Anatomical traits explain comparative drought response of seedlings from
wet tropical forests
Abstract
Water availability regulates plant community dynamics but the drought
response of seedlings remains poorly known despite their vulnerability,
especially for the Asian tropics. In particular, discerning how
functional traits of seedlings mediate drought response can aid
generalizable predictions of tree responses to global environmental
change. We assessed interspecific variation in drought response
explained by above- and below-ground seedling traits. We conducted a
dry-down experiment in the greenhouse using 16 tree species from the
humid forests of Western Ghats in southern India, chosen to represent
differences in seasonality affiliations–sites of high and low seasonal
drought. We compared seedling survival, growth, and photosynthetic
performance under drought and well-watered conditions, and assessed the
extent to which species responses were explained by seasonality
affiliation and 12 traits of root, stem and leaf. We found that the
species from seasonally dry forest reduced photosynthetic rate in
drought compared to well-watered conditions, but seasonality affiliation
did not explain differences in growth and survival. Performance changes
in drought vs well-watered conditions were best explained by anatomical
traits of xylem, veins and stomata. Species with larger xylem reduced
their growth and photosynthesis to tolerate desiccation. In drought,
species with smaller stomata showed reduced survival even though
photosynthetic activity decreased by a larger extent with larger
stomata. Our study shows that anatomical traits related to xylem and
stomata, directly related to water transport and gas-exchange, played a
more prominent role than commonly used soft traits (e.g., specific leaf
area, wood density) in explaining species response to drought, and may
offer a better proxy for physiological traits related to drought
tolerance of seedlings.