Summer drought survival and recovery in Microlaena stipoides

Microlaena stipoides (microlaena) is an important perennial grass in over 7 million hectares of native pastures in southern Australia and can survive and persist despite severe soil water deficits during summer. Many other pasture species survive similar conditions by relying on summer dormancy, which raises the possibility that microlaena may behave similarly. A field experiment using rainout shelters was conducted on an existing microlaena pasture in north-east Victoria. The experiment was a split-plot design with two watering treatments (‘summer storm’ or ‘summer dry’) as main plots and three defoliation treatments (nil, intense defoliation, strategic defoliation) as subplots. The ‘summer storm’ treatment resulted in the formation of new buds and tillers and increased basal cover from 1% in February to 18% in March. A glasshouse pot experiment examined the recovery of microlaena after different periods of drought and subsequent rewatering. In the pot experiment, microlaena withstood relatively short (up to 30 days) dry periods and then recovered when rewatered. Thus, it appears that microlaena is a persistent, perennial pasture plant that, although it survives very dry summers in Mediterranean areas, is not summer dormant. Microlaena does not exhibit summer dormancy in response to moisture stress and enter a quiescent stage, because normal growth is prevented by the lack of water, but it quickly recommences growth when soil water becomes available. The ability of microlaena to withstand summer soil water deficits and to recruit from seedlings make it a valuable pasture species across drought-prone environments, and this undoubtedly partly explains its very broad adaptation across eastern Australia.

Population biology of Microlaena stipoides in a south-eastern Australian pasture

Microlaena (Microlaena stipoides var. stipoides (Labill.) R.Br.) is a C3 perennial grass that is native to areas of south-eastern Australia. In this region, perennial grasses are important for the grazing industries because of their extended growing season and persistence over several years. This series of experiments focused on the population biology of Microlaena by studying the phenology (when seed was set), seed rain (how much seed was produced and where it fell), seed germination, germinable seedbank, seed predation and seedling recruitment in a pasture. Experiments were conducted at Chiltern, in north-eastern Victoria, on an existing native grass pasture dominated by Microlaena. Seed yields were substantial (mean 800 seeds m–2), with seed rain occurring over December–May. Microlaena has two distinct periods of high seed rain, in early summer and in early autumn. Seed predation is high. Within a 24-h period during peak seed production, up to 30% of Microlaena seed was removed from a pasture, primarily by ants. Microlaena seedlings recruited throughout an open paddock; however, seedling density was low (5 seedlings m–2). Microlaena represented only low numbers in the seedbank (0.01–0.05% of total); hence, any seedlings of Microlaena that germinate from the seedbank would face immense competition from other species. Management strategies for Microlaena-dominant pastures need to focus on the maintenance of existing plants.

Phosphorus content of the soil influences the growth and productivity of Themeda triandra Forssk. and Microlaena stipoides (Labill.) R.Br.

Despite native grasses occupying a large area of land in Australia, there has been limited work on the responses of these species to the addition of phosphorus (P). The main objective of this study was to investigate the effect of the addition of P to create a range of P contents in the soil on the productivity and morphology of two native grasses at two times of harvests. Two contrasting perennial native grasses, namely kangaroo grass (Themeda triandra Forssk. syn. T. australis R. Br. Stapf) and weeping grass [Microlaena stipoides var. stipoides (Labill.) R. Br.] were grown in a glasshouse with the addition of P to create five contents of P in the soil (7, 17, 32, 107 and 307 mg kg–1 soil) using a completely randomised design with four replicates per treatment. Grasses were harvested to 5 cm above the substrate surface, and the number of tillers and leaf area were recorded on Day 84 (harvest 1) and Day 112 (harvest 2) of the experiment. Dry matter production for kangaroo and weeping grass increased with P contents of the soil of 32 mg and ≥107 mg P kg–1 soil, respectively. Increased dry matter production for both species was the result of increased leaf area, tiller number and root growth. These results provide data that help to understand the disappearance sequence of kangaroo grass from more fertile soils and an increase in weeping grass, particularly in soils with greater fertility. Further research is required to determine if these results hold for other grass ecotypes.

Genetic diversity within a population of Microlaena stipoides, as revealed by AFLP markers

Microlaena stipoides (Labill.) R.Br. (microlaena), a C3 perennial grass, is common within grazed native pastures in the high-rainfall zone (>550 mm average annual rainfall) of south-eastern Australia. It has the ability to spread via seed production or vegetatively, using both rhizomes and stolons. This experiment aimed to determine how variable a microlaena population was within a single area, with the aim of determining whether microlaena relied on seed or vegetative spread to sustain populations. Leaf samples of microlaena were collected from 85 locations, sampling two transects, within a pasture at Chiltern, in north-eastern Victoria (36°12ʹS, 146°35ʹE). The genetic diversity among samples was analysed using amplified fragment length polymorphism (AFLP) markers. We obtained 1612 fragments, using 10 primers combinations. Polymorphism for the markers ranged from 47% to 65%. These results indicated that the populations of microlaena that exist within the pasture at Chiltern are likely to have undergone some degree of outcrossing (Fst = 0.0219). It is likely that recruitment is occurring from sexual reproduction as well as via clonal spread within the microlaena population examined. This ability to use vegetative spread as well as both sexual and asexual reproduction may make populations of microlaena more resilient in the longer term.

