DOI: 10.5061/dryad.kh1893264
title: Root allocation and foraging precision in heterogeneous soils

description: Root growth patterns respond to small-scale resource heterogeneity and the
 presence of roots of neighboring plants, but how a plant integrates its
 responses to these cues is not well understood. In the presence of
 neighbors, plants may shift allocation to roots as a consequence of plant
 size and root:shoot allometry, as a response to resource depletion by
 neighbors, or through a direct response to neighbor presence. The same
 response pathways also have the potential to alter proliferation in
 resource-rich patches in soil. Four species of grassland plants were grown
 in the greenhouse as single plants, monocultures, and mixtures. Root
 length allocation as a function of shoot mass was examined for background
 soil and fertilized patches. Plants grown with same-species neighbors
 followed the same allometric trajectory as single plants for root length
 in background soil, so any change in root allocation was due only to
 reduced plant size. Root proliferation in patches declined with neighbors,
 consistent with a response to resource depletion. Mixtures overproduced
 roots in both background soil and in patches, relative to plants of the
 same size in monocultures.
description: Four co-occuring grassland species were included in the
 experiment: two grasses, <em>Dactylis glomerata</em> L. and
 <em>Poa pratensis </em>L., and two forbs, <em>Centaurea
 jacea</em> L. and <em>Plantago lanceolata
 </em>L. Each pot (15 cm square x 30 cm deep) was
 filled with a background soil containing a mix of 50% (by volume)
 commercial topsoil, 30% sand, 10% milled peat, and 10% perlite. Two
 resource-rich patches were created in each pot by removing a soil core (1
 cm diameter x 15 cm deep), adding 0.5 g of Osmocote slow-release
 fertilizer (19-6-12 NPK; Scotts-Sierra Horticultural Products, Marysville,
 Ohio, USA) mixed with about 15 ml background soil, and refilling the rest
 of the core with background soil. Patches were placed in opposite corners
 of the pot, equidistant from the pot edge and center. Control cores
 containing only background soil with no fertilizer were removed and
 refilled in the two remaining corners. Seeds were
 germinated in background soil and transplanted into experimental pots
 after four weeks. Each pot was planted with a single plant, a monoculture
 (four individuals of the same species), or a mixture (one individual of
 each species). Each plant was positioned between a patch and a control
 core. Specific positions of single individuals and of species in mixtures
 were determined randomly. Pots were maintained in the greenhouse with
 natural light and watered daily. Plants were harvested
 after 60 days of growth in pots. Shoots were clipped at the soil surface,
 dried at 80 C for 48 hours and weighed. Shoots of all four individuals in
 monocultures were weighed together. Soil cores (2 cm diameter x 20 cm
 deep) were removed at the positions of resource-rich patches and control
 patches. Cores from the two patches of each kind were combined for each
 pot. The soil was air-dried for at least 48 hours and the roots were
 removed from the soil. Each root sample was scanned for determination of
 total root length using a WinRhizo root image analysis system (Regent
 Instruments, Quebec, Canada). Roots in mixtures could not be separated by
 species.