilizing Bacteria in Maize Monoculture and Intercropping *MM: Maize Monoculture; MI: Maize Intercropping

Table 2 .
Colony morphology of Phosphate Solubilizing Bacteria in Monoculture and Intercropping Maize *MM: Maize Monoculture; MI: Maize Intercropping

Table 3 .
Colony diversity and population density of phosphate solubilizing bacteria in peanut monoculture and intercropping

Table 4 .
Colony morphology of Phosphate Solubilizing Bacteria in Peanut Monoculture and Intercropping *PM: Peanut Monoculture; PI: Peanut Intercropping

Table 5 .
Results of AM spore density of maize and peanut plants in monoculture and intercropping cropping patterns

Table 6 .
Figure of AM spores of maize and peanut in monoculture and intercropping cropping patterns.

Table 7 .
Results of AM infectivity in monoculture and intercropping maize and peanut plants No. Plant type's