Beyond leaf color : comparing camera-based phenological metrics with leaf biochemical, biophysical, and spectral properties throughout the growing season of a temperate deciduous forest

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 119 (2014): 181-191, doi:10.1002/2013JG002460.Plant phenology, a sensitive indicator of climate change, influences vegetation-atmosphere interactions by changing the carbon and water cycles from local to global scales. Camera-based phenological observations of the color changes of the vegetation canopy throughout the growing season have become popular in recent years. However, the linkages between camera phenological metrics and leaf biochemical, biophysical, and spectral properties are elusive. We measured key leaf properties including chlorophyll concentration and leaf reflectance on a weekly basis from June to November 2011 in a white oak forest on the island of Martha's Vineyard, Massachusetts, USA. Concurrently, we used a digital camera to automatically acquire daily pictures of the tree canopies. We found that there was a mismatch between the camera-based phenological metric for the canopy greenness (green chromatic coordinate, gcc) and the total chlorophyll and carotenoids concentration and leaf mass per area during late spring/early summer. The seasonal peak of gcc is approximately 20 days earlier than the peak of the total chlorophyll concentration. During the fall, both canopy and leaf redness were significantly correlated with the vegetation index for anthocyanin concentration, opening a new window to quantify vegetation senescence remotely. Satellite- and camera-based vegetation indices agreed well, suggesting that camera-based observations can be used as the ground validation for satellites. Using the high-temporal resolution dataset of leaf biochemical, biophysical, and spectral properties, our results show the strengths and potential uncertainties to use canopy color as the proxy of ecosystem functioning.This research was supported by the Brown University– Marine Biological Laboratory graduate program in Biological and Environmental Sciences, Brown–ECI phenology working group, Brown Office of International Affairs Seed Grant on phenology, and Marine Biological Laboratory start-up funding for JT.2014-09-3

Contributions of photosynthetic organs to the seed yield of hybrid rice: The effects of gibberellin application examined by carbon isotope technology

The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Contributions of photosynthetic organs to the seed yield of hybrid rice: The effects of gibberellin application examined by carbon isotope technology. Seed Science and Technology, 46(3), (2018): 533-546, doi:10.15258/sst.2018.46.3.10.Changes in the structure and quality of a hybrid combination population have been observed after the application of gibberellins. Such changes would affect the accumulation and distribution of photosynthetic products, which would subsequently affect the yield during hybrid rice seed production. In this study, photosynthetic physiological characteristics and the distribution of photosynthetic products were evaluated in a field experiment. The transport of panicle photosynthetic products to grain was demonstrated using a 14C isotope tracer technique.The contribution ratios of the panicle and leaf to yield in the hybrid rice seed production were 32.3 and 42.1%, respectively. Through isotope tracing technology, it was determined that about 90% of the photosynthetic products of the panicle and 50% of those of the leaf were delivered to the panicle. During the filling period, the contribution of panicle to yield was concentrated in the early period (0–10 days after pollination), and the contribution of leaf to yield was more significant in the late period (10 days after pollination to maturity). These results suggest that the panicle makes an important photosynthetic contribution (equivalent to that of the flag leaf) during the process of grain filling, especially at 0–5 days after the heading stage.We are thankful to anonymous reviewers and editors for their helpful comments and suggestions. This research was part of the project for the National Natural Science Foundation of China (No. 31271666), “12th 5-year plan” Agro-Scientific Research in the Public Interest (Grant No. 201303002) and the Earmarked Fund for China Agriculture Research System (Grant No. CARS-01-26)

Short-term drought response of N2O and CO2 emissions from mesic agricultural soils in the US Midwest

