Pathways of Leymus chinensis Individual Aboveground Biomass Decline in Natural Semiarid Grassland Induced by Overgrazing: A Study at the Plant Functional Trait Scale

Abstract

Natural grassland productivity, which is based on an individual plant’s aboveground biomass (AB) and its interaction with herbivores, can obviously affect terrestrial ecosystem services and the grassland’s agricultural production. As plant traits have been linked to both AB and ecosystem success, they may provide a useful approach to understand the changes in individual plants and grassland productivity in response to grazing on a generic level. Unfortunately, the current lack of studies on how plant traits affect AB affected by herbivores leaves a major gap in our understanding of the mechanism of grassland productivity decline. This study, therefore, aims to analyze the paths of overgrazing-induced decline in the individual AB of Leymus chinensis (the dominant species of meadow-steppe grassland in northern China) on a plant functional trait scale. Using a paired-sampling approach, we compared the differences in the functional traits of L. chinensis in long-term grazing-excluded and experimental grazing grassland plots over a continuous period of approximately 20 years (located in meadow steppe lands in Hailar, Inner Mongolia, China). We found a highly significant decline in the individual height and biomass (leaf, stem, and the whole plant) of L. chinensis as a result of overgrazing. Biomass allocation and leaf mass per unit area were significantly affected by the variation in individual size. Grazing clearly enhanced the sensitivity of the leaf-to-stem biomass ratio in response to variation in individual size. Moreover, using a method of standardized major axis estimation, we found that the biomass in the leaves, stems, and the plant as a whole had highly significant allometric scaling with various functional traits. Also, the slopes of the allometric equations of these relationships were significantly altered by grazing. Therefore, a clear implication of this is that grazing promotes an asymmetrical response of different plant functional traits to variation in individual plant size, which influences biomass indirectly. Furthermore, we detected paths of individual AB decline in L. chinensis induced by grazing by fitting to a structural equation model. These results indicate that grazing causes AB decline primarily through a ‘bottom-up’ effect on plant height and stem traits. However, leaf traits, via the process of allometric scaling, affect plant AB indirectly.

Long-term effects of mowing on plasticity and allometry of Leymus chinensis in a temperate semi-arid grassland, China

“…Depending on the model and variable, it was necessary to alter the relationship between a measured L. chinensis functional trait and the rest of the model. We compared the utility of each functional trait index within the SEM based on a number of measures, including the power of the particular model for explaining the variation in L. chinensis biomass accumulation (R 2 ), measures of model significance and fit (χ 2 ), and the significance of the functional trait variables within the model (significance of regression weights) (Li et al, 2015b). SEM analysis was performed using IBM SPSS AMOS 18.0 software packages.…”

“…However, not all grassland plant species have the same phenotypic plasticity reaction (Díaz et al, 2007). For example, distinctions could be made between "mowing-susceptible" and "mowing-resistant" plants in their responses to long-term stresses in heterogeneous habitats, and L. chinensis is the dominant species in Inner Mongolian grassland that is mowing-susceptible (Li et al, 2015b). Therefore, the reduction in physical characteristics of L. chinensis will likely have a substantial effect on the structure and functioning of grassland ecosystems.…”

“…In general, grassland productivity, which primarily relies on plant biomass, is an important function of a grassland ecosystem (Li et al, 2015b). Under the pressure of human activity and climate change, the decrease of grassland productivity could have a substantial impact on the global ecosystem .…”

Long-Term Overgrazing-Induced Memory Decreases Photosynthesis of Clonal Offspring in a Perennial Grassland Plant

“…A growing body of experimental evidence suggests that grassland plants show rapid phenotypic plasticity when exposed to such biotic and abiotic stresses (Li et al, 2015a). For example, Couso and Fernandez (2012) reported that the most tolerant species had the highest morphological plasticity in an underlying trait in three Patagonian steppe grasses.…”

Comparison of Modeling Grassland Degradation with and without Considering Localized Spatial Associations in Vegetation Changing Patterns

“…Some human-induced factors, including overpopulation, overgrazing from livestock, and transportation, were also identified as being threatening factors for the grassland ecosystem [23][24][25][26]. Intensified human disturbance due to increased accessibility to remote regions, as a result of the construction of more road networks, have led to vegetation degradation in many parts of the world [17,[27][28][29].…”