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

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

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
  1. 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 Ncrit = 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