Chlorophyll meters are widely used to guide nitrogen (N) management by monitoring leaf N status in agricultural systems, but the effects of environmental factors and leaf characteristics on leaf N estimations are still unclear. In the present study, we estimated the relationships among SPAD readings, chlorophyll content and leaf N content per leaf area for seven species grown in multiple environments. There were similar relationships between SPAD readings and chlorophyll content per leaf area for the species groups, but the relationship between chlorophyll content and leaf N content per leaf area, and the relationship between SPAD readings and leaf N content per leaf area varied widely among the species groups. A significant impact of light-dependent chloroplast movement on SPAD readings was observed under low leaf N supplementation in both rice and soybean but not under high N supplementation. Furthermore, the allocation of leaf N to chlorophyll was strongly influenced by short-term changes in growth light. We demonstrate that the relationship between SPAD readings and leaf N content per leaf area is profoundly affected by environmental factors and leaf features of crop species, which should be accounted for when using a chlorophyll meter to guide N management in agricultural systems.

No abstract

No abstract

No abstract

Crop yields are largely influenced by air temperature and solar radiation, but the individual effects of these weather variables are difficult to distinguish because they are often not independent. Here, we demonstrate a large effect of temperature on rice grain yield when solar radiation and crop growth duration were not confounding factors for explaining yield difference across two locations in the tropical and subtropical environments. We found that grain yield of double-season rice crops in the subtropical environment of Wuxue County, Hubei Province, China was 9-66% higher than that in the tropical environment of International Rice Research Institute (IRRI), Philippines. Such yield difference was not caused by the difference in crop growth duration from transplanting to maturity. Biomass production rather than harvest index was responsible for the yield difference. Average daily minimum and maximum temperature from transplanting to maturity at IRRI was 3.4 and 1.9 ºC higher than that at Wuxue, respectively, whereas average daily solar radiation at Wuxue was lower or similar to that at IRRI. Crop's efficiency in converting solar radiation into biomass (i.e. radiation use efficiency, RUE) at Wuxue was 48% higher than that at IRRI, which was associated with the difference in temperature between the two environments. We concluded that lower rice yield in the tropical environment was associated with lower RUE, which was due to the higher temperature compared with the subtropical environment. Our results suggested the crop adaptation strategies for global climate changes should focus more on future warming.