Ecophysiological and foliar nitrogen concentration responses of understorey Acacia spp. and Eucalyptus sp. to prescribed burning Ling Ma, Xingquan Rao, Ping Lu, Shahla Hosseini Bai, Zhihong Xu, Xiaoyang Chen, Timothy Blumfield & Jun Xie Environmental Science and Pollution Research ISSN 0944-1344 Environ Sci Pollut Res DOI 10.1007/s11356-015-4223-2
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Author's personal copy Environ Sci Pollut Res DOI 10.1007/s11356-015-4223-2
RESEARCH ARTICLE
Ecophysiological and foliar nitrogen concentration responses of understorey Acacia spp. and Eucalyptus sp. to prescribed burning Ling Ma & Xingquan Rao & Ping Lu & Shahla Hosseini Bai & Zhihong Xu & Xiaoyang Chen & Timothy Blumfield & Jun Xie
Received: 29 October 2014 / Accepted: 9 February 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Eucalyptus spp. is a dominant tree genus in Australia and most Eucalyptus spp. are canopy dominant species. In Australian natural forests, Eucalyptus spp. commonly are associated with understorey legumes which play a crucial role for ecological restoration owing to their nitrogen (N) fixing ability for replenishing the soil N lost after frequent prescribed burning. This study aimed to explore to what extent Responsible editor: Philippe Garrigues L. Ma : X. Chen State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources; Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry, South China Agricultural University, Guangzhou 510642, People’s Republic of China L. Ma : X. Chen (*) : J. Xie Key Laboratory of Energy Plants Resource and Utilization, Ministry of Agriculture; Key Laboratory of Biomass Energy of Guangdong Regular Higher Education Institutions, Institute of New Energy and New Materials, South China Agriculture University, Guangzhou 510642, People’s Republic of China e-mail:
[email protected]
physiological responses of these species differ 7 and 12 years after last fire. Two most common understorey Acacia spp., Acacia leiocalyx and A. disparrima, as well as one nonleguminous Eucalyptus resinifera, were studied due to their dominance in the forest. Both A. leiocalyx and A. disparrima showed higher carbon (C) assimilation capacity, maximum photosynthetic capacity, and moderate foliar C/N ratio compared with E. resinifera. A. leiocalyx showed various advantages compared to A. disparrima such as higher photosynthetic capacity, adaptation to wider light range and higher foliar total N (TNmass). A. leiocalyx also relied on N2-fixing ability for longer time compared to A. disparrima. The results suggested that the two Acacia spp. were more beneficial to C and N cycles for the post burning ecosystem than the non-N2fixing species E. resinifera. A. leiocalyx had greater contribution to complementing soil N cycle long after burning compared to A. disparrima. Keywords Leaf gas exchange . Carbon and nitrogen isotope composition (δ13C and δ15N) . Acacia leiocalyx . A. disparrima . Eucalyptus resinifera . Symbiotic N2 fixation
X. Rao South China Botanical Garden of Chinese Academy of Sciences, Guangzhou 510650, People’s Republic of China P. Lu Energy Resources of Australia Ltd, GPO Box 2394, Darwin, NT 0801, Australia S. H. Bai : Z. Xu (*) : T. Blumfield Environmental Futures Research Institute, School of Natural Sciences, Griffith University, Nathan, Brisbane, QLD 4111, Australia e-mail:
[email protected] S. H. Bai Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Maroochydore, QLD 4558, Australia
Introduction Under global climate change (GCC), frequent extreme weather events have become a major concern of the international community. In subtropical Australia, prolonged drought is expected to be one of the consequences under GCC and leads to more frequent wild fires (Reverchon et al. 2012). Prescribed burning has been implemented as a treatment to reduce the wildfires and restore forests for decades, but it might result in
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nitrogen (N) volatilization losses (Smithwick et al. 2005; Burgoyne and DeLuca 2009; Reverchon et al. 2012) which might worsen the N-poor soils of this continent. However, Australia has a large number of understory legumes broadly distributed across the country, which can replenish the soil N lost after fire by N fixation through the associated N2-fixing bacteria (Guinto et al. 2000; Reverchon et al. 2012). Therefore, understory legumes play a crucial role for ecological restoration of Australian native forests (Guinto et al. 2000; Adams et al. 2010). Eucalyptus is a fast-growing species which dominate large forest area in Australia. The mixed species forest of Eucalyptus with understorey Acacia tend to have higher productivity, higher rates of nutrient cycling, as well as higher rates of N2-fixation than monocultures (Forrester et al 2006). Instantaneous photosynthesis related parameters are generally used to evaluate the ability of plants to fix C and accumulate biomass (Ghashghaie et al. 2001). However, photosynthetic capacity of plant is water and nutrient dependent (Martin and Thorstenson 1988). Farquhar et al. (1982) reported that foliar stable carbon (C) isotope composition (δ13C) of C3 plants was linearly correlated to water use efficiency (WUE). Therefore, δ13C is a time-integrated method and has widely used to investigate WUE of plants, higher δ13C value generally means higher WUE (Farquhar and Richards 1984), which has been used in different forest ecosystems of subtropical Australia (Hosseini