CSIRO PUBLISHING Australian Journal of Botany, 2021, 69,30–44 https://doi.org/10.1071/BT20118 Controls on myxomycete species and species assemblages Peter Wellman 17 Warragamba Avenue, Duffy, ACT 2611, Australia. Email: [email protected] Abstract. This paper uses data from previous worldwide myxomycete surveys to determine the controls on the occurrence of myxomycete species, and on species assemblages. The main findings are as follows. The effect of substrate pH can be modelled, in that each species has a preferred pH value relative to the mean of a survey; errors from the model are 0.2 pH units. The substrate physical properties, evaluated by subjective hardness, showed no correlation with pH measurements. Hence, myxomycete species seem to have distinct ecological niches in substrate, with preferred pH and preferred physical properties. Comparison of the species found from the liana stem substrate shows that the species association does not change within angiosperm forests. Further, the species association is the same as that found in other angiosperm litter substrates: twigs on trees or on the ground, and leaves. This and a previous finding are consistent with similar ecological environments around the world having the same myxomycete species association within sampling error. In mixed angiosperm forests around the world the pH of un-decayed wood is ~4.9, and for decayed wood and tree litter is ~6.5 in tropical latitudes, and ~5.5 at 35 latitude, so on decaying the change in pH varies with latitude. Keywords: acidity, latitude, myxomycete, pH, plasmodial slime mould, species assemblages. Received 11 September 2020, accepted 30 November 2020, published online 22 January 2021 Introduction substrate needs only ~30 diverse samples if five Petri dishes Myxomycetes (plasmodial slime moulds) are single celled are grown per sample (data of Wellman 2019; this paper). organisms in the phylum Amoebozoa. Their life cycle has A large number of myxomycete moist-culture surveys have two feeding stages; a relatively small uninucleate phase, and a been carried out. In a great majority of the surveys the larger multinucleate plasmodium. The life cycle ends with a objective was to obtain a listing of the species on one or fruiting body which contains spores. When there is moisture more substrates, particularly the rare species. In many cases the myxomycetes feed mainly on bacteria, but otherwise they the surveys included an analysis of the completeness of the survive as dormant stages (microcysts, sclerotia, and spores). species list. Some of the major surveys have also recorded There are ~1000 species (Stephenson and Rojas 2017), with environmental parameters and analysed the correlation within almost all species identified from their fruiting bodies in terms the survey area between the myxomycete species and the of a morphological species concept. A summary of our present various environmental niches (e.g. Schnittler 2001). There knowledge of myxomycetes is provided by Stephenson and have been many comparisons of species assemblages using Rojas (2017). measures of diversity. Previous papers by Wellman (2016, Myxomycetes can be obtained in the fruiting stage either by 2019) have tackled some general topics using Australian data collecting naturally occurring fruiting bodies in the field, or by from the bark substrate: the number of species associations collecting substrates with resting phases and cultivating the over Australia; the nature of the species association substrates. It is not practical to address most of the subjects boundaries; the effects of pH on the productivity; the discussed in this paper by using the fruiting bodies collected in variation over Australia of productivity and family the field, because where myxomycete fruiting bodies are found dominance; and the typical growth and decay over is not necessarily where they have fed. The moist culture four weeks of a large mixed myxomycete ‘population’.This method of cultivation is relatively easy: it can be applied to any paper uses both Australian and overseas data to investigate organic matter; a sample can be collected over a large part of other general myxomycete ecological topics which affect the year; the relation between the number of fruit and the myxomycete species. These topics include: the extent of feeding source is known; and the number of common species species associations around the world, the effects of pH and on a single type of substrate is ~30, so a survey to determine substrate physical properties on a species, and the average the relative abundance of the common species of a type of change of substrate acidity with latitude. Journal compilation Ó CSIRO 2021 Open Access CC BY www.publish.csiro.au/journals/ajb Controls on myxomycete species and assemblages Australian Journal of Botany 31 The study of myxomycete growth controls is important wood. The samples were collected from indigenous and exotic both to understanding