Can the Riparian Invader, Arundo Donax, Benefit
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DOI: 10.1111/wre.12036 Can the riparian invader, Arundo donax, benefit from clonal integration? L KUI*†, F LI*, G MOORE* & J WEST* *Department of Ecosystem Science and Management, Texas A & M University, College Station, TX, USA, and †College of Environmental Science and Forestry, State University of New York, Syracuse, NY, USA Received 30 April 2013 Revised version accepted 3 June 2013 Subject Editor: Francesco Tei, Perugia, Italy objective was to determine whether clonal integration Summary enhanced growth and survival of A. donax ramets. We Resource sharing through rhizomes of clonal plants compared growth-related responses in paired 1 m2 supplements locally available nutrients to enhance plots with severed and intact rhizomes. In the first recruitment and growth in resource-limited environ- 19 days, rhizome severing nearly doubled ramet ments. We investigated whether Arundo donax,an density, while by 77 days, the intact rhizomes pro- invasive clonal plant, can benefit from clonal integra- duced 67% taller stems with 49% greater diameter tion. Sharing resources between ramets can facilitate and showed higher survival rate after flooding. This resprouting from mowing, fire and herbicide treat- study provides initial evidence that physiological inte- ments, but it is unknown whether clonal integration gration could be an important mechanism in A. donax, contributes to A. donax invasion success. Our first which can enhance its competitive abilities, accelerate objective was to determine whether A. donax rhizomes rates of encroachment and strengthen its capability to transported water between ramets. Hydrogen isotopic– recolonise disturbed areas. Our results highlight an enriched water was applied on three 1 m diameter important consideration of clonal invasive species in areas, and rhizome and soil samples were collected weed management. beyond the watering zone after 5, 24 and 48 h of the Keywords: giant reed, translocation, invasive species, last watering. Logistic modelling indicated that water plant response, isotopes, rhizome severing. was able to move laterally at least 3.5 m. The second KUI L, LI F, MOORE G&WEST J (2013). Can the riparian invader, Arundo donax, benefit from clonal integration? Weed Research 53, 370–377. transport nitrogen through the interconnected rhizomes Introduction (de Kroon et al., 1996, 1998). Clonal plants that remain interconnected belowground Physiological integration among clones can signifi- have the potential for physiological integration, the cantly improve the survival of a local population (Xiao translocation of water resources, nutrients or carbohy- et al., 2011), enhance fitness (Du et al., 2010) and drates from a donor ramet to a recipient ramet (Caraco support the growth of ramets into harsher environments & Kelly, 1991; de Kroon et al., 1998). For example, (Yu et al., 2008). Despite all those benefits, the existence using stable isotope labelling in pot experiments, Carex and extent of physiological integration differs among hirta L. and Carex flacca Schreb. were found to species (Williams & Briske, 1991; Dong, 1999), size of Correspondence: L Kui, College of Environmental Science and Forestry, State University of New York, Syracuse, NY, USA. Tel: (+1) 3154704831; Fax: (+1) 3154706535; E-mail: [email protected] © 2013 European Weed Research Society 53, 370–377 Clonal integration of Arundo donax 371 ramet (Caraco & Kelly, 1991; Brezina et al., 2006), root many riparian areas may provide continuous access to development (Matlaga & Sternberg, 2009) and resource groundwater even during drought, and thus, integra- availability (de Kroon et al., 1996; Guo et al., 2011). tion may not exist under mesic or homogeneous Clonal integration may benefit rhizomatous plants conditions (Matlaga & Sternberg, 2009). growing in systems with pronounced resource gradients This study examined the existence and potential (Dong, 1999; Xiao et al., 2010). In semi-arid riparian benefits of clonal integration in A. donax on the flood- zones, water availability gradients provide conditions plain of lower Rio Grande River, USA. The first for clonal plants to transport water from river banks objective was to determine whether A. donax shared and distribute it throughout floodplains (Shumway, soil resources (here water) through its rhizome 1995). In turn, oxygen can be transported from terres- networks at lateral distances up to 3.5 m, using a trial ramets to the lower submerged ramets (Amsberry deuterium-labelling experiment. If clonal integration et al., 2000; Xiao et al., 2010). In some riparian habi- existed in A. donax, the second objective was to assess tats, clonal integration may allow clonal invasive the effects of clonal integration on plant’s recruitment plants to grow faster and expand more rapidly than and growth by conducting a rhizome-severing experi- the non-clonal native plants (Wang et al., 2009). Plant ment. Our goal was to better understand the mecha- invasion has become a serious ecological issue in ripar- nisms for successful invasion by large