Abstract
The ongoing changes in the global climate expose the world�s ecosystems not only to
increasing CO2 concentrations and temperatures but also to altered precipitation (P)
regimes. Using four well-established process-based ecosystem models (LPJ, DayCent,
ORCHIDEE, TECO), we explored effects of potential P changes on water limitation and
net primary production (NPP) in seven terrestrial ecosystems with distinctive vegetation
types in different hydroclimatic zones. We found that NPP responses to P changes
differed not only among sites but also within a year at a given site. The magnitudes of
NPP change were basically determined by the degree of ecosystem water limitation,
which was quantified here using the ratio between atmospheric transpirational demand
and soil water supply. Humid sites and/or periods were least responsive to any change in
P as compared with moderately humid or dry sites/periods. We also found that NPP
responded more strongly to doubling or halving of P amount and a seasonal shift in
P occurrence than that to altered P frequency and intensity at constant annual amounts.
The findings were highly robust across the four models especially in terms of the
direction of changes and largely consistent with earlier P manipulation experiments and
modelling results. Overall, this study underscores the widespread importance of P as a
driver of change in ecosystems, although the ultimate response of a particular site will
depend on the detailed nature and seasonal timing of P change.
