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DATA SET IDENTIFIER: Factors influencing decomposition of leaves for five plant species at El Verde

PROJECT TITLE : Decomposition Fungal - Plant Interactions (Factors influencing early-stage leaf litter decomposition in tropical forest with emphasis in the role of fungal - plant interactions)

PROJECT DESCRIPTION : Rates of decomposition depend on the particular interactions between producers and decomposer food webs. This interactions are determined by the intrinsic characteristics of both plant and decomposers and are as well influenced by abiotic factors. Field studies were designed to determine the influences of environmental parameters such as climate and microsite variation on the decomposition rates of five tree species from The Luquillo Experimental Forest (LEF). This also allowed us to determine the influence of leaf quality on the decomposer community and whether leaf physical, structural or phylogenetic relationships could be used as predictors of decomposition rates. Microcosms were used to separated the contribution of interactions between dominant plants and fungal species in decomposition rates. The rates of decomposition were determined by mass loss in both the field and microcosms experiments. In the microcosms systems, CO₂ evolution by the decomposition of each of the five leaf litter substrates, by fungal species isolated from that particular leaf or from any of the other litter types, was obtained by using sodium hydroxide traps. There were significant differences in decomposition rates among leaf litter types both in field and microcosms experiments. There was also a significant effect of dry and wet periods in decomposition rates. Leaf litter decomposed faster under their  tree sources than in a common plot. Among the leaf quality parameters, the lignin and nitrogen to lignin ratios were the best predictors of decomposition rates. Non polar elements, water soluble (simple sugars), P and Ca were positively correlated with percent mass loss (PML) while C was negatively correlated with PML. In the microcosms experiments we did not found specificity between fungi and their substrate (where the fungus was isolated), neither to substrates that were chemically, physically or structurally related to the plant were the fungi was originally isolated. Nevertheless, there were differential responses of particular fungi to plant substrates as well as influences of plant species on the fungal decomposers performance. The differential contributions of leaf species to carbon budgets (mass remaining and CO₂ release) may be important in determining management practices for forest and agricultural systems. We found that species such as Manilkara bidentata  may retain carbon in the ecosystem while other species such as Sapium laurocerasus  decomposed rapidly and therefore, released nutrients quickly but with greater carbon losses. The absence of tight links between plants and fungal decomposer may indicate adaptation of fungi to changes in resource availability in a disturbed forest. Alternatively, this might indicate that the presence of a fungi in a particular substrate does not depend on the substrate's chemical o physical composition but on the presence of other members of the detrivoral community. Although the presence of generalist basidiomycetes made an important contribution to the decomposition of leaf species, the diversity of the decomposer and detrivoral community might be important in maintaining nutrient balances in the ecosystems since random encounters of plants, decomposers and detrivores may determine the residence time of a substrate on the forest floor.

LTER CORE AREAS:Annotate all that apply

LEF LTER 1 RESEARCH TOPIC: (Annotate all that apply)

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RESEARCH LOCATION: The microcosms were incubated on the UPR campus in Rio Piedras - a lab experiment. The FIELD incubation occurred at El Verde in a common plot under Dacryodes excelsa, the Wadsworth plot, on the ridge above the footbridge over the Quebrada Sonadora.

INVESTIGATORS:

