Altered Rainfall Patterns, Gas Exchange, and Growth in Grasses and Forbs

Abstract

Although the potential for increased temperature is the primary and best-studied aspect of anthropogenic climate change, altered rainfall patterns, increased storm intensity, and more severe droughts are also predicted in most climate-change scenarios. We altered experimentally the rainfall regime in a native tallgrass prairie in northeastern Kansas and assessed leaf-level physiological activity and plant growth responses for C 3 and C 4 plant species. Our primary objective was to contrast the importance of reductions in rainfall quantity (30% smaller rain events, no change in rainfall pattern) with an altered, more extreme distribution of rainfall (no reduction in total growing-season quantity, 50% increased inter-rainfall dry intervals) for these dominant species from the two main plant functional groups (C 4 grasses, C 3 forbs) present in many grasslands. Leaf water potential (w l), net photosynthetic carbon gain (), specific leaf mass, leaf C : N ratio, growth rate A CO2 for Andropogon gerardii (C 4 grass) and Solidago canadensis (C 3 forb), vegetative and flowering stem densities, and canopy light penetration for grass and forb assemblages were intensively monitored during the 1999 growing season in a long-term rainfall manipulation study at the Konza Prairie Biological Station. Soil water content at 0-30 cm depth was more variable in response to the altered rainfall distribution compared to the reduced-quantity treatment. In S. canadensis, , g s (stomatal conductance), A : Ci (leaf stomatal [CO 2 ]), A CO2 and A : E (estimated leaf transpiration rate) were positively correlated with soil water content, but no relationship was seen for A. gerardii, indicating that even though this dominant grass species has most of its roots in the upper 30 cm of the soil, A. gerardii was buffered physiologically from increased resource variability. There were few significant responses in growth parameters in either grasses or forbs, but canopy light penetration increased with both rainfall treatments. We concluded (1) that the temporal variability in rainfall inputs can have as much impact on soil moisture as simple reductions in rainfall quantities with no change in temporal distribution, (2) that responses of A. gerardii and S. canadensis to altered rainfall distributions were not consistent with common views of soil resource partitioning between shallow-rooted grasses and deep-rooted forbs, and (3) that altered rainfall patterns may have the potential to offset elevated CO 2 impacts on grassland vegetation.

Plant ecophysiological responses to drought, nocturnal warming and variable climate in the Pannonian sand forest-steppe: results of a six-year climate manipulation experiment

“…A deeper root system and clonal integration for C. dactylon (through both stolons and rhizomes), and especially for P. alba (Magyar 1933, Forde 1966, Krízsik & Körmöczi 2000 may provide a greater ability for these species to reach water resources in deeper soil layers and exploit spatial environmental heterogeneity. Consistently, in other studies in arid or semiarid habitats, shallow rooted plants were found to be more constrained by severe drought than deep rooted species (Schwinning et al 2005, Wertin et al 2015), however such difference can be buffered physiologically (Fay et al 2002). In our experiment, the effective source-to-sink assimilate transport of C. dactylon (Forde 1966) and the production of root suckers of P. alba may reduce end-product limitation on photosynthesis.…”

“…This allows making investigations on one or a few, mostly dominant species as representatives of functional types. Different plant functional types, according to their life form, phenology, vegetative growth, rooting pattern or photosynthesis type, often respond differently to natural or experimentally simulated climatic stresses (Mamolos et al 2001, Fay et al 2002, Xia & Wan 2013, Wertin et al 2015, which may result in changes in the dominance structure and composition of the community (Alward et al 1999, Zavaleta et al 2003.…”

“…Parsons et al 1994, Suzuki & Kudo 1997, Hudson et al 2011, Xia & Wan 2013, or Mediterranean woody species , Prieto et al 2009a, Ogaya et al 2011, Liu et al 2016, less attention has been paid to the components of temperate continental or dryland grasslands and shrublands (e.g. Fay et al 2002, Maricle & Adler 2011, Wertin et al 2015, where soil water availability has a major role in plant responses to climate-induced changes.…”

Impacts of warming and changes in precipitation frequency on the regeneration of two Acer species

“…Dreesen et al, 2012;Carón et al, 2014a) and of soil moisture variability (e.g. Fay et al, 2002Fay et al, , 2012 on growth. However, it is possible that the high organic matter content (20%) of the potting soil used in this experiment induced a high water retention capacity, therefore, irrespective of the treatments applied, the seedlings never experienced strong drought stress related to the differences in watering frequency.…”

“…Precipitation frequency may change separately from rainfall totals when the total amount of rainfall over a certain period remains constant, but the number of rainfall events decreases and the precipitation amount in each rainfall event increases. Some of the few available studies on plants have shown that reduced rainfall frequencies can increase productivity, decrease root-to-shoot ratios or affect leaf senescence in grassland species (Fay et al, 2003(Fay et al, , 2002Schneider et al, 2014). Yet, more research is urgently needed to better understand the effect of changes in precipitation frequency on other plant growth parameters, functional groups, and ecosystems (Schneider et al, 2014).…”