Spatio-temporal variability in the photosynthetic characteristics of Zostera tasmanica measured by PAM
Introduction
Seagrass photosynthesis is highly dynamic on a variety of spatio-temporal scales. Differences have been observed at temporal scales ranging from hours to seasons and spatial scales ranging from within a leaf to across the bed. These changes have been linked to physical factors, such as the availability of light (Mazzella and Alberte, 1986), nutrients (Bulthuis et al., 1992) and temperature (Bulthuis, 1987), and/or biological processes such as age (Durako and Kunzelman, 2002, Alcoverro et al., 1995, Alcoverro et al., 1998, Modigh et al., 1998) and various endogenous regulatory mechanisms of the plant (Pirc, 1986, Mazzella and Alberte, 1986). A number of limitations have been identified in measuring such changes with traditional techniques such as O2 exchange and 14C labelling, particularly at smaller scales. Despite these difficulties, understanding the processes that generate small-scale variability in seagrass photosynthesis and how they operate over different scales of time and space remains an important process from which other models and hypotheses can be derived (Underwood, 1981).
One of the more recent developments in photosynthesis research is the submersible pulse amplitude modulated (PAM) fluorometer. This instrument was designed to make small-scale (minute and cms) assessments of chlorophyll a fluorescence, from which the relative electron transport rates (rETRs), quantum yield and maximal effective quantum yield (Fv/Fm ratio) can be determined. The photosynthetic parameters α, Pmax and Ik (initial slope, maximum photosynthetic rate and saturation irradiance) can also be calculated by plotting rETRs against photon flux. Studies investigating the use of this instrument in photosynthesis research have found a linear or curvilinear relationship between 14C labelling or O2 evolution and PAM fluorometry in a number of aquatic organisms (Beer et al., 1998a, Geel et al., 1997, Hartig et al., 1998, Hofstraat et al., 1994, Kromkamp et al., 1998, Schreiber et al., 1997, Ting and Owens, 1992) including six species of seagrass (Beer and Björk, 2000, Beer et al., 1998b).
Several studies have demonstrated that small-scale (i.e. within and between leaves and diurnal) spatio-temporal variability in photosynthesis can be significant for some seagrass species but not others (Ralph, 1996, Ralph et al., 1998, Ralph et al., 2005, Beer and Björk, 2000, Silva and Santos, 2003, Durako and Kunzelman, 2002, Enriquez et al., 2002). Their work suggests that recent light history plays a significant role in diurnal changes (Ralph, 1996, Ralph et al., 1998) while age is more important for small-scale spatial considerations (Durako and Kunzelman, 2002, Enriquez et al., 2002, Ralph et al., 2005). Small-scale variability has the potential to confound larger scale studies, when not taken into account. However, few studies have tested how these variables (light and age) influence the photosynthesis parameters (α, Pmax and Ik) and the Fv/Fm ratio at smaller spatio-temporal scale (cms and minutes) (Durako and Kunzelman, 2002, Enriquez et al., 2002). Moreover, beyond the work of Durako and Kunzelman (2002), no attempt has been to measure seagrass photosynthesis over a range of small spatio-temporal scales. Knowledge of the scale(s) at which there is predictable variation is important for designing sampling strategies and must be determined before PAM fluorometry is to be used as a routine tool for measuring seagrass photosynthesis and calculating primary productivity.
In this study, PAM fluorometry measurements of rapid light curves (RLCs) and the Fv/Fm ratio were used to investigate spatio-temporal variability in Zostera tasmanica photosynthesis. Our objectives were (1) to examine patterns of variability in the photosynthetic parameters (Ik, α, Pmax) and the Fv/Fm ratio over a range of spatial (within a leaf to across the bed) and temporal scales (minutes to hours); (2) to identify the scale(s) at which there was predictable variation and (3) to examine the role of light and age at the scale(s) identified.
Section snippets
Methods
Shoots of Zostera tasmanica G. Martens ex Asch. (formerly known as Heterozostera tasmanica, Les et al., 2002) were collected from an intertidal area (ranging between 0.2 and 5 m deep) at Avalon Beach, Port Phillip Bay, Vic., Australia, (54°14′N, 8°23′E) in June and August 1999. This seagrass reproduces vegetatively, producing both erect and rhizome shoots. Erect shoots bear the most leaves and may be branched or unbranched with a cluster of leaves at the apex of each branch. In this study only
Results
Both the hyperbolic tangent model (Jassby and Platt, 1976, Platt et al., 1980) and the non-linear model (Eilers and Peeters, 1988) showed similar spatial and temporal trends. Therefore, only data for the photosynthetic parameters calculated using the hyperbolic tangent model are shown here (Jassby and Platt, 1976, Platt et al., 1980).
