Fungal biomass and productivity in standing-decaying leaves of black needlerush (Juncus roemerianus)

Abstract

Ascomycetous fungal decomposers generate the major part of the microbial biomass on and in standing naturally decaying shoots for one (smooth cordgrass, Spartina alterniflora ) of the two major ramet-forming marsh plants of the south-eastern USA. Evidence from frequency of occurrence of sexual structures (ascomata) in the second major ramet-forming marsh plant (black needlerush, Juncus roemerianus ) suggests that fungi are major secondary producers in the needlerush decomposition system also. To test this, samples of needlerush blades at three stages of decay were collected seasonally for three years. Average living-fungal standing crop (as ergosterol) of needlerush blades (254 µ g g – 1 organic mass of decay system) was ~65%of a comparable average for smooth cordgrass, but fungal mass was equally active between the two species (near 30 pmol acetate incorporated into ergosterol µ g – 1 ergosterol h –1 ). Although maximum living-fungal crop for needlerush was found in winter, and in winter and spring for smooth cordgrass, in many other respects, patterns of change in needlerush fungal variables were quite different from those for smooth cordgrass. For example, living-fungal standing crop rose 1.5-fold with decay stage for needlerush, but was constant for cordgrass, perhaps because of lesser mycophagous activity and lesser competition from bacterioplankton associated with tidal flooding in the high-marsh, needlerush zones.

Species‐specific patterns of litter processing by terrestrial isopods (Isopoda: Oniscidea) in high intertidal salt marshes and coastal forests

“…Juncus roemerianus Scheele (Black Needlerush) is a dominant high‐marsh plant in south‐eastern US salt marshes (Wiegert & Freeman 1990). Leaves initially decompose while standing (Newell 2001), but eventually fall to the marsh surface and may form mats that provide habitat for a variety of invertebrates (M. Will & S. C. Pennings, unpublished data). Quercus virginiana Mill.…”

Fungal farming in a snail

“…Simulation of snail grazing demonstrates that the simple mechanical opening of grass tissue is ample engineering to promote invasion and growth of marine fungi (Fig. 2), whose spores are ubiquitous across the marsh surface (22). Seeding and͞or propagule transplantation is therefore not necessary for snail promotion of fungal growth.…”

“…To exclude fungi from plant tissue, we sprayed Spartina stems in fungal removal treatments once every 5 days with the systemic fungicide Daconil Ultrex Turf Care with Chlorothanlo (Zeneca, Wilmington, DE). This fungicide seemed ideal for marsh use, because plants take it up within 2 h and it is an effective killer of terrestrial fungi (G. Gilbert, University of California, Santa Cruz, personal communication) taxonomically similar to the dominant marsh fungi Phaeosphaeria and Mycosphaerella, which are typically Ͼ90% of marsh fungal biomass (22). Preliminary marsh experiments showed that Daconil application does not affect growth of uninjured Spartina plants (see Fig.…”

“…ʈ Mechanisms of growth enhancement are not exactly known, but nutrient transfer from fecal pellets is likely, given that snail pellets are high in nitrogen content and fungal growth on cordgrass is nitrogen-limited (17,18,22,23). Pellets could additionally provide fungal propagule supplements, given that 50% of mycelium in snail feces typically remains undigested and intact (25).…”

“…1) and feed on the senescent material surrounding those wounds [radulations (20)]. Microscopic examination of injured leaves indicates that ascomycete fungi [probably primarily ascomycetes in the genera Phaeosphaeria and Mycosphaerella (22,23)], the snails' preferred food (16,17), are more abundant in snail-maintained wounds than on green leaf surfaces and fungi dominate the microbial communities that invade radulated Spartina leaves [bacteria are typically Ͻ5%, by mass, of the microbial community on decomposing, standing Spartina leaves (22,23)]. Field observations also suggest that snails concentrate deposition of nitrogen-and hyphae-rich fecal pellets (24,25) on fungus-invaded wounds [Littoraria feces are typically dense with fungal hyphae, and snails digest only Ϸ50% of the mycelium they consume (25)].…”