Cluster Roots of Embothrium Coccineum (Proteaceae) Affect Enzyme Activities and Phosphorus Lability in Rhizosphere Soil
Total Page：16
File Type：pdf, Size：1020Kb
Plant Soil DOI 10.1007/s11104-015-2547-9 REGULAR ARTICLE Cluster roots of Embothrium coccineum (Proteaceae) affect enzyme activities and phosphorus lability in rhizosphere soil M. Delgado & A. Zúñiga-Feest & L. Almonacid & H. Lambers & F. Borie Received: 6 November 2014 /Accepted: 2 June 2015 # Springer International Publishing Switzerland 2015 Abstract Results The rhizosphere of senescing cluster roots pre- Background and aim Cluster roots have a profound sented the highest P-ase, β-glucosidase and dehydroge- effect on their rhizosphere. Our aim was to determine nase activities, and fastest rate of FDA hydrolysis, being the effect of cluster roots of Embothrium coccineum, 2.6-, 4.6-, 3.3- and 25.8-fold greater, respectively, than growing under natural conditions, on soil enzyme activ- those in the rhizosphere of mature cluster roots. The P ities and phosphorus (P) lability in its rhizosphere. fractionation showed that the inorganic P (Pi) fraction Methods We determined enzyme activities: acid phos- was 15 % greater in the rhizosphere of mature cluster phatase (P-ase), dehydrogenase and β-glucosidase, and roots than in that of other stages. Mature cluster roots the rate of hydrolysis of fluorescein diacetate (FDA), as showed the highest total [P], suggesting the fastest P well as P fractions in the cluster root rhizosphere at uptake. different cluster-root developmental stages (juvenile, Conclusion Cluster roots of E. coccineum modified mature, semi-senescent, senescent), in the non-cluster their rhizosphere depending on their developmental root rhizosphere, and in bulk soil. In addition, the con- stage, presenting lower soil enzyme activities at the centrations of total P and manganese Mn in roots was mature stage than at other development stages. In addi- measured. tion, mature cluster roots increased the Pi fraction in their rhizosphere, allowing the highest total root [P] at this developmental stage. Responsible Editor: Tim S. George. * : Keywords Enzymatic activities Phosphorus M. Delgado ( ) L. Almonacid . Programa de Doctorado en Ciencias de Recursos Naturales, fractionation Volcanic soils Southern South America Universidad de la Frontera, Casilla 54-D, Temuco, Chile e-mail: [email protected] M. Delgado : A. Zúñiga-Feest Introduction Laboratorio de Biología Vegetal, Instituto de Ciencias Ambientales y Evolutivas, Facultad de Ciencias, Universidad Cluster roots are a plant strategy to increase nutrient Austral de Chile, Valdivia, Chile acquisition, involving release of large amounts of or- F. Borie ganic compounds (e.g., citrate, malate) that mobilise Center of Amelioration and Sustainability of Volcanic Soil. phosphorus (P) through solubilisation of P sorbed onto BIOREN-UFRO, Temuco, Chile soil particles, making it available to be taken up by plants (Dinkelaker et al. 1995; Shane and Lambers H. Lambers School of Plant Biology, University of Western Australia, 2005a;Skene1998). These roots occur in most species Crawley (Perth), WA 6009, Australia belonging to the Proteaceae, but similar root structures Plant Soil occur in species in other families (Lambers et al. 2006; expressed just prior to citrate exudation. It is not known Lamont 2003), especially in actinorhizal species (Louis if similar mechanisms operate in other species bearing et al. 1991). cluster roots. Therefore, the first question we address is: Cluster roots are dense clusters of fine rootlets around do cluster roots of E. coccineam (Proteaceae) function amainaxis(Purnell1960); they are ephemeral struc- similarly to cluster roots of L. albus, decreasing micro- tures, living about 3 weeks, showing rapid carboxylate bial activity in active cluster roots? release just when the rootlets have stopped growing Release of organic acids is associated with several (e.g., in Lupinus albus: around 3 to 4 days after their changes in the rhizosphere, such as mobilisation of P, emergence (Watt and Evans 1999); in Hakea prostrata Mn and iron (Fe), decrease in pH, and metal detoxifica- R.Br., 12 to 13 days after emergence (Shane et al. tion through chelation (Jones 1998). However, most 2004a); in Embothrium coccineum J. R. Forst & G. studies involving these changes have been carried out Forst., 13 to 25 days after emergence (Delgado et al. under controlled conditions, which may be quite far 2014)). In contrast, in juvenile or senescent cluster roots, from those in a natural environment. So far, it is un- the release of carboxylates is very slow. Several authors known how cluster roots affect P lability in the rhizo- reported that these differences in carboxylate-exudation sphere in plants growing under natural conditions (in rates as dependent on cluster-root developmental stage this study, volcanic soils). Therefore, the second ques- lead to strong changes in bacterial community structure tion we address is: do exuding cluster roots mobilise P in the rhizosphere of cluster roots (Marschner et al. from non-labile fractions to more labile fractions in the 2005; 2002; Weisskopf