Page 279 - PC2019 Program & Proceedings

PLANT CANADA 2019

P131. Cold spring delays autumn senescence, elongates nutrient uptake period, but reduces
nitrogen storage for winter in Rhynchospora alba (Cyperaceae)
Byne, K.; P. Ryser
Laurentian University

Factors underlying variation in timing of fall senescence are not well known. We investigated how a
delay in the onset of the growth in spring affects senescence and N uptake in autumn, and the resulting
storage of N for the winter in Rhynchospora alba. This species develops each year its sole organ for
storage and overwintering, bulbils, anew. The plants were grown outdoors in a garden experiment with
two treatments, identical except for three weeks difference in start of the growth in May. Above and
below-ground growth and senescence, and N uptake were periodically recorded from August to
November. By August, plants that started their growth later had caught up in total size and N content, but
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had smaller bulbils. Their higher delta C indicated a higher stomatal conductance during growth.
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Senescence of leaves and roots was delayed, resulting in an extended period of N tracer uptake by four
weeks. Nevertheless, after senescence, plants with an early start in the growing season had 55% more N
in their overwintering bulbils, due to an earlier and more efficient remobilization. We conclude that
timing of senescence in R. alba is a result of an interplay between the status of winter storage and cold
temperatures, constrained by a trade-off between prolonged nutrient uptake and efficient remobilization
of nutrients.

Peter Ryser (pryser@laurentian.ca)

P132. Effects of drought, plant hormones and arbuscular mycorrhizal fungi on photosynthesis,
transpiration and plant growth in corn (Zea mays)
Singh, S.; M. Fu
University of British Columbia, Canada

Globally severe drought is projected to occur more frequently, which could negatively impact the growth
and development of plants. Arbuscular mycorrhizal (AM) fungi colonization and plant hormones have
been reported to enhance plant growth and development in some plant species. We investigated the
effects of AM colonization, severe drought, and exogenous applications of abscisic acid (ABA) and
benzylamino purine (BAP) on photosynthesis and transpiration rates, water potential, and fresh weight
corn (Zea mays cv. Honey select). Three-week-old corn seedlings inoculated with or without AM, and
with or without foliar hormone treatments were subjected to three weeks of drought stress. Our results
showed that severe drought significantly lowered photosynthesis and transpiration rates, water potential
and plant growth compared to well-watered treatments. However, AM and exogenous hormone
treatments did not have a significant effect on photosynthesis and transpiration rates, and plant growth. In
addition, AM and exogenous hormone treatments did not reverse the drought-induced decline in plant
growth. The role of AM colonization, and plant hormones in photosynthesis and transpiration, and growth
of corn plants grown under normal and drought-stress conditions will be discussed.

Santokh Singh (santokh.singh@botany.ubc.ca)

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