4.3. Distribution of N-P stocks in the different ecosystems
Forest stands varied significantly in the distribution of N and P stocks
in different vegetation components and soil layers. The forest
structure, vegetation biomass, and nutrient concentrations determined
the N and P stock in the vegetative components and different soil layers
(Frédéric et al., 2010; Phoenix et al., 2012; Joshi and Garkoti, 2021
b). Present vegetation biomass P (19.19 to 233.91 kg
ha-1) and N (346.77 to 4662.02 kg
ha-1 ) stocks are higher than the values reported
(60.5 kg ha-1 for P and 577 kg ha-1for N) by Zhang et al. (2018). Late succession forest stands have higher
vegetation biomass and nutrient concentrations and greater litter
biomass, which may enhance the forest nutrient dynamics (Joshi &
Garkoti 2021b). The high range of C/P and N/P ratio and the low P stock
in the soil in young stands (AER, ALR, and AYM) may affect the enzymatic
and microbial activities that decompose organic matter, which may, in
turn, limit the microbial activities and forest growth during early
stages of chronosequence (Richardson et al. 2004). The contribution of
soil N and P to the ecosystem N and P stocks ranged from 70.18-48.82 %
and 63.49-74.80 %, respectively, which indicate that soil TN and TP
stocks (including soil microbial biomass stocks) play a key role in
ecosystem N and P stock. Our results reveal the progressive increment in
vegetation and soil nitrogen and phosphorus stock along the forest
chronosequence. The order of the different N and P stocks in our study
sites follows the order: soil > trees > shrubs
> herb > litter (Figure 6). Hence, higher
litter amount, soil nutrients, and soil microbial biomass (e.g., Deiss
et al., 2018) may improve ecosystem N and P stocks. Finally, our
findings indicated that there was an interaction between N and P stocks
in the plant-soil system.