Tillandsia usneoides (L.) L. (Spanish moss) water storage and leachate characteristics from two maritime oak forest settings

Abstract

Along subtropical and tropical coastlines, Tillandsia usneoides L. (Spanish moss) can heavily cover tree crowns, altering the volume, timing and chemical composition of rainwater reaching soils as throughfall. It is well-established that throughfall amount, dissolved ion and dissolved organic matter (DOM) enrichment, as well as the chemical character of DOM, can influence a host of ecological processes -e.g. litter decomposition and fine root patterns. However, no study known to the authors has holistically examined the water storage capacity, dissolved ions and DOM derived from T. usneoides. This study examined 60 T. usneoides samples from two maritime live oak (Quercus virginiana Mill.) forest settings for water absorbency, maximum water storage capacity, dissolved solutes (Na + , NH 4, dissolved organic carbon, total dissolved nitrogen) and DOM optical properties using ultraviolet-visible and fluorescence spectrophotometry. Thirty samples were collected from each study site: downtown Savannah (SAV) and St. Catherine's Island (SCI), GA, USA. Results show that T. usneoides coverage can increase canopy water storage more markedly (up to 3 mm) than most other epiphyte communities, tree leaf forms or bark structures previously studied. Ion wash off/leaching was greater for N species from SAV samples; yet, base cation macronutrients (Mg 2+ , Ca 2+ ) and sea salts (Na + , Cl À ) were more enriched from SCI samples. Spectrophotometry revealed that T. usneoides leachates contained DOM with low-specific UV absorbance at 254 nm per unit carbon (SUVA 254 ) and high percentage of protein-like fluorescent material compared with literature values for other throughfall and vegetation leachates. In other natural waters, these optical characteristics indicate highly biolabile DOM, suggesting that T. usneoides DOM may also be highly biolabile (i.e. highly relevant to soil microbial functions, like mineralization). Cluster analysis linked fluorescent DOM (FDOM) to ion concentrations of primarily anthropogenic source (F À , SO 4 2À ). Correlation analyses including both sites' data indicated that log-transformed FDOM intensities indirectly relate ( p < 0.01, r = À0.5) -and enrichment of major sea salt ions directly relate (Na + : p < 0.000001, r = 0.83; Cl À : p < 0.000001, r = 0.80) -to T. usneoides maximum water absorbency.

Molecular and Optical Properties of Tree-Derived Dissolved Organic Matter in Throughfall and Stemflow from Live Oaks and Eastern Red Cedar

“…Research into the fluxes and quality of epiphyte DOM release is scarce. With respect to the dominant epiphytes encountered in our study, no data is available for resurrection ferns; while Spanish moss collected from nearby sites in coastal Georgia leached DOM with significantly lower SUVA 254 values (Van Stan et al, 2015) than for the current tree-DOM samples ( Table 1). The Spanish moss samples leached in Van Stan et al (2015) were cleaned of all canopy soil and any decaying or damaged moss.…”

“…With respect to the dominant epiphytes encountered in our study, no data is available for resurrection ferns; while Spanish moss collected from nearby sites in coastal Georgia leached DOM with significantly lower SUVA 254 values (Van Stan et al, 2015) than for the current tree-DOM samples ( Table 1). The Spanish moss samples leached in Van Stan et al (2015) were cleaned of all canopy soil and any decaying or damaged moss. As such, these leachates contained organics derived directly from Spanish moss rather than from the more diverse canopy ecosystem and potential organic sources that the presence of Spanish moss in a tree cultivates.…”

A review and evaluation of forest canopy epiphyte roles in the partitioning and chemical alteration of precipitation

“…Most insights on solute enrichment, depletion and transformation of throughfall and stemflow in epiphyte-laden canopies rely on indirect budgeting estimates from (1) epiphyte-scale in situ chemical spraying (Bates, 1990) or washing with purified water (Rodrigo et al, 1999) and ex situ washing with purified water (Prussia and Killingbeck, 1991;Van Stan et al, 2015); (2) individual tree canopy-scale epiphyte removals (Knops et al, 1991(Knops et al, , 1996 and stemflow monitoring (Awasthi et al, 1995;Levia, 2002;Turner et al, 2007); and (3) forest plot-scale throughfall sampling beneath epiphytes-both without alterations to wet/dry deposition chemistry (Coxson, 1991;Coxson et al, 1992;Cappellato et al, 1993;Cavelier et al, 1997;Godoy et al, 2001;Aubert et al, 2002;Woods et al, 2012;Rosier et al, 2015) and with altered N deposition (Gaige et al, 2007). Only one study each compared throughfall and stemflow collected from immediately above and below target epiphytes (Turner et al, 2007;Woods et al, 2012).…”

“…Of the various canopy surface types, epiphyte cover arguably has received less attention from the precipitation partitioning research community (Levia andFrost, 2003, 2006). This is surprising as epiphytes are ubiquitous across forest types (e.g., Hölscher et al, 2004;Husk et al, 2004;Zotz, 2005;Pypker et al, 2006a;Hauck, 2009;Lundström et al, 2013;Van Stan et al, 2015), and their coverage, patterns, and forms can significantly alter canopy structural attributes, by (1) closing canopy gaps and connecting edges across, and branches within, individual trees ( Fig. 1a), (2) filling voids in branch crotches and tree holes (Fig.…”

“…1a). Solute flux and character of throughfall and stemflow is affected by epiphytes' myriad of nutrient acquisition mechanisms and unique leaching behavior (Schlesinger and Marks, 1977;Carroll, 1980;Reiners and Olson, 1984;Veneklaas, 1990;Coxson, 1991;Farmer et al, 1991;Knops et al, 1991Knops et al, , 1996Prussia and Killingbeck, 1991;Coxson et al, 1992;Cappellato et al, 1993;Godoy et al, 2001;Levia, 2002;Liu et al, 2002;Husk et al, 2004;Oyarzún et al, 2004;Dezzeo and Chacón, 2006;Turner et al, 2007;Zimmermann et al, 2007;Winkler and Zotz, 2009;Hauck, 2010;Van Stan et al, 2015). Net precipitation chemistry is further modified by enhanced dry deposition and aerosol transformation on epiphyte surfaces (Denison, 1979;Coxson, 1991;Knops et al, 1991;Rodrigo et al, 1999;Aubert et al, 2002;Hietz et al, 2002;Gaige et al, 2007;Inselsbacher et al, 2007;Umana and Wanek, 2010;Woods et al, 2012), and the decomposition of bark, leaf and stem litter trapped in epiphytes (Benzing, 1990;Richardson et al, 2000;Hietz et al, 2002;Turner et al, 2007;Woods et al, 2012).…”