Trampling, defoliation and physiological integration affect growth, morphological and mechanical properties of a root-suckering clonal tree.
OBJECTIVE
Grazing is a complex process involving the simultaneous occurrence of both trampling and defoliation. Clonal plants are a common feature of heavily grazed ecosystems where large herbivores inflict the simultaneous pressures of trampling and defoliation on the vegetation. We test the hypothesis that physiological integration (resource sharing between interconnected ramets) may help plants to deal with the interactive effects of trampling and defoliation.


METHODS
In a field study, small and large ramets of the root-suckering clonal tree Populus simonii were subjected to two levels of trampling and defoliation, while connected or disconnected to other ramets. Plant responses were quantified via survival, growth, morphological and stem mechanical traits.


RESULTS
Disconnection and trampling increased mortality, especially in small ramets. Trampling increased stem length, basal diameter, fibrous root mass, stem stiffness and resistance to deflection in connected ramets, but decreased them in disconnected ones. Trampling decreased vertical height more in disconnected than in connected ramets, and reduced stem mass in disconnected ramets but not in connected ramets. Defoliation reduced basal diameter, leaf mass, stem mass and leaf area ratio, but did not interact with trampling or disconnection.


CONCLUSIONS
Although clonal integration did not influence defoliation response, it did alleviate the effects of trampling. We suggest that by facilitating resource transport between ramets, clonal integration compensates for trampling-induced damage to fine roots.
State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
Liang
L
Xu
Fei-Hai
FH
Yu
Elles
E
van Drunen
Feike
F
Schieving
Ming
M
Dong
Niels P R
NP
Anten
D018533:Biomass; D001696:Biomechanical Phenomena; D002681:China; D060434:Herbivory; D018515:Plant Leaves / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology; D018517:Plant Roots / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D018547:Plant Stems / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology; D032107:Populus / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D014197:Trees / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology