The$leaf$hydraulic$bo0leneck$$ in$Californian$chaparral$and$$ coastal$sage$scrub$ Alex%Pivovaroff% University%of%California%Riverside% Riverside,%California,%USA%

Plant%Hydraulic%Conductance% F K= ΔΨ •  Measures%water%flow% through%a%plant% •  Kplant%can%be%broken% down%into:% %%Kroot,%Kstem,%and%Kleaf% •  Each%organ%has%its%own% resistance% Tyree%&%Ewers%(1991)%New%Phytol.%

Plant%Hydraulic%Conductance%

Tyree%&%Ewers%(1991)%New%Phytol.%

Plant%Hydraulic%Conductance%

Tyree%&%Ewers%(1991)%New%Phytol.%

Hydraulic%SegmentaNon% Zimmermann%1983%

Tyree%&%Ewers%(1991)%New%Phytol.%

Hydraulic%SegmentaNon% Zimmermann%1983%

Tyree%&%Ewers%(1991)%New%Phytol.%

Hydraulic%SegmentaNon% Zimmermann%1983%

Leaves%=%% hydraulic%boTleneck;% “safety%valve”%

Tyree%&%Ewers%(1991)%New%Phytol.%

Hydraulic%SegmentaNon% Zimmermann%1983%

Leaves%=%% hydraulic%boTleneck;% “safety%valve”%

Distal%organs%are%% more%expendable% Tyree%&%Ewers%(1991)%New%Phytol.%

Hydraulic%SegmentaNon% Zimmermann%1983%

Leaves%=%% hydraulic%boTleneck;% “safety%valve”%

Distal%organs%are%% more%expendable% Tyree%&%Ewers%(1991)%New%Phytol.%

QuesNon%&%Hypotheses% •  Aim:%Test%the%relaNonship%between%water% movement%in%stems%and%leaves%in%a%droughtZ prone%environment,%in%the%context%of%HSH% •  H1:%Kleaf%would%be%negaNvely%correlated%with%Ks% •  H2:%Species%with%a%lower%hydraulic%safety% margin%would%have%lower%Kleaf%

MediterraneanZtype%Climate%

•  Only$5$regions$in$the$ •  20%$plant$biodiversity$ •  Dry,$warm$summers$&$ –  Biodiversity$hotspot$&$ wet$cool$winters$=$ conservaJon$priority$ annual$seasonal$drought$

MediterraneanZtype%Climate%

•  Only$5$regions$in$the$ •  20%$plant$biodiversity$ •  Dry,$warm$summers$&$ –  Biodiversity$hotspot$&$ wet$cool$winters$=$ conservaJon$priority$ annual$seasonal$drought$

•  36%cm%MAP% •  California%chaparral%and% coastal%sage%scrub%(n=17)%

•  36%cm%MAP% •  California%chaparral%and% coastal%sage%scrub%(n=17)%

Methods% •  •  •  •  • 

Water%potenNals% Kleaf%with%EvaporaNve%Flux%Method% Ks%% Hydraulic%safety%margin%(Ψstem%–%Ψ50)% Other%traits,%including%LA:SA,%LMA,%wood%density%

CoZoccurring%species%experience%a%wide%range%of% Nssue%water%status%on%an%annual%basis%

Pivovaroff%et%al.%New%Phytologist,%in%press.%

PrecipitaNon% Nov%–%Feb:%15.1%cm% June%–%Sept:%0.5%cm%

Species%with%!%Ks%have%"%Kleaf%=%hydraulic%segmentaNon%

"  Kleaf%=%hydraulic%boTleneck% May%place%limit%on%water%loss%during%maximum%gas%exchange%% Pivovaroff%et%al.%New%Phytologist,%in%press.%

Species%with%"%operaNng%safety%margin%have%"%Kleaf%%

Leaves%may%funcNon%as%“safety%valves”% Pivovaroff%et%al.%New%Phytologist,%in%press.%

Species%with%!%Kleaf%have%"%LA:SA%%

More%leaf%area%to%support%with%a%given%sapwood%area%=%% "%individual%Kleaf% Pivovaroff%et%al.%New%Phytologist,%in%press.%

Species%with%!%Ks%have%!%LA:SA%%

•  Shoot%hydraulic%architecture% •  Balance%of%transpiraNonal%demand% Pivovaroff%et%al.%New%Phytologist,%in%press.%

Species%with%!%LMA%have%!%wood%density%

!%LMA%&%wood%density%=%Greater%investment%in%structure%of%stems%and%leaves% "%LMA%&%wood%density=%Maximize%resource%acquisiNon% Pivovaroff%et%al.%New%Phytologist,%in%press.%

Summary% Traits$ Ψleaf%

RelaJonship$ Wide%range% Ψleaf%%more%neg.%than%Ψstem% Kleaf%&%Ks% −% Kleaf%&%hydraulic%safety%margin% +% Kleaf%&%LA:SA% −% Ks%&%LA:SA% +% LMA%&%wood%density% +%

THANK$YOU$ Acknowledgements% %%%Louis%SanNago%&% %%%Lawren%Sack% Field%work:% –  Larissa%Yates% –  Eric%Pivovaroff% –  Mark%De%Guzman% –  Sarah%Pasquini%

Funding%&%LogisNcs% –  NSF%GRFP% –  Pablo%Bryant%@% SMER% Lab%work:% –  Yong%Shen% –  Max%Brodie% –  Angelica%Nunez%