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Rice is a major crop that feeds more than half of global population. Rice paddy playscomplex roles in carbon cycle by emitting CH4 to the atmosphere while CO2 is sequesteredfrom or released to the atmosphere. Here, we present 3.5 years of eddy covariancemeasurements of CH4 and CO2 fluxes over an intermittently-irrigated rice paddy in Korea intandem with carbon stock measurements in leaf, stem, grain, and root. The interannualvariation of CO2 fluxes was little although the timings of transplantation and harvest weredifferent for each year. Rice paddy acted as a slight sink or neutral in CO2 (-47.3 ± 50.9 g Cm−2 y−1; mean ± 95% confidence interval) with 942.2 ± 129.4 g C m−2 y−1 and894.9 ± 106.5 g C m−2 y−1 for gross primary production (GPP) and ecosystemrespiration (Reco), respectively. Carbon stock in rice showed large interannualvariation (760.2 ± 183.7 g C m−2) with 70 ± 19.8 g C m−2, 232.1 ± 83.3 g Cm−2, 378.2 ± 75.5 g C m−2, and 79.8 ± 12.8 g C m−2 for leaf, stem, grain, androot, respectively. The rice paddy emitted 21.7 ± 2.5 g C m−2 y−1 of CH4. Whenconsidering the global warming potential of CH4 (197.3 g CO2-Ceq m−2 y−1),the paddy shift from carbon sink to source (150 g CO2-Ceq m−2 y−1). The CH4flux showed a bimodal seasonal pattern caused by the mid-season drainage whichturned the soils aerobic conditions so prohibited CH4 emissions. The irrigationpractices, which are different every year, resulted in the significant interannualvariation of CH4 emission (± 7%). These findings will be useful to understand carbonbudgets and cycles, and develop carbon and water managements in rice paddy. [ABSTRACT FROM AUTHOR]

Sun-induced chlorophyll fluorescence (SIF) has recently become an important topic in large scale photosynthesis research. This is mainly related to the selectivity of SIF for vegetation on the one hand and the close mechanistic relationships to photosynthesis on the other hand. The latter, however, is already nonlinear at the leaf level and further complicated by the canopy scattering of far-red SIF. This scattering process, which is strongly affected by the structure of the canopy, results in only a fraction of SIF photons emitted at the leaf-level to escape the canopy. The challenge for canopy-level SIF research is therefore to disentangle the contributions related to canopy structure and leaf physiology. While it is widely assumed that the latter has the stronger relationship to photosynthesis, this has not been tested experimentally at the canopy scale so far. We used a recently developed approach to estimate the canopy escape probability of far-red SIF to analyze the contributions of canopy structure and leaf physiology separately. For this, we conducted a combined analysis for three in-situ datasets from a rice paddy, a wheat and a corn field that all had fPAR, PAR, far-red SIF, GPP and canopy reflectance observations covering most of the growing season. Our analysis focused on half-hourly observations both at the level of fluxes involving the absorbed radiation as well as at the level of light use efficiencies, which excludes the radiation component.We found that canopy structure effects dominated the seasonal component of the SIF escape probability and that this was the cause of a positive correlation of the latter to photosynthetic light use efficiency. The estimated total SIF yield of all leaves in the canopy, in contrast, was dominated by diurnal variations and was almost entirely uncorrelated to photosynthetic light use efficiency. Furthermore, our findings confirm the strong relationships between NIRv to both SIF and GPP at short time scales and the site level that were previously only reported at large spatial and long temporal scales. Thus, our findings bridge gaps between spatio-temoral scales and challenge the widely held assumption that the leaf physiology component in SIF provides most of the additional information for photosynthesis estimation that goes beyond APAR. We think that our approach has the potential to unify previous findings into a coherent picture that could enable the community to more easily identify the advantages and limitations of different methods of estimating GPP from remotely sensed observations. [ABSTRACT FROM AUTHOR]

The emerging technique of remotely sensed Sun-Induced chlorophyll Fluorescence (SIF) hasadvanced our ability to estimate plant photosynthetic activity. However, continuousobservations of SIF and Gross Primary Productivity (GPP) at the canopy scale inevergreen needle leaf forests have been lacking so far. Here, we report continuouslyobserved far-red canopy SIF, GPP and Absorbed Photosynthetically Active Radiation(APAR) during the senescence period in an evergreen needle leaf forest. We installed ahigh-spectral-resolution spectrometer combined with a rotating prism system, whichmeasures up- and down welling irradiance with a single fiber, 20 m above the canopy. Weinvestigated the relationships between SIF, APAR and GPP separately for the followingthree periods; 1) before and 2) after understory vegetation leaf fall, 3) after thetemperature drops below zero. In addition, we examined the effects of diffuse light on therelationships. We found that the slope of the half-hourly SIF-APAR relationshipwas distinctly different in each period but this was not the case in the APAR-GPPand SIF-GPP relationships: while the APAR-GPP relationship showed a similarslope difference as APAR-SIF in the third period, the other two periods had a moresimilar slope value; the SIF-GPP relationship, in contrast had similar slope values inthe last two periods but a very different value in the first period. In addition, thehalf-hourly SIF-APAR relationship showed the highest correlation over the threeperiods (R2 = 0.83). On the other hand, regardless of sky condition, we confirmedthat for daily mean values, SIF-GPP relationship (cloudy: R2 = 0.83, clear: R2 =0.76) was stronger than the SIF-APAR relationship (cloudy: R2 = 0.66, clear: R2 =0.69). Overall, our results indicate that relationships between canopy SIF, GPP andAPAR can vary depending on the presence of understory vegetation, temperatureand the sky condition in an evergreen needle leaf forest. These findings will helpimprove canopy-level SIF-based GPP estimation across multiple temporal scales. [ABSTRACT FROM AUTHOR]