Comparison of the role of the foliar sheath in nutrient (ammonium and phosphate) acquisition by the seagrass Thalassia hemprichii (Ehrenb.) Aschers. at two different sites on tropical Hainan Island, China

Abstract

Comparison of the role of the foliar sheath in nutrient (ammonium and phosphate) acquisition by the seagrass Thalassia hemprichii (Ehrenb.) Aschers. at two different sites on tropical Hainan Abstract Generally, the foliar sheaths of seagrass contribute a large biomass to the dry weight of plants, and are found to be above-sediment biomass or, sometimes, below-sediment biomass. However, the role of foliar sheaths of seagrass in nutrient uptake has not yet been established. Thus, this study was performed to test whether the growth form of foliar sheaths affects the nutrient uptake properties of the seagrass. Two separate sets of morphotypes of the seagrass Thalassia hemprichii were collected from two different tropical meadows in coastal Hainan Island, China in the South China Sea. Ammonium (NH 4 ? ) and phosphate (P i ) uptake by solely blades and roots (experiment I), and above and belowsediment tissues (experiment II) of the two sets of specimens were examined in partitioned chambers using laboratory incubations. Curve profiles of the blade and root saturation uptake kinetics were shown to be similar for the two morphotypes of T. hemprichii. However, the above and below-sediment tissues uptake kinetics had different characteristics between the two morphotypes. For plants with above-sediment foliar sheaths, uptake by the above-sediment tissues contributed an important part of the whole plants' nutrient acquisition. In contrast, for plants with below-sediment foliar sheaths, the contribution of nutrient uptake by above-sediment foliar blade tissues seemed almost negligible. Therefore, the results demonstrated that foliar sheaths of the tropical seagrass T. hemprichii were able to absorb NH 4 ? and P i . Especially interesting is that the capacity for uptake by robust foliar sheaths growing beneath the sediment was remarkable (we termed this the Zhang-Huang-Thorhaug effect). The role of sheaths in nutrient acquisition found in this study is critical in elucidating seagrass nutrient uptake strategies.

Interaction between ammonium and phosphate uptake rates in the seagrass Zostera noltii

“…Although saturation kinetics have been reported for foliar phosphate uptake in seagrasses (Pérez-Lloréns & Niell 1995, Stapel et al 1996, Zhang et al 2011 Gras et al 2003). The observed disparity in Zostera noltii kinetics between our study (linear), and those of Pérez-Lloréns & Niell (1995) (saturation) for the same range of concentrations, could be caused by differences in the nutritional history of the plants (e.g.…”

Nitrogen enrichment decreases seagrass contributions to refractory organic matter pools

“…By contrast, amino acids in sheath and roots did not show significant correlations with nitrogen load in this study. Generally, nitrogen assimilation rate in seagrass sheath was low (Zhang et al 2011) and a large part of nitrogen absorbed by roots is allocated to leaves, mainly through radial transport (Nayar et al 2018), which may explain why amino acids in sheaths and roots were not significantly related to nitrogen load. Soluble sugars, such as glucose, fructose, sucrose, and fructan are dominant storage labile carbohydrates and metabolic substrates that response to environmental stress (Alcoverro et al 1999).…”

“…In contrast, the rhizome labile OM and cellulose‐associated OM had a maximum at 2.12–2.19% leaf nitrogen content, followed by a minimum (2.77~2.90% leaf nitrogen content) before increasing again. The sheath, which has vascular bundles for assimilates transport and functions in ammonia absorption (Kuo and Cambridge 1978; Zhang et al 2011), may initially increase its labile OM content with increasing nitrogen load. However, with further increases in nitrogen load, labile OM of the sheath may decrease due to reduced whole‐plant carbon reserves.…”

Home for Marine Species: Seagrass Leaves as Vital Spawning Grounds and Food Source

“…For instance, herrings on the pacific coast of the United States deposit their eggs on the blades of Z. marina (Hook et al, 1988). Meanwhile, leaf sheaths of seagrasses contribute substantially to biomass (Manzanera et al, 1998), and play a pivotal role in nutrient acquisition (Zhang et al, 2011). For land plants such as wheat, insect eggs are always oviposited on the leaf blades rather than the leaf sheath, which could be related to the distribution of stimulatory chemicals on plant surfaces (Kanno and Harris, 2000).…”