clonal plants ian zones, and riparian restoration and management such as A. donax. projects have been carried out to control the expansion of invasive species (Richardson et al., 2007). Efforts to Materials and methods restore riparian zones and manage non-native riparian vegetation would benefit from improved understanding Site description of physiological and biological characteristics of clonal invasive species. Clonal plants may be more difficult to Research sites were located on an c. 1300 m wide flood- control using fire, mowing or herbicide treatments plain on the lower Rio Grande River (29°14′ N, 100°47′ because of vigorous resprouting from rhizomes (De W) of the USA–Mexico border. All experimental plots Cauwer & Reheul, 2009), and clonal integration may were located within the lower/active floodplain terrace, further enhance resprouting potential by translocating which was occupied by a continuous, nearly monocul- resources from robust rhizomes to weaker ramets. ture stand of naturally populated A. donax with sparse This study focuses on Arundo donax L. (giant reed), (<1%) Prosopis glandulosa Torr. The land on the high a clonal perennial grass that invades in North America terrace outside of our study site is managed as range- and frequently inhabits riparian zones (Dudley, 2000). land with cattle and sheep grazing. However, grazing Like many clonal invasive species, it has robust persis- was excluded from our study area for the past several tent rhizomes and propagates solely by vegetative decades through the construction of fever tick perma- means (Khudamrongsawat et al., 2004). Arundo donax nent quarantine/buffer zones (Pound et al., 2010). Our is characterised by rapid growth rates (up to 70 cm per site is located on alluvial soils that are generally well week), high biomass production, a tendency towards stratified, calcareous, sandy to silt loams (SSURGO, community dominance in many habitats and tolerance 2013). Gravelly layers have been encountered at depth to a wide range of environmental conditions (Dudley, during soil coring operations for other research efforts 2000). Any of these might be attributed, at least in on the site. The soil surface elevations in our sites were part, to clonal integration (Cushman & Gaffney, about 3–5 m above the average river water level. Arun- 2010). Using the network of robust persistent rhi- do donax may have been promoted by fire (Coffman zomes, it is reasonable to expect A. donax can extend et al., 2010), which occur commonly in the region. growth during dry conditions by transporting water There was evidence of previous fire events at our site, from moist areas to the neighbour ramets on flood- although none occurred at our site during the study. plains. If this is true, clonal integration may provide Amistad Dam at Del Rio, TX, about 50 km upstream an important mechanism to explain why many semi- of our research site, was completed in 1969. Altered arid riparian zones have been extensively occupied by flow regimes following dam construction probably also A. donax (Yang et al., 2011). contributed to the expansion of exotic species, including On the other hand, although A. donax maintains A. donax, into the riparian zones (Purchase et al., physical connection between ramets, it may not be nec- 2001). essary for A. donax to maintain physiological integra- The climate in this region is semiarid with average tion in all riparian environments (Caraco & Kelly, annual rainfall of 470 mm (NOAA, 2010). In 2010, a 1991). Arundo donax roots can penetrate to a depth of summer flood happened from 7 to 15 July. It was up to about 3 m (personal observation), which in caused by significant releases from the Amistad Dam © 2013 European Weed Research Society 53, 370–377 372 L Kui et al. and heavy local precipitation associated with Hurri- cane Alex. The total precipitation from June to August was 152 mm, similar rainfall amount compared with 30-year averages for those months (NOAA, 2010). However, the precipitation in July was 120 mm, three times the average for July. Deuterium-labelling experiment The deuterium-labelling experiment was conducted in an area located c. 100 m from the water course within a continuous stand of A. donax. The experiment began in mid-August 2010, one month after the summer flood. The experimental site was not inundated during flood- ing but did experience shallow groundwater (~1.5 m Fig. 1 Plot layout for the watering experiment. The centre dark from the soil surface). After the flood receded and colour marks the 1 m diameter watering area. Outside rings 20 days had passed without precipitation, we set up were situated at four distances away from the labelled ramets. three replicate circular plots (Fig. 1) spaced 10 m apart. Samples were collected at the intersection of each ring along In each plot, five rhizome and five soil samples were col- five direction lines (N, NE, NW, SE, SW). lected for background isotopic determination prior to the experiment on 16 August 2010. Those background directions, which were treated as replicate samples for samples were located randomly along the 3.5 m ring of corresponding distances.