Carbon partitioning patterns of mycorrhizal versus non‐mycorrhizal plants: real‐time dynamic measurements using ¹¹CO₂

Abstract

S U M M A K ^•Oas exchnnj^e and c;irl">on ;illoc:ition piilterns were sttidied in two popiihitums of I'diiictiiii rolorotiiiii, :in .Mrica C-4 grass. The pUints were grown ni split-root pots, eontammg partially sterihzed soil, with one side either inoculated (I) or not inoculated (NI) with a \-esieuliir-iirbuscuhir (\'.A) ni\ corrliizal fungus, (iigaspora margarita. Net carbon exchange rates (CER) and stomatal conductances were measured with conventional gas exchange apparatus, and carbon assimilation, translocation, and allocation were measured using photosynthetically-fixed "CO,.Mycorrhizal infection on one half of the split-root system caused a 20",, increase in CI'"R. llie eflect on CHR was less in tillers on the opposite side of the plants from the infected balf of the roots. The rate at «hich photosynthates were stored in the leaves was 45",, higher. Sink activity (concentration of labelled photosynthates in stem phloem tis.sue) more tban doubled in 1 versus NI plants. CICR and stomatal conductances, along with most of the carbon allocation patterns, were nearly identical between the NI (control) bigb grazing and low grazing ecotypes. However, V.-\ m\corrhizal fungi catised a greater storage ot photosynthates in the low grazing ecot\|ic.

Mycorrhizal sink strength influences whole plant carbon balance of Trifolium repens L.

“…The additional amount of CO 2 respired by M compared with NM root systems as a percentage of the net amount of CO 2 assimilated by M plants was 15% on day 42. This is in good agreement with previous studies which have shown that the additional amount of 14 C respired by roots of 14 CO 2 -labelled M plants ranged from 4 to 20% of the total net CO 2 fixed by the plant (Pang & Paul 1980;Paul & Kucey 1981;Kucey & Paul 1982;Snellgrove et al 1982;Koch & Johnson 1984;Harris et al 1985;Douds et al 1988;Wang et al 1989).…”

“…The additional amount of CO 2 respired by M compared with NM root systems as a percentage of the net amount of CO 2 assimilated by M plants was 15% on day 42. This is in good agreement with previous studies which have shown that the additional amount of 14 C respired by roots of 14 CO 2 -labelled M plants ranged from 4 to 20% of the total net CO 2 fixed by the plant (Pang & Paul 1980;Paul & Kucey 1981;Kucey & Paul 1982;Snellgrove et al 1982;Koch & Johnson 1984;Harris et al 1985;Douds et al 1988;Wang et al 1989).By day 53, that the C budgets were still significantly different between M and NM plants when expressed on a per plant basis, could be attributed to the fact that M plants had, for the first time, become significantly larger than those in the NM condition. The fact that the growth of M plants did eventually outpace that of plants grown in the NM condition could indicate that the superior potential for nutrient capture was eventually expressed in colonized plants and may have masked any sink effects.…”

“…Comparison of the C economies of mycorrhizal (M) and non-mycorrhizal (NM) roots has shown that support of the symbiosis requires the transfer of an additional 4-20% of the total net C fixed by the plant (Pang & Paul 1980;Paul & Kucey 1981;Kucey & Paul 1982;Snellgrove et al 1982;Koch & Johnson 1984;Harris, Pacovsky & Paul 1985;Douds, Johnson & Koch 1988;Wang et al 1989). While this demand can be seen as the 'cost' of the symbiosis, it has been hypothesized that mycorrhizal colonization of the root, by increasing its sink strength, may stimulate the process of C assimilation so that the 'cost' imposed on the plant's C economy is reduced or eliminated and thus contribute to the overall benefit derived from association with mycorrhizal fungi (Fitter 1991;Tinker, Durall & Jones 1994).…”

Effects of low‐concentration sulphur dioxide fumigation and vesicular–arbuscular mycorrhizas on 14C‐partitioning in Phleum pratense L.

“…This will probably affect the availability-of photoassimilate for fungal metabolism. Root systems colonized by VA mycorrhiza] fungi acquire a greater percentage of photoassimilate than non-mycorrhizal roots (Koch & Johnson, 1984;Douds, Johnson & Koch, 1988;Wang et al, 1989). In our study there was a tendency for mycorrhizal plants to have a greater proportion of ^*C in the roots compared with non-mycorrhizal plants (Table 3).…”

Physiological responses of Festuca arundinacea to fungal endophyte infection

“…notatuni and Agrostis stolonifera act as an important sink for sucrose, converting it rapidly into sugar alcohols (Thrower & Lewis, 1973;Smith, Bacon & Luttrell, 1985). A strong sink for photosynthates might reduce or prevent feedback inhibition of photosynthetic rates, thereby' allowing higher average growth rates (Wang et al, 1989;Lyons, Evans & Bacon, 1990;Larson & Whitham, 1991).…”