myxomycetes (plasmodial slime trees growing in the city of Canberra (35S, south-east moulds), and, because the cultivation of myxomycetes is so Australia). The exotic trees originated in other temperate easy, to providing important pointers to growth controls in climates. Small pieces of the samples materials were placed other simple organisms which are more difficult to study. The in small plastic cups, 20 mm of de-ionised water was added, related cellular slime moulds (Distyostelia) are the model the cups were left for 24 h, and then the pH of the water was organism for investigating the workings of a single cell. determined by a pH meter that had been calibrated by standard solutions. Materials and methods Results The studies in this paper were initiated by a desire to compare the myxomycete species assemblage on Australian temperate Geographic extent of litter-substrate species assemblages liana substrates with the assemblage on tropical liana substrate. The aim of this study was to obtain the myxomycete species A temperate liana substrate survey was carried out as follows. assemblage for temperate rainforest liana stems, so the species The samples were collected near the coast in eastern New found could be compared with nine assemblages previously South Wales (NSW) at different months during the years reported on liana in the tropics. The results of the 10 available 2014–2018. They were selected from five areas over seven surveys are listed in Table 1 as columns 1–10, with the degrees of latitude to provide variety in location. They were temperate survey as column 3. The main difference in taken from 14 liana species and a wide range of families to species association between the temperate survey and provide variety in substrate pH and bark texture. In all species elsewhere is that in NSW Physarum oblatum is common, a section of the woody stem showed numerous wide water and the Stemonitis fusca is subspecies fusca not nigrescens. conduits. The liana samples were collected during a long The NSW data does not record Comatricha tenerrima (which period of dry weather, so the myxomycete material should apparently does not occur in Australia), or Perichaena be in a resting phase when collected. The material cultivated dictyonema and Physarum didermoides. These differences for myxomycetes was liana stem sections ~20–45 mm long are minor. Column 3 was from the temperate forest (bark and wood). Most of the stem material was of small reported above, column 1 was sampled well above the diameter so the stem was cultivated whole, but a few stems, ground at the very top of the rainforest, column 9 samples with a diameter >8 mm, were cut lengthwise, and the half a cloud forest at 1300–2700 m altitude with liana stems having sections were cultivated with the bark uppermost. a thick epiphyte covering, and in other surveys the samples Myxomycete fruit were obtained by the moist culture were collected close to the ground near sea level. After method (Stephenson and Stempen 1994). For each sample allowing for the effect of sampling errors, there appears to five Petri dishes were cultivated, each dish 90 mm in diameter be no difference between the species assemblages of these 10 and 10 mm high. Filter paper was placed at the base of each surveys; that is, the surveys are consistent with a liana Petri dish, and sections of the stem were placed on this with the myxomycetes species association being uniform across stem sides touching, to fill the Petri dish. In order to obtain as angiosperm closed rainforest. If we take the species which many myxomycete species as possible in each Petri dish, the occur on three or more surveys as forming the liana species pieces of stem used sampled the range of stem diameter, assemblage, then this assemblage consists of 22 species, and degree of decay and bark texture. For each selected stem a they occur with an abundance of 6–160 parts per thousand (‰) portion was placed in each Petri dish. The Petri dishes were This species assembly is listed in Table 1,column19. half filled with ‘distilled’ water, left for 24 h and then the water Table 1, columns 1–20 list the published myxomycete was drained. The Petri dishes were then maintained at ~22Cin species assemblages for four types of litter substrates in diffuse natural light. Every week the dishes were inspected, angiosperm forests: dead liana stems on the vine; dead mature fruiting bodies removed for drying and study, and twigs on the ground; dead twigs still on the tree or shrub, Petri-dish moistness was maintained by adding drops of water. and mainly dead leaves on the ground. If there are any Any pieces of substrate with significant fungus was discarded. differences between the species assemblages of the litter The duration of cultivation was 6–8 weeks. This procedure types, or at any particular location, then these differences aimed at getting a large diverse species assemblage and a large should show on the table.