Nitrogen addition stimulated compensatory growth responses to clipping defoliation in a Northern Tibetan alpine meadow

Abstract

Grazing and clipping defoliation are the most important human disturbances in natural grasslands. Compensatory growth is a common response to clipping defoliation, which is of great significance for forage production and livestock husbandry development. However, how clipping intensity affects plant compensatory growth and how nitrogen (N) addition regulates this response in alpine ecosystems are still unclear. A manipulative experiment including two clipping intensities (light and heavy) crossed with N addition was conducted in an alpine meadow ecosystem to examine the effects of how N addition regulated plant compensatory growth induced by clipping defoliation. Selective clipping was used to simulate animal feeding, that is, only grasses and sedges were clipped. Under the N addition treatment, the relative growth rate of grasses and total biomass after clipping were significantly higher than those under the no N addition treatment. The total community biomass showed over‐compensatory growth in light clipping under N addition treatment, while it showed equal‐compensatory growth under the other treatments. The over‐compensatory growth in light clipping under the N addition treatments mainly resulted from the stimulated growth of grasses. Regression analysis showed that the relative growth rate and biomass of grasses were positively correlated with soil inorganic N content, but increasing N availability was not conducive to the growth of sedges and other forbs. Divergent responses of different plant functional groups to clipping and N addition would lead to changes in community structure and functioning. Both community biomass and compensatory growth tended to increase first and then reach a stable state with the increase in soil N availability. Our results show that although light clipping could largely stimulate forage production under N addition, excessive clipping cannot lead to a continuous increase in compensatory growth of plant biomass, even under N addition conditions, in this semiarid alpine meadow ecosystem.

Monthly mowing frequency does not affect soil CO2 emissions of fertilized Bromus erectus‐dominated grasslands

“…This is because, conversely, these abiotic factors will probably have significant effects on the soil carbon cycle of such grasslands (Han et al, 2012; Hopkins & Del Prado, 2007). Many studies showed how different mowing frequencies applied to seminatural grasslands affect aboveground biomass production (Bernhardt‐Römermann et al, 2011; D'Ottavio & Ziliotto, 2003; Rose et al, 2012; Zong & Shi, 2019) that, despite variations in management, is positively correlated to soil respiration (Raich & Tufekcioglu, 2000). Other studies also show how the below ground biomass in grasslands affects soil CO 2 emission depending on several parameters (e.g., roots diameter, age, N concentration) (Bahn et al, 2006; Koncz et al, 2015).…”

“…Moreover, different studies have suggested that the response in terms of soil respiration of N‐fertilized grasslands subjected to different herbage removal frequencies depends on the actions and interactions of other direct factors (e.g., mowing effects on plant roots) and indirect factors (e.g., drivers of soil respiration: soil temperature, water content). For example, Zong and Shi (2019) reported that a higher mowing frequency for semiarid N‐fertilized grasslands might not result in continuous increases in plant compensatory growth. Interruptions to, or slowdowns of, plant compensatory growth can reduce the contributions of the root component to total soil respiration (Wei et al, 2016).…”

Shoot–Root Interplay Mediates Defoliation-Induced Plant Legacy Effect

“…For perennial plant species, the interaction between above and belowground organs are critical to both individual growth in the current growing season and population persistence in the next year ( Briske and Richards, 1995 ; Zong and Shi, 2019 ); thus, this may be the determining factor for the temporal stability of the whole ecosystem ( Zhang et al, 2017 ; Xu et al, 2020 ). Two-rounds of shoot defoliation directly reduced the remaining and accumulated biomass by 64.66 and 57.51%, and indirectly reduced the root biomass by 60.11% ( Figure 1 and Supplementary Figure 2 ).…”