Abstract
Plants that lack chlorophyll are rare and typically restricted to holoparasites that obtain their carbon, water and mineral resources from a host plant. Although not parasites in the traditional sense, albino foliage, such as the sprouts that sometimes develop from redwood tree trunks, are comparable in function. They occur sporadically, and can reach the size of shrubs and in rare cases, trees. Albino redwoods are interesting because in addition to their reduced carbon resources, the absence of chloroplasts may impede proper stomatal function, and both aspects may have upstream consequences on water transport and xylem quality. We examined the water relations, water transport and xylem anatomical attributes of albino redwoods and show that similar to achlorophyllous and parasitic plants, albino redwoods have notably higher stomatal conductance than green sprouts. Given that stem xylem tracheid size as well as water transport efficiency are nearly equivalent in both albino and green individuals, we attribute the increased leaf water loss in albino sprouts to lower leaf to xylem area ratios, which favour improved hydration relative to green sprouts. The stems of albino redwoods were more vulnerable to drought-induced embolism than green stems, and this was consistent with the albino's weaker tracheids, as characterized by wall thickness to lumen diameter measures. Our results are both complementary and consistent with previous research on achlorophyllous plants, and suggest that the loss of stomatal control and photosynthetic capacity results in substantial vascular and anatomical adjustments.
Highlights
The vast majority of plants are photosynthetic autotrophs, so encounters with achlorophyllous plants are uncommon and typically constrained to parasites
Albino redwood growth is typically small and inconspicuous with only a few woody shoots, but we identified four individuals with woody stems that were sufficiently comparable in size to adjacent green-leaved material
The water relations and hydraulics of albino redwoods those of green trees, so short sprouts and heaps of dead material comprise most of the biomass of even these relatively robust albino plants
Summary
The vast majority of plants are photosynthetic autotrophs, so encounters with achlorophyllous plants are uncommon and typically constrained to parasites. Rarer still are persistently achlorophyllous plants for which the absence of chloroplasts is the result of some genetic or developmental instability rather than an evolved life-history strategy. Such ‘albino’ vegetation is a sink for water and carbon, so its survival is entirely dependent on ready access to these resources. If the albino is attached to a photosynthesizing mother plant, it can survive indefinitely, often for decades. Such is the case with redwood albino Don) Endl., Cupressaceae) sprouts, which scarce, are persistent entities throughout California’s redwood forest range
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