SOURCE OF FUNDING(SPONSOR): NSF

DATA SET ABSTRACT : We evaluated the influences of leaf quality, climate and microsite on the decomposition of leaves of five tropical tree species. Single-species litterbags were used to determine weight loss during the first three months of decomposition in the Luquillo Experimental Forest, Puerto Rico. Significant differences were found in decomposition rates among leaf species (Inga fagifolia < I. vera < Manilkara bidentata < C-roton poecilanthus <<Sapium laurocerasus), but only S. laurocerasus differed significantly from the other species. Lignin had a suggestive negative correlation with leaf decomposition while carbon content and the lignin:N ratio were significantly correlated with mass loss. Content of N, P, Ca, and polyphenol were not significantly correlated with mass loss, but several of the litter quality variables were correlated with each other. Leaf species decomposed faster under canopies of their source trees than in a common plot where the source species were absent. Decomposition in two species in the Euphorbiaceae, S. laurocerasus and C. poecilanthus, was significantly affected by microsite. Leaching losses during the first three weeks were greater under source trees than in the common plot, and may have been associated with differences in canopy structure and throughfall. Differences in detrital communities, however, could have contributed to the differences in decomposition between microsites. Leaves of all species decomposed significantly faster in the wet than in the dry period (P = 0.001) despite little climatic variation in this subtropical wet forest type. This suggests that decomposition of tropical leaf litter might be sensitive to microclimatic changes on the forest floor resulting from either global climate change, or from natural or anthropogenic disturbances that open the canopy.

The plant species were paired based on their physical and chemical characteristics (Tables 1, 2) to facilitate comparisons. Species in the first pair, I. vera and I. fagifolia, share the same family and genus and have high N and lignin concentrations, but they differ slightly in their levels of polyphenols. Species in the second pair, M. bidentata and C. poecilanthus, share similar nutrient concentrations, leaf structure and latex, but they belong to different families. Species in the third pair, C. poecilanthus and S. laurocerasus, share the same family and have latex, but they differ in nutrient and lignin concentrations as well as leaf structure. Sapium laurocerasus leaves are thin and smooth while C. poecilanthus leaves are thicker and have a heavier cuticle with peltate hairs.

Thickness of the leaves, epidermal cells, epidermal cell walls, and waxy cuticles were measured on hand-cut cross-sections using an ocular micrometer at 200-600x (five leaves per species). Ten fresh leaves per species were weighed and their areas were estimated using a grid. Water uptake (g water/cm²) was then determined by submerging the same leaves in deionized water for two hours and re-weighing (Taylor & Parkinson, 1988b).

Leaf litter collection - Only recently fallen senescent leaves of the selected species were collected. These leaves represent the normal substrates for primary fungal decomposers. Most leaves were collected the same day they abscised, but some senescent leaves where collected directly from their trees. Leaf collection took place during April and in early May for the first experiment, and at the end of July for the second set of experiments. Leaves of each species were collected from at least five trees. For field experiments, leaves were dried at 50°4C for 72 h. The 50 >° C temperature was used to avoid major changes in plant chemistry and to control for differences in initial water content between leaf species (W. Silver, personal communication). Additional leaves were collected for chemical analyses and were dried according to each laboratory's protocols as described below.

Effects of leaf structure and quality on decomposition. - Litter bags (20 x 20 cm) made with 2 mm mesh plastic screening were used for these experiments. Litter bags containing three grams of oven-dried (50 >° C) leaves of a single species were placed in a common plot. The first experimental sets were decomposed from May through July 2000. A total of 45 bags were used, nine bags per plant species. Bags were placed in the field under a tree of their own species for the first week to allow colonization by their normal decomposers, and subsequently moved to the common plot located in mature tabonuco forest. Three replicates per plant species were collected after three, six and twelve weeks of decomposition. After each collection, bags with the decomposed leaves were oven dried at 65>° C for 72 h and weighed to calculate rates of decomposition (difference between the initial and the final dry weight). We used correlation analyses to determine the relationship between leaf quality and decomposition and correlations among leaf quality factors.

In addition, we compared early stage leaching losses in the two types of sites. The amount of rainfall during the first phase of decomposition (3 wks) did not differ significantly between the dry and wet period experiments described below (207 and 197 mm in the dry and wet period experiments, respectively). We were therefore able to compare initial mass loss attributed primarily by leaching between sites (two-way ANOVA), even though these experiments occurred at different times.

Influence of wet and dry periods on decomposition rates.- For these experiments, comparisons were made of decomposition rates during the dry and wet periods in the common plot. The dry period was from May through July 2000 and the wet period from August-November 2000 (Fig. 1). Five replicates were used in the experiment during the wet period, and three replicates were used per collection time during the dry period.

