Résumé
1. There is a fundamental trade-off between leaf traits associated with
either resource acquisition or resource conservation. This gradient of
trait variation, called the economics spectrum also applies to fine roots
but whether it is consistent for coarse roots or at the plant community
level remains untested. 2. We measured a set of morphological and chemical
root traits at a community level (functional parameters; FP) in 20 plant
communities located along land-use intensity gradients and across 3
climatic zones (Tropical, Mediterranean and Montane). We hypothesized (i)
the existence of a root economics spectrum in plant communities consistent
within root types (fine, < 2 mm; coarse, 2-5 mm) but that ii)
variations in root traits occur with soil depths (top 20 cm of soil and
100-150 cm deep) and iii) along land use gradients thus leading to
variation in root FP. 3. Root FP co-varied, in line with the resource
acquisition-conservation trade-off, from communities with root FP
syndromes associated to resource acquisition (e.g. high specific root
length, SRL; thin diameters and low root dry matter contents, RDMC) to
root FP syndromes associated with resource conservation (e.g. low SRL,
thick diameters and high RDMC). This pattern was consistent for both fine
and coarse roots indicating a strong consistency of a trade-off between
resource acquisition and conservation for plant roots. 4. Roots had
different suites of traits at different depths, suggesting a disparity in
root function and exploitation capacities. Shallow, fine roots were
thinner, richer in nitrogen and with lower lignin concentrations
associated to greater exploitation capacities compared to deep, fine
roots. However, shallow coarse roots were richer in nitrogen, carbon and
soluble concentrations than deep, coarse roots. 5. Fine root parameters of
highly disturbed, herbaceous dominated plant communities in poorer soils
were associated to foraging strategies, i.e. greater SRL and lower lignin
and RDMC than those from less disturbed communities. Coarse roots however,
were less sensitive to the land use gradient. 6. Synthesis This study
demonstrates the existence of a general trade-off in root construction at
a community level, which operates within all root types suggesting that
all plant tissues are controlled by the trade-off between resource
acquisition and conservation.