20 research outputs found
Restoration of photosystem II photochemistry and carbon assimilation and related changes in chlorophyll and protein contents during the rehydration of desiccated Xerophyta scabrida leaves
Recovery of photosynthesis in rehydrating desiccated leaves of the poikilochlorophyllous desiccation-tolerant plant Xerophyta scabrida was investigated. Detached leaves were remoistened under 12âh light/dark cycles for 96âh. Water, chlorophyll (Chl), and protein contents, Chl fluorescence, photosynthesisâCO2 concentration response, and the amount and activity of Rubisco were measured at intervals during the rehydration period. Leaf relative water contents reached 87% in 12âh and full turgor in 96âh. Chl synthesis was slower before than after 24âh, and Chla:Chlb ratios changed from 0.13 to 2.6 in 48âh. The maximum quantum efficiency recovered faster during rehydration than the photosystem II operating efficiency and the efficiency factor, which is known to depend mainly on the use of the electron transport chain products. From 24âh to 96âh of rehydration, net carbon fixation was Rubisco limited, rather than electron transport limited. Total Rubisco activity increased during rehydration more than the Rubisco protein content. Desiccated leaves contained, in a close to functional state, more than half the amount of the Rubisco protein present in rehydrated leaves. The results suggest that in X. scabrida leaves Rubisco adopts a special, protective conformation and recovers its activity during rehydration through modifications in redox status
Interannual variability of grasslandsâ carbon balance depends on soil type
Interannual variation of carbon fluxes of grasslands on sandy (5 years data) and heavy clay soils (4 years data) have been analysed. The sandy grassland was carbon sink in 3 (2004, 2005, 2006) out of the investigated 5 years. Its annual C-balance is precipitation limited, the relation seems strongly conservative, with r2
of 0.83. More than half of the net source activity fell to the summer droughts. The heavy clay grassland was net source of carbon in one year (2007) only with no whole year record from 2003, a drought and heat wave year. Dependence of the C-balance on precipitation was somewhat weaker (r2 =0.57) than in the sandy grassland. Length of growing period showed less variation here compared to the sandy grassland. Recovery of sink activity after rains was much slower for the heavy clay grassland than for the sandy grassland. The reason behind is that the amount of water required to reach optimal soil water content for plant functioning is several times larger for the mountain grassland. This fact and the low conductivity of the clay soil for water decrease the heavy clay grasslandâs recovery potential after droughts. Owing to these soil characteristics, the clay grassland may be more vulnerable to droughts in terms of decreased C-assimilation and (soil) carbon losses under the predicted drier summers even if the annual precipitation sum was higher by 10.7% on average for the mountain compared to the sandy grassland. The annual precipitation sum is close to the threshold, below which the grasslands may turn into source of carbon. While in one hand this can be viewed as an example of ecosystem scale adaptation to available water, drought events also involve loss of soil carbon and a potential positive feedback between source activity and decreasing net primary production, on the other