Spartina maritima decomposition in Odiel
Spartina maritima decomposition in Odiel Marshes
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CAPÍTULO 8.- Descomposición de Spartina maritima en las
Marismas del Odiel.
RESUMEN
Este trabajo cuantifica por primera vez la tasa de descomposición (k day-1) y el peso seco remanente en hojas, tallos y rizomas de Spartina maritima en el estuario conjunto de los ríos Tinto y Odiel (suroeste de la Península Ibérica). Las hojas mostraron menor peso seco remanente que tallos y rizomas. El peso seco remanente de las hojas de S. maritima tras un año fue del 27 ± 10 %. El peso seco remanente de los tallos y los rizomas fueron 59 ± 11 % y 57 ± 2 %, respectivamente. La mayor pérdida de peso para las hojas fue recogida al inicio del proceso de descomposición (33 ± 4 % en los primeros tres meses correspondiendo con primavera) y para los tallos y rizomas durante los segundos tres meses correspondientes a verano (21 ± 6 % y 17 ± 5 %, respectivamente). Las hojas de
S. maritima mostraron mayor k que los tallos y rizomas durante todo el estudio, siendo
estadísticamente significativo en primavera y otoño. La k anual para las hojas fue 0.0043 ± 0.0013 dias-1 y cerca de 0.0015 dias-1 para tallos y rizomas. Por tanto, concluimos que el ciclado de los nutrientes de S. maritima es muy activo, especialmente en hojas, en las Marismas del Odiel.
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CHAPTER 8.- Spartina maritima decomposition in Odiel
Marshes.
ABSTRACT
This work quantifies for the first time the decomposition rate (k day-1) and the remaining weight in leaves, stems and rhizomes of Spartina maritima in the joint estuary of the Odiel and Tinto rivers (south-west Iberian Peninsula). Leaves showed a lower remaining dry weight than stems and rhizomes. The remaining dry weight of S. maritima leaves was 27 ± 10 % after one year. The remaining dry weight for stems and rhizomes was 59 ± 11 % and 57 ± 2 %, respectively. The highest weight loss for leaves was recorded at the beginning of the decomposition process (33 ± 4 % for the first three months, corresponding to spring) and for stems and rhizomes during the second three months, corresponding to summer (21 ± 6 % and 17 ± 5 %, respectively). During the whole study,
S. maritima leaves showed a higher value of k than stems and rhizomes, with statistically
significant results during spring and autumn. The annual k value for leaves was 0.0043 ± 0.0013 days-1 and ca. 0.0015 days-1 for stems and rhizomes. We conclude that nutrient recycling of S. maritima is very active, especially on leaves, in the Odiel Marshes.
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8.1. INTRODUCTION
Plant decomposition is a key process in salt marshes, influencing the formation of soil particulate organic matter and releasing inorganic nutrients for plants (Adam, 1990). Decomposition is influenced by many environmental factors, such as sediment texture (De Boer, 2000), water availability (Menéndez & Sanmartí, 2007), salinity (Hemminga
et al., 1991) and the decomposer community (Pozo & Colino, 1992; Alkemade et al.,
1993).
Decomposition has been studied for Spartina alterniflora Loisel and Spartina
patens (Ait.) Muhl. in North American estuaries and in invasive Chinese populations
(White et al., 1978; Frasco & Good, 1982; Valiela et al., 1985; Foote & Reynolds,1997; Windham, 2001; Liao et al., 2008), and for Spartina anglica C.E. Hubbard and Spartina
maritima (Curtis) Fernald in European marshes (Buth & Wolf, 1985; Hemminga et al.,
1991; Pozo & Colino, 1992; Lillebø et al., 1999; Castro & Freitas, 2000; Caçador et al., 2007; Sousa et al., 2008).
This is the first study of the decomposition dynamic for S. maritima tissues (leaves, stems and rhizomes) in the Odiel Marshes in the joint estuary of the Odiel and Tinto rivers (southwest Iberian Peninsula). This is globally the most metal-polluted estuary (Elbaz-Poulichet et al., 2001; Grande et al., 2003), where S. maritima accumulates high heavy metals loads in its tissues (Luque et al., 1999).
8.2. MATERIALS AND METHODS
Our work was carried out in a restored salt marsh area (Chapter 2) from March 2010 to
March 2011. 2 g per organ of S. maritima (leaves, stems and rhizomes) were dried to a
constant weight (DW) at 80 °C over 48 h (n = 10). To determine the decomposition rate of S. maritima, 2 g per organ were placed into bags (10 cm x 20 cm) with a light mesh of
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1 mm (Castro & Freitas, 2000). 12 litter bags (4 bags per organ) were placed on the sediment surface in 6 salt marshes (n = 6) colonized by S. maritima and Sarcocornia
perennis (Mill.) A.J. Scott ssp. perennis. One bag per organ was collected from each
marsh every 3 months from March 2010 to March 2011. After collection, plant material was carefully cleaned, dried to constant weight and weighed. The remaining dry weight in percentage was calculated, as was decomposition rate (k) using the Olson equation (Olson, 1963):
Ln (final weight (DW) / initial weight (DW)) = -k * time (days).
