Control of tiller recruitment in bunchgrasses: uniting physiology and ecology

Abstract

Summary 1.Bunchgrasses are clonal plants whose dominance of moist grasslands worldwide is maintained largely through tiller recruitment. Tiller recruitment in clonal plants is a subset of the problem of lateral bud outgrowth in higher plants. This paper proposes that three currently competing hypotheses of lateral bud outgrowth -apical dominance; the nutrition hypothesis; and photosensitivity to the red : far-red light ratio -all operate in a manner dependent on environment and plant form. 2. The evidence for each hypothesis is reviewed, following which an integrated model is provided that links the three hypotheses into a cohesive strategy. Consequently we assess tiller recruitment by bunchgrasses in terms of the constraints of their functional growth form and their environment. Of the mineral nutrients, only nitrogen is considered because it is the only nutrient whose relationship with tiller recruitment is well established. 3. The integrated model maintains the accepted paradigm that actual bud release is hormonally controlled by the auxin : cytokinin ratio, although local nutrient concentrations may also be inhibitory. Importantly, each hormone is controlled by local signals in the shoots and roots, respectively, facilitating appropriate responses to environmental conditions. Auxin production and export from the shoots is moderated by phytochrome responses to red : far-red light ratios. Cytokinin production is mediated by root N concentration which, in turn, is a function of N absorption from the soil and seasonal reallocation of tissue N. 4. The growth form of bunchgrasses and the environment in which they are found emphasize that N has a strong mediatory role over tiller production which allows the grass plant to respond appropriately to shifts in this limiting resource. This suggests that control of lateral bud outgrowth may have an evolutionary basis in resource competition for N.

Belowground bud banks of tallgrass prairie are insensitive to multi‐year, growing‐season drought

“…The light cues that signal dormant buds to emerge as shoots may be blocked or altered by the detritus layer in unburned prairie. Based on studies of C 3 grasses, Tomlinson and O'Connor (2004) proposed that an interaction of light (red/far-red light ratio) and nitrogen regulate bud outgrowth and shoot emergence. Williamson et al (2012) tested the Tomlinson and O'Connor model and found that while C 3 grasses responded as predicted to light and nitrogen availability, with increased tillering under higher light and nitrogen levels, C 4 grasses did not.…”

“…Williamson et al (2012) tested the Tomlinson and O'Connor model and found that while C 3 grasses responded as predicted to light and nitrogen availability, with increased tillering under higher light and nitrogen levels, C 4 grasses did not. The primary controls over bud transition to shoots in tallgrass prairie are most likely temperature (Knapp and Hulbert 1986), light (Deregibus et al 1985, Tomlinson and O'Connor 2004, Williamson et al 2012, and nitrogen (Bonser and Aarssen 2003, Tomlinson and O'Connor 2004, Williamson et al 2012.…”

Short‐term effects of elevated precipitation and nitrogen on soil fertility and plant growth in a Neotropical savanna

“…Bunchgrasses reproduce in two distinct manners (1) through seedling recruitment and (2) production of lateral tiller (Tomlinson and O'Connor 2004). For our study we quantified reproduction based on measures of reproductive effort and allocation related to seedling recruitment by measuring (1) flowering vs. nonflowering individuals, (2) the number of flowering tillers per individual, (3) the total number of spikelets, and (4) allocation of spikelets per flowering tiller.…”

Effects of Planting Method on Enhanced Stand Establishment and Subsequent Performance of Forage Native Warm-Season Grasses

“…This also indicates that, among the four NWSGs, SG establishment was less susceptible to weed competition, and therefore, under comparable growing conditions, the productivity of fall-seeded new stands of similar varieties may benefit more from careful early defoliation management that promotes tillering than it might with intensive weed control alone. Defoliation usually favors the growth of auxiliary tillers through improved light environment (Assuero & Tognetti, 2010) and the removal of the reproductive tillers'' apical dominance (Richards, et al, 1988;Briske and Richards, 1995;Tomlinson and O'connor, 2004). However, when deciding on appropriate defoliation strategies, species differences in response to defoliation as in the case of SG in the current study should be taken into consideration.…”