Table 1.

Results of Poisson regression models relating the species richness of rare, subdominant and all plant species on grasslands and arable fields to N input. (In all models, confounding effects of environmental variables were corrected for by including the variables latitude and temperature. Comparison of models with all possible subsets of variables have shown that altitude, precipitation and landscape diversity had negligible additional effects on species richness and were therefore not included. Test statistics are t values for variables and deviance ratios for models.)

	estimate	test statistic	p-values
grasslands (n=130)
all species
latitude	−0.0216	−1.46	0.148
temperature	−0.0225	−1.79	0.076
annual nitrogen input	−0.0012	−3.40	<0.001
model		11.19	<0.001
rare species
latitude	−0.0137	−0.74	0.459
temperature	0.0060	0.38	0.701
annual nitrogen input	−0.0015	−3.88	<0.001
model		11.58	<0.001
subdominant species
latitude	−0.0425	−2.55	0.012
temperature	−0.1110	−7.75	<0.001
annual nitrogen input	−0.0009	−2.58	0.011
model		23.20	<.001
arable fields (n=141)
all species
latitude	−0.1015	−6.93	<.001
temperature	−0.1312	−4.82	<.001
annual nitrogen input	−0.0015	−4.77	<.001
model		46.50	<.001
rare species
latitude	−0.1036	−5.45	<.001
temperature	−0.1166	−3.29	0.001
annual nitrogen input	−0.0017	−4.00	<.001
model		38.00	<.001
subdominant species
latitude	−0.1206	−5.69	<.001
temperature	−0.1956	−4.96	<.001
annual nitrogen input	−0.0016	−3.58	<.001
model		19.42	<.001