Evaluation of arbuscular mycorrhiza with symbiotic and nonsymbiotic pea isolines at three sites in the Alentejo, Portugal

Abstract

Providing an appropriate negative control for the experimental factor arbuscular mycorrhiza (AM) is a fundamental methodological problem. Therefore, the nonmycorrhizal (myc –) and nonnodulating (nod –) pea (Pisum sativum L.) mutant P2 was studied together with the parental symbiotic isogenetic variety Frisson in three experiments: (1) growth response to water supply in a climate chamber under nonsymbiotic growth conditions, (2) field evaluation at three sites in the Alentejo, South Portugal, and (3) growth response to P supply in a soil low in available P in a greenhouse‐chamber experiment. In the climate chamber at high NPK levels, mutant P2 achieved the same biomass as Frisson at 80% and 40% water‐holding capacity, respectively. For the field evaluation, three sites were chosen with normal arable use (Évora), extensive use as Montado (Portel), and intensive horticultural use (Mitra). The colonization of pea roots with AM fungi ranged from 4% (Mitra) to more than 90% (Portel), probably caused by differences in P availability. The plant density of mutant P2 was generally 25% lower than that of Frisson. Yield indices were all lowest at Portel, despite the same NPK fertilization. Grain and shoot yield of mutant P2 did not reach the level of Frisson at any site. Differences in N and P concentrations between the two isolines were insignificant in most cases. Differences in the amount of shoot P per plant consistently mirrored the mycorrhizal status of the three sites. Roughly 50% of the yield depression per m2 could be attributed to the lower plant density of mutant P2, the remaining 50% must be caused by AM‐fungal colonization or other factors. In the final pot experiment using the soil with low P availability from Portel, the main benefit of AM for peas was enhanced P uptake. Central questions could not be answered using a nonmycorrhizal control. However, mutants remain one interesting tool, best be used in combination with other approaches to estimate the effects of mycorrhization.

Impact of pea growth and arbuscular mycorrhizal fungi on the decomposition of 15N-labeled maize residues

“…Although the mutation should only affect the genes for mycorrhizal and rhizobial infection (Duc et al 1989), further genetic defects cannot be fully excluded (Kleikamp and Joergensen 2006). Interactions with plant hormones may be involved in the mutation, as suggested by experiments with mutant P2 treated with an auxin-transport inhibitor (Müller 1999).…”

“…After rinsing with tap water, the samples were acidified with 2 M HCl for 20 min and then stained with 0.1% trypan blue in 90% lactic acid for 20 min at 65°C (Phillips and Hayman 1970;Kleikamp and Joergensen 2006). Subsequently, the roots were distained with lactic acid and stored in a solution containing lactic acid, glycerol, and water (1:1:1 by vol.)…”

“…It is well-known that AMF can improve nutrient acquisition and yield of host plants (Smith and Read 2008), especially that of P and N (Maeder et al 2000;Cavagnaro et al 2006). However, this positive AMF effect on plant decreases under conditions of non-limiting nutrient availability, especially P, after fertilizer application (Thingstrup et al 1998;Kleikamp and Joergensen 2006). The presence of AMF may have stimulatory or inhibitory effects on soil microorganisms by several mechanisms (Christensen and Jakobsen 1993;Wamberg et al 2003;Vestergård et al 2008), including (1) quantitative and qualitative changes in root exudation, (2) competition for nutrients and water, and (3) exudation of stimulatory or inhibitory substances.…”

“…The myc − mutants as nonmycorrhizal controls are available for tomatoes (Cavagnaro et al 2006) but also for peas (Duc et al 1989;Kleikamp and Joergensen 2006). Peas (Pisum sativum L.) are an important component of arable crop rotations in organic farming systems, and the bibliography about their rhizodeposition is extensive (Mayer et al 2003;Wichern et al 2007).…”

Evidence of considerable C and N transfer from peas to cereals via direct root contact but not via mycorrhiza

“…In such an experiment, the AMF-resistant winter-pea ( Pisum sativum L.) mutant P2 24 can most likely be used as an effective additional zero-control in comparison with its isogenetic and symbiotic isoline Frisson. The often lower belowground biomass of mutant P2 in comparison with Frisson 17 , 25 , 26 does not matter in this context, as the relative effects of root contact and diffusion are more important.…”