Enhanced interannual precipitation variability increases plant-functional diversity that in turn ameliorates
negative impact on productivity
Contact(s): Laureano A. Gherardi ([email protected]) and Osvaldo E. Sala ([email protected])
Long-term context: Climate change will result in increased precipitation variance due to higher water-holding
capacity of a warmer atmosphere and changes in atmospheric circulation modes. Increase precipitation variability
will occur at intra-annual, inter-annual and decadal scales. Although the importance of extreme events is part of
the public narrative and resulted in a special assessment from the Intergovernmental Panel on Climate Change on
extreme events, impacts of climate variability on ecosystem structure and functioning have received much less
attention than effects of changes in the mean state of climate. Most studies have focused on global warming,
atmospheric CO 2 concentration and drought effects overlooking precipitation variance per se as a driver of
community and ecosystem change. Here, we aim at studying the effect of interannual precipitation variability on
plant-functional diversity and its consequences for the functioning of a grassland ecosystem.
Our contribution to the understanding of
climate change effects on ecosystem
functioning is based on manipulative
experimentation complementing the data
mining and modeling approaches in the
larger LTER project. We experimentally
manipulated interannual precipitation
variance applying sequences of wet and
dry years for seven years. Precipitation
manipulations consisted of five levels of
precipitation: -80%, - 50%, ambient, +50%
and +80% relative to ambient
precipitation. We switched these
treatments every year resulting in 5 levels
of interannual precipitation coefficient of
variation during a six-year period while
keeping mean precipitation virtually
constant (Fig 1).
Fig 1. Growing-season precipitation per treatment, including
five different levels of precipitation manipulation +80%, +50%,
ambient, - 50% and -80% all relative to ambient precipitation
resulting in five levels of interannual precipitation coefficient of
variation. Treatments were switched every year from wet to dry
and dry to wet. Inset legend indicates mean and coefficient of
variation for growing season precipitation for each treatment
received during the six years of the experiment.
Three hypotheses guided our work:
(1) Increased temporal variability in
annual precipitation increases
functional diversity as a result of
nonlinear responses of plantfunctional types to precipitation.
(2) Enhanced functional diversity resulting from high precipitation variability increases ecosystem
productivity despite direct effects of precipitation.
(3) Increased functional diversity due to high precipitation variability enhances ecosystem stability.
Our results showed that increased coefficient of variation of interannual precipitation had a positive effect on
plant diversity (Fig 2a) (Gherardi and Sala 2015a). Changes in functional diversity resulted from changes in
functional evenness (Fig 2b) that were in turn explained by the increase in the relative abundance of rare plantfunctional types in high precipitation variance treatments (Fig 3).
Our results supported our second hypothesis showing that increased interannual precipitation variability resulted
in increased diversity, which in turn ameliorated the negative impact of enhanced precipitation variability on
ecosystem ANPP (Fig 4) (Gherardi and Sala 2015b). This positive biodiversity effect on ecosystem functioning may
be explained through species complementarity. Our data show temporal complementarity among plant-functional
types taking advantage of extreme years and dominant species outperforming other plant types during years with
modal conditions.
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Our results supported our third hypothesis showing that increased functional diversity increases ANPP stability.
The coefficient of variation of perennial grass ANPP matches the precipitation coefficient of variation (Fig 5).
Although ecosystem stability showed a trend in the same direction as that of dominant species, community ANPP
variation increased at one-half the perennial grass rate as precipitation variability increased. Therefore, the
response of the dominant plant-functional type was not fully driving ecosystem stability. On the other hand, the
ANPP coefficient of variation of rare plant-functional types decreased or did not change with increasing
precipitation variability. Increased relative abundance of rare-plant types led to a portfolio effect determining the
coefficient of variation of total ANPP to be much lower than expected based on dominant functional-type
response.
Relationship with the LTER VI proposal: This objective falls under Obj. 2-4 Plant-functional type transitions. ANPP
is also one of the LTER Core Topics.
Literature Cited:
Gherardi, L. A. and O. E. Sala. 2015a. Enhanced interannual precipitation variability increases plant functional
diversity that in turn ameliorates negative impact on productivity. Ecology Letters doi: 10.1111/ele.12523.
Gherardi, L. A. and O. E. Sala. 2015b. Enhanced precipitation variability decreases grass- and increases shrubproductivity. Proceedings of the National Academy of Sciences doi:10.1073/pnas.1506433112.
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