Abstract
Forage yield is the fundamental ecosystem service of grasslands. While the quantitative responses of forage yield to nitrogen (N) enrichment are well known, its qualitative responses remain unclear. Even less known is the relative contribution of changes in community composition to the quality of the yield at the community level. We examined the quantitative and qualitative responses of forage yield at both plant functional group and community levels with factorial treatments of N addition and mowing in a temperate steppe. Nitrogen addition significantly enhanced the community-level yield by favoring the growth of rhizomatous grass. Mowing tended to mediate the impacts of N addition on the yield. Nitrogen addition increased the concentrations of crude protein and crude fat in forage at the community level. Neither the main effects of mowing nor its interactive effects with N addition affected forage quality. The N-induced shifts in plant species composition significantly contributed to the effects of N addition on forage quality at the community level. Our results suggest that mowing wound weaken the positive effects of N deposition on the quantity but not the quality of forage yield. Changes in plant community composition are important in driving the qualitative responses of yield to N deposition.
Highlights
Grasslands play a key role in animal husbandry (O’Mara 2012; Luescher et al 2014), which are essential for meat and milk production (Sanderson et al 2004; Vetter 2005)
Nitrogen addition significantly increased the quantity of community-level forage yield (Fig. 1), mainly due to its positive effects on rhizomatous grass (Fig. 1b)
We found that N addition significantly increased quantitative forage yield and the concentrations of crude fat at the community level
Summary
Grasslands play a key role in animal husbandry (O’Mara 2012; Luescher et al 2014), which are essential for meat and milk production (Sanderson et al 2004; Vetter 2005). N inputs could increase forage yield by 30–50% in diverse grasslands (Yandjian et al 2011; DeMalach et al 2017) Such quantitative enhancements of forage yield at the community level in response to N deposition are accompanied by specific responses of different plant functional groups due to their large variation in functional traits (Suding et al 2005; Clark et al 2019). Given the substantial variation of forage quality among different plant functional groups (Licitra et al 1997; Duru et al 2008), it is reasonable to expect that N deposition would result in qualitative changes of forage yield by altering plant community composition. It remains an open question, for the relative importance of the intragroup variation (through enhancing forage quality at individual plant functional group level) and the inter-group variation (through changing the community composition) in driving the responses of community-level qualitative changes of forage yield to N deposition
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