C:N:P stoichiometry and nutrient limitation of the soil microbial biomass in a grazed grassland site under experimental P limitation or excess

Table 3 Regression model results for microbial nutrient limitation

Explanatory variable	Estimate	Std. Error	T value	P value
C-limitation
(Intercept)	1.898	0.184	10.33	<0.0001***
C:P_soil	−0.392	0.074	−5.27	<0.0001***
N:P_mic	1.088	0.30	3.63	0.0011**
C:P_soil × C_mic:DOC	0.021	0.005	4.0	0.0004***
N:P_mic × C_mic:DOC	−0.092	0.023	−4.03	0.0004***
CP-limitation
(Intercept)	0.622	0.071	8.74	<0.0001***
CN_lmt × N:P_mic × C:N_mic	0.013	0.003	3.79	0.0003***
CN-limitation
(Intercept)	13.239	3.534	3.75	0.0009***
N:P_soil	−1.048	0.339	−3.09	0.0047**
C_lmt	−6.749	2.306	−2.93	0.007*
C_lmt × N:P_soil	0.491	0.192	2.565	0.0164*
N:P_mic	−1.748	0.635	−2.753	0.0106*
N:P_mic × C_lmt	0.728	0.304	2.395	0.0241*
N:P_mic × N:P_soil	0.122	0.055	2.223	0.0351*
CNP-limitation
(Intercept)	0.842	0.129	6.56	<0.0001***
CN_lmt	0.573	0.079	7.26	<0.0001***

Minimum adequate model of a multiple regression on microbial C-, CP-, CN- and CNP-limitation as dependent variables respectively. Explanatory variables are as follows: for C-limitation: soil C:P ratio (C:P_soil), microbial N:P ratio (N:P_mic), interactions of these with the ratio of microbial C to dissolved organic C (C_mic:DOC) (r² = 0.671, F_[4,29] = 17.83, P < 0.0001); for CP-limitation: interaction of microbial CN-limitation (CN_lmt) × N_:P_mic × microbial C:N ratio (C_:N_mic) (r² = 0.164, F_[1,67] = 14.3, P = 0.0003); for CN-limitation: soil N:P ratio (N:P_soil), microbial C-limitation (C_lmt), N_:P_mic, and interactions between these variables (r² = 0.78, F_[6,26] = 19.58, P < 0.0001); for CNP-limitation: microbial CN-limitation (CN_lmt) (r² = 0.429, F_[1,68] = 52.8, P < 0.0001).