Indigenous sward restoration by oversowing Microlaena stipoides into kikuyu (Pennisetum clandestinum) pasture

Management plans for the grazed parklands of the Auckland volcanic cones call for revegetation to restore a more natural and historic vegetation cover. The native grass Microlaena stipoides has been identified as a relevant species, and a field experiment was undertaken to determine the best approach for establishing this species into existing pasture. Seed obtained locally was broadcast or hydro-seeded in May 2007 onto kikuyu pasture, at three sowing rates (100, 250 and 750 seeds/m2) following control of the resident pasture with turf stripping or mowing and spraying, in a replicated factorial trial. After 12 months, the highest levels of Microlaena plant density (mean 56 plants/m2), cover (mean 50%) and accumulated herbage mass were observed on broadcast/sprayed plots at the highest sowing rate. Recovery of the resident pasture (dominantly Pennisetum clandestinum) occurred to a level of ~25% after 12 months, but was inhibited at the highest Microlaena sowing rate. Keywords: broadcast, hydro-seeding, kikuyu, Microlaena stipoides, re-vegetation

Reproductive and vegetative responses of different accessions of Microlaena stipoides (Labill.) R.Br. to nitrogen applications and supplementary irrigation in southern Australia

Native grasses such as Microlaena stipoides (Labill.) R.Br. have the potential to play an important role in pastures, revegetation and as turfgrasses, but their use to date has been limited by seed supply. The purpose of this study was to investigate, (i) the effect of nitrogen fertilisation on M. stipoides seed production, (ii) the effect of irrigation on seed production, and (iii) the variation among accessions in response to these 2 factors. Microlaena stipoides accessions responded to added nitrogen with an increase in shoot growth, total amount of dry matter produced per plant and in reproductive characters at the end of the harvest season. Higher yields were recorded for high (split) nitrogen treatments in comparison to nil (control) or low nitrogen treatments, with added nitrogen extending seed production. Higher soil moisture regimes produced significantly more reproductive culms, more spikelets per culm, and more seeds per plant when compared to low soil moisture treatments. The frequency of irrigation had more effect on seed yield than the amount of water applied. Microlaena stipoides appears to have a 2–step mechanism for regulating the yield of its summer inflorescences namely; the plant initially responds to a high frequency of rainfall or irrigation events by initiating culms. Numbers of culms and florets per culm that reach maturity are dependent on the volume of water applied. Such a mechanism would assist in the adaptation of this grass to a southern Australian climate, which often exhibits an erratic summer rainfall. While there were differences among the accessions for both reproductive and vegetative characters, they gave a uniform response to the different nitrogen treatments. The responses of 3 accessions to different irrigation treatments were somewhat different but with respect to total number of spikelets produced per plant, they all responded in the same way. Different irrigation management schedules may be required for different cultivars for commercial seed production.

Variation in seed yield and its components in the Australian native grass Microlaena stipoides as a guide to its potential as a perennial grain crop

This research investigated the potential to domesticate an Australian native grass (Microlaena stipoides) to produce a perennial grain crop. Perennial grain crops offer a new solution to the long-standing problems of salinity and soil erosion associated with conventional cropping systems based on annual plants. Seed yield and its components (culm number, spikelet number per culm, seed set, seed weight) were measured in 46 accessions of Microlaena stipoides (microlaena, meadow or weeping rice grass) from Western Australia and New South Wales to quantify potentially useful variation in the species. A high degree of variability was found to exist, with a 20-fold range in seed yield (0.1–2.4 g/plant), 5-fold range in seed weight (129–666 mg per 100 seeds), 2-fold range in spikelet number (14–30 per culm), 8-fold range in seed set (12–98%), and a 5-fold range in culm number (11–59 per plant). Seed yield was positively and significantly (P < 0.05) correlated with culm number, seed set, and seed weight (r > 0.55 for all). No correlation was found between seed yield and spikelet number per culm (r = –0.14). The range in seed yield and its components suggests that there is sufficient variation within microlaena to make selections for higher yielding lines. This variation will enable breeders to exploit genetic diversity more efficiently and identify useful accessions for further work. High priority traits for future work include synchronous maturity and resistance to shattering.