Root trait responses to drought and warming

1.
Plant
species show a broad spectrum of plasticity in their covarying root traits in
response to soil water limitation, ranging from no change to shifts towards
traits that enhance the acquisition of water and nutrients. Knowledge of these
plant root trait correlations and associated trait plasticity under drought is
crucial to sustaining pasture and grassland productivity under future, drier
climates.
2.
Here, we
investigated belowground responses to drought in four C3
and three C4 pasture grasses and whether these explain aboveground
responses during extreme winter and spring drought, and post-drought recovery,
in a well replicated field manipulation experiment. We hypothesised that: 1) C3
and C4 functional groups differ in their belowground trait responses
to drought: C3 species shift their traits in line with a drought
avoidance strategy and C4 species shift towards drought tolerance
strategies; 2) post-drought
recovery is associated with belowground carbon reserves in both functional
groups.
3.
Root traits in C3 species were associated with higher values
for specific root length, nitrogen and soluble sugar concentrations, while
those in C4 species were more associated with higher mean diameter,
tissue density and starch concentrations. During drought, plasticity in root
traits in both C3 and C4 functional groups increased
values for specific root length, root soluble sugars, root nitrogen, and
reduced values for root tissue density, which we interpret as a drought
avoidance strategy. Aboveground productivity during drought was related
positively with root soluble sugars, crown nitrogen concentrations and
negatively with root tissue density and crown soluble sugars, and post-drought
recovery was correlated positively with soluble sugars in roots and crowns.

4.
These findings highlight the importance of understanding links between
root trait plasticity and plant productivity during drought and post-drought
recovery for predicting plant species’ responses to changes in a future
climate.