Soybean plants grown in controlled environment cabinets under light intensities of 220 w/m2 or 90 w/m2 (400–700 nm) and day to night temperatures of 27.5–22.5 C or 20.0–12.5 C in all combinations, exhibited differences in growth rate, leaf anatomy, chloroplast ultrastructure, and leaf starch, chlorophyll, and chloroplast lipid contents. Leaves grown under the lower light intensity at both temperatures had palisade mesophyll chloroplasts containing well‐formed grana. The corresponding leaves developed under the higher light intensity had very rudimentary grana. Chloroplasts from high temperature and high light had grana consisting of two or three appressed thylakoids, while grana from the low temperature were confined to occasional thylakoid overlap. Spongy mesophyll chloroplasts were less sensitive to growth conditions. Transfer experiments showed that the ultrastructure of chloroplasts from mature leaves could be modified by changing the conditions, though the effect was less marked than when the leaf was growing.
Monocultures and mixtures of perennial ryegrass ('Grasslands Nui') and paspalum (,Grasslands Raki') were grown at high (24°C day/18°C night) and low (14°C day/8°C night) temperatures either continuously for 24 weeks or transferred between temperatures at 12 weeks. Defoliation treatments applied were cutting at 2-and 4-weekly intervals and frequent cutting immediately after temperature changeover. The effects of these treatments on dry matter production, tiller number per plant, and light interception are reported. Averaged over both grasses and their mixtures, yields were highest under high temperature and infrequent cutting. There was marked species x temperature interaction. Paspalum yielded most at high temperature and ryegrass at low temperature. Ryegrass-paspalum mixtures outyielded the monocultures and mixtures provided more stable yields over the range of temperature conditions. Response of the grasses to temperature changed with time. Ryegrass initially grew more rapidly at high temperature, but after 12 weeks growth, had higher yields at low temperature. Paspalum growth was severely reduced when transferred from high to low temperature, and rapidly increased when transferred from low to high temperature. Canopy development and consequently light interception was restricted, especially for paspalum, by low temperatures and by frequent cutting. Ryegrass had fewer but larger tillers at high compared to low temperature, and it rapidly changed to the contrasting habit form after temperature transfer. Paspalum tillers were short, prostrate, and largely below cuttmg height at low temperature, but elongated rapidly above cutting height at high temperature. Frequent cutting increased the tiller number of paspalum and reduced the tiller number of ryegrass. Because mutual shading occurred amongst competing plants in a simulated sward situation, these results from controlled environment conditions are more closely applicable to the field situation than results obtained from isolated plants. Use ofryegrass-paspalum mixtures in northern New Zealand and management objectives to obtain efficient light interception and tiller populations are discussed.
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