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Agriculture, Ecosystems & Environment 212 (2015): 127-133, doi:10.1016/j.agee.2015.07.005.Climate change is causing the intensification of both rainfall and droughts in temperate climatic zones, which will affect soil drying and rewetting cycles and associated processes such as soil greenhouse gas (GHG) fluxes. We investigated the effect of soil rewetting following a prolonged natural drought on soil emissions of nitrous oxide (N2O) and carbon dioxide (CO2) in an agricultural field recently converted from 22 years in the USDA Conservation Reserve Program (CRP). We compared responses to those in a similarly managed field with no CRP history and to a CRP reference field. We additionally compared soil GHG emissions measured by static flux chambers with off-site laboratory analysis versus in situ analysis using a portable quantum cascade laser and infrared gas analyzer. Under growing season drought conditions, average soil N2O fluxes ranged between 0.2 and 0.8 μg N m−2 min−1 and were higher in former CRP soils and unaffected by nitrogen (N) fertilization. After 18 days of drought, a 50 mm rewetting event increased N2O fluxes by 34 and 24 fold respectively in the former CRP and non-CRP soils. Average soil CO2 emissions during drought ranged from 1.1 to 3.1 mg C m−2 min−1 for the three systems. CO2 emissions increased ∼2 fold after the rewetting and were higher from soils with higher C contents. Observations are consistent with the hypothesis that during drought soil N2O emissions are controlled by available C and following rewetting additionally influenced by N availability, whereas soil CO2 emissions are independent of short-term N availability. Finally, soil GHG emissions estimated by off-site and in situ methods were statistically identical.Financial support for this work was provided by the DOE Office of Science (DE-FC02-07ER64494) and Office of Energy Efficiency and Renewable Energy (DE-AC05-76RL01830), the US National Science Foundation LTER program (DEB 1027253), and MSU AgBioResearch. J. Tang and M. Cui were supported additionally by NSF/DBI-959333, Brown University seed funding, and the Brown University–Marine Biological Laboratory graduate program in Biological and Environmental Sciences

Performance of solar-induced chlorophyll fluorescence in estimating water-use efficiency in a temperate forest

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Remote Sensing 10 (2018): 796, doi:10.3390/rs10050796.Water-use efficiency (WUE) is a critical variable describing the interrelationship between carbon uptake and water loss in land ecosystems. Different WUE formulations (WUEs) including intrinsic water use efficiency (WUEi), inherent water use efficiency (IWUE), and underlying water use efficiency (uWUE) have been proposed. Based on continuous measurements of carbon and water fluxes and solar-induced chlorophyll fluorescence (SIF) at a temperate forest, we analyze the correlations between SIF emission and the different WUEs at the canopy level by using linear regression (LR) and Gaussian processes regression (GPR) models. Overall, we find that SIF emission has a good potential to estimate IWUE and uWUE, especially when a combination of different SIF bands and a GPR model is used. At an hourly time step, canopy-level SIF emission can explain as high as 65% and 61% of the variances in IWUE and uWUE. Specifically, we find that (1) a daily time step by averaging hourly values during daytime can enhance the SIF-IWUE correlations, (2) the SIF-IWUE correlations decrease when photosynthetically active radiation and air temperature exceed their optimal biological thresholds, (3) a low Leaf Area Index (LAI) has a negative effect on the SIF-IWUE correlations due to large evaporation fluxes, (4) a high LAI in summer also reduces the SIF-IWUE correlations most likely due to increasing scattering and (re)absorption of the SIF signal, and (5) the observation time during the day has a strong impact on the SIF-IWUE correlations and SIF measurements in the early morning have the lowest power to estimate IWUE due to the large evaporation of dew. This study provides a new way to evaluate the stomatal regulation of plant-gas exchange without complex parameterizations.This research was supported by U.S. Department of Energy Office of Biological and Environmental Research Grant DE-SC0006951, National Science Foundation Grants DBI 959333 and AGS-1005663, and the University of Chicago and the MBL Lillie Research Innovation Award to Jianwu Tang. This study was also supported by the open project grant (LBKF201701) of Key Laboratory of Land Surface Pattern and Simulation, Chinese Academy of Sciences

Using canopy greenness index to identify leaf ecophysiological traits during the foliar senescence in an oak forest

