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Nutrient supply enhanced the increase in intrinsic water‐use efficiency of a temperate seminatural grassland in the last century
Author(s) -
Köhler Iris H.,
Macdonald Andy,
Schnyder Hans
Publication year - 2012
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2012.02781.x
Subject(s) - fertilizer , nutrient , temperate climate , zoology , nitrogen , phosphorus , chemistry , agronomy , water use efficiency , environmental science , botany , biology , irrigation , organic chemistry
Under the increase in atmospheric CO 2 during the last century, variable increases in the intrinsic water‐use efficiency ( W i ), i.e., the ratio between carbon assimilation rate ( A ) and stomatal conductance ( g s ), of C 3 vegetation have been observed. Here, we ask if long‐term nutrient status and especially nitrogen supply have an effect on the CO 2 response of W i in a temperate seminatural C 3 grassland. This analysis draws on the long‐term trends (1915–2009) in W i , derived from carbon isotope analysis, of archived hay and herbage from the Park Grass Experiment at R othamsted ( S outh‐ E ast E ngland). Plant samples came from five fertilizer treatments, each with different annual nitrogen (N; 0, 48 or 96 kg ha −1 ), phosphorus (P; 0 or 35 kg ha −1 ) and potassium (K; 0 or 225 kg ha −1 ) applications, with lime as required to maintain soil pH near 7. Carbon isotope discrimination ( 13 Δ) increased significantly ( P < 0.001) on the Control (0.9‰ per 100 ppm CO 2 increase). This trend differed significantly ( P < 0.01) from those observed on the fertilized treatments ( PK only: 0.4‰ per 100 ppm CO 2 increase, P < 0.001; Low N only, Low N+PK , High N+PK : no significant increase). The 13 Δ trends on fertilized treatments did not differ significantly from each other. However, N status, assessed as N fertilizer supply plus an estimate of biologically fixed N, was negatively related ( r 2 = 0.88; P < 0.02) to the trend for 13 Δ against CO 2 . Other indices of N status exhibited similar relationships. Accordingly, the increase in W i at High N+PK was twice that of the Control (+28% resp. +13% relative to 1915). In addition, the CO 2 responsiveness of 13 Δ was related to the grass content of the plant community. This may have been due to the greater CO 2 responsiveness of g s in grasses relative to forbs. Thus, the greater CO 2 response of grass‐rich fertilized swards may be related to effects of nutrient supply on botanical composition.