CROSS-REFERENCES (other data sets related to this one): LTERDBAS 125; LTERDBAS 126;

SAMPLE LOCATION: ITES Facundo Bueso 104, Rio Piedras Campus, University of Puerto Rico

STORAGE SITES (of data files): Data Managers File; USDA Forest Service Sabana Luquillo

INVESTIGATOR'S ASSIGNED KEYWORDS: Leaf chemistry, site specificity, fungal decomposers, hurricanes, disturbance

LEF LTER OFFICIAL KEYWORDS  (See table): EL VERDE, TABONUCO, BIOGEOCHEMICAL CYCLES, CARBON, NITROGEN, DECOMPOSITION, LITTER FALL, SECOND FOREST, ASCOMYCETIES, BASIDIOMYCETES, THESIS

PUBLICATIONS : none

DISSEMINATION:

REASONS TO RESTRICT DATA IN THIS DATA SET BEYOND ITS TWO YEAR POLICY PERIOD*:

*WILL HAVE TO BE APPROVED BY  LTER PRINCIPAL INVESTIGATORS: J. ZIMMERMAN, A. LUGO , D.J. LODGE

FILING

_X_ "File data: Data Management will only file an electronic copy of the data file and its documentation
_ Enter" data on-line:Data Management will be in charge of entering the data on computer files (Contact Eda C. Meléndez)

SITES DESCRIPTIONS: This study was conducted in the Luquillo Experimental Forest (LEF) at the El Verde Field Station (18°20' N, 65°49' W) in Puerto Rico. The forest at El Verde is known as tabonuco forest and is classified as subtropical wet forest in the Holdridge system (1970, Ewel & Whitmore 1973). Mature tabonuco forest (MTF) is dominated by Dacryodes excelsa Vahl. (tabonuco), Sloanea berteriana Choise and Manilkara bidentata (A. DC.) Chev. Another part of the forest is a mid-successional forest (MSF). Elevation in the study area ranges from 250 to 350 m; mean monthly air temperatures are relatively constant through the year, with minimum monthly means of 21°C between December and January and maximum monthly means of 24°C between July and September (Vogt et al. 1996). In some recent years, however, the maximum mean monthly temperature has increased to as high as 26°C (Fig.1). Annual precipitation is about 3500 mm (Sullivan et al. 1999), and there is only slight seasonal variation. Two periods of reduced rainfall occur per year, the stronger one between January and April and a second one between June and July. In the year of our experiment (2000), the second period was drier than in other years (Fig. 1). Relative humidity in El Verde is high, between 96 and 100% (Brown et al. 1983). Soils are a complex of Ultisols and Oxisols (Brown et al. 1983, Huffaker 1995) and are mostly well-drained (Zimmerman et al. 1995).

Current sources of disturbance in the tabonuco forest are treefalls, landslides and hurricanes (Zimmerman et al. 1995). The forest was greatly affected by Hurricane Hugo in 1989, slightly by Hortense in 1996, and again severely by Georges in 1998 (Brokaw et al. in press). Scatena (1993) reported that leaf production had recovered to 50% of pre-hurricane levels two years after Hurricane Hugo. Data from Luquillo Experimental Forest (LEF) showed 73% recovery of leaf production after Hurricane Georges by 2000, the year of our experiment (LEF data was provided by Warren & Zou, personal communication).

Geographical positional system (GPS) Coordinates for each location:

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COMPUTATIONAL METHODS:

  FOR DATA MANAGER USE ONLY

DATE OF LAST REVIEW: November 4, 2008
DATE OF LAST ENTRY : November 17, 2000
STAGE OF DATA SET MANAGEMENT (dates) :
RECEIVED ENTERED: September 27, 2002
FILED ON-LINE April 1, 2003 (metadata only)
REVIEWED BY RESEARCHER
FILING MEDIA :
NAME OF DOCUMENTATION FILE :
NAME OF ON - LINE CATALOG : LTERDBAS
RECORD #: 124
DOCUMENT TYPE : data set (magnetic media)
PRIORITY TO BE ENTERED : N/A

Rev. date of this form: 15 July 2001