Carbon and Nitrogen Supply during Seed Filling and Leaf Senescence in Soybean

Abstract

Leaf senescence and N redistribution during seed fdiing may limit soybean [Glycine max (L.) Merr.] yield by restricting the seed filling period. Experiments were conducted in the field and greenhouse to evaluate the relationship between seed N demand and leaf senescence. Plants (cv. McCall) were grown under shade cloth (which reduced insolation by 63%) from R1 to R$ (beginning seed fill), then the shade was removed from some plants with the objective of increasing photosynthesis, seed dry matter, and N accumulation. Experiments included plants grown in soil with no nodules (NO~ as primary source), plants grown in soil with many nodules (N from NO~" and N2 fixation), and in a hydroponics system (NO~" as primary source) where N was removed from the media at 1~. Increasing photosynthesis at It5 increased seed dry matter accumulation and the response was larger when N was available. Seed N accumulation also increased if N was available. Increasing photosynthesis had no effect on seed N accumulation when N was not available to the plant. Temporal changes in chlorophyll and N of an upper leaf were measured to characterize leaf senescence. Increasing photosynthesis did not accelerate leaf senescence in any of the treatments. If N was available, N uptake increased when photosynthesis increased. If N was not available, seed N concentration decreased. The data suggest that leaf senescence does not occur because of seed N demand, but may be regulated by processes in the leaf.

Physiological and management factors contributing to soybean potential yield

“…However, previous efforts to supply N during seedfill did not prevent senescence or N redistribution (Egli et al, 1978a;Hayati et al, 1995Hayati et al, , 1996. Likewise, in a comparison of soybean maturity isolines, a maturity group (MG) 6 isoline had 73 to 100% more total N at the beginning of seedfill than the MG 4 isoline but N content in harvested seed was not different (Mastrodomenico and Purcell, 2012), indicating that N supply was not limiting yield.…”

“…Others also observed that N deficiency shortened the EFP and accelerated leaf senescence (Boon-Long et al, 1983;Hayati et al, 1995). The self-destruct hypothesis also explains why a lower DMAC (or ISGR) increases the EFP by slowing the daily demand for C and N remobilization (Salado-Navarro et al, 1986a, 1986b, 1993.…”

Differences in Leaf Senescence among Reciprocally Grafted Plants of Two Soybean Cultivars, Enrei and Tachinagaha

“…Properties of nuclei and cytoplasm in the line that stayed green, the transport of abscisic acid from pods to leaves, the accumulation of abscisic acid in leaves, and the translocation of nitrogen from leaves to pods were suggested as explanations for role of the above-ground parts of plants that was related to senescence (Guiamet et al, 1990;Nooden, 1984;Hayati et al, 1995). Delayed maturation of the stems of the Tachinagaha cultivar is observed in Tokyo and Chiba, namely, the southern parts of the Kanto district, but it is scarcely observed in northern areas, Nagano and Tochigi.…”

Genetic Improvement in Short Season Soybeans: I. Dry Matter Accumulation, Partitioning, and Leaf Area Duration

“…A number of researchers have attempted to identify critical periods for soybean yield determination (Egli, 1988; Board and Harville, 1993; Hayati et al, 1995; Board et al, 1996). Investigations on the vegetative period have reported no evidence to link either DM accumulation during the vegetative period or the duration of this period with yield (Weber et al, 1966; Egli, 1993).…”