Varietal difference in the correlation between leaf nitrogen content and photosynthesis in rice(Oryza sativa L.) plants is related to specific leaf weight

Increasing leaf photosynthesis per area（A） is of great importance to achieve yield further improvement. The aim of this study was to exploit varietal difference in A and its correlation with specific leaf weight（SLW）. Twelve rice cultivars, including 6 indica and 6 japonica varieties, were pot-grown under two N treatments, low N（LN） and sufficient N（SN）. Leaf photosynthesis and related parameters were measured at tillering stage. Compared with LN treatment, A, stomatal conductance（g_s）, mesophyll conductance（g_m）, leaf N content（N_（area））, and chlorophyll content were significantly improved under SN treatment, while SLW and photosynthetic N use efficiency（PNUE） were generally decreased. Varietal difference in A was positively related to both g_s and g_m, but not related to N_（area）. This resulted in a low PNUE in high N_（area） leaves. Varietal difference in PNUE was generally negatively related to SLW. Response of PNUE to N supply varied among different rice cultivars, and interestingly, the decrease in PNUE under SN was negatively related to the decrease in SLW. With a higher N_（area）, japonica rice cultivars did not show a higher A than indica rice cultivars because of possession of high-SLW leaves. Therefore, varietal difference in A was not related to N_（area）, and SLW can substantially interfere with the correlation between A and N_（area）. These findings may provide useful information for rice breeders to maximize A and PNUE, rather than over reliance on N_（area） as an indicator of photosynthetic performance.

A global meta-analysis of woody plant responses to elevated CO_(2):implications on biomass,growth,leaf N content,photosynthesis and water relations

Background:Atmospheric CO_(2)may double by the year 2100,thereby altering plant growth,photosynthesis,leaf nutrient contents and water relations.Specifically,atmospheric CO_(2)is currently 50%higher than pre-industrial levels and is projected to rise as high as 936μmol mol^(−1)under worst-case scenario in 2100.The objective of the study was to investigate the effects of elevated CO_(2)on woody plant growth,production,photosynthetic characteristics,leaf N and water relations.Methods:A meta-analysis of 611 observations from 100 peer-reviewed articles published from 1985 to 2021 was conducted.We selected articles in which elevated CO_(2)and ambient CO_(2)range from 600–1000 and 300–400μmol mol^(−1),respectively.Elevated CO_(2)was categorized into<700,700 and>700μmol mol^(−1)concentrations.Results:Total biomass increased similarly across the three elevated CO_(2)concentrations,with leguminous trees(LTs)investing more biomass to shoot,whereas non-leguminous trees(NLTs)invested to root production.Leaf area index,shoot height,and light-saturated photosynthesis(A_(max))were unresponsive at<700μmol mol^(−1),but increased significantly at 700 and>700μmol mol^(−1).However,shoot biomass and A_(max)acclimatized as the duration of woody plants exposure to elevated CO_(2)increased.Maximum rate of photosynthetic Rubisco carboxylation(V_(cmax))and apparent maximum rate of photosynthetic electron transport(J_(max))were downregulated.Elevated CO_(2)reduced stomatal conductance(g_(s))by 32%on average and increased water use efficiency by 34,43 and 63%for<700,700 and>700μmol mol^(−1),respectively.Leaf N content decreased two times more in NLTs than LTs growing at elevated CO_(2)than ambient CO_(2).Conclusions:Our results suggest that woody plants will benefit from elevated CO_(2)through increased photosyn-thetic rate,productivity and improved water status,but the responses will vary by woody plant traits and length of exposure to elevated CO_(2).