Stomatal conductance limited the CO2 response of grassland in the last century

Table 1 Summary characteristics of selected treatments from the Park Grass Experiment

Treatment	Plot No. (subplot)	P/K input (g m⁻² year⁻¹)	N input (g m⁻² year⁻¹)	Functional group composition (%-G/%-F/%-L)	Species richness	pH	Total herbage yield (g m⁻²)	NNI	PNI	N to P	Nutrient limitation
No nitrogen
CONTROL.L	2/2(a), 3(a)	0/0	0	Dicot-rich (48/40/12)	43	7.2	224	0.4	0.6	11.3	Co-limitation
CONTROL.U	3(d)	0/0	0	Dicot-rich (63/33/4)	41	5.2	149	0.4	0.5	12.9	Co-limitation
PK.L	7/2(a)	3.5/22.5	0	Dicot-rich (54/21/25)	29	6.8	501	0.5	1.2	4.9	N-limitation
Sodium nitrate
N*1.L	17(a)	0/0	4.8	Dicot-rich (62/36/2)	36	7.1	244	0.4	0.4	14.9	Co-limitation
N*1PK.L	16(a)	3.5/22.5	4.8	Dicot-rich (68/20/12)	26	6.7	496	0.5	1.2	4.8	N-limitation
N*2.PK.L	14/2(a)	3.5/22.5	9.6	Grass-rich (80/17/3)	31	6.9	487	0.5	1.2	5.2	Co-limitation
Ammonium sulfate
N1.L	1(b)	0/0	4.8	Dicot-rich (66/33/1)	30	6.2	208	0.5	0.5	15.6	Co-limitation
N1.U	1(d)	0/0	4.8	Grass-rich (97/3/0)	6	4.1	100	0.5	0.4	20.1	Co-limitation
N2PK.L	9/2(b)	3.5/22.5	9.6	Grass-rich (90/7/3)	19	6.3	545	0.5	1.1	5.3	N-limitation
N2PK.U	9/2(d)	3.5/22.5	9.6	Grass-rich (99/1/0)	5	3.7	355	0.5	0.8	7.9	N-limitation
N3PK.L	11/1(b)	3.5/22.5	14.4	Grass-rich (91/9/0)	16	6.2	560	0.6	1.1	6.0	N-limitation
N3PK.U	11/1(d)	3.5/22.5	14.4	Grass-rich (100/0/0)	2	3.6	374	0.6	0.7	9.9	Co-limitation

Lime application is represented with the letters “L” (limed) or “U” (unlimed) in the treatment name. Ground chalk was applied as necessary to maintain soil at pH 7 or 6 on sub-plots “a” and “b”, respectively; P amount applied to the plots was decreased from 3.5 to 1.7 g P m⁻² year⁻¹ since 2017; functional group composition was estimated from botanical separation data between 1915 and 1976, 1991 and 2000, and 2010 and 2012 (e-RA); species richness data report on a 10-year period from 1991 to 2000; total herbage yields and nitrogen nutrition index (NNI) data are given for the last 15 years of the study (2004–2018); phosphorus nutrition index (PNI) and N to P ratios are presented for a 10-year period (2000–2009); soil pH corresponds to samples taken in 1995; NNI was calculated as in Lemaire et al. [28], with parameters for C3 temperate grassland if yield > 100 g m⁻² and N_crit = 4.8%-N in dry matter if yield < 100 g m⁻². PNI was calculated according to Liebisch et al. [29]. Nutrient limitation was defined based on N to P ratios according to Güsewell [30], with N to P ratios < 10 and > 20 corresponding to N- and P-limitation and N to P ratios between 10 and 20 indicating N and P co-limitation

ISSN: 1741-7007