Festuca campestris alters root morphology and growth in response to simulated grazing and nitrogen form

Abstract

Summary1. Large herbivores are known to spatially concentrate and alter the form of nitrogen (N) in grassland systems, which can modify aboveground plant chemical composition and productivity, and result in shifts in grazing pressure in these areas. Root responses to grazing under high N inputs may facilitate these changes, but their responses are less well understood. 2. We examined biomass, root morphology and demography, and nitrogen pool responses of Festuca campestris Rydb. seedlings grown in pots in an environmental chamber and subject to heavy fertilization with isotopically-labelled N in a NO 3 -N or NH 4 -N fertilizer treatment, and to no clipping or clipping to 4 cm twice during the experiment. 3. Festuca campestris exhibited re-growth patterns after defoliation that reflected preferential allocation to aboveground shoots, with percent recovery of shoot biomass twice that of roots. Clipping did not increase the risk of root mortality. Instead, reduced root biomass in clipped plants resulted from slowed elongation and decreased production of new roots. Although roots with smaller diameters and at lower density had a greater risk of root mortality, clipping did not alter the mean root diameter or level of root branching. 4. Under high N fertilization, NH 4 -N increased the amount of aboveground biomass, ameliorated the effects of clipping on root production and further reduced the risk of root mortality in clipped plants. N-form had no effect on root morphology. 5. While total plant N uptake and the percent utilization of fertilizer were lower in clipped plants, total plant nitrogen accumulated per root biomass (g g)1 ) at harvest was higher in clipped plants. 6. Our findings indicate that where defoliation is coupled with high nitrogen return, Festuca campestris recuperates by increasing nitrogen uptake, shifting production to favour recovery of aboveground biomass, and mitigating carbon losses by decreasing investment in new, actively growing roots. Because application of a more mobile form of nitrogen (NO 3 -N) did not alter root morphology, root physiological responses may be most important for re-growth when nitrogen is not limiting. Root reductions associated with grazing may have a greater impact in locations where grazer-mediated nitrogen return is spatially decoupled from defoliation.

Independence of seasonal patterns of root functional traits and rooting strategy of a grass‐clover sward from sward age and slurry application

“…Response of perennial ryegrass roots to defoliation has been intensively investigated, and studies have demonstrated that defoliation had no effect on specific root length (Paterson and Sim, ), root C/N ratio (Paterson and Sim, ), root diameter (McInenly et al ., ), branching intensity (Dawson et al ., ) or turnover rate (Hill et al ., ). Hence, the differences in root growth between growth periods are likely to be related to season as well as growth stage (i.e.…”

Root growth and turnover in perennial forages as affected by management systems and soil depth

“…Root traits exhibit strong seasonal patterns (Chen et al 2016), which are likely to be modulated by soil depth and management practices (Fan et al 2016;Lazicki et al 2016) and, hence, to influence rootderived soil C fluxes (Poirier et al 2018). Defoliation in perennial grass pasture species was shown to increase root turnover, while also inducing a smaller root system (McInenly et al 2010;Reid et al 2015). Ensuing defoliation and under high N conditions, root architecture of grasses showed a reduced average root diameter (Dawson et al 2004).…”

Intra and inter-annual climatic conditions have stronger effect than grazing intensity on root growth of permanent grasslands

“…The contrasting results are possibly due to the variable abundance of defoliation-tolerant species or the combined effects of both defoliation and the level of soil fertility on the roots of grazed grasslands (Leuschner et al, 2013; Picon-Cochard et al, 2009; Yan et al, 2013; Ziter and McDougall, 2013). Thus, root growth reductions associated with grazing may have a greater impact in locations where the grazer-mediated N return is spatially decoupled from defoliation (McInenly et al, 2010). Furthermore, the higher SRA observed in the Ca-treatment than in the abandonment or Ca+ treatment should reflect a higher presence of species with fine roots, such as D. glomerata or H. lanatus (Picon-Cochard et al, 2012), because the soil fertility approximated by the NNI was similar across treatments.…”

“…In addition, comparing two contrasting grazed grasslands, Klumpp et al (2011) showed that during wet years extensive managed grassland (low stocking density combined with low soil fertility) had a higher storage capacity than intensive managed grassland (moderate stocking density combined with N fertilization), whereas the reverse was observed during dry years, as a result of higher canopy senescence in extensive vs. intensive management. Changes in root morphology and functioning may thus be an important mechanism in plant adaptive strategies to drought, and have been less well studied than above-ground plant responses (Biswell and Weaver 1933;Dawson et al 2000;McInenly et al 2010). However, there are not enough data to make generalizations about combined impacts of management and climatic conditions variability such as precipitation reduction on root and shoot biomass production and plant traits defining plant strategies related to resource use and grazing intensity.…”

“…However, there are few data on above- and below-ground biomass responses to drought for grassland (Byrne et al 2013; Wilcox et al 2015; Li et al 2018), although some evidence shows that the ‘slow’ trait strategy (resource conservation) is associated with drought tolerance (Pérez-Ramos et al 2012; Reich 2014). Changes in root morphology and functioning may thus be important determinants in plant adaptive strategies to drought, and have been less studied than above-ground plant responses (Biswell and Weaver 1933; Dawson et al 2000; McInenly et al 2010). However, there are not enough data to make generalizations about combined impacts of management and climatic conditions variability such as precipitation reduction on root and shoot biomass production and plant traits defining plant strategies related to resource use and grazing intensity.…”