Low temperature effects on leaf physiology and survivorship in the C3 and C4 subspecies of Alloteropsis semialata

Abstract

The species richness of C(4) grasses is strongly correlated with temperature, with C(4) species dominating subtropical ecosystems and C(3) types predominating in cooler climates. Here, the effects of low temperatures on C(4) and C(3) grasses are compared, controlling for phylogenetic effects by using Alloteropsis semialata, a unique species with C(4) and C(3) subspecies. Controlled environment and common garden experiments tested the hypotheses that: (i) photosynthesis and growth are greater in the C(4) than the C(3) subspecies at high temperatures, but this advantage is reversed below 20 degrees C; and (ii) chilling-induced photoinhibition and light-mediated freezing injury of leaves occur at higher temperature thresholds in the C(4) than the C(3) plants. Measurements of leaf growth and photosynthesis showed the expected advantages of the C(4) pathway over the C(3) type at high temperatures. These declined with temperature, but were not completely lost until 15 degrees C, and there was no evidence of a reversal to give a C(3) advantage. Chronic chilling (5-15 degrees C) or acute freezing events induced a comparable degree of photodamage in illuminated leaves of both subspecies. Similarly, freezing caused high rates of mortality in the unhardened leaves of both subtypes. However, a 2-week chilling treatment prior to these freezing events halved injury in the C(3) but not the C(4) subspecies, suggesting that C(4) leaves lacked the capacity for cold acclimation. These results therefore suggest that C(3) members of this subtropical species may gain an advantage over their C(4) counterparts at low temperatures via protection from freezing injury rather than higher photosynthetic rates.

Effect of shading by baobab (Adansonia digitata) and néré (Parkia biglobosa) on yields of millet (Pennisetum glaucum) and taro (Colocasia esculenta) in parkland systems in Burkina Faso, West Africa

“…That is why the highest HI of millet was observed in the area going from the crown edge to 3 m away where more light was available and soil fertility may be increased by tree effect. That also explains why the highest HI of taro was in the area close to the tree trunk where PAR was more reduced as this C 3 pathway crop was limited by photorespiration because of the high temperature and light saturation in the open field (Hay and Porter 2006;Osborne et al 2008;Yang et al 2004). …”

Leaf cold acclimation and freezing injury in C3 and C4 grasses of the Mongolian Plateau

“…A mechanistic link between freezing sensitivity and the C 4 pathway is also suggested by the occurrence of cold acclimation in the C 3 but not in the C 4 subspecies of A. semialata (Ibrahim et al , 2008; Osborne et al , 2008). However, cold acclimation has been observed previously in a minority of C 4 species.…”

“…The protocol for each freezing event followed Osborne et al (2008). Briefly, the root system of each plant was prevented from freezing by wrapping each pot in polythene, and immersing it in a water bath held at 15 °C.…”

“…Cold acclimation in the C 3 subspecies is associated with changes in the pattern of moisture release at low water potentials, compared with the C 4 type, indicating the possible involvement of water relations in the acclimation response. These data suggested that climatic extremes such as frost events, rather than photosynthetic responses to average climate conditions, may advantage the C 3 over the C 4 subspecies in cool climatic regions (Ibrahim et al , 2008; Osborne et al , 2008). …”

“…Recent experiments with C 3 and C 4 subspecies of the African grass Alloteropsis semialata showed that the C 4 subspecies suffers from freezing-induced mortality of its leaves during winter, which the C 3 subspecies avoids via cold acclimation (Ibrahim et al , 2008; Osborne et al , 2008). Cold acclimation in the C 3 subspecies is associated with changes in the pattern of moisture release at low water potentials, compared with the C 4 type, indicating the possible involvement of water relations in the acclimation response.…”