Root morphological responses to population density vary with soil
conditions and growth stages
Abstract
How plants cope with the increase of population density via root
plasticity is not well documented. Abiotic environments and plant
ontogeny may play an important role in determining plant response to
density and thus contribute to understanding this issue. We aimed to
investigate root plasticity in response to density under contrasting
soil conditions at three stages of plant growth in an annual herbaceous
species Abutilon theophrasti. We conducted a field experiment by
subjecting plant individuals to low, medium and high densities (13.4,
36.0 and 121.0 plants m-2, respectively) under fertile and infertile
soil conditions, and a series of root traits were measured at three
harvests when they had grown for 30, 50 and 70 d. Results revealed the
complexity of root response to density, which may increase, decrease or
canalize, depending on the strength of above- and below-ground
interactions, which varied with soil conditions or growth stage. The
intensity of above- and/or below-ground interactions increased with
decreased soil resources, but first increased then decreased with growth
stage. Facilitation is more likely to occur at low to moderate
below-ground interaction, when above-ground interaction is negligible,
and resources are abundant and at early stage of plant growth. Plants
may prefer to adjust biomass allocation to maintain total mass stable
initially, before suffering decreased total mass, in response to
intraspecific interactions.