Leaf photosynthesis of crops acclimates to elevated CO and temperature, but studies quantifying responses of leaf photosynthetic parameters to combined CO and temperature increases under field conditions are scarce. We measured leaf photosynthesis of rice cultivars Changyou 5 and Nanjing 9108 grown in two free-air CO enrichment (FACE) systems, respectively, installed in paddy fields. Each FACE system had four combinations of two levels of CO (ambient and enriched) and two levels of canopy temperature (no warming and warmed by 1.0-2.0°C). Parameters of the C photosynthesis model of Farquhar, von Caemmerer and Berry (the FvCB model), and of a stomatal conductance (g ) model were estimated for the four conditions. Most photosynthetic parameters acclimated to elevated CO , elevated temperature, and their combination. The combination of elevated CO and temperature changed the functional relationships between biochemical parameters and leaf nitrogen content for Changyou 5. The g model significantly underestimated g under the combination of elevated CO and temperature by 19% for Changyou 5 and by 10% for Nanjing 9108 if no acclimation was assumed. However, our further analysis applying the coupled g -FvCB model to an independent, previously published FACE experiment showed that including such an acclimation response of g hardly improved prediction of leaf photosynthesis under the four combinations of CO and temperature. Therefore, the typical procedure that crop models using the FvCB and g models are parameterized from plants grown under current ambient conditions may not result in critical errors in projecting productivity of paddy rice under future global change.

Water shortage has threatened sustainable development of agriculture globally as well as in the North China Plain (NCP). Irrigation, as the most effective way to increase food production in dry land, may not be readily available in the situation of drought. One of the alternatives is to supply plants with enough nutrients so that they can be more sustainable to the water stress. The objective of this study was to explore effects of irrigation and sulphur (S) application on water consumption, dry matter accumulation (DMA), and grain yield of winter wheat in NCP. Three irrigation regimes including no irrigation (rainfed, I 0) during the whole growth period, once irrigation only at jointing stage (90 mm, I 1), and twice respective irrigation at jointing and anthesis stages (90 mm plus 90 mm, I 2), and two levels of S application including 0 (S 0) and 60 kg ha-1 (S 60) were designed in the field experiment in NCP. Results showed that increasing irrigation times significantly increased mean grain yield of wheat by 12.5-23.7% and nitrogen partial factor productivity (NPFP) by 21.2-45.0% in two wheat seasons, but markedly decreased crop water use efficiency (YWUE). Furthermore, S supply 60 kg ha-1 significantly increased mean grain yield, YWUE, IWUE and NPFP by 5.6, 6.1, 23.2, and 5.6% (across two wheat seasons), respectively. However, we also found that role of soil moisture prior to S application was one of important greater factors on improving the absorption and utilization of storage water and nutrients of soil. Thus, water supply is still the most important factor to restrict the growth of wheat in the present case of NCP, S supply 60 kg ha-1 with once irrigation 90 mm at the jointing stage is a relatively appropriate recommended combination to improve grain yield and WUE of wheat when saving water resources will be considered in irrigated wheat farmlands of NCP.

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In order to investigate the effect of chromosome doubling on ozone tolerance, we compared the physiological responses of a diploid honeysuckle (Lonicera japonica Thunb.) and its autotetraploid cultivar to elevated ozone (O 3 ) exposure (70 ng g -1 , 7 h d -1 for 31 d). Net photosynthetic rate (P N ) of both cultivars were drastically (P<0.01) impaired by O 3 . Although there were significantly positive correlation between P N and stomatal conductance (g s ) in both cultivars under each treatment, the decreased g s in O 3 might be the result rather than the cause of decreased P N as indicated by stable or increasing the ratio of intercellular to ambient CO 2 concentration(C i /C a ). P N under saturating CO 2 concentration (P Nsat ) and carboxylation efficiency (CE) significantly decreased under O 3 fumigation, which indicated the Calvin cycle was impaired. O 3 also inhibited the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (F v /F m ), actual quantum yield of PSII photochemistry (Φ PSII ), electron transport rate (ETR), photochemical quenching coefficient (q P ), non-photochemical quenching (NPQ), the maximum in vivo rate of Rubisco carboxylation (V cmax ) and the maximal photosynthetic electron transport rate (J max ) which demonstrated that the decrease in P N of the honeysuckle exposed to elevated O 3 was probably not only due to impairment of Calvin cycle but also with respect to the lightharvesting and electron transport processes. Compared to the diploid, the tetraploid had higher relative loss in transpiration rate (E), (g s ), (P Nsat ), V cmax and J max . This result indicated that the Calvin cycle and electron transport in tetraploid was damaged more seriously than in diploid. A barely nonsignificant (P=0.086) interaction between O 3 and cultivar on P N suggested a higher photosynthetic sensitivity of the tetraploid cultivar.

Heat stress (HS) seriously restricts the growth and development of plants. When plants are exposed to extreme high temperature, the heat stress response (HSR) is activated to enable plants to survive. Sessile plants have evolved multiple strategies to sense and cope with HS. Previous studies have established that PHYTOCHROME INTERACTING FACTOR 4 (PIF4) acts as a key component in thermomorphogenesis; however, whether PIF4 regulates plant thermotolerance and the molecular mechanism linking this light transcriptional factor and HSR remain unclear. Here, we show that the overexpression of PIF4 indeed provides plants with a stronger basal thermotolerance and greatly improves the survival ability of Arabidopsis under severe HS. Via phylogenetic analysis, we identified two sets (six) of PIF4 homologs in wheat, and the expression patterns of the PIF4 homologs were conservatively induced by heat treatment in both wheat and Arabidopsis. Furthermore, the PIF4 protein was accumulated under heat stress and had an identical expression level. Additionally, we found that the core regulator of HSR, HEAT SHOCK TRANSCRIPTION FACTOR A2 (HSFA2), was highly responsive to light and heat. Followed by promoter analysis and ChIP-qPCR, we further found that PIF4 can bind directly to the G-box motifs of the HSFA2 promoter. Via effector–reporter assays, we found that PIF4 binding could activate HSFA2 gene expression, thereby resulting in the activation of other HS-inducible genes, such as heat shock proteins. Finally, the overexpression of PIF4 led to a stronger basal thermotolerance under non-heat-treatment conditions, thereby resulting in an enhanced tolerance to severe heat stress. Taken together, our findings propose that PIF4 is linked to heat stress signaling by directly binding to the HSFA2 promoter and triggering the HSR at normal temperature conditions to promote the basal thermotolerance. These functions of PIF4 provide a candidate direction for breeding heat-resistant crop cultivars.