Abstract
Understanding the mechanism of plant morphological plasticity in response to grazing and clipping of semiarid grassland can provide insight into the process of disturbance-induced decline in grassland productivity. In recent studies there has been controversy regarding two hypotheses: 1) grazing avoidance; and 2) growth limiting mechanisms of morphological plasticity in response to defoliation. However, the experimental evidence presented for the memory response to grazing and clipping of plants has been poorly reported. This paper reports on two experiments that tested these hypotheses in field and in a controlled environment, respectively. We examined the effects of long-term clipping and grazing on the functional traits and their plasticity for Leymus chinensis (Trin.) Tzvelev (the dominate species) in the typical-steppe grassland of Inner Mongolia, China. There were four main findings from these experiments. (i) The majority of phenotypic traits of L. chinensis tended to significantly miniaturize in response to long-term field clipping and grazing. (ii) The significant response of morphological plasticity with and without grazing was maintained in a hydroponic experiment designed to remove environmental variability, but there was no significant difference in L. chinensis individual size traits for the clipping comparison. (iii) Plasticity indexes of L. chinensis traits in a controlled environment were significantly lower than under field conditions indicating that plants had partial and slight memory effect to long-term grazing. (iv) The allometry of various phenotypic traits, indicated significant trade-offs between leaf and stem allocation with variations in plant size induced by defoliation, which were maintained only under grazing in the hydroponic controlled environment experiment. Taken together, our findings suggest that the morphological plasticity of L. chinensis induced by artificial clipping was different with that by livestock grazing. The miniaturization of plant size in long-term grazed grassland may reflect retained characteristics of dwarf memory for adaptation to long-term grazing by large herbivores.
Highlights
Grasslands occupy more than a third of the world’s land area, excluding Antarctica and Greenland, and support the livelihoods of approximately 1 billion people [1]
L. chinensis functional traits responded to field clipping and grazing
Long-term clipping and grazing had similar effects on the field functional traits of L. chinensis, with the majority traits significantly diminished by defoliation (Table 2; P
Summary
Grasslands occupy more than a third of the world’s land area, excluding Antarctica and Greenland, and support the livelihoods of approximately 1 billion people [1]. Plant functional traits are the features that represent ecological strategies and determine how plants respond to environmental factors, affect other trophic levels and influence ecosystem properties [4]. Until recently we have had relatively little knowledge about the response of grassland plant traits to over utilization [5] compared to responses at the landscape, ecosystem, community and population levels [3, 6] and in recent years there has been a focus on the response of functional traits to defoliation. Our previous study indicated that the functional traits of Leymus chinensis (Trin.) Tzvelev, the dominate species in eastern Eurasian temperate grassland, can adapt to long-term grazing by leaf and stem allometry [21]
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