Abstract
Identifying the linkages between nutrient properties and plant size is important for reducing uncertainty in understanding the mechanisms of plant phenotypic plasticity. Although the positive effects of grazing exclusion on plant morphological plasticity has been well documented, surprisingly little is known about the relationship of nutrient strategies with plant shoot size after long-term grazing exclusion. We experimentally investigated the impacts of grazing exclusion over time (0, 9, 15, and 35 years) on the relationships of nutrient traits (nutrient concentration, allocation, and stoichiometry) of with morphological plasticity in Leymus chinensis, which is a dominant species in grasslands of Inner Mongolia, China. Our results showed that there was a significantly negative correlation between the degrees of plasticity and stability of various morphological traits. Increases in plant size by 126.41, 164.17, and 247.47% were observed with the increase of grazing exclusion time of 9, 15, and 35 years, respectively. Plant size was negatively correlated with nitrogen (N) and phosphorus (P) concentrations, but was positively correlated with carbon (C) concentration. Biomass partitioning and leaf to stem ratios of nutrient concentrations contributed more than 95% of the changes in N, P, and C allocation in L. chinensis leaves and stems induced by grazing exclusions. Nine years’ grazing exclusion rapidly changed the nutrient concentrations (averaged by -34.84%), leaf to stem nutrient allocations (averaged by -86.75%), and ecological stoichiometry (averaged by +46.54%) compared to free-grazing, whereas there was no significant trend of these nutrient traits across the 9, 15, and 35 years’ grazing exclusion in L. chinensis individuals. Our findings suggest that with the increase of the duration of the grazing exclusion, time effects on plant performances gradually weakened both in plant morphological plasticity and nutrient properties. There is a significant negative effect between plant sizes and nutrient traits under long-term grazing exclusion.
Highlights
Phenotypic plasticity is defined as the ability of a single plant genotype to produce different phenotypes under various biotic and abiotic disturbances, including herbivore grazing, bio-invasion, elevated CO2, warming, and drought (Nicotra et al, 2010; Dostál et al, 2016; Wang D. et al, 2017)
We examined the effects of grazing exclusion on morphological plasticity, nutrient concentration, accumulation, allocation, and ecological stoichiometry of L. chinensis along a time series in a degraded pasture located in Xilinhot, Inner Mongolia, China
We found that N:P in L. chinensis individuals was lower than the threshold of 14:1 for N limitation, and that N:P gradually decreased with the increase of grazing exclusion time, especially in L. chinensis stems
Summary
Phenotypic plasticity is defined as the ability of a single plant genotype to produce different phenotypes (morphology, phenology, or physiology) under various biotic and abiotic disturbances, including herbivore grazing, bio-invasion, elevated CO2, warming, and drought (Nicotra et al, 2010; Dostál et al, 2016; Wang D. et al, 2017). The potential role of phenotypic plasticity on the change of ecosystem function has attracted the interest of grassland ecologists. It provides a new theoretical perspective for understanding how plant functional traits mediate the restoration of grassland ecosystem performance under grazing exclusion (Li et al, 2016a; Wang D. et al, 2017). Recent results from a long-term grassland trial indicated sheep grazing caused the decline of aboveground biomass of Leymus chinensis, primarily through a ‘bottom-up’ effect due to the asymmetrical response of different plant functional traits with the variations in individual plant size (Li et al, 2015a). The patterns of the phenotypic variations of plant species in a long-term study in a degraded pasture are largely unknown
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