The pattern of within-leaf variation showed that α and the Fv/Fm ratio decreased with distance from the leaf base (Fig. 1). Although there was considerable
Discussion
PAM fluorescence measurements of the photosynthetic parameters and Fv/Fm ratio of Z. tasmanica varied spatially and temporally. The covariates, distance from leaf base and leaf length, were significant for all parameters examined, excluding Pmax. At larger scales, Pmax and the Fv/Fm ratio differed significantly between shoots, clusters and leaves, Ik varied between shoots and leaves and α differed between clusters and leaves. Both Pmax, and the Fv/Fm ratio were found to vary with the in situ
Acknowledgement
We are grateful to EPA Victoria for the generous loan of their Underwater PAM and logistic support.
References (38)
- et al.
Seasonal and age-dependent variability of Posidonia oceanica (L.) Delile photosynthetic parameters
J. Exp. Mar. Biol. Ecol.
(1998) - et al.
Measuring rates of photosynthesis of two tropical seagrasses by pulse-amplitude modulate (PAM) fluorometry
Aquat. Bot.
(2000) - et al.
Photosynthetic characteristics of Thalassia testudinum measured in situ by pulse-amplitude modulated (PAM) fluorometry: methodological and scale-based considerations
Aquat. Bot.
(2002) - et al.
A model for the relationship between light intensity and the rate of photosynthesis in phytoplankton
Ecol. Modell.
(1988) - et al.
The relationship between the quantum yield of photosynthetic transport and quenching of chlorophyll fluorescence
Biochim. Biophys. Acta
(1989) - et al.
Distribution and spatial variation of benthic microalgal biomass in a temperate, shallow-water marine system
Aquat. Bot.
(1998) - et al.
Light adaptation and the role of autotrophic epiphytes in primary production of the temperate seagrass Zostera marina
J. Exp. Mar. Biol. Ecol.
(1986) Seasonal aspects of photosynthesis in Posidonia oceanica: influence of depth, temperature and light intensity
Aquat. Bot.
(1986)- et al.
Fluorescence imaging application: effects of leaf age on seagrass photokinetics
Aquat. Bot.
(2005) - et al.
Photosynthetic responses of the seagrass Halophila ovalis (R. Br.) Hook. f. to high irradiance stress, using chlorophyll fluorescence
Aquat. Bot.
(1995)
Quantum efficiency of photosystem II in relation to ’energy’-dependent quenching of chlorophyll fluorescence
Biochim. Biophys. Acta
Annual growth dynamics of Posidonia oceanica: contribution of large-scale versus local factors to seasonality
Mar. Ecol. Prog. Ser.
Use of pulse amplitude modulated (PAM) fluorometry for in situ measurements of photosynthesis in Red Sea Faviid corals
Mar. Biol.
Measuring photosynthetic rates in seagrasses by pulse amplitude modulated (PAM) fluorometry
Mar. Ecol. Prog. Ser.
Determination of the quantum efficiency of photosystem II and of non-photochemical quenching of chlorophyll fluorescence in the field
Oecologia
Effects of temperature on photosynthesis and growth of seagrasses
Aquat. Bot.
Growth of the seagrass Heterozostera tasmanica limited by nitrogen in Port Phillip Bay, Australia
Mar. Ecol. Prog. Ser.
Effects of ultraviolet and photosynthetically active radiation on five seagrass species
Mar. Biol.
Variation in the photosynthetic preformance along the leaves of the tropical seagrass Thalassia testudinum
Mar. Biol.
Cited by (10)
Systematical regulation involved in heterogeneous photosynthetic characteristics of individual leaf in pima cotton
2022, Journal of Integrative AgricultureCitation Excerpt :These studies reported that photosynthetic performance varies greatly from the tip to the base of the leaf (Deng et al. 2007; Nardini et al. 2008; Li et al. 2013; Xiong et al. 2015; Yuan et al. 2015). This longitudinal heterogeneity of leaf may be due to the fact that the leaf-base is constantly generated, leading to the leaf-base tissue being formed later than the tip or the margin of leaf (Strain et al. 2006; Deng et al. 2007). In addition, there are differences in light energy intercepted by the tip and the leaf base (Meinzer and Saliendra 1997; Xiong et al. 2015).
Conclusive remarks. Reliability and comparability of chlorophyll fluorescence data from several field teams
2011, Environmental and Experimental BotanyCitation Excerpt :The problem of the sampling strategy across a tree crown is discussed also within the pan-european programme for forests health monitoring (Luyssaert et al., 2002). The issues that need to be addressed are: the variability of the leaf responses within the crown, the scientific question to be investigated (assessment of the response in the whole tree, or just in a specific population of leaves assumed as target), as well as the sampling strategy taking in account the spatial heterogeneity of the photosynthesis (Sakai and Akiyama, 2005; Strain et al., 2006). This consideration may appear trivial, but the study of the variability and the sampling strategy are rarely stated in this kind of research.
Experimental analysis of the response and recovery of Zostera marina (L.) and Halodule wrightii (Ascher.) to repeated light-limitation stress
2009, Journal of Experimental Marine Biology and EcologyThe effect of salinity shock on the growth and rapid light curve of dunaliella salina
2021, Aquaculture ResearchVariation characteristics of chlorophyll fluorescence of two typical eremophytes under drought stress in the drift desert hinterland
2013, Advanced Materials Research