Application of Chlorophyll Fluorescence Analysis Technique in Studying the Response of Lettuce (Lactuca sativa L.) to Cadmium Stress.

To reveal the impact of cadmium stress on the physiological mechanism of lettuce, simultaneous determination and correlation analyses of chlorophyll content and photosynthetic function were conducted using lettuce seedlings as the research subject. The changes in relative chlorophyll content, rapid chlorophyll fluorescence induction kinetics curve, and related chlorophyll fluorescence parameters of lettuce seedling leaves under cadmium stress were detected and analyzed. Furthermore, a model for estimating relative chlorophyll content was established. The results showed that cadmium stress at 1 mg/kg and 5 mg/kg had a promoting effect on the relative chlorophyll content, while cadmium stress at 10 mg/kg and 20 mg/kg had an inhibitory effect on the relative chlorophyll content. Moreover, with the extension of time, the inhibitory effect became more pronounced. Cadmium stress affects both the donor and acceptor sides of photosystem II in lettuce seedling leaves, damaging the electron transfer chain and reducing energy transfer in the photosynthetic system. It also inhibits water photolysis and decreases electron transfer efficiency, leading to a decline in photosynthesis. However, lettuce seedling leaves can mitigate photosystem II damage caused by cadmium stress through increased thermal dissipation. The model established based on the energy captured by a reaction center for electron transfer can effectively estimate the relative chlorophyll content of leaves. This study demonstrates that chlorophyll fluorescence techniques have great potential in elucidating the physiological mechanism of cadmium stress in lettuce, as well as in achieving synchronized determination and correlation analyses of chlorophyll content and photosynthetic function.

Response of agricultural multifunctionality to farmland loss under rapidly urbanizing processes in Yangtze River Delta, China.

Agricultural multifunctionality is increasing interest and importance under the environmental change, which influences the sustainability of agricultural systems. However, research on how the agricultural multifunctionality is being temporally adjusted under the process of rapid urbanization remains limited. Here, we use the Yangtze River Delta, one of the newest metropolitan agglomerations globally, as study area to investigate the threats of modern urbanization to traditional agriculture. This study assessed changes to farmland area and the agricultural multifunctionality of 16 cities in the delta during 1995-2015. The results show that: (1) 87.1% (690, 200 hm2) of farmland area was lost because of urban sprawl over the last 20 years; (2) the total value of agricultural multifunctionality in the delta had increased by 23.2%, which was mainly attributed to a significant increase in food provision and cultural leisure values; (3) the key factor affecting the spatial differentiation of agricultural multifunctionality changed from agricultural labour in 1995 to gross domestic product in 2005 and 2015; and (4) Socio-economic conditions and natural resources determined the adaptive change model of agricultural multifunctionality in different groups of cities. These results illustrate that agricultural multifunctionality is being adjusted to rapid urbanization through the intensification and trade-off of the multiple functions in agricultural system. Therefore, to foster the sustainable development of agriculture in metropolitan agglomerations, future land use policy should focus on both urban control and promoting agricultural multifunctionality. Ongoing transformation practices, such as land consolidation, should aim to improve the bio-physical and socio-economic functions of farmland in the delta. Future research should focus on developing locally suitable strategies based on the adaptive mechanisms of agricultural multifunctionality under changing environments in different cities.