Table 3.

Linear regressions of seasonal isotopic composition of plant life forms and mean annual rainfall

Life form	β ln(rainfall)	α	n	R 2	P (R 2)	| t | (β)	P (β),	| t | (α)	P (α)
Annuals
δ15Na
W	−3.19	19.09	16	0.65	<0.001	1.117	0.277	1.368	0.186
D	−1.82	12.21	8	0.77	<0.01
δ13Cb
W	−1.35	−20.17	17	0.55	<0.001	1.273	0.216	4.374	<0.001
D	−0.71	−22.27	10	0.48	<0.05
Forbs
δ15N
W	−4.13	24.00	13	0.63	<0.01	0.153	0.894	0.189	0.852
D	−4.33	25.42	9	0.65	<0.01
δ13C
W	−1.04	−21.73	15	0.41	<0.05	0.581	0.568	5.388	<0.001
D	−0.64	−22.21	9	0.11	0.374
Geophytes
δ15N
W	−2.68	14.78	9	0.56	<0.05
δ13C
W	−1.22	−21.27	12	0.66	<0.01
Dwarf shrubs
δ15N
W	−4.71	26.95	14	0.70	<0.001	1.451	0.162	0.933	0.361
D	−2.98	16.33	10	0.81	<0.001
δ13C
W	−1.08	−21.34	13	0.61	<0.01	0.618	0.543	6.080	<0.001
D	−1.40	−17.76	11	0.49	<0.05
Shrubs and trees
δ15N
W	−4.49	26.03	10	0.78	<0.001	0.799	0.437	1.371	0.189
D	−3.65	22.71	9	0.87	<0.001
δ13C
W	−2.34	−12.28	6	0.92	<0.01	0.610	0.557	2.525	<0.05
D	−2.67	−3.65	7	0.35	0.159

β Slope, α intercept, n number of sites, |t | paired t test comparing wet and dry season regression line β and α; for other abbreviations, see Table 2

P values < 0.05 shown in bold

^aExposed ridge desert sites are excluded from the plant δ¹⁵N analysis

^bDry wash desert sites are excluded from the plant δ¹³C analysis