3.4. Driving factors of the ecosystem nitrogen and phosphorus
stock
The structural equation model (SEM) revealed that tree biomass (A.
nepalensis , R. arboreum , Q. leucotrichophora , and
associated species), understory (herbaceous, shrub), litter), and soil
(including microbial biomass) was the variable that influenced ecosystem
N and P stock (Figure 8). The SEM explained 92.1 % and 92.8 % of the
variation in ecosystem N and P stocks, respectively. A.
nepalensis biomass N stock, soil TN stock, and litter N stock had a
significant (P < 0.05) direct positive influence on ecosystem
nitrogen stocks, in which standardized effects were 0.161, 0.619, and
0.601, respectively. Meanwhile, Q. leucotrichophora biomass N
stock and associated species biomass N stock had a significant (P
< 0.05) direct negative influence on ecosystem N stock, in
which standardized effects were -0.142 and -0.112. Meanwhile, R.
arboreum biomass N stock, MBN stock, and understory (herbaceous, shrub
biomass) N stock had no direct influence on ecosystem N stock.
Similarly, A. nepalensis biomass P stock, Q.
leucotrichophora biomass P stock, associated species biomass P stock,
MBP stock, and soil TP stock had a direct positive influence on
ecosystem phosphorus stocks in which standardized effects were 0.497,
0.439, 0.112, 0.223 and 0.394, respectively. Meanwhile, R.
arboreum , Q. leucotrichophora, and associated species biomass N
and P stock had no direct effects on soil, microbial biomass, and
understory (herbaceous, shrub biomass) N and P stock. Furthermore,R. arboreum , and associated species biomass N and P stock had a
significant (P < 0.05) direct positive influence on litter
biomass N and P stock. The total influence of each driving factor on the
ecosystem N stock in ranked in the following order: 0.61 (soil TN stock)
> 0.601 (litter biomass N stock) > 0.161
(A. nepalensis biomass N stock) > -0.142 (Q.
leucotrichophora biomass N stock) > -0.112 (associated
species biomass N stock). The standardized total effect of each driving
factor on the ecosystem P stock in ranked in the following order: 0.497
(A. nepalensis biomass P stock) > 0.439 (Q.
leucotrichophora biomass P stock) > 0.394 (soil TP stock)
> 0.223 (MBP stock) > 0.112 (associated
species biomass P stock) > -0.132 (understory biomass P
stock). The results of standardized total influence revealed thatA. nepalensis biomass and soil N and P stocks were the most
important direct and indirect driving factors of ecosystem N and P
stocks (Figure 8).