Sex-specific non-structural carbohydrate variation and hydraulics explain differences in drought resistance of Populus euphratica females and males along an aridity gradient

Non-structural carbohydrates (NSC) are essential for the osmotic
adjustment and maintenance of the hydraulic functioning of trees, but
knowledge about the relationship between NSC dynamics and hydraulics
during drought stress is still limited, especially in dioecious plants. We
investigated photosynthetic carbon assimilation, xylem hydraulics and
related functional traits, and explored whether hydraulics are linked to
NSC dynamics in the leaves and branches of Populus euphratica
females and males along an aridity gradient in the Xinjiang Province,
China. Both sexes of P. euphratica had increased intrinsic water
use efficiency (WUE), percent loss of conductivity (PLC) and xylem
pressure inducing 50% loss of hydraulic conductivity (P50), but decreased
net photosynthetic rate (Pn), sapwood-specific hydraulic conductivity (Ks)
and hydraulic safety margin (leaf mid-day water potential-P50, HSM50)
associated with the reduction in the soil water content. Furthermore,
females and males have different hydraulic strategies related to NSC
dynamics under low soil water content conditions. Males had higher Ks,
wood density (WD), HSM50, Pn, WUE, leaf dry mass per area (LMA) and leaf
soluble sugar levels, and lower branch soluble sugar levels, PLC and P50
values than females under extreme drought conditions, indicating that
males had a more resistant xylem and can maintain water flow and leaf
turgor probably due to the greater availability of soluble sugars to be
used for osmotic adjustments. In addition, females had a lower Ks, WD and
LMA and higher branch soluble sugar levels and PLC, implying that females
were more vulnerable to cavitation and required higher branch soluble
sugar levels for embolism repair under extreme drought conditions.
Synthesis. Due to the spatial sexual segregation across resource
gradients, dioecious plants are more vulnerable to rapid climate change.
The different hydraulic strategies linked to NSC dynamics between females
and males may result in a situation that one sex is more prone to an
increasingly long and intense drought than the other one. This study
improves our predictions for future climate change impacts on dioecious P.
euphratica and provides theoretical knowledge for restoration and
afforestation in P. euphratica forests.