Artificial asymmetric warming reduces nectar yield in a Tibetan alpine species of Asteraceae.
OBJECTIVE
Asymmetric warming is one of the distinguishing features of global climate change, in which winter and night-time temperatures are predicted to increase more than summer and diurnal temperatures. Winter warming weakens vernalization and hence decreases the potential to flower for some perennial herbs, and night warming can reduce carbohydrate concentrations in storage organs. This study therefore hypothesized that asymmetric warming should act to reduce flower number and nectar production per flower in a perennial herb, Saussurea nigrescens, a key nectar plant for pollinators in Tibetan alpine meadows.


METHODS
A long-term (6 years) warming experiment was conducted using open-top chambers placed in a natural meadow and manipulated to achieve asymmetric increases in temperature, as follows: a mean annual increase of 0·7 and 2·7 °C during the growing and non-growing seasons, respectively, combined with an increase of 1·6 and 2·8 °C in the daytime and night-time, respectively, from June to August. Measurements were taken of nectar volume and concentration (sucrose content), and also of leaf non-structural carbohydrate content and plant morphology.


RESULTS
Six years of experimental warming resulted in reductions in nectar volume per floret (64·7 % of control), floret number per capitulum (8·7 %) and capitulum number per plant (32·5 %), whereas nectar concentration remained unchanged. Depletion of leaf non-structural carbohydrates was significantly higher in the warmed than in the ambient condition. Overall plant density was also reduced by warming, which, when combined with reductions in flower development and nectar volumes, led to a reduction of ∼90 % in nectar production per unit area.


CONCLUSIONS
The negative effect of asymmetric warming on nectar yields in S. nigrescens may be explained by a concomitant depletion of leaf non-structural carbohydrates. The results thus highlight a novel aspect of how climate change might affect plant-pollinator interactions and plant reproduction via induction of allocation shifts for plants growing in communities subject to asymmetric warming.
Ecological Security and Protection Key Laboratory of Sichuan Province, Mianyang Normal University, Mianyang 621000, China, Department of Biology, Nanjing University, Nanjing 210093, China.
Junpeng
J
Mu
Ecolab, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China and.
Youhong
Y
Peng
Ecolab, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China and.
Xinqiang
X
Xi
Department of Biology, Nanjing University, Nanjing 210093, China.
Xinwei
X
Wu
Ecolab, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China and.
Guoyong
G
Li
Section of Plant Biology, School of Integrative Plant Biology, Cornell University, Ithaca, NY 14853, USA.
Karl J
KJ
Niklas
Department of Biology, Nanjing University, Nanjing 210093, China, Ecolab, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China and shcs@nju.edu.cn.
Shucun
S
Sun
D000818:Animals; D019659:Asteraceae / Q000254:growth & development / Q000378:metabolism*; D057231:Climate Change; D035264:Flowers / Q000254:growth & development / Q000378:metabolism; D065948:Grassland; D007313:Insecta / Q000502:physiology*; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D057048:Plant Nectar / Q000378:metabolism*; D054817:Pollination; D012098:Reproduction; D012621:Seasons; D013559:Symbiosis; D013696:Temperature
D057048:Plant Nectar
Asteraceae; Global climate change; Saussurea nigrescens; alpine meadow; asymmetric warming; nectar rewards; nectar yield; non-structural carbohydrates; plant–pollinator interactions