Nutrient supply enhanced the increase in intrinsic water-use efficiency of a temperate seminatural grassland in the last century

Iris H. Köhler, Andy MacDonald, Hans Schnyder

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26 Scopus citations

Abstract

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 Rothamsted (South-East England). 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 ( 13Δ) 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 13Δ 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 13Δ 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 13Δ 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.

Original languageEnglish
Pages (from-to)3367-3376
Number of pages10
JournalGlobal Change Biology
Volume18
Issue number11
DOIs
StatePublished - Nov 2012
Externally publishedYes

Keywords

  • Atmospheric CO
  • C grassland
  • Carbon isotope discrimination ( Δ)
  • Climate change
  • Functional group
  • Hay and herbage
  • Nitrogen
  • Park Grass Experiment
  • Water-use efficiency

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