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecosphere 9 (2018): e02337, doi:10.1002/ecs2.2337.Camera‐based observation of forest canopies allows for low‐cost, continuous, high temporal‐spatial resolutions of plant phenology and seasonality of functional traits. In this study, we extracted canopy color index (green chromatic coordinate, Gcc) from the time‐series canopy images provided by a digital camera in a deciduous forest in Massachusetts, USA. We also measured leaf‐level photosynthetic activities and leaf area index (LAI) development in the field during the growing season, and corresponding leaf chlorophyll concentrations in the laboratory. We used the Bayesian change point (BCP) approach to analyze Gcc. Our results showed that (1) the date of starting decline of LAI (DOY 263), defined as the start of senescence, could be mathematically identified from the autumn Gcc pattern by analyzing change points of the Gcc curve, and Gcc is highly correlated with LAI after the first change point when LAI was decreasing (R2 = 0.88, LAI < 2.5 m2/m2); (2) the second change point of Gcc (DOY 289) started a more rapid decline of Gcc when chlorophyll concentration and photosynthesis rates were relatively low (13.4 ± 10.0% and 23.7 ± 13.4% of their maximum values, respectively) and continuously reducing; and (3) the third change point of Gcc (DOY 295) marked the end of growing season, defined by the termination of photosynthetic activities, two weeks earlier than the end of Gcc curve decline. Our results suggested that with the change point analysis, camera‐based phenology observation can effectively quantify the dynamic pattern of the start of senescence (with declining LAI) and the end of senescence (when photosynthetic activities terminated) in the deciduous forest.Priority Academic Program Development of Jiangsu Higher Education Institutions in Discipline of Environmental Science and Engineer in Nanjing Forest University; China Scholarship Council Grant Number: 201506190095; Brown University Seed Funds for International Research Projects on the Environmen

Seasonal variations of leaf and canopy properties tracked by ground-based NDVI imagery in a temperate forest

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 7 (2017): 1267, doi:10.1038/s41598-017-01260-y.Changes in plant phenology affect the carbon flux of terrestrial forest ecosystems due to the link between the growing season length and vegetation productivity. Digital camera imagery, which can be acquired frequently, has been used to monitor seasonal and annual changes in forest canopy phenology and track critical phenological events. However, quantitative assessment of the structural and biochemical controls of the phenological patterns in camera images has rarely been done. In this study, we used an NDVI (Normalized Difference Vegetation Index) camera to monitor daily variations of vegetation reflectance at visible and near-infrared (NIR) bands with high spatial and temporal resolutions, and found that the infrared camera based NDVI (camera-NDVI) agreed well with the leaf expansion process that was measured by independent manual observations at Harvard Forest, Massachusetts, USA. We also measured the seasonality of canopy structural (leaf area index, LAI) and biochemical properties (leaf chlorophyll and nitrogen content). We found significant linear relationships between camera-NDVI and leaf chlorophyll concentration, and between camera-NDVI and leaf nitrogen content, though weaker relationships between camera-NDVI and LAI. Therefore, we recommend ground-based camera-NDVI as a powerful tool for long-term, near surface observations to monitor canopy development and to estimate leaf chlorophyll, nitrogen status, and LAI.This research was supported by US Department of Energy Office of Biological and Environmental Research Grant DE-SC0006951, National Science Foundation Grants DBI-959333 and AGS-1005663, and the University of Chicago and the MBL Lillie Research Innovation Award to J.T. and China Scholarship Council (CSC) to H.Y

Heterotrophic respiration in disturbed forests : a review with examples from North America

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): G00K04, doi:10.1029/2010JG001495.Heterotrophic respiration (RH) is a major process releasing carbon to the atmosphere and is essential to understanding carbon dynamics in terrestrial ecosystems. Here we review what is known about this flux as related to forest disturbance using examples from North America. The global RH flux from soils has been estimated at 53–57 Pg C yr−1, but this does not include contributions from other sources (i.e., dead wood, heart-rots). Disturbance-related inputs likely account for 20–50% of all RH losses in forests, and disturbances lead to a reorganization of ecosystem carbon pools that influences how RH changes over succession. Multiple controls on RH related to climate, the material being decomposed, and the decomposers involved have been identified, but how each potentially interacts with disturbance remains an open question. An emerging paradigm of carbon dynamics suggests the possibility of multiple periods of carbon sinks and sources following disturbance; a large contributing factor is the possibility that postdisturbance RH does not always follow the monotonic decline assumed in the classic theory. Without a better understanding and modeling of RH and its controlling factors, it will be difficult to estimate, forecast, understand, and manage carbon balances of regions in which disturbance frequency and severity are changing. Meeting this challenge will require (1) improved field data on processes and stores, (2) an improved understanding of the physiological and environmental controls of RH, and (3) a more formal analysis of how model structure influences the RH responses that can be predicted.Support was provided by the U.S. Geologic Survey and the Kaye and Ward Richardson Endowment

