Plants in Mediterranean environments can adopt photoprotective mechanisms to cope with winter temperatures, thus avoiding photoinhibition. An increase in global temperature is expected in the future as a consequence of climate change. The aims of this work were (i) to analyse anatomy and photochemical activity in winter leaves of Cistus incanus L., to identify characters having a potential role in photoprotection under natural winter conditions, and (ii) to evaluate the effect of higher temperature on such traits. Leaves from plants grown in a greenhouse (indoor) were compared with those from plants grown outdoors on the basis of anatomical and photochemical traits, including indexes evaluating the exposure of chloroplasts at the cell surface. Leaves developed outdoors were characterized by anatomical traits related to the optimization of light harvesting and to gas-exchange control. Such traits were accompanied by a higher pigment content and an increase in the thermal dissipation of excess absorbed light. Indoor leaves showed physiological and morphoanatomical adjustments addressed to invest more of absorbed light in photochemistry. Overall, our analysis showed that (i) photoprotection in C. incanus relies on adaptive traits at both the morphoanatomical and physiological level and (ii) C. incanus leaves seem to be able to acclimatize to warmer winters.
We assessed the contribution of leaf movements to PSII photoprotection against high light and temperature in Robinia pseudoacacia. Gas exchange and chlorophyll a fluorescence measurements were performed during the day at 10:00, 12:00, 15:00 and 18:00 hours on leaves where paraheliotropic movements were restrained (restrained leaves, RL) and on control unrestrained leaves (UL). RL showed a strong decrease of net photosynthesis (A(n)), stomatal conductance (g(sH2O)), quantum yield of electron transport (PhiPSII), percentage of photosynthesis inhibited by O2 (IPO) and photochemical quenching (q(P)) in the course of the day, whereas, a significant increase in C(i)/C(a) and NPQ was observed. Contrary to RL, UL had higher photosynthetic performance that was maintained at elevated levels throughout the day. In the late afternoon, A(n), g(sH2O), PhiPSII and q(P) of RL showed a tendency to recovery, as compared to 15:00 hours, even if the values remained lower than those measured at 10:00 hours and in UL. In addition, contrary to UL, no recovery was found in F(v)/F(m) at the end of the study period in RL. Data presented suggest that in R. pseudoacacia, leaf movements, by reducing light interception, represent an efficient, fast and reversible strategy to overcome environmental stresses such as high light and temperature. Moreover, paraheliotropism was able to protect photosystems, avoiding photoinhibitory damage, leading to a carbon gain for the plant.
Soil N 2 O emissions were monitored throughout a 3-year crop rotation including maize, fennel and a ryegrass-clover sward, at Borgo Cioffi NitroEurope site. N 2 O emission rates were highly variable in time and space and controlled by soil nitrogen and soil water content. The N 2 O effluxes were low for most of the monitored period. The highest N 2 O emissions were recorded throughout the 2007 maize cropping season, ranged form 15.2 to 196.2 μg m −2 h −1 whereas the lowest ones ranged form −5 to 10 μg m −2 h −1 during the 2007-2008 ryegrass-clover winter crop. For the maize crops, N 2 O peaks were detected after fertilization but with a delay of some weeks from applications, probably due to the presence of DMPP nitrification inhibitor in the applied fertilizer. A properly designed ANOVA model was developed to explain the influence of the main chemical-physical factors. This model also allowed the quantification of the delay time in peak emissions following fertilization, which resulted variable over the years and ranged between 2 and 21 days. A dependence of emissions from soil temperature and moisture was found, with significant interactions in some instances. Calculated Emission Factors (maize 2007: 0.48%; ryegrass-clover sward 2007-2008: 0.05%; maize 2008: 0.14%; fennel: 0.28% 2008-2009; maize 2009: 0.015%) resulted well below the values reported in the literature and the 1% reference value indicated by IPCC, probably due to a suboptimal water regime inducing low Water Filled Pore Space (WFPS) values.
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