The influence of application hyperaccumulator plant straw on photosynthetic pigment content and photosynthetic parameter of lettuce under cadmium stress

Pot experiments were conducted to study the effects of straw application of three hyperaccumulator plants (Solanum nigrum, Bidens pilosa and Galinsoga parviflora) influence photosynthetic pigments content and photosynthetic parameters of lettuce (Lactuca sativa) under Cd stress. The results showed that: compared with no straw application, the photosynthetic pigment content of lettuce was increased by applying three kinds of hyperaccumulator plants straw (S. nigrum, B. pilosa and G. parviflora), but there was no significant difference among the three kinds of hyperaccumulator plant straws; also improved the net photosynthetic rate (Pn), Stomatal conductance (Gs), transpiration rate (Tr), intercellular CO2 concentration (Ci) of lettuce, among them, the effect of G. parviflora straw was the most obvious. Application of three kinds of hyperaccumulator plant straw promoted the growth of lettuce by increasing the photosynthetic pigment content and photosynthetic parameter of lettuce under Cd stress.

Prediction of crop productivity and evapotranspiration with two photosynthetic parameter regionalization methods

SUMMARYParameter regionalization is the foundation for the spatial application of an ecosystem model at the canopy level and has been improved greatly by remote sensing (RS). Photosynthetic rate is restricted by the carboxylation rate, which is limited by the activity of the enzyme Rubisco. By including RS normalized difference vegetation index (NDVI) and census data of grain yield at the county level in an ecosystem model (vegetation interface processes (VIP) model), the pattern of photosynthetic parameter Vcmax (maximum catalytic activity of Rubisco) of winter wheat was obtained and then used to simulate the wheat yield and evapotranspiration (ET) in the North China Plain (referred to as the Vcmax method). To evaluate its performance, the simulated yield and ET were compared with those derived by the leaf area index (LAI) method using the retrieved LAI from NDVI to drive the VIP model. The results showed that the Vcmax method performed better than the LAI method in highly productive fields, while the LAI method described the inter-annual variations of yield more favourably in fields with low productivity. Over the study area, average yield (4520 kg/ha) and seasonal ET (360 mm) simulated by the LAI method was slightly lower than those simulated using the Vcmax method (4730 kg/ha for yield and 372 mm for ET). Compared with the census data of yield, the relative root mean square error (RMSE) of grain yield with Vcmax method (0·17) was lower than that of the LAI method (0·20). In conclusion, the physical model with spatial Vcmax pattern from remote sensing is reliable for regional crop productivity prediction.

Influence of diel cycles of respiration, chlorophyll, and photosynthetic parameters on the summer metabolic balance of temperate lakes and rivers

Primary production, planktonic respiration, bacterial abundance, and chlorophyll a were measured in the epilimnion of two Canadian Shield lakes and in two large rivers to establish their metabolic balance and to contrast oligotrophic and oligo-mesotrophic systems. Pronounced diel respiration cycles were observed in all systems, with a minimum in the morning and a maximum in the evening. Respiration was positively correlated with water temperature, incident light, and chlorophyll a concentration. Diel cycles of chlorophyll a were discernible in both rivers and in the oligo-mesotrophic lake. Our results show that a single morning sampling underestimates both respiration and chlorophyll a, whereas a single sample taken at noon generally agrees better with the average of four daily measurements. In oligotrophic Lac Croche, the photosynthetic parameter αB remained constant throughout the day, whereas PBm increased by 12.5% between 0600 h and 1300 h. Ignoring the diel community respiration cycle resulted in a ~25% underestimation of daily respiration, whereas ignoring the PBm cycle induced a ~9% underestimation of the daily primary production. The net balance between production (P) and respiration (R) of the oligotrophic lake epilimnion remained positive during two summers, and the P:R ratio showed net autotrophy for all systems except for the oligotrophic river, which was slightly net heterotrophic.