SOIL NUTRIENT SUPPLY AND CHIONOCHLOA GRASSES

Abstract

Grasslands dominate the alpine zone in South Island, New Zealand. In this photo, mountain beech forests (Nothofagus spp.) transition to mixed scrubland and then alpine grasslands in Takahe Valley, a remote, hanging valley situated in the rugged Murchison Mountains, Fiordland. Lake Orbell in the background is situated at ~890 m above sea level, while the valley head basin reaches upward of 1250 m. Photograph by Andrew J. Tanentzap. The valley head basin consists of distinct communities, each dominated by one of four Chionochloa species. In most years, tussocks do not flower, such as along the transect of C. pallens shown in this photo. Photograph by William G. Lee. Synchronous and intermittent reproduction in long-lived plants, known as mast seeding, has rarely been studied along environmental gradients, despite its potential to be influenced by factors such as soil nutrients. Tanentzap et al. used a 37-year data set for five species of alpine Chionochloa grasses in New Zealand to test whether populations on nutrient-rich soils require less-favorable growing temperatures to flower. They found that flowering primarily depends on warm summer temperatures, and species on nitrogen-rich soils do require less favorable temperatures because they invest less nitrogen in seeds. These findings provide new evidence for ecological influences over evolutionary (i.e., distal) processes. Masting events are pronounced, with almost all plants in a population flowering. Here, 99% of C. teretifolia tussocks are flowering along a permanent transect in March 2011. Photograph by Andrew J. Tanentzap. Culms of C. crassiuscula. Masting in Chionochloa is postulated to have evolved ultimately in response to predator satiation. Photograph by Andrew J. Tanentzap Takahē, a flightless and endemic rail species, was presumed extinct in New Zealand in the early 20th century until a remnant population was discovered in Takahe Valley in 1948. The Murchison Mountains were thereafter protected for their conservation, and the species remains endangered in the wild. Birds primarily feed on Chionochloa during the summer, consuming the basal portions of tillers that are rich in starches. This photograph shows a bird with radio transmitter in the Ettrick Burn of the Murchison Mountains. Photograph by Sheila Dumesh. These photographs illustrate the article “Soil nutrient supply modulates temperatureinduction cues in mast-seeding grasses,” by Andrew J. Tanentzap, William G. Lee, and David A. Coomes, published in Ecology 93:462–469, March 2012.