Bai et al. 2014a, b; Huang et al. 2008a, b; Ibell et al. 2013; Tutua et al. 2014). Photosynthetic capacity of leaves is also highly responsive to N availability because the proteins of the Calvin cycle and thylakoids represent the majority of leaf N (Xu et al. 2000; Warren and Adams 2001; Hosseini et al. 2012). N is also the main component of the Robisco enzyme involved in photosynthesis (Evans 2001). Legumes may obtain more N in leaves for photosynthesis through N2 fixation (Kiers et al. 2003). Dry mass based total N (TNmass) as well as 15N signals of plant tissues are generally used to explain time-integrated N2-fixing ability of legumes (Houngnandan et al. 2008). Foliar N isotope composition (δ15N) has shown to be positively correlated with foliar TNmass which is an indicator of plant productivity (Xu et al. 2000; Warren and Adams 2001; Kiers et al. 2003; Houngnandan et al. 2008). Increased soil microbial N transformation leads to increased N availability but newly available N is vulnerable to loss through leaching or volatilization or other gaseous N such as N oxides via nitrification and denitrification. Lighter 14N would be expected to be lost more favorably from the system than heavier 15N and plant uptake from more 15N enriched will result in higher foliar δ15N, which explains such positive relationship (Yoneyama et al. 1993; Högberg 1997). The WUE, growth response and photosynthetic capacity of Acacia spp. and Eucalyptus spp. and N2-fixing ability of
Acacia spp. have been studied in both mixed specie plantations and revegetation sites (Akhter et al. 2005; Forrester et al. 2010; Hosseini Bai et al. 2014a, b). However, the knowledge on ecophysiological response of native understory legumes to prescribed burning is inadequate (Hoque et al. 2011). In addition, little is known about the temporal dynamics of physiological activity or N2-fixation ability of understory Acacia species during their lifecycle (Chapin et al. 1994; Crews et al. 2001; Hosseini Bai et al. 2012; Hyodo et al. 2013), while such information would be very useful for sustainable forest management. Hence, in this study, we selected two most common understorey Acacia spp., Acacia leiocalyx (Domin) Pedley and A. disparrima M.W.McDonald & Maslin and a Eucalyptus sp., Eucalyptus resinifera Smith dominating in Toohey Forest of subtropical Australia with different prescribed burning history. We examined their physiological performances such as photosynthesis, transpiration, instant water use efficiency (iWUE), and foliar δ13C, as well as foliar δ15N, C/N ratio and photosynthetic N-use efficiency (PNUE). These variables were used to compare physiological differences among plant species, plant size and their responses to different prescribed fire treatment (years since last burn). We hypothesized that (i) there might be some inter-site and inter-plant size differences between the two Acacia species but much less than among Acacia spp. and the non-N2-fixing Eucalyptus sp. (Guinto et al. 2000; Hosseini Bai et al. 2013); and (ii) the different prescribed fire treatments may have considerable effect on the foliar δ15N of all the plant species due to N limitation posed by frequent fire (Guinto et al. 2000; Reverchon et al. 2012). We also hypothesized that Eucalyptus resinifera may have higher WUE compared to the two Acacia spp. due to its ability to survive in harsh conditions. We aimed to provide insights into the species variation as well as prescribed fire treatment effect for forest management in subtropical Australia.
Materials and methods Experiment site The study was conducted at Toohey Forest (27o32′53″S; 153o03′21″E) located in Brisbane, southeast Queensland, Australia. Toohey Forest is a dry sclerophyll forest dominated by eucalypts with understories consisting of grasses and shrubs which are mainly Acacia sp. The mean annual temperature 1 year before this study was 27 °C and mean annual rainfall was 930 mm over the last 30 years in the study area (Fig. 1). The field experiment was undertaken in July 2008 at two sites (about 200 m apart) with different fuel reduction burning history. Toohey forest is subjected to frequent burning for the last 30 years. Site 1 was burnt in 1991 and 2001 while Site 2 was burnt in 1996.
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quantum efficiency (Qa, μmol μmol–1) and maximum photosynthesis (Amax, μmol m–2 s–1) were derived from these curves according to von Caemmerer and Farquhar (1981). A/Ci response curves were determined through the CO2 concentration order 350, 250, 200, 150, 100, 50, 350, 450, 600, 750, 900, and 1100 μmol mol−1, and from which CO2 compensation point (CCP, μmol m–2 s–1) was derived. Foliar total C, total N, and N isotope compositions
Fig. 1 Monthly mean value of a air temperature (close circles) and its daily range (gray area) and b actual rainfall (bars) and 30-year mean rainfall (line, 1977–2006) at the study site
At both experimental sites, 4 plots, 10–50 m away from each other, were randomly established with three replications per each category at each plot. In each plot, A. disparrima and A. leiocalyx were categorized into small size (S, basal diameter (BD) ≤1.0 cm) or medium size (M, BD >1.5 cm). However, since germination of Acacia spp. are triggered by fire, and Acacia spp. often killed by burning (Hosseini Bai et al. 2013), we assumed that Acacia spp. of the two sizes at each site had similar age. In addition, only one size of Eucalyptus resinifera (DBH
