4.4 Way of degradation influence AGB of grasses
Degradation significantly
decreased AGB of grasses both through direct way and indirect way in
those two types of grasslands. Degradation declined AGB of grasses
directly and through decreased Pn
indirectly in native grasslands, and declined AGB of grasses directly
and through decreased Pn, plant N and P indirectly in active restoration
grasslands. So, plant
Pn
plays important role in determining AGB of grasses both in native
grasslands and active restoration grasslands (Xu et al., 2018; Shen et
al., 2019, 2021). For the direct way, land degeneration decreased
biomass accumulation through restricting plant abundance, declining
plant individual height and plant richness (Xu et al., 2015, 2018; Li et
al., 2018; Guo et al., 2019). For the indirect way, in native
grasslands, land degeneration first decreased plant N concentration
(Elser et al., 2007; Güsewell and Gessner, 2009; Dlamini et al., 2014;
Peńuelas et al., 2015) and thus to decrease photosynthetic activity
(Wright et al., 2004, 2010; Güsewell, 2010; Sundqvist et al., 2014;
Castellano et al., 2016). In active restoration grasslands, the main
reason for the indirect way was that land degradation declined soil
nutrient content such as C, N and P and the gs and Ci of
grasses, the former declined plant N and P content and the later
inhibited plant photosynthetic rate (Sundqvist et al., 2014; Zhou et
al., 2021; Shen et al., 2019).
Conclusions
In conclusion, land degeneration
both the native and active
restoration grasslands significantly
influenced AGB, photosynthetic
capacity and nutrient concentration of grasses. In native grasslands,
the decline of Pn mainly caused by non-stoma limitation, and in active
restoration grasslands, the decline of Pn mainly caused by stoma
limitation. Plant photosynthetic properties and N and P concentration in
active restoration grasslands shows stronger association with its AGB
than native grasslands. Land degradation decreased AGB of grasses
through both direct way and indirect way in those two types of
grassland. Plant N and P are the two key nodes that matter in the way of
declining AGB of grasses and can indicate the of degradation level of
active restoration grasslands.