Sugar export limits size of conifer needles

Abstract

Plant leaf size varies by more than three orders of magnitude, from a few millimeters to over one meter. Conifer leaves, however, are relatively short and the majority of needles are no longer than 6 cm. The reason for the strong confinement of the trait-space is unknown. We show that sugars produced near the tip of long needles cannot be exported efficiently, because the pressure required to drive vascular flow would exceed the greatest available pressure (the osmotic pressure). This basic constraint leads to the formation of an inactive region of stagnant fluid near the needle tip, which does not contribute to sugar flow. Remarkably, we find that the size of the active part does not scale with needle length. We predict a single maximum needle size of 5 cm, in accord with data from 519 conifer species. This could help rationalize the recent observation that conifers have significantly smaller leaves than angiosperms, and provide a biophysical explanation for this intriguing difference between the two largest groups of plants.

Within‐crown plasticity in leaf traits among the tallest conifers

“…). The longest efficient length for P. menziesii leaves, before phloem would stagnate at the tip due to insufficient osmotic drive, is ~2.5 cm (based on mean phloem radius across trees 1–5, see Rademaker et al., ), which is similar to our observed maximum (2.2 cm) but considerably longer than our observed mean (1.8 cm) and minimum (1.3 cm) leaf lengths. In tree 6 from Washington, 86% of the variation in leaf length is explained by δ 13 C, a variable associated with the impacts of chronic water stress on stomatal and mesophyll CO 2 conductance (Table ; Hultine and Marshall, ).…”

“…Turgor in living cells is limited under conditions of low xylem Ψ, which in turn limits leaf length not only in trees, but also in other plants facing chronic water stress, forcing leaves to expand during nightly Ψ peaks (Boyer, ; Van Volkenburgh and Boyer, ; Boyer and Silk, ). The minimum phloem loading required for osmotically driven export of photosynthate over a given distance sets limits on maximum efficient leaf length in conifers, where a greater radius of phloem tissue can sustain transport through longer leaves without stagnation at the leaf tip (Rademaker et al., ). Nonetheless, ecological constraints may result in a realized leaf length below the maximum predicted given available phloem.…”

Wet-tip versus dry-tip regimes of osmotically driven fluid flow

“…Osmotically driven fluid transport has been studied in a series of mathematical models sprouting from the pioneering work by Kedem and Katchalsky 8 into describing simple cyst expansion 5,9–11 , phloem flow in plants 12–20 and fluid secretion in mammalian glands 4,21–23 . Recently, Rademaker et al .…”

Carbon Derived from Pine Needles as a Na+‐Storage Electrode Material in Dual‐Ion Batteries

“…The average leaf length of conifer is 2.3 cm with 75% of leaves shorter than 6 cm. The radius of the conduits that transport the sugar and water in the phloem cells is below 3 μm . Therefore, the vessels in the pine needle carbon (PNC) may help to construct pores that are accessible for Na + storage and transportation.…”

“…The radius of the conduits that transport the sugar and water in the phloem cells is below 3 μm. [46] Therefore, the vessels in the pine needle carbon (PNC) may help to construct pores that are accessible for Na + storage and transportation. Moreover, pine needles are so soft that the breaking machines used in the kitchen can grind them into a powder, which reduces fabricating costs.…”