Abiotic environment was characterized during March and April 2009 at the same points where S. maritima samples were placed for decomposition. Elevation relative to Spanish Hydrographic Zero (SHZ) was surveyed to a resolution of 2 cm with a Leica NA 820 theodolite (Singapore). Electrical conductivity and pH of the interstitial water of the sediment were measured in the laboratory with a conductivity meter (Crison-522) and a pH meter (pH/rédox Crison with electrode M-506), respectively (n = 6). Conductivity and pH were recorded after adding distilled water to the sediment (1:2 and 1:1 v/v, water/sediment, respectively). Sediment redox potential was determined in the field in triplicate sub-samples with a portable meter and electrode system (Crison pH/mV p-506) (n = 6). Each sediment characteristic was recorded for depths between 0–5 cm during spring.
Analyses were carried out using SPSS for Windows, release 17.0 (SPSS Inc., Chicago, IL). Deviations were calculated as the standard error of the mean (SEM). Data were tested for normality with the Kolmogorov–Smirnov test and for homogeneity of variance with the Levene test (P> 0.05). Variations in decomposition rate and remaining dry weight between organs were compared using a one-way analysis of variance (Anova). A Tukey t-test between means was calculated only if the F-test was significant (P > 0.05).
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8.3. RESULTS AND DISCUSSION
Decomposition samples were placed at a mean topographical elevation of +2.85 ± 0.08 m SHZ on sediments with a pH of 7.0 ± 0.1, a conductivity of 17 ± 3 mS cm-1 and a redox potential of +81 ± 38 mV.
Leaves showed lower remaining dry weight than stems and rhizomes during the whole study (Anova, P < 0.05), but these differences were not significant in summer due to a high data dispersion. The remaining dry weight of S. maritima leaves was 27 ± 10 % after 1 yr, being within the range of those reported previously for Spartina leaves (40 % and 12 % after 1 yr for S. maritima, following Pozo & Colino (1992) and Castro & Freitas (2000), respectively, and 12% for S. alterniflora in nine months, following Liao
et al. (2008)). The remaining dry weight for stems and rhizomes recorded in this study
(59 ± 11 % and 57 ± 2 %, respectively, after 1 yr) was also within the range reported previously for Spartina cynosuroides (L.) Roth., S. alterniflora and S. maritima (Hackney, 1980; Pozo & Colino, 1992; Liao et al., 2008; Sousa et al., 2008) (Fig. 8.1).
The highest weight loss for leaves was recorded at the beginning of the decomposition process (33 ± 4 % for the first three months, corresponding to spring) and for stems and rhizomes during the second three months, corresponding to summer (21 ± 6 % and 17 ± 5 %, respectively) (Fig. 8.1). Faster decomposition could be related to a higher C:N ratio at the ignition of decomposition (Sousa et al., 2008) and with warmer conditions during spring and summer in the Mediterranean climate (Pozo & Colino, 1992; Castro & Freitas, 2000).
S. maritima leaves showed higher k than stems and rhizomes during the whole
study, being statistically significant during spring and autumn (Anova, P < 0.05). Annual
k for leaves was 0.0043 ± 0.0013 days-1, being within the range recorded by Castro & Freitas (2000) for S. maritima (0.0050 days-1) and Liao et al. (2008) for S. alterniflora (0.0063 days-1). Annual k for stems and rhizomes (ca. 0.0015 days-1) was lower than
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those recorded previously (0.0024-0.0043 days-1, following Liao et al., 2008 and Sousa
et al., 2008) (Table 8.1).
*
*
*
3/2010 6/2010 9/2010 12/2010 3/2011 R emaini ng w eig ht (% ) 0 20 40 60 80 100 Leaves Stems RhizomesFigure 8.1. Litter mass remaining in different plants structures of Spartina maritima during one year in restored salt marshes in the joint estuary of the Odiel and Tinto rivers (n = 6). Asterisks indicate significant differences between leaves, and stems and rhizomes (Anova, P < 0.05).
This is the first study quantifying decomposition of S. maritima in the Odiel Marshes. Our results showed that decomposition of S. maritima tissues is similar to that recorded for Small Cordgrass and other Spartina species in other estuaries, even at the upper distribution limit of low salt marshes with less tidal influence and with very high loads of metals in plant tissues and sediments (see Chapter 7). We conclude that nutrient recycling of S. maritima is very active, especially on leaves, in the Odiel Marshes.
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Organ Decomposition rate (day-1)
0-3 months (spring) Leaves 0.0048 ± 0.0007a
Stems 0.0010 ± 0.0007b
Rhizomes 0.0013 ± 0.0004b 3-6 months (summer) Leaves 0.0060 ± 0.0020a
Stems 0.0018 ± 0.0002a
Rhizomes 0.0016 ± 0.0004a 6-9 months (autumn) Leaves 0.0043 ± 0.0008a
Stems 0.0021 ± 0.0004b
Rhizomes 0.0022 ± 0.0004b 9-12 months (winter) Leaves 0.0043 ± 0.0013a
Stems 0.0015 ± 0.0005a
Rhizomes 0.0014 ± 0.0001a
Table 8.1. Decomposition rate (day-1) in leaves, stems and rhizomes of Spartina maritima in the Odiel Marshes during one year. The letters indicate significant differences between organs for the same period (Anova, P < 0.05).
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