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Abstract Grasslands are expected to experience droughts of unprecedented frequency and magnitude in the future. Characterizing grassland responses and recovery from drought is therefore critical to predict the vulnerability of grassland ecosystems to climate change. Most previous studies have focused on ecosystem responses during drought while investigations of post‐drought recovery are rare. Few studies have used functional traits, and in particular bud or clonal traits, to explore the mechanisms underlying grassland responses to and recovery from drought.To address this issue, we experimentally imposed a four‐year drought in a C3‐dominated grassland in northeastern China and monitored recovery for 3 years post‐drought. We investigated the immediate and legacy effects of drought on total above‐ground net primary productivity (ANPP), ANPP of functional groups (rhizomatous grasses, bunch grasses and forbs), and how the legacy effects were driven by plant species diversity, clonal traits and vegetative traits.We found that drought progressively reduced total ANPP over the 4‐year period. The reductions in total ANPP in the first and third drought years were caused by the decrease in ANPP of bunch grasses only, while that of the second year was caused by declines in ANPP of bunch grasses and forbs, and the fourth year decline was linked to all three functional groups. The post‐drought recovery of ANPP, which occurred despite the continued loss of plant species diversity, was mainly driven by rapid recovery of rhizomatous and bunch grasses, which compensated for the slow response by forbs. The rapid post‐drought recovery of these grasses can be attributed to their relatively large, intact bud and shoot densities post‐drought, as well as the recovery of plant height and specific leaf area. The rapid recovery of grasses possibly restricted the growth and distribution of forbs, resulting in reduced forb ANPP and, consequently, lower species diversity during the recovery period.Synthesis. These results highlight the potential for positive legacy effects of drought on ANPP as well as the important and complementary roles of plant reproductive and vegetative traits in mediating ecosystem recovery from drought in a C3‐dominated grassland.
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Resolving the Dust Bowl paradox of grassland responses to extreme drought
During the 1930s Dust Bowl drought in the central United States, species with the C3photosynthetic pathway expanded throughout C4-dominated grasslands. This widespread increase in C3grasses during a decade of low rainfall and high temperatures is inconsistent with well-known traits of C3vs. C4pathways. Indeed, water use efficiency is generally lower, and photosynthesis is more sensitive to high temperatures in C3than C4species, consistent with the predominant distribution of C3grasslands in cooler environments and at higher latitudes globally. We experimentally imposed extreme drought for 4 y in mixed C3/C4grasslands in Kansas and Wyoming and, similar to Dust Bowl observations, also documented three- to fivefold increases in C3/C4biomass ratios. To explain these paradoxical responses, we first analyzed long-term climate records to show that under nominal conditions in the central United States, C4grasses dominate where precipitation and air temperature are strongly related (warmest months are wettest months). In contrast, C3grasses flourish where precipitation inputs are less strongly coupled to warm temperatures. We then show that during extreme drought years, precipitation–temperature relationships weaken, and the proportion of precipitation falling during cooler months increases. This shift in precipitation seasonality provides a mechanism for C3grasses to respond positively to multiyear drought, resolving the Dust Bowl paradox. Grasslands are globally important biomes and increasingly vulnerable to direct effects of climate extremes. Our findings highlight how extreme drought can indirectly alter precipitation seasonality and shift ecosystem phenology, affecting function in ways not predictable from key traits of C3and C4species.
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- Award ID(s):
- 1655499
- PAR ID:
- 10186357
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 36
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 22249-22255
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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