Cover crops and chicken grazing in a winter fallow field improve soil carbon and nitrogen contents and decrease methane emissions

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zheng, H., Zhou, L., Wei, J., Tang, Q., Zou, Y., Tang, J., & Xu, H. Cover crops and chicken grazing in a winter fallow field improve soil carbon and nitrogen contents and decrease methane emissions. Scientific Reports, 10(1), (2020): 12607, doi:10.1038/s41598-020-69407-y.Using symbiotic farming methods [cover crops and chicken grazing (+ C)] in a winter fallow field, we found that the soil organic matter and total nitrogen of the + C treatment were 5.2% and 26.6% higher, respectively, than those of a treatment with cover crops and no chicken grazing (− C). The annual rice grain yield of the + C treatment was 3.8% higher than that of the − C treatment and 12.3% higher than that of the bare fallow field (CK), while the annual CH4 emissions of the + C treatment were 26.9% lower than those of the − C treatment and 10.6% lower than those of the CK treatment. The 100-year global warming potential of the + C treatment was 6.2% lower than that of the − C treatment. Therefore, the use of winter cover crops and chicken grazing in a winter fallow field was effective at reducing CH4 emissions and significantly improving soil nutrients and rice yield.This study was supported by the Earmarked Fund for China Agriculture Research System (CARS-01-26), the China-UK joint Red Soil Critical Zone project from the National Natural Science Foundation of China (Grant No. 41571130053), and Hunan “A Hundred Scholars” Program

Soil CO2 efflux of a larch forest in northern Japan

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 7 (2010): 3447–3457, doi:10.5194/bg-7-3447-2010.We had continuously measured soil CO2 efflux (Rs) in a larch forest in northern Japan at hourly intervals for the snow-free period in 2003 with an automated chamber system and partitioned Rs into heterotrophic respiration (Rh) and autotrophic respiration (Rr) by using the trench method. In addition, we applied the soil CO2 concentration gradients method to continuously measure soil CO2 profiles under snowpack in the snowy period and to partition Rs into topsoil (Oa and A horizons) CO2 efflux (Ft) with a depth of 0.13 m and sub-soil (C horizon) CO2 efflux (Fc). We found that soil CO2 effluxes were strongly affected by the seasonal variation of soil temperature but weakly correlated with soil moisture, probably because the volumetric soil moisture (30–40% at 95% confidence interval) was within a plateau region for root and microbial activities. The soil CO2 effluxes changed seasonally in parallel with soil temperature in topsoil with the peak in late summer. On the other hand, the contribution of Rr to Rs was the largest at about 50% in early summer, when canopy photosynthesis and plant growth were more active. The temperature sensitivity (Q10) of Rr peaked in June. Under snowpack, Rs was stable until mid-March and then gradually increased with snow melting. Rs summed up to 79 gC m−2 during the snowy season for 4 months. The annual Rs was determined at 934 gC m−2 y−1 in 2003, which accounted for 63% of ecosystem respiration. The annual contributions of Rh and Rs to Rs were 57% and 43%, respectively. Based on the gradient approach, Rs was partitioned vertically into litter (Oi and Oe horizons) with a depth of 0.01–0.02 m, topsoil and sub-soil respirations with proportions of 6, 72 and 22%, respectively, on an annual basis. The vertical distribution of CO2 efflux was consistent with those of soil carbon and root biomass.This work was supported by the Global Environmental Research Fund (B-073), Ministry of the Environment, Japan and Grants-in-Aid for Scientific Research (No. 13480150) from JSPS