Evidence for a fungal loop in shrublands

Abstract

Dryland communities may mitigate the loss of limited resources by exchanging nutrients through subterranean fungal connections, termed fungal loops. In arid grasslands, fungal loops can influence community composition and primary productivity, yet their ecological significance across dryland systems remains unexplored. We investigated the functional role of fungal loops in nutrient translocation in a North American shrubland ecosystem. We traced the movement of 15N from moss‐dominated biocrusts to the dominant xeric shrub Larrea tridentata, and the movement of 13C from L. tridentata to biocrusts in plots established in situ in the Sonoran Desert. Measurements occurred at three time points spanning 1 week following a simulated 2.5 mm rainfall event, and at distances up to 1 m from tracer application. We also used ITS sequencing to investigate changes in fungal community composition in soils over the 1‐week period. We discovered movement of 15N from biocrusts into L. tridentata foliage as well as 15N movement to other spatially isolated moss‐dominated biocrust patches, yet this movement did not occur until 4–6 days post‐rainfall, when significantly higher δ15N was observed in L. tridentata and biocrusts compared to previous days. We did not observe consistent patterns of 13C movement from L. tridentata into neighbouring shrubs or biocrusts, suggesting differential environmental drivers for carbon movement in this system. Fungal communities exhibited a decrease in alpha diversity on the last day of the study, indicative of a delayed community response to rainfall concomitant with nutrient translocation. Fungal endophyte orders Pleosporales and Pezizales dominated all plot soils, and order Pleosporales was significantly more abundant in 15N enriched plots, suggesting that dark septate endophytic fungi were involved in nitrogen translocation. The delay in nutrient translocation may reflect a rainfall‐triggered rebuilding of mycelial networks between community members following drought. Synthesis. Our results point to fungal‐mediated nutrient exchange pathways in a previously uninvestigated vegetation type, shrublands, where nutrients are translocated between moss‐dominated biocrusts and nearby shrubs. We provide the first evidence that nutrient transfer may be delayed up to 6 days following rainfall, consistent with pulse‐dynamic responses in drylands, and that moss‐dominated biocrusts play a role in fungal loops.

Temporal Effects of Monsoon Rainfall Pulses on Plant Available Nitrogen in a Chihuahuan Desert Grassland

“…Dryland ecosystems are characterized by islands of fertility, where SOM, microbial ecoenzymatic activities, and nutrient availability are higher under and adjacent to plants compared to areas of unvegetated soil (Kieft et al., 1998; Ladwig et al., 2015; Schlesinger et al., 1990; Stursova et al., 2006). There is also some evidence that fungal hyphae can transport nitrogen fixed by biological soil crusts to plants located up to 1 m away (Carvajal Janke & Coe, 2021; Green et al., 2008). Prior to the summer monsoon we installed three soil collars (25.4 cm wide and 15 cm deep) per plot, each positioned around a randomly selected tussock of black grama to prevent plant roots and soil microbes from acquiring outside resources as well as to limit potential nitrogen losses through overland flow.…”

Rapid foliar uptake of inorganic and amino acid nitrogen in three dryland plant species

“…(3) Do plant species differ in the rate or form of short-term N uptake? We expected that individuals of all three species in this study would ultimately transport similar amounts of 15 N to leaves within 12 -48 h based on evidence from prior dryland 15 N tracer experiments that reported recovery of NH4 + , NO3 -, and amino acid-N forms in leaves of similar perennial grass and woody shrub/subshrub species < 72 h following application of water and N (Aanderud and Bledsoe 2009;BassiriRad et al 1999;Carvajal Janke and Coe 2021;Ivans et al 2003;James et al 2008;Zhuang et al 2015;Zhuang et al 2020). Finally, much of the key background literature comparing inorganic and organic N uptake among different plant functional types comes from studies performed in non-dryland ecosystems such as temperate grasslands (Bardgett et al 2003;Näsholm et al 2000;Näsholm et al 2009;Weigelt et al 2003;Wilkinson et al 2015) and tundra ecosystems (Ashton et al 2008;Ashton et al 2010;McKane et al 2002;Miller and Bowman 2003;Näsholm et al 2009).…”

Ecology and responses to climate change of biocrust-forming mosses in drylands

“…Unfortunately, there is still little known about the role of cyanosymbiosis in the nutrient status of moss-dominated biocrusts and how it interacts with soil N availability ( Coe et al , 2014 ). A recent study suggests that all these ways of acquiring N allow mosses to have enough N reserves even to transfer some of them to vascular plants through fungal loops without compromising their survival ( Carvajal Janke and Coe, 2021 ). Mosses can also enrich the soil through direct N leakage during the cyanobacterial N fixation, the decomposition of moss tissues ( Evans and Lange, 2001 ), or the phenomenon of ‘bryotic pulses’ ( Slate et al , 2019 ; Fig.…”