Data from: Responses of C4 grasses to aridity reflect species-specific strategies in a semiarid savanna

The C4 Poaceae are a diverse group both in terms of evolutionary lineage
and biochemistry. There is a distinct pattern in the distribution of C4
grass groups with aridity, however, the mechanistic basis for this
distribution is not well understood. Additionally, few studies have
investigated the functional strategies of cooccurring C4 grass species for
dealing with aridity in their natural environments. We explored the
coordination of leaf-level gas exchange, water use, and morphology among
five co-occurring semiarid C4 grasses belonging to divergent clades,
biochemical subtypes, and size classes at three sites along a natural
aridity gradient. More specifically, we measured pre-dawn and midday water
potential, stomatal conductance, water use efficiency, and photosynthesis.
Leaf tissue was also collected for analysis of stable isotopes of carbon
and oxygen as well as for measurement of specific leaf area (SLA) and leaf
width. Species differences in the responsiveness of stomata to changes in
vapor pressure deficit were also assessed. It was expected that NAD-me
species would maintain higher rates of photosynthesis, higher water use
efficiency, and have more responsive stomata than other cooccurring
species based on observed biogeographic patterns and past greenhouse
studies. We found that Aristidoideae and Chloridoideae NAD-me-type grasses
had greater stomatal sensitivity to VPD, consistent with a more isohydric
strategy. However, midgrasses had both greater apparent water access and
water use efficiency, regardless of subtype or lineage. PCK-type had less
responsive stomata and maintained lower levels of photosynthesis with
increasing aridity. There were strong interspecific differences
in 13C, leaf width, and SLA, however these were not significantly
correlated with water use efficiency. C4 grasses in our study did not fit
discretely into functional groups as defined by lineage, biochemistry, or
size class. Interspecific differences, evolutionary legacy, and
biochemical pathways are likely to interact to determine water use and
photosynthetic strategies of these plants. Control of water loss via
highly responsive stomata may form the basis for the dominance of certain
C4 grass groups in arid environments. These findings build on our
understanding of contrasting strategies of C4 grasses for dealing with
aridity in their natural environments.