02567nas a2200133 4500008004100000245011400041210006900155260001600224520205400240100002402294700001902318700001602337856008002353 2017 eng d00aPrecipitation and environmental constraints on three aspects of flowering in three dominant tallgrass species0 aPrecipitation and environmental constraints on three aspects of  cMar-05-20183 a
  1. Flower production can comprise up to 70% of aboveground primary production in grasslands. Yet we know relatively little about how the environment and timing of rainfall determine flower productivity. Evidence suggests that deficits or additions of rainfall during phenlologically relevant periods (i.e. growth, storage, initiation of flowering, and reproduction) can determine flower production in grasslands.
  2. We used long-term data from the Konza Prairie LTER to test how fire, soil topography, and precipitation amounts during four phenologically relevant periods of the growing season constrain three aspects of flowering in three dominant C4 grass species. Specifically, we examined the probability of flowering, flowering stalk density, and individual flowering stalk biomass for Andropogon gerardii, Schizachyrium scoparium and Sorghastrum nutans.
  3. We found that each of the three species responded to the amount of precipitation during phenologically relevant periods in unique ways. All aspects of A. gerardii flowering were sensitive to precipitation during the flowering stalk elongation period (June 20 – Aug 3). The probability of S. nutans flowering was partly determined by precipitation during the rapid growth phase (April 21 – June 4), whereas flowering stalk density of this species depended on rainfall during flowering stalk elongation (June 20 – Aug 3). In contrast, all aspects of flowering of S. scoparium were relatively independent of rainfall during any period.
  4. Our results demonstrate that three functionally similar, codominant C4 grass species respond differently to phenologically relevant precipitation periods. As a result, drought during any phenological window during the growing season can adversely impact biomass and flowering production of grasslands via species-specific reductions in flowering stalk density and biomass.
1 aLemoine, Nathan, P.1 aDietrich, J.D.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2435.1290402250nas a2200193 4500008004100000245008700041210006900128300001400197490000800211520160600219653004101825653002401866653001801890653002501908653002201933100001901955700001601974856006601990 2016 eng d00aThe effect of timing of growing season drought on flowering of a dominant C4 grass0 aeffect of timing of growing season drought on flowering of a dom a391 - 3990 v1813 a

Timing of precipitation is equally important as amount for determining ecosystem function, especially aboveground net primary productivity (ANPP), in a number of ecosystems. In tallgrass prairie of the Central Plains of North America, grass flowering stalks of dominant C4 grasses, such as Andropogon gerardii, can account for more than 70 % of ANPP, or almost none of it, as the number of flowering stalks produced is highly variable. Although growing season precipitation amount is important for driving variation in flowering stalk production, it remains unknown whether there are critical periods within the growing season in which sufficient rainfall must occur to allow for flowering. The effect of timing of rainfall deficit (drought) on flowering of A. gerardii, was tested by excluding rainfall during three periods within the growing season (starting in mid-April, mid-May and mid-June). Mid-summer drought (starting in mid-June) strongly reduced the flowering rate (e.g., density and biomass) of A. gerardii (e.g., as high as 94 % compared to the control), suggesting flowering is highly sensitive to precipitation at this time. This effect appeared to be related to plant water status at the time of flowering stalk initiation, rather than an indirect consequence of reduced C assimilation. Our results suggest that increased frequency of growing season drought forecast with climate change could reduce sexual reproduction in this dominant grass species, particularly if it coincides with timing of flowering stalk initiation, with important implications for ecosystem functioning.

10aAboveground net primary productivity10aAndropogon gerardii10aEcophysiology10aPrecipitation timing10atallgrass prairie1 aDietrich, J.D.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-016-3579-4