Patch–background contrast and patch density have limited effects on root proliferation and plant performance in Abutilon theophrasti

Abstract

Summary 1.We examined biomass and root proliferation responses of Abutilon theophrasti Medic. to the density of high nutrient patches and the patch-background contrast. Contrast in nutrient content between a patch and the background soil, as well as patch density, are important features of heterogeneous soil environments that have received little research attention. 2. Plants were grown in pots with no, one or two organic nutrient patches, and the equivalent nutrition of no, one or two patches in the background soil in a factorial design. Plant performance (root and shoot biomass) and root proliferation (root length inside and outside high-nutrient patches) were measured. 3. Root and shoot biomass increased with increasing nutrient heterogeneity, and root biomass declined with increased background soil nutrient availability. Patchbackground contrast did not alter root or shoot biomass, nor allocation to roots. Biomass responses appeared to be driven by heterogeneity, as plants with access to the same total nutrients were larger when nutrients were concentrated in patches. The root proliferation response was not affected by either the density of patches or the degree of contrast. 4. A conceptual model is presented describing how a plant's overall nutrient status could respond to changes in the patch-background contrast. The model predicts that nutrient-sufficient plants should not respond to patches, but nutrient-limited plants should proliferate roots proportionally to the contrast. The proliferation response should saturate when the total nutrients in both patch and background are no longer limiting.

Plant root growth and the marginal value theorem

“…Less data are available to test this prediction, although available data suggest this hypothesis may be supported. Lamb et al (20) found fewer roots were produced by plants as total habitat quality increased and when the total number of patches remained constant. However, there was only a nonsignificant trend toward reduced effort in patches as habitat quality increased (20).…”

“…Lamb et al (20) found fewer roots were produced by plants as total habitat quality increased and when the total number of patches remained constant. However, there was only a nonsignificant trend toward reduced effort in patches as habitat quality increased (20). Similar results have been found for competing plants that avoid areas of high competition in favor of root-free soil, where resource uptake is presumably higher (16).…”

“…Patterns of fine root biomass allocation in response to soil nutrient heterogeneity are well studied and there are studies in the literature that have similarly documented this relationship between patch quality and foraging effort, even if the original authors did not cast them in the context of MVT. Not all studies of root foraging measure patches of different quality, but when they do, almost every species studied expends foraging effort in proportion to patch quality (e.g., [20][21][22][23][24]. In other words, plants that focus root growth primarily in nutrient-rich soil, presumably maximize the benefits of foraging and minimize the costs of root growth and nutrient uptake.…”

Densely rooted rhizosphere hotspots induced around subsurface NH4 +-fertilizer depots: a home for soil PGPMs?

“…NH 4 + and HPO 4 2− /H 2 PO 4 − or CO(NH 2 ) 2 and HPO 4 2− /H 2 PO 4 − , the later under optimal ammonification conditions) [2,5] and are poorly mobile in soil [6][7][8][9], crops can more efficiently acquire fertilizer-depot nutrients, thus improving their yields [4]. Nevertheless, it has been shown that intense rooting may not occur around fertilizer depots based on manure or mineral N under greenhouse and field conditions [10]; (Müller et al 2009, unpublished results). The reasons for this are unclear.…”

Contrasting root behaviour in two grass species: a test of functionality in dynamic heterogeneous conditions

“…Selective root placement (also termed root foraging 'precision') is defined as the investment in roots placed into nutrient-rich zones, relative to root abundance in nutrient-poor zones. Selective root placement is ubiquitous among terrestrial species, but the benefits of this trait appear largely context-dependent, as species identity, nutritional composition of patches and duration of study influence the outcome (Hutchings and John 2004;Lamb et al 2004;de Kroon and Mommer 2006;Kembel et al 2008). This context-dependency exists for individually-grown plant species (Kembel and Cahill 2005), and also for plants under interspecific competition, where a high degree of selective root placement sometimes Robinson et al 1999), but not always, leads to the highest competitive ability (Bliss et al 2002;Cahill and Casper 1999;Rajaniemi 2007).…”