4.3 The optimum of N addition and its effects on
multifunctionality
Our previous study determined the optimal N addition rate was 90 to 120
kg N ha-1 in MSSL according to the hay yield and N use
efficiency (Huang et al. , 2015). The overall results of this
study strongly support this conclusion again from the quality ofL. chinensis and soil characteristics. Although L.
chinensis may have the maximum seed yield when N addition rate was 150
kg N ha-1 in MSSL(Huang et al. , 2019) and other
higher quality indicators, such as protein contents and
K+/Na+ ratio in this study,
comprehensive analysis indicated that this recommendation was still the
best. The relationship between L.chinensis quality and soil
chemical characteristics also fully illustrated that soil desalination
was consistent with the improvement of soil fertility and plant quality
(Fig.6), and N addition was beneficial to achieve the goal.
In recent years, there has seen a surge of interest in ecosystem
multifunctionality which including ‘ecosystem function
multifunctionality’ and ‘ecosystem service multifunctionality’ (Manninget al. , 2018). As a whole, the EMF has been widely studied in
natural ecosystem (Pfisterer & Schmid, 2002). In this study, the effect
of N addition on the EMF of L. chinensis showed a quadratic curve
relationship, and there was a positive correlation between the EMF and N
addition rates of more than 90 kg N ha-1(Fig.7). When
N addition rate was 120 to 210 kg N ha-1, there were
no significant changes on the EMF among different N treatments,
indicating that the EMF basically reached a steady state. Consequently,
N addition of 90-120 kg N ha-1 was also suitable in
moderately saline-sodic grassland of L. chinensis from the
perspective of the EMF.