et al. 2005). On the other hand, soil? it is widely recognised that many microorganisms are To answer the questions raised above, we studied the capable of stimulating plant growth through a variety of rhizosphere of cluster roots (at different cluster-root mechanisms that include improvement of plant nutri- development stages) of E. coccineum, a Proteaceae from tion, production of phytohormones, and suppression of the southern part of South America. This species forms pathogenic microorganisms (Goh et al. 2013;Martínez- small cluster roots, but with a rapid carboxylate- Viveros et al. 2010). Wenzel et al. (1994)havefoundP- exudation rate (Delgado et al. 2014). Thus, the aim of solubilising bacteria associated with the cluster-root rhi- this study was to assess the effect of cluster roots of zosphere of waratah (Telopea speciosissima (Sm.) R. E. coccineum on chemical (P lability) and biochemical Br). However, we do not know if such bacteria (or other activities (soil enzymes of both plant and microbial microorganisms stimultating plant growth) occur in the origin) associated with cluster roots. rhizosphere of exuding cluster roots, thus enhancing nutrient availability, or if microorganism are inhibited and thus prevented from immobilising nutrients, making Materials and methods them less available to plants. Organic compounds released into the rhizosphere are Study area and soil collection available as substrate for microorganisms, and rapidly assimilated into microbial biomass (Gregory 2006; Rhizosphere soil and cluster roots of E. coccineum were Pinton et al. 2001; Ryan and Delhaize 2001). Besides, collected in February 2014 from Puerto Chalupa, microorganisms may assimilate nutrients that are Comuna Puyehue, Región de los Lagos, Chile. The area mobilised by plants, generating strong competition for is mainly covered by scrub (Rubus ulmifolius)and nutrient uptake. However, Weisskopf et al. (2006)pro- second-growth forests with some mature trees such as posed that Lupinus albus has three mechanisms Drymis winteri (J.R. et. Forster), Lomatia hirsuta curtailing microbial degradation of citric acid exuded ((Lam.) Diels. Ex Macbr), Eucryphia cordifolia (Cav.), from its cluster roots: i) strong acidification of the Luma apiculata ((DC.) Burret) and E. coccineum. The cluster-root rhizosphere, decreasing bacterial abun- chemical characteristics and soil texture of the soil (de- dance, because most bacteria are sensitive to acidic rived from recent volcanic ash) were determined accord- environments; ii) exudation of phenolic compounds that ing to Sadzawka et al. (2004) and Schlatter et al. (2003), induce fungal sporulation, thus reducing potential citrate respectively (Table 1). The study area was a zone where consumption by fungi; iii) exudation of chitinase and E. coccineum forms pure second-growth forests. Sam- glucanase (enzymes degrading fungal cell walls), ples of roots and soils were collected around the stem at Plant Soil a b Table 1 Chemical analyses and texture of soil collected in the obtained from the rhizosphere soil of the three collection natural habitat of Embothrium coccineum at Puerto Chalupa, sites (n=3). However, due to the large amount of rhizo- Antillanca, X Región de los Lagos, Chile sphere soil used in these determinations and little N(mgkg−1)37amount of rhizosphere soil obtained in one of three Olsen-P (mgkg−1)4 collecting sites (site 1), rhizosphere soil collected from Total P (mgkg−1)2575 BSite 1^ was mixed with that collected at the other two K(mgkg−1)43sites (2 and 3). From this bulked soil, four replicates pH (H2O) 5.32 were obtained. Soil organic matter (%) 15 K(cmol+kg−1)0.11 Hydrolysis of fluorescein diacetate Na (cmol+kg−1)0.04 Ca (cmol+kg−1)0.57 This technique is widely used for estimating soil micro- Mg (cmol+kg−1)0.16 biological activities that reflect the activity of several Al (cmol+kg−1)0.07 enzymes catalysing the hydrolysis of chemical bonds Aluminium saturation (%) 7.37 such as ester (e.g., non-specific esterases, lipases) and Base saturation (cmol+/kg) 0.88 peptide bonds (e.g., proteases), all of which hydrolyse Soil texture Silt Loam (clay 15 %, FDA and are involved in organic matter degradation sand 20 %, silt 65 %) (Adam and Duncan 2001;Nannipierietal.2003; Ntougias et al. 2005; Schnürer and Rosswall 1982). This a b Determined according to Sadzawka et al. (2004). Determined was determined using fluorescein diacetate (FDA) as according to Schlatter et al. (2003) described by Adam and Duncan (2001). Briefly, 1 g rhizosphere soil was placed into 50 mL centrifuge tubes. the top 20 cm of soil. This collection was carried out at Then, 10 mL potassium phosphate buffer (pH 7.6) was three locations (within an area of approx. 0.5 ha), sepa- added. After 10 min, FDAwas added; tubes were sealed rated by at least 100 m. These samples were collected and incubated at 30 ° C for 1 h in an orbital incubator at and placed in boxes with ice bags inside, being subse- 100 rpm. After this, 10 mL acetone was added to each quently taken to the laboratory, sieved to 1 mm and tube. Finally, fluorescein absorbance was measured in a stored at 4 °C until later analysis.